论风浪的局域结构──Ⅰ.风浪的局域结构与局域小波能谱

LOCAL STRUCTURES OF WIND WAVES Ⅰ.LOCAL STRUCTURES OF WIND WAVES AND LOCAL WAVELET ENERGY SPECTRUM

基于小波变换，引入了能刻画风浪局域结构的局域小波能谱。论述了风浪的整体结构与局域结构。指出了在不同时间尺度上，风浪具有不同的局域化特征。提出了风浪场演化过程中整体的共振非线性相互作用是否存在的质疑。

Based on the wavelet transform, the present paper introduces a kind of wind waves energy distribution, the so-called local wavelet energy spectrum, into studies of wind waves. The wavelet spectrum, which can describe local structures of wind waves, is quite different from the normal wind wave frequency spectrum which can only describe global strutures of wind waves. The analyzed results from wind wave data measured in a wind wave channel show that wind waves energy exhibited localizations both in scales (frequency) and physical space, which implies that energy at a given frequency has significant fluctuations as time evolves. Almost all of the properties of wind waves are local, such as waves groupness and secondary peak. The looal structures of wave groupness are shown clearly in the three dimensional time-frequency spectrum. The local structurds of wind waves are due to the fact that, for realistic windwaves, the wind pressure has local strucures and cannot be considered as a constant, nor, can it be interpreted as a superposition of Fourier wave component since the Fourier transform has not resolution in physical space. Since in the weakly nonlinear theory the water wave flelds are represented by the Fourier tranform and whose spectral representation has long been used, the authors question the existence of globally nonlinear resonant interactions in the evolution of wind wave fields, and maintain that for realistic wind waves, the resonat interactions are local rather than global.