[FLASH-USERS] zoom-out simulations

[Sean M. Couch]

Hi Jon,

Depending on what exactly you are looking to do, it might already be possible with FLASH. FLASH4 already has the capability to reduce the maximum allowed refinement level as a function of radius. See the runtime parameter `gr_lrefineMaxRedDoByLogR` and `gr_lrefineMaxRedRadiusFact`. The latter is a bit arcane, but essentially sets the “angular” resolution of the resulting grid. But the value chose depends on the number of zones per block (`nxb`) since the resolution limiting is actually based on the _block_ size, not the _zone_ size directly.

The second already-implemented feature that could be of use here is the runtime param `gr_lrefineMaxRedDoByTime`. This, if True, decreases the maximum allowed refinement level anywhere on the grid as a function of time. The behavior is set by the params `gr_lrefineMaxRedLogBase`, `gr_lrefineMaxRedTRef`, and `gr_lrefineMaxRedTimeScale`. See appropriate documentation online or the code directly. Combined with `gr_lrefineMaxRedDoByLogR`, this means you can “de-resolve” the inner region of your grid as the feature you are interested in moves out in radius. This nets you not only a reduction in the total number of zones in the simulation but, usually, a nice increase in the time step size. We have been using these features, in various combinations, for years in our supernova simulations.

This all assumes that you are included the “large” scale region from the very start of your simulation. If you want to map an already-run simulation into a larger domain, literally zooming out, that’s harder. I did it a long time ago (with FLASH v2!) when I was a grad student but that code and capability are now part of the geological record, I fear.

Sean


----------------------------------------------------------------------
Sean M. Couch, Ph.D.
Assistant Professor
Department of Physics and Astronomy
Department of Computational Mathematics, Science, and Engineering
Facility for Rare Isotope Beams
Michigan State University
567 Wilson Rd, 3250 BPS
East Lansing, MI 48824
(517) 884-5035 --- couch at pa.msu.edu --- www.pa.msu.edu/~couch
On May 29, 2019, 1:45 PM -0400, Slavin, Jonathan <jslavin at cfa.harvard.edu>, wrote:
Hi all,

Often simulators will use zoom-in simulations - taking a part of a large simulation to focus on a small region of interest. I would like to do the opposite. I would like to take a fairly small scale simulation and embed it in a larger smooth background and reduce the refinement by a level or two. I imagine that this will require some significant coding, but I was wondering if anyone had tried something like this or could offer suggestions on how to do it. Thanks in advance for any help.

Regards,
Jon

--

Jonathan D. Slavin
Astrophysicist - High Energy Astrophysics Division
Center for Astrophysics | Harvard & Smithsonian
Office: (617) 496-7981 | Cell: (781) 363-0035
60 Garden Street | MS 83 | Cambridge, MA 02138


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