[HectorRedal]

Hi,

I would like to post the following question about how to calculate the integral of a surface in the finite element method.

As far as I know, when calculating, for example the stiff matrix, in the finite element formulation, the integral for such calculation is extended over the whole domain, for example a cube.

I am developing a software for cfd that uses the finite element formulation, and there are some integrals that should be performed over the surface of the domain (These integrals are surface integrals).

For integrals that are applied over the domain, the jacobi is used for differential transformation.

My doubt arises when trying to calculate the surface integrals. As far as I know, the jacobi could not be used.
Which kind of differential transformation should be used?

I would appreciate any kind of help / suggestion.

Thanks in advance,

Hector.