Frequency and phase lock-in behind circular cylinder in the presence of random irregular waves

In this paper, we present the influence of irregular random waves on the von Karman street in the wake of an elastically mounted cylinder. The flow is perpendicular to the long axis of the cylinder which is constrained to oscillate transversally. In our experiments, the generated waves are derived from Pierson-Moskowitz and Joint North Sea Wave Project (gamma = 3 or 7) spectra. It was found that the increase of the nonlinearity of the generated waves is accompanied by a decrease of the shedding frequency to half of the pic frequency of the generated waves. Furthermore, the Hilbert transformation was performed to calculate the continuous phases of irregular waves theta(eta) and that of the Karman vortex street theta(Vx). The temporal evolution of the phase combination theta = 2 theta(Vx) - theta(eta) has been investigated as well. It was found that the time evolution of theta has a steplike shape, i.e., when theta = 0, this corresponds to a synchronizationlike effect. This approach enables the temporal variability of the synchronization to be quantified in the presence of random irregular waves.