Creating volume mesh from Imported Surface Mesh without Geometry

Hello,

I need to be able to import surface meshes (without geometry) which define boundaries of a volume mesh that I would like to build.

For this, Salome seems to require an underlying "geometry" to be tied up to each surface mesh component, making the tool very inflexible.

For instance gmsh, which utilizes tetgen and netgen libraries, supports the feature I am after, however I prefer to stick to a complete CAE solution like Salome impressively offers.

I would appreciate insights, solutions or work arounds.

Best,

Albcem

Hi, Albcem,

I am also interested in knowing how to do this. Please let me know if you figure this out. I also use gmsh. I am not aware that gmsh can import surface mesh (without geometry), and then mesh the volume using the surface mesh. Can you point to me where I can find how this can be done? Thanks!

phsieh2005

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Hello,

The key to meshing surfaces bounded by STL or NAS files is to bring them in via a GEO file, which acts as a script to organize them into faces or volumes.

I actually looked at the demos/ directory where there is the example to define a sphere ready to volume mesh:

demos/sphere-discrete.geo
demos/sphere-surf.stl

The sphere-discrete.geo file script sources the spehere-surf.stl file to define a surface and then a volume:

// merge a surface mesh
Merge "sphere-surf.stl";

// add a geometrical volume
Surface Loop(1) = {1};
Volume(1) = {1};

So when you open the geo file in gmesh, the volume and faces/patches are already defined and ready to volume mesh.

So what you need to do is to collect all your stl shells, and write a 10-15line 'GEO' script, then open this as a GEO file for the volume mesh.

I hope this helps.

albcem

Hi, Alcem,

Thanks a lot for the answer!

But, I mis-understood your post eariler. What I am look to do is: using the nodes/elements on the imported surface mesh as starting point for the volume mesh. Hence, the resulting volume mesh will still have the same nodes/elments on the surfaces as the nodes/elements imported. Is this possible?

phsieh2005

Yes, this is exactly what I do in gmesh. So there is no misunderstanding on your part - I think our needs are the same..

The GEO file (rather script) is really a wrapper around the imported files in STL, NAS or some other surface mesh formats. These files include only the mesh points and surface facet definitions.

I don't know how to explain this further. You can look at the STL file of the sphere example I mentioned. You will see it is of surface mesh, nothing else. You can apply the same idea to a group of surface mesh files.

For instance, I surface meshed a vehicle in a tunnel geometry. So I obtained a Vehicle.stl and a Tunnel.stl file. I wrote a GEO script to define a volume utilizing the 2 stl files. I called it VehicleInTunnel.geo and loaded to gmesh. Then directly generated volume mesh.

Albcem

Hi, Albcem:

Thanks for your patience on this subject.

In your vehical and tunnel example, how did you surface mesh the parts, and how did you get the vehicle.stl and tunnel.stl files?

I build CAD model in SolidWorks. I can save the CAD model directly as stl format (that is no actual meshing done). Yes, the stl file contains nodes and facets. But, this nodes are not what I want.

What I am thinking is the following:

build the CAD part in SolidWorks. Mesh the surfaces using COSMOSWorks. For example, for a simple cube. I will have surface meshes on all 6 faces -- this is actually meshing step performed in COSMOS. I then export the surface mesh into I-DEAS unv format. I am hoping to read the surface mesh into gmsh (or Salome), them mesh the volume. Of course, I can mesh the volume in COSMOS, but, there are cases, I will only have surface mesh. I really do not want the nodes/facets from the stl files. Come to think of it, if I surface mesh the surfaces I want, save the surface mesh in ascii format, then, convert it to stl format. Then, read it into gmsh, mesh the volume - will this work?

phsieh