Inviscid Incompressible Flow in FreeFEM

[cmd (Chris)]

See the notes of @fb77 here:

Boundary condition

If you want to avoid using a Lagrange multiplier (because it enlarges the matrix to invert), some other ways to penalize the normal boundary conditions are possible. In 3D you can use for example the boundary vertices. You have to define first a continuous approximate normal on the boundary (label 1 is for boundary) fespace Vh1(Th,[P2,P2,P2]); varf bdryn([w1,w2,w3],[v1,v2,v3])=int2d(Th,1)(v1*N.x+v2*N.y+v3*N.z); Vh1 [normalappx,normalappy,normalappz]; normalappx[]=bdryn(0,Vh1); Then you can ad…