Statistics of Extreme Wind Waves

Chalikov D.V. ‎

This paper describes the results of more than 4,000 long-term (up to thousands of peak-wave periods) ‎numerical simulations of nonlinear gravity surface waves performed for investigation of properties and ‎estimation of statistics of extreme («freak») waves. The method of solution of 2-D potential wave’s equa-‎tions based on conformal mapping is applied to the simulation of wave behavior assigned by different ‎initial conditions, defined by JONSWAP and Pierson-Moskowitz spectra. It is shown that nonlinear wave ‎evolution sometimes results in appearance of very big waves. There are no predictors for appearance of ‎extreme waves, however, a height of dimensional waves is proportional to a significant wave height. The ‎initial generation of extreme waves can occur simply as a result of group effects, but in some cases the ‎largest wave suddenly starts to grow. It is followed sometimes by a strong concentration of wave energy ‎around a peak vertical. It is taking place throughout several peak wave periods. It happens to an ‎individual wave in a physical space, no energy exchange with surrounding waves taking place. Probability ‎function for steep waves has been constructed. Such a function can be used for development of ‎operational forecast of freak waves based on a standard forecast.

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