Numerical Prediction of Regular Wave Breaking on Very Gentle Slopes

Regular wave deformation and breaking on very gende slopes is calculated by Mixed-Eulerian-Lagrangian procedure. The velocity potentials and their normal derivatives on the boundary are calculated through the mixed 0-1 boundary element method. The wave elevation and the potentials of time-stepping integration are detertnined by the 2nd-order Taylor expansion at the nodes of free surface boundary elements. During calculation the x-coordinates of the free surface element nodes are supposed to remain unchanged, i.e. the partial derivatives of wave elevation and potentials with respect to x are considered as zero. The numerical results of asymmetric parameters of breaking waves are verified by experimental study. It is shown that when the wave asymmetry is weak, the maximum horizontal velocity of water particales occurs at the wave peak and, the average ratio of this maximum velocity to wave celerity is 0.96. However, when the wave asymmetry is strong, the maximum horizontal velocity of water particles occu     

平缓岸坡上波浪破碎的实验研究

在１／２００的缓坡上进行了规则波与不规则波破碎的实验研究。在本实验条件下,分析了波形的不对称必至波浪破碎指标的影响,并以此对合田良实和Ｎｅｌｓｏｎ关于极平缓坡上规则波破碎指标的分歧作了解释。本文的研究还表明,底坡坡度ｉ、相对水深ｄ／Ｌ。及波形的不对称必至不规则波的破碎指标的影响较小。合田对规则波的破碎指标在不规则波条件下仍然可用,但系数Ａ应取为０．１５。不规则波波长与同周期按线悸理论计算之波长的比     

规则波在缓坡上变形与破碎数值分析

通过在二维数值水槽内用边界元法直接求解Laplace方程,对规则波在缓坡上的变形及破碎进行了数值计算。分析了不同底坡及采用不同底摩阻系数时规则波的破碎特征,并对规则波破碎的极限坡度进行了研究。重点分析了规则波破碎时海底坡度、底摩阻系数及波形不对称性对破碎指标的影响。     

Breaking Criteria for Regular Waves on Gentle Slopes

Nelson pointed out that the wave breaking criterion(H/d)_b for gentle slopes(i<1/100),inwhich H is the wave height and d is the water depth at the breaking point,is smaller than that for beachslopes of i>1/100),i.e.,the value of(H/d)_b for gentle slopes may be smaller than 0.6.Goda indicatedthat the wave breaking criterion given by himself is a result based on theoretical study,so it should be alsocorrect and can be used for gentle beaches,i.e.,the value of(H/d)_b for gentle slopes may be still largerthan 0.7.By use of high order nonlinear wave theory,this problem is analyzed in this study and the reasonwhy there is a large difference between different studies is explained.Moreover,the bottom energy loss dur-ing wave propagation is considered and the critical slope for the absence of wave breaking is also analyzed.     

Wave Breaking Phenomena of Irregular Waves Combined with Opposing Current

- Experimental study and theoretical analysis show that the critical value of relative wave height (H/ d)b given by Goda and the critical wave steepness (H/ L)b given by Michell and Miche can be adopted as the spilling breaking indices of regular waves. According to the same principle, a systematic theoretical analysis and experiment of irregular waves have been done by the authors in order to solve the breaking problem of irregular waves. It is indicated that the authors' method for determining wave breaking of regular waves can also be used for irregular waves.     

Transformation and Breaking of Irregular Waves on Very Gentle Slopes

—Based on theoretical analysis.numerical calculation.and experimental study,this paper dis-cusses breaker indices of irregular waves.transformation of wave spectrum.characteristics and computa-tion of breaking waves.as well as the critical beach slope under which waves will not break.Computed re-sults are in good agreement with laboratory physical model test data and ocean wave field measurements.     

Numerical Simulation of Breaking Wave Based on Higher-Order Mild Slope Equation

The "surface roller" to simulate wave energy dissipation of wave breaking is introduced into the random wave model based on approximate parabolic mild slope equation in this paper to simulate the random wave transportation including diffraction, refraction and breaking in nearshore areas. The roller breaking random wave higher-order approximate parabolic equation model has been verified by the existing experimental data for a plane slope beach and a circular shoal, and the numerical results of random wave breaking model agree with the experimental data very well. This model can be applied to calculate random wave propagation from deep to shallow water in large areas near the shore over natu ral topography.     

Effects of Wave Breaking on Freak Wave Generation in Ramdom Wave Train

The experimental studies of the wave breaking effects on freak wave generation are presented within a finite-depth random wave train in a laboratory wave tank. The main attention is paid to the abnormal index, AI=Hmax/Hs, being used to characterize the freak waves, and the changes of the coefficient due to wave breaking. The results show that the occurence in deep water is larger than that in shallow water.     

Wave Transformation and Breaking in Diagonal Opposing Current

- When waves propagate into diagonal opposing current from non-current area, not only the wave parameters but also the direction of wave propagation will change, that is, wave refraction will occur. The authors have calculated the changes of wave parameters, including wave refraction, by Linear Wave Theory, and have also done systematic study on wave transformation and breaking in opposing current by means of experimental analysis and theoretical calculation. In order to know the effect of wave refraction, computation is done in this paper about wave transformation and breaking on gentle slopes in diagonal opposing current.     

Effects of Wave Breaking on Freak Wave Generation in Random Wave Train

The experimental studies of the wave breaking effects on freak wave generation are presented within a finite-depth random wave train in a laboratory wave tank. The main attention is paid to the abnormal index,AI=Hmax/Hs,being used to characterize the freak waves,and the changes of the coefficient due to wave breaking. The results show that the occurrence probability of freak wave events in non-breaking waves is much larger than that in breaking waves and such occurrence in deep water is larger than that in ...     

Experimental and Numerical Study of Wave-Induced Long-Shore Currents on A Mild Slope Beach

1.Introduction Long shorecurrenthasbecomethesubjectofextensiveworldwideresearchformanyyears.The purposeofthestudyistounderstandandpredicttheprocessesofsedimenttransport,shorelineevolu tionandpollutanttransportinthenear shorezoneundertheactionofwaves.Goda(2001)regarded thesuspendedsedimentastheprincipalloadinsedimenttransportandtheeffectoflong shorecurrents wasemphasized.Theeffectofwavesonpollutanttransportwasstudiedbynumericalmodelandfield experiment(TaoandHan,2002;Rodriguezetal.,1995),andth…     

波流水槽模拟波浪技术的研究

介绍了实验室的造波机系统和造波特性及其在模型试验中的应用,并讨论了实验室内模拟海浪的检验标准及其方法。并对造波机应用前景进行讨论,对不规则波造波机进行物模试验具有一定的现实意义。     

缓坡地形上内孤立波的破碎及能量分析

在大型重力式分层流水槽中对内孤立波沿缓坡地形的演化特征进行了实验研究,利用分层染色标识方法和多点组合探头阵列技术对其传播特性做了定性分析和定量测量。实验表明:下凹型内孤立波沿缓坡地形传播过程中的破碎先从波背部发生,继而演化出上凸型内孤立波;内孤立波破碎不仅与入射波波幅相关,而且受到地形坡度的强烈影响;入射波幅参数??0.4是内孤立波不稳定及破碎的实验判据,内孤立波能量损失出现跃升是其发生破碎的重要特征。研究进一步获得了内孤立波沿缓坡地形的三维演化结构、破碎发生条件和能量变化特性,对于复杂海洋环境中非线性内波传播特性认识及其动力学建模具有重要的科学意义。     

Experimental Study of Wave Energy Spectrum in Shallow Water

Wave energy spectrum in shallow water can be studied in wind wave channel in combination with irregular wave- maker. Fetch length is successfully extended and by "Relay" method the corresponding spectrum pattern and the wind velocity scale are obtained.     

Comparisons of Computational and Experimental Results of Solitary Wave Breaking

- In this paper, the solitary wave deformation along a gentle slope and the impact pressure, on the wall are investigated experimentally and the results are compared with numerical results obtained based on the volume of fluid (VOF) method. The topography used in the experiment consists of three segments. The left segment is a 1:4 slope, the middle segment 1 :SO slope and the right segment a horizontal bed. Both the wave heights and breaking points obtained from numerical simulation and experiments are in good agreement. Numerical results give reasonable pressure distributions of breaking waves on the wall.     

Development of A Fully Nonlinear Numerical Wave Tank

A fully nonlinear numerical wave tank (NWT) based on the solution of the σ-transformed Navier-Stokes equation is developed in this study. The numerical wave is generated from the inflow boundary, where the surface elevation and/or velocity are specified by use of the analytical solution or the laboratory data. The Sommerfeld/Orlanski radiation condition in eonjunetion with an artificial damping zone is applied to reduce wave reflection from the outflow boundary. The whole numerical solution procedures are split into three steps, i.e., advection, diffusion and propagation, and a new method, the Lagrange-Euler Method, instead of the MAC or VOF method, is introduced to solve the free surface elevation at the new time step. Several typical wave cases, including solitary waves, regular waves and irregular waves, are simulated in the wave tank. The robustness and accuracy of the NWF are verified by the good agreement between the numerical results and the linear or nonlinear analytical solutions. This research will be further developed by study of wave-wave, wave-current, wave-structure or wave-jet interaction in the future.     

Effect of Berm Width and Elevation on Irregular Wave Run-Up

This paper discusses the effect of berm width and elevation of composite slope on irregular wave run-up. Based on the data obtained from model tests, the formula and distribution of irregular wave run-up on composite slope are derived. The changing of wind speed, width and elevation of the berm are considered comprehensively. The wave run-up with various exceedance probability can be es-timated utilizing the distribution curves of irregular wave run-up.     

Experimental Study on the Bed Shear Stress Under Breaking Waves

The object of present study is to investigate the bed shear stress on a slope under regular breaking waves by a novel instrument named Micro-Electro-Mechanical System (MEMS) flexible hot-film shear stress sensor. The sensors were calibrated before application, and then a wave flume experiment was conducted to study the bed shear stress for the case of regular waves spilling and plunging on a 1:15 smooth PVC slope. The experiment shows that the sensor is feasible for the measurement of the bed shear stress under breaking waves. For regular incident waves, the bed shear stress is mainly periodic in both outside and inside the breaking point. The fluctuations of the bed shear stress increase significantly after waves breaking due to the turbulence and vortexes generated by breaking waves. For plunging breaker, the extreme value of the mean maximum bed shear stress appears after the plunging point, and the more violent the wave breaks, the more dramatic increase of the maximum bed shear stress will occur. For spilling breaker, the increase of the maximum bed shear stress along the slope is gradual compared with the plunging breaker. At last, an empirical equation about the relationship between the maximum bed shear stress and the surf similarity parameter is given, which can be used to estimate the maximum bed shear stress under breaking waves in practice.     

Experimental Investigation of Irregular Wave Uplift Force on Deck of Exposed High-Pile Jetties

A laboratory setup was developed to investigate irregular wave uplift loads on exposed high-pile jetties.It is shown that the dimensionless uplift load increases to the maximum with an increasing relative clearance and then decreases.The relative clearance corresponding to the peak force is linked to a range from 0.4 to 0.8.When the relative clearance exceeds a certain value,the wave can not reach the underside of the deck and the force becomes zero.Distinct trends of dimensionless force with a relative width of deck show that the force tends to decrease as the relative deck width increases,and then the decrease slows down after the relative deck width increases or decreases to a certain value.The pressure distribution length associated with the maximum uplift force is equivalent to the wave contact width x.When x is larger than the width of deck B,it is taken as B.The statistical distribution of loads obeys the Weibull distribution.The results from the analyses of the real data suggest a new dimensionless prediction model on wave-in-deck uplift loads and the conversion ratio between wave loads at different exceedance probabilities.A comparison is made between the new prediction model and the existing widely used three prediction models.These results are used as useful references for structural design of the jetty.     

Study of Wave and Tide Influence on Slope Stability of the Navigation Channel of Tianjin Port

The Tianjin Port is the largest man-made port in China.Since the navigation channel of the Tianjin Port is constructed by dredging,a very important problem,as many people concerned,is the submarine slope stability.As the environment on land is different from that in submarine,it is necessary to evaluate the influence of the environmental loading,such as wave and tide,on the stability of navigation channel slope.In the present study,based on the observed results,the characteristics of the navigation channel slope are summarized,and the causes of creating the special slope shape are analyzed.The roles of waves and tides are evaluated,and failure mechanics are discussed to helq us predict what will happen in the future.