论风浪的局域结构──Ⅱ.风浪局域小波能谱的性质及应用

LOCAL STRUCTURES OF WIND WAVES Ⅱ.PROPERTIES OF LOCAL WAVELET ENERGY SPECTRUM AND ITS APPLICATIONS

引入了局域小波能谱的局域间歇性度量，分析了不同风速下的风浪资料，结果表明，局域小波能谱可依局域频率分为三部分。风浪的群性在三维局域小波能谱图像下显示得更为明显，与风浪有关的一切性质都是局域的，包括风浪的群性。讨论了局域小波谱峰值与谱峰频率的涨落，指出了前者在工程设计中的重要意义，并发现了后者与风浪破碎有关的两种非线性现象。

Local intermittency measure is introduced to study the properties of local wavelet energy spectrum and to analyze the wind wave data obtained in a wind wave channel. It is shown that local wavelet energy spectrum of wind waves can be divided into three sections:(l) the section whose local frequencies are lower than the local peak frequency;(2) the section whose local frequencies are close to the local peak frequencies. In this section the local intermittency measure has significant and irregular fluctuations which indicate that waves energy has strong intermittency;(3)the section whose local frequencies are higher than the local peak frequency. This section corresponds to the equilibrium range of the Fourier spectrum and has regular intermittency.Fluctutions of spectral peak energy and peak frequency are also discussed in the present paper. The authors point out that wind waves may have instantaeously remarkble energy, which is much more than the average over the time interval determined by the dominant wave component and may cause great damage to offshore structures. In engineering designs, the variance of the fluctuations of the local peak should also be taken into considerations besides the mean value of the fluctuations described by the Fourier spectrum. In the later fluctuations they found two interesting phenomena closely related to waves breaking. One is called 'jump' wherein the peak frequency may jump abrubtly from one value to another value, and the other one is called 'stagnation' wherein the peak frequency remains constant, and may so over several sections.