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Indexed by:Journal Papers

Date of Publication:2015-08-01

Journal:OCEAN ENGINEERING

Included Journals:SCIE、EI、Scopus

Volume:104

Page Number:480-488

ISSN No.:0029-8018

Key Words:Freak waves; Wave groupiness; Benjamin-Feir instability; Wavelet transform

Abstract:In this investigation of the groupiness properties of unstable random wave trains, the evolution of wave groups in the process of freak wave generation and their scale-averaged wavelet power W(t) are analyzed. Wave groupiness is described in terms of two new groupiness parameters, group height GF(W) and group length GL(W), which are defined based on the wavelet transform. The relationship between GF(W), GL(W) and the kurtosis of the wave surface are also given. Detailed analyses show that wave groups play an important role in the process of freak wave generation. The group height parameter GF(W) reflects the wave train instability well. More unstable wave trains (i.e., those with a larger Benjamin-Feir index) are reflected in larger values of GF(W), which gradually increases with wave evolution during wave propagation; however, GL(W) is not obviously related to wave instability but is associated with the bandwidth of the frequency spectrum. The ratio of GF(W) to GL(W) is strongly related to kurtosis, implying that it is a good indicator of freak wave generation. (C) 2015 Elsevier Ltd. All rights reserved.