[nikos_]

Hello everyone,

I want to simulate the following case. Three parallel solid disks with fluid between them. The upper disk is moving downwards with a given axial velocity and the downer disk is fixed. Gravity is neglected.

I assume that i can describe upper and downer disk motion making a DEFINE_CG_MOTION udf.

My main problem is that i don't now what type of motion/boundary condition should i have for the middle disk and more general the interface between the disk and the fluid. It is supposed that the disk shall moved downwards due to a force applied to it by the fluid pressure. So i can't give my self a value of velocity to this disk and it somehow occur itself. Is it possible having a type of free, unconstrained solid body motion?

One option i thought of, is obtaining the velocity of the nodes that are in the upper edge of the middle disk and then give that value to the disk itself. Is it possible to do so and does that seems reasonable?

Ideally the boundary conditions would be:
1)Left and right surfaces : pressure outlets.
2)Upper disk: moving with given negative y velocity.
3)Downer disk: remain fixed (zero velocity)

Thank you very much.
Nikos