  In strongly nonequilibrium Bose-Einstein condensates described by the
generalized Gross-Pitaevskii equation, vortex motion becomes self-accelerated
while the long-range vortex-antivortex interaction appears to be repulsive. We
numerically study the impact of these rather unusual vortex properties on the
dynamics of multivortex systems. We show that at strong nonequilibrium the
repulsion between vortices and antivortices leads to a dramatic slowdown of
their annihilation. Moreover, in finite-size samples, relaxation of multivortex
systems can lead to the formation of metastable vortex-antivortex clusters,
whose shape and size depend, in particular, on the sample geometry, boundary
conditions and deviations from equilibrium. We further demonstrate that at
strong nonequilibrium the interaction of self-accelerated vortices with
inhomogeneous condensate flows can lead to generation of new vortex-antivortex
pairs.
