very good question indeed. Let me try to shed some light around this topic:
We have observed that the meshing software we are using sometimes creates invalid meshes which cannot be used in a simulation. The most common invalidity in hex-dominant meshing is that the mesh contains a face with 3 cells next to it. This is clearly invalid as it will break many assumptions made by FVM. In order to save our users from proceeding with data which won’t work, we show this error.
Some other checks we do are:
- All cells must have strictly positive volume > 0
- All faces must have strictly positive area > 0
- All boundary faces must have exactly 1 adjacent cell
- All internal faces must have exactly 2 adjacent cells
There are more checks but those are only for us to catch other inconsistencies early in the process (so called “contract checks”). They will not be caused by the mesher directly.
Regarding the time spent after meshing: besides the validity check (and a few other things) we also generate the visualization which you see in the 3D viewer inside the workbench after meshing. This takes some time because we need to read in the entire mesh and convert it to a different format. In order to reduce the loading time for our users and to improve the interaction performance, we also run it through an optimization pipeline. This can take some time - however the ratio you reported is very extreme. If you don’t mind, I’d like to take a look. Feel free to share the project with me (or support, which is even easier) and I’ll try to find out what the matter is.
I also want to mention that some massive performance improvements for meshing are in the making. I cannot tell more at this point (sorry!) but I can say that you are going to see some exciting improvements and much faster meshing in the coming weeks. Stay tuned