Internal boundaries with gmsh mesh and legacy fenics

[dokken]

For internal boundaries, you need to use the dS measure.
See for instance How to integrate on the surface of a subdomain (without making the surface its own subdomain) - #2 by dokken

Note that an internal facet integral needs a restriction to a given side, see:

Integrating over an interior surface

Hi, consider using restriction using + and -. Here foo('+') restricts foo to the positive cell and FacetNormal('+') is the outer normal of a positive cell. Following the discussion here the +, - side can be changed by providing a form which has a dx measure term which has specified subdomain_data by some cell function g. Then a positive cell for a facet is the one for which value of g is higher. This allows for the following from dolfin import * from mshr import * omega1 = Rectangle(Point(0, 0…