Periodic boundary condition

Set a Periodic condition.

Parameter	Description
Offset-1	Offset in coordinate direction 1 of the opposite periodic boundary.
Offset-2	Offset in coordinate direction 2 of the opposite periodic boundary.
Offset-3	Offset in coordinate direction 3 of the opposite periodic boundary.

The Periodic boundary condition is actually a little bit special in ChiDG in that it does not actually compute an exterior state \(Q_{BC}\) like all other boundary condition state functions are expected to do. Rather, any faces in a bc_patch_t that are associated with a Periodic boundary condition are reset from BOUNDARY faces to CHIMERA faces. Additionally, the offset parameters from the Periodic bc_state_t object are stored in the face_t object to inform the Chimera infrastructure to search for a donor, not at the original location, but at a location defined by the offset coordinates. In this way, the Periodic boundary supports fully non-matching boundaries through the Chimera infrastructure.

Note

In setting up Periodic boundaries, recognize that opposite boundaries will require opposite offset coordinates. To accomplish this, create two different boundary condition groups. Add a Periodic state function to each. When setting the coordinate offset parameters, make sure these parameters are opposite sign between the two groups.

Warning

A current limitation to the Periodic boundary condition implementation is that it shall not be used to specify Periodic boundaries that couple an element with itself. The Chimera infrastructure automatically throws the receiver element out as a potential donor candidate. This situation might be encountered when trying to run a ‘2D’ calculation with 3D elements, but only using 1 element in the 3rd dimension. One might consider applying Periodic boundaries in the 3rd dimension, however the infrastructure will not set up this coupling correctly. An alternative would be to apply Symmetry-like boundary conditions.