浅窄航道非线性兴波阻力数值计算

应用Rankine面元法计算船舶在浅窄航道中作匀速直航运动时的非线性兴波阻力．基于势流理论，在船体表面、自由面以及岸壁分布Rankine源来表达流场速度势，利用迭代方法满足非线性自由面边界条件，采用映像法满足水底边界条件，采用网格错位法满足辐射条件．以Wigley数学船型为例进行计算，通过改变航速和航道宽度参数，得到相应的兴波阻力．通过分析不同航速下航道宽度变化对兴波阻力的影响，得到了一些有意义的结论．     

基于Rankine源高阶面元法的船舶航行姿态与兴波阻力计算

针对航行船舶的兴波阻力和姿态预报,采用Rankine源高阶面元法求解船舶航行兴波问题。计算时采用叠模线性化自由面条件,对自由面影响系数奇异积分采用源点上置的方法处理,物面奇异积分和立体角则直接求解。就数学船型Wigley、S60和KCS集装箱船的航行兴波阻力与姿态分别进行了数值计算与分析,计算中根据姿态变化重新划分船体湿表面,进行迭代计算,不同航速下的姿态、兴波阻力和船侧波高与试验结果比较,吻合良好,自由面波形真实反映了物理现象,研究表明本文方法能准确地预报船舶航行姿态和兴波阻力,对不同船型和航行速度有着广泛的适用性。     

关于m-项及三维船舶在波浪中运动的一种数值计算方法(英文)

文章提出一种基于Rankine源分布的三维船舶运动数值计算方法。该方法可求解定常及非定常的船舶兴波势流场。自由表面条件利用迭模解进行线性化,而物面条件中包含了m-项。由于m-项是定常速度势的物面二阶导数,数值计算有一定困难。文中使用一种直接数值差分方法计算m-项。文中也提出一种满足远方辐射条件的数值差分方法。船舶的下沉和纵倾则通过迭代求解稳态兴波问题获得,从而确定船舶在有航速时的湿表面再进行耐波性计算。该方法的计算与现有模型试验进行了比较,结果令人满意。     

近自由面三维水翼的水动力分析及试验研究

采用面元法对近自由面三维水翼进行势流数值分析并进行了相关试验研究。在数值计算中,将Rankine源和偶极子置于边界面上,用时间步进法模拟水翼的势流场和自由表面波形。在自由面采用非线性自由面边界条件,在尾涡面上采用偶极子布置以满足Kutta条件。文中给出了数值计算模型的参数,对于不同浸深、不同航速和不同攻角下的水翼,计算了水翼表面上的压力分布,水翼的阻力和升力及自由表面波形。数值计算结果与试验结果进行了对比。结果表明,文中方法可用于水翼优化设计、近自由面振动翼运动及水翼船兴波等问题的研究。     

基于三维非线性区域分割法的船舶运动时域计算研究

基于三维势流理论,构建船舶在波浪中航行的非线性区域分割法。用假想的控制面将计算域分为内域和外域,其中外域采用自由面格林函数法,内域考虑自由面非线性,采用满足移动兴波线性化自由面条件的Rankine面元法,并通过过渡函数使内外域速度势及其导数在控制面上连续。内外域耦合求解得到扰动速度势及流体动压力。其中自由面运动学边界条件、动力学边界条件及物面条件m项中的移动兴波速度势及波面抬升是基于非线性兴波计算得到的,较线性化自由面条件更为精确。以数学船型Wigley-3为对象,讨论了不同因素对计算收敛性的影响,验证了该方法的可靠性和准确性;以S60和S175两种具有外飘的实际船型在波浪中的运动响应为例,将计算结果与试验及其他方法进行了对比,验证了三维时域非线性区域分割法在实船运动预报中的准确性。     

直接边界元法时域全非线性兴波计算

文章在时域中采用直接边界元的方法计算模拟了以稳定航速运动的近水面潜体全非线性兴波现象.从格林定理出发,在边界面上布置Rankine源和偶极子,采用时间步进的方法计算模拟潜体近自由面运动的兴波现象.每个时步自由面上的势和节点位置采用全非线性拉格朗日自由面边界条件求解,重新生成自由面网格准备下一个时步计算的初始条件.文中给出了数值计算的结果并与试验和线性计算的结果相比,证实了该方法是可靠的,并可以利用该方法建立数值波浪水池.     

一种计算非线性兴波阻力的基于NURBS的高阶面元法(英文)

文章开发了一种用于求解非线性兴波阻力问题的基于非均匀有理B样条(NURBS)的高阶面元法.该方法采用NURBS基函数表达物面几何和边界面上的源强分布.为了满足非线性自由面边界条件,开发了一个迭代算法;辐射条件通过采用网格错位的数值技术得到满足.以Wigley数学船型为例,在一系列的船速下计算了非线性兴波阻力.数值结果表明所提出的方法对于计算兴波阻力是精确和有效的.     

非线性船波问题的数值分析

通过对慢船兴波速度势重新进行分解，给出各分量新的量级假定，分析简化了船波问题的非线性自由面边界条件，利用耦合元方法对非线性船波问超进行了数值计算，重点讨论了自由面条件中各项的影响大小及其与船型的关系。     

浅水中下潜物体有航速辐射问题的数值解

开发了一种基于非均匀有理B样条(NURBS)的Rankine源高阶面元法用于求解浅水中下潜物体有航速辐射问题。基于势流理论,流场中的扰动速度势用物体表面和自由面上分布的Rankine源来表达,同时用映像法计及水底的影响;采用NURBS曲面精确表达物面和自由面,在求出边界面上的未知源强后,物体表面的速度势分布用B样条表示;采用配置方法对边界积分方程进行求解,采用高斯—勒让德公式计算方程中的积分,同时开发了一种解决数值积分中奇异性问题的方法。采用文中数值方法求解了浅水中下潜圆球的有航速辐射问题,计算得到了下潜圆球水动力系数和自由面波形,所得水动力系数计算结果和他人的计算结果进行了比较,其吻合程度良好,从而验证了文中开发方法的有效性。     

船舶在波浪中航行时绕射问题的线性时域解

本文研究了水面船舶(物体)在波浪中航行时的绕射问题,求得了有航速船舶绕射问题线性时域解的理论模型.提出了计算波浪绕射力的公式.对于细长形的船舶.作者给出了计算波浪扰动力的公式,使得在时域中有航速船舶波浪扰动力的计算,可以用辐射势和入射波势来表示,而不须求解绕射势.利用本文所提出的波浪扰动力公式.在求解波浪扰动力时,对于任意多的入射波频率,只要解算积分方程一从而大大节省了计算工作量。本文还证明了在波浪中航行的一般三维物体,如果在自由面条件简化时,假设定常兴波势为有限量价,则在波浪绕射力公式中,不存在水线积分项。从数学上证明了水线积分项在物理上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。在算例中,运用本文导出的波浪扰动力公式对 Wigley 船型进行了波浪扰动力的求解,与试验结果和现有理论方法的数值结果进行了比较,吻合良好.本文还对各种参数的影响进行了讨论,对计算结果所反映的物理现象作了分析。     

近水面椭球体非线性兴波的数值模拟

本文开发了一种去奇异面元法用于计算以定常前进速度运动的近水面椭球体引起的三维非线性自由面势流.采用求解非线性深水波的Stokes理论求解该定常非线性问题;物面用NURBS(非均匀有理B样条)表达;孤立的Rankine源分布在物体内部和自由面上方.给出了波型、波阻以及收敛特性随一些参数的变化规律.波阻计算结果和他人的其它数值结果进行了比较,其吻合程度令人满意.     

基于多次透射公式和无奇异边界元法模拟全非线性数值波浪水池

文章基于势流理论对全非线性的三维数值水池进行了模拟,其控制方程由无奇异边界积分方程法(Desingularized Boundary Integral Equation Method,DBIEM)进行离散求解,在求解全非线性的自由面微分方程时,文中采用混合欧拉—拉格朗日法(Mixed Eulerian-Lagrangian,MEL)和四阶Adams-Bashforth-Moulton(ABM4)预报—修正方法,为了避免结果发散即增强数值稳定性,文中采用B样条法来光顺波面.同时,在远方辐射控制面上采用多次透射公式方法(Multi-transmitting Formula,MTF)来进行消波,文中得到的结果与理论解进行了比较,结果表明该方法可用来有效模拟全非线性的数值波浪水池.     

A time-domain higher-order boundary element method for 3D forward-speed radiation and diffraction problems

A time-domain higher-order boundary element method for seakeeping analyses in the framework of linear potential theory is newly developed. Ship waves generated by two modified Wigley models advancing at a constant forward speed in calm water or incident waves and the resultant radiation and diffraction forces are computed to validate this code. A rectangular computational domain moving with the same forward speed as the ship is introduced, in which an artificial damping beach is installed at an outer portion of the free surface except the downstream side for satisfying the radiation condition. The velocity potential on the ship hull and the normal velocity on the free surface are calculated directly by solving the boundary integral equation. An explicit time-marching scheme is employed for updating both kinematic and dynamic free-surface boundary conditions, with an embedding of a second-order upwind difference scheme for the derivative in the x-direction to stabilize the calculation. Extensive results including the exciting forces, added mass and damping coefficients, wave profiles, and wave patterns for blunt Wigley and slender Wigley hulls with forward speed are presented to validate the efficiency of the proposed 3D time-domain approach. The corresponding physical tests of the radiation and diffraction problems in a towing tank are also carried out. Computed numerical results show good agreement with the corresponding experimental data and other numerical solutions.     

规则迎浪中船舶参数横摇的三维时域预报方法研究

参数横摇是船舶因复原特性改变而引起的典型非线性现象。文章采用三维时域方法预报规则迎浪中船舶的参数横摇运动。该方法引入匹配面将流域分为内域和外域,内域中采用Rankine源来满足物面条件和线性自由面条件,而外域中应用时域格林函数来满足线性自由面条件和远场辐射条件。数值方法中,Froude-Krylov力和恢复力是通过对船舶瞬时湿表面积积分获得,同时考虑了横摇、垂荡和纵摇三自由度之间的耦合作用,以及非线性横摇阻尼的影响。数值结果与试验结果吻合很好,说明该方法可以有效地预报参数横摇。     

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.     

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.     

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.     

Numerical simulation of nonlinear wave force on a quasi-ellipse caisson

A three dimensional numerical model of nonlinear wave action on a quasi-ellipse caisson in a time domain was developed in this paper. Navier-Stokes equations were solved by the finite difference method, and the volume of fluid (VOF) method was employed to trace the free surface. The partial cell method was used to deal with the irregular boundary typical of this type of problem during first-time wave interaction with the structure, and a satisfactory result was obtained. The numerical model was verified and used to investigate the effects of the relative wave height H/d, relative caisson width kD, and relative length-width ratio B/D on the wave forces of the quasi-ellipse caisson. It was shown that the relative wave height H/d has a significant effect on the wave forces of the caisson. Compared with the non-dimensional inline wave force, the relative length-width ratio B/D was shown to have significant influence on the non-dimensional transverse wave force.