海浪的特征波陡

在现有的海浪要素统计分布的理论框架下具体地推导了二维海浪波良与波长的联合统计分布,波长统计分布以及波陡的统计分布,在此基础上对上特征波陡的定义及期 承风要素的变化规律做了较为细致的讨论。     

Maxima for Gaussian seas

The probability distribution of the height of global maximum for a Gaussian random field evolving in time is studied. In particular, the effect of spreading is studied and the role of the wave kinematics is discussed. It is observed that taking into account time dynamics of spatial characteristics results in distributions different from those obtained for the static case. The results are illustrated by computing the derived distribution for different Gaussian seas for three distinct sampling schemes. The resulting distributions are also used to compute return periods for rogue waves.     

The statistical distribution of nearbed wave orbital velocity in intermediate coastal water depth

The statistical distribution of wave orbital velocity in intermediate coastal water depth has been quantitatively determined from the comprehensive field velocity data collected near the seabed in this study. Two ocean ADV current meters, which were mounted at 0.5 m above the seabed on two separate stainless steel tripods sitting on the seabed, were used to measure instantaneous water particle velocities at a 2 Hz sampling rate for 17.07 min every hour in two coastal water depths of 11 m and 23 m in nine field deployments over a period of 2 years. The zero-crossing method is applied to analyse the field velocity data collected in each field deployment to obtain a large sample of wave orbital velocity amplitudes of individual waves. Based on the collected field velocity data, it is found that the histogram of instantaneous wave orbital velocities perfectly follows the Gaussian distribution as commonly assumed, while the histogram of wave orbital velocity amplitudes is less accurately described by the Rayleigh distribution than the modified Rayleigh and the Weibull distribution. It is also found that large orbital velocity amplitudes are generally overestimated by the Rayleigh distribution, but well predicted by the modified Rayleigh and the Weibull distribution. The expected value of maximum orbital velocity in a velocity record of finite size is also derived from the three distributions and found to agree well with the present field data.     

On the distribution of crest to trough wave heights

In the present paper we derive the probability distribution function of crest to trough wave heights in a narrow-band, Gaussian stochastic process. It is shown that the distribution function is a one-parameter Rayleigh distribution where the parameter is expressed in terms of the correlation function of the given process. Comparison based on correlation values obtained via sea wave spectra indicate that the derived distribution function agrees well with observed data.     

Effect of Nonlinearity on Groupiness of Random Wave Fields

Theoretical studies so far on random wave groups have all been in linear ways.Methods to sim-ulate random wave groups,an important subject in ocean engineering,also employ relationship resulting froma Gaussian process.Many filed measurements have shown that the real sea surfase displacement deviatessomewhat from Gaussian distribution.Tayfun et al.have further depicted in theory that the envelope spectralpeak frequency is constantly zero for a Gaussian process which means that the groupiness factors will be con-stants,too.In this paper,the effect of nonlinearity on groupiness of a random wave field is examined via thetheoretical results derived by Tayfun et al.from an expression of amplitude-modulated Stokes waves.Whenthe surface displacement is treated as a non-Gaussian process,it is found that the group height factors GF_1and GF_2 proposed by Zhao et al.and Yu et al.,respectively,depend on a nonlinearity factor as well as aspectrum-bandwidth factor,deferring from the case of a Gaussion process.Compariso     

Probability distribution of random wave forces in weakly nonlinear random waves

Based on the second-order random wave theory, the joint statistical distribution of the horizontal velocity and acceleration is derived using the characteristic function expansion method. From the joint distribution and the Morison equation, the theoretical distributions of drag forces, inertia forces and total random wave forces are determined. The distribution of inertia forces is Gaussian as that derived using the linear wave model, whereas the distributions of drag forces and total random forces deviate slightly from those derived utilizing the linear wave model. It is found that the distribution of wave forces depends solely on the frequency spectrum of sea waves associated with the first order approximation and the second order wave–wave interaction.     

Hilbert变换在海浪波高与周期联合分布函数中的应用

Longuet-Higgins(1983)[1]导出了波高与周期的联合分布函数,此分布函数虽然与实际数据符合良好,但存在很大的缺陷,如:由此分布函数得出的波高分布为形式较为复杂的非Rayleigh分布,很难应用于工程计算中。孙孚(1988a)[2]应用射线理论导出了一种波高与周期联合分布,虽然弥补了Longuet-Higgins的一些缺陷,但推导过程过于复杂。本文在窄谱假定下通过应用Hilbert变换方法得出新的分布函数并与前两者比较,表明Hilbert变换的方法不但简便,而且完全克服Longuet-Higgins的不足,可以方便的应用于工程计算中。本文也为Hilbert变换的方法在工程中的应用提供了理论依据。     

基于LPB1-2型声学测波仪资料的近岸浪特征分析

为研究近岸浪的形态特征,利用LPB1-2型声学测波仪在某海域所测得的海浪数据对近岸浪特征要素进行统计分析,利用最大"熵"原理推导出了波高的最大"熵"分布,研究了状态参量对波高分布和波高"熵"的影响。研究表明,该海域的波主要以波高0.3~0.7 m,周期2.5~5.5 s的波为主,表示离散程度的特征值平均差为0.267,日极差值主要在0.1~0.4 m区间内,最大值为1.0 m,分布较为集中,波高分布近似为正态分布。     

The distribution of zero-crossing wave heights and periods in a stationary sea state

Existing theoretical distributions of wave height and period do not reflect measured joint distributions from field data. A simulation methodology is introduced to retain the essential features of the theoretical background in Gaussian random noise but to avoid further compromising assumptions in the interpretation of height and period in the amplitude domain. A joint distribution can be associated directly with an empirical or measured variance spectrum. Spectral shape appears to dominate the detail of predicted joint distributions. There is generally a much sharper decay in probability levels at higher periods than is predicted by theoretical models. For Jonswap spectra, there is a dominant central ridge and a distinct bimodal structure in the joint distribution, features that are not evident in symmetric Gaussian spectral forms. The wave height distributions for Jonswap spectra differ little from the Rayleigh distribution, except at extreme wave heights where Rayleigh overpredicts. The period distributions are strongly sensitive to spectral shape. In the conditional distribution of periods, given the height, the asymptotic median period at extreme wave heights is significantly longer than the mean period for Jonswap spectra, but not for symmetric Gaussian forms.     

白浪覆盖率模式中参量的研究

在波面位移为正态过程的假定下,推导出一种以平均周期和风速为参量的白浪覆盖率公式W=1-Φ[5.11094[-T/U10]0.7576].依据摩擦风速和U10的表达式,进一步推导出白浪覆盖率依赖于摩擦风速的形式W=1-Φ[0.5227[-T/U]0.7576]].考虑到在实际应用中,经常需要用波龄描述波浪的状态,将白浪覆盖率表示成一种形式简单的波龄的函数W=1-Φ(3.6496ξ0.7576),与Monahan等的海上测量数据符合良好.     

不规则波作用下沿岸流流速分布规律分析

基于MIKE21 PMS,对1/10、1/20、1/40、1/100四种不同坡度地形下不规则波浪产生的沿岸流进行数值模拟。将模拟得到的流速随着离开静水岸线距离的变化曲线进行无量纲化处理,并选用高斯分布函数对流速曲线进行拟合,进而得到高斯分布函数中流速最大值与其出现位置以及流速分布宽度等参数随着入射波浪要素和地形坡度的变化关系。研究结果表明,文中给出的高斯分布函数适用于描述不规则波浪作用生成的沿岸流流速分布规律。     

Statistical properties of successive wave heights and successive wave periods

Two successive wave heights are modeled by a Gaussian copula, which is referred to as the Nataf model. Results with two initial distributions for the transformation are presented, the Næss model [Næss A. On the distribution of crest to trough wave heights. Ocean Engineering (1985);12(3):221–34] and a two-parameter Weibull distribution, where the latter is in best agreement with data. The results are compared with existing models. The Nataf model has also been used for modeling three successive wave heights.Results show that the Nataf transformation of three successive wave heights can be approximated by a first order autoregressive model. This means that the distribution of the wave height given the previous wave height is independent of the wave heights prior to the previous wave height. Thus, the joint distribution of three successive wave heights can be obtained by combining conditional bivariate distributions. The simulation of successive wave heights can be done directly without simulating the time series of the complete surface elevation.Successive wave periods with corresponding wave heights exceeding a certain threshold have also been studied. Results show that the distribution for successive wave periods when the corresponding wave heights exceed the root-mean-square value of the wave heights, can be approximated by a multivariate Gaussian distribution.The theoretical distributions are compared with observed wave data obtained from field measurements in the central North Sea and in the Japan Sea, with laboratory data and numerical simulations.     

波面极大值处水质点水平加速度的统计分布

基于 L onguet- Higgins线性海浪模型 ,在二维情况下导出海浪波面极大值处水质点水平加速度分布律 ,其分布遵从正态分布。在分布中引入新的谱宽度参量 [(m2 m4 - m23 ) / m2 m4 ]12 。以Neumann谱为模式计算波面极大值处质点加速度分布。     

Probability distribution of random wave–current forces

Based on the second-order solutions obtained for the three-dimensional weakly nonlinear random waves propagating over a steady uniform current in finite water depth, the joint statistical distribution of the velocity and acceleration of the fluid particle in the current direction is derived using the characteristic function expansion method. From the joint distribution and the Morison equation, the theoretical distributions of drag forces, inertia forces and total random forces caused by waves propagating over a steady uniform current are determined. The distribution of inertia forces is Gaussian as that derived using the linear wave model, whereas the distributions of drag forces and total random forces deviate slightly from those derived utilizing the linear wave model. The distributions presented can be determined by the wave number spectrum of ocean waves, current speed and the second order wave–wave and wave–current interactions. As an illustrative example, for fully developed deep ocean waves, the parameters appeared in the distributions near still water level are calculated for various wind speeds and current speeds by using Donelan–Pierson–Banner spectrum and the effects of the current and the nonlinearity of ocean waves on the distribution are studied.     

Experimental Study on the Effects of A Breakwater on Wave Field Characteristics

Studies on the possible effects of a detached breakwater on the characteristics of the wavefield are carried out experimentally.A serpentine wave generator is used to generate both uni- andmulti-directional waves.Characteristics of the wave fields analyzed here include the wave fielddirectionality,and the probability distributions of surface elevations and of the wave heights.Owing to thepresence of the breakwater,waves outside the harbour are found to be reflected with,however,concen-trated energy within the harbour entrance.In general,wave heights can be approximated with a Rayleighdistribution,with occasional deviations from the theory.This occurs more frequently for waves with high-er peak frequency values than for those with lower values both for uni-and multi-directional waves.Sur-face elevations can be approximated with the Gaussian model.although the Edgeworth's form of the typeA Gram-Charlier series expansions would yield better fits.Wave directionality is found to have nodiscernible effects on     

微尺度滑动平均方法计算海浪谱奇阶矩的公式

Glazman提出了一种计算海浪谱高阶谱矩的微尺度平均方法,但是,他利用随机过程理论导出的计算偶阶矩的公式和参照偶阶矩结论定义的奇阶矩计算公式之间存在着内在的不一致性.本文在Glazman工作的基础上根据随机过程理论推导了“微尺度平均方法”计算奇阶谱矩的公式,纠正了他的错误.上述结论随即应用于讨论破碎对波面水质点水平速度分布的影响.通过破碎的加速度判据考虑了破碎对速度分布的限制,给出了未破碎波面上水质点水平速度的的统计分布的初步结果.该分布取决于谱宽度参数及白浪覆盖率的大小,当白浪覆盖率较大时明显偏离正态分布.     

Statistical characteristics of long waves nearshore

The random long wave runup on a beach of constant slope is studied in the framework of the rigorous solutions of the nonlinear shallow water theory. These solutions are used for calculation of the statistical characteristics of the vertical displacement of the moving shoreline and its horizontal velocity. It is shown that probability characteristics of the runup heights and extreme values of the shoreline velocity coincide in the linear and nonlinear theory. If the incident wave is represented by a narrow-band Gaussian process, the runup height is described by a Rayleigh distribution. The significant runup height can also be found within the linear theory of long wave shoaling and runup. Wave nonlinearity nearshore does not affect the Gaussian probability distribution of the velocity of the moving shoreline. However the vertical displacement of the moving shoreline becomes non-Gaussian due to the wave nonlinearity. Its statistical moments are calculated analytically. It is shown that the mean water level increases (setup), the skewness is always positive and kurtosis is positive for weak amplitude waves and negative for strongly nonlinear waves. The probability of the wave breaking is also calculated and conditions of validity of the analytical theory are discussed. The spectral and statistical characteristics of the moving shoreline are studied in detail. It is shown that the probability of coastal floods grows with an increase in the nonlinearity. Randomness of the wave field nearshore leads to an increase in the wave spectrum width.     

Parameterization and simulation of near bed orbital velocities under irregular waves in shallow water

A set of empirical formulations is derived that describe important wave properties in shallow water as functions of commonly used parameters such as wave height, wave period, local water depth and local bed slope. These wave properties include time varying near-bed orbital velocities and statistical properties such as the distribution of wave height and wave period. Empirical expressions of characteristic wave parameters are derived on the basis of extensive analysis of field data using recently developed evolutionary algorithms. The field data covered a wide range of wave conditions, though there were few conditions with wave periods greater than 15 s. Comparison with field measurements showed good agreement both on a time scale of a single wave period as well as time averaged velocity moments.     

Bragg scattering of centimeter electromagnetic radiation from the sea surface: The effect of waves longer than Bragg components

The effect of sea surface waves longer than Bragg components on the backscattering of centimeter electromagnetic radiation is studied on the basis of data on direct field measurements of sea-surface slopes. A situation in which waves with wavelengths greater than 10 cm are longer than the Bragg components is considered. The increase in the backscattering cross section that is due to the presence of long waves is numerically estimated for sounding at horizontal and vertical polarization. Nonlinear effects in the field of surface waves result in the departure of the distribution of sea-surface slopes from a Gaussian distribution and lead to a change in the backscattering cross section. At a sounding angle of 35°, this change may reach 15% with respect to the cross section calculated for a Gaussian surface.     

Nearshore Wave Field Analysis Using SAR Images

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