CFD数值分析三体船片体位置对阻力及兴波干扰影响

三体船的水动力性能是目前水动力学研究的热门。对于中高速三体船来说,其静水阻力的很大一部分由兴波阻力构成,而对于兴波最大的影响因素就是片体位置的布局。以一艘圆舭型三体船为研究对象,运用黏流计算流体力学(CFD)方法模拟分析4种不同片体位置对三体船静水阻力和兴波干扰的影响。数值计算采用自主研发的黏流CFD求解器naoe-FOAM-SJTU。数值预报得到三体船静水阻力结果与模型试验结果吻合较好,验证了当前CFD方法预报三体船阻力的可靠性。通过不同片体位置三体船阻力计算发现,方案4的船型方案阻力最优,且通过细节的主片体间兴波干扰流场的结果给出了不同片体布置方案对三体船阻力和兴波的影响。     

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.     

Dynamics of ships and fenders during berthing in a time domain

When designing fixed or semi-fixed structures used for berthing ships, it is generally assumed that the entire kinetic energy of the ship is absorbed by the fender or the system of fenders. The fenders have the functions of ensuring a safe berthing both for the ships and the piers by absorbing shock loads and preventing direct contact between the berthed ship and the pier. In this study, the problem is analyzed in the stages of berthing, collision and leaving. Each of the stages is analyzed and solved in the time domain. The system is assumed to consist of three components: pier, fender and the ship. Environmental effects that simultaneously affect berthing are wave, current and wind effects. Cummins equation was assumed to be a good representation of the problem and was solved in time domain taking various factors into account. Nonlinear effects related to the instantaneous values of forces, moments and ship motions, which are time dependent, were studied by the Cummins equation and its later developments by Ogilvie. Fender forces were added to the calculation scheme by the authors. A case study for a passenger ferry operating in Izmir bay is presented.     

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。     

Experimental investigation of blade and propeller loads: Steady turning motion

This paper is the continuation of the work described in [14], dedicated to the presentation of the results of propeller performance in behind-hull during straight ahead motion obtained by a novel experimental set-up for the measurements of single blade loads. In the present case, the study shows and discusses the single blade and propeller loads developed during steady turning conditions, that were simulated by means of free running, self propelled maneuvering tests for a twin screw configuration. Maneuvering conditions are critical for the ship propulsion system, because the performance of the propeller and the side effects related to its functioning (propeller–hull induced pressure and vibrations, noise) are completely different with respect to the design condition in straight ahead motion. Thrust and torque and generation of in-plane loads (force and moments), developed by the blade during the period, evolve differently for the two propellers, due to different propeller–wake interactions. The understanding and the accurate quantification of propeller loads, in these realistic operative scenarios, are pivotal to design low emission and comfortable ships, fulfilling the requirements of safety and continuity of operations at sea. The analysis is carried out revisiting the investigation in [14] for three different speeds (F_N = 0.26, 0.34 and 0.40) and a large set of rudder angles that span moderate and tight maneuvers.     

Initial attack of large-scaled tsunami on ship motions and mooring loads

In this paper, we propose a numerical simulation procedure of moored ship motions due to initial attack of large-scaled tsunamis and investigate the effects on the motions and mooring loads. The effect of methodology on selection of tsunami wave components and of the drag forces are then considered by using the numerical simulation method, applying to several case studies for LNG-carrier. Large ship motions and excessive mooring loads beyond the safe working loads are induced by the resonant tsunami wave components in the sway and surge motions and drag forces.     

THE COMPUTATION OF OPTIMUM OCEAN SHIP ROUTING

A computational method for the ocean ship routing based on optimization theory is presented in this paper. In the computational programme "breaking circle method" is used, by which a principal contradictory line can be obtained in the operations research. The automatic selection of calculating network and the initial values have been realized. The quantitative estimation for the change of navigating speed under the different conditions of ocean wave and current has been done. The objectivly quantitative computational method is provided for ocean ship routing and forecast service following ship tracks. The calculating examples and practical experiments of ships have proved that this computational method is highly effective.     

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。     

Experimental and Numerical Investigations of Ship Parametric Rolling in Regular Head Waves

Parametric rolling is one of five types of the ship stability failure modes as proposed by IMO. The periodic change of the metacentric height is often considered as the internal cause of this phenomenon. Parametric rolling is a complex nonlinear hydrodynamic problem, often accompanied by large amplitude vertical motions of ships. In recent years,the Reynolds-averaged Navier–Stokes(RANS) equation simulations for viscous flows have made great progress in the field of ship seakeeping. In this paper, the parametric rolling for the C11 containership in regular waves is studied both experimentally and numerically. In the experiments, parametric rolling amplitudes at different drafts, forward speeds and wave steepnesses are analyzed. The differences in the steady amplitudes of parametric rolling are observed for two drafts. The effect of the incident wave steepness(or wave amplitude) is also studied, and this supports previous results obtained on limits of the stability for parametric rolling. In numerical simulations, the ship motions of parametric rolling are analyzed by use of the potential-flow and viscous-flow methods. In the viscousflow method, the Reynolds-averaged Navier–Stokes equations are solved using the overset grid method. The numerical accuracies of the two methods at different wave steepnesses are also discussed.     

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.

     

3-D geometric modeler for rapid ship safety assessment

CAD systems are used broadly in the shipbuilding industry. CAD systems for naval architecture are a useful tool for hull form, internal arrangement and the structural design of ships. These systems require high precision and expertise for efficient use. Therefore, these systems are not appropriate in supporting emergency responses, which require rapid modeling even if it generates some errors.This paper describes a geometric modeler for rapid ship safety assessment. The modeler is developed based on the 3-D geometric modeling kernel ACIS. The definition of hull form, internal arrangement and major longitudinal structural members is a fundamental function of the modeler. The developed modeler is interfaced with other applications used for ship safety assessment such as hydrostatic calculation, ship motion analysis in wave condition, longitudinal strength analysis and so on. In addition, it can generate a new ship model by making variations in a previously defined ship model.     

Ships with ventilated cavitation in seaways and active flow control

Bottom ventilated cavitation has been proven as a very effective drag reduction technology for river ships and planning boats. The ability of this technology to withstand the sea wave impact usual for seagoing ships depends on the ship bottom shape and could be enhanced by some active flow control devices. Therefore, there is the need in numerical tools to estimate the effects of bottom changes and to design such devices. The fundamentals of active flow control for the ship bottom ventilated cavitation are considered here on the basis of a special model of cavitating flows. This model takes into account the air compressibility in the cavity, as well as the multi-frequency nature of the incoming flow in wavy seas and of the cavity response on perturbations by incoming flow. The numerical method corresponding to this model was developed and widely manifested with an example of a ship model tested in a towing tank at Froude numbers between 0.4 and 0.7.The impact of waves in head seas and following seas on cavities has been studied in the range of wavelengths from 0.45 to 1.2 of the model (or ship) length. An oscillating cavitator-spoiler was considered as the flow controlling devices in this study. The oscillation magnitude and the phase shift between cavitator oscillation and the incoming waves have been varied to determine the best flow control parameters. The main results of the provided computational analysis include oscillations of cavity surface, of the pressure in cavity and of the moment of hydrodynamic load on the cavitator. The major part of computations has been carried out for the flap oscillating at the frequency coinciding with the wave frequency, but the effect of a frequency shift is also analyzed.     

南黄海辐射沙洲近岸海域波浪特性研究

Errors will be caused in calculating the fatigue damages of details in liquid cargo tanks by using the traditional spectral analysis method which is based on linear system, for the nonlinear relationship between the dynamic stress and the ship acceleration. An improved spectral analysis method for the assessment of the fatigue damage in detail of a liquid cargo tank is proposed in this paper. Based on assumptions that the wave process can be simulated by summing the sinusoidal waves in different frequencies and the stress process can be simulated by summing the stress processes induced by these sinusoidal waves, the stress power spectral density (PSD) is calculated by expanding the stress processes induced by the sinusoidal waves into Fourier series and adding the amplitudes of each harmonic component with the same frequency. This analysis method can take the nonlinear relationship into consideration and the fatigue damage is then calculated based on the PSD of stress. Take an independent tank in an LNG carrier for example, the accuracy of the improved spectral analysis method is proved much better than that of the traditional spectral analysis method by comparing the calculated damage results with the results calculated by the time domain method. The proposed spectral analysis method is more accurate in calculating the fatigue damages in detail of ship liquid cargo tanks.     

Wave loads on large vertical cylinders: A design method

The finite element method based on linear diffraction theory proposed by Zienkiewicz and Bettess (1977) has been used to compute wave loads and moments about the bed of surface piercing cylinders of circular, square, rectangular and elliptical sections for different angles of wave incidence. On the basis of the results obtained, a design method is presented in the form of simple design charts for estimating wave forces and moments on large cylinders of arbitrary sections. The numerical solutions obtained have been checked for their validity by comparing with other theoretical solutions and experimental data. Further the application of the design method to a case study shows good correlation with experimental and other theoretical solutions.     

Slow drift oscillations of a ship in irregular waves

A procedure to calculate horizontal slow drift excitation forces on an infinitely long horizontal cylinder in irregular beam sea waves is presented. The hydrodynamic boundary-value problem is solved correctly to second order in wave amplitude. Results in the form of second order transfer functions are presented for different two-dimensional shapes. It is concluded that Newman's approximative method is a practical way to calculate slow drift excitation forces on a ship in beam sea and suggested that it may be used in a more general case. Applications of the results for moored ships are discussed.     

Simulation of Kelvin wakes in optical images of rough sea surface

Kelvin wake is one of the common wakes generated by moving ships and contains rich information about ships. In this paper, free wave elevations of Kelvin wake are calculated based on the Michell thin ship theory combined with a point source perturbation model. The probability density function of sea surface slopes is introduced to calculate the specular reflection of sunlight and skylight and the refraction of scattered light underwater. Satellite-detected Kelvin wakes are then simulated by adding surface specular reflectance and water-leaving reflectance. Simulation results agree well with satellite measurements. The specular reflection of sunlight is the decisive factor affecting the features of Kelvin wakes according to the simulation results. The main factors that influence the specular reflection of sunlight, such as the incident direction and observation direction, ship parameters, and background environment, are discussed. This study is helpful for wake detection and provides a preliminary theoretical method for the retrieval of ship information.     

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.     

Domain decomposition and matching for time-domain analysis of motions of ships advancing in head sea

A domain decomposition and matching method in the time-domain is outlined for simulating the motions of ships advancing in waves. The flow field is decomposed into inner and outer domains by an imaginary control surface, and the Rankine source method is applied to the inner domain while the transient Green function method is used in the outer domain. Two initial boundary value problems are matched on the control surface. The corresponding numerical codes are developed, and the added masses, wave exciting forces and ship motions advancing in head sea for Series 60 ship and S175 containership, are presented and verified. A good agreement has been obtained when the numerical results are compared with the experimental data and other references. It shows that the present method is more efficient because of the panel discretization only in the inner domain during the numerical calculation, and good numerical stability is proved to avoid divergence problem regarding ships with flare.