Parametric Finite Element Modeling Across Many
Contents
1. a part in TrueGrid can consist of many different materials by using the mate mt and mti commands For NASTRAN output the linear material is selected first Then the element type and non linear properties are added I beam With Hole Using Shell Elements This next example demonstrates the use of curves and replications to create a shell model of an I beam with holes The block command is used to define a block structured quad shell mesh It has the same syntax as above using index lists to form multiple blocks in all three directions with one exception A minus sign is used to identify the indices in these lists that correspond to shell faces in the mesh para r lt 65 c radius thw 2 c web thickness thp 25 oc plate thickness block c shell part I PF ABs Lge c i list TST Oe ec j list Sal Sp ABs ale c k list O 1 5 r sin 45 1 5 r sin 45 3 x list 1 0 1 y list O 1 5 r sin 45 1 5 r sin 45 3 oe z list The second partition in the j list is a shell face that forms the web of the I beam The first and last indices in the k list form the bottom and top plates of the I beam One block in the middle of the web of the I beam is deleted The four edges to this hole will be deformed to the shape of a circle dei 2 3 2 2 3 Shell I Beam part with holes The th and thi commands assign shell thicknesses The last argument to these commands is the thickness thi 1 0 42. log 1og10 Sin cos tan asin acos atan atan2 sinh cosh rand and norm Additional functions can be defined with the def command def function_name a b c expression The function can have many dummy arguments The expression should be dependent on the dummy arguments Once defined a function can be used in the same manner as the intrinsic functions The if elseif else endif conditional statement is also available with the same properties as in FORTRAN For example if sdensity gt 1 0 then block 1 5 op Sk2e2 Sp he4 Te2 73 else block 1 5 1 6 1 Sk2 Sdensity 2 5 1 4 7 2 7 endif The above commands issue a different block command depending on the density parameter A typical use of the conditional statement is to insert a new partition when the conditions warrant it For example if srad3 radl gt 0 1 then if i3 i1l 1t 6 then mseq i 6 11 13 c add elements in the i direction endif insprt 1 2 1 5 c insert a partition in the i direction endif The include command will transfer the input stream to another file After all the commands are read from this file the input stream is then returned to the original source If the file is parametric then the include feature is similar to a subroutine call in a programming language For example c rad is the radius of the sphere c x0 is the x component of the center of the sphere c yO is the y component of the center of the sphere c z0 is the z c
3. materials LS DYna MATerialS nastmats materials NASTran MATerialS mt i material assign a material number to a set of elements by Index progression mate material set the default material number Analysis Options abaqstep analysis ABAQus STEP for analysis ansyopts analysis ANSYs OPTionS lsdyopts analysis LS DYna OPTionS nastopts analysis NASTran OPTionS Merging stp merging Surface Tolerance with Printout Load Curve led 2D curve Load Curve Definition Beams and Shells ibm i element I direction BeaMs by Index progression jbm i element J direction BeaMs by Index progression kbm i element K direction BeaMs by Index progression bm element BeaMs along a 3D curve bsd element Beam cross Section Definition th i element shell THickness by Index progression Mesh Quality measure diagnostic MEASURE mesh quality elm diagnostic display ELements within a given range of Measure labels graphics display LABELS for objects in the picture condition graphics use tokens to display various boundary CONDITIONS mlabs graphics display Multiple LABels and conditionS for objects in the picture Viewing slice graphics SLICE the picture by removing everything beyond a plane Sets nset i sets modify a Node SET by Index progression fset i sets modify a Face SET by Index progression eset i sets modify a Element SET by Index progression Loads
4. thp th 1 2 1 4 2 4 Sthw ole Attaching to a 3D Curve A circle is needed to shape 4 edges of the mesh The curd CURve Definition command has many 3D curve types and is used in this case to define the circle This example also shows how parameters can be used to form geometry The first argument to the curd command is the curve identification number followed by the curve type and related arguments curd 1 arc3 c define a circle by 3 points whole re plesn srh OS CE 1252 OL Ser ct Lis Stor 0 eae The curs command attaches an edge of the mesh to a curve The curs command requires a region see the definition of a region above followed by the curve number The order of commands for a part does not matter The commands are ordered within TrueGrid so that all of the move commands such as pb mb mbi and tr are used first Then the commands to attach edges to curves are used The end nodes of the edge i e corners of the block mesh can be moved with the mouse to control the way an edge is attached to a curve Since the order in which commands are issued does not matter one can attach an edge to a curve and then interactively move the corners of the mesh into position For this simple example no move commands were needed because the coordinates in the block command were carefully chosen curs 2 23 3 2 3 curs 3 223 2 3 curs 2 2 2 32 2 curs 2222 2 3 Part Replication Two commands are needed to replicat
5. Proceedings 4 International Meshing Roundtable Sandia National Laboratories pp 179 191 October 1995 3 National Computer Graphics Association The Initial Graphics Exchange Specification IGES Version 5 1 IGES PDES Organization Fairfax Va 1991 4 MSC NASTRAN User s Guide The MacNeal Schwendler Corporation Los Angeles Ca 1994 5 ABAQUS Version 6 4 PDF Documentation User s Manual ABAQUS Inc Pawtucket RI 2003 6 ABAQUS Version 6 4 PDF Documentation Reference Manual ABAQUS Inc Pawtucket RI 2003 7 Ansys Inc Ansys 6 1 Documentation SAS IP Inc Canonsburg Pa 2002 8 LS DYNA Keyword User s Manual Version 970 Livermore Software Technology Corp Livermore Ca 1992 2002 9 J F Thompson Z U Z Warsi and C W Mastin Numerical Grid Generation North Holland NY 1985 10 J F Thompson B K Soni N P Weatherill Handbook of Grid Generation Chapter 32 Truncation Error on Structured Grids by C W Mastin pp 32 1 to 32 10 CRC Press NY 1999 Appendix Commonly Used TrueGrid Commands The following is a list of the most commonly used commands in TrueGrid The name of the submenu for a command is found in the parentheses next to the key word command Some of the commands have an optional i suffix for the index progression form of the command Parts block parts initiate a multi BLOCK part in Cartesian coordinates cylinder parts initi
6. and Constraints b i boundary nodal constraints or Boundary conditions by Index progression fd i dis vel acc Fixed Displacement by Index progression fc i force ForCe by Index progression Misc para misc define some PARAmeters interrupt misc INTERRUPT the batch file with interactively generated commands resume misc RESUME the batch file after being interrupted help provide HELP dialogue for the given command if then else misc conditional statements include misc INCLUDE commands from a file def misc DEFine an inline function Replication lct replicate define a list of Local Coordinate Transformations lrep replicate Local REPlications of a part using transformations from lct above
7. many simulation codes batch mode so that a template FEM can be easily modified material models and analysis options that only need to be defined once parameters and expressions used wherever they are needed high quality elements to minimize the effect of the mesh on the results smooth and predictable variations in the mesh loads and constraints NYDN BWNr The TrueGrid User s Manual and Examples Manual in electronic form are available Emailing requests to info truegrid com Input decks to the draw shell I beam and solid I beam are also available upon request As a final note TrueGrid supports many options for ABAQUS ANSYS LS DYNA and NASTRAN However these simulation codes are constantly improving and TrueGrid does not support every feature in every code If TrueGrid does not support a feature try two things First contact the support team at XYZ Scientific Applications at 925 373 0628 and ask if this feature can be added to TrueGrid Also try the verbatim command verbatim multi line block of text endverbatim This command will take any text within its scope and duplicate it verbatim in the output file References 1 TrueGrid Manual version 2 1 0 by XYZ Scientific Applications Inc Sept 7 2001 2 Benzley S E Perry E Merkley K Clark B and Sjaardama A Comparison of All Hexagonal and All Tetrahedral Finite Element Meshes for Elastic and Elasto Plastic Analysis
8. number For example the fd and fdi specify fixed displacements This identification number in the argument list is followed by an amplitude and a 3D displacement vector fdi 1 1 2 03 4 1 2 1 1 10 0 fdi 6 1 20 3 4 1 2 1 1100 Material Assignment Materials are identified with a positive number The properties of the material are defined below All elements are assigned a material number The default is 1 The mate command changes the default The mt and mti commands assign materials to different regions of the mesh In the draw model the elements to be drawn are assigned material 1 and the clamp elements are assigned material 2 by default mate 2 m 1216322 1 Other Parametric Features The para command defines parameters that can be used in place of any number The character must precede the use of any parameter para k2 7 density 2 236 c define k2 and density Algebraic expressions can be inserted wherever a number is needed to complete a command The expression must be enclosed by the open and close square brackets The syntax for operators and intrinsic functions match FORTRAN with the following exceptions 1 and can be used for exponentiation 2 Trigonometric functions use degrees not radians 3 The norm function generates a random variable with a normal distribution para k2 3 2 1 density sqrt 5 c define k2 and density The intrinsic functions are int nint abs mod sign max min sqrt exp
9. Parametric Finite Element Modeling Across Many Simulation Codes Robert Rainsberger XYZ Scientific Applications Inc 1324 Concannon Blvd Livermore CA 94550 rains truegrid com Abstract It is shown with TrueGrid that a finite element model can be created in a preprocessor and exported to many finite element codes such that the model is identical for each finite element code Parameters expressions and conditional statements in a template input file simplify smooth or discrete variations in the generation of the mesh material properties element properties loads and constraints Keywords ABAQUS ANSYS applied mechanics computational fluid dynamics computer models finite element analysis finite element modeling fluid mechanics hexahedral LS DYNA mathematical modeling mesh generation multi block structured NASTRAN parametric parametric finite element modeling projection quadrilateral simulation solid mechanics Introduction The finite element method FEM is an essential tool in the design and understanding of complex structures A typical finite element session starts with a simplified model to make quick and dirty simulations to gain basic insights into the structure These insights will lead to refinements in mesh density and detail This numerical testing of the structure may require numerous simulations with different loads and boundary conditions There may be significant changes during the evolut
10. at will be deformed The second material will be used for the hardened metal clamps Similar features are selected for each simulation code It is convenient to lump all of the code specific analysis options with the code specific material commands para ts 01 c time step term 1 c termination time The material models and analysis options in each simulation code are quite different Therefore the syntax of the commands to specify these properties in TrueGrid is different for each simulation code With the aid of the graphical user interface it is easy to create the same material model for all four simulation codes The graphical user interface produces the correct syntax that is then recorded in the session file There is a pattern to these commands A command is needed to select the output format It is usually the name of the simulation code The commands are abaqus ansys lsdyna keyword and nastran The 1sdyna command has an argument because older versions of LS DYNA allowed for a second format that is still available in TrueGrid The analysis commands are abaqstep ansyopts l1sdyopts and nastopts The ABAQUS analysis options command is different because it is needed for each step The other simulation codes option commands are usually issued only once The material commands are abaqmats ansymats lsdymats and nastmats Each use of these commands defines one material Both the analysis options and the material defini
11. ate a multi block part in CYLINDRical coordinates cycorsy parts Cylindrical Coordinate System frame of reference insprt mesh INSert a partition in the block part topology mseq mesh change the number of elements in one direction of the block part de i mesh DElete blocks Move Corners pb mesh Placement mb i mesh relative Move by Index progression tr i mesh generalize TRansformation by Index progression Attach to One 3D Curve curs mesh attach edgeS of the mesh to a CURve curd 3D curves CURve Definition Project to One Surface sf i mesh project faces to a SurFace by Index progression sd surfaces Surface Definition Gluing bb interface Block Boundary definition and assignment trbb interface TRansitional Block Boundary definition and assignment Smoothing unifm i mesh UNIForM relaxation of solids by Index progression tf i mesh invoke TransFinite interpolation by Index progression Input Output iges cad extract all entities from an IGES file readmesh parts READ a file containing a MESH abaqus output ABAQUS output format ansys output ANSYS output format lsdyna keyword output LS DYNA output format nastran output NASTRAN output format write output WRITE the output file postscript graphics direct output to a POSTSCRIPT file Materials abaqmats materials ABAQus MATerialS ansymats materials ANSYs MATerialS 1lsdymats
12. e a part The Let command defines the transformations to be applied to each copy of the part Then the lrep command identifies which transformations are to be used The 0 transformation is the identity transformation i e no transformation is applied to a copy of the part lct 3 mx 3 repe 3 lrep 0 3 I Beam With Hole Using Brick Elements A solid mesh of the same model requires two partitions for each of the web the bottom plate and the top plate This example shows the creation of a surface and the projection of the edges of the hole to that surface Projection to surfaces is preferred over attachment to curves because projection is a constrained Newton method that automatically calculates the intersection of surfaces wherever it is required As was mentioned above the order that commands are issued is not important The TrueGrid algorithm sorts the commands and uses them in the following order 1 move corners to points 2 attachment edges to curves 3 projection faces to surfaces The results of moves and attachments to curves are used to determine the points of projections on the surfaces This internal ordering of commands is referred to as the command hierarchy in TrueGrid The sd Surface Definition command is followed by a surface identification number a surface type and associated arguments In the definition below surface 1 is defined as a cylinder The axis of rotation is parallel to the y axis and passes through
13. e block command usually contains more blocks than are needed for a particular problem This is because it is usually easier to define an array of blocks and delete some of them then it is to define each required block separately For example para th 1 c sample thickness parameter block 113 17 31 35 47 i index list 15 10 14 j index list In 258 k index list F L6 th A ST GF Ce LZ 08 08 th oO x coordinate list y coordinate list z coordinate list ct ct qaqaaqaaaa oO Oo This part has 5 blocks in the i direction 3 blocks in the j direction and 1 block in the k direction in the computational domain Each number in the 1 index list specifies the end of one block and the beginning of the next The same is true about the j index and k index lists The interfaces between the blocks located at the node numbers in the index lists are referred to as partitions and they are numbered by their sequence in the index list The x y and z coordinate lists position the partitions in the 1 j and k directions respectively A few more commands will be introduced and added to this block command to build a simple model of a sample material being drawn between two clamps IQS RA O X Y RAK N N N ANANN N X RA Physical Mesh with 13 blocks of hex elements Computation Mesh with 13 blocks Starting with the block command above all unneeded blocks are removed with a dei dele
14. emonstrates the building and exporting of several simple TrueGrid models for nonlinear static analysis to be performed by ABAQUS 5 6 ANSYS 7 LS DYNA 8 and NASTRAN 4 Most commands used below to generate these models are not targeted for a particular simulation code because most simulation codes do non linear static simulations in a similar fashion Even in a dynamic simulation the differences in the commands to TrueGrid for the different simulation codes are quite limited Each of these simulation codes offers a different set of multi physics capabilities and consequently a different set of loads that can be applied The different loads will not be discussed in this paper The remaining differences are categorized as follows 1 Material models equation of state quadrature and element types each simulation code has a different set of material types They all include an isotropic plastic material Each code defines the yield curve differently The element type and equation of state are coupled to the material model and are selected at the same time the material properties are selected Only the hex solid or the quad shell type is selected If a prism pyramid tet or triangle is formed during the element generation phase the appropriate element type for that element is automatically selected The commands that define material properties end with mats The mate mt and mti commands are used to associate a group of eleme
15. es a grid with an i index ranging from 1 to 5 a j index ranging from to 6 and a k index ranging from 1 to 7 Each pair of numbers in the block command ends with a semi colon and is referred to as an index list The semi colon terminates each list It is shown in the next example that the block command can be used to create a part with many blocks For this reason the syntax for the block command must allow for each index list to have arbitrary length The three dimensional space containing the i j and k indices is sometimes referred to as the computational domain of the mesh The edges of this block are initially parallel to the coordinate axis and the faces are planar The remaining arguments of the block command assign x y and z coordinates to the mesh For example 2 35 c x coordinate list 1 4 7 c y coordinate list Ze kde c z coordinate list completes the block command above The first list of coordinates specifies the x coordinate for the 2 faces perpendicular to the x axis There must be one x coordinate for each index in the i index list The same is required for the y coordinates corresponding to the j index list and the z coordinates corresponding to the k index list Sometimes the three dimensional space containing the x y and z coordinates is referred to as the physical range of the mesh Creating a Multi Block Part The block command is generalized so that a single part can have any number of connected blocks Th
16. f the mesh either a region or an index progression can be moved as a rigid body using the pb mb and mbi commands The pb command assigns coordinates and the mb or mbi commands modify the coordinates by adding a component For example 08 c assign the y coordinate 3 3 08 c decrease the y coordinate oe pb il mb 4 The tr command is a more general method of manipulating the mesh These three commands change the coordinates of the corners of the blocks Then the edges faces and interior nodes are interpolated The graphical user interface can be used to create these commands with a click and drag of the mouse to move the corners of the block The arguments to these commands can then be replaced with parametric algebraic expressions using a text editor to modify the session file Nodal Constraints The b and bi commands assign nodal constraints In the command below the z displacement is constrained at the base of the clamps For some simulation codes with case control such as ABAQUS and NASTRAN a set identifier or case control number sid should be assigned to the constraint Notice that this command ends in a semicolon indicating this command has many options Any of the degrees of freedom can be constrained by adding options to the list bi 13 0 4 6 1 2 0 3 4 1 sid 1 dzi1 Fixed Displacement For historical reasons many commands imposing loads require a load curve number set identified or case control
17. ion of the design of a complex structure Altogether many finite element experiments will be required A preprocessor to the FEM should make it easy to evolve and modify the model The verification and validation of a finite element computer model places additional requirements on the preprocessor The identical model must be generated for each code being tested and compared in the verification and validation procedure Key features of the model need to be isolated so that their properties can be varied independently This is necessary so that a variance in the measurement of the physical model can be propagated to the numerical model and the results of the simulation This may also be useful in determining if a linear simulation is stable meaning a small change in the numerical model should produce small variations in the results of the simulation Some of the features to vary are material properties geometric shapes and mesh density Ideally it should be easy to vary these features smoothly or in a discrete manner It should also be possible to vary features using a random perturbation A hexahedral Presented at NIST 2004 Workshop on Verification amp Validation of Computer Models of High consequence Engineering Systems Nov 8 9 2004 mesh for a solid object and a quadrilateral mesh for a shell structure are considered by many to be the ideal elements for finite element analysis 2 This is particularly true for nonlinear analysis When
18. l element types properties should be selected that are available in all simulation codes The spd command specifies the material properties The degrees of freedom are specified when the element is defined with for example the spring command Point mass properties are defined at the time these elements are generated with for example the pm and npm commands In the examples below text in the Courier font indicate input to TrueGrid Bold Courier font indicates a keyword command The c command starts a comment TrueGrid accepts a batch file or runs interactively with menus and buttons A session file is generated to record both batch and interactively generated commands This session file can be used to reproduce the model in batch mode Typically the user creates a simple model interactively and then modifies the session file with a text editor for subsequent reruns in batch mode The interrupt and resume commands can be useful when making incremental changes interactively to the batch file Creating a Single Block Part The block command creates a three dimensional rectangular mesh The numbering of nodes in each of the three directions is independent starting with 1 This produces a three dimensional array of nodes Each node is uniquely identified by three indices They are referred to as the i J and k indices For example the command block c indices of a single block part T53 c i l Ist 6 j list TE ec k list produc
19. nts with a material model TrueGrid is a Registered Trademark of XYZ Scientific Applications Inc ABAQUS is a Trademark of ABAQUS Inc ANSYS is a Registered Trademark of SAS IP Inc LS DYNA is a Trademark of Livermore Software Technology Corp NASTRAN is a Registered Trademark of NASA 2 Analysis options initial time step number of iterations output and data base options solution method case selection and other global controls fall in this category The commands that specify the analysis options end with opts 3 Element cross sectional properties shell cross sectional properties are defined within the material model definition Variable shell thicknesses are not supported by all simulation codes and must be avoided when making validation and verification comparisons Beam cross section properties vary greatly and are defined with the bsd command These beam cross sectional properties are then referenced within the material definition or the commands that generate the beams such as ibm jbm kbm and bm A limited orthotropy feature is handled within the material model It is this author s wish that beam cross section properties be standardized The benefits would include translation of the model from one simulation code format to another and verification and validation of finite element models With a standard in beam cross sections one could have greater confidence in the comparison of results from many simulation codes Perhaps
20. omponent of the center of the sphere c n is the node density of the mesh para rad 1 0 x0 0 yO 0 z0 0n 10 ce set parameters for sphere 1 include sphere c include the spherical part file para rad 1 2 x0 2 yO 2 z0 2 n 12 set parameters for sphere 2 include sphere ce include the spherical part file produces two spheres using the commands in an included file called sphere The details of the sphere file are left to the reader Code Specific Material Models and Analysis Options Another important use of the if elseif else and endif statements are now shown with the material models for all the simulation codes mentioned above The outtyp parameter will be used to set the output format type so that only this parameter needs to be changed to switch from one output option to any other We adopt the following convention for the value of outtyp c 1 means output to ABAQUS c 2 means output to ANSYS c 3 means output to LS DYNA c 4 means output to NASTRAN para outtyp 1 In this example we will use the following material parameters including some isotropic plasticity constants to define the same material model for all four simulation codes para rho 7 0e 4 c density e 3 0e 7 c Young s Modulus pr 3 c Poisson s Ratio sigy 75000 c yield stress et 1 0e 5 c tangent modulus There will actually be two material models The first is for the material th
21. te command For example the command dei 3 4 12 0 3 4 1 2 delete 2 blocks removes two blocks Both blocks start at the 3 partition and end in the 4 partition in the i direction One block goes from the 1 to the 2 partition in the j direction The second block goes from the 3 to the 4 partition in the j direction Note that the 0 in the j index list is used to indicate a gap and can be interpreted as the word and Both blocks go from the 1 to the 2 partition in the k direction Commands that end with i require three index lists The three index lists are sometimes referred to as an index progression De is an alternative form of the delete command This command deletes one block The following accomplishes the same thing as the above dei command de 3 1 de 3 3 c delete first block 2 4 c delete second block 2 2 4 4 This type of command requires 6 numbers They are starting i partition number starting j partition number starting k partition number ending i partition number ending j partition number ending k partition number These six numbers are sometimes referred to as a region The region notation is an option because of its simplicity With large and complex models this notation becomes tedious and inefficient Typically a beginner chooses commands with a region notation and graduates to commands with an index progression as they become sophisticated users Large and complex struc
22. the beam cross sectional properties defined in the IGES 3 standard can be used as a standard If each simulation code supported at least these features then translations and comparisons could be assured 4 Contact surfaces methods used in the simulation codes vary greatly and continue to evolve The sid command is used to select the properties of the contact surfaces This author is not aware of any comparative studies of the contact surfaces available in these simulation codes An advanced verification and validation of finite element computer modeling should include contact surfaces One common characteristic of contact surfaces is a loss of accuracy In particular tied contacts used to glue two dissimilar faces of a material interface are unwarranted in TrueGrid The interface between two parts of the mesh can always be made to match The block boundary bb command is used to glue two similar parts The transitional block boundary trbb command will glue two dissimilar faces together using all hex elements for solids and all quad elements when using shells by automatically generating a transitional region at the interface There are some limitations to the trbb command that are easily met when the mesh topology is planned Example of a transition region between two blocks 5 Springs dampers and point masses material properties and degrees of freedom vary between the simulation codes If a model is to be run with these specia
23. the point 1 5 0 1 5 This cylinder has aradius r sd l c 1 501 501 0 block Sr surface 1 1 5 r sin 45 3 3 thp IF WS 19 E EF t32 9 15 21 237 0 1 5 r sin 45 1 thw 2 thw 2 1 Sthp 0 1 5 r sin 45 1 5 r sin 45 3 dei 1 4 ZO 3 4 2 bs dei 2 3 2 3 3 4 Y W W N NOAN WN M NW N NN v W vit AX XN WY N Ny WY SN A l WY Wy mm LW rate KV oe ae H SER en OOO ERN A Y al YA N W A A SESE eesseee ee AN H The sf and sfi project to SurFace commands constrain parts of the mesh to a single surface If an edge or a corner node is required along the intersection of several surfaces then these commands need to be issued at least once for each surface In this example the four faces of the hole are projected to surface 1 sfi 2 3 2 3 3 4 sd 1 Creating the FEM File The final step in the process is to assemble the mesh and write the output file for the appropriate simulation code Four commands are needed merge c enter the assembly phase stp 0001 c merge the coincident nodes write c write the output file quit Summary Simple examples have been used to demonstrate features in TrueGrid that can be of great value to verification amp validation of virtual prototyping Those features are output formats for
24. these types of elements form block structures the meshes tend to be nearly orthogonal These types of meshes usually reduce the order of the numerical error in the simulation 9 10 Such a mesh is desirable when comparing results from many simulation codes A poor quality mesh in the simulation will cause confusion when comparing the results of experiments using many simulation codes On the other hand a lower quality mesh may be needed to test the range of performance in the simulation codes Thus it is necessary that a preprocessor have the flexibility to vary the mesh quality It is also important that small changes to geometry cause only small changes in the mesh density If a small change in the geometry were to make a radical change in the mesh then any variation in the simulation results could be the results of the radical change in the mesh This is a strong argument for multi block structured meshes where the mesh topology is prescribed It is potentially a problem with automatic mesh generators that can undergo a radical change in the mesh topology when a small change is made to the geometry TrueGrid 1 is a commercial preprocessor for many FEA and CFD simulation codes It is used to generate high quality multi block linear or quadratic hexahedral solid quadrilateral shell or plate and beam or truss elements It can also generate prisms tetrahedrons and triangles in very small numbers as required for a good mesh This paper d
25. tions can have many options activated and each command is terminated with a semicolon After the commands to choose the output material models and analysis options have been issued the if elseif endif statements the parameters and comments can be added to the session file with a text editor to produce if Souttyp egq 1 then c ABAQUS specific abaqus c selects the output format abaqstep abstep 1 ce STEP definition static 0001 Sts Sterm ce select static analysis abcload blc 1 fd ce include displacements load curve 1 abagqmats 1 c elastic plastic material agqeltyp C3D aqdens rho agelas agelis e Spr agplas sigy sigy e Ssigy 1 Ssigy e et 1 abagqmats 2 c same as first material but stiffer ageltyp C3D aqdens rho agelas agqelis 10 e pr agqplas 100 sigy 100 sigy e 100 sigy 1 10 sigy e et 1 elseif Souttyp eq 2 then c ANSYS specific ansys c selects the output format ansyopts antype 0 e static analysis eqslv sparse 1 0e 8 ce solution method autots on c automatic time step andtime ts c time step size antime term c termination time ansymats 1 stif185 c plastic solid element prxy spr ex Se dens rho biso sigy et c Bi linear isotropic ansymats 2 stif185 c same as the first but stiffer prxy spr ex 10 e dens Srho biso 100 sigy et elseif Souttyp eq 3 then c LS DYNA specific lsdyna keyword e selects the output format lsdyopts c analysis options jautf 1 ce a
26. tures can be constructed using index progressions with a minimum number of commands The graphical user interface and in particular the computational window makes the selection of an index progression relatively intuitive Parametric Nature of the Block Command The block command is one of only two commands that specify the block structure or topology of the part The insprt command to insert a partition is the other command but is not detailed in this paper The block command is one of only two commands that specify the number of nodes within each block of the part The other is the mseq command that adds or removes nodes The insprt and mseg commands augment the block command so that the user can change the mesh without having to go back and modify the block command The mseq command is also not discussed in further detail because it is available only as a convenience and does not offer a fundamental capability If we ignore these two exceptional commands the block command is the only command that refers to the actual nodes in the mesh All subsequent commands in the part refer to partition numbers Essentially the numbers in the index progression and the region notation are numbered parameters whose true values are specified in the block command Thus the user can change the number of nodes in the mesh by modifying the index lists in the block command All other commands will be automatically adjusted Moving Corners of the Mesh Portions o
27. utomatically adjust time steps imflag 1 ce implicit dtO Sts initial time step nsolvr 2 ce BFGS updates implicit solver endtim term e termination time d3plot dtcycl 01 output interval isdymats 1 24 ce rate dependent isotropic plastic brick elfob csb ce element type and formulation rho rho e e pr spr sigy Ssigy et Set isdymats 2 24 brick elfob csb e same as the first but stiffer rho Srho e 10 Se pr Spr sigy 100 sigy et set elseif Souttyp eq 4 then c NASTRAN specific nastran c selects the output format nastopts sol 106 e type of solution nlparm 1 term ts c ID and number of increments auto c automatic stiffness updates nastmats 1 1 c isotropic elastic plastic e e nu pr rho Srho psolid plastic ce element type with plasticity hslope Set yidfun 1 inyldp Ssigy nastmats 2 1 c same as the first but stiffer e 10 e nu Spr rho Srho psolid plastic hslope Set yidfun 1 inyldp 100 sigy endif The ABAQUS element type is implied from the material options selected from the menus The ANSYS element type is selected first which then dictates the available material options The LS DYNA material type is selected first which dictates which options and element types are available LS DYNA s notion of a part is the same as a material in TrueGrid In contrast
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