潜堤后高阶自由谐波的研究

基于高阶边界元方法的完全非线性数值水槽模型模拟潜堤地形上波浪的传播变形,通过与实验值进行比较,考察数学模型的正确性.采用两点法分离得到堤后高倍频自由波来研究入射波参数、水深对堤后高倍频自由波的影响.研究发现:基频波、二阶和三阶自由波幅值分别与入射波波幅成线性、二次和三次函数关系,基频波幅值基本不随波浪周期变化,而二阶和...     

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。     

Numerical simulation of nonlinear dispersive waves propagating over a submerged bar by IB–VOF model

It is a good test for a numerical model to simulate progressive waves propagating over a submerged bar with a relatively high ratio of slopes. In this paper, the combined IB–VOF model is used to predict nonlinear dispersive waves propagating over a submerged bar with both slopes of 1:2. The predicted free surface elevations are compared with the experimental data and numerical results presented by other researchers. The comparison shows that the IB–VOF model is able to provide satisfactory wave profiles in the shallow water with strong nonlinear effects and in the wave transmitted region with strong wave dispersion in particular. Moreover, the wave evolution behind the submerged bar is described in detail, including the spatial wave profile modulation, spectral analysis of the time-series waves, flow velocity and pressure fields, and kinetic energy distribution. The effect of fluid viscosity on the numerical simulations is also studied, and it is found that the effect on the wave evolution considered in this paper is not significant. Finally, the hydrodynamic force acting on the bar is calculated using the IB–VOF model.     

Numerical Simulation of Wave Field near Submerged Bars by PLIC-VOF Model

Investigating the wave field near structures in coastal and offshore engineering is of increasing significance. In the present study, simulation is done of the wave profile and flow field for waves propagating over submerged bars, using PLIC-VOF （Pieeewise Linear Interface Construction） to trace the free surface of wave and finite difference method to solve vertical 2D Navier-Stokes （N-S） equations. A comparison of the numerical results for two kinds of submerged bars with the experimental ones shows that the PLIC-VOF model used in this study is effective and can compute the wave field precisely.     

Nonlinear Model of Mean Free Surface of Waves

-A nonlinear model of mean free surface of waves or wave set-up is presented.The model isbased on that of Roelvink(1993),but the numerical techniques used in the solution are based on theWeighted-Average Flux(WAF)method(Watson et al,1992),with Time-Operator-Splitting(TOS)usedfor the treatment of the source terms.This method allows a small number of computational points to beused,and is particularly efficient in modeling wave set-up.The short wave(or primary wave)energy equa-tion is solved by use of a more traditional Lax-Wendroff technique.A nonlinear wave theory(James,1974)is introduced.The model described in this paper is found to be satisfactory in most respects whencompared with the measurements conducted by Stive(1983)except in modeling the mean free surface veryclose to the mean shoreline.     

Interaction of non-breaking regular waves with a periodic array of artificial porous bars

A computational model is developed to investigate the wave damping characteristics of a periodic array of porous bars. The transmission and reflection coefficients as well as the wave energy dissipation are evaluated relating to the physical properties and geometric factors of bars. It is shown that the porosity, number, width and height of bars all play important roles in the wave damping characteristics, compared to other factors such as the intrinsic permeability. It is observed that like impermeable bars, permeable bars display Bragg phenomenon. However, Bragg reflection produced by permeable bars is smaller than that by impermeable bars. Permeable bars reflect smaller waves, transmit smaller waves and dissipate more wave energy. It is indicated that if the porosity increases, both the reflection and transmission coefficients decrease and more wave energy is dissipated. Further, it is found that the porosity controls the magnitude, but not the oscillation frequency of the reflection coefficient, which depends only on the number of bars.     

Wave decomposition phenomenon and spectrum evolution over submerged bars

Wave decomposition phenomenon and spectrum evolution over submerged bars are investigated by a previously developed numerical model. First, the computed free surface displacements of regular waves at various locations are compared with the available experimental data to confirm the validity of the numerical model, and satisfactory agreements are obtained. In addition, variations of decomposition characteristics with incident wave parameters and the change of energy spectrum for regular waves are also studied. Then the spectrum evolution of irregular waves over submerged bars, as well as the influence of incident peak wave period and the steepness of the front slope of the bar on spectrum evolution, is investigated. Wave decomposition and spectral shape are found to be significantly influenced by the incident wave conditions. When the upslope of the bar becomes 1:2, the length of the slope becomes shorter and will not benefit the generation of high frequency energy, so spectrum evolution is not significant.     

多个淹没水平圆柱诱发高阶谐波特性的数值与试验研究

基于势流理论采用时域高阶边界元方法建立了模拟非线性波浪与淹没水平双、三圆柱作用的数值水槽模型,其中采用混合欧拉-拉格朗日方法更新自由水面,四阶Runga-Kutta方法进行时间步进。利用两点法分离得到潜体下游高阶自由波,进而研究潜体间距、布置形式等对高倍频自由波的影响。同时在物理水槽内开展多潜体高阶谐波物理模型试验,并将试验结果与数值结果进行对比,吻合较好。研究发现:淹没双圆柱下游高阶谐波幅值随潜体间距呈现周期性振荡变化,其振荡的重现距离约为波长一半。而淹没三圆柱下游的高阶谐波随第一个间距呈周期性振荡变化,随第二个间距的增大而减小。     

水下平板与波浪相互作用完全非线性数值模拟(英文)

利用完全非线性数值波浪水槽技术研究水下平板与波浪的相互作用。假定水下平板厚度极薄、刚性,位于有限水深并且非常接近自由水面。应用四阶龙格库塔方法追踪每一时刻的波面形状,采用阻尼层来吸收反射波以保证算法的稳定性,同时引入平滑和重组的方法抑制自由表面控制点的较高梯度。通过对波浪与浮动圆柱相互作用的数值模拟证实了数值波浪水槽方法的有效性,计算结果与线性理论吻合良好。在波浪数值水槽方法中引入造波板模拟波浪产生并与水下平板发生相互作用,应用傅立叶解析方法对波面变形、波浪力作了分析。结果表明在板非常接近自由水面的情况下会表现出现很强的非线性,揭示了线性理论的局限性。     

孤立波与升沉水平板相互作用数值模拟研究

合理的刚度和潜深设计可以使升沉水平板获得优异的消浪性能。基于考虑流体黏性的二维不可压缩Navier-Stokes方程,以高阶紧致插值CIP(constrained interpolation profile)方法求解方程对流项,采用VOF(volume of fluid)方法重构自由液面,构建二维数值波浪水槽。采用试验数据验证模型后,研究孤立波与升沉水平板相互作用,分析相对刚度K*、相对潜深d/h、相对波高H/h对于升沉板的消浪性能和运动响应的影响,揭示升沉板对孤立波的消浪机理。研究表明:在孤立波通过时,升沉板会经历一个先上升后下降的运动,随后非线性自由振动,板下方水体近似均匀流动,且水流的垂向流动与板的垂荡方向一致;升沉板主要通过不对称涡旋脱落、浅水变形、波浪反射与辐射波转化等方式消耗孤立波能量;一定条件下,采用最优相对刚度K*=4.0和最优相对潜深d/h=0.52可以取得良好的消浪效果,此时透射系数最小,同时升沉板的运动响应在合理的范围内。     

孤立波与带窄缝双箱相互作用模拟研究

针对孤立波与带窄缝双箱的作用问题,应用时域高阶边界元方法建立了二维数值水槽。其中,自由水面满足完全非线性运动学和动力学边界条件,对瞬时自由表面流体质点采用混合欧拉-拉格朗日法追踪,采用四阶龙格库塔法对下一时刻的自由水面的速度势和波面升高进行更新。采用加速度势法求解物体湿表面的瞬时波浪力。采用推板方法生成孤立波。通过模拟孤立波在直墙上的爬高以及施加在直墙上的波浪力,并与已发表的实验和数值结果对比,验证本数值模型的准确性。通过数值模拟计算研究了窄缝宽度、方箱尺寸对波浪在箱体迎浪侧爬高,窄缝内波面升高,箱体背浪侧透射波高及箱体受波浪荷载的影响。同时研究了有一定时间间隔的双孤立波与带窄缝双箱系统作用问题。     

Analysis of submerged bar nourishment strategies in a wave-dominated environment using a 2DV process-based model

The present study aims to analyze the effects of different submerged bars nourishment strategies using a 2DV process-based morphodynamical model. A two-barred beach profile typical of the French Mediterranean micro-tidal storm-dominated coastline is chosen as a reference profile. Two different kinds of modified beach profiles are considered. (i) Only the outer bar is nourished, the inner bar being unchanged (ii) both bars are nourished. Three typical wave forcing regimes are considered. The behavior of the natural profile is first investigated under the 3 wave forcing regimes. Then the behavior of the various nourished profiles is analyzed in terms of wave dynamics and bars behavior. On the basis of the model results, the outer bar only nourishment strategy appears to be preferable.     

Modelling of Random Waves over Submerged Breakwaters and Its Application to Reflection Estimation

1.IntroductionGreat efforts have been devoted to the protection of coastal areas over many years by erectingdikes,seawalls,groin systems,and detached breakwaters.The sea walls,jetties,detached breakwa-ters,etc.are traditionally adopted as absorbingfacilit…     

Wave reflection, transmission and harmonics due to different submerged structures

I~IOXdifferent tabes of submerged structures restricting wave development are extensively appliedin coastal and barber engineering. Generally speaking, the submerged structures are classified intothree types (see Fig. 1 ): a submerged horizontal plate (fixed submerged structure), a submergedbreakwater (rectangular or trapezoidal) and a step-take structure (toPOgraphy). In order to get aclear understanding of the characteristics of wave motion around submemed structures, manyFig. 1. Fol'InS…     

A Finite Element Solution of Wave Forces on Submerged Horizontal Circular Cylinders

In this paper, a numerical model is established for estimating the wave forces on a submerged horizontal circular cylinder. For predicting the wave motion, a set of two-dimensional Navier-Stokes equations is solved numerically with a finite element method. In order to track the moving non-linear wave surface boundary, the Navier-Stokes equations are discretized in a moving mesh system. After each computational time step, the mesh is modified according to the changed wave surface boundary. In order to stabilize the numerical procedure, a three-step finite element method is applied in the time integration. The water sloshing in a tank and wave propagation over a submerged bar are simulated for the first time to validate the present model. The computational results agree well with the analytical solution and the experimental data.Finally, the model is applied to the simulation of interaction between waves and a submerged horizontal circular cylinder.The effects of the KC number and the cylinder depth on the wave forces are studied.     

Experimental investigation of the harmonic generation by waves over a submerged plate

Experiments in a wave flume have been performed to analyse the nonlinear interaction between regular gravity waves and a submerged horizontal plate used as breakwater. A new method, based on the Doppler shift generated by a moving probes, has been used to discriminate the incident fundamental mode and the reflected fundamental mode. The relationships of the reflection and transmission coefficients to the wave number at different submergence depth ratios are presented. The accurate discrimination, by this method, of the phase-locked and free modes allows the quantification of the higher harmonics generated by the breakwater and the analysis of the nonlinear interaction between the waves and the submerged plate. The transfer of energy from the fundamental mode to higher harmonics is very large in the cases of small submergence depth ratios. The vortices produced at the edges take part in the production of higher harmonics by interaction with the free surface but involve, at the same time, a dissipation process that increases the efficiency of the breakwater.     

Bragg Reflection of Waves by Different Shapes of Artificial Bars

Experiments are performed in a wave flume to demonstrate the Bragg reflection of linear gravity waves by artificial bars. Three different artificial bars with rectangular, triangular and rectified cosinoidal shapes are placed discretely on the seabed for measurement of the Bragg reflection. A series of experimental conditions including the number of bars, the pe-riodic bar spacing, the water depth and various wave conditions are tested. Key parameters influencing the Bragg resonances are investigated. The experimental data are compared with the values from both theoretical and numerical models. Some key parameters have proved to be effective in describing the primary resonances. Predictive equations of the charac-teristics for the Bragg reflection are proposed in this paper.     

潜堤上规则波辐射应力的数值研究

在近岸波浪相关研究中,辐射应力是波动在水体中引起的剩余动量流,是波浪运动的重要物理量。在波浪从深水逐渐传向浅水的过程中,波浪的非线性逐渐增强,甚至会发生破碎等剧烈变形,引起辐射应力的强烈变化,对次重力波生成等有重要贡献。应用OpenFOAM精细模拟波浪在潜堤上的传播,得出波浪运动的详细流场信息,计算了有波浪破碎情况下潜堤地形上波浪的辐射应力和波浪增减水情况。研究结果表明,在潜堤地形下,辐射应力值在堤前平底处受波幅变化影响较敏感,波浪完全破碎后其值在堤后坡面处呈增大趋势直至平底处趋于平稳。辐射应力沿程变化对波浪增减水的影响趋势与波浪增减水方程符合良好。     

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.     

Nonlinear numerical simulation on extreme-wave kinematics

A fully nonlinear numerical model based on a time-domain higher-order boundary element method (HOBEM) is founded to simulate the kinematics of extreme waves. In the model, the fully nonlinear free surface boundary conditions are satisfied and a semi-mixed Euler-Lagrange method is used to track free surface; a fourth-order Runga-Kutta technique is adopted to refresh the wave elevation and velocity potential on the free surface at each time step; an image Green function is used in the numerical wave tank so that the integrations on the lateral surfaces and bottom are excluded. The extreme waves are generated by the method of wave focusing. The physical experiments are carried out in a wave flume. On the horizontal velocity of the measured point, numerical solutions agree well with experimental results. The characteristics of the nonlinear extreme-wave kinematics and the velocity distribution are studied here.