[Users] Large junk radiation

[Zach Etienne]

Hi Deborah,

I'd be curious to see a comparison between the junk radiation you're seeing
now versus before, for the same physical scenario, grids, etc. Also, the
extra wiggles/reflections are typically caused not by junk radiation but by
a sharp gauge feature (https://arxiv.org/abs/1404.6523). The two can be
easily distinguished as the former propagates at c, and the latter at
sqrt(2) c (see paper for details).

-Zach

*     *     *
Zachariah Etienne
Assoc. Prof. of Physics, U. of Idaho
Adjunct Assoc. Prof. of Physics & Astronomy, West Virginia U.
https://etienneresearch.com
https://blackholesathome.net


On Tue, Aug 9, 2022 at 4:41 PM Erik Schnetter <schnetter at gmail.com> wrote:

> Deborah
>
> One one hand, TwoPunctures has parameters to choose the resolution of
> the spectral grid it uses. I assume you are aware of these, and that
> you also know how to choose the 3D AMR grid setup parameters.
>
> TwoPunctures only solves for the conformal factor. It does per se not
> directly choose a lapse and a shift, but their choice is important in
> practice. Choosing \alpha=1 and \beta^i=0 as initial conditions is
> often not good. Similarly, choosing the antisymmetry lapse (with
> \alpha=-1 at the puncture) is also a bad idea (it is ill-posed). The
> TwoPunctures toolkit in the Einstein Toolkit has several options for
> choosing the initial gauge conditions. Personally, I am partial to
> initial_lapse = "twopunctures-averaged", but I am sure that others
> have other preferences.
>
> Of course, the BSSN gauge parameters used during evolution will also
> play a role.
>
> You can look at the gallery example at
> <http://einsteintoolkit.org/gallery/bbh/index.html> for ideas.
>
> -erik
>
>
>
> On Tue, Aug 9, 2022 at 4:47 PM Ferguson, Deborah
> <deborah.ferguson at austin.utexas.edu> wrote:
> >
> > Hi,
> >
> >
> >
> > We had been using our own version of TwoPunctures, and I’ve recently
> switched to the ETK version since it doesn’t require solving for the masses
> separately. Junk radiation has always been present, but I’m finding that
> some of my recent simulations have particularly loud junk radiation, which
> also makes it harder avoid reflection of. So I’m guessing I’m not fully
> understanding the TwoPunctures parameters.
> >
> >
> >
> > I’ve attached a parfile and a psi4 plot for a simulation I’ve started
> that’s having this large junk radiation, and was hoping someone could point
> out any mistakes I may have in the TwoPunctures parameters.
> >
> >
> >
> > Thanks!
> >
> > Deborah
> >
> >
> >
> > --------------------------------------
> >
> > Deborah Ferguson
> >
> > Post Doc
> >
> > University of Texas at Austin
> >
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>
>
>
> --
> Erik Schnetter <schnetter at gmail.com>
> http://www.perimeterinstitute.ca/personal/eschnetter/
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