Evolution of random directional wave and rogue wave occurrence
Evolution of random directional wave and rogue wave occurrence
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发表时间：
2007
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通讯作者：
T. Waseda;H. Tamura
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作者：
T. Waseda;H. Tamura
极值海浪超过有效波高两倍的概率(即流氓海浪)被认为是波浪陡度和频率带宽的函数。组合参数被命名为“Benjamin-Feir”指数，表明非共振波-波相互作用(或某些情况下的Benjamin-Feir不稳定性)是导致无赖波发生增加的原因。然而，最近的研究表明，波谱的方向性抑制了非共振波与波的相互作用。初步研究表明，对于给定的陡度和频率带宽，峰度(因此出现流氓波的概率)随着频谱的展宽而迅速减小(早稻田，第9波WS)。在这份报告中，我们将介绍使用位于矩形盆地(长50米，宽10米，深5米，木下实验室IIS)一端的定向造波机进行的额外实验的结果。实验参数覆盖了传统JONSWAP-Mitsuyasu类型频谱的定向扩展(单向到宽)、陡度和频率带宽范围。还研究了其他方向分布，如Hwang&Wang(2001)观测到的方向分布和双峰分布。结果将讨论强非线性(即波浪破碎)的隔离效应，束缚波和不稳定性的相对重要性，以及频谱离散化的影响。尤其是波破裂引起的光谱下移对峰度的增大起着重要的作用。这些发现对利用第三代波模型进行无赖波预报的意义也将被讨论。
The probability of extreme waves exceeding twice the significant wave height (i.e. the rogue waves), is suggested to be a function of wave steepness and frequency bandwidth. The combined parameter is named the “Benjamin-Feir” index suggesting that the non-resonant wave-wave interaction (or the Benjamin-Feir instability in some cases) is responsible for the increased rogue wave occurrence. However, recent studies suggest that the non-resonant wave-wave interaction is suppressed by the directionality of the wave spectrum. Preliminary study suggested that for a given steepness and frequency bandwidth, the Kurtosis (and hence the probability of the rogue wave) rapidly decreases as the spectrum broadens (Waseda, 9th Wave WS). In this report, we will present results from the additional experiment conducted using the directional wave maker located at one end of a rectangular basin (50m long, 10 m wide, 5 m deep, Kinoshita lab IIS). The experimental parameters cover ranges of directional spreading (unidirectional to broad), steepness, and frequency bandwidth with a conventional JONSWAP-Mitsuyasu type spectrum. Other directional distributions such as the observed one by Hwang & Wang (2001) and bimodal distribution were studied as well. The results will be discussed isolating effects of strong nonlinearity (i.e. wave breaking), relative significance of bound waves and instability, and effects of discretization of the spectrum. In particular, the spectral downshifting due to wave breaking plays an important role in the increase of the Kurtosis. Implication of these findings to the rogue wave prediction utilizing 3rd generation wave models will be discussed as well.