[Users] problem using McLachlan with a NS-BH system

[Erik Schnetter]

Giulia

Let me make a few more guesses:

- How do the lapse gauge driver parameters look like? Did you rescale
them as well?
- How does the apparent horizon position / shape / coordinate radius
behave before this happens?

-erik

On Fri, Nov 29, 2019 at 6:33 AM Giulia Crotti
<g.crotti1 at campus.unimib.it> wrote:
>
> Dear all,
> thanks for the suggestions. Indeed the problem seems to be occurring
> on the finest grid, because the lapse is wrong on the finest level. We
> did try changing the ML_BSSN::BetaDriver parameter from 0.71 to 0.25
> (in order to make it ~1/M_BH), but the result was pretty much the
> same.
>
> Cheers,
> Giulia
>
> Il giorno mer 27 nov 2019 alle ore 16:27 Erik Schnetter
> <schnetter at cct.lsu.edu> ha scritto:
> >
> > The issue with the time step size (see probably
> > <https://arxiv.org/abs/1003.0859>) occurs on the coarsest levels only.
> > If the error occurs near the puncture on the fine grid, then this is
> > not the problem.
> >
> > Some of the gauge parameters have a dimension (e.g. 1/length). The
> > "standard" settings are optimized for M=1. If your black hole mass is
> > very different, then you might need to change them. If you have a
> > total mass of M=4, then the gauge might try to act four times faster
> > than usual, leading to an instability. The cure would then be
> > increased resolution, or changing the respective parameters.
> >
> > -erik
> >
> >
> >
> > On Wed, Nov 27, 2019 at 8:52 AM Wolfgang Kastaun <physik at fangwolg.de> wrote:
> > >
> > > Hi Bruno,
> > >
> > > Not sure if related, but I vaguely recall that the gamma-driver shift
> > > gauge condition can become unstable if the timestep exceeds a critical
> > > value related to the damping constant eta in the driver. This might
> > > happen with 9 levels if the timestep is also increasing by a factor 2
> > > with each level. The solution I remember was to use the same timestep
> > > for the few coarsest levels. Do you know if the first occurrence of NANs
> > > in the shift happens on the coarsest level?
> > >
> > > Cheers,
> > > Wolfgang.
> > >
> > > On 11/27/19 12:36 PM, Bruno Giacomazzo wrote:
> > > > Dear All,
> > > >   a student of mine (Giulia Crotti) is having issues running a NS-BH
> > > > simulation with GRHydro and McLachlan (parfile attached). The problem we
> > > > are having is with the metric evolution (see attached image for the
> > > > lapse produced just before the crash) and I don't think I ever saw such
> > > > a problem. Does any of you have any suggestio?
> > > >
> > > > Approximately around 2000 iterations the simulation crashes with the
> > > > following error:
> > > >
> > > > ERROR from host r168c12s01.marconi.cineca.it
> > > > <http://r168c12s01.marconi.cineca.it> process 0
> > > >
> > > >   while executing schedule bin CCTK_EVOL, routine
> > > > PunctureTracker::PunctureTracker_Track
> > > >
> > > >   in thorn PunctureTracker, file
> > > > /marconi/home/userexternal/gcrotti0/EinsteinToolkit/ET_2018_09/Cactus/arrangements/EinsteinAnalysis/PunctureTracker/src/puncture_tracker.cc:204:
> > > >
> > > >   -> Shift at puncture #0 is (-nan,-nan,-nan).  This likely indicates an
> > > > error in the simulation.
> > > >
> > > >
> > > > Something is wrong with the metric; indeed the lapse function gets
> > > > larger than 1. We have 9 refinement levels on the black hole, with a
> > > > resolution of 0.045 on the finest grid. The initial data have been
> > > > computed as to get a mass ratio = 3; so the black hole mass is ~4 solar
> > > > masses. The black hole is non-spinning.
> > > >
> > > >
> > > > Thanks,
> > > >
> > > > Bruno
> > > >
> > > >
> > > > --
> > > >
> > > > Prof. Bruno Giacomazzo
> > > > Department of Physics
> > > > University of Milano-Bicocca
> > > > Piazza della Scienza 3
> > > > 20126 Milano
> > > > Italy
> > > >
> > > > email: bruno.giacomazzo at unimib.it <mailto:bruno.giacomazzo at unimib.it>
> > > > phone: (+39) 02 6448 2321
> > > > web: http://www.brunogiacomazzo.org <http://www.brunogiacomazzo.org/>
> > > >
> > > > ----------------------------------------------------------------------
> > > > There are only 10 types of people in the world:
> > > > Those who understand binary, and those who don't
> > > > ----------------------------------------------------------------------
> > > >
> > > >
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> >
> >
> > --
> > Erik Schnetter <schnetter at cct.lsu.edu>
> > http://www.perimeterinstitute.ca/personal/eschnetter/
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/