To calculate a model created in Rhino

Could anyone point me in the direction for doing fem based on a model created in Rhino?

  • When exporting the model, I meshed the solid in Rhino and exported it as stl, but Prepomax read it as a solid needed to be meshed. I hope to find a format that can be recognised as a valid mesh by Prepomax. Could anyone let me know if there’s such a compatible format? Thanks!!

  • If there’s not such a format, the model needs to be meshed before calculation. Is it better to do meshing in Prepomax directly, or in other software (eg, Gmsh) and then import the mesh in Prepomax? My model is a small (<10cm) organic-shape solid with ununiform thickness (2~4mm), not extremely complex but with quite some details.

Thanks a lot!

Can Rhino export to STEP ? I guess it should be possible. That’s the best format to export to PrePoMax. You will still have to mesh the model but PrePoMax can easily handle this and Gmsh is needed pretty much only when hex elements are to be used.

Probably, it’s not surfaces but have thickness in Rhino 3D model before exported to STL format.

It seems Rhino 3D have many capabilities to export in several formats. Try using STEP or IGES whenever possible, STL format is the last resort due to limitation.

Also, STL format is hard to follow curve edge and surfaces, quadratic and coarsening. Someone can try NetGen GUI or TetWild mesher then importing as vol or inp format in PrePoMax.

Indeed but it’s typically used for such organic shapes due to the way they are obtained (e.g. from 3D scanning). Conversion to CAD geometry can be problematic and usually requires specialized software. But Rhino is one of a few applications that can handle this properly (including important conversion from surface mesh to NURBS surfaces).

Thank you! I’ll try step.

By hex element did you mean hex mesh? My model will need to bend by ~90 dg. Considering the large deformation, will it be better (accurate/efficient) for calculation if I convert the model to hex mesh? And do I do that in Gmsh?


Thanks for your information! I’ll try step and iges.

If I could convert the model to a geometry made of small flat faces, will that benefit the meshing process in Prepomax and Gmsh?

right, i miss to specific in generic workflow of another mesh based CAD software (e.g SketchUp and Blender) or 3D scanner output limitation.

Yes, hex mesh. It’s superior to tetrahedral mesh but definitely not a must. For complex shapes you can use tetrahedral meshes with no doubts. Just make sure the mesh is refined enough.

Actually, it’s not totally wrong to use tetrahedral meshes even for simple shapes when there’s no tool for hex meshing around. You just have to remember that much more elements will be needed.

Do you mean STL surface mesh ? No need for that if you can obtain a clean STEP file from Rhino.

Still an interesting topic, accuracy in results and speed of modeling also computational times.

Hexahedral mesh is advanced, need proper partitioning to eliminate skew or distorted mesh generated. Mesh refinement and transition can be problematic.

I mean STEP file. Instead of importing a geometry with smooth surfaces, if I pre-convert the geometry into a mesh-like shape (a geometry with flat faces) and then export it as STEP, will Prepomax maybe recognise the existing flat faces and take their edges as reference when converting the the geometry into a mesh?

I still think that it’s better to import a smooth geometry and do the meshing from scratch in PrePoMax. This way you will have more flexibility.

indeed, this happens for STEP/IGES based format but not for STL, the mesher NetGen in PrePoMax is capable to coarsening.

If you import a .step file, the edges of surfaces are hard constraints (the mesh will follow the edges) and cannot be removed while meshing. If you import an .stl file, the edges are detected using a 30° default angle. This can be changed using Geometry → Stl Part → Find Model Edges by Angle. These found edges by angle (the so-called feature edges) are then hard constraints for meshing.

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