Fluid structure interaction with contact assembly

Hi,

I need to model a 2 layer- laminar flow (level set) with fluid structure interaction. The structure are two plates floating at the 2 fluid interface (Imagine two ice sheets floating on water; the two fluids are air and water). I used FORM UNION initially but the model fails when the plates come in contact (collide). So I have tried using FORM ASSEMBLY (this time with only one sheet to begin with), with 'Identity Boundary Pairs' generated at the fluid structure interface. I have provided deforming domain for the fluid domains. The issue is I cannot select the solid boundary to apply multiphysics: Fluid Structure Interaction and Wetted wall.

May I know the issue for this, the model is attached?

Thanks in advance

Dharma