基于小波变换法定义的波群参数

通过小波变换分析的波能过程定义了两个描述波浪群性的参数,由数值模拟波浪和实测波浪资料对其与常用的波群参数进行对比分析,结果表明基于小波波能过程定义的群性参数是有效的,从而展示了小波变换用于在时频域上分析波群的能力。详细探讨了波浪记录长度对群性参数稳定性的影响,分析结果表明,波浪观测长度对于波群参数的影响较大,在考虑波浪群性的波浪模拟及分析时,建议模拟时间长度应在400~500个波以上。     

A new method for separation of 2D incident and reflected waves by the Morlet wavelet transform

A new method based on the Morlet wavelet transform for separating a 2D wave field into incident and reflected waves is proposed in this paper. The principle of this method, first, is derived for constant depths. Then, using the linear shoaling theory, the method is extended to an arbitrary sloping bathymetry. Owing to the time-frequency characteristic of wavelet transform, the present method can separate waves in the real time domain and is not confined by the stationary assumption of waves. The efficiency and accuracy of this method are demonstrated using numerical simulated data.     

Wave profile measurement by wavelet transform

A new technique for measuring wave profiles by wavelet transform using the Mexican Hat wavelet as the mother wavelet is introduced. This technique has the potential to provide low cost, high resolution field measurements of wave profiles in the laboratory. The experiments to capture the video image of the wave profile were carried out in a wave flume. Then, the Mexican Hat wavelet was adopted to trace out the exact profiles of the waves from the captured video images. The series of tests on numerical data and video images show promise as means of detecting two-dimensional profiles of waves.     

Wavelet analysis for processing of ocean surface wave records

Wavelet analysis is a relatively new technique and in the recent years enormous interest in application of wavelets has been observed. This modern technique is particularly suitable for non-stationary processes as in contrast to the Fourier transform, (FT), the wavelet transform (WT) allows exceptional localization, both in time and frequency domains. The wavelet transform has been successfully implemented in signal and image processing, ordinary and partial differential equation theory, numerical analysis, communication theory and other fields. On the other hand, the application of the WT to ocean engineering and oceanography is rare. In this paper the WTs capability to give a full time–frequency representation of the wave signals is demonstrated. The processing of the time series of the non-stationary deep water waves, waves breaking at the tropical coral reefs and mechanically generated waves in the wave flume demonstrates the ability of the wavelet transform technique to detect a complex variability of these signals in the time–frequency domain. Various spectral representations resulting from the wavelet transform are discussed and their application for wave signals is shown.     

Application of Wavelet Algorithm to Spectral Analysis of Oceanic Waves and Offshore Structure Responses

Fourier transform (FT) is a commonly used method in spectral analysis of ocean wave and offshore structure responses,but it is not suitable for records of short length.In this paper another method,wavelet transform (WT),is applied to analyze the data of short length.The Morlet wavelet is employed to calculate the spectral density functions for wave records and simulated Floating Production Storage and Offloading (FPSO) vessels' responses.Computed wave data include simulated wave data based on JONSWAP spectr...     

孤立内波对过渡海域声场干涉结构的影响分析

南海北部陆坡海域是孤立内波的活跃区,孤立内波在该海域能够引起水体环境较强烈的水平不均匀性,从而影响声场干涉结构。将描述宽带声信号强度干涉条纹斜率的波导不变量视为一种分布,能更准确地分析声场的距离*频率干涉结构。本文研究了孤立内波环境下过渡海域声场的距离*频率干涉结构,依据实测孤立内波海洋环境,得到孤立内波环境下随距离变化的声速剖面,利用抛物方程方法仿真过渡海域声场干涉结构。在此基础上,利用拉东变换和傅里叶变换结合的谱值分离方法在低信噪比环境下提取波导不变量分布。分析表明孤立内波环境下过渡海域的声场类影区、类会聚区的波导不变量取值更丰富。     

海滩碎波带波能振荡的多尺度分析

对不同波况条件下实测的一岬间海滩碎波带两个测站的波面数据 ,通过小波变换方法计算了小波能谱 ,并作了显著性检验。结果表明 :( 1 )碎波带波能存在典型的多尺度振荡特性 ;( 2 )在正常波况下 ,波能主要分布于风浪频域 ,入射波自外测站向内测站传播过程中 ,能量具有向低频方向转移的趋势 ;( 3)在高能波况下 ,能量均向长重力波频带增加 ,在长重力波显著尺度 ,二测站之间存在良好的位相一致关系     

论风浪的局域结构──Ⅰ.风浪的局域结构与局域小波能谱

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。提出了风场演化过程中整体的共振在线性相互作用是否存在的质疑。     

Application of the spectral decomposition technique for characterizing reservoir extensional system in the Abadan Plain, southwestern Iran

The Abadan plain in southwestern Iran has important petroleum reservoir potential but poorly defined structural setting. It is located at the Mesopotamian foredeep basin, bounded by the Arabian plate and the Dezful Embayment. The main reservoir in this field is the Fahliyan formation, composed of reef carbonates. Most of the Abadan area is flat and covered by recent alluvial deposits with no outcrops. Studies of the structures in this area have provided information about the structural history and allowed better reservoir and drilling management. Seismic spectral decomposition techniques have been utilized as a quick and effective interpretation tool. Fast Fourier transform (FFT) and continuous wavelet transforms (CWT) have been used to convert time to frequency domain, and have been applied to detect fault systems in the reservoir. Application of the Fast Fourier transform (FFT) and continuous wavelet transforms (CWT) indicate that the Abadan reservoir consists normal extensional system of the reservoir which display paralleling of contour common depth in two sides of extensional system in some regions and large displacement between two sides of contours indicate that system is normal in which hanging wall moved over footwall. Various displacements between sides indicate parallel strike-slip movements which are associated with reverse faulting and inversion tectonics.     

Wavelet transform based coherence analysis of freak wave and its impact

The present paper presents the results of a wavelet transform-based coherence analysis of freak wave and its impact. Wavelet transform has been used as a tool in analyzing signals in the time domain as well as in the frequency domain. The analysis was applied to laboratory-generated freak waves. The wavelet transform of the time history of the freak wave and its impact force revealed that a wide range of frequency components were contained in them. The coherence analysis was conducted on the wave and its impact force time histories. The coherence analysis revealed that some high-frequency components were highly correlated with the impact forces. The present study demonstrates that the wavelet transform can be an alternative tool in the analysis of strongly nonlinear freak wave and its impact.     

Pressure transfer function in time and time-frequency domains

In this paper, we define a time-domain pressure transfer function calculated from SIWEH (smoothed instantaneous wave energy history) transforms, and a time-frequency domain pressure transfer function calculated from wavelet transforms, of synchronized wave and pressure data. It is our objective to study whether the time-domain pressure transfer function and the time-frequency domain pressure transfer function can provide new interpretation of wind wave behaviors. The detail structure of local time-frequency pressure transfer function in three-dimensional plot from wavelet transform is not employed due to its large variations, instead the time-integral wavelet spectral pressure transfer function and frequency-integral wavelet SIWEH pressure transfer function are used. These two averaged pressure transfer functions are smooth approximations of frequency-domain Fourier and time-domain SIWEH pressure transfer functions, respectively.Application to real ocean waves reveals that in frequency-domain the measured Fourier and wavelet spectral pressure transfer functions can be approximated by the linear pressure transfer function in the dominant wave range. In time-domain, the wavelet SIWEH pressure transfer function is a better indicator of wind wave behaviors than the SIWEH pressure transfer function. A value higher than 0.5 for the wavelet SIWEH pressure transfer function is a good discriminator of relative shallow-water long waves and wave groups are mostly composed of relative low frequency long waves.     

Numerical study of nonlinear freak wave impact underneath a fixed horizontal deck in 2-D space

Freak waves are extreme and unexpected surface waves with huge wave heights that may lead to severe damage to ships and offshore structures. However, few researches have been conducted to investigate the impact underneath fixed horizontal decks caused by freak waves. To study these phenomena, a 2-D numerical wave tank is built in which nonlinear freak waves based on the Peregrine breather solution are generated. As a validation, a regular-wave-induced underneath impact is simulated and compared to the existing experimental measurements. Then the nonlinear freak-wave-induced impact is investigate with different values of deck clearance above the mean free surface. In addition, a comparative simulation of a “large” regular wave based on the 2nd-order Stokes wave theory with the same crest height and wave length of the nonlinear freak wave is carried out to reveal the unique features of the nonlinear freak-wave-induced impact. By applying a fluid–structure interaction (FSI) algorithm in which the bottom deck and front side wall are simplified as Euler beams in 2-D and discretized by the finite element method (FEM), the hydroelastic effects are considered during the impact event. The vertical force acting underneath the bottom deck, the transversal force acting on the front side wall, the structural displacements of the elastic deck and wall are analyzed and discussed respectively, from which meaningful conclusions are drawn.     

Nonlinear effects of the distribution of amplitudes of sea waves

The effect of nonlinearities, such as wave-breaking and vertical asymmetry associated with sea waves, on the distribution of wave amplitudes is explored. Semiclosed theoretical expressions are derived to describe the distributions of breaking-limited crest and trough amplitudes for Stokes-type nonlinear sea waves. These are compared with the conventional Rayleigh distribution appropriate to linear wave amplitudes. The construction of nonlinear wave envelopes with the fast Fourier transform technique is described. The technique can be utilized to enlarge the data base in empirical analyses of field records which typically contain limited information on amplitude characteristics. The theoretical distributions and the proposed data enlargement technique are demonstrated with the analysis of a nonlinear wave record.     

Solitary wave propagation influenced by submerged breakwater

The form of Boussinesq equation derived by Nwogu （1993） using velocity at an arbitrary distance and surface elevation as variables is used to simulate wave surface elevation changes. In the numerical experiment, water depth was divided into five layers with six layer interfaces to simulate velocity at each layer interface. Besides, a physical experiment was carried out to validate numerical model and study solitary wave propagation.“Water column collapsing”method （WCCM） was used to generate solitary wave. A series of wave gauges around an impervious breakwater were set-up in the flume to measure the solitary wave shoaling, run-up, and breaking processes. The results show that the measured data and simulated data are in good agreement. Moreover, simulated and measured surface elevations were analyzed by the wavelet transform method. It shows that different wave frequencies stratified in the wavelet amplitude spectrum. Finally, horizontal and vertical velocities of each layer interface were analyzed in the process of solitary wave propagation through submerged breakwater.     

The effect of wave–current interactions on the storm surge and inundation in Charleston Harbor during Hurricane Hugo 1989

The effects of wave–current interactions on the storm surge and inundation induced by Hurricane Hugo in and around the Charleston Harbor and its adjacent coastal regions are examined by using a three-dimensional (3-D) wave–current coupled modeling system. The 3-D storm surge and inundation modeling component of the coupled system is based on the Princeton ocean model (POM), whereas the wave modeling component is based on the third-generation wave model, simulating waves nearshore (SWAN). The results indicate that the effects of wave-induced surface, bottom, and radiation stresses can separately or in combination produce significant changes in storm surge and inundation. The effects of waves vary spatially. In some areas, the contribution of waves to peak storm surge during Hurricane Hugo reached as high as 0.76 m which led to substantial changes in the inundation and drying areas simulated by the storm surge model.     

Three-Dimensional Boundary Element Method Applied to Nonlinear Wave Transformation

For higher accuracy in simulating the transformation of three dimensional waves,in consid-eration of the advantages of constant panels and linear elements,a combined boundary elements is appliedin this research.The method can be used to remove the transverse vibration due to the accumulation ofcomputational errors.A combined boundary condition of sponge layer and Sommerfeld radiation condi-tion is used to remove the reflected waves from the computing domain.By following the water particle onthe water surface,the third order Stokes wave transform is simulated by the numerical wave flume tech-nique.The computed results are in good agreement with theoretical ones.     

Separation of obliquely incident and reflected irregular waves by the Morlet wavelet transform

An existing 2D time-domain method for separating irregular incident and reflected waves by wavelet transform [Ma et al., 2010. A new method for separation of 2D incident and reflected waves by the Morlet wavelet transform. Coastal Eng., 57(6):597–603] is extended to account for obliquely incident irregular waves propagating over sloping bottoms. The linear shoaling and refraction coefficients are adopted to determine the amplitude and phase changes of waves. The optimal central frequency of the Morlet wavelet is determined by the minimum Shannon wavelet entropy. Numerical tests show that the present method can accurately separate waves over horizontal depths. For waves at sloping bottoms, however, the separation errors increase as bottom slope increases and are significant for waves with incident angle larger than π/3.     

Investigation of nonlinear interactions in ocean swell waves usingthe reduced bispectrum

In this paper, a two-dimensional (2-D) reduced bicoherence function which can be calculated via the reduced bispectrum is introduced. The statistical and computational aspects of the 2-D reduced bicoherence function are compared with those of the conventional bicoherence function. It is shown that the proposed technique is less noise-sensitive than the conventional bicoherence estimate. The use of the 2-D reduced bicoherence function to investigate nonlinear interactions in ocean swell waves is also demonstrated. As the 2-D reduced bicoherence can be efficiently calculated, it is proposed to use this novel technique in oceanographic field experiments that require real-time data processing and interpretation     

Two-Dimensional Spectral Estimation: A Radon Transform Approach

A new technique for two-dimensional (2-D) spectral estimation of a stationary random field (SRF) is investigated in this paper. This is based on the extension of the Radon transform theory to stationary random fields (SRF's), proposed by Jain and Ansari [19]. Using the Radon transform, the 2-D estimation problem is reduced to a set of one-dimensional (1-D) independent problems, which could then be solved using 1-D linear prediction (LP) or by any other high-resolution estimation procedure. This is unlike previous methods which obtain the 2-D power spectral density OPSD) estimate by using 1-D high-resolution techniques in the spirit of a separable estimator [2]. Examples are provided to illustrate the performance of the new technique. Various features of this approach are highlighted.