Robin conditions

[dokken]

@Apoh

volume_marker = 6
model.add_physical(circ_outer.curve_loop.curves, "Outer")
model.add_physical(circ_inner.curve_loop.curves, "Inner")

You have not marked the physical surface (volume of the mesh, and thus it cannot load it), see for instance: Problem converting gmsh to xdmf for fenics - #2 by dokken