[Louisgirucl]

Hello everyone,

I am working on a project with specified displacement in complex biomedical geometry, and I am not using FSI; only the fluid surface is displaced.

The specified displacement applied to the surface is proportional to the average pressure on it and to a stiffness coefficient. The goal is to push the displacement to a maximum of 2mm.

I have come across negative element volume and divergence at about 1.2mm of displacement and can not explain why. I have attached two pictures from the monitor showing the divergence on the CFL and displacement ( see "DivergenceDisplacement.png" and "Divergence CFL Solver.png")

The mesh size is about 1.5-2mm in the region where the solver crashes.
I have looked at the CFL and reduced my dt from 1ms to 0.5ms and made the mesh coarser in the region to aim at lowering the CFL. However, it still diverges when the displacement rises close to 1.2mm.
Improvement of the CFL led to the same local divergence and the mesh to "bubble" (see "Divergence CFL.png").
I looked at the results time step per timestep close to the beginning of the divergence, and it looks like the CFL in the fluid regions peaks and leads the mesh displacement to diverge.

I am welcoming any tips that the community could provide as I find myself quite stuck on the issue.