防浪建筑物影响下珊瑚礁海岸波浪传播变形试验

通过测试一系列不规则波工况研究了防浪建筑物存在下珊瑚礁海岸附近短波、低频长波和增水的变化规律,并对比了防浪建筑物的不同位置情况。分析结果表明：波浪在沿礁传播过程中,短波波高沿礁坪持续衰减,低频长波波高沿礁坪逐渐增大,波浪增水则沿礁坪基本保持不变;海岸附近短波随着防浪建筑物与礁缘距离的变大而减小,低频长波则在防浪建筑物处于礁坪后部时达到最大,防浪建筑物位置的变化对于礁坪波浪增水的影响可以忽略。通过理论分析证明了珊瑚礁地形上低频长波是由于群波破碎造成的破碎点移动而产生的;当特定波况作用于特定位置的防浪建筑物时,低频长波在礁坪上会发生一阶共振效应导致其能量在海岸附近达到最大值。     

Probabilistic Distribution of the Maximum Wave Heigh

A new method of treating maximum wave height as a random variable in reliability analysis of breakwater caissons is proposed. The maximum wave height is expressed as the significant wave height multiplied by the so-called wave height ratio. The proposed wave height ratio is a type of transfer function from the significant wave height to the maximum wave height. Under the condition of a breaking wave, the ratio is intrinsically nonlinear. Therefore, the probability density function for the variable cannot be easily defined. In this study, however, it can be derived from the relationship between the maximum and significant waves in a nonbreaking environment. Some examples are shown to validate the derived probability density function for the wave ratio parameter. By introducing the wave height ratio into reliability analysis of caisson breakwater, the maximum wave height can be used as an independent and primary random variable, which means that the risk of caisson failure during its lifetime can be evaluated realistically.     

Probabilistic distribution of the maximum wave height

A new method of treating maximum wave height as a random variable in reliability analysis of breakwater caissons is proposed. The maximum wave height is expressed as the significant wave height multiplied by the so-called wave height ratio.The proposed wave height ratio is a type of transfer function from the significant wave height to the maximum wave height.Under the condition of a breaking wave, the ratio is intrinsically nonlinear. Therefore, the probability density function for the     

Experimental Study of Perforated Caisson Breakwater

This paper describes the design of a perforated caisson breakwater and presents the results of model test. Tests with regular and irregular waves have demonstrated that the perforated caisson breakwater has the advantages of low reflection coefficient, good wave-absorbing performance, relatively small wave height in front of the breakwater, and small amount of overtopping. Analyses have been made of the coefficient of reflection, wave height in front of the breakwater, and wave overtopping. Relevant figures and tables are presented for reference.     

Determination of wave energy dissipation factor and numerical simulation of wave height in the surf zone

Based on the time-dependent mild slope equation including the effect of wave energy dissipation, an expression for the energy dissipation factor is derived in conjunction with the wave energy balance equation. The wave height of regular and irregular waves is numerically simulated by use of the parabolic mild slope equation considering the energy dissipation due to wave breaking. Comparison of numerical results with experimental data shows that the expression for the energy dissipation factor is reasonable. The effects of the wave breaking coefficient on the breaking point and the distribution of wave height after breaking are discussed through the study of a specific experimental topography.     

Wave transmission by overtopping due to random waves

Experimental studies of wave transmission by overtopping for a smooth impermeable breakwater with 1:1.5 slope under both regular and random waves were conducted. A resulting relationship between the transmission coefficient (determined by wave height and wave period) and a breakwater height above mean water level normalized with the height of wave run-up measured directly by capacity wave meter is reported. Meanwhile, their discrepancies in both regular and random waves are also discussed in this study. The authors find also that the transmitted significant wave period by overtopping of random waves may be much longer than those of the incoming wave. This characteristic is especially prominent and probably creates the oscillation phenomenon in the wave basin at the back of breakwater when the breakwater height (above mean water level) to water depth ratio is greater than 0.23 and the incoming wave period is longer than 8 sec.     

一个新的破碎波统计模式

由运动方程和涡度方程所导得的两个首次积分估计给出了海波破碎的发生条件和破碎波的波面限制。由这两个条件所构造的新的破碎波统计模式，可导出海波的破碎面积率、破碎体积率和破碎能量损耗率的解析表达式，加之一个简单的白冠物理模型又导出了一个新的白冠覆盖率的解析表达式。     

涌浪作用下港内波况试验研究

基于秘鲁钱凯港的防波堤三维整体模型试验结果,研究了涌浪绕射、透射联合作用对港内波况的影响.分析了不同波向、不同谱峰周期的入射波条件下港内不同功能区的波况分布规律,并对比分析了具有不同周期的入射波对港内不同区域波高的影响,兼顾分析了波向的影响.结果表明,在涌浪作用下,受透射、绕射影响,不同入射波条件下港内比波高分布规律相...     

The visual estimation of shore-breaking wave heights

Although a number of programmes for the visual estimation of breaking wave height have been, or are being, operated in different parts of the world (USA-LEO, Australia-COPE), there has been little investigation of the reliability of such data to make precise evaluations of breaking wave height. Using a combination of field data for simultaneous visual estimations and measurements of breaking wave height, it can be shown that experienced observers are able to estimate mean height with only a 20% error. Also the moments of the breaking wave spectrum may be calculated, allowing quick and cheap measurements of extreme waves.LEO records from Florida and California indicate that almost 50% of the data are redundant as frequency of observation could be halved without loss. However, records appear to be filtered, inasmuch as extreme waves are underestimated.     

Risk Analysis of Breakwater Caisson Under Wave Attack Using Load Surface Approximation

A new load surface based approach to the reliability analysis of caisson-type breakwater is proposed. Uncertainties of the horizontal and vertical wave loads acting on breakwater are considered by using the so-called load surfaces, which can be estimated as functions of wave height, water level, and so on. Then, the first-order reliability method（FORM） can be applied to determine the probability of failure under the wave action. In this way, the reliability analysis of breakwaters with uncertainties both in wave height and in water level is possible. Moreover, the uncertainty in wave breaking can be taken into account by considering a random variable for wave height ratio which relates the significant wave height to the maximum wave height. The proposed approach is applied numerically to the reliability analysis of caisson breakwater under wave attack that may undergo partial or full wave breaking.     

Interaction Between Waves and A Comb-Type Breakwater

The characteristics of wave transmission, reflection and energy dissipation of comb-type caisson breakwaters are studied through laboratory physical model tests. Regular and irregular waves, with a wide range of wave heights and periods and a constant water depth, are considered. Different dimensions of each portion of the comb-type caisson breakwater are tested. Empirical formulae for calculating the reduction coefficient k, which is the ratio of horizontal wave force on unit length of the comb-type breakwater to that on unit length of the vertical wall breakwater, and for calculating the reflection coefficient of waves k, are obtained from the measurements. The comb-type caisson breakwater has been found to be very efficient in dissipating incident wave energy and in reducing wave reflection, and has already been used for the construction of an island breakwater in the Dayao Bay of Dalian Port, Liaoning Province, China. Compared with the cost of a common caisson breakwater, about 24. 5% of the investm     

Scour below marine pipelines in shoaling conditions for random waves

This paper provides an approach by which the scour depth below pipelines in shoaling conditions beneath non-breaking and breaking random waves can be derived. Here the scour depth formula in shoaling conditions for regular non-breaking and breaking waves with normal incidence to the pipeline presented by Cevik and Yüksel [Cevik, E. and Yüksel, Y., (1999). Scour under submarine pipelines in waves in shoaling conditions. ASCE J. Waterw., Port, Coast. Ocean Eng., 125 (1), 9–19.] combined with the wave height distribution including shoaling and breaking waves presented by Mendez et al. [Mendez, F.J., Losada, I.J. and Medina, R., (2004). Transformation model of wave height distribution on planar beaches. Coast. Eng. 50 (3), 97–115.] are used. Moreover, the approach is based on describing the wave motion as a stationary Gaussian narrow-band random process. An example of calculation is also presented.     

多向随机波浪反射的试验研究

试验研究了多向随机波浪在直立式防波堤和斜坡式防波堤前的反射情况。在试验中，改变波浪要素(波陡、周期)、波浪入射角度(正向、斜向)和方向分布以及防波堤的坡度，以充分研究这些因素对波浪反射的影响。遗传算法用来分析多向随机波从建筑物的反射。试验结果表明，直立堤的反射系数基本上不随入射波浪方向变化，斜坡堤的反射系数随波浪峰频的增大和堤坡的变缓而减小，且随波浪方向有一定变化。还探讨了多向随机波浪在斜坡式防波堤上的反射面位置问题。     

Intercomparison of wave-driven current models

Seven numerical models which simulate waves and currents in the surf-zone are tested for the case of a reduced-scale detached breakwater subjected to the action of regular waves with normal incidence. The computed wave heights, water levels and velocities are compared with measurements collected in an experimental wave basin. The wave height decay in the surf-zone is predicted reasonably well. Set-up and currents appear to be less well predicted. This intercomparison exercise shows that radiation stresses are systematically overestimated by formulations used in the models, mean bottom shear stresses are not always co-linear with the mean bottom velocity vector in shallow water, and turbulence modelling in the surf-zone requires a sophisticated     

Application of VOF in Calculating Wave Energy Loss due to Spilling Breaker

- A large amount of experimental analysis and systematical theoretical calculation has been done by the authors to solve the problem of wave transformation and breaking, considering the effect of both current and topography, but only the wave energy loss due to spilling breaker in the surf zone has been discussed in this paper. Based on test result analysis and calculation with the Stream Function Wave Theory, the wave velocity field at breaking points has been obtained, and it is used to calculate the wave heights after breaking by the VOF (Volume of Fluid) method, in which the governing equations are continuity equation and Navier-Stokes Equation for imcompressible fluids. In the present paper, the improved VOF technique is used to calculate the wave heights of stable regular waves after breaking. Results fit the test data well, which shows that the VOF method is suitable to numerical simulation of regular waves after breaking. Besides, the breaker coefficient B of regular waves in the bore model is a     

直立堤前波浪和波压力统计特征

基于1987年和1988年夏季在古镇口港直立堤前的实测资料,对波浪和波压力连续记录进行了统计分析和谱估计,研究了在堤前海浪不发生破碎条件下,堤前波浪和堤面不同高程上压力波的波面高度概率分布、堤前波浪波高和周期与波压力幅度和周期的概率分布特征、入射波行近提前过程中的谱变化及堤面不同高程上压力谱的变化特征。主要结果总结在本文最后一节。     

Deformation of multi-directional random waves passing over an impermeable submerged breakwater installed on a sloping bed

This study investigates the wave deformation of multi-directional random waves passing over an impermeable submerged breakwater installed on the slope. Experiments were conducted in a three-dimensional wave basin equipped with a multi-directional random wave generator. Measurements of the free surface elevations around an impermeable submerged breakwater were carried out using 19 capacitance-type wave gages. In addition, a numerical model is proposed in three-dimensional random wave field. It is shown that the numerical results reproduce the general trend of the experimental results well. Investigations are made to study the effect of the spreading parameter S_max and bottom topography (bottom slope and submerged breakwater) on the wave deformation. It is pointed out that concentration of wave energy with larger values of the spreading parameter S_max is located within narrow limits in onshore side of the submerged breakwater. Furthermore, the supplementary discussion is made by means of numerical results.     

直立式防波堤口门区海啸局部冲刷规律实验研究

海啸作为世界上最严重的自然灾害之一,其巨大的破坏力使得近海建筑物遭受了严重的损害。基于波浪水槽实验,开展海啸波作用下不同口门距离的防波堤局部冲刷机理实验研究。实验结果表明,在海啸波越顶水流产生的水跌以及海啸波通过防波堤口门时产生的扰流共同作用下,口门中心线处产生明显的局部冲刷坑,随着口门距离的增加,防波堤局部冲刷先加剧后减弱。建立防波堤局部最大冲刷深度与海啸波波高、防波堤宽度及出水高度、口门间距的关系式,揭示了最大局部冲刷深度与海啸波波高、防波堤尺寸、口门距离的内在关系。     

Wave forces on vertical cylinders upon shoals

An experimental study has been carried out on the forces from plunging breaking regular and irregular waves on a vertical cylinder on a shoal. Total as well as local wave forces have been measured. Engineering formulae for the calculation of the horizontal forces and overturning moments have been derived. The duration of the impact forces have been measured and compares fairly well with theoretical values.     

Numerical investigation on the dynamics of a vertical wall defenced by an offshore breakwater

The numerical and experimental investigations on the performance of an offshore-submerged breakwater in reducing the wave forces and wave run-up on vertical wall are presented. A two-dimensional finite-element model is employed to study the hydrodynamic performance of the submerged breakwater under the action of regular and random waves. The numerical prediction has been supported with experimental measurements. The wave forces and wave run-up on the vertical wall were measured for different breakwater configurations. The applicability of linear theoretical model in the prediction of wave forces on the wall by a submerged breakwater has been discussed.