[FLASH-USERS] ensuring div B = 0 when adjusting evolution
John ZuHone
jzuhone at gmail.com
Fri Jun 16 09:12:59 EDT 2017
I'll be honest, I've noticed this behavior with HLLC as well. It happens less, but it's still present.
Sent from my iPhone
> On Jun 9, 2017, at 7:51 PM, Dongwook Lee <dongwook at flash.uchicago.edu> wrote:
>
> 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?bibcode=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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