Lots of thanks for very useful forum.
I got a question about shell elements. Is it possible to have a shell element without any thickness as a rigid body. I need to do optimisation on the material properties of two different layers and a rigid element might help to measure the displacement of the second layer.I defined one shell element, however the model was not run.

I am also wondering if it is possible to do optimisation process based on displacement rather than force? More specifically, is it possible to apply force and compare displacement with a measured one?