The role of parametric noise in altering the nonlinear dynamical behaviour of a circular cylinder undergoing vortex induced vibrations (VIV) is examined. The analysis is done by using a wake
oscillator model as well as numerical simulations of a Navier Stokes solver. Parametric noise is seen to bring in major qualitative and quantitative changes in response dynamics of the VIV system. Noise
is seen to excite multiple frequencies in the responses and bring in new dynamical states. A low intensity noise gives rise to dynamics that resembles a quasi-periodic behaviour whereas Noise induced intermittency is observed with high intensity noise. Time series tools have been found effective in characterising the dynamical differences of different qualitative states. We also study the influence of noise on the phase dynamics of the system, in the framework of synchronisation theory. The stochastic VIV system manifests asynchronous and synchronous phase dynamics as well as regions of phase slips during the transition boundaries of stochastic bifurcations. The numerical
simulations using the Navier Stokes solver reveal that the time scale of the input noise is a major factor in deciding the wake and structural dynamics as well as the regime of lock-in. A short time scale invokes aperiodic dynamics whereas a long time scale noise invokes `switch' states in the responses. The temporal intermittency seen in the aerodynamic and cylinder responses is manifested as a spatio-temporal intermittency in the flow-field. In presence of long-time sale noise, the wake behind the body is a combination of strong Karman, weak Karman and the transition aperiodicities. With short time scale noise, the flow-field dynamics is predominantly characterised by
aperiodic phenomenon such as vortex pairing, vortex diffusion and deflected wakes.