[FLASH-USERS] MHD simulations Eint=0 problem
Seyit Hocuk
seyit at mpe.mpg.de
Tue Feb 7 03:21:30 EST 2017
Hi Jon,
Thanks for the quick response. I too have a sudden increase/decrease in
temperature and internal energy in a single cell (I assume that E_int
--> T --> P). It is possible that there is a single origin to this
problem. Let us notify one another about any progress on this matter,
and anyone else from the community.
Best wishes,
Seyit
On 06/02/17 19:24, Slavin, Jonathan wrote:
> Hi Seyit,
>
> I have had to put that problem aside for a while, though I hope to get
> back to it soon. I have not solved the problem that leads to negative
> or zero timesteps. What I found was that what leads to the problem is
> that suddenly in a single grid zone/pixel the thermal pressure jumps
> to a very high value, which thus leads to a very small timestep. I
> plan to probe the problem further as soon as I can.
>
> Regards,
> Jon
>
> On Mon, Feb 6, 2017 at 1:00 PM,
> <flash-users-request at flash.uchicago.edu
> <mailto:flash-users-request at flash.uchicago.edu>> wrote:
>
> From: Seyit Hocuk <seyit at mpe.mpg.de <mailto:seyit at mpe.mpg.de>>
> To: "flash-users at flash.uchicago.edu
> <mailto:flash-users at flash.uchicago.edu>"
> <flash-users at flash.uchicago.edu
> <mailto:flash-users at flash.uchicago.edu>>
> Cc:
> Date: Mon, 6 Feb 2017 10:56:22 +0100
> Subject: [FLASH-USERS] MHD simulations Eint=0 problem
> Hi community,
>
> Has anyone else encountered this problem before?
>
> Whenever I run MHD simulations with the USM solver (Flash4.4), I
> occasionally get Eint=0. This seems to occur only when I put a
> B-field > 0 (I often simulate mass-to-flux ratio of 2). The
> problem is bigger with higher magnetic field strength. I have
> played around with the "eintswitch" parameter, thereby reducing
> reducing the issue it as much as I can (eintswitch =< 1e-4), but
> the problem still persists. A high eintswitch, on the other hand,
> thereby reverting to an independent internal energy calculation
> was giving me crazy values. It is as if the magnetic energy is not
> considered for the internal energy calculations when derived from
> the total energy (Eint = E_tot - Ekin - Emag), or something along
> those lines, but this is just guessing.
>
> Optimizing the parameters helped a little. See parameter choices
> below. My initial guess was that the solver has a hard time
> solving, because the problem is stiff on occasion. Playing with
> these options and relaxing the solver still did not completely
> remove this issue.
>
> I initially thought that this happens after new cells are created,
> however, the problem does still occur when lrefine_min=lrefine_max.
>
> The problem also seems to persist if:
> ForceHydroLimit = .True. (but the B-field is not set to zero; in
> the tested case it is 10.0e-6)
> So, forcing hydrolimit did not help! This while when the B = 0
> (+Forcehydrolimit=true), the Eint does not become 0, but very low
> instead (which is a different issue?). While with B=0, I also get
> a different refinement. Therefore, I am not entirely sure what
> forcehydrolimit does actually. Clearly, there is still impact by
> the B-field.
>
> Another funny thing is enableMaskedGCFill. I usually have
> enableMaskedGCFill = .True.
> but the module that made use of this is turned off. Setting this
> to true or false gives me somewhat different kind of errors. With
> .False. I also get negative values, i.e., WARNING after gc
> filling: min. unk(EINT_VAR)=-1487770975.081508
>
> The end results is sometimes (especially if I don't constrain by
> "small" variables, i.e., make the "small" values really small):
> DRIVER_ABORT: Computed new time step smaller than dr_dtMinContinue!
> similar to a problem mentioned recently "dt not positive in MHD
> simulations" by Jon Slavin. Was any solution fouond for that?
>
> What does help is:
> cfl = crazy low, but normally lowering cfl only delays the issue.
>
> What doesn't help is:
> Turning off gravity
> Turning off particles
> Turning off refinement
> Turning of all my modules
> (Heating/Cooling/Chemistry/Colmndensities...)
> Changing boundaries from periodic/isolated to outflow
> Viscosity
> And many other things
>
> With kind regards,
> Seyit
>
>
> Normal conditions (but I tested them all):
> mfieldstrength = 5.0e-6
> killdivb = .True.
> E_upwind = .True.
> energyFix = .True.
> RiemannSolver = "HYBRID"
> slopeLimiter = "HYBRID"
> order = 3
> use_steepening = .False.
> use_flattening = .True.
> use_avisc = .True.
> shockDetect = .True.
> cfl = 0.6
>
> Libraries/Compilers:
> hdf5-serial/1.8.15
> ifort: intel/15.0
> impi/5.0.3
> x86_64 x86_64 x86_64 GNU/Linux
>
>
> --
> Dr. Seyit Hocuk
> Post-doctoral researcher
> Center for Astrochemical Studies (CAS)
> Max-Planck-Institute for Extraterrestrial physics (MPE)
> Giessenbachstrasse 1, 85748 Garching bei Munchen
> Phone: +49-8930000-3012 <tel:%2B49-8930000-3012> | Fax:
> +49-8930000-3569 <tel:%2B49-8930000-3569>
> Web : www.mpe.mpg.de/~seyit <http://www.mpe.mpg.de/%7Eseyit>
>
>
>
>
>
> --
> ________________________________________________________
> Jonathan D. Slavin Harvard-Smithsonian CfA
> jslavin at cfa.harvard.edu <mailto:jslavin at cfa.harvard.edu> 60
> Garden Street, MS 83
> phone: (617) 496-7981 Cambridge, MA 02138-1516
> cell: (781) 363-0035 USA
> ________________________________________________________
>
--
Dr. Seyit Hocuk
Post-doctoral researcher
Center for Astrochemical Studies (CAS)
Max-Planck-Institute for Extraterrestrial physics (MPE)
Giessenbachstrasse 1, 85748 Garching bei Munchen
Phone: +49-8930000-3012 | Fax: +49-8930000-3569
Web : www.mpe.mpg.de/~seyit
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