Problem with shell extrusion


I am a newbie on FreeFEM and I want to solve a squeeze problem. The problem is this:

Two rigid plates sandwich a curved plate made of elastic material, gradually move one of the rigid plates, and finally flatten the middle curved plate. I need to get the displacement of the middle curved plate.

I have completed the meshing of three plates, as shown below.

Which part of the doc should I refer to for this implementation?