NUMERICAL SIMULATION OF SOLITARY WAVE RUN-UP AND OVER-TOPPING USING BOUSSINESQ-TYPE MODEL

In this article,the use of a high-order Boussinesq-type model and sets of laboratory experiments in a large scale flume of breaking solitary waves climbing up slopes with two inclinations are presented to study the shoreline behavior of breaking and non-breaking solitary waves on plane slopes.The scale effect on run-up height is briefly discussed.The model simulation capability is well validated against the available laboratory data and present experiments.Then,serial numerical tests are conducted to study the shoreline motion correlated with the effects of beach slope and wave nonlinearity for breaking and non-breaking waves.The empirical formula proposed by Hsiao et al.for predicting the maximum run-up height of a breaking solitary wave on plane slopes with a wide range of slope inclinations is confirmed to be cautious.Furthermore,solitary waves impacting and overtopping an impermeable sloping seawall at various water depths are investigated.Laboratory data of run-up height,shoreline motion,free surface elevation and overtopping discharge are presented.Comparisons of run-up,run-down,shoreline trajectory and wave overtopping discharge are made.A fairly good agreement is seen between numerical results and experimental data.It elucidates that the present depth-integrated model can be used as an efficient tool for predicting a wide spectrum of coastal problems.     

NUMERICAL SIMULATION OF TWO-DIMENSIONAL OVERTOPPING AGAINST SEAWALLS ARMORED WITH ARTIFICIAL UNITS IN REGULAR WAVES

A new mathematical model for the overtopping against seawalls armored with artificial units in regular waves was established. The 2-D numerical wave flume, based on the Reynolds Averaged Navier-Stokes (RANS) equations and the standard k-ε turbulence model, was developed to simulate the turbulent flows with the free surface, in which the Volume Of Fluid (VOF) method was used to handle the large deformation of the free surface and the relaxation approach of combined wave generation and absorbing was implemented. In order to consider the effects of energy dissipation due to the armors on a slope seawall, a porous media model was proposed and implemented in the numerical wave flume. A series of physical model experiments were carried out in the same condition of the numerical simulation to determine the drag coefficient in the porous media model in terms of the overtopping discharge. Compared the computational value of overtopping over the seawall with the experimental data, the values of the effective drag coefficient was calibrated for the layers of blocks at different locations along the seawalls.     

LOCAL SCOUR AROUND A LARGE-SCALE VERTICAL CIRCULAR CYLINDER DUE TO COMBINED WAVE-CURRENT ACTION

The local scour around a large scale vertical circular cylinder due to combined wave-current action was experimentally and numerically studied in the present paper. Experiments were carried out to research the affect of the wave height, current velocity and the diameter of the cylinder on the scour process. The topography near the cylinder in various cases during scour was measured. The cylinder diameter affects the distribution of scour and deposition area. The maximum scour depth increases evidently when the current velocity increases, The maximum scour depth does not increase after the wave height retains a certain value. A numerical model using a finite element method for simulating the scour process was established. And the numerical results agree well with the measured data. The numerical model is more applicable in the case of large-scale cylinders.     

DuaISPHysics：A numerical tool to simulate real breakwaters

The open-source code DualSPHysics is used in this work to compute the wave run-up in an existing dike in the Chinese coast using realistic dimensions, bathymetry and wave conditions. The GPU computing power of the DualSPHysics allows simulating real-engineering problems that involve complex geometries with a high resolution in a reasonable computational time. The code is first validated by comparing the numerical free-surface elevation, the wave orbital velocities and the time series of the run-up with physical data in a wave flume. Those experiments include a smooth dike and an armored dike with two layers of cubic blocks. After validation,the code is applied to a real case to obtain the wave run-up under different incident wave conditions. In order to simulate the real open sea, the spurious reflections from the wavemaker are removed by using an active wave absorption technique.     

EXPERIMENTAL INVESTIGATION ON WAVE RUN-UP CHARACTERISTICS ALONG COLUMNS AND AIR GAP RESPONSE OF SEMI-SUBMERSIBLE PLATFORM

This article mainly concentrates on a large-volume drilling semi-submersible platform,aiming to reveal wave run-up characteristics along square columns and give the relationship between air gap distributions and wave parameters.The tests with fixed model were conducted firstly on its encountering a series of monochromatic waves.A wide range of wave slope (H /L) were selected to investigate the air gap response in detail.As can be seen,larger wave steepness will generally cause smaller air gap in the same wave period,which indicates nonlinear effects of incoming wave can amplify wave elevation.Model tests with mooring condition were also conducted in the same wave conditions.As was expected,the maximum relative wave elevation reduces obviously compared with the fixed one.However,wave shape close to columns show higher harmonic characteristics due to interaction between waves and the columns of semi-submersible platform.Meaningful conclusions from the model tests are drawn in this article,which is helpful in air gap design of floating offshore platform to a certain extent.In addition,the experimental results will provide an important reference for further research on validation and update of theoretical models of air gap.     

PIV MEASUREMENTS OF THE NEAR-WAKE FLOW OF AN AIRFOIL ABOVE A FREE SURFACE

The near-wake flow of a NACA0012 airfoils mounted above a water surface were experimentally studied in a wind/wave tunnel. The main objective of this study is to investigate the influence of the free surface on the structure of the airfoil trailing wake. The flow structure was measured with different ride heights between the airfoil and free surface using a Particle Image Velocimetry (PIV) system. The Reynolds number based on the chord length of the airfoil was about 3.5×103. For each experimental condition, large amount of instantaneous velocity fields were captured and ensemble-averaged to get the spatial distributions of mean velocity and mean vorticity, as well as turbulence statistics. The results show that the flow structures of the airfoil wake varies remarkably with the change in the ride height.     

A STUDY OF WAVE CHARACTERISTICS AFTER HYDRAULIC JUMP

An experimental study of wave characteristics after jump in energy dissipation ofhydraulic jump is presentedinthis paper.It was completed in a trough with a horizontal bed,40cm in width.Various elements of wave were measured,the wave form,period,spectrumand its attenuation along course are analyzed,and the physical mechanism of wave is discussed.An expression of the maximum wave height after jump is given,based on the measured data.Some measures to diminish wave are discussed preliminarily also.     

STUDY OF NON-BOUSSINESQ EFFCET ON SEA SURFACE HEIGHT

A set of equations was derived for a nonBoussinesq ocean model in this paper. A new time-splitting scheme was introduced which incorporates the 4th-order Runge-Kutta explicit scheme of low-frequency mode and an implicit scheme of high-frequency mode. With this model, potential temperature, salinity fields and sea surface height were calculated simultaneously such that the numerical error of extrapolation of density field from the current time level to the next one could be reduced while using the equation of mass conservation to determine sea surface height. The non-Boussinesq effect on the density field and sea surface height was estimated by numerical experiments in the final part of this paper.     

Application of CLEAR-VOF method to wave and flow simulations

A two-dimensional numerical model based on the Navier-Stokes equations and computational Lagrangian-Eulerian advection remap-volume of fluid (CLEAR-VOF) method was developed to simulate wave and flow problems. The Navier-Stokes equations were discretized with a three-step finite element method that has a third-order accuracy. In the CLEAR-VOF method, the VOF function F was calculated in the Lagrangian manner and allowed the complicated free surface to be accurately captured. The propagation of regular waves and solitary waves over a flat bottom, and shoaling and breaking of solitary waves on two different slopes were simulated with this model, and the numerical results agreed with experimental data and theoretical solutions. A benchmark test of dam-collapse flow was also simulated with an unstructured mesh, and the capability of the present model for wave and flow simulations with unstructured meshes, was verified. The results show that the model is effective for numerical simulation of wave and flow problems with both structured and unstructured meshes.     

ABRUPT DEFLECTED SUPERCRITICAL WATER FLOW IN SLOPED CHANNELS

The effect of the bottom slope on abrupt deflected supercritical water flow was experimentally and theoretically studied. Model tests were conducted in a flume of 1.2 m wide and 2.6 m long with sloped bottom at an angle 35.54°, its length of deflector was 0.2 m and the deflection angles were 15° and 30°. An approximate method for calculating the shock wave angle and depth ratio of the abrupt deflected supercritical water flow was suggested, and a correction coefficient for the hydrodynamic pressure was introduced to generalize the momentum equation in the direction perpendicular to the shock front. It must be noticed that in the sloped channel the shock wave angle and the depth ratio are no longer constant as those in the horizontal channels, but slowly change along the shock front. The calculated results are in good agreement with measured data.     

斜坡式海堤结构尺度对越浪量的影响研究

为系统研究坡式海堤结构尺度对越浪量的影响,开展了相关波浪水槽试验,在观察越浪量试验现象的基础上,分别研究了斜坡坡度、防浪墙顶超高、防浪墙高度对斜坡式海堤越浪量的影响。结果表明:防浪墙顶超高对越浪量的影响最为显著,越浪量随防浪墙顶超高的增大而减小,且减小趋势随之变缓,无量纲形式下的越浪量随相对防浪墙顶超高的增大呈现较明显的指数递减关系;随着斜坡坡度的增大,因斜坡面上损耗能量的增加大于反射能量的减少,越浪量总体呈现减小的变化趋势,斜坡坡度对越浪量的影响不及防浪墙顶超高;防浪墙顶超高一旦确定,防浪墙高度对越浪量的影响相对较小。     

高滩陡坡地形下电力设施海堤的越浪量试验

以浙江舟山某海岛高滩陡坡地形下的电力设施海堤为例,通过物理模型试验,分别研究了平台宽度、平台超高、防浪墙高度对海堤越浪量的影响,并采用方差分析法进行了敏感性分析。结果表明:平台超高对越浪量的影响最为显著,防浪墙高度次之,平台宽度影响最小;无量纲形式下的越浪量随防浪墙顶超高的增大呈现较明显的指数递减关系。据此提出了电力设施海堤防浪结构的合理设置方式。     

孤立波翻越防波堤流动的湍流数值模拟

应用湍流数学模型和流体体积法模拟孤立波翻越防波堤的流动和自由表面变化。数模成功地再现了波浪涌顶和喷射、射流入水、自由表面破碎和漩涡产生等复杂流动过程,并获得了孤立波翻越防波堤时的压力分布。     

数值模拟波浪翻越直立方柱

本文应用ＶＯＦ方法研究了孤立波翻越直立方柱流动的全过程。用人工压缩法和差分法求解二维Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程，用施主－受主法求解流体体积函数控制方程。通过数值计算得到了孤立波翻越直立方柱的流场和压力值，并成功地模拟出波浪涌顶，水柱喷射，冲击和界面破碎的过程。     

应对超高水位的海堤加高方案波浪模型试验研究

通过对波浪越浪量、波压力等要素的测定与分析,对超高水位及相应台风大浪下的海堤加高方案进行了初步探索。试验实例表明,在堤顶内侧设置一定高度的挡墙可挡住越浪水体下部的楔形连片水体,从而有效减少作用于海堤背坡的越浪量,该例中堤顶内侧挡墙的实测最大越浪压力达到148.8 kPa,作用位置可在挡墙底部或近底部。     

内河航道中船行波在岸坡爬高的数值模拟

该文基于RANS方程、RNG k-ε湍流模型建立数值波浪水池,用VOF法追踪自由面的位置,并模拟了内河航道中船行波的生成、传播、爬高和岸壁反射过程,且与典型断面航道中船行波在岸坡最大爬高和回落的现场测量值进行了比较,验证了数值模型的有效性。通过对航道中船行波进行数值模拟,获得了船行波的波形及其在岸坡上爬高与回落的最大值。分析了船舶吃水、航速和航道岸坡倾角对特征波高以及最大爬高与回落的影响。最后建立了计算船行波特征波高、爬高和回落的经验公式。     

不同护坡条件下波浪溢流海堤内坡水动力特征

波浪溢流指强风暴潮引起堤前水位超过堤顶,海堤受到的越浪与溢流联合作用。波浪溢流一旦发生,极易引起大范围的海堤内坡侵蚀乃至溃堤,产生灾难性后果。基于1:1的大型水槽试验,分析了波浪溢流过程中不同海堤内坡护坡条件下(碾压混凝土、铰接式护坡砖和高性能加筋草皮)海堤内坡水力学特征;建立了相应的内坡平均水深和平均流速计算模型,计算结果表明波浪溢流过程中海堤内坡上的波高分布仍符合瑞利分布,并分析了内坡上的特征波高和特征峰值水深之间的换算关系;提出了波浪溢流过程中海堤内坡上的均方根波高和波速经验计算式。     

带异形块体海堤越浪的数值模拟

该文在FLUENT软件平台上，发展了数值消波-造波技术，通过在动量方程里添加多孔介质源项，建立了带有多孔介质模型的二维数值波浪水槽。应用该数值波浪水槽，数值模拟了在斜坡堤坡面上铺设异形块体情况下的越浪过程，给出了越浪量。为了率定异形块体的等效惯性阻力系数，进行了典型工况的物理模型实验，给出了在斜坡堤坡面上不同位置处铺设一层异形块体情况下多孔介质模型的等效阻力系数。     

水库滑坡涌浪爬坡特征试验研究

由滑坡引起的涌浪灾害不仅严重威胁航运安全,还会冲毁码头、大坝等水工建筑物并造成沿岸居民生命财产的损失。采用物理模型试验的方法对散粒体滑坡涌浪的爬坡特性开展了研究。试验结果表明：影响涌浪爬坡高度的主要因素有滑坡入水速度、滑坡体规模、滑动面倾角、水深、传播距离和爬坡角度等;当涌浪远场传播形态类似椭圆余弦波或孤立波时,涌浪爬坡高度较高,岸坡处水流紊动剧烈,涌浪对岸坡的破坏能力也最强。根据试验结果还建立了近岸坡处涌浪最大波幅计算模型,并结合经典波浪爬坡经验公式推导出了新滑坡涌浪爬坡高度计算公式。以长江新滩滑坡为例,验证了新涌浪爬坡高度计算公式的精度。研究结果能为实际工程中可能存在的滑坡涌浪爬坡灾害范围预测和涌浪避险方案制定等提供一定参考。