dynamic mesh
 

Hi guys, I am trying to model the dropping of a cap of a solid body.I have five walls describing the whole object which is like a one side open cylinder. I want only three of the walls which describe the cap to move with 6dof and I want the remaining two to stay where they are, however while the cap drops the walls that should remain tends to elongate and after a while run crashes due to detection of negative wolume. I would appreciate it if you could give me some tips for such a case. Thanx in advance.