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论文类型：期刊论文

发表时间：2009-06-01

发表刊物：OCEAN ENGINEERING

收录刊物：SCIE、EI、Scopus

卷号：36

期号：8

页面范围：595-604

ISSN号：0029-8018

关键字：Higher-harmonic forces; Vertical cylinder; Nonlinear interactions; Wave transformation; Scale-averaged wavelet energy; Wavelet-based bicoherence

摘要：This paper considers higher-harmonic forces due to wave focusing on a vertical circular cylinder. A series of experiments has been conducted in a wave flume. The first six-harmonic components of the measured wave forces are analyzed using the scale-averaged wavelet spectrum. It is noted that due to the transient nature Of focused (freak) waves, Fourier analysis would not provide equivalent information to that gleaned from the analyses used herein. The results for the experiments with very steep wave crests show significant amplitudes at the fourth and fifth harmonics. These harmonics exhibit amplitudes that are the same order as the second harmonic, but much larger than those of the third harmonic. The wavelet-based bicoherence is used to detect the quadratic nonlinearity of the measured forces. And the bicoherence spectra reveal the primary mathematical reason for the existence of the striking amplitudes of the fourth and fifth harmonics: the interaction between the lower-harmonic components Couple more strongly with the fourth and fifth harmonics, thus the fourth and fifth harmonics glean more energy than those of the third-harmonic components. However, the physical explanation for this remains elusive. (C) 2009 Elsevier Ltd. All rights reserved.