应用时域格林函数方法模拟有限水深中波浪对结构物的作用

该文采用时域内满足自由水面条件的格林函数方法对无限和有限水深中波浪与任意形状三维物体相互作用所产生的绕射和辐射问题进行了理论研究和数值计算。建立了不包含自由水面积分的积分方程,消除了自由项系数。文中计算了各种形状三维物体在无限水深和有限水深情况下所受到的绕射和辐射波浪力,并与解析解以及频域理论进行了对比,结果符合良好,验证了本文所提理论的正确性。     

几何独立的高阶面元法在波-流-物相互作用问题mj项求解中的应用

mj项的计算是波-流-物相互作用问题的数值解的难点之一.该文给出了使用几何独立的高阶面元法求解mj项的方法,物面用任意的分片连续函数表示,定常兴波势用任意阶的B样条函数近似,直接对定常兴波势微分以得到mj项中定常兴波势的二阶导数.数值实例显示这一方法的计算结果非常准确.     

大型海洋结构物的非线性绕射效应

本文在空间上应用面源法,在时间域上应用步进法,数值处理了三维物体与非线性波浪的相互干扰,研究了结构物的非线性绕射效应。首先,作为比较,求解了正弦波列和孤立波绕射垂直桩柱的情形。接着,进一步求解了大振幅波浪绕射固定在自由面上的大型浮动码头的工程实例。结果表明,非线性波浪绕射力与线性结果,有一定的差别。有时,尽管从总体效应来看,这种差别不十分明显,但从上浪、出水和波的爬高以及局部应力等局部效应来看,这种差别可能很明显。     

波浪对三维浮体的二阶作用

本文通过求解二阶势的方法对波浪与任意形状三维物体的相互作用问题做了研究，波浪运动的二阶势应用高阶边界元方法进行计算，为了高阶边界元法的应用，本文给出了一个无速度势二阶空间导数，无奇异积分的新的积分方程。     

二阶波浪力的切片理论与潜体上的垂向定常力

二阶波浪力的三维理论基本上是对无航速的结构物建立起来的，航速的影响不甚清楚，一些理论问题，例如二阶绕射势辐射条件的提法，直到最近才得以澄清，即使如此，用三维方法完整地求取物体上的二阶波浪力仍十分费时，本文中对有航速的细长物体建立了二阶波浪力的切片理论，旨在提供理论上合理，实用上相对简便的二阶力计算方法，作为完整的二阶波浪力的一个组成部分，文中给出了细长潜体在不同潜深和浪向角时所受的垂向常力及变化趋     

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。     

大直径圆柱体上的二阶波浪力

在二阶波浪力的计算中,二阶绕射势满足的非齐次自由条件,其非齐次项在整个自由面上不是绝对可积的,给解析或数值求解造成了困难。本文推广了周清甫的工作,对有限水深引进了一个“局部扰动源”,用此局部扰动源在自由面上的分布,构造了满足非齐次自由面条件的二阶势的特解。并进一步证明,此特解在远处收敛得足够快,只剩下外传的自由波,后者在无穷远处满足通常的Som-mevfeld条件。 按这个方法,本文得到了大直径圆柱体在有限水深中的完整的二阶绕射势,计算了二阶波浪力,并与实验数据和现有的计算结果进行了比较。比较表明,在波长稍大的地方,本文的结果有明显改善。     

近水面三维物体运动的时域计算

本文提出了求解近水面三维物体作任意运动时受到的水动力和产生的波浪的压力波方法。运动可以是大振幅的,但自由面条件是线性的。整个问题由自由面上分布偶极子和物面上布置源汇来模拟后,就可以分解为自由面上布有压力的压力波解和无限流场的绕流解。本文导出了水面布有压力为一般函数时的解析解,然后利用特殊函数的各种性质和公式积出了其中的四重无限积分,大大地简化了。三维的计算主要是计算机速度和内存空间的限制,故本文的方法有较大的实用价值。作为例子,本文计算了突然起动的圆球和回转体作定常运动时的水动力以及它幅射的波浪。结果与其它数值和PMM试验结果比较证实了本方法的合理性和计算的准确性。     

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。     

波浪和水流对大直径圆柱的共同作用力

本文将波流共同对圆柱作用的速度势分成合模势（无自由表面的绕流速度势）、流兴波势和非定常波势三部分。忽略小量的流兴波势，考虑合模势对非定常波势的影响，用直接边界元法求出非定常波势，从而求出波流共同对圆柱的作用力，提出了沿流线的自由表面条件和波流共同作用下散射波的幅射条件。文中给出了波流对大直径圆柱作用力曲线，可供工程设计使用，适用条件是相对水深ｄ／Ｌ＞０．１５，相对流速Ｕ／ｃ＜０．２。     

TIME-DOMAIN ANALYSIS OF WAVE FORCES ON SHIPS WITH FORWARD SPEED

Analyses of wave forces on Wigley and Series 60 ships at forward speedare presented in time domain which is based on a free surface transient Green functionwith linearized condition. The main effort focus on the investigation of the numerical sta-bility of time stepping calculation and the waterline intergal contribution to the excitingforces. Numerical study shows that the stable results can be obtained when a wall-sided as-sumption is used at the stern only and the effect of waterline can be neglected. Compar-isons have been made between the present time domain calculations and other works. Nu-merical results for the added resistance on a C_B=0.8 ship in short waves are presentedbased on the assumption that the steady disturbance of ship hull can be neglected.     

A TIME-DOMAIN METHOD TO PREDICT SHIP MOTIONS IN OBLIQUE SEAS AT FORWARD SPEEDS

Time-domain analysis is used to predict wave loading and motion responses for a ship travelling at a constant speed in regular oblique waves.The combined diffraction and radiation perturbations,caused by the steady forward speed of the ship and her motions,are considered as a distribution of normal velocities on the wetted hull surface.The ship-hull boundary condition is exactly fulfilled by expressing the fluid normal velocities as a finite series in terms of the body geometry and the incident wave potential.As far as the authors are aware,no similar work is published todate. The new theory is applied to predict forces and motions at forward speed for a Wigley ship-hull in head waves and a catamaran-ferry in oblique waves.Predictions are compared with published theoretical and experimental results for the Wigley ship-hull,and the comparison is good.For the catamaran,a self-propelled model is built and tested in the large towing tank and seakeeping basin of the China Ship Scientific Research Centre,Wuxi     

Iterative Rankine HOBEM analysis of hull-form effects in forward-speed diffraction problem

A time-domain numerical algorithm based on the higher-order boundary element method and the iterative time-marching scheme is proposed for seakeeping analysis. The ship waves generated by a hull advancing at a constant forward speed in incident waves and the resultant diffraction forces acting on the hull are computed to investigate the hull-form effects on the hydrodynamic forces. A rectangular computational domain travelling at ship's speed is considered. An artificial damping beach for satisfying the radiation condition is installed at the outer portion of the free surface except the downstream side. An iterative time-marching scheme is employed for updating both kinematic and dynamic free-surface boundary conditions for numerical accuracy and stability. The boundary integral equation is solved by distributing higher-order boundary elements over the wetted body surface and the free surface. The hull-form effects on the naval hydrodynamics are investigated by comparing three different Wigley models. Finally, the corresponding unsteady wave patterns and the wave profiles around the hulls are illustrated and discussed.     

An iterative Rankine BEM for wave-making analysis of submerged and surface- piercing bodies in finite water depth

A 3-D iterative Rankine Boundary Element Method （BEM） for seakeeping problem in time domain is developed in the framework of linear potential theory. Waves generated by both submerged and surface-piercing bodies moving at a constant forward speed in otherwise calm water, and the resultant steady wave pattern, wave profile and resistance are computed to validate this newly-developed code. A rectangular computational domain moving with the same forward speed as the body 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 obtained directly by solving the boundary integral equation, with the Rankine source used as the kernel function. An iterative time-marching scheme is employed for updating both kinematic and dynamic free surface boundary conditions to stabilize the calculation. Extensive results including the wave patterns, wave profiles and wave resistances for a submerged spheroid and a Wigley hull with forward speed are presented to validate the efficiency of the proposed 3-D time-domain higher-order approach. Finally, the sensitivity of ship-generated waves to the water depth is investigated. Computed results show satisfactory agreement with the corresponding experimental data and other numerical solutions.     

An iterative Rankine boundary element method for wave diffraction of a ship with forward speed

A 3-D time-domain seakeeping analysis tool has been newly developed by using a higher-order boundary element method with the Rankine source as the kernel function. An iterative time-marching scheme for updating both kinematic and dynamic free-surface boundary conditions is adopted for achieving numerical accuracy and stability. A rectangular computational domain moving with the mean speed of ship is introduced. A damping beach at the outer portion of the truncated free surface is installed for satisfying the radiation condition. After numerical convergence checked, the diffraction unsteady problem of a Wigley hull traveling with a constant forward speed in waves is studied. Extensive results including wave exciting forces, wave patterns and pressure distributions on the hull are presented to validate the efficiency and accuracy of the proposed 3-D time-domain iterative Rankine BEM approach. Computed results are compared to be in good agreement with the corresponding experimental data and other published numerical solutions.     

Flexural-gravity wave resistances due to a moving point source on 2-D infinite floating beam

The flexural-gravity wave responses due to a load steadily moving or suddenly accelerated along a rectilinear orbit are analytically studied within the framework of the linear potential theory. A thin viscoelastic plate model is used for a very large floating structure. The initially quiescent fluid in the ocean is assumed to be homogenous, incompressible, and inviscid, and the disturbed motion be irrotational. A moving line source on the plate surface is considered as a moving point in the two-dimensional coordinates. Under the assumptions of small-amplitude wave motion and small plate deflection, a linear fluid-plate coupling model is established. The integral solutions for the surface deflections and the wave resistances are analytically obtained by the Fourier transform method. To study the dynamic characteristics of the flexural-gravity wave response, the asymptotic representations of the wave resistances are derived by the residue theorem and the methods of stationary phase. It shows that the steady wave resistance is zero when the speed of moving load is less than the minimal phase speed. The wave resistances due to the accelerate motion consist of two parts, namely the steady and transient wave responses. Eventually the transient wave resistance declines toward zero and the wave resistance approaches the steady component as the time goes to the infinity. Furthermore, the effect of the strain relaxation time for this viscoelastic plate is studied and it exhibits more influence for a high-speed motion.     

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.     

三体船在斜浪规则波中运动响应预报方法研究

对于三体船在波浪中的水动力预报,航速效应和主体与片体间水动力干扰效应是水动力载荷合理预报的关键之处,需合理考虑.二维半势流理论可较为准确反映上述效应,已在三体船顶浪中垂向运动响应理论预报上获得了较为满意的结果.在此基础上,该文探讨了该方法在三体船斜浪中运动特别是横摇预报上的应用.为较准确获得三体船横摇运动时粘性阻尼贡献,采用三体船模静水中自由横摇衰减试验获得了自由横摇运动衰减曲线,并经能量法处理获得了船舶横摇阻尼系数.然后,结合二维半理论,获得了三体船运动数值解.数值解与斜浪规则波中运动响应模型试验结果符合较好,反映本文所采用的数值方法可较好地预测三体船斜浪中水动力载荷和运动,可用于三体船在波浪中耐波性评估.