[FLASH-USERS] ensuring div B = 0 when adjusting evolution
Dongwook Lee
dongwook at flash.uchicago.edu
Fri Jun 9 19:51:55 EDT 2017
Hi Jon,
OK, I am glad to hear that your problem was resolved with a smaller dt,
which should help improving the numerical stability due to the second
explosion.
The reason I mentioned HLLD was because I've seen a couple of cases in
which fine-coarse block artifacts are triggered and amplified using the
HLLD solver, possibly due to (among many other scenarios) a switch that is
activated at degenerate case ~ line 215 or so.
I will need to look into this case more carefully in future and see how I
can improve the HLLD behavior. Until then, if this happens, switching to
HLLC will help.
Cheers,
Dongwook
On Fri, Jun 9, 2017 at 9:19 AM, Slavin, Jonathan <jslavin at cfa.harvard.edu>
wrote:
> Hi Dongwook,
>
> I was using HLLD. However my problem was solved when I set the initial
> time step after the second explosion to dtinit, which is a very small
> value. So I think it was related to the large pressure gradients present
> when the second explosion is initiated. As far as I can tell, the problem
> was between fine resolution pixels, not at a fine-coarse boundary.
>
> Jon
>
> On Thu, Jun 8, 2017 at 7:05 PM, Dongwook Lee <dongwook at flash.uchicago.edu>
> wrote:
>
>> Hi Jon,
>>
>> Do you see large B fluctuations aligned with the fine-coarse block
>> boundaries; and they get larger over time?
>>
>> Just to add one quick suggestion: what Riemann solver you've been using?
>> If HLLD, can you try to switch to HLLC or HLL and see if the fluctuations
>> still persist?
>>
>> Cheers,
>> Dongwook
>>
>> On Fri, May 26, 2017 at 1:38 PM, Slavin, Jonathan <
>> jslavin at cfa.harvard.edu> wrote:
>>
>>> To answer Sean and Ernesto's questions:
>>> I am using the USM solver and AMR. I have now determined that div B is
>>> still 0 after the second explosion, which is not too surprising since, for
>>> this run, I have not changed the magnetic field and include div B cleaning
>>> (killdivb = .true.). So the problem is not with non-zero div B but with the
>>> large B fluctuations that are initiated. I noticed that there are small
>>> scale fluctuations in the region where the second explosion is initiated
>>> before the explosion, though the field is weak ~ 0.01 muG. The
>>> fluctuations after the explosion go from ~ -1000 muG - +1000 muG. I do
>>> expect amplification of B field fluctuations at the shock, but not to that
>>> extent.
>>>
>>> The way I'm initiating the second explosion is (almost) the same way I
>>> initiate the first one - I set the pressure of parcels within a given
>>> radius to a value such that the sum of the energy in those parcels is equal
>>> to the value I want for the explosion (1.E51 ergs). I set the density to a
>>> value so as to have the mass total to 8 solar masses. So all the energy is
>>> thermal at first. I'll see about calling the EOS unit, since I haven't
>>> done that. Any additional info on how to do that would be appreciated.
>>>
>>> Thanks,
>>> Jon
>>>
>>> On Fri, May 26, 2017 at 1:00 PM, <flash-users-request at flash.uchicago.edu
>>> > wrote:
>>>>
>>>> ---------- Forwarded message ----------
>>>> From: ERNESTO ZURBRIGGEN <ezurbriggen at unc.edu.ar>
>>>> To: flash-users at flash.uchicago.edu
>>>> Cc:
>>>> Bcc:
>>>> Date: Fri, 26 May 2017 10:56:45 -0300
>>>> Subject: Re: [FLASH-USERS] ensuring div B = 0 when adjusting evolution
>>>> Hi Jon!
>>>>
>>>> Have you tried to set off a less intense second supernova explosion?
>>>> Have you observed the same problems in that case? The second explotion
>>>> might be much too intense.
>>>>
>>>> On the other hand, how do you set the later explotion? I mean, applying
>>>> the explotion, are you consistently modifying the thermodynamical
>>>> variables? For example, if you instantaneously modify the density and the
>>>> temperature, then you also should call the Eos unit to keep the
>>>> consistence. I have experimented situations in which just modifying
>>>> velocities and keeping the thermodynamics unaltered, I also had to call the
>>>> Eos unit in order to maintain consistence
>>>>
>>>> Some runtime parameter that might help being on are 'shockDetect' and
>>>> 'shockLowerCFL' (this last one I think is just in realease 4.4).
>>>>
>>>>
>>>> Best!
>>>>
>>>> --
>>>> *Ernesto Zurbriggen*
>>>>
>>>> *Instituto de Astronomía Teórica y Experimental (IATE). *
>>>> *Observatorio Astronómico de Córdoba (OAC), **Universidad Nacional de
>>>> Córdoba **(UNC)**. *
>>>> *Teléfono: +54 0351 4331064-5, interno 222. *
>>>> *Córdoba, Argentina.*
>>>>
>>>>
>>>> ---------- Forwarded message ----------
>>>> From: "Sean M. Couch" <couch at pa.msu.edu>
>>>> To: "Slavin, Jonathan" <jslavin at cfa.harvard.edu>, flash-users <
>>>> flash-users at flash.uchicago.edu>
>>>> Cc:
>>>> Bcc:
>>>> Date: Fri, 26 May 2017 14:07:22 +0000
>>>> Subject: Re: [FLASH-USERS] ensuring div B = 0 when adjusting evolution
>>>> Hi Jon,
>>>>
>>>> Can you give a little more info? Are you using the USM solver? Are you
>>>> using AMR? Have you actually checked that divB>0 in the output data? A log
>>>> file from a representative run would be useful.
>>>>
>>>> In my experience, the USM solver in cylindrical R-Z coordinates with
>>>> AMR can be….touchy. But it should work and maintain divB=0! (See, e.g.,
>>>> http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibco
>>>> de=2013ApJ...773..136J&link_type=EJOURNAL).
>>>>
>>>> Cheers,
>>>> Sean
>>>>
>>>>
>>>> ------------------------------------------------------------
>>>> ----------------------------------------------
>>>> Sean M. Couch
>>>> Assistant Professor
>>>> Department of Physics and Astronomy
>>>> Department of Computational Mathematics, Science, and Engineering
>>>> National Superconducting Cyclotron Laboratory/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 25, 2017 at 4:41:45 PM, Slavin, Jonathan (
>>>> jslavin at cfa.harvard.edu) wrote:
>>>>
>>>> Hi all,
>>>>
>>>> I'm running MHD simulations where I set off a second supernova
>>>> explosion within a pre-existing remnant. I'm using
>>>> Simulation_adjustEvolution for this. However, I'm running into a problem
>>>> with the magnetic field just after initiating the second explosion. I'm
>>>> getting very large pixel-to-pixel variations in Bx and By at the edge of
>>>> the new expanding blast wave. I'm thinking that it could be because of
>>>> non-zero div B in the region in which the explosion is generated. So my
>>>> question is, does anyone have a suggestion for div B cleaning at the point
>>>> that the explosion is started, i.e. within Simulation_adjustEvolution, to
>>>> prevent the problems I'm having? I don't really expect the B field to be
>>>> dynamically important inside the remnant (beta >> 1), so accuracy of the B
>>>> field is probably not important there. I should add that I'm doing these
>>>> calculations in 2D cylindrical symmetry (R-Z). Thanks in advance for any
>>>> help.
>>>>
>>>> Regards,
>>>> Jon
>>>>
>>>>
>>>> _______________________________________________
>>>> flash-users mailing list
>>>> flash-users at flash.uchicago.edu
>>>> http://flash.uchicago.edu/mailman/listinfo/flash-users
>>>>
>>> --
>>> ________________________________________________________
>>> 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
>>> ________________________________________________________
>>>
>>>
>>
>>
>> --
>>
>> =========================================
>> Dongwook Lee, Ph.D., Assistant Professor
>> Applied Mathematics and Statistics
>> University of California, Santa Cruz
>> Baskin Engineering, Room 353C
>> 1156 High Street, Santa Cruz, CA 95064
>> https://users.soe.ucsc.edu/~dongwook/
>>
>>
>
>
> --
> ________________________________________________________
> 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
> ________________________________________________________
>
>
--
=========================================
Dongwook Lee, Ph.D., Assistant Professor
Applied Mathematics and Statistics
University of California, Santa Cruz
Baskin Engineering, Room 353C
1156 High Street, Santa Cruz, CA 95064
https://users.soe.ucsc.edu/~dongwook/
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