REFLECTION OF OBLIQUE INCIDENT WAVES BY PERFORATED CAISSONS WITH TRAVERSE WALL

The interaction of oblique incident waves with infinite number of perforated caissons is investigated. The fluid domain is divided into infinite sub-domains by the caissons, and eigen-function expansion is applied to expand velocity potentials in each domain. A phase relation is introduced for wave oscillation in each caisson, and the structure geometry is considered in constructing the models of reflection waves. The reflected waves with the present analysis include all of the waves traveling in different directions when incident wave period is short. Numerical examinations show that velocities at the inner and outer sides of the front walls of caissons are close to each other, and reflection coefficients satisfy the energy conservation relation very well when porous effect parameter is infinite. Numerical results show that the reflection coefficients of oblique incident waves are smaller for shorter caissons at low frequency, and decrease with the increase of wave incident angle.     

Three-dimensional numerical simulation of wave interaction with perforated quasi-ellipse caisson

The finite difference method and the volume of fluid (VOF) method were used to develop a three-dimensional numerical model to study wave interaction with a perforated caisson.The partial cell method was adopted to solve this type of problem for the first time. The validity of the present model, with and without the presence of caisson structures, was examined by comparing the model results with experimental data. Then, the numerical model was used to investigate the effects of various wave and structure parameters on the wave force and wave runup of the perforated quasi-ellipse caisson. Compared with the solid quasi-ellipse caisson, the wave force on the perforated quasi-ellipse caisson is significantly reduced with increasing porosity of the perforated quasi-ellipse caisson. Furthermore, the perforated quasi-ellipse caisson can also reduce the wave runup, and it tends to decrease with the increase of the porosity of the perforated quasi-ellipse caisson and the relative wave height.     

施工期台风浪作用下沉箱碰撞破坏分析

以“莎莉嘉”台风引起施工期沉箱碰撞破坏为背景,研究台风浪作用下施工期沉箱碰撞破坏模式及机理。提出基于台风浪作用下沉箱碰撞反应分析两步走的数值模拟方法,该方法利用高精度流体模拟软件Flow-3D的造波技术模拟台风引起的波浪传播过程,并与沉箱结构作用获取沉箱波浪力时程曲线;建立沉箱精细化有限元模型,将上述波浪力时程曲线施加于沉箱结构,利用LS-DYNA显式求解器分析沉箱结构的碰撞反应。应用该方法对“莎莉嘉”台风引起施工期沉箱碰撞破坏进行分析,结果表明:数值模拟的沉箱结构在不同波浪方向作用下发生不同角度的碰撞会导致不同的沉箱碰撞破坏模式,波浪作用方向与沉箱前后壁夹角为60°时,沉箱碰撞破坏模式与“莎莉嘉”台风作用期间的现场情况吻合较好。     

局部开孔防波堤对斜向波反射的理论分析和试验研究

本文通过理论分析和试验研究相结合的方法，探讨了斜向规则波与局部开孔防波堤的相互作用。流体运动的计算域被分成两个子域，一个区位于开孔沉箱结构物外侧，另一个区位于结构物内。在每个子区域内，应用分离变量法和特征函数展开法以求得相应的速度势，在速度势的特征展开中考虑了非传播模态波。理论计算与试验结果对比表明，二者符合较好。基于对不同因素影响的分析，给出了斜向规则波在局部开孔结构前反射率的简化计算公式，在工程设计中可用于预估类似条件下结构物前的波浪反射率。     

新型透空组合板式防波堤结构型式及消浪特性分析

为提高透空式防波堤的消浪性能并减小结构受力,在前人研究基础上提出了一种新型透空组合板式防波堤,比较分析了该型式的防波堤(模型c)与另外两种型式的防波堤(模型a和模型b)的结构特点。通过物理模型试验,探讨了模型c在不同影响因素下的消浪特性,并对比分析了模型a与模型c的透射系数、反射系数和能量耗散系数在不同相对堤宽下的变化关系,比较了两种模型的消浪效果。分析得出,由于模型c兼具开孔水平板式防波堤和开孔挡板式防波堤的作用,模型c的波浪反射小于模型a,消浪效果优于模型a,且模型c这种结构能有效减小防波堤结构受力;当模型宽度和相对间隙比同时较大时消浪效果更好,防波堤出水后的消浪性能要优于淹没状态下的防波堤。     

多层水平板衰减波浪的影响因素分析

基于线性波浪理论,进行多层水平板对波浪的反射和透射作用研究。通过分解速度势为对称势和反对称势,结合特征函数展开法,在考虑水平板厚度的条件下由匹配条件确定速度势展开式中的待定系数,进而得到结构对波浪的反射系数和透射系数。所得结果与现有相关的理论解、数值解以及试验结果吻合较好。对相对水深、相对宽度、相对厚度以及水平板层数等对结构衰减波浪的影响进行了深入探讨和分析,给出了反射系数和透射系数随上述参数的变化规律。     

斜坡上封闭水平板波浪上托力试验研究

波浪对平板的上托力是海上透空结构物设计的重要依据，不同布置形式的平板波浪上托力有不同的变化规律。本文通过系列模型试验，对斜坡上尾部封闭的水平板波浪上托力产生的机理进行了详细的分析和论述，认为影响其大小的直接因素与尾部透空情况相同，仍为几何因素、动力因素和空气垫层因素，但各因素对波浪上托力的影响程度发生了很大变化。试验结果表明，板下最大冲击压强与最大总上托力并不总是同步发生，其压强分布形式也不尽相同，应分别考虑。     

吸力式沉箱组合基础承载特性研究

基于吸力式沉箱基础应用于桥梁工程的背景, 考虑不同数量的沉箱组合和沉箱间距, 通过数值模拟的方法研究了吸力式沉箱组合基础的承载特性, 重点分析了组合基础与单个基础承载性状的差异, 以及连接各沉箱的顶板对基础承载力的贡献。计算结果表明, 沉箱组合基础与单个沉箱基础的荷载-位移曲线类型都相同; 受类似于“群桩”效应的影响, 竖向荷载作用下组合基础中的沉箱承载力不能完全发挥, 但由于沉箱之间的连接顶板可以提供阻力, 所以当沉箱间距较大时组合基础的承载力会大于相应数量单个基础的承载力之和, 且随着沉箱间距的增大而增大; 对于水平荷载作用下的吸力式沉箱组合基础, 其承载力大于相应数量单个基础的承载力之和, 连接顶板底部与土体之间的摩擦和挤压对于组合基础承载力的提高可以忽略不计。     

潮汐电站浮运法施工技术综述

在潮汐电站建设中，浮运法施工起着降低造价，缩短工期，改善施工条件等重要作用。本文简要介绍潮汐电站浮运法施工各阶段（预制，拖运，地基处理，沉放）的关键技术，包括选择预制场，控制拖运，开挖和地基加固，定位和安放沉箱等。浮运法施工技术在河床式水电站、码头、海上采油平台、过江（海底）隧道、桥梁、水闸等工程中也有广泛的应用前景。     

箱型结构物封堵溃坝水力学特性试验研究

介绍了用箱型结构物通过爆破下沉方法封堵溃坝的水力学模型试验。基于相似理论，研究堵口过程中的水力学特性变化，得到了溃口附近的流速、流态规律，以及箱体周边的流速情况。成果为实际确定沉箱堵口方案提供了依据，同时也为今后其它堵口技术方案的研究提供参考。     

倾斜荷载作用下吸力桶承载性能分析

以砂土地基中吸力桶为分析对象,建立能够考虑主应力方向旋转的本构模型,通过数值分析方法进行积分,在不同荷载倾斜角度条件下研究等效塑性应变分布及土体主应力方向的旋转变化,分析倾斜荷载对吸力桶承载性能的影响。研究结果表明:等效塑性应变主要在桶壁外围和桶端下部等区域集中分布,桶体内部土体处于弹性变形状态;荷载倾斜角度对竖向荷载-位移关系的影响比较微弱,对水平荷载-位移关系的影响则比较显著;土体主应力方向在变形初期的旋转非常显著,随着倾斜角度的增加,主应力方向的旋转逐渐显著;当竖向位移在(0.05～0.10)D范围时,主应力方向达到稳定状态,不再旋转。     

竖向荷载下裙式吸力基础周围土体变形研究

对饱和细海砂中传统吸力基础与裙式吸力基础开展了竖向单调加载试验和有限元模拟的对比研究,获得了基础周围砂土的变形规律及基础破坏形式,讨论了"裙"结构对基础周围土体变形的影响。研究发现:极限状态下,传统吸力基础周围土体变形范围小于裙式吸力基础周围土体变形范围,减少幅度为31%~55%,说明裙式吸力基础调动了较大范围土体发挥作用以提高其水平承载力。裙宽会引起土体的变形增大,而裙高可以对周围土体进行约束;裙宽相同时,土体变形范围随裙高的增大逐渐减小。在竖向压力荷载作用下,传统吸力基础与裙式吸力基础在砂土中的破坏形式符合Prandtl整体剪切破坏。     

堤坝护面开孔砌块抗浪稳定性试验研究

护面砌块作为堤坝结构的组成部分,其抗浪能力对堤坝的整体稳定起着重要作用。通过较大比尺物理模型,针对我国堤坝设计的具体情况,对一种新型开孔勾连块体的抗浪稳定性进行试验研究,分析砌块厚度、戗台、波浪周期等因素的影响,得到砌块抗风浪稳定厚度计算式。建议护岸设计中应采用均衡设计的理念,综合考虑波浪荷载,将其平衡分配给护面、垫层和基土,对海岸、河流、大型湖泊和水库等水利工程的护岸和堤坝抗浪稳定设计具有指导意义。     

向家坝水电站围堰基础沉井施工下沉阻力监测

 以金沙江向家坝水电站围堰沉井基础为研究对象,对沉井下沉过程中的刃脚土压力、井壁侧摩阻力进行了全面监测。根据大量现场的实测资料,系统地分析了沉井下沉过程中的受力特征,得出了沉井下沉过程中,经过不同深度、不同地层时的刃脚土压力及井壁摩阻力的大小及侧阻力呈抛物线形分布规律,同时提出了下沉系数K值的计算方法。据实测,3次下沉的K值均小于1.15时,表示下沉到位困难。     

A NEW MEASURE FOR DIRECT MEASUREMENT OF THE BED SHEAR STRESS OF WAVE BOUNDARY LAYER IN WAVE FLUME

In this article, a shear plate was mounted on the bottom in a wave flume and direct measurements of the smooth and rough bed shear stress under regular and irregular waves were conducted with the horizontal force exerted on the shear plates by the bottom shear stress in the wave boundary layer. Under immobile bed condition, grains of sand were glued uniformly and tightly onto the shear plate, being prevented from motion with the fluid flow and generation of sand ripples. The distribution of the bottom mean shear stress varying with time was measured by examining the interaction between the shear plate and shear transducers. The relation between the force measured by the shear transducers and its voltage is a linear one. Simultaneous measurements of the bottom velocity were carried out by an Acoustic Doppler Velocimeter (ADV), while the whole process was completely controlled by computers, bottom shear stress and velocity were synchronously measured. Based on the experimental results, it can be concluded that (1) the friction coefficient groews considerably with the increase of the Reynolds number, (2) the shear stress is a function varying with time and linearly proportional to the velocity. Compared with theoretical results and previous experimental data, it is shown that the experimental method is feasible and effective, A further study on the bed shear stress under regular or irregular waves can be carried out. And applicability to the laboratory studies on the initiation of sediments and the measurement of the shear stress after sediment imigration.     

浅论多级孔板消能问题

本文论述了孔板的消能机理、能量损失等消能特性。并通过试验分析找出了影响多级孔板消能各项因素与孔板消能系数之间的关系,为龙抬头泄洪洞选用多级孔板消能设计提供了依据。     

有限深水中沉井的水动力计算

本文提出用特征函数展开和匹配方法计算圆筒形沉井在有限深水中的流体动力系数,其中包括垂荡、纵荡(横荡)、纵摇(横摇)及纵荡与纵摇(横荡与横摇)偶合的附加质量和阻尼系数。用文中推导的公式编制的计算程序,对已发表的有三维源汇分布法计算和实验结果的例子的计算表明本方法有效。本方法的优点是计算速度大大快于其它数值方法,而且计算结果准确。文中对一些形状的沉井进行了计算,得到了其水动力系数的若干变化规律。本文对海洋工程中沉井这一结构物在波浪中的运动估算和结构设计提供了有效手段。     

柔性浮式防波堤消浪特性研究

针对圆柱形柔性浮式防波堤的消浪效果展开断面试验研究,分析其在规则波和不规则波作用下的消浪特性。通过大量水槽试验给出了圆柱形柔性浮式防波堤透射系数、反射系数、衰减系数与锚固方式、试验水深、相对宽度的变化关系。研究结果表明:该结构形式的浮式防波堤对短周期波浪消浪效果明显,而对长周期波浪消浪效果不佳;锚固方式和水深对消浪效果的影响较小;相对宽度是影响消浪效果的主要因素。研究成果可为由该结构连接成的"V"形浮式防波堤的锚固方式和摆放角度的设计提供参考。     

Extreme wave loads on submerged water intakes in shallow water

This paper provides new guidance concerning the hydrodynamic loads on submerged intake structures located in shallow water under breaking and non-breaking waves. Results from a series of experiments conducted in a large wave flume at 1:15 scale to study the hydrodynamic forces exerted on a generic intake structure located on a sloping seabed in shallow water below breaking and non-breaking irregular waves are presented. Based on analysis of the experimental data, empirical relationships are developed to describe the peak loads in terms of characteristic wave parameters such as significant wave height and peak wave period. The distribution of the peak loads across different parts of the intake structure is also described. Drag and inertia force coefficients for the horizontal forcing on the intake structure and for the main structural sub-components are derived and presented. It is shown that the well-known Morison equation, with appropriate drag and inertia force coefficients, can provide reasonable estimates of the moderate horizontal loads, but the peak loads are less well predicted.     

NUMERICAL SIMULATION OF IRREGULAR WAVE-SIMULATING IRREGULAR WAVE TRAIN

In real sea states, damage incidents on offshore floating structures are not due to the whole time series of wave elevation characterized as statistical one but due to few extreme waves or wave groups in irregular wave train. So, using CFD tools to precisely simulate predetermined irregular wave train will lay sound basis for understanding the local characteristic of the flow field and impact loads on offshore floating structures when damage incidents occur. In this article, the generation of single extreme wave is investigated in a numerical wave tank. First, experimental irregular wave train is decomposed into certain number of small-amplitude waves. The Fourier series expansion is performed to determine the amplitude and initial phase angle of each wave component. A hydrodynamic transfer function is used to calculate the amplitude of wave-maker motion associated with each wave component. Then superposition is carried out on all of the wave-maker motion components to get the final wave-maker motion. With the wave-maker motion as input, simulation of the single extreme irregular wave train is modeled successfully. Then the method is applied to simulating a much more complicated irregular wave train. Once again main features of the complicated irregular wave train are reproduced compared with experiment carried out in the new deepwater experimental basin at Shanghai Jiao Tong University. In the simulation, dynamic mesh method is enabled to model the piston-type wave-maker, the Volume Of Fluid (VOF) method is employed to capture the free surface and a dissipation zone is introduced to deal with wave reflection.