MESH, CONNECT & SET UP MY MODEL FOR FEA STUDIES by D Duraikannu Graphics Systems Corporation

1. MESH, CONNECT & SET UP MY MODEL FOR FEA STUDIESby D DuraikannuGraphics Systems Corporation

2. MESH, CONNECT & SET UP What is SolidWorks Simulation? • Design, Analysis Systems fully integrated within SolidWorks • SolidWorks Simulation provides one screen solution for several types of analysis • Powered by fast solvers, SolidWorks Simulation enables you to solve large problems quickly using your personal computer. • SolidWorks Simulation comes in several bundles to satisfy your analysis needs. • SolidWorks Simulation shortens time to market by saving time and effort in searching for the optimum.

3. 2011 SolidWorks Simulation Product Bundles • Simulation Premium Advanced Dynamics SolidWorks Premium Simulation Professional Static Design Study, Optimization Sustainability Frequency/ Buckling • Flow • Simulation • Electronics • HVAC Fatigue Composites Drop Test Event Based Motion Thermal Pressure Vessel SolidWorks Motion Nonlinear

4. Two Meshers: Standard Vs. Curvature

5. Meshing Stages • Evaluating Geometry • Geometry errors may cause failure • Processing boundary • Surface meshing • Creating mesh • Volume filling • Failure Diagnosis • Complex single body component causes problems • Improved a lot in 2011 SolidWorks

6. Preparing a Model for Analysis • Simplify geometry • Suppress cosmetic features • Be careful in selecting stress concentration areas • Check for rebuild errors • Assembles: Interferences • Often result of a poor modeling technique • Thickness Interferences in the case of shells, use correct “Shell offset method” – new in 2011 • Allowed only for Shrink fit

7. Example: Interference • Meshing problems due to interference are quite common • Always check for interference in assembly • Tools -> Interference Detection • Interferences prevent compatible mesh • Re-mesh failed parts with incompatible mesh is not always a good option

8. Importance of Good Quality mesh • Stress Concentrations • Application of mesh control is a manual process • Stress singularities: The more mesh is refined, higher the stress valves • Adaptive Meshing • Available for Solids in Static Studies • Depends on loading types

9. Viewing Mesh and Results • Useful approach for checking behavior of the model and mesh refinement level • Settings: Mesh boundary options • VON: Edit Definition -> Advanced Options -> Element Valves • Stress is calculated at Gaussian points within element • Element stress is an average of just the element • Nodal stress is an average of adjacent elements • Energy Norm Error • Shows % difference between element and nodal stress for each element

10. Importance of Tolerance • For Standard Mesher: Tolerance is the valve below which adjacent nodes will be merged • For Curvature based Mesher: In 2011, it is defined based on Min/Max size, number elements around holes and element ratio • Can be particularly importance for small features being resolved • If global tolerance is 30% greater than the smallest element size specified in mesh control, global tolerance value is changed to 30% of smallest element size

11. Tolerance and small features • Can be the cause of “Restraint transfer failed” or “No loads applied” error when running a study • Has to do with mismatch between geometry used in actual definition (faces/edges) and mesh generated • When getting restraint transfer failed error, check defined restraint, and then “show mesh” to see if area is resolved by mesh • Beware of the model that have small features compared to overall dimensions

12. Example: Mesh Tolerance • Tolerance Too large: feature is not resolved • Tolerance made smaller (tighter) so nodes are not merged

13. Mesh Type Selection in 2011 • Treat as Beam • Treat as Solid / Beam • Can treat Solid Extrusion as beams but must specify treat as beam • Define Shell By Selected Faces • At mid surface • At Top Surface • At Bottom Surface • Specify Ratio • Treat as Remote mass

14. Automatic Shell Realignment • Uses an algorithm to attempt to line up shell top and bottom surfaces so they are consistent • Option to turn OFF / ON is available through “Simulation Options” dialog • Note: Having option enabled may cause meshing to take longer time if there are many elements – possible to flip shells manually

15. Detecting Bad Geometry • Use SolidWorks Utilities Geometry Analysis tool • Requires SolidWorks Premium • Short edges, sliver faces, etc will often cause mesh failure • Does not work on imported geometry • Try exporting into IGES file and importing into SolidWorks • Can often heals problems areas (gaps / faces)

16. Compatible / Incompatible Mesh • Affects solid/solid, solid/shell or shell/shell that are touching • Compatible mesh with touching surfaces • ‘Imprint’ of each face on the other – nodes line up at the surface • Incompatible mesh with touching surfaces • Each component is mesh as if other is not there • “Improve accuracy for contacting surfaces with incompatible mesh” option – mortar bonding

17. Contact / Gap Elements • No Penetration contact • Node to Node • Must touch initially • No sliding – forces applied parallel to contact normal force • Requires compatible mesh • Node to Surface • Each source node is assigned a target element • Slower than node to node • Surface to Surface • Most general option • Most resource intensive • Supported for Nonlinear studies

18. Contact Analysis tips • Direct Spare solver is preferred for Contact problems • Set global contact to free to ensure no undesired bonding occurs – contact hierarchy • Node to Surface is default option • Shell thickness is taken into account for No penetration or virtual wall contact

19. Bonding Diagnosis • Two possible error messages • Direct Sparse: “Model is unstable. Restraints may not be adequate” • FFEPlus: “Iterative solver stopped” • Analysis fails – no results • Enable soft spring option • Large displacement flag may be thrown • Say “No” (do not rerun this large displacement option on) and save the results and check the animation

20. Locating a node or element • Helpful for error messages referencing a node/element • In Nonlinear Analysis check *.OUT file • Problems with convergence can have to do with specific region and that can be due to meshing or contact definition • Solver places a notes that reference specific nodes/elements in *.OUT file • Right click on Mesh -> List selected • Node / Element location is annotated • Alternative approach: export as *.geo and search for node number in notepad and get coordinates then insert a point

21. Beam Contact • Beam to beam contact is defined by joints • No contact sets for beam to beam contact • Can bond a beam joint or beam to a shell / solid face • Beam joint or beam as set 1 • Shell / solid face as set 2 • Joints created at intersections of neutral axes and free ends • Joint colors • Purple: joint connecting two or more beams • Olive: free or disconnected joint

22. Additional contact analysis tips • If vertices and edges are involved in contacts, use node to Surface • Mesh should be finer on set1 entity than on set 2 • Can have convergence problems if set2 has finer mesh • Split lines reducing the source area can help speed up the convergence • For nonlinear contact problems with nonlinear material models, try draft quality • In linear static analysis, remember that only initial and final positions are saved – animation may show interference

23. Diagnostics using “Frequency Study” • Test for Rigid body motion (RBM) • FFEPlus with soft spring enabled • Combinations of restraints and bonding with improper contacts could result in RBM • Rigid body mode shows frequency valves as closes to zero • Test for bonding behavior • Look at mode shapes animations • Loads can be suppressed for this study • Copy study information from ‘static’ to ‘frequency’ or vice-versa

24. Thank You • For any questions/comments/feedbacks • dd@gxsc.com& joe.janik@gxsc.com • Phone: 1-800-454-2233 • Many thanks to WIILSSUG Leader: Brain Kinnune and Ruud Lighting, Inc. • See you all in Nov 2011 for next WI/IL Simulation User group (WIILSSUG) meeting