[billyCFD]

Hello, I have a problem regarding a situation that apparently seems simple but I have difficulty in solving.

I'm analyzing the deflation of a cubic component made of rubber. It can be seen as the deflating of a balloon: at time 0 the cube has a certain volume and internal pressure. This pressure decreases and with it also the volume until the internal pressure is equal to the external one.

The initial idea was to make a 2-way FSI but the resources it requires are too high (RAM, etc ...) so I had to fall back on a kind of 1-way FSI.

The idea is to get the volume of my cube as a function of pressure from Mechanical, which I did, and use this relationship in Fluent. In this way I can take into account the volume variation that inevitably affects the deflation process.

Since the geometry can be considered cubic, it would be enough for me to move a wall to simulate the change in volume as in a piston.

I wrote a UDF that relates the internal pressure with the size of the cube and the time to obtain a speed to be applied to a wall, unfortunately, this approach does not work due to instability problems.

The thing I would like to try is to assign a position to a wall of my cube as a function of pressure across a UDF.

The question is: what can I use as a UDF to define the position (say the height Y of my wall) as a function of the internal pressure? There is a simple way to assign a position (that change in time) to a wall?