Wavelet ridge analysis of nonlinear dynamic spar responses

In this work it is demonstrated that the wavelet ridge technique is applicable for tracking the time-dependent frequencies and corresponding amplitude envelopes of natural modes of spar platforms. This preliminary study examines the case where nonlinear mooring line stiffness induces time-dependent frequency behavior for a numerically modeled spar platform. Free decay tests of the spar are performed and the wavelet ridge technique is applied to track the instantaneous frequencies of the surge and pitch modes. Finally, frequency tracking of the natural modes of a spar platform subject to irregular wave loading is considered.