Discussion Forum

I'm working on a simple solution for a closure problem related to developing the governing equations for mass transfer in a porous media. This requires a solution to Laplace's equation in a cubic unit cell with a single sphere cut from its center. The sphere has a specified flux based on the surface normal vector, and the faces of the cube have a periodic boundary condition since we model our medium as an array of these unit cells in the closure problem.

I've tried specifying periodic boundary conditions on opposing faces of the cube, but they do not overwrite the default zero flux condition. How do I impose a periodic condition on the opposing faces of the cube in the PDE solver?

I realize that the boundary conditions will specify the solution up to an arbitrary constant--we have an additional condition that the integral of the result over the cube minus the sphere is zero which we can use to find the desired solution--does COMSOL require a specified value somewhere?

The computer I work at runs version 4.1, but also have access to a supercomputer running version 4.2 which I will use for more complicated geometries in the future. If there is any difference between the two please let me know. Thanks.