[asking]

Hi,

I am trying to model a 2D cylinder vibration. I wrote a UDF to move the cylinder depending on the forces on the cylinder.

I separated the fluid mesh zone into two areas called "near" and "out". The "near" area its located around the cylinder and it's for the boundary layer. The "out" area is for the rest of the fluid. My intention is to move the cylinder with the "near" zones together as a block. The "out" area will deform and absorb the mesh motion.

One option is to apply the UDF on the cylinder and select the "deform adjacent boundary layer with zone" option, which forces me to select the spring smoothing method. I thought that if I wanted to use the diffusion method (where the "deform adjacent BL" option is not available), I could write a dumy UDF for the "near" zone and select the relative motion - cylinder option. That way both, the "near" zone and the cylinder, would move as a block. Unfortunately, I get negative mesh volume within the "near" zone after a few iterations.

Anyone have any suggestion/idea to make both zones move as a block?
Thank you.