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meshing large CAD file

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15 years 1 week ago #3217 by Kay
meshing large CAD file was created by Kay
hi

I would like to create a 3D volume mesh from a large stl file, about 6MB. Since Salome does not import stl, I had to convert it to igs using BRL-CAD but the igs is now 60MB, plus I have to repair it using sewing before I can even create a mesh. The entire process takes days.

Is there a way to modify Salome for it to import stl format? or even vtk format?

Is there another open source stl to igs converter?

Thank you
Kay
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15 years 1 week ago #3219 by Joël Cugnoni
Replied by Joël Cugnoni on topic Re:meshing large CAD file
Hi,

meshing from STL geometry (thousands of small triangles) usually requires specific algorithms that are able to simplify the geometry: a computational mesh cannot use all the triangles of the STL surface, it will be just too big. This is why, I think that using CAD-based mesh generators is not suitable to the meshing of STL geometry: CAD-based meshers MUST put at least one element on each edge => with STL kind of geometry, this means several million of elements at least!!!

So, the best tool for this task is probably Netgen: it can load STL geometries, repair it if necessary, and then mesh the surface and volume with some abstraction of the STL triangulation (it keeps the sharp edges, but produces a smooth surface mesh everywhere else).

If your STL mesh was already "computationnally" acceptable (element quality & size), you could also use Tetgen to "fill" the surface with tetrahedra (and possibly also GMSH).

Joël Cugnoni - a.k.a admin
www.caelinux.com
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15 years 1 week ago #3234 by Kay
Replied by Kay on topic Re:meshing large CAD file
hi

Thank you for your advice. Netgen works nicely. But I have 2 volume meshes that I would like to merge such that the (nearly) overlapping surfaces share nodes. Salome has a "Merge nodes" feature that Netgen don't seem to have. I guess I'll poke around at the Netgen forum.

Thanks
Kay
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15 years 1 week ago #3245 by Joël Cugnoni
Replied by Joël Cugnoni on topic Re:meshing large CAD file
I don't know which code you will use to solve the problem, but some codes like Code-Aster let you define "tied" surfaces that will be linked with additional equations (Lagrange multipliers) to ensure continuity.. this may be a good solution.

Or alternativelly, you can try to :
1. export your Netgen Meshes in UNV format
2. then import both meshes in Salome
3. Create a "compound mesh" (union)
4. Merge coincident nodes

Good luck

Joël

Joël Cugnoni - a.k.a admin
www.caelinux.com
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15 years 3 days ago #3271 by Kay
Replied by Kay on topic Re:meshing large CAD file
hi Joel

Thank you for your reply.

I'm using Elmer for now, but I may switch later.

The alternative method you had suggested does work but it seems Netgen does not export to UNV format. So I'm hoping to convert Netgen's neutral format to UNV format and I need more information into UNV format definitions. I read in one of the posts that you have such a document. Can you please email me a copy at:

ksun [at] intio [dot] us

Thank you
Kay
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