全非线性方法对于沉浸双圆柱定常前行运动引起自由表面流的研究（英文）

The free surface flow generated by twin-cylinders in forced motion submerged beneath the free surface is studied based on the boundary element method. Two relative locations, namely, horizontal and vertical, are examined for the twin cylinders. In both cases, the twin cylinders are starting from rest and ultimately moving with the same constant speed through an accelerating process. Assuming that the fluid is inviscid and incompressible and the flow to be irrotational, the integral Laplace equation can be discretized based on the boundary element method. Fully-nonlinear boundary conditions are satisfied on the unknown free surface and the moving body surface. The free surface is traced by a Lagrangian technique. Regriding and remeshing are applied, which is crucial to quality of the numerical results. Single circular cylinder and elliptical cylinder are calculated by linear method and fully nonlinear method for accuracy checking and then fully nonlinear method is conducted on the twin cylinder cases, respectively. The generated wave elevation and the resultant force are analysed to discuss the influence of the gap between the two cylinders as well as the water depth. It is found that no matter the kind of distribution, when the moving cylinders are close to each other, they suffer hydrodynamic force with large absolute value in the direction of motion. The trend of force varying with the increase of gap can be clearly seen from numerical analysis. The vertically distributed twin cylinders seem to attract with each other while the horizontally distributed twin cylinders are opposite when they are close to each other.     

流体与结构砰击的全非线性模拟:综述（英文）

This paper presents a review of the work on fluid/structure impact based on inviscid and imcompressible liquid and irrotational flow. The focus is on the velocity potential theory together with boundary element method(BEM). Fully nonlinear boundary conditions are imposed on the unknown free surface and the wetted surface of the moving body. The review includes(1) vertical and oblique water entry of a body at constant or a prescribed varying speed, as well as free fall motion,(2) liquid droplets or column impact as well as wave impact on a body,(3) similarity solution of an expanding body. It covers two dimensional(2D), axisymmetric and three dimensional(3D) cases. Key techniques used in the numerical simulation are outlined, including mesh generation on the multivalued free surface, the stretched coordinate system for expanding domain, the auxiliary function method for decoupling the mutual dependence of the pressure and the body motion, and treatment for the jet or the thin liquid film developed during impact.     

紧致插值曲线CIP方法及其应用

波浪与建筑物的相互作用过程会涉及到波浪破碎、水气掺混和结构物的动力响应等复杂过程,对数值算法提出了更高要求。文章基于紧致插值曲线CIP（Constrained Interpolation Profile）方法建立了可模拟波浪破碎、翻滚等自由面大变形流动问题的数学模型。模型以CIP方法为流场基本求解器,离散了纳维—斯托克斯（Navier-Stokes：N-S）方程,同时还以CIP方法捕捉了自由面,通过多相流理论描述了流—固—气之间的相互作用。对强非线性自由表面流动问题的典型算例溃坝问题开展了数值模拟,并通过与他人实验结果的比较验证了模型的有效性。最后开展了极端波浪对浮式结构冲击过程的模拟,准确地预测了甲板上浪和结构的动力响应等问题。     

Fully nonlinear simulation for fluid/structure impact: A review

This paper presents a review of the work on fluid/structure impact based on inviscid and imcompressible liquid and irrotational flow. The focus is on the velocity potential theory together with boundary element method （BEM）. Fully nonlinear boundary conditions are imposed on the unknown free surface and the wetted surface of the moving body. The review includes （1） vertical and oblique water entry of a body at constant or a prescribed varying speed, as well as free fall motion, （2） liquid droplets or column impact as well as wave impact on a body, （3） similarity solution of an expanding body. It covers two dimensional （2D）, axisymmetric and three dimensional （3D） cases. Key techniques used in the numerical simulation are outlined, including mesh generation on the multivalued free surface, the stretched coordinate system for expanding domain, the auxiliary function method for decoupling the mutual dependence of the pressure and the body motion, and treatment for the jet or the thin liquid film developed during impact.     

纵摇容器中液体晃荡的非线性数值模拟

在海洋工程领域,液体晃荡是一种普遍存在的物理现象。对于船舶而言,转动比平动有着更重要的影响。该文针对纵摇容器中的液体晃荡问题,采用高阶边界元方法建立自由水面满足完全非线性边界条件的时域数学模型。通过大地坐标系和随体坐标系之间的坐标变换,使得计算域仅控制在随体坐标系内。求解中采用半混合欧拉—拉格朗日方法追踪流体瞬时水面,运用四阶龙格库塔方法更新下一时间步的波面和速度势。通过与已发表试验和数值结果的对比,验证了建立模型的准确性。进而开展大量数值试验研究容器纵摇运动频率、纵摇转动中心和容器中布置一竖直隔板对晃动波面与荷载的影响。     

浅水中低速斜航船舶水动力预报及验证与确认分析

浅水中的斜航船舶受到浅水阻塞效应和不对称流的综合影响。为预报该运动中的船舶水动力,文章采用基于定常雷诺平均纳维—斯托克斯方程的计算流体动力学方法,对浅水中做斜航运动的船舶粘性绕流场进行数值模拟。考虑低航速运动的特点,忽略航速影响下的自由面兴波,由数值计算得到水动力系数在漂角影响下的变化规律。针对计算精度问题,在数值模拟中从验证和确认角度分析和评估计算结果：通过网格收敛性分析分析数值误差与不确定度;结合试验数据考察计算模型的误差。此外,从计算区域尺度、湍流模型、边界条件、船体下沉和纵倾作用方面对模型误差的影响因素进行探讨,可为改进计算模型、提高数值模拟精度提供参考依据。     

Time-domain TEBEM method for mean drift force and moment of ships with forward speed under the oblique seas

A numerical method for solving 3D unsteady potential flow problem of ship advancing in waves is put forward. The flow field is divided into an inner and an outer domain by introducing an artificial matching surface. The inner domain is surrounded by ship wetted surface and matching surface as well as part of the free surface. The free surface condition for the inner domain is formulated by perturbation about the double-body flow or uniform incoming flow assumption. The outer domain is surrounded by matching surface and the rest free surface as well as infinite far-field radiation boundary. The free surface condition for the outer domain is formulated by perturbation about uniform incoming flow. The simple Green function and transient free surface Green function are used to form the boundary integral equation (BIE) for the inner and outer domains, respectively. Taylor Expansion Boundary Element Method (TEBEM) is utilized to solve the double-body flow and inner domain and outer domain unsteady flow BIE. Matching conditions for the inner domain flow and outer domain flow are enforced by the continuity of velocity potential and normal velocity on the matching surface. Direct pressure integration on ship wetted surface is used to obtain the first-order and second-order wave forces (moments). The numerical predictions on the displacement, added resistance, sway mean drift force and yaw mean drift moment of the modified KVLCC2 ship at different forward speeds are investigated by the proposed TEBEM method. It is also compared with the other numerical results. The physical tank experiment results are also developed to validate the accuracy of numerical tank results. Compared with the experiment solutions, a good agreement can be obtained by TEBEM method.

     

溃坝问题的数值仿真和实验(英文)

In this paper, two novel numerical computation methods are introduced which have been recently developed at Research Institute for Applied Mechanics ( RIAM ), Kyushu University, for strongly nonlinear wave-body interaction problems, such as ship motions in rough seas and resulting green-water impact on deck. The first method is the CIP-based Cartesian grid method, in which the free surface flow is treated as a multi-phase flow which is solved using a Cartesian grid. The second method is the MPS method, which is a so-called particle method and hence no grid is used. The features and calculation procedures of these numerical methods are described. One validation computation against a newly conducted experiment on a dam break problem, which is also described in this paper, is presented.     

水面舰船附近气泡运动数值模拟

当气泡在自由面和水面舰船附近运动时,两者的存在均会对气泡脉动产生影响。基于不可压缩势流理论,采用边界元方法对边界积分方程进行求解。针对建立自由面需要大量的网格,且处理自由面与水面结构交界面时数值不稳定,采用考虑自由面效应的格林函数取代基本格林函数,通过与自由面附近气泡轴对称模型的计算结果进行对比,验证了该方法的有效性。通过对舰船结构附近的气泡运动射流特性进行模拟,发现当药包在舷侧和自由面附近爆炸时,气泡射流可能不会完全作用在舰船上,自由面效应的存在削弱了气泡的打击能力。     

A CIP-based method for numerical simulations of violent free-surface flows

A CFD model is proposed for numerical simulations of extremely nonlinear free-surface flows such as wave impact phenomena and violent wave–body interactions. The constrained interpolation profile (CIP) method is adopted as the base scheme for the model. The wave–body interaction is treated as a multiphase problem, which has liquid (water), gas (air), and solid (wave-maker and floating body) phases. The flow is represented by one set of governing equations, which are solved numerically on a nonuniform, staggered Cartesian grid by a finite-difference method. The free surface as well as the body boundary are immersed in the computation domain and captured by different methods. In this article, the proposed numerical model is first described. Then to validate the accuracy and demonstrate the capability, several two-dimensional numerical simulations are presented, and compared with experiments and with computations by other numerical methods. The numerical results show that the present computation model is both robust and accurate for violent free-surface flows.     

挟沙水流引起底床冲淤变化的数值模拟

本模型为垂向二维数学模型,以修正的NS方程为基础,采用粒子Level Set方法和对流扩散方程分别模拟自由水面和悬沙运动,根据底床物质质量平衡的原则计算底床变形,可模拟水流引起的底床冲淤变化.该模型将水流模型扩展到泥沙运动领域,以二相流概念简化自由水面边界条件,模拟悬沙、底沙和底床变形;采用固定的笛卡尔坐标,不需重新划...     

Water entry of a bow-flare ship section with roll angle

The two-dimensional water entry of a bow-flare ship section with constant roll angle, or heel angle, was studied by using a boundary element method. The fully nonlinear free surface conditions and exact body boundary conditions were satisfied. Nonviscous flow separation from the knuckles of the section or from the curved bottom could be simulated. The numerical calculations were compared with existing experimental results. First, the effects of roll angle were investigated and then the characteristics associated with large roll angles were examined in particular. The evolution of the free surfaces and the pressure distributions on the section surface are illustrated and the influence of nonviscous flow separation from the leeward section surface is discussed.     

波浪与带有窄缝结构作用的非线性数值模拟

针对波浪与带有窄缝结构作用产生的流体共振问题,采用基于域内源造波技术的时域高阶边界元方法并在窄缝内流体引入人工阻尼,建立了自由水面满足完全非线性边界条件的二维时域数值波浪水槽模型。求解中采用混合欧拉-拉格朗日方法追踪流体瞬时水面,运用四阶龙格库塔方法更新下一时间步的波面和速度势,利用加速度势的方法来求得作用结构上的瞬时波浪荷载。通过与已发表文献的数值与实验结果对比,验证了模型的准确性。同时通过大量的数值计算研究了共振条件入射波浪非线性对反射波高、透射波高和窄缝内波高、及结构波浪荷载和压力分布的影响。     

规则波作用下方形排柱附近水流特性数值模拟

为研究规则波作用下方形排柱附近流动特性,基于计算流体力学软件FLOW-3D,运用质量源造波方法,离散RNG k-ε方程控制下的雷诺时均Navier-Stokes方程建立无反射三维数值波浪水槽.与物理模型试验结果对比,建立的数值模型性能良好.运用数值计算结果,分析排柱周围自由表面三维运动特征和方形排柱周围速度场与涡量场分...     

简单Green函数法求解三维水动力系数

本文提出用简单Green函数1/r求解无航速的三维物体在水面、水下或在无界域中作各向振荡时水动力系数的数值方法。对于无穷远处扩散条件转换成辐射面条件的问题作了专门的考虑,即用圆柱将物体包围在其内部,该圆柱将流场分成内、外两部分,外部域中速度势的特征函数展开式与内部域中用Green公式求得的解相匹配。 根据本计算方法编制的程序对一些典型情况作了试算,其中包括在水面振荡的半球、方盒和圆盘的水动力系数曲线;水面及水底对圆球水动力系数的影响等。为考核本方法,与其它计算方法得到的结果作了比较。对方盒的三维结果与切片法作了比较。     

潜艇应急上浮稳性研究

通过对应急上浮运动及高压空气吹除主压载水舱规律的简化,给出了潜艇应急上浮运动方程.将上层建筑的背水量作为临时加载,推导出应急上浮稳性计算方法.将非定常势流理论用于应急上浮运动流场分析与水动力计算.考虑了非线性自由表面条件,在应急上浮运动中随时进行流场以及自由表面的运动计算,从而实现了应急上浮运动与流场的耦合求解.采用将艇体及自由表面划分成四边形单元的方法计算流场,用Adams方法计算自由表面运动和艇体上浮运动.文中给出了某潜艇应急上浮运动和稳性的算例,计算结果验证了方法的可靠性.     

Numerical analysis on free surface waves and stern viscous flow of a ship model

This paper deals with numerical techniques for computing the viscous flow past a ship hull with and without a free surface using a Reynolds-averaged Navier-Stokes solver with global conservation. In the first technique, a coarse grid is used to find an approximate solution to the free surface problem. Interpolation of a fine grid is subsequently carried out, and a more exact solution, particularly in the boundary layer and wake, is obtained. In the second technique, a modified Baldwin-Lomax model is introduced to compute the viscous flow with and without a free surface. These numerical techniques are applied to simulations of the flow around a Series 60 and an SR196C ship model. The results are compared with measurement data, and the usefulness of the numerical techniques is demonstrated.     

A finite pointset method for the numerical simulation of free surface flow around a ship

In this paper, we present a Finite pointset method (FPM) for the numerical simulation of free surface flow around a ship in calm water. It is a Lagrangian and meshless particle scheme which is applied to the projection method for the incompressible governing equations. This requires the solution of Poisson problems in each time step, so a moving least squares (MLS) interpolants is used for the spatial derivatives in order to discretize the Poisson equation with pressure-Dirichlet condition of free surface flow in meshless structure. Meanwhile, an additional problem of the periodic particle locations redistribution in the present approach is still handled by MLS interpolants. With the proposed FPM technique, problems associated with the free surface flow around a ship are circumvented. A verification of numerical modeling is made using the Wigley hull and the validity of the proposed methodology is examined by comparing the detail of wave profile and wave-making resistance with Series 60 model. The results demonstrate that FPM is able to perform efficient and stable simulations of free surface flow around a ship.     

浅水中船舶水动力特性数值计算

本文对浅水中船舶水动力特性进行数值计算研究.采用RANS方程结合RNG K-ε两方程湍流模型,对一方形系数0.6的系列60船模在浅水中的阻力、升沉、纵倾和兴波进行数值计算,其中自由面采用VOF方法处理;计算中,水深Froude数范围0.6～1.8,包含了临界和超临界水深Froude数.数值计算得到的阻力、升沉和纵倾与模型试验结果及采用三维扩展Boussinesq方程的计算结果进行了比较分析,吻合较好,部分计算结果得到改进.