[Users] Noise outburst in ET waveforms

[Antoni Ramos Buades]

Hi,

my name is Antoni Ramos Buades, I am PhD student at 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 modes 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  ), indeed I cannot even
attach some snapshots because then the message exceeds the limit of 1000KB
and the message gets stuck on the moderator approval procedure of the
mailing list ( two days have already passed ...). So I have sent a minimal
version without the snapshots. In the movie or the snapshots one observes
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 somebody has ever seen this thing happening
before and if somebody knows how one could solve this problem, if adding
some additional parameters to the parameter file (attached to this email)
can prevent this from happening, 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 it does. 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.
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