[FLASH-USERS] Checkboard of Magnetic Monopoles

[Aaron Froese]

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>

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