Rigid body‘s motion in a viscous fluid with 6 dof and dynamic mesh function
 

Hi everybody,
I am trying to model the sedimentation motion of a rigid body in a viscous fluid under effect of gravity using 6dof and dynamic mesh function in Fluent. However, the terminal velocity of this body is quite different from the theory. So I am wondering anybody has a experience of using 6 dof and viscous force calculation?
Thanks a lot