[FLASH-USERS] Checkboard of Magnetic Monopoles

[Aaron Froese]

Hi Nathan,

Thanks for the suggestion.  It tried adding magnetic energy, but it doesn't change the placement of the checkboards.  I'm not sure magnetic energy belongs in ENER_VAR because the related section in Simulation_initBlock reads:

           ! total specific gas energy
           enerZone = eintZone + ekinZone

I have also tried turning EnergyFix on and off, but there it has no discernible effect.

Thanks,
Aaron
________________________________________
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>