海浪的群性及其主要特征参数

本文综述了目前研究波群的三类主要方法——包线理论、连的统计理论和波能过程线法及其描述群性的主要参数,结合实测资料,从波群的高度和长度两个方面对它们进行了分析比较,建议了能较好描述波浪群性的方法和参数。给出了三个测站处海浪的群性参数。探讨了群性对波高分布和组成波相位分布的影响以及波浪记录长度对计算群性参数的影响。     

二维海浪波包跨水平特征量及其应用

将Adler关于二维随机波场跨水平特征量的理论应用于二维线性随机海浪,严格导出了二维海浪波包的跨水平特征量表达式,并利用该式讨论了给定时刻二维海浪的一种几何结构——大波簇集情况。对于海面上波高均超过较高参考水平的一簇大波,给出了一个计算其中波峰平均个数的公式,它与Glazman所给出的公式不同另外还给出计算上述大波簇平均面积的公式。最后结合现有的海浪万向谱给出一些具体计算结果,并对这些结果进行了讨论。     

岬间海湾滨面带波浪结构和外观统计特征

对中等波能条件下收集的粤东两个岬间海湾滨面带4个站点的波浪数据作了滨面带波面、波包和长重力波的基本特征的分析，得到如下主要结果：（1）滨面带波谱由多峰频构成，从海向岸波高增大，波周期减小，谱宽度加大，谱尖度减小；（2）入射波群性较强，表征入射波群性的相对均方根群高与谱宽度无关；（3）长波振幅与波浪能量增大，其形成主要与组成波间的非线性相互作用有关。     

旋转层化二维海洋波动连续谱的波包特征分析

对旋转层化二维海洋波动中重力惯性波和涡旋波连续谱波包的结构以及演变特征作了计算和分析,并得到以下结论:这两类波动的结构与演变各不相同。连续谱波包的演变不但依赖基本场的分布,而且还依赖初始扰动的结构。根据初始场的不同,扰动可衰减,也可先增长、再衰减,有时增长还很大,但其最终是衰减的。连续谱波包的结构随时间变化,然而构成该波包的连续谱其结构则不随时间变化,这是两者的最大差异。连续谱波包的上述演变特性表明,在有限时段扰动的演变中连续谱是不能被忽略的,在海洋波动演变中连续谱和离散谱的作用均须予以考虑和重视。     

三阶非线性海浪波面斜率的联合概率统计分布

从Longuet-Higgins于1963年建立的非线性随机海浪模型出发,对各向同性波面斜率的联台概率统计分布进行了理论研究.结果表明,在三阶近似下,波面斜率联合概率统计分有为截断的Gram-Charlier级数,截断的项数取决于非线性近似的阶数,每一阶近似均对前一阶近似结果有所修正如果不考虑非线性耦合相互作用的影响,则分布蜕化为高斯分布.     

随机海浪群性的研究

从随机海浪群因子的定义出发,分别研究将海浪视作正态过程和非正态过程时海浪的群性。研究结果发现按正态过程描述海浪时其群因子的值为常值,而按非正态过程描述海浪时其群因子的值不再是常值,它与海浪的非线性因子及谱宽度参数有关,并随这两个因子变化而变化。文中并给出了海上实测资料的验证结果     

海浪预报现状与未来

值此国家海洋环境预报中心成立40周年之际,回顾40年来我国海浪研究和海浪预报历程,我国已经在海浪研究和海浪预报方面有了较大进展,尤其在海浪预报方面已经获得了一些较成熟的理论和方法.本文简要介绍在发展和完善海浪数值诊断模式与海浪数值预报模式,实现海浪预报方法客观化,预报手段自动化和系统化方面的现状和未来.     

对近岸海浪非势函数、势函数型缓坡方程的初步探讨

针对目前缓坡方程中势函数假设比较多的问题,本文利用二维浅水方程来描述海浪水质点运动的有势假设,采取WKBJ方法推导缓坡方程在缓变地形下的波包方程,对势函数缓坡方程进行修正,以建立更全面更实用的近岸波浪传播计算模式。同时,文中还采用非势函数型模拟波浪传播。     

海浪数值模式研究回顾与进展

本文简单介绍了海浪的生成、发展理论,以及海浪数值模式的分类;回顾总结了国内外在海浪数值模式研究方面取得的成果。     

胶州湾双峰谱型波浪的统计特征

本文对胶州湾实测双峰海浪谱的资料进行了统计分析和谱分析，探讨了双峰谱型海浪的波要素概率分布及其群性特征，并与单峰谱型海浪进行了比较，最后通过双峰谱的合成波高，周期与实测值的比较，对采用能量迭加式的式（９）和式（８）进行一些讨论，主要结果列于本文最后一节。     

A discrete correction scheme for envelope approach of wave group statistics

The existence of empty envelope excursions (EEE) brings error to the envelope approach of wave group statistics, which identifies wave group by envelope upcrossing of a critical level. A group number correction scheme is suggested in this paper to exclude EEE from wave group statistics. To this end, the Ditlevson and Lindgren [J. Sound Vib. 122 (1988) 571] theory about the fraction of empty excursion envelopes (FEEE) is examined to see if it fits for ocean waves. The sea waves are simulated with Monte Carlo method and with P-M and JONSWAP spectrums. The values of FEEE of the simulated waves are investigated and compared with the theory of Ditlevson and Lindgren. The comparison shows that, at the second-order approximation, theoretical predictions of FEEE are close to those derived from simulations. This approximate analytical expression of FEEE is then employed to form a group number correction scheme. Comparisons between numerical and theoretical results of wave group properties show that this correction scheme is quite effective.     

Numerical analysis on random wave-induced porous seabed response

Research on the response of random wave on offshore structures has received great deal of attention of many researchers and engineers in the design of marine structures. Most previous investigations have been limited to the regular waves. In this paper, based on Longuet–Higgins random wave theory and finite element method, a numerical model for random wave-induced seabed response is established. The seabed is treated as poroelastic medium and characterized by Biot’s partly dynamic equations (u–p model). The JONSWAP spectrum is adopted in Longuet–Higgins model, which is based on the cumulative superposition of linear diffraction solution. Based on the numerical results, the effects of random wave on seabed response are investigated by comparing with the corresponding Stokes wave and cnoidal wave. Then, a parametric study is conducted to examine the effect of wave and soil characteristic on the seabed.     

随机波作用下海床动态响应分析

真实的海洋波浪是随机的,而前人对海床的动态响应分析大都是选用线性波或者Stokes波理论,对海床的模拟大都采用Biot拟静力模型,忽略了流体速度及土体位移加速度的影响。联合使用Longuet-Higgins随机波模型(采用Jonswap谱)以及动力u-p形式的海床响应计算模型,使用COMSOL Multiphysics多场耦合软件的PDE模块输入方程进行有限元计算,得到随机波作用下整体海床动态响应结果。将随机波结果与一阶Stokes波和椭圆余弦波结果进行对比,并对渗透系数和饱和度进行参数分析,研究表明渗透系数和饱和度对于随机波作用下海床动态响应影响显著。     

The difference between the joint probability distributions of apparent wave heights and periods and individual wave heights and periods

The joint distribution of wave heights and periods of individual waves is usually approximated by the joint distribution of apparent wave heights and periods. However there is difference between them. This difference is addressed and the theoretical joint distributions of apparent wave heights and periods due to Longuet-Higgins and Sun are modified to give more reasonable representations of the joint distribution of wave heights and periods of individual waves. The modification has overcome an inherent drawback of these joint PDFs that the mean wave period is infinite. A comparison is made between the modified formulae and the field data of Goda, which shows that the new formulae consist with the measurement better than their original counterparts.     

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     

Momentum balance in shoaling gravity waves: Comment on ’shoaling surface gravity waves cause a force and a torque on the bottom’ by K. E. Kenyon

In a recent paper, Kenyon (2004) proposed that the wave-induced energy flux is generally not conserved, and that shoaling waves cause a mean force and torque on the bottom. That force was equated to the divergence of the wave momentum flux estimated from the assumption that the wave-induced mass flux is conserved. This assumption and conclusions are contrary to a wide body of observations and theory. Most importantly, waves propagate in water, so that the momentum balance generally involves the mean water flow. Although the expression for the non-hydrostatic bottom force given by Kenyon is not supported by observations, a consistent review of existing theory shows that a smaller mean wave-induced force must be present in cases with bottom friction or wave reflection. That force exactly balances the change in wave momentum flux due to bottom friction and the exchange of wave momentum between incident and reflected wave components. The remainder of the wave momentum flux divergence, due to shoaling or wave breaking, is compensated by the mean flow, with a balance involving hydrostatic pressure forces that arise from a change in mean surface elevation that is very well verified by observations.     

波浪水槽中随机波的模拟

根据线性系统理论,首先由给定的靶谱模拟海浪信号,再把此信号转换为造波控制输入信号,最后在水槽中指定的截面处产生具有给定靶谱的随机波。这种模拟方法已在青岛海洋大学物理海洋实验室的大型水槽中实现,并取得良好的效果。     

A study on kinematics characteristics of freak wave

Based on the 3rd-order Stokes wave theory, the speed of freak waves is formulated in terms of the period and the wave height. Finite modified wave steepness gives rise to a significant enhancement of the nonlinear contributions to the freak wave speed in comparison with the 3rd-order Stokes wave theory. For a fix modified wave steepness, the estimated amplification of the nonlinear contributions due to the deviation from the 3rd-order Stokes wave theory is 0.22～0.99. In addition, the velocity and acceleration fields are also documented in detail. In the present simulation, the horizontal velocities are smaller than the wave speed, and the freak wave exhibits a maximal horizontal velocity up to 37% of the wave speed and a maximal vertical acceleration up to about 20% of the gravitational acceleration.     

二阶Boussinesq方程的孤立波解

基于同量阶迭代法，在保留同阶面的前提下，对林建国等（1998a)得到的二阶Boussinesq类方程进行了求解，得到了与其量阶相对应的取立波解，并春与Euler方程的二阶孤立波解进行了比较，结果显示，本文解比传统Boussinesq方程的孤立波解有明显的改善，扩大了孤立的适用范围。     

非线性效应对风浪波面极大值和极小值分布的影响

通过分析实验室风浪观测结果研究非线性效应对波面极大值和极小值分布的影响。波面极大值和极小值累积概率的差异表明 ,与线性理论相比 ,波面极小值在平均波面以下的位置偏高。对实验结果的进一步分析表明 ,非线性效应使波面极大值在平均波面以上总概率高于线性理论结果 ,而概率密度峰值处波面极大值高度略低于线性理论结果。波面极小值在平均波面以上各位置出现的概率均高于线性理论结果 ,在平均波面以下的较低位置 ,波面极小值出现概率明显低于线性理论结果。