[FLASH-USERS] Divergence of magnetic field

[Slavin, Jonathan]

Hi Lucas,

I'm surprised that you're getting this result.  I've been using nearly the
same setup - i.e. 2D cyclindrical symmetry, uniform B = Bz, USM,  with
those same parameter settings.  I haven't had any problems with divb.  I
think the only difference is the magnitude of B - as well as whatever else
you're setting up in terms of densities, pressures and velocities.  Which
version of FLASH are you using?  I'm using FLASH 4.3.  I'm wondering if
something strange could be happening when the energy is dominated by the
magnetic field.

Regards,
Jon

On Tue, Apr 24, 2018 at 1:00 PM, <flash-users-request at flash.uchicago.edu>
wrote:

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>    1.  Divergence of magnetic field (Lucas Rubio Fermoso)
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> ---------- Forwarded message ----------
> From: Lucas Rubio Fermoso <l.rubiof at alumnos.upm.es>
> To: flash-users at flash.uchicago.edu
> Cc:
> Bcc:
> Date: Tue, 24 Apr 2018 11:43:49 +0200
> Subject: [FLASH-USERS] Divergence of magnetic field
> Dear all,
>
> I am trying to run a 2D cylindrical simulation with a high uniform initial
> magnetic field in the "Z" direction (~100 T), but I am getting very high
> divergence values that cascade in other errors forward in the simulation.
>
> This divergence is generated at the cells in the block boundaries
> perpendicular to the field, while being 0 everywhere else.
>
> Divergence values are created at the first step and they evolve during
> "nrefs" steps, after that the values get frozen for the rest of the
> simulation.
>
> For example: For "nrefs"=2 initial divergence is 0 everywhere, divergence
> changes at steps 1, 2 and 3 and then keeps the same values of step 3.
>
> For "nrefs"=4 is the same but evolves up to step 5.
>
> The problem seems related to how paramesh handles fluxes before it starts
> refining.
>
> I have tried to restart the simulation on the initial checkpoint so
> paramesh redistributes blocks on start, but did not work.
>
> Some parameters that may be important:
> Grid is Paramesh4
> Prolongation methods: injection and balsara, both used with little
> difference (It should be used balsara since the simulation is cylindrical)
> Solver: Unsplit Staggered Mesh
> killdivb = true
> flux_correct = true
> E_modification = true
> energyfix = true
>
> In simulation_initBlock magnetic field face values and magnetic field cell
> values are declared with the same value.
>
> Thanks in advance for your help.
>
> Best regards,
> --
> Lucas Rubio Fermoso
> Universidad Politecnica de Madrid
>
>
>
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-- 
________________________________________________________
Jonathan D. Slavin                 Harvard-Smithsonian CfA
jslavin at cfa.harvard.edu       60 Garden Street, MS 83
phone: (617) 496-7981       Cambridge, MA 02138-1516
cell: (781) 363-0035             USA
________________________________________________________
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