Laboratory Study on the Interaction Between Regular Obliquely Incident Waves and Vertical Walls

The characteristics of wave forces are studied based on physical model tests with regular waves. The ratio of obliquely incident wave forces to normally incident wave forces on unit length of a vertical wall is related with various factors. A linear reduction of the mean force of obliquely incident waves is confirmed with an increase in the relative caisson length. Also the characteristics of reflection coefficient of diagonal waves are discussed.     

Wave Forces Acting on Vertical Walls

Regular and irregular wave forces acting on vertical walls are studied by a previously developed numerical model. The computed wave forces are compared with the available experimental data to verify the numerical model, and satisfactory agreements are obtained. The variation of wave forces with incident angles and the shape of simultaneous pressure distribution are investigated, and the comparisons between numerical results and Goda＇ s predictions are also carried out. It is concluded that the maximum wave forces acting on the unit length of vertical wall is often induced by the obliquely incident waves instead of normally incident waves, while Goda＇ s formula may be inapplicable for oblique wave incidence. The shape of simultaneous pressure distribution is not significantly influenced by incident angles, and it can be favorably predicted by Goda＇ s formula. When regular wave heights are taken as the same as irregular wave height H1%, the irregular wave forces Ph. 1% are slightly larger than regular wave forces in most cases.     

开孔沉箱在斜向入射波作用下受力研究

应用透空壁内流体速度与壁两侧的压力差成正比的线性模型,研究了斜向波与无限多个开孔沉箱的相互作用.依照结构物的几何形状,把整个流域分成无限多个子域,在每个子域内应用特征函数展开法对速度势进行展开.对于沉箱内的波浪运动,引入相位差概念;在构造反射波模型时,考虑了结构物的几何形状影响.列举出物理模型实验结果与数值实验结果的比较,可以看出两者吻合较好.进一步的数值计算验证表明,当孔隙系数无限大时,开孔墙前后的速度非常接近.在低频入射波作用下,垂直于沉箱的水平力随角度的变大而减小,平行于沉箱排列方向的力则变大.     

开孔沉箱与斜向波作用的理论研究和实验验证

应用透空壁内流体速度与壁两侧的压力差成正比的线性模型,研究了无限多个开孔沉箱在斜向波作用下的反射问题。整个流域被分成无限多个子域,在每个子域内应用特征函数展开法对速度势进行展开。对于沉箱内的波浪运动,根据沉箱位置引入相位差概念。在构造反射波模型时,考虑了结构物几何形状周期性的影响。结果表明,当孔隙系数无限大时,开孔墙前后的速度非常接近,反射系数符合能量守恒定律。在低频入射波作用下,沉箱越短,其反射系数越小,反射系数随着角度的变大而减小。     

Three-dimensional numerical simulation of oblique wave action on vertical walls

1 Introduction A vertical wall is one of the typical maritime sheltering structures in the coastal region, which is mainly subjected to wave forces. It has been a com- mon engineering assumption adopted for design pur- poses that normally incident wave fo…     

Action of Cnoidal Waves on Vertical Walls

Based on the 2nd order cnoidal wave theory, the characters of shallow water standing waves and their action on vertical walls are studied in this paper. The theoretical expressions of the wave surface elevation in front of and the wave pressure on the vertical wall are obtained. In order to verify the theoretical results, model tests were made in the State Key Laboratory of Coastal and Offshore Engineering at DUT. For the wave surface elevation in front of the wall and the wave forces on the wall at the moment when the wave surface at the wall surface goes down to the bottom of the wave trough, the calculated results coincide quite well with the experimental results. For the wave forces on the wall at the moment when the wave surface at the wall surface goes up to the top of the wave crest, the theoretical expressions are modified by the experimental results. For the convenience of practical use, calculations are made for the wave conditions which usually occur in enginering practice by use of the inves     

Calculation of Wave Pressure and Pressure Spectrum for Perforate-Pipe Breakwater

Standing waves are formed due to the reflection when waves meet vertical wall,thereforestrong structures are needed to keep the wall stability under the serious wave attack.For the improvementof the working condition and increase of the stability of the wall,the lower reflecting breakwaters have at-tracted close attention Reports mostly from Japanese researchers are often concerned with the wall ofcaisson equipped with open windows.In this paper a kind of hollow-pipe perforated breakwater is exam-ined which waves may partially perforate into the harbour basin.The wave in front of the wall can onlyform partial standing wave and wave force is reduced obviously.And the theoretical calculation of waveforce and analysis of wave force spectrum are all derived.Comparison between the results from theoreticalcalculation and hydraulic modeling shows reasonable agreement.     

A Three-Point Method for Separating Incident and Reflected Waves over A Sloping Bed

This study presents a three-point method for separating incident and reflected waves to explain normally incident waves' propagating over a sloping bed. Linear wave shoaling is used to determine changes in wave amplitude and phase in response to variations of bathymetry. The wave reflection coefficient and incident amplitude are estimated from wave heights measured at three fixed wave gauges with unequal spacing. Sensitivity analysis demonstrates that the proposed method can predict the reflection and amplitude of waves over a sloping bed more accurately than the two-point method.     

Oblique wave interaction with a floating structure near a wall with stepped bottom

Diffraction of obliquely incident waves by a floating structure near a wall with step-type bottom topography is investigated under the three-dimensional small amplitude wave theory. Full solution of the problem under the potential flow approach is obtained by the matched eigenfunction expansion method. The wave-induced forces on the structure and on the wall, the reflection and transmission characteristics and the wave elevations in the free surface regions are studied for different incident wave angles, water depth ratios and dimension of the structure and the distance of the wall from the center of the structure. The problem is reformulated under shallow water approximations and results are compared with the finite depth results.     

完全非线性孤立波的直墙反射

报道了应用边界积分方法模拟完全非线性孤立波的传播与直墙反射,给出了波形演变过程。结果表明,本模型对计算孤立波的传播与直墙反射是有效的。三阶Boussinesq方程的孤立波解比低阶方程的孤立波解更接近完全非线性的数值解.当来波波高增大时,孤立波直墙反射的相位滞后变小。若考虑大波高孤立波的直墙反射或波——波相互作用,一阶理论预报的相位滞后往往低估实际情况。     

波浪作用下大尺径圆柱周围局部冲刷

通过系列模型试验，对波浪作用下墩柱周围局部冲刷地形及其形成机理进行了分析，认为最大冲刷深度发生在墩柱前方，与防波堤前冲淤形态类似，分为细沙型和粗沙型。在对各影响因子分析基础上，提出墩柱周围最大冲刷深度计算公式，试验资料表明，该公式与试验值有着良好的一致性。     

不完全立波的二维数值波浪水槽模拟

利用二维数值波浪水槽研究波浪在防波堤前的运动状态.模型选用Navier-Stokes方程作为基本方程,以有限元法对基本方程进行离散.以直立堤前完全立波和越浪条件的不完全立波、斜坡堤前的不完全立波等典型情况的模拟为基础,组合这些典型情况模拟削角堤前不完全立波运动,探讨其堤前波面、波节点及波腹点位置、波压力等特性变化.     

规则波和不规则波作用下消波建筑物前的波高分析

消波建筑物在国内外已得到广泛应用。本文采用近似方法分析了明基床上直立式消波建筑物前的波高及消波室内的波高，从而确定建筑物的消波效果。并在规则波的基础上将成果推广至不规则波作用下的情况。     

Experimental investigating on the reflected waves from the caisson-type vertical porous seawalls

The hydrodynamic efficiencies of caisson-type vertical porous seawalls used for protecting coastal areas were calculated in this study. Physical models were developed to compare the wave reflection from vertical plane, semi-porous, and porous seawalls caused by both regular and random waves. Tests were carried out for a wide range of wave heights, wave periods, and different water depths (d=0.165, 0.270 and 0.375 m). The performance regarding the reflected waves from porous and semi-porous seawalls showed improvement when compared with those from the plane seawall. The reflection coefficients of the porous and semi-porous seawalls were calculated as 0.6 and 0.75, respectively, while the coefficient for the fully reflecting plane vertical wall was significantly higher (0.9). It was also observed that the reflection coefficient decreases with increase in wave steepness and relative water depth. In addition, the reduction in the reflection coefficient of porous and semi-porous seawalls, as compared to that of a plane seawall, was observed for both regular and random waves. New equations were also proposed to calculate the reflection coefficient of different types of seawalls with the aid of laboratory experiments. By verifying the developed equations using some other experimental data, it was validated that the equations could be used for practical situations. The results of the present study can be applied to optimize the design of vertical seawalls and for coastal protecting schemes.     

斜向不规则波入、反射波分离的实验研究

斜向入射的不规则波在海岸结构物前发生反射形成入、反射波共存的波浪场,对这种物理场的入、反射波的分离是海岸工程研究的一个重要课题.改进了一种可用于斜向入射的不规则波分离的两点法,使得测波阵列的两波高仪可布置在结构物前任何方向上.将此方法应用于三维波浪水池的物理模型试验研究,试验了不同的两波高仪的组合、不同的基床高度、不同的入射方向和不同的波浪要素等各种条件对分离结果的影响,结果表明,各种情况在满足非奇异条件下可得到较好的分离结果.该方法计算简便,可以给出较准确的反射系数和入、反射波的频谱.     

NWF: Propagation of Tsunami and its Interaction with Continental Shelf and Vertical Wall

In this article, tsunamis represented as solitary waves was simulated using the fully nonlinear free surface waves based on Finite Element method developed by Sriram et al. (2006). The split up of solitary wave while it propagates over the uneven bottom topography is successfully established. Wave transmission and reflection over a vertical step introduced in the bottom topography is in good agreement with the experimental results from Seabra-Santos et al. (1987). The wave transformation over a continental shelf with different smooth slopes reveals that the solitary wave reflection increases while the continental slope varies from flat to steep. The interaction of the solitary wave with a vertical wall for different wave steepness has been analysed. The reflected shape of the profile is in good agreement with the observation made by Fenton and Rienecker (1982) and an increase in wave celerity is observed.     

Sediment by-passing across coastal inlets by natural means

The problem of shoals and sand spits at harbour and river mouths is ubiquitous. Because of the pulsative nature of littoral drift no adequate solution has been found for this problem. If one could be found utilising the natural swell energy at the site it could save billions of dollars annually in dredging costs. One solution worthy of consideration and further research is to reflect the persistent waves obliquely across the entrance. These reflected waves interact with the incident component to form a short-crested wave system that suspends sediment and aids its transmission downcoast. Tests with varying lengths of reflecting wall have shown the effectiveness of this concept. Further research is indicated to overcome subsidiary problems such as navigability.     

Numerical Modeling of Water Wave Interaction with A Soft Mud Bed

A vertical 2-D numerical model is presented for simulating the interaction between water waves and a soft mud bed. Taking into aceotmt nonlinear theology, a semi-empirical theological model is applied to this water-mud model, reflecting the combined visco-elasto-plastic properties of soft mud under such oscillatory external forces as water waves. In order to increase the resolution of the flow in the neighborhood of both sides of the inter-surface, a logarithmic grid in the vertical direction is employed for numerical treatment. Model verifications are given through comparisons between the calculated and the measured mud mass transport velocities as well as wave height changes.     

Analysis of Wave Height in Front of a Wave Absorbing Structure with Rubble Foundation

Wave absorbing structures have been widely applied in many countries. In the present paper, the wave heights in front of a vertical wave absorbing structure with rubble foundation as well as in the wave chamber of the structure are analysed using an approximative calculation method, and the dissipating effect of the structure is verified. On the basis of the results of regular waves, the relative wave heights of irregular waves in front of the wave absorbing structure as well as in the chamber have also been analysed.     

Breaking of Solitary Waves on Uniform Slopes

The propagation,shoaling and breaking of solitary waves on mild slopes are simulated byboundary element method.In this paper,the criterion of breaking solitary waves on mild slopes is discussed.The criterion is that the ratio of horizontal velocity of water particles on the wave crest to wave celerity equalsone.However,the case that the ratio of horizontal velocity of water particles on the wave crest to wave ce-lerity is below one but the front face of wave profile becomes vertical is also considered as a breaking criteri-on.According to the above criteria,the breaking index for slopes 1:10 to 1:25 is studied.The result is com-pared to other researchers'.The deformation of solitary waves on slopes is discussed and the distribution offluid velocities at breaking is shown.