Modeling motion in Ansoft Maxwell 3D

Hi everybody,

I'm trying to model the motion of conductive objects through spatially variant magnetic field and compute corresponding Lenz's forces. for the beginning I have a very simple set up: a current carrying solenoid made of a solid cylinder produces a uniform magnetic field along its z axis, I have put a ring inside the solenoid, with its surface initially parallel to the field direction and I rotate the ring (non-cylindrical rotation) 180 degree around a fixed point on its periphery, so its surface becomes perpendicular and again parallel to the field in the course of motion (I have attached a snapshot).
the problem is no matter how small I make the time step, I do not get a smooth force changing over time. the plots are very noisy with extremely rapid changes.

anyone can help me with this? I really appreciate...