A Two-Dimensional Numerical Simulation of Sprial Density Waves In Thin Accretion Disks
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**Session 40 -- Computational Astrophysics I**
*Display presentation, Wednesday, 1, 1994, 9:20-6:30*

## [40.14] A Two-Dimensional Numerical Simulation of Sprial Density Waves In Thin Accretion Disks

*N. A. Hillis, S. P. Ruden (Univ. of California, Irvine)*

We are interested in examining the energy and angular momentum
transport of spiral density waves (SDWs) in gaseous disks. The
influence of gravitating bodies within the disk generates waves which
propagate throughout the disk and dissipate through natural viscous
damping processes. To achieve an accurate simulation of this
transport mechanism it is necessary to understand the propagation of
waves on a numerical grid. It can be shown that the group velocity of
a SDW on a mesh vanishes when the wavelength equals twice the grid
spacing. SDWs, which wind up and decrease their radial wavelength as
they propagate, will reflect off the numerical grid at these locations
where the group velocity vanishes. We dub these positions in the
disk *Nyquist Barriers*
because they spuriously reflect wave
energy and angular momentum. To control this effect we have developed
an artificial wave viscosity that damps these waves before they
reflect and minimizes their impact on the subsequent evolution of the
system. This wave viscosity is equivalent to giving the disk a
vertical scale height comparable to the radial grid spacing. We
present numerical simulations of the reflection process.

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