Nonlinear spiral density waves - Viscous damping

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[[abstract]]The authors calculate the viscous damping of nonlinear density waves in Saturn's rings using various kinetic formulations to estimate the collisional change (δP/δt)c of the vertically integrated pressure tensor P in a particulate disk. The pressure tensor is computed as a function of two parameters: (1) the ratio of the average collision frequency to the epicyclic frequency, and (2) a measure of how close streamlines are to crossing when perturbed by nonaxisymmetric forces. When parameters approximately correct for the density waves excited by Mimas's 5:3 resonance in the A ring are used, the authors obtain a satisfactory fit with the observed profile, providing one uses a coefficient of restitution that is appropriate to crystalline ice and providing one uses an extreme Krook formulation to evaluate (δP/δt)c. When a similar calculation is made for the density waves in the B ring excited by the comparably strong 2:1 resonance of the so-called co-orbital satellites, the results are more mixed. It is speculated that the densities in the actual peaks of the density waves in Saturn's B ring are limited, not by viscosity, but by the condition of excluded volumes when ice balls are packed tightly against one another. Finally, the authors discuss the problems of mass and angular momentum transport in a disk with externally deposited resonant torques, and of opening gaps and maintaining sharp edges in planetary rings. --------------------------------------------------------------------------------[[fileno]]2010118010094[[department]]物理

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