How to specify Boundary conditions when the mesh is imported from GMSH?

[dokken]

As you have written the boundary data to xdmf, you can read it in as described in:

Transitioning from mesh.xml to mesh.xdmf, from dolfin-convert to meshio

This can be done using meshio and writing the explicit data to xdmf file. import meshio msh = meshio.read("test.msh") meshio.write("mesh.xdmf", meshio.Mesh(points=msh.points, cells={"tetra": msh.cells["tetra"]})) meshio.write("mf.xdmf", meshio.Mesh(points=msh.points, cells={"triangle": msh.cells["triangle"]}, cell_data={"triangle": {"name_to_read": msh.cell_data["triangle"]["gmsh:physical"]}})) from dolfin import * mesh = Mesh() with XDMFFile("mesh.xdmf") …

and use the mesh function in the boundary condition as described in

Boundary markers for moving mesh

Here is an example of what you would like to do: from dolfin import * mesh = UnitSquareMesh(10,10) V = VectorFunctionSpace(mesh, "CG", 1) x = SpatialCoordinate(mesh) u = project(as_vector((0.05*sin(pi*x[1]), 0)), V) class LeftOnBoundary(SubDomain): def inside(self, x, on_boundary): return x[0] < DOLFIN_EPS and on_boundary mf = MeshFunction("size_t", mesh, 1, 0) LeftOnBoundary().mark(mf, 1) bc = DirichletBC(V, u, mf, 1) u_boundary = Function(V) bc.apply(u_boundary.vector()) prin…