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Old   June 22, 2014, 12:24
Default Mesh Boundary Assignment Question
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I am currently using a free tetrahedral mesh generator(Tetgen) to create a 3D mesh. Tetgen supports a few types of mesh descriptions. I currently use the .smesh format as an input to Tetgen. The .smesh format involves listing all of the nodes on the surface of the mesh as well as the faces of the surface of the mesh. The most important thing is that the node and faces have boundary markers that tell which boundary they belong to. Manually putting those boundary markers into the .smesh file via a script isn't hard when I'm dealing with a simple geometry like a sphere in a cube, but it becomes almost impossible when dealing with complex geometries.

Tetgen outputs a series of .node, .face, and .ele files that contain the 3D mesh information, and I use those files in a CFD code, but the important thing is that I need those output files to have distinct boundary markers, which will only happen if the input file to Tetgen has the proper boundary markers.

My question is this: is there a way to use any software to create a surface mesh of a geometry and have the boundaries marked with a unique identifier so that I can then input it into Tetgen? I'm even open to using any free(or maybe even licensed) that can create a 3D mesh from a surface mesh, as long as it outputs the .node, .face, and .ele files. I would greatly appreciate any input or guidance on this issue. I am very new to mesh generation, so I am open to suggestions of better ways to handle this issue.

What I have tried: I tried modeling a complicated geometry in a CAD program and then exporting the model as a .STL file. Tetgen then reads in this boundary description of the model and creates a 3D mesh from the surface. The only problem is that there is no distinction between the different boundaries that were given by the input .stl file, and I do not see a feasible way to go in and assign appropriate boundary markers to the meshed surface after meshing is finished.

Additional Thoughts: I'm thinking that a program that can either create or read in .stl(or some other boundary description file format) and then assign boundary markers to user selected boundaries would be optimal. I have access to StarCCM+, which seems like it can handle assignment of boundary markers to a surface mesh, but it does not export a mesh in a format that my CFD program can read. I would most likely need to export the surface mesh from some program in a format that can be either read by Tetgen or read directly by my CFD program.

Here is a list of file formats that my CFD program can read:

Note 1: the old starCD format does not seem to be the same as the new starccm+ mesh format.

Note 2: The CFD program was developed in the 2000s, so the other supported file formats for commercial software may not be compatible)

1.) CENTAUR ASCII format.
2.) VGRIDns format.
3.) MESH3D format.
4.) TETMESH format. <---Tetgen output works for this format.
5.) Cobalt format.
6.) GAMBIT format. Only GAMBIT files in ASCII neutral file format are supported.
7.) StarCD format. Only StarCD files in ASCII format are supported.
8.) CENTAUR binary format.
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Old   June 13, 2016, 17:19
Default A good surface mesh generator
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I eventually found a wonderful addon to Sketchup(free) that allows you to draw up your model in the super user-friendly Sketchup program and then use the addon to specify boundary conditions/markers for mesh generation programs like Tetgen or gmesh.

The addon is called MeshKit. It's made by someone who uses these forums. It's completely free, and it is remarkably easy to use. I wish I had known about this tool a long time ago.

Link to MeshKit Page(Note: You must have Sketchup installed in order to add MeshKit to it):
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boundary markers, surface mesh, tetgen, tetrahedral mesh

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