Relativistic simulations of superluminal sources

We present numerical simulations of the radio emission from hydrodynamical relativistic jets. The quiescent-state jet emission consists of quasi-periodic knots of high emission, associated with internal recollimation shocks. Superluminal components can be reproduced by introducing a square-wave perturbation in the injection velocity of the jet. Strong interactions of the resulting moving shock and the standing recollimations result in a 'drag' and increase in emission of the latter.