Wrong transmission conditions in Tutorial 11

[santiagobadia]

@oriolcg (I think you did this test)

I was looking at Tutorial 11.

You consider a steady FSI problem where us is the solid velocity. I think it does not make sense, because the solid velocity should be zero.

I think that we want to solve the solid problem using the solid displacement ds. In fact, the constitute model you are using makes sense for the displacement, not the velocity.

Then, we want to impose uf = 0 on the interface.

That would solve the problem, but then the problem is only coupled in one direction. The matrix is upper triangular, since $A_u^{f,s}$ is zero now. It is ok, I would just clarify in the text.

I wanted to agree on this, before starting to make changes.