海浪双峰方向分布的一种物理解释

PHYSICAL EXPLANATION OF BIMODAL DIRECTIONAL DISTRIBUTION OF OCEAN WAVES

用 １８个波高计组成的直径为 ４０ｃｍ的圆形阵列在大型风浪槽内系统地测量了风浪和涌浪方向谱。用两种分辨力较高的方向谱估计方法最大似然法（ＭＬＭ）和贝叶斯方法（ＢＤＭ）分析的结果表明：风浪高频域出现的依赖于估计方法的双峰方向分布是一种物理假象；在较成长的涌浪低频域，得到跟传播方向对称、两峰间隔大约６０°－９０°非常规则的双峰方向分布，它跟频率和涌浪的成长状态有关，而跟估计方法无关，这种现象可以用非线性波－波相互作用过弱，在不同方向之间不能有效传递能量来解释。

Measured data from a circular array of 18 wave gauges in a large wind flume are used to analyze the directional spectra of wind waves and swells by the Maximum Likelihood Method (MLM) and Bayesian Method (BDM). The results show that diretional spreading functions for these spectra are unimodal and the narrowest in the region of the spectral peak freunecy; the younger the waves, the broader the directional spreading width. At frequencies higher than the peak frequency of wind waves, the unimodal spreading becomes bimodal or multimodal depending on the estimating mehtod (MLM or BDW used and relates to the frequency. At frequencies lower than the peak frequency of the swell, the directional spreading becomes regularly bimodal and is symmetrical about the propagating direction. The bimodal sidelobes are independent of the estimating method, continuing to separate by 60°to 90° with a decreasing frequency and becoming larger in magnitude with the decay of the swell. It is inferred that the nonlinear wave-wave interations are too weak to transfer senergy effectively in different directions and maintain trimodal directional distributions in the region of low freqarencies of the swell.