Yon can apply rotational body force from the load manager by providing the angular velocity and the corordinate point on the axis of rotation. To visualize the rotational displacement only, select the rotations UR from the field output request.
· First, you can define a reference point in the center of the ring and create the coupling constraint between the point and the ring. Then, apply the “Displacement/Rotation” boundary condition.
· Second, create a rigid plane, place it on top of the ring, make tie constraint, and then apply rotation on the reference point of the plane.
· Third, create a rigid cylinder and place it in the ring. Make tie contact between the inner surface of the ring and the outer surface of the cylinder. Then, apply rotation on the reference point of the cylinder.
I think the last two are better because local deflections may occur in the first solution.
Also, check the link below. You may find it helpful for your current and future problems.