I am working on a nasal cavity which has a complex geometry. I have generated a hex mesh using the popular SnappyHexMesh. The problem is that I am getting several meaningless edges connecting the non-neighbours vortices. This obviously results in skewed (negative volume/Jacobian) cells. I used the debug=1 option and observed the problem happens in the snapping phase of the meshing. I played around with the different parameters in the SnappyHexMeshDict and could reduce the number of skewed cells down to 81 considering the 5M total cells. Does anybody knows how to fix/remove the skewed cells? Is this to be done manually? If somebody has/knows a C++ code for automatizing the procedure and can be shared it would be highly appreciated.
Thanks Daniel,
Actually the idea is to use an open source mesh generator.
The surface mesh which is the Snappy's input is an STL file so it is bunch of triangles and it gets indeed quite dense at some locations. So you are suspecting that to be the reason.
Dear Milad,
Meshers are often able to create 3D meshes in some geometries from the nothing. Sometimes, particularly for complex geometries, this process may have problems. Sometimes, the geometry is so complex that, prior to attempting the meshing, the mesher needs you to "help him" by manually making the 1D mesh of some edges, or the 2D meshes of some faces, etc. Sometimes, even if the mesher has no problem in meshing the 3Dgeometry, you may want to do that also to control the cell size in areas of particular interest.
In your case, if the mesher (be it either open source or copyrighted like Gambit, etc) generates a 3D mesh featuring low quality (like having too many elements with unacceptable skewness) which may jeopardize convergence of the solution, the traditional way to fix this problem is to create manually the 2D meshes (or 1D meshes) in the faces (or the edges) that are close to the high-skewness cells. After creating these meshes manually, then you attempt the automatic meshing for the remaining faces and the 3D geometry. You may need to make several attempts (i.e., several different 2D meshings of the involved faces) before you obtain a high quality mesh.
Most of the time it is better to improve your cad geometry in catia or solid work
ts better to merge some faces or remove them. Most of time this kind of edges have not any effect on your results
so make your geometry simpler
Also it is recommended to use .stp rather .igs when you want import your geometry to generate mesh
Could you post a screenshot of the bad cells? Are you using explicit or implicit snapping?
Sometimes it helps to refine/coarsen the background mesh or the specific patches.
Regards, Martin
Any improvement on the topic?
I am facing a similar problem. Snappy generate 59 highly skewed (identified by checkMesh) cells for my problem, however skewed cells are not reported during the snap-process.
Best regards
Bastian
Bastian, have you checked if the meshQualityDict (or settings) used in Snappy is the same used in checkMesh?
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