Publications

Cherneva, Z. and Guedes Soares, C. (2008), “Non-Linearity and Non-Stationarity of the New Year Abnormal Wave”, Applied Ocean Research, Vol. 30, pp. 215-220

Wigner spectrum, generalized Wigner bispectrum and trispectrum are used here to investigate the non-stationarity and non-linearity of the New Year freak wave. It is shown that for a short series of 7 waves the second peak of the Wigner spectrum exists probably due to Benjamin-Feir instability. There are five peaks of energy during the freak wave in the Wigner spectrum calculated using 4min series. Frequencies of two pairs of peaks are related like frequencies of fourth-order resonant interactions. The Wigner third-order moment spectrum is used to describe how the bispectrum of wind waves is changing in the time. The results are compared with these for stationary bispectrum investigated in our previous works. It is shown that phase coupling takes place preliminary in the front side of the waves. The time-frequency trispectrum is constructed too. It is found that before the freak wave fourth-order moment spectrum shows very intensive non-linear interactions. This process is stronger before the freak wave than after it.

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