Vortex structures in dilute quantum fluids

Vortex structures in dilute quantum fluids are studied using the time-indep endent Gross-Pitaevskii equation. The velocity and momentum of vortex rings with multiple circulation are determined and their core structures analyse d. For flow around a spherical object, we study the encircling and pinned r ing solutions, and determine their excitation energies as a function of vel ocity for both penetrable and impenetrable objects. The ring and laminar fl ow solutions converge at a critical velocity, which decreases with increasi ng object size. We also study the vortex solutions associated with flow pas t a surface bump which indicate that surface roughness also reduces the cri tical velocity. This effect may have important implications for the thresho ld of dissipation in superfluids and superconductors.