基于NURBS的三维船体曲面重构

针对重大件货仿真系统中船体曲面造型问题，给出了基于NURBS(非均匀有理B样条方法)技术重构船体曲面的主要步骤。对于给定的船舶型值点，用累加弦长参数化方法构造节点矢量，用非均匀有理B样条方法进行横剖线和水线的全局插值，并构造出规整的船体曲面的插值点网格，进而重构出以NURBS为统一数学表达式的船体曲面。仿真结果表明应用NURBS方法重构出的三维船体具有高度真实感。     

基于傅汝德-克雷洛夫力非线性法的规则波浪中船舶运动数学模型

为准确预报规则波浪中船舶的运动, 提出基于四叉树划分的自适应网格法, 以生成船舶瞬时湿表面, 在船舶瞬时湿表面上计算傅汝德-克雷洛夫(F-K)力与静恢复力; 对于与波面相交的面元, 由于F-K力在波面处剧烈波动, 采用四叉树划分法进一步细分面元; 基于线性理论, 采用瞬时自由面格林函数在船舶平均湿表面上计算扰动力; 为避免瞬时自由面格林函数在自由液面处剧烈波动产生严重数值误差, 舍去扰动势所满足边界积分方程中的水线项, 并对迎浪前进速度为傅汝德数0.2的WigleyⅠ型船舶进行数值计算。计算结果表明: 对低于瞬时波面以下的船体部分, F-K力非线性法所需面元数更少, 为细网格法的1/4~1/8;除不规则频率外, 舍去与未舍去水线项所得水动力系数与试验值的相对误差分别小于33.4%、54.8%, 因此, 舍去水线项所得水动力系数更接近试验结果; 当入射波波幅为0.018 m, 波长与船长比为1.25时, 采用F-K力非线性法与线性法所得纵摇幅值响应因子的计算结果分别比试验值低3.2%、17.0%, 波长与船长比为2.00时, 采用F-K力非线性法与线性法所得纵摇幅值响应因子的计算结果分别比试验值低6.7%、13.5%, 可见, 采用F-K力非线性法能够准确地仿真规则波浪中船舶的运动。      

Numerical study on bank effects for a ship sailing in shallow channel

A numerical study on bank effects in shallow channels is carried out by using a first-order Rankine source panel method. A container ship sailing along a vertical bank and a sloping bank at different forward speeds, different water depths and different distances between the bank and the ship hull is taken as example. The sway force and yaw moment acting on the hull are calculated and the influences of the speed, water depth and distance between the bank and ship hull on the hydrodynamic force and moment are analyzed. This study can provide insight into the bank effects, as well as to give guidance on ship manoeuvring and control in restricted waterways, which is helpful to the navigation safety.     

Geometry modeling of ship hull based on non-uniform B-spline

In order to generate the three-dimensional (3-D) hull surface accurately and smoothly, a mixed method which is made up of non-uniform B-spline together with an iterative procedure was developed. By using the iterative method the data points on each section curve are calculated and the generalized waterlines and transverse section curves are determined. Then using the non-uniform B-spline expression, the control vertex net of the hull is calculated based on the generalized waterlines and section curves. A ship with tunnel stern was taken as test case. The numerical results prove that the proposed approach for geometry modeling of 3-D ship hull surface is accurate and effective.     

基于三维时域Green函数法的船舶在规则波浪中的运动数学模型

在小时间区域采用级数展开法, 在大时间区域采用渐进展开法, 在大、小时间过渡区域采用精细积分法, 对三维时域Green函数进行数值计算; 采用线性叠加原理求解船舶辐射与绕射问题, 构造出船舶在规则波浪中的运动数学模型, 并采用数值方法计算WigleyⅠ型船舶和S60型船舶以Froude数为0.2迎波浪航行时的水动力系数、波浪激励力与运动时间历程。计算结果表明: 由于不规则频率的影响, 当量纲一频率为1.7时, WigleyⅠ型船舶的垂荡附加质量计算结果比试验结果小44%, 当量纲一频率为2.5时, S60型船舶的纵摇阻尼系数计算结果比试验结果小43%;随着入射波频率的增加, WigleyⅠ型船舶和S60型船舶的水动力系数和波浪激励力的大部分计算结果与试验结果的相对误差小于30%, 且二者的变化趋势一致; 对于WigleyⅠ型船舶, 当波长与船长比为1.25时, 采用三维时域方法计算的垂荡幅值响应因子和纵摇幅值响应因子分别比试验值小11.3%和4.8%, 采用三维频域方法计算的垂荡幅值响应因子比试验值大48.4%, 纵摇幅值响应因子比试验值小48.4%, 当波长与船长比为1.50时, 采用三维时域方法计算的垂荡幅值响应因子和纵摇幅值响应因子分别比试验值小3.0%和11.3%, 采用三维频域方法计算的垂荡幅值响应因子比试验值大9.8%, 纵摇幅值响应因子比试验值小23.6%。可见, 采用三维时域方法能准确地仿真船舶在波浪中的运动时间历程。      

基于NURBS的船体曲面自适应三角网格剖分

针对面向曲面的三维船体性能计算和真实感图形显示问题,应用NURBS曲线、曲面理论,提出一种新颖的船体NURBS曲面三角形网格自动生成算法,运用四角编码方法和改进的曲面片平坦性检验方法,保证在递归分割船体NURBS曲面时,能够快速有效地分割出四边形网格,在曲面片的高度方向和边界处同时满足给定的精度要求,在此基础上,应用割角剖分算法将一个四边形网格剖分成两个或多个三角形网格。应用结果表明,应用该算法生成的三角形平面片能够较好地逼近船体曲面,避免出现网格间的裂缝,与二叉树、四叉树方法相比,四角编码方法明显节省了时间和空间,提高了算法效率。     

A Methodology for Curve and Surface Fitting with Adaptive Fairing for Digitized Points

Introduction In the process of part or product design, re-verse engineering is a method for constructing aCAD model from the physical part that already ex-ists[1-4]. The whole process starts from digitizingthe part, i.e., the measuring of coordinates of t…     

用面元法预报船舶的兴波阻力及波型

采用基于开尔文源的面元法求解航行于均匀流场中的船舶兴波问题．在船体湿表面上布置开尔文源，使其严格满足船体表面条件．数值计算中，首先采用分部积分对被积函数进行简化处理，然后采用高斯积分实现面元和线元上的积分，避免了被积函数为高频振荡函数所带来的数值计算的复杂性和不确定性．计算结果表明，其波型及兴波阻力系数与试验结果和其他数值方法相比均吻合较好．     

潜体非定常兴波问题的数值求解

开发了一种求解非定常兴波问题的基于非均匀有理B样条(NURBS)的三维面元法，应用该方法对潜体加速航行的情况进行了数值计算研究．基于势流理论，建立了线性边值问题．在物面上分布时域Kelvin源，物面和物面上的源强分布都用NURBS来表示．用时间步进的方法求解这一边值问题．对潜体中低速航行的情况进行了计算，给出了即时的波阻和波型。     

Computation of the viscous hydrodynamic forces on a KVLCC2 model moving obliquely in shallow water

The viscous hydrodynamic force and moment on ships moving obliquely in shallow water axe important for ship navigation safety. In the paper, the viscous flow field around a KVLCC2 model moving obliquely in shallow water is simulated and the hydrodynamic drag, lateral force and yaw moment acting on the hull are obtained by a general purpose computational fluid dynamics (CFD) package FLUENT with shear-stress transport (SST) k-w turbulence model. The numerical computation is performed at different drift angels and water depths. The numerical results are compared with experimental results, and a good agreement is demonstrated.     

Numerical research on wave-making resistance of trimaran

A 3D rankine panel method was developed for calculating the linear wave-making resistance of a tri-maran with Wigiey hulls. In order to calculate the normal vector and derivative of the body surface accurately,non-uniform rational B-spline (NURBS) was adopted to represent body surface and rankine source density.The radiation condition is satisfied using the numerical technology of staggered grids. Numerical results showthat the linear wave-making resistance of the trimaran can be calculated effectively using this method.     

Method to calculate resistance of high-speed displacement ship taking the effect of dynamic sinkage and trim and fluid viscosity into account

A method is presented to calculate the resistance of a high-speed displacement ship taking the effect of sinkage and trim and viscosity of fluid into account. A free surface flow field is evaluated by solving Reynolds averaged Navier-Stokes (RANS) equations with volume of fluid (VoF) method. The sinkage and trim are computed by equating the vertical force and pitching moment to the hydrostatic restoring force and moment. The software Fluent, Maxsurf and MATLAB are used to implement this method. With dynamic mesh being used, the position of a ship is updated by the motion of ??ship plus boundary layer?? grid zone. The hull factors are introduced for fast calculating the running attitude of a ship. The method has been applied to the ship model INSEAN2340 for different Froude numbers and is found to be efficient for evaluating the flow field, resistance, sinkage and trim.     

Application of method of fundamental solutions in solving potential flow problems for ship motion prediction

A novel panel-free approach based on the method of fundamental solutions (MFS) is proposed to solve the potential flow for predicting ship motion responses in the frequency domain according to strip theory. Compared with the conventional boundary element method (BEM), MFS is a desingularized, panel-free and integration-free approach. As a result, it is mathematically simple and easy for programming. The velocity potential is described by radial basis function (RBF) approximations and any degree of continuity of the velocity potential gradient can be obtained. Desingularization is achieved through collating singularities on a pseudo boundary outside the real fluid domain. Practical implementation and numerical characteristics of the MFS for solving the potential flow problem concerning ship hydrodynamics are elaborated through the computation of a 2D rectangular section. Then, the current method is further integrated with frequency domain strip theory to predict the heave and pitch responses of a containership and a very large crude carrier (VLCC) in regular head waves. The results of both ships agree well with the 3D frequency domain panel method and experimental data. Thus, the correctness and usefulness of the proposed approach are proved. We hope that this paper will serve as a motivation for other researchers to apply the MFS to various challenging problems in the field of ship hydrodynamics.     

局部气垫双体船阻力性能及片体间距优化研究

基于流体计算软件STAR-CCM＋,使用VOF法模拟自由液面,联立求解N-S方程及运动方程,并结合湍流模型RNGk-ε及DFBI六自由度模型,对局部气垫双体船型阻力性能进行数值模拟计算,计算结果与船模水池试验结果吻合,精度可信,验证了此该数值方案的可行性.在此基础上,针对局部气垫双体船的片体间距对阻力性能的影响进行数值仿真计算,并对结果进行对比分析,得到了不同片体间距下的阻力变化趋势.针对该局部气垫双体船,综合考虑越峰性能及高速段、低速段阻力性能对片体间距进行选取,认为0.34m的片体间距较为合理.文中使用的CFD方法能够有效模拟局部气垫双体船的阻力性能,可用于船型优化设计.     

The numerical simulation of a towing cylinder based on immersed body boundary method

An immersed body boundary method is adopted to track the motions of a towing cylinder, and a homogenous multiphase Eulerian-Eulerian fluid approach is used to capture the free surface. The Reynolds average Navier-Stockes (RANS) solver is applied to all gird nodes to deal with different velocities of the nodes that are in the body boundary, near the boundary and out of the boundary and their effect on the fluid. The towing cylinder resistance at different submerged depths in the tank is presented. The simulation results are compared with the experimental data, and the method is verified and validated. Finally, the hydrodynamic characters of the cylinder are discussed further. The numerical and experimental results show that at high speeds, the deeper the cylinder submerges, the lower resistance it suffers. The resistance coefficient trough is obtained at Froude number in the range of 0.3 < F r < 0.4. These phenomena can provide some suggestions on the small waterplane area twin hull (SWATH) design.     

小水线面双体船兴波阻力特性研究

介绍了基于米切尔Michell瘦船理论的一种小水线面双体船SWATH兴波阻力计算基本原理．运用敞篷函数对船体表面及流场进行了线性近似,建立了数值计算模型,对一类直／斜支柱SWATH兴波阻力进行计算,重点分析了支柱间距、倾角变化对兴波阻力的影响,并将计算结果与实验测试进行对比,二者基本吻合,证明该方法用于计算SWATH的兴波阻力是可行和有效的．     

基于NURBS高阶面元法的浅水船舶兴波阻力计算

实现了一种船舶兴波阻力和兴波波形的数值计算方法，将CFD与CAD技术联系在一起，应用NURBS曲面造型技术将船体曲面表达为统一的数学模型，使性能计算的真实物面条件得以满足，应用高阶面元法数值模拟单、双体船在浅水航道中定常直航状态下的兴波阻力与兴波波形，并与瑞典ShipFlow软件的计算结果进行比较分析，表明该方法是可行的．     

Numerical investigation on the hydrodynamic difference between internal and external turret-moored FLNG

Motion responses of the floating liquefied natural gas（FLNG）hull and the mooring loads in a 100-year return environmental condition are predicted with the help of the well known coupled dynamic analysis code DeepC.A ship-shaped turret-moored FLNG moored by 4×3 chain-polyester-chain lines in 1.5 km depth of water is studied.Two types of turrets such as internal and external turrets,resulting from diferent locations of the turrets,are adopted respectively in the numerical simulations.Motion responses of the FLNG hull and forces of the mooring lines obtained from the internal turret case and external turret case are compared with each other.Significant diferences are obtained.Statistic analysis is also used to analyze the comparison results,and efects of the turret location on the FLNG hydrodynamic characteristics are summed up.The conclusion regarding the hydrodynamic diferences between internal and external turret-moored FLNG systems would provide help for design of the FLNG system.     

船舶调度闸外编排算法

为了提高船闸的通过能力,优化船舶进闸调度,分析了三峡船闸船舶的平均过闸间隔时间,提出了闸外编排的概念,分析了船舶在进闸调度中的操作流程,以安全性和进闸耗时为目标,建立了闸外编排的数学模型,设计了相应的启发式求解算法,将模型的目标和约束条件通过启发式方法生成船舶在闸外的排序法则。数值试验分析结果表明闸外编排数学模型切实可行,排序算法可以生成安全高效的进闸方案,闸外编排的实现考虑了船舶进闸时间和安全性原则,缩短了闸次间隔时间,提高了日开闸次数,有效地提高了通航设施的整体通过能力。     

Numerical study on water depth effects on hydrodynamic forces acting on berthing ships

Due to the restrictions of ports, maneuverability of berthing ships will be affected significantly by water depth. In the present study, numerical simulation of the berthing maneuver of a ship with prescribed translational motion is performed by solving the Reynolds-averaged Navier-Stokes (RANS) equations based on overset grid, and the effects of the quaywall and freesurface are taken into consideration. To validate the present numerical method, comparison is performed between our results and the other results or measurements. It is found that the agreement is significantly better than that resulting from previous CFD-based approach. Subsequently, the effects of various water depths are investigated to evaluate their influences on hydrodynamic forces. The present results can provide helpful guidance on safe maneuvering for vessels’ berthing and fender system design in quays.