[Umut]

Dear all,

I’m trying to generate a 3D hybrid mesh on a fairly simple geometry using gmsh. I added all images, input and geo files below.

The geometry is a box without a lid with air inside, meaning two concentric boxes. I want structured mesh on box solid and unstructured tetrahedral and pyramid cells in fluid domain (air inside the box).

The mesh visibly generated as expected (please check images below). However gmsh gives warning about 36 ill-conditioned cells. When I export it as .msh and converted to Openfoam polyMesh folder, the mesh metrics are beyond terrible with all sorts of errors.

I would highly appreciate if anyone can help (educate) me if and how I can generate hybrid mesh using gmsh (or in any opensource tool really).

Cheers

Input geometry files:
https://drive.google.com/file/d/1P-S...ew?usp=sharing
https://drive.google.com/file/d/1IVy...ew?usp=sharing

Images:


https://drive.google.com/file/d/1p0g...a2ppq5fKL/view
https://drive.google.com/file/d/1a9Y...fMSeYD6JL/view

Gmsh .geo file:
If you download and try meshing it, don't forget to edit the Merge "Path/to/*.brep"; lines.

//Hybrid mesh example
SetFactory("OpenCASCADE");

// Merge geometries
Merge "Path/to/outer.brep";
Merge " Path/to/inner.brep";
Coherence;

// *** Structured Region *** //

// Define Transfinite Curves (Ib)
Transfinite Curve {103, 100, 97, 93, 68, 65, 72, 71, 32, 36, 40, 45, 29, 42, 37, 31, 83, 87, 101, 98, 57, 55, 41, 20, 16, 13, 38, 15} = 40 Using Progression 1;
Transfinite Curve {88, 92, 104, 73, 62, 61, 46, 28, 24, 21, 43, 23, 76, 81, 96, 67, 53, 48, 35, 10, 6, 1, 30, 3, 91, 86, 80, 79, 51, 52, 63, 56, 8, 12, 19, 27, 2, 22, 14, 4} = 5 Using Progression 1;

// Transfinite and Recombination for Surfaces 
For s In {1:74}
  Transfinite Surface{s};
  Recombine Surface{s};
EndFor

// Transfinite and Recombination for Volumes
For v In {1:17}
  Transfinite Volume{v};
  Recombine Volume{v};
EndFor

// *** Un-Structured Region *** //
//surface 75 and volume 18 should be unstructured (pyramid & tetrahedral cells)

Mesh.OptimizeNetgen = 3;  // or 2, 3
Mesh 3;