I am still working on this issue. I have a UDF working, but when I set up the dynamic mesh and the rigid body moves down (negative z direction), the sides that the rigid motion face is connected to do not adjust accordingly. I have tried various settings and no matter what the sides do not move with the top. I always get the error 'negative cell volume'. I was reading that layering and remeshing are not compatible with 3D cubic mesh, only tetrahedral, is this true?