Okay, I'll quit body force weighted scheme. And as what I know is that FSI also includes moving structure without deforming, so hmm it has a generalised definition. Well let's think about six DOF Properties; Another subscriber and I have discussed what the possible problem might be. We suspect that maybe Moment of Inertia should be filled in moment of inertia about the axis of rotation instead of its CG. Since the user guide only claims that in Inertia Tensor field those components (Ixx, Iyy,.etc.) are defined relative to the CG. What do you think?