Reliable method for 3D hybrid mesh generation

I found that structured & unstructured hybrid mesh generation not so reliable with Salome. I wanted to check with the community that if the method I use is wrong. All files and images are attached below.

Explanation:

dividedBox case:
In shaper I added a box and split it with a plane.

  • Created groups for sub-volumes and some surfaces.
  • Created mesh using 3D tetrahedralization method and maximum size.
  • Created sub-mesh on one volume group, set 3D Mapped Hexahedralization and on 1D edgeSize.

The mesh is generated as expected. Sub-mesh is entirely consist of structured hexahedral cells, where the other volume-group meshed with unstructured tetrahedral cells and pyramids where the two volumes meet.

Now my problem starts here.

innerOuter case:

  • I created another box. This time I cut it with 5 planes. Think of it like a thick walled box without a lid and the air inside.
  • I created inner and outer volume groups.
  • Followed same meshing procedure. 3D tetrahedral mesh with structured sub-meshed volume group.

The mesh was not as expected. I was expecting strict structured hexahedral mesh on the sub-meshed volume. But instead seemingly random hexahedral regions and mostly tetrahedral mesh.

I uploaded the both images below.

So my question: Is there a reliable way to get expected hybrid mesh on every time and on every valid geometry?

Below figures show the first “dividedBox” case.

dividedBox_mesh1
dividedBox_mesh2

Below figures show the geometry and mesh of unexpected result from “innerOuter” case.


Here are both case files:

dividedBox_unmeshed.hdf (262.0 KB)
innerOuter_unmeshed.hdf (216.1 KB)