Time-domain numerical and segmented ship model experimental analyses of hydroelastic responses of a large container ship in oblique regular waves

Real sea conditions are characterized by multidirectional sea waves. However, the prediction of hull load responses in oblique waves is a difficult problem due to numeral divergence. This paper focuses on the investigation of numerical and experimental methods of load responses of ultra-large vessels in oblique regular waves. A three dimensional nonlinear hydroelastic method is proposed. In order to numerically solve the divergence problem of time-domain motion equations in oblique waves, a proportional, integral and derivative (PID) autopilot model is applied. A tank model measurement methodology is used to conduct experiments for hydroelastic responses of a large container ship in oblique regular waves. To implement the tests, a segmented ship model and oblique wave testing system are designed and assembled. Then a series of tests corresponding to various wave headings are carried out to investigate the vibrational characteristics of the model. Finally, time-domain numerical simulations of the ship are carried out. The numerical analysis results by the presented method show good agreement with experimental results.     

基于南海波浪要素的波浪滑翔机翼板参数优化设计与仿真

针对南海不同波浪要素条件下波浪滑翔机翼板参数设计的问题进行研究。基于欧洲中尺度天气预报中心大气和海洋全球再分析数据集(ERA5), 对南海不同季节以及台风经过时的波高波周期进行统计。并利用FLUENT软件研究南海不同波浪要素条件下翼板最大偏转角度、转轴位置以及翼板间距对波浪滑翔机水下翼板平均推力的影响。仿真结果表明, 波高越大, 翼板最大偏转角度也应相应增大, 才能保证翼板获得更大的推力; 在南海波浪要素条件下, 翼板转轴位置选取在翼板前端1/5处较佳; 适当增加翼板间距能够提高翼板获得的推力。通过对翼板被动摆动进行仿真, 得到了翼板在不同参数设置下产生的推力, 为波浪滑翔机翼板设计提供参考。     

Prediction of design wave loads of the ocean structure by equivalent irregular wave approach

The present study is employing the equivalent irregular wave approach to predict the wave loads for a ship encountering the worst sea state with respect to the critical dynamic loading parameter. Two different hydrodynamic numerical models, i.e. 3D pulsating source technique and 3D translating pulsating source technique, are applied to calculate the corresponding RAO of the ship moving in waves. Incorporating the RAO of the related physical properties, we can calculate the extreme value for the corresponding ship loading factor, which can be regarded as the worst sea state in the service lifetime of the ship. With the time and period of the occurrence of the corresponding extreme value, we can simulate the time history of the wave load in this period, which is so-called equivalent irregular wave approach. Comparing with the results calculated by the traditional equivalent regular wave approach, we find that the equivalent irregular wave approach can simulate the corresponding wave load more realistic, especially for dynamic pressure. Using the equivalent irregular wave approach can offer the effective and practical base for the ship structural analysis.     

Model test and simulation of a ship with wavefoils

The paper describes model tests of a tanker with two fixed bow-mounted foils (wavefoils), for resistance and motion reduction in waves. Measured ship resistance, wavefoil thrust and ship motions were compared with time-domain simulations. The wavefoil forces were calculated using a slightly modified Leishman–Beddoes dynamic stall model, with a two-way coupling to the ship motions. In typical sea states in head seas, employing the wavefoils reduced ship resistance by 9–17%, according to scaled model test resistance. Heave and pitch were reduced by −11% to 32% and 11% to 25%, respectively. The foils affect the flow around the hull. This should be considered when selecting the wavefoil location in the design process.     

船载波浪发电设备设计及其性能研究

为解决小型无人船由于船体空间紧凑,携带燃料较少导致的续航力差、航程短等问题,本文以三体船为平台,将摆式波浪能发电技术与多体船相结合,提出了一种新型船载波浪发电设备设计方案。该发电设备可由主侧船体之间的波浪运动响应差异驱动,在海上航行时捕获波浪能并转化为电能,以此来补充船上能源。通过数值软件对三体船进行性能预报,结果表明,在四级海况下迎浪航行时,三体船平均波浪能捕获功率可达3.57 kW,波浪能一级转换效率为7.32%,能够有效的补充船上能源。同时,安装船载波浪发电设备具备减摇减荡的效果,提升了三体船的航行稳定性,进一步体现了该装置的可行性和实用性。     

Research on Design Method of the Full Form Ship with Minimum Thrust Deduction Factor

In the preliminary design stage of the full form ships, in order to obtain a hull form with low resistance and maximum propulsion efficiency, an optimization design program for a full form ship with the minimum thrust deduction factor has been developed, which combined the potential flow theory and boundary layer theory with the optimization technique. In the optimization process, the Sequential Unconstrained Minimization Technique(SUMT) interior point method of Nonlinear Programming(NLP) was proposed with the minimum thrust deduction factor as the objective function. An appropriate displacement is a basic constraint condition, and the boundary layer separation is an additional one. The parameters of the hull form modification function are used as design variables. At last, the numerical optimization example for lines of after-body of 50000 DWT product oil tanker was provided, which indicated that the propulsion efficiency was improved distinctly by this optimal design method.     

深远海养殖工船最小推进功率研究

针对十万吨级深远海养殖工船在波浪中的阻力和运动响应开展了船模试验与模拟计算,并对其最小推进功率进行了校核。以试验流体力学（EFD）模型试验与模型尺度计算流体力学（CFD）模拟计算的结果进行对比作为方法验证,将实尺度CFD模拟计算的结果直接用于最小推进功率的校核。结果显示,EFD模型试验结果与模型尺度CFD计算结果误差在10%左右,计算精度满足工程要求。在规定的恶劣海况下该船型波浪增阻占总阻力的比例最高可达56.3%,螺旋桨转矩可达最大转矩的63.9%。等级2简化评估法得到的最小推进功率为等级1线评估法给出的最小功率线值的58.9%。研究表明实尺度CFD模拟计算可直接用于船舶最小推进功率的校核,此深远海养殖工船使用等级2简化评估方法进行校核更容易满足规范要求,其最小推进功率应不小于6 833 kW。     

Transformation of a wave energy spectrum from encounter to absolute domain when observing from an advancing ship

The article presents a practical approach to transform a wave energy spectrum from encounter domain to absolute domain. This problem has its specific relevance, when shipboard sea state estimation is conducted by the wave buoy analogy; notably for some particular implementation solving for the sea state directly in the encounter domain. In this context, the encounter domain is that observed from a ship when it advances in a seaway, whereas the absolute domain is that corresponding to making observations from a fixed point in the inertial frame. Spectrum transformation can be uniquely carried out if the ship sails “against” the waves (beam to head sea) but in following sea conditions there exists no unique solution to the problem. Instead, a reasonable approach valid for practical engineering must be applied, and the article outlines one viable solution that can be used to transform a wave spectrum from encounter to absolute domain. Specifically, two pseudo algorithms are presented, and good performance is achieved with both algorithms when they are tested at different operational scenarios.     

Calculation Methods of Added Resistance and Ship Motion Response Based on Potential Flow and Viscous Flow Theory

To improve the energy efficiency of ships and to predict ship motion response under actual sea conditions, the far-field theory, strip theory, and Fujii and Takahashi’s modified semi-empirical method are based and studied to calculate the wave-induced added resistance. Firstly, a new modified formula based on the Maruo method is presented to calculate the radiation added resistance for the ship with a complex surface. Meanwhile, some calculation details such as the Green function, the shape of the sections (shape below the still water level or shape below the wave level) in the strip theory, and so on are discussed. Finally, the CFD method is used to simulate the motions of the hull and the added resistance, and the results of the CFD method and those of other numerical methods are analyzed and compared with the experiment results. The modified method in the paper can predict the added resistance in waves for the complex-hull-surface ships well and quickly.

     

Effects of flexibility on propulsive force acting on a heaving foil

The hybrid Cartesian/immersed boundary method is applied to simulate effects of flexibility on propulsive force acting on a heaving foil in a viscous flow. Immersed boundary nodes are distributed inside an instantaneous fluid domain. Velocity vector is reconstructed at the immersed boundary node based on an interpolation along a local normal line. Using the staggered/non-staggered grid method, the demand for pressure at boundary nodes is removed. Elastic deformation of the flexible foil is modelled based on the dynamic thin-plate mechanics. The developed code is validated through comparisons with other computations on flow fields around a flapping foil. The generation of the reverse Karman vortex street is investigated. Forces acting on heaving foils are compared for flexible and rigid cases and the increased thrust of the flexible foil is attributed to the deformed configuration near the tip. The flexibility of the heaving foil decreases vertical force and improves propulsion efficiency. The variations of force and deformation are investigated according to bending stiffness of the foil.     

涌浪作用下港内大型集装箱船运动特性数值研究

随着船舶大型化和港口建设深水化发展,外海不同周期波浪作用下大型系泊船泊稳问题与小型系泊船相比出现了新的特点。为此,利用数值模型方法研究了在不同入射角度和周期的涌浪作用下港内大型系泊船的水动力响应,针对系泊船的泊稳情况探讨了船舶的运动规律和运动特性。研究发现,在涌浪周期较大的情况下,限定波高的泊稳标准不足以用来确定系泊船的正常作业条件,港内泊船的水平运动（纵荡、横荡和艏摇）极易超出运动标准值并影响装卸作业效率,并且船舶的水平运动表现出主要由次重力波主导的低频运动特性,而垂直运动（垂荡、横摇和纵摇）表现出主要由短波主导的波频运动特性。     

A parametric study of wave loads on trimaran ships traveling in waves

In this paper, we present a spectral analysis based on wave loads to select suitable side-hull arrangements for a trimaran ship traveling in waves. Neglecting the steady flow effect, the three-dimensional source-distribution method, using a pulsating source potential incorporating the panel method, is adopted to solve the corresponding hydrodynamic coefficients. The significant values for wave loads, including shear forces, bending moments, and torsion moments at different locations on the main hull and connected deck with respect to different staggers and clearances, are derived by the spectral analysis. Several ship speeds and wave headings are also considered for comparison. This study offers more information for selecting the side-hull arrangement from the viewpoint of wave loads on trimaran ships, which may be regarded as helpful references for seakeeping design of these types of ships.     

An experimental method to identify a component of wave orbital motion in propeller effective inflow velocity and its effects on load fluctuations of a ship main engine in waves

Improvements of estimation accuracy on propeller torque fluctuations in waves will contribute assessments on safe operation of a ship main engine as in adverse sea condition. The propeller torque and thrust in waves can be estimated by propeller effective inflow velocity in waves, using the propeller open-water characteristics. Fluctuation components in the mathematical model of the propeller effective inflow velocity in waves can be composed of two components, respectively caused by ship surge motion and wave orbital motion at propeller position. In this study, an experimental method by the model test to directly identify the characteristics of the component by the wave orbital motion is newly proposed. Furthermore, the free-running model test in regular waves, using a simulator of the marine diesel engine which manages the shaft speed of the motor on a ship model as behaving the actual diesel engine, is carried out to obtain realistic torque fluctuations for comparisons of the estimated results applying the proposed identification method. Through comparisons of estimated fluctuations with the measured results, the proposed approach for the component of the inflow velocity due to wave orbital motion is successfully validated.     

摆动尾鳍水动力性能的试验和数值研究

鱼类能够在水下高速度、低噪音、高效率地游动。鱼类出色的推进性能通过其摆动尾鳍实现。这种摆动尾鳍推进方式已经用在了水下无人航行器上。因此研究摆动尾鳍的水动力性能是非常有意义的。对摆动尾鳍的推进水动力性能进行了详尽的研究。设计、装配了一套仿尾鳍推进系统,并对其进行了相应的水动力试验。在试验中研究了运动参数对摆动尾鳍水动力性能的影响。与此同时,采用基于雷诺平均N-S方程的数值方法对摆动尾鳍的水动力性能进行了研究。在数值计算中采用了k-ωSST湍流模型和有限体积法。数值计算结果和水动力试验结果进行了比较。对尾鳍表面的压力分布和流场中的尾涡结构进行了分析。水动力试验和数值计算都表明摆动尾鳍可以产生推进力和较高的推进效率。     

Response Characteristics of Load on Vessels in Waves

Considering the requirement of direct design and fatigue test for ships and floating structures byuse of FEM technique,a computational procedure of spectral analysis for wave load on the hull surface is de-veloped in this paper.The response of hydrodynamic pressure on the body surface to a designated sea state forships and floating structures is calculated by use of the revised strip method with the hull bound perturbationflow concept.The spectral function of wave load for the defined point on the body surface can be determinedfrom the Wiener-Khinhin theorem and the characteristic load value can be also obtained from spectral mo-ment analysis.A container ship is taken as a computational example and the sample of wave load with a cer-tain probability and corresponding encountered frequency is provided.     

波浪滑翔机推进装置翼片的启动阶段水动力学分析

波浪滑翔机直接利用波浪能实现大范围长距离的机动运动观测,在海洋环境观测中可以发挥重要的作用。本文对波浪滑翔机推进装置在启动阶段的翼片的水动力学行为进行了研究。以波浪滑翔机水下推进装置的翼片为研究对象,运用雷诺平均Navier-Stokes方程(RANS),对给定垂荡和摆动运动的翼片水动力学进行了水动力分析和仿真,模拟了单个翼片、纵向阵列多翼片的运动状况,得到推进装置翼片附近的压力分布和整体推进动力,分析翼片间距变化在启动阶段对推进力的影响作用。通过该研究工作为深入理解波浪滑翔机推进装置工作状态提供了理论依据。     

单体喷水推进船舶动力定位控制方法研究

面向一型喷水推进器为动力定位执行机构的单体喷水推进船舶,开展了船舶仿真模型建立、推力分配及进一步动力定位相关控制算法设计与仿真模拟。针对传统的定步长Kalman滤波提出了改进方案,同时考虑到单体喷水推进船舶的特殊性,对推力分配算法进行了优化,并基于荷载前馈的PD控制算法开展了不同工况下的仿真试验。试验结果表明,所提出的喷水推进推力分配算法能够有效控制一型单体喷水推进船舶实现定点、定艏向、移位、转艏等动力定位典型功能,并具备一定抗外部干扰能力。     

Full scale CFD seakeeping simulations for case study ship redesigned from V-shaped bulbous bow to X-bow hull form

Increasing propulsion efficiency, safety, comfort and operability are of the great importance, especially for small ships operating on windy sites like the North Sea and the Baltic Sea. Seakeeping performance of ships and offshore structures can be analysed by different methods and the one that is becoming increasingly important is CFD RANS. The recent development of simulation techniques together with rising HPC accessibility enables performance of advanced seakeeping simulations for ships in a full scale. The paper presents CFD seakeeping analysis for a case study vessel in two variants: V-shaped bulbous bow hull form (as built) and innovative hull form (X-bow type). The study presents the influence of redesigning the ship on selected seakeeping aspects. The advanced CFD model, with the application of overset mesh technique, was described in detail. Selected numerical results were validated on the basis of experimental testing in a towing tank and showed good agreement. The approach demonstrated here of performing the CFD seakeeping simulations for the analysis of ship performance in a full scale and close to real loading conditions has direct application to the design process as well as in determination of optimal operational parameters of any ship.     

动态海面上方船舶六自由度运动仿真

在Fudide-Krylov假设条件下,依据船舶分离建模理论在固定和运动坐标系中计算海面船只六自由度运动数学模型。主要包括:对风、浪、流的单独建模并进行矢量叠加,并在风浪流联合作用下对船舶六自由度运动构建简化的数学建模,完成实时仿真。基于Simulink和V-Realm Builder虚拟现实技术创建船舶运动模型、海洋表面环境及船只的几何模型,对船舶六自由度运动进行视景仿真,给出了有风无浪、有浪无风和风浪兼有三种情况下船只旋回路径和船舶运动轨迹。在VR视景浏览器中创建动态海面上船舶六自由度运动模型,不仅易于实现且结果逼真。得到的结果为进一步研究动态船只目标声散射特性的精确预报提供基础。     

A shipborne- type wave-height meter for oceangoing vessels, using microwave Doppler radar

A wave-height meter using a simple microwave Doppler radar,simeq10mW in power and 10.525 GHz in frequency, is proposed so that we can measure oceanic waves effectively while the ship is steaming. It was first applied to the measurement of the variation of water level generated in a wave tank, which suggested that it is adequately applicable to the measurement of oceanic waves. A field test was carried out off the cape of Nojimazaki by installing the Doppler radar 5 m above the sea level at the bow of the ship. The result agreed reasonably well with that measured simultaneously by the ultrasonic wave-height meter installed at the same position. Another test is running successfully on a larger ship with the wave-height meter installed at 9 m above the sea level. The significant wave height measured by the present meter is being compared with that observed visually by the navigation officers.