Higher-harmonic focused-wave forces on a vertical cylinder

Yuxiang Ma, Guohai Dong, Marc Perlin, Shuxue Liu, Jun Zang, Yiyan Sun

Research output: Contribution to journalArticle

23 Citations (Scopus)

Abstract

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.
Original languageEnglish
Pages (from-to)595-604
Number of pages10
JournalOcean Engineering
Volume36
Issue number8
DOIs
Publication statusPublished - Jun 2009

Keywords

  • Wave transformation
  • Vertical cylinder
  • Wavelet-based bicoherence
  • Scale-averaged wavelet energy
  • Higher-harmonic forces
  • Nonlinear interactions

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