transport of diluted species and laminar flow

Hi all!
I want to simulate a cylinder moving in the water, and it can generate some species on the bottom of the cylinder. So the move of the cylinder will influence the transportation of the diluted species. I set the moving wall boundary condition to the outer surface of the cylinder, but when i set the magnitude of the velocity too big, there is an error says"failed to find a solution. Maximum number of newton iterations reached, returned solution is not conberged"
can anybody help me, thanks a lot!