Metastable states in the planar 2d XY model and dissipation in superfluid flow

We use the Metropolis algorithm to study the stability of superfluid flow in a model system, namely the two-dimensional planar XY model. Flow properties are examined by studying the behaviour of the system in meta-stable ``twisted'' states. We demonstrate the stability of superfluidity in this model and we discuss the Meissner effect and velocity quantization. We also study the critical velocity and dissipation by vortex creation and rotational flow and their dependence on the geometry of the system. An expression for the average superfluid velocity as a function of time, ${\bar v}_s(t)$, is obtained and compared with experimental results.