离岸式潜堤对海堤越浪量影响的实验研究

外海波浪作用下海堤越浪是一个复杂的水动力学过程,越浪量则是评估海堤安全的重要因素之一。离岸式潜堤作为一种典型的护岸工程结构物,已被应用于淤泥质海岸复合式海堤工程,其主要作用是促淤保滩和降低越浪量。本文针对不同的潜堤与海堤距离以及不同的潜堤高程,进行了规则波作用下越浪量系列物理模型实验,给出了各工况下的实测越浪量。实验结果表明:潜堤是否导致波浪破碎是控制海堤越浪量的主要因素之一;当潜堤使得波浪破碎时,潜堤位置对海堤越浪量有较大影响。潜堤与海堤距离接近1/2波长时越浪量偏大。     

孤立波斜坡堤堤顶及后坡越浪流数值分析

孤立波往往被用来模拟海啸等浅水大波.运用基于RANS方程、VOF方法以及Goring造波方法建立了二维数值波浪水槽,进行了孤立波在简单斜坡堤上越浪过程的数值模拟.通过数值模拟,研究了不同相对堤顶宽及不同相对波高条件下对孤立波越堤流基本特征,包括堤顶前缘水层厚度及速度、堤顶末端水层厚度及速度、堤顶流厚度及速度沿程分布、后坡流厚度及速度沿程分布.依据数值实验结果,建立了堤顶流最大厚度分布及最大速度分布的经验公式.计算结果表明,堤顶流厚度沿程减小,而堤顶流速度则沿程增大;后坡流厚度先增大,随后再沿程缓慢减小;后坡流速度先减小,随后再沿程缓慢增大.     

基于VPM-THINC/QQ模型的波浪高保真模拟

为实现波浪传播的高保真数值模拟,采用包含单元均值和点值(volume-average/point-value method,VPM)的有限体积法求解纳维-斯托克斯方程和具有二次曲面性质和高斯积分的双曲正切函数(THINC method with quadratic surface representation and Gaussian quadrature,THINC/QQ)方法来重构自由面,建立以开源求解库OpenFOAM底层函数库为基础的VPM-THINC/QQ模型.在本模型中添加推板造波法实现波浪的产生功能,采用松弛法实现消波功能,构建高精度黏性流数值波浪水槽.分别采用VPM-THINC/QQ模型和InterFoam求解器(OpenFOAM软件包中广泛使用的多相流求解器)开展规则波的数值模拟,重点探究网格大小和时间步长等因素对波浪传播过程的影响,定量地分析波高衰减程度;为验证本模型的适应性,对长短波进行模拟.结果表明,在相同网格大小或时间步长条件下,VPM-THINC/QQ模型的预测结果与参考值吻合较好,波高衰减较少,且无相位差,在波浪传播过程的模拟中呈现出良好的保真性.本文工作为波浪传播的模拟研究提供了一种高精度的黏性数值波浪水槽模型.     

基于VPM-THINC/QQ模型的波浪高保真模拟

为实现波浪传播的高保真数值模拟,采用包含单元均值和点值(volume-average/point-value method,VPM)的有限体积法求解纳维-斯托克斯方程和具有二次曲面性质和高斯积分的双曲正切函数(THINC method with quadratic surface representation and Gaussian quadrature,THINC/QQ)方法来重构自由面,建立以开源求解库OpenFOAM底层函数库为基础的VPM-THINC/QQ模型. 在本模型中添加推板造波法实现波浪的产生功能,采用松弛法实现消波功能,构建高精度黏性流数值波浪水槽. 分别采用VPM-THINC/QQ模型和InterFoam求解器(OpenFOAM软件包中广泛使用的多相流求解器)开展规则波的数值模拟,重点探究网格大小和时间步长等因素对波浪传播过程的影响,定量地分析波高衰减程度;为验证本模型的适应性,对长短波进行模拟. 结果表明,在相同网格大小或时间步长条件下,VPM-THINC/QQ模型的预测结果与参考值吻合较好,波高衰减较少,且无相位差,在波浪传播过程的模拟中呈现出良好的保真性. 本文工作 为波浪传播的模拟研究提供了一种高精度的黏性数值波浪水槽模型.      

二层密度分层流体重力流的数值模拟

从RANS方程和RNGk-ε湍流模型出发,采用流体体积法(VOF)来模拟密度分层流动,对盐水和淡水因密度差异导致的分层重力流动现象进行了数值模拟.文中报道了平底水槽重力流、狭孔交换流的数值模拟结果,分层重力流锋面运动速度的计算值与现有的半理论半经验公式一致.为了揭示地形变化对分层重力流的影响,对设有缓变潜堤的水槽内分层重力流动的形成过程进行了数值模拟,给出了重力头推进速度和局部流场的计算结果,并讨论了分层流界面、流量和锋面附近的流速分布特征.     

波浪与新型双排开孔圆筒防波堤相互作用三维数值模拟

双排开孔圆筒防波堤是基于圆筒、板式结构的一种复合式新型结构型式;基于不可压缩两相流模型建立三维数值波浪水槽,通过RNG k-ε湍流模型进行湍流封闭,并采用TruVOF方法捕捉自由液面,开展波浪与双排开孔圆筒防波堤相互作用数值模拟,探究相对排间距、开孔率对新型双排开孔圆筒防波堤消浪性能的影响,分析了后排开孔圆筒防波堤附近的复杂水动力现象和流动特性.结果表明,在本文研究工况范围内,沿程平均波高随相对排间距的增大先增大后减小,随开孔率的增大而增大,周期对沿程平均波高的影响没有明显规律;当B/D=9, e=23.11%时,新型双排开孔圆筒防波堤消浪效果最优,反射系数在0.4～0.46之间,透射系数在0.3～0.35之间,耗散系数在0.8～0.85之间;自由液面破碎、水气掺混、环状涡运动演化是新型双排开孔圆筒防波堤紊动耗能消波的主要原因;相对排间距会引起后排防波堤附近涡量分布以及剪切层形态的变化,从而导致不同的紊动特性,影响双排开孔圆筒防波堤消浪特性.研究结果可以为新型双排开孔圆筒防波堤工程设计与消浪机理研究提供理论支撑.     

波浪破碎的一种混合湍流模拟模式

近岸波浪的变形与破碎,一方面影响水体与泥沙运输,另一方面对消波护岸具有指导意义.本文提出一种三维混合湍流模拟模式方法,将求解区域分为造波区、波浪传播区和消波区.造波区采用层流模式,通过基于Fluent的二次开发的UDF方法在边界进行速度造波.这种方法在给定入口速度的条件下,根据已知波高进行精准插值,从而控制水的体积分数.在波浪传播区域,采用大涡模拟进行模拟研究,在消波区,采用RANS模型并利用多孔介质消波法进行消波.模型通过VOF方法捕捉波浪破碎过程中的自由面变化.本文对波高为5.5 cm的规则波(M1)、波高为13.5cm的规则波(M3)、有效波高为7.75cm的TMA谱单向不规则波(U1)和有效波高为19cm的TMA谱多向不规则波(B5)展开了模拟研究,并与前人的相关实验结果作比较,各条件下模拟结果与实验结果吻合.模拟结果说明本文提出的模型能够准确模拟出波浪传播过程中的折射和绕射现象,并且能够捕捉的波浪破碎过程中的自由面变化,为三维波浪的传播与破碎的数值模拟提供一种模拟方法.     

INTERNAL SOLITARY WAVE LOADS EXPERIMENTS AND ITS THEORETICAL MODEL FOR A CYLINDRICAL STRUCTURE

在大型重力式密度分层水槽中, 对内孤立波与圆柱型结构的相互作用特性开展了系列实验. 基于两层流体中 内孤立波的KdV,eKdV和MCC理论, 建立了圆柱型结构内孤立波载荷的理论预报模型, 给出了该载荷理论预报模型中3类内孤立波理论的适用性条件.研究表明, 圆柱型结构内孤立波水平载荷包括水平Froude-Krylov力、附加质量力和拖曳力3个部分, 可以由Morison公式计算, 而内孤立波垂向载荷主要为垂向Froude-Krylov力, 可以由内孤立波诱导动压力计算.系列实验结果表明, 附加质量系数可以取为常数1.0, 拖曳力系数与内孤立波诱导速度场的雷诺数之间为指数函数关系, 而且基于理论预报模型的数值结果与系列实验结果吻合.     

波浪破碎的一种混合湍流模拟模式

近岸波浪的变形与破碎,一方面影响水体标识码运输,另一方面对消波护岸具有指导意义.本文提出一种三维混合湍流模拟模式方法,将求解区域分为造波区、波浪传播区和消波区. 造波区采用层流模式,通过基于 Fluent 的二次开发的 UDF 方法在边界进行速度造波.这种方法在给定入口速度的条件标识码据已知波高进行 精准插值,从而控制水的体积分数. 在波浪传播区域,采用大涡标识码行模拟研究,在消波区,采用 RANS 模型并利用多孔介质消波法进行消波. 模标识码 VOF 方法捕捉波浪破碎过程中的自由面变化.本文对波高为 5.5cm 的规则波 (M1)、波高为 13.5cm 的 规则波 (M3)、有效标识码 7.75cm 的 TMA 谱单向不规则波 (U1) 和有效波高为 19cm 的 TMA 谱多向不规则波 (B5) 展开标识码研究,并与前人的相关标识码果作比较,各条件下模拟结果与实验结果吻合.模拟结果说明本文提出的模型能够准确模拟出波浪传播过程中的折射和标识码象,并且能够捕捉的波浪破碎过程中的自由面变化,为三维波浪的传播与破碎的数值模拟提供一种模拟方法.      

横浪中的波浪二阶力计算

本文提出了用基于多极展开的切片法来计算横浪规则波中的波浪二阶力。把本文的计算方法和实验与其它方法相比较结果是令人满意的，并且计算量不大。因而这是一种实用的数值计算方法。     

Scale effects in subaerial landslide generated impulse waves

Hydraulic scale modelling involves scale effects. The limiting criteria for scale models of subaerial landslide generated impulse waves including solid, air, and water are discussed both based on a literature review and based on detailed two-dimensional experimentation. Seven scale series based on the Froude similitude were conducted involving the intermediate-water wave spectrum. Scale effects were primarily attributed to the impact crater formation, the air entrainment and detrainment, and the turbulent boundary layer as a function of surface tension and fluid viscosity. These effects reduce the relative wave amplitude and the wave attenuation as compared with reference experiments. Wave amplitude attenuation was found to be more than 70 times larger than predicted with the standard wave theory. Limitations for plane impulse wave generation on the basis of the present research are given by which scale effects can be avoided.     

Numerical simulation of solitary waves overtopping on a sloping sea dike using a particle method

Sea dikes, as a commonly used type of coastal protection structures, are often attacked or damaged by violent waves overtopping under tsunamis and storm surges. In this study, the behavior of solitary waves traveling on a sloping sea dike is simulated, and solitary wave overtopping characteristics are analyzed using a complete Lagrangian numerical method, the moving particle semi-implicit (MPS) method. To better describe the complicated fluid motions during the wave overtopping process, the original MPS method is modified by introducing a new free surface detection method, i.e., the area filling rate identification method, and a modified gradient operator to provide higher precision. Meanwhile, the approximation method for sloping boundaries in particle methods is enhanced, and a smooth slope approximation method is proposed and recommended. To verify the improved MPS method, a solitary wave traveling over a steep sloping bed is studied. The entire solitary wave run-up and run-down processes and exquisite water movements are reproduced well by the present method, and are consistent with the corresponding experimental results. Subsequently, the improved MPS method is applied to investigate the overtopping process of a single solitary wave over a sloping sea dike. The results show that the hydraulic jump phenomenon is also possible to occur during the run-down motion of the solitary wave overtopping. Finally, the characteristics of the propagation and overtopping of two successive solitary waves on a sloping sea dike are discussed. The result manifests that the interaction between adjacent solitary waves affects wave overtopping patterns and overtopping velocities.     

微重力条件下部分充液贮箱气液界面波动特性的数值模拟

微重力环境中部分充液贮箱内气液界面和气、液两相介质在残余重力或加速度干扰下的运动特征是先进空间流体管理技术的基础. 本文针对空间贮箱常用构型和实际尺寸, 基于邦德数相似准则设计了3个缩比模型, 数值模拟了原型贮箱和缩比模型中加速度变化引起的贮箱内气液两相流动及气液界面上界面波的传播. 数值模拟结果验证了原型和模型间的运动相似性, 发现在满足邦德数相似准则的前提下, 系统还近似满足韦伯数相似准则, 或等价地, 近似满足弗劳德数相似准则. 此外, 数值模拟结果也表明原型和模型间的运动存在细微偏差, 这主要源于黏性耗散作用的差异. 由韦伯数相似准则可知, 缩比加大, 贮箱尺寸减小, 重力突变后由表面张力释放出来的驱动力增强, 相同韦伯数下流动速度增大, 黏性耗散作用随之增强, 本文的数值模拟结果证实了该结论. 相关结果可以用于指导空间贮箱流体管理技术的地面模拟试验的方案设计等.      

Generation of two-dimensional steep water waves on finite depth with and without wind

This paper reports on a series of numerical simulations designed to investigate the action of wind on steep waves and breaking waves generated through the mechanism of dispersive focusing on finite depth. The dynamics of the wave packet propagating without wind at the free surface are compared to the dynamics of the packet propagating in the presence of wind. Wind is introduced in the numerical wave tank by means of a pressure term, corresponding to the modified Jeffreys' sheltering mechanism. The wind blowing over a strongly modulated wave group due to the dispersive focusing of an initial long wave packet increases the duration and maximal amplitude of the steep wave event. These results are coherent with those obtained within the framework of deep water. However, steep wave events are less unstable to wind perturbation in shallow water than in deep water.Furthermore, a comparison between experimental and numerical wave breaking is presented in the absence of wind. The numerical simulations show that the wind speeds up the wave breaking and amplifies slightly the wave height.The wall pressure during the runup of the steep wave event on a vertical wall is also investigated and a comparison between experimental and numerical results is provided.     

Incompressible SPH simulation of wave breaking and overtopping with turbulence modelling

In this paper a truly incompressible version of the smoothed particle hydrodynamics (SPH) method is presented to investigate the surface wave overtopping. SPH is a pure Lagrangian approach which can handle large deformations of the free surface with high accuracy. The governing equations are solved based on the SPH particle interaction models and the incompressible algorithm of pressure projection is implemented by enforcing the constant particle density. The two‐equation k–ε model is an effective way of dealing with the turbulence and vortices during wave breaking and overtopping and it is coupled with the incompressible SPH numerical scheme. The SPH model is employed to reproduce the experiment and computations of wave overtopping of a sloping sea wall. The computations are validated against the experimental and numerical data found in the literatures and good agreement is observed. Besides, the convergence behaviour of the numerical scheme and the effects of particle spacing refinement and turbulence modelling on the simulation results are also investigated in further detail. The sensitivity of the computed wave breaking and overtopping on these issues is discussed and clarified. Copyright © 2005 John Wiley & Sons, Ltd.     

Evolution of wide-spectrum unidirectional wave groups in a tank: an experimental and numerical study

Evolution of unidirectional nonlinear wave groups with wide spectra is studied experimentally and numerically. As an example of such an evolution, focusing of an initially wide wave train that is modulated both in amplitude and in frequency, to a single steep wave at a prescribed location along the laboratory wave tank is investigated. When numerous frequency harmonics arrive at the focusing location in phase, a very wave steep single emerges. The experimental study was carried out in two wave flumes that differ in size by an order of magnitude: a 330 m long Large Wave Channel in Hanover, and in 18 m long Tel-Aviv University wave tank. The spatial version of the Zakharov equation was applied in the numerical simulations. Detailed quantitative comparison is carried out between the experimental results and the numerical simulations. Spectra of the 2nd order bound waves are calculated using the theoretical model adopted. It is demonstrated that with the contribution of bound waves accounted for, a very good agreement between experiments and simulations is achieved.     

Experimental and numerical analysis of solitary waves generated by bed and boundary movements

This paper is an experimental and numerical study about propagation and reflection of waves originated by natural hazards such as sea bottom movements, hill slope sliding and avalanches. One‐dimensional flume experiments were conducted to study the characteristics of such waves. The results of the experimental study can be used by other researchers to verify their numerical models. A finite volume numerical model, which solves the shallow water equations, was also verified using our own experimental results. In order to deal with reflection on sloping surfaces and overtopping walls, a new condition for the treatment of the coastline is suggested. The numerical simulation of wave generation is also studied considering the bed movement. A boundary condition is proposed for this case. Those situations when the shallow water equations are valid to simulate this type of phenomena have been studied, as well as their limitations. Copyright © 2004 John Wiley & Sons, Ltd.     

Multi‐scale simulation with a hybrid Boussinesq‐RANS hydrodynamic model

A hybrid wave model is developed for simulation of water wave propagation from deep water to shoreline. The constituent wave models are the irrotational, 1‐D horizontal Boussinesq and 2‐D vertical Reynolds‐averaged Navier–Stokes (RANS). The models are two‐way coupled, and the interface is placed at a location where turbulence is relatively small. Boundary conditions on the interfacing side of each model are provided by its counterpart model through data exchange. Prior to the exchange, a data transformation step is carried out due to the differences in physical variables and approximations employed in both models. The hybrid model is tested for both accuracy and speedup performance. Tests consisting of idealized solitary and standing wave motions and wave overtopping of nearshore structures show that: (1) the simulation results of the current hybrid model compare well with the idealized data, experimental data, and pure RANS model results and (2) the hybrid model saves computational time by a factor proportional to the reduction in the size of the RANS model domain. Finally, a large‐scale tsunami simulation is provided for a numerical setup that is practically unapproachable using RANS model alone; not only does the hybrid model offer more rapid simulation of relatively small‐scale problems, it provides an opportunity to examine very large total domains with the fine resolution typical of RANS simulations. Copyright © 2009 John Wiley & Sons, Ltd.     

Numerical simulations of wave interactions with vertical wave barriers using the SPH method

This paper focuses on the fluid boundary separation problem of the conventional dynamic solid boundary treatment (DSBT) and proposes a modified DSBT (MDSBT). Classic 2D free dam break flows and 3D dam break flows against a rectangular box are used to assess the performance of this MDSBT in free surface flow and violent fluid–structure interaction, respectively. Another test, water column oscillations in a U‐tube, is specially designed to reveal the applicability of dealing with two types of particular boundaries: the wet–dry solid boundary and the large‐curvature solid boundary. A comparison between the numerical results and the experimental data shows that the MDSBT is capable of eliminating the fluid boundary separation, improving the accuracy of the solid boundary pressure calculations and preventing the unphysical penetration of fluid particles. Using a 2D SPH numerical wave tank with MDSBT, the interactions between regular waves and a simplified vertical wave barrier are simulated. The numerical results reveal that the maximum horizontal force occurs at the endpoint of the vertical board, and with the enlargement of the relative submerged board length, the maximum moment grows linearly; furthermore, the relative average mass transportation under the breakwater initially increases to 11.14 per wave strike but is later reduced. The numerical simulation of a full‐scale 3D wave barrier with two vertical boards shows that the wave and structure interactions in the practical project are far more complicated than in the simplified 2D models. The SPH model using the MDSBT is capable of providing a reference for engineering designs. Copyright © 2014 John Wiley & Sons, Ltd.