规则波中圆形承台对桩基波浪力的影响

近海软基条件中跨海桥梁和风电场工程大多采用承台桩基结构.圆形承台波浪力的计算采用基于线性势流理论和特征函数展开的解析方法,桩柱波浪力的计算采用Morison公式,讨论并发展了波浪对圆形承台及其下部桩柱的作用力的工程计算方法.研究了承台的存在对桩基波浪力的影响,针对某典型桩基结构布置形式给出了承台效应系数和群桩系数随相对水深、无量纲承台半径、相对浸深等参数的变化规律.     

非周期波浪与直墙作用的非线性数值研究

基于时域高阶边界元方法,建立了完全非线性二维数值波浪水槽,对非周期波浪与直墙的相互作用问题进行了模拟和研究.自由表面满足完全非线性自由水面运动学和动力学边界条件,采用混合欧拉-拉格朗日方法追踪瞬时自由面流体质点,采用四阶Runge-Kutta法对下一时间步的波面和自由面速度势进行更新.采用加速度式法求解直墙表面速度势的时间导数,对瞬时物体湿表面上的水动力压强积分,得到作用在物体上的瞬时波浪力.首先,将全非线性与Serre-Green-Naghdi(SGN)模型的结果进行了对比分析,发现对于大幅值双入射波问题,仅满足弱色散关系的SGN模型大大低估了最大波浪爬高;其次,研究了双入射波与直墙的非线性作用问题,发现线性预报对波浪最大爬高有较大低估,而波浪的非线性成分不只导致了自由面爬高的异常增大,也引起了局部自由面的高频振荡,该物理过程中,直墙所受的波浪载荷,也展示出了与波浪爬高相似的非线性特性;最后,对波浪爬升和波浪力的时间历程进行了频谱分析,发现入射主频波的部分能量传递给了更高频的波浪成分,反映出该问题具有典型的非线性特性.     

短峰波与双层开孔圆筒柱相互作用的数值分析

应用比例边界有限元法（SBFEM）研究了短峰波与双层开孔圆筒柱相互作用。该方法将整个计算域划分成两个有限子域和1个无限子域,利用SBFEM使空间维数降低一阶,并在降维方向保持解析的特点,只需对求解域外圆柱边界进行离散。通过比例坐标与直角坐标之间的转换,并利用变分原理推导了各个子域的SBFEM方程。然后,SBFEM针对有限域和无限域分别采用贝塞尔函数和汉克尔函数作为基函数来求解对应域的解,并将计算结果与解析解进行比较,验证了该方法是一种用很少单元便能得到精确结果的高效方法。进一步研究了诸如相对波数ka、内外柱半径比a/b和内外壁孔隙影响系数G等对双层开孔圆筒柱结构所受波浪荷载、结构内外侧波浪爬升及绕射波轮廓的影响。为双层开孔圆筒柱水动力分析和结构设计提供了有价值的参考。     

三维波浪-流-串行桩柱相互作用的数值分析

为探讨波浪-流-串行桩柱的相互作用,建立了三维数值模型,采用大涡模拟(LES)方法对湍流进行模拟。研究了波浪-流-串行桩柱相互作用下的拖曳系数,对波浪-流靠近结构时的非线性相互作用引起的拖曳力和涡的变化,以及在结构前后自由面的变化进行了分析,并且与波浪-流与孤立桩柱相互作用的研究进行比较。结果表明:由于桩柱的存在,在波浪-流的传播过程中出现了时间延迟,这就导致了桩柱前后附近自由面水位存在较大的位移差;由于桩柱之间互相干扰,下游桩柱的存在导致上游桩柱附近不能形成非对称的周期性涡脱落,上游桩柱横向拖曳力受到影响最大,顺方的拖曳力也受到明显影响;下游桩柱横向和顺向的拖曳力都受到较大的影响;同时涡的脱落会把其附近的自由面吸入。     

波浪引起的海底土层中的应力场和位移场

本文分析了波浪压力引起的海底土层中孔隙水流动的状况,给出了简化的力学模型来描述海底土层中孔隙水流动所引起的应力场和位移场.对波浪的分析采用了线性波的理论假设,波浪引起的压力计算采用高斯分布理论.孔隙流体和土骨架都假设为可压缩的,孔隙水在海底土层中的流动满足达西定律.由表示质量守恒的连续性方程与应力平衡方程出发,得到了由位移所表示的高阶微分方程,并给出了海底土层中位移场和应力场的解.其解依赖于孔隙流体和土骨架的相对压缩性,土的泊桑比和剪切模量,以及土介质的渗透率和各向异性等特性.文章还结合实际情况进行了计算,并分析了上述参数的影响.对如何应用上述结果提出了相应的参考意见.     

孤立波与淹没平板相互作用的三维波面和水动力实验研究

在波浪水池中进行了孤立波作用下有限长度和有限宽度淹没平板的三维模型水池实验. 首次应用多目视觉立体重构技术测量局部三维自由表面变形, 该系统的有效测量水平范围为1.7 m$\times $1.6 m. 用4个三分力测力传感器组成水下测力系统, 在不影响波面的情况下测量孤立波对平板的作用力和力矩. 针对波浪不破碎的情况, 选择0.4 m水深和0.16 m波高的来波条件, 平板淹没深度为0.1 m. 实验结果表明, 孤立波经过淹没平板时自由面有明显的三维变形, 导致孤立波波幅的时空变化. 波幅在平板尾缘中心线处达到最大值, 并沿展向逐渐减小. 利用多目视觉立体重构系统得到的波面变化过程与浪高仪给出定点波面时间序列相互印证, 表明建立标识码波面测量方法是有效的. 孤立波对淹没平板作用的水动力载荷变化分为6个典型阶段, 并与利用波面三维重构得到的波面测量标识码并讨论. 基于多目视觉立体重构技术得到了垂向力和俯仰力矩极值点出现时的三维波面形态. 建立的多目视觉立体重构系统将为海洋工程结构物的水池物理模型实验提供新的波面测量手段.      

规则波作用下垂直圆柱局部波浪力

在ＫＣ为４０～３５，雷诺数Ｒｅ为６×１０３～２×１０４参数范围内就规则波作用下垂直圆柱局部波浪力进行了实验研究．给出横向力随ＫＣ数类型变化的划分．基于Ｓｔｏｋｅｓ二阶波理论和Ｍｏｒｉｓｏｎ公式得到圆柱阻力系数ＣＤ，惯性力系数ＣＭ和最大升力系数ＣＬｍａｘ沿桩柱的分布及其随ＫＣ数的变化规律．结果表明，在波表面间歇区的桩柱的局部水动力系数变化显著，越向波峰位水动力系数ＣＤ和ＣＬｍａｘ越减小，而ＣＭ值却越增高．     

潜堤对波浪在直立式防浪墙上爬高的影响

对直立式防浪墙前潜堤的空间布置对波浪在直墙上爬高的影响进行了研究.建立简化模型,即直立式防浪墙前海床设计为平底,潜堤设计为直立薄板. 改变潜堤高度及其与防浪墙之间距,研究不同的潜堤布置对波浪在直墙上爬高的影响. 针对线性波浪场,利用数值波浪水槽模拟了潜堤作用下直墙上波浪的爬高现象. 同时建立了理论模型,系统地分析了潜堤布置形式对直墙上波浪爬高的影响. 研究结果表明潜堤相对于水深的高度越大,对波浪在直墙上爬高的影响越大,而在一定的相对高度条件下,潜堤与直立墙之间距对波浪爬高的影响呈现出一定的规律性.      

有限厚度砂床对波浪载荷的响应

本文采用水-土两相介质混合物的连续介质力学理论分析了有限厚度砂床对波浪载荷的响应。土床看作饱和孔隙弹性介质,用Biot理论来描述流动和变形的耦合效应,波浪用线性水波描述。在上述假设下得到了描述土床对波浪载荷响应的基本方程。用解沂-数值方法给出了土床中位移、应力和孔隙水压力的分布并将理沦计算结果与波浪-砂床模型试验的实验资料进行了比较。文章还对影响土床对波浪响应的参量特性进行了分析和讨论。根据参量研究、理论计算与实验资料比较的结果,可以得出结论:本文所提供的理论模型和计算方法能用来估算海床对波浪载荷的影响。     

基于相平均方法的折射绕射联合波浪模型

近岸带波浪运动的研究具有很重要的工程意义，近年来已获得了较丰硕的研 究成果并发展了许多波浪模型，而基于不同理论的波浪模型往往具有特定的适用性. 在海岸 工程中应用比较广泛的一类波浪模型以波能(波作用量)守恒为基本依据，如SWAN模型. 该 类模型在实际工程中已经得到了大量的应用，但该类模型未计及波浪绕射效应，成为其突出 的缺陷之一. 如何对模型做适当的改进，使之适用于波浪绕射的模拟，从而在原有基础上拓 广模型的应用范围是一项具有实际意义的研究工作. 该文采用波能(波作用量)守恒方程描 述近岸带波浪运动，通过引入绕射因子，得到折射、绕射联合波浪模型，从而拓广了模型的 应用范围. 通过实际算例验证，表明所建立的模型计及了波浪折射、绕射作用，对相平 均波浪模型在波浪绕射效应模拟方面的改进具有一定的意义.     

Hydrodynamic forces and moments due to interaction of linear water waves with truncated partial-porous cylinders in finite depth

An exact analytical method is employed for studying the diffraction problems in an ocean due to the presence of a specific type of cylinders. In this current work, two models are studied: (i) a floating surface-piercing truncated partial-porous cylinder, (ii) a surface-piercing truncated partial-porous cylinder placed at the bottom. In both cases, the configuration of the composite cylinder is such that it consists of an impermeable inner cylinder rising above the free surface and a coaxial truncated porous cylinder around the lower part of the inner cylinder with the top of the porous cylinder being impermeable. By using linear water wave theory, a three-dimensional representation of the problem is developed based on eigenfunction expansion method. The condition on the porous boundary is defined by applying Darcy’s law. Pressure and velocity satisfy continuity conditions across the linear interface between the adjacent fluid domains. Hydrodynamic force, moment and wave run-up are calculated by using the velocity potentials. Comparisons are carried out with results of wave diffraction by a floating and bottom-mounted compound cylinder, i.e., when the whole cylinder is non-porous. Handy agreements are observed from these comparisons. Through numerical tests, various experiments are carried out to investigate the impact of various parameters, such as porous coefficients, draft ratio, the ratio of inner and outer radii, the water depth etc., on hydrodynamic force, moment and wave run-up. The results clearly indicate that an appropriate optimal ratio for various parameters may be considered in designing practical ocean structures with minimum adverse hydrodynamic effect. The appearance of resonance in the results and role of porosity in mitigating resonance effect are explained. Proposal to select various appropriate parameters for the best possible effect is put forward.     

Hydrodynamic interactions of water waves with a group of independently oscillating truncated circular cylinders

In this study, we examine the water wave radiation by arrays of truncated circular cylinders. Each cylinder can oscillate independently in any rigid oscillation mode with a prescribed amplitude, including translational and rotational modes such as surge, sway, heave, pitch, roll, and their com-binations. Based on the eigenfunction expansion and Graf ’s addition theorem for Bessel functions, we developed an ana-lytical method that includes the effects of evanescent modes in order to analyze such arrays of cylinders. To investi-gate the effects of several influential factors on convergence, our objective is to dramatically reduce the number of tests required and determine the influencing relationships between truncation number and convergence behavior for different factor combinations. We use the orthogonal test method to fulfill the objective. Lastly, we present our results regarding the effects of evanescent modes on hydrodynamic coeffi-cients.     

Hydroelastic analysis of surface wave interaction with concentric porous and flexible cylinder systems

The present study deals with the hydroelastic analysis of gravity wave interaction with concentric porous and flexible cylinder systems, in which the inner cylinder is rigid and the outer cylinder is porous and flexible. The problems are analyzed in finite water depth under the assumption of small amplitude water wave theory and structural response. The cylinder configurations in the present study are namely (a) surface-piercing truncated cylinders, (b) bottom-touching truncated cylinders and (c) complete submerged cylinders extended from free surface to bottom. As special cases of the concentric cylinder system, wave diffraction by (i) porous flexible cylinder and (ii) flexible floating cage with rigid bottom are analyzed. The scattering potentials are evaluated using Fourier–Bessel series expansion method and the least square approximation method. The convergence of the double series is tested numerically to determine the number of terms in the Fourier–Bessel series expansion. The effects of porosity and flexibility of the outer cylinder, in attenuating the hydrodynamic forces and dynamic overturning moments, are analyzed for various cylinder configurations and wave characteristics. A parametric study with respect to wave frequency, ratios of inner-to-outer cylinder radii, annular spacing between the two cylinders and porosities is done. In order to understand the flow distribution around the cylinders, contour plots are provided. The findings of the present study are likely to be of immense help in the design of various types of marine structures which can withstand the wave loads of varied nature in the marine environment. The theory can be easily extended to deal with a large class of problems associated with acoustic wave interaction with flexible porous structures.     

Second-order interaction of irregular waves with a truncated column

A complete semi-analytical solution is obtained for second-order diffraction of plane bichromatic waves by a fixed truncated circular column. The fluid domain is divided into interior and exterior regions. In the exterior region, the second-order velocity potential is expressed in terms of ‘locked-wave’ and ‘free-wave’ components, both are solved using Fourier and eigenfunction expansions. The resulting ‘locked wave’ potential is expressed by one-dimensional Green's integrals with oscillating integrands. In order to increase computational efficiency, the far-field part of the integrals are carried out analytically. Solutions in both regions are matched on the interface by the potential and its normal derivative continuity conditions. Based on the present approach, the sum-and difference-frequency potentials are efficiently evaluated and are used to generate the quadratic transfer functions which correlates sum-frequency QTFs for a TLP column are present, which are compared for some frequency pairs with those from a fully numerical procedure. Satisfactory agreement has been obtained. QTF spectra for a case study TLP column, generated using the semi-analytical solution are presented. Also given are the results for nonlinear wave field around the column.     

MODELLING AND CALCULATION OF THE TURBULENT BOUNDARY LAYER ON A ROTATING CYLINDER SURFACE WITH STRONG SUCTION 1)

提出了湍流边界层的一种简单、快速计算方法, 用以求解强吸气作用下旋转圆筒表面边界层流动. 首先, 理论分析了同心圆筒间的旋转流体运动, 外筒静止、内筒旋转且为多孔吸气条件. 强吸气情况下旋转流动主要表现为内筒壁面附近的边界层流动, 基于这一事实得到了周向速度分布的解析表达式. 其次, 通过引入新参数扩展Cebeci-Smith代数湍流模型, 使其能考虑流线曲率、壁面吸气、低Reynolds数效应等因素. 针对这些因素的综合影响, 采用解析修正和经验参数对模型进行调整. 同时, 基于Reynolds应力湍流模型的仿真结果, 校准代数湍流模型中的经验参数. 最后, 给出基于广义Cebeci-Smith湍流模型的旋转壁面边界层流动的迭代算法, 该算法适用于需要特殊迭代过程的轴向及周向流动均匀情况. 计算了不同旋转速度和吸气强度组合工况下的边界层流动, 其周向速度和湍流强度分布与基于Reynolds应力湍流模型的计算结果非常接近. 并且表明, 当Reynolds应力湍流模型数值模拟预测内筒边界层为稳定层流时, 该方法也再现了相同初始条件下的层流边界层.     

Short crested wave–current forces around a large vertical circular cylinder

An analytical solution for the diffraction of short crested incident wave along positive x-axis direction on a large circular cylinder with uniform current is derived. The important influences of currents on wave frequency, water run-up, wave force, inertia and drag coefficients on the cylinder profiles are investigated for short-crested incident wave. Based on the numerical results, we find wave frequency of short crested wave system is affected by incident angle and the strength of the currents. The wave frequency increases or decreases with increasing current speed following or opposing wave propagating direction. It shows that the effects of current speeds, current directions on water run-up on the circular cylinder with different radius for different wave numbers are very conspicuous when the incident wave changes from long crested plane waves to short-crested waves. With the increase of current speed, the water run-up on the cylinder becomes more and more high, and will exceed that of long crested plane wave and short crested wave case without currents even though the current speed is small. The total wave loads, inertia coefficient and drag coefficient exerted on a cylinder with currents would be larger compared to the wave loads exerted pure short-crested waves. Therefore, ocean engineers should consider the short crested wave–current load on marine constructs carefully.     

等波高双孤立波直墙爬高的数值模拟

基于RANS方程、VOF方法以及修正的Goring造波方法建立了模拟活塞式推波板运动的二维数值波浪水槽,实现了双孤立波直墙爬高的数值模拟．利用动边界技术模拟造波机推波板的运动,有效地实现了不同波峰间距双孤立波的造波方法．在验证单孤立波直墙爬高的基础上,模拟了不同相对波高、相对波峰间距的等波高双孤立波的直墙爬高过程,给出了波面、速度场及波动能量的变化规律．数值模拟结果表明：对于等波高的双孤立波,当入射波波高较大及两个波峰间距相对较小时,跟随在后孤立波的爬高放大系数小于先导孤立波的爬高放大系数;双孤立波在直墙爬高过程中,波动场的势能时间过程线呈现三峰形态,其中居中的最大势能峰值出现在第二个孤立波与经直墙反射后反向传播的第一个孤立波完全对撞的时刻．