2015-05-26 2:06 GMT+10:00 David Love <[email protected]>: > Dear Sir/Madam, > > I have been experiencing difficulties generating a volume mesh (.geo and > .msh) from a surface mesh (.stl) generated in matlab. The main issue is that > I end up with zero volume tetrahedra (elements with four collinear points) > which causes difficulties in subsequent finite element simulations. > > I have attached an example of a surface mesh (.stl) that I start off with. I > then use the procedure outlined in the following link to create the volume > mesh (.geo and .msh): > http://fengl.org/2012/05/21/converting-stl-surface-mesh-to-volume-mesh-using-gmsh/ > > My questions are: > - Is there a way to avoid zero volume tetrahedra or does the issue originate > from the matlab generated stl file? Do you have a suggestion to avoid this > issue?
Hello. I had a go at your STL surface and it seemed to work here. I meshed it with the attached, no frills, .geo file. To check that the mesh was O. K., I solved a Poisson problem on the volume with uniform forcing and zero Dirichlet conditions using P1 elements in FreeFem++, using the attached .edp script. It computes the volume as 0.54956, the area as 15.7748, and the integral of the solution as 0.000286442. I don't think that this would work if there were degenerate elements. Is it possible that the error is in the solver rather than the mesh? > - Is there a possibility of generating a volume mesh in GMSH by defining the > surface boundary in an equation? For instance if I describe my shape in form > of a triple sinusoidal (as done in the matlab code) and then tell GMSH to > mesh the inner volume. If so could you point me towards some examples? I don't think that this can be done in a .geo file, but your first approach of generating the STL externally and merging it into Gmsh should work as you expected. I'm using gmsh 2.9.4 (compiled under 64-bit Debian from SVN sources), in case that matters.
Plane111_UnitCellCountXYZ331_VolumeFraction13_NetworkNR1.geo
Description: Binary data
poisson.edp
Description: Binary data
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