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

[Attal, Nitesh]

Hello,

I tried using periodic BC (in y-direction) for a 2D thermal conduction
problem (Temperature gradient was imposed only in x-direction). I found
that the temperature at the y-boundary drops rapidly even though there is
no gradient present.
I tracked down the routine (gr_hypreApplyBcToFace) responsible for applying
the BC for HYPRE matrix. Here appropriate modification to the Bmatrix is
made to implement Dirichlet, Vacuum and other BC.

I was wondering if there could be a quick-fix to get the wraparound
solution variables to modify Bmatrix, i.e. a way to access appropriate
neighbors (blocks) that contain the periodic BC.

Thanks,
Nitesh

On Mon, Aug 31, 2015 at 1:53 PM, Klaus Weide <klaus at flash.uchicago.edu>
wrote:

> 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
>
>
>
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