[Users] weird behavior with some ET simulations

[Haas, Roland]

Hello all,

as Zach said, there have been updates to Carpet since then. Though the
behaviour is a bit odd.

Carpet will merge refined boxes (eg the two boxes tracking the black
holes) if they overlap and form a single large enclosing box. This can
lead to a situation where, when the boxes are aligned in x or y, the do
not overlap but do when eg they are at 45 degree angels (since they
their corners overlap) eg:


xxxxxxxxxxxx  ++++++++++++
x          x  +          +
x          x  +          +       
x          x  +          +
x          x  +          +
xxxxxxxxxxxx  ++++++++++++

where everything is fine, vs:

 xxxxxxxxxxxx
 x          x
 x          x
 x          x
 x         ++++++++++++
 xxxxxxxxxx+x         +
           +          +
           +          +
           +          +
           ++++++++++++

where there is overlap and Carpet will make one large box like so:

 **********************
 *          x         *
 *          x         *
 *          x         *
 *         +++++++++++*
 *xxxxxxxxx+x         *
 *         +          *
 *         +          *
 *         +          *
 **********************

that encloses both black holes.

You will be easily able to see this if you have 2d or 3d output, the
load it into eg VisIt, create a slice in the xy plane, then add a
"Mesh" plot.

Similar effects can happen if the outer corner of one of the moving
boxes (think in 3d here, the outer edge is not on the xy plane but off
the xy plane by the height of the moving box) intersects with the
inner_sphere radius of Llama.

Right now this is just guess but may expain the observed behaviour if
each of the bursts you saw is due to a bit of grid being created or
destroyed.

Yours,
Roland

> Hi Toni,
> 
> The problem you report seems to be related to the AMR, which is a
> separate module from Llama. There have been multiple updates to the
> AMR infrastructure since 2017.
> 
> -Zach
> 
> *     *     *
> Zachariah Etienne
> Assistant Professor of Mathematics
> West Virginia University
> *https://math.wvu.edu/~zetienne/ <https://math.wvu.edu/~zetienne/>*
> https://blackholesathome.net
> 
> 
> On Wed, Mar 6, 2019 at 1:42 PM Antoni Ramos Buades <
> antoniramosbuades at gmail.com> wrote:  
> 
> > Hi,
> >
> > we are using a version of the EinsteinToolkit of 2017, particularly,
> >
> > !DEFINE ET_RELEASE = ET_2017_06
> >
> > so it is not one of the newest versions, but as far as I know in
> > the last releases there has not been updates on the Llama thorn.
> > Although we can try to run with older or newer versions if you
> > think it can help to solve the problem.
> >
> > Best Regards,
> > Toni.
> >
> >
> > El mié., 6 mar. 2019 a las 18:29, Zach Etienne
> > (<zachetie at gmail.com>) escribió:
> >  
> >> Hi Antoni,
> >>
> >> This is a worrisome finding, thanks for sharing. It would be
> >> useful if you would let us know what version of the ET you are
> >> using. Further, if you could attempt the simulation with earlier
> >> versions of the ET (e.g., the first version with Llama included),
> >> it would help to determine if this issue arose due to some recent
> >> commit.
> >>
> >> -Zach
> >>
> >> *     *     *
> >> Zachariah Etienne
> >> Assistant Professor of Mathematics
> >> West Virginia University
> >> *https://math.wvu.edu/~zetienne/ <https://math.wvu.edu/~zetienne/>*
> >> https://blackholesathome.net
> >>
> >>
> >> On Wed, Mar 6, 2019 at 9:40 AM Antoni Ramos Buades <  
> >> antoniramosbuades at gmail.com> wrote:  
> >>  
> >>> Hi,
> >>>
> >>> my name is Antoni Ramos Buades, I am PhD student in the
> >>> University of the Balearic Islands working with Sascha Husa. We
> >>> have been using ET with the Llama thorn to produce waveforms. We
> >>> have observed in some simulations strange behaviors in the
> >>> waveforms. For example, I have attached a plot of the amplitude
> >>> of the psi4 of a non-spinning q1 simulation, for different higher
> >>> order modes, where you can see that the 22, 32 and 44 show weird
> >>> spikes. We have rerun this simulation outputting 2D data in the
> >>> x-y plane. We have plotted the Hamiltonian constraint and made a
> >>> movie (I cannot attach the movie because its size is 42Mb ) but I
> >>> can attach some snapshots where you can observe that there seems
> >>> to be an outburst of noise when the boxes are aligned, and this
> >>> continues happening in the simulation each time the boxes are
> >>> aligned with each other. Geraint Pratten is also investigating
> >>> this issue  adding some new parameters in the parameter file
> >>> (attached to the email) for the carpet mesh refinement like
> >>> freeze_unaligned_parent_levels, freeze_unaligned_levels, ... and
> >>> running some tests.
> >>>
> >>> We would like to ask you if somebidy has ever seen this thing
> >>> happening before and if somebody knows how one could solve this
> >>> problem, because with the same Carpet settings we have observed
> >>> that for some configurations (mass ratio and spins) this does not
> >>> happen, but for others, like the one presented in this email we
> >>> do. I have additional quantities as a 2D output like the
> >>> curvature, metric, horizon, ... in case you think they could be
> >>> used to check something.
> >>>
> >>> Thanks and best regards,
> >>> Toni.
> >>> _______________________________________________
> >>> Users mailing list
> >>> Users at einsteintoolkit.org
> >>> http://lists.einsteintoolkit.org/mailman/listinfo/users
> >>>  
> >>  



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