This command solves a boundary value problem to determine the stationary flow through the media. If all material IDs present in the 3D structure model describe either fluid or solid materials, the Stokes equation is solved. If some material IDs represent unresolved porous materials, the Stokes-Brinkman equation is solved.

These equations are valid for small Reynolds numbers, as is the case for slow laminar flows, or for fluids with high viscosity, such as oil. For faster flows (higher Reynolds numbers), you must use the Navier-Stokes(-Brinkman) command.

In the Stokes(-Brinkman) command, the flow boundary conditions are aligned with the space direction - one side of the domain is the inflow area and the opposite side of the domain is the outflow area. As boundary conditions, you can prescribe flow rate, inflow velocity, or pressure.

The permeability of the media is determined as a post-processing step. You can select to compute the permeability in one space direction only, or compute the full 3D tensor by solving the boundary value problems for each space direction.