[aspect-devel] Problems with periodic boundary conditions (Wolfgang Bangerth)

[Max Rudolph]

Wolfgang,
Thanks for following up on this problem. I gave up trying to make aspect
work using periodic boundary conditions and we're using my finite volume
code for this project instead, but if the problem with aspect could be
fixed, we might go back to using aspect. The problems that I encountered
with aspect occurred regardless of whether I invoked the option to subtract
the null space associated with net translation. The problems only occurred
at high Ra. If you take the cookbook example with periodic boundary
conditions and increase Ra to 10^7 (if memory serves), the error will occur.

Cheers,
Max


On Wed, Dec 10, 2014 at 12:00 PM, <aspect-devel-request at geodynamics.org>
wrote:
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>    1. Re: Error when trying to run a cookbook example
>       (Wolfgang Bangerth)
>    2. Re: Problems with periodic boundary conditions (Wolfgang Bangerth)
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> Message: 2
> Date: Wed, 10 Dec 2014 10:45:48 -0600
> From: Wolfgang Bangerth <bangerth at tamu.edu>
> To: aspect-devel at geodynamics.org
> Subject: Re: [aspect-devel] Problems with periodic boundary conditions
> Message-ID: <548878BC.5090503 at tamu.edu>
> Content-Type: text/plain; charset=windows-1252; format=flowed
>
> On 11/06/2014 06:51 PM, Max Rudolph wrote:
> > Thanks for your help. Another way of dealing with the null space
> > associated with a net translation (or net rotation in 3D spherical
> > geometry) would be to fix the horizontal velocity for one vx degree of
> > freedom (essentially a dirichlet boundary condition for one dof). I
> > suppose that it would be key to do this in such a way as to keep the
> > stiffness matrix symmetric. Then, calculate the net translation or
> > linear momentum in the x-direction and subtract it after solving the
> > momentum and continuity equations. Would this solve the problem?
>
> Max, did you figure out how to deal with your situation? I recognize
> that it's been a while since you asked your question :-( but still
> wanted to point out that there are parameter settings to allow you to
> remove this null space -- see the null space parameters for the input file.
>
> Best
>   W.
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                  www: http://www.math.tamu.edu/~bangerth/
>
>
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> End of Aspect-devel Digest, Vol 37, Issue 3
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