[Users] Black hole excision

[Roland Haas]

Hello Ken,

> I am following the Parma group's par file to simulate binary neutron stars
> merging into a black hole. In particular I adopt the following lines into
> my parfile but it looks like everything is "excised" at the very first
> iteration (the maximum density suddenly becomes ~10e-11, basically the
> atmosphere density settings).
> 
> Could someone please guide me how this should be done properly? or what
> parameter settings do I need to set as well?
Sorry for the long delay.

We had a bit of a discussion about this in the last Einstein Toolkit
call and you should be able to find some suggestions in the minutes:

http://lists.einsteintoolkit.org/pipermail/users/2021-June/008034.html

Namely:

-8<-
** Black Hole Excision by Hon Ka Hui needs to be answered.  They added
some lines to the *.par and then excision seemed to occur.  Looks like
a problem with the Spherical Surface being registered but not set, so
it has an infinite radius.  They need to set the number of spherical
surfaces, perhaps.
-8<-

basically it is suggested that you need some parameters for
SphericalSurface to be set. See eg the binary black hole star gallery
example
https://bitbucket.org/einsteintoolkit/einsteinexamples/raw/master/par/GW150914/GW150914.rpar :

SphericalSurface::nsurfaces             = 5
SphericalSurface::maxntheta             = 66
SphericalSurface::maxnphi               = 124
SphericalSurface::verbose               = no

# Surfaces 0 and 1 are used by PunctureTracker

# Horizon 1
SphericalSurface::ntheta            [2] = 41
SphericalSurface::nphi              [2] = 80
SphericalSurface::nghoststheta      [2] = 2
SphericalSurface::nghostsphi        [2] = 2

# Horizon 2
SphericalSurface::ntheta            [3] = 41
SphericalSurface::nphi              [3] = 80
SphericalSurface::nghoststheta      [3] = 2
SphericalSurface::nghostsphi        [3] = 2

# Common horizon
SphericalSurface::ntheta            [4] = 41
SphericalSurface::nphi              [4] = 80
SphericalSurface::nghoststheta      [4] = 2
SphericalSurface::nghostsphi        [4] = 2

to make sure that the spherical surface used by AHFinderDirect is
actually initialized by making sure nsurfaces is large enough and
giving ntheta, nphi etc values for it.

Yours,
Roland

-- 
My email is as private as my paper mail. I therefore support encrypting
and signing email messages. Get my PGP key from http://pgp.mit.edu .
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 833 bytes
Desc: OpenPGP digital signature
Url : http://lists.einsteintoolkit.org/pipermail/users/attachments/20210618/45a306f5/attachment-0001.bin