# COMSOL Multiphysics. Set fixed constraint for a face in only one direction

I'm making a solid mechanics study for a steel plate (like a box). I'm applying a normal force on one face, and I'd like to fix the opposite face during the deformation. However, I need it to be fixed only in direction of the force, not completely. That is, let the force be along 'y' axis. Then I want to fix the opposite face along 'y' direction, but leave it free in other directions — 'x' and 'z'.

The boundary conditions for it are these: $u_y=0$. The default fixed constraint condition assumes those: $\vec{u} = \vec{0}$ (all three components at once). I heard something about weak constraints, but haven't found much info about it.

Pictures for clarity:

• Symmetric condition could be an option by slicing the body in half in y direction. That would make the problem constrained and more efficient. – BalazsToth Sep 15 at 7:39