Self-propulsion computations using a speed controller and a discretized propeller with dynamic overset grids

A method that can be used to perform self-propulsion computations of surface ships is presented. The propeller is gridded as an overset object with a rotational velocity that is imposed by a speed controller, which finds the self-propulsion point when the ship reaches the target Froude number in a single transient computation. Dynamic overset grids are used to allow different dynamic groups to move independently, including the hull and appendages, the propeller, and the background (where the far-field boundary conditions are imposed). Predicted integral quantities include propeller rotational speed, propeller forces, and ship’s attitude, along with the complete flow field. The fluid flow is solved by employing a single-phase level set approach to model the free surface, along with a blended k−ω/k−ɛ based DES model for turbulence. Three ship hulls are evaluated: the single-propeller KVLCC1 tanker appended with a rudder, the twin propeller fully appended surface combatant model DTMB 5613, and the KCS container ship without a rudder, and the results are compared with experimental data obtained at the model scale. In the case of KCS, a more complete comparison with propulsion data is performed. It is shown that direct computation of self-propelled ships is feasible, and though very resource intensive, it provides a tool for obtaining vast flow detail.     

基于三维势流理论的耐波性数值预报

准确预报船体运动响应对于砰击等波浪载荷的计算以及合理结构设计具有重要意义。船舶在大幅波浪中的运动呈明显的非线性,而现阶段耐波性预报多采用线性切片方法。三维水动力分析软件 WASIM基于时域势流理论,采用 Rankine面元法预报船舶在波浪中的运动响应,并考虑了多种非线性因素。本文以标模 DTMB5512为对象,采用 WASIM预报其在不同航速下的耐波性,并与基于线性切片理论的计算结果和模型试验结果进行对比。结果表明：利用 WASIM计算得到的船体运动响应比其他方法更接近试验值,合理体现了船舶在风浪中的实际耐波性能。因此,利用 WASIM能够较好地评估船舶在波浪中的非线性耐波特性。     

几种千吨级高性能船耐波性对比分析

为了对比分析千吨级单体圆舭船型、深V船型、穿浪双体船型、三体船的耐波性能,采用二维半理论方法计算各船型在迎浪规则波中的摇荡及首中尾部垂向加速度的频率响应函数,其中应用时域格林函数求解水动力系数,应用谱分析计算各船型在不规则波中的运动有义值.结果表明,几种千吨级高性能船在波浪中的纵向运动性能均比常规圆舭船型优,其中三体船纵向运动性能最佳.计算结果可为该吨级舰船平台选型提供技术支持.     

小水线面双体船在波浪中的运动响应预报

用切片理论方法发展了SWATH船耐波性预报程序，提供了390t方案的油田小水线面交通船计算分析结果，包括规则波中纵向运动频率响应函数的计算及不规则波中各种海况下的运动有义值预报。     

静水中并行两船水动力干扰数值研究

为比较分析单船与两船并行航行的水动力差异,探讨静水中两船并行时漂角、船船相对位置对船体阻力、侧向力及摇首力矩的影响规律,文章基于RANS方程采用SST k-棕湍流模型,数值分析了某两船静水并行时船船相互作用。研究表明：不同漂角下两船中对中并行时,船体所受阻力均较单船航行时有所增大且受到指向两船中间的附加侧向力;当两船并行斜航的漂角相反时,同一船舶位于迎流侧较背流侧时船体受力存在一定差异;两船并行直航时,船船相对位置对船体受力有较大的影响,当两船纵向间距小于一倍船长时,船船相互作用较为显著,在不同横向间距下,船体受力随纵向间距的变化规律相同,在一定纵向间距下,船间横向间距越小船船相互作用越强。     

某豪华游轮在波浪中的耐波性能预报(英文)

The seakeeping performance of a luxury cruise ship was evaluated during the concept design phase. By comparing numerical predictions based on 3-D linear potential flow theory in the frequency domain with the results of model tests, it was shown that the 3-D method predicted the seakeeping performance of the luxury cruise ship well. Based on the model, the seakeeping features of the luxury cruise ship were analyzed, and then the influence was seen of changes to the primary design parameters (center of gravity, inertial radius, etc.). Based on the results, suggestions were proposed to improve the choice of parameters for luxury cruise ships during the concept design phase. They should improve seakeeping performance.     

大型豪华邮轮在迎浪中非线性运动预报方法研究

目前工程上通常采用的线性理论耐波性预报方法尚不能够准确地预报船舶非线性运动,而全非线性理论预报又因为耗时长不能广泛应用于实际工程中。现将基于切片理论的频域线性预报方法加以扩展,考虑湿表面变化的非线性因素,在时域中求解船舶非线性运动。通过对某艘大型豪华邮轮的非线性运动耐波特性研究,对其理论计算结果与试验结果比较,表明该预报方法能够较好地评估该船的非线性运动耐波特性。给出的计算方法简便、实用,适用于船舶纵向非线性运动预报,对船舶设计阶段的耐波性能评估具有一定的工程实用价值。     

Large-amplitude motion responses of a Ro–Ro ship to regular oblique waves in intact and damaged conditions

This article presents a nonlinear time-domain simulation method for the prediction of large-amplitude motions of a Ro–Ro ship in regular oblique waves in an intact and a damaged condition. Numerical computations and model tests have been carried out to investigate the dynamic motion responses of Ro–Ro ship Dextra to various wave amplitudes at three different wave headings. The results of numerical and experimental investigations for stern quartering waves are reviewed. Comparisons between predictions and measurements show good agreement except in the roll-resonant region. Nonlinear effects are significant in horizontal modes of motion, and resonant roll motion, and there is strong coupling between all modes of motion in the roll-resonant region for large-amplitude responses. On the other hand, the time-domain simulation technique suffers from numerical drift in horizontal modes of motion as wave amplitude increases. This is due to nonlinear equations of motion and the lack of a restoring force and moment in horizontal motion. Received: April 30, 2002 / Accepted: August 9, 2002 Acknowledgments. II Programme of the European Community Commission under contract No. BRPR-CT97-0513. Address correspondence to: H.S. Chan (hoi-sang.chan@ncl.ac.uk)     

Forecasting fishing vessel responses in coastal areas

A system for forecasting the operability of ships was developed by extending a wave forecasting system with the ship responses to the forecast sea states. The system produces 4-day wave forecasts in an implementation for the Portuguese Exclusive Economic Zone, where the vessels’ seakeeping performance is forecast, although the method presented could well be applied to any other coastal region. The proposed procedure requires the knowledge of the transfer functions for different ship speeds and headings. The computations are made for two different types of fishing vessels that currently operate in the Portuguese coast. Ship motions and derived responses are evaluated with a strip theory code and compared with the prescribed values of relevant seakeeping criteria that represent the limit conditions that still allow standard operational conditions for those vessels. For each forecast sea state at each grid point at a given time, the response spectrum is calculated and operability indexes are computed and compared with the maximum allowed values for a specific operation criterion. The results are presented as operational index maps for various areas of the Portuguese coast, and the information provided by system will help ship masters to plan the operation of their ships, namely to decide the areas to operate in anticipation. In this way, they can identify areas in which the level of operationally of their ships will be degraded due to weather conditions and avoid them.     

一种有效近似建模方法及船舶耐波性代理模型构建

船舶耐波性能预报计算过程复杂,会受到诸多设计变量的影响;且采用高精度商业软件如CFD预报船舶性能的计算代价非常高。文章采用拉丁超立方方法进行了设计空间抽样。定义了一个新的综合衡准指标来表达船舶耐波性能,即短期和长期作用下船舶非工作时间百分数。考虑了船舶耐波性能中的五个运动方向：横摇、纵摇、转艏、横荡和升沉。为提高船舶耐波性能计算效率,一种有效的近似建模方法—单参数Lagrangian 支持向量回归算法被用于训练并构建代理模型以预报船舶耐波性能,且该算法是由作者在过去的研究工作中首次提出。以海洋平台支援船（OSV）为例,采用SPL-SVR算法预报船舶耐波性能,并与基于NAPA计算仿真结果、人工神经网络和经典支持向量回归算法进行对比。该文考虑OSV的两种速度,建立了海洋平台支援船短期作用下非工作时间百分数的耐波性能响应面模型,结果显示采用SPL-SVR算法建立的船舶耐波性能响应面模型比较适合船型初步设计的工程实际应用,并具有较高的计算效率。     

Surf-riding and oscillations of a ship in quartering waves

The behavior of a ship encountering large regular waves from astern at low frequency is the object of investigation, with a parallel study of surf-riding and periodic motion paterns. First, the theoretical analysis of surf-riding is extended from purely following to quartering seas. Steady-state continuation is used to identify all possible surf-riding states for one wavelength. Examination of stability indicates the existence of stable and unstable states and predicts a new type of oscillatory surf-riding. Global analysis is also applied to determine the areas of state space which lead to surf-riding for a given ship and wave conditions. In the case of overtaking waves, the large rudder-yaw-surge oscillations of the vessel are examined, showing the mechanism and conditions responsible for loss of controllability at certain vessel headings.List of symbols c wave celerity (m/s) - C(p) roll damping moment (Ntm) - g acceleration of gravity (m/s²) - GM metacentric height (m) - H wave height (m) - I _x ,I _z roll and yaw ship moments of inertia (kg m²) - k wave number (m^–1) - K _H ,K _W ,K _R hull reaction, wave, rudder, and propeller - K _p forces in the roll direction (Ntm) - m ship mass (kg) - n propeller rate of rotation (rpm) - N _H ,N _W ,N _R hull reaction, wave, rudder, and propeller - N _P moments in the yaw direction (Ntm) - p roll angular velocity (rad/s) - r rate-of-turn (rad/s) - R(,x) restoring moment (Ntm) - Res(u) ship resistance (Nt) - t time (s) - u surge velocity (m/s) - U vessel speed (m/s) - v sway velocity (m/s) - W ship weight (Nt) - x longitudinal position of the ship measured from the wave system (m) - x _G ,z _G longitudinal and vertical center of gravity (m) - x _S longitudinal position of a ship section (S), in the ship-fixed system (m) - X _H ,X _W ,X _R hull reaction, wave, rudder, and propeller - X _P forces in the surge direction (Nt) - y transverse position of the ship, measured from the wave system (m) - Y _H ,Y _W ,Y _R hull reaction, wave, rudder, and propeller - Y _p forces in the sway direction (Nt) - z _Y vertical position of the point of action of the lateral reaction force during turn (m) - z _W vertical position of the point of action of the lateral wave force (m) Greek symbols angle of drift (rad) - rudder angle (rad) - wavelength (m) - position of the ship in the earth-fixed system (m) - water density (kg/m³) - angle of heel (rad) - heading angle (rad) - _e frequency of encounter (rad/s) Hydrodynamic coefficients K roll added mass - N _v ,N _r yaw acceleration coefficients - N _v N _r N _rr N _rrv ,N _vvr yaw velocity coefficients K. Spyrou: Ship behavior in quartering waves - X _u surge acceleration coefficient - X _u X _vr surge velocity coefficients - Y _v ,Y _r sway acceleration coefficients - Y _v ,Y _r ,Y _vv ,Y _rr ,Y _vr sway velocity coefficients European Union-nominated Fellow of the Science and Technology Agency of Japan, Visiting Researcher, National Research Institute of Fisheries Engineering of Japan     

一型小水线面双体船的水动力性能与结构设计

简要介绍了中国船舶重工集团公司(CSIS)建立和发展的一种小水线面双体船(SWATH)优化设计工程技术系统.主要包括SWATH船型的概念设计、主尺度与线型优化、有效功率预报、纵向运动稳定性校验及稳定鳍设计、耐波性预报、结构载荷评估、波浪中的船体结构动、静响应分析等有关设计、预报与评估的系统方法.并以一型1500吨级小水线面双体型海洋调查船设计和评估为例对有关设计方法进行了说明和验证,在该船设计中,采用线性和非线性三维水弹性理论来预报载荷与评估在波浪中航行船体的结构安全性,同时在中国船舶科学研究中心(CSSRC)的拖曳水池与耐波性水池中进行了阻力与自航、耐波性与操纵性、波浪载荷等船模拖曳及自航试验.文中还给出了该船有关优化设计及模型试验结果.     

Comparison of CFD and EFD for the Series 60 C B= 0.6 in steady drift motion

 This paper presents comparisons of computational and experimental fluid dynamics results for boundary layers, wakes, and wave fields for the Series 60 C _B= 0.6 ship model in steady drift motion. The numerical method solves the unsteady Reynolds-averaged Navier–Stokes and continuity equations with the Baldwin–Lomax turbulence model, exact nonlinear kinematic and approximate dynamic free-surface boundary conditions, and a body/free-surface conforming grid. The experimental and computational conditions, i.e., Froude numbers of 0.16 and 0.316 for the experiments, and Froude numbers of 0 and 0.316 for the computations, allow comparisons of low and high Froude number results, respectively, which allows an evaluation of Froude number effects and validation of the computational fluid dynamics at both low and high Froude numbers. This article gives an overview of this numerical approach, and the computational conditions and uncertainty analysis are described. Results are presented for the wave and flow fields, with emphasis on the important flow features of drift- and wave-induced effects in comparison with the experiments. Finally, conclusions from the present study are given, together with recommendations for future work. Received: August 31, 2001 / Accepted: March 25, 2002     

近水面波浪力作用下潜体的非线性运动响应

通过对潜体近水面航行波浪力作用下非线性运动响应进行建模和计算，揭示了由于二阶波浪力民低速时潜艇操纵面舵力之不足，潜体的定深控制可能难于实现，产生逐渐上浮与露出波面的非线性现象。计算结果与自由自航模的试验结果相当吻合。     

基于AQWA计算规则波中新型海工船的运动响应

本文应用三维势流理论的水动力软件AQWA分析一种新型工程船舶在波浪中的运动响应,新型船为改造的波兰中型集装箱船B-573,设计搭载Pram型艉和POD吊舱式推进系统的新型海工船.本文计算此船在规则波中不同浪向角条件下的六个自由度的频域和时域的运动响应,得到在不同浪向角下船体的响应振幅算子RAO,计算船舶顺浪下不同船速的垂荡RAO以及纵荡、垂荡和纵摇三个自由度的一阶、二阶波浪力,分析结果显示该新船型具有良好的耐波性.     

船舶垂荡与纵摇耦合运动频率散射机制研究

针对船舶纵向速度振荡对垂荡与纵摇耦合运动建立运动响应模型,基于弗劳德-克雷洛夫假定,采用切片法推导切片的浮力、阻尼力和惯性力,通过对切片的积分得到了船体垂荡与纵摇的水动力(矩),推导并得到垂荡与纵摇耦合运动响应方程。以某隐身船为实例,初步分析遭遇频率散射强度和散射频率对耦合运动的影响,得到增大散射强度和散射频率可以减弱耦合运动及其剧烈程度的初步结论。     

Study on real-time estimation of the ship motion cross spectra

 Time-varying coefficient vector autoregressive (T-VVAR) modeling with instantaneous responses is applied to spectrum analysis based on the nonstationary motion data of ships. Because of the ship's maneuvers, changes such as course and speed, the ship motions in waves are regarded as a nonstationary random process, although the seaway can be considered as a stationary stochastic process. The T-VVAR model is transformed into a state space model, and the time-varying coefficients can be evaluated by using the Kalman filter algorithm. Using the estimated time-varying coefficients, the instantaneous cross spectra of the ship motions can be calculated at every moment. In order to examine the reliability of the proposed procedure, on-board tests were carried out. Under stationary conditions, at a constant speed and course, the proposed method shows good agreement with stationary vector autoregressive (SVAR) modeling analysis. Moreover, it is confirmed that the proposed method can estimate the instantaneous cross spectra of the ship motions even under nonstationary conditions, showing that this is a powerful tool for on-line analysis of the nonstationary motion data of ships. Received: August 2, 2002 / Accepted: November 28, 2002 Acknowledgments. The authors thank the captain and crew of the training ship Shioji Maru, Tokyo University of Mercantile Marine. Address correspondence to: T. Iseki (iseki@ipc.tosho-u.ac.jp) Updated from the Japanese original, which won the 2002 SNAJ prize (J Soc Nav Archit Jpn 2001;190:161–168)     

Broaching prediction in the light of an enhanced mathematical model,with higher-order terms taken into account

 We have attempted to develop a more consistent mathematical model for capsizing associated with surf-riding in following and quartering waves by taking most of the second-order terms of the waves into account. The wave effects on the hull maneuvring coefficients were estimated, together with the hydrodynamic lift due to wave fluid velocity, and the change in added mass due to relative wave elevations. The wave effects on the hydrodynamic derivatives with respect to rudder angles were estimated by using the Mathematical Modelling Group (MMG) model. Then captive ship model experiments were conducted, and these showed reasonably good agreements between the experiments and the calculations for the wave effects on the hull and the rudder maneuvring forces. It was also found that the wave effects on restoring moments are much smaller than the Froude–Krylov prediction, and the minimum restoring arm appears on a wave downslope but not on a wave crest amidship. Thus, an experimental formula of the lift force due to the heel angle of the ship is provided for numerical modelling. Numerical simulations were then carried out with these second-order terms of waves, and the results were compared with the results of free-running model experiments. An improved prediction accuracy for ship motions in following and quartering seas was demonstrated. Although the boundaries of the ship motion modes were also obtained with both the original model and the present one, the second-order terms for waves are not so crucial for predicting the capsizing boundaries themselves. Received: June 20, 2002 / Accepted: October 10, 2002 Acknowledgments. This research was supported by a Grant-in-Aid for Scientific Research of the Ministry of Education, Culture, Sports, Science and Technology of Japan (No. 13555270). The authors thank Prof. N. Rakhmanin of the Krylov Ship Research Institute for providing the Russian literature, as well as Mr. H. Murata of NHK (Japan Broadcasting Corporation) for translating it into Japanese. Address correspondence to: N. Umeda (e-mail: umeda@naoe.eng.osaka-u.ac.jp)     

保证耐波性能的目标函数的Wigley船型优化(英文)

The research performed in this paper was carried out to investigate the computational procedure to design seakeeping optimized ship hull form. To reach the optimized hull form, four stages should be done, which consists of: generate alternative hull form, seakeeping calculations, objective functions and optimization techniques. There are many parameters that may be determined in ship hull form optimization. This paper deals with developed strip theory for determining the seakeeping performance, genetic algorithm(GA) as optimization method, high order equations for curve fitting of the hull form and finally reaching to the minimum bow vertical motion in regular head waves. The Wigley hull is selected as an initial hull and carried to be optimized. Two cases are considered. For the first case, the only form coefficients of the hull(C B, C M, C W, C P) are changed and main dimensions(L, B, T) are fixed. In the second case both hull form and main dimensions are varied simultaneously. Finally, optimized hull form and its seakeeping performances are presented. The results of optimization procedure demonstrate that the optimized hull forms yield a reduction in vertical motion and acceleration.     

Manoeuvring characteristics of twin-rudder systems: rudder-hull interaction effect on the manoeuvrability of twin-rudder ships

With a recent increase in ship capacity and propulsion performance, a wide-beam ship fitted with a twin-rudder system has been adopted in many cases. However, to improve ship manoeuvring, it is still necessary to have a better understanding of rudder-hull interactions in twin-rudder ships. Captive model tests (oblique towing and circular motion test) as well as free-running tests with a single-propeller twin-rudder ship and a twin-propeller twin-rudder ship are carried out. The effect of drift angle on the rudder forces and some peculiar phenomena concerning rudder normal force for twin-rudder ships are evaluated. A method for estimating the hull-rudder interaction coefficients based on free-running experimental results is proposed.