UDF for oscilliating ball in a ball check valve
 

I am trying to simulate the motion of a ball in a check valve using a 2D model in Fluent.

From my research and several iterations I was able to define the DOF of the ball using the DEFINE_SDOF UDF, however that does not simulate my problem. But rather just gives the ball the freedom to translate or rotate independent of the inlet velocity.

I tried to use DEFINE_CG_MOTION but i am not sure what to define for the velocity.

I only want motion in the y-direction to be completely dependent on pressure or velocity.

Any suggestions would be appreciated. ANd yes I did check the tutorial on this forum but it is for a specific problem.