2 way FSI - constraining
 

I am new to workbench; modelling a solid ball in pipe, looking for stresses and deformation on the ball when it is in the flow.Its a 2 way FSI problem.
Ideally there should not be any constraints on the ball when modelling,it flows freely in the flow. But when i do that, simulation asks for the constraints in order to solve.
Any suggestions on constraining? or another way to counter this problem.

Thanks in advance.

First of all, how to you model the flowing ball?
Do you use 6DOF section in your flow model?
why don't you use 1way FSI? not a bad approach for your problem
you must see FSI in 6DOF modeling, I have found a good tutorial on internet, but unfortunately I don't have it right now.
regards

Thanks for replying.
Yes that is my doubt. I am not able to model flowing ball.It asks for constraint for ball,so i approached following way.
I modeled 2 systems; transient structural and fluid. Kept ball fixed, and put inlet velocity of flow equal to relative vel of flow over ball.
To constrain ball,
method 1, i sliced ball in 3 planes. Constrained XY plane in Z direction,XZ plane in Y direction,YZ plane in X direction. Definitely its not practical way.
method 2, created a very very small hollow sphere inside ball at its center. Constrained that surface.

1 way FSI would be simpler but there will be similar problem of constraining the ball.

Thanks in advance.