Trouble with Multilayer boundaries in 2D mesh

Hi @Ali_Rajabi,

I believe this would work but it is difficult to tell without a minimum working example. Note that FacetNormal can be used without a SubMesh, as detailed in Integrating over an interior surface - #4 by MiroK. You can control which way the FacetNormal points by using the domain markers and a restriction (either ('+') or ('-')).