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TGrid 5.0 User's Guide

1. 3 20 3 6 2 Opening the User s Guide Index 3 21 3 6 3 Accessing the Other Manuals 005 3 21 SGA Usine Help ep se he nes e OR EE Se RE AES S 3 22 3 6 5 Accessing the User Service Center Web Site 3 22 3 6 6 Accessing the Online Technical Support Web Site 3 22 3 6 7 Obtaining a Listing of Other TGrid License Users 3 22 4 Sample Session 4 1 Gls Preparation s a oem sorod Ge O88 ee Oe By we oe ee ee ere os 4 1 4 2 Reading the Boundary Mesh 02 0 20204 4 2 4 3 Examining the Boundary Mesh 4s 4 h oeio eee ee EnS es 4 3 4 4 Generating the Interior Mesh 020 02 0008 4 5 io Displaying the Meshi sc sac noes How a sha Cage eee iri 4 6 4 6 Reporting the Mesh Statistics o a a a a a a a 4 8 A Checking the Mesh sas oe par ee ee eS ER ee EE Se eS 4 12 4 8 Saving the Mesh and Exiting TGrid 0 4 4 12 5 Text User Interface 5 1 S Text Menu Systemi oy we Ree ee Pa RAR Be RAD RSE ES 5 1 5 1 1 Command Abbreviation 2 2 00 000 5 3 TOC 2 ANSYS Inc April 15 2008 CONTENTS Coded Scheme Evaluatio sersa Gg ee we Bae ee Sw ee eS 5 4 glg Aliases a dge 84 KOR C4 KO Oe DR e C ede OH OSS 5 4 52 leet Prompt System ssas spies Cai ky g aob ee yh gai 5 4 Sal Numbers oh ek PS RE Ba eee oe Pelee 5 5 Ba Booleans g 0 4559 2 b ote g Saw eh ee ee bee be BSS 5 5 Gad DINES ce bee Rede RSE RS24ESE4
2. 2 7 70 Projecting Boundary Zones 4 lt b nee da eG 6 YP eee ae ee eS 7 70 7 11 1 The Project Face Zone Panel 2302 anew hanea avn e e s 7 71 7 11 2 Text Commands for Projecting Boundary Zones 7 72 Creating Gate s r eek ee eee ER PORE ee SRP EAE Ee 7 72 7 12 1 The User Defined Groups Panel 2 2 200 7 73 7 12 2 Text Commands for User Defined Groups 7 74 Manipulating Boundary ZonES e roce soste ee YY ws 7 75 7 13 1 The Manage Face Zones Panel 2 004 7 75 7 13 2 Text Commands for Manipulating Boundary Zones 7 78 Creating SUr aces s s se eo ee eRe ee Rew EES 7 79 14 1 Creatine a Bounding Box gt o ne s wy oe dee ee ORE AS 7 79 7 14 2 Creating a Planar Surface Mesh 00 7 82 T143 Creating es Cylinder so ocg che de dbo ee bh bGR eR eS 7 86 T 14 4 Creatine a Swept Surface e se oe s cee ee ee ee we 7 88 7 14 5 Creating Periodic Boundaries 4 lt cso ec a Yee eae ee eS 7 90 ANSYS Inc April 15 2008 CONTENTS 7 14 6 Text Commands for Creating Surfaces 7 15 Additional Boundary Mesh Text Commands 8 Wrapping Boundaries 8 1 The Boundary Wrapper s lt eop s soii paue doe aia oe we eS 8 1 1 Applications of Wrapper o oo a 8 2 The Wrapping Process 26544454454 444 58445 8 3 Examining and Repairing the Input Geometry aaa 8 4 Initializing the Cartesian Grid 8 5 Examining the Cartesian G
3. Controls Selections contains a list of the selected entities You need to ensure the appropriate entities are selected in the Selections list before clicking the required button in the Operation group box Filter lists the types of entities that can be selected Only entities of the type selected in the Filter list can be selected To select entities of more than one type select the appropriate option in the Filter list and select the required entities of the same type Then change the selection in the Filter list and continue to select the entities as required Operation contains buttons for performing cell modification operations Smooth repositions the selected node based on the average of the surrounding nodes Clear removes the selected entities from the Selections list Split refines the selected cell by adding a node at the centroid and splitting the cell into four cells Undo undoes the previous operation 13 16 ANSYS Inc April 15 2008 13 6 Modifying Cells Move To moves the selected node to the specified position Move By moves the selected node by the specified increment Swap swaps the cell configuration 3 2 or 2 3 according to the entities selected Centroid reports the centroid for the entity selected in the Selections list Set defines the projection line or plane determined by the entities selected in the Selections list Distance reports the distance between the two entities selected
4. Figure 9 1 9 Example of a Non Conformal Interface Boundary gt Manage 4 Write the grid to a file 5 Read the combined grid file into FLUENT and create the non conformal inter face using the Grid Interfaces option 9 1 7 Inserting Isolated Nodes into a Tri or Tet Mesh To add nodes to the mesh without also specifying the faces you can create a boundary zone in the boundary mesh in the program that created it just for this purpose Then in TGrid you can introduce the nodes associated with these faces This feature is useful for clustering nodes and therefore cells in a controlled manner Figure 9 1 10 shows a grid that was generated using this method to cluster the nodes behind the wedge A grid that was generated for the same geometry without clustering is shown in Figure 9 1 11 You can follow either of the two procedures to insert isolated nodes into a mesh e Delete the face zone before meshing e Introduce the nodes using face zones after meshing ANSYS Inc April 15 2008 9 9 Creating a Mesh Delete the Face Zone Before Meshing This procedure is as follows 1 Delete the face zone but leave the associated nodes Disable Delete Nodes in the Manage Face Zones panel to retain these nodes Fa By default the unused nodes are deleted when the faces of the zone are deleted 2 Disable Delete Unused Nodes in the Tri Tet panel and generate the volume mesh i By default unused nodes wi
5. 4 Display the boundary mesh Display gt Grid al r r r r F F Figure 4 3 2 The Display Grid Panel The Display Grid panel has capabilities for displaying free multi connected and un meshed faces It is useful to display unmeshed faces when the initial mesh generation process fails and you want to locate the problem areas easily a Select all the boundary zones in the Face Zones selection list b Click Display see Figure 4 3 3 The boundaries are color coded according to their type c Close the Display Grid panel 4 4 ANSYS Inc April 15 2008 4 4 Generating the Interior Mesh Figure 4 3 3 Display of Wedge Boundary Faces 4 4 Generating the Interior Mesh When you are satisfied with the boundary mesh generate the interior mesh For most cases the automatic mesh generation procedure will create an good quality mesh Mesh Auto Mesh Auto Mesh Boundary Layer Mesh l Prisme Quad Ye Transition A poramido v Nes Confonnais Volume Fill TrisTet v Hexeere v No Fill Options _4 Merge Cell Zones paeoh Aacty Giese tow Figure 4 4 1 The Auto Mesh Panel 1 Click Mesh in the Auto Mesh panel ANSYS Inc April 15 2008 4 5 Sample Session A Working dialog box will appear during the mesh generation You can click Cancel in the Working dialog box to stop the mesh gen
6. Controls Face Zones contains a list of boundary face zones from which you can select the bound ary zone to be remeshed Edge Zones contains a list of edge loops that have been created for one or more face zones using the Apply button Edge Zone Groups contains a list of edge zone types If you select a zone type from this list e g boundary edge all edge zones of that type will be selected in the Edge Zones list This shortcut allows you to easily select all zones of a certain type without having to select each zone individually Face Zone Groups contains a list of face zone types If you select a zone type from this list e g boundary all face zones of that type will be selected in the Face Zones list This shortcut allows you to easily select all zones of a certain type without having to select each zone individually Edge Modify contains buttons for applying the edit operations to the edge loop s selected in the Edge Zones list ANSYS Inc April 15 2008 7 6 Creating and Modifying Features Delete deletes the selected edge loops Note that you should not delete exte rior edge loops for non manifold surfaces i e surfaces with clearly defined borders Copy copies each selected edge loop including its nodes to a new edge loop Toggle changes a boundary edge loop to an interior edge loop or vice versa Group associates the selected edge loops with the selected face zone for subse quent remeshing UnG
7. ANSYS Inc April 15 2008 14 27 Examining the Mesh Display Timeout enables the setting of a timeout for displaying the geometry Timeout in seconds specifies the value for the timeout When TGrid fails to display the geometry within the time specified an error message will be displayed in the TGrid console indicating that the model could not be displayed within the specified time Graphics Window allows you to open and close graphics windows Active Window indicates the graphics window to be opened closed or set active Its title displays the graphics window ID Open Close opens or closes the window with the ID shown in the Active Window box If the indicated window is open the Close button will appear If the indicated window is not open the Open button will appear Set sets the window with the ID shown in the Active Window box to be the active graphics window Lighting Attributes controls lighting attributes for all lights in the active graphics win dow Lights On allows you to enable disable all lights in the active graphics window Lighting specifies the method to be used in lighting interpolation Flat Gouraud or Phong Flat is the most basic method There is no interpolation within the individual polygonal facets Gouraud and Phong have smoother gradations of color because they interpolate on each facet Layout controls the display of captions axes and the colormap in the graphics display window Titles ena
8. 10 11 12 Specify advanced options if required By default TGrid considers self proximity during the wrapping process You can ignore self proximity detection during wrapper initialization if required In order to have a smooth transition from fine to coarse cells you can set the number of additional layers of cells to be included during refinement When you specify the number of Buffer Layers TGrid marks additional layers of cells adjacent to those marked for refinement by the size requirement Select the face zone s you want to wrap from the Tri Boundary Zones list e If the input geometry does not have face zones of the geometry type and you do not select any zone in the Tri Boundary Zones list all the available face zones will be considered for wrapping e Ifthe input geometry has face zones of the geometry type and you do not select any zone in the Tri Boundary Zones list only the face zones of the geometry type will be considered for wrapping e If you select specific zone s in the Boundary Zones list irrespective of whether or not the input geometry has geometry type face zones only the selected zone s will be considered for wrapping Click Init to initialize the Cartesian grid After creating the Cartesian grid the wrapper virtually partitions all the cells into several volumetric regions based on the intersecting and isolated cells These regions are ordered according to descending order of their sizes
9. 12 13 10 12 13 12 34 13 51 13 3 6 13 74 4 2 28 0 1 3 0 O0 1 a 0 0 180 2 C7 1 3 4 By 2122 2 3353 2 10 2 0 3 0 4 6 8 3 2 30 20 1 0 ANSYS Inc April 15 2008 B 13 Mesh File Format 13 5 9 9 c 2 8 5 1 0 13 1aa82 6 7 3 0 18 1 15 1 9 a 10 1 1812 1 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 OWWONNEF Example 3 FrRrOOrF OF O 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 Figure B 11 3 illustrates a simple quadrilateral mesh with hanging nodes bn13 bf15 bn7 bf14 bng bf12 bn2 bf13 bn12 f6 e6 f1c3 bfl7 bf16 c1 f5 c2 nget f2 bn3 f1 f3c4 bf18 Wio be Tni bf9 bno BELT pra FLO pn11 Figure B 11 3 Quadrilateral Mesh with Hanging Nodes The following describes this mesh 0 Grid 0 Dimensions 2 2 ANSYS Inc April 15 2008 B 11 Example Files 12 13 10 12 12 58 OMNADFrR FRAN aona AUN 13 a 6 6 9 4b NOANA aNND OW 13 da 13 3c b 3 13 c 8 13 O 1 O 1 7 1 4 7 7 N 1 ONrFPOBWOD AN AON AD OT amp W kaui Na 38 oao ANEA O O O G Noa WY 4c 6 3 2 1 gt O Or 5 10 1 0 6 11 30 4 0 b 13 7 0 a
10. Edit updates the edited text in the active graphics window This button will replace the Add button when you are editing an existing text string from the Names list Clear removes all annotation text and attachment lines from the active graphics win dow 14 11 2 Text Commands for Text Annotation Text commands related to annotation are display annotate adds annotation text to a graphics window It will prompt you for a string to use as the annotation text A dialog will prompt you to select a screen location using the mouse probe button on your mouse For more information on setting the mouse buttons see Section 14 9 2 Text Commands for Selecting Mouse Buttons display clear annotations removes all annotations and attachment lines from the active graphics window ANSYS Inc April 15 2008 14 51 Examining the Mesh 14 12 Shortcuts for Selecting Zones The panels opened from the Display menu and some other panels contain lists of zones present in the model You can choose one or more face cell node or edge zones from these lists If a large number of zones are present in the model it becomes difficult to find and select the required zone The Zone Selection Helper panel allows you to easily find and select the zone s you want You can either select the required zones by their naming pattern or by number of entities present in them Although the panel is opened from the Display menu it can be used with all panels
11. Max Angle specifies the maximum angle between two adjacent faces allowed for performing swapping ANSYS Inc April 15 2008 8 41 Wrapping Boundaries Max Skew specifies the maximum allowable skewness value after swapping Improve allows you to improve the wrapper surface based on the Quality Measure selected Quality Measure contains the available options for improving the quality of the wrapper surface Skewness allows you to improve the wrapper surface quality based on the skewness Size Change allows you to improve the wrapper surface quality based on size change Aspect Ratio allows you to improve the wrapper surface quality based on the aspect ratio Iteration specifies the number of improving attempts Max Angle specifies the maximum allowable angle between two ad jacent face normals Quality Limit specifies the quality limit for the improvement opera tion All elements above the specified quality limit will be improved Preserve Boundary allows you to preserve the original locations of the zone boundary nodes Zone contains options for the recovery of zones from the wrapper surface Recover Zone separates the wrapper surface into zones based on the original geometry Rezone smoothes the separated zones by adjusting the node position on the zone boundaries Reprojection enables the projection of nodes onto the geometry af ter smoothing Rename allows you to rename the boundary zones From sp
12. Reading Multiple T Grid Files If the mesh is contained in two or more separate files you can read them together in TGrid and assemble the complete mesh For example if you are creating a hybrid mesh by reading in a triangular boundary mesh and a volume mesh consisting of hexahedral cells read both files at the same time using the File Read Mesh menu item or the file read multiple mesh or file read multiple case text commands You can also use the file read meshes by tmerge text command This command uses the tmerge utility Reading 2D Mesh Files in the 3D Version of T Grid It is also possible to read 2D meshes from FLUENT into the 3D version of TGrid To read a 2D mesh into the 3D version of TGrid use the File Import Fluent 2D Mesh menu item or the file import fluent 2d mesh text command Reading 3D Mesh Files in the 2D Version of T Grid It is also possible to read 3D meshes from FLUENT into the 2D version of TGrid To read a 3D mesh into the 2D version of TGrid use the File Import Fluent 3D Mesh menu item or the file import fluent 3d mesh text command 6 1 3 Appending Mesh Files You can also read multiple mesh files one by one instead of reading all of them at a time This process is called as appending the mesh files To do so read in the first mesh file using the Select File panel Reopen the panel and enable Append File s check button and read the remaining files one by one For details see Section 3 2 6 Select F
13. The status message indicates that the mesh file information is being piped into the gzip command and that the output of the compression command is being redirected to the file with the specified name In this particular example the msh extension was added automatically Note The writing of compressed file will fail if the compress or GNU gzip compression routine is not available on your platform 6 3 Reading Scheme Source Files A Scheme source file can be loaded in three ways e Through the menu system as a scheme file e Through the menu system as a journal file e Through Scheme itself For large source files use the Select File panel invoked by selecting the File Read Scheme menu item or the Scheme load function gt load file scm Shorter files can also be loaded with the File Read Journal menu item or the file read journal command in the text interface or its or source alias gt falessem gt source file scm In this case each character of the file is echoed to the console as it is read in the same way as if you were typing the contents of the file ANSYS Inc April 15 2008 6 7 File Types 6 4 Journal Files TGrid creates a journal file by recording everything you type on the command line or enter through the GUI The GUI commands are recorded as Scheme code lines in journal files You can also create journal files manually with a text editor The purpose of a journal file is to autom
14. boundary surfer smoothing iterations specifies the number of smoothing itera tions to be performed after surface triangulation boundary surfer smoothing relaxation specifies the surface smoothing relaxation factor boundary surfer swapping iterations specifies the number of swapping iterations to be performed after surface triangulation 7 60 ANSYS Inc April 15 2008 7 8 Faceted Stitching of Boundary Zones 7 8 Faceted Stitching of Boundary Zones TGrid allows you to to repair surfaces having internal cracks or free edges using the Faceted Stitch option You can specify an appropriate tolerance value within which the free edges will be stitched The Self Stitch only option allows you to stitch the edges within the same boundary zone The faceted stitching operation is available only for triangular boundaries Figure 7 8 1 shows the repair of a surface with internal cracks Ov A B Figure 7 8 1 Mesh A Before and B After Using the Faceted Stitch Option The command boundary remesh faceted stitch zones allows you to perform the faceted stitching of zones Note Featues may not be maintained when using the faceted stitching operation ANSYS Inc April 15 2008 7 61 Manipulating the Boundary Mesh 7 8 1 The Faceted Stitch Panel The Faceted Stitch panel contains options for repairing cracks in the surface mesh Controls Boundary gt Mesh F
15. driver gl opengl null pex sbx x11 xgl J sets the graphics driver available drivers vary by platform env show environment variables g run without gui or graphics gu run without gui gr run without graphics help this listing i journal read the specified journal file ANSYS Inc April 15 2008 2 3 Starting Dual Process Build of TGrid n no execute nocheck disable checks for valid license file and server project x write project x start and end times to license log Y list all releases rx specify release x v list all versions VX specify version x version if given must be first On Windows systems only env gu with restrictions help i journal r rx v and vx are available The first three options are for specifying arguments for TGrid and Cortex Cortex is a process that provides the user interface and graphics for TGrid When you start TGrid you actually start Cortex which then starts TGrid On Windows systems tgrid gu will run TGrid keeping it in its iconified form The GUI will be available if you expand it This option can be used in conjunction with the i journal option to run a job in background mode Options Description cx host pl p2 Used only when you start TGrid manually see Section 2 2 Start ing TGrid tgrid driver Allows you to specify the graphics driver to be used in the TGrid session e g tgrid driv
16. e One sweep at the appropriate skewness threshold for that particular level of refine ment e Another sweep with a high skewness threshold and a relaxed Min Boundary Closeness set in the Tri Tet Refine Controls panel see Section 11 5 2 The Tri Tet Refine Controls Panel This sweep attempts to reduce highly skewed cells in confined regions of the geome try Boundary slivers will be removed after the refinement sweeps are complete if the Remove Slivers option is enabled in the Refinement tab of the Tri Tet panel In some rare cases it may happen that the first sweep of the first refinement level will never finish because more skewed cells are formed due to refinement which will be further refined to create more skewed cells and so on Such a problem may occur when there is a problem with the boundary mesh such as rapid mesh transition in small gaps etc This problem can be avoided by using the incremental improvement option for the refinement parameters or by increasing the Min Node Closeness value in the Tri Tet Refine Controls panel see Section 11 5 2 The Tri Tet Refine Controls Panel You can select the fast transition option for the refinement parameters in order to generate a mesh with a smaller number of cells When this option is selected TGrid will use the appropriate refinement parameters to generate fewer cells during meshing The rate of change of the cell size is increased in order to reduce the number of cells generate
17. quality range enable Quality in the Options group box set the appropriate Minimum and Maximum values and click Display or Apply Use the Report Face Limits panel see Section 15 2 1 The Report Face Limits Panel to determine an appropriate range Minimum sets the minimum value for the quality range This value should be greater than or equal to zero and less than the Maximum value Maximum sets the maximum value for the quality range This value should be greater than the Minimum value If the quality measure being used is skewness it should also be less than or equal to one Quality Measure opens the Quality Measure panel see Section 15 5 2 The Qual ity Measure Panel in which you can select the measure of quality to be used skewness aspect ratio change in size etc Face Zones contains a list of face zones from which you can select those to be drawn Face Zone Groups contains a list of face zone types Selecting a zone type from this list e g inlet will select all face zones of that type pressure inlet 3 velocity inlet 5 etc in the Face Zones list This shortcut allows you to easily select all zones of a certain type without having to select each zone individually You can also select multiple zone types in the Zone Groups list to select all zones of different types e g wall and symmetry Cells contains options for displaying cells Display Grid Nodes Faces cens Bounds Attributes Opti
18. square of the circumcenter radius relevant for triangular and tetrahedral cells only the quality of the cell The default measure of quality is skewness but you can use the Quality Measure panel see Section 15 5 2 The Quality Measure Panel to specify aspect ratio or change in size instead 15 6 5 Face report gt print info entity 32 32 4 n95 bni97 n90 c4599 c1279 ANSYS Inc April 15 2008 15 17 Reporting Mesh Statistics The following information is listed for a face e associated zone ID e the nodes forming the face e the neighboring cells Due to the manner in which the algorithm maintains memory not all indices will have values that is an empty slot can be caused by a delete operation Empty slots are reused in subsequent operations so the actual entity at a particular index may change as the mesh is generated 15 7 Additional Text Commands for Reporting Text interface commands related to the Report menu that are not available in the GUI are listed below report cell distribution reports the distribution of cell quality report cell zone a location reports the cell zone at the specified location report cell zone volume reports the volume of the specified cell zone in the console report edge size limits reports the edge size limits report face distribution reports the distribution of face quality report face zone area reports the area of the specified face zone in the console
19. 4 4 2 64 224 e224 a 44 15 3 15 2 2 Text Commands for Reporting Face Limits 15 5 15 3 Reporting Cell Limits sbs s ean ee eed Pa HAV Be Rees 15 5 15 3 1 The Report Cell Limits Panel 15 5 15 3 2 Text Commands for Reporting Cell Limits 15 6 154 Reporting Boundary Cell Limits o 4 2 v oh eeu ae ewe REE 15 6 15 4 1 The Report Boundary Cell Limits Panel 2 2 2 15 7 15 4 2 Text Commands for Reporting Boundary Cell Limits 15 8 15 5 Mesh Quality e seais ea Ow entes mE ee ORE HEE a 15 8 15 5 1 Quality Measures Available in TGrid 15 9 15 5 2 Specifying the Quality Measure o oaa a a 15 13 15 5 3 Text Commands for Selecting the Quality Measure 15 15 15 6 Printing Grid Iniormatigi lt s seis 6 Se ER 6D pion oe oe we REEDE KE i 15 15 i56 Boundary Node 42 5 ey oe aa eee E ia E ace ee eS 15 15 156 2 Node 4 4 emort ssa KS oe RPE EK Rw wD i 15 16 15 6 3 Boundaty Pate bak ee eee we na iee LA ee ee See 15 16 1 64 Cell eag soc be ead oa eB oh a i oh Re SAS a 15 17 PG Wee bee eh ke a eS Be Be Be bask Ga Se Oe eG 15 17 15 7 Additional Text Commands for Reporting 15 18 Importing Boundary and Volume Meshes A 1 A 1 GAMBIT Meshes 2 002 eee eee eee eee A 1 A 2 TetraMesher Volume Mesh aoaaa aaa 2 000 eee eee A 1 A 3 Meshes from Third Party CAD Packages aoaaa a A 1 A 3 1 Using the fe2ram Filter to Convert Files
20. A 1 A 3 2 l deas Universal Files 2 aaa a A 2 A 3 3 PATRAN Neutral Files aa aaa aa A 4 AA ANSYS Files kee sarea Re Ow OS CRW ES CR ORO ORS a A 5 ANSYS Inc April 15 2008 CONTENTS ASS ARIES Fil s 2246 4 oo a eae eee GE Ke a A 3 6 NASTRAN Files 2 04 B Mesh File Format By COmMent pes s 24 44 ee ee ea Se ee eS Se S B2 Header sss p eed wwe ba ee be ee 6 oy ww ae B 3 Dimensions 2 de eee RRR EEL EG SEE ES ERG BA Nodes x cae AM Be eee ea ewe oo eR ow a B Periodic Shadow Faces 2 2 24 62 6 ebb ee BA Celle sod eee ee eh es BEGG AEE oe Reh ER GOS Br ER ec eB ec ee Be ee he oe i n B Face Tree lt lt poies Ou eee A ee ee p E ee p e p gi G B9 Cel Troe prora gta s Oe a OBS HH EH a HERS B 10 Interface Face Parents oaoa aaa a B 11 Example Files lt eed en ee hee eRe Rd eae a ee C Shortcut Keys C1 Arow Keys ieoa riaa Ge DEG RAG KS ES G2 Help RES es ee ce Ph ec ee 6 Oe ee oi C3 Hot a eek Be ee h Bie OE kos Oe ES ee Be G D Query Functions D 1 Using Boolean Operations with Query Functions D2 Examples oe eee ee ek oe eee ee eS Ow a E Tips Et Reading Files dk a ao he ow Oe SLR E2 Watine Files ss s grede ee eee wee oe ee SE SE a E3 Saving Hard Copy Wiles lt a s re teata diu ee os E 4 Importing Meshes anaana aa e E5 Oreste a Mesh sacs ace Ree pera EP we RR ow ANSYS Inc April 15 2008 TOC 15 CONTENTS TOC 16 EG Grouping Elements so ce ney ce
21. ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh First finds the triangular face with the worst quality in the entire grid or the active group when Quality Limit is selected The worst face will be displayed in the graphics window and the quality and zone ID will be reported in the console The selected node will appear in the Selections list along with the longest edge of the face and its opposing vertex node When Mark is selected the first of the marked faces will be displayed in the graphics window The selected node will appear in the Selections list along with the longest edge of the face and its opposing vertex node Modify the display region in the Bounds section of the Display Grid panel see Section 14 1 3 The Display Grid Panel If the zone in which the face lies is not currently included in the display include it by selecting the zone in the Face Zones selection list in the Faces tab of the Display Grid panel If you have not yet displayed the grid TGrid will report in the console the worst face its skewness and the zone in which it lies Next finds the triangular face having the next highest quality value after that of the worst face in the grid or the active group when Quality Limit is selected Every time you click this button the triangular face having the next highest quality value will be displayed in the graphics window This option will help you to view the locations of the skewed cells i
22. Figure 15 5 1 Smooth and Non Smooth Transitions in Cell Size Aspect Ratio The aspect ratio of a face or cell is the ratio of the longest edge length to the shortest edge length The aspect ratio applies to triangular tetrahedral quadrilateral and hexahedral elements and is defined differently for each element type The aspect ratio can also be used to determine how close to ideal a face or cell is e For an equilateral face or cell e g an equilateral triangle or a square the aspect ratio will be 1 e For less regularly shaped faces or cells the aspect ratio will be greater than 1 since the edges differ in length e For triangular and tetrahedral faces and cells and for pyramids you can usually focus on improving the skewness and the smoothness and aspect ratio will conse quently be improved as well ANSYS Inc April 15 2008 15 9 Reporting Mesh Statistics e For prisms including 2D quadrilateral cells it is important to check the aspect ratio and or the change in size in addition to the skewness because it is possible to have a large jump in cell size between two cells with low skewness or a high aspect ratio low skew cell such as the quadrilateral on the right in Figure 15 5 2 Figure 15 5 2 Large Change in Size Between Low Skew Quadrilaterals Skewness Skewness is one of the primary quality measures for a mesh Skewness determines how close to ideal i e equilateral or equiangular a
23. For automatic adjustment of intersecting colliding prism layers while growing prisms do the following 1 Specify the prism growth parameters 2 Click the Growth Options button in the Growth tab to open the Prisms Growth Options panel see Section 10 10 1 The Prisms Growth Options Panel 3 Enable the appropriate options in the General Options group box 4 Specify the parameters required for the proximity calculation and controlling the prism layer height Enable Allow Shrinkage to allow shrinkage of prism layers in areas of proximity This option is enabled by default Enable Keep First Layer Offsets if required This option allows you to keep the original first offset height and scale the offset heights for the remaining layers in case of intersecting prism layers Specify an appropriate value for Gap Factor Enable Allow Ignore to ignore the prism growth parameters in areas of proximity Enter an appropriate value for Max Aspect Ratio or Max Shrink Factor as re quired Click Apply and close the Prism Growth Options panel 5 Click Create in the Prisms panel ANSYS Inc April 15 2008 10 9 Generating Prisms 10 3 4 Ignoring Invalid Normals Some geometries may contain regions where the normals considered while growing prisms may be invalid The normal at a particular node may be nearly tangential to the sur rounding faces in the geometry and as a result the prism generation may fail For such cases
24. Graphical User Interface 3 1 Console The TGrid Console is the main window that controls the execution of the program JE TGrid 3D Jal File Boundary Mesh Display Report Help nodes 684 reading 63 Ea three dimensional nodes id 1 type 1 ascii aces reading bee mixed faces Cid 2 type 3 ascii type 3 ascii type 3 ascii reading 228 mixed faces id 5 type 3 ascii reading 228 mixed faces id 6 type 3 ascii reading 226 mixed faces id 7 type 3 ascii no cells zone default interior doesn t exist skipping zone variables generating pointers don extracting boundary entities 84 boundary nodes 1361 boundary faces ERLIE interior boundary nodes extracting internal boundaries boundary exit mesh display file report Figure 3 1 1 The Console You can interact with TGrid through the Console in either of the following ways e graphical user interface GUI e text user interface TUI The Console contains a terminal emulator for the TUI and a menu bar for the GUI 3 1 1 Terminal Emulator The terminal emulator behaves in a similar manner as the xterm or other UNIX com mand shell tools or to the MS DOS Command Prompt window on the Windows sys tem It allows you to interact with the TUI menu For more information on the TUI see Chapter 5 Text User Interface All textual output from the program is printed in the terminal emulator and all typing is displayed on the
25. Select the appropriate actions to be performed during initialization from the Options group box The Merge Free Nodes and Delete Unused Nodes options are enabled by default You can also include improving the surface mesh in the mesh initialization process by enabling the Improve Surface Mesh option Select the appropriate option from the Non Fluid Type drop down list Enable Delet Dead Zones if required When the initial mesh is generated all the cells are grouped into contiguous zones separated by boundaries TGrid considers the mesh to comprise a single fluid zone and one or more dead regions The zone just inside the outer boundary is set to be active and is labeled a fluid zone All other non fluid zones will be inactive Only active zones will be considered for refinement during the mesh generation process You can refine different groups of zones using different refinement parameters for each group by toggling the zones between active and inactive If however you need to use the same refinement parameters for all the zones you can change the specification of Non Fluid Type to a type other than dead e g solid When the Non Fluid Type is set to a type other than dead all the zones will be activated after initialization Hence you can set the appropriate refinement parameters without setting all the zones to be active Specify additional initialization parameters if required These parameters are avail able in the Tri
26. i You should slit the boundary face after you generate the volume mesh so that TGrid will not place cells inside the gap There may be some inaccuracies when you graphically display solution data for a grid with a slit boundary in FLUENT boundary auto slit faces slits all boundary faces with cells on both sides these cells must be in the same cell zone A displacement can be specified to provide thickness to the boundary see Figure 7 15 1 7 94 ANSYS Inc April 15 2008 7 15 Additional Boundary Mesh Text Commands ie gap Figure 7 15 1 Slitting a Boundary Face Zone ANSYS Inc April 15 2008 7 95 Manipulating the Boundary Mesh 7 96 ANSYS Inc April 15 2008 Chapter 8 Wrapping Boundaries TGrid allows you to create a good quality boundary mesh using a bad quality surface mesh as input This can be done using the wrapper utility in TGrid The following sections discuss the procedure to use the wrapper and the parameters associated with it e Section 8 1 The Boundary Wrapper e Section 8 2 The Wrapping Process e Section 8 3 Examining and Repairing the Input Geometry e Section 8 4 Initializing the Cartesian Grid e Section 8 5 Examining the Cartesian Grid for Leakages e Section 8 6 Extracting the Wrapper Surface e Section 8 7 Checking the Quality of the Wrapper Surface e Section 8 8 Post Wrapping Improvement Operations e Section 8 9 The Boundary Wrapper Panel e Section 8 10 Text Commands for the
27. none determines the cell size distribution based on the Max Cell Volume and skewness This option is available only for the skewness based refinement Growth Rate specifies the growth factor for determining the cell size distri bution when the geometric method is selected from the Cell Size Function drop down list ANSYS Inc April 15 2008 11 19 Generating Triangular Tetrahedral Meshes Controls opens the Tri Tet Refine Controls panel see Section 11 5 2 The Tri Tet Refine Controls Panel Refine refines the mesh based on the specified parameters and activated regions Local Region opens the Tri Tet Refinement Region panel see Section 11 5 3 The Tri Tet Refinement Region Panel Init amp Refine initializes and refines the mesh Apply applies the parameters set in the Tri Tet panel 11 5 1 The Tri Tet Init Controls Panel The Tri Tet Init Controls panel allows you to set additional parameters to control the initial mesh generation Tri Tet Init Controls 4 Defaults Sliver Size 3 1556e 15 Node Tolerance 0 00644539 Controls Defaults enables the use of the default parameter values for mesh initialization Sliver Size is the smallest cell size which can be determined accurately Cells having a calculated size less than the specified sliver size will be assigned a size of zero This option is available only when the Defaults option is disabled Node Tolerance is the smallest d
28. report face zone at location reports the face zone at the specified location report list cell quality reports a list of cells with the specified quality measure within a specified range report memory usage reports the amount of memory used for all nodes faces and cells and the total memory allocated report mesh statistics writes mesh statistics such as range of quality range in size and number of cells faces and nodes to an external file report unrefined cells reports the number of cells that have not been refined report update bounding box updates the extents of the bounding box report verbosity level specifies how much information should be displayed during mesh initialization and refinement and other operations Changing the value to 2 from the default value of 1 will result in more messages while changing it to 0 will disable all messages 15 18 ANSYS Inc April 15 2008 Appendix A Importing Boundary and Volume Meshes The volume mesh generation scheme of TGrid requires sets of line segments 2D or tri angular and or quadrilateral elements 3D defining the boundaries of the computational domain In addition to the basic capability provided in GAMBIT data interfaces have been written to popular CAD CAE software packages for use by TGrid A 1 GAMBIT Meshes GAMBIT can create 2D and 3D surface and volume meshes See the GAMBIT Modeling Guide for details A 2 TetraMesher Volume Mesh ICEM CFD Engine
29. the adjacent nodes will be slightly more orthogonal to their faces For uniform distances this places the nodes for the first layer as shown in Figure 10 8 1 The dashed line connecting the new nodes begins to pinch inward at the corner The distances between parent and child nodes are still all the same but the angles of the direction vectors introduce this pinching effect Without some sort of correction such crevices can eventually collapse Minimum Height Offset Distance Method In this method child nodes are guaranteed to be at least as far from their parent nodes as the distance computed for the current layer from the growth inputs TGrid will also try to retain the shape of the original boundary a Fry Figure 10 8 2 Minimum Height Offset Distance Method For a perfect 90 degree corner this results in a perfect 90 degree corner for the next layer see Figure 10 8 2 Thus in this method the shape is better preserved if no additional smoothing is applied The minimum height method have some limitations If the angle of the direction vector at the corner is not 45 degrees i e if it does not exactly bisect the angle between the faces the minimum height method can increase skewness Aspect Ratio Method This method allows you to control the aspect ratio of the prism cells that are extruded from the base boundary zone The aspect ratio is defined as the ratio of the prism base length to the prism layer height The
30. 10 and 30 respectively nesh tritet improve smooth interior sliver smoothes non boundary nodes on sliver cells having skewness greater than the specified threshold value The default value for the skewness threshold is 0 985 ANSYS Inc April 15 2008 13 9 Improving the Mesh 13 5 The Tri Tet Improve Panel Tri Tet Improve CellZones General Slivers fuid 44 s Options Method Smooth Nodes y v Swap Faces 1 Weighted v Improve Improve Min Cell Skewness 0 3 Iterations 5 Y Min Improvement Cell Zone Groups 5 3 dead Relaxation Apply Controls Cell Zones contains a list from which you can select the cell zones to be improved Cell Zone Groups contains a list of the cell zone types If you select a cell type from the list e g fluid all cell zones of that type will be selected in the Cell Zones list General contains optios for smoothing nodes swapping faces and improving cells Options contains a list of the options available for improving the mesh Smooth Nodes smoothes the nodes to improve the mesh quality Method contains a list of the smoothing methods available in TGrid Weighted implies that the cell size as given by the cell size function at the neighboring nodes for the Laplace method or the circumcenter for the variational method is used to weight the influence of each node or circumcenter when computing the average node locat
31. 2008 Using This Manual How To Use This Manual Depending on your familiarity with computational fluid dynamics CFD and the TGrid software you can use this manual in different ways For the Beginner The suggested readings for the beginner are as follows e For information about how TGrid relates to and interacts with other products or about the motivation for unstructured grid generation read Chapter 1 Introduction to TGrid e To learn more about the user interface read Chapters 3 and 5 e To learn about reading and writing files see Chapter 6 File Types e For information about checking and improving a boundary mesh see Chapter 7 Ma nipulating the Boundary Mesh e To find out about the different types of meshes that TGrid can generate the meshing processes and how to solve or avoid meshing problems see Chapters 9 12 e To learn about checking the quality of the mesh see Chapters 14 and 15 e To find out how to use the on line help in TGrid read Section 3 6 Using the GUI Help System Depending on the characteristics of your particular problem and the tools you want to employ use the table of contents and the indexes to find the relevant information For the Experienced User If you are an experienced user who needs to look up specific information there are different tools that allow you to use the TGrid User s Guide as a reference manual e The table of contents lists topics that are discussed in a
32. ANSYS Inc April 15 2008 11 7 Generating Triangular Tetrahedral Meshes i By default the Non Fluid Type is set to dead as TGrid considers the grid to comprise a single fluid region and one or more dead regions The active zone is considered to be the fluid zone and only this fluid zone will be considered for refinement during the automatic meshing process When the Non Fluid Type is set to a type other than dead e g solid all the zones will be active after the initialization is complete Hence all the zones will be considered for refinement If required you can change the zone type using the Manage Cell Zones panel see Section 13 9 3 The Manage Cell Zones Panel Step 3 Refining the Mesh You will refine the initial mesh by adding cells at the boundary and in the interior The refinement methods available are the skewness based method and the advancing front method You can also define local refinement regions using the Tri Tet Refinement Region panel You can modify the parameters in the Refinement tab of the Tri Tet panel and select additional refinement options for skewness based refinement in the Tri Tet Refine Controls panel if required Step 4 Improving the Mesh You can improve the skewness by smoothing swapping and refining the mesh further to improve the quality of the volume mesh At any point in the mesh generation process you can compute and or plot the cell skewness distribution using the Cell Distribution pa
33. April 15 2008 14 1 Examining the Mesh 14 1 Displaying the Grid In TGrid you can manipulate the display of grid entities and modify the way in which they appear in the graphics window TGrid allows you to draw selected boundary zones unmeshed faces free or multiply connected faces and unused nodes You can also control the display of items using intrinsic parameters such as skewness When you specify a range for a particular parameter TGrid will display entities that satisfy that condition If more than one range limitation is specified then only those entities that match all specified range limitations are drawn You can also specify information regarding color display of solid filled faces and shrink age of faces and cells These features can help you visualize your mesh effectively and quickly determine the cause of any problems in the mesh You can perform these opera tions using the Display Grid panel and the associated set of panels or using the associated text commands The Display Grid panel consists of a series of tabbed frames within the main panel Each tab has a set of related controls and the active tab is indicated by the labeled button which appears depressed The Nodes Faces and Cells tabs contain controls and zone lists specific to those entity types The Bounds tab contains controls allowing you to limit the display to objects within specific coordinate ranges or within a distance to a selected objec
34. April 15 2008 6 17 File Types Click Apply instead of Save to save the current hardcopy settings instead of saving a hardcopy The applied settings will become the defaults for subsequent hardcopies Choosing the Hardcopy File Format To choose the hardcopy file format select one of the following options in the Format list EPS Encapsulated PostScript output is the same as PostScript output with the addition of Adobe Document Structuring Conventions v2 statements Currently no preview bitmap is included in EPS output Often programs which import EPS files use the preview bitmap to display on screen although the actual vector PostScript information is used for printing on a PostScript device You can save EPS files in raster or vector format IRIS Image is the native raster image file format on SGI computers The IRIS Image driver may not be available on all platforms JPEG is a common raster file format PP M output is a common raster file format PostScript is a common vector file format You can also choose to save a PostScript file in raster format TIFF is a common raster file format The TIFF driver may not be available on all PN VR platforms G is a common raster file format ML is a graphics interchange format that allows export of 3D geometrical entities that you can display in the TGrid graphics window This format can commonly be used by VR systems and in particular the 3D geometry c
35. Direction allows you to specify the direction of the light the position on the unit sphere from which the light emanates by entering the X Y and Z coordinates or by computing the coordinates based on the current view in the graphics window ANSYS Inc April 15 2008 14 37 Examining the Mesh X Y Z specify the direction of the light For example the direction 1 1 1 means that the rays from the light will be parallel to the vector from 1 1 1 to the origin Use View Vector updates the X Y Z fields with the appropriate values for the current view in the active graphics window and shines a light in that direction Instead of entering the X Y Z values for a light s direction vector use the mouse to change the view in the graphics window so that the position in reference to the geometry is the position from which you would like a light to shine Then click on the Use View Vector button to update the X Y Z fields with the appropriate values for the current position and update the graphics display with the new light direction This method is convenient if you know where you want a light to be but you are not sure of the exact direction vector Color allows you to specify the light color with sliders You can create your desired color by increasing and decreasing the slider values for the colors Red Green and Blue You can also enter a descriptive string e g lavender in the Color field Active Lights shows the position and
36. Display updates the display according to the options selected in all frames in the Display Grid panel All options are saved before the display is updated as if you had clicked the Apply button Apply saves the options selected in all frames of the Display Grid panel but does not update the display The Display and Applybuttons along the bottom of the panel apply to all controls in all frames of the panel i e for all tabs For example you can change some controls in the Faces tab then click the Bounds tab and change some controls there and then click Display to draw the grid with the new settings Even though a tab s controls are not visible its current settings affect the display 14 1 4 Text Commands for Displaying the Grid The following text interface commands are similar in functionality to the controls in the Display Grid panel display all grid displays the grid according to the currently set parameters display boundary cells displays boundary cells attached to the specified face zones display boundary grid displays only boundary zones according to the currently set parameters display draw cells using faces draws cells that are neighbors for the selected faces display draw cells using nodes draws cells that are connected to the selected nodes ANSYS Inc April 15 2008 14 11 Examining the Mesh display draw face zones using entities displays the neighboring face zones of the selected entity display d
37. E 6 merging 7 16 move by 7 17 move to 7 17 moving 7 17 radius 15 16 Bib 9 Index smoothing 7 18 unmeshed 14 6 15 1 unused 14 5 nodes deleting 7 75 Non Conformals panel 9 22 non conformal meshes 9 8 non manifold 14 6 normals displaying 14 10 flipping 7 76 10 3 10 28 orienting 7 76 10 3 10 28 smoothing 10 17 offset distance 10 18 smoothing 10 21 offset scaling 9 18 online help 3 19 orientation 10 40 orienting boundary faces 7 76 normals 7 76 orienting normals 10 3 10 28 orthogonality 10 10 orthographic view 14 35 Outer Box Zones panel 12 10 Page Setup panel 3 16 Pan Regions panel 8 43 panel layout 6 24 panels 3 9 Annotate 14 49 Auto Node Move 13 20 Axes Histogram 14 22 Boundary Wrapper 8 30 Bounding Box 7 80 Bounding Frame 14 44 Call Distribution 14 20 Camera Parameters 14 33 Cavity Remesh 13 24 Create Boundary Zones 7 27 Display Grid 14 4 Display Options 14 24 Display Properties 14 41 Bib 10 Domains 13 34 Face Distribution 14 17 Feature Modify 7 49 Grid Colors 14 13 Hexcore 12 8 Intersect Boundary Zones 7 10 Lights 14 36 Make Periodic Boundaries 7 90 Manage Cell Zones 13 28 Manage Face Zones 7 74 Mirror Planes 14 32 Modify Boundary 7 22 Modify Cells 13 15 Mouse Buttons 14 45 Mouse Probe 14 48 Pan Regions 8 43 Plane Surface 7 83 Project Face Zone 7 70 Quality Measure 15 13 Refine Boundary Zones 7 37 Report Bo
38. Gray Scale wv Monochrome Radio buttons are a set of check buttons that allow only one to be set in the on position at a time When you click the left mouse button on a radio button it will turn on and all others will be turned off Text Entry Hame outlet A text entry lets you type the text input It will often have a label associated with it to indicate what the entry is for Integer Number Entry Iteration 25 ANSYS Inc April 15 2008 3 11 Graphical User Interface An integer number entry is similar to a text entry except it allows only integer numbers to be entered e g 10 10 50000 and 5e4 The integer number entry also has arrow buttons that allow you to increase or decrease its value Click on the up or down arrow button to increase or decrease the value by one You can increase the size of the increment by holding down a keyboard key while clicking the arrow button The keys used are Key Factor of Increase Shift 10 Ctrl 100 Real Number Entry Max Allowable Skewness Oo 95 A real number entry is similar to a text entry except it allows only real numbers to be entered e g 10 10 538 50000 45 and 5 e 4 In most cases the label will show the units associated with the real number entry Single Selection List Face Zones bottom inlet left outlet right top 3 12 ANSYS Inc April 15 2008 3 3 Panels A single selection
39. Neighborhood settings Center changes the display to place the selected object in the center of the view ANSYS Inc April 15 2008 14 9 Examining the Mesh Compute sets the range to include the entire geometry Reset restores the controls to their default settings i e no limits on x y or z range The previously set maximum and minimum values for each range will remain visible but they will be grayed out indicating that they are not in effect Attributes contains options for customizing the display H Display Grid Nodes Faces Cells Bounds Attributes Edge Type Label Scale Edges All 1 F Filled v Feature tiarmoi Seale Colors F Lights i wy Outline 1 Lights Shrink Factor Circumcircles aaa Rendering Feature Angie _t Labels 9 z Rendering 135 _ Normals Styles Options allows you to select one or more of the following options Edges enables display of face edges Filled enables faces and cells to be drawn with filled polygons This is most useful when the Lights option is enabled Lights enables display lighting to make the display realistic This is only useful if Filled is enabled Circumcircles allows you to display face circumcircles for triangular faces Labels allows you to display labels You can control the size of the labels using an appropriate Label Scale Normals enables the display of face normals You can control the size of the normal ve
40. The surface that you want to wrap or recover is region 1 Display each region created during the Cartesian grid initialization process using the Draw button below the Region list in the Region tab of the Boundary Wrapper panel Ensure that region 1 is the largest region and forms a faceted watertight representation of the boundaries of the input geometry Examine region 1 and make sure that the cell sizes are according to your require ment If you are not satisfied with the cell size distribution of the Cartesian grid specify appropriate values for Zone Specific Size and Local Size Functions for the individual or required zones to obtain an appropriate Cartesian grid in the cor responding zones Refine the Cartesian grid if required Before wrapping the boundary regions examine the configuration of the Cartesian grid around critical zones of the domain such as sharp curves and edges If the cell size after the automated grid initialization is too large around such zones reduce the cell sizes a Select the zone s for which you want to specify local size functions from the Tri Boundary Zones selection list ANSYS Inc April 15 2008 8 5 Examining the Cartesian Grid for Leakages b Specify appropriate Zone Specific Size parameters and Local Size Function pa rameters Fa If you specify Zone Specific Size as well as Local Size Function parameters for a particular boundary zone the Cartesian grid will take the minimu
41. Vector supports PostScript EPS and VRML formats For the quickest print time save vector files for simple 2D displays and raster files for complicated scenes For raster hardcopy files you can control the resolution of the hardcopy image by specifying the size in pixels ANSYS Inc April 15 2008 E 3 Tips E 4 Most monochrome PostScript devices will render Color images in shades of gray To ensure that the color ramp is rendered as a linearly increasing gray ramp select Gray Scale For all formats except the window dump you can specify which type of Coloring you want to use for the hardcopy file For all hardcopy formats except the window dump you can control two additional settings under Options For PostScript and EPS files specify the resolution in dots per inch DPI instead of setting the width and height Each time you create a new window dump the value of n will increase by one so you there is no need to track numbers onto the hardcopy filenames manually If you are planning to make an animation save the window dumps into numbered files using the n variable To do this use the Window Dump Command Enter myfile n xwd as the filename in the Select File dialog box If you use the ImageMagick animate program save the files in MIFF format the native ImageMagick format It is more efficient When saving window dumps remember that the window dump will capture the window exactly as it is displayed inclu
42. at atime This is useful when handling a large and complicated mesh 8 7 Checking the Quality of the Wrapper Surface The quality of the wrapper surface can be checked using the options available in the Reports tab You can display the contours of Distance Normal or Composite and check the deviation of the wrapper surface from the original geometry You can also iden tify problems like crossover configurations insufficient geometry representation using the contours of quality 1 Click the Reports tab and select the wrapper surface in the Tri Boundary Zones list 2 Enable Node Value and or Auto Range as appropriate in the Contour Options group box 3 Select Distance Normal or Composite as appropriate in the Contours of drop down list 4 Set the Levels as appropriate and click Draw Contours Figure 8 7 1 shows a sample display of contours of distance of the wrapper surface from the input geometry The red patches in the display indicate that at such locations wrapper surface does not exactly represent the input geometry You will use the available post wrapping operations to improve the wrapper surface at such locations 8 8 Post Wrapping Improvement Operations The wrapper surface created after imprinting is of good quality and it represents the input geometry very well in most regions However you can improve it further in some regions of the geometry such as sharp corners and curves The post wrapping improvement operations allow
43. button in the Display Grid panel to open the Grid Colors panel By default the Color by Type option is selected allowing you to assign colors based on zone type 2 To change the color assigned to a particular zone type select the zone type in the Types list 3 Select the required color in the Colors list 4 If you prefer to assign colors based on the zone ID select the Color by ID option You can set colors individually for the grid displayed on each of the zones using the Scene Description panel see Section 14 8 1 The Scene Description Panel Adding Features to an Outline Display For closed 3D geometries the standard outline display may not show sufficient details to accurately depict the shape This is because for each boundary only the edges on the outside of the geometry i e those used by only one face on the boundary are drawn You can capture additional features using the Feature option in the Display Grid panel see Section 14 1 3 The Display Grid Panel Specify an appropriate value for the Feature Angle to obtain the outline display required Shrinking Faces and Cells in the Display To distinguish individual faces or cells in the display you may want to enlarge the space between adjacent faces or cells by increasing the Shrink Factor in the Display Grid panel see Section 14 1 3 The Display Grid Panel The default value of zero produces a display in which the adjacent faces or cells overlap A value of 1 cr
44. height offset method is used this direction method may introduce spikes and pits in the advancing layer surfaces surface average is similar to face average but handles sharp edges better This is the default method in 3D mnesh prism controls normal orthogonal layers specifies the number of layers to preserve orthogonality All smoothing is deferred until after these layers have been generated mesh prism normal smooth enables or disables smoothing of normal direction vec tors ANSYS Inc April 15 2008 10 37 Generating Prisms mesh prism normal smooth converged sets the convergence criterion in degrees for normal smoothing If the normal directions are changing by less than this value smoothing iterations will stop mnesh prism normal smooth iter specifies the maximum number of normal smooth ing iterations to be performed for the normal vectors on each layer These iterations will be performed until the convergence criterion is reached mesh prism controls offset smooth enables disables offset distance smoothing nesh prism controls offset smooth converged sets the convergence criterion for offset smoothing If the offset heights change by less than this value smoothing iterations will stop nesh prism controls offset smooth iter sets the maximum number of offset smooth ing iterations to be performed These iterations will be performed until the con vergence criterion is reached nesh prism controls pr
45. menu and the menu prompt is simply a caret ANSYS Inc April 15 2008 5 1 Text User Interface To generate a listing of the submenus and commands in the current menu press lt RETURN gt gt file mesh report boundary display exit By convention submenu names end with a to differentiate them from menu commands To execute a command type its name or an abbreviation Similarly to move down into a submenu enter its name or an abbreviation When you move into the submenu the prompt will change to reflect the current menu name display display gt set display set gt To move back to the previously occupied menu type q or quit at the prompt display set gt display gt You can move directly to a menu by giving its full pathname display gt file display file gt In the above example control was passed from display to file without stopping in the root menu Therefore when you quit from the file menu control will be passed directly back to display display file gt display gt If you execute a command without stopping in any of the menus along the way control will again be returned to the menu from which you invoked the command 5 2 ANSYS Inc April 15 2008 5 1 Text Menu System display gt file start journal jrnl Input journal opened on file jrnl display gt
46. menu item or the text command file read mesh e If the boundary mesh is contained in two or more separate files you can read them together TGrid will assemble the complete boundary mesh for you e To read a 2D mesh into the 3D version of TGrid use the File Import Fluent 2D Mesh menu item or the file import fluent 2d mesh text command ANSYS Inc April 15 2008 E 1 Tips To read a 3D mesh into the 2D version of TGrid use the File Import Fluent 3D Mesh menu item or the file import fluent 3d mesh text command Read a compressed file using the text interface by entering the file name First TGrid attempts to open a file with the input name If it cannot find a file with that name it attempts to locate files with default suffixes and extensions appended to the name The compressed file read will fail if the compress or GNU gzip compression routines are not available on your platform Scheme source files can be loaded in three ways through the menu system as a scheme file through the menu system as a journal file through Scheme itself TGrid cannot read grids from the solvers that have been adapted using hanging nodes If you wish to read one of these grids into TGrid you will need to coarsen the mesh within the solver until you have recovered the original unadapted grid Only one journal file can be open for recording at a time but you can write a journal and a transcript file simultaneously You can also
47. panel will be highlighted The highlighting will be updated when you click on the Change button after modifying your selections in the Boundary Zones list For Node Zones Cell Zones and Face Zones you cannot modify the face zones in a given domain by changing this list This list shows by highlighting the node zone cell zones and face zones respectively that are contained in the domain as you have defined it Activate sets the domain selected in the Domains list to be the active domain When you create the volume mesh only those zones that are in the active domain will be meshed When you display the grid the zones available for display will be only those zones that are included in the active domain Similarly diagnostic reports will report information about only those zones If you want to check a subset of the global domain you can create and activate a domain that includes the desired zones and then proceed with the display or report If you want your grid display or report to include all zones in the domain be sure to activate the global domain The Activate button will be disabled as soon as a domain is activated It will become available again if you select a different domain When a new domain is created it will automatically be identified as the active domain and the Activate button will be disabled Draw displays the grid for the selected Boundary Zones based on the current settings in the Display Grid panel see
48. solid all the zones will be active after the initialization is complete Hence all the zones will be considered for refinement If required you can change the zone type using the Manage Cell Zones panel see Section 13 9 3 The Manage Cell Zones Panel Select the appropriate type from the Non Fluid Type drop down list in the Tri Tet Zones group box in the Tri Tet panel before initializing the mesh 11 1 4 Automatic Meshing for Hybrid Meshes The Auto Mesh tool in TGrid can also create prisms and pyramids automatically allowing automatic generation of hybrid meshes e If a mix of surface mesh types quadrilateral and triangular is present in the domain TGrid will create pyramid cell zones on the quadrilateral boundary faces before meshing the tetrahedral domain e If prism growth parameters have been attached to a boundary zone using the Prisms panel see Section 10 10 The Prisms Panel TGrid will automatically ex trude the prism layers before meshing the tetrahedral domain When pyramids or prisms are generated using the automatic mesh generation fea ture the intermediate boundary zones will be merged automatically after the tetra hedral mesh generation is complete This enhancement avoids the creation of addi tional boundary zones such as prism side and pyramid cap Sections 10 4 and 9 3 2 e TGrid also allows you to transition from quad to tri faces using the Non Conformals option This option is useful when you want to
49. that define the boundaries of the domain and have been grouped within ANSYS using node and element selection For volume meshes the filter reads a 2D or 3D mesh that has its boundary nodes grouped within ANSYS using node and element selection All boundary zones will be considered wall zones you can set the appropriate boundary types in TGrid or in the solver See Section A 3 1 Using the fe2ram Filter to Convert Files for information about using the fe2ram grid filter Recognized Datasets The following datasets are recognized by the grid filter NBLOCK node block data EBLOCK element block data CMBLOCK element node grouping The elements must be STIF63 linear shell elements In addition if element data without an explicit element ID is used the filter assumes sequential numbering of the elements when creating the zones Periodic Boundaries In general it is difficult to generate a valid grid with periodic boundaries in ANSYS However a special feature exists in TGrid that allows you to generate a grid in a domain with periodic boundaries See Section 7 14 5 Creating Periodic Boundaries for further details ANSYS Inc April 15 2008 A 5 Importing Boundary and Volume Meshes A 3 5 ARIES Files ARIES provides a filter to TGrid or you may write a Prep7 file from ARIES and use the fe2ram filter with arguments for an ANSYS file For more information on importing ANSYS files see Section A 3 4 ANSYS Files In general t
50. the triangulation tends towards equilateral cells providing the most equilateral grid for the given node distribution 13 2 2 Tetrahedral Grids For tetrahedral grids swapping involves searching for a specific configuration of cells and replacing it by an alternative configuration The default option is a 3 2 swap configu ration where three tetrahedra are replaced by two tetrahedra after swapping The other possible combinations are the 2 3 swap configuration replacing two tetrahedra by three and the 4 4 swap configuration replacing four existing tetrahedra with four alternate tetrahedra 13 4 ANSYS Inc April 15 2008 13 3 Improving the Mesh Figure 13 2 3 shows the 2 3 and 3 2 swap configurations The two tetrahedra on the left having a common interior face can be replaced by three tetrahedra having a common interior edge The common face will be replaced by three interior faces and an interior edge during swapping Conversely the three tetrahedra on the right have two interior faces each and share a common interior edge During swapping for a 3 2 configuration three interior faces and the common interior edge will be replaced by a single face This results in two tetrahedra having a common interior face 2 3 Swap gt 3 2 Swap Figure 13 2 3 2 3 and 3 2 Swap Configurations Another possible swap configuration is the 4 4 swap confguration where four tetrahedra will be replaced by four
51. there will be multiply connected edges Note Duplicate faces can be handled in TGrid and hence it is not necessary to remove them Extra Nodes or Faces Nodes that are not used by any face are called unused nodes The unused nodes can easily be found and deleted using the operations described in Section 7 1 2 The Merge Boundary Nodes Panel if they are not required However there are cases where these additional nodes may be useful see Section 9 1 7 Inserting Isolated Nodes into a Tri or Tet Mesh Extra faces can be identified and removed using the method described for duplicate faces Intersecting Faces If there are intersecting faces in the mesh TGrid will not be able to generate a mesh until the problem faces are removed Most intersecting faces can be located using the boundary mark face intersection command Also TGrid will report boundary face intersection if encountered during initialization After the meshing fails the unmeshed faces can be drawn to see the problem area Usually since the intersecting face will have been meshed it will not be drawn and some additional sleuthing will be required Draw all the faces near the unmeshed faces by setting display bounds see Section 14 1 3 The Display Grid Panel Click the Mark button in the Intersect Boundary Zones panel see Section 7 2 5 The Intersect Boundary Zones Panel to highlight the face intersection Alternatively you can use the command boundary mark face interse
52. various growth methods constant linear geometric and exponential can be used to specify the aspect ratio of the first layer When a non constant growth method is used the aspect ratio for subsequent layers will change accordingly The heights of the prism cells will vary according to the local face sizes in the surface mesh providing a convenient way to automatically vary prism heights across a zone Last Ratio Method This method also allows you to control the aspect ratio of the prism cells that are extruded from the base boundary zone You can spec ify First Height for the first prism layer If you select this method the various ANSYS Inc April 15 2008 10 8 Offset Distances growth methods will not be accessible The last aspect ratio method is explained in Figure 10 8 3 Local base Imesh size Last layer offset height Figure 10 8 3 Last Ratio Method Local base mesh size is used to find out the offset height for the last layer For example if you specify 80 as the Last Percent value the offset height of the last layer will be 0 8 times the local base mesh size Local growth rate is used to calculate the other intermediate offset heights exponentially Offset Smoothing The purpose of offset smoothing is to eliminate spikes and dips in the new surface layer Smoothing is applied iteratively Figure 10 8 4 shows how the nodes are moved during offset smoothing node position after of
53. 11 14 ANSYS Inc April 15 2008 11 4 Refining the Tri Tet Mesh 5 Modify the refinement control parameters if required e For the skewness method click the Controls button to open the Tri Tet Refine Controls panel see Section 11 5 2 The Tri Tet Refine Controls Panel Select the appropriate option from the Preset Parameters drop down list Verify the parameter values in the Tri Tet Refine Controls panel and modify the values as appropriate e For the advancing front method use the commands available in the mesh tritet controls adv front method menu You can also specify the targeted skewness for the refinement process see Section 11 4 Refinement Controls for details 6 To refine specific regions of the mesh click the Local Regions button to open the Tri Tet Refinement Region panel see Section 11 5 3 The Tri Tet Refinement Region Panel Define the refinement region s and activate them The number of activated regions will be reported in the Message field in the Refinement tab of the Tri Tet panel 7 Click Refine to refine the mesh 11 4 3 Text Commands for Setting Refinement Controls The text interface commands for setting refinement parameters are as follows mesh tritet refine refines the initialized mesh mesh tritet controls adv front method first improve params defines the refin ing front improvement parameters for the advancing front method mesh tritet controls adv front method second improve
54. 15 10 27 height 10 24 meshing problems 10 39 growing too far 10 42 ANSYS Inc April 15 2008 high skewness 10 41 large jumps in prism height 10 42 left handed faces 10 41 negative volume 10 41 orientation 10 40 retriangulation failure 10 40 too few nodes 10 40 too many nodes 10 40 unknown face combinations 10 40 orthogonality 10 10 proximity detection 10 7 side faces 10 11 two sided walls 10 6 prism meshing problems 10 39 free nodes 10 40 growing too far 10 42 high skewness 10 41 large jumps in prism height 10 42 left handed faces 10 41 negative volume 10 41 orientation 10 40 retriangulation failure 10 40 too few nodes 10 40 too many nodes 10 40 unknown face combinations 10 40 Prisms Growth Options panel 10 32 Prisms panel 10 23 problems prism meshing 10 39 program capabilities 1 4 program capabilities 1 4 program structure 1 2 Project Face Zone panel 7 70 projection 10 13 pull down menu 3 4 pyramid 9 1 generation 9 14 new zones created during 9 16 problems 9 20 meshing problems 9 20 side faces 9 16 pyramids Bib 11 Index cap faces 9 16 Pyramids panel 9 17 quadrilateral 9 1 quality 15 8 cell 14 8 14 20 face 14 6 14 17 measures 15 8 specifying 15 13 mesh 15 8 plotting cell distribution 14 19 face distribution 14 17 reporting 15 3 15 5 15 6 Quality Measure panel 15 13 quality measures 15 9 aspect ratio 15 9 clustering 15 9 dihedra
55. 2D and 3D is mouse zoom Right sets the function associated with the right button This is not used on a two button mouse The default setting for both 2D and 3D is mouse probe FLUENT Defaults sets the mouse button functions according to FLUENT defaults Workbench Defaults sets the mouse button functions according to Workbench defaults The predefined button functions available are follows mouse rotate allows you to rotate the view by dragging the mouse across the screen Dragging horizontally rotates the object about the y axis of the screen vertical mouse movement rotates the object about the x axis of the screen The function completes when the mouse button is released or the cursor leaves the graphics window mouse dolly allows you to translate the view by dragging the mouse while holding down the button The function completes when the mouse button is released or the cursor leaves the graphics window mouse zoom allows you to draw a zoom box anchored at the point at which the button is pressed by dragging the mouse with the button held down When you release the button e If the dragging was from left to right a magnified view of the area within the zoom box will fill the window e If the dragging was from right to left the area of the window shrinks to fit into the zoom box resulting in a zoomed out view e If the mouse button is clicked not dragged the selected point becomes the center of the window mouse ro
56. 2D or 3D mesh that has its boundary nodes grouped by named component to create boundary zones All boundary zones will be considered wall zones you can set the appropriate boundary types in TGrid or in the solver See Section A 3 1 Using the fe2ram Filter to Convert Files for information about using the fe2ram grid filter Recognized PAT RAN Datasets The following Neutral file datasets are recognized by the grid filter Node Data Packet Type 01 Element Data Packet Type 02 Distributed Load Data Packet Type 06 Node Temperature Data Packet Type 10 Name Components Packet Type 21 File Header Packet Type 25 ANSYS Inc April 15 2008 A 3 Meshes from Third Party CAD Packages Grouping Elements to Create Zones In PATRAN named components are applied to the nodes to create groups of faces called zones In FLUENT boundary conditions are applied to each zone For instance all nodes on a curve or patch may be put in a Name Component For 2D volume meshes an additional constraint is placed on the elements existence in the Z 0 plane Periodic Boundaries In general it is difficult to generate a valid grid with periodic boundaries in PATRAN However a special feature exists in TGrid that allows you to generate a grid in a domain with periodic boundaries See Section 7 14 5 Creating Periodic Boundaries for further details A 3 4 ANSYS Files For ANSYS surface meshes the filter reads triangular and quadrilateral linear elements
57. 6 0 ba eV OS we HS 14 13 14 1 6 Text Commands for Grid Colors lt e e lt s sss eee bee aws 14 14 14 1 7 The Style Attributes Panel o a aaa a 14 15 14 1 8 Text Commands for Style Attributes aaoo aaa 14 17 14 2 Checking Face Distribution s ec sc ressor besedo tleas 14 17 14 2 1 The Face Distribution Panel s oc o coi e ce bod sedd ee eG 14 18 14 22 Face Distribution Text Interface 24 ss sde ha tae oa rs 14 20 14 3 Checking Cell Distrib ti n s lt seo de oe eed E eed ew BO es 14 20 1424 Te Cell Distribution Panel 2 5046 s s aeg en ackoa ad 14 21 14 3 2 Cell Distribution Text Interface 14 22 14 4 Modifying the Attributes of the Plot Axes 14 22 14 4 1 The Axes Histogram Panel u lt 4 22s kk eae ee Deda 14 23 14 4 2 Text Interface for Modifying Axes Attributes 14 25 14 5 Controlling Display Opti ns s s cs st soem 4 2 44 eaa HG e442 04 14 25 14 5 1 The Display Options Panel oaoa aaa GH eH HD 14 26 14 5 2 Text Commands for Controlling Display Options 14 29 14 6 Modifying the View 24 2266 2 4 444 424445 raat eo 14 31 14 6 1 Whe Views Panel 2 24444 a rond 64446 4444444 5 14 32 14 6 2 The Write Views Panel 29 24 2204 2 lt 4 me lt 8 dee eae 14 33 TOC 12 ANSYS Inc April 15 2008 CONTENTS 14 6 3 The Mirror Planes Panel 2 2 14 6 4 The Camera Parameters Panel 14 6 5 Text Commands for Modifying
58. 6 9 Saving Hardcopy Files Save opens the Select File dialog box where you can specify a name for the hardcopy file and then save it The resulting file will contain a hardcopy of the active graphics window Apply saves the current settings TGrid will use these settings when making subsequent hardcopies Preview applies the saved settings to the currently active graphics window so the effects of different options may be investigated interactively 6 9 3 Text Interface for Saving Hardcopy Files Text commands for saving hardcopy files and modifying hardcopy options are display hard copy saves a hardcopy file of the active graphics window display set hardcopy color mode contains the available color modes display set hardcopy color mode color selects full color display set hardcopy color mode gray scale selects gray scale i e various shades of gray display set hardcopy color mode mono chrome selects black and white display set hardcopy color mode list displays the current hardcopy color mode display set hardcopy driver contains the available hardcopy formats display set hardcopy driver dump window sets the command to dump a graphics window to a file display set hardcopy driver eps sets Encapsulated PostScript format display set hardcopy driver image sets IRIS image format display set hardcopy driver jpeg sets JPEG image format display set hardcopy driver post script sets PostScript format display set hardcopy
59. 6 Using Adjacent Zones as the Sides of Prisms 10 7 Direction Vectors s scos soret oe 4 Roo Keds e 10 8 Offset Distances 2 oa a ee ene Be a 10 9 Improving Prism Quality 2 04 ee sed Ba RW ee eed 10 9 1 Edge Swapping and Smoothing 1002 Node Smoothing s esda ssr 244544444 4 109 3 Improving Warp ue ye se he eee Se ES 10 10 The Prisms Pomel coros ghi e ee a Reed ee RE eed 10 10 1 The Prisms Growth Options Panel 10 11 Text Interface for Generating Prisms 10 12 Prism Meshing Problems gt i ee es eee doa ee renei 11 Generating Triangular Tetrahedral Meshes 11 1 Automatically Creating a Tri or Tet Mesh 11 1 1 Automatic Meshing Procedure for Tri Tet Meshes 11 1 2 Using the Auto Mesh Tool 11 1 3 Automatic Meshing of Multiple Cell Zones 11 1 4 Automatic Meshing for Hybrid Meshes 11 1 5 Further Mesh Improvements 11 2 Manually Creating a Tri or Tet Mesh 11 2 1 Manual Meshing Procedure for Tri Tet Meshes 11 3 Initializing the Tri Tet Mesh vecse onei sarei sarei 11 3 1 Using the Tri Tet Panel aces fee ea dus 11 3 2 Text Commands for Initializing the Mesh 11 4 Refining the Tri Tet Mesh xc ee ee a ee eS eS 11 4 1 Using Local Refinement Regions 11 4 2 Using the Tri Tet Panel 11 4 3 Text Commands for Setting Refinement Controls 11 5 The Tri Tet Patel ocr ce sb
60. 7 36 7 5 2 The Refine Boundary Zones Panel 2 7 38 7 5 3 Text Commands for Boundary Zone Refinement 7 42 7 6 Creating and Modifying Features 2 02004 7 42 7a Grea ting Edge Loops ses iee po oe hee ee ORE As 7 43 7 6 2 Modifying Edge Loops sc ss srir SAE Pa ESS 7 47 7 6 3 The Feature Modify Panel aaau 7 50 7 6 4 Text Commands for Creating and Modifying Features 7 53 ta Reme shing Boundary Zones oao ee Se dd ae EK Ph ORE SR eS 7 54 ANSYS Inc April 15 2008 TOC 5 CONTENTS TOC 6 7 8 to 7 10 TAa 1 12 7 13 7 14 titel Creating Edge Loops seori s eb ee wee ee HEH oe eS 7 54 toa Modifymg Edge Logps c s lt e sea e nba temma bos OES 7 55 7 7 3 Remeshing Surface Zones 2 0 ee es 7 55 7 7 4 Remeshing Zones Using the Surface Retriangulation Panel 7 56 7 7 5 The Surface Retriangulation Panel 0 7 57 7 7 6 Text Commands for Remeshing 7 59 Faceted Stitching of Boundary Zones 5 lt 2 use oe v4 bee ey eo 7 61 feel The Faceted Stitch Panel oe giie 4 lt 4 as ee bee RR HRS 7 62 Triangulating Boundary Zones lt 2 4 444 ds ediad edatia tani 7 63 7 9 1 The Triangulate Zones Panel ooa aaa 7 63 Separating Boundary Zones 6 3 6 rrea resed resetear du 7 64 7 10 1 Methods for Separating Face Zones oaoa aa a 7 64 7 10 2 The Separate Face Zones Panel o oo a aaa a 7 68 7 10 3 Text Commands for Separating Face Zones
61. Adjacent Zone Angle in the Project tab of the Prisms panel The default threshold value is 45 degrees For example if you are growing prisms from the bottom surface in Figure 10 6 1 using the default maximum adjacent zone angle of 45 degrees the zone on the left will be excluded but the zone on the right will be used as it is A new zone will be created for the left sides of the prisms create new zone for prism side F use adjacent zone growth direction han adjacent zone angle 0 adjacent zone angle 60 Figure 10 6 1 Effect of Adjacent Zone Angle To fill in the gap on the left side of Figure 10 6 1 in 2D create a domain enclosing the gap and generate triangular cells or in 3D create pyramids using the prism side faces create a domain and generate tetrahedral cells 10 14 ANSYS Inc April 15 2008 10 6 Using Adjacent Zones as the Sides of Prisms Projecting to Adjacent Triangular Face Zones If an adjacent zone has triangular faces TGrid will perform two additional steps to incorporate the zone into the prism layers projection and retriangulation TGrid will project the outer nodes of the prisms onto the triangular faces of the adjacent zone provided it satisfies the following requirements e It must share nodes with the boundary zone from which you are building the prisms That is there must be no free nodes see Section 7 1 1 Free and Isolated Nodes where the zones touch e The angle
62. Aspect Ratio Max Skewness and Max Size Change 4 Click Apply TGrid will report the improvement operations performed and the quality at the end of the auto improvement in the console Recovering a Single Surface Certain geometries may have sheet metal components which have a small thickness and which are connected to other components The post wrapping improvement options include the recovery of such thin sheets as a single surface after wrapping You can either use the Automatic option to mark the thin parts or manually select the faces on opposite sides of the thin part The marked faces will then be merged to obtain a single surface You can also remove unmerged island regions after recovering the surfaces To recover a single surface for thin parts do the following 1 Select Expert in the Options drop down list and Recover Single Surface in the Sub Options list respectively 2 Select Single Surface in the Recover Options list 3 Enable Automatic and click Mark to mark the faces to be merged in thin parts Alternatively disable Automatic and click the Select button in the Parameters group box Select the seed faces as appropriate and click Mark to mark the faces to be merged 4 Specify appropriate values for Critical Thickness and Critical Angle 8 30 ANSYS Inc April 15 2008 8 8 Post Wrapping Improvement Operations 5 Click Merge to merge the thin surfaces into a single surface Figure 8 8 5 shows the recover
63. CTRIA3 tetrahedral and triangular elements ANSYS Inc April 15 2008 A 3 Meshes from Third Party CAD Packages CHEXA CQUAD4 CPENTA hexahedral quadrilateral and wedge elements Since TGrid uses linear elements you should use linear elements in the mesh generation process If parabolic elements exist in the dataset the filter ignores the mid side nodes This assumption is valid if the edges of the element are near linear However if this is not the case an incorrect topology may result from this assumption For example in regions of high curvature the parabolic element may look much different than the linear element For 2D volume meshes an additional constraint is placed on the elements existence in the Z 0 plane Periodic Boundaries In general it is difficult to generate a valid grid with periodic boundaries in NASTRAN However a special feature exists in TGrid that allows you to generate a grid in a domain with periodic boundaries See Section 7 14 5 Creating Periodic Boundaries for further details Deleting Duplicate Nodes NASTRAN often generates duplicate nodes in the process of creating triangular elements These must be removed by using the Merge button in the Boundary Nodes panel or the boundary merge duplicates text command in TGrid ANSYS Inc April 15 2008 A 7 Importing Boundary and Volume Meshes ANSYS Inc April 15 2008 Appendix B Mesh File Format B 1 This document describe
64. File Import NASTRAN Volume 6 10 File Import Options 6 14 File Import PATRAN neutral Surface 6 10 File Import PATRAN neutral Volume 6 10 file import stl 6 13 File Import STL 6 10 file read boundary mesh 6 2 file read case 6 3 file read domains 6 10 file read journal 6 9 file read mesh 6 2 E 1 file read meshes by tmerge 6 3 file read multi bound mesh 6 2 file read multiple case 6 3 file read multiple mesh 6 3 File Read Boundary Mesh 6 2 File Read Domains 6 10 ANSYS Inc April 15 2008 Index File Read Journal 6 8 File Read Mesh 6 2 File Save Layout 6 24 file start journal 6 9 file start transcript 6 9 file stop journal 6 9 file stop transcript 6 9 file write case 6 4 E 2 file write domains 6 10 file write mesh 6 4 E 2 File Write Boundaries 6 5 File Write Domains 6 10 File Write Mesh 6 4 File Write Start Journal 6 8 File Write Start Transcript 6 9 File Write Stop Journal 6 8 File Write Stop Transcript 6 9 filenames 5 6 files 6 1 append 6 3 hardcopy 6 17 importing from CAD packages 6 11 journal 6 8 log 6 8 reading compressed 6 6 reading and writing 6 1 compressed 6 6 reading multiple boundary mesh 3 7 6 2 reading multiple mesh 6 3 searching for 3 7 selecting 3 6 transcript 6 9 writing compressed 6 7 Filter Options panel 6 14 filters 6 16 A 1 finding worst face 7 20 fixed angle criteria 7 4
65. Grid Nodes contains options for displaying nodes Options allows you to select one or more of the following options All draws all nodes in the node zones selected from the Node Zones list col ored by their zone type Select one or more zones for any to be displayed Unused draws nodes that are not currently used by any faces or cells The unused nodes are usually displayed with a different color and marker symbol to distinguish them from nodes in use Node Zones contains a list of node zones from which you can select those to be drawn Node Zone Groups contains a list of node zone types Selecting a zone type from this list e g boundary node will select all node zones of that type boundary node 1 boundary node 2 etc in the Node Zones list This shortcut allows you to select all zones of a certain type without having to select each zone individually Faces contains options for displaying faces Display Grid Nodes Faces Cells Bounds Attributes Face Size Range F all Minimum Joo Free Multi iat aay 1 Unmeshed Face Quality Range Left Handed Minimum 0 9 I Size WE Quality Maximum 1 Quality Measure Dis e Dome ie Options allows you to select one or more of the following options All draws all faces in the selected face zones colored by their zone type Select one or more zones from the Face Zones list for any to be displayed Free draws free faces face
66. NZ 0 A i aN TATAN N avs NENN i if A SEBS Ma LES aay BO AS fs INA vy IN LN ata KA AAAA AAAS NY ma VAAAAA CA A S a A LAVA A AALAY ZIN AAV AT AY A N K Figure 13 9 1 Copying and Translating a Cell Zone 13 9 3 The Manage Cell Zones Panel The Manage Cell Zones panel allows you to change the cell type of a zone set active cell zones delete zones and merge two or more zones into one It also allows you to rename rotate scale or translate one or more cell zones The default zone name consists of a cell type dead fluid or solid and a zone ID number Mesh Manage Manage Cell Zones Options Type v Activate Change Type v Copy v Delete v Merge v Rename v Rotate v Scale v Translate Cell Zone Groups Fie dead fluid solid Aaj f ej j e ANSYS Inc April 15 2008 13 29 Improving the Mesh Options contains the following zone manipulation options Activate activates the selected zone s e When you click Apply the selected zone s will be made active and the zone s that are not selected will be made inactive e When you refine the mesh only cells in active zones will be refined e When you display the grid the cells including boundary cells interior nodes and interior faces that are displayed are those in the active zones See Section 13 9 1 Active Zones and Cell Types for details Chang
67. Normal specifies the direction of the face with respect to the original geom etry Composite specifies the value calculated by linearly combining above two values Levels sets the number of contour levels that are displayed Min shows the minimum value of the scalar field Max shows the maximum value of the scalar field Draw Contours displays the contours in the active graphics window Post Improve contains the parameters to improve the quality of the wrapper surface v A A A A A A A A Options contains various options that are available to improve the quality of the wrapper surface ANSYS Inc April 15 2008 8 39 Wrapping Boundaries Coarsen allows you to coarsen the wrapper surface This option can also be used for wrapper boundary zones after zone recovery Total Face Count reports the face count for the zone selected in the Tri Boundary Zones list The value in this field is informational only Edge Length Change specifies the maximum allowable edge length change Max Angle Change specifies the maximum allowable angle change Min Length Max Length specify the minimum and maximum values range for the average length of faces to be considered for coarsening Preserve Boundary allows you to preserve the original locations of the zone boundary nodes Post Wrap contains options for the post wrapping operations available in TGrid Auto Post Wrap allows you to perform a pre defined sequence of post w
68. Number Meshed option is enabled Report Number Meshed toggles the reporting of the number of nodes and faces that have been meshed Update updates the reported values 15 1 2 Text Commands for Reporting Mesh Size Text commands for reporting the size of the mesh are as follows report mesh size reports the number of nodes faces and cells report number meshed reports the number of elements that have been meshed 15 2 ANSYS Inc April 15 2008 15 2 Reporting Face Limits 15 2 Reporting Face Limits Before generating a 3D volume mesh check the quality of the faces to get an indication of the overall mesh quality The default quality measure is skewness but you can also report the aspect ratio limits or the range in size change for a face zone For 2D a maximum skewness less than 0 5 and an average of 0 1 are good For 3D a maximum less than 0 9 and an average of 0 4 are good The lower the maximum skewness the better the mesh See Section 15 5 Mesh Quality for information on face and cell quality measures in TGrid You can check face size and quality limits using the Report Face Limits panel or the associated text commands Before creating a layer of pyramid cells check the aspect ratio of the quadrilateral faces that will form the base of the pyramids This aspect ratio should be less than 8 Otherwise the triangular faces of the pyramids will be highly skewed If the aspect ratio is greater than 8 regenerate the qu
69. Properties Panel To modify the color visibility and other display properties for individual geometric objects in the graphics display use the Display Properties panel Click Display in the Scene Description panel see Section 14 8 1 The Scene Description Panel to open this panel S Display Properties Geometry Name Colors Group Visibility Visible Lighting Faces Outer Faces Edges d Perimeter Edges 1 Feature Edges F Lines 1 Nodes Transparency wa e e Controls Geometry Name displays the name of the object you selected for modification in the Scene Description panel see Section 14 8 1 The Scene Description Panel Visibility contains check buttons that control options related to the visibility of the selected object Visible toggles the visibility of the selected object e If the option is enabled the object will be visible in the display e Ifthe option is disabled the object will be invisible 14 42 ANSYS Inc April 15 2008 14 8 Describing a Scene Lighting turns the effect of lighting for the selected object on or off You can choose to have lighting affect only certain objects instead of all of them Faces toggles the filled display of faces for the selected grid or surface object Enabling Faces on has the same effect as enabling the Filled option in the Display Grid panel see Section 14 1 3 The Display Grid Panel Outer Faces toggles the display of outer faces Ed
70. RIS CORA A A DNAS Aa AE VATA N V PCAN VA ANAP ON ATS MATL SN AED es SNE AAT AN PSP ADI ICH DES ATE FE PRA ATO CIPI Y SOCK AA eas OP SH ps DJ SEI a DTT Ay AAI ay CRT NNE APA RSIOZS SSDS Aare A a I as Na SCOP GTH SAREE TAA BARRE OR SER TE KEK AER DEAD ES DRS SESS Rad ae EOE EST SERS ISTE Figure 11 4 1 Local Refinement Region for the Tetrahedral Mesh 11 4 2 Using the Tri Tet Panel You can refine the mesh using the options available in the Refinement tab of the Tri Tet panel Mesh gt Tri Tet 1 Select the appropriate refinement method from the Refine Method drop down list 2 Enable the appropriate options in the Options group box 3 Specify an appropriate value for Max Cell Volume 4 Select the appropriate option from the Cell Size Function drop down list Ensure that none of the cells in the interior are larger than required by selecting the appropriate option in the Cell Size Function list the following options are available none specifies that the cell size is determined based on the Max Cell Volume and skewness This option is available only for the skewness based refinement method linear specifies that the cell size in the interior is linearly interpolated from the size of the boundary triangles geometric specifies that the cell size in the interior of the domain is obtained by a geometric growth from the closest boundary according to the growth rate specified
71. Refine Controls Panel If it is desirable to have a small highly skewed cell than a large one two modifica tions are introduced The face centroid is used not the circumcenter The distance from the face is limited by the length of the longest face edge The basic strategy is to refine the cells with the highest skewness starting with the boundary cells then interior cells and then conclude each refinement pass with swapping and smoothing In each subsequent refinement the cell skewness refine ment parameters are lowered to increase the mesh density and gradually improve the quality of the mesh Sometimes there can be flat cells with two boundary faces that cannot be removed with face swapping However by claiming the two interior faces to be boundary faces the cell is effectively eliminated E 12 Using the GUI E 10 e If you have used domains to generate the mesh or group zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces you can report the face distribution only for those face zones that are in the active domain The Wireframe Animationoption is turned on by default It uses a wireframe rep resentation of all geometry during mouse manipulation Turn it off only if your computer has a graphics accelerator Otherwise the mouse manipulation may be very slow Double Buffering turns double buffering on or off if it is supported by the driver Double buffering dras
72. Section 7 14 3 The Zone Prefix Panel where you can specify the prefix for the heat exchanger zones to be created Preview allows you to preview the heat exchanger to be created ANSYS Inc April 15 2008 Chapter 10 Generating Prisms This chapter describes the automatic and manual procedure for creating prisms in TGrid It also discusses the solution to some common problems that you may face while creating prisms This chapter comprises the following sections e Section 10 1 Overview e Section 10 2 Procedure for Generating Prisms e Section 10 3 Prism Meshing Options e Section 10 4 Zones Created During Prism Generation e Section 10 5 How TGrid Builds Prisms e Section 10 6 Using Adjacent Zones as the Sides of Prisms e Section 10 7 Direction Vectors e Section 10 8 Offset Distances e Section 10 9 Improving Prism Quality e Section 10 10 The Prisms Panel e Section 10 11 Text Interface for Generating Prisms e Section 10 12 Prism Meshing Problems 10 1 Overview In TGrid you can create 3D prism cells starting from either quadrilateral or triangular boundary faces or both The 2D prism cells quadrilateral can be created starting from linear faces Prisms can be used to resolve a boundary layer region of a triangular or tetrahedral mesh They can be used to extend some portion of a domain for which the volume mesh already exists e g increase the length of an inlet pipe or to create a volume mesh by extrusio
73. TGrid Text interface commands that control the display and are not found in the GUI are as follows display clear clears the active graphics window This option is useful when you redo an overlay display set re render re renders the current window after modifying the variables in the set menu display set colors background sets the background window color display set colors foreground sets the foreground text and window frame color display set colors user color allows you to change the color for the specified zone display xy file allows you to choose a file from which to create an xy plot display xy set plot to file allows you to write xy plot values to a file 14 6 Modifying the View TGrid allows you to control the view of the scene that is displayed in the graphics window You can modify the view by scaling centering or rotating the scene You can also save a view that you have created or restore or delete a view that you saved earlier These operations are performed in the Views panel or with the associated text commands ANSYS Inc April 15 2008 14 31 Examining the Mesh 14 6 1 The Views Panel With the Views panel you can make various modifications to the view displayed in the active graphics window Display gt Views Views Actions Mirror Planes Define Plane Peviedic Repeats Apply Camera Close Help Controls Views lists the cur
74. TUI command can be used to detect holes in the geometry by tracing the path between the two specified cells mesh tritet trace path between cells A path between the selected cells will be highlighted Interior Node Near Boundary During refinement a node may be placed too close to a boundary face resulting in a highly skewed cell You can detect this situation by displaying the highly skewed cells You can then smooth the grid to eliminate the problem If the interior node is constrained by the boundary faces increase the Min Boundary Closeness in the Tri Tet Refine Controls panel see Section 11 5 2 The Tri Tet Refine Controls Panel and regenerate the mesh Refer to Sections 13 5 and 13 7 3 for details ANSYS Inc April 15 2008 11 27 Generating Triangular Tetrahedral Meshes 11 28 ANSYS Inc April 15 2008 Chapter 12 Generating the Hexcore Mesh Hexcore meshing is a hybrid meshing scheme that generates Cartesian cells inside the core of the domain and tetrahedral cells close to the boundaries Hanging node or H refinements on the Cartesian cells allow efficient cell size transition from boundary to interior of the domain This results in fewer cells with full automation and can handle complex geometries internal walls and gaps The hexcore meshing scheme is applicable to all volumes but is useful mainly for volumes with large internal regions and few internal boundaries such as intrusions or holes The Hexcore
75. Tet Init Controls panel Click the Controls button to open the Tri Tet Init Controls panel see Section 11 5 1 The Tri Tet Init Controls Panel Click Init to initialize the mesh ANSYS Inc April 15 2008 11 3 Initializing the Tri Tet Mesh A Working dialog box will appear informing you that the initialization is in progress Click the Cancel button in the Working dialog box to abort the mesh initialization process Canceling the initialization will leave the mesh incomplete e If you try to initialize the mesh after canceling an initial attempt TGrid will ask you in a Question dialog box if it is OK to clear the incomplete mesh After you approve TGrid will begin the initialization process again e If you try to initialize the mesh when duplicate nodes exist the initialization will fail You must clear the mesh and merge the duplicate nodes before attempting the initialization again e If you try to initialize the mesh when a volume mesh already exists a Question dialog box will appear asking if you want to clear the existing mesh If you click Yes TGrid will clear the volume mesh and proceed to initialize the mesh If you click No the operation will be canceled e If you need to preserve the existing mesh during the meshing process use the command mesh tritet preserve cell zone to specify the cell zone s to be preserved and click the Init button to proceed with the initialization e If the initial mesh gene
76. The text menu system provides on line help for menu commands The text menu on line help system is described in Section 5 6 Using the Text Interface Help System 5 1 1 Command Abbreviation To select a menu command you need not type the entire name you can type an abbre viation that matches the command e A command name consists of phrases separated by hyphens e A command is matched by matching an initial sequence of its phrases Matching of hyphens is optional A phrase is matched by matching an initial sequence of its characters A character is matched by typing that character The rules for matching a command are e If an abbreviation matches more than one command then the command with the greatest number of matched phrases is chosen e If more than one command has the same number of matched phrases then the first command to appear in the menu is chosen For example each of the following will match the given command set ambient color set ambient color s a c sac and sa e When abbreviating commands sometimes your abbreviation will match more than one command In such cases the first command is selected e Occasionally there is an anomaly such as lint not matching lighting interpolation because the li gets absorbed in lights on and then the nt doesn t match interpolation This can be resolved by choosing a different abbreviation such as liin or 1 int ANSYS Inc April 15 2008 5 3 Text
77. This option is used by while remeshing overlapping zones and retriangulating prisms By default this option is enabled boundary remesh controls intersect feature angle allows you to specify the min imum feature angle that should be considered while retriangulating the boundary zones ANSYS Inc April 15 2008 7 13 Manipulating the Boundary Mesh boundary remesh controls intersect join match angle specifies the allowed max imum angle between the normals of the two overlapping surfaces to be joined This parameter is used to control the size of the join region boundary remesh controls intersect refine region toggles the refinement of the intersecting regions after performing any of the intersection operation By default this option is disabled boundary remesh controls intersect retri improve allows you to improve the mesh After performing any intersection operation the slivers are removed along the curve of intersection Laplace smoothing is performed and followed by the edge swapping Laplace smoothing is also performed for insert edge zone remesh overlapped zones and prism retriangulation options Smoothing is performed again The smooth swap operations can be controlled by changing the various defaults such as swapping iterations smoothing iterations etc boundary remesh controls intersect separate toggles the automatic separation of intersected zones boundary remesh controls intersect stitch preserve indi
78. User Interface 5 1 2 Scheme Evaluation If you enter an open parenthesis at the menu prompt then that parenthesis and all characters up to and including the matching closing parenthesis are passed to Scheme to be evaluated The result of evaluating the expression is then displayed define a 1 a 2 8 4 5 1 3 Aliases Command aliases can be defined within the menu system As with the UNIX csh shell aliases take precedence over command execution The following aliases are predefined in Cortex error pwd chdir 1s and alias error displays the Scheme object that was the irritant in the most recent Scheme error interrupt pwd prints the working directory in which all file operations will take place chdir changes the working directory 1s lists the files in the working directory alias displays the list of symbols currently aliased 5 2 Text Prompt System Commands require various arguments including numbers filenames yes no responses character strings and lists A uniform interface to this input is provided by the text prompt system A prompt consists of a prompt string followed by an optional units string enclosed in parentheses followed by a default value enclosed in square brackets filled grids no lt RETURN gt shrink factor 0 1 lt RETURN gt line weight 1 lt RETURN gt title lt RETURN gt ANSYS Inc April 15 2008 5 2 Text Prompt Sy
79. a create operation places a delete on the stack and a delete adds a create operation The excep tions are merge and collapse which cannot be undone Theoretically if no merge or collapse operations are performed you can undo all previous operations In reality certain sequences of operations are not ANSYS Inc April 15 2008 7 25 Manipulating the Boundary Mesh 7 26 reversible The undo operation requires that the name of the object exist when the action is undone If the name does not exist then the undo will fail i Usually you can undo the last few operations but if many operations are being performed it is recommended that you save the mesh periodically particularly before merge and collapse operations Centroid reports the coordinates of a node or the centroid of a face or cell Distance calculates the distance between any two selected entities face node cell etc Set defines a reference line or plane for the Project operation Project projects selected nodes onto the projection line or plane defined by the Set operation Enter Selection allows you to type in the name of an object or zone or the coordinates of a position This provides an alternative to selecting objects zones and locations in the graphics window For example if you have created a new zone and want to use Rezone to move some faces into it there is no way to display the new zone In such cases enter the zone name in this field To
80. a solution using FLUENT d Close the Report Cell Limits panel 3 Open the Report Mesh Size panel Report gt Mesh Size You can use this panel to check the number of nodes faces and cells This panel separates the number of nodes faces and cells into two groups boundary and interior a Click Update The number of cells is 664 see Figure 4 6 3 Report Mesh Size Boundary Interior Nodes A zs Faces 3 fa Cells 664 d Report Number Meshed Figure 4 6 3 The Report Mesh Size Panel b Close the Report Mesh Size panel 4 Plot the histogram Use the Cell Distribution panel to plot a histogram of the distribution of cell quality skewness by default to get an overall feel of the quality of the mesh Display gt Plot Cell Distribution a Select Quality in the Options list b c d Select fluid 7 in the Cell Zones selection list Enter 0 5 for Maximum and 50 for Partitions Not MY RR Enable Percent of Total 4 10 ANSYS Inc April 15 2008 4 6 Reporting the Mesh Statistics e Click Plot TGrid will plot the histogram shown in Figure 4 6 4 Cells wl ot eet Onan m 0 00 005 010 016 020 026 050 035 040 045 0 60 Quality Histogram of Cell Quality Equilateral Volume Deviation Method Figure 4 6 4 Histogram of Cell Quality Skewn
81. allows you to modify the selected region according to specified parameters Init creates a default region encompassing the entire geometry Draw displays the selected region in the graphics window Refine refines the selected region Delete deletes the selected region 8 9 2 The Pan Regions Panel The Pan Regions panel allows you to observe and analyze the region you want to wrap created during the Cartesian grid initialization S Pan Regions Direction Start End Increment ax 424 6154 3415 385 38 4 v Y Value A 1533 785 ap a EJ I Overlay Graphics Region F All A v Negative ANSYS Inc April 15 2008 8 45 Wrapping Boundaries Controls Direction allows you to select the direction in which you want pan the selected re gion s Start specifies the frame number from which you want to start the plane movement End specifies the frame number at which you want to stop the plane movement Increment specifies the interval of the cutting plane coordinate during panning Overlay Graphics allows you to display either the Cartesian grid surface or the geom etry along with the pan plane while panning through the selected region s Positive displays the surfaces on the positive side of the cutting plane Negative displays the surfaces on the negative side of the cutting plane Region allows you to select the regions you want to pan through All enables panning through all regions When this option
82. alternate tetrahedra In Figure 13 2 4 either the common interior edge or two common faces can be replaced resulting in four alternate tetrahedra 13 2 3 Text Interface for Smoothing and Swapping Text command for smoothing and swapping on the grid is as follows mesh tritet improve swap faces performs interior face swapping to improve cell skewness 13 3 Improving the Mesh The Improve operation is an automated procedure for sliver removal or for reducing the maximum skewness in the mesh The improvement is carried out by removing cells above the specified skewness threshold by collapsing cells swapping faces smoothing nodes and inserting new nodes iteratively Each operation is specialized and the mesh will be modified only if the mesh is noticeably improved The skewness before and after ANSYS Inc April 15 2008 13 5 Improving the Mesh Figure 13 2 4 4 4 Swap Configuration an operation is taken into account to determine the improvement Hence the lower the skewness of the cells involved the larger the improvement will have to be in order for the mesh to be modified The improve operation is a more elaborate version of the Remove Slivers option invoked from the Refinement tab in the Tri Tet panel see Section 11 5 The Tri Tet Panel 13 4 Removing Slivers from a Tetrahedral Mesh A sliver typically denotes a flat tetrahedral cell Figure 13 4 1 shows an acceptable tetrahedron Figure 13 4 1 Sliver F
83. and arguments used with a specified filter For example if you have saved the PATRAN files with a NEU extension instead of neu you can either substitute or add NEU to the extension list For some filters one of the arguments will be the dimensions of the grid When you use the filter options command 6 8 Exporting Files You can save the mesh to a file that can be read by HYPERMESH NASTRAN PATRAN and ANSYS 6 8 1 Exporting HYPERMESH Files To save your mesh to a file that can be read by HYPERMESH select the File Export HYPERMESH menu item or use the file export hypermesh TUI command and specify the name for the HYPERMESH file 6 8 2 Exporting NASTRAN Files To save the mesh to a file that can be read by NASTRAN select the File Export NASTRAN menu item or use the file export nastran TUI command and specify the name for the NASTRAN file 6 8 3 Exporting PAT RAN Files To save the mesh to a file that can be read by PATRAN select the File Export PATRAN menu item or use the file export patran TUI command and specify the name for the PATRAN file 6 16 ANSYS Inc April 15 2008 6 9 Saving Hardcopy Files 6 8 4 Exporting ANSYS and STL Files To save the mesh to a file that can be read by ANSYS select the File Export ANSYS menu item or use the file export ansys TUI command and specify the name for the ANSYS file To save the mesh to a file that can be read by third party packages use the file export stl TU
84. boundary type from this list e g inlet all boundary zones of that type for this example all pressure inlet and velocity inlet boundaries will be selected in the Boundary Zones list This shortcut allows you to easily select all boundary zones of a certain type without having to select each zone individually Note that you can select multi ple boundary types in the Boundary Zone Groups list to select all zones of several different types e g inlet and outlet Print reports the distribution of face size or quality in the text window Plot plots a histogram of boundary face size or quality Compute determines the minimum and maximum face size or quality ANSYS Inc April 15 2008 14 19 Examining the Mesh 60000 00 4 50000 00 4 40000 00 4 Gells 50000 00 4 20000 00 4 10000 00 47 0 00 r r r r r r r 1 D 1 0 00 010 020 030 040 O50 060 O70 O80 O90 160 Quality Histogram of Cell Quality Equilateral Volume Deviation Method Figure 14 2 2 Histogram with 100 Partitions 14 2 2 Face Distribution Text Interface Text commands with functionality similar to that of the controls in the Face Distribution panel are display xy face distribution plots a histogram of face quality boundary face distribution reports the distribution of face quality in the text win dow display xy set xy percent y toggles whether the y coordinate should be scaled to show a percent of total
85. boundary faces boundary count free nodes reports the number of boundary nodes associated with edges having only one attached face boundary merge nodes merges duplicate nodes If two nodes of a face are merged the face is deleted ANSYS Inc April 15 2008 7 5 Manipulating the Boundary Mesh 7 2 Intersecting Boundary Zones TGrid allows you to perform connection of boundary zones present in the geometry using the set of intersection commands availables These commands can be used to resolve intersections overlaps and for connections along free boundaries Intersection of faces is possible only for boundary zones meshed with triangular cells The intersection options available in TGrid are e Intersect for connecting intersecting zones e Join for connecting overlapping zones e Stitch for connecting adjacent zones along free edges 7 2 1 Intersect The intersect option is used to connect intersecting boundary zones Figure 7 2 1 shows an example where the intersect option can be used The connection is made along the curve or line of intersection of the boundary zones You can use the intersection operation on multi connected faces as well as in regions of mesh size discrepancy A mesh siz discrepancy ke ulti connection Figure 7 2 1 Intersection of Boundary Zones You can intersect boundary zones having a gap between them by specifying an appropri ate Tolerance value All zones with the distance b
86. cell the face is left handed Since the solver assumes a right handed relation ship between faces and cells left handed faces introduce errors into the solution Left handed faces may be created if there are problems with the generation of prismatic cells See Section 10 12 Negative Volumes Left Handed Faces High Skewness for details Size draws faces within the size range indicated by the Face Size Range limits Quality draws faces within the quality range indicated by the Face Quality Face S fied Range limits The default measure of quality is skewness but you can use the Quality Measure panel see Section 15 5 2 The Quality Measure Panel to specify aspect ratio or change in size instead ize Range limits the faces displayed to those with a size within the speci range To specify a face size range enable Size in the Options group box set the appropriate Minimum and Maximum values and click Display or Apply Minimum sets the minimum value for the size range in the physical dimen sions of the mesh This value should be less than the Maximum value Maximum sets the maximum value for the skewness range in the physical dimensions of the mesh This value should be greater than the Minimum value Face Quality Range limits the faces displayed to those with a quality measure value skewness by default within the specified range To specify a face 14 6 ANSYS Inc April 15 2008 14 1 Displaying the Grid
87. cells Refinement improves the mesh by adding cells e To get the best possible mesh with the smallest number of cells perform smoothing and swapping before refining the mesh any further e Since 2D meshes do not suffer from the problems that occur in 3D swapping and smoothing have no effect in 2D so they need not be performed e After initializing the mesh you can improve the quality and density of the grid using global and local refinement The global refinement visits all cells in the active zones while the local refinement only visits cells within a specified region In most applications use only the global refinement to create an acceptable dis cretization of the volume The local refinement is used to modify the grading away from boundaries or increase the resolution of an interior region of the grid e Swapping is not performed if it will significantly alter the geometry defined by the original boundary mesh e If the pyramids of the pyramid cell zone are on the wrong side delete the newly created zones related to the pyramids ANSYS Inc April 15 2008 E 9 Tips e Each refinement level actually consists of two sweeps through the refinement pro cedure One sweep at the appropriate skewness thresholds for that particular level of refinement Another sweep with high skewness thresholds and a relaxed Min Boundary Closeness set in the Tri Tet Refinement Controls panel see Section 11 5 2 The Tri Tet
88. cells etc This section describes the generic procedure for modifying the cells using the Modify Cells panel You will also use the Display Grid panel see Section 14 1 3 The Display Grid Panel during the modification of the cells 13 6 1 Using the Modify Cells Panel 1 Display the cell s or cell zone s to be modified using the options in the Display Grid panel 2 Select the type of entity cell face node etc you want to select in the Filter list in the Modify Cells panel 3 Select the objects to be modified in the graphics window 4 Click the appropriate button in the Operation group box 5 Repeat the procedure to perform different operations on the cells A Save the mesh periodically since not all operations are reversible The operations available in the Modify Cells panel for modifying cells are Smoothing Nodes During node smoothing the selected node will be repositioned based on the average of the surrounding nodes Do the following to smooth a node 1 Select the node s to be smoothed 2 Click Smooth in the Operation group box ANSYS Inc April 15 2008 13 13 Improving the Mesh Splitting Cells During splitting the selected cell will be refined by the addition of a node at the centroid of the cell Moving Nodes You can move the selected node either to a specified position or by a specified magnitude Do the following to move a node to a particular position 1 Select node in the F
89. color of all defined directional lights and allows you to change the position of a light All directional lights in TGrid are assumed to be at infinity and pass through the unit sphere at the position shown All light rays arriving at the scene from one light are parallel The colored markers on the surface of the sphere represent the color and direction of these distant lights These lights point towards the center of the sphere the origin which is usually where the geometry is Lighting Method specifies the method to be used in lighting interpolation Off Flat Gouraud or Phong Flat is the most basic method There is no interpolation within the individual polygonal facets Gouraud and Phong have smoother gradations of color because they interpolate on each facet When Off is selected lighting effects are disabled Headlight On turns on a light that moves with the camera This option is not especially relevant for TGrid Reset resets the light definitions to their last saved state i e the lighting that was in effect the last time you opened the panel or clicked on Apply 14 38 ANSYS Inc April 15 2008 14 8 Describing a Scene 14 7 2 Text Commands for Adding Lights Text interface commands with the same functionality as the controls in the Lights panel are display set lights headlight on turns the light that moves with the camera on off display set lights lights on turns all lights on off display set ligh
90. controls improve face smooth converged specifies the convergence cri teria for cap face smoothing mnesh prism controls improve face smooth rings specifies the number of rings to propagate skewness during smoothing of cap faces nesh prism controls improve face smooth skew specifies the minimum skewness to smooth cap faces mesh prism improve improve warp enables disables improving of face warp during prism generation This option is disabled by default nesh prism controls improve left hand check specifies checking for left handedness of faces A value of 0 implies face handedness will not be checked 1 implies only cap faces will be checked while 2 implies faces of all cells in current layer will be checked nesh prism controls improve max allowable skew specifies the maximum allow able skewness for cap faces after smoothing Prism layer growth will be stopped if any cap face has skewness greater the specified value nesh prism controls improve node smooth allows you to enable node driven smooth ing to improve skewness nesh prism controls improve node smooth angle refers to the maximum devia tion of a node s sharpest angle i e the most acute angle between adjacent faces that use the node from 180 degrees The node will be smoothed only if its sharpest angle falls within this range For example if the specified value is 45 degrees nodes with sharpest angles between 135 and 225 degrees can be smoothed ANSYS
91. deleting 7 75 merging 7 75 Boundary Create Bounding Box 7 78 Bib 3 Index Boundary Create Cylinder 7 85 Boundary Create Periodic 7 89 Boundary Create Plane Surface 7 81 Boundary Create Swept Surface 7 87 Boundary Feature 7 42 Boundary Intersect 7 5 Boundary Merge Nodes 7 2 Boundary Mesh Improve 7 32 Boundary Mesh Refine 7 35 Boundary Mesh Triangulate 7 62 Boundary Modify 7 14 Boundary Remesh 7 53 boundary remesh triangulate 9 7 Boundary Separate 7 63 Boundary Zone Project 7 69 Boundary Zones 7 74 bounding box creating 7 78 Bounding Box panel 7 80 Bounding Frame panel 14 44 browse 3 7 buttons 3 10 CAD import 6 11 Camera Parameters panel 14 33 cancelling 3 5 a display operation 3 15 cap faces 9 16 10 11 10 12 capabilities of TGrid 1 4 captions 14 27 editing 14 49 E 7 E 11 Cavity Remesh panel 13 24 cell aspect ratio 14 20 15 5 15 8 degenerate 2 2 13 6 distribution 14 19 quality 14 8 14 20 15 5 15 8 size 14 8 15 5 change in 15 5 15 8 skewness 11 22 14 8 14 20 15 5 smoothness 15 8 zones 13 26 active 11 24 13 28 14 4 changing type 13 29 Bib 4 copying 13 27 13 29 creating new 13 29 deleting 13 29 merging 13 30 moving 13 27 preserving 11 1 renaming 13 30 rotating 13 30 scaling 13 30 translating 13 30 Cell Distribution panel 14 20 CGNS 6 11 character strings 5 5 check box
92. do so enter the name of the desired object or zone or the coordinates of the desired location and press the return or enter key on your keyboard TGrid will verify your entry and add it to the Selections list if it is valid To select cells faces edges or nodes enter their simplified names e g bf213 for the boundary face numbered 213 To select zones enter their names e g wal1 7 To enter positions type their coordinates e g 1 5 2 4 5 6 Auto Redisplay toggles the automatic update of the display after a boundary modifi cation operation is performed If the Auto Redisplay option is enabled TGrid will automatically redisplay the grid after you make a change to the boundary allowing you to immediately see the effect of your change If Auto Redisplay is disabled click Redisplay to see the effect of your change The Auto Redisplay option is enabled by default Local Delta toggles the automatic limiting of the grid display to a neighborhood around the skewed face If the Local Delta option is enabled TGrid will auto matically display the skewed face along with some of the faces around it allowing you to locate the exact position of the skewed cell in the geometry You can also use the hot keys up arrow and down arrow to increase or decrease the bound limits in the display respectively Quality Limit allows you to find the face with the worst quality in the entire grid Mark allows you to find the marked faces
93. during refinement 11 16 ANSYS Inc April 15 2008 11 4 Refining the Tri Tet Mesh mesh tritet controls skewness method smooth mesh toggles the automatic smooth ing of the mesh during refinement mesh tritet controls skewness method sort boundary faces toggles the auto matic sorting of boundary faces by size during refinement mesh tritet controls skewness method sort cells toggles the automatic reverse sorting of cells by skewness during refinement mesh tritet controls skewness method swap faces toggles the automatic swap ping of faces during refinement mesh tritet controls skewness method type allows you to select the appropriate pre defined skewness refinement parameters You can select default fast transition or incremental improve as required mesh tritet local regions activate activates the specified region s for refinement mesh tritet local regions deactivate deactivate the specified region s for refine ment mesh tritet local regions define defines the refinement region according to the specified parameters mesh tritet local regions delete deletes the specified refinement region mesh tritet local regions ideal vol reports the volume of an ideal tetrahedron for the edge length specified mesh tritet local regions init defines the default refinement region encompass ing the entire geometry mesh tritet local regions list all regions lists all refinement region parame ters and the
94. ee Click Draw and check if the normal vectors for each zone are pointing in the direction that you want to build the prisms e If the vectors for the faces on each zone do not point in the same direction i e if some point on one side of the zone and others point on the other side click the Orient Normals button to reorient them e If the vectors point in the wrong direction click the Flip Normals button to reverse the direction d Display the zone s to verify that the normals now point in the correct direc tion e Specify the method for determining the direction of the prisms e Select Normal in the Method list to compute normal direction vectors This method takes into account the change in direction required for a curved region Specify the values for the maximum angle change e Select Uniform in the Method list to use a constant uniform direction for flat prism regions Specify the appropriate direction vector 5 Set the parameters for prism improvement and prism projection available in the Improve and Project tabs respectively as required ANSYS Inc April 15 2008 10 3 Generating Prisms 10 Click Apply to save your settings Save the mesh File Write Mesh i It is a good practice to save the mesh at this point If you are dissatisfied with the prisms generated you can read in this mesh and modify the prism parameters to regenerate the prisms Click C
95. ee a 13 2 13 1 1 Laplacian Smoothing 22 24 44424444 4 44 h44 245 13 2 13 12 Variational Smoothie 2 x u lt vay lt 2 ese Seed ewe EG 13 2 13 1 3 Skewness Based Smoothing 4 13 2 13 1 4 Text Commands for Smoothing ss s s s asc eseas teet 13 3 13 2 SWAPPING ses ck ee e Ue ee R e p OR p ORES g e i E g 13 3 1321 Triangular Gids eoe goe e liegia e ee ge ee a See Geya 13 3 TOC 10 ANSYS Inc April 15 2008 CONTENTS 1322 Tetrabhedral Grids sa e oh oe ee Se ee Ee eee ee eS 13 4 13 2 3 Text Interface for Smoothing and Swapping 13 5 13 3 Improving the M sh lt o e soo ccs eee eee ER ee kadd eaw yee 13 5 13 4 Removing Slivers from a Tetrahedral Mesh 13 6 13 4 1 Automatic Sliver Removal a a a 13 7 13 4 2 Removing Slivers Manually a aaa 13 7 13 4 3 Text Interface for Sliver Removal 13 9 13 5 The Try tet improve Panel 2 os 44 5 e ee Gg e ep e SOE De pea 13 10 13 6 Moditying Cele 2446264258 48288448245 84 e264 G RES DS 13 13 13 6 1 Using the Modify Cells Panel 13 13 13 6 2 The Modify Cells Panel e sei eea sosea posta atir dn 13 16 13 6 3 Text Commands for Modifying Cell Zones aaau aa 13 18 13 7 M vine Nodes gt e siora ma ri ka rii bee dG See EERE a aa 13 19 13 71 Automatic Correction s s s es d kosi doe SA ee EA wi 13 19 13 7 2 Semi Automatic Correction as sa a s ae p i E ie E a ee a D 13 20 13 7 3 The Auto Node Move Panel aaa
96. element 2 10 lt RETURN gt element 3 100 lt RETURN gt element 4 lt RETURN gt element 5 Q lt RETURN gt Then it leaves only 1 and 10 in the list element 1 1 lt RETURN gt element 2 10 lt RETURN gt element 3 100 Subsequently entering creates a five element list 1 10 11 12 and 13 element 1 1 11 12 13 ANSYS Inc April 15 2008 5 7 Text User Interface Finally a single empty list removes all elements element 1 1 10O 5 2 7 Evaluation All responses to prompts except filenames are evaluated by the Scheme interpreter before they are used Therefore you can enter any valid Scheme expression as the response to a prompt For example to enter a unit vector with one component equal to 1 3 without using your calculator do the following foo gt set xy x component 1 0 1 3 y component 0 0 sqrt 8 9 You can also first define a utility function to compute the second component of a unit vector as follows gt define unit y x sqrt 1 0 x x unit y foo gt set xy x component 1 0 1 3 y component 0 0 unit y 1 3 5 2 8 Default Value Binding The default value at any prompt is bound to the Scheme symbol _ underscore so that the default value can form part of a Sc
97. enabled by default When this option is disabled TGrid will generate more than one thread per base thread mesh prism normal bisect angle is required for growing prisms out of sharp interior corners When the value of this angle is set the normals are automatically projected onto the plane bisecting the angle between faces having an interior angle less than this angle mnesh prism normal converge locally specifies whether or not the normal smooth ing at each node is frozen once convergence is satisfied at that node If not all normals are continuously smoothed until all of them have converged mesh prism controls normal direction method specifies whether the prism layers should be grown normal to surfaces or along a specified direction vector mnesh prism controls normal ignore invalid normals allows you to ignore nodes which have poor normals mesh prism controls normal intersect detect enables the adjustment of normals to avoid their intersection 10 36 ANSYS Inc April 15 2008 10 11 Text Interface for Generating Prisms mesh prism controls normal intersect detect angle specifies the angle based on which normal intersection is determined The normal intersection is determined in cases when the feature angle of the manifold of a node is less than the value specified mesh prism controls normal max angle change specifies the maximum angle by which the normal direction at a node can change during smoothing mesh pr
98. enter the number Matching Zones contains a list of the zones of the specified Zone Type that match the specified Zone Name Pattern or Max Zone Entities Select selects the zones in the Matching Zones list in all open panels Deselect deselects the zones in the Matching Zones list in all open panels ANSYS Inc April 15 2008 14 53 Examining the Mesh 14 54 ANSYS Inc April 15 2008 Chapter 15 Reporting Mesh Statistics The quality of a mesh is determined more effectively by looking at various statistics such as maximum skewness rather than just performing a visual inspection Unlike structured grids unstructured grids are nearly impossible to comprehend with only a graphical plot The types of mesh information that TGrid can report include minimum maximum and average values of cell size skewness aspect ratio or change in size warp squish edge ra tio and the total number of each element type These reporting operations are described in the following sections e Section 15 1 Reporting the Mesh Size Section 15 2 Reporting Face Limits Section 15 3 Reporting Cell Limits Section 15 4 Reporting Boundary Cell Limits e Section 15 5 Mesh Quality Section 15 6 Printing Grid Information Section 15 7 Additional Text Commands for Reporting 15 1 Reporting the Mesh Size The Report Mesh Size panel and associated text commands allow you to check the size of your mesh by reporting the number of node
99. for individual zones in the console nesh prism improve improve prism cells smoothes cells by considering rings of cells around the prism cells nesh prism improve smooth brute force forcibly smooth cells if cell skewness is still high after regular smoothing nesh prism improve smooth cell rings specifies the number of cell rings to be con sidered around the skewed cells to be used by improve prism cells nesh prism improve smooth prism cells specifies optimization based smoothing of prism cells nesh prism improve smooth sliver skew specifies the skewness above which prism cells will be smoothed nesh prism list parameters lists all prism mesh parameters in the console mesh prism reset parameters resets the prism parameters to their defaults i If you read in a mesh file created in a previous version of TGrid you can reset all the prism parameters using this command before proceeding with setting the prism parameters mesh revolve face zone generates prisms by revolving a specified face zone through a specified angle about a specified rotation origin and axis to produce a polar mesh 10 12 Prism Meshing Problems This section discusses a number of common problems that you may encounter when gen erating prismatic meshes A appropriate solution is also recommended for each problem If the prism generation fails or is unsatisfactory read in the mesh you saved before start ing the prism generation in step 6 of Secti
100. freeze boundary cells freezes the boundary cells during mesh improvement and sliver removal operations mesh tritet controls advanced keep virtual entities toggles the automatic delet ing of virtual entities after mesh initialization mesh tritet controls improve mesh improve toggles the automatic improvement of the mesh during the meshing process mesh tritet controls improve mesh laplace smooth sets the parameters for Lapla cian smoothing in order to improve mesh quality 11 24 ANSYS Inc April 15 2008 11 7 Common Tri Tet Meshing Problems nesh tritet controls improve mesh skewness smooth sets the parameters for skewness based smoothing in order to improve mesh quality mesh tritet controls improve mesh swap sets the parameters for swapping in or der to improve mesh quality mesh tritet controls remove slivers angle specifies the maximum dihedral an gle for considering the cell to be a sliver nesh tritet controls remove slivers attempts specifies the number of attempts overall to remove slivers mesh tritet controls remove slivers iterations specifies the number of itera tions to be performed for the specific sliver removal operation mesh tritet controls remove slivers remove toggles the automatic removal of slivers mesh tritet controls remove slivers skew specifies the skewness threshold for sliver removal mesh tritet delete virtual cells deletes virtual cells created due to the use of the ke
101. gen eration and describes the way in whichTGrid interacts with other products e Chapter 2 Getting Started gives an overview of the problem setup steps In this chapter you will also find information about starting TGrid e Chapter 3 Graphical User Interface describes the using of the graphical user inter face It also explains how to use the TGrid on line help system e Chapter 4 Sample Session presents a sample TGrid session that you can work through at your own pace e Chapter 5 Text User Interface describes the use of the text interface and options associated with it See the separate Text Command List for information about specific text interface commands e Chapter 6 File Types contains information about the files that TGrid can read and write including hardcopy files e Chapter 7 Manipulating the Boundary Mesh explains the need for a high quality boundary mesh and describes various options available to create such mesh ANSYS Inc April 15 2008 UTM 1 Using This Manual e Chapter 8 Wrapping Boundaries contains information about creating a high quality boundary mesh starting from bad surface mesh using the surface wrapper tool e Chapter 9 Creating a Mesh describes the meshing strategy and creation of pyra mids non conformals and heat exchanger mesh e Chapter 10 Generating Prisms describes the procedure to create prism mesh It also explains how to deal with common problems that can be faced while creat
102. grid adapted to the gaps and curvatures of the input geometry The size functions are established while initializing the Cartesian grid i If you initialize the Cartesian grid without enabling Proximity or Curvature a grid of uniform size the default size will be created throughout the domain You can control the sensitivity of the size functions using the following TUI commands e boundary wrapper set curvature factor e boundary wrapper set proximity factor The default values of the curvature factor and the proximity factor are set to 0 5 and 0 25 respectively If you reduce these values the wrapper will generate a finer mesh in the affected regions ANSYS Inc April 15 2008 8 7 Wrapping Boundaries A The size functions can produce strange results if the input mesh contains cells with skewness greater than 0 99 b Set Min Length and Max Length by changing the Level as appropriate The Min Length is the minimum allowable cell length in the Cartesian grid A smaller size captures details more accurately and also reduces the crossover configurations although it increases the number of holes in the geometry Hence it is recommended to specify a Min Length value less than half the required mesh size Panning the regions also helps in deciding the Min Length value It is rec ommended to specify a value 3 4 times smaller than the size of an important narrow gap present in the geometry See Section 8 9 2 The Pan Regi
103. hardcopy x resolution sets the width of raster format images in pixels 0 implies that the hardcopy should use the same resolution as the active graphics window display set hardcopy y resolution sets the height of raster format images in pixels 0 implies that the hardcopy should use the same resolution as the active graphics window 6 10 Saving the Panel Layout The Save Layout command in the File pull down menu allows you to save the existing panel and window layout You can arrange panels and graphics windows on your screen in a preferred configuration and invoke the Save Layout command A cxlayout file is written in your home directory If you subsequently arrange different panels and save the layout again the positions of these panels will be added to the positions of the panels that you saved earlier If you move a panel for which a position is already saved and then you save the layout the new position will be written to the cxlayout file In subsequent sessions when you invoke a panel or create a graphics window it will be positioned based on the saved configuration Any panel or window not specified in the saved configuration will use the default position The cxlayout file in your home directory applies to all Cortex applications i e TGrid FLUENT FLUENT UNS RAMPANT NEKTON and MixSim 6 24 ANSYS Inc April 15 2008 6 11 The tgrid File 6 11 The tgrid File When starting up TGrid looks in your hom
104. into two or more wall zones 7 10 1 Methods for Separating Face Zones There are six methods available for separating a boundary face zone They are e Separating using angle e Separating using regions e Separating based on the neighboring cell zone Separating based on the face element shape e Separating using a seed element e Separating based on marked cells Using Angle For geometries with sharp corners it is often easy to separate face zones based on the significant angle Faces with normal vectors that differ by an angle greater than or equal to the specified angle value will be placed in different zones For example if the grid consists of a cube and all 6 sides of the cube are in a single wall zone you would specify a significant angle of 89 Since the normal vector for each cube side differs by 90 from the normals of its adjacent sides each of the 6 sides will be placed in a different wall zone 7 64 ANSYS Inc April 15 2008 7 10 Separating Boundary Zones Using Regions You can also separate face zones based on contiguous regions For example if you want to generate the mesh in different regions of the domain using different meshing parameters you may need to split up a boundary zone that encompasses more than one of these regions Separating based on region splits non contiguous boundary face zones i e zones that are separated into two or more isolated groups into multiple zones This command wi
105. is disabled you can select a particular region to pan Pan starts the movement of the plane from one end to the other in the specified direction through the Cartesian grid 8 9 3 The Trace Path Panel The Trace Path panel allows you to locate the position of the hole or leak in the Cartesian grid or input geometry by tracing the path connecting the cells corresponding to specified locations Trace Path Locations X Pos Pos Z Pos Start 1533 78 786 4937 726 6909 End 1533 78 1059 644 910 128 Select Points 8 46 ANSYS Inc April 15 2008 8 10 Text Commands for the Wrapper Controls Locations specifies the positions X Pos Y Pos Z Pos of the Start and End points between which the path is to be traced You can either enter the position values or select the points using the mouse Select Points allows you to select the start and end points of the trace using the mouse Trace highlights the shortest possible path between the specified Start and End points 8 10 Text Commands for the Wrapper The text interface command for wrapping boundary zones is listed below boundary wrapper delete all cells allows you to delete the Cartesian mesh This command is available only after initializing the Cartesian grid boundary wrapper imprint edges imprints the wrapper surface on recovered feature edges that you recover This command is available only after creating the wrapper
106. left mouse button 3 Move the pointer along the slider bar to change the value 4 Release the left mouse button OR 1 Place the pointer over the slider and click the left mouse button 2 Using the arrow keys on the keyboard move the slider bar left or right to change the value Drop Down List Offset Method mirom __ aspect ratio last ratio minimum height A drop down list is a hidden single selection list that shows only the current selection to save space To change the selection do the following 1 Click on the arrow button to display the list 2 Place the pointer over the new list item 3 Click the left mouse button on the item to make the selection and close the list To abort the selection operation while the list is displayed move the pointer anywhere outside the list and click the left mouse button 3 14 ANSYS Inc April 15 2008 3 4 Graphics Display Windows 3 4 Graphics Display Windows Graphics display windows e g Figure 3 4 1 are separate windows that display the graphical output of the program e Use the Display Options panel to change the attributes of the graphics display or to open another display window e Use the Mouse Buttons panel to set the action taken when a mouse button is pressed in the display window E tgrid 1 ANSYS Inc Figure 3 4 1 Graphics Display Window e To cancel a display operation press lt Control C gt while the data is be
107. list contains two or more items Each item is printed on a separate line in the list You can select an item by placing the pointer over the item line and clicking with the left mouse button The selected item will be highlighted Selecting another item will deselect the previously selected item in the list Many panels will also accept a double click in order to invoke the panel action that is associated with the list selection Multiple Selection List Face Zones FEP bottom interior 14 left outlet right top A multiple selection list is similar to a single selection list but allows you to select more than one item at a time Click on an item to toggle its selection state Click on an unselected item to select it and click on a selected item to deselect it There are three small push buttons in the upper right corner of the multiple selection list which accelerate the task of selecting or deselecting items from the selection list e Click to select all the items in the selection list e Click to deselect all the items in the selection list e Click to invert the selection of items in the selection list Scale 127 Blue ANSYS Inc April 15 2008 3 13 Graphical User Interface The scale is used to select a value from a predefined range by moving a slider The number shows the current value To change the value do the following 1 Place the pointer over the slider 2 Press and hold down the
108. of the fe2ram filter will indicate the CAD package used to create the file The name selected in the Filters list e g ideas2tgrid identifies the CAD package that created the file and whether the file is a boundary mesh or volume mesh For example ideas2tgrid is used for importing a boundary mesh from I deas and ideas2ram is used for importing a volume mesh from I deas When you select a filter name in the Filters list the appropriate file extension and arguments for the fe2ram filter will appear under Extension and Options Extension is the extension of the third party mesh file to be imported Options are the arguments used by the filter selected in the Filters list or by the fe2ram filter ANSYS Inc April 15 2008 6 15 File Types For some filters one of the arguments will be the dimensionality of the grid For such filter TGrid will show a default dimensionality argument of d a TGrid will automatically determine if the grid is 2D or 3D So you need not substitute 2 or 3 for a For information about the import filters and their related arguments see Appendix A Importing Boundary and Volume Meshes Text Commands for Setting Filter Options To import mesh files from third party packages use the following text commands file filter list lists the names of the converters that are used to change third party mesh files to TGrid format file filter options allows you to change the extension e g cas msh neu
109. of the specified boundary zone s boundary manage id specifies a new boundary zone ID If TGrid detects a conflict it will ignore the change boundary manage list prints information about all boundary zones 7 78 ANSYS Inc April 15 2008 7 14 Creating Surfaces boundary manage merge merges face zones You can use the alphabetic order first zone or larger area as appropriate boundary manage name gives a face zone a new name boundary manage orient consistently orients the faces in the specified zones boundary manage origin specifies a new origin for the mesh to be used for face zone rotation and for periodic zone creation The default origin is 0 0 or 0 0 0 boundary manage rotate rotates all nodes of the specified face zone s boundary manage scale scales all nodes of the specified face zone s boundary manage translate translates all nodes of the specified face zone s boundary zone type changes the boundary type of the specified face zone 7 14 Creating Surfaces TGrid allows you to create specific types of surfaces within the existing geometry These surfaces can be created using one of the options available in the Boundary Create menu The following sections explain how to create surfaces using TGrid e Creating a bounding box Section 7 14 1 Creating a Bounding Box e Creating a planer surface mesh Section 7 14 2 Creating a Planar Surface Mesh e Creating a cylinder Section 7 14 3 Creatin
110. output as a single zone It is important not to group nodes of internal faces with nodes of boundary faces One technique is to generate groups automatically based on curves or mesh areas i e every curve or mesh area will be a different zone in TGrid or FLUENT Another technique is to create the groups manually generating groups consisting of all nodes related to a given curve 2D or mesh area 3D ANSYS Inc April 15 2008 A 3 Importing Boundary and Volume Meshes Periodic Boundaries In general it is difficult to generate a valid grid with periodic boundaries in l deas However a special feature exists in TGrid that allows you to generate a grid in a domain with periodic boundaries See Section 7 14 5 Creating Periodic Boundaries for further details Deleting Duplicate Nodes I deas often generates duplicate nodes in the process of creating triangular elements These must be removed by using either the remove coincident node command in l deas or the Merge button in the Boundary Nodes panel or the boundary merge duplicates text command in TGrid The node merging process is usually faster in TGrid but more visual in I deas A 3 3 PATRAN Neutral Files For PATRAN surface meshes the filter reads triangular and quadrilateral linear elements that define the boundaries of the domain and have been grouped by named component or identified by property ID s within PATRAN to create zones For volume meshes the filter reads a
111. params defines the cell zone improvement parameters for the advancing front method mesh tritet controls adv front method refine parameters defines the refinement parameters for the advancing front method mesh tritet controls adv front method skew improve attempts specifies the num ber of overall improvement attempts for the advancing front method nesh tritet controls adv front method skew improve boundary sliver skew specifies the boundary sliver skewness for the advancing front method This parameter is used for removing sliver cells along the boundary mnesh tritet controls adv front method skew improve iterations specifies the number of improvement iterations in each attempt for the advancing front method ANSYS Inc April 15 2008 11 15 Generating Triangular Tetrahedral Meshes mesh tritet controls adv front method skew improve sliver skew specifies the sliver skewness for the advancing front method This parameter is used for removing sliver cells in the interior mnesh tritet controls adv front method skew improve target skew specifies the targeted skewness during improvement for the advancing front method mesh tritet controls adv front method skew improve target allows you to en able targeted skewness based refinement for the advancing front method This op tion allows you to improve the mesh until the targeted skewness value is achieved mesh tritet controls advanced max cells sets the maximum number of c
112. read a journal file at any time On Windowssystems only env gu with restrictions help i journal r rx v and vx are available Journal files are always loaded in the main i e top level text menu regardless of where you are in the text menu hierarchy when you invoke the read command The read journal command always loads the file in the main i e top level menu regardless of where you are in the menu hierarchy when you invoke it To start TGrid and immediately read a _ journal file type tgrid i jou replacing jou with the name of the journal file you want to read E 2 Writing Files e When TGrid writes a mesh file msh will be added to the name you type unless the name already ends with msh e To write a mesh file that can be read by TGrid use the File Write Mesh menu item or the text commands file write mesh or file write case File Write Mesh ANSYS Inc April 15 2008 E 3 Saving Hard Copy Files To write a mesh file in the format that can be read by FLUENT use either the File Write Mesh menu item or the text command file write mesh File Write Mesh The Filter Options panel allows you to change the extension e g cas msh neu and arguments used with a specified filter For example if you save the PATRAN files with a NEU extension instead of neu you can either substitute or add NEU to the extension list Onl
113. respective mesh elements prisms pyramids or non conformals tri tet or hex using either the respective panels or the associated text commands prior to using the auto mesh command TGrid will prompt you to specify the mesh elements required when the auto mesh command is invoked The previously set parameters will be used to create the mesh 9 2 1 The Auto Mesh Panel The Auto Mesh panel allows you to automatically create the volume mesh You can specify the mesh elements to be used and set appropriate parameters for the same 9 12 Auto Mesh Boundary Layer Mesh F Prisms Set Quad Tet Transition Pyramids v Non Conformals Set Volume Fill TrisTet v Hexcore v No Fill Set Options J Merge Cell Zones ANSYS Inc April 15 2008 9 3 Generating Pyramids Controls Boundary Layer Mesh contains options for creating the boundary layer prism mesh Prisms allows you to create prism layers in the geometry Set opens the Prisms panel Note The Prisms option in the Auto Mesh panel will be visible only after applying zone specific growth by clicking Apply in the Zone Specific Growth group box in the Prisms panel see Section 10 10 The Prisms Panel Quad Tet Transition contains options for specifying the quad tet transition elements for a hybrid mesh Pyramids specifies that pyramids will be created as transitional elements between the quadril
114. search the preceding material The menu selections that will lead you to a particular panel are also indicated usually within a paragraph using a For example Display Grid tells you to choose Grid from the Display menu Contacting Technical Support The support engineers can help you to plan your CFD modeling projects and to overcome any difficulties you encounter while using TGrid If you encounter difficulties we invite you to call your support engineer for assistance However there are a few things that we encourage you to do before calling UTM 4 Read the section s of the manual containing information on the commands you are trying to use or the type of problem you are trying to solve Recall the exact steps you were following that led up to and caused the problem ANSYS Inc April 15 2008 Using This Manual e Write down the exact error message that appeared if any e For particularly difficult problems save a transcript file of the TGrid session in which the problem occurred This is the best source that we can use to reproduce the problem and thereby help to identify the cause ANSYS Inc April 15 2008 UTM 5 Using This Manual UTM 6 ANSYS Inc April 15 2008 Chapter 1 Introduction to TGrid 1 1 This chapter provides an introduction to TGrid an explanation of its capabilities and instructions for starting TGrid e Section 1 1 Introduction e Section 1 2 Program Structu
115. selected You can also create a plane surface enclosing the boundaries of the selected face zone using this method e Planar Points Method In this method you will select three coordinate points in the geometry using mouse and TGrid creates a plane surface mesh using them The concept of planar points method is shown in Figure 7 14 1 After specifying the planar points TGrid connects the first point P1 and second point P2 to ANSYS Inc April 15 2008 7 14 Creating Surfaces each other by a line line 1 Another line line 2 is drawn through third point P3 parallel to the first line Perpendiculars are drawn from points P1 and P3 on line 2 and line 1 respectively line 2 line 1 Figure 7 14 1 Planar Points Method This process creates a rectangular surface which can be later meshed as per re quirement Using the Plane Surface Panel The procedure to create a surface mesh is as follows 1 Under Options if you select Axis Direction for creating a plane surface mesh do the following a Under Face Zones select the zone s on which you want to create a plane surface mesh b Under Direction select appropriate axis c Click Compute This will update the minimum and maximum extents of the selected face zones in X Y and Z text entry fields It will also update Mesh Size tert entry box with a value of 1 10th of the minimum distance along the coordinate azes d Click Draw This will draw a
116. surface mesh In some rare cases the sliver size which is automatically computed may need to be changed This may happen for domains in which the minimum boundary face size is very small as compared to the domain extent When changing the sliver size the rule of thumb is that the specified value should be of the order 1e 12 times the minimum face area The automatic refinement procedure comprises the following steps 1 Sorting the boundary faces by size 3D only 2 Refining the boundary cells 3 Reverse sorting cells by skewness 4 Refining the active cell zone s 5 Swapping cells based on skewness 6 Reverse sorting cells by skewness 7 Smoothing the mesh 8 Removing boundary slivers 11 2 ANSYS Inc April 15 2008 11 1 Automatically Creating a Tri or Tet Mesh You can select either the advancing front refinement or the skewness based refinement of the tetrahedral mesh The refinement procedure is repeated a number of times You can control the number of repetitions for skewness based refinement by setting the Number of Levels in the Tri Tet Refine Controls panel see Section 11 5 2 The Tri Tet Re fine Controls Panel For each subsequent level of refinement the cell skewness thresholds are lowered Additional refinement levels increase the grid resolution and the number of cells and decrease the average cell skewness Each refinement level actually consists of two sweeps through the refinement procedure
117. the Boundary Zones list This shortcut allows you to easily select all boundary zones of a certain type without having to select each zone individually You can select multiple boundary types in the Tri Boundary Zone Groups list to select all zones of several different types e g inlet and outlet Apply performs the selected operation Draw displays the zones selected in the Tri Boundary Zones list Limits prints a report in the console window of the minimum and maximum size of each zone that is selected in the Tri Boundary Zones list This report will also tell you how many faces on each selected zone have been marked for refinement 7 40 ANSYS Inc April 15 2008 7 5 Refining the Boundary Mesh The Boundary Refinement Region Panel Boundary Refinement Region Max Face Area Center Length Orient X deg Jo deg Z deg fo Controls Regions contains a list of the defined regions Name reports the name of the selected region You can specify a new name by entering it in the text entry box Max Face Area sets the maximum face area for the selected region You can change the value by entering a new value in this field Center allows you to specify the coordinates of the center of the region you want to create Length allows you to specify the absolute size of the region in the x y and z directions Orient allows you to specify the orientation of the region Note TGr
118. the original geometry To rename the wrapper surfaces do the following 1 Select the surfaces to be renamed in the Tri Boundary Zones list 2 Retain the selection of Zone in the Options drop down list and select Rename in the Sub Options list 3 Specify the prefix as appropriate in the From and To fields in the Change Prefix group box 4 Click Apply 8 8 4 Expert Options The Expert options contain advanced post wrapping improvement options available in TGrid e Auto post impovement e Recovering a single surface e Removing crossovers ANSYS Inc April 15 2008 8 29 Wrapping Boundaries Auto Post Improvement TGrid allows you to use a pre defined sequence of improvement operations to improve the wrapper surface after recovering and rezoning the wrapper surface based on the original geometry The improvement operations include the splitting and merging of nodes to remove small areas improving the boundary surface quality collapsing skewed faces and removing duplicate and intersecting faces The automatic improvement procedure performs these improvement operations in a pre defined sequence based on the parameters specified in the Boundary Wrapper panel To use the automatic post improvement procedure do the following 1 Select Expert in the Options drop down list and Auto Post Improve in the Sub Options list respectively 2 Enter an appropriate value for Min Triangle Area 3 Enter appropriate values for Max
119. the prism layers as described in Sec tion 10 9 1 Edge Swapping and Smoothing Note Edge swapping is not available for quadrilateral faces Finding Coordinates of the Centroid To find the location of the centroid of a face or cell do the following 1 Set Filter to face or cell as appropriate 2 Select the face or the cell using the mouse probe button 3 Click the Centroid button hot key lt Ctrl gt L The face or cell centroid location will be printed in the console window Calculating Distance Between Objects To compute the distance between two objects do the following 1 Set Filter to face edge or cell as appropriate 2 Select two objects 7 20 ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh 3 Click Distance hot key lt Ctrl gt D For details about using the Modify Boundary panel see Section 7 3 3 The Modify Boundary Panel For example if an edge or face or cell and a node are selected the distance between the centroid of the edge or face or cell and the node is computed and printed to the console window Projecting Nodes To reconstruct features in the surface mesh that were not captured in the surface mesh generation project selected nodes onto a specified line or plane To do so perform the following The Create Boundary Zone panel will appear automatically when you create a new face zone Section 7 3 3 The Modify Boundary Panel You can specify the name and typ
120. the quadrilateral base zone to the appropriate type if necessary Boundary Manage Since you built cells next to the quadrilateral base zone its original boundary type may no longer be correct ANSYS Inc April 15 2008 9 15 Creating a Mesh The pyramids should be automatically created on the appropriate side of the specified boundary zone s If the pyramids are on the wrong side do the following 1 Delete the newly created zones related to the pyramids 2 Reverse the normal direction on the quadrilateral boundary where the pyramids are being built using the Flip Normals option in the Manage Face Zones panel 3 Recreate the pyramids 9 3 2 Zones Created During Pyramid Generation When TGrid generates pyramids it will create at least two new zones a cell zone con taining the pyramid cells and a face zone containing the triangular faces of the pyramids TGrid will create the following zones e The cell zone containing the pyramids pyramid cells n e The face zone containing the triangular faces of the pyramid cells base zone pyramid cap n For example if the pyramids were built from the quadrilateral face zone wall 4 they will be placed in a new zone called wall 4 pyramid cap 9 where the 9 is the zone number assigned by TGrid e The face zones containing the pyramid sides which use existing faces from the orig inal boundary mesh base zone pyramid side n where n is the zone nu
121. the wrapped zones in the Tri Boundary Zones selection list Match Selections selects the edge loop s associated with the selected zone s in Tri Boundary Zones list This feature can be used only if the Auto Edge Select option is disabled ANSYS Inc April 15 2008 8 37 Wrapping Boundaries Auto Edge Select automatically selects edge loop s associated with the zones selected in the Tri Boundary Zones selection list Edge Zones contains a list of edge loops that have been created for one or more face zones With Advanced Tracking enables advanced tracking of the node path correspond ing to a feature edge on the wrapper surface duing imprinting of features Draw displays the edge loops selected in the Edge Zones list Delete deletes the edge loops selected in the Edge Zones list Imprint projects the nodes of the wrapper surface onto the selected Edge Zones Reports contains the parameters to check the quality of the wrapper surface Contour Options contains the various contour display options Node Values toggles between using scalar field values at nodes and at face centers for computing the contours Auto Range toggles between automatic and manual setting of the contour range 8 38 ANSYS Inc April 15 2008 8 9 The Boundary Wrapper Panel Contours of contains a list from which you can select the parameters to be con toured Distance specifies the distance of face center to the original geometry
122. the wrapper surface in the Tri Boundary Zones selection list 2 Select Expert in the Options drop down list and Remove Crossover in the Sub Options list ANSYS Inc April 15 2008 8 31 Wrapping Boundaries 3 Enable Automatic and click Apply to automatically remove crossovers The automatic crossover removal resolves the crossover faces throughout the do main You may need to manually resolve some configurations that could not be resolved during the automatic crossover removal 4 Disable Automatic and specify the following crossover removal parameters a Specify the number of crossover removal attempts in the Iteration field b Select the seed face as appropriate c d Figure 8 8 6 shows crossovers connecting separate parts of the wrapper surface These faces will be deleted during the crossover removal Enter appropriate values for Max Faces and Relaxation Click Apply y AN Vise RI pers 7 a AN SVATA RAZ RSS Figure 8 8 6 Wrapper Surface A Before and B After Crossover Removal 8 32 ANSYS Inc April 15 2008 8 9 The Boundary Wrapper Panel 8 9 The Boundary Wrapper Panel The Boundary Wrapper panel allows you to preprocess geometries that contains gaps and overlaps See Section 8 2 The Wrapping Process for more details about using the Boundary Wrapper panel Boundary gt Wrap Tri Boundary Zones contains a list of exi
123. to select with the mouse edge node position etc in the Filter list in the Modify Boundary panel ANSYS Inc April 15 2008 7 15 Manipulating the Boundary Mesh 3 Select the objects you want to operate on using the mouse probe button the right button by default in the graphics window You can select individual objects one at a time or select a group of them by defining a selection region See Section 14 10 Controlling the Mouse Probe Functions for details The selected objects will appear in the Selections list in the Modify Boundary panel 4 Click the appropriate Operation button to perform the boundary modification 5 Repeat the process to perform different operations on different objects A Save the mesh periodically as it is not always possible to undo an operation 7 3 2 Operations Performed Modify Boundary Panel You can perform the following operations using the Modify Boundary panel Creating a Node To create a node do the following 1 Select the required position or enter node coordinates explicitly in the Enter Se lection box 2 Select node in the Filter list or use the hot key lt Ctrl gt N 3 Click the Create button or press F5 on the keyboard Note You can select or specify multiple positions Creating a Face To create a face do the following 1 To create a face in 2D select 2 nodes and optionally the zone in which you want the new face to be 2 To create a face in 3D sel
124. to undo the last n operations Note You can use the boundary modifcation operations to fix holes in the geometry Refer to Section 8 8 Detecting and Filling the Holes Manually for details 7 3 3 The Modify Boundary Panel The Modify Boundary panel is used in conjunction with the mouse probe The Filter list allows you to specify which type of object you want to select with the mouse node zone face etc Each selected object is stored in the Selections list You can perform the required operation on the selected items e g merge nodes swap faces or move a node using one of the Operation buttons Then the selection list is cleared ANSYS Inc April 15 2008 7 23 Manipulating the Boundary Mesh Boundary gt Modify Controls Selections lists the objects nodes faces zones etc that have been selected To deselect an object either click on it once more in the graphics window or select it in the Selections list and then click on the Clear button under Operation Modify Boundary Selections Filter Operation bn2145 bf18 edge12 Enter Selection Auto Redisplay F Local Delta Skew Report Zone v Mark Reset Reset Move Nodes Redisptas Close Help ja Filter lists the types of objects nodes faces zones etc that can be selected by the mouse Only objects of the type highlighted in this list can be selected You can select one or more objects o
125. translated to create zone 2 The node distribution on the left boundary of zones 1 and 2 is the same as the distribution on the right boundary Since the left boundary of zone 2 is overlaid on the right boundary of zone 1 there will be duplicate nodes It is important that you merge these duplicate nodes The procedure for doing this is as follows 1 Open the Merge Boundary Nodes panel see Section 7 1 2 The Merge Boundary Nodes Panel 2 Compare all nodes on both boundaries To do this select the two zones in both the Compare and With group boxes 3 Disable Only Free Nodes for both the zones 4 Click the Merge button to merge the duplicate nodes After the duplicate nodes on the two boundaries are merged one of the two boundary face zones will be deleted automatically Since duplicate faces are merged when the duplicate nodes are merged one zone will no longer have any faces 13 28 ANSYS Inc April 15 2008 13 9 Manipulating Cell Zones VASAYAVAYAVAYATANS VAITATA ATATA Fs ITATTA KA F AP Wi AAAS SY pay AS yyy arava Fava MSENM NINI BR R V Two overlaid boundaries between N BEM NSAAAA zone 1 and zone 2 contain duplicate zone 1 nodes and faces that must be merged i 2 F WS A R TK gt VA AAA AEE AVA AAY CAA AE AD BAA Sia Vo ran a fA PARAS F SAA SORES s i AS c KES IFORALBEG PADD PARASN ALAA AA zone 1 zone 2
126. types If you select a zone type from this list e g fluid all cell zones of that type will be selected in the Cell Zones list This shortcut allows you to easily select all zones of a certain type without having to select each zone individually You can select multiple types in the Cell Zone Groups list to select all zones of several different types e g fluid and solid Print reports the distribution of cell quality or size in the text window Plot plots a histogram of cell distribution Compute determines the minimum and maximum cell size or quality 14 3 2 Cell Distribution Text Interface Text commands with functionality similar to that of the controls in the Cell Distribution panel are display xy cell distribution plots a histogram of cell quality report cell distribution reports the distribution of cell quality in the text window display xy set xy percent y toggles whether the y coordinate should be scaled to 14 4 show a percent of total values being plotted Modifying the Attributes of the Plot Axes You can modify the appearance of the axes by changing the parameters that control the labels scale range numbers and tick marks These operations are available in the Axes panel and in the associated text interface menu 14 22 ANSYS Inc April 15 2008 14 4 Modifying the Attributes of the Plot Axes 14 4 1 The Axes Histogram Panel The Axes panel allows you to independently control the characteri
127. view O 1 front back String input can also provide an easy way to create aliases within TGrid For example to create an alias that will display the grid you can type the following alias dg lambda ti menu load string di gr Then any time you enter dg from anywhere in the menu hierarchy the grid will be drawn in the active window ti menu load string evaluates the string argument in the top level menu It ignores any menu you may be in when you invoke ti menu loadstring Therefore the com mand ti menu load string open window 1 gr incorrect usage 5 10 ANSYS Inc April 15 2008 5 6 Using the Text Interface Help System will not work even if you type it from within the display menu The string itself must cause control to enter the display menu as in ti menu load string display open window 1 grid 8 play op 8 5 6 Using the Text Interface Help System The text user interface provides context sensitive on line help Within the text menu system a brief description of each of the commands can be invoked by entering a followed by the command in question Example gt dis display Enter the display menu You can also enter a lone to enter help mode In this mode you need only enter the command or menu name to display the help message To exit help mode type q or quit as for a normal menu Example help mode gt di display Ente
128. with the hole will be merged and the hole information will be deleted a Enter the appropriate value for Region e g 1 for region 1 and click Select to select the potential holes for the region of interest b Click the button to select all the holes other than those in region 1 c Click Open 2 Select all the holes in the Automatic selection list and click Fix The fix operation automatically fills the holes using triangular patches The patches created will be added into the geometry and cell intersections will be updated accordingly The newly added patches will serve as part of the geometry in the subsequent wrapping process 8 5 2 Manual Leak Detection The manual leak detection procedure involves using the Pan Regions panel to examine the region the Trace Path panel to detect the exact location of the hole and the various methods described in Section 8 3 Detecting and Filling the Holes Manually to fill the hole Using the Pan Regions Panel The Pan Regions panel allows you to observe and analyze the region to be wrapped created during the Cartesian grid initialization A plane can be passed through the selected region or all available regions along the X Y or Z direction as required The interior of the region s on every position of the plane is displayed on the plane You can view the interior of the Cartesian grid on the plane You can also overlay the boundary surfaces while panning and clip the boundary su
129. wrap 8 50 ANSYS Inc April 15 2008 8 10 Text Commands for the Wrapper boundary wrapper post improve resolve nonmanifoldness allows you to resolve non manifold configurations on the wrapper surface boundary wrapper post improve resolve self intersection removes the self in tersecting faces boundary wrapper post improve rezone smoothes the zones separated from the wrap per surface for better representation of the geometry boundary wrapper post improve smooth folded faces smoothes the folded faces on the wrapper surface boundary wrapper post improve smooth wrapper surf smoothes the wrapper sur face boundary wrapper post improve swap wrapper surf swaps the nodes of the wrap per surface to improve its quality ANSYS Inc April 15 2008 8 51 Wrapping Boundaries 8 52 ANSYS Inc April 15 2008 Chapter 9 Creating a Mesh After reading the boundary mesh and performing the necessary modifications e g du plicate node merging edge swapping you will create the volume mesh Depending on the type of mesh you are starting from boundary mesh only boundary mesh with hexahedral cells in one or more regions etc you can automatically generate the mesh manually generate the mesh step by step or use a combination of manual and automatic commands TGrid allows you to create several types of meshes The meshing strategy and the use of the Auto Mesh tool are described in this chapter The quad te
130. wrapper region modify region holes allows you to fix or open holes re lated to the specified region boundary wrapper region open holes opens the specified hole s See Section 8 5 1 Au tomatic Leak Detection for details boundary wrapper region refine refines the Cartesian grid based on the zone spe cific sizes and local size functions This command is available only after initializing Cartesian grid boundary wrapper region refine enclosing region refines the region enclosing the specified point boundary wrapper region refine region refines the specified region boundary wrapper region refine zone cells refines the cells associated with the specified boundary zone This command is available only after initializing the Cartesian grid boundary wrapper region update regions updates the regions to account for the changes made to the original geometry during manual hole fixing boundary wrapper region wrap enclosing region generates the wrapper surface for the region enclosing the specified point boundary wrapper region wrap region generates the wrapper surface for the speci fied region This command is available only after initializing the Cartesian grid boundary wrapper region wrapper region at location reports the region at the specified location boundary wrapper set clear size clears all the zone specific size parameters boundary wrapper set curvature allows you to enable or disable the curvature size fun
131. you can change this type later When refining the mesh only the active zones are refined By toggling the zones between active and inactive you can refine different groups of zones independently using different mesh parameters for the different groups If you plan to refine all cell zones using the same refinement parameters change the Non Fluid Type in the Tri Tet panel see Section 11 5 The Tri Tet Panel before initializing the mesh If you change the Non Fluid Type to any type other than dead all zones will be set active automatically after the initialization occurs This eliminates the need for you to set all zones to be active in the Cell Zones panel See also the automatic activation method available through the text interface described in Section 13 9 4 Text Commands for Manipulating Cell Zones 13 9 2 Copying and Moving Cell Zones If you are creating a mesh for a geometry that repeats periodically you can simplify the meshing tasks To do this create the boundary and volume mesh for just one of the repeated sections Copy the appropriate cell zone s to the required location s If the copy shares a boundary with the original zone i e if the two zones are connected ensure that the distribution of nodes is the same on the two overlaid boundaries A simplified case copying a triangular cell zone for a 2D rectangular geometry is illus trated in Figure 13 9 1 Here the volume mesh was created for zone 1 and then copied and
132. you have disabled edge swapping or normal offset or edge smoothing turn them back on ANSYS Inc April 15 2008 10 41 Generating Prisms e If you are using the minimum height offset method enabled with the mesh controls prism offset method text command switch back to the uni form method e Lower the Skewness for Swapping and Smoothing in the Improve section of the Prisms panel e Increase the number of Layers in the Improve section of the Prisms panel if it is smaller than the number of layers being grown e Enable Smooth Nodes in the Improve section of the Prisms panel You can also increase the number of smoothing rings using the following TUI commands mesh controls prism node smooth rings e If you are growing simultaneously from multiple zones use zone specific growth controls Use smaller initial heights and or growth rates for zones that are having problems Growing Too Far The problem here is growing too many layers Ideally to provide for a smooth transition to the nearly equilateral tetrahedra the volume of the tetrahedra should be the local growth rate times the volume of the last layer prism cells Solution To ensure this does not happen verify that the prism parameters satisfy the above condition Large Jumps in Prism Height If the prisms use quadrilateral faces of adjacent zones and the node spacings on these faces are very different from the layer heights the prism heights jump at the oute
133. you to improve the wrapper surface by performing various operations such as smoothing swapping inflating thin regions removing crossovers etc The improvement operations are available in the Post Improve tab in the Boundary Wrap per panel They are grouped as follows e Coarsening options e Post wrapping options e Zone options e Expert options 8 18 ANSYS Inc April 15 2008 8 8 Post Wrapping Improvement Operations Contour of Wrapped Surface Quality Distance Figure 8 7 1 Contours of Distance of a Wrapper Surface When you perform a particular post wrap operation TGrid will indicate in the console the completion of the operation performed along with the zone s on which the operation was performed 8 8 1 Coarsening the Wrapper Surface The wrapper surface created may be finer than you require in some regions You can coarsen the mesh in such regions or globally for the entire wrapper surface This operation also reduces the cell count of the mesh thereby reducing the computation time To coarsen the wrapper surface do the following 1 Select the boundary zone s that you want to coarsen 2 Select Coarsen in the Options drop down list 3 Enter an appropriate value for Edge Length Change The Edge Length Change value specifies the allowable change in edge length during the coarsening operation 4 Enter an appropriate value for Max Angle Change The Max Angle Change value specifies the mazimum all
134. you to refine the face zone based on the proximity with respect to other faces in the current domain The outer edges of the boundary face zones are also refined to allow better quality meshes after refinement ANSYS Inc April 15 2008 7 39 Manipulating the Boundary Mesh Regions contains a list of the refinement regions that have been defined Click the Local Regions button to open the Boundary Refinement Region panel and define the refinement region Max Face Area shows the maximum acceptable face area for the refinement re gion selected in the Regions list faces on the selected zones that are larger than this will be refined The Max Face Area is defined in the Boundary Refinement Region panel Local Regions opens the Boundary Refinement Region panel see Section 7 5 2 The Boundary Refinement Region Panel in which you can define the refinement re gion Relative Distance specifies the relative distance for determining the region to be refined based on proximity Iterations specifies the number of face splitting passes to be performed dur ing the proximity refinement Tri Boundary Zones contains a list from which you can select individual boundary zones to be operated on Tri Boundary Zone Groups contains a list of boundary zone types If you select a boundary type from this list e g inlet all boundary zones of that type for this example all pressure inlet and velocity inlet boundaries will be selected in
135. 10 The Prisms Panel Growth displays the controls for computing the height of each layer of prisms This is the default tab of the Prisms panel Offset Method contains a drop down list of the methods available for computing the offset distance See Section 10 8 Offset Distances uniform specifies the uniform offset method aspect ratio specifies the aspect ratio offset method last ratio specifies the last ratio offset method minimum height specifies the minimum height offset method Growth Method contains a drop down list of the methods available for computing the prism height Figure 10 10 1 shows layer heights for all four methods using a first height of 1 and a slope rate exponent of 1 2 A geometric C constant B linear D exponential D 120 B Layer 49 Height A C 0 Figure 10 10 1 Layer Heights Computed Using the Four Growth Methods constant enables the specification of a constant height for all prism layers When this method is selected you will need to specify the First Height and the Number of Layers The height of all prisms will be the First Height hi ANSYS Inc April 15 2008 10 25 Generating Prisms linear enables the specification of a variable height that decreases or in creases linearly for each layer of prisms hn hy s n 1 10 10 1 When this method is selected you will need to specify the First Height h the Number of Layers and the Slope s geometric enables
136. 14 7 0 16 0 d 0 2 6 1 3 7 7 20 3 1 7 3 7 2 2 b 3 2 f 3 2 10 a 2 12 24 2 13 1f 2 14 1f 2 ANSYS Inc April 15 2008 B 15 Mesh File Format b c 7 0 13 9 15 15 1f 2 9 b70 13 8 16 16 1f 2 9 8 2 7 59 13 13 b 4 2 d c 59 14 14 a 6 2 12 11 59 15 15 9 3 2 ba 59 16 16 8 2 27 6 10 1 1d12 50000000e 00 50000000e 00 00000000e 00 50000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 OWWONNRrFPRFRNNWHN ND FPrRPoOoOoOOrRrrFPF OHO MF A B 16 00000000e 01 00000000e 00 00000000e 01 00000000e 00 00000000e 01 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 ANSYS Inc April 15 2008 Appendix C Shortcut Keys Creating a mesh and modifying and or repairing it involves number of operations TGrid provides tools for making boundary repairs enabling you to perform primitive opera tions on the boundary mesh such as creating and deleting nodes faces moving nodes swapping edges merging smoothing nodes collapsing nodes edge s and face s etc These operations can be performed using the appropriate panels However if you are handling a large and complicated mesh you may find it difficult to perform these oper ations repetitively usin
137. 2 flipping normals 7 76 10 3 10 28 FLUENT 1 2 free ANSYS Inc April 15 2008 edges 7 2 faces 14 5 nodes 7 2 free nodes 10 40 GAMBIT 1 2 6 13 A 1 getting started 2 1 global domain 13 35 graphical user interface GUI 3 1 customizing the 3 17 graphics display windows 3 14 Windows features 3 15 hardcopy files 6 17 window dumps 6 20 Grid Colors panel 14 13 Group Name panel 7 73 GUI 3 1 customizing the 3 17 hardcopy coloring 6 19 file format 6 18 file type 6 19 options 6 20 resolution 6 19 saving files 6 17 Hardcopy panel 6 21 Heat Exchanger Mesh panel 9 24 Help 3 19 help text interface 5 10 help keys C 1 hexahedron 9 1 hexcore generation 12 1 Hexcore panel 12 8 Hexcore Refinement Region panel 12 11 high skewness 10 41 histogram boundary face quality 14 17 boundary face size 14 17 cell quality 14 19 cell size 14 19 Bib 7 Index hole filling 8 4 hot keys C 2 hybrid mesh 9 1 merging duplicate nodes 7 4 viscous 9 2 zonal 9 3 HYPERMESH export 6 16 HYPERMESH 6 13 I deas 6 12 A 1 A 2 importing mesh files 6 11 Information dialog box 3 5 initial mesh generating the 11 2 11 9 integer entry 3 11 interrupt 5 8 Intersect Boundary Zones panel 7 10 intersecting boundary zones 7 5 isolated nodes 7 2 9 9 E 6 journal files 6 8 keyboard shortcuts C 1 arrow keys C 1 help keys C 1 hot keys C 2 labels 14 13 14 22 Laplacian sm
138. 23 Examining the Mesh Minor Rules toggles the display of minor rules on the active axis Minor rules are the horizontal or vertical lines that mark the secondary data divisions and span the whole plot window to produce a grid Number Format contains commands for changing the format of the data labels on the active axis Data labels are the character strings used to define the primary data divisions on the axes Type sets the form of the data labels You may select from a drop down list of options including the following general displays the real value with either float or exponential form based on the size of the number and the defined Precision float displays the real value with an integral and fractional part e g 1 0000 where the number of digits in the fractional part is determined by Precision exponential displays the real value with a mantissa and exponent e g 1 0e 02 where the number of digits in the fractional part of the mantissa is determined by Precision Precision defines the number of fractional digits displayed in the data labels Range contains the range or extents of the active axis To set the range manually you must turn off Auto Range Otherwise the extents are computed automatically Minimum sets the minimum data value for the active axis Maximum sets the maximum data value for the active axis Major Rules contains commands for modifying the appearance of the major rules To use these command
139. 3 10 checking mesh files 4 11 checking the mesh 13 37 child node 10 18 clearing a mesh 13 37 clustering 9 9 15 9 collapsing edges 7 17 faces 7 17 nodes 7 17 colors 14 23 14 30 compressed files 6 6 console 2 2 3 2 conventions used in this manual UTM 4 copying boundary zones 7 75 Cortex 5 4 CPU time 2 6 Create Boundary Zone panel 7 27 creating edge loops 7 53 angle criteria adaptive angle 7 42 fixed angle 7 42 face seec approach 7 43 face zone approach 7 43 customizing GUI 3 17 cxlayout file 6 24 cylinder ANSYS Inc April 15 2008 Index creating 7 85 Cylinder panel 7 86 degenerate cells 2 2 13 6 Delaunay violation 7 32 deleting boundary zones 7 75 9 9 cell zones 13 29 dead zones 7 92 13 29 faces 7 16 7 29 isolated nodes 7 5 nodes 7 16 7 29 7 75 refinement regions 11 24 the mesh 13 37 unused boundary faces 7 92 dialog box 3 4 dihedral angle 15 13 display 14 1 cell size 14 19 colors 14 13 face size 14 17 grid 14 2 magnifying 14 46 mesh 14 2 options 14 24 properties 14 40 quality distribution 14 17 14 19 rotating 14 46 styles 14 15 translating 14 46 Display Grid panel 14 4 Display Options panel 14 24 Display Properties panel 14 41 Display Annotate 14 49 Display Grid 14 4 Display Lights 14 36 Display Mouse Buttons 14 45 Display Mouse Probe 14 47 Display Options 14 24 Display Plot Cell Di
140. 4EESSGBEE ES I 5 5 ei SUNS ace ee es ee o ee oO a E aE S E 5 6 Be Filenames sa eo 5 ee ee be ee be bee hee Se Ged 5 6 Bo Lits lt 2 246825 89 BSED ESAS REARS eGREEY ESS 5 7 2i Eyaluatiom seos s e ke ee Eee ee REE wee ES 5 8 5 2 8 Default Value Bindin e csi onea sesed be we de eee dS 5 8 Oe U oe ee ee e a Ee Bee ES eS See eS a N F 5 8 g4 Systemi C mimands s e bb eked eee 4 ee EERE EES 5 9 5 5 Text Menu Input trom Character Strings e gt s socor 66 scene koeni es 5 10 5 6 Using the Text Interface Help System aoaaa 5 11 6 File Types 6 1 CLE Mesk Files s opare gon a e ee eee eee ee NTa 6 1 6 1 1 Reading Boundary Mesh Files 6 2 6 1 2 Reading TGrid Mesh Files 0000 6 2 6 1 3 Appending Mesh Files 2 00000004 6 3 Ole Writing Mesh Pie eee Beebe SRL eS Rs CHES G 6 4 6 1 5 Writing Boundary Mesh Files 6 5 G2 Compressed Files lt sc s ca sp adet poredi AER 4 ee a o ESS 6 6 6 2 1 Reading Compressed Files ice aaa e 6 6 6 2 2 Writing Compressed Files aa aa 244 a 6 7 6 3 Reading Scheme Source Files ooa aaa 00000 pees 6 7 Om Journal Files so 2 e tocea oee a aa bose 4 eS e e a EES 6 8 Oa Using the GU asieran inea oe BY AR OS RRs 6 8 ANSYS Inc April 15 2008 TOC 3 CONTENTS 64 2 Using Text Commands lt 4 ceed waded weP ee ee aS 6 9 Geo Transeript Files ecs oo eee hoe Se RE a CR whe Pewee Boe ees 6 9 Go Alem the ca eee ew ee a Eee ek e
141. 7 for details about this parameter This option is available only when the Normal method is selected 10 28 ANSYS Inc April 15 2008 10 10 The Prisms Panel Vector specifies the uniform direction for all layers of prisms You can either enter values in the X Y Z fields or click the Compute button to get the average normal direction of the selected zone s This option is available only when the Uniform method is selected Compute computes the average normal direction to the selected zone or zones i e the average of the unit normals of all the faces in the zones This direction is usually a good choice for the uniform direction especially if the zone is planar This option is available only when the Uniform method is selected A If you use the Compute button to calculate the average normal direction do not change the sign of the displayed Vector It is important for the uniform direction vector to have the same sign as the normal direction for the face zone Orthogonal Layers specifies the number of layers that should remain orthogonal to the original boundary For an orthogonal layer TGrid will perform no edge swapping or normal edge or node smoothing See Section 10 3 5 Preserv ing Orthogonality for details This option is available only when the Normal method is selected and it is set to zero by default Improve contains the controls for various procedures used to improve the quality of the prisms These controls ar
142. Blake and G S Spragle A 3D Delaunay Unstructured Grid Generator Applied to Trains Planes and Automobiles Technical Report AIAA 93 0673 American Institute of Aeronautics and Astronautics 1993 A Bowyer Computing Dirichlet Tessellations The Computer Journal 24 2 162 166 May 1981 M Garland and P S Heckbert Surface Simplification Using Quadric Error Metrics In 24th Annual Conference on Computer Graphics and Interactive Techniques pages 209 216 1997 D G Holmes and D D Snyder The Generation of Unstructured Triangular Meshes Using Delaunay Triangulation In S Sengupta J Hauser P R Eiseman and J F Thompson editors Numerical Grid Generation in Computational Fluid Mechanics 88 pages 643 652 Pineridge Press Limited 1988 Y Kallinderis A Khawaja and H McMorris Hybrid Prismatic Tetrahedral Grid Generation for Complex Geometries Technical Report AIAA 95 0211 AIAA 33rd Aerospace Sciences Meeting and Exhibit Reno Nevada 1995 Y Kallinderis and S Ward Prismatic Grid Generation for Three Dimensional Com plex Geometries ATAA Journal 31 10 1850 1856 October 1993 L Kobbelt J Vorsatz U Labsik and H P Seidel A Shrink Wrapping Approach to Remeshing Polygonal Surfaces Computer Graphics Forum 18 3 119 130 1999 C L Lawson Properties of n dimensional Triangulations Computer Aided Geomet ric Design 3 231 246 December 1986 R Lohner and P Parikh Generation of Three Dimensional Unstructu
143. Compute button next to the Max Cell Length field to obtain the optimal maxi mum cell length for the mesh Alternatively specify the maximum cell length as required TGrid generates the initial Cartesian cells based on the maximum cell length 12 3 5 Buffer Layers The Cartesian cells are marked and subsequently subdivided to satisfy the size require ment on the boundary mesh When there is large disparity in size distribution between the boundary mesh and the initial Cartesian cells there will be a rapid transition from fine to coarser cells To avoid this TGrid marks additional layers of cells adjacent to those marked by the size requirement see Figure 12 3 4 You can control the number of additional layers by setting the Buffer Layers in the Hexcore panel The default number of buffer layers is set to 1 Setting the number of buffer layers to zero may result in a poor quality mesh 12 6 ANSYS Inc April 15 2008 12 3 Controlling Hexcore Parameters Figure 12 3 4 Hexcore Mesh Using A Buffer Layers 1 B Buffer Layers 2 12 3 6 Peel Layers The peel layers control the gap between the hexahedra core and the geometry After the Cartesian cells are subdivided to meet the size requirement TGrid deletes the cells intersected by boundary mesh and those within some distance to the closest face on the boundary mesh The default value for Peel Layers is 1 hence TGrid assumes this distance to be the height of an ideal tetrahed
144. Draw to view the selected zones If the quadrilateral zone you require does not appear in the list use the boundary reset element type text command to update the type of the zone ANSYS Inc April 15 2008 9 3 Generating Pyramids It is possible that TGrid may not recognize the quadrilateral zone due to changes made to the boundary mesh For example if you separate a mixed tri and quad face zone into a tri face zone and a quad face zone TGrid will continue to identify each of these as a mixed zone You need to reset the element type for the quad zone for TGrid to recognize it and include it in the Boundary Zones selection list 3 Select the appropriate method for determining the pyramid vertex location in the Options list The skewness method is selected by default and is appropriate for most cases 4 Specify the height of the pyramids by setting the Offset Scaling value 5 Enable Fill Cap if required The Fill Cap option inserts a tetrahedral cell between the exposed pyramid faces satisfying the Face Angle criterion see Figure 9 3 2 A Figure 9 3 2 Pyramid Cap A Using the Fill Cap Option B Without the Fill Cap Option 6 Click Create TGrid will report the new pyramid cell zone and the new face zones in the console window You can then use the Display Grid panel see Section 14 1 3 The Display Grid Panel to view these new zones Display Grid 7 Change the boundary type of
145. E EHR ee Ee Oe ERS 2 2 23 Starting Dual Process Build of Tord cs sst ssar 4448 624444 2 3 2 0 1 Startup OPO osa sa iie seneo e e g op Ee SE 2 4 3 Graphical User Interface 3 1 Ql COM teissa spedi pradip reisi kaa eaei 3 2 Ql Term nal Emulator scos ses cies aie ea o ee eS Yo 3 2 fil Menu Bars ive ais ee See aa e e e SE es 3 3 3 2 Dialog TOMES acr m ee Soke Se Coe Hee ee a a ee ee a 3 4 32 1 etror Dialog Boe se s ra bbb eS KES EA EEEGR GER ES 3 4 3 22 Informati w Dialog Boe sis 444684 oeio k ee ok ye 3 5 3 23 Warning Dialog Box s lt uk auc Bod ees Bok ee ea a E eS 3 5 324 Working Dighe BOX soe se noa 4 254 4 a gb oe a 6 44 3 5 3 2 5 Question Dialog Box 4 26144 dee iu dea bud weeds 3 6 32 6 Select File Dialog Boe caos ead oe ORV oo KRY a SES A 3 6 ANSYS Inc April 15 2008 TOC 1 CONTENTS Gee SOM p46 a Gree ee eee eee ee ee Se eee ee eS 3 9 3 3 1 Categories Of Panels oc s se soa smoro 0a wba eas ood 3 9 3 3 2 Controls ofa Panel oon ssis dacos e ad ey a eo 3 10 3 4 Graphics Display Windows 54 6 seca i parei paor eiie Garda d 3 15 3 4 1 Printing the Contents of the Graphics Display Window Windows Oye ace no ee he ee re ES eee 3 16 342 Whe Page Setup Panel se lt 4 oe amp lt amp we E 4 wre So Se eS 3 16 3 5 Customizing the GUI UNIX Systems 44 24428 444 ee de4 es 3 18 3 6 Using the GUI Help System 2 2264 cb ee eee eee ees 3 19 3 6 1 Opening the User s Guide Table of Contents
146. Edge To split an edge do the following 1 Select the edge s you want to split 2 Click Split or press the F7 key on the keyboard All faces sharing the edge will be split into two faces If you select multiple edges and they share a face TGrid may not be able to complete the split operation That is if the face referenced by the split operation for the second edge has already been split by the operation on the first edge the second split operation will not be possible because TGrid looks for a face that no longer exists If this happens redisplay the grid and reselect the edge that was not split In such cases it may be easier to split the face rather than the edge ANSYS Inc April 15 2008 7 19 Manipulating the Boundary Mesh Splitting a Face To split one or more faces do the following 1 Select the face s you want to split 2 Click Split or press the F7 key Each triangular face splits into three faces by adding a node at the centroid Perform edge swapping after this step to improve the quality of the local refinement Each quadrilateral face will be split into two triangularfaces Swapping an Edge To swap a boundary edge of a triangular face do the following 1 Select the edge s as appropriate 2 Click Swap or press the F8 key on the keyboard If the triangular boundary face on which you perform edge swapping is the cap face of a prism layer the swap ping will automatically propagate through
147. Grid session by selecting Exit in the File menu File Exit Alternatively you can type exit in the TGrid console ANSYS Inc April 15 2008 4 13 Sample Session 4 14 ANSYS Inc April 15 2008 Chapter 5 Text User Interface TGrid user interface also consists of a textual command line reference The text user interface TUTI is written in a dialect of Lisp called Scheme Users familiar with Scheme will be able to use the interpretive capabilities of the interface to create customized commands The TUI is described in the following sections e Section 5 1 Text Menu System e Section 5 2 Text Prompt System Section 5 3 Interrupts Section 5 4 System Commands Section 5 5 Text Menu Input from Character Strings Section 5 6 Using the Text Interface Help System 5 1 Text Menu System The text menu system provides a hierarchical interface to the program s underlying procedural interface e You can easily manipulate its operation with standard text based tools input can be saved in files modified with text editors and read back in to be executed because it is text based e The text menu system is tightly integrated with the Scheme extension language so it can easily be programmed to provide sophisticated control and customized functionality The menu system structure is similar to the directory tree structure of UNIX operating systems When you first start TGrid you are in the root
148. Grid will perform smoothing as described in Section 10 9 2 Node Smoothing to move the nodes e If the sharpest angle is far from 180 degrees TGrid will limit the smoothing so that the nodes are only allowed to move along the face s longest edge This method will prevent the collapse of sharp corners in the mesh Smoothing does not propagate downward it is performed only on the skewed cap faces themselves This edge swapping smoothing procedure is not performed on quadrilateral cap faces 10 9 2 Node Smoothing If the edge swapping and smoothing are not sufficient to reduce the skewness of some faces include an additional smoothing operation In this method if any of the faces surrounding a new node have a skewness greater than the specified threshold the node is smoothed 10 22 ANSYS Inc April 15 2008 10 9 Improving Prism Quality Instead of moving only the node this method will also move the surrounding nodes to make space for the node to move nodes on target node nodes on ring 1 Figure 10 9 1 Node Smoothing in Rings The surrounding nodes are grouped and smoothed in rings see Figure 10 9 1 The nodes on the outermost ring are smoothed first etc until the target node on ring zero is finally smoothed This type of smoothing is helpful in concave areas where the advancing layers continually decrease the available surface area causing squashing of triangular faces By smoothing outer rings of node
149. I command and specify the name for the STL file Note This option is only available in TUI 6 9 Saving Hardcopy Files Graphics window displays can be saved in various formats such as TIFF EPS and PostScript There may be slight differences between the hardcopies and the displayed graphics windows This is because hardcopies are generated using the internal software renderer while the graphics windows may utilize specialized graphics hardware for opti mum performance Many systems provide a utility to dump the contents of a graphics window into a raster file This is generally the fastest method of generating a hardcopy since the scene is already rendered in the graphics window and guarantees that the hardcopy will be identical to the window 6 9 1 Using the Hardcopy Panel Use the Hardcopy panel to set the hardcopy parameters and to save the hardcopy files The controls and the equivalent text interface commands are described in Sections 6 9 2 and 6 9 3 The procedure for saving a hardcopy file is as follows 1 Open the Hardcopy panel 2 Select the appropriate file format 3 Specify the file type if applicable optional 4 Set the coloring 5 Define the resolution if applicable optional 6 If you are generating a window dump specify the command to be used for the dump 7 Preview the result optional 8 Click the Save button and enter the filename in the resulting Select File dialog box ANSYS Inc
150. Inc April 15 2008 13 4 Removing Slivers from a Tetrahedral Mesh 13 4 3 Text Interface for Sliver Removal The text interface commands for removing boundary slivers are mesh tritet improve collapse slivers attempts to collapse the nodes of a skewed sliver cell on any one of its neighbors nesh tritet improve refine boundary slivers attempts to increase the volume of boundary slivers to create a valid tet cell TGrid identifies tetrahedra having one or two faces on the boundary and then splits the appropriate edge The split node is then smoothed such that the volume of the tetrahedron increases thereby creating a valid tet cell mesh tritet improve refine slivers attempts to remove the sliver by placing a node at or near the centroid of the sliver cell TGrid then performs swapping and smoothing to improve the skewness You can also specify whether boundary cells are to be refined Refining the boundary cells may allow you to carry out further improvement options such as smoothing swapping and collapsing slivers mnesh tritet improve sliver boundary swap removes boundary slivers by moving the boundary to exclude the cells from the zone nesh tritet improve smooth boundary sliver smoothes nodes on sliver cells hav ing all four nodes on the boundary until the skewness value is less than the specified value The default values for the skewness threshold minimum dihedral angle be tween boundary faces and feature angle are 0 985
151. Inc April 15 2008 10 35 Generating Prisms nesh prism controls improve node smooth converged sets the convergence crite rion for node smoothing If the node positions are changing by less than this value smoothing iterations will stop nesh prism controls improve node smooth iter specifies the maximum number of node smoothing iterations to be performed for the nodes on each layer These iterations will be performed until the convergence criterion is reached nesh prism controls improve node smooth local allows you to enable node smooth ing to converge locally This is useful for large geometries nesh prism controls improve node smooth rings controls the locality of node smooth ing by setting the number of rings around each node to be smoothed e If zero only a node itself is smoothed If one the node and all of its neighbors are smoothed e If two the neighbors of the neighbors are also smoothed and so on nesh prism controls improve shrink left handed cap allows you to enable shrink ing of prism layers to get rid of left handed faces nesh prism controls improve swap smooth skew specifies the skewness threshold for edge swapping and edge and node smoothing The faces with skewness greater than or equal to the specified value will be swapped and or smoothed nesh prism controls merge ignored threads allows you to automatically merge all ignored zones related to a base thread into a single thread This option is
152. MBIT Neutral Mesh Files To read a GAMBIT neutral file use either of the following e Select the File Import GAMBIT neutral menu item and then select the Surface menu item to read a surface mesh or the Volume menu item to read a volume mesh e Use the file import gambit surf mesh or file import gambit vol mesh text interface commands 6 7 4 Grid Import Filter Options The filter is used by TGrid to import mesh files from third party packages can take different arguments see Appendix A Importing Boundary and Volume Meshes You can control these arguments and the extensions of the files to be converted using the Filter Options panel or the related text commands File Import gt Options The Filter Options Panel The Filter Options panel allows you to change the extension e g cas msh neu and arguments used with a specified filter 6 14 ANSYS Inc April 15 2008 6 7 Importing Files Filter Options Filters uns2ram ideas2tgrid ideas2ram patran2tgrid patran2ram ansys2tgrid ansys2ram nastran2tgrid Extension ineu pat out Options utility fe2ram tPATRAN s d a OK Cancel Help Controls Filters contains a list of the available file converters When you select a name from this list the corresponding Extension and Options will be displayed A single filter fe2ram is used for files from all CAD packages The arguments
153. Percent specifies the percentage to be used along with the First Height when the last ratio offset method is selected Slope sets the slope s of the linear function used to compute the heights of the prism layers when the linear growth method is selected 10 26 ANSYS Inc April 15 2008 10 10 The Prisms Panel Rate sets the rate of growth r of the geometric function used to compute the heights of the prism layers when the geometric growth method is selected Exponent sets the exponent p for the exponential function used to compute the heights of the prism layers when the exponential growth method is selected Growth Options opens the Prisms Growth Options panel see Section 10 10 1 The Prisms Growth Options Panel Edge Size Limits displays in an Information dialog box and in the console the minimum maximum and average edge lengths for all selected Boundary Zones The First Height should usually be smaller than the minimum length reported Zone Specific Growth allows you to simultaneously grow prisms from multiple zones using different growth parameters By default this option will be enabled if you read in a mesh for which separate growths were specified for different zones and then subsequently saved It will be disabled if you read in a mesh that does not have saved prism parameters You need not use any of these controls if you are building prisms from just one zone building them from multiple zones using the
154. RMESH 6 16 file export nastran 6 16 File Export NASTRAN 6 16 file export patran 6 16 File Export PATRAN 6 16 file export stl 6 17 File Hardcopy 6 17 file import patran surf mesh 6 12 file import patran vol mesh 6 12 File Import ANSYS prep7 cdb Surface 6 10 File Import ANSYS prep7 cdb Volume 6 10 file import ansys surf mesh 6 11 file import ansys vol mesh 6 11 file import cgns surf mesh 6 11 file import cgns vol mesh 6 11 File Import CGNS Surface 6 10 File Import CGNS Volume 6 10 File Import FIDAP neutral Surface 6 10 File Import FIDAP neutral Volume 6 10 file import fidap surf mesh 6 13 Bib 6 file import fidap vol mesh 6 13 File Import Fluent 2D Mesh 6 3 File Import Fluent 3D Mesh 6 3 file import fluent 2d mesh 6 3 E 1 file import fluent 3d mesh 6 3 E 2 File Import GAMBIT neutral Surface 6 10 File Import GAMBIT neutral Volume 6 10 file import gambit surf mesh 6 13 file import gambit vol mesh 6 13 File Import HYPERMESH Ascii Surface 6 10 File Import HYPERMESH Ascii Volume 6 10 file import hypermesh surf mesh 6 13 file import hypermesh vol mesh 6 13 File Import IDEAS universal Surface 6 10 File Import IDEAS universal Volume 6 10 file import ideas surf mesh 6 12 file import ideas vol mesh 6 12 file import nastran surf mesh 6 12 file import nastran vol mesh 6 12 File Import NASTRAN Surface 6 10
155. S Inc April 15 2008 14 17 Examining the Mesh 14 2 1 The Face Distribution Panel The Face Distribution panel allows you to generate a histogram of boundary face size or quality Display Plot Face Distribution El Face Distribution Options Minimum Boundary Zones E zj ouaity 6 113612e 07 gg inlet vas left 0 4014939 outlet Quality Measure ght Percent of Total HP Axes Partitions 100 Y Boundary Zone Groups far field a geometry f Print Plot Compute Close Help The number of faces on the selected zones with a size or quality measure value e g skewness in the specified range in each of the regularly spaced partitions is displayed in a histogram format The x axis shows the size or quality and the y axis gives the number of faces or the percentage of the total number of faces Note If you have used domains to generate the mesh or group zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces you can report the face distribution only for those face zones that are in the active domain Options specifies a histogram of face Quality or Size The default measure of quality is skewness but you can use the Quality Measure panel see Section 15 5 2 The Quality Measure Panel to specify aspect ratio or change in size instead Quality Measure opens the Quality Measure panel see Section 15 5 2
156. Section 14 1 3 The Display Grid Panel 13 36 ANSYS Inc April 15 2008 13 11 Checking the Mesh Create creates a new domain Change changes the definition of the selected domain to the definition currently shown in the panel Delete deletes the selected domain definition The individual zones that were in the domain are not affected You can only delete the grouping of these zones that was defined by the domain 13 10 4 Text Commands for Domains Text commands for domain creation and activation are as follows mesh domains activate activates the specified domain for meshing reporting opera tions mesh domains create creates a new domain based on the specified boundary face zones mesh domains create from creates a new domain based on the specified cell zones mesh domains delete deletes the specified domain mesh domains draw displays the boundary face zones of the specified domain mesh domains print prints the zones comprising the specified domain 13 11 Checking the Mesh When you have completed the mesh generation process you need to check the mesh before saving it Mesh gt Check Alternatively you can use the command mesh check to check the mesh When you select the Mesh Check menu item TGrid will check the mesh connectivity and the orientation of the faces face handedness which should be right handed for all faces because the solvers use a right handed system TGrid will report
157. Specify the Local Size Function The parameters in this group box allow you to enable or disable proximity and curvature size functions locally to any boundary zone you want 8 8 ANSYS Inc April 15 2008 8 4 Initializing the Cartesian Grid a Enable Proximity and or Curvature b Set the Level as appropriate c Click Apply 6 Click Draw Sizes This is to ensure whether or not the specified cell sizes are sufficient TGrid high lights the cells of the specified Max Length and Min Length on the selected face zone s in the graphics window e Two different sized red boxes representing the minimum and maximum cell length will be displayed on the boundary zones for which you applied Global Size Function and Local Size Function e Uniform sized red boxes will be displayed on the boundary zones for which you applied Zone Specific Size If the highlighted cell sizes in a zone are too large reduce the values before creating the wrapper surface See Figure 8 4 1 You can use the following TUI command to change the number of cells to be highlighted boundary wrapper set number of size boxes The default value for the number of cells to be displayed is set to 20 You can increase or decrease the value as required Hh Poad i hel way i i Max Size Min Size Figure 8 4 1 Display of Min and Max Cell Sizes ANSYS Inc April 15 2008 8 9 Wrapping Boundaries 8 10 T
158. T BEAT OED A Aan AAAA ARNT EA 4 LEA ERG LISLE aS ti rat Kae CK av AN SOS oe oe if Mas wae oy Ay N Ne i vay a K fe atl IAN AVAN AA RE SSS ee Ser avs Nide DKS a S Boundary Mesh Figure 9 1 7 Hexcore Mesh Wedge elements are created only when boundary layers are attached on faces pre meshed with triangular elements It combines the automation and geometric flexibility of tet hybrid meshes with greatly reduced cell counts in many applications Hexcore is most beneficial in geometries with large open spaces as in automotive aerospace and HVAC applications See Chapter 12 Generating the Hexcore Mesh for details 9 1 6 Additional Meshing Tasks Additional meshing tasks that TGrid can handle are e If you have a complete volume mesh and want to extend some portion of the domain e g increase the length of an inlet pipe you can grow one or more layers of prisms from the current external quadrilateral or triangular boundary to be extended Figure 9 1 8 shows a region of prisms wedges extended from the triangular face zone that bounds a tetrahedral region e Unless there is a reason to use hexahedral cells in the quad regions it is preferable to convert a mixed tri quad boundary mesh to an all tri boundary mesh and then create a tet mesh for a 3D boundary mesh consisting of only triangular faces ANSYS Inc April 15 2008 Creating a Mesh Figu
159. TGrid 5 0 User s Guide April 2008 Copyright 2008 by ANSYS Inc All Rights Reserved No part of this document may be reproduced or otherwise used in any form without express written permission from ANSYS Inc Airpak ANSYS ANSYS Workbench AUTODYN CFX FIDAP FloWizard FLUENT GAMBIT Icechip Icemax Icepak Icepro Icewave MixSim POLYFLOW TGrid and any and all ANSYS Inc brand product service and feature names logos and slogans are registered trademarks or trademarks of ANSYS Inc or its subsidiaries located in the United States or other countries All other brand product service and feature names or trademarks are the property of their respective owners CATIA V5 is a registered trademark of Dassault Systemes CHEMKIN is a registered trademark of Reaction Design Inc Portions of this program include material copyrighted by PathScale Corporation 2003 2004 ANSYS Inc Centerra Resource Park 10 Cavendish Court Lebanon NH 03766 Contents Preface UTM 1 1 Introduction to TGrid 1 1 Li Tatroduction oS 24 ee oe be Re ee Cw Be Ew Be Ge Dee 1 1 t2 Program Dire ss suoro Ze a ie be ee oe ee Oo ee eee es 1 2 1 3 Program Cap bilitieSs o o o cae ee ee Le eee Ce eee ee bs 1 3 14 Accessing TGrid Manuals 144 6 ead Oe OV ow eR Hal a 1 4 2 Getting Started 2 1 21 Usime WAG sers e grea 4 ERED ERS EE RAED ES RE HERES 2 1 Zell Grid Generation Shape 2 64 k Pe eiei oe He D a N 3 2 1 22 Shortie TGNA oor ew bo ES RE a R
160. The Quality Measure Panel in which you can select the measure of quality to be reported skewness aspect ratio or change in size Axes opens the Axes panel see Section 14 4 1 The Axes Histogram Panel in which you can set parameter ranges number formats rules etc Minimum specifies that only faces with a quality measure value skewness by default greater than this value will be plotted 14 18 ANSYS Inc April 15 2008 14 2 Checking Face Distribution Maximum specifies that only faces with a quality measure value skewness by default less than this value will be plotted Percent of Total specifies that the number of faces as a percentage of the total number of faces counted will be plotted By default the actual number of faces is plotted Partitions specifies the number of partitions in the histogram Increasing the number of partitions will improve the resolution of the plot see Figures 14 2 1 and 14 2 2 120000 00 100000 00 4 e T 80000 00 4 Cells s0000 00 4 40000 00 r pepego 0 00 r 7 z a 0 00 010 020 030 040 050 060 070 080 090 1 00 Quality Histogram of Cell Quality Equilateral Yolume Deviation Method Figure 14 2 1 Histogram with 50 Partitions Boundary Zones contains a list from which you can select one or more zones to be used to generate the histogram Boundary Zone Groups contains a list of boundary zone types If you select a
161. Tri Tet Refine Controls panel The refinement controls for the advancing front method are available in the mesh tritet controls adv front method menu The mesh tritet controls adv front method skew improve target command is important as it allows you to enable targeted skewness based refinement for the advanc ing front method The refinement process will attempt to reach the targeted skewness specified by the command mesh tritet controls adv front method skew improve target skewness Though the default values work well in most situations it may be advantageous to increase the target skewness value in some cases e g cases where a combination of a poor surface mesh and narrow gaps will result in poor cells in the mesh to increase the meshing speed Refer to Section 11 4 3 Text Commands for Setting Refinement Controls for the list of commands available 11 4 1 Using Local Refinement Regions A refinement region limits refinement to specific cells inside the domain When you use the Refine option in the Tri Tet Refinement Region panel TGrid refines the cells within the activated region s The primary use of refinement regions is to reduce the cell size in the region to less than it would be normally Currently the only possible region shape is a box which can be oriented as required The region is defined by an x y and z range and its orientation about the x y and z axes Any cell within the region or which intersects the region wi
162. Wrapper 8 1 The Boundary Wrapper Geometries migrated from various CAD packages often contain gaps and overlaps between the surfaces due to algorithm and tolerance differences of the CAD packages Repairing such geometries manually is a tedious and time consuming process The wrapper provides the ability to create reliable meshes for such geometries without extensive manual clean up and reduces the time required for preprocessing The wrapper can take account of gaps and overlaps at the expense of certain degree of geometry details of the model It can handle unclean geometries and does not require a water tight representation of the geometry ANSYS Inc April 15 2008 8 1 Wrapping Boundaries 8 1 1 Applications of Wrapper The wrapper is useful in the following industrial applications Automotive Underhood thermal management engine only front car full car Cabin HVAC External aerodynamics Brake cooling and engine cooling Aerospace Engine core compartment Cockpit HVAC cabin HVAC Landing gear Drill bit applications Smoke and fire spread Bio medical applications Other applications with bad input geometries 8 2 The Wrapping Process The wrapping process is based on the Cartesian grid or overlay grid approach The general procedure for creating a wrapper surface is as follows 1 A coarse Cartesian grid is overlaid on the input geometry including gaps and overlaps This Carte
163. You can use TGrid to generate a triangular tetrahedral hexcore or hybrid volume mesh from an existing boundary mesh created by GAMBIT or a third party CAD CAE package An ordered group of boundary faces that have the same boundary conditions and are treated as a unit Note The term thread has been replaced by zone Any division of 2 space into triangles This term is also commonly used to refer to an n dimension simplical division of n space The specific term in 3D is tetrahedralization Nodes that are not used by any faces are called unused nodes They can easily be found and deleted A map showing the locus of points region for each node that are closer to the node than any other node Its dual is a Delaunay mesh A list of nodes faces or cells that have some commonality For instance they may all be inlet faces or they may be contiguous cells not separated by a boundary ANSYS Inc April 15 2008 Bibliography 1 7 T J Baker Three Dimensional Mesh Generation By Triangulation of Arbitrary Point Sets Technical Report AIAA 87 1124 American Institute of Aeronautics and Astronautics 1987 T J Barth Wiltberger N L and A S Gandhi Three Dimensional Unstructured Grid Generation via Incremental Insertion and Local Optimization In Software Sys tems for Surface Modeling and Grid Generation Langley Research Center Hamp ton Virginia April 1992 NASA Conference Publication 3143 K R
164. a new mesh This feature is available with the Clear menu item in the Mesh pull down menu Mesh Clear You can also use the text command mesh clear mesh To delete the boundary mesh use the text command mesh reset mesh When you use either of these commands TGrid will ask you to confirm that you want to clear or reset the mesh i If you have used domains to generate the mesh or group zones for report ing as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces only the mesh in the active domain will be cleared 13 38 ANSYS Inc April 15 2008 Chapter 14 Examining the Mesh The following sections explain how to examine the mesh You can specify various pa rameters that control the display environment display the mesh view histograms of cell and face distribution modify the mouse button functions and manipulate the lighting and view in the graphics window Section 14 1 Displaying the Grid e Section 14 2 Checking Face Distribution e Section 14 3 Checking Cell Distribution e Section 14 4 Modifying the Attributes of the Plot Axes e Section 14 5 Controlling Display Options e Section 14 6 Modifying the View e Section 14 7 Adding Lights e Section 14 8 Describing a Scene e Section 14 9 Controlling the Mouse Buttons e Section 14 10 Controlling the Mouse Probe Functions e Section 14 11 Annotating the Display e Section 14 12 Shortcuts for Selecting Zones ANSYS Inc
165. a periodic shadow boundary for each zone selected and change each of the selected zones to a periodic boundary zone Boundary gt Create gt Periodic Make Periodic Boundaries Options Axis Zones s wel E core v wel a degrees Controls Options selects the type of periodicity rotational or translational For Rotational periodicity you will specify the Angle and Axis For Translational periodicity you will specify the Shift Depending on the periodicity selected Shift or Axis will appear in the panel Angle specifies the angle of rotation for rotational periodicity Axis specifies the axis of rotation for rotational periodicity The Axis label appears when the Rotational option is selected Shift specifies the translational shift for translational periodicity The Shift label appears when the Translational option is selected Boundary Zones contains a list from which you can select the zone s to be made periodic Apply creates a periodic shadow boundary for each zone selected and changes each of the selected zones to a periodic zone ANSYS Inc April 15 2008 7 91 Manipulating the Boundary Mesh Draw displays the selected zones in the active graphics window List reports in the text window the zone ID name type and number of faces in the zone for each selected zone 7 14 6 Text Commands for Creating Surfaces The text interface comman
166. a version or wait and specify it later when prompted by TGrid tgrid v Lists the available versions tgrid vx Runs version x of TGrid Note Type tgrid n or use the n option in conjunction with any of the others to see where the specified executable is without actually running it 64 Bit Version The 64 bit version of TGrid is required only when your problem size exceeds the 32 bit process address space Most problems with less than two million cells will fit within a 32 bit address space To use the 64 bit version add the 64 option to the command line when starting the program ANSYS Inc April 15 2008 Chapter 3 Graphical User Interface The graphical user interface GUI is made up of four main components a console control panels dialog boxes and graphics windows When you use the GUI you will be interacting with one of these components at all times This chapter describes the GUI components and explains the procedure to customize the attributes of the GUI including colors and text fonts on UNIX systems to better match your platform environment It also explains the procedure to use the help system in TGrid The following sections are described in this chapter Section 3 1 Console Section 3 2 Dialog Boxes Section 3 3 Panels Section 3 4 Graphics Display Windows Section 3 5 Customizing the GUI UNIX Systems Section 3 6 Using the GUI Help System ANSYS Inc April 15 2008 3 1
167. abs are hidden The Prisms panel consists of a series of tabbed frames within the main panel listed horizontally across the top of the panel Each frame has a name and a set of related controls Mesh Prisms Prisms Boundary Zones HE Growth Direction l Improve l Project n Offset Method Growth Method et x yl i a First Aspect Ratio Number of Layers top 4 2 T Last Aspect Ratio Rate 1 929012 41 2 Zone Specific Growth Growth Options Boundary Zone Groups Grow on Two Sided Wall Edge Size Limits far field Apply Clear List geometry inlet Controls Boundary Zones contains a selection list of all of the boundary zones in your mesh You will select the zone s from which you want the prisms to be built Boundary Zone Groups contains a list of boundary zone types and user defined groups If you select a boundary type or group from this list e g inlet all boundary zones of that type or group will be selected in the Boundary Zones list This shortcut allows you to easily select all boundary zones of a certain type without having to select each zone individually You can select multiple boundary types in the Boundary Zone Groups list to select all zones of several different types e g inlet and outlet You can also select tri or quad in this list to select all triangular or quadrilateral boundary zones 10 24 ANSYS Inc April 15 2008 10
168. aces with nodes of boundary faces In PATRAN named components are applied to the nodes to create groups of faces called zones In FLUENT boundary conditions are applied to each zone E 7 Deleting Duplicate Nodes e deas often generates duplicate nodes in the process of creating triangular elements They can be removed by using one of the following The remove coincident node command in I deas ANSYS Inc April 15 2008 E 5 Tips The Merge button in the Merge Boundary Nodes panel in TGrid the boundary merge duplicates text command The node merging process is usually faster in TGrid but more visual in I deas NASTRAN often generates duplicate nodes in the process of creating triangular elements These can be removed by using the Merge button in the Merge Boundary Nodes panel or the boundary merge duplicates text command in TGrid E 8 Manipulating the Boundary Mesh File In TGrid modify the boundary mesh to improve its quality The quality of the boundary mesh influences the interior mesh generation and the numerical analysis Quality is measured based on four criteria clustering smoothness skewness and aspect ratio Smoothness is particularly critical in regions where surfaces intersect or where they are in close proximity Skewness of the cells can have a dramatic influence on the accuracy and convergence characteristics of the numerical integration technique Highly skewed cells decrease acc
169. aceted Stitch Faceted Stitch Tri Boundary Zones Sa Tri Boundary Zone Groups go Ey far field geometry inlet f Tolerance 9 05 J Self Stitch only Tri Boundary Zones contains a list from which you can select individual boundary zone s to be stitched Tri Boundary Zone Groups contains a list of the default bounday zone types and user defined groups If you select a zone type group from this list all zones of that type group will be selected in the Tri Boundary Zones list You can also select multiple types to select all the zones of different types e g inlet and outlet Tolerance specifies the tolerance within which the free edges will be stitched Self Stitch only allows you to stitch the edges within the same boundary zone Stitch stitches the free edges in the zone Draw displays the selected zones in the graphics window 7 62 ANSYS Inc April 15 2008 7 9 Triangulating Boundary Zones 7 9 Triangulating Boundary Zones Some operations like intersection joining stitching and wrapping are limited only to triangular boundary zones TGrid allows you to remesh a quadrilateral face zone with triangular faces Figure 7 9 1 You can either copy the quad zone s and triangulate the copied zones or replace the original quad zone s with the triangulated zone p quad zone A triangulated zone A Figure 7 9 1 Triangulating a Boundary Zone 7 9 1 The Triangulate Zones Pan
170. activated regions in the TGrid console mesh tritet local regions refine refines live cells inside the specified region based on refinement parameters ANSYS Inc April 15 2008 11 17 Generating Triangular Tetrahedral Meshes 11 5 The Tri Tet Panel The Tri Tet panel allows you to set the parameters controlling tri tet meshing TrifTet Initialization Refinement Options Tri Tet Zones Controls E Merge Free Nodes _t Delete Dead Zones pea Delete Unused Nodes Non Fluid Type Init I Improve Surface Mesh yi IniteRefine Apply Close Help Controls Initialization contains options for initializing the mesh Options contains options to be included excluded in the mesh initialization pro cess Merge Free Nodes merges free nodes see Section 7 1 1 Free and Isolated Nodes Delete Unused Nodes deletes nodes which are not referenced by any faces see Section 7 1 1 Free and Isolated Nodes Improve Surface Mesh performs edge swapping based on the Delaunay cri terion to improve the quality of the surface mesh Tri Tet Zones contains parameters for tri tet cell zone initialization Delete Dead Zones toggles the automatic deleting of dead zones Non Fluid Type allows you to select the non fluid cell type TGrid will set the non fluid zones to the selected type after initializing the mesh Controls opens the Tri Tet Init Controls panel see Section 11 5 1 The Tri Tet Init Contro
171. adrilateral faces e If they were created in a different preprocessor return to that application and try to reduce the aspect ratio of the faces in question e If they were created by TGrid during the building of prism layers rebuild the prisms using a more gradual growth rate Check the skewness of triangular faces on a boundary from which you are going to build prisms to ensure that the quality of the prism cells will be good After you create the prisms check the skewness of the triangular faces that were created during the prism generation 15 2 1 The Report Face Limits Panel The Report Face Limits panel reports on the size or quality limits of selected face zones The minimum maximum and average values are reported If you used domains to generate the mesh or group zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces you can report face limits only for the face zones that are in the active domain ANSYS Inc April 15 2008 15 3 Reporting Mesh Statistics Report gt Face Limits Controls fl Report Face Limits Options Face Zones E Pil Quality v Size interior 14 let Quality Measure outlet right top Maximum ass ar ups eer aee z boundary Average far field oorz7sos1 geometry Compute Close Help Options specifies either Quality or Size to be computed Skewness is the default mea sure of quality Qualit
172. ahedral mesh generation 11 1 tetrahedron 9 1 TetraMesher A 1 text annotation 14 47 entry 3 11 prompts 5 4 userinterface 5 1 TGrid 1 2 capabilities 1 4 tgrid file 6 24 tgrid help 2 4 tmerge append files 6 3 too few nodes 10 40 too many nodes 10 40 Trace Path panel 8 44 transcript files 6 9 Transformations panel 14 42 transforming objects in a scene 14 42 Bib 13 Index translating the display 14 46 translating zones 7 76 13 30 Tri Tet Improve panel 13 9 Tri Tet Init Controls panel 11 19 tri tet meshing refinement controls 11 12 refinement controls 11 12 Tri Tet panel 11 17 Tri Tet Refine Controls panel 11 20 Tri Tet Refinement Region panel 11 22 triangle 9 1 triangular mesh generation 11 1 Triangulate Zones panel 7 62 TUI 5 1 unknown face combinations 10 40 unmeshed faces 14 6 15 1 nodes 14 6 15 1 unused nodes 14 5 User Defined Groups panel 7 71 user interface 3 1 graphical 3 1 text 5 1 using Auto Mesh tri tet meshing 11 4 using the manual UTM 1 vector file 6 19 views 14 30 Views panel 14 30 virtual zone 13 26 viscous hybrid mesh 9 2 visibility 14 40 Warning dialog box 3 5 warp 15 13 wedge 9 1 window dumps 6 20 windows 3 14 Windows systems graphics display window features 3 15 Working dialog box 3 5 Bib 14 worst face 7 20 wrapper 8 1 applications 8 2 automatic improvement 8 28 checking quality 8 17 coarsening 8 18 8 37 de
173. ain file to be read 6 10 ANSYS Inc April 15 2008 6 7 Importing Files 6 7 Importing Files TGrid allows you to import the following file formats e ANSYS Prep7 cdb files e CGNS files e FIDAP neutral files e GAMBIT neutral files e HYPERMESH ASCII files e deas Universal files e NASTRAN files e PATRAN neutral files e STL files Importing Multiple Files You can also import multiple files into TGrid using the File Import menu Select the file format e g ANSYS prep7 cdb and the mesh type surface or volume to open the Select File dialog box Select the appropriate files from the Files selection list and click OK Alternatively use the appropriate TUI command e g file import ansys surf mesh and specify the names of the files to be imported Appending Multiple External Files You can also add files of any external format to an existing mesh This is known as appending files To append external files read or import the first file Use the File Import menu and select the appropriate file format e g ANSYS prep7 cdb and the mesh type surface or volume Enable Append File s in the Select File dialog box and import the necessary files 6 7 1 Importing Mesh Files Generated by Third Party Packages TGrid also allows you to import mesh information generated by some CAD packages ANSYS I deas NASTRAN PATRAN and HYPERMESH as well as mesh information in the CGNS CFD general notation system format These fil
174. ain with the specified do main mesh cavity region allows you to create a cavity to improve the existing volume mesh in the specified region mesh cavity remove zones allows you to create a cavity for removing zone s from an existing volume mesh mesh cavity replace zones allows you create a cavity for removing a set of zones from an existing volume mesh and replacing them with a new set of zones 13 9 Manipulating Cell Zones When TGrid creates a volume mesh of any cell shape from a boundary mesh these cells will be grouped into cell zones contiguous zones separated by boundaries You can manipulate these zones to control further mesh generation or to duplicate an existing volume mesh to model a repeated geometry 13 9 1 Active Zones and Cell Types After the initial mesh is generated all the cells are grouped into contiguous zones sep arated by boundaries An artifact of the meshing algorithm is that a virtual zone is created outside the outer boundary and it is always given a cell type of dead This zone is automatically deleted upon completion of the initial mesh generation If the initial mesh generation is interrupted for some reason this zone will remain in the mesh until the initialization is completed Other zone types available are fluid and solid ANSYS Inc April 15 2008 13 27 Improving the Mesh The zone just inside the outer boundary is automatically set to be active and labeled a fluid zone although
175. al Files 1 Select the File Import PATRAN neutral menu item 2 Select the Surface menu item to read a surface mesh or the Volume menu item to read a volume mesh OR Use one of the following TUI commands e file import patran surf mesh e file import patran vol mesh Reading HYPERMESH ASCII Files 1 Select the File Import HYPERMESH Ascii menu item 2 Select the Surface menu item to read a surface mesh or the Volume menu item to read a volume mesh OR Use one of the following TUI commands e file import hypermesh surf mesh e file import hypermesh vol mesh ANSYS Inc April 15 2008 6 13 File Types Reading STL Stereo Lithography Format Files Select the File Import STL menu itemor use the file import stl TUI command For information about the format of these files and details about importing them if the import commands are not available on your computer see Appendix A Importing Boundary and Volume Meshes For information about changing the options related to grid import see Section 6 7 4 Grid Import Filter Options 6 7 2 Importing FIDAP Neutral Mesh Files To read a FIDAP neutral file use either of the following e Select the File Import FIDAP neutral menu item and then select the Surface menu item to read a surface mesh or the Volume menu item to read a volume mesh e Use the file import fidap surf mesh or file import fidap vol mesh text interface commands 6 7 3 Importing GA
176. al Volume Based Skewness In the equilateral volume deviation method skewness is defined as Optimal Cell Size Cell Size 15 5 1 Optimal Cell Size Skewness where the optimal cell size is the size of an equilateral cell with the same circumradius Quality grids have a skewness value of approximately 0 1 for 2D and 0 4 for 3D Ta ble 15 5 1 provides a general guide to the relationship between cell skewness and quality In 2D all cells should be good or better The presence of cells that are fair or worse indicates poor boundary node placement You should try to improve your boundary mesh as much as possible because the quality of the overall mesh can be no better than that of the boundary mesh In 3D most cells should be good or better but a small percentage will generally be in the fair range and there are usually even a few poor cells ANSYS Inc April 15 2008 15 11 Reporting Mesh Statistics Normalized Equiangular Skewness In the normalized angle deviation method skewness is defined in general as Omax be be Omin 15 5 2 max I80 0 O aa where Omax largest angle in the face or cell Omin Smallest angle in the face or cell be angle for an equiangular face cell e g 60 for a triangle 90 for a square For a pyramid the cell skewness will be the maximum skewness computed for any face An ideal pyramid skewness 0 is one in which the 4 triangular faces are equilateral and equi
177. allows you to remesh boundary faces Refer to Sec tion 7 7 4 Remeshing Zones Using the Surface Retriangulation Panel for details Boundary Mesh Remesh Surface Retriangulation Face Zones Edge Zones Edge Create intersect 8 5 12 Angle Criterion intersect 9 5 6 xl Feature Angle 40 Feature Modify Face Remesh Options F Auto Edge Select Edge Zone Groups E Reconstruction Order boundary edge y F Draw Faces interior edge Replace Face Zone ANSYS Inc April 15 2008 7 57 Manipulating the Boundary Mesh Controls Face Zones contains a list of boundary face zones from which you can select the bound ary zone to be remeshed Edge Zones contains a list of edge loops that have been created for one or more face zones using the Create button Edge Zone Groups contains a list of edge zone types If you select a zone type from this list e g boundary edge all edge zones of that type will be selected in the Edge Zones list This shortcut allows you to easily select all zones of a certain type without having to select each zone individually Auto Edge Select selects the edge zones associated with a particular face zones auto matically Draw Faces includes the selected face zone in the display when you click the Draw button Edge Create contains parameters to create delete and modify edge loops Angle Criterion contains a drop down list to choos
178. also in hexadecimal so that they match the indices in the bodies of the grid connectivity sections The zone id and type are also in hexadecimal for consistency B 5 Periodic Shadow Faces Index 18 Scheme symbol xf periodic face C macro XF_PERIODIC_FACE Codes FLUENT TGrid Status required only for grids with periodic boundaries This section indicates the pairings of periodic faces on periodic boundaries Grids without periodic boundaries do not have sections of this type B 4 ANSYS Inc April 15 2008 B 5 Periodic Shadow Faces The format of the section is as follows 18 first index last index periodic zone shadow zone foo f01 10 21 20 21 where first index is the index of the first periodic face pair in the list last index is the last periodic face pair in the list periodic zone is the zone ID of the periodic face zone shadow zone is the zone ID of the corresponding shadow face zone These are in hexadecimal format The indices in the section body f refer to the faces on each of the periodic bound aries in hexadecimal the indices being offsets into the list of faces for the grid The first index and last index do not refer to face indices They refer to indices in the list of periodic pairs A partial example of such a section is as follows 18 1 2b ac 12 1f 13 21 ad 1c2 ANSYS Inc April 15 2008 Mesh File Format B 6 Cells Index 12 Scheme symb
179. alue after the currently displayed cell Clicking the Next Skew button repeatedly will display the skewed cells in the descending order of skewness The Next Skewbutton will be activated only after the Skew button has been clicked in the Modiy Cells panel Reset Skew resets the skewness values When you click Reset Skew both the Next Skew and Reset Skew buttons will be deactivated Click Skew and then Next Skew to display the skewed cells again ANSYS Inc April 15 2008 13 17 Improving the Mesh Redisplay updates the display in the display window This button is activated only when the Auto Redisplay option is disabled i You can disable Auto Redisplay for large meshes or when the graphics per formance of your computer is slow You can then use the Redisplay button to view the updated display Skew displays the cell with the worst highest skewness The cell will also be added to the Selections list Draw displays the cells connected to the selected node s or face s according to the options enabled in the Draw Cells group box 13 6 3 Text Commands for Modifying Cell Zones Text interface commands for modifying cell zones are as follows mesh modify clear selections deseclects the selected entities mesh modify deselect last deseclects the last selected entity mesh modify extract unused nodes extracts the unused nodes into a separate inte rior node zone mesh modify list selections lists the selected entities i
180. an be viewed and manipulated in a web browser graphics window Non geometric entities such as text titles color bars and orientation axis are not exported In addition most display or visibility characteristics set in TGrid such as lighting shading method transparency face and edge visibility outer face culling and hidden line removal are not explicitly exported but are controlled by the software used to view the VRML file Window Dump UNIX systems only selects a window dump operation for generating 6 18 the hardcopy With this format you will need to specify the appropriate Window Dump Command ANSYS Inc April 15 2008 6 9 Saving Hardcopy Files Choosing the File Type To save a PostScript or EPS file you can choose either of the following file types e Raster A raster file defines the color of each individual pixel in the image Raster files have a fixed resolution Raster supports IRIS image JPEG PostScript EPS and TIFF formats e Vector A vector file defines the graphics image as a combination of geometric primitives like lines polygons and text Vector files are usually scalable to any resolution Vector supports PostScript EPS and VRML formats Note For the quickest print time save vector files for simple 2D displays and raster files for complicated scenes Specifying the Color Mode For all formats except the window dump you can specify which type of Coloring you want to use for the hardcopy f
181. anage revolve face zone generates cells by revolving a face thread mesh manage rotate rotates all nodes of specified cell zones by a specified angle mesh manage scale scales all nodes of specified cell zones by a specified factor 13 32 ANSYS Inc April 15 2008 13 10 Using Domains to Group and Mesh Boundary Faces mesh manage set active sets the specified cell zones to be active mesh manage translate translates all nodes of specified cell zones by a specified vec tor mesh manage type allows you to changes the type of the cell zone mesh separate separate cell by face separates cells that are connected to a spec ified face zone into another cell zone This separation method applies only to prism cells mesh separate local regions define allows you to define the local region mesh separate local regions delete deletes the specified local region mesh separate local regions init creates a region encompassing the entire geom etry mesh separate local regions list all regions lists all the local regions defined mesh separate separate cell by mark separates cells within a specified local region into another cell zone mesh separate separate cell by region separates contiguous regions within a cell zone into separate cell zones mesh separate separate cell by shape separates cells with different shapes pyra mids tetrahedra etc into separate cell zones mesh separate separate cell by size separates
182. and employs various types of input controls that make up the form The various types of controls you will see are described in the following sections 3 3 1 Categories of Panels After entering the data using the controls of a panel you can either apply the changes you have made or abort the changes Each panel falls into one of two behavioral categories depending on how it was designed for applying or aborting the changes e Some panels are used in situations where you have to apply the changes and im mediately close the panel Mouse Buttons ua poeme Middle mouse zoom y FLUENT Defaults Workbench Defaults This type of panel includes two push button controls OK applies any changes you have made to the panel and closes the panel Cancel ignores the changes you have made and closes the panel e Some panels are used in situations where you have to keep the panel displayed on the screen after changes have been applied This helps to quickly go back to that panel and make more changes Panels used for mesh generation and display often fall into this category ANSYS Inc April 15 2008 3 9 Graphical User Interface S Scene Description Names E Geometry Attributes Scene Composition top e A Grerters Sate Srour let phi de inlet Hsin Frame Options bottom ise Yahin Pathlines hae Sten Delete Geometry This type of panel includes
183. and any hexahedral cells into TGrid and continue the mesh generation process there The first step in producing an unstructured grid is to define the shape of the domain boundaries Surface grids created in CAD CAE packages can be read into TGrid using the appropriate menu item in the File Import pull down submenu or the associated text commands or converted using the appropriate stand alone grid filter When the grid generation is completed you can read the 3D grid created by TGrid into the solver After a grid is read into the solver the remaining operations are performed there These include setting boundary conditions defining fluid properties executing the solution and viewing and postprocessing the results 1 3 Program Capabilities TGrid is a robust and a highly automated unstructured volume mesh generator with the following meshing capabilities e Generates triangles tris and quadrilaterals quads in 2D e Generates tets hexcore prisms pyramids in 2D e Generates volume mesh that is accepted by FLUENT e Uses Delaunay triangulation method for tris tets e Uses advancing layer method for prisms e Generates hexcore mesh e Has a robust boundary wrapper tool e Can export polyhedral cells e Has tools for checking repairing and improving boundary mesh to ensure a good starting point for the mesh e Is capable of manipulating face cell zones e Is flexible it allows the most appropriate cell type to be used to gene
184. and cap faces for the simultaneously grown prism layers If you want to retain individual prism cell zones and cap faces enable Grow Individually in the General Options group box in the Prisms Growth Options panel 4 Click Apply in the Prisms panel 5 Repeat this procedure for other zones for which you want to apply different growth controls 6 Click Create A Before you click the Create button ensure that all the zones for which you want to grow prisms are selected in the Boundary Zones list 10 3 2 Growing Prisms on a Two Sided Wall Two sided walls may be present in some geometries To grow prisms on both sides of a two sided wall e g growing prisms on dangling walls do the following 1 Select the two sided wall on which you want to grow prisms from the Boundary Zones selection list 10 6 ANSYS Inc April 15 2008 10 3 Prism Meshing Options 2 Specify the prism growth parameters as required 3 Enable Grow on Two Sided Wall in the Growth tab of the Prisms panel 4 Click Create See Figure 10 3 2 for details Figure 10 3 2 Prism Growth on a Dangling Wall 10 3 3 Detecting Proximity and Collision If the zones on which you want to grow prisms are very close to each other the prism layers from zones may intersect or collide with each other This results in bad quality of prism layers For example in Figure 10 3 3 the prism layers grown from proximal surfaces intersect each other The Allow Shrinkage opti
185. ane for a nonsymmetric domain Camera opens the Camera Parameters panel see Section 14 6 4 The Camera Param eters Panel 14 6 2 The Write Views Panel The Write Views panel allows you to save selected views to a view file This feature allows you to transfer views between mesh files Write Views Views to Write H Controls Views To Save is a selectable list of the defined views The selected views will be saved to a view file when you click OK ANSYS Inc April 15 2008 14 33 Examining the Mesh 14 6 3 The Mirror Planes Panel The Mirror Planes panel allows you to define a symmetry plane for a nonsymmetric domain for use with graphics Controls Plane Equation contains inputs for specifying the equation for the mirror plane AX BY CZ Distance Mirror Planes contains a list of all mirror planes you have defined using this panel Mirror planes that exist in the domain due to symmetry will not appear in this list since they cannot be modified Add adds the plane defined by the Plane Equation to the Mirror Planes list Delete deletes the plane s selected in the Mirror Planes list 14 6 4 The Camera Parameters Panel The Camera Parameters panel allows you to modify the camera through which you are viewing the graphics display 14 34 ANSYS Inc April 15 2008 14 6 Modifying the View Controls Camera contains a drop down list of the parameters that defi
186. ange this using the command mesh prism controls merge ignored threads which will generate more than one thread per base thread To merge one or more prism cell zones with other cell zones and merge the corresponding face zones use the Merge option in the Manage Cell Zones panel see Section 13 9 3 The Manage Cell Zones Panel By default the prism cap n zones will be wall zones If you do not want to include these walls in the model change them to interior zones or any other type using the Manage Face Zones panel see Section 7 13 1 The Manage Face Zones Panel 10 5 How T Grid Builds Prisms TGrid follows the following steps to build the prism and to create a high quality mesh 10 12 1 Boundary mesh analysis Analyze the initial surface mesh to determine if any adjacent zones should be projected to and retriangulated if triangular or if their faces should be used as the sides of new prism cells if quadrilateral ANSYS Inc April 15 2008 10 5 How T Grid Builds Prisms For details on how TGrid determines whether to use existing boundary zones or not see Section 10 6 Using Adjacent Zones as the Sides of Prisms 2 Prism layer growth Grow layers of prisms one by one based on the layer height specification This is a multi step procedure and hence you can modify or skip some of the steps a Determine the initial direction vectors so that TGrid will know the direction in which to build the prisms Severa
187. angular and the quadrilateral base face is a square The guidelines in Table 15 5 1 apply to the normalized equiangular skewness as well Size Change Size change is the ratio of the area or volume of a cell in the geometry to the area or volume of each neighboring face or cell This ratio is calculated for every face or cell in the domain The minimum and maximum values are reported for the selected zones Squish Squish is a measure used to quantify the non orthogonality of a cell with respect to its faces It is defined as follows l A re re 15 5 3 where A face unit area vector re the vector connecting the adjacent cell centroids for face squish or and the cell face centroid for cell squish Edge Ratio The edge ratio is defined as the ratio of maximum length of the edge of the element to the minimum length of the edge of the element By definition edge ratio is always greater than or equal to 1 Higher the value of the edge ratio the less regularly shaped is its associated element For equilateral element shapes the edge ratio is always equal to 1 15 12 ANSYS Inc April 15 2008 15 5 Mesh Quality Warp Face warp applies only to quadrilateral elements and is defined as the variation of normals between the two triangular faces that can be constructed from the quadrilateral face The actual value is the maximum of the two possible ways triangles can be created Mathematically it is express
188. any problems it finds along with the domain extents and the maximum and minimum cell volumes which must not be negative The sample output is as follows ANSYS Inc April 15 2008 13 37 Improving the Mesh Domain extents x coordinate min 1 016026e 02 max 2 621100e 02 y coordinate min 3 513216e 02 max 2 000000e 02 z coordinate min 1 016057e 02 max 1 016057e 02 Volume statistics minimum volume 6 357072e 03 maximum volume 1 990373e 03 total volume 7 620820e 06 Face area statistics minimum face area 5 638886e 02 maximum face area 2 900312e 02 average face area 1 963704e 01 Checking number of nodes per cell Checking number of faces per cell Checking cell faces Checking face handedness Done If any problems are reported use the Display Grid panel see Section 14 1 3 The Dis play Grid Panel to find out where the problem faces or cells are located If you have used domains to generate the mesh or group zones for reporting as described in Sec tion 13 10 Using Domains to Group and Mesh Boundary Faces only the mesh in the active domain will be checked 13 12 Clearing the Mesh If you are dissatisfied with the mesh generated you can choose to clear the mesh and start again from the boundary mesh When TGrid clears the mesh it deletes all interior nodes and faces and all cells both live and dead Only the boundary nodes and faces will be left After the mesh is cleared you can generate
189. apping Select allows you to select the seed faces when the Automatic option is disabled Mark marks the faces to be merged Merge merges the thin surfaces into a single surface Post Single Surface allows you to remove unmerged island regions after recovering the thin surface Start Seed Face specifies the seed face to be used for marking the unmerged regions You need to specify the seed face while marking the unmerged regions manually Max Face Count specifies the maximum allowable face count for the removal of the unmerged regions Mark marks the unmerged regions to be removed Delete deletes the marked faces Reset clears the previously selected seed face Auto automatically marks and deletes the unmerged regions Remove Crossover allows you to remove the crossover configurations the wrapper surface ANSYS Inc April 15 2008 8 43 Wrapping Boundaries Automatic automatically removes the crossover configurations Seed Face specifies the seed face for determining the crossover con figuration Max Faces specifies the maximum number of faces to be collected and deleted after performing this operation Iteration specifies the number of attempts to remove the crossover configuration in case of failure Relaxation specifies the relaxation factor for node smoothing in making different number of attempts Modify opens the Modify Boundary panel Mark marks the cells to be considered for the selected post w
190. arately The User Defined Groups panel allows you to define new face and or edge groups update existing groups activate or delete a particular group Although the panel is opened from the Boundary menu it can be used with all panels that contain zone lists Note When a user defined group is activated the wild cards used for zone selection in all the TUI commands will return zones contained in the active group For example the command display boundary grid will display all the boundary zones contained in the active group 7 72 ANSYS Inc April 15 2008 7 12 Creating Groups 7 12 1 The User Defined Groups Panel The User Defined Groups panel allows you to create groups of surfaces which will be available in all the TGrid panels Boundary gt Zone Group User Defined Groups Options Face Zones Face Groups 4 eng guard 3 eng top v Edges engine front axle front wheels front wing front wing sides guard 1 rear wheels axle rear wing Face Zone Groups 5 Activate Update Delete front wheel axle Faces EPEE glo wing front wing rear geometry f Controls Options contains options for creating groups Faces specifies the creation of a group containing one or more face zones Edges specifies the creation of a group containing one or more edge zones Face Zones contains a list of available face zones from which you ca
191. are described in briefly in this section The basic measures include clustering smoothness skewness and aspect ratio The default quality measure is skewness You can check the quality of faces and cells using the following panels e Report Face Limits panel see Section 15 2 1 The Report Face Limits Panel e Report Cell Limits panel see Section 15 3 1 The Report Cell Limits Panel e Report Boundary Cell Limits panel see Section 15 4 1 The Report Boundary Cell Limits Panel To specify the quality measure skewness aspect ratio change in size etc use the Quality Measure panel see Section 15 5 2 The Quality Measure Panel 15 8 ANSYS Inc April 15 2008 15 5 Mesh Quality 15 5 1 Quality Measures Available in T Grid Clustering The requirement for clustering is that the mesh be fine enough to resolve the primary features of the flow being analyzed The resolution depends on the boundary mesh that you start from and also the parameters controlling the generation of the interior mesh Smoothness In a high quality mesh the change in size from one face or cell to the next should be gradual smooth Large differences in size between adjacent faces or cells will result in a poor computational grid because the differential equations being solved assume that the cells shrink or grow smoothly Figure 15 5 1 illustrates different changes in size for triangular cells Smooth Change in Large Jump in Cell Size Cell Size
192. ary Zones list You can also select multiple types to select all the zones of different types e g inlet and outlet Options contains options for defining the direction of node movement Seed Normal specifies node movement in the direction of the seleted seed node normal Local Normal specifies node movement in the direction of the individual node normals Seed Node specifies the seed node selected Node Count determines the nodes to be moved Move by specifies the distance by which the node is to be moved Flip flips the normal direction Draw displays the direction and distance of the node movement Move moves the node s according to the parameters specified 7 3 4 Text Commands for Boundary Modification The tools for modifying the boundary work in conjunction with the mouse To use them 1 Select the appropriate entity in the graphics window using the mouse or the selec tion commands 2 Enter the command in the text window 3 First set the selection probe to select Each object that you pick is stored in a list 4 Monitor this list of selected items using list selections The list can be modified using clear selections and deselect last commands After you perform an operation on the selected items the selection list is cleared These text commands perform the same functions as the Modify Boundary panel see Section 7 3 1 Using the Modify Boundary Panel The following operations are available ANSYS Inc A
193. ary modify merge merges pairs of nodes The first node selected is retained and the second is the duplicate that is merged boundary modify move moves the selected node to the specified position boundary modify next skew finds the triangular face having the next highest skewness value after that of the worst skewed face in the grid or the active group The face ID its skewness the longest edge ID and the node ID opposite to the longest edge are displayed in the console boundary modify rezone moves the selected faces from their current zone into the se lected zone if the selection list contains a zone and one or more faces 7 30 ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh boundary modify select filter selects a filter The possible filters are off cell face edge node zone and position If off is chosen then when a selection is made it is first checked to see if it is a cell then a face an edge and so on When the node filter is used if a cell or face is selected the node closest to the selection point is picked Thus nodes do not have to be displayed to be picked boundary modify select probe selects the probe function The possible functions are off label select and print When the function is off mouse probes are disabled label prints the selection label in the graphics window select adds the selection to the selection list and print prints the information on the selection in the console wind
194. ate a series of commands instead of entering them repeatedly on the command line It can also be used to produce a record of the input to a program session for later reference although transcript files are often more useful for this purpose see Section 6 5 Transcript Files Command input is taken from the specified journal file until its end is reached at which time control is returned to the standard input usually the keyboard Each line from the journal file is echoed to the standard output usually the screen as it is read and processed Note A journal file by design is a simple record playback facility Hence it knows noth ing about the state in which it was recorded or the state in which it is being played back Therefore recreate the state in which the journal was written before you read it into the program For example if the journal file includes an instruction for TGrid to save a new file with a specified name check that no file with that name exists in your directory before you read in your journal file If a file with that name exists and you read in your journal file it will prompt for a confirmation to overwrite the old file when the program reaches the write instruction The journal file contains no response to the confirmation request Hence TGrid will not be able to continue following the instructions of the journal file Other conditions that may affect the ability of the program to perform the instructions contained
195. ateral face or cell This is the default method that was available in previous releases of TGrid Normalized Equiangle Deviation selects the skewness method that is based on the deviation from a normalized equiangular angle This method is always used for pyramids and prisms 15 5 3 Text Commands for Selecting the Quality Measure The following text command can be used for specifying the quality measure report quality method specifies the method to be used for reporting face and cell quality 15 6 Printing Grid Information The report print info text command allows you to obtain information about indi vidual components of the mesh This command also appears in the boundary menu When you use this command TGrid will prompt you for an entity i e a node face or cell An entity name consists of a prefix and an index The valid prefixes are bn boundary node n node bf boundary face f face and c cell Hence the name of the first boundary node would be bn1 If the first node is a boundary node then both bni and n1 refer to the same node The output for each type of entity is as explained in this section 15 6 1 Boundary Node report gt print info entity bni bn1 3 0 0 0 0 1 b 2099 bf1093 bf193 ANSYS Inc April 15 2008 15 15 Reporting Mesh Statistics The following information is listed for the boundary node e associated zone ID e Cartesian coordinates of the node e node radiu
196. ateral and triangular cells Non Conformals specifies that a non conformal interface will be created as a tran sition between the quadrilateral and triagular cells Set opens the Pyramids panel see Section 9 3 3 The Pyramids Panel or the Non Conformals panel see Section 9 4 1 The Non Conformals Panel as ap propriate Volume Fill contains options for volume meshing Tri Tet allows you to mesh the geometry with triangular tetrahedral hybrid mesh Hexcore allows you to mesh the geometry with tetrahedral hybrid mesh adjacent to the walls and hexahedral mesh in the core flow region No Fill allows you to mesh the boundary layers with prisms and pyramids or non conformals as specified without creating tetrahedral hexahedral cells Set opens the Tri Tet panel see Section 11 5 The Tri Tet Panel or the Hex core panel see Section 12 4 The Hexcore Panel as appropriate Options contains additional meshing options Merge Cell Zones toggles the merging of cell zones during meshing 9 3 Generating Pyramids A pyramid has a quadrilateral face as its base and four triangular faces extending from the sides of the quadrilateral up to a single point above the base See Figure 9 3 1 To generate a conformal mesh with a region of tetrahedral cells adjacent to a region of hexahedral cells in TGrid you will first create a layer of pyramids as a transition from quadrilateral faces to triangular faces After creating a single laye
197. available in the Edge Create group box in the Surface Retriangulation panel You can create the edge loops according to your requirement by specifying an appro priate combination of the edge loop creation approach and angle criteria refer to Sec tion 7 6 1 Creating Edge Loops for details The procedure for creating the edge loops using the Surface Retriangulation panel is as follows 1 Select the required zone from the Face Zones list 7 54 ANSYS Inc April 15 2008 7 7 Remeshing Boundary Zones 2 Select the appropriate option from the Angle Criterion drop down list in the Edge Create group box Specify an appropriate value for the Feature Angle when using the Fixed angle criterion 3 Click Create to create the edge loops Alternatively you can use the Feature Modify panel to create the edge loops Refer to Section 7 6 1 Creating Edge Loops Using the Feature Modify Panel for details The Face Seed approach is available only when you use the Feature Modify panel for creating edge loops Click the Feature Modify button to open the Feature Modify panel You can also draw the edge loops to determine their direction i e which end is the start point and which is the end point 7 7 2 Modifying Edge Loops You can modify the node distribution on the edge loops using the Feature Modify panel which is opened using the Feature Modify button in the Surface Retriangulation panel If you want to assign different node dis
198. avoid pyramids on quad faces when growing prisms from a boundary For mix surface mesh types quadrilateral and triangular you can select Non Conformal in the Quad Tet Transition list in the Auto Mesh panel TGrid will copy the surfaces containing quad cells and triangulate them keeping the original faces intact The free nodes of the triangulated surface will then be merged with the nodes of the original surface mesh and both the surfaces will be converted to interface type ANSYS Inc April 15 2008 11 5 Generating Triangular Tetrahedral Meshes 11 1 5 Further Mesh Improvements Examine the following after generating the mesh using the automatic mesh generation process e The cell distribution see Section 15 4 Reporting Boundary Cell Limits e The cell limit reports see Sections 15 3 and 15 4 e The mesh size see Section 15 1 Reporting the Mesh Size For 2D problems it is possible to reduce the maximum skewness to 0 4 In 3D it is typically possible to reduce the maximum skewness to the range 0 8 0 9 Skewness values higher than 0 9 are typically obtained due to constraints imposed by the surface meshes If you still have highly skewed cells apply additional swapping and smoothing to improve the quality see Sections 13 1 and 13 2 To increase the density of the grid locally use refinement regions see Section 11 4 1 Using Local Refinement Regions A Do not over refine the grid in TGrid The volume mesh produced in TGri
199. awing the selected type of node Size specifies the size of the symbol Styles contains a list of all the different types of nodes and faces that can be displayed The settings under Faces Edges and Nodes will apply to the node or face type selected in the Styles list These types correspond to the options in the Display Grid panel see Section 14 1 3 The Display Grid Panel The default style attributes are listed in Table 14 1 1 refine indicates boundary faces to be refined free indicates free nodes or faces left handed indicates faces that do not follow the right hand rule with respect to their cell neighbors multi indicates multiply connected nodes or faces unmeshed indicates unmeshed nodes or faces unused indicates unused nodes or faces mark indicates marked objects for expert users tag indicates tagged objects for expert users face size indicates faces within the specified face size range cell size indicates cells within the specified cell size range face quality indicates faces within the specified face quality range cell quality indicates cells within the specified cell quality range 14 16 ANSYS Inc April 15 2008 14 2 Checking Face Distribution Styles Faces Edges Nodes Visible Color Visible Color Weight Visible Color Symbol Size left handed yes red yes red 2 yes red o 0 5 refine yes magenta yes yellow 2 yes magenta o 0 5 free yes cya
200. ax Y Max Z Max specifies the maximum values of physical dimensions of the bounding box in X Y and Z direction respectively This option is available only if you have selected Absolute Delta X Min Delta Y Min Delta Z Min specifies the clearance values that you want to specify from X Min Y Min or Z Min respectively This option is available only if you have selected Relative Delta X Max Delta Y Max Delta Z Max specifies the clearance values that you want to specify from X Max Y Max or Z Max respectively This option is available only if you have selected Relative Create creates a bounding box of specified values 7 14 2 Creating a Planar Surface Mesh In some cases you may need to create a plane surface mesh in the input geometry e g creating a baffle like surface inside a hollow tube TGrid allows you to create a plane surface and mesh the surface using triangular cells of required size using the Plane Surface panel It is possible to create a planar surface of rectangular shape only You cannot create a planar surface of any other shape There are two methods available for creating planar surface mesh 7 82 e Axis Direction Method This method allows you to create the plane surface perpendicular to any of the coordinate axes Select the axis perpendicular to which you want to create a pla nar surface mesh and then specify the coordinates of the points that will form a rectangular surface perpendicular to the axis
201. ay Grid panel will be in effect in the resulting grid display ANSYS Inc April 15 2008 9 19 Creating a Mesh 9 3 4 Text Interface for Generating Pyramids Text commands for creating pyramid cells are as follows mesh pyramid controls fill angle specifies the dihedral angle between adjacent pyramid faces for which tetrahedral cells should be created when the fill cap option is enabled mesh pyramid controls fill cap enables the filling of the space between pyramids with tetrahedra mesh pyramid controls neighbor angle sets the threshold dihedral angle used to limit the neighboring faces considered for pyramid creation For example if the value is set to 110 degrees and the angle between a given quadrilateral face and the neighboring triangular face is greater than 110 degrees the resulting pyramid will not include the triangular face mesh pyramid controls offset factor specifies the fraction of the computed pyra mid height offset by which the pyramid heights will be randomly adjusted The default value is 0 indicating that all pyramids will have the exact height computed by TGrid A value of 0 1 for example will limit each adjustment to 10 of the computed height mesh pyramid controls offset method specifies the method by which offset distances are determined mesh pyramid controls offset scaling specifies the scaling s to be used to deter mine the height of the pyramid See Equation 9 3 1 mesh p
202. bels sets the strings that define the x and y axis labels display xy set lines sets the pattern weight and color of the plot lines display xy set log toggles the log scaling on the x and y axis display xy set markers sets parameters for the data markers display xy set numbers sets the format and precision of the data numbers displayed on the x and y axis display xy set rules sets the visibility line weight and color of the major and minor rules in the x and y axis directions 14 5 Controlling Display Options When examining graphics you may want to change some of the attributes of the display window For example you can open a number of windows to look at several different displays simultaneously control the lighting attributes in a scene or modify rendering parameters These and other options are available in the Display Options panel or with the associated text commands ANSYS Inc April 15 2008 14 25 Examining the Mesh 14 5 1 The Display Options Panel The Display Options panel provides an interactive mechanism for setting attributes or options that control how and where a scene is rendered Display gt Options Controls Rendering allows you to modify characteristics of the display that are related to the way in which scenes are rendered Line Width controls the thickness of lines The default is 1 Point Symbol sets the symbol used for nodes and data points Animation Option
203. between the adjacent zone and the prism growth direction must be less than the specified threshold Max Adjacent Zone Angle in the Project section of the Prisms panel The default threshold value is 45 degrees In Figure 10 6 1 the zone on the right will be projected to and retriangulated while the zone on the left will be excluded Retriangulation As shown in Figure 10 1 1 the sides of the prism will always be quadrilateral faces regardless of the type of face from which a 3D prism is built triangular or quadrilateral If the prism side nodes are projected to an adjacent triangular boundary face zone 1 The prism side faces on the shared boundary will be overlaid on the triangular faces of the existing boundary zone 2 TGrid will retriangulate the triangular boundary zone so that the triangular portion of the zone ends at the border of the portion now filled with quadrilateral faces This is done to obtain a conformal mesh where all the nodes match up at face edges 3 The triangles that were overlapping the quadrilateral prism side faces will be deleted Figure 10 6 2 shows the initial boundary mesh for a car and the symmetry boundary beside it If the prisms are generated from the car body without retriangulation of the triangular symmetry boundary the resulting boundary mesh will be as shown in Figure 10 6 3 With retriangulation the boundary mesh will appear as in Figure 10 6 4 Though it is possible to disable retriangula
204. bles disables the display of captions in the graphics display window Axes enables disables the display of the axis triad Colormap enables disables the display of the colormap Colormap Alignment allows you to adjust the alignment of the colormap in the graphics window Select the side i e Left Top Right Bottom where you want to align the colormap from the drop down list Apply applies the specified attributes and re renders the scene in the active graphics window with the new attributes To see the effect of the new attributes on other graphics windows redisplay them Info prints out information about the graphics driver in the console Lights opens the Lights panel see Section 14 7 1 The Lights Panel which allows you to create delete and modify directional light sources 14 28 ANSYS Inc April 15 2008 14 5 Controlling Display Options 14 5 2 Text Commands for Controlling Display Options Text commands with functionality similar to the controls in the Display Options panel are listed below display open window opens a graphics window display close window closes a graphics window display set window sets the specified window as the active graphics window display set line weight sets the line width factor display set reset graphics resets the graphics system display set title sets the problem title display set rendering options contains the commands that allow you to set op tions that determine how th
205. bottom line As the number of text lines grows the lines will be scrolled off the top of the window The scroll bar on the right allows you to go back and look at the preceding text Use lt Control C gt to interrupt the program while it is working You can also copy and paste operations between the Console and other X Window or Windows applications that support copy and paste ANSYS Inc April 15 2008 3 1 Console To perform the copy and paste operation on a UNIX system do the following 1 Select the text by highlighting it 2 Release the left mouse button 3 Move the pointer to the target window 4 Press the middle mouse button to paste the text To copy the text to the clipboard on a Windows system do the following 1 Select the text by highlighting it 2 Release the left mouse button 3 Press the lt Ctrl gt and lt Insert gt keys together 3 1 2 Menu Bar The menu bar organizes the GUI menu hierarchy using a set of pull down menus see Figure 3 1 2 Menu items are arranged in a logical order to correspond to the sequence of actions that you perform in TGrid Figure 3 1 2 The TGrid Menu Bar A pull down menu contain items that perform commonly executed actions Figure 3 1 3 shows the UNIX Report pull down menu Using the Mouse To select any item from the pull down menu do the following 1 Click the pull down menu using the left mouse button 2 Move the pointer to the item you want to
206. canceled Fal You can use the command mesh tritet preserve cell zone to specify the cell zone s to be preserved during mesh generation and click the Mesh button to proceed with the automatic mesh generation 11 1 3 Automatic Meshing of Multiple Cell Zones The Auto Mesh tool allows you to mesh multiple cell zones automatically This is useful when the mesh has multiple cell zones e g the problem requires a fluid zone and one or more solid zones You can refine the mesh using refinement parameters specific to individual zones if required The procedure for meshing multiple cell zones comprises the following steps 1 Initialize the mesh 2 Activate the appropriate zones using the Manage Cell Zones panel see Section 13 9 3 The Manage Cell Zones Panel 3 Set the zone specific refinement parameters and refine the active zones If you want to mesh all the zones included in the mesh with the same refinement parameters modify the Non Fluid Type in the Tri Tet panel see Section 11 5 The Tri Tet Panel 11 4 ANSYS Inc April 15 2008 11 1 Automatically Creating a Tri or Tet Mesh i By default the Non Fluid Type is set to dead as TGrid considers the grid to comprise a single fluid region and one or more dead regions The active zone is considered to be the fluid zone and only this fluid zone will be considered for refinement during the automatic meshing process When the Non Fluid Type is set to a type other than dead e g
207. cates that the geom etry and location of the intersect zone the zone in the left gui zone list is to be preserved This option is enabled by default boundary remesh controls intersect tolerance allows you to specify the toler ance value boundary remesh controls intersect within tolerance performs the intersection operation only within the specified tolerance value It is useful only for the Intersect option boundary remesh clear marked faces clears the highlighting of the triangles that are marked boundary remesh create edge loops allows you to create edge loops for the selected face zone boundary remesh create intersect loop creates edge loop along the line or curve of intersection boundary remesh create join loop creates edge loop on boundary of the region of overlap of two surfaces boundary remesh create stitch loop creates edge loops for connecting two surfaces along their free edges boundary remesh delete overlapped edges deletes overlapped edges created during remeshing 7 14 ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh boundary remesh insert edge zone allows you to insert an edge zone into a trian gulated boundary face zone boundary remesh mark intersecting faces highlights the triangles in the neighbor hood of the line of intersection boundary remesh mark join faces highlights the triangles in the neighborhood of the join edge loop boundary remesh mark stitch fa
208. cedure is repeated for the specified iterations per face You can also set the number of repetitions through the automatic correction procedure as required By default TGrid performs the correction procedure twice ANSYS Inc April 15 2008 13 19 Improving the Mesh 13 7 2 Semi Automatic Correction The semi automatic correction is available only for skewness based improvement The generic procedure for using the semi automatic correction is as follows 13 20 Select the appopriate zones in the Cell Zones drop down list and the Boundary Zones selection list Specify values for Max Skew Iterations Node and Feature Angle as appropriate Enable Restrict Boundary Nodes Along Surface if required When this option is enabled the movement of the boundary node will be limited to the plane containing the boundary faces sharing the boundary node see Figure 13 7 1 A Boundary Node Movement B Boundary Node Movement not Restricted in Plane Restricted in Plane Figure 13 7 1 Movement of Boundary Nodes Click Skew to display the cell with the maximum skewness depending on the skew ness threshold specified TGrid will display the cell having maximum skewness and cells faces within a pre defined range of the cell Click Propose TGrid will highlight the node to be moved and the alternative position The improvement in the skewness will also be reported in the TGrid console Click Accept if the proposed pos
209. cells based on the specified mini mum and maximum cell sizes mesh separate separate cell by skew separates cells based on the specified cell skewness 13 10 Using Domains to Group and Mesh Boundary Faces Domains allow you to group different boundary zones together so that you can create tetrahedral meshes in the region they enclose or you can limit the zones available for a display or report to only those zones in a selected subset of the domain rather than the entire domain ANSYS Inc April 15 2008 13 33 Improving the Mesh 13 10 1 Using Domains If you are generating a hybrid mesh containing quads and tris in 2D or hexas tets and pyramids in 3D identify a domain of the global mesh as the region in which you want to generate triangular or tetrahedral cells You can also use domains to group boundary zones so that you can perform diagnostics on them or display them When you display the grid the zones available for display will be only those zones that are included in the active domain Similarly diagnostic reports will report information about only those zones e If you want to check a subset of the global domain you can create and activate a domain that includes the desired zones and then proceed with the display or report e If you want your grid display or report to include all zones in the mesh be sure to activate the global domain in the Domains panel 13 10 2 Defining Domains The procedure for defin
210. ces Number sets the number of boundary nodes or faces depending on the selection in the Boundary list The quality of cells containing this number of boundary nodes or faces will be reported when you click on Compute ANSYS Inc April 15 2008 15 7 Reporting Mesh Statistics Quality Measure opens the Quality Measure panel see Section 15 5 2 The Quality Measure Panel in which you can select the measure of quality to be reported skewness aspect ratio etc Minimum shows the reported minimum quality measurement skewness by default of the cells with the specified number of boundary nodes or faces Maximum shows the reported maximum quality measurement skewness by default of the cells with the specified number of boundary nodes or faces Compute calculates the minimum and maximum quality measurement for boundary cells with the specified number of boundary nodes or faces 15 4 2 Text Commands for Reporting Boundary Cell Limits The following TUI command is associated with reporting boundary cell limits report boundary cell quality reports the quality of boundary cells If you spec ify zero for number of boundary faces you will be prompted for number of boundary nodes 15 5 Mesh Quality The quality of the mesh guarantees the best analysis results for the problem minimizes the need for additional analysis runs and improves one s predictive capabilities Mesh quality is determined by some measures which
211. ces highlights the triangles in the neighborhood of the stich edge loop boundary remesh remesh overlapping zones allows you to remesh overlapping face zones boundary remesh stitch face zones allows you to connect two surfaces along their free edges boundary remesh intersect face zones allows you to connect two intersecting sur faces boundary remesh join face zones allows you to connect two overlapping faces boundary remesh stitch zone allows you to connect free edges of a group of surfaces There must be some initial connection to start with 7 3 Modifying the Boundary Mesh TGrid provides tools for making boundary repairs enabling you to perform primitive operations on the boundary mesh such as creating and deleting nodes and faces moving nodes swapping edges merging and smoothing nodes collapsing nodes edge s and face s splitting faces and moving faces to another boundary zone 7 3 1 Using the Modify Boundary Panel This section describes the generic procedure for modifying the boundary mesh using the Modify Boundary panel In addition to the Modify Boundary panel you will also use the Display Grid panel see Section 14 1 3 The Display Grid Panel during the modification process 1 Display the boundary zone s that you want to modify using the Display Grid panel If you need to modify many zones display them one at a time to make the graphics display less cluttered 2 Select the type of entity you want
212. ces using the boundary create tri surface text command and then create pyramids pyramids pierce boundary pyramids pierce boundary Figure 9 3 5 Pyramid Cells Intersecting Each Other and Boundary The skewness based pyramid creation will use the existing triangular faces and avoid the intersection problem see Figure 9 3 6 High Aspect Ratio Creating pyramids on quadrilateral faces with very high aspect ratios results in highly skewed triangular faces Subsequent attempts to create a tetrahedral mesh from these elements will produce a poor quality mesh ANSYS Inc April 15 2008 9 21 Creating a Mesh pyramids do not pierce boundary Figure 9 3 6 Fixed Intersecting Pyramid Cells Using Triangular Faces Irrespective of the method used to generate the quadrilaterals modify the meshing strat egy to reduce the aspect ratio using an external grid generation package or the prism layer capability 9 4 Creating a Non Conformal Interface For meshes containing both hexahedral and tetrahedral elements you can generate a non conformal interface to avoid creating intermediate pyramids as transition elements between the quadrilateral and triangular surfaces You can also choose to create a non conformal interface when growing prisms from a boundary on a surface mesh to avoid quad faces in the domain to be meshed TGrid will copy the surfaces containing quad elements and triangulate them while keeping the original surfaces in
213. cified Max Angle and Max Skew parameters Max Angle specifies the maximum angle between two adjacent face normals When the Swap option is active only faces with an angle below this value will be swapped This restriction prevents the loss of sharp edges in the geometry The valid range of entries is 0 to 180 degrees and the default is 10 degrees The larger the angle the greater the chance that a face swap will occur that may have an impact on the flow solution See Section 13 2 Swapping for details about swapping When the Smooth option is active the nodes on a face will be smoothed only if one of the angles between the face normals is less than Max Angle Relax used with the Smooth option specifies the relaxation factor by which the com puted change in node position should by multiplied before the node is moved A value of zero results in no node movement and a value of 1 results in movement equivalent to the entire computed increment Max Skew used only with the Swap option specifies the maximum allowable face skewness as a result of edge swapping If a swap will cause the skewness of a face to exceed this value TGrid will not perform the swap See Section 13 2 Swapping for details about swapping Refinement contains controls for defining refinement parameters Type allows you to specify refinement based or marking or proximity when the Refine option is selected Mark allows you to refine the marked faces Proximity allows
214. cter then the name must be surrounded with double quotes One consequence of this convenience is that filename prompts do not evaluate the re sponse For example the following sequence will end up writing a hardcopy file with the name fn not valve ps define fn valve ps Since the filename prompt did not evaluate the response fn did not get a chance to evaluate valve ps as it would for most other prompts 5 6 ANSYS Inc April 15 2008 5 2 Text Prompt System 5 2 6 Lists Some functions in TGrid require a list of objects such as numbers strings booleans etc A list is a Scheme object that is a sequence of objects terminated by the empty list Lists are prompted for an element at a time and the end of the list is signaled by entering an empty list This terminating list forms the tail of the prompted list and can either be empty or can contain values For convenience the empty list can be entered as as well as the standard form Normally list prompts save the previous argument list as the default To modify the list overwrite the desired elements and terminate the process with an empty list For example the following creates a list of three numbers 1 10 and 100 element 1 Q EL element 2 0 110 element 3 1100 element 4 lt RETURN gt Subsequently it adds a fourth element as shown below element 1 1 lt RETURN gt
215. ction boundary wrapper set curvature factor allows you to specify the curvature factor for initializing the wrapper 8 48 ANSYS Inc April 15 2008 8 10 Text Commands for the Wrapper boundary wrapper set default face size allows you to specify the default face size for the Cartesian grid boundary wrapper set feature threshold allows you to specify the critical range within which the nodes of the wrapper will be projected onto the feature edges boundary wrapper set ignore feature skewness specifies the critical skewness to preserve feature lines during the face improvement Only faces with skewness greater than the specified value will be modified The default value is such that no feature lines will be modified during the face improvement boundary wrapper set ignore self proximity allows you to enable or disable the self proximity calculation during the refinement boundary wrapper set list size lists the current zone specific sizes of the domain boundary wrapper set local size function allows you to set local size functions for refining the Cartesian grid boundary wrapper set max refine level specifies the maximum allowable refine ment level boundary wrapper set maximum size level specifies the largest cell size in the Carte sian grid boundary wrapper set minimum proximity gap specifies the minimum gap within which the proximity will be ignored boundary wrapper set number of size boxes specifies
216. ction for details on the manual hole fixing procedure Features contains the parameters to recover the distinctive feature lines in the geom etry 8 36 ANSYS Inc April 15 2008 8 9 The Boundary Wrapper Panel Boundary Wrapper Tri Boundary Zones Face Size Region Features Reports Post Improve airintake Feature Methods Edge Zones Bai i wheels_19 by cylinder left Fixed Angle cylinder right generator Adaptive Angle top left Feature Angle top right 80 wheels HSppe ST 2T extract Features Feature Modify Wrapped Tri Zones Match Selections I Auto Edge Select _4 With Advanced Tracking _Draw Delete _ imprint Tri Boundary Zone Groups far field geometry Le Feature Methods specifies the methods available to create edge loops Fixed Angle specifies the feature edge should be preserved only if the angle between adjacent triangular faces is greater that the specified value Feature Angle specifies the minimum feature angle that should be pre vented while remeshing operation Adaptive Angle specifies the feature edge should be preserved using adaptive angle criteria Extract Features extracts the edge loops for the zones selected in the Tri Boundary Zones selection list and lists them in the Edge Zones list Feature Modify opens the Feature Modify panel using which you can mod ify remesh edge loops Wrapped Tri Zones selects
217. ction to highlight the face intersection 11 26 ANSYS Inc April 15 2008 11 7 Common Tri Tet Meshing Problems Poor Boundary Node Distribution Some meshing problems can be caused by a poor quality surface mesh The surface mesh may have highly skewed faces or two or more boundaries in close proximity may have very different face sizes In the latter case the boundaries can be connected e g in a corner or completely separate Either way the boundary mesh cannot be created without considering the impact of other nearby boundaries If the gap between two boundaries is D the largest edge on a face should not exceed D The mesh quality is extremely important when a coarse mesh is required in a small gap Non Closed Boundaries You can generate an initial mesh even if there is a hole in a boundary either due to missing faces or a gap between two zones In this case instead of having two separate zones on opposite sides of the boundary you will have just one combined zone This situation is evident because you will have very few zones e Ifthe hole is in the outer boundary the cells outside the boundary will be combined with the cells inside resulting in an error The edges around the hole will be marked as free edges and therefore can be displayed e Ifthe problem is caused by a small gap between boundaries and the duplicate nodes have already been merged increase the tolerance and perform additional merging The following
218. ctors using an appropriate Normal Scale Edge Type contains options controlling the display of edges These options are available only when the Edges option is enabled See Section 14 1 2 Adding Features to an Outline Display for details All enables the display of all grid edges Feature enables feature lines in an outline display Outline enables the display of the grid outline 14 10 ANSYS Inc April 15 2008 14 1 Displaying the Grid Feature Angle controls the amount of detail added to a feature outline display This item is available only when Feature is selected in the Edge Type list See Section 14 1 2 Adding Features to an Outline Display for details Label Scale controls the size of the labels displayed Normal Scale controls the size of the face normals displayed Shrink Factor specifies the amount by which to shrink faces and cells Colors opens the Grid Colors panel see Section 14 1 5 The Grid Colors Panel using which you can specify colors for different grid zones Lights opens the Lights panel see Section 14 7 1 The Lights Panel using which you can control the lighting used in the display Rendering opens the Display Options panel see Section 14 5 1 The Display Options Panel using which you can control various rendering options Styles opens the Style Attributes panel see Section 14 1 7 The Style Attributes Panel where you can change how various types of grid objects are displayed
219. custom host executable listen custom prompts you for a version that is not in the menu i e a version that is not part of the standard distribution You can also use it to add options to a standard version name e g custom 2d option executable sets the name of the program to be run The default is tgrid You can use this option to give a full pathname if the executable is not in your search path e g executable Fluent Inc bin tgrid host sets the machine and username on which TGrid is to be run If necessary you will be prompted for a password in the window in which Cortex was started The default is to run on the same machine on which Cortex is running listen tells Cortex to wait a specified period of time for a TGrid session to start up instead of starting TGrid itself 2 2 ANSYS Inc April 15 2008 2 3 Starting Dual Process Build of TGrid Starting T Grid on Windows system There are two ways to start TGrid on a Windows system Click on the Start button select the Programs menu select the Fluent Inc menu and then select the TGrid program item If the default Fluent Inc program group name was changed when TGrid was installed you will find the TGrid menu item in the program group with the new name that was assigned rather than in the Fluent Inc program group Start from an MS DOS Command Prompt window by typing tgrid 2d or tgrid 3d at the prompt Before doing so first modify your user environmen
220. d Alternatively you can specify an appropriate cell size function with a sufficiently large value for the growth rate Various steps in the automatic meshing process can be added or eliminated using the Tri Tet panel see Section 11 5 The Tri Tet Panel In addition most aspects of the automatic meshing process can be changed dynamically through the Scheme interface Contact your Fluent support engineer for details ANSYS Inc April 15 2008 11 3 Generating Triangular Tetrahedral Meshes 11 1 2 Using the Auto Mesh Tool Mesh Auto Mesh The Auto Mesh tool can be used to automatically do either of the following functions e Generate a triangular or tetrahedral volume mesh starting from a boundary mesh e Generate a triangular or tetrahedral volume mesh in an unmeshed domain of a mesh that contains other cell shapes The Auto Mesh tool allows you generate the tri tetvolume mesh automatically When you select Tri Tet in the Volume Fill list and click the Mesh button in the Auto Mesh panel e If the volume mesh does not exist TGrid will perform all the steps listed in Sec tion 11 1 1 Automatic Meshing Procedure for Tri Tet Meshes e If a volume mesh already exists a Question dialog box will appear asking if you want to clear the existing mesh If you click Yes TGrid will clear the volume mesh and perform the active steps in the automatic mesh generation process If you click No the operation will be
221. d all cell zones of that type will be selected in the Cell Zones list This shortcut allows you to easily select all zones of a certain type without having to select each zone individually You can select multiple types in the Cell Zone Groups list to select all zones of several different types e g fluid and solid Compute calculates the Minimum Maximum and Average values for the selected option size or quality 15 3 2 Text Commands for Reporting Cell Limits Text commands with the same functionality as the controls in the Report Cell Limits panel are listed below report cell size limits reports the cell size limits report cell quality limits reports the cell quality limits report neighborhood quality reports the maximum skewness aspect ratio or size change of all cells using a specified node 15 4 Reporting Boundary Cell Limits For boundary layer flows boundary cells with low skewness are very important e In 2D triangular meshes most boundary cells will be equilateral except in corners or if there is another boundary close by If there are cells with a skewness above 0 25 the nodes are probably poorly dis tributed on the boundary 15 6 ANSYS Inc April 15 2008 15 4 Reporting Boundary Cell Limits e For 3D tetrahedral meshes the maximum skewness will not be lower than the maximum face skewness because the boundary cell skewness is limited by the boundary face skewness Highly skewed 3D cells with two bou
222. d as shown in Figure 7 6 5 Creating Edge Loops Using the Feature Modify Panel The procedure for creating edge loops using the Feature Modify panel is as follows 1 Select the required zone s from the Face Zones selection list 2 Select Create from the Options list 3 Select the appropriate option from the Approach drop down list Select the appro priate Seed Face when using the Face Seed approach 4 Select the appropriate option from the Angle Criterion drop down list Specify an appropriate value for the Angle when using the Fixed angle criterion 5 Click Apply to create the edge loops You can also use the Surface Retriangulation panel to create edge loops using the Face Zone appoach Refer to Section 7 7 5 The Surface Retriangulation Panel for details 7 46 ANSYS Inc April 15 2008 7 6 Creating and Modifying Features Figure 7 6 5 Edge Loops for Face Seed Approach and Fixed Angle 55 or Adaptive Angle 7 6 2 Modifying Edge Loops The edge modification options available in TGrid are e Deleting edge loops e Copying existing edge loops including the modes to a new edge loop e Toggling the edge loop type between boundary and interior e Grouping and ungrouping edge loops e Orienting the edges on the edge loop to point in the same direction e Reversing the direction of the edge loop Note The direction of a boundary edge loop determines the side from which new faces are formed The di
223. d should be of sufficient density to resolve the shape of the geometry The mesh can be improved more effectively using the solution adaptive mesh capability provided in FLUENT 11 2 Manually Creating a Tri or Tet Mesh In addition to the Auto Mesh tool TGrid allows you to control the tri tet mesh generation process by modifying parameters at each step The basic operations are described here and the methods for modifying the associated parameters are described in Sections 11 3 and 11 4 11 2 1 Manual Meshing Procedure for Tri Tet Meshes The basic components of the manual meshing process are examining and repairing the surface mesh creating an initial mesh refining the mesh and improving the mesh The following steps describe the recommended meshing procedure Step 1 Examining the Surface Mesh The first step in the mesh generation process is to examine the validity and quality of the surface mesh The recommended approach includes the following steps e Checking for free and isolated nodes see Section 7 1 1 Free and Isolated Nodes 11 6 ANSYS Inc April 15 2008 11 2 Manually Creating a Tri or Tet Mesh e Checking and improving the surface mesh quality see Section 7 4 Improving Boundary Surfaces e Visually examining the surface mesh for free multiply connected skewed and or close proximity faces see Section 14 1 Displaying the Grid e Making local repairs if required see Section 7 3 Modifying the Bounda
224. d while the graphics window is displayed with a black background and white foreground respectively ANSYS Inc April 15 2008 3 17 Graphical User Interface 3 5 Customizing the GUI UNIX Systems On UNIX systems you can customize the GUI by changing the attributes such as text color background color and text fonts The program will try to provide default text fonts that are satisfactory for the display size of your platform In some cases customization may be necessary if the default text fonts make the GUI too small or too large on your display or if the default colors are undesirable The GUI in TGrid is based on the X Window System Toolkit and OSF Motif The at tributes of the GUI are represented by X Window resources If you are unfamiliar with the X Window System Resource Database please refer to any documentation you may have that describes how to use the X Window System or OSF Motif applications The default X Window resource values for a medium resolution display are as follows General resources Fluent geometry 0 0 Fluent fontList helvetica bold r normal 12 Fluent MenuBar fontList helvetica bold r normal 12 Fluent XmText fontList fixed medium r normal 13 Fluent XmTextField fontList fixed medium r normal 13 Fluent foreground black Fluent background gray 5 Fluent activeForeground black Fluent activeBackground gray85 Fluent disabledTextColor gray55 Fluent XmToggleButton
225. d by wall zones the wall zone bounding one cell zone will be merged with the adjacent wall zone bounding the other cell zone Rename allows you to change the name of the selected zone Name specifies the new name for the zone selected in the Cell Zones list 13 30 ANSYS Inc April 15 2008 13 9 Manipulating Cell Zones Rotate rotates the selected zone s through the specified angle See Section 13 9 2 Copy ing and Moving Cell Zones for details Angle specifies the angle of rotation through which you want to rotate the selected zone s axis allows you to specify the axis about which you want to rotate the selected zone s pivot allows you to specify a pivot point about which you want to rotate the selected zone s Copy Zone s allows you to copy the nodes of the selected zone s thereby creating new zone s of the same type before positioning the copied zone s per the specified Angle and axis or pivot Scale scales the selected zone s by multiplying each of the node coordinates by the specified Scale Factors The cell sizes will increase or decrease accordingly Scale Factors specifies the scale factors applied to the grid in each of the Cartesian coordinate directions X Y and in 3D Z Copy Zone s allows you to copy the nodes of the selected zone s thereby creating new zone s of the same type before scaling the copied zone s per the specified scale factors Translate translates the selected zone s b
226. d in a mesh file created in a previous version of TGrid it is recommended that you reset all the prism parameters using the command mesh prism reset parameters before proceeding with setting the prism parameters 10 2 ANSYS Inc April 15 2008 10 2 Procedure for Generating Prisms 3 Specify prism growth parameters in the Growth tab a Select the appropriate Offset Method and Growth Method for growing prisms See Sections 10 8 and 10 10 for details b Define the height of the first prism layer First Height First Aspect Ratio c Set the growth method related parameter Slope Rate or Exponent as appli cable and the Number of Layers d Specify options for proximity detection and ignoring prisms in regions of prox imity and invalid normals in the Prisms Growth Options panel opened using the Growth Options button if required Refer to Section 10 3 Prism Mesh ing Options for details e Click the Plot or Print button to preview the height distribution For information on setting different growth parameters for different zones see Section 10 3 1 Growing Prisms Simultaneously from Multiple Zones 4 Specify the direction for prism growth see Section 10 7 Direction Vectors a Enable the display of normals in the Attributes section of the Display Grid panel and click Apply Display Grid b Click the Direction tab in the Prisms panel to view the direction parameters O
227. d read it back into the previous TGrid session using the Append File s option d Connect the meshed cavity to the parent mesh and merge the cavity domain with the parent domain 3 Enter an appropriate value for Scale and click Compute The extents of the bound ing box will be computed based on the zones selected in the Remove Boundary Zones and Add Boundary Zones selection lists and the scale factor specified and 13 24 ANSYS Inc April 15 2008 13 8 Cavity Remeshing reported in the Cavity Remesh panel Alternatively you can specify the extents of the bounding box as required A You need to manually specify the extents of the bounding box when using the cavity remeshing feature to improve a region of skewed cells 4 Specify the orientation of the bounding box in the Orient group box 5 Click Draw to preview the cavity domain to be created 6 Click Create to create the cavity domain The cavity domain will comprise the new zone s to be added and the boundary zones touching the domain defined by the bounding box Any zone s to be removed will not be included in the cavity domain The existing volume mesh in the cavity will be removed and boundary zone s extracted from the interior zone s if any will be changed to wall type and included in the cavity domain 7 Connect the new zone s with the boundaries of the cavity domain using node merging or intersect operations when removing adding or replacing zones in the v
228. d second nodes will be merged then the third and fourth and so on Note To merge multiple pairs select an even number of nodes and ensure that you select them in the correct order 2 Click Merge or press F9 The first node selected is retained and the second node is merged onto the first node Save the boundary mesh before merging nodes because merging is not reversible i e clicking Undo will not undo a merge operation ANSYS Inc April 15 2008 7 17 Manipulating the Boundary Mesh Moving a Node To move the node to any position in the domain do the following Choose node in the filter list hot key lt Ctrl gt N 2 Select the node you want to move 3 Choose position in the filter list hot key lt Ctrl gt X 4 Select the position coordinates or click on the position in the graphics window to which you want to move the selected node 5 Click Move To To move the node by specifying the magnitude of the movement do the following 1 Select the node you want to move 2 Enter the magnitude by which you to move the selected node 3 Click Move By Rezoning a Face To change the zone type of one or more faces do the following 1 Select the face s you want to move 2 Select the zone to which you want the selected faces to move 3 Click Rezone hot key lt Ctrl gt 0 You can create a zone if you need to move faces to a new zone Collapsing Nodes Edges Faces To collapse no
229. d value the faces are assumed to be folded Relaxation specifies the relaxation factor for node smoothing Reprojection enables the projection of the adjusted nodes back on the geometry edges after smoothing Inflate Thin Regions improves the wrapper surface by pushing apart the overlapping faces to a certain thickness Critical Thickness specifies the critical distance within which the faces are assumed to be overlapped Critical Angle specifies the critical angle between the faces below which the faces are assumed to be overlapped Preserve Boundary allows you to preserve the original locations of the zone boundary nodes Remove Self Intersection moves apart the intersecting faces in the wrap per surface Iteration specifies number of attempts to remove self intersecting faces Relative Thickness specifies the distance upto which the separation of self intersecting faces takes place Delete Island deletes islands faces having a face count less than or equal to the specified critical face count Critical Face Count specifies the critical face count for deleting the island faces Absolute Count specifies the absolute face count below which the non contiguous region can be treated as an island configuration Relative Count specifies the face count relative to the largest re gion below which the non contiguous region can be treated as an island configuration Swap allows you to perform node swapping on the wrapper surface
230. des edges or faces do the following 1 Select the appropriate Filter 2 Select the two nodes or edge s face s you want to collapse Note To collapse multiple pairs of selected entity select an even number of nodes and ensure that you select them in the correct order 3 Click Collapse hot key lt Ctrl gt 7 18 ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh While collapsing e If a pair of nodes is selected both the nodes are moved towards each other at the midpoint and collapsed into a single node e If an edge is selected the two nodes of the edge collapse onto the midpoint of the edge and surrounding nodes get connected to the newly created node e If the triangular surface is selected the new node at the centroid of the triangle is created and the selected triangular face gets deleted You can also collapse multiple pairs of nodes by selecting more than two nodes before clicking Collapse The first and the second node will collapse then the third and the fourth and so on Save the boundary mesh before performing this operation because col lapsing is not reversible i e the Undo button will not undo a collapse operation Smoothing a Node To smooth a node do the following 1 Select the node s you want to smooth 2 Click Smooth or press the F6 key on the keyboard The node will be placed at a position computed from the average of the surrounding nodes Splitting an
231. ding resolution colors transparency etc For this reason all of the inputs that control these characteristics are disabled in the Hardcopy panel when you enable the Window Dump format You can save your mesh to a file that can be read by HYPERMESH NASTRAN PATRAN and ANSYS Importing Meshes e A single filter fe2ram allows you to convert files created by several finite element packages to the grid file format used by TGrid This filter allows you to convert surface or volume meshes from ANSYS I deas NASTRAN PATRAN or other pack ages The ARIES files can be converted if they are first saved as ANSYS Prep7 files as described in Section A 3 5 ARIES Files ARIES provides a filter to TGrid or you may write a Prep7 file from ARIES and use the fe2ram filter with arguments for an ANSYS file For more information on importing ANSYS files see Section A 3 4 ANSYS Files When you read the mesh into the solver it will ignore the dead cell zones If you have a very large mesh and there are many cells in a dead zone delete them To do so use the Manage Cell Zones panel This reduces the memory requirements ANSYS Inc April 15 2008 E 5 Creating a Mesh E 5 Creating a Mesh e If cells e g prisms or pyramids have already been created in some portion of your computational domain create a domain encompassing the region to be meshed with triangular or tetrahedral cells before you can begin the tri tet mesh generatio
232. displayed is Group Display opens the Display Properties panel see Section 14 8 4 The Display Prop erties Panel which allows you to change the color visibility and other prop erties for the selected object Transform opens the Transformations panel see Section 14 8 5 The Transfor mations Panel which allows you to translate rotate and scale the selected object IsoValue is not available in TGrid Pathlines is not available in TGrid Time Step is not available in TGrid 14 40 ANSYS Inc April 15 2008 14 8 Describing a Scene Scene Composition contains controls for enabling overlays and bounding frames Overlays activates the superimposition of a new geometry onto a currently dis played geometry Draw Frame activates the display of a bounding frame in the graphics display Frame Options opens the Bounding Frame panel see Section 14 8 6 The Bound ing Frame Panel in which you can define properties of the bounding frame Delete Geometry deletes the geometric object that is currently selected in the Names list The ability to delete individual objects is especially useful if you have overlays on and you generate an unwanted object e g if you generate contours of the wrong variable You can simply delete the unwanted object and continue your scene composition instead of starting over from the beginning Apply saves the status of Overlays and Draw Frame When you turn Overlays or Draw Fra
233. driver ppm sets PPM format display set hardcopy driver tiff sets TIFF format display set hardcopy driver list displays the current hardcopy format display set hardcopy driver options allows you to set hardcopy options such as landscape orientation and physical size The options may be entered on one line if you separate them with commas ANSYS Inc April 15 2008 6 23 File Types display set hardcopy driver post format contains commands for setting the PostScript driver format display set hardcopy driver post format fast raster enables a raster file that may be larger than the standard raster file but will print much more quickly display set hardcopy driver post format raster enables the standard raster file display set hardcopy driver post format rle raster enables a run length encoded raster file that will be about the same size as the standard raster file but will print slightly more quickly This is the default file type display set hardcopy driver post format vector enables the standard vector file display set hardcopy invert background toggles the exchange of foreground and or background colors for hardcopy files display set hardcopy landscape toggles between landscape or portrait orientation display set hardcopy preview applies the settings of the color mode invert background and landscape options to the currently active graphics window to preview the ap pearance of printed hardcopies display set
234. ds for creating surfaces are as follows boundary create bounding box allows you to create the bounding box for the spec ified zones You can specify the zone type name edge length and the extents of the box as required boundary create cylinder allows you to create a cylinder by specifying the axis radius and edge length You can also specify the prefix for the zone being created as arequired boundary create plane surface allows you to create a plane surface by specifying either the axis direction axial location and the extents of the surface or three nt defining the plane boundary create swept surface allows you to create a surface by sweeping the spec ified edge in the direction specified You need to specify the distance to sweep through and the number of offsets as required boundary make periodic allows you to make the specified boundaries periodic You can specify the type of periodicity rotational or translational the angle and axis of rotation for rotational periodicity or the translational shift for translational periodicity For each of the zones specified a corresponding periodic shadow boundary zone will be created 7 15 Additional Boundary Mesh Text Commands Some commands for checking and modifying the boundary mesh are not available in the GUI The text interface commands for these operations are listed below boundary clear marked faces clears faces that were marked with the boundary mark face prox
235. e You can use the bounday unmark selected faces command hot key lt Ctrl gt U to unmark the faces ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh To improve the skewed face do the following operations e Click Smooth to smooth the node opposite the longest face e Click Merge to collapse the shortest edge of the face merging the other two edges together The longer of the remaining two edges is retained and the shorter one is merged with it e Click Swap to swap the selected edge e Click Split to refine the face by bisecting the selected edge If the entities that TGrid selects are not appropriate clear them choose the appropriate items and perform the desired operations Deselecting a Selected Object If you select an object and then decide that it is not the correct one you can click on the object again in the graphics window to deselect it You can also select it in the Selections list in the Modify Boundary panel and click Clear You can use the hot key F2 to deselect all objects selected A Deselect operations are performed only on the items selected in the Selec tions list Undoing an Operation To undo any operation except a merge click the Undo button or press the F12 key on the keyboard In some cases a particular sequence of operations will not be able to be undone Hence make sure that you save the mesh periodically between the modifications i Click Undo or press F12 n times
236. e Index 59 Scheme symbol xf face tree C macro XF_FACE_TREE Codes FLUENT Status only for grids with hanging node adaption This section indicates the face hierarchy of the grid containing hanging nodes The format of the section is as follows 59 face idO face idi parent zone id child zone id number of kids kid id O kid id 1i kid id n where face id0 is the index of the first parent face in section face id1 is the index of the last parent face in section parent zone id is the ID of the zone containing the parent faces child zone id is the ID of the zone containing the children faces number of kids is the number of children of the parent face kid id n are the face IDs of the children These are in hexadecimal format TGrid can read files that contain this section B 9 Cell Tree Index 58 Scheme symbol xf cell tree C macro XF_CELL_TREE Codes FLUENT Status only for grids with hanging node adaption This section indicates the cell hierarchy of the grid containing hanging nodes ANSYS Inc April 15 2008 B 9 Mesh File Format The format of the section is as follows 58 cell idO cell idi parent zone id child zone id number of kids kid id 0 kid id 1 kid id n where cell id0 is the index of the first parent cell in section cell id1 is the index of the last parent cell in section parent zone id is the ID of the zone containing the parent cells child zone id is the ID o
237. e sults in the separation of wall 1 into two zones wall 1 and wall 1 6 one on either side of wall 2 and the separation of wall 2 into two zones a circular zone inside the pipe section of wall 1 wall 2 9 and a zone with the remaining part of wall 2 ANSYS Inc April 15 2008 7 2 Intersecting Boundary Zones Figure 7 2 9 Boundary Mesh A Before and B After Intersection Using the Separate Option 7 2 6 Text Commands for Boundary Intersection The text interface commands for intersecting boundary zones are listed below boundary remesh intersect all face zones allows you to intersect all the face zones boundary remesh intersect face zones allows you to intersect the specified face zones boundary remesh join all face zones allows you to join all the face zones boundary remesh join face volume allows you to join a face zone connected to a volume mesh with another tri face zone boundary remesh join face zones allows you to join the specified face zones boundary remesh stitch all face zones allows you to stitch all the face zones boundary remesh stitch face zones allows you to stitch the specified face zones boundary remesh controls intersect absolute tolerance allows you to switch between the use of absolute and relative tolerance By default TGrid uses relative tolerance value boundary remesh controls intersect delete overlap toggles the automatic dele tion of region of overlap of the two surfaces
238. e Modified Octree Technique International Journal for Numerical Methods in Engineering 20 1965 1990 1984 ANSYS Inc April 15 2008 Index file write boundaries 6 5 TGrid dual process 2 3 accessing manuals 1 5 active cell zones 11 24 13 28 14 4 adaptive angle criteria 7 42 Annotate panel 14 49 annotated text 14 47 ANSYS 6 11 A 1 A 5 export 6 17 append mesh files 6 3 ARIES A 6 arrow keys C 1 aspect ratio 15 9 cell 14 20 15 5 15 6 face 14 17 15 3 plotting cell distribution 14 19 plotting face distribution 14 17 Auto Mesh panel 9 12 Auto Node Move panel 13 20 automatic mesh generation hybrid meshes 11 5 tri tet meshing 11 2 axes 14 21 Axes Histogram panel 14 22 axis direction method 7 81 booleans 5 5 boundary cell size 15 6 cell skewness 15 6 closeness 11 22 features 7 42 layer 9 2 9 5 ANSYS Inc April 15 2008 manipulating 7 2 mesh 7 1 examining 4 3 modifying 7 14 quality 15 3 refinement 7 35 repair 7 14 nodes 7 2 periodic 7 89 refinement 7 35 remeshing 7 53 repair 7 14 separation 7 63 wrapper 8 1 wrapping 8 1 zones 7 74 changing type 7 74 intersecting 7 5 manipulating 7 74 projecting 7 69 remeshing 7 53 renaming 7 75 rotating 7 76 scaling 7 76 separating 7 63 translating 7 76 Boundary Improve panel 7 32 Boundary Refinement Region panel 7 40 Boundary Wrapper panel 8 30 boundary zones copying 7 75 creating new 7 75
239. e Panel in which you can enter the name for the group to be created Draw displays the group selected in the Face Zones or Edge Zones list The Group Name Panel The Group Name panel allows you to specify the name for the group to be created Group Name Name front wheel axle Controls Name specifies the name of the group to be created i You cannot create a new group having the name global or having the same name as one of the default TGrid groups You also cannot create a new group having the same name as an existing group 7 12 2 Text Commands for User Defined Groups The text commands for manipulating user defined groups are as follows boundary manage user defined groups activate allows you to activate the speci fied user defined group boundary manage user defined groups create allows you to create a group of face or edge zones comprising the specified zones boundary manage user defined groups delete deletes the specified group boundary manage user defined groups list lists the groups in the TGrid console boundary manage user defined groups update allows you to modify an existing group 7 74 ANSYS Inc April 15 2008 7 13 Manipulating Boundary Zones 7 143 Manipulating Boundary Zones Boundary zones are groups of boundary faces Usually the grouping collects boundary faces with the same boundary conditions but further subgroupings are often used to preserve a sharp edge in th
240. e Refine Boundary Zones panel allows you to refine the triangular boundary zones that touch a local refinement region before you refine the volume mesh in the refinement region Boundary Mesh Refine Refine Boundary Zones Options Refinement Tri Boundary Zones amp SE v Clear Type Mark Mark Refine v Proximity vy Smooth Reyiens v Swap Max agit Tri Boundary Zone Groups los far field 4 Max Face amp rea geometry Bax Skew inlet oe e Lecai Regions Apply Draw Limits Close Help These commands are described in Section 7 15 Additional Boundary Mesh Text Commands 7 38 ANSYS Inc April 15 2008 7 5 Refining the Boundary Mesh Controls Options contains a number of operations related to the boundary zone refinement The selected operation will be performed when you click Apply Clear clears all refinement marks from all boundary faces Mark marks faces that are larger than the Max Face Size Only faces that border the refinement region will be marked Refine refines the marked faces by dividing them into three faces as shown in Figure 7 5 1 Smooth smooths the nodes of the boundary faces using Laplacian smoothing as described in Section 13 1 1 Laplacian Smoothing based on the specified Max Angle and Relax parameters to try to lower the maximum skewness Swap swaps the edges of the boundary faces based on the spe
241. e Surface Retriangulation panel is as follows Select the face zone you want to remesh in the Face Zones selection list Select the appropriate option from the Reconstruction Order drop down list in the Face Remesh Options group box You can select None to specify no reconstruc tion order The Second Order reconstruction is recommended for coarse surface remeshing while the Third Order reconstruction is recommended for fine surface remeshing Enable Replace Face Zone if required TGrid will create a new zone for the remeshed face When Replace Face Zone is enabled the newly remeshed face zone will be retained while the original face zone will be deleted You should ensure that the new face zone is acceptable before deleting the original zone Click Remesh Before remeshing face zones make sure that you are satisfied with the edge loops TGrid cannot remesh non manifold faces Before proceeding with remesh ing ensure that the geometry does not contain such faces 7 7 4 Remeshing Zones Using the Surface Retriangulation Panel The generalized procedure for remeshing surface zones is as follows 7 56 Select the face s for which you want to create edge loops in the Face Zones selection list Select the appropriate option from the Angle Criterion drop down list By default TGrid uses the Face Zone approach to create edge loops Therefore you can only specify the required Angle Criterion in the Surface Retrian
242. e Type sets the type of the selected cell zone to the type selected in the Type drop down list Type contains a drop down list of available cell zone types dead fluid and solid FLUENT will read in the two live cell zone types fluid and solid and assign default conditions as described in the FLUENT User s Guide Dead cell zones are regions that are not part of the computational domain They will not be read by FLUENT Copy copies all nodes faces and cells of the selected zone or zones creating a new zone of the same type at the same location Delete deletes the selected cell zone s along with the associated faces and nodes You may want to delete dead zones to free up some memoryin your com puter Commands for checking and deleting these faces are described in Sec tion 7 15 Additional Boundary Mesh Text Commands This operation is irreversible After deleting cell zones check to see if there are any boundary faces located between two deleted zones Such faces must be removed if you are generating a mesh for FLUENT Merge merges two or more selected zones into one The resulting cell zone will have the name type and ID of the first selected zone that appears in the Cell Zones list This operation is irreversible Merge Sub Zones controls whether or not same type face zones and same type node zones associated with the cell zones being merged should also be merged For example if you merge two cell zones that are bounde
243. e a Gs 6 9 6 52 Using Text Commands ossos scak Sa sisii ee oe He S ee 2 6 9 66 Domain File i esw ree adek gi ae a ee ee be oe 2S 6 10 6 6 1 Reading Domain Files 222 42 64 4445446854845 6 10 6062 Welw Domain Wiles se yuo va 6 mY SR YES SEES 6 10 Oa Amiportne Wiles por pa ec es 8 ee Se ey ee ew amp ee Pe eee S 6 11 6 7 1 Importing Mesh Files Generated by Third Party Packages 6 11 6 7 2 Importing FIDAP Neutral Mesh Files 6 14 6 7 3 Importing GAMBIT Neutral Mesh Files 6 14 6 7 4 Grid Import Filter Options o s sa se ea seau ee ees 6 14 Ge Exporting Fil g gt saora dae edad ee 2G doei EERE a Ra 6 16 68 1 Egporting HYPERMESH Fil s s lt e s sos Meee aca wre o krans ea 6 16 68 2 Exporting NASTRAN Files grs e d 0044 4 ie ack ee e G 6 16 6 8 3 Exporting PATRAN Files 444 426 0 28044 4 444 6 16 6 8 4 Exporting ANSYS and STL Files 6 17 69 Saving Hardcopy Wile secs eed eee eo hE Pee kPa de Sas 6 17 6 9 1 Using the Hardcopy Panel 2 424 f2 ba hee eee ee 6 17 6 9 2 The Hardcopy Panel 22 2244 444444445446 846 543 6 22 6 9 3 Text Interface for Saving Hardcopy Files 6 23 6 10 Sayine the Panel Layout oee s moane popacp a we biep ew p ee Goes 6 24 611 The ered File sa cead 4th ea dba Pe Geb aaa Cee ea 6 25 6 12 Exiting VGA a ccas escoar es baa RR RR we Ee e e a 6 25 7 Manipulating the Boundary Mesh 7 1 7 1 Manipulating Boundary Nodes aoaaa a 7 2 7 1 1 F
244. e a single fluid region and one or more dead regions The active zone is considered to be the fluid zone and only this fluid zone will be considered for refinement during the automatic meshing process If the mesh includes multiple regions e g the problem for which you are creating a grid includes a fluid zone and one or more solid zones and you intend refining all of them using the same refinement parameters modify the Non Fluid Type before generating the hexcore mesh When the Non Fluid Type is set to a type other than dead e g solid all the zones will be active after the initialization is complete Hence TGrid will refine all zones automatically during the refinement process 12 10 ANSYS Inc April 15 2008 12 4 The Hexcore Panel Tet Controls opens the Tri Tet panel see Section 11 5 The Tri Tet Panel where you can set the parameters for tetrahedral meshing Local Regions opens the Hexcore Refinement Region panel see Section 12 4 2 The Hexcore Refinement Region Panel Create creates the hexcore according to the parameters specified in the Hexcore panel Apply applies the parameters specified in the Hexcore panel 12 4 1 The Outer Box Zones Panel The Outer Box Zones panel allows you to select the boundaries comprising the bounding box of the domain Outer Box Zones Boundary Zones HER mirror outlet outlet side outlet top symmetry wheel arch front Boundary Zone Groups fa
245. e allows you to deactivate the specified local region s mesh hexcore local regions define defines the local region according to the spec ified parameters mesh hexcore local regions delete deletes the specified refinement region mesh hexcore local regions ideal hex vol reports the ideal hex volume for the given edge length mesh hexcore local regions init creates a default region encompassing the entire geometry mesh hexcore local regions list all regions lists the defined and active regions in the TGrid console 12 14 ANSYS Inc April 15 2008 Chapter 13 Improving the Mesh A volume mesh created from a high quality surface mesh may contain some high skewness cells The poor cells may result from unsuitable mesh size distribution over the domain or more often caused by constraints imposed by the boundaries This chapter describes the options available in TGrid to improve the mesh quality by removing highly skewed cells e Section 13 1 Smoothing Nodes e Section 13 2 Swapping e Section 13 3 Improving the Mesh e Section 13 4 Removing Slivers from a Tetrahedral Mesh e Section 13 5 The Tri Tet Improve Panel e Section 13 6 Modifying Cells e Section 13 7 Moving Nodes e Section 13 8 Cavity Remeshing e Section 13 9 Manipulating Cell Zones e Section 13 10 Using Domains to Group and Mesh Boundary Faces e Section 13 11 Checking the Mesh e Section 13 12 Clearing the Mesh After creating a triangular tetrah
246. e allows you to rotate the view by dragging the mouse across the screen mouse dolly allows you to translate the view by dragging the mouse across the screen mouse zoom allows you to zoom in or out on the display mouse roll zoom allows you to zoom in or out of the view by rolling the mouse while the button is pressed mouse probe allows you to perform the specified mouse probe function The mouse probe function can be set to one of the values described for the boundary modify select probe command in Section 7 3 4 Text Commands for Boundary Modification mouse annotate allows you to insert text into the graphics window 14 10 Controlling the Mouse Probe Functions TGrid allows you to assign a specific function to the mouse probe button Click the mouse probe in the graphics window for the appropriate action to take 14 48 ANSYS Inc April 15 2008 14 10 Controlling the Mouse Probe Functions 14 10 1 The Mouse Probe Panel The Mouse Probe panel is used to set the actions taken when the mouse probe button is clicked in a graphics window Display Mouse Probe Mouse Probe Function Filter Controls Function selects the function to be performed when the mouse probe is clicked in the graphics window The available functions are off disables the mouse probe label displays the label for the selected entity in the graphics window select saves the selected entity in a list
247. e boundary mesh file to be read e Use the file read boundary mesh text command and specify the name of the boundary mesh file to be read This is convenient if you want to read in a large volume mesh and recreate it by starting from the boundary mesh Reading Multiple Boundary Mesh Files If the boundary mesh is contained in two or more separate files you can read them in together and have TGrid assemble the complete boundary mesh Alternatively you can use the file read multi bound mesh text command for reading multiple boundary mesh files 6 1 2 Reading TGrid Mesh Files To read a TGrid mesh you can use either of the following e Select the File Read Mesh menu item to open the Select File panel and select the TGrid mesh file to be read e Use the file read mesh text command and specify the name of the mesh file to be read 6 2 ANSYS Inc April 15 2008 6 1 Mesh Files You can also use either of these commands to read a FLUENT mesh file created with GAMBIT or to read the mesh file contained in a FLUENT case file To do the latter you can also use the text command file read case The commands discussed here are used to read a 2D mesh into the 2D version of TGrid or a 3D mesh into the 3D version of TGrid i TGrid cannot read grids from solvers that have been adapted using hanging nodes To read one of these grids into TGrid coarsen the mesh within the solver until you have recovered the original unadapted grid
248. e directory for an optional file called tgrid If it finds the file TGrid loads the file with the Scheme load function This file may contain Scheme functions that customize the operation of the code 6 12 Exiting TGrid To exit TGrid do one of the following e Select Exit in the File pull down menu File Exit e Type exit within any menu If the present TGrid state has not been written to a file you will receive a warning message You can either cancel the exit and write the mesh or continue to exit without saving the file ANSYS Inc April 15 2008 6 25 File Types 6 26 ANSYS Inc April 15 2008 Chapter 7 Manipulating the Boundary Mesh The first step in producing an unstructured grid is to define the shape of the domain boundaries Using a preprocessor GAMBIT or a third party CAD package you will create a boundary mesh in which the boundaries are defined by line segments 2D or triangular or quadrilateral facets 3D and then create a mesh in TGrid TGrid allows you to modify the boundary mesh to improve its quality It also allows the creation of surface meshes on certain primitive shapes The following sections discuss mesh quality requirements and various techniques for gen erating an adequate boundary mesh for numerical analysis e Section 7 1 Manipulating Boundary Nodes e Section 7 2 Intersecting Boundary Zones e Section 7 3 Modifying the Boundary Mesh e Section 7 4 Improvin
249. e ee Kae ROE KE OER ee eS E 5 Ey WDeletime Duplicate Nodes 24 46 soca Roa ck eta feaa aoe aes E 5 E 8 Manipulating the Boundary Mesh File E 6 E9 Examining the Meshi se ee eee son ee Boe ORE ae RPA eda a E 7 E 10 Reporting Mesh Statistics 22 2 o sa 4 ek ee ee ee eb a oe E 7 Ed Refining the Mesh 22 222 4 22 de dK EEE ERED RES ERS E 8 E12 Usme the GUI ek ee Be Po hw REE REE Se eS E 10 ANSYS Inc April 15 2008 Using This Manual The Contents of This Manual The TGrid User s Guide tells you what you need to know to use TGrid Chapters 6 through 15 describe the menus that appear at the top of the TGrid window and explain the use of the associated graphical user interface menu items and the text interface menu items The appendices contain information about importing boundary and volume meshes the mesh file format tips troubleshooting and the shortcut keys and query functions available in TGrid to make your task easier At the end of the User s Guide you will find a glossary a bibliography and the index Ei Under U S and international copyright law ANSYS Inc is unable to distribute copies of the papers listed in the bibliography other than those published internally by ANSYS Inc Please use your library or a document delivery service to obtain copies of copyrighted papers A brief description of what s in each chapter follows e Chapter 1 Introduction to TGrid gives you an overview of unstructured grid
250. e mesh file and is written as a separate file It contains a list of node face and cell zone IDs that comprise each domain in the mesh By convention domain file names are composed of a root with the suffix dom If you conform to this convention you do not have to type the suffix when prompted for a filename it will be added automatically When TGrid reads a domain file it first searches for a file with the exact name you typed If a file with that name is not found it will search for a file with dom appended to the name When TGrid writes a domain file dom will be added to the name you type unless the name already ends with dom 6 6 1 Reading Domain Files To read the domain files into TGrid do either of the following e Select the File Read Domains menu item to invoke the Select File panel and specify the name of the domain file to be read e Enter the file read domains text command and specify the name of the domain file to be read If a domain that is being read already exists in the mesh a warning message is displayed TGrid verifies if the zones defining the domains exist in the mesh If not it will display a warning message 6 6 2 Writing Domain Files To write the domain files into TGrid do either of the following e Select the File Write Domains menu item to invoke the Select File panel and specify the name of the domain file to be written e Enter the file write domains text command and specify the name of the dom
251. e not used if the Uniform direction method is selected Prisms Boundary Zones Ba cal cee ieee au I Swap Edges Skewness _t Improve Smooth Edges 9 7 Max Her ace _4 Smooth Nodes oe v Rerationrs Check Quality ma Max Allowable Skewness 0 95 Boundary Zone Groups 5 far field 4 geometry inlet f Swapping and Smoothing contains controls for the edge swapping and smoothing and node smoothing ANSYS Inc April 15 2008 10 29 Generating Prisms Swap Edges enables disables edge swapping see Section 10 9 1 Edge Swap ping and Smoothing to decrease the skewness of highly skewed faces This option is enabled by default Smooth Edges enables disables edge smoothing see Section 10 9 1 Edge Swapping and Smoothing to decrease the skewness of highly skewed faces This option is enabled by default Smooth Nodes enables disables node smoothing see Section 10 9 2 Node Smoothing to decrease the skewness of highly skewed faces This option is disabled by default Skewness specifies the face skewness above which edge swapping and smooth ing are triggered Only faces having skewness greater than this value are evaluated for these operations The default value is 0 7 Warp contains options for improving face warp Improve allows you to improve face warp see Section 10 9 3 Improving Warp during prism generation This option is disabled by default Max Iter Face sp
252. e of the new zone in this panel 1 Define the projection line or plane For a projection line select two entities and for a projection plane select three entities If edges faces or cells are selected their centroidal locations will be used 2 Click Set hot key lt Ctrl gt S and the projection line or plane will be shown in the graphics display 3 Select the nodes to be projected 4 Click Project hot key lt Ctrl gt P The selected nodes will be projected onto the projection line or plane that you defined with the Set button Simplifying Boundary Modification The following functions simplify the boundary modification process Finding the Worst Marked Faces To find the face having the worst quality in the grid select Quality Limit and click the First button or press the F11 key on the keyboard e TGrid displays the triangular face having worst quality in the graphics window and reports its quality and zone ID in the TGrid console e TGrid also selects the longest edge of the face and the node opposite it and updates the grid display limiting it to the neighborhood of the highly skewed face ANSYS Inc April 15 2008 7 21 Manipulating the Boundary Mesh e If the grid has not been displayed TGrid reports in the console the worst face its quality and the zone in which it lies You can display the faces in the descending order of their quality as follows 1 Select Quality Limit and click First hot
253. e options are available in the display set hardcopy driver post format text menu Window Dumps UNIX Systems If you select the Window Dump format the program will use the specified Window Dump Command to save the hardcopy file For example if you want to use xwd to capture a window set the Window Dump Command to xwd id w gt TGrid will automatically interpret w to be the ID number of the active window when the dump occurs e To save the file in the Select File dialog box enter the filename for the output from the window dump e g myfile xwd e To make an animation save the window dumps into numbered files using the n variable To do this enter the Window Dump Command xwd id w gt and type myfile n xwd as the filename in the Select File dialog box Note Each time you create a new window dump the value of Zn will increase by one so you do not need to track numbers to the hardcopy filenames manually 6 20 ANSYS Inc April 15 2008 6 9 Saving Hardcopy Files If you use the ImageMagick animate program saving the files in MIFF format the native ImageMagick format is more efficient In such cases use the ImageMagick tool import For the Window Dump Command enter the default command import window w Specify the output format to be MIFF by using the miff suffix at the end of the filename The window dump feature is both system and graphics driver specific The commands available for dumping windows depe
254. e quadrilateral mesh with no periodic boundaries or hanging nodes bn8 bf8 bn2 bf7 bn4 bf6 bn7 e a bf9 c1 fl e2 f2 3 bf10 e o o bn5 bf3 bn1 bf4 bn3 bf5 bn6 Figure B 11 1 Quadrilateral Mesh ANSYS Inc April 15 2008 B 11 Mesh Fi le Format The following describes this mesh O 0 Dimensions 2 12 13 10 12 13 12 34 13 5 1 13 3 6 13 74 42 28 13 8 5 13 6 7 10 OWWONNF FB B 12 Grid 2 0 1 3 0 O 1a 0 0 180 2 7131 3 2 4 9 9 9 12 2 3 3 3532 1 0 2 0 3 0 4 6 8 3 2 30 20 1 0 699 a 2 1 0 6 aa 24 2 3 0 1 1812 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 Fro Or OF OO 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 00000000e 00 ANSYS Inc April 15 2008 B 11 Example Files Example 2 Figure B 11 2 illustrates a simple quadrilateral mesh with periodic boundaries but no hanging nodes In this example bf9 and bf10 are faces on the periodic zones bng E br brs bts cl b3 bna i bri bt b4 brnd bna brs bt5 bry bn bf10 Figure B 11 2 Quadrilateral Mesh with Periodic Boundaries The following describes this mesh 0 Dimensions 2 2 0 Grid
255. e scene is rendered display set rendering options animation option allows you to specify the ani mation option as appropriate all uses a solid tone shading representation of all geometry during mouse manip ulation level of detail uses a simplified representation of the geometry during mouse manipulation by drawing the geometry using fewer elements wireframe uses a wireframe representation of all geometry during mouse manipu lation This is the default option display set rendering options auto spin enables mouse view rotations to con tinue to spin the display after the button is released display set rendering options device info prints information about the graphics driver in the TGrid console display set rendering options double buffering allows you to enable disable dou ble buffering Double buffering dramatically reduces screen flicker during graphics updates If your display hardware does not support double buffering and you enable this option double buffering will be done in software Software double buffering uses extra memory display set rendering options driver contains commands for changing the cur rent graphics driver ANSYS Inc April 15 2008 14 29 Examining the Mesh display set rendering options face displacement sets the face displacement in Z buffer units along the camera Z axis for the displayed geometry when both faces and edges are displayed simultaneously Quite often faces and ed
256. e surface mesh or simply as an artifact of the boundary mesh generation process The options described here can be used to find information about each zone identify which zone is which merge zones or delete them change the boundary type of all faces in a zone rename zones and rotate scale or translate zones Each zone has a unique ID which must be a positive integer 7 13 1 The Manage Face Zones Panel The Manage Face Zones panel allows you to manipulate boundary zones You can use the panel to change the boundary type of a zone delete zones combine merge zones display draw them print list information about them copy them rename them and change their position Boundary gt Manage Manage Face Zones Options Type Face Zones HESA 4 Change Type Yall bottom inlet v Copy Sente Factors interior 14 Delet Seta 3 outlet v Merge i right top Rename y v Flip Normals as Orient v Orie z Rotate y i Face Zone Groups H v Scale bamda 3 v Translate far field e geometry f Apply Draw List Close Help Controls Options selects the operationt o be performed by clicking the Apply button Change Type sets the boundary type of the selected zone s to be the type se lected in the Type drop down list ANSYS Inc April 15 2008 7 75 Manipulating the Boundary Mesh Type contains a drop down list of boundary types The boundary types that app
257. e the angle criteria used for creating edge loops Fixed specifies the use of fixed angle criteria while creating edge loops See Section 7 6 1 Creating Edge Loops for details Feature Angle specifies the minimum feature angle that should be pre served while creating edge loops Adaptive specifies the use of adaptive angle criteria for creating edge loops See Section 7 6 1 Creating Edge Loops for details Create creates the edge loops for the face zone selected in the Face Zones list Exterior edge loops are automatically generated on the borders of the face zone and interior edge loops are generated based on the specified Feature Angle or if the edges are multiply connected Delete deletes the edge loop for the face zone selected in the Edge Zones list Feature Modify opens the Feature Modify panel using which you can modify the edge loops Face Remesh Options contains parameters for controlling mesh quality of the face zones Reconstruction Order contains a drop down list for the reconstruction order that you want to use for the surface you want to remesh None specifies no reconstruction oder 7 58 ANSYS Inc April 15 2008 7 7 Remeshing Boundary Zones Second Order specifies the use of second order reconstruction for remeshing It is recommended to use this option for a coarse surface remeshing Third Order specifies the use of third order reconstruction for remeshing It is recommended to use this option fo
258. e value specified for minimum improvement TGrid will compare the maximum change in cell skewness with the specified value for minimum improvement When the maximum change in cell skewness is less than or equal to the value specified for minimum improvement further smoothing iterations will no longer yield appreciable improvement in the mesh TGrid will stop the smoothing at this point even if the requested number of iterations has not been completed This skewness based smoothing process can be very time consuming so it is advisable to perform smoothing only on cells with high skewness Improved results can be obtained by smoothing the nodes several times There are internal checks that will prevent a node from being moved if moving it causes the maximum skewness to increase but it is common for the skewness of some cells to increase when a cell with a higher skewness is being improved Hence you may see the average skewness increase while the maximum skewness is decreasing You should consider whether the improvements to the mesh due to a decrease in the maximum skewness are worth the potential increase in the average skewness Performing smoothing only on cells with very high skewness e g 0 8 or 0 9 may decrease the adverse effects on the average skewness 13 1 4 Text Commands for Smoothing Text commands for smoothing the grid are as follows mesh laplace smooth nodes applies a Laplacian smoothing operator to the grid nodes This com
259. each zone have been marked for refinement boundary refine local regions define defines the refinement region according to the specified parameters boundary refine local regions delete deletes the specified region boundary refine local regions init creates a region encompassing the entire ge ometry boundary refine local regions list all regions lists all the refinement regions in the TGrid console boundary refine mark marks the faces for refinement boundary refine refine refines the marked faces 7 6 Creating and Modifying Features Geometric features such as ridges curves or corners should be preserved while per forming various operations e g smoothing remeshing on the boundary mesh TGrid allows you to create edge loops for a face zone If required you can also modify the node distribution on the edge loop The Feature Modify panel panel contains options available for creating and modifying edge loops You can also draw the edge loops to determine their direction i e determine the start and the end points i You can also use the Surface Retriangulation panel see Section 7 7 Remesh ing Boundary Zones for creating edge loops before remeshing the face zones The Surface Retriangulation panel allows you to use the face zone approach only 7 42 ANSYS Inc April 15 2008 7 6 Creating and Modifying Features 7 6 1 Creating Edge Loops Edge loops can be created according to the specified combinatio
260. ead to left handed faces and or neg ative volumes See Section 10 12 Negative Volumes Left Handed Faces High Skewness for details ANSYS Inc April 15 2008 10 11 Generating Prisms 10 4 Zones Created During Prism Generation When TGrid generates prisms several new cell and face zones are created You can identify the new zones by their default names The cell zone containing the prisms will be named prism cells n The face zone created at the end of the last prism layer will be named prism cap n If the prism layers are bounded by one or more existing triangular face zones each of these will be retriangulated so that the faces of the zone that are adjacent to the prisms will become quadrilateral faces while the rest of the faces in the zone remain triangles If an original triangular face zone is called symmetry the portion of it that still con tains triangles will be retained as symmetry while the portion containing quadri lateral faces will be named symmetry quad n Any faces that were not projected to adjacent zones see Section 10 6 Using Adja cent Zones as the Sides of Prisms are collected into a zone named prism side n For a zone wall n the zone created by ignoring prism growth in the region of proximity will be named as wall n ignore where n is the zone number assigned by TGrid i TGrid will merge all the ignored threads related to a base thread into a single thread by default You can however ch
261. ear in the list are used only as descriptive names in TGrid You can change them in FLUENT where you will also set the related boundary conditions See the FLUENT User s Guide for information about valid boundary types i The periodic boundary type is not available since it is not possible to change a non periodic boundary to a periodic boundary using this panel See Section 7 14 5 Creating Periodic Boundaries for information about creating periodic boundaries in TGrid Copy copies all nodes and faces of the selected zone or zones creating a new zone of the same type at the same location You can then use the Rotate and Translate options to place the new zone in the appropriate position If the copy is placed so that it is connected to an original zone you will need to merge the duplicate nodes on the original boundary zone and the new boundary zone This is similar to when you copy a cell zone See Figure 13 9 1 for details Compare free nodes on both boundary zones with all nodes on both boundary zones using the Merge Boundary Nodes panel see Section 7 1 2 The Merge Boundary Nodes Panel Delete deletes all the selected face zone s You can also delete the unused nodes associated with the selected face zone s A To avoid invalidating the mesh you cannot delete face zones that are con nected to a cell zone Delete Nodes allows you to delete the unused nodes associated with face s that are being deleted Merge combines a
262. east critical and then move the boundary sliver to that zone The default values for the skewness threshold and the minimum dihedral angle between faces are 0 95 and 10 respectively Refining Boundary Slivers This operation attempts to increase the volume of boundary slivers to create a valid tet cell TGrid identifies tetrahedra having one or two faces on the boundary and then splits the edge opposite the boundary face s The edge opposite the face pair with the largest dihedral angle will be split for a tet with one boundary face while the edge opposite the boundary faces will be split for a tet having two boundary faces The split node is then smoothed such that the volume of the tetrahedron increases thereby creating a valid tet cell Refining Interior Slivers This operation attempts to remove the sliver by placing a node at or near the centroid of the sliver cell TGrid then performs swapping and smoothing to improve the skewness Collapsing Slivers This operation attempts to collapse the edge of a skewed sliver cell on any one of its neighbors The default skewness threshold is 0 985 Notes e If you are not using a two sided wall condition for the boundary you can slit the face zone containing the sliver using the boundary slit boundary face command and then perform the sliver removal operation e Multiple slivers may exist on top of each other thus requiring multiple operations to remove them all 13 8 ANSYS
263. eates the opposite extreme where each face or cell is represented by a point and there is a considerable space between entities A small value such as 0 01 may be sufficient to allow you to distinguish a face or cell from its neighbor Figure 14 1 1 shows displays with different Shrink Factor values ANSYS Inc April 15 2008 14 3 Examining the Mesh A Figure 14 1 1 Grid Display A With Shrink Factor 0 B With Shrink Factor 0 01 14 1 3 The Display Grid Panel The Display Grid panel allows you to select the grid zones to be drawn You can also display unmeshed free or multiply connected faces or unused nodes and you can limit the display to objects within certain quality and or size ranges These controls may help you in determining the causes of boundary mesh problems Cells including boundary cells interior nodes and interior faces will be displayed only if they are in the active cell zones In addition if you have used domains to generate the mesh or grouped zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces only the cells faces etc in the active domain can be displayed Display gt Grid Controls Display Grid l Nodes Faces Cells Bounds Attributes Options Node Zones Bz F al boundary node 11 node 1 1 Unused Node Zone Groups gS boundary node node 14 4 ANSYS Inc April 15 2008 14 1 Displaying the
264. ecified tol erance The intersection curve is remeshed with a local spacing calculated from from the inter secting surfaces The next step is to insert the intersection curve into the surfaces The insertion will result in a retriangulation of the surfaces along the intersection curve The boundary remesh remesh overlapping zones TUI command extracts the bound ary loops from the zone to imprint The intersecting curve is inserted into the zones During the insertion the zones are retriangulated To perform any of the intersection operations do the following 1 Select the boundary zone s you want intersect in the Intersect Tri Zone list 2 Select the boundary zone s with which you want to intersect the selected boundary zone in the With Tri Zone list 7 10 ANSYS Inc April 15 2008 7 2 Intersecting Boundary Zones 3 Select the appropriate operation from the Operation list 4 Specify the appropriate Tolerance value only in the case of surfaces having gap between them 5 Enable Absolute Tolerance Refine or Separate as appropriate 6 Click Mark TGrid highlights the cells that will be affected by the intersection operation This also helps you to decide whether or not the specified tolerance is sufficient 7 Click Apply 7 2 5 The Intersect Boundary Zones Panel The Intersect Boundary Zones panel allows you to connect two triangular boundary zones See Section 7 2 Intersecting Boundary Zones for detail
265. ecifies the maximum number of attempts for improving a particular face Iterations specifies the number of iterations through the warp improvement procedure Check Quality enables disables the checking of face and cell quality after each prism layer is created When this option is enabled the default setting TGrid will check the cell volume of every new cell the face handedness of every face on every new cell the skewness of all new cap faces 3D only and the skewness of all new cells 2D only If any new cell has zero or negative volume or any left handed faces or if the skewness exceeds the specified Max Allowable Skewness prism layer creation will be stopped See Section 10 12 Negative Volumes Left Handed Faces High Skewness for details Max Allowable Skewness specifies the maximum skewness allowed for a prism cap face in 3D or a prism cell in 2D If the skewness exceeds the specified value TGrid will stop the meshing process and warn you that the skewness for that layer is too high You can then examine the skewed faces or cells make appropriate corrections and recreate the prisms See Section 10 12 Negative Volumes Left Handed Faces High Skewness for details 10 30 ANSYS Inc April 15 2008 10 10 The Prisms Panel Project contains controls for projection and retriangulation Prisms Boundary Zones Baz Growth Direction Improve Project J Retriangulate Adjacent Zones Side Feature An
266. ecifies the prefix of the existing zone names that you want to rename To specifies the prefix of the new zone names Expert contains advanced improvement options Auto Post Improve performs a pre defined sequence of improvement op erations like splitting and merging of nodes to remove small areas improving the boundary surface quality collapsing skewed faces and removing duplicate and intersecting faces 8 42 ANSYS Inc April 15 2008 8 9 The Boundary Wrapper Panel Min Triangle Area specifies the minimum face area to be considered while removing small areas Max Aspect Ratio specifies the maximum allowable aspect ratio Max Skewness specifies the maximum allowable skewness Max Size Change specifies the maximum allowable size change Recover Single Surface contains options for recovering thin surfaces and removing any remaining overlapping regions Single Surface allows you to recover a single thin surface Automatic enables the automatic marking and merging of thin regions for recovering the single surface First Seed Face Second Seed Face specify the seed faces to be used for marking the thin regions Critical Thickness specifies the critical thickness of the surface to be recovered Critical Angle specifies the maximum angle between a pair of op posing faces while checking for overlapping faces Any pair of faces whose normal vectors form an angle greater than the spec ified value will be regarded as non overl
267. ect 3 or 4 nodes and the optional zone Use the hot keys lt Ctrl gt N and lt Ctrl gt F to select node and face as Filter respectively 3 Click Create or press F5 7 16 ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh While creating a face e If you do not select a zone the new face will be in the same zone as an existing face that uses one of the specified nodes e If the nodes you use to create a face are used by faces in different zones make sure that the new face is in the right zone e If you create a face and it is in the wrong zone use the rezoning feature Creating a Zone To create a new zone do the following 1 Select zone in the Filter list hot key lt Ctrl gt Z 2 Click Create or press F5 key The Create Boundary Zone panel will open prompting you for the zone name and type 3 Specify the name and zone type as appropriate in the Create Boundary Zone panel 4 Click OK The new zone will automatically be added to the Selections list in the Modify Boundary panel Deleting a Node Face Zone To delete the node s or face s do the following 1 Select the node s or face s or zone s to be deleted 2 Click Delete or press lt Ctrl gt W on the keyboard Merging Nodes To merge the nodes do the following 1 Select the two nodes to be merged You can merge multiple pairs of nodes by selecting more than two nodes before clicking Merge or pressing F9 The first an
268. ect projects the edges of the selected edge loop onto the selected face zone using the specified controls Method contains the methods that can be used for projecting edges Closest Point specifies that each edge should be projected to the closest point on the selected face zone Specific Direction specifies that each edge should be projected in a spec ified direction onto the selected face zone Direction specifies the X Y Z vector for the direction in which edges should be projected when the Specified Direction projection method is used Intersect computes the intersection of the selected edge loops and creates a new edge loop containing the common edges Delete enables the automatic deletion of all overlapping edges before the intersection is computed If you want to delete individual overlapping edges use the delete overlapped edges text command mentioned in Section 7 7 6 Text Commands for Remeshing 7 52 ANSYS Inc April 15 2008 7 6 Creating and Modifying Features Intersection Tolerance specifies the tolerance for determining if two edges intersect Apply executes the parameter that you have selected in the Options list List reports in the text window the zone ID name boundary type and number of faces in each selected edge loop Size Limits reports in the Information dialog box the minimum maximum and av erage edge length for each selected edge loop 7 6 4 Text Commands for Creating and Modif
269. ected Target Face Zone contains a list from which you can select a boundary zone to be the target of projection from the source zone Projection Method contains options for defining the method of projection Normal specifies that the projection occurs in the direction normal to the source face zone Direction allows you to specify the direction of projection from the source face zone Closest specifies that for each node being projected the projection occurs in the direction of the closest point on the destination face zone ANSYS Inc April 15 2008 7 71 Manipulating the Boundary Mesh Projection Direction specifies the direction of projection X Y Z when Direction is selected in the Projection Type list Project completes the zone projection Draw displays the zones selected in the Source Face Zone and Target Face Zone lists Default resets all controls in the panel to their default settings 7 11 2 Text Commands for Projecting Boundary Zones The text interface command for projecting boundary zones is boundary project face zone allows nodes on a selected face zone to be projected onto a target face zone Projection can be performed based on normal direction closest point or specified direction 7 12 Creating Groups TGrid allows you to create groups of surfaces which will be available in all the panels along with the default groups e g boundary tri quad etc Both face and edge zones are grouped sep
270. ection initial zones final zones to delete the geometry e Smoothing the prism cap zone created during the prism creation operation 1 Use the command define initial zones get face zones of filter prism cap to obtain a list of the zones named prism cap 2 Apply appropriate prism parameters and create prisms 3 Use the command define final zones get face zones of filter prism cap to obtain a list of the zones named prism cap after the prism creation opera tion 4 Use the command boundary improve smooth eval expr list subtract final zones initial zones to smooth the recently created prism cap zone D 4 ANSYS Inc April 15 2008 Appendix E Tips This appendix contains tips on the following topics e Section E 1 Reading Files e Section E 2 Writing Files e Section E 3 Saving Hard Copy Files e Section E 4 Importing Meshes e Section E 5 Creating a Mesh e Section E 6 Grouping Elements e Section E 7 Deleting Duplicate Nodes e Section E 8 Manipulating the Boundary Mesh File e Section E 9 Examining the Mesh e Section E 10 Reporting Mesh Statistics e Section E 11 Refining the Mesh e Section E 12 Using the GUI E 1 Reading Files e When TGrid reads a mesh file it first searches for a file with the exact name you typed If a file with that name is not found it will search for a file with msh appended to the name e You can read a TGrid mesh file using the File Read Mesh
271. ectory either for TGrid or for Cortex and it is therefore not useful Typing chdir with no arguments will move you to your home directory in the console Examples of system commands entered in the console are as follows pwd Ils valve The screen output will appear in the window in which TGrid was started If you start the program remotely it will appear in the window in which Cortex was started home cfd run valve valvei cas valvei msh valve2 cas valve2 msh ANSYS Inc April 15 2008 5 9 Text User Interface 5 5 Text Menu Input from Character Strings When writing a Scheme extension function for TGrid it is convenient to be able to include menu commands in the function This can be done with ti menu load string For example to open graphics window 1 use ti menu load string di ow 1 A Scheme loop that will open windows 0 and 1 and display the front view of the grid in window 0 and the back view in window 1 is given by for each lambda window view ti menu load string format f di ow a gr view rv a window view 0 1 gt front back This loop makes use of the format function to construct the string used by menu load string This simple loop can also be written without using menu commands but you need to know the Scheme functions that get executed by the menu commands to do it for each lambda window view cx open window window draw mesh cx restore view
272. ed Absolute do the following a Click Compute This will update the minimum and maximum extents absolute values of the selected face zones in the X Y and Z text entry fields These values repre sents a bounding box that encloses the selected boundary zones touching its extremeties in all three directions This will also update the Mesh Size text en try box with a value of 1 10th of the minimum length of the computed bounding boz b Click Draw This will draw a bounding box of computed values in the graphics window If you want bounding box of parameters of your choice then specify X Y and Z coordinates accordingly c optional Specify appropriate Mesh Size Mesh Size tert entry box gets updated when you click Compute in the previous step If you want finer or coarser mesh than the default mesh size change this value appropriately d Click Create to create a bounding box of specified parameters 3 If you have selected Relative do the following Initially all the Delta entry fields will be set to 0 This implies that the bounding box touching the boundaries of the selected face zone will be created 7 80 ANSYS Inc April 15 2008 7 14 Creating Surfaces a Specify the required clearance values in Delta entry fields Positive values in these fields mean bounding box outside the initial bounding box will be created and negative values in these fields mean bounding box inside the initial bounding box wi
273. ed as follows Z minja b oe where Z the deviation from a best fit plane that contains the element a b the lengths of the line segments that bisect the edges of the element The value of face warp ranges between 0 and 1 A value of 0 specifies an equilateral element and a value of 1 specifies a highly skewed element Dihedral Angle Dihedral angle applies only to the faces and not cells It highlights the faces with the dihedral angle between them in the range specified in the Cell Quality Range group box in the Cells tab of the Display Grid panel You can specify a range of values from 0 180 This quality measure is useful in locating the sharp corners in complicated geometries 15 5 2 Specifying the Quality Measure You can specify the quality measure in the Quality Measure panel The Quality Measure Panel The Quality Measure panel allows you to specify the measure used to evaluate the quality of your mesh skewness change in size edge ratio aspect ratio squish warp or dihedral angle For triangular and tetrahedral faces cells you can also select the method to be used to report and display skewness ANSYS Inc April 15 2008 15 13 Reporting Mesh Statistics Report Quality Measure Quality Measure Skewness v Size Change v Edge Ratio wv Aspect Ratio v Squish wv Warp v Dihedral Angle Tri Tet Skewness Method Equilateral Volume Deviation v Normal
274. ed surface for a thin part Enable the display of multiply connected faces in the Display Grid panel see Section 14 1 3 The Display Grid Panel to see the remaining unmerged regions recovered surface Figure 8 8 5 Recovering a Single Surface The unmerged regions can be removed using the Post Single Surface option 6 Select Post Single Surface in the Recover Options list 7 Enter an appropriate value for Max Face Count and click the Auto button in the Parameters group box to automatically remove the remaining unmerged regions Most unmerged faces will be deleted when the automatic option is used Any remaining unmerged faces can be deleted manually Select the seed face as appro priate and click the Mark button in the Parameters group box TGrid will mark the regions and report the number of faces to be deleted Click Delete to delete the marked faces Removing Crossovers If the geometry has small gaps between two separate faces the wrapper can create crossover configurations The crossovers are unwanted faces that connect parts of the wrapper surface separated by a small gap The crossover faces have one vertex on one side of the gap and the other two nodes on the other side of the gap You need to remove the crossovers to make the wrapper surface represent the original geometry precisely TGrid allows you to remove crossover faces either automatically or manually To remove crossover configurations do the following 1 Select
275. edral or hybrid mesh you can improve the quality of the mesh by smoothing nodes and swapping faces Smoothing and face swapping are tools that help to improve the quality of the final numerical mesh You can also use the improve command which combines operations like collapsing cells node smoothing face swapping and inserting nodes Tetrahedral mesh improvement options are available in the Tri Tet Improve panel see Section 13 5 The Tri Tet Improve Panel ANSYS Inc April 15 2008 13 1 Improving the Mesh 13 1 Smoothing Nodes Smoothing repositions the nodes to improve the mesh quality The smoothing methods available in TGrid are e Laplace smoothing e Variational smoothing e Skewness based smoothing 13 1 1 Laplacian Smoothing Laplace smoothing is used to improve reduce the average skewness of the mesh In this method a Laplacian smoothing operator is applied to the unstructured grid to reposition nodes The new node position is the average of the positions of its node neighbors The relaxation factor a number between 0 0 and 1 0 multiplies the computed node position increment A value of zero results in no movement of the node and a value of unity results in movement equivalent to the entire computed increment This node repositioning strategy improves the skewness of the mesh but usually relaxes theclustering of node points In extreme circumstances the unchecked operator may create grid lines that cross ov
276. een entities 1 Select the appropriate option in the Filter list and select the two entities between which the distance is to be determined 2 Click Distance in the Operation group box The distance between the selected entities will be printed in the TGrid console Projecting Nodes You can project nodes onto a specified projection line or plane Do the following to project nodes 1 Define the projection line or projection plane as appropriate a Select the appropriate option in the Filter list b Select two entities to define the projection line or three entities to define the projection planne c Click Set in the Operation group box to define the projection line or plane The line coordinates or plane position will be repoted in the TGrid console 2 Select the node s to be projected The projection line plane will be highlighted in the display window 3 Click Project in the Operation group box ANSYS Inc April 15 2008 13 15 Improving the Mesh 13 6 2 The Modify Cells Panel The Modify Cells panel allows you to perform operation such as smoothing nodes moving nodes swapping cells etc Mesh Tools Cell Modify S Modify Cells Selections Filter Operation Enter Selection Auto Redisplay Draw Cells Quality Measure F Local Delta Using Nodes skew Report Zone tse tanta azo Next Skew Heset Skew Hedisptas Skew Brew Close Help
277. el The Triangulate Zones panel contains the options available for triangulating quad zones Boundary gt Mesh Triangulate Triangulate Zones Boundary Zones Ba Boundary Zone Groups gg far field a geometry inlet f Replace Controls Boundary Zones contains a list of the quadrilateral boundary zone s available ANSYS Inc April 15 2008 7 63 Manipulating the Boundary Mesh Boundary Zone Groups contains a list of the default boundary zone groups and user defined groups available in TGrid If you select a zone group from this list all zones of that group will be selected in the Boundary Zones list You can also select multiple types to select all the zones of different types e g inlet and outlet Replace toggles the automatic deleting of the original quadrilaleral boundary zone When this option is enabled the quadrilateral boundary zone will be replaced by the newly triangulated zone 7 10 Separating Boundary Zones There are several methods available in TGrid that allow you to separate a single boundary face zone into multiple zones of the same type If your grid contains a zone that you want to break up into smaller portions you can make use of these features For example if you created a single wall zone when generating the grid for a duct but you want to generate different mesh shapes on specific portions of the wall you will need to break that wall zone
278. el if required Click the Feature Modify to open the Feature Modify panel see Section 7 6 3 The Feature Modify Panel Refer to Sections 7 6 1 and 7 6 2 for details about using this panel e Project the nodes of the wrapper surface on the edge loops that you have created i Select the wrapper surface wrapper surf xx in the Tri Boundary Zones list ii Select the edge loops on which you want to project nodes of the initial wrapper surface in the Edge Zones selection list Deselect the edges to be ignored during imprinting from the Edge Zones list iii Enable With Advanced Tracking to allow recovery of more features if re quired Click Imprint Imprinting is carried out by tracking a node path on the wrapper surface corresponding to a feature edge in the geometry The nodes on the wrap per surface close to the feature edge are projected onto the edge loop See Figure 8 6 1 to see the effect of imprinting i You may have to click Imprint more than once B E amp A B Figure 8 6 1 Wrapper Surface A Before and B After Imprinting The nodes outside the critical range will not be projected because the projection of such nodes creates flipped or highly skewed triangles ANSYS Inc April 15 2008 8 17 Wrapping Boundaries If the features are not extracted properly after the imprint operation you can separate the wrapper surface zone by zone and click Imprint by selecting all the separated zones
279. ell length Section 12 3 4 Maximum Cell Length e Buffer layer Section 12 3 5 Buffer Layers e Peel layers Section 12 3 6 Peel Layers e Local refinement regions Section 12 3 7 Local Refinement Regions 12 3 1 Keep Outer Domain TGrid allows you to create hexcore mesh until the boundary of the domain instead of creating a tetrahedral mesh at the boundary This feature is useful for the hexcore grid generation for external flow domains e g external aerodynamics cases where the boundary conformity is not needed for far field boundaries You can generate the hexcore mesh till the far field boundary of the domain by enabling Keep Outer Domain in the Hexcore panel The minimum and maximum domain extents will be automatically updated with values slightly greater than the bounding box of the surface mesh in the domain In Figure 12 3 1 the hexcore mesh has been extended until the domain boundary and does not have a tetrahedral mesh at the far field boundary ANSYS Inc April 15 2008 12 3 Generating the Hexcore Mesh il Hexcore mesh extends upto user defined domain extents If the gap be tween user defined domain extents and geometric boundaries is less than 20 of size of the bounding box which contains the given geometry TGrid gives warning Figure 12 3 1 Hexcore Until the Far Field Boundary 12 3 2 Hexcore Upto Boundaries The Hexcore Upto Boundaries option can be used when the boundary of a domain touches the geo
280. ell or face is from its ideal form similar to aspect ratio A skewness of zero is equilat eral equiangular and a skewness of 1 is degenerate A boundary sliver is a flat boundary cell containing two boundary faces It is a tetrahedron in which the 4 forming nodes are nearly coplanar and also nearly lie on a circle The circumcenter of a sliver is also found to be nearly coplanar with the forming nodes In a high quality mesh the change in size from one face or cell to the next should be gradual smooth Large differences in size between adjacent faces or cells will result in a poor computational grid because the differential equations being solved assume that the cells shrink or grow smoothly Squish is a measure used to quantify the non orthogonality of a cell with respect to its faces Squish is defined as 1 A re rel where A is the face unit area vector and re is the vector connecting the adjacent cell centroids for face squish or connecting the cell centroid and the cell face centroid for cell squish Glo 5 Glossary TGrid Thread Triangulation Unused Nodes Voronoi Regions Zone Glo 6 A highly efficient easy to use unstructured grid generation pro gram that can handle grids of virtually unlimited size and complex ity consisting of triangular tetrahedral hexahedral prismatic or pyramidal cells It is an additional preprocessor that can generate volume meshes from existing boundary meshes
281. ells does not provide much useful information about the mesh Hence you need to rely primarily on grid statistics 1 Open the Report Boundary Cell Limits panel Report gt Boundary Cell Limits a Click Compute The maximum cell skewness of cells having 1 boundary face is 0 47 A skewness of zero indicates an equilateral cell You can click the Quality Measure button to open the Quality Measure panel see Section 15 5 2 The Quality Measure Panel where you can report additional measures of quality aspect ratio and ANSYS Inc April 15 2008 4 6 Reporting the Mesh Statistics Figure 4 6 1 The Report Boundary Cell Limits Panel change in size by selecting them The default measure of skewness is sufficient for analyzing the quality of triangular and tetrahedral cells b Close the Report Boundary Cell Limits panel 2 Open the Report Cell Limits panel Report gt Cell Limits Figure 4 6 2 The Report Cell Limits Panel You can use this panel to determine the best minimum worst maximum and average cell quality skewness by default a Select Quality in the Options list ANSYS Inc April 15 2008 4 9 Sample Session b Select the fluid 7 zone in the Cell Zones selection list c Click Compute The worst cell has a skewness of 0 488 The average skewness is approximately 0 12 These values are typical for 2D problems and are suitable for obtaining
282. ells in the mesh mesh tritet controls advanced max nodes sets the maximum number of nodes in the mesh A Be careful when you set upper limits on the number of cells or nodes TGrid will stop adding nodes or cells when it reaches the prescribed limit and may leave the mesh unevenly refined and less than adequate mesh tritet controls cell size function specifies the cell size function for refine ment You can select geometric linear or none as appropriate mesh tritet controls compute max cell volume computes the maximum cell vol ume for the current mesh mesh tritet controls max cell volume specifies the maximum allowable cell vol ume mesh tritet controls refine method allows you to select the refinement method You can select either skewness based refinement or the advancing front method mesh tritet controls skewness method levels specifies the number of refinement levels for skewness based refinement mesh tritet controls skewness method max skew improve toggles the skewness based improvement during refinement mesh tritet controls skewness method must improve skewness toggles the mod ification of the default auto refinement parameters in order to improve skewness after refinement mesh tritet controls skewness method refine boundary cells toggles the au tomatic refinement of boundary cells during refinement mesh tritet controls skewness method refine cells toggles the automatic re finement of cells
283. ent Utilize this time to login to the faster machine and to start TGrid ANSYS Inc April 15 2008 2 3 Getting Started 3 Press Enter on your keyboard again A message will prompt you to start TGrid on remote machine with the following arguments cx host p1 p2 where host is the name of the host local machine on which the Cortex is running on pi and p2 are the two integers indicating the connecting port numbers that are used to communicate information between the Cortex on the host machine and TGrid on the remote machine 4 Login to the remote machine and set the display to the host machine 5 Start TGrid from remote machine using the following command tgrid version cx host p1 p2 Replace version by the version that you wish to run 2d or 3d The host and port numbers are displayed in the TGrid console window The GUI commands related to the File menu e g reading file importing file and other Select File dialogs do not work for dual process build Therefore use the TUI commands 2 3 1 Startup Options Before starting TGrid you can obtain information about the available releases Type tgrid help in an xterm window on UNIX systems or the MS DOS Command Prompt window on Windows systems The options available are Usage version help options options cl following argument passed to tgrid cxarg following argument passed to cortex cx host p1 p2 connect to the specified cortex process
284. entric Boundary Cell Cell CFD Convergence ANSYS Inc April 15 2008 The aspect ratio of a face or cell is the ratio of the longest edge length to the shortest edge length The aspect ratio applies to triangular tetrahedral quadrilateral and hexahedral elements and is defined differently for each element type The axial component of force acting tangential to the surface due to friction Barycentric coordinates are the set of weighting factors w i that represent a location in space relative to a fixed set of points p i The location is given by the sum of w i x p i for all i where 0 lt w t lt 1 and the sum of all w i is 1 A cell that contains one or more boundary faces An n simplex in n dimensions It has n 1 nodes and faces In 2D a cell is a triangle and in 3D a cell is a tetrahedron Computational Fluid Dynamics The property of a numerical method to produce a solution which approaches the exact solution as the grid spacing control volume size or element size is reduced to zero Glo 1 Glossary Circumcenter Circumcircle Circumradius Clustering Dead Cell Edge Swapping Edge Element Face Glo 2 The point equidistant from each of the n 1 forming nodes of a cell or face A circle sphere that passes through the n 1 forming nodes of a cell The radius of a circumcircle circumsphere The requirement for clustering is that the mesh be fine enough to resolve the p
285. ep virtual entities option mesh tritet preserve cell zone allows you to specify the cell zones to be preserved during the meshing process 11 7 Common Tri Tet Meshing Problems Most problems with the mesh generation process become manifest in the failure to gen erate an initial mesh There are two sources of such problems e An invalid surface mesh e Incorrect sliver size specified Some of the common problems and suggestions for checking and fixing the mesh are described in this section To look at the nodes and faces that have not been meshed enable Unmeshed in the Display Grid panel ANSYS Inc April 15 2008 11 25 Generating Triangular Tetrahedral Meshes Duplicate Nodes or Faces Some codes create multiple copies of the same node where two boundary curves or surfaces meet resulting in a connectivity problem This problem can be detected by reporting the number of free nodes or by drawing the free edges If the geometry does not contain infinitely thin walls then there should not be any free nodes or edges You can remove duplicate nodes using the boundary delete duplicate nodes command described in Section 7 15 Additional Boundary Mesh Text Commands The presence of duplicate faces can be detected in one of two ways e If the nodes of the duplicate faces are not shared by the non duplicate faces the duplicate faces may have free edges that can be displayed e If the nodes are not distinct or have been merged
286. eparates a face zone by defining a seed face on the surface 7 11 Projecting Boundary Zones Another mesh refinement method involves projecting the nodes of one face zone onto another possibly non planar face zone to create a new face zone that has the same connectivity as the original face zone This new face zone is created after the projection and no cell zones are created The face zone that is projected is not modified in any way Projecting a face zone is used mainly to fill in gaps by extending the domain through the projection The original connectivity is maintained after the projection with the effect being that elements on the connected side zones will be stretched to cover the projection distance Affected side zones should then be remeshed to obtain regular size 7 70 ANSYS Inc April 15 2008 7 11 Projecting Boundary Zones elements on them Such a remeshing results in a new side zone after which you can and should delete the original side zone Finally you can mesh the domain to get the volume elements 7 11 1 The Project Face Zone Panel The Project Face Zone panel allows you to project nodes from a selected face zone onto a target face zone Project Face Zone Source Face Zone Target Face Zone Projection Method Projection Direction v Nomal mE u Direction v Closest Controls Source Face Zone contains a list from which you can select a boundary zone to be proj
287. er The prisms extends throughout the entire region bounded by the quadrilateral faces but only a few of them are shown here A ROS ASA N 5 Ne TSI Y O NUV Ve ae ae a se TRESS We NIM ei Pee See tS ELIE aera CSS IBS ey BRN PORK KA aaah A iy Figure 9 1 2 Grid with Prisms in a Boundary Layer Region The surface mesh originally contained only triangular faces The quadrilateral faces are created automatically when the prisms are built on the triangular faces If the quadrilateral faces of the prisms do not lie on the external boundary of the domain i e if the prism region begins and or ends in the interior of the domain create a layer of transitional pyramids between steps 1 and 2 See Section 9 3 Generating Pyramids for details If you have no special boundary layer resolution requirements you can generate a mesh consisting entirely of tets see Figure 9 1 3 You can use the automatic tet mesh gener ation procedure the manual procedure or a combination of both See Chapter 11 Gen erating Triangular Tetrahedral Meshes for details 9 1 2 3D Boundary Mesh Start from a 3D boundary mesh containing triangular and quadrilateral faces as well as hexahedral cells in the quadrilateral face regions The resulting mesh is referred to as a zonal hybrid mesh 1 Add a layer of pyramids to the quadr
288. er mesh improve ment options You can initialize and refine the tri tet mesh in a single step by clicking the Init amp Refine button in the Tri Tet panel after setting the appropriate parameters in the Initialization and Refinement tabs Alternatively you can set the appropriate parameters in the Initial ization tab and click the Init button to create the initial mesh You can then refine the initial mesh by setting the appropriate parameters in the Refinement tab and clicking the Refine button If you need to refine a particular region you can define the region to be refined using the Tri Tet Refinement Region panel see Section 11 5 3 The Tri Tet Refinement Region Panel ANSYS Inc April 15 2008 11 9 Generating Triangular Tetrahedral Meshes 11 3 Initializing the Tri Tet Mesh The first step in the volume mesh generation process is initialization The initial mesh consists of the nodes and triangles of the boundary surface mesh For some 3D geometries it is not possible to create a tetrahedral mesh from the boundary nodes alone In such cases TGrid automatically adds a small number of nodes in the interior of the domain Interior nodes may also have to be added to resolve numerical problems associated with the D elaunay criterion 11 3 1 Using the Tri Tet Panel You can initialize the mesh using the options available in the Initialization tab of the Tri Tet panel Mesh Tri Tet 11 10
289. er surface in the Tri Boundary Zones list 2 Select Post Wrap in the Options drop down list and Auto Post Wrap in the Sub Options list respectively 3 Enter an appropriate value for Distance Tolerance The value specified for Distance Tolerance will be considered for the removal of duplicate nodes on the wrapper surface 4 Enter an appropriate value for Relative Thickness The value specified for Relative Thickness will be considered for the removal of self intersecting surfaces on the wrapper surface 5 Enter an appropriate value for Critical Thickness The value specified for Critical Thickness will be considered for the inflating of thin regions on the wrapper surface 6 Enter an appropriate value for Max Improve Angle 7 Click Apply TGrid will report the operations performed and the quality at the end of the auto post wrapping in the console Removing Duplicate Nodes The initial wrapper surface created after imprinting may contain duplicate nodes two nodes having the same Cartesian coordinates Multiple copies of the same node may cause problems in connectivity of the final wrapper surface To remove the duplicate nodes do the following 1 Select the wrapper surface in the Tri Boundary Zones selection list 2 Select Post Wrap in the Options drop down list and Remove Duplicate in the Sub Options list respectively ANSYS Inc April 15 2008 8 21 Wrapping Boundaries 3 Enter an appropriate value for Di
290. er the boundary creating negative cell volumes To pre vent such cross overs the skewness of the resulting cells is checked before the node is repositioned This makes the smoothing operation time consuming The smoothing operator can also be applied repeatedly but as the number of smoothing iterations increases the node points have a tendency to pull away from boundaries and the grid tends to lose any clustering characteristics 13 1 2 Variational Smoothing Variational smoothing is available only for triangular and tetahedral meshes It can be considered as a variant of Laplace smoothing The new node position is computed as a weighted average of the circumcenters of the cells containing the node The variational smoothing method is provided as a complement to Laplace smoothing 13 1 3 Skewness Based Smoothing Skewness based smoothing is available only for triangular and tetrahedral grids When you use skewness based smoothing TGrid applies a smoothing operator to the grid repo sitioning interior nodes to lower the maximum skewness of the grid TGrid will try to move interior nodes to improve the skewness of cells with skewness greater than the specified minimum skewness You can also specify an appropriate value for the minimum improvement if required This allows you to stop performing the smoothing iterations 13 2 ANSYS Inc April 15 2008 13 2 Swapping when the maximum change in cell skewness is less than or equal to th
291. er tutorial 7 i Zier Plaise iA Select An I Write Binary Files F Write As Polyhedra Mesh File s Bo temave home user tutorial myfile msh Case File myfile caJ OK Filter Cancel A Read Form B Write Form Figure 3 2 1 The Select File Dialog Box Note In the Directories list the dot represents the current directory and the double dots represents the parent directory 2 Specify the file name by selecting it from the Files list or entering the file name in the File text entry box if available at the bottom of the dialog box The name of this text entry box will change depending on the type of file you are selecting Mesh File Journal File etc If you are searching for an existing file with a non standard extension you may have to modify the search pattern at the end of the path in the Filter text entry box e If you are reading a mesh file the default extension in the search path will be msh MSH cas and only those files that have one of these extensions will appear in the Files list e If you want files with a grd extension to appear in the Files list change the search pattern to grd e If you want all the files in the directory to be listed in the Files list enter as the search pattern ANSYS Inc April 15 2008 3 7 Graphical User Interface 3 Read multiple boundary mesh or volume mesh files e If you are reading multip
292. er xgl tgrid env Lists all environment variables before running TGrid tgrid g Runs Cortex without graphics and without the graphical user interface This option is useful if you are not on an X Window display or if you want to submit a batch job tgrid gu Runs Cortex without the graphical user interface tgrid gr Runs Cortex without graphics To start TGrid and immediately read a journal file enter the command tgrid i journal replacing journal with the name of the journal file you want to read ANSYS Inc April 15 2008 2 5 Getting Started Options Description nocheck Speeds up the startup by not checking to see if the license server is running This is useful if you know that the license daemon is running project x Allows you to record CPU time for individual projects sepa rately tgrid project x where x is replaced by the name of the project Extra information related to CPU time will be written to the license manager log file usually license log in the license subdirectory of your TGrid installation directory To determine the CPU time for the project add the USER CPU and SYSTEM CPU values that appear in license log See the installation notes for more information about the license man ager tgrid version r Replaces version with the desired version and lists all releases of the specified version tgrid rx Runs release x of TGrid You may either specify
293. eration TGrid will report the progress of the mesh generation in the console Figure 4 4 2 E C lt A E File Boundary Mesh Display Report Help Number of Cells Number of Nodes Nodes Sec 495 211 4 Number of Cells Number of Nodes Nodes Sec 629 278 smooth cells with skewness gt 0 75 for 10 iterations faces swapped moved nodes most improvement O 629 cells min skew 4 112162e 15 max skew 0 72758774 avg skew 0 15876303 swap cells with skewness gt 0 2 for 5 iterations smooth cells with skewness gt 0 75 for 5 iterations faces swapped smooth cells with skewness gt 0 3 for 3 iterations moved nodes most improvement 0 moved 178 nodes rms 0 114148 moved 123 nodes rms 0 0530185 moved 31 nodes rms 0 0327698 629 cells min skew 5 2864892e 06 max skew 0 48732538 avg skew 0 1173402 Tone Figure 4 4 2 Text Output from Auto Mesh 2 Close the Auto Mesh panel This example describes the generation of the mesh using the default triangular mesh generation parameters You can modify the mesh generation parameters in the Tri Tet panel see Section 11 5 The Tri Tet Panel if required 4 5 Displaying the Mesh You can display the mesh using the Display Grid panel Figure 4 5 1 Display Grid 1 Click the Cells tab at the top of the panel 2 Select fluid 8 in the Cell Zones selection list Alternatively you can select fluid in the Cell Zone Groups list to select the fluid
294. ering writes a RAMPANT file from TetraMesher This file can be read by TGrid using the File Read Mesh menu item or the file read mesh text com mand TetraMesher generates tetrahedral volume grids using a recursive subdivision octree scheme that interfaces with ICEM CFD A 3 Meshes from Third Party CAD Packages A single filter allows you to convert files created by several finite element packages to the grid file format used by TGrid This filter fe2ram allows you to convert surface or volume meshes from ANSYS l deas NASTRAN PATRAN or other packages ARIES files can be converted if they are first saved as ANSYS Prep7 files as described in Section A 3 5 ARIES Files A 3 1 Using the fe2ram Filter to Convert Files When you import one of these types of grid files using the menu items in the File Import pull down menu the changes are transparent and you can follow the instructions provided in Section 6 7 Importing Files If you choose to convert the file manually before reading it into TGrid enter the following command utility fe2ram dimension read format merge zoning write format input file output file The items enclosed in square brackets are optional ANSYS Inc April 15 2008 A 1 Importing Boundary and Volume Meshes dimension indicates the dimension of the dataset Replace dimension by d2 to indicate that the grid is two dimensional For a 3D grid do not enter anything for dimension because 3D is the de
295. ermined by the shortest distance from the centroid of face B to its nodes The marked faces will appear in the grid display when faces are displayed For a list of faces in proximity to each other set the report verbosity level to 2 before using the mark face proximity command boundary merge small face zones merges the face zones having area less than the specified minimum area with the adjacent zone boundary print info prints information about the grid in the text window See Sec tion 15 6 Printing Grid Information for more information boundary reset element type resets the element type mixed tri or quad of a bound ary zone If you have separated a mixed tri and quad face zone into one tri face zone and one quad face zone for example TGrid will continue to identify each of these as a mixed zone Resetting the element type for each of these new zones will identify them as respectively a triangular zone and a quadrilateral zone boundary scale nodes applies a scaling factor to all node coordinates You can use this command to change the units of the grid boundary slit boundary face slits a boundary face zone by duplicating all faces and nodes except those nodes that are located at the edges of the boundary zone A displacement can be specified to provide thickness to the boundary see Fig ure 7 15 1 The slit command only works when it is possible to move from face to face using the connectivity provided by the cells
296. ernatively use the TUI command mesh non conformals controls enable to enable the creation of a non conformal interface If this option is enabled all the surfaces having quad elements will be copied and remeshed with triangular cells The free nodes of the triangular mesh will be merged ANSYS Inc April 15 2008 12 3 Controlling Hexcore Parameters with the original surface mesh The method to be used for retriangulation can be specified using the command mesh non conformals controls retri method The quad split method is the default method used for retriangulation You can select prism quad split or remesh as appropriate 3 Specify the hexcore parameters in the Hexcore panel See Section 12 3 Controlling Hexcore Parameters for details TGrid automatically calculates the parameters e g maximum cell length required during the hexcore meshing These parameters can be changed using the Hexcore panel or using the commands in the mesh hexcore text menu 4 Click Create in the Hexcore panel to generate the hexcore mesh 12 3 Controlling Hexcore Parameters The parameters that control the hexcore mesh generation can be changed using the Hexcore panel The following options are available to control the hexcore mesh generation in the domain e Keep outer domain Section 12 3 1 Keep Outer Domain e Hexcore upto boundaries Section 12 3 2 Hexcore Upto Boundaries e Only hexcore Section 12 3 3 Only Hexcore e Maximum c
297. es are imported into TGrid using the menu items in the Import submenu or using the associated text commands ANSYS Inc April 15 2008 6 11 File Types Reading ANSYS Prep7 Files 1 Select the File Import ANSYS prep7 cdb menu item 2 Select the Surface menu item to read a surface Prep7 file or the Volume menu item to read a volume Prep file OR Use one of the following TUI commands e file import ansys surf mesh e file import ansys vol mesh Reading CGNS Files 1 Select the File Import CGNS menu item 2 Select the Surface menu item to read a surface mesh or the Volume menu item to read a volume mesh OR Use one of the following TUI commands e file import cgns surf mesh e file import cgns vol mesh Reading deas Universal Files 1 Select the File Import IDEAS universal menu item 2 Select the Surface menu item to read a surface Universal file or the Volume menu item to read a volume Universal file OR Use one of the following TUI commands e file import ideas surf mesh e file import ideas vol mesh 6 12 ANSYS Inc April 15 2008 6 7 Importing Files Reading NASTRAN Files 1 Select the File Import NASTRAN menu item 2 Select the Surface menu item to read a surface file or the Volume menu item to read a volume file OR Use one of the following TUI commands e file import nastran surf mesh e file import nastran vol mesh Reading PAT RAN Neutr
298. es of the layers are moved to zones of the same types as the zones to which their nodes are projected Unprojected faces are collected in a single prism side zone 4 Retriangulation Adjacent triangular zones that have been projected to are auto matically retriangulated Triangles that are overlapped by new quadrilateral faces from the prism layers are removed Most of the original nodes are used in the new triangulation The result is a conformal interface between the sides of the prism layers and the adjacent triangular zones An analogous procedure is used in 2D ANSYS Inc April 15 2008 10 13 Generating Prisms 10 6 Using Adjacent Zones as the Sides of Prisms For each zone adjacent to the zone s from which you grow prisms TGrid will check the angle between the prism growth direction and the adjacent zone Depending on the size of this angle TGrid will decide whether to use the adjacent zone for the prism sides or create a new zone Using Adjacent Quadrilateral Face Zones If an adjacent zone has quadrilateral faces it will be used without modification as the prism side boundary and it satisfies the following requirements e It must share nodes with the boundary zone from which you are building the prisms i e there must be no free nodes see Section 7 1 1 Free and Isolated Nodes where the zones touch e The angle between the adjacent zone and the prism growth direction must be less than the specified threshold Max
299. es on sliver cells having skew ness greater than the specified threshold value Swap Boundary removes boundary slivers by moving the boundary to ex clude the cells from the zone Refine Boundary refines the boundary slivers by edge splitting Refine Interior remove the sliver by placing a node at or near the centroid of the sliver cell Collapse attempts to collapse the nodes of a skewed sliver cell on any one of its neighbors Skew Threshold specifies the skewness threshold above which sliver cells will be removed Relaxation specifies the relaxation factor for smoothing boundary and interior slivers Iteration specifies the number of iterations for the smoothing of boundary and interior slivers 13 12 ANSYS Inc April 15 2008 13 6 Modifying Cells Min Skewness specifies the skewness above which the boundary slivers will be swapped Dihedral Angle specifies the threshold dihedral angle If the dihedral angle be tween two boundary faces is below the specified value the cell is considered to be a valid boundary sliver which cannot be improved Feature Angle specifies the angle defining the features for smoothing of boundary slivers Boundary Freeze allows you to fix the boundary during the sliver removal oper ations Apply performs the selected operation 13 6 Modifying Cells TGrid provides tools enabling you to perform primitive operations on the cells such as smoothing nodes swapping cells splitting
300. eset the skewness values Propose highlights the node to be moved and the alternative node position The improvement in the skewness will also be reported in the TGrid console Accept allows you to accept the proposed node movement Refuse allows you to reject the proposed node movement Quality Measure opens the Quality Measure panel see Section 15 5 2 The Quality Mea sure Panel Improve Warp contains options for using the automatic correction procedure for warp based improvement 13 7 4 Text Commands for Moving Nodes The text commands for improving the mesh by moving nodes are as follows mesh modify auto node move allows you to improve the mesh quality by node move ment mesh modify auto improve warp allows you to improve face warp by node movement 13 22 ANSYS Inc April 15 2008 13 8 Cavity Remeshing 13 8 Cavity Remeshing Cavity remeshing is useful in parametric studies since it allows you add remove and replace different parts of the existing mesh You can compare alternative designs by creating a cavity around the object to be replaced and then inserting the new object and connecting it to the existing mesh Prisms can be grown using appropriate parameters and the cavity can be filled with tet cells You can also improve the quality of the volume mesh by creating an appropriate cavity around the skewed cells and remeshing it TGrid allows you to create a cavity in an existing mesh by removing tet cells
301. ess Close the Cell Distribution panel ANSYS Inc April 15 2008 4 11 Sample Session 4 7 Checking the Mesh Before saving the mesh file check it to make sure it has no negative cell volumes or left handed faces See Section 13 11 Checking the Mesh for details Mesh gt Check Domain extents x coordinate min 1 000000e 01 max 1 000000e 01 y coordinate min 1 000000e 01 max 1 000000e 01 Volume statistics minimum volume 1 246947e 03 maximum volume 2 172626e 00 total volume 3 999559e 02 Face area statistics minimum face area 1 022265e 02 maximum face area 2 254692e 00 average face area 9 797752e 01 Checking number of nodes per cell Checking number of faces per cell Checking cell faces Checking face handedness Checking periodic face pairs Checking face children Checking face zone boundary conditions Checking for invalid node coordinates Done The printed results of the check do not show any problem hence the mesh is valid for use in FLUENT 4 8 Saving the Mesh and Exiting T Grid File Write Mesh 1 Enter the file name wedge final msh in the Mesh File field 2 Click OK to write the file The default file name is the same as the input file name 4 12 ANSYS Inc April 15 2008 4 8 Saving the Mesh and Exiting T Grid chome user tutorial mshy id Figure 4 8 1 Writing the Mesh File 3 End the T
302. essing the Online Technical Support Web Site You can access the Online Technical Support web site by selecting the Online Technical Support menu item in the Help pull down menu Help Online Technical Support TGrid will direct your web browser to the appropriate web address 3 6 7 Obtaining a Listing of Other TGrid License Users You can obtain a listing of current TGrid users when you select the License Usage menu item in the Help pull down menu Help License Usage TGrid will display a list the current users of the TGrid license feature in the console window 3 22 ANSYS Inc April 15 2008 Chapter 4 Sample Session This chapter describes a sample session to illustrate the basic procedure for examining and creating the mesh in TGrid This sample session consists of the following steps e Section 4 1 Preparation e Section 4 2 Reading the Boundary Mesh e Section 4 3 Examining the Boundary Mesh e Section 4 4 Generating the Interior Mesh e Section 4 5 Displaying the Mesh e Section 4 6 Reporting the Mesh Statistics e Section 4 7 Checking the Mesh e Section 4 8 Saving the Mesh and Exiting TGrid In this session you will generate a triangular volume mesh for a simple wedge shaped geometry The boundary mesh file is provided with TGrid on the CD 4 1 Preparation 1 Copy wedge zip from the TGrid documentation CD to your working directory e For UNIX systems locate the fi
303. et a definitive answer The tolerance is used to define a thickness for the boundary of the circumsphere If a node is on this boundary it is neither inside nor outside of the circumsphere and hence will be treated specially mesh tritet controls advanced defaults toggles the use of the default values for the initialization parameters mesh tritet controls advanced node tolerance defines the smallest distance be tween two distinct nodes This command is available only when you disable the use of the default values for the initialization parameters mesh tritet controls advanced sliver size is the smallest cell whose size can be determined accurately This command is available only when you disable the use of the default values for the initialization parameters 11 4 Refining the Tri Tet Mesh After initializing the mesh you can improve the quality and density of the grid using global and local refinement Global refinement allows you to refine all cells in the active zones while local refinement allows you to refine cells within a specified region In most applications you will use only global refinement to create an acceptable dis cretization of the volume Local refinement is used to modify the grading away from boundaries or increase the resolution of an interior region of the grid You need to define and activate the regions to be refined before proceeding The refinement process comprises a series of sweeps through a sequence of
304. et shrink factor sets shrinkage of both faces and cells A value of zero indicates no shrinkage while a value of one would shrink the face or cell to a point 14 1 5 The Grid Colors Panel You can opn the Grid Colors panel by clicking on the Colors button in the Attributes tab frame of the Display Grid panel see Section 14 1 3 The Display Grid Panel It controls the color of the zones that are displayed using the Display Grid panel You can color zones by their type or by their ID number You can see the effect of these changes the next time you display the grid ANSYS Inc April 15 2008 14 13 Examining the Mesh Grid Colors Options Types Color by Type Color by ID free surface intemal Options contains options for setting the colors Color by Type allows you to set the color for each type of zone outlet wall etc Color by ID modifies the grid colors so that each zone wall 1 wall 2 outlet 3 etc will be assigned one of the colors from the Colors list If there are more zones than colors some zones will be the same color Sample displays a sample of the currently selected color Types contains a selectable list of zone types You can select the zone type for which you want to set the color Note that you can set colors separately for each zone grid using the Scene Description panel see Section 14 8 1 The Scene Description Panel Colors contains a list from which yo
305. ete deletes the selected region 12 5 Text Commands for Hexcore Meshing Text commands with the same functionality as the Hexcore Auto Mesh menu item and the controls in the Hexcore Controls panel along with additional text commands related to meshing are as follows mesh hexcore controls boundary merge tolerance specifies the tolerance for merg ing zones aligned to domain boundaries mesh hexcore controls buffer layers sets the number of additional cells to mark for subdivision mesh hexcore controls delete dead zones toggles the deleting of dead zones dur ing hexcore meshing mesh hexcore controls keep outer domain allows you to enable the creation of Cartesian cells until the boundary of the domain during hexcore meshing mesh hexcore controls maximum cell length sets the maximum cell length for the hex cells in the domain mesh hexcore controls maximum initial cells specifies the maximum number of cells in the initial Cartesian mesh mesh hexcore controls maximum subdivisions number of change in size hanging node subdivisions allowed in the hex mesh region The default value is 50 mesh hexcore controls mesh rel island count specifies the threshold cell count relative to the total cell count for islands to be deleted when separating cells by region during hexcore meshing The default value is 1 of the total cell count ANSYS Inc April 15 2008 12 13 Generating the Hexcore Mesh mesh hexcore controls
306. etween them less the specified tolerance value will be intersected The tolerance can be either relative or absolute When inter secting zones having different mesh size you can enable the Refine option to obtain a better graded mesh around the intersecting faces see Figure 7 2 2 ANSYS Inc April 15 2008 7 2 Intersecting Boundary Zones A Figure 7 2 2 Intersection Without A and With B Using the Refine Option 7 2 2 Join The join option is used to connect two overlapping boundary zones Figure 7 2 3 The overlapping areas of both the boundary zones are merged and the mesh at the boundary of the region of overlap is made conformal To join surfaces that are on top of each other but not connected with a small gap specify an appropriate Tolerance value The part of the surfaces within the tolerance value join The boundary zone selected in the Intersect Tri Zone defines the shape of the combined surface in the overlap region The shape in the With Tri Zone may be changed to perform the join operation Figure 7 2 3 Partially Overlapping Faces Figures 7 2 4 and 7 2 5 show the overlapped faces after joining and after remeshing the joined faces ANSYS Inc April 15 2008 7 7 Manipulating the Boundary Mesh Figure 7 2 4 Joining of Overlapping Faces Figure 7 2 5 Remeshing of Joined Faces 7 8 ANSYS Inc April 15 2008 7 2 Intersecting Boundary Zones 7 2 3 Stitch The stitch opt
307. evel specifies the refinement level for the local region defined Center allows you to specify the coordinates of the center of the region you want to create Length allows you to specify the absolute size of the new region in the x y and z directions Orient allows you to specify the orientation of the new region Note TGrid orients the region by rotation first about the x axis then the y axis and finally the z axis You need to take this into account while specifying the orientation of the region as rotation in any other order will produce different results Activate activates the region s selected in the Regions list Deactivate deactivates the region s selected in the Regions list ANSYS Inc April 15 2008 12 5 Text Commands for Hexcore Meshing Select Activated selects the activated regions in the Regions list Deselect Activated deselects the activated regions in the Regions list Define creates a new region according to the specified parameters It also allows you to modify the selected region according to the specified changes Init creates a default region encompassing the entire geometry Draw draws the region s in the graphics window The maximum cell size for the refinement regions will also be displayed If the boundary grid was displayed using the Display Grid panel see Section 14 1 3 The Display Grid Panel before drawing the refinement region the grid will also be included in the display Del
308. example 4 1 initialization 11 9 manual 11 6 multiple zones 11 4 refinement 11 12 mesh improvement 13 1 Mesh Auto Mesh 11 2 11 4 Mesh Check 13 37 Mesh Clear 13 37 mesh clear mesh 13 38 Mesh Domains 13 33 13 34 Mesh Hexcore 12 1 12 8 Mesh Manage 13 26 13 28 Mesh Prisms 10 1 Mesh Pyramids 9 14 mesh reset mesh 13 38 Mesh Tools Auto Node Move 13 20 Mesh Tools Cavity Remesh 13 22 13 24 Mesh Tools Cell Modify 13 15 Mesh Tools Tet Improve 13 7 Mesh Tools Tri Tet Improve 13 2 13 3 13 9 meshing problems pyramids 9 20 tri tet 11 25 procedure hybrid 9 2 9 3 9 5 9 6 pyramids 9 14 ANSYS Inc April 15 2008 tri tet 11 6 meshing problems prisms 10 39 meshing procedure prisms 10 2 Mirror Planes panel 14 32 Modify Boundary panel 7 22 Modify Cells panel 13 15 mouse buttons 14 45 manipulation 14 46 14 48 probe 14 46 14 47 filter 7 23 14 9 function 7 23 14 9 select 7 23 14 9 Mouse Buttons panel 14 45 Mouse Probe panel 14 48 Move Nodes panel 7 27 moving node 7 17 multiple mesh files 3 7 6 2 6 3 multiple selection list 3 13 multiple zones 11 4 multiply connected 14 5 naming zones 7 75 13 30 NASTRAN 6 12 A 1 A 6 export 6 16 negative cell volume 10 41 negative volume 10 41 node boundary 7 2 closeness 11 22 clustering 9 9 collapsing 7 17 creation 7 15 deletion 7 16 duplicate 7 2 11 25 free 7 2 isolated 7 2 9 9
309. excore generation see Figure 12 3 3 However the tetrahedral mesh domain is created and activated during the hexcore meshing procedure You can manually create the tetrahedral mesh in a separate step Figure 12 3 3 Only Hexcore ANSYS Inc April 15 2008 12 5 Generating the Hexcore Mesh Hex cell islands may be created when the Only Hexcore option is used You can delete small islands which may be created by setting the minimum allowable size for the hex cell islands using the command mesh hexcore controls post relative island count This command is available only when the Only Hexcore option has been enabled in the Hexcore panel You can also use the command mesh hexcore controls only hexcore to enable only hexcore meshing The default value for post relative island count is 10 All hex cell islands whose size is less than the specified percentage in the default case 10 of the largest hex cell zone will be automatically deleted No islands will be removed if you set the value to 0 A You may need to verify that hex cells are created only in the domain of interest since TGrid cannot identify whether the cells are within the domain without tet meshing Also all the non fluid type zones are created as separate fluid zones You need to retain the fluid zone s of interest and delete the others 12 3 4 Maximum Cell Length TGrid can automatically calculate an optimal maximum cell length for a particular mesh Click the
310. f one type then change the Filter and continue selecting objects of a different type Changing the Filter automatically changes the mouse probe function to Select It is also possible to select a group of entities by defining a rectangular or polygonal selection region See Section 14 10 1 The Mouse Probe Panel for details Operation contains the buttons that perform the boundary modification operations Create creates nodes if the Selections list contains positions creates boundary faces if the list contains 2 in 2D or 3 or 4 in 3D nodes and optionally a zone or creates a new zone if Filter is first set to zone e If you create a face without selecting a zone the new face will be in the same zone as an existing face that uses one of the specified nodes e If you select a zone as well as the nodes the new face will be in the selected zone 7 24 ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh e If the nodes used to create a face are used by faces in different zones select a zone to be sure that the new face is in the desired zone Merge merges pairs of nodes or face edges e If a pair of node is selected the first node selected is retained and the second is the duplicate that is merged e If a triangular face is selected its shortest edge is collapsed merging the other two edges together The longer of the remaining two edges is retained and the shorter one is merged with it Collapse collapse
311. f the zone containing the children cells number of kids is the number of children of the parent cell kid id n are the cell IDs of the children These are in hexadecimal format TGrid cannot read files that contain this section B 10 Interface Face Parents Index 61 Scheme symbol xf face parents C macro XF_FACE_PARENTS Codes FLUENT Status only for grids with non conformal interfaces This section indicates the relationship between the intersection faces and original faces The intersection faces children are produced from intersecting two non conformal sur faces parents and are some fraction of the original face Each child will refer to at least one parent The format of the section is as follows 61 face idO face id1 parent id O parent id 1 B 10 ANSYS Inc April 15 2008 B 11 Example Files where face ido is the index of the first child face in the section face id1 is the index of the last child face in the section parent id 0 is the index of the right side parent face parent id 1 is the index of the left side parent face These are in hexadecimal format TGrid will skip this section if you read a non conformal grid from the solver into TGrid So it will not maintain all the information necessary to preserve the non conformal interface When you read the grid back into the solver you will need to recreate the interface B 11 Example Files Example 1 Figure B 11 1 illustrates a simpl
312. f your graphics window can affect the size of the clipboard picture For best results experiment with the graphics window size and examine the resulting clipboard picture using the Windows clipboard viewer Bitmap is a bitmap copy of the graphics window DIB Bitmap is a device independent bitmap copy of the graphics window Metafile is a Windows Metafile Enhanced Metafile is a Windows Enhanced Metafile Picture Format allows you to specify a raster or a vector picture Vector creates a vector picture This format will have a higher resolution when printed but some large 3D pictures may take a long time to print Raster creates a raster picture This format will have a lower resolution when printed but large 3D pictures may take much less time to print Printer Scale controls the amount of the page that the printed picture will cover Decreasing the scaling will effectively increase the margin between the picture and the edge of the paper Options contains options that control other attributes of the picture Landscape Orientation Printer specifies the orientation of the picture If se lected the picture is made in landscape mode Otherwise it is made in por trait mode This option is applicable only when printing Reverse Foreground Background specifies that the foreground and background colors of the picture will be swapped This feature allows you to make a copy of the picture with a white background and a black foregroun
313. face or cell is see Figure 15 5 3 Equilateral Triangle Highly Skewed Triangle Equiangular Highly Skewed Quad Quad Figure 15 5 3 Ideal and Skewed Triangles and Quadrilaterals Table 15 5 1 lists the range of skewness values and the corresponding cell quality According to the definition of skewness a value of 0 indicates an equilateral cell best and a value of 1 indicates a completely degenerate cell worst Degenerate cells slivers are characterized by nodes that are nearly coplanar collinear in 2D 15 10 ANSYS Inc April 15 2008 15 5 Mesh Quality Value of Skewness Cell Quality 1 degenerate 0 9 lt 1 bad sliver 0 75 0 9 poor 0 5 0 75 fair 0 25 0 5 good gt 0 0 25 excellent 0 equilateral Table 15 5 1 Skewness Ranges and Cell Quality Highly skewed faces and cells are unacceptable because the equations being solved assume that the cells are relatively equilateral equiangular Two methods for measuring skewness are e Based on the equilateral volume applies only to triangles and tetrahedra e Based on the deviation from a normalized equilateral angle This method applies to all cell and face shapes e g pyramids and prisms The default skewness method for triangles and tetrahedra is the equilateral volume method But you can change to the angle deviation method using the Quality Measure panel see Section 15 5 2 The Quality Measure Panel Equilater
314. fault For a surface mesh replace dimension by surface read format indicates the format of the file you wish to convert Replace read format by tANSYS for an ANSYS file tIDEAS for an I deas file tNASTRAN for a NASTRAN file or tPATRAN for a PATRAN file For a list of conversion capabilities from other CAD packages type utility fe2ram cl help merge indicates the grid tolerance The default is 107 1 0e 06 and you can reset the tolerance to this value by replacing merge by m To set another tolerance value replace merge by mTOLERANCE where TOLERANCE is an appropriate real number value zoning indicates how zones were identified in the CAD package Replace zoning by zID for a grid that was zoned by property ID s or zNONE to ignore all zone groupings For a grid zoned by group do not enter anything for zoning because zoning by groups is the default write format indicates the output format for the file you wish to convert Replace write format by oFIDAP7 to write the grid in FIDAP format To write the grid for use in FLUENT or TGrid do not enter anything for write format because it is the default selection input file and output file are the names of the original file and the file to which you want to write the converted grid information respectively For example to convert the 2D l deas volume mesh file sample unv to an output file called sample grd enter the following command utility fe2ram d2 tIDEAS sample
315. fied bound ary condition identifiers In addition to reading and writing TGrid mesh files you can also import mesh files from various CAD packages and write mesh files for FLUENT For information about the format of the CAD package files see Appendix A Importing Boundary and Volume Meshes and for details on the mesh file format for TGrid and FLUENT see Appendix B Mesh File Format ANSYS Inc April 15 2008 6 1 File Types i If the mesh information is contained in two or more separate files generated by one of these CAD packages you can read them one by one using the Append File s check button in the Select File panel You can also read them together and have TGrid assemble the complete mesh for you By default TGrid saves the mesh files with the suffix msh You need not type the suffix while saving the mesh file it will be added automatically For example if you enter the file name gumby TGrid will write to the file gumby msh When TGrid reads a mesh file it first searches for a file with the exact name you typed If a file with that name is not found it will search for a file with msh appended to the name 6 1 1 Reading Boundary Mesh Files To read a FLUENT boundary mesh contained in a FLUENT mesh file created with GAMBIT or a boundary mesh contained in a FLUENT case file into TGrid you can do either of the following e Select the File Read Boundary Mesh menu item to open the Select File panel and select th
316. fied value may not always be adhered to in the final mesh as the value may be relaxed during the prism improvement operations such as smoothing etc 10 11 Text Interface for Generating Prisms Text commands for generating prisms are listed below Some of them allow additional control that is not available in the Prisms panel mesh prism create creates prism layers on the specified face zone s according to the specified parameters mesh prism controls adjacent zone project adjacent angle sets the tolerance used to determine whether or not to use an adjacent zone If a zone shares outer nodes with any of the zones from which the layers are being grown the base zones its angle with respect to the growth direction is compared with this value If the angle is less than or equal to this value then the zone will be used See Section 10 6 Using Adjacent Zones as the Sides of Prisms for details mesh prism controls adjacent zone project converged sets the convergence cri terion for iterative projection This is non dimensionalized by the offset height at each local node ANSYS Inc April 15 2008 10 33 Generating Prisms nesh prism controls adjacent zone project iter sets the maximum number of iterations to perform when projecting to multiple zones Most projections converge in only a few iterations There is normally no need to change this value mesh prism controls adjacent zone project enables disables projection of ou
317. filter Returns a list of the node zones whose names con tain the specified filter string get face zones of filter gt boundary node get wrapped zones Returns a list of the wrapped face zones D 1 Using Boolean Operations with Query Functions You can also perform Boolean operations on lists returned by the query functions The following Boolean operations can be performed e Union of lists list union list 1 list 2 e Intersection of lists list intersection list 1 list 2 e Subtraction of lists list subtract list 1 list 2 Note Only two lists can be used as arguments for a subtraction operation For example list 1 1234 list 2 1 56 list 3 147 then list union list 1 list 2 list 3 list intersection list 1 list 2 list 3 list subtract list 1 list 2 ANSYS Inc April 15 2008 1234567 ROA Query Functions D 2 Examples Some examples of using query functions are e Deleting the geometry while retaining the wrapper surface after wrapping opera tions 1 Use the command define initial zones get zones of group boundary to obtain a list of the boundary zones 2 Perform the wrapping operations as required 3 Use the command define final zones get zones of group boundary to obtain a list of the boundary zones after the wrapping operations 4 Use the command boundary manage delete eval expr list inters
318. filter ignores the mid side nodes This assumption is valid if the edges of the element are near linear However if this is not the case an incorrect topology may result from this assumption For example in regions of high curvature the parabolic element may look much different than the linear element For volume meshes note that mesh area mesh volume datasets are not recognized This implies that writing multiple mesh areas mesh volumes to a single Universal file may confuse fe2ram TGrid or FLUENT For 2D volume meshes an additional constraint is placed on the elements existence in the Z 0 plane Grouping Elements to Create Zones for a Surface Mesh The Group command in I deas is used to create the boundary zones needed by TGrid All faces grouped together are listed together in the output as a single zone In FLUENT boundary conditions are set on a per zone basis One technique is to generate groups automatically based on mesh areas i e every mesh area will be a different zone in TGrid Although this method may generate a large number of zones the zones can be merged in TGrid or in FLUENT Another technique is to create a group of elements related to a given mesh area manually This allows you to select multiple mesh areas for one group Grouping Nodes to Create Zones for a Volume Mesh The Group command is used in I deas to create the boundary zones needed by TGrid or FLUENT All nodes grouped together are listed together in the
319. following products FLUENT the solver GAMBIT the preprocessor for geometry modeling and mesh generation TGrid the additional preprocessor that can generate volume meshes from existing boundary meshes Filters translators for import of surface and volume meshes from CAD CAE packages such as ANSYS I deas NASTRAN PATRAN and others Figure 1 2 1 shows how TGrid relates to these products GAMBIT Geometry Mesh Other CAD CAE Packages lt Geometry set up 2D 3D Mesh Generation Boundary Mesh Faceted geometry Boundary and or TGrid Volume Mesh 2D triangular mesh 3D triangular surface mesh 2D 3D triangular tetrahedral hybrid mesh Hexcore mesh 2D 3D Mesh Mesh FLUENT V5 or later Mesh import and adaption Physical models Material properties Boundary conditions Calculation Postprocessing Figure 1 2 1 Program Structure 1 2 ANSYS Inc April 15 2008 1 3 Program Capabilities You can use TGrid to generate a triangular tetrahedral hexcore or hybrid volume mesh from an existing boundary mesh To create a mesh in TGrid first use a preprocessor GAMBIT or a third party CAD pack age to create a boundary mesh in which the boundaries are defined by line segments 2D or triangular or quadrilateral facets 3D To create tetrahedral prismatic or pyra midal cells read the boundary mesh
320. for information about installing the files from the documentation CD ROM This section focuses on the Help menu in TGrid and how you can use it and the Help button in each panel to access the HTML based on line help from within TGrid 3 6 1 Opening the User s Guide Table of Contents To see a list of the chapters in the User s Guide select the User s Guide Contents menu item in the Help pull down menu Help gt User s Guide Contents Selecting this item will open the web browser to the contents page of the User s Guide Figure 3 6 1 Each chapter in the list is a hypertext link that you can click to view that chapter There is also an Expanded Contents link which will display a list of contents including all section titles in addition to the chapter titles Each of these is a link to the corresponding chapter or section of the manual A TGrid 5 0 User s Guide Microsoft Internet Explorer File Edit View Favorites Tools Help ay x aA LA JO search Sie Favortes amp A w yo ins Qsnagt A e a Return to Home Index Contents Previous Up Next TGrid 5 0 User s Guide e Expanded Contents e Using This Manual e 1 Introduction to TGrid e 2 Getting Started e 3 Graphical User Interface e 4 Sample Session o 5 Text User Interface e 6 File Types o 7 Manipulating the Boundary Mesh e 8 Wrapping Boundaries e 9 Creating a Mesh e 10 Generating Prisms o 11 Generating Tr
321. fore it will be separated into two wall zones ANSYS Inc April 15 2008 7 65 Manipulating the Boundary Mesh wall 1 wall 5 wall 4 z all 3 wals CHL CELL ZONE 1 ZONE 2 wall 2 wall 1 is separated because it borders two different cell zones The same is true for wall 2 wall 1 wall 6 wall 5 wall 4 z all 3 ks CELL CELL ZONE 1 ZONE 2 wall2 wall7 wall 1 wall 5 wall 4 wall 3 CELL CELL ZONE 1 ZONE 1 wall 2 wall 1 is not separated because it borders only one cell zone The same is true for wall 2 wall 1 wall 5 wall 4 wall 3 CELL CELL ZONE 1 ZONE 1 wall 2 Figure 7 10 2 Face Separation Based on Cell Neighbor Based on the Face Element Shape You can also separate face zones based on the shape of the faces For example if a face zone contains both triangular and quadrilateral faces you can separate the zone into two zones one containing the triangular faces and the other containing the quadrilateral faces Using Seed Element TGrid allows you to separate face zones by specifying a face element in the face zone as a seed face You can also separate different faces of a single face zone using this method The surface on which you define a seed face gets separated from rest of the face zone There are two criterion using which you can separate face zones using the seed element These criterion are as follows 7 66 e Feature Angle Criteria This method allows you to sepa
322. fset smoothing ld Figure 10 8 4 Effect of Offset Smoothing L node position before offset smoothing ANSYS Inc April 15 2008 10 21 Generating Prisms 10 9 Improving Prism Quality TGrid performs the following to improve the skewness of prism faces e Edge swapping and smoothing Section 10 9 1 Edge Swapping and Smoothing e Node smoothing Section 10 9 2 Node Smoothing 10 9 1 Edge Swapping and Smoothing After the new triangular cap faces are created for the new layer the skewness is compared with the specified skewness threshold Skewness in the Swapping and Smoothing group box in the Improve tab of the Prisms panel If the skewness of a face is too high TGrid performs the following improvement procedure 1 Swap the longest edges of highly skewed faces When edge swapping occurs on a cap face swapping propagates downward Swap ping must be performed on the corresponding faces on all prism layers including the face on the original boundary mesh so that the grid lines within the prism layers do not cross Swapping is not performed if it will significantly alter the geometry defined by the original boundary mesh 2 If swapping is not performed TGrid will try to improve the skewness by smoothing the nodes of the skewed faces using one of the following operations e If the sharpest angle at the node i e the most acute angle between adjacent faces that use the node is nearly 180 degrees T
323. fy face cell zones closest to a specified point using the query functions You can also use the query functions to determine the zones created during a particular operation by performing Boolean operations on lists returned by specific query functions You can use the eval expr function to evaluate the lists returned by the query functions in order that they may be used as input in the text user interface commands Refer to Section D 2 Examples for examples on the use of query functions The query functions available in TGrid are described in the following table Query Function Description Examples get face zone at location x y z Returns the face zone at or closest to the specified lo cation get cell zone at location x y z Returns the cell zone at or closest to the specified lo cation get zones of type type Returns a list of zones of the spec ified default face zone type get zones of type symmetry Returns a list of zones of the spec ified default edge zone type get zones of type gt boundary edge Returns a list of zones of the spec ified default cell zone type get zones of type fluid Returns a list of zones of the spec ified default node zone type get zones of type gt boundary node ANSYS Inc April 15 2008 D 1 Query Functions Query Function Description Examples get zones of grou
324. g Boundary Surfaces e Section 7 5 Refining the Boundary Mesh e Section 7 6 Creating and Modifying Features e Section 7 7 Remeshing Boundary Zones e Section 7 8 Faceted Stitching of Boundary Zones e Section 7 9 Triangulating Boundary Zones e Section 7 10 Separating Boundary Zones e Section 7 11 Projecting Boundary Zones e Section 7 12 Creating Groups e Section 7 13 Manipulating Boundary Zones e Section 7 14 Creating Surfaces e Section 7 15 Additional Boundary Mesh Text Commands ANSYS Inc April 15 2008 7 1 Manipulating the Boundary Mesh 7 1 Manipulating Boundary Nodes Manipulation of boundary nodes is an effective way to influence the boundary mesh quality Operations for deleting unwanted boundary nodes can be performed in the Merge Boundary Nodes panel or with the associated text commands 7 1 1 Free and Isolated Nodes The mesh generation algorithm does not permit duplicate nodes i e two nodes with the same Cartesian coordinates Duplicate nodes may be created by grid generators that preserve the node locations at adjoining edges of adjacent surfaces but give different labels to the two sets of nodes The nodes and edges at which these surfaces meet are termed free nodes and free edges N31 C3 N32 N42 QS ATAT OGO N22 C4 T C2 N41 0ce SOSON21 N11 C1 N12 Figure 7 1 1 Free Nodes Figure 7 1 1 shows a simple 2D geometry in which the free nodes are marked Although the node at the end of cur
325. g a Cylinder Creating a swept surface Section 7 14 4 Creating a Swept Surface Creating periodic boundaries Section 7 14 5 Creating Periodic Boundaries i The various options for creating surfaces are available only in the 3D ver sion of TGrid 7 14 1 Creating a Bounding Box In some cases you may want to create a box that encloses the input geometry e g creating a wind tunnel around a geometry TGrid allows you to create a bounding box around the input geometry or only the selected zones of the geometry using the Bounding Box panel You can also specify the required clearance values of the bounding box from the boundaries of the geometry i The option for creating bounding box is available only in 3D version of TGrid ANSYS Inc April 15 2008 7 79 Manipulating the Boundary Mesh There are two methods available for creating bounding box Using Absolute Values This method allows you to create the bounding box by specifying the minimum and maximum extents of the bounding box in X Y and Z directions Using Relative Values This method allows you to create the bounding box by specifying the relative coordinate values with reference to the selected face zone Using the Bounding Box Panel The procedure to create a bounding box is as follows 1 Under Face Zones select the zone s around which you want to create a bounding box and select appropriate Method of creating bounding box 2 If you have select
326. g the panels To make your task easy several keyboard shortcuts are available in TGrid e Section C 1 Arrow Keys e Section C 2 Help Keys e Section C 3 Hot Keys il To make use of the shortcut keys display the geometry in the graphics window Click in the graphics window and then press the key you want to use C 1 Arrow Keys The arrow keys used in TGrid are described in the following table Arrow Keys Description Up arrow Increases display bounds in the Display Grid panel Down arrow Decreases display bounds in the Display Grid panel Right arrow This allows you to view the skewed faces in the decreasing order of their skewness by finding the triangular face of next highest skewness value after the worst skewed face in the mesh active group or the marked faces When you press this button the triangular face of the next highest skewness value will be displayed in the graphics window Left arrow Clears the selection of skewed faces ANSYS Inc April 15 2008 C 1 Shortcut Keys C 2 Help Keys The various help keys available in TGrid are described in the following table Help Description Keys F2 Clears the previously selected entities in the Selections list of the Modify Boundary panel F3 Toggles between the mouse dolly and the option currently selected for right mouse button in the Mouse Buttons panel F4 Toggles the selection of the mouse probe func
327. ges may be displayed at the same location causing bad edges known as edge stitching Parts of an edge become invisible due to overlapping portions of the face Setting the face displacement can help alleviate the problem by pushing the faces back by a small amount so that the complete edge becomes visible A value of 0 for the face displacement does not displace the faces at all If the value is set too high it may cause the hidden edges to show up in front of the displayed faces You can adjust the display by specifying an appropriate value for the face displacement The default value of face displacement is set to 8 Z buffer units display set rendering options hidden lines allows you to enable disable hidden line removal display set rendering options hidden surfaces turns hidden surfaces removal on or off display set rendering options hidden surface method allows you to choose from among the hidden surface removal methods that TGrid sup ports These options listed below are display hardware dependent hardware z buffer is the fastest method if your hardware supports it The ac curacy and speed of this method is hardware dependent painters will show less edge aliasing effects than hardware z buffer This method is often used instead of software z buffer when memory is limited software z buffer is the fastest of the accurate software methods available es pecially for complex scenes but it is memory intensive z sort is a fa
328. ges toggles the display of interior and exterior edges of the geometric object Perimeter Edges toggles the display of the outline of the geometric object This option has no effect on the display of grids Feature Edges not applicable for TGrid Lines toggles the display of the lines if any in the geometric object Nodes toggles the display of the nodes if any in the geometric object Colors contains controls for setting face edge line and node colors and transparency for faces Color specifies the face edge line or node color for modification When you turn on this button the color scales below will show the current color specification which you can modify by moving the sliders on the color scales Red Green Blue are color scales with which you can specify the RGB compo nents of the face edge or line color Transparency sets the relative transparency of the selected object An object with a transparency of 0 is opaque An object with a transparency of 100 is transparent 14 8 5 Transforming Geometric Objects in a Scene When composing a scene in your graphics window it is helpful to move a particular object from its original position or to increase or decrease its size For example you may want to temporarily move an interior portion of the grid outside the grid boundaries where it can be seen and interpreted more easily You can also move an object by rotating it about a specified point If you want to display one
329. gh skewness Left handed faces are faces that have collapsed into their cells You can view them by turning on the Left Handed option in the Faces section of the Display Grid panel Very high skewness occurs when the value of skewness is greater than the specified Max Allowable Skewness in the Improve section of the Prisms panel These problems can occur where prism layer fronts are advancing too quickly in areas of high curvature For example the first layer height may be greater than the minimum edge length of your original surface mesh You should compare the First Height with the results of clicking the Edge Size Limits button in the Growth section of the Prisms panel The First Height should usually be smaller than the minimum edge size Solution If the First Height is reasonable but TGrid is unable to successfully generate your requested Total Height try one of the following solutions e Reduce the First Height or the parameter used for the growth Method i e Slope Rate or Exponent and increase the Number of Layers Extra layers allow smoothing to compensate better for sharp edges and corners e If you have specified a nonzero value for Orthogonal Layers in the Direct section of the Prisms panel change it to zero Increasing orthogonality can reduce robustness e If you have reduced the Max Angle Change in the Direct section of the Prisms panel from its default of 70 degrees to improve orthogonality reset it to 70 e If
330. gle nee Boundary Zone Groups far field geometry inlet f Retriangulate Adjacent Zones specifies whether or not the triangular face zones adjacent to which outer nodes have been projected will be automatically retri angulated This option is enabled by default See Section 10 6 Retriangulation for details about this procedure Max Adjacent Zone Angle sets the tolerance used to determine whether or not to use an adjacent zone If a zone shares outer nodes with any of the zones from which the layers are being grown the base zones its angle with respect to the growth direction is compared with the specified value If the angle is less than or equal to this value then the zone will be used See Section 10 6 Using Adjacent Zones as the Sides of Prisms for details The default is 45 degrees Side Feature Angle specifies the angle used for computing the feature normals Create creates the prisms using the settings specified in the panel Apply applies all current settings for prism growth without creating the prisms If you wish to set the parameters in advance and return later to generate the prisms click Apply before closing the Prisms panel There is no need to click Apply before moving from one tab in the panel to another e g from the Growth tab to the Direct tab Note Clicking Apply only applies the parameters set in the Prisms panel When setting prism parameters for use with the Auto Mesh opti
331. gle through which you want to rotate the selected zone s axis allows you to specify the axis about which you want to rotate the selected zone s pivot allows you to specify a pivot point about which you want to rotate the selected zone s Copy Zone s allows you to copy the nodes and faces of the selected zone s thereby creating new zone s of the same type before positioning the copied zone s per the specified Angle and axis or pivot Scale scales the selected zone s by multiplying each of the node coordinates by the specified Scale Factors The face sizes will increase or decrease accordingly Scale Factors specifies the scale factors applied to the grid in each of the Cartesian coordinate directions X Y and in 3D Z Copy Zone s allows you to copy the nodes and faces of the selected zone s thereby creating new zone s of the same type before scaling the copied zone s per the specified scale factors Translate translates the selected zone s by the specified translation offsets ANSYS Inc April 15 2008 7 77 Manipulating the Boundary Mesh Translation specifies the translation offsets X Y Z to be added to the Cartesian coordinate of every node in the selected zone s Copy Zone s allows you to copy the nodes and faces of the selected zone s thereby creating new zone s of the same type before positioning the copied zone s per the specified translation offsets Face Zones contains a list from wh
332. group box set the appropriate Minimum and Maximum values and click Display or Apply Use the Report Cell Lim its panel see Section 15 3 1 The Report Cell Limits Panel to determine an appropriate range Minimum sets the minimum value for the quality range This value should be greater than or equal to zero and less than the Maximum value Maximum sets the maximum value for the quality range This value should be greater than the Minimum value If the quality measure being used is skewness it should also be less than or equal to one Quality Measure opens the Quality Measure panel see Section 15 5 2 The Qual ity Measure Panel in which you can select the measure of quality to be used skewness aspect ratio change in size etc Cell Zones contains a list of cell zones from which you can select those to be drawn Cell Zone Groups contains a list of cell zone types Selecting a zone type from this list e g solid will select all cell zones of that type solid 4 solid 5 etc in the Cell Zones list You can select multiple zone types in the Zone Groups list to select all zones of several different types e g fluid and solid 14 8 ANSYS Inc April 15 2008 14 1 Displaying the Grid Bounds contains options allowing you to limit the items drawn in the display to those objects inside specified bounds or passing through them Display Grid Nodes Faces Celts Bounds Attributes F Limit by X Lim
333. gulation is likely to fail Solution To verify this problem check the messages printed before the first prism layer It should contain a list of all the zones connected to the zones from which you are growing the prisms 1 Make sure there are no free nodes in the surface mesh before growing any prisms 2 Use the Count Free Nodes button in the Merge Boundary Nodes panel see Sec tion 7 1 2 The Merge Boundary Nodes Panel to check for free nodes 3 Turn on the Free option in the Faces section of the Display Grid panel to see where the free nodes are located 10 40 ANSYS Inc April 15 2008 10 12 Prism Meshing Problems Too Many Few Nodes or Unknown Face Combinations If you receive the following type of messages then you are most likely growing prisms into existing cells Warning wedge cell c887 has too many nodes Warning wedge cell c1928 has too few nodes Warning base_mask 7 0x7 unknown face combinations Either you have already grown prisms from the selected zones or you are growing them in the wrong direction into cells on the other sides of the selected zones In the latter case click the Flip Normals button in the Direct section of the Prisms panel before growing the layers See step 4 in Section 10 2 Procedure for Generating Prisms Negative Volumes Left Handed Faces High Skewness TGrid will automatically stop the prism layer creation process if it detects negative cell volumes left handed faces or hi
334. gulation panel If however you want to use Face Seed approach you can use the Feature Modify panel to create the edge loops instead see Section 7 6 1 Creating Edge Loops Using the Feature Modify Panel Click Create The edge loops created will now be available in the Edge Zones selection list Select the appropriate zone s in the Edge Zones selection list and click Draw to display them The selected edge zone s will be displayed in the graphics window If you are not satisfied with the edge loops and you want to modify them open the Feature Modify panel ANSYS Inc April 15 2008 7 7 Remeshing Boundary Zones 5 Click the Feature Modify button to open the Feature Modify panel 6 Modify the edge loops as required using the options available in the Feature Modify panel Refer to Section 7 6 2 Modifying Edge Loops Using the Feature Modify Panel for details When you are satisfied with the edge loops you can proceed to remesh the faces 7 Select the appropriate options from the Reconstruction Order drop down list in the Face Remesh Options group box 8 Enable Replace Face Zone if required il Remeshing can be performed on both triangular and quadrilateral face zones However it will always result in a triangular face zone 9 Click Remesh to remesh the face zones Note Edge loops are saved when TGrid writes a mesh file 7 7 5 The Surface Retriangulation Panel The Surface Retriangulation panel
335. hat are in the active domain Controls Options specifies a histogram of cell Quality or Size The default measure of quality is skewness but you can use the Quality Measure panel see Section 15 5 2 The Quality Measure Panel to specify aspect ratio or change in size instead Quality Measure opens the Quality Measure panel see Section 15 5 2 The Quality Measure Panel in which you can select the measure of quality to be reported skewness aspect ratio or change in size Axes opens the Axes panel see Section 14 4 1 The Axes Histogram Panel in which you can set parameter ranges number formats rules etc Minimum specifies that only cells with size or quality measure value skewness by default greater than this value will be plotted ANSYS Inc April 15 2008 14 21 Examining the Mesh Maximum specifies that only cells with size or quality measure value skewness by default less than this value will be plotted Percent of Total specifies that the number of cells as a percentage of the total number of cells counted will be plotted By default the actual number of cells is plotted Partitions specifies the number of partitions in the histogram Increasing the number of partitions will improve the resolution of the plot see Figures 14 2 1 and 14 2 2 Cell Zones contains a list from which you can select one or more zones to be used to generate the histogram Cell Zone Groups contains a list of cell zone
336. he Boundary Mesh Controls Total Distance specifies the total distance through which the edge is to be projected No of Offsets specifies the number of Edge Zones contains a drop down list of all the existing edge zones Face Zones contains a list of existing face zones in the geometry Vector specifies the direction in which the selected edge is to be swept Split Quad Faces toggles the creation of tri quad faces for the swept surface Apply creates the faces corresponding to the swept surface 7 14 5 Creating Periodic Boundaries If the preprocessor used to create the boundary mesh for TGrid does not allow you to generate periodic boundaries that are identical and contain either face or node correspon dence information you can create the periodic boundaries in TGrid In the preprocessor create only one of the periodic boundaries and assign it any non periodic boundary type In TGrid change this boundary to a periodic boundary and create the corresponding periodic shadow boundary TGrid will assign a zone type of periodic to both the periodic and the periodic shadow zones and generate the face node correspondence Note This is the only way to create periodic boundaries in TGrid it is not sufficient to simply set a zone type to be periodic You can specify either rotational or translational periodicity For rotational periodic ity you need to enter an angle of rotation and the axis of rotation For translational periodicity yo
337. he Mesh File s list 4 2 ANSYS Inc April 15 2008 4 3 Examining the Boundary Mesh 3 Click OK TGrid will read the mesh file and it s console shows the progress as the file is read 4 3 Examining the Boundary Mesh After reading the mesh file you can check the boundary mesh for topological problems such as free and multi connected nodes and faces All these operations can be performed in the Merge Boundary Nodes panel You can display the grid using the Display Grid panel Boundary gt Merge Nodes S Merge Boundary Nodes Compare With Only Free Nodes Only Free Nodes Boundary Face Zones Boundary Face Zones Tolerance Count Free Nodes 5 26315e 05 Count Unused Nodes i Percent of shortest connected edge length Delete Unused Nodes Message Figure 4 3 1 The Merge Boundary Nodes Panel 1 Click Count Free Nodes to see if any free nodes exist TGrid reports in the Message field that none were found You can click Merge to merge the free nodes if any exist 2 Click Count Unused Nodes to see if any unused nodes exist You can click Delete Unused Nodes to delete unused nodes if any exist 3 Close the Merge Boundary Nodes panel For a 8D surface mesh you can use the Boundary Improve panel also opened from the Boundary menu to check the boundary mesh quality and make improvements ANSYS Inc April 15 2008 4 3 Sample Session
338. he effect of these changes the next time you display the grid Style Attributes Edges Nodes JY Visible Visible I Visible Color Color Color rte y remma y matey Weight 2 F size o5 en size Faces contains parameters that control the display of faces Visible indicates whether or not the selected type of face should be visible in the graphics display If a face is visible its interior will be filled To see the outline of a face you can make Edges visible ANSYS Inc April 15 2008 14 15 Examining the Mesh Color specifies the color to be used for drawing the selected type of face Choose the color you want from the drop down list Edges contains parameters that control the display of edges Visible indicates whether or not the edges of the selected type of face should be visible in the graphics display Color specifies the color to be used for drawing the edges of the selected type of face Choose the color you want from the drop down list Weight specifies the thickness of edge lines as a multiple of the default thickness Nodes contains parameters that control the display of nodes Visible indicates whether or not the selected type of node should be visible in the graphics display Color specifies the color to be used for drawing the selected type of node Choose the color you want from the drop down list Symbol specifies the symbol to be used for dr
339. he normal direction at a node can change up to 45 degrees during normal edge and node smoothing For example if you reduce this parameter to 10 degrees the change in normal direction will be more gradual and the mesh near the original boundary will be nearly orthogonal Specify an explicit number for Orthogonal Layers in the Direction tab of the Prisms panel When you specify orthogonal layers you should decrease the Max Angle Change to approximately 10 degrees This will prevent sudden sharp changes in normal direction at the first non orthogonal layer For a non orthogonal layer TGrid will perform edge swapping normal edge or node smoothing so that the layer is orthogonal to the original boundary For example if you specify 5 orthogonal layers no smoothing will be performed on the first 5 layers resulting in direction vectors that are normal to the original surface mesh faces Full smoothing is used on the sixth and subsequent layers If you are preserving orthogonality near the original boundary make sure that the prism layers do not grow too quickly Use small layer heights relative to the sizes of the faces on the original boundary If prism layers grow quickly the nearly orthogonal direction vectors are likely to cross at sharp concave corners causing the prism generation to fail TGrid will stop the prism layer generation at this point See Section 10 7 Normal Smoothing Preserving orthogonality can affect skewness and l
340. he original position enter 0 in all three integer number fields Rotate About specifies the point about which to rotate the object Scale contains X Y and Z real number fields in which you can enter the amount by which to scale the selected object in each direction ANSYS Inc April 15 2008 14 8 Describing a Scene e To avoid distortion of the shape of the object be sure to specify the same value for all three entries Scaling is not cumulative so you can easily return to a known state e To return the object to its original size enter 1 in all three real number fields 14 8 6 The Bounding Frame Panel To open this panel click on the Frame Options push button in the Scene Description panel see Section 14 8 1 The Scene Description Panel Bounding Frame Frame Extents Axes Domain Display The Bounding Frame panel allows you to add a bounding frame with optional measure markings to the display of the domain e g Figure 14 8 1 Cees Le ery a Sy WY m O E Qy w wY w Figure 14 8 1 Graphics Display with Bounding Frame 14 45 ANSYS Inc April 15 2008 Examining the Mesh Controls Frame Extents indicates the extents of the bounding frame Domain specifies that the frame should encompass the domain extents Display specifies that the frame should encompass the portion of the domain that is shown in the display Axes contains control
341. heme expression For example if you want to decrease a default value by one third you could enter shrink factor 0 8 _ 3 5 3 Interrupts The execution of the code can be halted using lt Control C gt at which time the present operation stops at the next recoverable location 5 8 ANSYS Inc April 15 2008 5 4 System Commands 5 4 System Commands If you are running TGrid in a UNIX operating system you can execute system commands with the bang shell escape character All characters following the up to the next newline character will be executed in a subshell Any further input related to these system commands must be entered in the window in which you started the program and any screen output will also appear in that window If you start TGrid remotely this input and output will be in the window in which you started Cortex Irm junk Ivi script rp The 1s and pwd aliases invoke the UNIX 1s and pwd commands in the working directory The chdir alias changes the current working directory of the program The 1s and pwd commands will execute the UNIX commands in the directory in which Cortex was started The screen output will appear in the window in which you started TGrid unless you started it remotely in which case the output will appear in the window in which you started Cortex Note Commands chdir or cd executes in a subshell so it will not change the working dir
342. her swap the edges or smoothen the surface All faces having area smaller than the specified minimum absolute size will be collapsed You can also specify the minimum relative size size of the neighboring entity to be considered while using the Collapse and Swap option 7 4 2 Smoothing the Boundary Surface Smoothing of the surface mesh allows you to control the variation in the size of the mesh elements thereby improving the accuracy of the numerical analysis Smoothing is critical in regions of proximity or regions where surfaces intersect and the accuracy of the approximations used in numerical analysis techniques deteriorates with rapid fluctuations in the element size The smoothing procedure involves relocating of the mesh nodes without changing the mesh topology 7 4 3 Swapping Face Edges Edge swapping can be used to improve the triangular surface mesh The procedure involves checking each pair of faces that shares an edge and identifying the connecting diagonal that results in the most appropriate configuration of faces within the resulting quadrilateral For a face considered if the unshared node on the other face lies within 7 32 ANSYS Inc April 15 2008 7 4 Improving Boundary Surfaces its minimal sphere the configuration is considered to be a Delaunay violation and the edge is swapped The procedure makes a single pass through the faces to avoid cyclic swapping of the same set of edges Thus the edge swapping proces
343. hexcore to the tet cell regions Smoothing the interface faces if interface smoothing is enabled Initializing and refining the tet cells between the interface faces and the boundary mesh The maximum skewness reported at the end of the refinement process is not neces sarily the final maximum skewness Sliver cells on the interfaces can be removed at a later stage Removing sliver cells on the interface faces Merging Cartesian cells with tet and wedge if present cells to form contiguous cell zones i If prism parameters have been attached to boundary zones TGrid will first generate the prism layers The hexcore meshing procedure will then be applied to the resulting prism caps along with the other boundary zones that were not involved in the prism mesh generation You can control the general shape size and density of the core as well as the size of ele ments created at the outer boundary of the core using the parameters in the Hexcore panel see Section 12 4 The Hexcore Panel and the TUI commands in the mesh hexcore menu 12 2 Manual Hexcore Meshing Procedure To create a hexcore mesh manually do the following 12 2 1 2 Read in a boundary mesh and check and improve its quality if necessary optional Split any quad faces in the boundary mesh into triangular faces using the boundary remesh triangulate command By default TGrid does not allow quad faces while initializing the hexcore mesh Alt
344. i ave piee ee Sed oa aed ANSYS Inc April 15 2008 TOC 9 CONTENTS 115 1 The Tri Tet Init Controls Panel sosa cis siet oeie e404 0e445 11 20 11 5 2 The Tri Tet Refine Controls Panel 0 11 21 11 5 3 The Tri Tet Refinement Region Panel 11 23 11 6 Additional Text Commands for Tri Tet Mesh Generation 11 24 11 7 Common Tri Tet Meshing Problems 4 11 25 12 Generating the Hexcore Mesh 12 1 12 1 Automatic Hexcore Meshing Procedure 04 12 1 12 2 Manual Hexcore Meshing Procedure 2 12 2 12 3 Controlling Hexcore Parameters gt 2 4 64 ceh 44445 244 staci 12 3 123 1 Keep Outer Dome e socs van RYE Se A RYE eh ES 12 3 12 2 2 Hexcore Upto Boundari s o c soe eosa s oep ru p eS ee eS 12 4 123 3 Only Hextores 2 scp n eo 24 4 ae oe a BOS a oe aa e i 12 5 12 3 4 Maximum Cell Length c c s raea ea peene p ur a ha 12 6 12335 Buller Layers s 2 o6 bee eek ee dee Sew pee dee pied 12 6 123 0 Peel Layee s i rop aw bt Oe Rh eS eh ee SE ee ee 12 7 12 3 7 Local Refinement Regions soos sesde 648248 24 644 12 8 124 TheHegcore Panel ss coc sco ee Ae ee SLA ido a Ka es 12 9 124 1 The Outer Box Zones Panel lt rs e sa Geno dP aie E ace eue d 12 11 12 4 2 The Hexcore Refinement Region Panel 12 12 12 5 Text Commands for Hexcore Meshing 12 13 13 Improving the Mesh 13 1 13 1 Smoothing Nodes ss estds a oe ee ee eds Be ee
345. ially keyboard and GUI input output from TGrid usually all screen output The GUI commands are recorded as Scheme code lines in transcript files TGrid creates a transcript file by recording everything typed as input or entered through the GUI and everything printed as output in the text window The purpose of a transcript file is to produce a record of the program session for later reference The transcript file cannot be read back into the program because they contain messages and other output transcript files i At a time only one transcript file can be open for recording But you can write a transcript and a journal file simultaneously You can also read a journal file while a transcript recording is in progress 6 5 1 Using the GUI To start the transcripting process select the File Write Start Transcript menu item Enter a name for the file in the Select File panel The transcript recording begins and the Start Transcript menu item becomes the Stop Transcript menu item You can end transcript recording by selecting Stop Transcript or by exiting the program 6 5 2 Using Text Commands In the text interface start the transcripting process with the file start transcript command and end it with the file stop transcript command or by exiting the program ANSYS Inc April 15 2008 6 9 File Types 6 6 Domain Files Each mesh file written by TGrid has a domain section A domain file is the domain section of th
346. iangular Tetrahedral Meshes e 12 Generating the Hexcore Mesh e 13 Improving the Mesh e 14 Examining the Mesh Figure 3 6 1 User s Guide Contents ANSYS Inc April 15 2008 3 6 Using the GUI Help System 3 6 2 Opening the User s Guide Index To see the index for the User s Guide select the User s Guide Index menu item in the Help pull down menu Help User s Guide Index Selecting this menu item will open the web browser to the A page of the index Fig ure 3 6 2 You can use the links at the top and bottom of the page to accessthe index pages for other letters of the alphabet Next to each entry in the index you will find one or more numbers which are links Clicking on one of these links will bring you to the corresponding place in the User s Guide where the index entry topic is discussed Index A Microsoft Internet Explorer BEE Fie Edt View Favorites Tools Help a gt x a EA JO search She Favorites amp B a i veo inks snao A e a Return to Home Contents Previous Up Next ABCDEFGHIJKLMNOPORSTUVWXZ Index A accessing manuals 14 active cell zones 306 319 258 adaptive angle criteria 138 Annotate panel 360 annotated text 354 ANSYS 413 409 95 ANSYS export 103 append mesh files 78 ARIES 414 arrow keys 429 aspect ratio 378 cell 329 371 374 face 326 368 plotting cell distribution 328 plotting face distribution 325 Aut
347. ich you can select the zone s to be modified Face Zone Groups contains a list of the default boundary zone types and the user defined groups If you select a boundary type group from this list e g inlet all boundary zones of that type group for this example all pressure inlet and velocity inlet boundaries will be selected in the Face Zones list This shortcut allows you to easily select all boundary zones of a certain type without having to select each zone individually You can select multiple boundary types in the Face Zone Groups list to select all zones of several different types e g inlet and outlet Apply applies the option to the selected zones Draw displays the selected zones in the active graphics window List reports in the console the zone ID name boundary type and the number of faces for each selected zone 7 13 2 Text Commands for Manipulating Boundary Zones Text interface commands with the same functions as the controls in the Manage Face Zones panel are as follows boundary manage auto delete nodes specifies whether or not unused nodes should be deleted when their face zone is deleted boundary manage change prefix allows you to change the prefix for the specified face zones boundary manage copy copies the nodes and faces of the specified face zones boundary manage create creates a new face zone boundary manage delete deletes the face zone boundary manage flip reverses the normal direction
348. icular location You can also move the plane to any position by moving the slider bar to any position using the mouse Figure 8 5 2 shows how the leakage can be detected using the Pan Regions panel When the plane passes through the Cartesian grid the interior of the Cartesian ANSYS Inc April 15 2008 8 13 Wrapping Boundaries grid is displayed at every position on the plane If at any position of the plane the color of the region is seen inside the geometry there may be a leak or hole in the Cartesian grid a GG RSNA TY A Pan Plane Passing Through All B Pan Plane Overlaid With Geometry Regions Figure 8 5 2 Leak Detection Using the Pan Regions Panel 8 Adjust the plane at the position where the leak is seen on the plane A The Pan Regions panel only allows you to know whether or not there is a leak or hole in the geometry If the geometry has a hole or leak you need to find its exact location and fill it Using the Trace Path Panel To locate the hole or leak using the Trace Path panel do the following 1 Display the pan plane at a position where there is an indication of a possible leak You can overlay the geometry to allow easier location of the leak 2 Click the Trace Path button in the Region tab of the Boundary Wrapper panel to open the Trace Path panel 3 Specify a pair of points one inside and the other outside the geometry see Figure 8 5 3 You can either enter the locations
349. id orients the region by rotation first about the x axis then the y azis and finally the z axis You need to take this into account while specifying the orientation of the region as rotation in any other order will produce different results Define creates a new region according to the specified parameters It also allows you to modify the selected region according to the changes made Init creates a default region encompassing the entire geometry Draw draws the region in the graphics window If the grid was displayed using the Display Grid panel see Section 14 1 3 The Display Grid Panel before drawing the region the grid will also be included in the display Delete deletes the selected region ANSYS Inc April 15 2008 7 41 Manipulating the Boundary Mesh 7 5 3 Text Commands for Boundary Zone Refinement The text commands for boundary zone refinement are as follows boundary refine auto refine automatically refines a face zone based on proximity The original face zone is treated as a background mesh Faces are refined by multiple face splitting passes so that no face is in close proximity to any face in the current domain boundary refine clear clears all refinement marks from all boundary faces boundary refine count counts the number of faces marked on each boundary zone boundary refine limits prints a report of the minimum and maximum size of each specified zone This report will also tell you how many faces on
350. ide of a thin region The angle between the two faces is less than the Critical Angle specified e When inflating the thin region the nodes of the faces are moved away from each other and the marked region will be inflated e If you enable Preserve Boundary the node on the feature edge will not be moved e If you disable Preserve Boundary the node on the feature edge will also be moved 8 24 ANSYS Inc April 15 2008 8 8 Post Wrapping Improvement Operations Feature Edge Facel Face2 y z Critical Thickness sea A A Using Preserve Boundary B Without Preserve Boundary Figure 8 8 3 Preserving the Feature Edge While Inflating Thin Regions Removing Self Intersections TGrid removes most invalid configurations and improves the face quality when you smooth and swap the wrapper surface However configurations such as self intersecting faces may remain To remove self intersecting faces do the following 1 Select the wrapper surface in the Tri Boundary Zones selection list 2 Select Post Wrap in the Options drop down list and Remove Self Intersection in the Sub Options list 3 Specify the number of attempts for resolving self intersecting configurations in the Iteration field 4 Specify an appropriate value for Relative Thickness The relative thickness is the maximum distance by which the self intersecting faces should be separated 5 Click Apply ANSYS Inc April 15 2008 8 25 W
351. ificant angle to be used when you separate a face zone based on angle Faces with normal vectors that differ by an angle greater than or equal to the specified significant angle will be placed in different zones when the separation occurs Local Region contains a list of local refinement regions that have been defined using the Boundary Refinement Region panel see Section 7 5 2 The Boundary Refinement Region Panel You can select one of these to be used with the Mark option as described in Section 7 10 1 Methods for Separating Face Zones Face Seed specifies the label of the face element that you have selected as a seed TGrid automatically picks up the label of the face element when you select it in the graphics window Flood Fill Options contains options for selecting the method of seed element based separation Angle specifies the significant angle to be used as a feature angle for the for the face zone separation Edge Loop allows you to separate the face zones based on the edge thread loop associated with the face on which you have defined a seed face element Boundary Face Zones contains a list of face zones from which you can select the zone to be separated Local Regions opens the Boundary Refinement Region panel see Section 7 5 2 The Boundary Refinement Region Panel where you can define a local region to be used in conjunction with the Mark option See Section 7 10 1 Methods for Separating Face Zones for details Se
352. ification lines in an application defaults resource file called Fluent This file should then be installed in a directory such as usr 1ib X11 app defaults or on SUN work stations the directory may be usr openwin lib app defaults See documentation regarding your platform for more information 3 6 Using the GUI Help System TGrid includes an intergrated HTML based on line help system that provides an easy access to the documentation Using the graphical user interface you can access the entire User s Guide and other documentation The User s Guide and other manuals are displayed in your web browser and you can use the hypertext links and the browser s search and navigation tools to find the information you need There are many ways to access the information contained in the on line help e You can get reference information from within a panel on UNIX machines e You can also request context sensitive help for a particular menu item or panel e You can go to the User s Guide contents page or index and use the hypertext links there to find the information you are looking for ANSYS Inc April 15 2008 3 19 Graphical User Interface 3 20 e You can also access the other TGrid documentation e g the Tutorial Guide TGrid s help system is HTML based so you need to have access to a web browser In stall the HTML files from the documentation CD ROM See the separate installation instructions for your platform type
353. iguration contains a list of the possible configurations for swapping Skewness specifies the skewness above which cells will be considered for face swapping Iterations specifies the number of swapping iterations Improve improves the mesh quality based on the specified parameters Skew Threshold specifies the skewness threshold for improving the mesh quality Dihedral Angle specifies the threshold dihedral angle If the dihedral angle between two boundary faces is below the specified value the cell is considered to be a valid boundary sliver which cannot be im proved Max Attempts specifies the number of improvement attempts Apply performs the selected operation Slivers contains the options available and parameters required for sliver removal ANSYS Inc April 15 2008 13 11 Improving the Mesh Tri Tet Improve Cell Zones General Slivers fwid 44 7 Options Skew Threshold 9 985 Smooth Boundary y Smooth Interior Relaxation v Swap Boundary 0 2 Refine Boundary Iteration Refine Interior 5 A AA azarae Dihedral Angle _4 Boundary Freeze Feature Angle Cell Zone Groups 5 dead fluid solid Options contains a list of the operations available for sliver removal Smooth Boundary smoothes nodes on sliver cells having any node on the boundary such that skewness of the surrounding cells is improved Smooth Interior smoothes non boundary nod
354. ilateral boundary face zone that lies between the hexahedral region and the adjacent region to be meshed with tets This creates the triangular boundary face zone that is required to create tets in the adjacent region See Section 9 3 Generating Pyramids for details ANSYS Inc April 15 2008 Creating a Mesh H AISETA i pi POs Re Samadi i SN TOS A j WA RS AVS nt SO So EAN ava AAOS ZSO AAA SEINN ASANA A FNY WS Noe SKY eal AN VASA A 16a ea Ke AA ara WS Figure 9 1 3 Surface Mesh for a Grid Containing Only Tetrahedra 2 Create a domain encompassing the region to be meshed with tets See Section 13 10 Us ing Domains to Group and Mesh Boundary Faces for details 3 Generate the tets in the selected domain using either automatic or manual tet mesh generation or a combination of both See Chapter 11 Generating Triangu lar Tetrahedral Meshes for details Figure 9 1 4 shows the surface mesh for a portion of a grid containing hexahedra pyra mids tetrahedra and prisms that was created on a plenum feeding a valve port cylinder Figure 9 1 4 Surface Mesh 9 4 ANSYS Inc April 15 2008 9 1 Choosing the Meshing Strategy e The less complicated plenum pipe on the left of the figure is meshed using hexahe dral cells e The more complex valve port valve not visible because it is inside the surrounding
355. ile e Select Color for a color scale copy e Select Gray Scale for a gray scale copy e Select Monochrome for a black and white copy Most monochrome PostScript devices will render Color images in shades of gray Select Gray Scale to ensure that the color ramp is rendered as a linearly increasing gray ramp Defining the Resolution For raster hardcopy files you can control the resolution of the hardcopy image by speci fying the size in pixels Set the desired Width and Height under Resolution If the values of Width and Height are both zero the hardcopy is generated at the same resolution as the active graphics window Note For PostScript and EPS files specify the resolution in dots per inch DPI instead of setting the width and height ANSYS Inc April 15 2008 6 19 File Types Options For all hardcopy formats except the window dump you can control two additional set tings e Specify the orientation of the hardcopy using the Landscape Orientation option If this option is enabled the hardcopy is made in landscape mode default otherwise it is made in portrait mode e Control the background color using the White Background option This feature allows you to make hardcopies with a white background and a black foreground while the graphics windows are displayed with a black background and white foreground TGrid also provides options that allow you to save PostScript files that can be printed more quickly Thes
356. ile Dialog Box You can also append the files using the following TUI command e file append meshes by tmerge allows you to append the mesh files using tmerge There is no GUI item in TGrid for this TUI command ANSYS Inc April 15 2008 6 3 File Types e file append mesh allows you to append the mesh files This command is same as that of the Append File s check button in the Select File dialog box The Append File s check button is not accessible while reading the first mesh file 6 1 4 Writing Mesh Files To write a mesh file in the format that can be read by FLUENT do either of the following e Select the File Write Mesh menu item to open the Select File panel and specify the name of the mesh file to be written e Use the file write mesh text command and specify the name of the mesh file to be written To write a case file in the format that can be read by FLUENT do either of the following e Select the File Write Case menu item e Use the file write case text command and specify the name of the mesh file to write Selecting the File Write Mesh and File Write Case menu item will invoke the Select File panel where you will specify the name of the mesh or case file to be written By default a binary file will be written when you write a mesh or case file Binary files take up less memory than text files and can be read and written by TGrid more quickly You can disable the Write Binary Files optio
357. ill be merged If this option is enabled the distance between two nodes is compared against the shortest attached edge length If the separation distance is less than the specified percentage specified in the Tolerance field times the shortest attached edge length then the nodes will be merged The allowable maximum value of this parameter is 90 Count Free Nodes reports in the Message box the number of free nodes Count Unused Nodes reports in the Message box the number of nodes that are not used by any boundary faces i e the number of isolated nodes Delete Unused Nodes deletes all unused nodes Message shows the information reported by TGrid when the Count Free Nodes or Count Unused Nodes button is clicked Merge finds and merges duplicate nodes according to the parameters specified in the Compare and With group boxes If two nodes of a face are merged the face is deleted Draw draws all zones that are selected in the Compare and or With gropu boxes Default resets all controls in the panel to their default settings 7 1 3 Text Commands for Manipulating Boundary Nodes The TUI commands performing the same functions as the controls in the Boundary Nodes panel are boundary count unused bound node counts unused boundary nodes in the domain boundary count unused nodes counts unused boundary and interior nodes in the do main boundary delete unused nodes deletes boundary nodes that are not used by any
358. ilter list and select the node to be moved 2 Select position in the Filter list and select the appropriate poistion 3 Click Move To in the Operation group box Do the following to move a node by a specified magnitude 1 Select node in the Filter list and select the node to be moved 2 Enter the magnitude by which you want to move the node in the Enter Selection field and press lt Enter gt The incerement will now be selected in the Selections list 3 Click Move By in the Operation group box Swapping Cells You can perform either a 3 2 configuration swap or a 2 3 configuration swap Refer to Section 13 2 2 Tetrahedral Grids for details on the swap configurations Do the following to swap cells 1 Select the appropriate option in the Filter list and select the entities to be swapped e Select 3 cells or the common edge in order to perform a 3 2 swap e Select 2 cells or the common face in order to perform a 2 3 swap 2 Click Swap in the Operation group box 13 14 ANSYS Inc April 15 2008 13 6 Modifying Cells Determining the Coordinates of the Centroid Do the following to determine the centroid 1 Select the appropriate option in the Filter list cell face edge or node and select the required entity 2 Click Centroid in the Operation group box The centroid coordinates will be printed in the TGrid console Determining the Distance Between Entities Do the following to determine the distance betw
359. imity or boundary mark face intersection com mand boundary check duplicate geom displays the names of the duplicate surfaces and prints maximum and average distance between them 7 92 ANSYS Inc April 15 2008 7 15 Additional Boundary Mesh Text Commands boundary clear marked nodes clears nodes that were marked with the boundary mark duplicate nodes command boundary count unused faces lists the number of boundary faces that are not used by any cell boundary delete duplicate faces searches for faces on a specified zone that have the same nodes and deletes the duplicates Duplicate faces may be present if you generated your boundary mesh using a third party grid generator or if you have used the slit boundary face command described below to modify the boundary mesh and then you merged nodes You can detect duplicate faces by displaying multiply connected faces using the Display Grid panel see Section 14 1 3 The Display Grid Panel boundary delete all dup faces searches for faces on all boundary zones that have the same nodes and deletes the duplicates boundary delete unused faces deletes all boundary faces that are not used by any cell You should use this command after creating a mesh and deleting any dead zones This command will remove any faces located between two deleted cell zones Such faces should be removed if you are generating a mesh for FLUENT but the solver will delete them if you do not bounda
360. in a defined bounded region The cells intersecting the bounded region will be marked and TGrid will extract the cavity boundaries from the marked cells The marked cells will then be deleted to create the cavity Figure 13 8 1 shows a cavity created around the rear view mirror of a car You can see the original mesh and the remeshed cavity created around the mirror The bounding box defined for the cavity is also shown Original mirror cavity i bounding box Figure 13 8 1 Remeshed Cavity Around a Mirror The various options available in TGrid are e Removing zones This option allows you to specify zones to be removed from the existing volume mesh e Adding zones This option allows you to add new zones to the existing volume mesh e Replacing zones This option allows you to remove a set of zones and replace them with a new set of zones e Improving a region This option allows you to define a cavity around skewed cells in the existing mesh You can modify the mesh as appropriate and then remesh the cavity ANSYS Inc April 15 2008 13 23 Improving the Mesh Remeshing a Cavity The generic procedure for remeshing a cavity using the Cavity Remesh panel is as follows 1 Select the appropriate zones from the Remove Boundary Zones and Add Boundary Zones selection lists e Removing Zones Select the zone s to be removed in the Remove Boundary Zones selection list Make sure that no zones have been selected
361. in a journal file can be created by modifications or manipulations that you make within the program At a given time only one journal file can be open for recording But you can read a journal file at any time You can also write a journal and a transcript file simultaneously 6 4 1 Using the GUI To start the journal file select the File Write Start Journal menu item Enter a name for the file in the Select File panel The journal recording begins and the Start Journal menu item becomes Stop Journal menu item You can stop journal writing by selecting Stop Journal or by exiting the program You can read a journal file into the program using the Select File dialog box invoked by selecting the File Read Journal menu item 6 8 ANSYS Inc April 15 2008 6 5 Transcript Files 6 4 2 Using Text Commands To start the journaling process using the file start journal command and end it with the file stop journal command or by exiting the program To read a journal file into the program use the file read journal command Note The read journal command always loads the file in the main i e top level menu regardless of where you are in the menu hierarchy when you invoke it The standard period alias is the same as the file read journal definition and is defined by alias lambda ti read journal 6 5 Transcript Files A transcript file contains a complete record of all standard input to TGrid spec
362. in the Add Boundary Zones list e Adding Zones Select the zone s to be added in the Add Boundary Zones selection list Make sure that no zones have been selected in the Remove Boundary Zones list e Replacing Zones Select the zone s to be removed in the Remove Boundary Zones selection list and the zone s to be added in the Add Boundary Zones selection list e Improving a Region Make sure that no zones have been selected in the Remove Boundary Zones and Add Boundary Zones selection lists 2 Enable Create Face Group if you want to create a user defined group UDG com prising the zones defining the cavity domain TGrid will create the cavity UDG and the corresponding cavity domain but retain the global domain as active when the Create Face Group option is enabled When this option is disabled the cavity domain will be activated when the cavity is created i The Create Face Group option is useful when using the cavity remeshing feature for large cases For such cases you can avoid frequent switching between domains by enabling the Create Face Group option when creating the cavity The basic procedure is as follows a Create a UDG for the cavity and save the boundary mesh for the cavity group defined using the File Write Boundaries option see Section 6 1 5 Writing Boundary Mesh Files b Read this boundary mesh in a separate TGrid session and create the volume mesh in the cavity as appropriate c Save the volume mesh an
363. in the Selections list Project projects the selected node s onto to the defined projection line or plane Quality reports the quality of the selected entitiy according to the Measure se lected in the Quality Measure panel see Section 15 5 2 The Quality Measure Panel Enter Selection allows you to enter the name of an entity or the coordinates of a par ticular position as an alternative to selecting the entity from the graphics window Auto Redisplay toggles the automatic update of display after a cell modification opera tion has been performed When Auto Redisplay is enabled TGrid will automatically update the display allowing you to see the change effected by the operation Local Delta toggles the limiting of the grid display to a neighborhood around the selected entity When Local Delta is enabled TGrid will display the selected entity and some faces around it Draw Cells contains options for drawing cells Using Nodes enables the display of cells comprising the selected node s Using Faces enables the display of cells comprising the selected face s Quality Measure opens the Quality Measure panel see Section 15 5 2 The Quality Measure Panel Skew Report Zone contains a drop down list of the cell zones for which you can locate skewed cells This allows you to select the cell zone of interest instead of locating the skewed cells for all zones Next Skew displays the cell having the next highest skewness v
364. ing prisms e Chapter 11 Generating Triangular Tetrahedral Meshes describes the meshing pro cedures for triangular and tetrahedral meshes e Chapter 12 Generating the Hexcore Mesh describes the procedure and options for creating hexcore meshes e Chapter 13 Improving the Mesh describes the options available for improving the quality of a volume mesh e Chapter 14 Examining the Mesh describes the methods available for checking the mesh graphically e Chapter 15 Reporting Mesh Statistics describes methods for checking the mesh diagnostically e Appendix A Importing Boundary and Volume Meshes describes filters that you can use to convert data from various software packages to a form that TGrid can accept e Appendix B Mesh File Format describes the format of the TGrid mesh file e Appendix C Shortcut Keys lists all the hotkeys shortcut keys available in TGrid e Appendix D Query Functions lists the query functions available in TGrid e Appendix E Tips contains information on tips that will be useful to you while working on TGrid The Contents of Other Manuals In addition to this User s Guide there are two more manuals available to help you use TGrid e The Tutorial Guide contains example problems Each tutorial contains detailed instructions on performing the tasks associated with it e The Text Command List provides a brief description of the commands in the TGrid text interface UTM 2 ANSYS Inc April 15
365. ing Using Nodes e Fixing holes by selecting positions Figure 8 3 3 1 Select the position filter hot key lt Ctrl gt X 2 Select the positions around the hole 3 Press F5 to create the surface that closes the hole ANSYS Inc April 15 2008 8 5 Wrapping Boundaries Figure 8 3 3 Hole Filling Using Positions e Fixing multiple holes near each other by creating a planar surface 1 Open the Plane Surface panel 2 Select three positions 3 Specify appropriate mesh size and click Create See Section 7 14 2 Creating a Planar Surface Mesh for details Figure 8 3 4 Hole Filling Using a Plane Surface The TUI command boundary check duplicate geom can be used to identify duplicate surfaces The duplicate surfaces and the maximum and average distance between them will be printed in the TGrid console 8 4 Initializing the Cartesian Grid The first step in the wrapping procedure is to overlay a Cartesian grid onto the input geometry The accuracy of the wrapping depends on the cell size distribution of the Cartesian grid TGrid allows you to specify the cell size of the Cartesian grid according to your requirement Finer cells give better results but require longer computational time Therefore it is very important to use a Cartesian grid of optimum cell size distribution 8 6 ANSYS Inc April 15 2008 8 4 Initializing the Cartesian Grid Before specifying these parameters you need to identify the zone
366. ing a new domain is as follows 1 Deselect all zones in the Boundary Zones list and click New It is quicker to create an empty domain and then add the zones you want instead of creating a domain with many zones and then removing those you do not want 2 In the Boundary Zones list select the zones you want to include in the new domain If you are not sure about the zones click Draw to display the zones that are currently selected in the Boundary Zones list It is possible to select all triangular or quadrilateral boundary face zones by choosing tri or quad in the Boundary Zone Groups list e If you are creating a domain within a hybrid mesh to create triangles or tetra hedra make sure that the domain contains all zones required to enclose the region that is to be meshed with tris tets and only those zones e If the zones you select do not completely enclose the region or if you include additional zones that do not bound this region the tri tet meshing is likely to fail or be incorrect 3 Click on the Change button TGrid will update the panel so that the node face and cell zones highlighted in their respective lists are those that are affiliated with the boundary zones in the domain 4 Select the domain that you want to mesh or display or report on in the Domains list and then click the Activate button This domain is then considered to be the active domain and the Activate button is disabled until you select another domai
367. ing processed in preparation for graphical display i You cannot cancel the operation after the program begins to draw in the graphics window For Windows systems there are special features for printing the contents of the graphics window directly These features are not available on UNIX systems ANSYS Inc April 15 2008 3 15 Graphical User Interface 3 4 1 Printing the Contents of the Graphics Display Window Windows Systems Only If you are using the Windows version of TGrid the system menu of the graphics window displayed by clicking in the upper left corner of the graphics window contains the usual system commands move size and close Along with the system commands TGrid adds three more commands to the menu for printer and clipboard support Copy to Clipboard places a copy of the current picture into the Windows clipboard Some attributes of the copied picture can be changed using the Page Setup panel The size of your graphics window affects the size of the text fonts used in the picture For best results experiment with the graphics window size and examine the resulting clipboard picture using the Windows clipboard viewer Print opens the Windows Print dialog box which enables you to send a copy of the picture to a printer Some attributes of the copied picture can be changed using the Page Setup panel More attributes of the final print can be specified within the Microsoft Windows Print and Print Setup dial
368. ints button a Working dialog box will open prompting you to select the points defining the cylinder axis By Nodes allows you to specify the nodes corresponding to the points defining the cylinder axis Select Nodes allows you to select the nodes corresponding to the points defin ing the cylinder axis using the mouse When you click the Select Nodes button a Working dialog box will open prompting you to select the nodes defining the cylinder axis Radius specifies the radius of the cylinder to be created Mesh Size specifies the size of the cells to be created for the cylindrical surface mesh Preview allows you to preview the cylinder to be created Create opens the Zone Prefix panel see Section 7 14 3 The Zone Prefix Panel where you can specify the prefix for the zones to be created The Zone Prefix Panel The Zone Prefix panel allows you to specify the prefix for the zones created e g cyl for the cylinder zones hxc for the heat exchanger zones etc Zone Prefix Zone Name Prefix cy Controls Zone Name Prefix specifies the prefix to be used for the zones being created 7 14 4 Creating a Swept Surface In some cases you may want to create a swept surface You can create a swept surface using the options available in the Swept Surface panel il The option of creating a swept surface is available only in the 3D version of TGrid You can create a swept surface by projecting a
369. ion This option is available only when variational or laplace is selected in the Method drop dowm list 13 10 ANSYS Inc April 15 2008 13 5 The Tri Tet Improve Panel Improve implies that the node will be repositioned only when the max imum skewness of the cells connected to the node is reduced This option is available only when variational or laplace is selected in the Method drop dowm list Min Cell Skewness specifies the skewness above which the nodes will be smoothed Iterations specifies the number of smoothing iterations Min Improvement specifies the convergence criterion for smoothing For skewness based smoothing smoothing will be stopped when the largest change in skewness is below the limit specified For Laplace and vari ational smoothing the convergence criterion is the root mean square of the distance the nodes were moved during smoothing Relaxation specifies the factor used for computing the smoothing dis tance The value varies between 0 and 1 A value of 0 results in no movement while a value of 1 results in movement equivalent to the computed distance A smaller value will result in a more grad ual change in the mesh A reduced value may also result in a higher quality mesh but at the expense of more smoothing iterations This option is available only when variational or laplace is selected in the Method drop dowm list Swap Faces swaps the faces of the cells to improve the mesh quality Swap Conf
370. ion is used to connect two boundary zones along their free edges You cannot use this option to connect the surfaces at a location other than the free edges in the mesh Gaps within the given tolerance are closed using closest point projection Consider the intersection example shown in Figure 7 2 6 Face 2 Face 1 Figure 7 2 6 Nearest Point Projection for Stitching It shows a cut through the two surfaces Face 1 and Face 2 which are separated by a gap The points of nearest projection will determine the location of the intersection curve Therefore point 1 will be connected to point 2 or point 3 All the three connect operations allow a small gap within the tolerance specified between the intersecting boundary zones However the gap should not distort the shape of the geometry Figure 7 2 7 Surfaces Before Stitch ANSYS Inc April 15 2008 7 9 Manipulating the Boundary Mesh Figure 7 2 8 Surfaces After Stitch 7 2 4 Using the Intersect Boundary Zones Panel In general all the three connect operations calculate the intersection curve or line between the two surfaces to be connected The intersection curve is constructed as follows e Intersect constructs the curve as the intersection of two zones e Join constructs the curve as the outer boundary of the overlapping region within the specified tolerance of the two surfaces e Stitch constructs the curve along the free boundaries and within the sp
371. iple files for reading or writing You can use it to look at your system directories and to select a file The appearance of the Select File dialog box will not always be the same e When you select the File Read Mesh or File Read Boundary Mesh menu item to read a mesh file the Select File dialog box will look as shown in Figure 3 2 1 A e If you are writing a case file the dialog box will look as shown in Figure 3 2 1 B e If you are reading or writing any other type of file the dialog box will be similar to that in Figure 3 2 1 B except that the Write Binary Files and Write As Polyhedra buttons will not appear To select files on UNIX systems do the following 1 Go to the appropriate directory You can do this in two different ways e Enter the path to the desired directory in the Filter text entry box and press the lt RETURN gt key or click the Filter button Note Include the final character in the pathname before the optional search pattern e Double click a directory and then a subdirectory etc in the Directories list until you reach the directory you want You can also click once on a directory and then click Filter instead of double clicking 3 6 ANSYS Inc April 15 2008 3 2 Dialog Boxes Select File R E Select File F Filter Filter homeduser tutorial imsh MSH cas chome user tutorial cas Directories Files Directories Files b home user tutorial home us
372. is operation separates the wrapper surface into several zones based on the input geometry The newly created zones will be listed in the Tri Boundary Zones selection list prefixed by wrap The boundaries of the separated zones are not smooth you need to smooth them using the Rezone option Rezoning Faces The zones separated from the single wrapper surface can be smoothed by adjusting the node positions on the zone boundaries Very small zones islands will be merged to bigger adjacent zones To rezone the faces on the separated wrapper zones do the following 1 Select the boundary zone s to be rezoned in the Tri Boundary Zones selection list 2 Retain the selection of Zone in the Options drop down list and select Rezone in the Sub Options list The Rezone option allows you to smooth the boundaries of the separated zones and removes the island zones Figure 8 8 4 3 Enable Reprojection if required This is useful in recovering the distinctive zone boundary in the original geometry 4 Click Apply Multiple rezone operations may be required for better recovery of the boundaries of the wrapper zones You may also need to rezone each wrapper zone separately 8 28 ANSYS Inc April 15 2008 8 8 Post Wrapping Improvement Operations A B Figure 8 8 4 Wrapper Surface A Before and B After Rezoning Renaming Zones By default the separated wrapper zones are prefixed by wrap to distinguish them from
373. ism Region Specify the uniform direction vector or click Compute in the Vector group box TGrid will use this constant vector for all prism layers instead of computing a new direction for each layer see Figure 10 7 1 ANSYS Inc April 15 2008 10 17 Generating Prisms e Normal Method For regions with curvature TGrid determines the appropriate normal direction vector at each node since it may be different for each node and each layer see Figure 10 7 2 Select Normal in the Method group box in the Direct tab of the Prisms panel normal direction vectors Figure 10 7 2 Normal Direction Vectors for a Curved Prism Region Normal Smoothing The normal direction vectors obtained using the methods described in Section 10 7 Di rection Vectors are smoothed so that there is a gradual change in direction from one node to the next This will reduce the chance of direction vector intersection which causes the prism generation to fail This step is not necessary when a uniform direction vector is used since there is no change in direction from one node to the next Figure 10 7 3 shows normal direction vectors in the vicinity of a sharp 90 degree corner Figure 10 7 3 Normal Direction Vectors Before Smoothing The direction vector is at an angle of 45 degree at the corner while elsewhere it is 0 or 90 degrees These direction vectors will intersect and prisms cannot be generated Figure 10 7 4 shows the normal direction
374. ism controls normal normal method specifies the method to use for normal direction computation see Section 10 7 Direction Vectors acute bisection is a variation of that proposed by Kallinderis et al 7 8 7 8 The faces surrounding a node are analyzed to find those whose planes form the most acute angle The resulting normal lies on the plane bisecting those two planes This method is computationally more expensive than surface averaging but is less robust at singular points where convex edges meet smooth surfaces For example if a box is sitting on the table such a point would be where one of the box s corners meets the table top face average computes the normal at a node by averaging the normals of the surrounding faces This is the only method available in 2D hybrid normal computes the normal by all the methods available and uses the best quality normal obtained This is the default method in TGrid minimized angle is a variation of that proposed by Pirzadeh 14 15 An initial normal at a node is determined by averaging the normals of the surrounding faces the face average method Iterations are then performed to minimize the largest angle between the node normal and the normals of the surrounding faces This method is a computationally more expensive than surface averaging and can produce slightly better normals when the uniform offset method is used and the surface mesh does not contain sharp edges When the minimum
375. ist of available boundary zones from which you can select the zones to be removed from the volume mesh Add Boundary Zones contains a selection list of available boundary zones from which you can select the zones to be added to the volume mesh Create Face Group allows you to create a UDG comprising the zone s defining the cavity domain Bounding Box defines the extents of the cavity to be created Scale specifies the scale factor to be applied while calculating the bounding box for the zones selected in the Remove Boundary Zones and Add Boundary Zones selection lists Compute computes the bounding box extents according to the zones selected in the Remove Boundary Zones and Add Boundary Zones selection lists and the scale factor specified 13 26 ANSYS Inc April 15 2008 13 9 Manipulating Cell Zones Center specifies the coordinates of the center of the cavity Length specifies the length of the cavity bounding box along the X Y and Z axes Orient specifies the orientation of the cavity bounding box about the center of the cavity Create creates a cavity according to the bounding box defined Draw allows you to preview the cavity to be created 13 8 2 Text Commands for Cavity Remeshing The text interface commands for cavity remeshing are as follows mesh cavity add zones allows you to create a cavity for adding new zone s to the existing volume mesh mesh cavity merge cavity merges the specified cavity dom
376. istance between two distinct nodes If the distance between two nodes is less than the specified node tolerance the nodes are considered to be duplicates This option is available only when the Defaults option is disabled 11 20 ANSYS Inc April 15 2008 11 5 The Tri Tet Panel 11 5 2 The Tri Tet Refine Controls Panel The Tri Tet Refine Controls panel allows you to set additional parameters to control the skewness based refinement of the mesh Controls Preset Parameters contains a drop down list of the preset refinement control parame ters available default specifies the default refinement parameters fast transition specifies the refinement parameters which will result in quicker mesh gradation away from the boundaries and will generate fewer cells as compared to the default option incremental improve specifies the refinement parameters which will result in in cremental lowering of skewness Number of Levels specifies the number of refinement levels List displays the refinement parameters for the specified number of levels in the con sole ANSYS Inc April 15 2008 11 21 Generating Triangular Tetrahedral Meshes Parameters contains input fields for the refinement parameters Level specifies the level of refinement for which refinement parameters are dis played Each refinement level consists of two sweeps through the refinement procedure Max Boundary Cell Skew specifies the maximum acceptable ske
377. it by Limit by Z Minimum 2 5 Minimum 9 Maximum 2 5 Maximum 2 Neighborhood Object Name Delta Compute e Set Ranges Center Reset X Range allows you to limit the display of grid objects to the specified x coor dinate range To use the range enable Limit by X then enter the required Minimum and Maximum values in the physical dimensions of the mesh Y Range allows you to limit the display of grid objects to the specified y coor dinate range To use the range enable Limit by Y then enter the required Minimum and Maximum values in the physical dimensions of the mesh Z Range allows you to limit the display of grid objects to the specified z coor dinate range To use the range enable Limit by Z then enter the required Minimum and Maximum values in the physical dimensions of the mesh Neighborhood allows you to set the range to be within a specified neighborhood of a specified grid object Specify the Object Name and Delta and click Set Ranges Object Name specifies the name of the object on which the specified range is based You can select objects with the mouse in the graphics window if the mouse probe function see Section 14 10 Controlling the Mouse Probe Functions is currently select and the filter is currently node edge face cell or zone Delta specifies the neighborhood range about the specified object Set Ranges sets the X Y and Z Range to the values determined by the
378. ition is appropriate Else click Refuse and then Propose to obtain the next suggestion Click Next Skew to proceed with the node correction for the next highly skewed cell ANSYS Inc April 15 2008 13 7 Moving Nodes 13 7 3 The Auto Node Move Panel The Auto Node Move panel contains options for moving nodes to improve the mesh quality Auto Node Move Cell Zones Quality Limit y 0 9 Boundary Zones Ba Max Iter Node outlet outlet side 50 outlet top Dihedral Angle prism side 24 prism side 24 intf 19 Restrict Boundary Nodes Along Surface symmetry Auto Correction Semi Auto Correction Skew Mexi skee Reset skee Iterations E Y Propose Secon Refase Apply Quality Measure 1 Improve Warp Controls Parameters contains the parameters for node movement Quality Limit specifies the quality limit for triangular tetrahedral cells All cells above the specified limit will be considered for improvement Max Warp specifies the maximum allowable warp for quadrilateral faces All quad cells having faces with warp greater than this value will be considered for improvement This option is available only when the Improve Warp option is enabled Max Iter Node specifies the number of attempts to improve the skewness by moving a particular node Max Iter Face specifies the number of attempts to improve the warp of a face This option is a
379. ized Equiangle Deviation Controls Measure contains the available measures that you can use to check the quality of your mesh See Section 15 5 Mesh Quality for details about these choices Skewness specifies that skewness is the quality measure to be reported or dis played Size Change specifies that change in face or cell size is the quality measure to be reported or displayed Edge Ratio specifies that edge ratio is the quality measure to be reported or displayed Aspect Ratio specifies that aspect ratio is the quality measure to be reported or displayed Squish specifies that squish is the quality measure to be reported or displayed Warp specifies that warp is the quality measure to be reported or displayed Dihedral Angle highlights the faces having the dihedral angle between them in the specified range in the Cell Quality Range box of the Display Grid panel For details see Section 15 5 1 Aspect Ratio Tri Tet Skewness Method indicates which method you want to use to report and dis play the skewness of triangles and tetrahedra 15 14 ANSYS Inc April 15 2008 15 6 Printing Grid Information il The skewness method you choose will only affect reports and displays based on skewness The triangular and tetrahedral meshing procedure will always be based on the equilateral volume skewness method Equilateral Volume Deviation selects the skewness method that is based on the volume of an ideal equil
380. key F11 to find the face with the worst quality The worst face will be displayed in the graphics window The Next button will replace the First button Click Next hot key right arrow key The triangular face having the next highest quality will be displayed in the graph ics window When you subsequently click Next the face having the next highest quality after that of the previously displayed or reported face will be displayed or reported Click Reset hot key left arrow button to reset the display to the worst quality element You can also find the worst face within a subset of zones by activating a group containing the required zones using the User Defined Groups panel see Section 7 12 1 The User Defined Groups Panel and then clicking First When you click the Next button after activating a particular group the triangular face having the next highest quality within the active group will be displayed To display the marked faces in succession do the following 7 22 1 Select Mark and click First hot key F11 to find the first marked face The face will be displayed in the graphics window The Next button will replace the First button Click Next hot key right arrow key The next marked face will be displayed in the graphics window When you subse quently click Next the next face will be displayed or reported Click Reset hot key left arrow button to reset the display to the first marked fac
381. l active zones mesh manage adjacent face zones lists all face zones that refer to the specified cell zone mesh manage auto set active sets the active zone s based on points that are defined in an external file For each zone you want to activate specify the coordinates of a point in the zone the zone type e g fluid and a new name This command is valid only for tri tet meshes A sample file is as follows 1550 50 466 58 896 41 fluid heater 1535 83 643 14 874 71 fluid below heater 1538 73 444 28 952 69 fluid above heater 1389 18 775 51 825 97 fluid plenum Here four fluid zones are identified renamed and activated Any zone that you identify in the file will automatically be activated The hash sign indicates that TGrid should append the appropriate ID number for the zone mesh manage change prefix allows you to change the prefix of the cell zone mesh manage copy copies all nodes and faces of specified cell zones mesh manage delete deletes a cell zone along with its associated nodes and faces mesh manage id specifies a new cell zone ID If a conflict is detected the change is ignored mesh manage list prints information on all cell zones mesh manage merge merges two or more cell zones mesh manage name allows you to rename a cell zone mesh manage origin specifies a new origin for the mesh to be used for cell zone rota tion The default origin is 0 0 or 0 0 0 mesh m
382. l advancement direction methods are available as discussed in Section 10 7 Direction Vectors b Smooth the initial direction vectors See Section 10 7 Normal Smoothing for details c Determine the initial offset distances so that TGrid will know how far from the corresponding nodes on the previous layer to place the new nodes that define the prisms See Section 10 8 Offset Distances for details d Smooth the offset distances are smoothed to eliminate spikes and dips in the new prism layer See Section 10 8 Offset Smoothing for details e Project new nodes along the outer edges of the prism layer to adjacent zones based on the analysis in step 1 f Create prism faces and cells using the new nodes The new faces at the top of the prism layer are referred to as cap faces g The new cap faces of skewness value greater than the specified threshold are improved by edge swapping or edge node smoothing See Section 10 9 1 Edge Swapping and Smoothing for details h Apply global smoothing across the new surface This is also skewness driven but is based on the nodes not the faces See Section 10 9 2 Node Smoothing for details i Check the quality of all new cells and faces j If quality problems are detected prism layer creation is stopped If more layers are to be grown the process is repeated starting from substep a 3 Zone clean up After all the prism layers have been grown the new faces along the outer sid
383. l angle 15 13 edge ratio 15 12 size change 15 12 skewness 15 10 smoothness 15 9 squish 15 12 warp 15 13 query functions D 1 Question dialog box 3 6 radio buttons 3 11 raster file 6 19 reading mesh files compressed 6 6 reading and writing files 6 1 real number entry 3 12 Refine Boundary Zones panel 7 37 refinement regions 11 13 refining 11 2 11 12 automatically 11 2 locally 7 35 11 13 manually 11 12 triangular boundary faces 7 35 remeshing boundary zones 7 53 remote execution 2 2 Bib 12 removing duplicate nodes 8 21 renaming zones 7 75 13 30 Report Boundary Cell Limits panel 15 7 Report Cell Limits panel 15 5 Report Face Limits panel 15 3 Report Mesh Size panel 15 1 Report Boundary Cell Limits 15 6 Report Cell Limits 15 5 Report Face Limits 15 3 Report Mesh Size 15 1 report print info 15 15 Report Quality Measure 15 13 reporting 15 1 aspect ratio boundary cell 15 6 cell 15 5 face 15 3 change in size boundary cell 15 6 cell 15 5 face 15 3 mesh information 15 15 mesh size 15 1 quality boundary cell 15 6 cell 15 5 face 15 3 size boundary cell 15 6 cell 15 5 face 15 3 skewness boundary cell 15 6 cell 15 5 face 15 3 resolution 15 9 retriangulation 10 13 10 14 retriangulation failure 10 40 rotating the display 14 46 zones 7 76 rotating zones 13 30 sample session 4 1 ANSYS Inc April 15 2008 Index saving domai
384. l be skipped by TGrid If a zone is of mixed type element type 0 it will have a body that lists the element type of each cell B 6 ANSYS Inc April 15 2008 B 7 Faces In the following example there are 3d hexadecimal 61 cells in cell zone 9 of which the first 3 are triangles the next 2 are quadrilaterals and so on 19 9 1 3da 0 0 111331131 The cell section is not required for TGrid when the file contains only a surface mesh B 7 Faces Index 13 Scheme symbol xf face C macro XF_FACE Codes FLUENT TGrid Status required The face section has a header with the same format as that for cells but with a section index of 13 13 zone id first index last index type element type A zone id of zero indicates a declaration section with no body and element type indicates the type of faces in that zone The body of a regular face section contains the grid connectivity and each line appears as follows nO ni n2 cr cl where n are the defining nodes vertices of the face and c are the adjacent cells This is an example of the triangular face format the actual number of nodes depends on the element type The ordering of the cell indices is important The first cell cr is the cell on the right side of the face and cl is the cell on the left side Direction is determined by the right hand rule It states that if you curl the fingers of your right hand in the order of the nodes your thumb will
385. l layers to be added in order to have a smooth transition from fine to coarse cells Local Regions opens the Wrapper Refinement Region panel see Section 8 9 1 The Wrapper Refinement Region Panel Init allows you to initialize the Cartesian grid Refine refines the Cartesian grid according to the specified Zone Specific Size and or Local Size Function parameters Region contains the parameters to examine the region of interest among the several regions created during the wrapper initialization process E Boundary Wrapper Tri Boundary Zones iJ Face Size l Region l Features l Reports l Post Improve l FE Eb interface H amp cate regions 5 e cylinder right region 2 region 3 region 4 region s top right wheels 1 Overlay Graphics Wrap Extract _ Wrap Fix Holes Automatic HER 3 Pan Regions Tri Boundary Zone Groups TEE nial Update Regions Region al A Select Region contains a list of the regions generated during the wrapping process Overlay Graphics displays the Cartesian grid overlaid with the current dis play Wrap wraps the selected region s Extract extracts the interface s from the selected region s Draw displays the selected region s ANSYS Inc April 15 2008 8 35 Wrapping Boundaries Refine refines the selected region s Clear clears all the regions Deleting the regions reduces the peak memory and improves the speed of further operations Yo
386. l volume cells If required you can extend the com putational domain by generating more prisms ANSYS Inc April 15 2008 2 1 Getting Started e For grids containing only triangles or tetrahedra you can either use the auto matic mesh generation procedure or perform each step yourself 4 Check the mesh for problems quality and location The presence of degenerate cells will prevent you from obtaining a solution and poor cells in critical areas will cause serious accuracy and convergence problems If such cells cannot be removed or improved you will have to generate a new mesh by modifying the boundary mesh and or using different mesh parameters 5 Write the mesh to a new file for input to the solver 2 2 Starting TGrid The installation process described in a separate booklet is designed to ensure that the TGrid is installed properly so that the program can be launched when you follow the appropriate instructions If not consult your computer systems manager or your support engineer The way you start TGrid will be different for UNIX and Windows systems Starting T Grid on UNIX system To start TGrid type tgrid 2d or tgrid 3d in the command line of an xterm window When TGrid starts it will display a text window and the main menu bar This is called the console window If you start TGrid on UNIX systems without specifying 2d or 3d press the return key to see the following list of options TGrid version gt
387. l wrapper surface and imprint it on the feature edges of the input geometry 1 Select the region to be wrapped and click the Wrap button below the Region list to extract the initial wrapper surface Alternatively you can select the region to be wrapped and click the Extract button to extract the interface The extracted interface will be available in the Interface list 2 Select the appropriate interface in the Interface list and click Wrap You may want to clear the regions created during the initialization of the Cartesian grid before proceeding to extract the wrapper surface Deleting the regions reduces the peak memory and improves the speed of further operations When creating the wrapper surface directly from the region TGrid will ask if you want to delete all the regions Click Yes in the Question dialog box to clear the regions When creating the wrapper surface from an interface click Clear below the Region selection list before extracting the initial wrapper surface from the interface TGrid creates a wrapper surface having a face zone type wrapper The newly created wrapper surface will be listed in the Tri Boundary Zones selection list It takes the name wrapper surf xx where xx is a random number The wrapper surface can be displayed using the either the Display Grid panel or the Boundary Wrapper panel AN You can perform the imprinting and post wrapping improvement opera tions only on surfaces having the type wrappe
388. le boundary mesh or volume mesh files the selected file will be added to the list of Mesh File s You can then select another file which will also be added to this list e If you have put only the required files in the working directory and want to read all of them click the Select All button All the files available in the directory will be added to the list of Mesh File s e If you accidentally select the wrong file select it in the Mesh File s list and click the Remove button to remove it from the list of files to be read Repeat until only the required files are in the Mesh File s list e You can also read multiple boundary mesh or volume mesh files using the Append File s option Open the Select File dialog box and read the first mesh file in TGrid Open the Select File dialog box again enable the Append File s check button and read the remaining mesh files one after the other The Append File s option will not be accessible while reading the first mesh file It will be accessible only after reading the first mesh file 4 To write a mesh file enter the file name in the Mesh File text entry box and click OK A The Write Binary Files check button is enabled by default Binary files take up less space and can be read and written by TGrid more quickly The binary files are written in double precision You can disable the Write Binary Files option to write the file in text format You can read and edit the text file but it wi
389. le by inserting the CD into your CD ROM drive and going to the following directory cdrom tgrid5 0 help tutfiles Replace cdrom by the name of your CD ROM drive e For Windows systems locate the file by inserting the CD into your CD ROM drive and going to the following directory cdrom tgrid5 0 help tutfiles Replace cdrom by the name of your CD ROM drive e g E ANSYS Inc April 15 2008 4 1 Sample Session Alternatively download wedge zip from the FLUENT User Services Center to your working directory This file can be found from the Documentation link on the TGrid product page 2 Unzip wedge zip The file wedge msh can be found in the wedge folder created on unzipping the file 3 Start the 2D version of TGrid see Section 2 2 Starting TGrid 4 2 Reading the Boundary Mesh 1 Read in the mesh file File Read Boundary Mesh The Select File dialog will open Select File Filter Jhome user tutori Ahomeduser tutorial imsh HSHcasPX al imsh MSH cas Ahomeduser tutorial imsh HSHcasPX Directories home user tutorial al amp ppead Rete Select Mesh File s Remove home user tutorial wedge msh Is see m p Figure 4 2 1 Reading the Mesh File The Filter and Directories that appear in the dialog box depend on the location of working directory 2 Select wedge msh in the Files list The file wedge msh will be added to t
390. leting islands 8 25 duplicate nodes 8 21 examining Cartesian grid 8 11 geometry 8 4 hole filling 8 4 improving quality 8 26 8 37 inflating thin regions 8 22 8 37 prewrapping operations 8 4 recovering a single surface 8 29 recovering zones 8 26 8 37 removing crossovers 8 30 8 37 duplicate 8 37 self intersection 8 37 removing self intersection 8 24 renaming zones 8 27 reports 8 17 rezoning faces 8 27 smooth folded 8 37 smoothing 8 21 smoothing folds 8 22 swapping 8 25 working 8 1 Wrapper Refinement Region panel 8 42 wrapping boundaries 8 1 process 8 2 Write Boundaries panel 6 5 Write Views panel 14 32 writing mesh files 6 4 compressed 6 7 writing case files polyhedra 6 4 XY plots 14 21 ANSYS Inc April 15 2008 Index zonal hybrid mesh 9 3 Zone Prefix panel 7 87 Zone Selection Helper panel 14 51 zones 7 74 active 11 24 13 28 14 4 changing type 7 74 13 29 copying 13 27 13 29 creating new 7 16 13 29 deleting 13 29 merging 13 30 moving 13 27 multiple 11 7 projecting 7 69 remeshing 7 53 renaming 7 75 13 30 rotating 7 76 13 30 scaling 7 76 13 30 separating 7 63 translating 7 76 13 30 zooming 14 46 ANSYS Inc April 15 2008 Bib 15
391. ll also split zones that are divided by another face zone A 2D example would be two face zones touching in a T Using this command on the top zone e g wall 1 in Figure 7 10 1 would split it into two zones In the analogous 3D case individual faces in the corners at the T junction may be put in their own zones To check for this problem list the new face zones using the List button in the Boundary Zones panel looking for zones with a single face in them You can then merge these faces into the appropriate zone wall 1 wall 5 wall 4 wall 3 REGION 1 REGION 2 wall 2 wall 1 is separated because it is divided by its intersection with wall 5 The same is true for wall 2 wall 1 wall 6 wall 5 wall 4 wall 3 REGION 1 REGION 2 wall 2 wall 7 Figure 7 10 1 Face Separation Based on Region Based on Neighboring Cell Zones Region separation will split wall 1 in Figure 7 10 1 into two zones regardless of whether the two regions are in the same cell zone However neighbor based separation will yield different results If both regions are in the same cell zone wall 1 is not separated see Figure 7 10 2 If they are in different cell zones it will be separated When neighbor separation is used wall 1 needs to be separated only if it is adjacent to more than one cell zone If the two regions are in two different cell zones then wall 1 has two different neighboring cell zones and there
392. ll be created b optional Specify the required Mesh Size c Click Draw to visualize the bounding box that is created d Click Create This will open Zone Type panel in which you can select the Boundary Type of the plane surface mesh that you have created i The new surface created will always be meshed using a triangular mesh The Bounding Box Panel The Bounding Box panel allows you to create a box that encloses the input geometry Boundary gt Create Bounding Box Bounding Box Face Zones Method Edge Length interior 14 v Relative outlet Mi Min Z Min Compute Create Draw Close Help Face Zones contains a list of existing face zones in the geometry Method contains options for selecting the method for creating bounding box Absolute allows you to create a bounding box by specifying the extents along the coordinate axes Relative allows you to create a bounding box by specifying the clearance values from the boundaries of the selected face zones ANSYS Inc April 15 2008 7 81 Manipulating the Boundary Mesh Mesh Size allows you to specify the maximum size of the triangular cells that you want to create for the bounding box X Min Y Min Z Min specifies the minimum values of physical dimensions of the bound ing box in X Y and Z direction respectively This option is available only if you have selected Absolute X M
393. ll be deleted during the automatic meshing The nodes will be introduced when you initialize the mesh When you use this procedure all nodes must be inserted into the mesh or the initialization will fail A Do not place isolated nodes too close to the boundary or to other nodes ALY TRARY Shee lt DRR n Figure 9 1 10 Mesh Generated Using Isolated Nodes to Concentrate Cells Introduce the Nodes Using Face Zones After Meshing This procedure is as follows 1 Create a subdomain that does not include the face zones used to control the mesh density 9 10 ANSYS Inc April 15 2008 9 2 Using the Auto Mesh Option SK SX O o AA IS S K ROA V7 Figure 9 1 11 Mesh Generated Without Using Isolated Nodes 2 Create the volume mesh using the subdomain 3 Activate the global domain 4 Introduce the additional nodes using the text command mesh modify mesh nodes on zone i The mesh modify mesh nodes on zone command will delete the faces associated with the face zone 9 2 Using the Auto Mesh Option The Auto Mesh panel see Section 9 2 1 The Auto Mesh Panel allows you to automatically create the volume mesh in TGrid using the different mesh elements available The generic procedure for using the Auto Mesh panel for creating the mesh comprises the following steps 1 Determine the mesh elements required for the particular case Refer to Sections 9 1 1 9 1 5 for detai
394. ll be subjected to the refinement criteria You can control the concentration of interior nodes by specifying the maximum cell volume in the refinement region It is possible to save different values for the Maximum Cell Volume when you save each region You can also specify an outer region with the required volume growth to have a smooth transition between the original and the refined cells Note In addition to the use of refinement regions for refinement during the mesh gen eration process they can also be used as a postprocessing tool to refine a region of an existing mesh You can create multiple regions that overlap each other and the geometry To create additional regions you can copy an existing region and then modify the parameters as required The default region includes the entire geometry Figure 11 4 1 shows the refinement region and outer region The maximum cell size for the refinement and outer regions is displayed based on the maximum cell volume and ANSYS Inc April 15 2008 11 13 Generating Triangular Tetrahedral Meshes outside volume growth specified For information on refining triangular boundary faces in anticipation of local refinement refer to Section 7 5 Refining the Boundary Mesh OCT NERA PR TATATATA UNE ICSC PKR DSRS EL AVAN Ie AS No SEK RIVER IC AV FAY AN P lt ra A AS TT O Rea a A AN A a Ra KANTAS NE OA AN ER eae EEIEIE ERASED RIDE ASIDES Sistas SSO AE NENE re RK gt SRS my BOR
395. ll require more storage space than the corresponding binary file You can also use the following TUI command to toggle the Write Binary Files option file file format 5 To write a hexcore mesh enable Write As Polyhedra check button in the Select File panel to allow TGrid to handle polyhedral cells Polyhedral cells are created when hex and tet cells are merged with each other Enabling this option allows TGrid to export these cells instead of nonconfomal meshes Fa This option is available only for hexcore meshes 6 Click OK to read or write the specified file s Shortcuts for this step are as follows e If the file appears in the Files list and you are not reading a mesh double click on it instead of just selecting it This will automatically activate the OK button 3 8 ANSYS Inc April 15 2008 3 3 Panels e If you are reading a mesh you will always have to click OK Clicking or double clicking will just add the selected file to the Mesh File s list e If you entered the name of the file in the File text entry box press the lt RETURN gt key instead of clicking OK File selection on Windows systems can be done using the standard Windows Select File dialog box For further instructions see documentation regarding your Windows system 3 3 Panels A panel is similar to a dialog box but working with a panel is like filling out a form Panels are used to perform more complicated input tasks Each panel is unique
396. ll selected zones into the first zone selected This operation is useful if you have several different zones that you would like to treat as a single zone Merge Options lists the options available for merging the selected zones Alphabetic Order allows you to retain the name of the zone which comes first in alphabetic order Larger Area allows you to retain the name of the zone having a bigger area A The Delete and Merge operations are irreversible Rename allows you to change the name of the selected zone Name specifies the new name for the zone selected in the Face Zones list 7 76 ANSYS Inc April 15 2008 7 13 Manipulating Boundary Zones Change Prefix allows you to change the prefix for the selected face zones From specifies the current prefix for the selected face zones To specifies the required prefix for the selected face zones Flip Normals reverses the normal direction of the selected boundary zone s Orient orients contiguous faces i e faces that touch each other in a selected zone so that their normals are all consistently pointing on the same side of the zone See Figure 7 13 1 This consistent orientation is especially important if you are going to build prisms from the boundary zone inconsistent orientation consistent orientation Figure 7 13 1 Inconsistently and Consistently Oriented Contiguous Faces Rotate rotates the selected zone s through the specified angle Angle specifies the an
397. ll zoom allows you to zoom in or out of the view by rolling the mouse while the button is pressed mouse probe allows you to perform the specified mouse probe function The mouse probe function can be set in the Mouse Probe panel see Section 14 10 1 The Mouse Probe Panel ANSYS Inc April 15 2008 14 47 Examining the Mesh mouse annotate allows you to insert text into the graphics window If you drag the mouse button an attachment line is drawn When you release the button after dragging or clicking a cursor is displayed in the graphics window and you can enter the text Press lt RETURN gt or move the cursor out of the graphics window To remove annotated text and attachment lines use the Clear push button in the Annotate panel or the display clear annotation command as described below in Section 14 11 Annotating the Display These commands will delete all annotated text from the window OK saves the current settings and closes the panel The appropriate function will be executed when a mouse button is subsequently clicked in a graphics window You do not have to redraw the graphics window for the new button functions to take effect 14 9 2 Text Commands for Selecting Mouse Buttons Text interface commands with the same functionality as the controls in the Mouse Buttons panel are display set mouse buttons prompts you to select a function for each of the mouse buttons The options available are mouse rotat
398. ls Panel Init initializes the mesh 11 18 ANSYS Inc April 15 2008 11 5 The Tri Tet Panel TrifTet Initialization Refinement Refine Method Cell Size y Max Cell Volume Controls Options 0 0002767174 Compute me J Improve Mesh Cell Size Function Growth Rate 1 Remove Slivers y 1 6 Message 1 active tet refinement region Local Regions Init amp Refine Apply Close Help Refinement contains options for refining the mesh Refine Method allows you to select the refinement method to be used Options contains options to be included excluded in the refinement process Improve Mesh improves the mesh during refinement see Sections 13 1 and 1 Remove Slivers removes slivers see Section 13 4 Removing Slivers from a Tetrahedral Mesh Cell Size contains parameters controlling the tri tet cell size Max Cell Volume specifies the maximum acceptable volume for a cell Any active cell with a size greater than the specified value will be refined Compute computes the maximum cell volume based on the longest edge in the boundary mesh Cell Size Function allows you to control the cell size distribution in the in terior of the mesh geometric determines the cell size distribution by geometric growth from the closest boundary according to the specified growth factor linear determines the cell size distribution by linear interpolation from the boundary cell size
399. ls on choosing the meshing strategy 2 If you need to grow prisms for the geometry under consideration click the Set button in the Boundary Layer Mesh group box to open the Prisms panel Set the appropriate prism parameters and click Apply in the Prisms panel Refer to Sec tion 10 3 Prism Meshing Options for details on the prism meshing options available ANSYS Inc April 15 2008 9 11 Creating a Mesh in TGrid Verify that the Prisms check box is enabled in the Boundary Layer Mesh group box in the Auto Mesh panel Select the appropriate quad tet transition elements from the Quad Tet Transition list Click the Set button to open the Pyramids panel see Section 9 3 3 The Pyramids Panel or the Non Conformals panel see Section 9 4 1 The Non Conformals Panel depending on the selection and specify the appropriate parameters Refer to Sections 9 3 1 and 9 4 for details Select the appropriate option from the Volume Fill list Click the Set button to open the Tri Tet panel see Section 11 5 The Tri Tet Panel or the Hexcore panel see Section 12 4 The Hexcore Panel depending on the selection and specify the appropriate parameters Refer to Sections 11 3 11 4 and 12 3 for details Enable Merge Cell Zones if desired Click Mesh to automatically create the mesh Alternatively you can use the command mesh auto mesh to generate the mesh auto matically You need to specify the meshing parameters for the
400. m cell size specified by both the options c Click Refine to update the Cartesian grid for the new set of parameters d Define local region s if required and refine them Currently the only possible shape is a box either aligned with the coordinate axes or oriented as required The region is defined by an x y and z range You can specify the level of refinement required for each local region You can visualize the regions defined using the Draw button in the Wrapper Refinement Region panel see Section 8 9 1 The Wrapper Refinement Region Panel The size of the elements in the defined region will be indicated in the graphics window e optional Refine regions for better representation of the geometry Select the region s to be refined in the Regions selection list and click the Refine button 8 5 Examining the Cartesian Grid for Leakages When the Cartesian grid you are using to create the wrapper surface contains a hole or niche of geometry whose size is greater than the size of the Cartesian cells in that zone a leakage or hole is created in the resulting wrapper surface Examine the region you want to wrap for mesh density leakages etc before extracting the wrapper surface You can use either the automatic leak detection feature or fix the leaks manually and update the region accordingly 8 5 1 Automatic Leak Detection When you refine an existing region or specify additional sizing functions for better rep resentation
401. mand can be used for smoothing of all cell types including prismatic cells mesh tritet improve skew smooth nodes applies skewness based smoothing to nodes on the tetrahedral cell zones to improve the mesh quality mnesh tritet improve smooth nodes allows you to apply either Laplacian or varia tional smoothing to nodes on the tetrahedral cell zones to improve the mesh quality 13 2 Swapping Swapping can be used to improve the quality of triangular or tetrahedral grids 13 2 1 Triangular Grids The approach for triangular grids is to use the Delaunay circle test to decide if a face shared by two triangular cells should be swapped A pair of cells sharing a face satisfies the circle test if the circumcircle of one cell does not contain the unshared node of the second cell ANSYS Inc April 15 2008 13 3 Improving the Mesh fo ee a os l ie 4 Si 7 lt Pa Figure 13 2 1 Cell Configurations Satisfying and Not Satisfying the Circle Test Figure 13 2 1 illustrates cell neighbors that satisfy and do not satisfy the circle test In cases where the circle test is not satisfied the diagonal or face is swapped as illustrated in Figure 13 2 2 San SE Figure 13 2 2 Swapped Face Satisfying the Delaunay Circle Test Repeated application of the swapping technique will produce a constrained Delaunay mesh A Delaunay grid is a unique triangulation that maximizes the minimum angles in the mesh Thus
402. manually or click the Select Points button and select the points using the mouse 4 Click Trace Figure 8 5 3 TGrid highlights the path connecting the cells corresponding to the points specified This traced path will always pass through the hole leak 8 14 ANSYS Inc April 15 2008 8 5 Examining the Cartesian Grid for Leakages Figure 8 5 3 Trace Path 5 Display the original geometry and click the Trace button in the Trace Path panel Figure 8 5 4 The traced path will now be visible along with the original geometry You can zoom in to the region where the trace path enters the geometry Figure 8 5 4 Figure 8 5 4 Display of Geometry with Highlighted Trace Path Close the hole or leak using the methods described in Section 8 3 Detecting and Filling the Holes Manually Select the surfaces in the Tri Boundary Zones selection list and click the Update Regions button in the Manual group box The regions will be updated to account for the fixed hole You can click the Trace button in the Trace Path panel to verify that the region has been updated for the fixed hole TGrid will report that there is no path between the two positions Examine the updated region for further leaks or holes Fill any remaining leaks or holes before proceeding ANSYS Inc April 15 2008 8 15 Wrapping Boundaries 8 6 Extracting the Wrapper Surface In this section you will learn how to extract the initia
403. mber assigned by TGrid For example if TGrid uses triangular boundary faces from the zone wall 3 they will be placed in a new zone called wall 3 pyramid side 6 where the 6 is the zone number assigned by TGrid ga If you include the pyramid side boundary zone s when defining the do main in which you are going to generate a tetrahedral mesh the tetrahedral meshing will fail 9 3 3 The Pyramids Panel The Pyramids panel allows you to specify all the parameters required for pyramid creation and to create the pyramids See Section 9 3 1 Creating Pyramids for details about using the options in the Pyramids panel 9 16 ANSYS Inc April 15 2008 9 3 Generating Pyramids Mesh Pyramids Pyramids Options Boundary Zones Bay Skewness quad inlet Neighbor v Centroid quad side Offset Scaling 4 Offset Factor F Fill Cap Boundary Zone Groups J far field Face Angle geometry 7 Controls Options contains the options for determining the location of the new vertex of the pyramid Skewness specifies that the new vertex of a pyramid should be placed just above the centroid of the quadrilateral base or the pyramid should share the vertex of a neighboring pyramid or a node on an adjacent boundary face whichever will yield the best skewness see Figures 9 3 3 and 9 3 4 This is the default option and is the best choice for most cases Neighbor specifie
404. me boolean values true or false These are entered with the Scheme symbols for true t and false f 5 2 3 Strings Character strings are entered in double quotes as in red Plot titles and plot legend titles are examples of character strings Character strings can include any characters including blank spaces and punctuation ANSYS Inc April 15 2008 5 5 Text User Interface 5 2 4 Symbols Symbols are entered without quotes Zone names surface names and material names are examples of symbols Symbols must start with an alphabetical character i e a letter and cannot include any blank spaces or commas You can use wild cards to specify zone names when using the TUI Some examples are e display boundary grid allows you to display all the boundary zones in the mesh e boundary delete island faces wrap allows you to delete island faces on all wrapper zones prefixed by wrap If you use a wild card for an operation that requires a single zone as input you will be prompted to specify a single zone from the list of those that match the expression specified boundary manage name wall lt RETURN gt wall 1i wall 2 wall 3 wall 4 wall 5 wall 6 Zone Name 5 2 5 Filenames Filenames are actually character strings For convenience filename prompts do not require the string to be surrounded with double quotes If for some exceptional reason a filename contains an embedded space chara
405. me on or off click Apply to see the effect of the change on subsequent display operations 14 8 2 Text Commands for Scene Description The following text commands are related to scene description display update scene draw frame enables disables the drawing of the bounding frame display update scene overlays enables disables the overlays option display update scene select geometry allows you to select the geometry to be up dated display update scene set frame allows you to change the frame options 14 8 3 Changing the Display Properties To enhance the scene in the graphics window you can change the color visibility and other display properties of each geometric object in the scene e You can specify different colors for displaying the edges and faces of a grid object to show the underlying mesh edges when the faces of the grid are filled and shaded e You can also make a selected object temporarily invisible If for example you are displaying the entire grid for a complicated problem you can make objects visible or invisible to display only certain boundary zones of the grid without regenerating the grid display using the Display Grid panel ANSYS Inc April 15 2008 14 41 Examining the Mesh e You can also use the visibility controls to manipulate geometric objects for efficient graphics display These features along with several others are available in the Display Properties panel 14 8 4 The Display
406. metry In such cases you can also create the hexcore mesh extending exactly until the boundaries of the domain When you enable Grow Upto Boundaries the minimum and maximum domain extents will be automatically updated with values exactly equal to the bounding box of the surface mesh in the domain The hexcore mesh will extend upto the boundary aligned with the X Y and Z axes An example is shown in Figure 12 3 2 where the hexcore mesh has been generated upto the bounding box for the geometry A TGrid will report an error if you attempt to use this option when the geometry is completely within the domain Enable Grow Upto Boundaries and specify the domain extents for the bounding box You can either enter the values manually or select the zones comprising the bounding box in the Outer Box Zones panel see Section 12 4 1 The Outer Box Zones Panel You can also specify the outer box zones using the command mesh hexcore controls outer box zones 12 4 ANSYS Inc April 15 2008 12 3 Controlling Hexcore Parameters Figure 12 3 2 Hexcore Upto Boundaries A The outer box zones specified should comprise a bounding box You cannot specify zones that are individual faces of the bounding box The hexcore mesh generated using this option will have hex cells generated upto all the boundaries defining the bounding box 12 3 3 Only Hexcore The Only Hexcore option allows you to prevent the automatic creation of the tetrahedral mesh after h
407. mon edge is created since the specified value for Angle is smaller than the feature angle Alternatively if you use the Adaptive angle criterion the change in angle will be detected automatically and the interior edge thread will be created as shown in Figure 7 6 3 Figure 7 6 4 shows the single edge loop created by using the Face Seed approach and Fixed angle criterion with the angle specified as 65 degrees The edge thread at the common edge is not created since the specified value for Angle is greater than the feature angle ANSYS Inc April 15 2008 7 6 Creating and Modifying Features Figure 7 6 2 Edge Loop for Face Zone Approach and Fixed Angle 65 Figure 7 6 3 Edge Loops for Face Zone Approach and Fixed Angle 55 or Adaptive Angle ANSYS Inc April 15 2008 7 45 Manipulating the Boundary Mesh Figure 7 6 4 Edge Loop for Face Seed Approach and Fixed Angle 65 e Figure 7 6 5 shows the edge loops created by using the Face Seed approach and Fixed angle criterion with the angle specified as 55 degrees The boundary edge thread is created based on the seed face selected The interior edge thread at the common edge is created since the specified value for Angle is smaller than the feature angle Alternatively if you use the Adaptive angle criterion the change in angle will be detected automatically and the boundary and interior edge threads will be create
408. mple Cartesian cell with the specified Max Length is also displayed at the center of the refinement box Figure 12 3 6 Local Refinement Region for the Hexcore Mesh 12 8 ANSYS Inc April 15 2008 12 4 The Hexcore Panel 12 4 The Hexcore Panel The Hexcore panel allows you to control the hexcore meshing procedure Mesh gt Hexcore Controls Parameters contains options that control the hexcore meshing in the domain Keep Outer Domain allows you to create Cartesian cells until the boundary of the domain Only Hexcore allows you to prevent the automatic creation of the tetrahedral mesh after hexcore generation When the Only Hexcore option is enabled the hexcore is created and the tetrahedral domain is activated You can manually create the tet mesh separately Max Cell Length sets the maximum length for the hex cells in the domain The final length may not be the specified value as it is also limited by other pa rameters Compute computes the maximum cell length based on the surface mesh ANSYS Inc April 15 2008 12 9 Generating the Hexcore Mesh Buffer Layers specifies the number of additional layer of cells to subdivide In creasing the buffer layers will significantly increase the number of cells Refer to Section 12 3 5 Buffer Layers for details Peel Layers controls the gap between the hexahedra core and the geometry Refer to Section 12 3 6 Peel Layers for details Grow Upto Bo
409. n 13 34 ANSYS Inc April 15 2008 13 10 Using Domains to Group and Mesh Boundary Faces By default the most recently created domain is automatically set to be the active domain so you only need to explicitly set the active domain if it is not the one you just created Note If you are unsatisfied with a domain definition delete it using the Delete button Then either start over or modify it by selecting it and performing steps 2 and 3 13 10 3 The Domains Panel The Domains panel allows you to create domains encompassing the region s of a hybrid mesh that are to be meshed with tetrahedra or triangles or domains containing boundary zones that you wish to group for other reasons See Sections 13 10 1 and 13 10 2 for details Mesh Domains domain 1 Controls Domains contains a selectable list of all domains that have been defined including the global domain containing all zones in the mesh Name sets the name of the new domain you are about to create by clicking on the New button or the name of the selected domain that you are about to change by clicking on the Change button ID shows the number of the selected domain The global domain has an ID of 0 the next domain to be created has an ID of 1 and so on Boundary Zones contains a list from which you can select the zone s to be included in the domain ANSYS Inc April 15 2008 13 35 Improving the Mesh B
410. n See Section 13 10 Using Domains to Group and Mesh Boundary Faces for details All automatic or manual meshing actions will apply only to the active domain e To improve the speed and reduce the number of potential problems introduce nodes in a scattered manner It is more effective than consecutively introducing nodes in close proximity e After the mesh is initialized TGrid will set any non fluid zones to Non Fluid Type If your mesh includes multiple regions e g the problem for which you are creating a grid includes a fluid zone and one or more solid zones and you plan to refine all of them using the same refinement parameters modify the Non Fluid Type before initializing the mesh e If there are intersecting faces in the mesh TGrid will not be able to generate a mesh until the problem faces are removed If there are no free or multiply connected edges then it will not be possible to identify the faces until meshing is attempted E 6 Grouping Elements e All boundary types are considered as wall zones You can set the appropriate boundary types in TGrid or in the solver e The Group command in I deas is used to create the boundary zones needed by TGrid All faces grouped together are listed together in the output as a single zone In FLUENT boundary conditions are set on a per zone basis All nodes grouped together are listed together in the output as a single zone It is important not to group nodes of internal f
411. n Regions Name Outside Range Growth Rate region 1 10 1 35 Center Length Orient x o x 10 v Ot v 50 Y dea 60 Activate Deactivate Z teg o Select Activated Deselect Activated Max Cell Volume 0 00027672 Cell Volume Limits X deg o Controls Regions contains a list of the defined regions Activate activates the region selected in the Regions list Deactivate deactivates the region selected in the Regions list Select Activated selects the activated regions in the Regions list Deselect Activated deselects the activated regions in the Regions list Name reports the name of the selected region You can specify a new name by entering it in this text entry box Outside Range defines the size of the outer transition region in which the geometric growth factor is applied to obtain a smooth transition between the original and the refined cells Growth Rate is the geometric growth factor applied in the outer transition region Center allows you to specify the coordinates of the center of the region you want to create This is useful when you know the region in which refinement is required Specify the coordinates of a point in that region as a center of the region to be created ANSYS Inc April 15 2008 11 23 Generating Triangular Tetrahedral Meshes Length allows you to specify the absolute size of the new region in x y and z directions Orient allows you
412. n To create prisms you need to specify the boundary zone s from which the prisms will be built their heights and the direction in which you want to build them ANSYS Inc April 15 2008 10 1 Generating Prisms TGrid also allows you grow prisms on dangling walls You can also specify different growth methods on adjacent walls in the domain TGrid can automatically detect the collision between the prisms layers and avoid the collision by adjusting the height of the colliding prism layers Figure 10 1 1 shows the types of prisms that TGrid can generate we 4 prism with prism with quadrilateral base triangular base hexahedron wed ge 2D prism quadrilateral Figure 10 1 1 Prism Shapes that TGrid Creates Instructions for building prisms are provided in Section 10 2 Procedure for Generating Prisms Details about how TGrid uses your inputs to generate the prisms are provided in Section 10 5 How TGrid Builds Prisms Problems related to prism generation are discussed in Section 10 12 Prism Meshing Problems 10 2 Procedure for Generating Prisms The procedure for creating prisms from boundary zones is as follows 1 Check the boundary mesh to ensure that free nodes or faces with high skewness do not exist See Sections 7 1 and 14 2 for details 2 Select the boundary zone s from which you want to grow prisms in the Boundary Zones selection list in the Prisms panel Mesh Prisms If you rea
413. n 2 1 Using TGrid e Section 2 2 Starting TGrid e Section 2 3 Starting Dual Process Build of TGrid Using T Grid Starting from a given boundary mesh or a boundary mesh with some 2D quadrilateral or 3D hexahedral cells TGrid generates an unstructured triangular or tetrahedral or hybrid grid In 2D the boundary mesh consists of nodes and straight edges whereas in 3D it consists of nodes and triangular and or quadrilateral faces A boundary mesh file can be obtained from a number of sources including GAMBIT TGrid creates an interior mesh from the boundary mesh and writes it to a new file This file can then be read into the solver where the solution process and postprocessing occur 2 1 1 Grid Generation Steps The basic steps for using TGrid are as follows 1 Read a simple boundary mesh file or a boundary mesh containing some 2D quadri lateral or 3D hexahedral cells into TGrid 2 Examine the boundary mesh for topological problems such as free edges and du plicate nodes When the boundary is topologically correct you can check a 3D surface mesh for poor face quality Many quality related problems can be solved easily with edge swapping but more difficult problems may require direct manipulation of the faces and nodes 3 Generate the volume mesh You can do this automatically or by proceeding through a series of steps e For hybrid grids first generate prisms or pyramids and then generate the triangular or tetrahedra
414. n edge loop along a specified linear distance in a specified direction 7 88 ANSYS Inc April 15 2008 7 14 Creating Surfaces Using the Swept Surface Panel The procedure for creating a swept surface is as follows 1 Create the edge loops for the required surface using either the Feature Modify panel or the Surface Retriangulation panel see Section 7 6 1 Creating Edge Loops for details 2 Open the Swept Surface panel Create Boundary o o NN QA Oo A OQ The Swept Surface Panel gt Swept Surface Enable Split Quad Faces if required Click Apply to create the swept surface Select the edge loop to be swept from the Edge Zones drop down list Select the corresponding face s from the Face Zones selection list Specify the distance along which the edge is to be swept in the Total Distance field Specify the appropriate value in the No of Offsets field Specify the Vector defining the direction in which the edge is to be swept The Swept Surface panel allows you to create a swept surface i Boundary gt Create Swept Surface S Swept Surface Total Distance E998 Zones 4 intersect 8 5 12 Face Zones No of Offsets A bottom ae inlet intevior 14 Vector left outlet x right top I Split Quad Faces Draw Edges HEF ANSYS Inc April 15 2008 7 89 Manipulating t
415. n files 6 10 hardcopy files 6 17 mesh files 4 11 6 1 panel layout 6 24 scale in a GUI panel 3 13 scaling zones 7 76 13 30 scene description 14 38 Scene Description panel 14 38 Scheme 1 1 5 1 5 4 5 5 5 9 loading source files 6 7 search pattern 3 7 Select File dialog box 3 6 selecting files 3 6 separate face zones based on shape 7 64 using angle 7 63 using marked cells 7 66 using neighboring cell zones 7 64 using regions 7 63 using seed element 7 64 Separate Face Zones panel 7 67 separating boundary zones 7 63 shadow 7 89 shortcut keys C 1 arrow keys C 1 help keys C 1 hot keys C 2 shrinking elements 14 11 side faces 9 16 10 11 single selection list 3 12 size cell 14 8 change in 15 9 face 14 6 plotting cell distribution 14 19 plotting face distribution 14 17 size change 15 12 skewness 4 8 11 22 15 10 cell 14 8 14 20 face 14 6 14 17 plotting cell distribution 14 19 plotting face distribution 14 17 ANSYS Inc April 15 2008 sliver 13 6 removal 13 6 smoothing Laplacian 13 2 normals 10 17 skewness based 13 2 variational 13 2 smoothing nodes 13 2 smoothness 7 35 15 9 squish 15 12 starting TGrid 2 2 on a remote machine 2 2 STL 6 13 strings 5 5 Style Attributes panel 14 15 Surface Retriangulation panel 7 56 swapping 13 3 sweep surface creating 7 87 Swept Surface panel 7 88 symbols 5 6 14 16 system commands 5 8 terminal emulator 3 2 tetr
416. n in the Select File dialog to write the file in text format The text file can be edited but it will require more storage space than the corresponding binary file You can also use the TUI command file file format to toggle the writing of binary files Since FLUENT has the same mesh file format as TGrid you will be able to read this file back into TGrid using the File Read Mesh menu item or the file read mesh text command if you should need to modify the mesh at a later time If you are writing a hexcore mesh enable the Write As Polyhedracheck button in the Select File panel This allows TGrid to create polyhedral cells Polyhedral cells are created when hex and tet cells are merged with each other Enabling this option allows TGrid to export these cells instead of non conformal meshes A Case files containing polyhydral cells cannot be read in TGrid ANSYS Inc April 15 2008 6 1 Mesh Files 6 1 5 Writing Boundary Mesh Files TGrid allows you to write a mesh file comprising specific boundary zones This is useful for large cases where you may want to mesh different parts of the mesh separately and then merge them together This allows you to avoid frequent switching between domains for such cases You can write out selected boundaries to a mesh file and then create the volume mesh for the part in a separate TGrid session You can then read the saved mesh into the previous TGrid session using the Append File s opti
417. n of the edge loop creation approach and the angle criterion The angle criteria used for creating edge loops are as follows e Fixed angle criterion This method considers the feature angle between adjacent faces when creating edge loops You can specify the minimum feature angle between adjacent faces as a parameter for edge loop creation The common edge thread between two faces will be created when the feature angle is greater than the value specified e Adaptive angle criterion This method compares the angle at the edge with the angle at neighboring edges If the relation between the angles matches the typical patterns of the angles in the neighborhood of the feature edge the edge in question is considered to be a feature edge You do not need to specify a value for the feature angle in this case The approaches available for edge loop creation are as follows e Face zone approach The edge thread is created on the entire face zone based on the specified angle criteria The face zone approach is useful when creating edge threads on common edges where two surfaces of the zone intersect each other The common edge is considered to be a feature edge when the angle value specified fixed angle criterion is less than the feature angle Alternatively the edge thread at the common edge can be created by detecting the change in the feature angle automatically adaptive angle criterion e Face seed approach The edge thread is created s
418. n panel to control XY plot and histogram displays Controls Names contains a list of the geometric objects that currently exist in the scene in cluding those that are presently invisible ANSYS Inc April 15 2008 14 39 Examining the Mesh You can specify the object or objects to be manipulated by selecting names in this list If you select more than one object at a time any operation transformation color specification etc will apply to all the selected objects You can also select objects by clicking on them in the graphics display using the mouse probe button The default is the right mouse button For information about mouse button functions see Section 14 9 Controlling the Mouse Buttons To deselect a selected object click on its name in the Names list Scene Description Names g Geometry Attributes Scene Composition tp e a eaters outlet Group let plac lien inte Display Frame Options bottom Transform fse Vais PRBUBSS fhos Vep Delete Geometry Geometry Attributes contains information about the type of the selected geometric object and push buttons which open panels for modifying the object Type reports the type of the selected object Possible types include grid and Group This information is especially helpful when you need to distinguish two or more objects with the same name When more than one object is selected the type
419. n select one or more zones to create a group The Face Zones list is replaced by the Edge Zones list when Edges is selected in the Options group box Face Zone Groups contains a list of the default face zone types and user defined groups If you select a zone type group from this list all zones of that type group will be selected in the Face Zones list You can also select multiple types to select all the zones of different types e g inlet and outlet The Face Zone Groups list is replaced by the Edge Zone Groups list when Edges is selected in the Options group box Face Groups contains a list of all existing face groups The Face Groups list is replaced by the Edge Groups list when Edges is selected in the Options group box A global group containing all the respective zones is created by default The global group cannot be updated or deleted 7 73 ANSYS Inc April 15 2008 Manipulating the Boundary Mesh Activate activates the zone group selected in the Face Groups or Edge Groups selection list Only the zones from the active group will be available in all TGrid panels You need to activate the global group to have all the zones available in the TGrid panels Update updates the selected group according to the current selections in the Face Zones or Edge Zones selection list Delete deletes the selected group from the Face Groups or Edge Groups list New opens the Group Name panel see Section 7 12 1 The Group Nam
420. n the TGrid console mesh modify list skewed cells lists the cells which are within the specified skew ness limits mesh modify mesh node introduces a new node into the existing mesh mesh modify mesh nodes on zone inserts the nodes associated with a particular face or node thread into the volume mesh For a specified face thread TGrid will delete the faces before introducing the nodes into the mesh mesh modify neighboring skew reports the skewness of all cells using the specified node mesh modify refine cell refines the cells specifed mesh modify select entity selects the specified entity mesh modify smooth node performs Laplace smoothing on the specified nodes 13 18 ANSYS Inc April 15 2008 13 7 Moving Nodes 13 7 Moving Nodes Highly skewed meshes can be improved by moving the nodes of the cells Moving nodes manually is a time consuming process TGrid has a tool which automates the node move ment process for improving the mesh quality You can specify quality improvement based on the skewness triangular tetrahedral elements or the warp quadrilateral elements You can also choose between the automatic correction process and the semi automatic correction process for the skewness based correction 13 7 1 Automatic Correction The automatic correction allows you to improve all the cells in the selected fluid zone based on the specified criteria You can improve the cells based on the skewness or the wa
421. n the TGrid console Limits reports the minimum and maximum face area for the zone s selected in the Tri Boundary Zones selection list Apply performs the operation selected in the Options drop down list Draw displays the selected zones in the graphics window 7 4 5 Text Commands for Improving Boundary Surfaces The text commands available for improving boundary surfaces are boundary improve collapse bad faces allows you to collapse the short edge of faces having a high aspect ratio or skewness in the specified face zone s boundary improve improve allows you to improve the boundary surface quality using skewness size change aspect ratio or area as the quality measure ANSYS Inc April 15 2008 7 35 Manipulating the Boundary Mesh boundary improve smooth allows you to improve the boundary surface using smooth ing boundary improve swap allows you to improve the boundary surface using edge swap ping 7 5 Refining the Boundary Mesh To use refinement regions for local refinement in some portion of the domain e g to obtain a high mesh resolution in the wake of an automobile you may refine the associated boundary zones as well When you perform the local refinement the boundary faces that border the refinement region will not be refined It is therefore possible that you will have a jump in face size where a small cell touches a large boundary face To improve the smoothness of the mesh use the Refine Bounda
422. n the descending order of their quality When Mark is selected the next marked face will be displayed in the graphics window Reset allows you to reset the quality values displayed in the graphics window when Quality Limit is selected When Mark is selected TGrid will reset to the first marked face When you click this button only the First button will be accessible Click First and then Next to start viewing faces in descending order of their quality Skew Report Zone contains a drop down list to choose the particular zone in the ge ometry for which you want to find the skewed cells This option allows you to find the skewed cells only in the zone of your interest instead of finding it for the whole mesh Redisplay forces a redisplay of the mesh This button is only available when Auto Redisplay is disabled If the mesh being displayed is very large or the graphics performance of your computer is slow disabling Auto Redisplay can greatly improve performance You can then click this button whenever you want to see the updated mesh For details about using the Modify Boundary panel see Section 7 3 1 Using the Modify Boundary Panel ANSYS Inc April 15 2008 7 27 Manipulating the Boundary Mesh The Create Boundary Zone Panel The Create Boundary Zone panel will appear automatically when you create a new face zone Section 7 3 1 Using the Modify Boundary Panel You can specify the name and type of the new zone in this
423. n the zone having feature angle greater than the specified Feature Angle are retained This option is useful for preserving the shape of the intersecting boundary zones The default value of Feature Angle is 40 however a value in the range of 10 50 degrees is recommended A large value may distort the shape of the intersecting boundary zones Mark highlights the triangles in the neighborhood of the line of intersection This helps you to ensure whether or not all faces along the line of intersection are considered for intersection This also helps you to be sure about the specified tolerance value Apply executes the operation selected in the Operations list Absolute Tolerance toggles the use of absolute tolerance Refine toggles the refinement of the intersecting face zones after the intersection is performed This option is useful for intersecting surfaces having a discrepancy in mesh sizes Enabling Refine yields a smoother mesh having better gradation i For complicated geometries with highly skewed elements the refinement can make overall mesh quality bad Separate allows you to separate the intersecting zones at the edge loop of the intersec tion while performing any one of the three intersection operations The intersecting zones are separated based on the edge loop criteria For example the mesh shown in Figure 7 2 9 has two boundary zones wall 1 and wall 2 Enabling the Separate option while intersecting these boundary zones r
424. n yes foreground 2 yes orange o 0 5 multi yes yellow yes foreground 2 yes magenta o 0 5 unmeshed no yes orange 2 yes red o 0 5 unused no yes green 2 yes green x 0 5 mark yes magenta yes yellow 2 yes magenta o 0 5 tag yes magenta yes yellow 2 yes magenta o 0 5 face size yes blue yes foreground 1 no cell size no yes red 1 no face quality yes red yes foreground 1 no cell quality no yes red 1 no Table 14 1 1 Default Style Attributes 14 1 8 Text Commands for Style Attributes The following text interface commands perform functions similar to those in the Style Attributes panel display set grid node size sets the node symbol scaling factor display set grid node symbol specifies the node symbol display set styles contains commands for setting the display style for the different types of nodes and faces that can be displayed 14 2 Checking Face Distribution When checking the quality of the mesh you may find it useful to look at a histogram of boundary face quality You can generate such a plot or report using the Face Distribution panel or the associated text commands This feature is available only in 3D When a histogram plot is displayed in the graphics window you can use any of the mouse buttons to add text annotations to the plot See Sections 14 9 and 14 11 for more information about using the mouse buttons and annotation features ANSY
425. ndary faces will be removed using the Tri Tet Improve panel see Section 13 5 The Tri Tet Improve Panel To check the skewness of boundary cells use the Report Boundary Cell Limits panel or the associated text commands 15 4 1 The Report Boundary Cell Limits Panel The Report Boundary Cell Limits panel reports the quality of cells containing a specified number of boundary faces The minimum and maximum skewness aspect ratio or size change values are reported Though this panel can be used to check all quality measures and all boundary cell shapes it is used primarily to check the skewness of triangular and tetrahedral boundary cells EA If you have used domains to generate the mesh or group zones for report ing as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces the report will apply only to the active domain Report gt Boundary Cell Limits Report Boundary Cell Limits Boundary Number Minimum 4 2 536493e 06 v Nodes Faces Maximum 0 6508578 Quality Measure Compute Close Help Controls Boundary allows you to specify whether you want to set the number of boundary nodes or faces Select Nodes or Faces and specify the number of nodes faces in the Number field To obtain information about cells that touch the boundary but do not actually have any boundary faces specify the number of boundary nodes instead of the number of boundary fa
426. nds on your system configuration Ea The window dump will capture the window exactly as it is displayed in cluding the resolution colors transparency etc For this reason all of the inputs that control these characteristics are disabled in the Hardcopy panel when you enable the Window Dump format If you are using an 8 bit graphics display you might want to use one of the built in raster drivers e g TIFF to generate higher quality 24 bit color output rather than dumping the 8 bit window On the other hand if your hardware supports transparency a window dump is the only method to generate a hardcopy with transparent surfaces If you save any other type of hardcopy file the transparency effects will not be captured in the resulting image Previewing the Hardcopy Image Before saving a hardcopy file you can preview the image to be saved Click Preview to apply the the current settings to the active graphics window so that you can see the effects of different options interactively before saving the hardcopy ANSYS Inc April 15 2008 6 21 File Types 6 9 2 The Hardcopy Panel The Hardcopy panel allows you to set graphics hardcopy parameters and save hardcopy files of graphics windows Hardcopy Format Coloring File Type Resolution 4 v EPS wv Color Raster DPI 75 wv JPEG Gray Scale v Vector Heigh 72 amp v PPM v Monochrome EE e y PostScript v TIFF v PNG Options v VRML I Landscape Orienta
427. ne the camera Position Target Up Vector and Field and X Y and Z fields in which you can define the coordinates or field distances for the parameter selected in the drop down list Figure 14 6 1 illustrates the definition of the camera by these parameters view plane Se up vector 4 position l i target x field y field Figure 14 6 1 Camera Definition Projection contains a drop down list that allows you to select a Perspective or Ortho graphic view Dial allows you to rotate the graphics display respectively e The dial controls rotation about the axis at the center of and perpendicular to the screen Sliders allows you to scale the graphics display respectively e The slider on the scale to the left of the dial rotates the display about the horizontal axis at the center of the screen e The slider on the scale below the dial rotates the display about the vertical axis at the center of the screen e The slider on the scale to the right of the dial zooms in or out in the display i When using the sliders and dial to manipulate the view select All in the Display Options panel see Section 14 5 1 The Display Options Panel so that you can watch the display move interactively while you move the slider or the dial indicator ANSYS Inc April 15 2008 14 35 Examining the Mesh 14 6 5 Text Commands for Modifying the View Text interface commands with the same functionality as the controls in
428. nel during the wrapping process See Section 8 9 The Boundary Wrapper Panel for details about the use of the parameters available in the Boundary Wrapper panel The wrapping process consists of the following tasks e Examining and repairing the input geometry Section 8 3 Examining and Repairing the Input Geometry e Initializing the Cartesian grid Section 8 4 Initializing the Cartesian Grid e Creating the wrapper surface e Recovering Boundary zones and features Section 8 7 Checking the Quality of the Wrapper Surface ANSYS Inc April 15 2008 8 3 Wrapping Boundaries e Using the post wrapping improve operations Section 8 8 Post Wrapping Improve ment Operations 8 3 Examining and Repairing the Input Geometry Before performing the wrapping operation you need to examine the input geometry and repair it to some extent so that the final wrapper surface is of good quality The geometry repair operations include the following operations e Checking for duplicate nodes e Converting quad zones into tri zones e Detecting and filling the holes in the geometry Checking and Removing Duplicate Nodes 1 Read the geometry in TGrid and check for free or duplicate nodes 2 If the mesh contains free duplicate nodes delete merge them using the Merge Boundary Nodes panel before proceeding to the wrapping operation Free nodes may cause trouble during the wrapping process because the wrapper assumes each edge to be a
429. nel see Section 14 3 1 The Cell Distribution Panel This will give you an idea of the improvement required For 2D problems it is usually possible to reduce the maximum skewness to 0 4 In 3D however it is typically possible to reduce it to 0 8 0 85 for simple geometries or 0 9 0 95 for more complex geometries Step 4a Swapping and Smoothing without Refining Swapping and smoothing improve the mesh by manipulating the nodes and faces without increasing the total number of cells Refinement on the other hand improves the mesh by adding nodes which typically increases the number of cells To get the best possible mesh with the minimum number of cells perform only smoothing and swapping before refining the mesh any further Smoothing repositions interior nodes to lower the maximum skewness of the grid For swapping given n 2 nodes in dimension n there are at most two triangulations of the nodes depending on the configuration of the nodes In cases where two triangulations exist TGrid examines the two alternatives selecting the one that has the lowest maximum skewness TGrid will automatically perform smoothing and swapping to improve the mesh when the Improve Mesh option is enabled in the Refinement tab of the Tri Tet panel 11 8 ANSYS Inc April 15 2008 11 2 Manually Creating a Tri or Tet Mesh Refer to Sections 13 1 and 13 2 for details on improving the mesh by swapping and smoothing Step 4b Further Refinement Y
430. ng face zones of the selected entity Ctrl h Prints the available hot keys in the TGrid console window Ctrl Finds the centroid of the selected face Ctrl n Selects node as the Filter in the Modify Boundary panel Ctrl o Performs the rezone operation on the selected zone Ctrl p Projects selected nodes onto the selected zones Ctrl s Allows you to set a plane or line on which you can project the nodes Set the plane or line either by selecting nodes or by selecting positions in the mesh Ctrl u Clears the marked faces selected Ctrl v Allows you to move the nodes from one position to another Ctrl w Deletes the selected entity without confirming Ctrl x Selects position as the Filter in the Modify Boundary panel Ctrl z Selects zone as the Filter in the Modify Boundary panel Ctrl A Performs the collapse operation on the selected nodes edges or faces Ctrl Displays the previous view in the graphics window Use Esc key to deselect the previously selected entity You can also use the Ctrl shortcut key ANSYS Inc April 15 2008 C 3 Shortcut Keys C 4 ANSYS Inc April 15 2008 Appendix D Query Functions When performing a series of operations in TGrid you may want to list all the zones of a particular type group or containing a particular text string TGrid allows you to query zones through the TUI based on a regular expression and a specified variable You can identi
431. ng prisms and modify the prism parameters Refer to Sections 10 5 10 12 for details on modifying the prism generation parameters to create a better mesh 10 4 ANSYS Inc April 15 2008 10 3 Prism Meshing Options 10 3 Prism Meshing Options This section describes various the options available in TGrid while creating a prism mesh for the domain 10 3 1 Growing Prisms Simultaneously from Multiple Zones You can select multiple face zones for simultaneously growing prism layers If the face zones are connected the prisms grown will also be connected A single zone of prism cells and a single zone of cap faces will be created for each set of simultaneously grown layers To retain the individual prism cell zones and cap face zones enable Grow Individually in the Prisms Growth Options panel opened by clicking the Growth Options button TGrid allows you to grow prisms from multiple zones with the same or different growth parameters e To use the same growth parameters for all zones follow the steps in Section 10 2 Pro cedure for Generating Prisms In this case the same number of layers are grown from all zones and all other parameters growth method offset method direction method etc will remain the same e To use different growth parameters for different zones apply different growth meth ods offset methods first height and other growth parameters as required for the growth method selected individually for each
432. nimum and maximum limits of the surface mesh in X direction Y Min Y Max allows you to specify the minimum and maximum limits of the surface mesh in Y direction Z Min Z Max allows you to specify the minimum and maximum limits of the surface mesh in Z direction Axial Location allows you to specify the location of the surface mesh along the selected axis This parameter is available only if you have selected Axis Direction under Options Planar Points contains the options to specify coordinate points that forms a planar surface X Pos Y Pos Z Pos specifies X Y and Z locations of the planar points P1 P2 P3 specifies three planar points Select Points allows you to select planar points using mouse When you click on this button a Working dialog box opens up prompting you to select three points to define a plane After you select the three points this dialog box closes automatically and the Planar Points fields gets updated i Make sure you have displayed the geometry in the graphics window before clicking Select Points button Mesh Size allows you to specify the size of the triangular cells that you want to create for the plane surface ANSYS Inc April 15 2008 7 85 Manipulating the Boundary Mesh Scale displays a rectangular surface having diagonal sizes 1 25 times of the existing planar surface that you have created in the graphics window Select the plane surface that you have created in the Face Zone
433. ning free edges is non manifold A face containing a free edge In 3D a node that is on a free edge In 2D a node used by only one boundary face A mesh containing free nodes is non manifold The preprocessor for geometry modeling and mesh generation The mesh of all the boundary nodes in which all of the boundary faces are present A face that is not part of the boundary A face that is inside the domain A node that is not on a boundary A node that is inside the domain A node that is not used by any boundary faces A cell in which solution equations are to be solved Live cells can represent either fluid or solid material Glo 3 Glossary Mach Number Manifold Multiply Connected Node Node Radius Periodic Periodic Shadow Refinement Region Scheme Glo 4 Mach Number is defined as the ratio of velocity of a fluid to the local velocity of sound in the medium A manifold boundary mesh is a mesh in which each edge is shared by two and only two boundary faces A condition on the boundary where more than two faces share a common edge A boundary mesh containing multiply connected edges is non manifold A zero dimensional entity defined by a coordinate location Also a 0 simplex or vertex For boundary nodes the average distance to neighboring boundary nodes For interior nodes the distance weighted average of the surrounding nodes A periodic boundary can be used to reduce a geometr
434. non fluid type allows you to set the cell zone type for the non fluid cell zones mesh controls hexcore only hexcore allows you to create only the hexcore mesh and activates the tet mesh domain without tet mesh generation This option is disabled by default mesh hexcore controls peel layers specifies the distance for the hexcore interface to peel back from the boundary The default value is 0 The higher the value of peel layer the greater the distance between the hexcore interface and the boundary mesh hexcore controls outer box zones allows you to specify the zones comprising the bounding box when using the Grow Upto Boundaries option mesh hexcore controls post relative island count specifies the threshold cell count relative to the cell count of the largest zone containing hex cells for islands to be deleted after generating the hexcore mesh using the Only Hexcore option The default value is 10 mesh hexcore controls smooth interface enables smoothing of the hexcore inter face mesh hexcore controls smooth iterations sets the number of smoothing iterations on the hexcore mesh hexcore controls smooth relaxation sets the smoothing under relaxation on the hexcore interface mesh hexcore create allows you to create the hexcore mesh according to the specified parameters mesh hexcore local regions activate allows you to activate the specified local re gion s for refinement mesh hexcore local regions deactivat
435. ns available for sliver removal are Smoothing Boundary Slivers This operation involves smoothing nodes on sliver cells having atleast one node on the boundary During smoothing the nodes will be repositioned so long as the skewness of the surrounding cells is improved The nodes on features will also be smoothed but will not be projected on to the original geometry However nodes at branch points more than two feature edges at the node and end points one feature edge at the node will be fixed The nodes will be smoothed until the skewness value is less than the specified value The default values for the skewness threshold minimum dihedral angle between boundary faces and feature angle are 0 985 10 and 30 respectively Smoothing Interior Slivers This operation involves smoothing non boundary nodes on sliver cells having skewness greater than the specified threshold value The default value for the skewness threshold is 0 985 ANSYS Inc April 15 2008 13 7 Improving the Mesh Swapping Boundary Slivers A flat boundary cell containing two boundary faces can be removed by moving the bound ary to exclude the cell from the zone in which it is located effecting a minor change in the geometry However if there is another live zone on the other side of the boundary this operation will result in the cell being moved to the other zone In such cases e g conjugate heat transfer problems you can decide which live zone is l
436. ntrols improve check allowable skew allows you to check the skew ness of the prism cap for every layer nesh prism controls improve check size enables the checking of cell size during the generation of each prism layer TGrid will report an error if zero area prism cells are generated and prism layer growth will be stopped When the check size option is disabled the zero area prism cells generated can be removed during the improvement smoothing operations performed at the end of the prism generation procedure mesh prism controls improve edge smooth enables disables local smoothing of nodes of the longest edges of skewed faces 10 34 ANSYS Inc April 15 2008 10 11 Text Interface for Generating Prisms nesh prism controls improve edge smooth angle specifies the maximum allowable angle between the normals of adjacent cap faces for skewness driven edge smooth ing mesh prism controls improve edge swap enables disables edge swapping to de crease the skewness of highly skewed faces mnesh prism controls improve edge swap base angle specifies the maximum allow able angle between a pair of base face normals for skewness driven edge swapping nesh prism controls improve edge swap cap angle specifies the maximum allow able angle between a pair of cap face normals for skewness driven edge swapping nesh prism controls improve face smooth allows you to enable face driven smooth ing to improve skewness nesh prism
437. nzip is imported into TGrid via an operating system pipe Reading gunzip flow msh gz You can also read a compressed file using the text interface by entering the file name First TGrid attempts to open a file with the input name If it cannot find a file with that name it attempts to locate files with default suffixes and extensions appended to the name For example if you enter the name file name TGrid traverses the following list until it finds an existing file e file name e file name gz e file name Z e file name suffix e file name suffix gz e file name suffix Z where suffix is a common extension to the file such as cas or msh TGrid reports an error if it fails to find an existing file with one of these names Note For Windows systems only files that were compressed with gzip i e files with a gz extension can be read Files that were compressed using compress cannot be read into TGrid on a Windows machine 6 6 ANSYS Inc April 15 2008 6 3 Reading Scheme Source Files 6 2 2 Writing Compressed Files You can write a compressed file using the text interface by entering the file name with the appropriate extension For example if you are prompted for a file name and you enter a file name with a gz extension a compressed file will be written The following TUI command can be used file gt wm mesh file name flow gz Writing gzip cfv gt flow msh gz
438. o Mesh panel 205 Auto Node Move panel 298 a Figure 3 6 2 User s Guide Index 3 6 3 Accessing the Other Manuals In addition to the User s Guide you can access other manuals through the on line help You can also access the User s Guide in Adobe Acrobat PDF format which is recom mended if you want to print an entire chapter or a long section Select the More Docu mentation menu item in the Help pull down menu to see other TGrid manuals Help More Documentation ANSYS Inc April 15 2008 3 21 Graphical User Interface When you select this item the web browser will open to the TGrid documentation home page 3 6 4 Using Help You can obtain information about using on line help by selecting the Using Help menu item in the Help pull down menu Help Using Help When you select this item the web browser will open to the beginning of this section 3 6 5 Accessing the User Service Center Web Site You can access the Fluent Users Service Center USC web site by selecting the User Services Center menu item in the Help pull down menu Help User Services Center TGrid will direct your web browser to the USC web address Note To link to the USC on UNIX platforms first install the contents of the TGrid Documentation CD which contains the files necessary to launch the browser so that you can automatically view the appropriate web pages 3 6 6 Acc
439. o limits or the range of change in cell size You can check cell size and quality limits using the Report Cell Limits panel or the associated text commands 15 3 1 The Report Cell Limits Panel The Report Cell Limits panel reports the size or quality limits of the selected cell zones The minimum maximum and average values are reported If you used domains to generate the mesh or group zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces the report will apply only to the active domain Report Cell Limits Report Cell Limits Options Cell Zones Ba Quality flud 13 000 v Size Quality Measure Minimum 2 5365e 06 Maximum me 0 7495732 eds ES dead Average fluid 0 2963164 solid Compute Close Help ANSYS Inc April 15 2008 15 5 Reporting Mesh Statistics Controls Options specifies either Quality or Size to be computed Skewness is the default mea sure of quality Quality Measure opens the Quality Measure panel see Section 15 5 2 The Quality Measure Panel in which you can select the measure of quality to be reported skewness aspect ratio change in size etc Minimum Maximum Average report the computed values for size or quality Cell Zones contains a list from which you can select the zones of interest Cell Zone Groups contains a list of cell zone types If you select a zone type from this list e g flui
440. o write a Prep7 file within ARIES the following criteria must be met e Name the part in the Geom module e Create a material or read one from the mat_lib in the Material module To create a material you must supply density Poisson s ratio and elastic modulus e Generate face pressures for the surface in the Environment module Later when you write the Prep7 file these will be transferred to the individual elements e Generate at least one restraint in the Environment module e Set the element type to be STIF63 triangular shell elements and specify some finite thickness e Write the Prep7 file making sure you let it automatically assign the pressure to the elements The Prep7 file can be filtered using the ARIES or Fluent Inc filter whichever you find most convenient A 3 6 NASTRAN Files For NASTRAN surface meshes the filter reads triangular and quadrilateral linear elements that define the boundaries of the solution domain For volume meshes the filter reads a 2D or 3D mesh All boundary zones will be considered wall zones you can set the appropriate boundary types in TGrid or in the solver See Section A 3 1 Using the fe2ram Filter to Convert Files for information about using the fe2ram grid filter Recognized NASTRAN Bulk Data Entries The following NASTRAN bulk entries are recognized by the grid filter GRID single precision node coordinates GRID double precision node coordinates CBAR line elements CTETRA
441. object more prominently than the others scale its size All these capabilities are available in the Transformations panel ANSYS Inc April 15 2008 14 43 Examining the Mesh The Transformations Panel You can use the Transformations panel to translate rotate or scale individual objects in the graphics display To open this panel click on the Transform push button in the Scene Description panel see Section 14 8 1 The Scene Description Panel 14 44 Transformations Geometry Name Group _ Meridional Translate Rotate by Rotate about Scale Controls Geometry Name displays the name of the object you selected for modification in the Scene Description panel see Section 14 8 1 The Scene Description Panel Meridional enables the display of the meridional view This option is especially useful in turbomachinery applications Translate contains X Y and Z real number fields in which you can enter the distance by which to translate the selected object in each direction Translations are not cumulative so you can easily return to a known state To return to the original position enter 0 in all three real number fields Rotate By contains X Y and Z integer number fields in which you can enter the number of degrees by which to rotate the selected object about each axis You can enter any value between 360 and 360 Rotations are not cumulative so you can easily return to a known state To return to t
442. odes ANSYS Inc April 15 2008 Manipulating the Boundary Mesh Controls Compare With contain control parameters used for merging duplicate nodes using the Merge button When searching for duplicate nodes TGrid will compare node A defined in the Compare group box with node B defined in the With group box Only Free Nodes allows you to limit the search to free nodes e If you enable Only Free Nodes only in the Compare group box TGrid will compare node A with node B only if node A is a free node e If you enable Only Free Nodes only in the With group box TGrid will compare node A with node B only if node B is a free node e If you enable Only Free Nodes in both the Compare and With group boxes the default setting TGrid will compare the two nodes only if both are free nodes If you disable this option in both group boxes TGrid will compare all nodes Since free nodes are a small subset of all nodes it is much faster to compare free nodes only with other free nodes To merge nodes that are not on a free edge disable Only Free Nodes in the Compare or With group box or in both group boxes For example if you read a hybrid mesh containing hexahedral cells and quadrilateral boundary faces and triangular boundary faces into TGrid there may be some duplicate nodes on adjacent quadrilateral and triangular boundary zones To merge them compare free nodes on both zones with all n
443. odes on both zones i e select both zones in the Compare and With group boxes and disable Only Free Nodes in one of them Boundary Face Zones is a selection list comprising all boundary zones in the domain You can limit the search for free nodes by selecting a subset of these zones By default all boundary zones are selected in both the Compare and With group boxes so node A on any boundary will be compared with node B on any boundary For example if you want to compare the nodes on only the inlet and top select inlet in the Compare group box and top in the With group box TGrid will then compare the nodes on these two boundaries according to the specification of Only Free Nodes for the selected boundary zones Selecting a subset of all boundary zones for node comparison will save time TGrid will be able to search for duplicate nodes and merge them more quickly if it does not need to check the nodes on all boundaries Tolerance specifies the tolerance for finding duplicate nodes If the position of two nodes differs by less than this Tolerance value the nodes are considered duplicate nodes and will be merged when you click the Merge button The default tolerance value is computed by dividing the shortest boundary edge by 1000 7 4 ANSYS Inc April 15 2008 7 1 Manipulating Boundary Nodes Percent of shortest connected edge length is used as an alternative to the Tolerance for determining whether two nodes w
444. of the geometry the minimum size may be reduced to a size smaller than some existing leakages These leakages can be detected automatically using the auto matic hole detection tool in TGrid The refinement of a region may result in the joining of previously separate regions through cells newly introduced by the refinement region collision While refining a region TGrid will automatically detect cells causing region collision and group them Such groups of cells will be identified as holes in the region The number of holes exposed by the current refinement will be reported in the TGrid console The following operations allow you to automatically detect holes e Refining a single region e Specifying local size function and additional zone specific sizes after initialization ANSYS Inc April 15 2008 8 11 Wrapping Boundaries e Refining local regions defined according to requirements The options for automatic detection and fixing of leaks are available in the Region tab of the Boundary Wrapper panel The Automatic selection list in the Fix Holes group box lists the potential holes for all regions The generic procedure for detecting and fixing holes leaks automatically is as follows 1 Open all holes other than the holes for the region of interest The Open operation can be used when the identified group of cells does not represent an actual hole or is not relevant in the subsequent wrapping process The regions associated
445. of the grid e There are no coordinates following The parentheses for the coordinates are not there either For example 10 0 1 245 0 2 If zone id is greater than zero it indicates the zone to which the nodes belong In such a case e first index and last index are the indices of the nodes in the zone in hexadec imal e last index in each zone must be less than or equal to the value in the declaration section e type indicates the type of nodes in the zone TGrid uses the value of types to indicate the following types Zero for virtual nodes ANSYS Inc April 15 2008 B 3 Mesh File Format One for no any type Two for boundary nodes TGrid ignores nodes of type zero and read all others but these codes write only type one e ND is an optional argument that indicates the dimensionality of the node data where ND is 2 or 3 If the number of dimensions in the grid is two as specified in the Section B 3 Dimensions or in the node header then only x and y coordinates are present on each line Example of a two dimensional grid 10 1 1 2d5 1 2 1 500000e 01 2 500000e 02 1 625000e 01 1 250000e 02 1 750000e 01 0 000000e 00 2 000000e 01 2 500000e 02 1 875000e 01 1 250000e 02 Grid connectivity is composed of integers representing pointers see Sections B 7 and B 6 hence using hexadecimal conserves space in the file and provides faster file input and output The header indices are
446. og boxes see documentation for Windows and your printer for details Page Setup opens the Page Setup panel which allows you to change attributes of the picture copied to the clipboard or to a printer 3 4 2 The Page Setup Panel To open the Page Setup panel select the Page Setup menu item in the system menu of the graphics display window Page Setup Color Clipboard Formats Color Bitmap Gray Scale DIB Bitmap Monochrome Metafile Enhanced Metafile Color Quality True Color Mapped Color C Yector f Picture Format Raster Printer Scale 90 v Options IV Landscape Orientation Printer IV Reverse Foreground Background OK Cancel Help 3 16 ANSYS Inc April 15 2008 3 4 Graphics Display Windows Controls Color allows you to specify a color or non color picture Color selects a color picture Gray Scale selects a gray scale picture Monochrome selects a black and white picture Color Quality allows you to specify the color mode used for the picture True Color creates a picture defined by RGB values This assumes that your printer or display has at least 65536 colors or unlimited colors Mapped Color creates a picture that uses a colormap This is the right choice for devices that have 256 colors Dithered Color creates a dithered picture that uses 20 colors or less Clipboard Formats allows you to choose the desired format copied to the clipboard The size o
447. ol xf cell C macro XF_CELL Codes FLUENT TGrid Status required The declaration section for cells is similar to that for nodes 12 zone id first index last index type element type When zone id is zero it indicates that it is a declaration of the total number of cells If last index is zero then there are no cells in the grid This is useful when the file contains only a surface mesh to alert the solvers that it cannot be used The type is ignored in a declaration section and is usually given as zero while the element type is ignored completely For example 12 0 1 3e3 0 states that there are 3e3 hexadecimal 995 cells in the grid This declaration section is required and must precede the regular cell sections The element type in a regular cell section header indicates the type of cells in the section as follows element type description nodes cell faces cell 0 mixed 1 triangular 3 3 2 tetrahedral 4 4 3 quadrilateral 4 4 4 hexahedral 8 6 5 pyramid 5 5 6 wedge 6 5 Regular cell sections have no body but they have a header of the same format where first index and last index indicate the range for the particular zone type indicates whether the cell zone is an active zone solid or fluid or inactive zone currently only parent cells resulting from hanging node adaption Active zones are represented with type 1 while inactive zones are represented with type 32 A type of zero indicates a dead zone and wil
448. olume mesh Refer to Sections 7 1 and 7 2 for details Modify the boundary mesh if required when improving a region in the volume mesh Refer to Chapter 7 Ma nipulating the Boundary Mesh for details on the various mesh improvement options 8 Activate the cavity domain and create the volume mesh as appropriate 9 Activate the global domain and delete the boundary zone s which are no longer required Merge the cavity domain with the parent domain using the command mesh cavity merge cavity During the merging operation the cavity cell zone s will be merged with the cell zone s in the parent domain The wall boundaries extracted from the interior zones will be converted to interior type and merged with the corresponding zone s in the parent domain Other boundary zones included in the cavity domain will be merged with the parent face zones ANSYS Inc April 15 2008 13 25 Improving the Mesh 13 8 1 The Cavity Remesh Panel The Cavity Remesh panel contains options for creating a cavity in an existing volume mesh Cavity Remesh Remove Boundary Zones Add Boundary Zones j car ground inlet mirror mirror 28 outlet outlet side outlet side outlet top outlet top 1 Create Face Group Bounding Box Scale 1 5 Compute Center Length x 0 3715596 x 9 075 X deg 9 Y 0 4851047 v 0 075 deg o z 0 4646883 z 0 2194692 Z deg 0 Controls Remove Boundary Zones contains a selection l
449. on click Apply in the Zone Specific Growth group box for TGrid to retain the growth parameters on specific zones in memory The Prisms option in the Auto Mesh panel will be visible only after applying zone specific growth ANSYS Inc April 15 2008 10 31 Generating Prisms Draw displays the boundary zone s selected in the Boundary Zones list All current settings in the Display Grid panel see Section 14 1 3 The Display Grid Panel will be reflected in the resulting grid display You may find it useful to enable the display of normal vectors so that you can easily determine the normal direction s of the selected boundary zone s 10 10 1 The Prisms Growth Options Panel The Prisms Growth Options panel allows you to specify the parameters needed for detect ing proximity collision retaining the first layer offset and growing prisms individually from multiple zones Prisms Growth Options General Options Remove Invalid Layer _4 Grow Individually _4 Ignore Invalid Normals Proximity Options F Allow Shrinkage i Keep First Layer Offsets Gap Factor 9 5 1 Allow Ignore bifax Shyink factay Max Aspect Ratio Controls General Options contains additional options for prism growth Remove Invalid Layer allows you to retain the valid prism layers grown before TGrid reports prism layer failure Grow Individually indicates whether individual prism cell zones and prism cap face zones
450. on 10 2 Procedure for Generating Prisms and repeat the process incorporating the appropriate corrections The most common prism meshing problems are e Orientation e Retriangulation failures e Too many or too few nodes or unknown face combinations ANSYS Inc April 15 2008 10 39 Generating Prisms e Negative volumes left handed faces or high skewness e Growing too far e Large jumps in prism height at the edges of layers Orientation If the faces of the boundary zone from which you are building prisms are not all ori ented in the same direction Figure 7 13 1 TGrid will stop the prism generation process immediately and will alert you that it has reoriented the faces Solution In this case do the following 1 Check the normal direction vectors on the boundary zone to ensure that they have not been oriented to face in the wrong direction 2 Follow the instructions in step 4 in Section 10 2 Procedure for Generating Prisms to check and if necessary correct flip the normal direction 3 Click Create to restart the prism generation process In this case there is no need to reread the mesh because TGrid stops before it actually creates any prism layers Retriangulation Failures If nodes where adjacent zones meet the zones from which prisms are growing are duplicated TGrid will be unaware that the zones are connected It will ignore such zones when considering nodes for projection and hence retrian
451. on and merge the part with the rest of the mesh To write a mesh file comprising selected boundaries do either of the following e Use the File Write Boundaries menu item to invoke the Write Boundaries panel see Section 6 1 5 The Write Boundaries Panel and specify the boundaries to be written e Use the file write boundaries text command and specify the name of the file to be written and the boundaries to be written The Write Boundaries Panel The Write Boundaries panel allows you to specify the boundaries to be written to a mesh file Write Boundaries Boundary Zones 5 5 Boundary Zone Groups far field geometry a Le Controls Boundary Zones contains a list of the boundary zones available Boundary Zone Groups contains a list of the boundary zone groups and user defined groups available ANSYS Inc April 15 2008 6 5 File Types 6 2 Compressed Files TGrid allows you to read and write compressed files Use the Select File dialog box to read or write the files that have been compressed using compress or gzip 6 2 1 Reading Compressed Files If you select a compressed file with a Z extension TGrid will automatically invoke zcat to import the file If you select a compressed file with a gz extension TGrid will invoke gunzip to import the file For example if you select a file named flow msh gz TGrid will report the following message indicating that the result of the gu
452. on in TGrid allows you to avoid the intersection of prism layers by adjusting the height of the prism layers in closely placed zones Fig ure 10 3 4 shows the use of this option to avoid intersection of the prism layers by ad justing the prism layer height A value of n for Gap Factor implies that a gap equal to n times the maximum base edge length at the node in question will be maintained Hence a value of 1 implies that the gap maintained is equal to the maximum base edge length at the node considered i Offset heights are scaled only in the regions where the intersection of prism layers takes place For the remaining regions the prisms are created ac cording to the specified parameters You can also ignore prisms regions of close proximity during prism generation The area of proximity will be determined based on the shrink factor specified Prism layers will be grown from the remaining geometry according to the specified parameters ANSYS Inc April 15 2008 10 7 Generating Prisms colliding prism layers Figure 10 3 3 Collision of Prism Layers adjusted prism layers Figure 10 3 4 Prism Layers Shrunk to Avoid Collision 10 8 ANSYS Inc April 15 2008 10 3 Prism Meshing Options Figure 10 3 5 shows a portion of the geometry where the region of proximity in a sharp corner has been ignored while creating prisms prisms ignored in region of proximity Figure 10 3 5 Ignoring Areas of Proximity
453. only when the two triangles form a angle close to planar and the swapped configuration gives better skewed cells To perform swapping on the wrapper surface do the following 1 Select the wrapper surface in the Tri Boundary Zones selection list 2 Select Post Wrap in the Options drop down list and Swap in the Sub Options list 3 Specify an appropriate value for Max Angle The maximum angle specifies the maximum angle between two adjacent face nor mals This restriction prevents the loss of sharp edges in the geometry while swap ping wrapper surface 8 26 ANSYS Inc April 15 2008 8 8 Post Wrapping Improvement Operations 4 Specify an appropriate value for Max Skew All the faces having a skewness value greater than the specified value will be swapped 5 Click Apply Improving the Quality This Improve operation allows you to further improve the quality of the wrapper surface To improve the wrapper surface do the following 1 Select the wrapper surface in the Tri Boundary Zones selection list 2 Select Post Wrap in the Options drop down list and Improve in the Sub Options list 3 Select the appropriate option from the Quality Measure drop down list 4 Specify the number of attempts to improve the wrapper surface quality in the Iteration field 5 Specify an appropriate value for Max Angle The maximum angle is the maximum allowable angle between two adjacent face normals This restriction prevents the los
454. ons Cell Size Range Cell Zones Cell Zone Groups HE Quality Measure Options allows you to select one or more of the following options ANSYS Inc April 15 2008 14 7 Examining the Mesh All draws all cells in the selected cell zones colored by their zone type Select one or more zones from the Cell Zones list for any to be displayed Size draws cells within the size range indicated by the Cell Size Range limits Quality draws cells within the quality range indicated by the Cell Quality Range limits The default measure of quality is skewness but you can use the Quality Measure panel see Section 15 5 2 The Quality Measure Panel to specify aspect ratio or change in size instead Cell Size Range limits the cells displayed to those having a size within the spec ified range To specify a cell size range enable Size in the Options group box set the appropriate Minimum and Maximum values and click Display or Apply Minimum sets the minimum value for the size range in the physical dimen sions of the mesh This value should be less than the Maximum value Maximum sets the maximum value for the skewness range in the physical dimensions of the mesh This value should be greater than the Minimum value Cell Quality Range limits the cells displayed to those with a quality measure value skewness by default within the specified range To specify the cell quality range enable Quality in the Options
455. ons Panel for details By default the Max Length is the same as the Default Length If the resulting Cartesian grid is very fine you can coarsen it at a later stage Cell lengths for each Level are determined relative to the Default Length For example if the Default Length is 76 46942 then the first Level will have a cell length of 76 46942 2 the second will have a cell length of 76 46942 2 and so on 4 Specify the Zone Specific Size To have a finer or coarser mesh for a particular boundary zone in the domain you can manage the cell size by using the parameters in the Zone Specific Size group boz This option creates a Cartesian grid of the specified length throughout the selected boundary zone a Select the zone s for which you want to specify a local cell length according to your requirement from the Tri Boundary Zones selection list You can specify the Zone Specific Size in terms of Level only b Increase or decrease the Level as required The cell length for each Level will be displayed in the Length boz c Click Apply to apply the value of the Length specified in the Zone Specific Size group box to the selected boundary zone s d Click Clear to clear the previously saved size e Click List to display the zone s and corresponding size s applied to them Fee Bh x Click Select to select the boundary zones of the selected Level in the Tri Bound ary Zones list Click Deselect to deselect them 5
456. oothing 13 2 large jumps in prism height 10 42 left handed faces 10 41 13 37 14 6 lights 14 36 Lights panel 14 36 list drop down 3 14 multiple selection 3 13 single selection 3 12 local refinement 7 35 11 13 log files 6 8 magnifying the display 14 46 Make Periodic Boundaries panel 7 90 Manage Cell Zones panel 13 28 Bib 8 Manage Face Zones panel 7 74 manifold 14 6 manipulating boundary nodes 7 2 manipulating cell zones 13 26 manual access 1 5 using the UTM 1 manual meshing 11 6 maximum cell length 12 6 menu bar 3 3 Merge Boundary Nodes panel 7 2 merging boundary zones 7 75 cell zones 13 30 duplicate nodes 7 3 7 16 mesh append 6 3 automatic tri tet generation 11 2 checking 13 37 clearing 13 37 display 14 2 domains 11 1 13 33 E 5 file format B 1 files for FLUENT 6 4 from CAD packages 6 11 importing 6 11 reading and writing 6 1 reading multiple 3 7 6 2 6 3 writing 6 4 find worst face 7 20 information 15 15 orthogonality 10 10 quality 15 8 resolution 15 9 size 15 1 smoothing nodes 13 2 surface repair 11 6 write boundaries 6 5 mesh files writing 6 4 mesh generation 9 1 ANSYS Inc April 15 2008 Index automatic hexcore 12 1 hybrid meshes 11 5 basic steps 2 1 hexcore 12 1 hybrid 9 2 9 3 9 5 9 6 13 33 viscous 9 2 zonal 9 3 nonconformal 9 8 prisms 10 1 pyramids 9 14 strategies 9 1 tri tet 9 3 9 6 11 1 automatic 11 2
457. or example will limit each adjustment to 10 of the computed height Fill Cap specifies that the space between the pyramids will be automatically filled with tetrahedra This option is enabled by default since filling the pyramid cap with tetrahedra makes it easy to initialize the tetrahedral mesh based on these faces Face Angle specifies the dihedral angle between adjacent pyramid faces for which tetra hedral cells should be created when the Fill Cap option is on The default value of 120 is acceptable for most cases With a larger value for Face Angle TGrid will create more tetrahedral cells in the pyramid cap With a smaller value fewer tetrahedral cells will be created Boundary Zones contains a list from which you can select the zone s to be operated on Boundary Zone Groups contains a list of boundary zone types If you select a boundary type from this list e g inlet all boundary zones of that type for this example all pressure inlet and velocity inlet boundaries will be selected in the Boundary Zones list This allows you to easily select all boundary zones of a certain type without having to select each zone individually You can select multiple boundary types in the Boundary Zone Groups list to select all zones of several different types e g inlet and outlet Create creates the pyramids you have defined Draw displays the boundary zone s selected in the Boundary Zones list All current settings in the Displ
458. ording to the specified parameters Apply applies the specified parameters to the zones selected Draw displays the zones selected in the Boundary Zones selection list in the graphics window ANSYS Inc April 15 2008 9 23 Creating a Mesh 9 4 2 Text Interface for Creating a Non Conformal Interface The text commands for creating a non conformal interface are as follows mesh non conformals controls enable toggles the creation of a non conformal in terface mesh non conformals controls retri method specifies the method to be used for retriangulating the quad faces on the non conformal zones prism remeshes all the quad zones named prism side n quad split splits the quad faces diagonally into tri faces remesh remeshes all the quad faces based on the edge and surface feature angle specified mesh non conformals create creates the non conformal interface on the specified face zone s using the specified retriangulation method 9 5 Creating a Heat Exchanger Zone Many engineering systems including power plants climate control and engine cooling systems typically contain heat exchangers However for most engineering problems it is impractical to model individual fins and tubes of the heat exchanger core TGrid allows you to create a heat exchanger volume mesh using the Mesh Create Heat Exchanger menu item The heat exchanger mesh in TGrid comprises prisms generated from a quad split surface mesh You need to s
459. ormat For example O Variables 37 relax mass flow 1 default coefficient default method 0 B 2 Header Index 1 Scheme symbol xf header C macro XF HEADER Codes FLUENT TGrid Status optional Header sections appear anywhere in the file except within other sections Although it can appear anywhere it is typically one of the first sections in the file It appear as 1 TGrid ND 3 5 1 where N is 2 or 3 The purpose of this section is to identify the program that wrote the file Additional header sections indicate other programs that may have been used in generating the file and thus provide a history mechanism showing where the file came from and how it was processed B 3 Dimensions Index 2 Scheme symbol xf dimension C macro XF_DIMENSION Codes FLUENT TGrid Status optional The dimensions of the grid is expressed as 2 ND where ND is 2 or 3 This section is currently supported as a check that the grid has the appropriate dimensions ANSYS Inc April 15 2008 B 4 Nodes B 4 Nodes Index 10 Scheme symbol xf node C macro XF_NODE Codes FLUENT TGrid Status required 10 zone id first index last index type ND x y1 z1 x2 y2 z2 If zone id is zero it provides the total number of nodes in the grid In such a case e first index will be one e last index will be the e Total number of nodes in hexadecimal type is meaningless ND is the dimensionality
460. ormation 13 6 ANSYS Inc April 15 2008 13 4 Removing Slivers from a Tetrahedral Mesh If the top node of the tetrahedron were to travel along the path of the dotted line in the direction of the arrow as it approached the end of the line the resulting cell would be a degenerate tetrahedron or a sliver In the following sections the term sliver is used to denote all types of poorly shaped cells There are several commands in TGrid to remove slivers or to reduce the maximum skewness of the mesh 13 4 1 Automatic Sliver Removal Sliver removal operations can be invoked during the tri tet mesh refinement process The Remove Slivers option in the Refinement tab of the Tri Tet panel see Section 11 5 The Tri Tet Panel controls the removal of slivers during the meshing process The Remove Slivers option comprises operations such as collapsing cells to remove nodes face swap ping smoothing and point insertion which are invoked iteratively Usually the sliver cells will be removed during refinement but occasionally a few might be left behind In such cases you can use the options in the Slivers tab in the Tri Tet Improve panel see Section 13 5 The Tri Tet Improve Panel to remove the slivers manually The Improve command uses an automated procedure to remove slivers or to improve the mesh quality in general 13 4 2 Removing Slivers Manually The Tri Tet Improve panel contains options for removing slivers manually The operatio
461. ou can further refine the cells in the active zones by changing parameters such as Max Cell Volume and Max Cell Skew and Max Boundary Cell Skew available only for skewness based refinement Fa Changing mesh size controls other than Max Cell Volume will have no effect on a mesh that has already been refined Alternately use local refinement regions Refer to Section 11 4 1 Using Local Refinement Regions for de tails Refining with skewness parameters reduced to values less than 0 5 will rarely improve a 3D mesh and will be very time consuming For a 2D mesh you may try reducing these parameters further to see if any improvement results Do not over refine the grid in TGrid The volume mesh produced in TGrid should be of sufficient density to resolve the shape and any intuitive flow features e g wall boundary layers Additional resolution can be more effectively produced using the solution adaptive mesh capability provided in FLUENT At this step you will have an acceptable grid for most geometries Step 4c Boundary Slivers and Other Sources of Lingering High Skewness When viewing the cell distribution plot if you find that there are a few cells with very high skewness check to see where they are located i e on the boundary or in the interior To do so use the Report Boundary Cell Limits panel see Section 15 4 1 The Report Boundary Cell Limits Panel Refer to Sections 13 4 and 13 7 for details on removing slivers and oth
462. oundary Zone Groups contains a list of boundary zone types If you select a boundary type from this list e g inlet all boundary zones of that type for this example all pressure inlet and velocity inlet boundaries will be selected in the Boundary Zones list This allows you to easily select all boundary zones of a certain type without having to select each zone individually It is also possible to select all triangular or quadrilateral face zones by choosing tri or quad in the Boundary Zone Groups list You can select multiple boundary types in the Boundary Zone Groups list to select all zones of several different types e g inlet and outlet Node Zones shows the names of all node zones in the domain Those that are included in the currently selected domain based on your selections in the Boundary Zones panel will be highlighted The highlighting will be updated when you click on the Change button after modifying your selections in the Boundary Zones list Cell Zones shows the names of all cell zones in the global domain Those that are included in the currently selected domain based on your selections in the Boundary Zones panel will be highlighted The highlighting will be updated when you click on the Change button after modifying your selections in the Boundary Zones list Face Zones shows the names of all face zones in the domain Those that are included in the currently selected domain based on your selections in the Boundary Zones
463. ow boundary modify select position allows you to add a position to the selection list by entering the coordinates of the position boundary modify select entity allows you to add a cell face or node to the selection list by entering the name of the simplex boundary modify select zone allows you to add a zone to the selection list by entering the zone name or ID boundary modify show filter shows the current filter boundary modify show probe shows the current probe function boundary modify skew finds the face with the highest worst skewness selects it in the graphics window and reports its skewness and zone ID in the console window boundary modify skew report zone allows you to select the zone for which you want to report the skewness You can either specify zone name or zone ID boundary modify smooth uses Laplace smoothing to modify the position of the nodes in the selection list The new position is an average of the neighboring node coor dinates and is not reprojected to the discrete surface boundary modify split face splits the selected face into three faces boundary modify swap swaps boundary edges of triangular faces if the selection list contains edges boundary modify undo undoes the previous operation When an operation is per formed the reverse operation is stored on the undo stack For example a create operation places a delete on the stack and a delete adds a create operation The merge and collapse op
464. owable change in the angle between adjacent faces during the coarsening operation This allows you to prevent the appropriate curvatures from over coarsening ANSYS Inc April 15 2008 8 19 Wrapping Boundaries Specify appropriate values for Min Length and Max Length These values specify the minimum and maximum edge length Only faces within this range will be considered for coarsening Enable Preserve Boundary if required Click Apply A B Figure 8 8 1 Wrapper Surface A Before and B After Coarsening Figure 8 8 1 shows the coarsening of the wrapper surface 8 8 2 Post Wrap Options The following post wrapping operations are available in TGrid 8 20 Auto post wrap Remove duplicate nodes Smoothing Smoothing folded faces Inflating thin regions Removing self intersections Deleting islands Swapping Improving the quality ANSYS Inc April 15 2008 8 8 Post Wrapping Improvement Operations Auto Post Wrap TGrid allows you to use a pre defined sequence of post wrapping operations to improve the wrapper surface The automatic post wrapping procedure performs the various post wrapping operations in a pre defined sequence based on the parameters specified in the Boundary Wrapper panel You can also use the individual post wrapping operations in the order required as described in the subsequent sections To use the automatic post wrapping option do the following 1 Select the wrapp
465. oximity allow ignore allows you to ignore nodes where specified maximum shrink factor cannot be maintained nesh prism controls proximity allow shrinkage allows you to enable shrinkage while growing prism layers mesh prism controls proximity gap factor specifies the gap between prism layers in the proximity region nesh prism controls proximity keep first layer offsets allows you to retain first layer offsets while performing proximity detection nesh prism controls proximity max aspect ratio specifies the minimum offset to avoid degenerate cells This option is available only when the allow ignore option is disabled nesh prism controls proximity max shrink factor specifies the shrink factor de termining the maximum shrinkage of the prism layers This option is available only when the allow ignore option is enabled nesh prism controls proximity smoothing rate specifies the rate at which shrink age is propagated in lateral direction mesh prism controls remove invalid layer removes the last prism layer if it fails in the quality check mnesh prism controls zone specific growth apply growth applies the zone specific growth parameters specified 10 38 ANSYS Inc April 15 2008 10 12 Prism Meshing Problems mesh prism controls zone specific growth clear growth clears the zone specific growth specified nesh prism controls zone specific growth list growth lists the zone specific growth parameters specified
466. p group Returns a list of the face zones in the specified default face zone group get zones of group geometry Returns a list of the edge zones in the specified de fault edge zone group get zones of group gt boundary edge Returns a list of the cell zones in the specified default cell zone group get zones of group fluid Returns a list of the node zones in the specified de fault node zone group get zones of group gt boundary node Returns a list of face or edge as appropriate zones in the spec ified user defined group get zones of group inlets returns a list of all inlets in the geometry where inlets is the user defined group comprising all inlets get face zones of filter filter Returns a list of the face zones whose names con tain the specified filter string get face zones of filter gt prism cap get cell zones of filter filter Returns a list of the cell zones whose names con tain the specified filter string get cell zones of filter gt prism cells get edge zones of filter filter Returns a list of the edge zones whose names con tain the specified filter string get edge zones of filter gt prism cap ANSYS Inc April 15 2008 D 1 Using Boolean Operations with Query Functions Query Function Description Examples get node zones of filter
467. p allows you to improve the selected zones by edge swapping Quality Measure contains the available options for improving the quality of the bound ary surfaces This option is available only when Improve is selected in the Options drop down list Skewness allows you to improve the boundary surface quality based on the skew ness Size Change allows you to improve the boundary surface quality based on size change Aspect Ratio allows you to improve the boundary surface quality based on the aspect ratio Area allows you to improve the boundary surface quality based on the area Quality Limit specifies the quality limit for the improvement operation when using the Improve option with Skewness Size Change or Aspect Ratio selected as the Quality Measure All elements above the specified quality limit will be improved Angle specifies the maximum allowable angle between two adjacent face normals see Figure 7 4 1 when using the Improve option with Skewness Size Change or Aspect Ratio selected as the Quality Measure Figure 7 4 1 Angle Between Adjacent Face Normals Iteration specifies the number of improving attempts when using the Improve option with Skewness Size Change or Aspect Ratio selected as the Quality Measure Preserve Boundary allows you to preserve the geometry of the surface when using the Improve option with Skewness Size Change or Aspect Ratio selected as the Quality Measure Area Options contains options for imp
468. p face zone by mark To clear marked faces use the TUI command boundary clear marked faces These commands are described in Section 7 15 Additional Boundary Mesh Text Commands 7 10 2 The Separate Face Zones Panel The Separate Face Zones panel allows you to separate a single face zone into multiple zones of the same type See Section 7 10 1 Methods for Separating Face Zones for details Boundary gt Zone gt Separate Separate Face Zones Options Angle Boundary Face Zones Bs Angle 90 Neighbor Face Seed v Region v Mark ketai Region wv Shape v Seed Lecal Regions Separate Draw Report Close Help Controls Options specifies the method on which the face separation is to be based Angle indicates that the face zone is to be separated based on significant angle specified in the Angle field Neighbor indicates that the face zone is to be separated based on the cell zones that are adjacent to it Region indicates that the face zone is to be separated based on contiguous re gions 7 68 ANSYS Inc April 15 2008 7 10 Separating Boundary Zones Mark indicates that the face zone is to be separated based on faces marked Shape indicates that the face zone is to be separated based on the face shape triangular or quadrilateral Seed indicates that the face zone is to be separated by specifying a seed face element Angle specifies the sign
469. panel Create Boundary Zone Name Type D cma e Controls Name specifies the name of the newly created face zone The default name that appears is the selected Type followed by the TGrid assigned zone ID number For example if the selected Type is wall the default Name will be wall indicating that TGrid should append the new zone ID number to wall to name the zone e g wall 12 You can enter a name that does not include the if you prefer e g inside wal1 Type contains a drop down list of all available boundary zone types When you select an item from this list the Name will be updated to reflect the new Type The Move Nodes Panel The Move Nodes panel allows you to move the selected node s by a specified distance either in the Seed Normal or Local Normal directions Move Nodes Boundary Zones Options Kottom L Seed Normal inlet eT Local Normal outlet ight Seed Node top bn3600 Node Count 3 Y Move by 0 001 Boundary Zone Groups far field 4 Flip geometry f 7 28 ANSYS Inc April 15 2008 7 3 Modifying the Boundary Mesh Controls Boundary Zones contains a list from which you can select individual boundary zone s Boundary Zone Groups contains a list of the default boundary zone types and user defined groups If you select a zone type group from this list all zones of that type group will be selected in the Bound
470. parate separates the selected face zone based on the specified parameters Draw displays the zones selected in the Boundary Face Zones list Report reports the result of the separation without actually separating the face zone ANSYS Inc April 15 2008 7 69 Manipulating the Boundary Mesh 7 10 3 Text Commands for Separating Face Zones Text commands for separating face zones are listed below boundary separate local regions define defines the refinement region according to the specified parameters boundary separate local regions delete deletes the specified region boundary separate local regions init creates a region encompassing the entire geometry boundary separate local regions list all regions lists all the refinement regions in the TGrid console boundary separate mark faces in region marks the faces that are contained in a specified local refinement region boundary separate sep face zone by angle separates a face zone based on signifi cant angle boundary separate sep face zone by cnbor separates a face zone based on the its cell neighbors boundary separate sep face zone by mark separates a face zone by moving marked faces to a new zone boundary separate sep face zone by region separates a face zone based on con tiguous regions boundary separate sep face zone by shape separates a face zone based on the shape of the faces triangular or quadrilateral boundary separate sep face zone from seed s
471. pecific Direction method Click Apply to project the edge onto the slected face zone e Intersecting edge loops Select Intersect from the Options list Select the appropriate zone s in the Edge Zones selection list Enable Delete in the Overlapped Edges group box if you want to automatically delete all the overlapping edges You can use the delete overlapped edges text command to delete individual overlapping edges Specify an appropriate value for Intersection Tolerance 5 Click Apply to intersect the selected edge loops ANSYS Inc April 15 2008 7 49 Manipulating the Boundary Mesh 7 6 3 The Feature Modify Panel The Feature Modify panel allows you to create and modify edge loops See Sections 7 6 1 and 7 6 2 for details Boundary gt Mesh F eature 7 50 Feature Modify Face Zones EdgeZones j Edge Modify default wall 12 Copy UnGroup Separate default wall 14 default wall 19 intersect 33 12 5 Toggle Orient Merge default wall 25 intersect 7 25 3 default wall 26 Options Approach default wall 33 default wall 7 default wall 9 w Remesh Angle Criterion ja Face Zone Create v Project Face Z Groups Edge Zone Groups Se p A ae P v Intersect Seed Face boundary boundary edge far field z interior edge Angle 40 1 Draw Faces Draw Edges Apply Draw List Size Limits Close Help LE
472. pecify four points either by selecting the locations or nodes and the required intervals between the first selected point and the each of the remaining points to create the heat exchanger mesh TGrid creates a meshed plane using the first three specified points and the corresponding intervals Prisms are created on the meshed plane using the fourth point and the corresponding interval The order of selection of the points is important since the heat exchanger zone is created based on the intervals specified between the first selected point and each of the remaining points If the points are not specified in the correct order you will get a heat exchanger zone that is different from the required one Alternatively you can use the TUI command mesh create neat exchanger to create the heat exchanger mesh You need to specify the method for selecting the points by location or by nodes the points the intervals and the zone name prefix as required You can preview the heat exchanger zones and modify the parameters if you are dissatis fied with the results TGrid creates the heat exchanger zones prefixed by hxc as shown 9 24 ANSYS Inc April 15 2008 9 5 Creating a Heat Exchanger Zone in Figure 9 5 1 You can specify the prefix for the zones as required in the Zone Prefix panel see Section 7 14 3 The Zone Prefix Panel Figure 9 5 1 Creating the Heat Exchanger Mesh 9 5 1 The Heat Exchanger Mesh Panel The Heat Exchange
473. per panel is opened from the Display menu it can be used with all panels that contain zone lists e g Cell Zones and Boundary Zones panels e To look at the nodes and faces that have not been meshed turn on the Unmeshed option in the Display Grid panel e If you use the Compute button to calculate the average normal direction be sure that you do not change the sign of the displayed Vector It is important for the uniform direction vector to have the same sign as the normal direction for the face zone e In the Prisms panel lowering the value of layer below the number of layers to be grown can save computation time But this should only be done when high skewness is not an issue e If any new cell has zero or negative volume or any left handed faces or if any skewness exceed the specified Max Allowable Skewness prism layer creation will be stopped e Face swapping and skewness based smoothing apply only to triangular and tetra hedral cells Laplace smoothing however can be applied to all the cell shapes e To prevent such cross overs the skewness of the resulting cells is checked before the node is repositioned This makes the smoothing operation time consuming so you should limit the smoothing to highly skewed cells ANSYS Inc April 15 2008 E 11 Tips E 12 ANSYS Inc April 15 2008 Glossary The terms defined in this glossary are those used in the text Aspect Ratio Axial Wall Shear Stress Baryc
474. pipe is meshed using tetrahedra e Pyramids are used as a transition between the hexahedral grid for the plenum and the tetrahedral grid for the valve port This transition occurs where the triangular and quadrilateral faces meet in the middle of the figure Additionally the quadrilateral faces produced by extending triangular faces in the cylinder i e the quadrilateral sides of the resulting prism wedges can be seen in the far right of the figure 9 1 3 2D Boundary Mesh If you want to have a high mesh resolution in some portion of the domain such as a boundary layer you can obtain a better quality and more efficient mesh by meshing that portion with prisms and then meshing the rest of the domain with triangles tris Figure 9 1 5 shows a grid created in this manner Figure 9 1 5 2D Mesh Containing Prisms Quadrilaterals and Triangles 1 Build one or more layers of prisms since it is a 2D domain the prisms will be quadrilateral cells starting from the required boundary boundaries See Chap ter 10 Generating Prisms for details 2 Create a domain encompassing the region to be meshed with tris See Section 13 10 Us ing Domains to Group and Mesh Boundary Faces for details ANSYS Inc April 15 2008 9 5 Creating a Mesh 3 Generate the tris in the selected domain using either automatic or manual tri mesh generation or a combination of both See Chapter 11 Generating Triangu lar Tetrahedral Meshes for detail
475. planar surface perpendicular to the selected axis with its sides on the computed values along the other two axes which are not selected under Direction e Specify the coordinates to form a rectangular surface of the size that you want Planar surface of computed values will be displayed in the graphics window If you want surface of different size than that of the computed values enter appropriate coordinate values as per requirement ANSYS Inc April 15 2008 7 83 Manipulating the Boundary Mesh If you have selected X Axis then text entry box for specifying coordinates in X direction will not be accessible This also applies to other two axes f Optional specify appropriate Mesh Size Mesh Size tert entry box gets updated when you click Compute in the previous step But if you want finer or coarser mesh than that of the default mesh size change this value appropriately g Specify Axial Location of the planar surface 2 Under Options if you have selected Points do the following a Click Select Points This opens a Working dialog box prompting you to select three coordinate points to define a plane b Select three points in the geometry using the right mouse button When you click on the point the graphics window its corresponding x y and z coordinates will be updated in the Planar Points field c Click Compute This updates only Mesh Size text entry field d optional Specify appropriate Me
476. play view camera up vector sets the camera up vector display view camera zoom camera adjusts the camera s field of view This operation is similar to dollying the camera in or out of the scene Dollying causes objects in front to move past you Zooming changes the perspective effect in the scene and can be disconcerting 14 36 ANSYS Inc April 15 2008 14 7 Adding Lights 14 7 Adding Lights In TGrid you can add lights with a specified color and direction to your display These lights can enhance the appearance of the display especially when it contains 3D geome tries 14 7 1 The Lights Panel The Lights panel provides an interactive mechanism for placing colored directional lights in a scene Display Lights Lights Light ID Color Active Lights o Color y F Light On 127 Direction Red 127 xio J ETET 6 Green 127 Zz 16 55135 J Use View Vector Lighting Method y i Headlight On Controls Light ID indicates the light that is being added deleted or modified By default light 1 is defined to be dark gray with a direction of 1 1 1 Light On indicates whether or not the light specified in Light ID is on or off By turning off the Light On option for a particular light you can remove this light from the display while still retaining its definition To add it to the display again simply turn on the Light On button
477. point to the right side of the face In 2D grids the k vector pointing outside the grid plane is used to determine the right hand side cell cr from k x ANSYS Inc April 15 2008 B 7 Mesh File Format If there is no adjacent cell then either cr or cl is zero All cells faces and nodes have positive indices For files containing only a boundary mesh both these values are zero If it is a two dimensional grid n2 is omitted If the face zone is of mixed type element type 0 the body of the section will include the face type and will appear as follows type vO v v2 cO cl where type is the type of face as defined in the following table element type face type nodes face 0 mixed 2 linear 2 3 triangular 3 4 quadrilateral 4 The current valid boundary conditions types are defined in the following table bc name bc id interior 2 wall 3 pressure inlet inlet vent intake fan 4 pressure outlet exhaust fan outlet vent 5 K 8 symmetry periodic shadow pressure far field 9 velocity inlet 10 periodic 12 fan porous jump radiator 14 mass flow inlet 20 interface 24 parent hanging node 31 outflow 36 axis 37 For non conformal grid interfaces the faces resulting from the intersection of the non conformal grids are placed in a separate face zone A factor of 1000 is added to the type of these sections e g 1003 is a wall zone B 8 ANSYS Inc April 15 2008 B 8 Face Tree B 8 Face Tre
478. ppropriate zone s from the Edge Zones selection list 3 Select an appropriate spacing method from the Method drop down list You can specify a constant spacing of nodes or select either the arithmetic or the geometric method for node spacing 4 Specify values for First Spacing and Last Spacing as required Note For the Constant method the value specified for First Spacing will be the constant node spacing Also the Last Spacing option is not relevant for the Constant method and will not be available 5 Specify an appropriate value for Feature Angle 6 Enable Quadratic Reconstruct if required The quadratic reconstruction option allows you to reconstruct the edge by fitting a quadratic polynomial between the original edge nodes 7 Click Apply to remesh the edge loop 7 48 ANSYS Inc April 15 2008 7 6 Creating and Modifying Features e Projecting edge loops 6 1 Select Project from the Options list 2 Select the appropriate zone s in the Edge Zones selection list 3 4 Select the appropriate projection method from the Method drop down list Select the appropriate face zone from the Face Zones selection list The Closest Point method specifies that the edge should be projected to the closest point on the face zone selected The Specific Direction method allows you to project the edge on the face zone in a specific direction Specify the direction in which the edge s should be projected when using the S
479. pril 15 2008 7 29 Manipulating the Boundary Mesh boundary modify analyze bnd connectivity finds and marks free edges and nodes and multiply connected edges and nodes This process is necessary if the boundary mesh has been changed with Scheme functions boundary modify auto redisplay toggles the automatic redisplay of the modified mesh boundary modify clear selections clears all selections boundary modify clear skew faces clears faces that were marked using the boundary modify mark skew face command boundary modify create creates a boundary face if the selection list contains 2 2D or 3 3D nodes and an optional zone If the selection list contains positions then nodes are created boundary modify create mid node creates a node at the midpoint between two se lected nodes boundary modify delete deletes all selected faces and nodes boundary modify delta move allows you to move the selected node by specified mag nitude boundary modify deselect last removes the last selection from the selection list boundary modify hole feature angle allows you to specify the feature angle for con sideration of holes in the geometry boundary modify list selections lists all of the selected objects boundary modify mark skew face marks faces that should be skipped when the worst skewed face is reported using the Skew button in the Modify Boundary panel This allows you to search for the next skewed face with the Skew button bound
480. procedural order enabling you to find material relating to a particular procedural step e The Index allows you to access information about a particular subject ANSYS Inc April 15 2008 UTM 3 Using This Manual Typographical Conventions Used In This Manual Several typographical conventions are used in the text of this manual to facilitate your learning process An informational icon Ea marks an important note A warning icon Ay marks an important note or warning Different type styles are used to indicate graphical user interface menu items and text interface menu items e g Display Grid panel display grid command The text interface type style is also used when illustrating exactly what appears on the screen or exactly what you need to type into a field in a panel A mini flow chart is used to indicate the menu selections that lead you to a specific panel For example Display Grid indicates that the Grid menu item can be selected from the Display pull down menu at the top of the TGrid console window The words surrounded by boxes invoke menus or submenus and the arrows point from a specific menu toward the item you should select from that menu In this manual mini flow charts usually precede a description of a panel or a screen il lustration showing how to use the panel They allow you to look up information about a panel and quickly determine how to access it without having to
481. quality based on skewness size change or aspect ratio boundary wrapper post improve inflate thin regions allows you to push apart the overlapping faces in thin regions boundary wrapper post improve post single surface allows you to clean up un merged island regions after recovering the single surface boundary wrapper post improve recover feature projects nodes from the wrap per surface on to the extracted features e Use the mark option to mark the nodes to be projected e Use the project option to project the nodes to the extracted features A You need to use the mark option and examine the tracked line before using the project option If you attempt to project the nodes without mark ing them first TGrid will display a warning about missing feature path information indicating that the nodes were not marked for projection boundary wrapper post improve recover single surface allows you to recover thin surfaces as a single surface after wrapping boundary wrapper post improve recover zone separates the wrapper surface into zones based on the original geometry boundary wrapper post improve remove crossover config allows you to remove crossover configurations boundary wrapper post improve remove duplicated nodes removes the duplicate nodes on the wrapper surface boundary wrapper post improve rename wrapper zones allows you to rename the wrapper zones by specifying an appropriate prefix instead of the default prefix
482. r If the mesh file contains the wrapper surface created in TGrid 4 0 you need to change the type of the surface from internal to wrapper before performing these operations TGrid will report an error if you perform operations like imprinting features or post wrapping improvements on a surface having type other than wrapper It is a good practice to save the mesh at this point 3 Modify the wrapper surface to represent the input geometry more closely The initial wrapper surface created will not be the exact representation of the input geometry Some of the distinctive features such as sharp edges between the zones will be ignored In this step you will recover the feature edges of the input geometry and imprint the wrapper surface onto these edge loops a Select the zones for which you want to recover the feature edges from the Tri Boundary Zones selection list b Select the method to be used for feature extraction from the Feature Methods list Refer to Section 7 6 1 Creating Edge Loops for details on the feature extraction methods 8 16 ANSYS Inc April 15 2008 8 6 Extracting the Wrapper Surface c Click Extract Features The edge loops edge zones will be created for the selected boundary zones These edge loops will be listed in the Edge Zones list You can display each of them by selecting each one and clicking the Draw button d Modify create feature edges using advanced options using the Feature Modify pan
483. r Mesh panel allows you to specify the parameters required to create the heat exchanger mesh Mesh Create gt Heat Exchanger Heat Exchanger Mesh By Locations By Locations X Pos Pos Z Pos v By Nodes P1 js js aa a piisi 182 a ey oy Y Intervals between 1 amp 3 P3 js laa Jo 10 Intervals SA amp 4 a ae be 5 Select Points Create Preview Close Help Controls Parameters contains inputs to be specified for heat exchanger mesh creation By Locations allows you to specify the locations X Pos Y Pos Z Pos of the four points P1 P2 P3 and P4 You can either enter the position values or select the points using the mouse ANSYS Inc April 15 2008 9 25 Creating a Mesh 9 26 By Nodes allows you to specify the nodes to be used You can either enter the Node ID or select the points using the mouse Intervals between 1 amp 2 specifies the number of intervals between points 1 and 2 Intervals between 1 amp 3 specifies the number of intervals between points 1 and 3 Intervals between 1 amp 4 specifies the number of intervals between points 1 and 4 Select Points allows you to select the points by selecting the locations or nodes using the mouse When you click this button a Working dialog box will open prompting you to select 3 points to define the plane and the 4th point to grow prisms Create opens the Zone Prefix panel see
484. r a fine surface remeshing Replace Face Zone toggles the creation of a new zone for the remeshed face and keeping a old one along with the new zone If this option is turned on the newly remeshed face zone is preserved and the original face zone is deleted i Before deleting the original face zone ensure that the new face zone is acceptable Remesh retriangulates the selected face zone using the edge loops in the Edge Zones list A new face zone will be created upon successful completion of the surface retriangulation i If you want to exclude an edge loop from the retriangulation delete it from the Edge Zones list before remeshing Draw displays the selected Edge Zones using the display settings that are currently de fined in the Display Grid panel Arrowheads on the edge loops indicate the direction of the loop 7 7 6 Text Commands for Remeshing Text commands for remeshing face zones are boundary remesh create edge loops creates edge loops for a specified face zone based on feature angle boundary remesh create intersect loop creates an interior edge loop at the inter section between two adjacent face zones boundary remesh delete overlapped edges deletes edges that overlap selected edge loops boundary remesh remesh face zone remeshes a specified face zone by automatically extracting edge loops If edge loops are present in the current domain e g if they were created using the create edge loops command they are
485. r edges Solution To fix this problem replace the adjacent quadrilateral face zones with trian gular face zones using the boundary create tri surface text command When you reattempt the prism generation TGrid will project to and retriangulate the zone Since TGrid projects the outer nodes of the prisms to the adjacent boundary zone and discards the original nodes on that portion of the zone the different node spacing on the adjacent zone will not affect the prism heights at the outer edges 10 42 ANSYS Inc April 15 2008 Chapter 11 Generating Triangular Tetrahedral Meshes This chapter describes the procedure to create the triangular tetrahedral mesh in the domain It also describes some of the common problems faced during tri tet meshing It contains the following sections e Section 11 2 Manually Creating a Tri or Tet Mesh e Section 11 3 Initializing the Tri Tet Mesh Section 11 4 Refining the Tri Tet Mesh e Section 11 5 The Tri Tet Panel Section 11 6 Additional Text Commands for Tri Tet Mesh Generation Section 11 7 Common Tri Tet Meshing Problems You can use one of the following techniques to generate triangular or tetrahedral meshes e Automatic mesh generation Section 11 1 Automatically Creating a Tri or Tet Mesh e Manual mesh generation Section 11 2 Manually Creating a Tri or Tet Mesh e A combination of manual and automatic commands Sections 11 3 11 4 If the cells e g prisms or pyramids ha
486. r field w TH Controls Boundary Zones contains a list of the boundary zone s available Boundary Zone Groups contains a list of the default boundary zone groups and user defined groups available in TGrid If you select a zone group from this list all zones of that group will be selected in the Boundary Zones list You can also select multiple types to select all the zones of different types e g inlet and outlet Apply defines the bounding box based on the zones selected in the Boundary Zones selection list Draw draws the zones selected in the Boundary Zones selection list ANSYS Inc April 15 2008 12 11 Generating the Hexcore Mesh 12 4 2 The Hexcore Refinement Region Panel Hexcore Refinement Region Regions CEN Max Length Level regions 7 5 z A Center Length Orient xfo fo xj so X deg o Activate deg 60 __ Deactivate Z deg E _Select Activated Activated Deselect Activated Activated The Hexcore Refinement Region panel provides options for creating modifying and acti vating deactivating a local region for hexcore mesh refinement 12 12 Controls Regions contains a list of the defined regions Name specifies the name of the region selected in the Regions list or the name of the region to be created Max Length specifies the maximum cell length in the region The Max Length value is determined by the specified refinement level L
487. r of pyramids TGrid will use the resulting triangular faces to create tetrahedra ANSYS Inc April 15 2008 9 13 Creating a Mesh tetrahedron hex ahedral prism Figure 9 3 1 Pyramid Cell Transition from a Hexahedron to a Tetrahedron To create pyramids you need to specify the boundary from which the pyramids will be built the method for determining the top vertex of each pyramid and the pyramid height 9 3 1 Creating Pyramids The procedure for creating a layer of pyramids from a quadrilateral boundary zone is as follows 9 14 1 Check the aspect ratio limits of the boundary face zones on which you need to build pyramids Report gt Face Limits The use of a high aspect ratio quadrilateral for the base of a pyramid produces skewed triangular faces that can cause problems during the tetrahedral mesh gen eration If the maximum quadrilateral face aspect ratio is much greater than 10 you will need to regenerate them e If the faces were created in a different preprocessor return to that application and try to reduce the aspect ratio of the faces in question e If the faces were created by TGrid during the building of prism layers rebuild the prisms using a more gradual growth rate Select the appropriate quadrilateral boundary zone s in the Boundary Zones selec tion list in the Pyramids panel see Section 9 3 3 The Pyramids Panel Mesh Pyramids Click
488. r the display menu help mode gt pwd pwd alias LAMBDA cx send system pwd help mode gt q gt ANSYS Inc April 15 2008 5 11 Text User Interface Help can also be obtained when you are prompted for information by typing a at the prompt Example gt display annotate Annotation text Enter the text to annotate the plot with Annotation text 5 12 ANSYS Inc April 15 2008 Chapter 6 File Types 6 1 During a TGrid session you may need to read and write several kinds of files You can read mesh journal Scheme and domain files and write mesh journal transcript and domain files TGrid also allows you to save hardcopy files save panel layouts and write the current Scheme images These files and features are described in the following sections Section 6 1 Mesh Files e Section 6 2 Compressed Files e Section 6 3 Reading Scheme Source Files e Section 6 4 Journal Files e Section 6 5 Transcript Files e Section 6 6 Domain Files e Section 6 7 Importing Files e Section 6 8 Exporting Files e Section 6 9 Saving Hardcopy Files e Section 6 10 Saving the Panel Layout e Section 6 11 The tgrid File e Section 6 12 Exiting TGrid Mesh Files A mesh file includes a list of the node coordinates boundary faces and sometimes interior faces and cells The boundary faces are grouped into zones with speci
489. r the refinement sweeps you can try boundary sliver removal e Canceling the meshing process during refinement will cause the algorithm to exit at the next reasonable stopping place leaving the mesh in an acceptable state e The default value of Minimum Skewness is 0 85 You may increase this value but do not decrease it since smoothing operations are very time consuming and the lower the value of the Minimum Skewness the smoothing process will take more time e For some meshes the first sweep of the first refinement level will never finish because more skewed cells are formed due to refinement which will then be further refined to create more skewed cells and so on This problem can be avoided by turning on the Incremental Improvement option e Various steps in the automatic meshing process can be added or eliminated as required In addition most aspects of the automatic meshing process can be changed dynamically through the Scheme interface e Do not over refine the grid in TGrid The volume mesh produced in TGrid should be of sufficient density to resolve the shape of the geometry The mesh can be improved more effectively using the solution adaptive mesh capability provided in FLUENT e There are situations where it may be undesirable to introduce additional nodes to eliminate highly skewed cells In these situations face swapping is used to improve the grid quality E 8 ANSYS Inc April 15 2008 E 11 Refining the Me
490. ral cell on the boundary face If Peel Layers is set to 0 TGrid will allow the gap size to be smaller than the ideal height The resulting hexcore mesh will contain the maximum number of Cartesian cells possible for the chosen parameters Figure 12 3 5 shows the hexcore mesh generated for different values of Peel Layers A Figure 12 3 5 Hexcore Mesh Using A Peel Layers 0 B Peel Layers 2 ANSYS Inc April 15 2008 12 7 Generating the Hexcore Mesh 12 3 7 Local Refinement Regions You can use local refinement regions to refine specific cells within the domain During the hexcore meshing procedure TGrid will refine the cells within the activated local refinement region s Currently the only possible region shape is a box either aligned with the coordinate axes or oriented as required The region extents are defined by the center and the length of the region The cell size within the region can be manipulated by setting the level of refinement relative to the maximum cell length in the hexcore domain You can also orient the region as required You can create multiple regions that overlap each other and the geometry To create additional regions you can copy an existing region and then modify the parameters as required The default region includes the entire geometry You can use the Draw button in the Hexcore Refinement Region panel to display the defined region Figure 12 3 6 shows a refinement region defined A sa
491. rapping Boundaries TGrid will check for the presence of self intersecting faces and report the number of such faces in the console The self intersecting configurations will be removed from the wrapper surface Most self intersecting configurations will be removed by TGrid but there may be some faces that may not be resolved Such faces will also be reported in the console Deleting Islands The Delete Islands option allows you to delete faces in a non contiguous region of a face zone You can delete islands having a face count less than or equal to the specified critical face count The critical face count is determined from the values specified for Absolute Count and Relative Count The value for the critical face count is taken as the absolute count specified or the product of the relative count specified and the face count of the largest region whichever is lower To delete island faces do the following 1 Select the wrapper surface in the Tri Boundary Zones list 2 Select Post Wrap in the Options drop down list and Delete Island in the Sub Options list 3 Enter appropriate values for Absolute Count and Relative Count in the Critical Face Count group box 4 Click Apply to delete the island faces Swapping Swapping is another operation to improve the skewness of the faces in the wrapper surface It allows you to swap the common edge of two adjacent triangles into the other diagonal directions The swapping is carried out
492. rapping im provement operation The Mark option is available Apply executes the operation selected in the Options list Draw displays the zones selected in the Tri Boundary Zones list in the graphics window 8 9 1 The Wrapper Refinement Region Panel The Wrapper Refinement Region panel allows you to define local regions to be refined Wrapper Refinement Region Regions Max Length Level z region 1 7 45 z Center Pe Orient X deg o deg 60 Z deg OOo Controls Regions contains a list of the defined regions Name specifies the name of the region selected in the Regions list or the region to be created Max Length specifies the maximum cell length in the region The Max Length value is specified by the Level specified 8 44 ANSYS Inc April 15 2008 8 9 The Boundary Wrapper Panel Level specifies the refinement level for the local region defined Center specifies the coordinates of center of the refinement region Length specifies the extent of the refinement region in the x y z directions Orient specifies the orientation of the refinement region Note TGrid orients the region by rotation first about the x axis then the y axis and finally the z axis You need to take this into account while specifying the orientation of the region as rotation in any other order will produce different results Define creates a new region according to the specified parameters It also
493. rapping operations on the wrapper surface Distance Tolerance specifies the tolerance value for removing dupli cate nodes Relative Thickness specifies the distance for the separation of self intersecting faces Critical Thickness specifies the critical thickness for inflating thin regions Max Improve Angle specifies the maximum angle considered for im proving the wrapper surface Remove Duplicate deletes the duplicate nodes within the proximity of the tolerance value Distance Tolerance specifies the tolerance value to be considered while removing duplicate nodes Smooth allows you to smooth the wrapper surface Iteration specifies the number of smoothing attempts Relaxation specifies the node smoothing relaxation factor Reprojection enables the projection of nodes onto the geometry af ter smoothing Rel Reproject Range specifies the maximum relative distance of the nodes from geometry within which the nodes are projected onto the geometry Preserve Boundary allows you to preserve the original locations of the zone boundary nodes 8 40 ANSYS Inc April 15 2008 8 9 The Boundary Wrapper Panel Smooth Folded allows you to fix the folded faces on the wrapper sur face Iteration specifies the number of node smoothing attempts for re solving folded configurations Critical Angle specifies an angle between the pair of adjacent faces If the feature angle between the two faces is smaller than the spec ifie
494. rate the volume mesh ANSYS Inc April 15 2008 1 3 Introduction to TGrid Tri tet meshes are suitable for complex geometries Hexcore meshes can combine the flexibility of tet hex and prism meshes with smaller cell count e Hybrid meshes Prism layers near walls allow proper boundary layer resolution Allows flow alignments with grid lines Generates smaller volume mesh with highly stretched prismatic elements e Non conformal meshes Suitable for parametric studies Meshes generated separately can be glued together 1 4 Accessing T Grid Manuals The on line help gives you access to the TGrid User s Guide through HTML files These files can be viewed with any web browser To see the User s Guide select User s Guide Contents in the Help pull down menu in the TGrid GUI This will open the User s Guide contents page You can access the required information by using the Table of Contents that displays a list of chapters including all section and subsection titles Each of these is a link to the corresponding chapter or section or subsection of the manual You can also use the Index to take you to the relevant section of the User s Guide For details on using GUI help system see Section 3 6 Using the GUI Help System 1 4 ANSYS Inc April 15 2008 Chapter 2 Getting Started 2 1 This chapter provides an overview of using TGrid and instructions for starting it e Sectio
495. rate the surface on which you have defined a seed face from the surfaces around it based on the specified value of the feature angle The feature angle is the angle between the normal vectors of the cells To separate the face zones based on this criteria do the following 1 2 3 Under Options select Seed Under Flood Fill Options select Angle Specify a seed element in the Face Seed text entry field Right click on the face you want to choose as a seed element in the graphics window The Face Seed text entry field gets updated automatically ANSYS Inc April 15 2008 7 10 Separating Boundary Zones 4 Specify the required feature angle in the Angle text entry field 5 Click Separate The surface on which you have defined a seed face will be separated from other surfaces of the zone for which the feature angle change is greater than or equal to the specified value For example if the grid consists of a cube and all 6 sides of the cube are in a single wall zone specify a significant angle of 89 and specify a seed face on any one of the walls Since the normal vector for each cube side differs by 90 from the normals of its adjacent sides the face on which you have defined a seed cell will be placed in a different wall zone Therefore two zones will be created one zone will have a face on which you defined a seed face and the second zone will have remaining faces e Edge Loop Criteria This method allows you
496. ration fails check the validity of the surface mesh In some rare cases you may need to change the sliver size parameter see Section 11 5 1 The Tri Tet Init Controls Panel Refer to Section 11 7 Common Tri Tet Meshing Problems for more information on meshing problems 11 3 2 Text Commands for Initializing the Mesh The text commands for initializing the mesh have the same functionality as the initial ization parameters available in the Initialization tab of the Tri Tet panel mesh tritet init meshes boundary nodes generating the initial Delaunay mesh mesh tritet controls delete dead zones toggles the automatic deleting of dead zones during mesh initialization mesh tritet controls delete unused nodes toggles the deleting of unused nodes during mesh initialization mesh tritet controls improve surface mesh toggles the improving of the surface mesh during mesh initialization mesh tritet controls merge free nodes toggles the merging of free nodes during mesh initialization mnesh tritet controls non fluid type selects the non fluid cell zone type ANSYS Inc April 15 2008 11 11 Generating Triangular Tetrahedral Meshes mesh tritet controls advanced circumsphere tolerance defines the thickness of the circumsphere boundary In a Delaunay meshing algorithm the most basic operation is checking to see if a node is inside or outside of the circumsphere of a cell Due to numerical errors it is not possible to g
497. raw zones draws the boundary cell zones using the zone ID as input display redisplay redraws the grid in the graphics window display set grid all cells toggles the display of all cells display set grid all faces toggles the display of all faces display set grid all nodes toggles the display of all nodes display set grid circumcircles toggles the display of face display set grid free toggles the drawing of faces nodes that have no neighboring face on at least one edge display set grid left handed toggles the display of left handed faces display set grid multi toggles the display of those faces nodes that have more than one neighboring face on an edge display set grid refine toggles the display of those faces that have been marked for refinement display set grid unmeshed toggles the display of nodes and faces that have not been meshed display set grid unused toggles the display of unused nodes display set grid marked toggles the display of marked nodes display set grid tagged toggles the display of tagged nodes display set grid cell quality sets the lower and upper limits of quality for cells to be displayed Only cells with a quality measure value e g skewness within the specified range will be drawn display set grid face quality sets the lower and upper limits of quality for faces to be displayed Only faces with a quality measure value e g skewness within the specified range will be drawn display
498. re e Section 1 3 Program Capabilities e Section 1 4 Accessing TGrid Manuals Introduction TGrid is a highly efficient easy to use unstructured grid generation program that can handle grids of virtually unlimited size and complexity consisting of triangular tetrahe dral hexahedral prismatic or pyramidal cells Unstructured grid generation techniques couple basic geometric building blocks with extensive geometric data to highly automate the grid generation process In addition the generalized data structures used in these schemes permit the addition and removal of cells to maximize accuracy and minimize memory and CPU requirements For input TGrid requires a discretized boundary mesh consisting of either nodes and edges in 2D or nodes and triangular quadrilateral faces in 3D TGrid contains a number of tools for checking and repairing the boundary mesh to ensure a good starting point for the mesh A complete mesh can be generated from the boundary mesh automatically or by exercising control of the process The user interface to TGrid is written in the Scheme language which is a dialect of LISP Most features are accessible through the graphical interface or the interactive menu interface The advanced user can customize and enhance the interface by adding or changing the Scheme functions ANSYS Inc April 15 2008 1 1 Introduction to TGrid 1 2 Program Structure TGrid is part of the FLUENT package which includes the
499. re 9 1 8 Extending an Existing Tetrahedral Mesh Using Prisms Use the Triangulate Zones panel see Section 7 9 1 The Triangulate Zones Panel or the command boundary remesh triangulate to convert quad face zones to tri face zones You can then use the Boundary Improve panel to improve the skewness of the tri angular boundary zone created You may choose to use a non conformal interface to define the computational do main This type of interface allows you to relax the requirement for point to point matching at the interface between the grids as illustrated in Figure 9 1 9 This feature of relaxing the requirement for point to point matching at the interface between the grids is particularly useful in parametric studies where you want to change an isolated region of the domain without changing the entire mesh The procedure is as follows 1 Prepare two separate grids These grids should not share nodes edges faces or cells 2 Read both the grids into TGrid 3 For surface grids define a domain for each independent grid region and mesh the individual domains using an appropriate meshing strategy Mesh Domains For volume grids change the face zone type of the two surfaces that will be treated nonconformally to interface ANSYS Inc April 15 2008 9 1 Choosing the Meshing Strategy
500. re gradual growth rate For 2D a maximum skewness less than 0 5 and an average of 0 1 are good For 3D a maximum skewness less than 0 9 and an average of 0 4 are good To check the skewness of boundary cells use the Report Boundary Cell Limits panel or the associated text commands If you have used domains to generate the mesh or group zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces the report will apply only to the active domain ANSYS Inc April 15 2008 E 7 Tips e The skewness method you choose in the Quality Measure panel will only affect reports and displays based on skewness The triangular and tetrahedral meshing procedure will always be based on the equilateral volume skewness method E 11 Refining the Mesh e The refinement procedure is repeated a number of times You can control the number of refinement levels by setting the Number of Levels see Section 11 5 2 The Tri Tet Refine Controls Panel For each subsequent level of refinement the cell skewness thresholds are lowered Additional refinement levels increase the grid resolution increase the number of cells and lower the cell skewness average e Each refinement level actually consists of two sweeps through the refinement proce dure where in the second sweep only refines a cell if the local skewness is improved This sweep attempts to reduce highly skewed cells in confined regions of the geom etry Afte
501. reate to generate the prisms Refer to Section 10 12 Prism Meshing Problems for suggestions on solving problems occurring during prism generation Check the maximum face skewness value reported in the TGrid console when the final prism layer is created to ensure that the value is acceptable This is only for 3D and is especially important if you are going to generate tetra hedral or pyramidal cells using this new boundary zone The new zone should not have highly skewed triangles or quadrilaterals For more information about the quality of quadrilateral faces used for creating pyramids see Section 9 3 1 Creating Pyramids If the reported maximum skewness is too high read the mesh file you saved after setting the prism parameters and try again with different parameters For details see Section 10 12 Prism Meshing Problems A number of new zones are created when the prism generation is complete see Section 10 4 Zones Created During Prism Generation If the prism cap or prism side face zones are not supposed to be walls e g if they are supposed to be simple interior zones change them to the appropriate boundary type Boundary Manage For most cases performing these steps will result in an acceptable mesh of prismatic cells but for some complex geometries you may have to modify the procedure If you are not satisfied with the prisms generated by TGrid you can read in the mesh you saved before generati
502. rection of a boundary edge loop should be right handed with respect to the average normal of the face zone to be remeshed However the direction is not so important in the case of interior edge loops since faces are always formed on both sides of the loop e Separating the edge loop based on the connectivity and feature angle specified e Merging multiple edge loops into a single loop Note Only edge loops of the same type boundary or interior can be merged ANSYS Inc April 15 2008 7 47 Manipulating the Boundary Mesh e Remeshing the edge loops to modify the node distribution e Projecting the edges of the edge loop onto a face zone You can select the closest point method or specify the direction in which the edge should be projected onto the selected face zone e Intersecting edge loops to create a new edge loop comprising the common edges Modifying Edge Loops Using the Feature Modify Panel The Feature Modify panel can be used for modifying the edge loops as follows e Operations such as deleting copying grouping ungrouping orienting separating and merging edge loops toggling the edge loop type and reversing the edge loop direction 1 Select the appropriate zone s in the Edge Zones selection list A You can select only one edge zone when separating an edge loop 2 Click the appropriate button in the Edge Modify group box e Remeshing edge loops 1 Select Remesh from the Options list 2 Select the a
503. red Grids by the Advancing Front Method Technical Report AIA A 88 0515 American Institute of Aeronautics and Astronautics 1988 ANSYS Inc April 15 2008 Bib 1 BIBLIOGRAPHY 12 13 14 15 16 17 18 19 Bib 2 D J Mavriplis Adaptive Mesh Generation for Viscous Flows Using Delaunay Tri angulation Journal of Computational Physics 90 12 271 291 October 1990 J D M ller P L Roe and Deconinck H A Frontal Approach for Node Generation in Delaunay Triangulations International Journal For Numerical Methods in Fluids 17 3 241 255 August 1993 S Pirzadeh Unstructured Viscous Grid Generation by the Advancing Layers Method ATAA Journal 32 8 1735 1737 August 1994 S Pirzadeh Three Dimensional Unstructured Viscous Grids by the Advancing Layers Method AJAA Journal 34 1 43 49 January 1996 J Z Wang and K Srinivasan An Adaptive Cartesian Grid Generation Method for Dirty Geometry International Journal For Numerical Methods in Fluids 39 703 717 2002 D F Watson Computing the n dimensional Delaunay tesselation with application to Voronoi polytopes The Computer Journal 24 2 167 172 May 1981 N P Weatherill A Method For Generating Irregular Computational Grids in Mul tiply Connected Planar Domains International Journal For Numerical Methods in Fluids 8 2 181 197 February 1988 M A Yerry and M S Shephard Automatic Three Dimensional Mesh Generation by th
504. ree and Isolated Nodes 02 00 004 7 2 7 1 2 The Merge Boundary Nodes Panel 2 4 7 3 TOC 4 ANSYS Inc April 15 2008 CONTENTS 7 1 3 Text Commands for Manipulating Boundary Nodes 7 5 7 2 Intersecting Boundary Zones ss s se sos serora Hm RES Ew dso 7 6 Cot IMNGISECE s erica Bh ee Bee Ek Lee ee 7 6 Co MOM 3 5 eae eee eee Ee Ok ee oe ee 2 7 7 Te OG 2 gio gD 2S eb ee awe ek be ee be oe BSG 7 9 7 2 4 Using the Intersect Boundary Zones Panel 7 10 7 2 5 The Intersect Boundary Zones Panel 7 11 7 2 6 Text Commands for Boundary Intersection 7 13 7 3 Modifying the Boundary Mesh 4 5 44 lt 244420 42 4 24 7 15 7 3 1 Using the Modify Boundary Panel 7 15 7 3 2 Operations Performed Modify Boundary Panel 7 16 7 3 3 The Modify Boundary Panel 2 266 be eee ee ees 7 23 7 3 4 Text Commands for Boundary Modification 7 29 ie Improving Boundary Surfaces s ss s k oe wee He ee He eS 7 32 7 4 1 Improving the Boundary Surface Quality 7 32 7 4 2 Smoothing the Boundary Surface 2 24 sae eee eanees 7 32 7 4 3 Swapping Face Edges 0 000 eee ee ees 7 32 144 The Boundary Improve Panel soes ses ei ee eka de eas 7 33 7 4 5 Text Commands for Improving Boundary Surfaces 7 35 7 5 Refining the Boundary Mesh 2 02 02000 7 36 7 5 1 Procedure for Refining Boundary Zone s
505. rently defined views Clicking on a view name highlights that name and enters it into the Name field Double clicking on a view name restores that view in the active graphics window Save Name specifies the name to use when saving a view Actions contains buttons for performing various actions related to the Views list and the Save Name Default restores the front view in the active graphics window Auto Scale modifies the view in the active graphics window by scaling and cen tering the current scene without changing its orientation Save stores the view in the active graphics window with the name in the Save Name box Restore sets the view of the active graphics window to be the view selected in the Views list Delete removes the selected view name from the Views list Be careful not to delete any of the predefined views Read opens the Select File dialog box see Section 3 2 6 Select File Dialog Box in which you can specify the name of a view file to be read 14 32 ANSYS Inc April 15 2008 14 6 Modifying the View Write opens the Write Views panel see Section 14 6 2 The Write Views Panel in which you can select the views to be saved to a view file Mirror Planes displays a list of all symmetry planes in the domain Mirror images are drawn for all selected symmetry planes Define Plane opens the Mirror Planes panel see Section 14 6 3 The Mirror Planes Panel in which you can define a mirror pl
506. rfaces on either side of the cutting plane 8 12 ANSYS Inc April 15 2008 8 5 Examining the Cartesian Grid for Leakages To pan through all the region s of your choice do the following 1 Display the required region using the Draw button below the Regions list 2 Click the Pan Regions button to open the Pan Regions panel 3 Select the appropriate axis along which you want to pan through the selected region s from the Direction list The Start End and Increment fields will be updated automatically based on the cell size distribution of the Cartesian grid You can change these values as appropriate 4 Enable Overlay Graphics if you want to see the geometry along with the pan plane Select Positive or Negative to clip the surfaces on the positive or negative side of the cutting plane Figure 8 5 1 shows the geometry on the positive side of the cutting plane Figure 8 5 1 Overlaid Geometry Clipped with the Pan Plane 5 Enable All in the Region group box to pan through all regions Alternatively disable All and select the required region to pan 6 Click Pan to start the plane movement through the selected region s The interior of the Cartesian grid is displayed on every position of the plane during its movement through the region Increase or decrease the Increment value to increase or decrease the speed of movement of the plane 7 Use the E and E buttons to observe the interior of the region at a part
507. rid for Leakages 8 5 1 Automatic Leak Detection 8 5 2 Manual Leak Detection 4 8 6 Extracting the Wrapper Surface 8 7 Checking the Quality of the Wrapper Surface 8 8 Post Wrapping Improvement Operations 8 8 1 Coarsening the Wrapper Surface 8 8 2 Post Wrap Options ssc coa eet Gu 6 a ha ee bas 8 8 3 Zone OPONE sis a e kh ee RS ee Re de ia 88 4 Expert Opie s dg se rd o448 4 Pee EP ie E 8 9 The Boundary Wrapper Panel 8 9 1 The Wrapper Refinement Region Panel 8 9 2 The Pan Regions Panel 2 lt 2 6224 6282 eee kes 8 9 3 The Trace Path Panel 2 22 225 ea heb babes 8 10 Text Commands for the Wrapper 9 Creating a Mesh 9 1 Choosing the Meshing Strategy 9 1 1 3D Boundary Mesh Containing Only Triangular Faces 9 1 2 3D Boundary Mesh 4 624 44 4624886 44 9 13 2D Boundary Mesh ps eol ose 24 4 p 2 eee be eS ANSYS Inc April 15 2008 TOC 7 CONTENTS 9 1 4 2D Boundary Mesh with Some Quadrilateral Cells 9 6 9 1 5 Generating a Hexcore Volume Mesh 9 6 9 1 6 Additional Meshing Tasks 000 9 7 9 1 7 Inserting Isolated Nodes into a Tri or Tet Mesh 9 9 9 2 Using the Auto Mesh Option 22 454 624 8b ee bw ee oe 9 11 9 2 1 The Auto Mesh Panel 2 02 0 2 0008 9 12 Oe Generating Pyramids s ay oce
508. rimary features of the flow being analyzed You can control the resolution with the boundary mesh that you start from and also with the parameters that control the generation of the interior mesh A cell that is not intended for use in the flow solver Dead cells are a by product of the meshing algorithm which does not know which cells are inside the domain of interest and which are outside or inside an internal region Face swapping on a surface mesh Edge swapping is performed on a 3D boundary mesh to reduce problems in generating the initial mesh The 1 simplex a line segment defining the bounds of a 3D face Same as simplex General name for a node face or cell An n 1 simplex in dimension n It defines the boundary of an n simplex cell A face has exactly two sides termed left and right In 2D a face is a line segment and in 3D a face is a triangle ANSYS Inc April 15 2008 Glossary Face Swapping Filters Free Edge Free Face Free Node GAMBIT Initial Mesh Interior Face Interior Node Isolated Node Live Cell ANSYS Inc April 15 2008 Switches to the alternate triangulation of n 2 nodes in dimension n based on some parameter such as skewness There are at most two such triangulations Are translators for import of surface and volume meshes from CAD CAE packages such as ANSYS I deas NASTRAN PATRAN and others An edge used by only one boundary face A mesh contai
509. roup ungroups loops that were grouped with the Group button Orient orients the edges on the selected edge loops so that they are all pointing in the same direction Reverse reverses the direction of the edge loop Note that the direction of a boundary edge loop determines the side from which new faces are formed The direction should be right handed with respect to the average normal of the face zone to be remeshed Faces are always formed on both sides of interior edge loops so direction is not important for interior loops Separate separates the selected edge loops based on connectivity and the speci fied Feature Angle Merge merges the selected edge loops into a single loop Options contains options and controls for the edge remeshing projection and intersec tion operations that are executed with the combination of Remesh Project Create and Intersect check buttons and Apply button Create contains parameters to create edge loops again Approach contains a drop down list to choose the approach used for creating edge loops Face Zone specifies the edge loops will be created for the selected face zone in the Face Zones list Face Seed specifies the edge loops will be created around a selected seed face Angle Criterion contains a drop down list to choose the angle criteria used for creating edge loops Fixed specifies the use of fixed angle criteria while creating edge loops See Section 7 6 1 Creating Edge Loops for de
510. roving the boundary surface based on the area 7 34 ANSYS Inc April 15 2008 7 4 Improving Boundary Surfaces Collapse and Swap allows you to collapse faces having face area smaller than the minimum absolute size specified or relative to the minimum absolute size and then perform edge swapping Collapse and Smooth allows you to collapse faces having face area smaller than the minimum absolute size specified and then perform smoothing Min Absolute Size specifies the minimum absolute size All faces having area smaller than the specified value will be collapsed Min Relative Size specifies the minimum relative size for the Collapse and Swap option only All faces having area smaller than the value relative to the minimum absolute size will be collapsed Max Angle specifies the maximum allowable angle between two adjacent face normals Figure 7 4 1 The Max Angle option is available only when Smooth or Swap is selected in the Options drop down list Relax specifies the relaxation factor used for smoothing This option is available only when Smooth is selected in the Options drop down list Max Skew specifies the maximum allowable skewness value for the swapping operation All faces having skewness greater than the specified value will be considered during the swapping operation Check reports the number of unused nodes in the TGrid console Skew reports the face with the maximum skewness and the corresponding skewness value i
511. rp values Skewness Based Improvement For the skewness based correction you can specify the skewness threshold feature angle and the number of iterations per node to be moved TGrid will select the cells which have a skewness greater than the specified maximum skewness For boundary nodes you can restrict the node movement in the plane containing each of the boundary faces sharing the node being moved The node to be moved for a particular cell will be selected based on the selection of zones in the Boundary Zones selection list and an alternative position for the node will be determined The node will be moved to the new position only if the skewness of the cell and its neighbors is improved by the change in node position The procedure is repeated for the specified iterations per node You can also set the number of repetitions through the automatic correction procedure as required By default TGrid performs the correction procedure only once Warp Based Improvement For the warp based correction you can specify the maximum warp and the number of iterations per face to be improved TGrid will select the quadrilateral faces which have a warp value greater than the specified maximum warp The ideal position for the node to be moved will be determined based on the remaining three nodes The node will be moved to the new position only if the warp of the face decreases and the cell skewness does not increase by the change in node position The pro
512. ry Mesh After obtaining a valid ideally high quality surface mesh you can proceed to create the volume mesh Step 2 Creating the Initial Mesh The first step in generating the volume grid is creating the initial mesh This process first creates a pre meshed box encompassing the entire geometry and then sequentially intro duces each boundary node into the mesh As the nodes of a boundary face are inserted into the mesh any necessary mesh modifications needed to insert the face are performed effectively inserting both boundary nodes and faces into the mesh simultaneously For more information see Section 11 3 Initializing the Tri Tet Mesh Activating Multiple Zones for Multi zone Grids Only If the mesh has multiple regions e g the problem requires a fluid zone and one or more solid zones you can refine the mesh using refinement parameters specific to individual zones if required The procedure for meshing multiple cell zones comprises the following steps 1 Initialize the mesh 2 Activate the appropriate zones using the Manage Cell Zones panel 3 Set the zone specific refinement parameters and refine the active zones If you want to mesh all the zones included in the mesh with the same refinement parameters modify the Non Fluid Type in the Tri Tet panel see Section 11 5 The Tri Tet Panel Select the appropriate type from the Non Fluid Type drop down list in the Tri Tet Zones group box in the Tri Tet panel
513. ry Zones panel to appropriately refine the boundary zones that border the refinement region before performing the refinement of the volume mesh Boundary refinement can be performed only on triangular boundary zones 7 5 1 Procedure for Refining Boundary Zone s To refine boundary zones based on marked faces do the following 1 Open the Refine Boundary Zones panel Boundary Mesh Refine 2 Select Mark in the Options list and define the refinement region Click the Local Re gions button to open the Boundary Refinement Region panel see Section 7 5 2 The Boundary Refinement Region Panel Define the refinement region as appropriate 3 Select the zones to be refined in the Tri Boundary Zones list 4 Select the region to be refined in the Regions list The Max Face Area will be updated based on the value specified in the Boundary Refinement Region panel 5 Click Apply to mark the faces to be refined TGrid marks the faces in the selected zones having face area greater than the Max Face Area specified 6 Select Refine in the Options list and Mark in the Refinement group box 7 Click Apply TGrid refines the marked faces by dividing them into three faces see Figure 7 5 1 7 36 ANSYS Inc April 15 2008 7 5 Refining the Boundary Mesh Figure 7 5 1 Refining a Triangular Boundary Face To refine boundary zones based on proximity do the following 1 Open the Refine Boundary Zone
514. ry edge limits prints the length of the shortest and longest edges on the boundary This information can be useful for setting initial mesh parameters and refinement controls boundary jiggle boundary nodes randomly perturbs all boundary nodes based on an input tolerance Some nodes will be perturbed less than the tolerance value while others will be perturbed by half of the tolerance value in all three coordinate directions boundary mark duplicate nodes marks duplicate nodes see Section 7 1 Manipulat ing Boundary Nodes for information about duplicate nodes The marked nodes will appear in the grid display when nodes are displayed For a list of duplicate nodes set the report verbosity level to 2 before using the mark duplicate nodes com mand boundary mark face intersection marks intersecting faces Intersection is detected if the line defined by any two consecutive nodes on a face intersects any face in the current domain The marked faces will appear in the grid display when faces are displayed For a list of intersecting faces set the report verbosity level to 2 before using the mark face intersection command boundary mark face proximity marks faces that are in proximity to each other Face A is considered to be in proximity to face B if any of the nodes on face A are inside ANSYS Inc April 15 2008 7 93 Manipulating the Boundary Mesh a sphere centered at the centroid of face B The radius of the sphere is det
515. s ntersect Boundary Intersect Boundary Zones v Stitch Intersect Tri Zone With Tri Zone Operation Tolerance Intersect pi v Join Feature Angle 40 Mark Apply Intersect Tri Zone contains a list of triangular boundary zones from which you can select the zone s to be intersected With Tri Zone contains a list of triangular boundary zones from which you can select the zone s with which the zone s selected in the Intersect Tri Zone list are to be intersected Operation contains a list where you can select the appropriate connect operation Intersect performs the intersect operation Join performs the join operation Stich performs the stitch operation 7 11 ANSYS Inc April 15 2008 Manipulating the Boundary Mesh 7 12 Tolerance specifies the tolerance value for the surfaces to be intersected Faces within the specified tolerance value are considered for intersection stich or join The default value of Tolerance is 0 05 By default TGrid assumes the relative tolerance but you can change it to absolute tolerance by enabling Absolute Tolerance in the Intersect Boundary Zones panel Alternatively use the TUI command boundary remesh controls intersect absolute tolerance to use the absolute tolerance Feature Angle specifies the minimum angle between the feature edges that should be preserved while retriangulation All the edges i
516. s If you have no special boundary layer resolution requirements you can generate a mesh consisting entirely of tris Figure 9 1 6 Use the automatic tri mesh generation procedure the manual procedure or a combination of both Figure 9 1 6 2D Mesh Containing Only Triangles 9 1 4 2D Boundary Mesh with Some Quadrilateral Cells 1 Create a domain encompassing the region to be meshed with tris Section 13 10 Us ing Domains to Group and Mesh Boundary Faces 2 Generate the tris in the selected domain using either automatic or manual tri mesh generation or a combination of both Chapter 11 Generating Triangu lar Tetrahedral Meshes The result of this procedure is similar to the example shown in Figure 9 1 5 The only difference is that the quadrilateral cells in Figure 9 1 5 are created in TGrid while here they are considered to be created elsewhere and imported 9 1 5 Generating a Hexcore Volume Mesh The hexcore mesh features a tet hybrid mesh adjacent to walls and a Cartesian mesh in the core flow region Figure 9 1 7 shows the typical hexcore mesh The hexcore meshing scheme creates a mesh consisting of two regions 9 6 ANSYS Inc April 15 2008 9 1 Choosing the Meshing Strategy e An inner region composed of regular Cartesian cells e An outer region consisting of tetrahedral elements Tet Cells Interface 5 a DSA wae SEAN ARNa i AANA A inva ASS MS ray fe K Mal LIA AACE O
517. s e faces using the node For boundary nodes the node radius is the average distance to neighboring boundary nodes 15 6 2 Node report gt print info entity n30 n30 5 2 433799 0 078610075 0 52846689 0 12702106 The following information is listed for a node e associated zone ID e Cartesian coordinates of the node e the node radius For interior nodes the node radius is the distance weighted average of the surrounding nodes 15 6 3 Boundary Face report gt print info entity bf17 bf17 2 bn1308 bn1314 bn1272 c1533 0 014393554 The following information is listed for a boundary face e associated zone ID e the nodes forming the face e the neighboring cells 15 16 ANSYS Inc April 15 2008 15 6 Printing Grid Information e the periodic shadow null if not periodic e the quality of the face The default measure of quality is skewness but you can use the Quality Measure panel see Section 15 5 2 The Quality Measure Panel to specify aspect ratio or change in size instead 15 6 4 Cell report gt print info entity c26 c26 1 n262 n34 bn204 bn205 4743 5372 1822 3426 0 00020961983 2 7032523 0 32941867 0 072823988 0 0081779587 0 44769606 The following information is listed for a cell zone ID the nodes forming the cell the faces forming the cell the size the coordinates of the circumcenter relevant for triangular and tetrahedral cells only
518. s faces and cells in it 15 1 1 The Report Mesh Size Panel The Report Mesh Size panel reports the number of nodes faces and cells Nodes and faces are grouped into those defining the boundaries and those used inside cell zones If the generation of the initial mesh fails you can determine how many boundary nodes and faces were not meshed by enabling Report Number Meshed in the Report Mesh Size panel The total number of boundary nodes and faces will be reported along with the number that were meshed The headings Boundary and Interior will be replaced by Total and Meshed respectively when you use this option and the reported information will appear in the appropriate boxes ANSYS Inc April 15 2008 15 1 Reporting Mesh Statistics Fal If you used domains to generate the mesh or group zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces the report will apply only to the active domain Report gt Mesh Size Report Mesh Size Boundary Interior Nodes z so Faces z 2507 Cells azs 1 Report Number Meshed Controls Boundary indicates the number of boundary nodes and boundary faces Interior indicates the number of interior nodes faces and cells Total indicates the total number of nodes and faces when the Report Number Meshed option is enabled Total indicates the number of nodes and faces that have been meshed when the Report
519. s i e walls with fluid or solid cells on both sides Hidden Line Removal allows you to enable disable hidden line removal If you do not use hidden line removal TGrid will not try to determine which lines in the display are behind others It will display all of them resulting a cluttered display Disable this option if you are working with a 2D problem or with geometries that do not overlap Hidden Surface Removal allows you to enable disable hidden surface removal If you do not use hidden surface removal TGrid will not try to determine which surfaces in the display are behind others It will display all of them resulting a cluttered display Disable this option if you are working with a 2D problem or with geometries that do not overlap Hidden Surface Method lists the methods available for hidden surface removal These options vary in speed and quality depending on the device you are using The choices available are as follows Hardware Z buffer is the fastest method if supported by your hardware The accuracy and speed of this method is hardware dependent Painters will show fewer edge aliasing effects than hardware z buffer This method is often used instead of software z buffer when memory is limited Software Z buffer is the fastest of the accurate software methods available especially for complex scenes but it is memory intensive Z sort only is a fast software method but it is not as accurate as software z buffer
520. s contains a list of the animation options available All uses a solid tone shading representation of all geometry during mouse manipulation Wireframe uses a wireframe representation of all geometry during mouse manipulation This option is selected by default Select an alternative option only if your computer has a graphics accelerator otherwise the mouse manipulation may be very slow 14 26 ANSYS Inc April 15 2008 14 5 Controlling Display Options Level of Detail uses a simplified representation of the geometry during mouse manipulation by drawing the geometry using fewer elements You can use this option to enable fast rendering of large models Double Buffering allows you to enable disable double buffering if it is supported by the driver Double buffering dramatically reduces screen flicker during graphics updates If your display hardware does not support double buffering and you enable this option double buffering will be done in software Software double buffering uses extra memory Outer Face Culling allows you to disable enable the display of outer faces in wall zones Outer face culling is useful for displaying both sides of a slit wall By default when you display a slit wall one side will bleed through to the other When you enable the Outer Face Culling option the display of a slit wall will show each side distinctly as you rotate the display This option can also be useful for displaying two sided wall
521. s first more space is provided for the nodes that need to be moved in order to reduce the skewness Thus this method performs regional smoothing around faces of high skewness The node smoothing procedure can be performed on both tri and quad faces 10 9 3 Improving Warp Improving warp in prisms is a postprocessing step which is carried out after all the required prism layers are created TGrid allows you to improve the warp in the generated prism faces by moving the nodes of the face to make it planer When the Improve option is enabled in the Warp group box in the Improve tab of the Prisms panel see Section 10 10 The Prisms Panel TGrid identifies the prism layer s having faces with warp gt 0 5 The nodes on the identified faces are moved and the new location of the node is updated only when 1 The overall maximum warp of the faces connected to the node has decreased 2 The overall maximum skewness of the cells connected to the node has decreased or remained the same This is useful in regions having complex sharp corners where the nodes of a prism cell may have drastic normal change ANSYS Inc April 15 2008 10 23 Generating Prisms 10 10 The Prisms Panel The Prisms panel allows you to specify parameters needed for prism cell creation and then create the prisms When you press any of the tab buttons along the top of the panel the panel contents change to show the related controls The controls for all inactive t
522. s for specifying the frame boundaries and measurements Display updates the active graphics window with the current frame settings 14 9 Controlling the Mouse Buttons A convenient feature of TGrid is that it allows you to assign a specific function to each of the mouse buttons According to your specifications clicking a mouse button in the graphics window will cause the appropriate action to be taken 14 9 1 The Mouse Buttons Panel The mouse button is used to set the actions taken when you click the mouse button in a graphics window Clicking any mouse button in a graphics window will make that window the active window Display Mouse Buttons Mouse Buttons ae Middle mouse zoom y FLUENT Defaults Workbench Defaults Each mouse button can be associated with a different function The predefined functions include mouse rotate mouse dolly mouse zoom mouse probe and mouse annotate These functions apply only to the graphics windows they are not active when an XY plot or histogram is displayed Clicking any mouse button in a graphics window will make that window the active window 14 46 ANSYS Inc April 15 2008 14 9 Controlling the Mouse Buttons Controls Left sets the function associated with the left button In 2D the default setting is mouse dolly and in 3D it is mouse rotate Middle sets the function associated with the middle button The default setting for both
523. s is repeated until no further improvement is possible At this stage even if a few Delaunay violations exist the differences resulting from continual swapping are marginal i If the triangular boundary zone selected is the cap face zone of a prism layer the edge swapping will automatically propagate though the prism layers 7 4 4 The Boundary Improve Panel The Boundary Improve panel allows you to improve the overall mesh quality Boundary Improve Tri Boundary Zones Options bottom hi inlet ES Cty Meare me see v op Quality Limit 0 7 Angle 30 Tri Boundary Zone Groups Iteration far field 4 z geometry inlet Preserve Boundary Controls Tri Boundary Zones contains a list from which you can select individual boundary zone s to be improved Tri Boundary Zone Groups contains a list of the default bounday zone types and user defined groups If you select a zone type group from this list all zones of that type group will be selected in the Tri Boundary Zones list You can also select multiple types to select all the zones of different types e g inlet and outlet Options contains the options available for improving boundary surfaces Improve allows you to improve the selected zones based on the Quality Measure selected ANSYS Inc April 15 2008 7 33 Manipulating the Boundary Mesh Smooth allows you to improve the selected zones by smoothing Swa
524. s list This will create a temporary surface of larger size and its corresponding coordinates will be updated in the Planar Points field Scale displays a rectangular surface having diagonal sizes 0 8 times of the existing planar surface that you have created in the graphics window Select the plane surface that you have created in the Face Zones list This will create a temporary surface of smaller size and its corresponding coordinates will be updated in the Planar Points field Create creates a planar surface mesh of specified parameters 7 14 3 Creating a Cylinder In some cases you may want to create a cylinder within the existing geometry e g creating an MRF zone for problems involving moving parts such as rotating blades or impellers TGrid allows you to create a cylindrical surface and mesh it using triangular cells You can create a cylindrical surface using the options available in the Cylinder panel i The option of creating a cylindrical surface is available only in the 3D version of TGrid You can create a cylindrical surface by specifying the radius r of the cylinder and two points P1 and P2 defining the axis see Figure 7 14 2 The axis can be defined by specifying the location X Y Z of the points or by specifying the appropriate boundary nodes corresponding to the axial points P1 and P2 Using the Cylinder Panel The procedure for creating a cylindrical surface is as follows 1 Select the appropriate op
525. s of sharp edges in the geometry while improving the wrapper surface 6 Specify an appropriate value for Quality Limit The quality limit is the limit above which the wrapper surface will be improved 7 Click Apply 8 8 3 Zone Options The wrapper surface created by TGrid comprises only a single boundary zone It is a good practice to separate the wrapper surface into several zones based on the zones of the original geometry This is particularly useful when boundary conditions are to be applied for certain zones during the fluid simulation You will then rezone the separated wrapper zones for better recovery of the zones in the geometry You can also rename the zones as required ANSYS Inc April 15 2008 8 27 Wrapping Boundaries Recovering Zones The wrapper surface will be separated into boundary zones based on the zones in the orig inal geometry When you separate the wrapper surface into different zones the boundary zones associated with the original geometry will be retained and the newly created bound ary zones will be prefixed by wrap For example for the boundary zone rear wing the corresponding zone created from the wrapper surface will be wrap rear wing xx where xx is a random number The original wrapper surface will be deleted To separate the zones of the wrapper surface do the following 1 Select Zone in the Options drop down list and Recover Zone in the Sub Options list 2 Click Apply Th
526. s pairs of nodes edge s or face s If a pair of nodes is selected both the nodes are deleted and a new node at the midpoint of the two nodes is created If a triangular face is selected complete face is collapsed into a single node at the centroid of the face i Merge and Collapse operations are irreversible Save the mesh before per forming a merge or collapse in case you want to return to the pre merge or pre collapse boundary mesh Move To moves the selected node to the specified position Move By moves the selected node by the specified magnitude of the deviation Rezone moves the selected faces from their current zone into the selected zone No physical change is made to the mesh just the zone type of the selected face is changed Smooth moves the selected node to a position computed from an average of its node neighbors The new position is an average of the neighboring node coordinates and is not reprojected to the discrete surface Split refines a triangular face by bisecting a selected edge or by adding a node at the center of a selected face Swap performs swapping on the selected edge s of a triangular face Edge swapping is not available for quadrilateral faces Clear removes the selected entities from the Selections list Delete deletes all selected faces and nodes Undo undoes the previous operation When an operation is performed the re verse operation is stored on the undo stack For example
527. s panel Boundary gt Mesh Refine 2 Select Refine in the Options list and Proximity in the Refinement group box 3 Select the zone from which the proximity is to be determined in the Tri Boundary Zones selection list 4 Specify the Relative Distance and number of refinement iterations as appropriate 5 Click Apply TGrid refines the faces in the proximity of the specified zone Figure 7 5 2 A Figure 7 5 2 Boundary Mesh A Before and B After Refining Based on Proximity ANSYS Inc April 15 2008 7 37 Manipulating the Boundary Mesh To further improve the quality of the refined boundary mesh do the following 1 Select Swap in the Options list and specify the Max Angle and Max Skew as appro priate see the description in Section 7 5 2 The Refine Boundary Zones Panel 2 Click Apply 3 If the geometry of the boundary is close to planar you can improve the mesh quality further by selecting the Smooth option specifying the Max Angle and Relax parame ters as appropriate see the description in Section 7 5 2 The Refine Boundary Zones Panel and clicking Apply A If the geometry is far from planar smoothing is not recommended since it may modify the shape of the boundary If you wish to repeat the process for another refinement region first select the Clear option and click Apply to clear all marks 7 5 2 The Refine Boundary Zones Panel Th
528. s selected the node closest to the selection point is picked Thus nodes do not have to be displayed to be picked 14 10 2 Text Commands for Mouse Probe Selection Text interface commands with the same functionality as the controls in the Mouse Probe panel are boundary modify select probe and boundary modify select filter 14 11 Annotating the Display Text annotations with optional attachment lines may be added to the TGrid graphics windows The text is added to the window at a location chosen with the mouse using the mouse probe button see Section 14 9 Controlling the Mouse Buttons for information on setting the mouse buttons Dragging with the mouse probe button pressed will draw an attachment line from the point where the mouse was first clicked to the point where it was released The annotation text will be placed at the point where the mouse button was released The annotation text is associated with the active graphics window it is removed only when the annotations are explicitly cleared You can edit the text in the graphics win dow s caption block by the left mouse button in the desired location When a cursor appears you can type the new text or delete the existing text Text in the caption block will not be deleted when you clear annotations 14 11 1 The Annotate Panel You can use the Annotate panel to add text with optional attachment lines to the graphics windows It can also be used to remove all annotations from the acti
529. s that if the pyramid is adjacent to a triangular boundary face and the angle formed by the quadrilateral base and the triangular boundary face is not greater than 115 degrees The pyramid should not use a node on that boundary as its new vertex Figure 9 3 3 Otherwise the new vertex should be placed just above the centroid of the quadrilateral base If the node of a neighboring boundary face is used as the vertex the height specification will be ignored for that pyramid Centroid specifies that the new vertex of the pyramid should always be placed just above the centroid of the quadrilateral base of the pyramid See Fig ure 9 3 4 9 17 ANSYS Inc April 15 2008 Creating a Mesh existing vertex existing triangular boundary face Figure 9 3 3 Using an Existing Node as the Pyramid Vertex new vertex LRT centroid Figure 9 3 4 Pyramid Vertex Placed Above the Centroid 9 18 ANSYS Inc April 15 2008 9 3 Generating Pyramids Offset Scaling specifies the scaling s to be used to determine the height of the pyra mid The height h is computed from the following equation h 9 3 1 aS where L VA A area of the quadrilateral base of the pyramid Offset Factor specifies the fraction of the computed pyramid height offset by which the pyramid heights will be randomly adjusted The default value is 0 indicating that all pyramids will have the exact height computed by TGrid A value of 0 1 f
530. s that require smaller cell sizes You can specify the parameters required to initialize the Cartesian grid in the Face Size tab of the Boundary Wrapper panel The process of specifying the parameters required to initialize the Cartesian grid is as follows 1 Open the Boundary Wrapper panel Boundary gt Wrap The existing face zones in the geometry will be listed in the Tri Boundary Zones list The zones listed in the Tri Boundary Zones list may be face zones in the input geometry before wrapping or the wrapper surface after wrapping 2 Specify an appropriate value for Default Length The Default Length is the largest allowable cell length in the Cartesian grid De pending on the shape and size of the input geometry TGrid automatically computes an appropriate value for the Default Length However you can also specify the value manually 3 Specify the Global Size Function a Enable Proximity and or Curvature The Proximity and Curvature size functions calculate the required cell length on each facet of the input geometry within the upper Max Length and lower Min Length limit of the refinement The Cartesian grid will be refined based on these sizes The curvature size function is applied whenever there is a change in angle between the two faces The proximity size function is applied to all the faces within the zone as well as between two zones Enabling these options allows you to create a Cartesian
531. s the content and format of TGrid and FLUENT mesh files These files are broken into several sections depending on the following guidelines e Each section is enclosed in parentheses and begins with an integer in decimal indicating its type e All groups of items are enclosed in parentheses This makes skipping to ends of sub sections and parsing them very easy It also allows for easy and compatible addition of new items in future eleases e Header information for lists of items is enclosed in separate sets of parentheses preceding the items which are in their own parentheses Grid sections are stored in the case file A grid file is a subset of a case file containing only those sections pertaining to the grid Currently defined grid sections are explained in the following sections The section ID numbers are indicated in both symbolic and numeric forms The symbolic representations are available as symbols in a Scheme source file xfile scm or as macros in a C header file xfile h Both these files are available from Fluent Inc Comment Index 0 Scheme symbol xf comment C macro XF_COMMENT Codes FLUENT TGrid Status optional Comment sections can appear anywhere in the file except within other sections It appear as O comment text It is recommended that each long section or group of related sections be preceded by a comment section explaining what is to follow ANSYS Inc April 15 2008 B 1 Mesh File F
532. s with no neighboring face on at least one edge on the selected zones Multi draws multiply connected faces on the selected zones along with their nodes ANSYS Inc April 15 2008 14 5 Examining the Mesh U e In 3D a multiply connected face is a boundary face that shares an edge with more than one other face and a multiply connected node is a node that is on a multiply connected edge i e an edge that is shared by more than two boundary faces e In 2D a multiply connected face is a boundary face that shares a node with more than one other face and a multiply connected node is a node that is shared by more than two boundary faces Multiply connected faces or nodes are usually an indication that some thing is wrong with the surface mesh and it needs to be regenerated Such a surface mesh is often referred to as non manifold However if you are creating a mesh with more than one fluid solid or porous zone you can expect multiply connected faces or nodes to occur at the edges of adjacent zones This does not indicate any problem nmeshed draws unmeshed faces on the selected zones along with their nodes Unmeshed nodes and faces are those that were not inserted into the initial mesh If any unmeshed nodes or faces are displayed you need to regenerate the initial mesh Left Handed draws left handed faces on the selected zones If the normal on a face defined using the right hand rule does not point into the
533. s you must activate Major Rules in the Options list Color sets the color of the major rules from a drop down list with numerous color selections Weight sets the line thickness of the major rule A line of weight 1 0 is normally 1 pixel wide A weight of 2 0 would make the line twice as thick i e 2 pixels wide Minor Rules contains commands for modifying the appearance of the minor rules To use these commands you must activate Minor Rules in the Options list Color sets the color of the minor rules from a drop down list with numerous color selections Weight sets the line thickness of the minor rule A line of weight 1 0 is 1 pixel wide A weight of 2 0 would make the line twice as thick i e 2 pixels wide 14 24 ANSYS Inc April 15 2008 14 5 Controlling Display Options 14 4 2 Text Interface for Modifying Axes Attributes Text interface commands with functionality similar to that of the controls in the Axes panel are display xy set auto scale sets the range for the x and y axis If auto scaling is not activated for a particular axis you are prompted for the minimum and maximum data values display xy set background color sets the color of the field within the abscissa and ordinate axes display xy set key sets the visibility and title of the description box that displays the markers and or lines with their associated data The key can be positioned and resized using the left mouse button display xy set la
534. same growth parameters or growing layers for multiple zones at different times Grow on Two Sided Wall allows you to grow prisms on both sides of a two sided wall Apply applies the specified growth parameters to the selected Boundary Zones Note When setting prism parameters for use with the Auto Mesh option it 1s necessary to apply the prism growth parameters on spe cific zones for TGrid to retain the growth parameters in memory The Prisms option in the Auto Mesh panel will be visible only after applying zone specific growth by clicking Apply in the Zone Specific Growth group boz Clear clears the zone specific growth settings attached to the zones se lected in the Boundary Zones list List lists the zone specific growth settings for the zones selected in the Boundary Zones list in the console Plot displays in the active graphics window an illustration of the prism layers allowing you to preview the layer heights before actually creating the prisms The plot will show the layer heights for all selected boundary zones and if different the heights for the current settings in the panel Print reports the growth parameters prism height for each layer and total height in the TGrid console The report will show the data for all selected zones and if different the data for the current settings in the panel ANSYS Inc April 15 2008 10 27 Generating Prisms Direction displays the controls for computing the grow
535. select and click it 3 Release the left mouse button ANSYS Inc April 15 2008 3 3 Graphical User Interface Report Mesh Size Face Limits Cell Limits Boundary Cell Limits Quality Measure Figure 3 1 3 The Report Pull down Menu Using the Mnemonic Windows Systems Only You can also select a pull down menu item using the keyboard Each pull down menu label or menu item contains one underlined character known as the mnemonic 1 Press the lt Alt gt key and the mnemonic character of the pull down menu to display a menu 2 When the pull down menu is displayed type the mnemonic character associated with an item to select that item If at any time you want to cancel a menu selection while the pull down menu is displayed press the lt ESC gt key 3 2 Dialog Boxes A dialog box is a separate temporary window that is displayed to perform the dialog The dialog boxes are used to perform simple input output tasks such as issuing warning and error messages or asking a question requiring a yes or no answer When a dialog box appears on your screen you should take care of it before moving on to other tasks Different types of dialog boxes are described in the following sections 3 2 1 Error Dialog Box ie Error File myfile not found o 3 4 ANSYS Inc April 15 2008 3 2 Dialog Boxes The Error dialog box is used to alert you of an error that has occ
536. selectColor green Fluent XmToggleButtonGadget selectColor green Fluent XmText translations override lt Key gt Delete delete previous character Fluent XmTextField translations override lt Key gt Delete delete previous character Console resources Fluent ConsoleText rows 24 Fluent ConsoleText columns 80 Fluent ConsoleText background linen Help Viewer resources Fluent Hyper foreground black 3 18 ANSYS Inc April 15 2008 3 6 Using the GUI Help System Fluent Hyper background linen Fluent Hyper hyperColor SlateBlue3 Fluent Hyper normalFont new century schoolbook medium r normal 12 Fluent Hyper hyperFont new century schoolbook bold r normal 12 Fluent Hyper texLargeFont new century schoolbook bold r normal 14 Fluent Hyper texBoldFont new century schoolbook bold r normal 12 Fluent Hyper texFixedFont courier bold r normal 12 Fluent Hyper texItalicFont new century schoolbook medium i normal 12 Fluent Hyper texMathFont symbol medium r normal 14 Fluent Hyper texSansFont helvetica bold r normal 12 To customize one or more of the resources for a particular user place appropriate resource specification lines in that user s file HOME Xdefaults or whatever resource file is loaded by the X Window System on the user s platform To customize one or more of the resources for several users at a site place the resource spec
537. set grid neighborhood sets the x y and z range to be within a specified neighborhood of a specified grid object display set grid x or y or z range limits the display of grid objects to the spec ified range display set grid normals toggles the display of face normals 14 12 ANSYS Inc April 15 2008 14 1 Displaying the Grid display set grid normal scale sets the scale factor for face normals display set grid labels toggles the display of labels display set grid label alignment sets the alignment of labels that appear in the graphics window By default the label is centered on the node cell etc to which the label refers You can specify v lt gt for center top bottom left or right respectively You can also combine symbols for example v for bottom center display set grid label font sets the label font By default all labels appear in sans serif font Some other choices are Roman typewriter and stroked display set grid label scale scales the size of the label display set grid list lists all the grid display settings display set grid default resets the grid display parameters to their default values display center view on sets the camera target to be the center centroid of an entity display set edges turns the display of face cell edges on and off display set filled grid turns the filled grid option on and off When a grid is not filled only its outline is drawn display s
538. sh e Smoothing is a very time consuming process so you should only perform smoothing on cells with high skewness Improved results can be obtained by smoothing the nodes several times e Carefully consider whether the improvements to the mesh due to a decrease in the maximum skewness are worth the potential increase in the average skewness Performing smoothing only on cells with very high skewness e g 0 8 or 0 9 may lessen the adverse effects on the average skewness e After obtaining an initial triangulation of the boundary nodes the final volume mesh is produced by introducing additional nodes and swapping interior triangular faces This step is separated into two parts refining a cell with one or more boundary faces and refining non boundary cells e It is undesirable to add a node too close to a boundary because if a highly skewed cell is created it will be almost impossible to remove it e Be careful when you set upper limits on the number of cells or nodes TGrid will stop adding nodes or cells when it reaches the prescribed limit and may leave the mesh unevenly refined and less than adequate e Near the boundaries there will often be cells of higher skewness because of the limitations placed on node placement These can be removed with face swapping e Of the three methods available for improving skewness swapping and smoothing improves the mesh by manipulating the nodes and faces without increasing the total number of
539. sh Size 3 Click Create to create a plane surface mesh of specified parameters This will open Zone Type panel in which you can select the Boundary Type of the plane surface mesh that you have created i The new surface created will always be meshed using a triangular mesh The Plane Surface Panel The Plane Surface panel allows you to create a planar surface mesh Boundary gt Create Plane Surface Plane Surface Face Zones Options Direction X Min X Mex Axis Direction interior 14 Points Y Min Y Max left 2 outlet Edge Length Ace Ea Axial Location a ca Seale Seate E Compute Create Draw Close Help 7 84 ANSYS Inc April 15 2008 7 14 Creating Surfaces Face Zones contains a list of existing face zones in the geometry Options contains methods available for creating a plane surface Axis Direction allows you to create a planar surface mesh perpendicular to any coordinate axes Points specifies the selection of planar points method to create a plane surface mesh Direction contains check buttons for specifying the axis about which you want to create a perpendicular plane surface X Axis Y Axis Z Axis allows you to create the perpendicular plane surface about the selected axis direction These parameters are available only if you have selected Axis Direction under Options X Min X Max allows you to specify the mi
540. should be retained or merged with like zones By default this option is disabled so a single zone of prism cells and a single zone of cap faces will be created for each set of simultaneously grown layers See Sec tion 10 3 1 Growing Prisms Simultaneously from Multiple Zones for details 10 32 ANSYS Inc April 15 2008 10 11 Text Interface for Generating Prisms Ignore Invalid Normals allows you to ignore regions of invalid normals while cre ating prisms Proximity Options contains options for proximity detection Allow Shrinkage enables the shrinking of prism layers in areas of proximity to avoid prism collision Keep First Layer Offsets allows you to retain the original first offset height while scaling offset heights in case of intersecting prism layers Gap Factor controls the gap between the intersecting prisms layers with respect to the cell size of the prisms Allow Ignore allows you to ignore prism growth parameters in areas of proximity to avoid prism collision Max Shrink Factor determines the shrinkage of prism layers to avoid collision This option is available only when the Allow Ignore option is enabled Max Aspect Ratio specifies the maximum aspect ratio to determine the limit for the shrinkage of prism layers This option is available only when the Allow Ignore option is disabled A The value specified for Max Aspect Ratio is only used as a guideline for limiting the shrinkage of the prism layers The speci
541. sian grid is used to automatically clean the input geometry and to create the water tight representation The intersection between the Cartesian grid and the input geometry is calculated and TGrid identifies and marks the intersecting cells A watertight faceted representation is created along the boundary of the intersecting cells The nodes on this faceted representation are projected on to the faces and fea ture edges of the input geometry which then results in a wrapper surface closely representing the input geometry The wrapper surface quality is improved by post wrapping operations such as smoothing swapping etc ANSYS Inc April 15 2008 8 2 The Wrapping Process Figure 8 2 1 shows schematic representation of wrapping procedure 6 Figure 8 2 1 Schematic Representation of Wrapping Process Note The dimensions of the distortion e g hole gap etc in the input geometry should be smaller than that of the size of the Cartesian cells created by the wrapper If there is significant distortion in the input geometry repair it to the extent that the distortion becomes smaller in size Large holes if present in the initial geometry should be filled Otherwise such holes will be ignored in the wrapping process The Boundary Wrapper panel allows you to perform wrapping operation In addition to the Boundary Wrapper panel you will also use the Display Grid panel see Section 14 1 3 The Display Grid Pa
542. sorting refin ing reverse sorting and swapping and smoothing of the cells You can specify the number of refinement levels to be performed for skewness based refinement Each refinement level consists of two iterations through the refinement procedure For each subsequent level of refinement the cell skewness thresholds are lowered Additional refinement levels will increase the grid resolution and the number of cells and decrease the average cell skewness The preset refinement control parameters are available in the Tri Tet Refine Controls panel see Section 11 5 2 The Tri Tet Refine Controls Panel Alternatively you can select the advancing front refinement method Specify whether the mesh has to be improved or if the slivers have to be removed during refinement The Improve Mesh option performs additional smoothing and swapping with lowered skewness thresholds attempting to improve the average skewness of the mesh The Remove Slivers option attempts to lower the maximum skewness by improving highly skewed sliver cells The boundary mesh is fixed during the mesh improvement and sliver removal operations 11 12 ANSYS Inc April 15 2008 11 4 Refining the Tri Tet Mesh Refinement Controls The refinement controls for the skewness method are available in the Tri Tet Refine Controls panel see Section 11 5 2 The Tri Tet Refine Controls Panel Click the Controls button in the Refinement tab of the Tri Tet panel to open the
543. special feature of the geometry Also curvature calcula tions cannot be performed on disconnected edges 3 Analyze the geometry and remove unnecessary details if any 4 Display the geometry using the Display Grid panel Triangulate Quad Zones Triangulate the quad zones present in the input geometry using the Triangulate Zones panel see Section 7 9 1 The Triangulate Zones Panel You can also use the command boundary remesh triangulate to triangulate the quad zones i The boundary wrapper does not support quad zones Detecting and Filling the Holes Manually Examine the geometry and fill any unwanted holes using the Modify Boundary panel You will mainly try to locate and fix the major holes in the geometry If you miss smaller holes you can fix them later using the automatic hole detection feature 8 4 ANSYS Inc April 15 2008 8 3 Examining and Repairing the Input Geometry There are several ways in which you can fix the holes in the geometry e Fixing holes by selecting edges Figure 8 3 1 1 Select the edge filter hot key lt Ctrl gt E 2 Select any edge on the hole boundary 3 Press F5 to create the surface that closes the hole Figure 8 3 1 Hole Filling Using Edge e Fixing holes by selecting nodes Figure 8 3 2 1 Select the node filter hot key lt Ctrl gt N 2 Select the nodes around the hole 3 Press F5 to create the surface that closes the hole Figure 8 3 2 Hole Fill
544. st software method but it is not as accurate as software z buffer list lists the current hidden surface method display set rendering options outer face cull turns the display of outer faces on and off display set rendering options surface edge visibility controls whether or not the mesh edges are drawn display set rendering options wireframe animation turns the use of wireframes during mouse manipulation on or off display set windows contains commands that allow you to customize the relative positions of subwindows inside the active graphics window The menu structure for the axes main scale text and xy submenus is similar The in the following descriptions stands for any one of these submenus 14 30 ANSYS Inc April 15 2008 14 6 Modifying the View display set windows contains commands for changing the location of the subwin dow display set windows border draws a border around the subwindow display set windows bottom sets the bottom boundary of the subwindow display set windows left sets the left boundary of the subwindow display set windows right sets the right boundary of the subwindow display set windows top sets the top boundary of the subwindow display set windows visible sets the visibility of the subwindow display set windows axes clear sets the transparency of the axes window display set windows video contains options for modifying a video This command is not relevant for
545. stance Tolerance The Distance Tolerance specifies the minimum distance between two distinct nodes on the wrapper surface If the distance between two nodes is less than the value specified the nodes will be considered to be duplicate nodes Click Mark to highlight the duplicate nodes on the wrapper surface Alternatively you can use the command boundary mark duplicate nodes to view the dupli cate nodes Click Apply The nodes within the specified tolerance value will be removed Smoothing This operation improves the skewness of the faces in the wrapper surface Smoothing allows you to reposition the nodes to improve the cell connectivity and quality To perform node smoothing do the following 8 22 1 2 3 4 5 6 Select the wrapper surface in the Tri Boundary Zones selection list Select Post Wrap in the Options drop down list and Smooth in the Sub Options list Specify the number of smoothing attempts in the Iteration field Enter an appropriate value for Relaxation Enable Reprojection if required Specify an appropriate value for Rel Reproject Range The smoothing operation repositions the nodes on the wrapper surface The new position of the node may not be on the original geometry This parameter specifies the maximum allowable distance between the new location of the node and the original geometry The local mesh size say D is computed by averaging edge lengths at the node If the new node posi
546. stem e The default value for a prompt is accepted by typing a lt RETURN gt or a comma A comma is not a separator It is a separate token that indicates a default value The sequence 1 2 results in three values the number 1 for the first prompt the default value for the second prompt the number 2 for the third prompt e A short help message can be displayed at any prompt by entering a See Sec tion 5 6 Using the Text Interface Help System e To abort a prompt sequence press lt Control C gt 5 2 1 Numbers The most common prompt type is a number Numbers can be either integers or real numbers Valid numbers are for example 16 2 4 9e5 and 1e 5 e Integers can also be specified in binary octal and hexadecimal form e The decimal integer 31 can be entered as 31 b11111 037 or x1f e In Scheme integers are a subset of reals so you do not need a decimal point to indicate that a number is real 2 is just as much a real as 2 0 e If you enter a real number at an integer prompt any fractional part will be trun cated That is 1 9 will become 1 5 2 2 Booleans Some prompts require a yes or no response A yes no prompt will accept either yes or y for a positive response or no or n for a negative response These prompts are used for confirming potentially dangerous actions such as overwriting an existing file exiting without saving case data mesh etc Some prompts require actual Sche
547. stics of the ordinate and abscissa on an XY plot or histogram You can change the labels scale range number format and major and minor rules visibility and appearance The title following Axes in the panel indicates which plot environment you are changing You can set different parameters for each type of plot that TGrid can generate Axes Histogram Axis Number Format Major Rules x Type Color vy foot a roma v Label Precision Weight Options Log _ 1 Auto Range Major Rules Minor Rules Axis contains check buttons that allow you to set abscissa x axis or ordinate y axis characteristics X allows you to specify the abscissa characteristics Y allows you to specify the ordinate characteristics Label defines the character string that will label the active axis the one selected in Axis in the display Options contains check buttons for scale range major rules and minor rules Log toggles logarithmic scaling of the active axis By default decimal scaling is used Auto Range toggles automatic computation of the range of the active axis If you deactivate this option you can enter the Minimum and Maximum values in the Range box Major Rules toggles the display of major rules on the active axis Major rules are the horizontal or vertical lines that mark the primary data divisions and span the whole plot window to produce a grid ANSYS Inc April 15 2008 14
548. sting tri face zones The zones may be face zones in the input geometry or the wrapper surface generated after wrapping Face Size contains parameters for creating and controlling the initial Cartesian grid Default Length specifies the size of the largest cells in the Cartesian grid Draw Sizes displays red boxes of the specified default size over the selected boundary zone Global Size Function allows you to specify the Cartesian grid initialization size function parameters to be applied globally Proximity allows you to automatically refine the Cartesian cells based on the proximity of the zone to other faces in the current domain ANSYS Inc April 15 2008 8 33 Wrapping Boundaries Curvature allows you to automatically refine the Cartesian cells based on the curvature of the zone in the current domain Max Length Min Length specify the maximum and minimum size of the cells in the Cartesian grid respectively These are only informative boxes and you cannot make any change to the values displayed here Level allows you to select the level of refinement The cell size for each level is determined relative to the Default Length Zone Specific Size contains the parameters for modifying the Cartesian grid cell configuration for each zone Length specifies the size of the cells in the Cartesian grid that you want to create for the zone s selected in the Tri Boundary Zones list The value in the Length can only be modified b
549. stribution 14 19 Display Plot Face Distribution 14 17 Display Scene 14 38 Display Selection Helper 14 51 ANSYS Inc April 15 2008 Display Views 14 30 domain files 6 10 domains 11 1 13 33 E 5 Domains panel 13 34 drop down list 3 14 dual process build 2 3 duplicate faces 11 25 nodes 7 2 11 25 edge collapsing 7 17 loop 7 53 creating 7 42 criteria 7 66 face seed approach 7 43 face zone approach 7 43 modifying 7 46 splitting 7 18 swapping 7 19 13 3 edge ratio 15 12 Error dialog box 3 4 error messages 3 4 exit 6 24 exiting 6 24 export polyhedral cells 3 8 extrusion 10 15 face aspect ratio 14 17 15 3 collapsing 7 17 creation 7 15 deleting 7 75 deletion 7 16 distribution 14 17 duplicate 11 25 free 14 5 handedness 10 41 13 37 left handed 10 41 13 37 14 6 normals 7 76 10 3 14 10 projecting 7 69 quality 14 6 14 17 15 3 remeshing 7 53 rezoning 7 17 Bib 5 Index separation 7 63 size 14 6 15 3 change in 15 3 skewness 14 6 14 17 15 3 slitting 7 93 splitting 7 19 swapping 13 3 unmeshed 14 6 15 1 Face Distribution panel 14 17 face warp 15 13 Facted Stitch panel 7 60 feature angle criteria 7 65 Feature Modify panel 7 49 FIDAP 6 13 file write boundaries 6 5 file append mesh 6 4 file append meshes by tmerge 6 3 file export ansys 6 17 File Export ANSYS 6 17 file export hypermesh 6 16 File Export HYPE
550. submenu contains options to control the hexcore mesh generation The starting point is a valid surface mesh e Section 12 1 Automatic Hexcore Meshing Procedure Section 12 2 Manual Hexcore Meshing Procedure e Section 12 3 Controlling Hexcore Parameters Section 12 4 The Hexcore Panel Section 12 5 Text Commands for Hexcore Meshing 12 1 Automatic Hexcore Meshing Procedure The automatic hexcore mesh generation process comprises the following steps 1 Generating initial Cartesian cells inside a bounding box or the region specified around the volume to be meshed 2 Marking the Cartesian cells that intersect the boundary mesh and those cells having sizes larger than the average size of the faces they intersect 3 Marking additional buffer layer cells adjacent to the cells marked in Step 2 if specified 4 Marking additional cells to enforce one level refinement difference between adjacent cells 5 Subdividing all marked in steps 2 4 cells and repeating steps 2 5 until the local face size criteria is met ANSYS Inc April 15 2008 12 1 Generating the Hexcore Mesh 6 10 11 Deleting cells that intersect or are within some distance to the closest face on the surface mesh Triangulating the the external surface of the hexcore by converting quads into tri interface faces The quad faces become parents with type parent face of the interface faces TGrid does not use pyramids to transition from the
551. surface boundary wrapper initialize creates a Cartesian mesh of the specified parameters boundary wrapper local regions define allows you to define the local refinement region boundary wrapper local regions delete deletes the specified refinement region boundary wrapper local regions init creates a region encompassing the entire ge ometry boundary wrapper local regions list all regions lists all the refinement regions in the TGrid console boundary wrapper local regions refine refines the specified region according to the refinement parameters specified boundary wrapper pre smooth allows you to enable or disable smoothing of nodes during wrapping This command is available only after initializing the Cartesian grid boundary wrapper region draw holes draws the holes detected by TGrid See Sec tion 8 5 1 Automatic Leak Detection for details boundary wrapper region extract enclosing region extracts the interface for the region enclosing the specified point ANSYS Inc April 15 2008 8 47 Wrapping Boundaries boundary wrapper region extract interface extracts the interfaces for the speci fied regions boundary wrapper region fix holes fixes the specified hole s See Section 8 5 1 Au tomatic Leak Detection for details boundary wrapper region list holes lists the existing holes boundary wrapper region list regions lists the region created when the Cartesian grid is initialized boundary
552. t The Attributes tab contains controls allowing you to change how the objects are displayed and add labels circumcircles and normal vectors 14 1 1 Generating the Grid Display The procedure for generating the grid display is as follows 1 Select the entities to be displayed in the zone lists in the Nodes Faces or Cells tabs as appropriate You can also select several entities of the same group by selecting the required group in the respective zone groups lists in the Nodes Faces or Cells tabs 2 Select the display options as appropriate from the Options group box in the Nodes Faces or Cells tabs 3 Set the range for limiting the display to a specific coordinate range or within a specific distance from a selected object if required 4 Set the display options as appropriate in the Attributes tab 5 Click Display to draw the grid in the active graphics window 14 2 ANSYS Inc April 15 2008 14 1 Displaying the Grid 14 1 2 Grid Display Options The grid display options include modifying the grid colors adding the outline of impor tant features to a display displaying normals circumcircles shrinking the faces and or cells in the display adding lights for filled grid displays etc Modifying the Grid Colors You can control the colors used to render the grid for each zone type or entity You can modify the colors using the Grid Colors panel see Section 14 1 5 The Grid Colors Panel 1 Click the Colors
553. t so that the MS DOS command utility will find TGrid 2 3 Starting Dual Process Build of T Grid The dual process build allows you to run Cortex on your local machine and TGrid on a remote machine The advantage of using dual process build is faster response to graphic actions performed when you use TGrid from a remote machine For example if you are handling a big mesh e g underhood mesh and running TGrid on a faster remote machine with only the display set to your local machine In this case the graphics actions e g zoom in zoom out opening a panel etc can be slow if the remote machine is located very far away or if the network connectivity is slow To avoid the slow response of the graphics actions run the dual process build of TGrid When running a dual process build ensure that the both machines remote and host have similar platforms either both IBM platforms or both non IBM platforms You can not use dual process build for IBM host machine and non IBM remote machine or vice versa To start the dual process build of TGrid do the following 1 2 Start TGrid on your local machine using the command tgrid serv It will open the TGrid window with the version prompt in the console Type listen and press Enter on your keyboard You will be prompted for a timeout the period of time to wait for a connection from remote TGrid The default value is 300 seconds You can also specify the timeout as per your requirem
554. t transition elements pyramid and non conformal meshing and creation of a heat exchanger zone are also described Advanced meshing techniques such as prism meshing triangular tetrahedral and hexcore meshing options etc are described in subsequent chapters e Section 9 1 Choosing the Meshing Strategy Section 9 2 Using the Auto Mesh Option Section 9 3 Generating Pyramids Section 9 4 Creating a Non Conformal Interface Section 9 5 Creating a Heat Exchanger Zone 9 1 Choosing the Meshing Strategy TGrid offers a variety of cell shapes that can be used to mesh the domain e g tetrahedra prisms hexahedra and pyramids in 3D and triangles and quadrilaterals 2D prisms in 2D These shapes are shown in Figure 9 1 1 A mesh consisting entirely of triangular elements is referred to as a triangular mesh a mesh with only tetrahedral elements is a tetrahedral mesh and a mesh with any combination of cell shapes is referred to as a hybrid mesh Before generating a volume mesh determine the shapes that are appropriate for the case you are solving Then follow the instructions for creating the required cell types Most cases will fall into one of the following categories e Starting from a 3D boundary mesh containing only triangular faces see Sec tion 9 1 1 3D Boundary Mesh Containing Only Triangular Faces ANSYS Inc April 15 2008 9 1 Creating a Mesh Z triangle tetrahedron 2D prism pyramid quadrila
555. tact The free nodes of the triangulated surface will then be merged with the nodes on the original surface mesh Both surfaces will then be converted to interface type 9 4 1 The Non Conformals Panel The Non Conformals panel allows you to specify the method to be used for retriangulating the quad faces on the non conformal zones 9 22 ANSYS Inc April 15 2008 9 4 Creating a Non Conformal Interface Non Conformals Retriangulation Method Boundary Zones quad inlet v Prism Quad Split quad side v Remesh Edge featere Angie Sarface featere Angie Boundary Zone Groups far field geometry Le Controls Retriangulation Method contains a list of methods available for retriangulating the quadrilateral faces on the non conformal zones Prism remeshes all quad zones named prism side n Quad Split splits the quad faces diagonally into tri faces Remesh remeshes all the zones comprising quad faces based on the edge and surface feature angle specified Boundary Zones contains a list of the boundary zones Boundary Zone Groups contains a list of the available boundary zone groups including the user defined groups Edge Feature Angle specifies the edge feature angle for remeshing when the Remesh method is selected Surface Feature Angle specifies the surface feature angle for remeshing when the Remesh method is selected Create creates the non conformal interface acc
556. tails Feature Angle specifies the minimum feature angle that should be considered while creating edge loops Adaptive specifies the use of adaptive angle criteria for creating edge loops See Section 7 6 1 Creating Edge Loops for details ANSYS Inc April 15 2008 7 51 Manipulating the Boundary Mesh Seed Face specifies the ID of the face that will be used as a seed face Remesh modifies the node distribution on the selected edge loops using the method and spacing defined Method contains the methods that can be used for the node distribution on the edge loops selected in the Feature Modify panel You can choose a Constant spacing method an Arithmetic spacing method or a Geometric spacing method First Spacing specifies the node spacing at the beginning of the edge loop or if the Constant method is used the constant node spacing If a value of 0 is specified the default TGrid will determine the spacing based on the surrounding edges Last Spacing specifies the node spacing at the end of the edge loop If a value of 0 is specified the default TGrid will determine the spacing based on the surrounding edges This input is not relevant for the Constant method so it will not be available Feature Angle specifies the minimum feature angle that should be prevented while remeshing Quadratic Reconstruction enables the reconstruction of edges by fitting a quadratic polynomial between the original edge nodes Proj
557. ter nodes to adjacent zones mesh prism controls adjacent zone retri feature angle allows you to specify the feature angle that should be prevented while generating prisms mesh prism controls adjacent zone retriangulate adjacent specifies whether or not adjacent triangular face zones to which outer nodes have been projected will be automatically retriangulated This option is on by default nesh prism controls adjacent zone side feature align angle specifies the an gle used for aligning projected normals along a feature edge nesh prism controls adjacent zone side feature angle specifies the angle used for computing the feature normals mnesh prism controls adjacent zone side topology align angle specifies the an gle used for aligning projected normals along a particular feature edge based on the topology This is particularly useful when the side feature angle specified is not sufficient to decide the feature edge to align the projected normals mesh prism controls auto separate cells toggles automatic movement of the cells extruded from different face zones to different cell zones mesh prism controls check quality enables disables the checking of volume skew ness and handedness of each new cell and face mesh prism controls grow individually specifies whether TGrid should grow prisms from multiple zones individually so that the individual prism cell zones and the in dividual cap face zones are retained nesh prism co
558. teral prism with quadrilateral base hexahedron hea prism with triangular base wedge Figure 9 1 1 Different Cell Shapes Starting from a 3D boundary mesh see Section 9 1 2 3D Boundary Mesh Starting from a 2D boundary mesh see Section 9 1 3 2D Boundary Mesh Starting from a 2D boundary mesh with some quadrilateral cells see Section 9 1 4 2D Boundary Mesh with Some Quadrilateral Cells e Generating a hexcore volume mesh see Section 9 1 5 Generating a Hexcore Volume Mesh 9 1 1 3D Boundary Mesh Containing Only Triangular Faces If you require a high mesh resolution in some portion of the domain such as a boundary layer you can obtain an efficient and better quality mesh by meshing that portion with prisms wedges and then meshing the rest of the domain with tetrahedra tets The resulting mesh is referred to as a viscous hybrid mesh The procedure is as follows 1 Build one or more layers of prisms starting from the appropriate boundary or boundaries See Chapter 10 Generating Prisms 2 Create a domain encompassing the region to be meshed with tets 3 Generate the tets in the selected domain using either automatic or manual tet mesh generation or a combination of the two See Chapter 11 Generating Trian gular Tetrahedral Meshes ANSYS Inc April 15 2008 9 1 Choosing the Meshing Strategy Figure 9 1 2 shows several layers of prisms in a portion of a mesh created in this mann
559. th directions for the nodes on each layer of prisms Prisms Boundary Zones Ba ae a l saloa l Nomal v Uniform Orthogonal Layers Flip Normals jo Orient Normals Boundary Zone Groups far field geometry inlet f Method lists the available methods for specifying the prism growth direction See Section 10 7 Direction Vectors for details about these methods Normal enables the computation of direction vectors normal to the bound ary zones from which you are growing Uniform enables a uniform direction specification for all nodes on all prism layers When you select this method you need to specify the direction Vector TGrid will use this constant vector for all nodes on all prism layers instead of computing a new direction for each node on each layer Therefore this option is most useful for creating straight sided prism regions without any curvature Flip Normals reverses the normal directions on the faces of the selected boundary zone s The normal directions will determine the side of the boundary zone on which prisms will be built Orient Normals orients contiguous faces i e faces that touch each other in a selected zone so that their normals are all consistently pointing on the same side of the zone see Figure 7 13 1 Max Angle Change specifies the maximum angle by which the normal direction at a node can change during smoothing See Sections 10 3 5 and 10
560. that can be used in conjunction with the boundary modification functions see Section 7 3 Modifying the Boundary Mesh print prints information about the selected entity in the text window see Sec tion 15 6 Printing Grid Information box enables the selection of a group of entities within a box to be used in con junction with the boundary modification functions see Section 7 3 Modifying the Boundary Mesh To define the selection box click the mouse probe but ton at one corner of the region to be selected drag the mouse to the opposite corner and release the mouse probe button polygon enables the selection of a group of entities within a polygonal region to be used in conjunction with the boundary modification functions see Sec tion 7 3 Modifying the Boundary Mesh To define the selection polygon click the mouse probe button at one vertex of the polygonal region to be selected and use the left mouse button to successively select each of the remaining vertices Click the mouse probe button again anywhere in the graphics window to complete the polygon definition ANSYS Inc April 15 2008 14 49 Examining the Mesh Filter indicates what the mouse probe button is to select The available filters are off cell face edge node zone and position If off is chosen when a selection is made it is first checked to see if it is a cell then a face an edge and so on When the node filter is used if a cell or face i
561. that contain zone lists e g Cell Zones and Boundary Zones panels 14 12 1 The Zone Selection Helper Panel The Zone Selection Helper panel allows you to find and select zones with a certain pattern in their names or with the number of zone entities present in them Display Selection Helper l Zone Selection Helper Options Matching Zones wrap f_v8 airintake 56 wrap f_v8 block 55 wrap f_v8 cylinder left 5 wrap f_v8 cylinder right By Zone Name v By Zone Entities Zone Type wrap f_v8 generator 52 y wrap f_v8 manfold 51 wrap f_v8 top left 50 Zone Name Pattem wrap f_v8 top right 49 wrap f_v8 wheels 48 Select Deselect Close Help Controls Options contains options to choose zone selection criteria By Zone Name specifies the use of zone selection criteria based on zone name pattern By Zone Entities specifies the use of zone selection criteria based on the number of selected zone entities present in them Zone Type contains a drop down list of types of zones face node edge cell Zone Name Pattern specifies the pattern to look for in the names of zones of the se lected Zone Type Press lt RETURN gt after you enter the pattern 14 52 ANSYS Inc April 15 2008 14 12 Shortcuts for Selecting Zones Max Zone Entities specifies the maximum number of zone entities to look for in the zones of the selected Zone Type Press lt RETURN gt after you
562. the View 14 7 Adding Lights s sanean eon eRe a RE a WE Be 14 71 The Lights Panel 2 2 sste se ee ee dee ee ae 14 7 2 Text Commands for Adding Lights 14 8 Describing a SeGne oo aoe ee ee ba ee Se SES 14 8 1 The Scene Description Panel 14 8 2 Text Commands for Scene Description 14 8 3 Changing the Display Properties 14 8 4 The Display Properties Panel 2 2 14 8 5 Transforming Geometric Objects ina Scene 14 8 6 The Bounding Frame Panel 14 9 Controlling the Mouse Buttons 2 46 6 bone Hoe bes 14 9 1 The Mouse Buttons Panel 14 9 2 Text Commands for Selecting Mouse Buttons 14 10 Controlling the Mouse Probe Functions 14 10 1 The Mouse Probe Panel 14 10 2 Text Commands for Mouse Probe Selection 14 11 Annotating the Display 0 1411 1 The Annotate Panel 2 5 24 244 akos 4 4 eos 14 11 2 Text Commands for Text Annotation 14 12 Shortcuts for Selecting Zones 22 2484 14 12 1 The Zone Selection Helper Panel 15 Reporting Mesh Statistics 15 1 Reporting the Mesh Size 2 2 2 eee ees 15 1 1 The Report Mesh Size Panel 202 15 1 2 Text Commands for Reporting Mesh Size ANSYS Inc April 15 2008 TOC 13 CONTENTS TOC 14 15 2 Reporting Face Limits s sce aoe ee a a ee ee a ee eS 15 3 15 2 1 The Report Face Limits Panel
563. the Views panel are display view auto scale scales and centers the current scene without changing its orientation display view default view resets the view to front and center display view delete view deletes a named view from the list of stored views display view last view returns to the camera position before the last manipulation display view list views lists all predefined and saved views display view restore view sets the current view to one of the stored views display view read views reads views from an external view file display view save view saves the currently displayed view into the list of stored views display view write views writes views to an external view file display view camera dolly camera allows you to move the camera left right up down in and out display view camera field allows you to set the field of view width and height of the scene display view camera orbit camera allows you to move the camera around the target Gives the effect of circling around the target display view camera pan camera gives you the effect of sweeping the camera across the scene The camera remains at its position but its target changes display view camera position sets the camera position display view camera projection lets you switch between perspective and orthographic views display view camera roll camera lets you adjust the camera up vector display view camera target sets the point the camera will look at dis
564. the number of boxes to be displayed when using the Draw Sizes button in the Face Size tab boundary wrapper set proximity allows you to enable or disable the proximity size function boundary wrapper set proximity factor allows you to specify the proximity factor for initializing the wrapper boundary wrapper set read local sizes reads the zone specific sizes written to a file boundary wrapper set refinement buffer layers allows you to specify the specific number of additional cell layers that you want to refine boundary wrapper set relative island count allows you to specify a critical cell count for island regions generated during wrapping boundary wrapper set write local sizes writes the zone specific sizes to a file boundary wrapper set zone specific size allows you to specify zone specific sizes ANSYS Inc April 15 2008 8 49 Wrapping Boundaries boundary wrapper post improve auto post improve improves the wrapper surface using a pre defined sequence of operations boundary wrapper post improve auto post wrap performs a pre defined sequence of post wrapping operations on the wrapper surface boundary wrapper post improve coarsen wrapper surf allows you to coarsen the wrapper surface boundary wrapper post improve imprint geom surf allows you to imprint the ge ometry on the wrapper surfaces manual zone recovery boundary wrapper post improve improve allows you to improve the wrapper surface
565. the original geometry if required 6 Click Apply Inflating Thin Regions If the geometry to be wrapped contains regions of very small thickness e g zero thickness walls the wrapper surface around it forms a thin region configuration Such type of configurations may cause problems in further volume meshing The Inflate Thin Regions option allows you to resolve such configurations by pushing apart the nodes of the faces very close to each other To inflate thin regions do the following 1 Select the wrapper surface in the Tri Boundary Zones selection list 2 Select Post Wrap in the Options drop down list and Inflate Thin Regions in the Sub Options list 3 Specify an appropriate value for Critical Thickness The critical thickness 1s the maximum distance the nodes can be moved away from each other ANSYS Inc April 15 2008 8 23 Wrapping Boundaries 4 Specify an appropriate value for Critical Angle The critical angle is the angle between the faces below which the faces are considered for inflating Increasing this value will include more faces to be inflated 5 Enable Preserve Boundary if required 6 Click Mark to highlight the thin regions 7 Click Apply Figure 8 8 2 shows the inflating of thin regions on the wrapper surface A B Figure 8 8 2 Wrapper Surface A Before and B After Inflating Thin Re gions In Figure 8 8 3 Facel and Face2 are the faces of the wrapper surface on either s
566. the specification of a variable height that decreases or increases geometrically for each layer of prisms hn r thi 10 10 2 When this method is selected you will need to specify the First Height h the Number of Layers and the Rate r exponential enables the specification of a variable height that decreases or increases exponentially for each layer of prisms hn hye DP 10 10 3 When this method is selected you will need to specify the First Height h the Number of Layers and the Exponent p First Height specifies the height of the first prism layer h The computed heights of subsequent prism layers will be based on this height depending on the Growth Method selected Number of Layers sets the total number of prism layers to be created Total Height reports the total height of the prisms to be grown You can use this information to check if the specified prism heights will yield a mesh of the required height If you want to see the updated Total Height press the lt Enter gt key after entering a new value for the other growth parameters If you do not press lt Enter gt after entering the value the Total Height reported will not reflect the changed value First Aspect Ratio specifies the first aspect ratio to be used when the aspect ratio offset method is selected Last Aspect Ratio reports the last aspect ratio based on the specified first aspect ratio for the aspect ratio offset method Last
567. thod ANSYS Inc April 15 2008 7 53 Manipulating the Boundary Mesh boundary feature remesh edge zones remeshes the specified edge loop s modify ing the node distribution according to the specified remeshing method spacing values and feature angle You can also enable quadratic reconstruction if required boundary feature reverse edge direction reverses the direction of the edge loop boundary feature separate edge zones separates the specified edge loop based on connectivity and the specified feature angle boundary feature toggle edge type toggles the edge type between boundary and interior boundary feature ungroup ungroups previously grouped edge zones 7 7 Remeshing Boundary Zones In some cases you may need to regenerate the boundary mesh on a particular boundary face zone You may find that the mesh resolution on the boundary is not high enough or that you want to generate triangular faces on a boundary that currently has quadrilateral faces Remeshing of boundary faces can be accomplished using the Surface Retriangulation panel To remesh the face zones do the following e Create edge loops e Modify edge loops e Remesh surface zones TGrid allows you to remesh the boundary face zones by taking account of edge angle curvature and proximity 7 7 1 Creating Edge Loops To remesh a face zone you first need to generate edge loops or edge zones on the borders of the face zones using the parameters
568. tically reduces screen flicker during graphics updates If your display hardware does not support double buffering and you turn this option on double buffering will be done in the software Software double buffering uses extra memory Hidden Line Removal turns hidden line removal on or off If you do not use hidden line removal TGrid will not try to determine which lines in the display are behind others it will display all of them and a cluttered display will result ANSYS Inc April 15 2008 E 12 Using the GUI Turn this option off if you are working with a 2D problem or with geometries that do not overlap Hidden Surface Removal works in a similar manner hiding displaying the surfaces instead of lines e In the Views Panel the Delete button removes the selected view name from the views list Be careful not to delete any of the predefined views e When using the sliders and dial to manipulate the view turn off Wireframe Ani mation in the Display Options panel see Section 14 5 1 The Display Options Panel to watch the display move interactively while you are moving the slider or the dial indicator e You can edit the text in the graphics window s caption block by clicking your left mouse button in the desired location A cursor will appear and you can then type new text or delete the text that was originally there Text in the caption block will not be deleted when you clear annotations e Although the Zone Selection Hel
569. tion Wisder Dump Cesnnasd v Window Dump White Background Sme D Poo cee o Format allows you to select the format of hardcopy files Coloring specifies the color mode for hardcopies Hardcopies may be made in Color Gray Scale or Monochrome black and white Most monochrome PostScript devices will render Color images in shades of gray Select Gray Scale to ensure that the color ramp is rendered as a linearly increasing gray ramp File Type specifies whether a Raster or Vector type hardcopy file is to be saved You can choose either of these if you are saving a PostScript or EPS file See Sec tion 6 9 1 Choosing the File Type for details Resolution specifies the size of raster hardcopies in pixels If the Width and Height are both zero the hardcopy is generated at the same resolution as the active graphics window For PostScript and EPS files specify the resolution in dots per inch DPI Options specifies whether or not to use the following options Landscape Orientation specifies the orientation of the hardcopy If selected the hardcopy is made in landscape mode otherwise it is made in portrait mode White Background specifies that the white background should be used in the hardcopy This feature allows you to make hardcopies with a white background and a black foreground while the graphics windows are displayed with a black background and white foreground 6 22 ANSYS Inc April 15 2008
570. tion by disabling the Retriangulate Adjacent Zones option in the Project tab of the Prisms panel it is not always recommended Expert users experimenting with different settings may temporarily turn off retriangulation ANSYS Inc April 15 2008 10 15 Generating Prisms AK WALI i Punta SSS ee a c a pct A N i AANA HM ii hy W M M W vi J Yy AN 9 Z A AA gt S A AW AY Lin AN ey ZV S S Q ERS I ARS KA TY SS NN SAY ML KI Ky NKS Rand VN AANA S a AAR ia KDR va Anan pP LS eee NZ S ERE pee ios Figure 10 6 2 Symmetry Zone and Car Wall Before Prism Generation Figure 10 6 3 Symmetry Zone and Car Wall After Prism Generation Without Retriangulation 10 16 ANSYS Inc April 15 2008 10 7 Direction Vectors Figure 10 6 4 Symmetry Zone and Car Wall After Prism Generation and Retriangulation 10 7 Direction Vectors As TGrid builds each layer of prisms it needs to know which direction to build in There are two methods available for determining the direction vectors e Extrusion Method For creating straight sided prism regions without any curva ture you can specify a uniform direction vector for all prism layers Select Uniform in the Method list in the Direction tab of the Prisms panel uniform direction vector Figure 10 7 1 Uniform Direction Vector for a Straight Sided Pr
571. tion between polygon and the option selected in the Mouse Probe panel F5 Creates the selected entity in the Filter list in the Modify Boundary panel F6 Smoothes the selected entity in the Filter list F7 Performs the split operation on the selected entity only face and edge in the Filter list F8 Performs the swap operation on the selected entity only face and edge in the Filter list F9 Allows you to merge the selected pair of nodes F11 Allows you to locate the worst skewed face in the mesh active group When you press this hot key the graphics window will be updated to show only the worst skewed face and its ID The skewness value is printed in the TGrid console F12 Undoes the latest operation performed on the mesh When modifying the boundary mesh it is not always possible to undo an operation ANSYS Inc April 15 2008 C 3 Hot Keys C 3 Hot Keys Hot Keys Description Ctrl a Adjusts the mesh position so that the mesh fits in the graphics window Ctrl c Selects cell as the Filter in the Modify Boundary panel This option does not work on Windows version of TGrid Ctrl d Calculates the distance between the two selected entities and displays it in the TGrid console Ctrl e Selects edge as the Filter in the Modify Boundary panel Ctrl f Selects face as the Filter in the Modify Boundary panel Ctrl g Displays the neighbori
572. tion for defining the cylinder axis 2 Specify the points defining the cylinder axis You can specify the locations or node IDs manually Alternatively you can click the Select Points or the Select Nodes button and select the points using the mouse Specify an appropriate value for the Radius of the cylinder Specify the appropriate Mesh Size if required Click Preview to preview the cylinder to be created QO oO AeA WwW When you are satisfied with the settings click Create to create the cylindrical surface 7 86 ANSYS Inc April 15 2008 7 14 Creating Surfaces PI X Y4 Z P2 X5 Y5 Z 9 Figure 7 14 2 Defining a Cylinder The Cylinder Panel The Cylinder panel allows you to create a cylindrical surface mesh Boundary Create gt Cylinder Cylinder Node ID First Node bn5023 v By Locations By Nodes Radius zi Second Node bn4688 T Edge Length Select Nodes o b Create Preview Close Help Controls Parameters contains parameters to be specified for creating the cylindrical surface mesh By Locations allows you to specify the locations X Pos Y Pos Z Pos of the points P1 and P2 defining the cylinder axis 7 87 ANSYS Inc April 15 2008 Manipulating the Boundary Mesh Select Points allows you to select the points defining the cylinder axis using the mouse When you click the Select Po
573. tion is within the Rel Reproject Range x D the node will be projected back on the original geometry Others are left at their locations Enable Preserve Boundary if required If you perform the smoothing operation after separating the zones of the wrapper surface the nodes on the boundaries of the separated zones will not be moved or repositioned during smoothing ANSYS Inc April 15 2008 8 8 Post Wrapping Improvement Operations Smoothing Folded Faces The presence of folded faces on the wrapper surface may cause problems in calculating the CFD solution TGrid allows you to resolve folded faces by performing node smoothing and reprojection of nodes on the original geometry To smooth the folded faces do the following 1 Select the wrapper surface in the Tri Boundary Zones selection list 2 Select Post Wrap in the Options drop down list and Smooth Folded in the Sub Options list 3 Specify the number of attempts to be made to resolve the folded faces in the Iteration field 4 Specify an appropriate value for Critical Angle The critical angle is the angle between adjacent faces If the feature angle between the two faces is less than the value specified the faces are considered as folded The default value for this parameter is 30 You can specify an appropriate value for the critical angle however it is recommended that you not specify a very large value 5 Enable Reprojection to allow projection of nodes onto
574. tions cannot be undone Theoretically if no merge or collapse operations are performed you could undo all previous operations In reality certain sequences of operations are not reversible ANSYS Inc April 15 2008 7 31 Manipulating the Boundary Mesh 7 4 Improving Boundary Surfaces The quality of the volume mesh is dependent on the quality of the boundary mesh from which it is generated TGrid allows you to improve boundary surfaces to improve the overall mesh quality The improvement operations are relevant only for triangular boundary zones of 3D grids You can improve the boundary mesh by specifying an appropriate quality limit depending on the quality measure considered You can also smooth and swap faces on the boundary surfaces to improve the mesh quality You can use the Boundary Improve panel to improve the surfaces You can diagnostically determine the boundary mesh quality using the Check and Skew buttons available when the Swap option is selected 7 4 1 Improving the Boundary Surface Quality You can improve the boundary surface quality using skewness size change aspect ratio or area as the quality measure e For improving the the boundary surface quality based on skewness size change and aspect ratio specify the quality limit the angle and the number of improvement iterations All the elements above the specified quality limit will be improved e For improving based on the area collapse faces and then eit
575. to separate the surface on which you have defined a seed face from the other faces in the zone based on the existing edge thread loops associated with it You must create edge thread loop for the given mesh If you have not created the edge thread loops you will not be able to separate the zones using this method To separate the face zones based on this criteria do the following 1 Under Options select Seed 2 Under Flood Fill Options select Edge Loop 3 Select a seed element in the Face Seed text entry field In this method you will only specify a seed element in the Face Seed text entry field The Angle text entry field will not be accessible 4 Click Separate Fa Create edge threads on the surface zones again using Surface Retriangulation panel after performing above operations Marked Cells You can separate face zones by placing faces that have been marked in a new zone To use this option in the Separate Face Zones panel explicitly define a subregion of the domain using the Refinement Region panel then separate face zones based on whether or not each face in the specified zone is in the selected local region ANSYS Inc April 15 2008 7 67 Manipulating the Boundary Mesh In the text interface mark faces for separation using the following TUI commands e boundary mark faces in region e boundary mark face proximity e boundary mark face intersection Then separate the marked faces using the TUI command se
576. to specify the orientation of the new region Note TGrid orients the region by rotation first about the x axis then the y axis and finally the z axis You need to take this into account while specifying the orientation of the region as rotation in any other order will produce different results Max Cell Volume sets the maximum cell volume for the selected region You can change this value by entering a new value in this text entry box Cell Volume Limits reports in an Information dialog box and the console the number of cells in the selected region and the minimum maximum and average size of these cells Define creates a new region according to the specified parameters It also allows you to modify the selected region according to the specified changes Init creates a default region encompassing the entire geometry Draw draws the region s in the graphics window The maximum cell size for the refinement and outer regions will also be displayed If the boundary grid was displayed using the Display Grid panel see Section 14 1 3 The Display Grid Panel before drawing the refinement region the grid will also be included in the display Refine refines active cells inside the selected region based on the specified refinement parameters Delete deletes the selected region 11 6 Additional Text Commands for Tri Tet Mesh Generation mesh tritet init refine generates the triangular tetrahedral mesh mesh tritet controls advanced
577. tributions to two or more portions of an edge loop you can separate the loop based on a specified feature angle between consecutive edges Separation is performed automatically at multiply connected nodes After creating edge loops using an appropriate combination of the edge loop creation approach and angle criteria modify the edge loops as required You can modify the edge loops using the options available in the Feature Modify panel Refer to Section 7 6 2 Mod ifying Edge Loops Using the Feature Modify Panel for details on using the various options available in the Feature Modify panel It is also possible to modify the edges of the loop using the operations in the Modify Boundary panel Any edges you create must have the same direction as the edge loop i You cannot remesh a continuous edge loop You must first separate it into two or more non continuous edge loops i e edge loops with start and end points 7 7 3 Remeshing Surface Zones If the mesh resolution on the boundary is not enough or you want to create triangular faces on a boundary that currently has quadrilateral faces you must remesh that boundary You can remesh the face zones using the Surface Retriangulation panel You can remesh face zones using the parameters available in the Face Remesh Options group box in the Surface Retriangulation panel ANSYS Inc April 15 2008 7 55 Manipulating the Boundary Mesh The procedure for remeshing face zones using th
578. ts lighting interpolation sets the lighting interpolation method to be used You can choose flat gouraud or phong The first one is the most basic method and the others are more sophisticated and provide smoother gradations of color display set lights set ambient color sets the ambient color for the scene The ambient color is the background light color in a scene display set lights set light adds or modifies a directional colored light 14 8 Describing a Scene After displaying a grid or parts of a grid in your graphics window you may want to overlay an additional display or move objects around and change their characteristics to increase the effectiveness of the scene displayed You can use the Scene Description panel the Display Properties and Transformations panels which are opened from within it to rotate translate and scale each object individually as well as change the color and visibility of each object You can make geometric objects visible and invisible thereby adding or deleting objects from the scene one at a time 14 8 1 The Scene Description Panel The Scene Description panel allows you to turn overlays on and off select geometric objects in the display for modification or deletion and open panels that control various characteristics of the selected object s Display Scene This menu item becomes available after you display a grid in the graphics window You cannot use the Scene Descriptio
579. two push button controls Apply applies any changes you have made to the panel but does not close the panel The name of this button is often changed to something more descriptive for example Sort for the sorting panels Close closes the panel All panels include the Help push button used to access on line help It displays infor mation about the controls in the panel The help information will appear in the web browser 3 3 2 Controls of a Panel Different types of controls in the panels are described in the following sections Tab Growth Direction Improve Project Tabs in the panel are used to mark the different sections into which the panel is divided The panel may be divided into different sections to reduce the amount of screen space it occupies Click on a tab to access that particular section of the panel Button Close 3 10 ANSYS Inc April 15 2008 3 3 Panels A button is used to perform a function indicated by the button label Click on the button to perform the action associated with it Check Box EF Landscape Orientation A check box also referred to as check button is a dialog element that is used to select or deselect an option It is located on forms and can appear alone or in groups of two or more and is used to enable disable an item or action indicated by the label of the check box Click the left mouse button on the check box to toggle the state Radio Buttons Color
580. u aaa aaa aaa 13 21 13 7 4 Text Commands for Moving Nodes 13 22 13 8 Cavity Remeshing ior ecos ke eee RP oe REP eS SRP e a s 13 23 13 8 1 The Cavity Remesh Panel oaa aa 13 26 13 8 2 Text Commands for Cavity Remeshing 13 27 13 9 Manipulating Gell ZONES 2 0 e yey oe hee a A EES S 13 27 13 9 1 Active Zones and Cell Types 4 4406 es es wa ee Rw Hew 13 27 13 9 2 Copying and Moving Cell Zones 004 13 28 13 9 3 The Manage Cell Zones Panel 2 000 13 29 13 9 4 Text Commands for Manipulating Cell Zones 13 32 13 10 Using Domains to Group and Mesh Boundary Faces 13 33 1310 1 Using Domains ss se rnia rodic oo hS be REG E DEES 13 34 1310 2 Were Domains se gO eee eee we kee NA 13 34 To The Domains Panel gretas grania ee HP eR Bae ee eS 13 35 ANSYS Inc April 15 2008 TOC 11 CONTENTS 13 104 Text Commands for Domains e ss s lt b pas edd eee ae ee eS 13 37 13 11 Checking the Meshi s Gs eae bo ok ROG Paha Ma ee RM alee 13 37 13 12 Clearing the Mesh i eee ew ee eee ee we ye 13 38 14 Examining the Mesh 14 1 14 1 Displaying the Gid o ecr ecd s a oe eee we dru we Bae ww hee eo 14 2 14 1 1 Generating the Grid Display 14 2 142 Grid Display Options 24 4 ec eed Ba snek oe seaweed ea 14 3 14 1 3 The Display Grid Panel 2242 4 6 e ee ee ee 14 4 14 1 4 Text Commands for Displaying the Grid 14 11 14 1 5 The Grid Colors Panel
581. u can not recover the regions after they have been deleted Interface contains a list of the interface surfaces extracted from the regions The Interface list is available only after you have extracted an interface from any region Wrap creates the wrapper surface from the selected interface s Draw displays the selected interface s List lists the face count for all extracted interface s in the console Delete deletes the selected interface s Fix Holes contains options for fixing holes in the Cartesian grid Automatic lists the holes detected for all regions Draw draws the hole s selected in the Automatic selection list List lists the ID location and the region for the hole s selected in the Automatic selection list Fix closes the holes selected in the Automatic selection list Open allows you to ignore holes in regions other than the region of interest Region specifies the region to be considered for automatic hole fixing Select selects the holes detected for the region specified in the Region field Manual contains options for manual hole fixing Pan Regions opens the Pan Regions panel using which you can ex amine the Cartesian grid Trace Path opens the Trace Path panel using which you can trace the leaks or holes in the existing geometry Update Regions updates the selected region for the modifications made to the zones selected in the Tri Boundary Zones list See Section 8 5 2 Manual Leak Dete
582. u can select a color for the selected type Reset Colors clears any colors you have set in the Scene Description panel so that all colors will revert to their definition by type or by ID as indicated under Options 14 1 6 Text Commands for Grid Colors The following text interface commands are similar in functionality to the controls in the Grid Colors panel display set colors color by type allows you to specify that the entities should be colored by their zone types The individual zone type colors can be set using the various text menu options e grid far e grid inlet e grid interior 14 14 ANSYS Inc April 15 2008 14 1 Displaying the Grid grid internal grid outlet grid periodic grid symmetry grid axis grid free surface grid traction grid wall surface display set colors list lists the colors available for the selected zone type display set colors reset colors resets the individual grid surface colors to the de faults 14 1 7 The Style Attributes Panel The Style Attributes panel is opened by clicking on the Styles button in the Attributes tab frame of the Display Grid panel see Section 14 1 3 The Display Grid Panel It controls the appearance of faces edges and nodes that are displayed using the Display Grid panel To modify the attributes of a certain type of face edge or node e g unmeshed select the appropriate item in the Styles list change the parameters and click Apply You can see t
583. u need to specify only a translational shift When the periodic shadow boundary is created from the original periodic boundary the nodes around the outer edges of the shadow zone will be duplicates of existing nodes These duplicates will be marked as free so they can be verified by counting them and drawing them Before generating the initial mesh you must merge these nodes i To ensure that the periodic shadow boundary creation works properly in TGrid you must define the node distribution correctly in the preprocessor that generates the boundary mesh In 3D you must be sure that the distribution of nodes on the boundaries that will be shared by the shadow zone and the surfaces adjacent to it is the same as the distribution on the boundaries shared by the original periodic zone and its adjacent surfaces In 2D however you need not worry about this requirement 7 90 ANSYS Inc April 15 2008 7 14 Creating Surfaces The Make Periodic Boundaries Panel The Make Periodic Boundaries panel allows you to create a matched pair of periodic periodic shadow boundaries from an existing zone You can select more than one zone for which periodic pairs should be created if appropriate For translationally periodic problems specify the translational shift and for rotationally periodic problems specify the angle of rotation and the axis of rotation After setting the appropriate parameters click on the Apply button TGrid will create
584. undaries allows you to create the hexcore mesh extending upto the boundaries of the domain Refer to Section 12 3 2 Hexcore Upto Boundaries for details Boundaries opens the Outer Box Zones panel see Section 12 4 1 The Outer Box Zones Panel where you can specify the boundaries comprising the bounding box X Min Y Min Z Min X Max Y Max Z Max specify the extents of the domain Draw Domain draws the defined domain Interface Smoothing specifies the parameters controlling interface smoothing Smooth Interface toggles smoothing at the hexcore interface Number of Iterations sets the number of smoothing iterations on the parent face Increasing the number of iterations will increase the value of maximum skew ness of the hex cells near the boundary It also helps initializing the tets and obtaining lower maximum skewness in the tet region The default number of iterations is zero When the number of smoothing iterations is zero the nodes at the parent face will be perturbed Relaxation Factor sets the value of under relaxation for smoothing the parent face Zones contains parameters that related to the zones created during hexcore meshing Delete Dead Zones toggles the deleting of the dead zones Non Fluid Type selects the default non fluid cell zone type After the mesh is initialized TGrid will set any non fluid zones to the specified type By default the non fluid type is set to dead as TGrid considers the grid to compris
585. undary Cell Limits 15 7 Report Cell Limits 15 5 Report Face Limits 15 3 Report Mesh Size 15 1 Scene Description 14 38 Separate Face Zones 7 67 Style Attributes 14 15 Surface Retriangulation 7 56 Trace Path 8 44 Transformations 14 42 Tri Tet Improve 13 9 Views 14 30 Wrapper Refinement Region 8 42 Write Views 14 32 Zone Prefix 7 87 Zone Selection Helper 14 51 categories 3 9 parent node 10 18 PATRAN 6 12 A 1 A 4 export 6 16 periodic 7 89 periodic shadow 7 89 perspective view 14 35 ANSYS Inc April 15 2008 Index planar points method 7 81 planar surface axis direction method 7 81 planar points method 7 81 plane surface creating 7 81 Plane Surface panel 7 83 plot axes 14 21 plotting cell distribution 14 19 face distribution 14 17 polyhedra 6 4 post improve automatic improvement 8 28 improving quality 8 26 inflating thin regions 8 22 recovering a single surface 8 29 recovering zones 8 26 remove duplicate nodes 8 21 remove self intersection 8 24 removing crossovers 8 30 renaming zones 8 27 rezoning faces 8 27 smoothing 8 21 smoothing folds 8 22 post wrap coarsening 8 18 deleting islands 8 25 swapping 8 25 preserving cell zones 11 1 Print panel 3 15 prism 9 1 cap faces 10 11 10 12 collision detection 10 7 dangling walls 10 6 generation 10 1 details 10 12 from multiple boundary zones 10 5 new zones created during 10 11 growth direction 10 3 10
586. unv sample grd After the output file has been written you can read it into TGrid using the File Read Mesh menu item For volume meshes the resulting output file can also be read into FLUENT i All boundary types are considered as wall zones You can set the appro priate boundary types in TGrid or in the solver A 3 2 deas Universal Files For deas surface meshes the filter reads triangular and quadrilateral elements that define the boundaries of the domain and have been grouped within I deas to create zones For volume meshes the filter reads a 2D or 3D mesh that has its boundary nodes or 2D boundary elements appropriately grouped to create boundary zones Do not include nodes and boundary elements in the same group All boundary zones will be considered wall zones you can set the appropriate boundary types in TGrid or in the solver See Section A 3 1 Using the fe2ram Filter to Convert Files for information about using the fe2ram grid filter A 2 ANSYS Inc April 15 2008 A 3 Meshes from Third Party CAD Packages Recognized deas Datasets The following Universal file datasets are recognized by the grid filter Node Coordinates dataset number 15 781 2411 Elements dataset number 780 or 2412 Permanent Groups dataset number 752 2417 2429 2430 2432 2435 Since TGrid uses linear elements you should use linear elements to generate the grid inside the mesh areas If parabolic elements exist in the dataset the
587. uracy and slow convergence A detailed discussion of skewness can be found in Section 15 5 Mesh Quality Free edges are acceptable if you are modeling a zero thickness wall thin wall in the geometry e g Figure 7 1 2 Improving the boundary mesh not only makes mesh generation easier but also im proves the final mesh quality and provides a better solution See Section 7 3 Mod ifying the Boundary Mesh for boundary mesh improvement utilities You can either retain the isolated nodes nodes that are not used by any bound ary faces to influence the generation of the interior mesh or delete them See Section 9 1 7 Inserting Isolated Nodes into a Tri or Tet Mesh To merge or collapse multiple pairs select an even number of nodes and ensure that you select them in the correct order Select a subset of all boundary zones for node comparison to save time TGrid will be able to search for duplicate nodes and merge them more quickly if it does not need to check the nodes on all boundaries If the initial mesh generation is not successful the nodes that failed to be inserted are moved to the front of the node list so that they will be inserted first in the next attempt ANSYS Inc April 15 2008 E 9 Examining the Mesh E 9 Examining the Mesh After reading the mesh file check the boundary mesh for topological problems such as free and multiply connected nodes and faces When TGrid initializes the mesh it automaticall
588. urred After reading the error information click OK to close the dialog box 3 2 2 Information Dialog Box Information Edge Size Limits wall Minimum 0 99447779 Maximum 20 257125 Average 838 0415928 o The Information dialog box is used to report some information to you After reading the information click OK to close the dialog box 3 2 3 Warning Dialog Box Warning The file myfile msh already exists OK to overwrite pi jem The Warning dialog box is used to alert you of a potential problem and ask you whether or not you want to proceed with the current operation Click OK to proceed with the operation Click Cancel to cancel the operation 3 2 4 Working Dialog Box working Refining mesh poet The Working dialog box is displayed when TGrid is busy performing a task When the task is done the dialog box will close automatically ANSYS Inc April 15 2008 3 5 Graphical User Interface This is a special dialog box because it requires no action by you However you can abort the task that is being performed by clicking the Cancel button 3 2 5 Question Dialog Box The Question dialog box is used to ask you a question that requires an answer Yes or No Click on the appropriate button to answer the question 3 2 6 Select File Dialog Box The Select File dialog box allows you to select a file or mult
589. urrounding the surface on which the seed face is defined based on the specified angle criteria The common edge is considered to be a feature edge when the angle value specified fixed angle criterion is less than the feature angle Alternatively the edge thread at the common edge can be created by detecting the change in the feature angle automatically adaptive angle criterion The Face Seed approach is available only when you use the Feature Modify panel for creating edge loops If you use the Surface Retriangulation panel instead the Face Zone approach will be used for creating the edge loops Figure 7 6 1 shows a surface mesh with two faces connected at a common edge and having a feature angle of 60 degrees Both faces are in the same face zone ANSYS Inc April 15 2008 7 43 Manipulating the Boundary Mesh Figure 7 6 1 Surface Mesh Feature Angle 60 Figures 7 6 2 7 6 5 show the edge loops created for different combinations of approach and angle criterion 7 44 e Figure 7 6 2 shows the single edge loop created by using the Face Zone approach and Fixed angle criterion with the angle specified as 65 degrees The edge thread at the common edge is not created since the specified value for Angle is greater than the feature angle Figure 7 6 3 shows the edge loops created by using the Face Zone approach and Fixed angle criterion with the angle specified as 55 degrees The interior edge thread at the com
590. used to remesh the specified face zone boundary remesh remesh overlapping zones remeshes overlapping face zones The non overlapping region is remeshed using the edge loops created from the overlap ping face zones ANSYS Inc April 15 2008 7 59 Manipulating the Boundary Mesh boundary remesh controls delete overlapped enables disables the deleting of over lapped edges boundary remesh controls direction specifies the direction of the edge loop projec tion boundary remesh controls project method specifies the method for projecting edge loops boundary remesh controls quadratic recon enables disables quadratic reconstruc tion of edge loops during remeshing boundary remesh controls remesh method specifies the method to be used for the node distribution on the edge loop boundary remesh controls spacing sets the node spacing for the edge loop boundary remesh controls tolerance sets the tolerance for determining if two edges intersect boundary surfer degree iterations specifies the number of degree swapping itera tions to be performed after surface triangulation boundary surfer grading sets the surface triangulation grading factor boundary surfer max elements on face sets the maximum number of faces allowed for surface triangulation boundary surfer selection interval sets the surface triangulation selection inter val boundary surfer shape tolerance sets the surface triangulation shape tolerance
591. vailable only when the Improve Warp option is enabled Dihedral Angle specifies the feature angle to be considered when moving bound ary nodes and allows you to maintain features of the geometry A boundary node will not be moved if the angle between the faces sharing the boundary node is less than the specified value ANSYS Inc April 15 2008 13 21 Improving the Mesh Cell Zones contains a drop down list of the cell zones from which you can select those to be considered for improvement Boundary Zones contains a list of the boundary zones from which you can select those to be considered for improvement Restrict Boundary Nodes Along Surface allows you to restrict the movement of bound ary nodes within the plane caontaining the faces sharing the node This option is available only for the skewness based improvement Auto Correction contains options for using the automatic correction procedure for skewness based improvement Iterations specifies the number of repetitions through the automatic correction procedure Apply performs the automatic correction procedure according to the number of iterations specified Semi Auto Correction contains options for using the semi automatic correction proce dure for skewness based improvement Skew displays the cell with the maximum skewness and cells faces within a pre defined range of the cell Next Skew displays the cell with the next highest skewness Reset Skew allows you to r
592. values being plotted 14 3 Checking Cell Distribution You can check cell size or quality by using the controls in the Cell Distribution panel or the associated text commands to generate a histogram plot or report When a histogram plot is displayed in the graphics window you can use any of the mouse buttons to add text annotations to the plot For more information about the annotation features see Sections 14 9 and 14 11 14 20 ANSYS Inc April 15 2008 14 3 Checking Cell Distribution 14 3 1 The Cell Distribution Panel The Cell Distribution panel allows you to generate a histogram of cell size or quality Display gt Plot Cell Distribution Cell Distribution Options Minimum Cell Zones 5 4 j Quality Tr heta fluid 13 0 v Size Maximum 0 7495732 Quality Measure Percent of Total Axes Partitions 100 y Cell Zone Groups 5 dead a fluid Print Plot Compute Close Help The number of cells in the specified range in each of the regularly spaced partitions is displayed in a histogram format The x axis shows either the size or the quality and the y axis gives the number of cells or the percentage of the total Note If you have used domains to generate the mesh or group zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces you can report the cell distribution only for those cell zones t
593. ve C1 N12 is located in the same position as the node at the beginning of curve C2 N21 each is a free node because it is not connected in any way to the adjoining curve Although the nodes have the same location TGrid knows only that they have different names and thus is unaware that the curves meet at this location Similarly if extrapo lated into 3D a free edge is a surface edge that is used by only one boundary face To check the location of free nodes see Section 14 1 3 The Display Grid Panel Free edges are acceptable when modeling a zero thickness wall thin wall in the ge ometry e g Figure 7 1 2 Isolated nodes are nodes that are not used by any boundary faces You can either retain these nodes to influence the generation of the interior mesh see Section 9 1 7 Inserting Isolated Nodes into a Tri or Tet Mesh or delete them ANSYS Inc April 15 2008 7 1 Manipulating Boundary Nodes ay COKER ASSIA RYRNSP ERAS y BA ay N 7 s a ATATA AA 0 ERTO KL K RNIN i AY unl HAY N N N 7 f A YAVA VV ZVN VAVA 7 oO AA V 2 7 KK lt gt AV KA N Figure 7 1 2 Example of a Thin Wall 7 1 2 The Merge Boundary Nodes Panel The Merge Boundary Nodes panel provides reports on free or isolated boundary nodes and options for removing duplicate and or isolated nodes Boundary gt Merge N
594. ve already been created in some portion of the computational domain you need to create a domain encompassing the region to be meshed with triangular or tetrahedral cells before starting with the tri tet mesh generation See Section 13 10 Using Domains to Group and Mesh Boundary Faces for details In such cases all automatic and or manual meshing actions will apply only to the active domain Alternatively instead of creating a new domain you can specify the cell zone s to be pre served while generating the tet mesh before proceeding with the mesh generation You can use the command mesh tritet preserve cell zone to specify the cell zone s to be preserved ANSYS Inc April 15 2008 11 1 Generating Triangular Tetrahedral Meshes 11 1 Automatically Creating a Tri or Tet Mesh The Auto Mesh submenu in the Mesh menu contains commands that encapsulate the recommended volume mesh generation strategy The starting point for this procedure is a valid surface mesh 11 1 1 Automatic Meshing Procedure for Tri Tet Meshes The automatic tri tet mesh generation process is divided into two fundamental tasks initialization and refinement The automatic initialization procedure comprises the fol lowing steps 1 Merging free nodes 2 Deleting unused nodes 3 Improving the surface mesh 4 Initializing the mesh 5 Generating and separating cell regions i If the mesh fails to initialize typically this indicates a problem with the
595. ve graphics window Display Annotate Annotate Names Annotation Text XEON inlet Font Specification Name Weight Sans Serif y Medium Y Color Slant Size Delete Text foreground F Regular y 16 x 14 50 ANSYS Inc April 15 2008 14 11 Annotating the Display Names contains a selectable list of all annotation text strings that have been defined You can choose a text string to be deleted or edited Delete Text deletes the text strings selected in the Names list from the display Annotation Text contains the annotation text string you wish to add or the annotation text string for the item selected in the Names list Font Specification contains controls for defining or modifying the font in the annotation text string Name contains a drop down list of various font styles Weight contains a drop down list from which you can select Medium or Bold Size contains a drop down list of font sizes in points Color contains a drop down list of colors that can be used for the text Slant contains a drop down list from which you can select Regular Italic or Oblique as the slant type Add adds the current Annotation Text to the active graphics window A dialog will prompt you to select a screen location using the mouse probe button For more information on setting the mouse buttons see Section 14 9 Controlling the Mouse Buttons
596. vectors near the corner after they have been smoothed After smoothing the normal direction changes more gradually from node to node 10 18 ANSYS Inc April 15 2008 10 8 Offset Distances or ir a yfftt S Figure 10 7 4 Normal Direction Vectors After Smoothing It is possible to create very thin prism layers using the direction vectors shown in Fig ure 10 7 3 as long as the last layer lies below the point where the vectors cross 10 8 Offset Distances The offset distance for a given node is the distance between adjacent layers at that node This distance is based on the prism layer height computed from the specified prism growth parameters The new node for a prism layer is placed at this distance along the direction vector There are four methods available for determining the offset distances e Uniform Offset Distance Method In this method every new node child is initially the same distance away from its parent node i e the corresponding node on the previous layer from which the direction vector is pointing Paii l a Figure 10 8 1 Uniform Offset Distance Method Uniform distances are fine for planar surface meshes but they result in crevices at sharp corners for example the 90 degree corner in Figure 10 8 1 The direction vector at the corner node will be at an angle of 45 degrees while the vectors at ANSYS Inc April 15 2008 10 19 Generating Prisms 10 20
597. wness for a bound ary cell All active boundary cells with skewness greater than this value will be refined Max Cell Skew specifies the maximum acceptable skewness for a cell All active cells with skewness greater than this value will be refined Min Node Closeness specifies the distance from an interior node normalized by the local mesh size within which it is appropriate to add a node This re striction prevents a node from being added too close to another node Min Boundary Closeness specifies the distance from a boundary node normalized by the local mesh size within which it is appropriate to add a node Do not add nodes too close to the boundary because it will be nearly impossible to remove a highly skewed cell if created Smooth Min Skew specifies the minimum skewness required to perform smooth ing Max Smooth Iteration specifies the maximum number of smoothing iterations Swap Min Skew specifies the minimum skewness required to perform swapping Max Swap Iteration specifies the maximum number of swapping iterations Apply applies the specified refinement parameters Default restores all parameters to their default values 11 22 ANSYS Inc April 15 2008 11 5 The Tri Tet Panel 11 5 3 The Tri Tet Refinement Region Panel The Tri Tet Refinement Region panel provides options for creating modifying and acti vating deactivating refinement regions for tri tet mesh refinement Tri Tet Refinement Regio
598. y Measure opens the Quality Measure panel see Section 15 5 2 The Quality Measure Panel in which you can select the measure of quality to be reported skewness aspect ratio etc Minimum Maximum Average report the computed values for size or quality Face Zones contains a list from which you can select the zones for the report Face Zone Groups contains a list of face zone types If you select a face type from this list e g inlet all face zones of that type for this example all pressure inlet and velocity inlet boundaries will be selected in the Face Zones list This allows you to easily select all face zones of a certain type without selecting each zone individually Select multiple types in the Face Zone Groups list to select all zones of several different types e g inlet and outlet Compute calculates the Minimum Maximum and Average values for the selected option size or quality on the selected face zones 15 4 ANSYS Inc April 15 2008 15 3 Reporting Cell Limits 15 2 2 Text Commands for Reporting Face Limits Text commands with the same functionality as the controls in the Report Face Limits panel are report face size limits reports the face size limits report face quality limits reports the face quality limits 15 3 Reporting Cell Limits TGrid allows you to report the quality of the cells in your volume mesh The default quality measure is skewness but you can also report the aspect rati
599. y changing the Level Level allows you to specify the cell length for the zones selected in the Tri Boundary Zones list Apply applies the specified level of refinement to the selected boundary zone Clear clears the specified level of refinement to the selected boundary zone Select selects the geometry zones on which specified zone sizes are defined Deselect deselects the geometry zones on which specified zone sizes are defined List reports the name level and cell size of the zone s selected in the Tri Boundary Zones list Local Size Function allows you to define local size functions and to refine local cells based on the size functions Proximity allows you to automatically refine the local cells based on the proximity of the zone to other faces in the domain Curvature allows you to automatically refine the local cells based on the curvature of the zone in the domain Min Length specifies the minimum allowable size of the cells in the Carte sian grid Level allows you to specify the minimum cell length for local refinement Apply computes required sizes based on the input geometry zones as well as parameters and updates size functions Options contains additional options for wrapping Ignore Self Proximity allows you to ignore self proximity during wrapping By default this option is disabled 8 34 ANSYS Inc April 15 2008 8 9 The Boundary Wrapper Panel Buffer Layers specifies the number of additiona
600. y makes the cell zone with the largest volume or the cell zone that contains a boundary zone with type pressure outlet the active fluid zone TGrid treats the rest of the cell zones non fluid zones as dead zones If any unmeshed nodes or faces are displayed you will need to regenerate the initial mesh If you have used domains to generate the mesh or group zones for reporting as described in Section 13 10 Using Domains to Group and Mesh Boundary Faces you can report the face distribution only for those face zones that are in the active domain When using the sliders and dial to manipulate the view turn off Wireframe Anima tion in the Display Options panel see Section 14 5 1 The Display Options Panel to watch the display move interactively while you move the slider or the dial indicator You can edit the text in the caption block of the graphics window by clicking your left mouse button in the desired location A cursor will appear and you can then type new text or delete the text that was originally there Text in the caption block will not be deleted when you clear annotations E 10 Reporting Mesh Statistics If the quadrilateral face skewness is much greater than 8 regenerate them If they were created in a different preprocessor return to that application and try to reduce the aspect ratio of the faces in question If they were created by TGrid during the building of prism layers rebuild the prisms using a mo
601. y one journal file can be open for recording at a time but you can write a journal and a transcript file simultaneously You can also read a journal file at any time Only one transcript file can be open for recording at a time but you can write a transcript and a journal file simultaneously You can also read a journal file while a transcript recording is in progress The compressed file write will fail if the compress or GNU gzip compression rou tines not available on your platform E 3 Saving Hard Copy Files For the quickest print time save vector files for simple 2D displays and raster files for complicated scenes For raster hardcopy files you can control the resolution of the hardcopy image by specifying the size in pixels Non geometric entities such as text titles color bars and orientation axis are not exported using the VRML option In addition most display or visibility character istics set in TGrid such as lighting shading method transparency face and edge visibility outer face culling and hidden line removal are not explicitly exported but are controlled by the software used to view the VRML file Before saving a hardcopy file you can have a preview of the saved image Click Preview to apply the the current settings to the active graphics window so that you can see the effects of different options interactively before saving the hardcopy Raster supports IRIS image JPEG PostScript EPS and TIFF formats
602. y the specified translation offsets See Section 13 9 2 Copying and Moving Cell Zones for details Translation specifies the translation offsets X Y Z to be added to the Cartesian coordinate of every node in the selected zone s Copy Zone s allows you to copy the nodes of the selected zone s thereby creating new zone s of the same type before positioning the copied zone s per the specified translation offsets Cell Zones contains a list from which you can select the zone s to be modified Cell Zone Groups contains a list of cell zone types If you select a cell type from this list e g fluid all cell zones of that type will be selected in the Cell Zones list This method allows you to easily select all cell zones of a certain type without having to select each zone individually You can select multiple cell types in the Cell Zone Groups list to select all zones of several different types e g solid and fluid Apply performs the selected option on the selected zones Draw displays the boundaries that define the selected cell zones If any faces of a boundary are used in defining the zone then the entire boundary is displayed List reports in the console the ID name type and number of cells for each selected zone ANSYS Inc April 15 2008 13 31 Improving the Mesh 13 9 4 Text Commands for Manipulating Cell Zones Text interface commands for manipulating cell zones are mesh manage active list lists al
603. y with a re peating component to its smallest non repeating section The pe riodicity can be either rotational about an axis through the origin or translational Every periodic boundary actually consists of two boundaries the primary boundary and its shadow The matching periodic boundary zone of the primary periodic zone Each periodic zone must have a unique shadow See Periodic A process of introducing additional nodes into the mesh in an effort to improve the mesh quality A contiguous group of cells enclosed by boundary faces A statically scoped and properly tail recursive dialect of the Lisp programming language invented by Steele and Sussman ANSYS Inc April 15 2008 Glossary Shrink Factor Simplex Size Skewness Sliver Smoothness Squish ANSYS Inc April 15 2008 It specifies the amount by which you can shrink faces and cells It is often difficult to select a face or cell without selecting its neighbor instead Increasing the shrink factor enlarges the space between adjacent faces or cells enabling you to choose the desired entity more easily An n simplex is the convex hull of n 1 points A 0 simplex is a node a 1 simplex line segment is a face in 2D and an edge in 3D a 2 simplex triangle is a cell in 2D and a face in 3D and a 3 simplex tetrahedron is a cell in 3D Length area or volume depending on the dimensionality of the object The normalized measure of how far a c
604. ya ee we EE SAREE SE EM RS 9 13 Oo Creating Pyramids 52 6 gorai eieo be bee eee Se Goei 9 14 9 3 2 Zones Created During Pyramid Generation 9 16 9 3 0 The Pyramids Panel 4 465 64462 oe ee a Se RS 9 16 9 3 4 Text Interface for Generating Pyramids 9 20 9 3 5 Pyramid Meshing Problems 4 2 2 466 seod we eee ee eS 9 20 9 4 Creating a Non Conformal Interface 004 9 22 9 41 The Now Contormals Panel gt lt gt sco rsk he wR eo 9 22 9 4 2 Text Interface for Creating a Non Conformal Interface 9 24 9 5 Creating a Heat Exchanger Zone 2 2 00 0202 Ge 9 24 9 5 1 The Heat Exchanger Mesh Panel 2 9 25 10 Generating Prisms 10 1 10 1 OVervieW a sor oe Sek we ee Se ee ee ede ee eds Re a ana 10 1 10 2 Procedure for Generating Prisms 2 0 048 10 2 10 3 Prism Meshing Options os s eas scs on ere Bee SRD Roe EW Ew ia 10 5 10 3 1 Growing Prisms Simultaneously from Multiple Zones 10 5 10 3 2 Growing Prisms on a Two Sided Wall 10 6 10 3 3 Detecting Proximity and Collision os t s co eto o n 45 10 7 10 3 4 Ignoring Invalid Normale s e qis coe eis poep ie p ayat ie Gere ys 10 10 10 3 5 Preserving Orihoponality s t 24 244445 44444 erine Ho 10 11 10 4 Zones Created During Prism Generation 10 12 10 5 How Tord Builds Pristis see nce how mosia RS OR we ORES 10 12 TOC 8 ANSYS Inc April 15 2008 CONTENTS 10
605. ying Features The text commands for creating and modifying features are boundary feature create edge zones extracts edge loops for the specified face zone s based on the feature method specified You also need to specify an appropriate value for feature angle when using the fixed angle method Note The Face Seed approach cannot be used when creating edge loops using text commands boundary feature copy edge zones copies the specified edge zone s to new edge zone s boundary feature delete edge zones deletes the specified edge zone s boundary feature edge size limits reports the minimum maximum and average edge length for the specfied edge zone s in the console boundary feature group associates the specified edge zone s with the specified face zone boundary feature intersect edge zones intersects the specified edge loops to create a new edge loop comprising the common edges You can enable automatic deleting of overlapped edges and specify an appropriate intersection tolerance boundary feature list edge zones lists the name ID type and count for the spec ified edge zone s boundary feature merge edge zones merges multiple edge loops of the same type into a single loop boundary feature orient edge direction orients the edges on the loop to point in the same direction boundary feature project edge zone projects the edges of the specified loop onto the specified face zone using the specified projection me
606. you can choose to ignore regions of the geometry where invalid normals exist dur ing prism generation Prism layers will be grown from the remaining geometry according to the specified parameters Figure 10 3 6 shows a portion of the geometry where the normal at the highlighted node will be nearly tangential to some of the surrounding faces You can see that the region around this node has been ignored while creating prisms invalid normal region ignored based on normal 77 Figure 10 3 6 Ignoring Invalid Normals You can ignore regions based on normals while creating prisms as follows 1 Specify the prism growth parameters 2 Select the Boundary Zone containing the invalid normal and click the Growth Op tions button to open the Prisms Growth Options panel a Enable Ignore Invalid Normals in the General Options group box b Click Apply and close the Prism Growth Options panel 3 Grow prisms as required 10 10 ANSYS Inc April 15 2008 10 3 Prism Meshing Options 10 3 5 Preserving Orthogonality In some cases it may be important for the prismatic mesh to be orthogonal near the original boundary For such cases there are two ways to preserve orthogonality Decrease the value specified for the Max Angle Change in the Direction tab of the Prisms panel to a lower value to limit the change in normal direction in each prism layer This parameter is set to 45 degrees by default This means t
607. yramid create creates a layer of pyramid cells on the specified quadrilateral face zone 9 3 5 Pyramid Meshing Problems Most problems associated with creating pyramid layers manifest themselves in the sub sequent process of generating the tetrahedral mesh Rapid Changes in Volume Rapid changes in the sizes of cells have a negative influence on the convergence and accu racy of the numerical solution The pyramid layer creation can produce rapid variations in cell volume In any of the following situations e If the quadrilateral surface mesh has faces with rapid changes in size 9 20 ANSYS Inc April 15 2008 9 3 Generating Pyramids e If there is great disparity between the sizes of the quadrilateral faces and the neigh boring triangular faces used in the pyramid creation You can avoid the rapid variation in volume by creating quadrilateral and neighboring triangular grids with smooth variations in face size Intersecting Faces If the quadrilateral surface used to create pyramids has highly concave corners the result ing pyramids may pierce each other and or neighboring boundary faces see Figure 9 3 5 In such cases you can either increase the resolution to prevent the intersections or alter the meshing strategy An alternative is to separate the quadrilaterals in the concave cor ner into another zone using the Separate Face Zones panel or the Modify Boundary panel create triangular faces from the quadrilateral fa
608. zone in the Cell Zones selection list 4 6 ANSYS Inc April 15 2008 4 5 Displaying the Mesh Figure 4 5 1 The Display Grid Panel Cells Tab 3 Enable All in the Options group box 4 Click Display see Figure 4 5 2 Figure 4 5 2 Grid Display 5 Close the Display Grid panel The Cell Zones list has a dead zone When TGrid initializes the mesh it automatically makes the cell zone with the largest volume or the cell zone that contains a boundary zone with type pressure outlet the active fluid zone ANSYS Inc April 15 2008 4 7 Sample Session TGrid treats the rest of the cell zones non fluid zones as dead zones In this case there is a dead zone for the region inside the wedge see Figure 4 5 3 Since the cells in the dead zone are not in the computational domain they can be ignored When you read the mesh into the solver the dead cell zones will be ignored If you have a large mesh with many cells in a dead zone you can delete the dead zones using the Manage Cell Zones panel This reduces the memory requirements You can zoom in on the wedge using the middle mouse button to create a zoom box around it see Section 14 9 Controlling the Mouse Buttons for details The resulting display is shown in Figure 4 5 3 Figure 4 5 3 Grid Zoomed View 4 6 Reporting the Mesh Statistics It is important to examine the grid statistics in the Report menu Looking at tetrahedral c
609. zone and click the Apply button in the Zone Specific Growth group box in the Prisms panel If you specify different growth parameters for different zones all other parameters direction method offset method etc can be set separately for each zone In this case the offset height of each node that is shared by multiple zones will be the average of the heights applied on the separate zones This produces a continuous transition between the zones Figure 10 3 1 Offset smoothing see Section 10 8 Offset Smoothing is recommended in these cases to avoid sharp height changes at such edges To assign different growth controls and different offset types to different face zones replace steps 2 and 3 in Section 10 2 Procedure for Generating Prisms with the following steps 1 Select the zone s for which you want to specify a set of growth parameters in the Boundary Zones list in the Prisms panel 2 Set the appropriate Offset Method Growth Method First Height and the related growth parameters as required in the Growth tab ANSYS Inc April 15 2008 10 5 Generating Prisms Zone 1 Zone 2 Uniform Aspect Ratio Uniform Aspect Ratio Method Method Figure 10 3 1 Different Growth Methods on Adjacent Zones 3 Specify parameters for proximity collision detection in the Prisms Growth Options panel see Section 10 3 3 Detecting Proximity and Collision for details i By default TGrid generates a single zone of prism cells

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