A discrete correction scheme for envelope approach of wave group statistics |
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Authors: | Zheng Guizhen Huang Xuren Xu Delun |
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Affiliation: | a Department of Oceanography, China Ocean University, 5 Yushan RD, Qingdao 266003, PR China;b 2nd College of Aviatic Engineering of China Navy, Qingdao 266041, PR China |
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Abstract: | The existence of empty envelope excursions (EEE) brings error to the envelope approach of wave group statistics, which identifies wave group by envelope upcrossing of a critical level. A group number correction scheme is suggested in this paper to exclude EEE from wave group statistics. To this end, the Ditlevson and Lindgren [J. Sound Vib. 122 (1988) 571] theory about the fraction of empty excursion envelopes (FEEE) is examined to see if it fits for ocean waves. The sea waves are simulated with Monte Carlo method and with P-M and JONSWAP spectrums. The values of FEEE of the simulated waves are investigated and compared with the theory of Ditlevson and Lindgren. The comparison shows that, at the second-order approximation, theoretical predictions of FEEE are close to those derived from simulations. This approximate analytical expression of FEEE is then employed to form a group number correction scheme. Comparisons between numerical and theoretical results of wave group properties show that this correction scheme is quite effective. |
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Keywords: | Random waves Wave group Wave envelope Empty excursion envelope Wave statistics |
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