实验室长波引起的风浪低频频移

Low frequency shift of wind waves induced by long waves in the laboratory tank

利用实验室波浪水槽观测规则长波对风浪的影响。谱分析显示,较之纯风浪谱,除已被广泛关注的长波抑制风浪这一现象外,当长波波陡较小,且频率远离风浪峰频时,长波还使得风浪谱向低频移动。利用Longuet-Higgins&Stewart(1960)理论,并考虑到风浪破碎的约束,计算了规则长波的存在对风浪谱的影响,发现可以较好地解释这一现象。表明当长波波陡小且频率远离风浪峰频时,长波对短波的二阶调制及其引起的破碎加强可能是长波影响风浪的主要机制。

The influences of long regular wave on wind wave are examined in the laboratory tank. The wind wave spectra when there is and there is not long waves are compared. Besides the widely addressed suppression of wind wave by long wave, it is also found that, the presence of long regular wave induces low frequency shift of wind wave when long wave slope is small and also its frequency s quite apart from wind wave peak frequency. The effect of long wave modulation on the wind wave spectra is estimated according to Longuet-Higgins＆amp;Stewart （1960） （abbreviated as LS60 afterwards） , which is found to be prominent at the large ratio of fp/fl. It＆#39; s also found that, when the limitation of wave breaking on wind wave steepness is taken into account, the LS60 theory can explain the low frequency shift satisfactorily. These work suggests that, at the small long wave slope and large ratio of fp/fl, the LS60 modulation mechanism together with the enhanced wave breaking may dominate the influence of long waves on wind waves.