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Abstract

We describe a method of implementing the axisymmetric evolution of
general-relativistic hydrodynamics and magnetohydrodynamics through
modification of a multipatch grid scheme. In order to ease the computational
requirements required to evolve the post-merger phase of systems involving
binary compact massive objects in numerical relativity, it is often beneficial
to take advantage of these system's tendency to rapidly settle into states that
are nearly axisymmetric, allowing for 2D evolution of secular timescales. We
implement this scheme in the Spectral Einstein Code (SpEC) and show the results
of application of this method to four test systems including viscosity,
magnetic fields, and neutrino radiation transport. Our results show that this
method can be used to quickly allow already existing 3D infrastructure that
makes use of local coordinate system transformations to be made to run in
axisymmetric 2D with comparable results.