we have a problem with mesh motion in OpenFOAM (for FSI applications with CalculiX), especially when the fluid mesh is to be compressed into a gap by displacing the solid domain.
Here, the displacementLaplacian displacement approach in OpenFOAM shows a strong compression of individual cells in the domain in a wave-like structure up to the crash. I use hex grids and planar simulations. I have encountered this problem frequently and I wonder if anyone has already found a solution for a better mesh motion in OpenFOAM for cases like this.
Dear Makis, thanks a lot. I will try this. I tried meanwhile SBRStress solver which is directly available in OpenFOAM.The SBRStress solver gives also a pretty nice mesh with good orthogonality. But I’m not yet at the end of my mesh desired compression. I will check out which solver then allows the highest grid compression.
The RBF-MotionSolver seems to always set the grid points at the boundaries to fixedValue, so that no sliding of the grid on the boundaries is possible. However, a working “slip” condition on some walls would be mandatory for us. We have tried it with different settings in dynamicMeshDict (static/moving/fixed patches) as well as with different entries in the pointDisplacement file, but it seems that it is not used at all.
Do you know if and how a slip boundary condition for the grid displacement on some boundaries can be realised in the RBFMotion solver?
Thanks a lot
Dear Makis, thanks for your reply.
With sliding I mean a “*slip”-conditions in the pointDisplacement. For the Laplacian and SBRStress solver we can use e.g. “slip” or “fixedNormalSlip” to allow a sliding of the mesh nodes along wall patches. This is quite important, if a deformed structure comes close to a wall. Please see attached figure with an initial solid in blue and a deformed solid in brown: If the nodes stick at the wall, the mesh gets highly deformed (see red line). In a closing gap situation (deformed solid reaches the wall boundary) it is very important that the nodes on the wall-patch can slide along the wall (see green line): The mesh is compressed but it remains more or less orthogonal. For this we don’t see an option in the RBF-motion solver. But we contacted Philip as you suggested.