基于速度势分离法的波物相互作用完全非线性数值模拟

该文基于势流理论和高阶边界元方法,建立了开敞水域波浪与三维物体相互作用的完全非线性数值模型。采用速度势分离技术,将总速度势分离成入射势和散射势,入射势通过理论解给定。采用混合欧拉-拉格朗日方法追踪流体瞬时水面,引进虚拟函数耦合求解波浪力和运动方程,自由水面网格仅在初始时刻生成一次,随后采用弹簧近似法在不改变网格节点排列的情况下对瞬时水面进行网格重构。利用所建立模型模拟完全非线性波浪对固定圆柱的绕射作用,并对规则浪三倍频作用下漂浮圆柱的共振响应进行了研究。     

双浮体自由垂向振荡响应特性

双圆柱体系统在波能装置和防波构件中得到应用，该系统是一个多自由度受迫阻尼振荡系统，阻力和激励力都来自于波浪力。本文采用线性波理论和特征函数展开皮配法，在平面入射波条件下，求解了双圆柱体垂荡运动辐射速度势和圆柱体固定不动时的绕射速度势，推导了附加质量、阻尼系数、波浪激励力表达式，列出了浮体垂荡运动微分方程。最后讨论了下浮体尺度及位置对系统响应特性的影响。数值计算表明无论下浮体尺度及位置如何变化，它只影响到浮体垂荡响应在低频端的值，下浮体的振幅值总是小于入射波的振幅值，而且它在一个较窄的频率范围内从较大的值很快变化接近于零。下浮体半径与上浮体半径之比的变化不仅影响到两个浮体的响应幅值，而且也影响到曲线的变化趋势；两浮体距离的变化对曲线的变化趋势影响不大，但对曲线的幅值有影响；下浮体厚度的变化只少许改变了响应曲线的幅值。     

波流联合作用下的物体上的波浪绕射力

本文研究了在波流联合作用下的任意三维物体的波浪绕射问题,建立了求解物体上的波浪绕射力的时域解理论模型。本文证明了对于任意三维物体,如果在自由面条件简化时,假设定常兴波势为有限量阶,则在波浪绕射力公式中,不存在含有绕射势的水线积分项。从数学上证明了水线积分项反映了自由面条件中定常兴波势和不定常势之间的耦合效应。在此基础上,本文提出了在波流联合作用情况下,作用在物体上的绕射力与辅助辐射势之间的关系式,从而不须求解绕射势便可得到绕射力。     

基于时域格林函数的有航速船舶与波浪相互作用的数值模拟

基于深水时域格林函数的数值处理方法及开发的计算程序,采用三维时域数值模拟方法,在线性势流理论框架内对深海波浪中航行船舶的辐射问题和绕射问题进行了求解,研究探讨了航行船舶与波浪相互作用问题.研究中对不同航行速度的Wigley型船水动力系数和波浪力进行了数值计算,通过与试验及文献计算结果的比较,验证了三维时域数值计算程序的有效性.     

两层黏性流体中直立圆柱体绕流的三维数值模拟

研究了两层流体中直立贯底圆柱体的三维黏性绕流问题.以不可压缩Navier-Stokes方程为控制方程,应用VOF方法追踪两层流体的内界面,建立了该问题的数值模拟方法.成功地数值模拟了两层流体中圆柱体黏性绕流产生的三维尾涡特征,表明了流体的密度分层效应对直立贯底圆柱体的尾涡特性和阻力系数都是有影响的.在海洋立管涡激振动的研究中,考虑流体的密度分层效应是重要的.     

大尺度柱状结构物波流荷载研究

大型深水工程往往面临水深、浪大以及流急等复杂自然条件,将受到巨大的水平波流力,在工程设计中需准确考虑波流力的大小.通过在波流水槽进行圆柱、方柱和矩形柱波流力系列试验,进行大尺度柱状结构物波流荷载研究,同时建立数学模型,应用边界元法求解大尺度柱体上的波浪荷载,编写了Fortran程序计算波浪力,运用柱体绕流理论计算水流力.对比分析试验结果和数值计算结果提出了波流力工程计算方法:对于深水大尺度柱状结构物波流力可由波浪力线性迭加水流力再乘以1.04得到,计算中波浪要素采用水流影响下的要素,水流力采用柱体绕流求得.按此方法计算波流力,并与物理模型试验结果进行对比,两者误差较小,满足工程设计的精度要求.     

V形贯底式防波堤上波浪作用力的解析研究

用解析方法计算V形贯底式防波堤在波浪绕射作用下周围流域任意点的速度势,研究波浪作用在V形贯底式防波堤上的波浪力。假定防波堤刚性、薄壁、不透浪、水深恒定。假想的圆柱面将整个流场划分为三个区域,分别在每个区域内将速度势用特征函数展开,然后在公共边界上按照速度连续,速度势连续的原则进行匹配,求得流域中任意一点的速度势和作用在V形贯底式防波堤上的总波力和总波力矩。数值结果给出了作用在防波堤上的波浪力随防波堤张角、入射波波长、入射角变化的曲线。结果表明:作用在V形贯底式防波堤上的波浪力与水深、防波堤的张角、入射波的波长等因素有关。     

二维浮体的低频作用力

本文用缓慢调制的Stokes波模拟入射波群,并采用多重尺度方法研究了波群对二维浮体的低频绕射问题,得到了一阶和二阶纸频绕射势,求得了相应的低频作用力,证明了由一阶低频绕射势所产生的二阶低频力垂直于静止自由表面,它与入射波包络波幅的平方以及浮体水线面的宽度成正比,而与浮体具体形状无关,低频绕射所产生的水平力来源于二阶低频绕射势,通过求解两个线性边值问题就可以计算它。     

脉冲波作用下竖直弹性板的水弹性响应

基于线性势流理论,将流场分为3个部分:入射势与反射势部分、辐射势的记忆部分、辐射势的瞬时部分,竖直弹性板的时域振动基于模态叠加法,利用傅里叶与拉普拉斯变换求解流场控制方程,与板的振动方程耦合,推导得出波浪作用下竖直弹性板的时域耦合方程,并利用二级四阶隐式Runge-Kutta法求解方程。首先给定竖直板一个初始弯曲,得到的结果与解析解和数值解结果吻合良好,验证了方法的正确性。其次对脉冲波作用下弹性竖直板的响应进行研究,分析了板的刚度系数、质量系数、脉冲幅值和边界条件对其水弹性响应的影响。研究结果表明,刚度系数对板的振动频率影响很大,脉冲幅值与板的振动幅度正相关,两边固定时对竖直弹性板的疲劳损伤最严重。     

六附属旋转小圆柱对主圆柱绕流特性的影响

基于计算流体动力学方法,对雷诺数Re=200条件下,六附属旋转小圆柱与主圆柱体二维绕流进行了数值模拟.考虑来流攻角(θ=0°-60°)与附属圆柱旋转速率(α=0.0-2.0)两个关键参数对主圆柱体流体力系数,以及流场特性的影响,最后分析了附属圆柱临界转速与来流攻角之间的变化.结果 表明:来流攻角和附属圆柱旋转速率的变化...     

THE RADIATION AND DIFFRACTION OF WATER WAVES BY A BOTTOM-MOUNTED CIRCULAR CYLINDER IN A TWO-LAYER FLUID

An analytical method was proposed to analyze the radiation and diffraction of water waves by a bottom-mounted circular cylinder in a two-layer fluid. Analytical expressions for added mass and damping coefficients, as well as the wave excitation forces of the circular cylinder were obtained by an eigenfunction expansion method. The hydrodynamic forces on the bottom-mounted circular cylinder in a two-layer fluid include not only the added mass and damping coefficients, but also the wave forces of the surface and internal-wave modes. This is different from the case of a homogenous fluid. Some examples were given, showing that density stratification can have a relative large effect on these hydrodynamic forces over a wide range of frequencies.     

用时域法求解二维二阶非线性水波的绕射问题

本文用二阶理论在时期围内研究非线性水波的绕射问题。一、二阶问题分别满足各自的自由表面条件和物面条件。用一阶Ａｄａｍｓ格式并配合时步处理来计算自由表面上的波高和速度势，而流场内的速度势通过求解有限元方法得到。采用人工阻尼区来吸收反射波，对水平半圆柱在水面的绕射问题进行了计算，得到了自由表面波高时间历程和圆柱所受到的波浪力，计算结果和有关文献进行了比较，其符合程度是令人满意的。     

A 3-D numerical study of solitary wave interaction with vertical cylinders using a parallelised particle-in-cell solver

This paper aims to provide a better understanding of the interaction between solitary waves and vertical circular cylinders. This is achieved via process based numerical modelling using the parallel particle-in-cell based incompressible flow solver PICIN. The numerical model solves the Navier-Stokes equations for free-surface flows and incorporates a Cartesian cut cell method for fluid-structure interaction. Solitary waves are generated using a piston-type wave paddle. The PICIN model is first validated using a test case that involves solitary wave scattering by a single vertical cylinder. Comparisons between the present results and experimental data show good agreement for the free surface elevations around the cylinder and the horizontal wave force on the cylinder. The model is then employed to investigate solitary wave interaction with a group of eleven vertical cylinders. The wave run-up and wave forces on the cylinders are discussed.     

The hydrodynamic interactions of an array of truncated circular cylinders as each cylinder oscillates independently with different prescribed modes

An analytical method based on the eigenfunction expansion and the Graf’s addition theorem for Bessel functions is developed to study the hydrodynamic interactions of an array of truncated circular cylinders with each cylinder oscillating independently in different prescribed modes. The hydrodynamic radiation and diffraction of linear waves by such an array of cylinders are investigated and the analytical solutions of the velocity potentials are obtained. After comparisons for degenerated cases and program verifications, several cases for an array of truncated cylinders with each cylinder oscillating independently in surge, sway, heave, roll, and pitch modes with different prescribed amplitudes, are studied and the hydrodynamic forces and moments acting on the cylinders are obtained.     

NONLINEAR DIFFRACTION OF BICHROMATIC WAVES BY A VERTICAL CYLINDER

We present in this paper a semi-analytical solution for second-order wave diffraction by a vertical circular cylinder in bichromatic waves.On the base of the usual assumption of an irrotational flow,the wave-diffraction problems at second-order sum-fre-quency and difference-frequency are considered.The corresponding second-order diffrac-tion potentials are decomposed into three parts,these are associated with the second-order incident wave,the quadratic forcing terms on the free-surface due to the first-order poten-tial,and the linearised'free-wave'component resulting from the boundary condition on the body surface.A particular solution which exactly satisfies the inhomogeneous free-sur-face condition has been derived.Numerical results for the quadratic transfer functions of the second-order force components are given,and are compared with those obtained using numerical solutions(Kim & Yue,1990,Moubayed & Williams 1995).These quadratic functions are useful in calculating the exciting forces on a circula     

RADIATION AND DIFFRACTION OF WATER WAVES BY A SUBMERGED CIRCULAR CYLINDER AT FORWARD SPEED

The wave radiation and diffraction by a submerged circular cylinder in deepwater is analysed by the multipole expansion method.The theory is based on the inviscid andlinearized potential flow.     

非线性波浪绕射问题的数值计算

本文给出非线性波浪绕射问题的计算模型,并用时间步进和边界元法求解。该模型能适用于严重非线性情形,且能满足初始条件和辐射条件。作为对该模型的检验,我们对孤立波绕过穿刺水面的直立圆柱的算例进行了计算,并同Isaacson的解析解、李宝元的差分解进行了比较,结果吻合很好。此外我们还用数值方法同时模拟造波机造波和求该波与直立圆柱的相互作用。结果表明,数值波浪水池能够以尽可能短的暂态过程,模拟波浪与物体的相互作用,提供良好的初始条件。数值波浪水池还能用于任意水深、任意水底形状下的相互作用问题。本文的计算模型和算法具有机时省,计算稳定的优点。     

部分可渗透直立圆柱的消波作用研究

本文导出了线性波浪作用于上部可渗透的直立刚性圆柱体上的水动力的解析解。在线性有势流的假定下，用特征函数展开方法求出了内部和外部流场的解。给出了不同波浪要素及结构尺寸参数下的数值结果。由结果可知，提高可渗透性可以有效消减波幅。     

Numerical simulation of wave interacting with a submerged cylinder using a 2D RANS model

A 2D RANS numerical model (IH2VOF) is employed to study wave interacting with a circular cylinder with a diameter of 0.02 m in a water depth of 0.27 m, with a wave period of 1.08 s and a wave height of 0.047 m. The influence of the wall proximity on the forces is analyzed for ratios between the pipe (i.e. circular cylinder) distance from the bottom and the pipe diameter varying from 0.04 to 1.5. Results of lift forces and streamlines are compared with the experimental results of Jarno-Druaux et al. (1995) and good agreement is found. Lift, drag and inertia coefficients are also compared with experimental results and the same trend of fundamental quantities with the gap between the cylinder and the bottom was obtained with the model giving slightly larger values. Finally, the influence of the method to estimate the drag and inertia coefficients in the force calculated using Morison equation is analyzed and Morison method shows the better agreement.     

规则波作用下倾斜桩柱的受力研究

本文通过实验研究,测试了水平桩柱及倾斜桩柱在规则波作用下的波浪力。基于Morison方程和Stokes二阶波理论,分析研究了不同埋深情况下水平桩柱的受力及其水动力系数C_D、C_M随K_C数的变化规律;分析研究了不同倾角情况下,倾斜桩柱的受力及其水动力系数C_D、C_M随K_O数的变化规律,同时还探讨了在同一倾角情况下,桩柱在一端出水和全部埋于水下时,水动力系数C_D、C_M的差别。