2D boundary condition problem

problem: This is the 2D incompressible Navier-Stokes in Fenics. I do not know why the boundary conditions cannot be imposed. Please help me!


If the desired BCs include no-slip conditions on the triangular “teeth” along the bottom side of the domain, a solution might be to alter the geometric bounds of cylinder to extend down to the bottom of the domain, e.g.,

#cylinder = "on_boundary && x[0]>0.10 && x[0]<2.15 && x[1]>0.05 && x[1]<0.35"
cylinder = "on_boundary && x[0]>0.10 && x[0]<2.15 && x[1]<0.35"

With the current lower bound on x[1] in cylinder, the bottom parts of the teeth (viz., where x[1] <= 0.05) are left with no Dirichlet BCs. Assuming a typical weak form for incompressible flow, these boundaries would then have traction-free Neumann BCs, if nothing else is integrated on the boundary.

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