Add more supported elements to CHT simulations

[boris-martin]

As of now, CHT simulations (more generally, simulations needing element face centers instead of nodes) only work with tetrahedrons. (Probably only first order tetrahedrons but I haven't tested) Using different elements (Say brick hexaedrons elements) crashes with no explicit messages but a segfault.

This part is problematic:

https://github.com/precice/calculix-adapter/blob/4496e8f160ec121481653baf44ec032813409ac6/adapter/PreciceInterface.c#L466-L472

• Function PreciceInterface_ConfigureFaceCentersMesh assumes tetrahedrons but should be adaptable +/- easily, as it calls a subroutine getTetraFaceCenters which is tetrahedron-specific
• PreciceInterface_ConfigureTetraFaces seems to be only required for connectivity but is always called (why?). This code is of course quite specific to the geometry.

I'd like to try to improve that in the near future, but I'm not 100% sure of the best approach:

• How do we detect element type ? Should we dive deeper into CalculiX code to detect each element and treat it accordingly ?
• Should we instead have only one type of elements (tetra or hexa) allowed (in the sense of "no mix") ? If so, is it detectable automatically, or should we add this as an option in the config.yml file?
• What about higher order elements ? wedge elements ? Supporting all elements could be complex.
• For connectivity, I read that supporte for quad elements on the interface is experimental. Is it safe to use ?

[MatthiasFreimuth]

Hi Boris, I actually already implemented some way of support for hexahedral elements, in my case I needed it for a DLOAD card, so to apply pressure values in CalculiX. I'm about to make a pull request with my changes soon and then we can use this as a starting point for further discussions about this topic.

[boris-martin]

Looking forward to it, thanks! It can probably wait for the actual PR, but how do you handle mixed meshes ? Do you detect for each element what kind it is? Do you only detect the element type of a single-type mesh? Or is that a configuration thing ?

[MatthiasFreimuth]

Actually I only use single-type meshes, so no mixed meshes. One can detect the element type directly from the CalculiX variable lakon. You can find it in the list of variables in the CalculiX documentation.