[FLASH-USERS] Periodic boundary conditions for diffusion/conduction

[Klaus Weide]

On Fri, 28 Aug 2015, Evan Scannapieco wrote:

> I am wondering if anyone has had success implementing conduction with the unsplit solver with periodic boundary conditions.
> 
> 
> 
> HYPRE/Grid_advanceDiffusion says only OUTFLOW, VACUUM, and DIRICHLET are 
> supported, but I would think that, at least in principle, periodics 
> would be easy as there is nothing special to do on boundaries of the 
> box, just treat them the same as other block boundary.  I would 
> appreciate input from anyone who has tried this.

Evan,

Although we have never tried periodic boundaries with 
Grid_advanceDiffusion at the Flash Center AFAIK (thus cannot claim that 
it's supported), my expectation is that this should just work.

Or at least, it MIGHT just work. At the level of the routines under 
GridSolvers/HYPRE (which basically act as an adapter between FLASH and 
HYPRE), periodic boundaries should not even be visible as such: the code 
should handle the coupling of local cells to cells in neighboring blocks 
the same way, whether these neighbors are adjacent directly or across a 
wrapped-around periodic boundary.  (Note I am referring to the "paramesh" 
case, not "UG".)

As long as the HYPRE matrix that the adapter constructs and ultimately 
passes to HYPRE for solving stays sane (does not become singular, stays
symmetric if you are using HYPRE_PCG as your gr_hypreSolverType, etc.),
everything should work as before.

If you try this, please let us know how it goes!

Klaus