[FLASH-USERS] Checkboard of Magnetic Monopoles

Tue Apr 17 20:31:04 EDT 2012

Update:

The monopole checkerboard is only present when using the USM solver, the 8wave solver is unaffected.  None of the following numerical parameters have any affect on the structure of the checkboard: number of guard cells, solver order, E_modification, energyFix, prologation method, Riemann solver, nblockx, boundary conditions, computational volume, and cooling rate.  The monopoles typically appear in the top right quarter of each CPU's domain, but can vary slightly (see pictures).
________________________________________
From: Nathan Goldbaum [goldbaum at ucolick.org]
Sent: Tuesday, April 17, 2012 2:29 PM
To: Aaron Froese
Subject: Re: [FLASH-USERS] Checkboard of Magnetic Monopoles

Hi Aaron,

This is a wild guess, but I think the error you're seeing is because you're not including the magnetic energy when you update the solnData vector.

Instead of

solnData(ENER_VAR,i,j,k) = ei + ek

You should have

solnData(ENER_VAR,i,j,k) = ei + ek + emag

where

emag = .5*dot_product(solnData(MAGX_VAR:MAGZ_VAR,i,j,k),solnData(MAGX_VAR:MAGZ_VAR,i,j,k))

I suggest you look closely at hy_uhd_energyFix.F90 (located in source/physics/Hydro/HydroMain/unsplit/MHD_StaggeredMesh/) before you make further modifications.

Hope that helps!  If any other users of the unsplit solver have a more solid understanding of what's happening in Aaron's simulation, please chime in.

Cheers,

Nathan Goldbaum
Graduate Student
Astronomy & Astrophysics, UCSC
goldbaum at ucolick.org
http://www.ucolick.org/~goldbaum

On Apr 17, 2012, at 2:20 PM, Aaron Froese wrote:

> Hi Mark,
>
> I have been able to recreate the checkboarding problem on the OrszagTang example using the USM solver.  I have included the necessary changes, which just involve including a modified cooling module to reduce the local internal energy by a small factor each time step.  I have included plots of divB at the first checkpoint for two cases: one with a static AMR and the internal energy dropping by a factor of 1e-6 each time step, the other with a dynamic AMR and the internal energy dropping by a factor of 1e-3 each time step.  The monopoles always appear on the borders of 8x8 squares.
>
> Thanks,
> Aaron
> ________________________________________
> From: Mark L Richardson [Mark.L.Richardson at asu.edu]
> Sent: Thursday, April 12, 2012 4:20 PM
> To: Aaron Froese
> Cc: flash-users at flash.uchicago.edu
> Subject: Re: [FLASH-USERS] Checkboard of Magnetic Monopoles
>
> Hi Aaron,
>  Are you able to overlay the grid so we can see how these features relate to the blocksize?
>
> Cheers,
>  -Mark
>
> On Thu, Apr 12, 2012 at 3:54 PM, Aaron Froese <aaron.froese at generalfusion.com<mailto:aaron.froese at generalfusion.com>> wrote:
> I am using the USM MHD solver with flash3 and I noticed that I am getting very large magnetic monopoles appearing in my solution, of the same order as the magnetic fields.  The monopoles appear in a somewhat random checkboard-like pattern, which I believe has something to do with the block-structure of the mesh.  I have attached two plots which show the magnitude of divb and posted copies online in case the mailing list does not allow file attachments.
>
> Cylindrical Shell Compression 2D - abs(divb)
> http://oi40.tinypic.com/1zeihbp.jpg
>
> Spherical Shell Compression 3D - abs(divb)
> http://oi39.tinypic.com/34grldv.jpg
>
> The central circle where the checkboard pattern appears is the only volume that is magnetized.  I am using a static AMR mesh with a uniform resolution across the magnetized volume, and less refinement in the surrounding non-magnetized fluid.  Has anyone observed similar behaviour?  It is definitely numerical in nature, but I do not know what part of the code is responsible..
>
> Thanks,
> Aaron
>
>
>
> --
> Mark Richardson,
> Mark.L.Richardson at asu.edu<mailto:Mark.L.Richardson at asu.edu>
> Ph.D. Candidate: Astrophysics
> PSF 271
> School of Earth and Space Exploration
> Arizona State University
> 480 318-4449
> www.public.asu.edu/~mlricha4<http://www.public.asu.edu/~mlricha4>
>
>
>
> !DSPAM:10175,4f8ddebf128361398417114!
> <OrszagTang-Cool-AMR_abs-divb.png><OrszagTang-Cool-uniform_abs-divb.png><Cool.F90><Config>

-------------- next part --------------
A non-text attachment was scrubbed...
Name: OrszagTang-Cool_abs-divb_cpu01.png
Type: image/png
Size: 71002 bytes
Desc: OrszagTang-Cool_abs-divb_cpu01.png
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20120417/426e3a69/attachment-0005.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OrszagTang-Cool_abs-divb_cpu02.png
Type: image/png
Size: 71493 bytes
Desc: OrszagTang-Cool_abs-divb_cpu02.png
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20120417/426e3a69/attachment-0006.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OrszagTang-Cool_abs-divb_cpu04.png
Type: image/png
Size: 71146 bytes
Desc: OrszagTang-Cool_abs-divb_cpu04.png
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20120417/426e3a69/attachment-0007.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OrszagTang-Cool_abs-divb_cpu08.png
Type: image/png
Size: 74507 bytes
Desc: OrszagTang-Cool_abs-divb_cpu08.png
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20120417/426e3a69/attachment-0008.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: OrszagTang-Cool_abs-divb_cpu16.png
Type: image/png
Size: 74172 bytes
Desc: OrszagTang-Cool_abs-divb_cpu16.png
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20120417/426e3a69/attachment-0009.png>