GMO model in FLOW-3D 9.2

xigema

I am using GMO model of FLOW-3D. There is a problem when I set up a simulation of one moving object coupled with fluid: the model geometry includes two parts: the bottom component is solid and non-moving, a sphere solid is solid with coupled motion, and the boundary condition is fluid velocity. But when the simulation starts, the sphere particle always sinks into bottom. I did not active collision model, and these two solid components should not have these reaction. Very appreciate if somebody can help me to figure out what is reason of my problem?