pressure bc in dolphin flow?

Question

does anyone know what is the boundary condition for pressure in the "flow past a dolphin" demo:
http://fenicsproject.org/featured/2011/pdesys.html

some pressure fix is needed, either \int p dx = 0 or a Dirichlet condition somewhere, otherwise pressure is only unique up to a constant.

I can't see the pressure bc in the code.

thanks in advance, achim.

Answer 1

There is nothing on pressure in this example, and you're correct, the pressure is ony determined up to a constant. It works with the current direct solver, but I would probably run into trouble with an iterative.

Comments

Classically, you'd expect the LU solvers to fail with singular systems.
Krylov solvers naturally deal with null spaces if the system is consistent. If you're preconditioning, you might not want to use ILU or any solver that involves (I)LU at some point.