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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.
