[airwarriorg91]

Hello !
I am trying to make a tetrahedral mesh in GMSH. The geometry is imported in GMSH in step format and subtracted from a box to create a domain.

I tried using fields and mesh control from points but it is not working. Any suggestions why it is not working. I have attached the .geo code. Thanks for the help !

SetFactory("OpenCASCADE");
Merge "geo.step";

//Meshing Settings
Mesh.Algorithm = 1;
Mesh.Algorithm3D = 7;
Mesh.SubdivisionAlgorithm = 2;
Mesh.MeshSizeFromPoints = 1;
Mesh.MeshSizeFromCurvature = 0;
Mesh.MeshSizeExtendFromBoundary = 1;
Mesh.MeshSizeMin = 1;
Mesh.MeshSizeMax = 20;
Mesh.ElementOrder = 2;

Box(2) = {-350, -250, -150, 700, 500, 300};

BooleanDifference (3) = {Volume{2}; Delete;} {Volume{1}; Delete;};

//Points 1 to 8 are the end points of the domain boundary.

For i In {1:8}
    MeshSize{Point{i}} = 400;
EndFor

Physical Surface("Inlet", 1) = {4};
Physical Surface("Outlet", 2) = {2};
Physical Surface("Top", 3) = {3};
Physical Surface("Bottom",4) = {5};
Physical Surface("Left", 5) = {6};
Physical Surface("Right", 6) = {1};
Physical Surface("Wall", 7) = {7:65};
Physical Volume("Fluid", 8) = {3};

[klausb]

I am also looking into 3D meshing using Gmsh and am struggling with mesh size settings. The way to approach 3D meshes is by using fields. I recommend to use python scripts rather than geo files. I import a CAD geometry in igs format, assign a surface mesh sizes to the individual surfaces... my problem is currently, that the mesh size on one of the surfaces is not as defined which may have to do with underlying mesh size definition hierarchies Gmsh applies automatically. I recommend to work through related python tutorials and examples available at: https://gitlab.onelab.info/gmsh/gmsh...r/examples/api to get started.

Also, you need to synchronize the opencascade and geo kernels before applying certain operations, maybe that's causing the issue - just a guess.

[airwarriorg91]

Hii,
I solved the issue in .geo file by using Transfinite Curve and specify the number of elements I wanted. I think the transfinite property is enforced even when the point size is defined. So, kind of a hack. Also, another issue I ran into is improving the tet mesh quality in GMSH. I tried NETGEN but it is not that useful. Any other steps to improve the mesh quality. Also how could I add prism boundary layer here in GMSH ? Is that possible ?

[klausb]

3D boundary layers are possible:

See: https://gitlab.onelab.info/gmsh/gmsh...ry_layer_3d.py


The boundary layer is extruded from the surface mesh. You can even create 2nd order i.e. curved cells which takes a lot of time as it's not yet running in parallel.

[airwarriorg91]

Thanks, I will check it out. It seems it is a python example. Is the command valid in .geo file too ?

[klausb]

Yes, it's a python example. I recommend to move to using python scripts when using Gmsh as it's more and more common and provides more flexibility. There's no geo version of the example to my knowledge.

[airwarriorg91]

Sure ! I will try to move to the Python workflow. I need to learn that. Thanks !