Planetary ring dynamics is reviewed, based on the results of local 3-dimensional simulations, which utilize a co-moving calculation cell with periodic boundary conditions. Various factors affecting the local balance between collisional dissipation and viscous gain of energy from the systematic velocity field are considered, including gravitational encounters and collective gravitational forces besides physical impacts. Simulation examples of the effects of different forms of the coefficient of restitution are given. Viscous stability properties are also discussed: examples of both instabilities and overstabilities are given and briefly discussed in the context of observed structures in Saturn's rings.
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