深水极端波浪非线性几何特征试验分析

Experimental analysis of the nonlinear geometric characteristics for extreme wave in deep water

为了解极端波浪非线性特征,明确波群在演化过程中的水动力学特性,针对一系列高斯波群进行了深水物理试验分析。试验结果显示,增加波陡或波群宽度,均可使波面偏度Sk发生明显变化,尤其当波浪发生破碎后,在破碎区域内,波面偏度变化范围剧烈增大,说明该偏度极大值可能作为判断破碎的一个指标。波陡和波群宽度对波面不对称度影响程度不同:当波陡或波群宽度增加后,波峰不对称度所受影响最大,波峰前端波谷不对称度次之,波峰后端波谷不对称度所受影响最小,但仍不可忽略。在波浪演化过程中,幅值谱出现不同程度频带下移,波浪破碎后,会出现永久频带下移;当调制不稳定发生时,随着调制不稳定指数增加,频带下移量呈现快速增长趋势。

To study the nonlinear characteristics of the extreme waves and identify the dynamic characteristics of wave groups during the evolution,a series of Gaussian wave groups are analyzed in deep water experimentally.The experimental results show that increasing the wave steepness or the wave group width can make the skewness Sk change obviously,especially when the wave is broken,the variation range of skewness increases dramatically within the breaking region,and the maximum value of skewness may be used as an indicator to judge the wave breaking.Wave steepness and wave group width have different effects on asymmetry.When the wave steepness or the width of the wave group is increased,the asymmetry of the crest is affected the most,followed by the asymmetry of the trough at the front of the crest and the asymmetry of the trough at the back of the crest being affected the least,which however is still not negligible.During the wave evolution,the amplitude spectrum shifts down to different degrees,and after the wave breaking,it shifts down permanently.When the modulation instability occurs,with the increase of the modulation instability index,the frequency band downshift presents a rapid growth trend.