[tobiasS]

Just one comment about the original problem with not solving U. I think there is a semicolon missing after the solver of the first block, I think it was rho. I don't know if you have already added it or not. If not.. Just do it
Cheers!

[obiscolly50]

Thanks very much Bruno. Your explanation makes total sense. I like the idea of replicating the same vertex points for the interface for both regions in both stl files. I'll try that, but my guess is that there might be mismatching vertexes at connection points to other regions of the stl as you said due to round off, especially if they were generated independently. In Salome, it's possible to export stl after mesh generation, so I believe there should be a way to make vertexes from both surface coincide. I'll look into this and update the thread if I find anything useful.

Thanks a lot!

[obiscolly50]

I thought I'd update the thread on my findings regarding generating STL's for multiregion cases. From my various tests, a guaranteed way of preventing multiple unwanted regions in chtMultiRegion simulations (assuming a watertight geometry) is having a conformal mesh at the interface. That is, a geometry in which all vertexes from the bodies in contact coincide. This can be achieved by meshing the geometry in Salome. Note that this meshing is not one that will be used directly in your simulation, but rather used to generate the points (vertexes) which will be exported to the STL file.

A conformal mesh at the interface can be achieved in Salome by creating a partition or submesh consisting of all the bodies interfacing. Since all the vertexes at the interface will coincide, this will prevent the creation of multiple unwanted regions.

Just exporting the STL directly from geometry creation might also work without the extra step of meshing. But in case it doesn't, and you're getting hundreds of unwanted regions after splitMeshRegions, then getting a conformal meshing in Salome or any other capable software should be the last guaranteed resort. Hope this helps someone.

Cheers,
Obi