How to Pre-Process Tire Model: Option 2 (Manually)
In some cases, STPtoOBJ.exe may not generate the required input files from a STEP file for PM FlexTire™, or you may wish to have greater control over mesh resolution for your tire model. In these situations, you can use Altair SimLab® to manually generate the necessary Nastran BDF file.
After creating the BDF file, you will still need to run STPtoOBJ.exe to generate the .obj and .off files required for PM FlexTire™ simulations.
Key Considerations for Meshing
When generating the mesh in SimLab®:
- PM FlexTire™ requires:
- A surface mesh with triangular elements.
- A volumetric mesh with tetrahedral elements.
- Shared nodes between surface and volume meshes.
- Recommended minimum mesh resolution:
- At least 5 elements across the tire sidewall height.
- At least 2 elements across the lug height.
Using the minimum mesh count will yield faster simulation times. However, depending on your analysis objectives, a finer mesh may be needed, with the trade-off of increased computational cost.
Step-by-Step: Generating a Nastran BDF File in SimLab®
Import the CAD File
- File > Import > CAD > Select File > OK
Create Regions for Mesh Control
- Left-click Model > Right-click > Select > Faces By RegionType
Cylinder > Define Cylinder > Straight/Arc Edge
Round Up Radius > OK > Select In (only)
Create Group > Label (e.g., Sidewall) > Apply
Apply Mesh Controls
- Mesh > Mesh Controls > Face > Select Face > Set Average Element Size > OK
Generate Surface Mesh
- Mesh > Surface Mesh > Tra3 > Average Element Size (e.g., 60 mm) > OK
Generate Volume Mesh
- Mesh > Tet4 > Average Element Size (e.g., 30 mm) > OK
Replace existing mesh in model > OK
Ensure Shared Nodes Between Surface and Volume Meshes
- Geometry > Create > From Faces
Duplicate and ensure shared faces between surface and volume mesh
Export as Nastran BDF
- Analysis > Export and Solve
Solver: Nastran
Analysis: None
Format: Small Field
Enable Renumber
Export > Yes (create default property)
Generate .obj and .off Files
After exporting the Nastran BDF, use STPtoOBJ.exe to generate the necessary .obj and .off files for your PM FlexTire™ simulation.
- Update the STEP file name in your
mesh.bat file:
"C:\Program Files\Altair\2024\EDEM\bin\STPtoOBJ.exe" -c mesher_config.yml -i Tractor_Tire.stp -hm -tol 5.0E-02 -max 50.0 -min 25.0 -dbelt 0.84 -x 0.0 -y 0.0 -z 1260.0 -b313 0.0 -90.0 0.0
- Execute
mesh.bat from the command prompt to generate the outputs and review the execution details.
How to Video
The Step-by-step video can be access here: Altair How-to-Video
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