Predicting the breaking onset of wave groups in finite water depths based on the Hilbert-Huang transform method

Abstract

This experimental study focuses on the nonlinear characteristics and breaking onset of extreme waves. The critical value of the first-order instantaneous frequency f1 obtained by the Hilbert-Huang transform method is proposed to determine the wave breaking onset. Specifically, when the normalized instantaneous frequency f1/fp ≥ 2 (fp denotes the dominant frequency), the wave breaks; otherwise, it is less likely to break. For the wave groups considered in this study, the normalized maximum crest height shows an exponential growth as the normalized instantaneous frequency increases. Moreover, it was found that there is a close logarithmic growth relationship between the normalized instantaneous frequency and the local wave steepness. Thus, the instantaneous frequency can be an effective indicator for evaluating extreme wave nonlinearity.