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Black hole excision with multiple grid patches

Thornburg, Jonathan (2004) Black hole excision with multiple grid patches Classical and Quantum Gravity, 21, (15), pp. 3665-3691. (doi:10.1088/0264-9381/21/15/004).

Record type: Article


When using black-hole excision to numerically evolve a black-hole spacetime with no continuous symmetries, most 3+1 finite differencing codes use a Cartesian grid. It is difficult to do excision on such a grid because the natural r = constant excision surface must be approximated either by a very different shape such as a contained cube, or by an irregular and non-smooth `LEGO1 sphere' which may introduce numerical instabilities into the evolution. In this paper I describe an alternate scheme which uses multiple {r × (angular coordinates)} patches, each patch using a different (nonsingular) choice of angular coordinates. This allows excision on a smooth r = constant 2-sphere. I discuss the key design choices in such a multiple-patch scheme, including the choice of ghost-zone versus internal-boundary treatment of the interpatch boundaries (I use a ghost-zone scheme), the number and shape of the patches (I use a 6-patch `inflated-cube' scheme), the details of how the ghost zones are `synchronized' by interpolation from neighbouring patches, the tensor basis for the Einstein equations in each patch, and the handling of non-tensor field variables such as the BSSN ??? (I use a scheme which requires ghost zones which are twice as wide for the BSSN conformal factor ? as for ??? and the other BSSN field variables). I present sample numerical results from a prototype implementation of this scheme. This code simulates the time evolution of the (asymptotically flat) spacetime around a single (excised) black hole, using fourth-order finite differencing in space and time. Using Kerr initial data with J/m^2 = 0.6, I present evolutions to t ? 1500m. The lifetime of these evolutions appears to be limited only by outer boundary instabilities, not by any excision instabilities or by any problems inherent to the multiple-patch scheme.

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Published date: 7 August 2004


Local EPrints ID: 45845
ISSN: 0264-9381
PURE UUID: 95f3ff5f-d78b-4f00-9d98-951e4fe9dbe3

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Date deposited: 16 Apr 2007
Last modified: 17 Jul 2017 15:10

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Author: Jonathan Thornburg

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