CFD performance prediction simulation for hull-form design of sailing boats

A new simulation method is developed for the design of sailing boats. A time-accurate, finite-volume method is combined with the equations of motion, and the hydrodynamic properties of sailing boats are predicted. The hull configuration is designed by a CAD system, and a boundary-fitted grid system is generated for the finite-volume method. Six components of forces and moments are derived by integrating surface pressure and tangential stress, and input into the equations of motion. The translational or rotational motions obtained are represented by the deformation of the grid system. This is repeated in a time-marching procedure. This system is applied to the prediction of both steady and unsteady sailing performance of boats. The degree of accuracy is examined, and two examples of performance simulation are presented.     

滑行艇波浪中运动性能试验研究

为了探究自主开发的滑行艇耐波性能,在拖曳水池中进行该滑行艇模型不同航速下的静水阻力试验、不同航速下变波长顶浪规则波试验与对应不同海况的不规则波试验,试验过程中记录阻力值和纵向运动响应值。对试验结果处理分析后发现:在排水体积傅氏数Fr=3.713时,滑行艇在5倍于船长的波长附近具有强烈的运动响应,出现了抨击和出水现象;与传统深V滑行艇相比,短波中该滑行艇具有更小的运动响应,滑行艇阻力增值较深V滑行艇有所减小;垂荡响应与航速与波高具有较好的线性关系,纵摇响应航速与波高具有弱非线性。     

单体半滑行穿浪船船型与静水航行性能

半滑行穿浪船是一种结合了混合式内倾型穿浪船艏和半滑行式水下船体的高速单体穿浪船,同时具有穿浪船的穿浪特性和半滑行船的航行特性,拥有良好的快速性和适航性.半滑行穿浪船采用具有折角设计的压浪型干舷,折角线在船长方向上与水线之间存在夹角.压浪干舷具有抑制内倾型船舶的干舷上浪、提供升力、增加储备浮力和减摇的作用.通过基于动网格的数值计算,对压浪干舷的纵向倾角及优选纵向倾角下的半滑行穿浪船在静水中的航行特性进行研究.计算结果表明:拥有较小纵向倾角的压浪干舷的使用效果较好;半滑行穿浪船同排水型穿浪船相比其在高速段的阻力和姿态得到了很大改善.     

新型高速艇的CFD模拟和对比分析

高速艇具有体积小、航速高、智能等优点,可以完成搜救、探测、导航和作战等多种任务,广泛应用于军民用领域。研究高速艇的阻力性能对艇体的型线设计和艇体的流体动力学性能分析都显得十分重要。设计一种新型高速艇,通过NUMECA系列软件对不同的高速艇进行数值模拟计算,以研究此类新型高速艇的水动力性能。研究表明：加装水翼或防飞溅条均可增加艇体的升力,使艇体更快地处于滑行状态,安装了防飞溅条的翼滑艇的阻力性能良好。     

Finite-volume simulation of flows about a ship in maneuvering motion

A finite-volume method of computing the viscous flow field about a ship in maneuvering motion was developed. The time-dependent Navier-Stokes equation discretized in the generalized boundary-fitted curvilinear coordinate system is solved numerically. A third-order upwind differencing scheme, a marker and cell (MAC)-type explicit time marching solution algorithm and a simplified subgrid scale (SGS) turbulence model are adopted. The simulation method is formulated, including the movement of a computational grid fitted to the body boundary that allows computation of the flow field around a body under unsteady motion. To estimate the maneuvering ability of a ship, the accurate prediction of the hydrodynamic forces and moments of the hull is important. Therefore, experimental methods of finding the hydrodynamic forces of a ship in maneuvering motion, such as the oblique towing test, the circular motion test (CMT) and planar motion mechanism (PMM) test, were established. Numerical simulation methods for those captive model experiments were developed introducing computational fluid dynamics (CFD). First, numerical methods for steady oblique tow and steady turn simulation were developed and then extended to unsteady forced motion. Simulations were conducted about several realistic hulls, and the results were verified by comparisons with measured results obtained in model experiments. Hydrodynamic forces and the moment, the longitudinal distribution of the hydrodynamic lateral force, and the pressure distribution on the hull surface showed good agreement.     

Three-dimensional numerical analysis of shipping water onto a moving ship using a particle method

The objective of this study was to develop a numerical analysis method based on the moving particle semi-implicit method for simulating shipping water on a moving ship. Towing tests of a very large crude carrier were numerically analyzed for three typical wavelengths. The ship was forced to move in order to express previously measured ship oscillations, and the calculated fluid behavior and the impact pressure on the deck were compared with the experimental results.     

Numerical simulation of wave-induced nonlinear motions of a two-dimensional floating body by the moving particle semi-implicit method

The moving particle semi-implicit (MPS) method was applied to compute nonlinear motions of a floating body influenced by the water on deck. To compute the motions of a rigid body, the fluid pressure at the position of each particle on the body surface was directly integrated in space and the equations of translational and rotational motions were integrated in time to determine the correct position of the rigid-body surface at each time step of the time-domain calculation. The performance of this method was validated through a comparison with measured results in an experiment that was newly conducted using a model of a box-shaped floating body with a small freeboard. Although the overall agreement was good, some discrepancies were observed for a shorter wave period, especially for the drift motion in sway. The effect of numerical resolution on the results was checked by changing the number of particles. With a higher number of particles, no obvious improvement was seen in the global body motions, but the resolution of the local free-surface profile, including the water on deck, was improved.     

面元法预估导管螺旋桨水动力性能的一种新方法

采用一种新的方法预估导管螺旋桨的水动力性能;导管和螺旋桨均采用基于速度势的面元法,它们间的影响通过相互的诱导速度势数值迭代来体现．与诱导速度体现相互影响的方法相比,本文方法可节省编程及计算时间;对JD系列导管螺旋桨的计算与实验结果的比较表明,该方法可以有效地预估导管螺旋桨的水动力性能．     

基于速度势迭代的面元法预报对转桨性能

采用基于诱导速度势迭代的面元法预报对转桨的定常水动力性能,在计算中,前桨和后桨的相互干扰通过影响系数实现;前桨尾涡面距后桨表面太近时的异变影响系数通过Lagrange插值求出。同时采用基于诱导速度迭代的面元法预报对转桨水动力性能,并与基于诱导速度势法进行对比,计算结果表明,采用诱导速度势迭代的方法计算的结果与试验值吻合良好。与基于诱导速度迭代的方法相比,计算结果精确,且可以节省计算时间。     

某型辅助船液压网机失力故障诊断与维修

针对某型辅助船液压传动绞网机失力(输出转矩大幅降低)故障,综合分析系统结构及工作原理,探究故障原因,维修工作采取重点控制措施,有效解决了失力问题。     

Mixed analysis of shell and solid elements using the overlaying mesh method

 This article presents a mixed method of analyzing shell elements and solid elements using the overlaying mesh method. In the structural design of a ship's hull, the shell elements are used for the global model. However, the solid elements are necessary to analyze the stress concentration zones or the vicinity of a crack. In such cases, the models are analyzed using zooming analysis, in which the results of a global model analysis are transferred to a local model analysis by imposing boundary conditions. This method is more advantageous than zooming analysis in terms of the accuracy of the solution and the modeling flexibility. Some examples of a plate model with a cracked surface or with a projection are shown in order to demonstrate the effectiveness of the method. Received: August 6, 2002 / Accepted: November 25, 2002 Address correspondence to: S. Nakasumi (sumi@nasl.t.u-tokyo.ac.jp) Updated from the Japanese original, which won the 2002 SNAJ prize (J Soc Nav Archit Jpn 2001;189:219–224; and 190:655–662)     

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。     

面元法预估导管螺旋桨定常性能的一种简便方法

用基于速度势的低阶面元法建立预估导管螺旋桨定常性能的计算方法,即对导管和螺旋桨都采用面元法,在计算面元的影响系数时计入导管和螺旋桨的相互影响。将对JD简易导管桨的计算与实验结果进行比较表明,该方法可以有效地应用于导管桨的定常性能计算。     

Structural safety assessment of a pontoon-type VLFS considering damage to the breakwater

 A structural safety assessment of a pontoon-type very large floating structure (VLFS) surrounded by a gravity-type breakwater was carried out for extreme wave conditions by considering the damage to the breakwater. Bending and shear collapses are considered to be a failure mode of the floating structure, while overturning damages the breakwater. The probability of the breakwater overturning, and the transmitted wave height before and after damage to the breakwater, are evaluated using design formulae for port and harbor facilities in Japan. The ultimate bending and shear strengths of the floating structure are calculated by the idealized structural unit method (ISUM) and FEM, respectively. The calculated failure probability for the floating structure is compared with the specified target safety level. It was found that the floating structure under consideration is most likely to fail by bending in transverse waves, and that the corresponding failure probability satisfies the target level. Received: September 12, 2002 / Accepted: October 4, 2002 Acknowledgment. The authors are grateful to Dr. Shigeo Ohmatsu, National Maritime Research Institute, Japan, for allowing us to use the program of hydroelastic response analysis. Address correspondence to: M. Fujikubo (e-mail: fujikubo@naoe.hiroshima-u.ac.jp) Updated from the Japanese original, which won the 2002 SNAJ prize (J Soc Arthit Jpn 2002;190:337–345)     

CFD方法预报螺旋桨敞水性能及CFD方法不确定度分析

螺旋桨作为船舶最常用的推进装置,在船舶高速化发展中发挥着举足轻重的作用。随着船舶载荷的增加,螺旋桨的水动力性能和敞水特性引起了国内外研究人员的广泛关注。螺旋桨在正常运行时,会受到非均匀尾流场的振动和空泡效应,使螺旋桨受到的脉动压力剧增,产生大量噪声的同时对螺旋桨的结构和性能造成损害。本文针对螺旋桨的水动力性能,采用CFD数值模拟技术和Fluent软件,对螺旋桨的敞水特性、噪声特性和不确定度等因素进行了系统的分析,对船舶螺旋桨的结构和流体力学设计具有重要的研究价值。     

A comparative study of the dynamic behaviour of a fast patrol boat travelling in rough seas

This paper describes a comparative study between full scale measurements recorded on a fast patrol boat encountering heavy winter seas, south of the Isle of Wight and theoretical predictions accounting for the slamming behaviour of the flexible hull. A hydroelastic approach is adopted and satisfactory agreement between measured and predicted responses demonstrated.     

动网格方法在螺旋桨非定常轴承力数值计算中的应用

为了探究螺旋桨轴承力的非定常变化特性,研究了动网格(DM)方法在螺旋桨非定常轴承力(UBF)数值计算中的适用性问题。首先,通过3套不同质量网格的数值计算比较,进行网格无关性检验,选出合适的计算网格。进一步采用所选网格DM数值模拟,并将结果与滑移网格(SM)方法、势流(PM)方法及试验方法得到的结果进行对比。分析结果显示了DM方法得到的螺旋桨UBF结果与SM方法以及试验的结果吻合较好,且优于PM方法。同时,DM方法与SM方法得到的流场分布也几乎一致。研究表明:DM方法应用于螺旋桨UBF数值计算是可行的。     

Long-term prediction method for the green water load and volume for an assessment of the load line

 To develop a practical prediction method for the green water load and volume on the bow deck in irregular waves, model tests were conducted using a tanker and a cargo ship on a domestic Japanese voyage. The relation between green water load and relative water height at the stem was considered. Based on the finding that the maximum value of the green water load is proportional to the square of the maximum value of the water elevation over the bow top, the probability density functions of the green water load and volume in short-term predictions were proposed. It was verified that the proposed functions show good agreement with the measured distributions, especially in the tails, and were better than conventional functions. Using these functions, long-term predictions of the green water load were carried out. It was confirmed that the present method is more rational than the conventional one for estimating the long-term probability of the green water load. An assessment of the bow height of a domestic Japanese ship from the viewpoint of deck wetness was carried out using these prediction methods. This research was used as the technical background for the revision of domestic rules on load lines, which was enforced in October 2001. Received: July 19, 2002 / Accepted: October 30, 2002 Acknowledgment. Some of the present study was carried out as part of a cooperation project (RR45) with the Shipbuilding Research Association of Japan, supported by the Nippon Foundation. Address correspondence to: Y. Ogawa (e-mail: ogawa@nmri.go.jp)     

Higher-order boundary element method for the interaction of a floating body with both waves and slow current

A hybrid boundary element method is suggested to solve the problem of the interaction of floating structures with both waves and slow current. A pulsating source and its mirror image referring to the sea bottom are adopted as the Green's function. The velocity potentials are expanded into an eigenfunction expansion in the outer region of the fluid domain while higher order elements are used to discretize the boundary surface surrounding the inner region. The method is validated by comparing calculated results for a circular cylinder with the semi-analytical solutions. The method is then applied to ellipsoids of various breadth and draft to investigate the influence of body shape on the wave drift damping.     

A study on the estimation of the seaquake response of a floating structure considering the characteristics of seismic wave propagation in the ground and the water

 Seaquakes, which are characterized by the propagation of vertical earthquake motion at the sea bottom as a compression (longitudinal) wave, are reported to cause damage to ships, and their effect on floating structures is a matter of great concern. To comprehend the basic properties of seaquakes, we first discuss a method to calculate the displacement of the seabed when it is subjected to hydrodynamic pressure. To investigate the interrelationship between the vibration of a floating structure and the deformation of the seabed, a new boundary integral equation is derived which assumes that the seabed is a semiinfinite homogeneous elastic solid in order to analyze the seaquake-induced hydrodynamic pressure acting on the floating structure. By considering the propagation of the seismic wave in the ground and in the water, the incident wave potential in seaquake problems is also deduced and its characteristics are discussed. Finally, the response of a very large floating structure in a seaquake is investigated using a fluid force analysis method, and considering the interrelationship between the vibration of the floating structure and the deformation of the seabed. Received: August 19, 2002 / Accepted: November 11, 2002 Address correspondence to: H. Takamura (hiroaki_takamura@nishimatsu.co.jp) Updated from the Japanese original, which won the 2002 SNAJ prize (J Soc Nav Archit Jpn 2001;189:87–92,93–100 and 190:381–386)