Study of Resistance Performance of Vessels with Notches by Experimental and Computational Fluid Dynamics Calculation Methods

Owing to the special working characteristics and operation requirements,lots of working ships have notches in different sizes and shapes in their hulls.In order to study the resistance performance of the vessel with notches,a series of model resistance tests were performed in respect to the 4 500 m 3 /h cutter suction dredger,and the tests were simulated based on the computational fluid dynamics software FLUENT.Based on analysis to the experimental data and the computational fluid dynamics(CFD) calculation results,the change of the flow field and the resistance performance caused by the notches were studied,and the reliability of the software in simulation of viscous flow around the hull was proved.It provides the basis for the future study and the design optimization of this kind of working ships.

CFD-Based Method of Determining Form Factor k for Different Ship Types and Different Drafts

The value of form factor k at different drafts is important in predicting full-scale total resistance and speed for different types of ships. In the ITTC community, most organizations predict form factor k using a low-speed model test. However, this method is problematic for ships with bulbous bows and transom. In this article, a Computational Fluid Dynamics(CFD)-based method is introduced to obtain k for different type of ships at different drafts, and a comparison is made between the CFD method and the model test. The results show that the CFD method produces reasonable k values. A grid generating method and turbulence model are briefly discussed in the context of obtaining a consistent k using CFD.

CFD Analysis of Ship-to-Ship Hydrodynamic Interaction

A numerical study of ship-to-ship interaction forces is performed using a commercial CFD code,and the results are compared with experimental data and with the results of a panel method analysis.Two ship models have been used in the interaction forces analysis:a tug and a tanker,advancing parallel to each other with different lateral distances and two different values of the fluid depth.Computations are carried out with four different flow models:inviscid and viscous flow with the free surface modeled as a rigid wall and inviscid and viscous flow with the deformable free surface.A fair agreement was obtained with available experimental data and results obtained by panel method.The influence of viscosity in the computations is found to be comparatively weak,while the wavemaking effects may be important,at small magnitude of the horizontal clearance.

Influence of Ship Motion on Flow Field over Modified Simple Frigate Shapes

When the frigate moves forward,due to the ship motion such as pitching and rolling,the flow over the flight deck becomes very complex,which may seriously threaten the taking off and landing of the ship-borne helicopter.The flow fields over the different modified simple frigate shape(SFS)models,consisting of the hangar and flight deck,were numerically studied by changing the ratio of hangar height and length in the static state and pitching state.For different models,the contours of velocity and pressure above the flight deck,as well as the variations of velocity components of the observation points and line in static state and pitching state were compared and analyzed.The results show that the size of recirculation zone and the location of the reattachment point have distinct differences for diverse models,and reveal the tracks of recirculation zone’s center and reattachment position in a pitching period.In addition,the velocity components at two observation positions also change periodically with the periodic motion.Furthermore,the deviations of the velocity components in static state and pitching state are relatively large,therefore,the flow fields in static state cannot be used to simulate that in pitching state correctly.

Sloshing-Coupled Ship Motion Algorithm for Estimation of Slosh-Induced Pressures

The effect of coupling between sloshing and ship motions in the evaluation of slosh-induced interior pressures is studied. The coupling between sloshing loads and ship motions is modelled through a hybrid algorithm which combines a potential flow solution based on transient Green function for the external ship hydrodynamics with a viscous flow solution based on a multiphase interface capturing volume of fluid(VOF) technique for the interior sloshing motion. The coupled algorithm accounts for full nonlinear slosh forces while the external forces on the hull are determined through a blended scheme of linear radiationdiffraction with nonlinear Froude-Krylov and restoring forces. Consideration of this level of nonlinearities in ship motions is found to have non-negligible effects on the slosh-coupled responses and slosh-induced loads. A scheme is devised to evaluate the statistical measure of the pressures through long-duration simulation studies in extreme irregular waves. It is found that coupling significantly influences the tank interior pressures, and the differences in the pressures between coupled and uncoupled cases can be as much as 100% or more. To determine the RAO over the frequency range needed for the simulation studies in irregular waves, two alternative schemes are proposed, both of which require far less computational time compared to the conventional method of finding RAO at each frequency, and the merits of these are discussed.

Numerical Study on Flow Around Modern Ship Hulls with Rudder-Propeller Interactions

Reducing the fuel consumption of ships presents both economic and environmental gains. Although in the past decades,extensive studies were carried out on the flow around ship hull, it is still difficult to calculate the flow around the hull while considering propeller interaction. In this paper, the viscous flow around modern ship hulls is computed considering propeller action. In this analysis, the numerical investigation of flow around the ship is combined with propeller theory to simulate the hull-propeller interaction. Various longitudinal positions of the rudder are also analyzed to determine the effect of rudder position on propeller efficiency. First, a numerical study was performed around a bare hull using Shipflow computational fluid dynamics(CFD) code to determine free-surface wave elevation and resistance components.A zonal approach was applied to successively incorporate Bpotential flow solver^ in the region outside the boundary layer and wake, Bboundary layer solver^ in the thin boundary layer region near the ship hull, and BNavier-Stokes solver^in the wake region. Propeller open water characteristics were determined using an open-source MATLAB code Open Prop, which is based on the lifting line theory, for the moderately loaded propeller. The obtained open water test results were specified in the flow module of Shipflow for self-propulsion tests. The velocity field behind the ship was recalculated into an effective wake and given to the propeller code that calculates the propeller load. Once the load was known, it was transferred to the Reynolds-averaged Navier-Stokes(RANS) solver to simulate the propeller action. The interaction between the hull and propeller with different rudder positions was then predicted to improve the propulsive efficiency.

Evaluation of Hydrodynamic Coefficients of Ships Oscillating in A Numerical Wave Tank

A technique for the evaluation of the hydrodynamic coefficients of ships is outlined for ship oscillating in a numerical wave tank, which is established on Computational Fluid Dynamics （CFD） theories. The numerical simulation of ship sections and bodies forced oscillating in the tank are carried out. The added mass and damping coefficients are obtained by the decomposition of the computational results, which agree well with the corresponding ones of potential theories.

Numerical Investigation of the Effect of Surface Roughness on the Viscous Resistance Components of Surface Ships

Recently,computational fluid dynamics(CFD)approaches have been effectively used by researchers to calculate the resistance characteristics of ships that have rough outer surfaces.These approaches are mainly based on modifying wall functions using experimentally pre-determined roughness functions.Although several recent studies have shown that CFD can be an effective tool to calculate resistance components of ships for different roughness conditions,most of these studies were performed using the same ship geometry(KRISO Container Ship).Thus,the effect of ship geometry on the resistance characteristics of rough hull surfaces is worth investigating.In this study,viscous resistance components of four different ships are calculated for different roughness conditions.First,flat plate simulations are performed using a previous experimental study for comparison purposes.Then,the viscous resistance components of three-dimensional hulls are calculated.All simulations are performed using two different turbulence models to investigate the effect of the turbulence model on the results.An examination of the distributions of the local skin friction coefficients of the DTMB 5415 and Series 60 showed that the plumpness of the bow form has a significant effect on the increase in frictional resistance with increasing roughness.Another significant finding of the study is that viscous pressure resistance is directly affected by the surface roughness.For all geometries,viscous pressure resistances showed a significant increase for highly rough surfaces.

高速槽道双体艇船型设计与阻力性能评估

[目的]槽道双体艇是一种中部贯通含有两个滑行片体的特殊滑行艇船型,中部槽道受到气旋抬升作用能使艇体脱离水面达到更高的航速,具有良好的快速性,同时在高速航行时能很快进入稳定状态。针对高速槽道双体艇的艇型参数化设计与阻力性能评估对于高性能船舶的船型开发与设计具有重要意义。[方法]采用clamped B样条曲线定义槽道双体艇的主要型线进行艇体船型参数化构型,并通过STAR-CCM+软件设置多船型方案对比,研究双体艇槽道尺寸和斜升角大小对艇体阻力性能的影响。[结果]得到比初始设计船型阻力降低17.3%的优选船型方案。[结论]与同尺度同排水量单体滑行艇对比,结果证明,在中高速工况下,本文所研究的高速槽道双体艇具有更加优良的航行性能。

组合式降液管塔板的流体力学性能研究及其流场CFD模拟

开发了一种液相处理能力大、结构简单且安装方便的组合式降液管塔板,可在不动火的前提下对常规双溢流塔板进行扩能改造。以空气和水为物系,在内径1219 mm的有机玻璃塔内,研究了组合式降液管塔板的流体力学性能。对塔板上液相流场的流体流动特性进行了计算流体力学(CFD)模拟,并将模拟结果与常规双溢流塔板进行对比。实验结果表明,相较于常规双溢流塔板,组合式降液管塔板的湿板压降低5%~25%、干板压降低20%~30%,而漏液率略高;在大液相负荷下,组合式降液管塔板的雾沫夹带率明显低于常规双溢流塔板。CFD模拟结果显示,组合式降液管塔板上液相流场比常规双溢流塔板更均匀,在扩大处理能力的同时不会影响塔板效率。

新型双体无人测量艇静水阻力性能预报与航态优化

为得到一艘新型双体无人测量艇的阻力性能和经济航态,分别利用模型试验、经验公式和计算流体力学(CFD)方法对该艇进行阻力预报和阻力成分分析.运用CFD方法进一步探究工作航速下船体的不同重心纵向位置对船体阻力、纵倾和船周波形的影响,还为多波束声学设备选取了合适的船体安装位置.结果表明,CFD方法能精确完整地预报双体测量艇从低航速排水到高航速滑行的航态变化和阻力特性,而经验公式法主要适用于测量艇航速较低(F_(r▽)<1.5)时的阻力预报.在4~6 kn测量航速下,该艇的阻力经济航态约为尾倾1.4°,此时在片体间距离船尾约0.3~0.5个船长位置处存在一个相对稳定的高液位区域,适合作为无人测量艇多波束声学设备的安装位置.

表面粗糙度对潮流能涡轮机水动力性能的影响

为探究由生物附着所引起的表面粗糙度效应对涡轮机水动力性能的影响,采用计算流体动力学方法对不同粗糙度和不同局部粗糙度分布条件下的水平轴涡轮机进行了数值模拟.研究结果表明:在相同尖速比(TSR)下,随着粗糙度的增大,涡轮机的功率和推力损失逐渐增大.而在相同粗糙度下,涡轮机的功率和推力损失也随着TSR的增大而增大,其中涡轮机在TSR=6.00的功率损失是TSR=3.00的2.3倍左右.局部粗糙度分布越靠近叶尖对涡轮机功率和推力损失的影响就越明显,其中分布在叶片半径(R)为0.75R~1.00R的局部粗糙度所造成的功率损失超过整体的一半以上.叶片背流面局部粗糙度分布相比迎流面局部粗糙度分布对涡轮机功率和推力的影响更明显.同时,涡轮机的粗糙度效应并不是各局部粗糙度的简单叠加,而是综合影响的结果.涡轮机一旦被生物附着,其设计条件下的最佳TSR范围将不再适用.

基于CFD的协同AUV编队队形研究

为了研究自主水下航行器(AUV)编队协同航行的减阻效果,对3个典型编队开展水动力性能研究。采用计算流体动力学(CFD)对3艘AUV以串列队形、并列队形和三角队形等开展水动力计算。通过改变各队形下AUV之间的间距,找到最佳队形间距位置,得出对各AUV的阻力影响。利用多目标遗传算法(MOGA)对三角队形进行优化,得出阻力最小的航行间距。结果表明:在串列队形中,当横向距离为3.80m和3.50m时,系统阻力达到最小;在并列队形中,系统阻力随纵向距离增大而减小,但系统内各AUV相比单体AUV无法获得阻力收益;在三角队形中,当横向距离为2.46 m、纵向距离为1.21 m时,系统阻力达到最小。研究成果可为多AUV编队航行提供一定参考。

考虑跨洋特征及碎冰对快速性影响的极地探险邮轮型线优化

[目的]全球减碳背景下,为应对极地船舶设计建造的环保要求,需开展跨洋航行时碎冰水域对极地探险邮轮船体型线优化设计的影响规律研究,以获得最佳节能型线。[方法]针对极地探险邮轮的跨洋航行特征,采用航区权重方法进行量化评估,分析碎冰对阻力和推进效率的影响。应用计算流体力学耦合离散元法(CFD-DEM)来分析螺旋桨的碎冰水域性能,建立以联合自航功率为目标的优化模型,进而对全船参数化模型开展设计航速下的优化计算。[结果]计算结果表明,优化后的船型可以满足排水量要求,有效降低了2种水域下的航行功率,其联合自航功率降低了9.71%。[结论]研究成果验证了基于权重优化方法的可行性和合理性,可为极地探险邮轮的型线和推进器优化设计提供参考。

SHIP HYDRODYNAMICS BASIC RESEARCH IN THE UNITED STATES

An overview of basic research on ship hydrodynamics in the United States ispresented. The focus is on leading edge research of high scientific interest bUt with ship hydrodynamics applicability. The research topic areas are briefly discussed, representative highlights from recent research are presented, and scientific hurdles to improved ship hydrodynamics technology are delineated. The purpose of the paper is to stimulate international cooperation in solving the basic research problems of common interest to all hydrodynamicists.

Rapid prediction of damaged ship roll motion responses in beam waves based on stacking algorithm

Accurate modeling for highly non-linear coupling of a damaged ship with liquid sloshing in waves is still of considerable interest within the computational fluid dynamics(CFD)and AI framework.This paper describes a data-driven Stacking algorithm for fast prediction of roll motion response amplitudes in beam waves by constructing a hydrodynamics model of a damaged ship based on the dynamic overlapping grid CFD technology.The general idea is to optimize various parameters varying with four types of classical base models like multi-layer perception,support vector regression,random forest,and hist gradient boosting regression.This offers several attractive properties in terms of accuracy and efficiency by choosing the standard DTMB 5415 model with double damaged compartments for validation.It is clearly demonstrated that the predicted response amplitude operator(RAO)in the regular beam waves agrees well with the experimental data available,which verifies the accuracy of the established damaged ship hydrodynamics model.Given high-quality CFD samples,therefore,implementation of the designed Stacking algorithm with its optimal combination can predict the damaged ship roll motion amplitudes effectively and accurately(e.g.,the coefficient of determination 0.9926,the average absolute error 0.0955 and CPU 3s),by comparison of four types of typical base models and their various forms.Importantly,the established Stacking algorithm provides one potential that can break through problems involving the time-consuming and low efficiency for large-scale lengthy CFD simulations.

Study of the Lift Force Induced by An Interceptor on A High-Speed Mono-Hull:The Affecting Factors and Estimation Formula

To find a better way to estimate the lift force induced by an interceptor on a high-speed mono-hull ship,a series of high-speed mono-hull ship models are designed and investigated under different conditions.Different lift forces are obtained by numerical calculations and validated by a model test in a towing tank.The factors that influence the force are the interceptor height,velocity,draft,and deadrise angle.The relationship between each factor and the induced lift force is investigated and obtained.We found that the induced lift mainly depends on the interceptor height and advancing velocity,and is proportional to the square of the interceptor height and velocity.The results also showed that the effects of the draft and deadrise angle are relatively less important,and the relationship between the induced lift and these two factors is generally linear.Based on the results,a formula including the combined effect of all factors used to estimate the lift force induced by the interceptor is developed based on systematic analysis.The proposed formula could be used to estimate the lift force induced by interceptors,especially under high-speed condition.

Numerical study on roll dynamics of damaged ship in beam waves and calm water

Computational fluid dynamics is used to study the roll dynamics of a damaged ship in beam waves with various steepnesses and in calm water.The wave-making method,which combines the velocity-inlet boundary and momentum source with the fifth-order Stokes theory,is employed for wave generation.The SST k-ωturbulence model with a modification to the turbulent viscosity in Reynolds stress is adopted to prevent the over-production of turbulence in the numerical wave tank.The lateral drift restrained model with a combined dynamic mesh strategy is utilized to deal with the coupled heave-sway-roll motions of the ship.First,benchmarking tests are performed,including wave generation and roll response of the damaged ship in regular beam waves.Then,the effects of incident wave steepness on the roll response of the damaged ship are analyzed.For different wave steepnesses,the ship roll motion is dominated by the first-order harmonic component.The second-order component increases with the increase of wave steepness.Finally,the roll hydrodynamic coefficients for different parts of the damaged ship are investigated with different rolling parameters.The added moment of inertia for the whole damaged ship is mainly attributed to the external hull composition and changes slightly with the change of roll amplitude and frequency.The added moment of inertia for the compartments could be negative in particular cases.The damping coefficients of the whole damaged ship and external hull increase with the increase of roll amplitude and frequency,while that of the compartments appears complicated with the change of roll amplitude and frequency.

基于CFD的浅水条件下工程船水阻力快速预报方法

为准确预报工程船的流阻力,以杭州湾铁路桥施工中的“水欣麒”号打桩船为研究对象,参考同类型船的阻力系数试验值,采用计算流体力学(CFD)方法对考虑锚泊约束的打桩船阻力进行预报。数值计算结果表明:在深水条件下,相比采用悬链线约束船舶得到的船舶阻力,完全限制船舶运动的计算误差不超过1.52%;在浅水条件下,锚泊无法完全限制船舶运动,船舶升沉、横倾和横摇对船舶阻力计算的影响较大,此时不考虑船舶运动得到的阻力相比悬链线约束条件下的阻力计算结果偏小,其误差最大达到26.6%;完全放开船舶的升沉和横摇自由度之后,计算得到的船舶横倾和横摇值比锚泊约束下的结果更大导致船舶兴波更剧烈,兴波阻力变大导致计算得到的总阻力偏大;考虑到不同锚泊方案对船舶运动的限制程度不同,从安全性的角度考虑,进行较为保守的阻力修正是有必要的。

双阿基米德螺旋水轮机阵列特性

为了探究阿基米德螺旋水轮机双机组的阵列特性,从而实现该型水轮机的高效利用,采用计算流体力学方法对不同排列方式及间距下的双机组阵列进行了三维数值模拟研究.结果表明,在并列排布中,两机组都将获得高于单独机组的性能指标,且二者之间的水动力相互作用的增益效果在达到峰值后随着并列间距的增大而逐渐减弱.反向旋转设置中的两机组的叶尖涡将出现类似于齿轮的啮合效应,而同向旋转设置中的两机组的叶尖涡相互冲突且交织在一起,导致一侧机组的叶尖涡在向下游发展的过程中过早地出现破碎.在串列排布中,当串列间距大于5 D后,上游机组的性能基本不受影响,下游机组的性能随着串列间距的减小而下降明显.反向旋转设置的下游机组的涡流结构较为混乱,出现了一定程度的尾流畸变,而同向旋转设置的下游机组几乎完美地与来自上游的涡流进行了融合,其尾流更像是对上游涡流的一种延伸和继承.研究结果为阿基米德螺旋水轮机的优化布置提供了一定的参考.