【作者】 马玉祥；

【导师】 董国海；

【作者基本信息】 大连理工大学 ， 港口、海岸及近海工程， 2010， 博士

【摘要】 小波变换是对非平稳信号进行时频分析的理想工具,目前该方法在许多科学和工程领域中得到了广泛的应用。然而,小波变换在波浪非线性特征分析中的应用研究却相对匮乏,有关方面的应用研究尚不深入,没有充分展示小波变换的优越性。本文的目的是将Morlet小波变换及其相关概念应用到波浪的非线性特征分析研究中,深入地挖掘Morlet小波变换在分析波浪非线性特征中的潜力,寻求基于Morlet小波变换的处理非线性波浪信号的新方法。本文首先对数据处理方法进行了简单的回顾,并详细介绍了Morlet小波变换的概念、特性以及优越性。然后,基于Morlet小波变换,通过对几种典型的非线性波浪信号进行了分析研究,取得了创新性研究成果：1.基于小波局部波能过程线提出了一个新的量化波浪群性程度的波群因数GF,与以往的GF的相比,本文提出的GF受计算时参数选取的影响几乎可以忽略,更加适合用来统一量化波浪的群性程度。2.引入小波二阶相关谱分析短时／瞬态非平稳波浪的非线性特征,从而解决了传统傅里叶二阶相关谱方法不能应用于短时／瞬态信号非线性耦合分析的问题。并用该小波二阶相关谱研究了不规则波浪在曲线形潜堤上的非线性传播变形、波浪局部的非线性特征变化以及非线性聚焦波浪在等水深下的传播演化过程,取得了理想的研究结果。3.提出用小波局部尺度平均波能来量化局部瞬态高阶谐波,从而解决了传统方法不能很好地量化局部瞬态谐波能量的问题。4.采用小波脊方法提取波浪瞬时峰频并用其表示波浪的瞬时频率,从而解决了用传统方法定义复杂信号的瞬时频率所遇到的困难。并用该方法首次分析研究了波浪在沿空间变化逆水流中的非线性频率调制过程,对波浪在逆水流中频带下移的条件以及频带下移的特征和机理进行了详细的分析研究,取得了重要的研究进展。5.根据Morlet小波变换的解析性质,提出了一种适合在变水深情况下分离非平稳入、反波浪的时域方法,从而解决了以往基于傅里叶变换的分离方法不能精确分离非平稳波浪场的问题。提出了一个新的分离低频波浪的时域方法,应用该方法能够准确地得到约束长波和入、反射自由长波的时间序列,为研究在变浅过程中约束长波滞后于短波包络的相位变化提供了很好的分析方法。更多还原

【Abstract】 Wavelet transform is an ideal tool for time-frequency analysis of nonstational signals. In recent years, this method has been used successfully in many scientific and engineering applications. However, applications of wavelet transform in nonlinearity of ocean waves are rare. Even though some studies have used the new method to slove some issues, the advantages of it are not revealed in depth. The goal of this dissertation is to apply the Morlet wavelet transform and some related definitions for analyzing the nonlinear ocean waves, digging the advantages of the new method in analyzing the nonlinear signals deeply. Furthermore, some new methods, which are suitable to process signals in nonlinear ocean wave analysis, will be proposed based on the Morlet wavelet transform.In this thesis, based on a brief introduction of the signal processing technology, the definition, properties and advantages of the Morlet wavelet transform are introduced carfully. Then, some typical nonstational signals in physical experimental models are analyzed in detail using the Morlet wavelet transform. The major creative contributions of this dissertation are summarized as follows:1. A new groupiness factor(GF), which is the main parameter to measure groupiness of waves, is proposed based on the local wavelet energy history. The main advantage of the new GF is that the effect of the operational definition on it is much smaller than on other GF. Therefore, this new GF is much more suitable to unify wave groupiness.2. To analyze the nonlinear phase coupling in short duration series, the wavelet bicoherence spectrum is introduced. Thus, the concept of bispectrum can be used to analysis series of physical models in ocean engineering. Then, the wavelet bicoherence spectrum is used to study the nonlinear evolutions of both irregular waves propagating over a submerged sill and focusing waves over a constant depth.3. A new method to measure the instantaneous harmonic components of nonstational signals, which can not be resolved using the traditional methods, is proposed using the local wavelet scale-averaged energy.4. The evolution of wave modulations on a spatially varying, opposing current has been studied experimentally. In this study, the wave frequency modulations are represented by the instantaneous peak frequencies which are extracted by the Morlet wavelet ridges, avoiding the difficulties for obtaining instaneaneous frequencies of complicated signals using the traditional methods. The criterion for the occurrence of frequency downshift in opposing currents has been investigated. Furthermore, the characteristic and the physical mechanism for frequency downshift have also been studied.5. A new method for separating nonstationary waves into incident and reflected low-frequecy waves in time domain has been proposed based on the Morlet wavelet transform. Hence, the problem about separating nonstational wave fields accuately by the methods based on Fourier transform is sloved. A new method for separating low-frequency waves in time domain has also been proposed. The method can accurately obtain the time series of bound low-frequency waves, incident and reflected low-frequecy waves. Hence, this method can be used to investigate the cross-shore variations of phase lag of bound low-frequency waves behind short wave envelops.更多还原