1. MESH, CONNECT & SET UP MY MODEL FOR FEA STUDIES by D Duraikannu Graphics 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
Nonlinear
Flow
Simulation
Electronics
HVAC
Simulation Professional
SolidWorks Premium
Static
SolidWorks
Motion
Frequency/
Buckling
Fatigue
Design Study,
Optimization
Composites
Sustainability
Thermal
Event Based
Motion
Drop Test
Pressure
Vessel
Advanced
Dynamics

4. Two Meshers: Standard Vs. Curvature
Standard Mesh
Curvature Based Mesh
Supports all possible contacts/component types
Default mesher in SolidWorks 2011
Activates Veronoi-Delaunay scheme for subsequent operations
Activates Curvature-based meshing scheme for subsequent operations
Creates uniform mesh all around the model
Creates more elements in higher-curvature areas automatically curved
Uses “Global Size and Tolerance”
Uses “Min/Max size, number of elements, growth ratio”

5. Meshing Stages Evaluating Geometry Processing boundary Creating mesh
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
&
Phone:
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