[FLASH-USERS] Initializing B-fields on AMR domains

[Paul Ricker]

Why not use the projection method with the AMR
Poisson solver? This is the kind of difficulty
it is designed to cope with.

Paul


On Fri Jul 29 2011 10:26:02 AM CDT, John ZuHone <jzuhone at cfa.harvard.edu> wrote:

> Hi all,
> 
> Just a general AMR question that I have been struggling with for a while
> and I wanted to see if anyone here had any insights (I run both Enzo and
> FLASH and this *should* apply to both, I think, with subtle
> modifications). 
> 
> Suppose you have a general, non-analytic magnetic field configuration
> (say, initially tangled or something). Suppose you want to initialize it
> on a grid such that it is divergence-free. If you have a uniform grid,
> one could try:
> 
> 1) Setting up a vector potential on the grid and then taking the curl
> 2) Setting up a magnetic field, transforming to Fourier space, and
> removing the divergence terms in Fourier space, then transforming back
> to real space. 3) The projection method using a Poisson solver 
> 
> All of these strategies have worked well for me in terms of setting up
> divergenceless fields on uniform grids. However, when interpolating this
> field onto an *initial* AMR grid, this gets tricky. I have tried
> modifications of the above proposals but have not really had that much
> luck. I always seem to end up with divergence terms at refinement
> boundaries. 
> 
> I have been setting up divergenceless magnetic fields in my FLASH sims
> so far by interpolating a low-res, uniformly-gridded field onto the
> minimum fully-refined level (root grid in Enzo parlance), then using the
> code interpolation machinery to interpolate this field to the other
> refinement levels. So far this has worked, but it is a tad
> unsatisfactory since I would prefer my initial field to sample the
> higher resolution elements from the get-go. Unfortunately, I need to
> have the grid with a non-uniform refinement from the start. 
> 
> Has anyone else had to deal with this problem, and how did you? 
> 
> Best,
> 
> John ZuHone
> 

-- 
Paul M. Ricker
University of Illinois