[Users] Large junk radiation

[Erik Schnetter]

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/