Foundations of FEA Modeling with Femap and NX
Contents
1. FINITE ELEMENT ANALYSIS Predictive Engi ineerin g Foundations of FEA Modeling with Femap and NX Nastran A broad introduction to modern finite element analysis and modeling techniques using Femap and NX Nastran 2011 All Rights Reserved GES iow sZ NN RS INITE ELEMENT ANALYSIS Predictive Engineerin Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Day 1 Course Outline Finite Element Technology Basics a The concept of finite element analysis nodes DOF elements b Basic element types a quick overview c Linear elastic FEA d F K U e Workshop I Introduction to Femap and NX Nastran f Femap Productivity Notes Il Finite Element Technology Beam and Isoparametric Elements a Beam Elements i Theory ii Workshop II Introduction to Beam Elements b lsoparametric Solid Elements i Theory ii Workshop III Element Quality c lsoparametric Plate Elements i Theory ii Workshop IV Introduction to Plate Elements iii Workshop V Mesh Refinement 2011 All Rights Reserved PANN FINITE ELEMENT ANALYSIS KZ A redictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Day 1 Course Outline continued Ill Foundations a Units and Managing Model Visibility i Background on FEA Units Usage ii Workshop VI Blanking Grouping and Visibility Day 2 Course Outline2. Thus one of the most common error messages in NX Nastran has nothing to do with loads and everything to do with your constraints 3 Au If the matrix is not constrained properly the solution will abort 2011 All Rights Reserved Se OK y PAD FINITE ELEMENT ANALYSIS PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology Workshop Introduction to Femap and NX Nastran Pre Processing Workflow e Walk through Interface Introduce concept of Panes Tool Bars Menus e Talk about Preferences and setting up one directory Scratch to store all of the modeling files e Femap is 100 Windows Undo Redo e Import Geometry Clean up Geometry using Geometry Solid Remove Face e Apply 1e4 load in Z direction e Apply Constraints Radial and Fixed e Analyze Analysis Workflow e Geometry e Material e Property e Mesh Sizing Note All analysis e Meshing examples in this class e Loads follows this general e Constraints analysis outline e Analyze A N Import Geometry File Workshop 1 Landing Gear Link LANDING GEAR LINK X_T Movie File Workshop 1 Landing Gear Link Workshop 1 wmv 2011 All Rights Reserved FINITE ELEMENT ANALYSIS Predictive Engineering PredictiveEngineering com Foundations of FEA Modeling with Femap and NX Nastran Femap
3. F H S oO OL S A A dominate contribution to the inaccuracy of a FEA model is loads All Rights Reserved 2011 FINITE ELEMENT ANALYSIS PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Analysis Concepts Nodes are used to define the geometry of the finite element that is to say its spatial characteristics Nodes have degrees of freedom and can translate 3 DOF TX TY amp TZ and rotate 3 DOF RX RY amp RZ in space Finite elements can be classed as point line surface and solid elements Another way to think of these elements is as having 0 D 1 D 2 D and 3 D characteristics D dimensional e 0 D elements are created on one node and can be meshed on geometric points e 1 D elements are created on two nodes and can be meshed on geometric lines e 2 D elements are created on three or four nodes triangular or quad and can be meshed on geometric surfaces e 3 D elements are created on a minimum of four nodes tetrahedral or eight nodes brick or hexahedral and can be meshed on geometric solids Examples of various element types are e 0 D elements are mass elements used to simulate concentrated weight without stiffness e 1 D elements are beam elements used to model space frame structures e g bus frames e 2 D elements are plate elements used to model thin walled structures e g pressure vessels airplane skins s
4. Productivity Notes Femap and NX Nastran Productivity RTM Reading the User manual can provide insight into how Femap functions The complete set of NX Nastran PDF manuals are provided Explore online help under User Manual Short cut key and Dialog boxes Look at Using the Mouse B Using the Mouse Mozilla Firefox Archivo Editar Yer Historial Marcadores Herramientas Ayuda lt 2 O fie 1170 Femap931 fhelp wwhelp wnhimplfiavahtrljwwhelp htm context Btopic SUCLLE index Search Favorites EM FEMAP NewFeatures Commands Proprietary and Restricted Rights Notic 1 Introduction 2 Product Configurations 3 Getting Started 4 User Interface 4 1 Overview ww 4 2 Accessing FEMAP Commands 4 2 1 FEMAP Main Menu 4 2 2 FEMAP Toolbars 4 2 3 Quick Access Menu Right 2 4 Shortcut Keys 2 6 Status Bar 2 6 The Select Toolbar 2 7 Context Sensitive Menus 2 8 Dackable Pane Icons 3 FEMAP Dialog Boxes 4 3 1 Entity Selection 4 3 2 Coordinate Definition 3 3 Vector Definition 3 4 Plane Definition 3 5 Color Palette 3 6 Library Selection 4 4 The Workplane and Other Tools 5 The FEA Process 6 Element Reference 7 Translation Tables for Analysis Prog 8 9 1 Analysis Program Interfaces Geometry Interfaces 0 Customization A Using the Keyboard IB Using the Mouse C Function Reference i 1E D Converting Old Models B E Other Analysis Program Interfaces Exam
5. Vector to match the beam s Y axis e The nodes are placed by default at the beam s shear center thus applied forces do not induce a twist or warping in the beam e The neutral axis is the center of gravity Moments are calculated through the neutral axis elem i Define BEAM Element Enter Nodes or Select with Cursor pi wia TE Orientation Nod Property 1 L Section Beam Offsets de Vector On E N Neutral Axis Title L Section Beam for Class Discussion Color 110 Layer 1 Property Values E Tapered Beam End A Area A 1 1875 Moment of Inertia I1 or Izz 0 391876 I2 or Iyy 1 087188 112 or Izy 0 379934 Torsional Constant J 0 0243636 Y Shear Area 0 391485 Z Shear Area 0 630896 Nonstruct mass length 0 Warping Constant 0 O SO SO O oOl oO lol o o oOo Perimeter 10 Y Neutral Axis Offset 0 36959 0 36959 Z Neutral Axis Offset 0 844446 0 844446 toad save Copy Material 1 2024 T351 Al Plate 25 v a Elem Property Type Stress Recovery 2 to 4 Blank Square Y Z End A1 0 123831 0 148975 2 1 876169 0 148975 3 0 126169 2 851025 4 0 123831 2 851025 0 0 0 0 3 0 0 0 0 Change Shape Draw Section V Compute Shear Center Offset E Compute Warping Constant Section Evaluat
6. are applied to the structure and likewise its stiffness K The unknowns are the displacements u within the structure after a load is applied Hence the method inverts the stiffness matrix and solves for the displacements With displacements one can calculate strains and with strains you have stresses and so on and so forth A simple rod example is provided showing how this process works 2011 All Rights Reserved redictive Engineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology X 0 EO _ Step 1 Satisfy static equilibrium YF F F 0 c AL u u L L Step 2 Relate strain to displacements Step 3 Relate stress to strain o Ee X X 2011 All Rights Reserved Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology Step 4 Relate force to stress Step 5 Relate force to displacement F Using the prior equations and performing a little o JK and O2 2 substitution yields xl A The minus sign is required since a positive tensile stress at End 1 is in the negative x direction F O A Ee A A tt u EA EA F u u L L Step 6 Assemble matrix i 2 k F a which give us iF K fu If u and u are non zero then an infinite number of solutions are possible or in mathematical terms the determinant of the stiffness matrix K
7. choose the Category from the drop down list then highlight the command from the Commands list After the command is highlighted click in the Press new shortcut key field and press a key or keyboard combination Once you have chosen the correct key or keyboard combination click the Assign button Ifthe key or keyboard combination has already been defined FEMAP will let you know and bring up a dialog box stating This shortcut is currently assigned Do you want to re assign this shortcut By clicking the Yes button the key or keyboard combination will be added to the Key assignments list and REMOVED from the command that was previously using that shortcut key or keyboard combination Clicking the No button allows you to select an unused shortcut key or keyboard combination and leaves all other shortcut keys unchanged Shortcut keys can be manually removed by highlighting a key or keyboard combination from the Key Assignments list and then clicking the Remove button The Reset Ai button will return all shortcut keys to their default commands This shortcut is currently assigned Defining shortcut keys for your most used commands you can save time moving through the FEMAP menu structure Shortcut keys are only available Do you want to re assign this shortcut from the FEMAP menu level Ifyou are already in another command or dialog box pressing these keys will not have the desired effect In most cases it will simply result in typing the
8. e Beams have their own coordinate system The beam s x direction is down its length from End A first node to End B second node e When meshed the beam is always located at its shear center and is graphically drawn w r t to this shear center e Beams can be offset to account for being attached to other thick structures i e stiffened plates Numerically a rigid link is used to offset the beam away from its neutral axis e DOF can be released at the beam ends to model a pinned joint or other types of behavior See Modify Update Element Beam Bar Releases Edge HX Ary oz N Yelem Grid Point A gt Xelem Plane 1 P End B gt ANN Wa 7 p Wb Fy Ox Grid Point B ooo Plane 2 NGG QM Mw _ 5s p 0 Zelem A schematic showing standard beam conventions for orientation and beam end offsets Pin flags end releases can be used for a variety of modeling tricks e g a bridge pinned connection 100 100 OO De A 30 40 30 Release Y SS Y 30 gt a 40 gt a 30 2011 All Rights Reserved FINITE ELEMENT ANALYSIS PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology Basic Concepts on Working with Beams e Beams need to be told how to orient themselves e The beam orientation is provided when you create the beam property You define the Element Orientation
9. excessively stiff and can easily generate bad numbers Note That is why the default tetrahedral element is the parabolic formulation with mid side nodes A warping element is shown below of a pressurized thin shelled vessel The hoop pressure should be a uniform 100 psi In the mesh region with no warping and good element quality the hoop stress is exactly 100 psi Where the warping is the worst the stress drops by 20 Check Element Quality Maximum Allowable Values to 1 tol Alternate Taper to 1 Internal Angles i deg Skew Warping Nastran Warping Tet Collapse Jacobian Combined Explicit Time Step 1 E 7 f ee 4P f ve IS 2a g i a A As F i tA X ti H 1 Output Set NX NASTRAN Cask T Warping Contour Plate Top MajorPrn Stress Make Group with Distorted Elements Check Fixup Invalid Elements ermanent cnc Open Model File Instructor s Models Plate Theory Heavily Warped Cylindrical Model modfem Femap Command Manual 7 4 5 6 Tools Check Element Quality 2011 All Rights Reserved Se la peal z FINITE ELEMENT ANALYSIS f J e e PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Slide Reserved for Participating Predictive Engineering Clients If you would like full access to these notes they can b
10. is singular So although we have the matrix terms we don t have a FEA solution 2011 All Rights Reserved PARA FINITE ELEMENT ANALYSIS WZ A redictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology This example demonstrates how the FEA method works and illustrates one of the most common errors that new users encounter when they submit their models for analysis On the right we start with a two spring model that has one DOF at each node We develop the matrix and one will note that with three nodes we have a matrix that is 3x3 e p Fad 1 23 p Es b_ ll a S L 1 L l b F P 2 0 u Where nodes share elements they share stiffness terms Off diagonal terms _ are zero For a very large matrix the F 2 2 1 l U5 majority of the terms are zero Hence 0 the name for NX Nastran s default solver F E u Sparse Matrix 2011 All Rights Reserved ANN FINITE ELEMENT ANALYSIS KZ redictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology F 9 _9 0 u In this form K is singular or there is no one unique solution the determinant is 0 0 In mechanics the structure can F 2 2 u move in space and hence any number of solutions could be obtained To fix this problem the matrix must be constrained
11. letter that you pressed Cis A few of the more useful but less obvious shortcut keys are listed below These keys work within a text or drop down list box in a FEMAP dialog box or list boxes in FEMAP They do not apply to other Windows applications except for those noted as Windows commands For a complete list of shortcut keys see Section A Using the Keyboard See Section 4 2 2 2 Customizing toolbars for same more information on creating shortcut keys Keys Function era Measure an angle exe Copy Windows command CiD Measure a distance Cte Display FEMAP Equation Editor for interactive definition of variables and equations NASTRAN Analysis FEMAP Structural Analysis Toolkit ews List functions FEMAP Thermal and Flow Ctr G Snap cursor selections to snap grid MoreResources owe Display a list of the existing entities of the desired type Ctr iv Snap cursor selections to nearest node Ctr Snap cursor selections to nearest point Cir Snap cursor selections to screen snap of ew 7 Redefine snap arid crey Paste Windows command Cir W Redefine workplane etx Cut Windows command Crez Use standard coordinate selection dialog boxto define location One ofthe most commonly used options is to use these keys to perform measurements when you want to input coordinates Since these keys are available when you are in another dialog box you can pe
12. F 0O 1 1 Ju F 2 _ P 0 0 The U DOF is set to 0 0 constrained and this wipes out row 1 and column 1 This allows us to write the matrix in a more F _ 2 2 J _ u condensed form as shown below The force at F will be recovered later as a reaction force F 0O 1 1j F 3 uy The determinant of the stiffness matrix is no longer zero Z i e 2 and a solution can be found using any number of F i u matrix technologies Usually mathematicians will say that the matrix can be decomposed instead of inverted since the actually process is one of matrix segmentation and multiplication 2011 All Rights Reserved ANN FINITE ELEMENT ANALYSIS WZ A redictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology Starting from where we left off we then can apply our loads In this simple 0 3 _ l u case we are pulling on the end of the system with a force of 1 0 This would then imply the following F 0 and F 1 0 We can then solve for our l l U unknowns u and u 1 1 In this section the matrix is transposed which is really difficult with larger matrices us O 1 l i K and Kf E 2 1 3 and we can solve for the unknowns Once displacements are generated it is not hard to then calculate F 2 gt uy the strain in each element apply the elastic modulus and then calculate stresses o fe
13. IV Constraints and Loads Modeling a Engineering Assessment of Constraints i Theory ii Workshop VII Constraints Loads and Non Manifold Geometry V Assembly Modeling Basics a Nastran RBE2 and RBE3 Elements i Theory ii Workshop VIII Nastran Rigid Links RBE2 versus Nastran Force Interpolation RBE3 b Application of RBE Elements i Workshop IX Tying Together Different Element Types 2011 All Rights Reserved KEAN FINITE ELEMENT ANALYSIS KZ A redictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Day 2 Course Outline continued VI Assembly Modeling Basics a Idealization of Engineering Systems i Workshop X Introduction to Normal Modes Analysis VII Results Validation a Understanding Stress Results i Theory of von Mises versus principal stresses ii Workshop XI Understanding of Von Mises versus Principal versus Transformed iii Workshop XII Understanding Averaging and Contouring Stress Data VIII Fatigue a Concepts of Basic Fatigue in Metal Materials IX Extra Material 2011 All Rights Reserved FINITE ELEMENT ANALYSIS PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Analysis A numerical analysis technique for obtaining approximate solutions to many types of engineering problems The need for numerical methods arises from the fact that
14. Members Calendar Promote Groups Labs Message History s Beta PEPEE Group Email Addresses Chat Description For all users of FEMAP Ask and answer questions Share tips tricks YAHOO Autos and complaints Femap with NX Nastran Topology Optimization Femap Thermal Solver Femap Advanced Thermal Solver Femap Flow Solver Femap Third Party Applications 15 26 Post message 43 29 FEMAP USERS yahoogroups com Subscribe mio Settings ZA ee FEMAP USERS an Es subscribe yahoogroups com Group Information 28 35 Unsubscribe FEMAP USERS unsubscribe yahoogroups com List owner Founded Feb 16 2002 3 FEMAP USERS owner yahoogroups com Language English Demos Interested In This Product x A Members 726 18 47 LA ILA Category Engineering Femap Real FEA Made Easy Quick Links News Features Ev n e r e el O Leading companies use Femap to analyze complex engineering problems a and accelerate design Other simulation gt Femap Case Studies tos ether ont otter enough gt Femap Resource Lira section are some capabdtes to simulate reatife gt Request Further Information engineering problems or haven t kept gt Download FEA for Engineers White Pap gt Aberdeen Group The Simulation driven or quite useful little tips and tricks gt Want to purchase Femap find a Partne 2011 All Rights Reserved GAS ite ECeNENP ANAS Predictive Engineering Foundations of FEA Modeling wit
15. Process amp 6 Element Reference 7 Translation Tables for Analysis Prog 8 Analysis Program Interfaces amp 9 Geometry Interfaces 10 Customization A Using the Keyboard B Using the Mouse C Function Reference FEMAP has both certain keys defined as commands for quick implementation as well as providing you the capability to define your own shortcut keys Commands which can be accessed through standard shortcut keys have the shortcut key listed next to their name Some of the most commonly used shortcut keys include F5 for View Select F6 for View Options and Ctri Q for View Quick Options These shortcut keys enable you to access these commands without going through the menu substructure In addition to the standard shortcut keys FEMAP also allows you to define letter keys in FEMAP as FEMAP commands You can also assign currently unused function keys and keyboard combinations i e CTRL SHIFT ALT letter or function keys as FEMAP commands as well You can therefore quickly customize FEMAP to use letter and function keystrokes as well as keyboard combinations to represent your most often used FEMAP commands To set up your own shortcut keys click the customize triangle on any toolbar and choose the Customize command or use the Tools Toolbars Customize menu In both cases the Customize command is at the bottom of the menu Once in Customize dialog box choose the Keyboard tab To define a shortcut key first
16. bsequent slides Although the theory is given in 2 D it can be directly leveraged into the third dimension One starts with a random region that is normalized into a 1 to 1 coordinate system and two formulas that use a simple linear shape function to define interior coordinates and interior displacements 4 Xxp gt N NW Xx i 4 4 up 2Ni S Us N is known as the shape function which does double duty as the interpolation function for both coordinates X and displacements U This is the cleient iso in the isoparametric With these formulas oe i we can map displacements in the interior of our s n element and also map any coordinates X u K u fhe n eta An example of a linear shape function for a four E xj node quadrilateral element see FEA textbooks N la E for quadratic shape functions use in parabolic 1 4 n eight node quadrilateral elements 2011 All Rights Reserved FA INITE ELEMENT ANALYSIS Paineen Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology Isoparametric Elements General Theory We start with basic mechanics and apply the isoparametric method to these equations Step 1 Satisfy static equilibrium Step 2 Relate strain to displacements simple 2D example 0 or 0U x Voy Ey t O A E l 9y This is where it gets a little complicated To Y xy 2 vA get our
17. e purchased from Predictive Engineering Please contact Training PredictiveEngineering com or call 503 206 5571 2011 All Rights Reserved
18. el using the Selector Entity set to Node Turn on gt x P Output Set NX NASTRAN Case 1 the Entity Info Pane Verify maximum node displacements for each Peformed2 56 Total Translation plate formulation e Increase the mesh density of the beam element using Mesh gt Remesh gt Refine then reanalyze and check the results e Increase the mesh density of all the isoparametric elements by a factor of 2 using the Mesh Toolbox Note Use Dialog Select within Meshing Toolbox to pick opposing curves to maintain quad mesh 2 56 12 144 24 57 refinement Rerun the model and interrogate the results Make note 4 12 144 of relative numerical cost versus improved convergence 48 2 304 T2 DOF Translation Matrix Model File Instructors Models lsoparametric Convergence Ilsoparametric Element Comparison for Bending with One Beam Element Start modfem A x y b 2011 All Rights Reserved FINITE ELEMENT ANALYSIS PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology lsoparametric Elements CQUAD 4 versus CTRIA3 Warping Distortion The Nastran CQUAD4 provides the accuracy of a eight node CQUAD for the price of a four node However this trick of an embedded extra shape function only works for rectangular 2D or hex 3D elements Triangular 2D and tetrahedral 3D elements remain linear and are well known to be
19. es that will Springs CELAS versus CBUSH e Siemens Web Site under Velocity Series or www Femap com E a E E Training Consulting greater Choose from the categories on the left There is no versus the only spring element that use is the CBUSH Why If you use the e Call Technical Support Predictive Engineering or GTAC e ranean sic a mene gel Predictive Engineerin g g New User Plate Modeling the potential to suck force out of your model SOLUTIONS that is your OLOAD won t match your TUTORIALS F F 4 Ya h O O G ro u S h a S Fe m a J S e r S 4128 SE Crystal Springs Bivd This tutorial walks the new user through the steps SPCFORCE in the F06 file and your model is p p Portland Oregon 97202 7917 Modeling amp to turn a 3D CAD file into a FEA plate model from thus garbage made this mistake once and 503 206 5571 Idealization t t to finish using the new Femap v10 02 was schooled by senior analyst at Navistar 888 316 3603 FAX Sa 7 interface when she noticed that my model had some email us Meshing E strange stresses This technical note Analyste gt Click to download 27 MB Zip file provides the necessary foundation to easily Techniques use CBUSH spring elements in all types of FE Beam Modeling models mar Build a simple beam model of a pickup bed cargo gt Click to download 2 6 MB Zipped File Customizing rack This tutorial covers beam modeling Settings techniques and using the Femap interface Program
20. es which is located near the center of the dialog box Enter Entity IDs here Preview selected entities Bring up list of entities Select picking method Entity Select Solid s to List bon Choose entire groups here Use More to A select multiple List of selected entities aninag Use Method Use OK Add Remove toselectan when you x Exclude alternate are done approach Since this box appears whenever you need to select entities for the command you have chosen itis very important that you become familiar with this dialog box You will see some form of it over and over again A brief explanation of each feature is provided below 2011 All Rights Reserved FINITE ELEMENT ANALYSIS predictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com F P d t it N t j Predictive Engineering s e C www predictiveengineering com downloads tutorials html emap Productivity Notes The New York Tim KLCC Eugene orez E Perfil a Metts com m lanacion com No PE Predictive Enginee Pecci Enonesa Other Resources Finite ELEMENT Anatysis Predictive engineering Mechanical Engineering Solutions Ext ra M ate ria Is at the e nd of th ese class n otes HOME ABOUTUS y NEWS PRODUCTS RESOURCES y CONTACT FEA CONSULTING SERVICES e Predictive Engineering Website PRODUCTS pa l hed a of and training fil
21. for most practical engineering problems analytical solutions do not exist While the governing equations and boundary conditions can usually be written for these problems difficulties introduced by either irregular geometry or other discontinuities render the problems intractable analytically To obtain a solution the engineer must make simplifying assumptions reducing the problem to one that can be solved or a numerical procedure must be used In an analytic solution the unknown quantity is given by a mathematical function valid at an infinite number of locations in the region under study while numerical methods provide approximate values of the unknown quantity only at discrete points in the region In the finite element method the region of interest is divided up into numerous connected sub regions or elements within which approximate functions usually polynomials are used to represent the unknown quantity The physical concept on which the finite element method is based has its origins in the theory of structures The idea of building up a structure by fitting together a number of structural elements see illustration was used in the early truss and framework analysis approaches employed in the design of bridges and buildings in the early 1900s By knowing the characteristics of individual structural elements and combining them the governing equations for the entire structure could be obtained This process produces a set of simultaneous algeb
22. generalized displacements u v the y i shape functions discussed on the prior slide are used to take corner point displacements Step 2 Relate strain to displacements nodes u and v and generate u displacements anywhere within the element V u N 0 N 0 u vV O N O N v2 or wu Nd 2011 All Rights Reserved Se la peal z FINITE ELEMENT ANALYSIS f J e e PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Slide Reserved for Participating Predictive Engineering Clients If you would like full access to these notes they can be purchased from Predictive Engineering Please contact Training PredictiveEngineering com or call 503 206 5571 2011 All Rights Reserved INITE ELEMENT ANALYSIS dinaon Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology Isoparametric Elements General Theory Numerical Quadrature To numerically integrate the Ilsoparametric element a technique known as Gauss Quadrature is employed This technique is based on the element having a normalized coordinate system of 1 1 Essentially the inner terms of the stiffness equation given below are only solved at discrete points within the element and weighting functions based on Gauss Quadrature are then applied The discrete points where this numerical integration is carried out are called Gauss P
23. h Femap and NX Nastran PredictiveEngineering com Finite Element Technology Beam Elements Nastran s Most Challenging Element 2D _ model for discussion t e The equations AO this 2D PEP can be developed from straight mechanics S e g see Timoshenko This is the fundamental concept about beams they are exact elements A standard beam has six DOF at each node F You are a beam expert 1 6 3L 6 3L Vv y l e What dimension rows columns would M IEI 3L oh Des 3L 2 9 1 the matrix have for one beam element 3 with two nodes L 6 3L 6 3L V gt e Ifyou wanted to determine the stress at M 3T 12 _ 3h oh Be Q 5 the base of a cantilevered beam having an end load would you obtain better numbers by increasing the mesh density e How would you model a drilled hole in the web of your I Beam shown above 2011 All Rights Reserved FINITE ELEMENT ANALYSIS PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology Basic Concepts on Working with Beams e Beams are used when you have long slender structural members with constant cross sectional properties e g structural steel tubing e One common rule of thumb is that the length to width is 10 1 e An excellent review of beam nomenclature can be found in the NX Nastran s Element Library Reference PDF file in the NX Nastran documentation
24. heet metal ships or structural steel framing e 3 D elements are solid elements used to model thick contoured objects e g castings 2011 All Rights Reserved Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology Linear Elastic Static Analysis 99 of the world e Stresses can be scaled as a linear function of the loads e The structure is elastic e Displacements can be scaled as a ratio of elastic moduli SSO1 S Strain Stress is independent of your material choice Application If the load is a force pressure then the resulting stress is just a function of geometry and not the material i e homogeneous materials Static means no acceleration Application Your structure must be constrained in all six DOF s translation and rotation If it is not constrained correctly it can t be solved 2011 All Rights Reserved PH LASN INITE ELEMENT ANALYSIS TA PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology The following section describes how the finite element method works It shows how basic mechanics are used to generate the finite element displacements and stresses from a structure FEA is based on the displacement method which boils down to VF y LK hus Typically one knows something about the loads F that
25. ing fly out While the Data Table window is flown out will change the Data Tabie window from Docked and Tabbed Retracted to simply Docked Model Info tree Click left mouse button in Mode info tree on an entity Selects and highlights the entity in the tree the cursor is currently over Also can be used to expand and collapse the different branches of the tree by pressing the toggle Click right mouse button in Modes info tree on an entity Displays Context Sensitive menu for the entity which is currently highlighted in the Modet info tree 4 2 4 Shortcut Keys Mozilla Firefox BEK Archivo Editar Yer Historial Marcadores Herramientas Ayuda o A O Aiestio sFemap991 hetoyhetimbinpliaveyhtniwuhelp mPcontext 2topiom B L 4 2 4 Shortcut Keys B Vv FEMAP 9 3 4 2 4 Shortcut Keys amp NewFeatures Commands Proprietary and Restricted Rights Notic 1 Introduction 2 Product Configurations 41 Overview w 4 2 Accessing FEMAP Commands 4 2 1 FEMAP Main Menu 4 2 2 FEMAP Toolbars 4 2 3 Quick Access Menu Right 4 2 5 Status Bar 4 2 6 The Select Toolbar 4 2 7 Context Sensitive Menus 4 2 8 Dockable Pane Icons 3 FEMAP Dialog Boxes 4 3 1 Entity Selection 4 3 2 Coordinate Definition 4 3 3 Vector Definition 4 3 4 Plane Definition 4 3 5 Color Palette 4 3 6 Library Selection 4 4 The Workplane and Other Tools 5 The FEA
26. ion Origin inal oisson Rat 0 3 Standard NASTRAN Shape Angle L Section X Size Height na Width 2 Thick Bottom 0 25 Thickness 0 25 Stress Recovery mi fs ha T 72 m E Reference Point Ie Iw Orientation Direction y Left Right Smart and experienced engineers struggle with beam theory and its application It is not exactly the most intuitive When in doubt build a small pilot model to guide your investigation 2011 All Rights Reserved Se la peal z FINITE ELEMENT ANALYSIS f J e e PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Slide Reserved for Participating Predictive Engineering Clients If you would like full access to these notes they can be purchased from Predictive Engineering Please contact Training PredictiveEngineering com or call 503 206 5571 2011 All Rights Reserved PARA FINITE ELEMENT ANALYSIS KZ redictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology lsoparametric Elements What Everybody Uses But Few Understand lsoparametric having the same parameters under different coordinate systems are the bedrock of modern FEA Simple functions are used to discretize oddly shaped surfaces or volumes The basis of this method is given in the su
27. ming O S B REALFEA COM LINKS h FEMAP USERS FEMAP tech groups yahoo com group FEMAP USERS Recommended View Settings for gt Click to download 22 MB Zip file Femap Added to Tutorials Customizina Settings The New York Tim Q KLCC Eugene Ore Perfil y Clar n com ln lanacion com No Predictive Enginee PE Predictive Enginee New User Register Signin Help Trending Mariah Carey Yahoo bJ Mail cd YAHOO GROUPS A Femap Siemens PLM Sc we e www plm automation siemens com en_us products velocity femap index shtn wh THE BEST PLACE TO START YOUR SEDAN SEARCH The New York Tim KLCC Eugene Ore Perfil Clarin com M lanacion com No Predictive Enginee Predictive Enginee Predictive Enginee SIEMENS FEMAP USERS Home yy Try Yahoo naan Chat Beta Now available on the left menu Read more Members Only YOUR NEXT CAR Messages Home Post Files Join This Group Photos Enk Activity within 7 days 1 New Member 5 New Messages New Questions es gt Start Your Search Femap Velocity Series The Femap Advanced Thermal Solver adds a number of What is Femap more advanced thermal modeling and simulations to the Try Femap for 45 Days FREE Femap Thermal Solver package including fluid duct Femap V10 3 modeling coupled convection and fluid flow analysis Database Polls
28. ndow Click left mouse button in Messages window Select the line that you were pointing at for transfer via File Messages Copy or File Messages Save Also press Shift the left mouse button to select a range of lines Press and drag left mouse button in Messages window Select all lines between where you press and release the mouse button Click right mouse button in Messages window Brings up a Context Sensitive menu for the Messages window Double click left mouse button on Messages window Title Bar Docked or Floating Toggles the Messages window between Docked and Floating Double click left mouse button on Messages window Title Bar Docked and Tabbed during fly out While the Messages window is lown out will change the Messages window from Docked and Tabbed Retracted ta simply Docked Entity Editor Click left mouse button in any field Entity Editor Makes the field active for editing except Read Only fields Clicking on the Down arrow button will bring up a drop down menu and clicking on the Action button will bring up a dialog box Press and drag left mouse button in any field Entity Editor Selects all characters in the field between where you press and release the mouse button Double click left mouse button on Entity Editor Title Bar Docked or Floating Toggles the Entity Editor between Docked and Floating Double click left mouse button on Enti
29. oints or in long form Guassian Integration Points An example of the location of Guass Points in a quadrilateral element is given below 1 4 Guassian integration is at its best i e most accurate when ik f if By E B J Agan the element is as near as possible to a perfect square During the integration process tabulated weighting values are used J3 terms Wi and Wj to arrive at the final integrated value I for the elements area or volume I 5 S WWO Eini l j The location of these Guass Points are also used for strain recovery and with strain we have stress That is in lsoparametric elements stresses are calculated at the Guass Points and extrapolated out to the nodal points for contouring Hence a high quality element low Jacobian will provide double benefits with a more accurate K and cleaner stress calculation 2011 All Rights Reserved PredictiveEngineering Foundations of FEA Modeling with Femap and NX Nastran PredictiveEngineering com Finite Element Technology lsoparametric Convergence Verification Element Assessment CQUAD4 CTRIA3 CQUADS cova ASE y The test models given on the right represent an idealization of a cantilevered beam with a unit load at their ends The theoretical displacement is 2 56 The beam element is exact while all other isoparametric formulations have values that approach this number to various degrees Student Tasks e interrogated the mod
30. ples E NASTRAN Analysis E FEMAP Structural Analysis Toolkit E FEMAP Thermal and Flow E MoreResources C cooge amp J B Using the Mouse a FEMAP 9 3 B Using the Mouse At the FEMAP Menu Level While FEMAP is waiting for you to choose a command you can perform certain FEMAP specific functions with the mouse These are in addition to the normal Windows functions that you can perform by clicking and dragging the mouse in the window borders and menus All references to left and right are for a standard right handed mouse configuration Action a General Click button in window Activate that window If you have multiple graphics windows on the screen the one you click on will become active All view changes will be made to that window Graphics Window Click hold and drag left mouse button in Graphics window Render mode Dynamic Rotate Pan and Zoom Works identical to View Align by Dynamic and the Dynamic Rotate Pan and Zoom View Toolbar command except you do not have to enter a command to do it Double click left mouse button in Graphics window Redraws that window Click right mouse button in Graphics window Select Toolbar not active Display quick access menu Click right mouse button in Graphics window Select Toolbar active Displays Context Sensitive menu for the entity type which is currently active in the Select Toolbar Messages wi
31. raic equations The limitation on the number of equations that could be solved posed a severe restriction on the analysis The introduction of the digital computer has made possible the solution of the large order systems of equations The finite element method is one of the most powerful approaches for approximate solutions to a wide range of problems in mathematical physics The method has achieved acceptance in nearly every branch of engineering and is the preferred approach in structural mechanics and heat transfer Its application has extended to soil mechanics heat transfer fluid flow magnetic field calculations and other areas From McGraw Hill Science and Technology Encyclopedia 5th Ed a typical two dimensional lt member B gt Y lt _ b R Structures modeled by fitting together structural elements a truss structure b two dimensional planar structure 2011 All Rights Reserved Bi WW van VA 4 th Femap and NX Nastran ing wi rh D o a o fitim f oo a Foundations of FEA Model Four things to consider about FEA e Visualization of structural constraints into modeling constraints e idealization of geometry into a numerical model e Discretization of continua into a finite element analysis grid e Engineering assessment of loads N n i Ed Z lt x Z Ww Ww al Lu w Z LL De O 8 oO cs ET C W dD
32. rform the measurement and obtain the result as the input to the dialog box value There is no need to perform your measurements write the information down and then go into the 4 3 1 Entity Selection In FEMAP just as in other Windows applications when a dialog box is displayed you are presented with one or more options or requests for textinumeric input To select an option or specify some input you first move to that field control using either the keyboard TAS Direction or Ait underlined_letter keys or more directly by selecting it with the cursor Ifthe current control is a button or list box you can select an option using either the keyboard or the cursor If the current control is a text box or drop down list box many applications give you no choice butto go back to your keyboard and type your input With FEMAP you can still do that but in most cases IDs and coordinates you can also enter the textinumeric input graphically using the cursor FEMAP has several standard dialog boxes but the most common box is the Entity Selection dialog box shown below Many FEMAP commands require you to select one or more entities which will be used for the command For all commands which support the selection of multiple entities FEMAP uses a common entity selection dialog box With this dialog box you can select any combination and any number of entities from your model As entities are selected or removed they are noted in the list of selected entiti
33. ty Editor Title Bar Dacked and Tabbed during fly out While the Entity Editor window is flown out will change the Messages window from Docked and Tabbed Retracted to simply Docked Data Table Click left mouse button in Date Tabie on a row Selects and highlights the row the cursor is currently over Press Ctrl the left mouse button to select multiple rows one at a time or Shift the left mouse button to select a range of rows Click left mouse button in Data Tabie on a column heading Toggles the Sort Method from lowest to highest numerical and alphabetical and vice versa Click left mouse button in Date Tabie on a column heading and drag the heading Allows you to move the column headings around and place them in the order you wish Also dragging a column header off the row of column headers until an IX appears over the column heading will remove the column from the Data Tabie Click right mouse button in Data Tabie on a row Brings up a Context Sensitive menu allowing you to perform show filter or delete the selected rows Click right mouse button in Data Tabie on a column heading Brings up a Context Sensitive menu with sorting alignment and other options Double click left mouse button on Data Table window Title Bar Docked or Floating Toggles the Data Table between Docked and Floating Double click left mouse button on Data Table window Title Bar Docked and Tabbed dur
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