Surface normal

[Nikhil Vaidya]

Hello,

I have a question regarding the surface normal vector when using the term:

dw_surface_flux

In my problem, I have an interface between two materials. For each material, the weak form contains the above term. Now, I have defined the interface as a facet region, and I pass this to the term in both equations. I think that the normal vector for the surface in the respective materials is not defined. How can I define this?

Best regards,
Nikhil

[Robert Cimrman]

You mean you have an interface in the domain? The normals are defined even for
internal facets, but the problem is, that each facet has two possible normals
in opposite directions. To choose a particular direction, you need to set a
parent region of the interface (facet) region, as in [1] - there, the normals
of Gamma_12_1 are w.r.t. Omega_1, and the normals of Gamma_12_2 are w.r.t. Omega_2.

Does that help?

r.

[1] http://sfepy.org/doc-devel/examples/acoustics/acoustics3d.html

> Best regards,
> Nikhil
>