波浪反射系数谱的特征分析

应用斜向不规则波反射系数的改进两点法(MTPM),用模型试验研究了混凝土护面堤和块石护面堤波浪反射系数的频率谱和方向谱,结果表明,分析的反射系数随入射波频率的增加、结构坡度的减小和入射角的加大而减小.给出了波浪反射系数频率谱及其随Iribarren数变化的规律,提出了反射系数三维谱的经验公式,由此可定量地描述斜向不规则波的反射系数随无量纲特征参数Iribarren数和入射波角度的变化规律.     

On reflection and diffraction due to a detached breakwater

Wave reflection and diffraction due to the presence of a detached breakwater are studied with the aid of directional wave fields. At first, experiments were carried out for the case where a breakwater is the sole factor affecting the wave field. It is shown that, estimated directional spectra in front of a detached breakwater can be separated into two parts in the spatial domain. Denoting these as the incident and reflected part of the total energy, an estimate of the reflection coefficient can be obtained. An empirical equation is proposed. This equation relates the reflection coefficients with the distances of the measuring stations away from the breakwater, as well as directionality of the wave field. This equation was then applied to the experiments where the fishing harbour Ba-Do-Zhi (BDZ) was used as model. It is shown that favorable results are obtained. On the other hand, diffraction due to the detached breakwater was also studied in a similar way. It is shown that predictions based on the empirical equation are in quantitative agreements with measurements. It is proposed that these empirical equations can be used in engineering applications.     

新型消能结构物边界形状对波浪反射特性影响研究

为了使消能结构在多频率波浪作用下都能有一个较低的反射率,提出一种新型消能结构——双层板与双列开孔结构复合结构。考虑了面积约束条件下结构物边界对波浪反射特性的影响,运用数值模拟方法模拟了波浪与结构物的相互作用,计算了消能结构在不同边界形状下的反射系数,对比波浪反射系数结果获得了最佳的消能结构物边界形状。反射系数研究结果及消能结构周围流场的分析表明:消能结构物的反射特性及流场特性对波候有一定的依赖性,也依赖于消能结构物的边界特性。因此开展消能结构物边界排布及形状的研究是很有必要的。     

A three-point method for estimating wave reflection of obliquely incident waves over a sloping bottom

A three-point method for estimating wave reflection is proposed to account for monochromatic oblique incident waves propagating over a sloping beach. The amplitudes of reflected wave and incident wave are separated using wave amplitudes measured at three fixed wave gauges with a distance. The applicability of the theory is verified by comparing the simulated results with the available theoretical, numerical and experimental results for the estimation of wave reflection. The sensitivity is also tested to provide a more accurate prediction of the reflection coefficient.     

Wave reflection in 3D conditions

Based on recent experiments carried out in wave basin on breakwaters with armour layer of rocks and cubes, this paper examines the dependence of the reflection coefficient on wave directional spreading and obliquity. Results suggest that long-crested and short-crested waves give similar reflection. The reflection coefficient is markedly dependent on the wave angle of incidence. The performance of formulae available in the literature is checked against the new dataset and a significant improvement is proposed by including the wave obliquity factor that appears in the traditional expression for the overtopping discharge.     

明基床开孔沉箱不规则波反射系数试验研究

通过二维波浪水槽物模试验,在考虑消浪室相对宽度、相对水深、相对波高、开孔率对反射系数的影响基础上,针对明基床开孔沉箱的工程应用,引入相对基床高度新的影响因素,通过控制单一变量原则分析各因素和反射率的关系,采用多元回归给出明基床开孔沉箱不规则波浪反射系数的计算公式,对明基床开孔沉箱的消浪机理进行了有益的探索,研究成果为工程设计及应用提供了一种简捷可靠的计算方法。     

斜向波浪入射角和反射系数确定方法

在海岸工程和水池实验中常常需要同时确定斜向波浪的传播方向和与海岸结构物相遇时的反射系数。应用三点浪高仪测波和迭代求解方法,建立了同时确定斜向波浪入射角和反射系数的分析方法。通过模拟数值信号,研究了测点不同排列方式、不同波浪入射方向、不同入射频率下本方法的分析灵敏程度。数值研究表明当测点间距指标p和q不同时趋于零时,任何一种排列方式求得的波浪反射系数和波浪入射角均具有很高的分析精度。     

双层局部开孔板沉箱对波浪反射的理论研究

提出了一种用于研究由双层开孔板和一个不透水后板的开孔结构对斜向波反射率的理论分析方法。整个流域被分成三个子域，在每个子域内应用特征函数展开法以得到该域内包含未知展开系数的势函数的表达式，在速度势的展开中，考虑了非传播模态波浪的影响。通过匹配开孔板处的边界条件可以求解待定的展开系数，继而求解双层开孔板防波堤结构对斜向波的反射率。数值计算结果与试验结果进行了比较，符合较好。并进一步讨论了几个重要因素对反射系数的影响。     

空间节省型堰式沉箱波浪反射与结构优化试验研究

为了同时提升消浪效果和节省海岸空间,对低反射防波堤进行改进,提出了一种空间节省型堰式沉箱结构。通过物理模型试验研究了堰式沉箱在规则波作用下的消能机理,然后采用单因子分析法分析了相对淹没深度、波陡和相对波高对反射系数的影响,并且利用SPSS软件对无因次参数进行非线性回归分析得到了反射系数计算公式。结果表明,内堰消浪室可以形成良好的波能耗散机制,随着有效消浪室个数的增多,消浪效果逐渐增强,使得反射系数的最小值和最大值较非透空直立结构分别降低了60%～90%和10%～30%。基于以上研究成果,给出关于特征水位与内堰的相对位置关系的合理建议,并总结了堰式沉箱结构的优化设计要点,对实际工程应用具有一定的指导意义。     

Wave reflection from natural beaches

The reflection of wave energy from natural beaches is a quantity that is rarely measured. This paper addresses the question as to whether the reflected wave energy from a beach is an important component of energy flux from an engineering point of view. Wave run-up and wave set-up are important nearshore processes in which wave reflection appears to play a major role and, consequently, the prediction of reflected wave energy from the offshore forcing irregular wave train energy at natural beaches is a first step in a better understanding of these processes. The present paper reports on wave reflection measurements at two natural beaches with different characteristics. The issue of wave reflection is addressed via separation of input and output signals using coincident pressure and velocity measurements. In the present limited analysis, reflected wave energy was not found to be significant.     

Wave kinematics of partial reflection from a vertical wall

A third-order perturbation approximation for the partial reflection from a vertical wall is presented in this paper. The wave parameters are expressed in terms of the amplitude of incident waves. The reflection coefficient is defined as the ratio of the height of reflected waves to incident waves. The numerical results demonstrate the significant influences of reflected coefficient on the wave profile and wave frequency bifurcation. For example, the critical angle of wave frequency bifurcation with partial reflection is about 7.5 degrees, not 21 degrees as reported previously for fully reflection.     

Wave reflection from perforated-wall caisson breakwaters

Analytical models for predicting wave reflection from a perforated-wall caisson breakwater have been developed. Most of the existing models deal with the case in which the waves are normally incident to the caisson lying on a flat sea bottom. In the present paper, using the Galerkin-eigenfunction method, an analytical model is developed that can predict the reflection coefficient of a perforatedwall caisson mounted on a rubble mound foundation when waves are obliquely incident to the breakwater at an arbitrary angle. The developed model is compared with other theoretical results and hydraulic experimental data.     

Further improvements to the higher-order Boussinesq equations: Bragg reflection

Enhancements for the Bragg reflection are introduced for three sets of 2D higher order Boussinesq equations to improve the prediction of the Bragg reflection. The extension of the approach to other sets of Boussinesq equations is discussed. The analytical solutions for the Bragg reflection over an infinite number of sinusoidal bars are derived for these Boussinesq models and compared to the exact theoretical solution in order to determine the optimized values of the parameters in the new enhancement terms. Numerical simulations are also carried out for the Bragg reflection over a finite number of sand bars and compared with corresponding measurements to validate the enhancements. Comparisons with other forms of Boussinesq models are made to discuss the applicability of different forms of Boussinesq models to rapidly varying topography with sand bars. The effects of the mild slope assumption on the prediction of Bragg reflection and of wave reflection on a plane self are also discussed.     

OBS广角反射地震及其意义

在蒸发岩、玄武岩等高阻抗岩层发育地区 ,常规反射地震往往难以获取高阻抗层以下的地层地质信息。而使用海底地震仪 ( OBS)进行广角反射地震测量 ,可较好地解决高阻抗层屏蔽问题 ,它是开展海上地质构造勘查的一种行之有效的方法。对 OBS广角反射地震法的原理 ,海上测量方法 ,资料处理 ,时间剖面解释及地下地质构造计算机模拟方法作了阐述 ,对 OBS广角反射地震勘探法的成功范例——苏伊士湾高蒸发岩发育区结晶基底勘探作一扼要介绍。     

Investigations on the reflection behaviour of a slotted seawall

Based on the linear wave theory and the eigenfunction expansion method, the interaction between waves and a slotted seawall is studied analytically as well as experimentally. The analytical investigations show that the reflection characteristics of a slotted seawall depend mainly on the porosity of the slotted plate and the incident wave height. It is found that the reflection coefficient reaches its minimum value as the chamber width is about a quarter of the incident wavelength. The reflection behaviour becomes optimal when the porosity is moderate (about 0.2 in the present study). The immersed depth has some effect on the reflection coefficient of the seawall structure, but the improvement is small when the immersed depth is larger than the half of the water depth. A series of physical model experiments are carried out to examine the analytical results. Comparisons between the analytical and experimental results of reflection coefficients are made for some comparable cases and show good agreement provided certain parameters of this model are suitably chosen. This demonstrates that the analytical model is able to account adequately for energy dissipation by the slotted plate and can provide instruction for the design of such seawalls.     

Wave reflection from vertical breakwater with porous structure

This paper presents numerical solutions for the wave reflection from submerged porous structures in front of the impermeable vertical breakwater. A new time-dependent mild-slope equation involves the parameters of the porous medium including the porosity, the friction factor and the inertia coefficient, etc. is derived for solving the boundary value problem. A comprehensive comparison between the present model and the existing analytical solution for the case of simple rectangular geometries of the submerged structure is performed first. Then, more complicated cases such as the inclined and trapezoidal submerged porous structures in front of the vertical breakwater with sloping bottom are considered. This study also examines the effects of the permeable properties and the geometric configurations of the porous structure to the wave reflection. It is found that the submerged porous structure with trapezoidal shape has more efficiency to reduce the wave reflection than that of triangular shape. The numerical results show that the minimum wave reflection is occurred when the breakwater is located at the intermediate water depth.     

Wave reflection from partially perforated-wall caisson breakwater

In 1995, Suh and Park developed a numerical model that computes the reflection of regular waves from a fully perforated-wall caisson breakwater. This paper describes how to apply this model to a partially perforated-wall caisson and irregular waves. To examine the performance of the model, existing experimental data are used for regular waves, while a laboratory experiment is conducted in this study for irregular waves. The numerical model based on a linear wave theory tends to over-predict the reflection coefficient of regular waves as the wave nonlinearity increases, but such an over-prediction is not observed in the case of irregular waves. For both regular and irregular waves, the numerical model slightly over- and under-predicts the reflection coefficients at larger and smaller values, respectively, because the model neglects the evanescent waves near the breakwater.     

Closed-form solutions for wave reflection and transmission by vertical slotted barrier

In this paper, we introduce the closed-form solution developed by Kim in 1998 for calculating the reflection and transmission coefficients of a vertical slotted barrier, which is not well known because it is presented in his thesis. It is then compared with other closed-form solutions developed by different authors. It is shown that all the solutions give a wrong result for long waves, i.e., large reflection and small transmission. It is also shown that the inertia term is important for intermediate-depth and deep water waves so that the solution including the inertial effect gives better prediction than those neglecting the inertial effect. The accuracy of the existing closed-form solutions is not satisfactory, even though they have been developed based on fundamental fluid mechanics principles. We propose a hybrid solution several parameters of which are based on empirical formulas. The hybrid solution better predicts the reflection and transmission coefficients than the existing solutions. Moreover, it gives a correct result, i.e., small reflection and large transmission, for long waves.     

渗透海床上矩形Bragg防波堤对波浪反射的研究

与海床不可渗透的情况相比,波浪在可渗透海床上传播时会发生波能衰减。本文将基于可渗透海床上一维修正型缓坡方程,建立方程求解的有限差分模型。将通过与不可渗透海床上矩形Bragg防波堤对波浪反射系数解析解的对比,验证有限差分模型的正确性和适用性。将进一步研究海床可渗透情况下,海床的渗透性参数、坝体的相对宽度、数量、浸没度对波浪反射系数的影响及其与海床不可渗透情况下的差异。本文研究发现,Bragg共振发生时的反射系数随坝体数量的增多而增大,随海床渗透性参数和坝体浸没度的增大而减小,并且存在一个坝体相对宽度值会使Bragg共振反射达到最大。相较于海床不可渗透的情况,发生Bragg共振反射的波浪频率几乎相同,但反射系数减小,而且零反射（或全透射）现象不再存在。