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Veltcheva, A. e Guedes Soares, C. (2007), “Analysis of Abnormal Wave Records by the Hilbert Huang Transform Method”, Journal of Atmospheric and Oceanic Technology, Vol. 24, pp. 1678-1689

The Hilbert–Huang transform method is used in this work to analyze wave records from the North Sea, which include abnormal waves. The analysis of the characteristics of abnormal waves is based on the local decomposition of wave data by using the intrinsic mode functions. The variations of amplitude of intrinsic mode functions around the time of the occurrence of abnormal waves are examined in order to investigate the contribution of different intrinsic mode functions on the abnormal waves’ profile, in an attempt to find relationships between them. The changes of local frequency of each intrinsic mode function in the vicinity of abnormal waves are examined. The essential nonlinearity of abnormal waves is considered as intrawave frequency modulation, a variation of the instantaneous frequency within one oscillation cycle. The Hilbert spectrum is used as a detector of abnormal waves. 1. Introduction Abnormal, freak, or rogue waves are local, primary transient phenomena with uncertain and unpredictable occurrence. A while ago, Draper (1964) referred to the existence of freak waves, but until recently they were thought to rarely occur and very little was known about their characteristics. During the last several years, various research groups have studied freak, rogue, or abnormal waves. While in earlier publications these waves were designated as freak, later the designation of rogue waves was adopted. However, as these waves are being defined as the ones that are outside of the normal population of expected waves, they are also called abnormal waves.

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