两相流相互作用下的船模微气泡减阻性能数值仿真

基于两相流理论,对集装箱船船模进行微气泡减阻性能数值仿真研究。分析船模在不同喷气口位置、流体含气率、不同喷射速度和角度下的流场分布和减阻效果。结果表明：当流体微气泡含量过高时,会增大船体摩擦阻力,流体含气率为10%~20%时,有较好的减阻效果,喷气口位置在距离球鼻艏后缘约三分之一船长附近具有较高的空气覆盖率,喷气口喷气方向垂直向下所产生的减阻效果比喷气方向偏向船侧效果要好,且船速较高时可允许较高含气率流体注入流场并增大减阻效果。     

Ship resistance of quadramaran with various hull position configurations

Multihull ships are widely used for sea transportation, and those with four hulls are known as quadramarans. Hull position configurations of a quadramaran include the diamond, tetra, and slice. In general, multihull vessels traveling at high speeds have better hydrodynamic efficiency than monohull ships. This study aims to identify possible effects of various quadramaran hull position configurations on ship resistance for hull dimensions of 2 m length, 0.21 m breadth, and 0.045 m thickness. We conducted a towing test in which we varied the hull spacing and speed at Fr values between 0.08 and 0.62 and measured the total resistance using a load cell transducer. The experimental results reveal that the lowest total resistance was achieved with a diamond quadramaran configuration at Fr = 0.1-0.6 and an effective interference factor of up to 0.35 with S/L = 3/10 and R/L = 1/2 at Fr = 0.62.     

采用微气泡缩减高速船拖曳阻力(英文)

Ship hull form of the underwater area strongly influences the resistance of the ship.The major factor in ship resistance is skin friction resistance.Bulbous bows,polymer paint,water repellent paint(highly water-repellent wall),air injection,and specific roughness have been used by researchers as an attempt to obtain the resistance reduction and operation efficiency of ships.Micro-bubble injection is a promising technique for lowering frictional resistance.The injected air bubbles are supposed to somehow modify the energy inside the turbulent boundary layer and thereby lower the skin friction.The purpose of this study was to identify the effect of injected micro bubbles on a navy fast patrol boat(FPB) 57 m type model with the following main dimensions:L=2 450 mm,B=400 mm,and T=190 mm.The influence of the location of micro bubble injection and bubble velocity was also investigated.The ship model was pulled by an electric motor whose speed could be varied and adjusted.The ship model resistance was precisely measured by a load cell transducer.Comparison of ship resistance with and without micro-bubble injection was shown on a graph as a function of the drag coefficient and Froude number.It was shown that micro bubble injection behind the mid-ship is the best location to achieve the most effective drag reduction,and the drag reduction caused by the micro-bubbles can reach 6%-9%.     

基于Fluent的船体界面阻力分析

基于 Fluent对船体界面阻力进行仿真分析,采用 VOF的方法模拟船体在空气和水两相中的运动情况,获得不同航速下船体摩擦阻力和压差阻力的关系。考虑方型系数对于船体阻力的影响,建立多个方型系数不同的模型来实现Fluent仿真模拟,获得一定傅汝德数下船体方形系数与船体阻力的关系,得到船舶阻力相对优化的船型。该方法通过更加精确的建模可为船体型线减阻提供更多的依据。     

Resistance analysis of unsymmetrical trimaran model with outboard sidehulls configuration

The application of multi-hull ship or trimaran vessel as a mode of transports in both river and sea environments have grown rapidly in recent years.Trimaran vessels are currently of interest for many new high speed ship projects due to the high levels of hydrodynamic efficiency that can be achieved,compared to the mono-hull and catamaran hull forms.The purpose of this study is to identify the possible effects of using an unsymmetrical trimaran ship model with configuration（S/L） 0.1-0.3 and R/L=0.1-0.2.Unsymmetrical trimaran ship model with main dimensions： L=2000mm,B=200 mm and T=45 mm.Experimental methods（towing tank） were performed in the study using speed variations at Froude number 0.1-0.6.The ship model was pulled by an electric motor whose speed could be varied and adjusted.The ship model resistance was measured precisely by using a load cell transducer.The comparison of ship resistance for each configuration with mono-hull was shown on the graph as a function of the total resistance coefficient and Froude number.The test results found that the effective drag reduction could be achieved up to 17% at Fr=0.35 with configuration S/L=0.1.     

平头方尾运输船舶开槽减阻研究

传统的平头方尾型运输船舶具有载重大、吃水浅的优点,但航行阻力大,航速低。本文针对该船型开展了开槽减阻的研究,通过在船底开设纵向槽道对艏部高压区进行引流减阻,来实现该船型高航速运输的要求。船体流场及阻力采用RANS方法进行数值模拟,并计及航行姿态的变化。通过改变槽道长度、宽度以及槽道顶板的形状,研究了减阻效果与槽道几何尺度的关系。针对某型船船的研究表明,船底槽道的引流量是影响减阻效果的主要因素,当采用纵向贯穿的槽道,且槽道顶板的折角点设在船中时,可使原船30节时的减阻率达到24%以上。     

超大型集装箱船能效设计指数优化研究

采用船型优化方法就超大型集装箱船10 000TEU的能效设计指数(EEDI)进行优化.文中以降低对主机功率的需求、提高能效设计水平为目标,优化该超大型集装箱船的阻力性能.优化时利用平移法和径向基函数方法进行船体曲面重构,并分别采用基于Rankine源非线性势流理论和边界层动量积分计算兴波阻力和摩擦阻力,最后同时使用遗传算法(NSGA-Ⅱ)和序列二次规划算法(NLPQL)在设计空间中探索满足约束条件的阻力最优船型.结果表明,通过该优化方法获得的最优船型,其能效设计指数优化程度明显,能够满足现阶段IMO对新造集装箱船计及折减系数后的强制要求.     

Resistance analysis of a semi-SWATH design concept in shallow water

Resistance analysis is an important analytical method used to evaluate the hydrodynamic performance of High Speed Craft (HSC). Analysis of multihull resistance in shallow water is essential to the performance evaluation of any type of HSC. Ships operating in shallow water experience increases in resistance because of changes in pressure distribution and wave pattern. In this paper, the shallow water performance of an HSC design concept, the semi-Small Waterplane Area Twin Hull (semi-SWATH) form, is studied. The hull is installed with fin stabilizers to reduce dynamic motion effects, and the resistance components of the hull, hull trim condition, and maximum wave amplitude around the hull are determined via calm water resistance tests in shallow water. These criteria are important in analyzing semi-SWATH resistance in shallow water and its relation to flow around hull. The fore fin angle is fixed to zero degrees, while the aft fin angle is varied to 0°, 5°, 10°, and 15°. For each configuration, investigations are conducted with depth Froude numbers (Fr _H ) ranging from 0.65 to 1.2, and the resistance tests are performed in shallow water at the towing tank of UTM. Analysis results indicate that the resistance, wave pattern, and trim of the semi-SWATH hull form are affected by the fin angle. The resistance is amplified whereas the trim and sinkage are reduced as the fin angle increases. Increases in fin angle contribute to seakeeping and stability but affect the hull resistance of HSCs.     

重庆—上海江海直达船船型优化

为提升重庆—上海过闸型江海直达船的航行性能和经济性,以满足通过三峡船闸船舶吃水要求的江海直达船型为研究对象,以排水体积和浮心纵向位置为约束条件,采用理论设计与数值计算相结合的方法优化船型。采用Rhinoceros软件进行船体建模,采用CAESES（FRIENDSHIP-Framework）软件进行半参数化模型优化,采用计算流体动力学（Computational Fluid Dynamics, CFD）技术进行阻力预报。通过2轮优化对比,优化船型在10 kn、13 kn和16 kn航速下的总阻力相比原始船型分别减小10.76%、8.18%和1.86%。研究表明：垂直艏+下凸艉组合的减阻效果要优于尖直艏+平直艉组合,且航速越低,减阻效果越明显;采用多航速验证方法能有效避免固定航速船型优化的局限性。研究结果可供江海直达船的船型设计和建造参考。 关键词：型线优化;总阻力;多航速;江海直达船;SBD技术     

滑行艇气层减阻试验

通过对三种艇型及不同的喷气方式的模型试验，研究了断阶滑行艇模型气层减阻的实施途径及减阻效果，取得了总阻力减少25％以上 结果，提出了一种适合于采用气层减阻技术且阻力性能优良的艇型。垂向舭板可减少滑行艇的高速阻力，但阻力减少的程度与艇型有关。底部斜升角较小时，有利于气层减阻。气层减阻率大于舭板减阻率，对底部斜升角较大且艇底扭曲、艏部设置适当的纵向防溅条、舯部设置楔形板的深Ⅴ型艇，垂向舭板对其阻力的影响不大，这种深Ⅴ型艇的阻力性能较佳，若喷气，其总阻力还可进一步减少15％。孔喷时，孔径采0.5mm或1.3mm对模型阻力的影响甚微，采用0.4mm缝叶的模型阻力比用孔喷时略大，采用较大孔喷或缝喷有利于工程上的喷气实施。     

Added resistance acting on hull of a non ballast water ship

In this paper, added resistances acting on a hull of non ballast water ship(NBS) in high waves is discussed. The non ballast water ships were developed at the laboratory of the authors at Osaka Prefecture University, Japan. In the present paper, the performances of three kinds of bow shapes developed for the NBS were theoretically and experimentally investigated to find the best one in high waves. In previous papers, an optimum bow shape for the NBS was developed in calm water and in moderated waves. For a 2 m model for experiments and computations, the wave height is 0.02 m. This means that the wave height is 15% of the draft of the ship in full load conditions. In this paper, added resistances in high waves up to 0.07 m for a 2 m model or 53% of the full load draft are investigated. In such high waves linear wave theories which have been used in the design stage of a ship for a long time may not work well anymore, and experiments are the only effective tool to predict the added resistance in high waves. With the computations for waves, the ship is in a fully captured condition because shorter waves, λ/Lpp0.6, are assumed.     

CFD-based method of determining form factor <Emphasis Type="Italic">k</Emphasis> 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.     

大型半潜船球首设计及阻力性能对比分析

在船速较低的肥大型船舶上,安装球鼻艏会在很大程度上降低船舶受到的阻力,球艏对艏部型线有缓和的作用,使船舶艏部水流发生改变,减少艏底漩涡,从而降低形状阻力,进而改善船舶的水动力性能。根据设计的10万吨级半潜船船型的船模静水阻力试验情况,该船舶船首由直立型改为球鼻艏型式,通过对原型和改进后的船型的阻力试验结果进行对比,检验了新船型的减阻性能,同时对船尾伴流场进行了研究,发现船首形状改变对尾部半流场影响不大     

Determining the Scour Dimensions Around Submerged Vanes in a 180° Bend with the Gene Expression Programming Technique

Submerged vanes are installed on rivers and channel beds to protect the outer bank bends from scouring. Also, local scouring occurs around the submerged vanes over time, and identifying the effective factors on the scouring phenomena around these submerged vanes is one of the important issues in river engineering. The most important aim of this study is investigation of scour pattern around submerged vanes located in 180° bend experimentally and numerically. Firstly, the effects of various parameters such as the Froude number (Fr), angle of submerged vanes to the flow (α), angle of submerged vane location in the bend (θ), distance between submerged vanes (d), height (H), and length (L) of the vanes on the dimensionless volume of the scour hole were experimentally studied. The submerged vanes were installed on a 180° bend whose central radius and channel width were 2.8 and 0.6 m, respectively. By reducing the Froude number, the scour hole volume decreased. For all Froude numbers, the biggest scour hole formed at θ?=?15°. In all models, by increasing the Froude number, the scour hole volume significantly increases. In addition, by increasing the submerged vanes’ length and height, the scour hole dimensions also grow. Secondly, using gene expression programming (GEP), a relationship for determining the scour hole volume around the submerged vanes was provided. For this model, the determination coefficients (R²) for the training and test modes were computed as 0.91 and 0.9, respectively. In addition, this study performed partial derivative sensitivity analysis (PDSA). According to the results, the PDSA was calculated as positive for all input variables.     

半滑行船扰流板阻力试验研究

半滑行船的航行姿态对船体阻力影响较大。为研究扰流板对半滑行船的降阻作用,首先在3种典型载况下,确定了船模未加扰流板的阻力、纵倾及升沉;然后在这3种载况下,于船模艉部添加扰流板,与静水未添加扰流板时船模的阻力和航态作比较,且不同航速时扰流板的设置不同。实验结果表明:合理的扰流板高度可以减小半滑行船的纵倾角和阻力;扰流板的降阻效果与船模的压载有关,其中满载情况下的降阻效果最为明显,最大可达6%。     

船体艏部水动力性能优化

提出一种以势流兴波阻力理论Rankine源方法为基础,结合SHIPFLOW软件为计算工具,利用CAD-CFD集成平台FRIENDSHIP-Framework软件进行变形优化,研究船舶的最小兴波阻力型线优化设计的方法,并考察了兴波优化得到的船型总阻力变化情况。在型线优化过程中,以兴波阻力系数为目标函数,排水量变化范围为约束条件,在Wigley船体前端增加一个利用Feature建模技术参数化生成的球艏并调整艏部型线使得船体表面光顺。选取球鼻艏形状的各项参数作为基本设计变量,利用DOE方法对船艏进行优化,获得了设计航速下兴波阻力较小的船型,验证了所提方法进行船艏型线优化的有效性。相应的考察变形及优化前后总阻力变化情况表明:在高傅汝德数情况下增加球艏所带来的粘性阻力的增加小于兴波阻力的减小量,总阻力得到了改善,优化后得到的球艏能在进一步减小兴波的同时减小总阻力。此外,还运用所提方法对3100TEU船型的船艏,利用Delta Shift方法进行变形,在设计航速下,将变形的参数作为设计变量,利用DOE方法进行优化设计。结果显示:在排水量限制范围内当球鼻艏向上向前伸展一定长度时可以降低兴波阻力。与此同时,由于优化前后船体湿表面积变化很小,粘性阻力的变化并不明显,兴波的减小则使得总阻力得到了改善。     

船用梯形微沟槽表面减阻效应的仿真分析与实验验证

基于微沟槽减阻机理,采用改变船体表面微结构形貌尺寸的方法,以期降低船舶运行中的航行阻力,提高船舶航行效率,节约能源。利用流体软件FLUENT对梯形肋条和梯形沟槽两种微结构表面流场进行模拟仿真,分析了沟槽深宽比h/d1的减阻效果。仿真结果表明,对于梯形肋条,在h/d1时均具有减阻效果,当h/d为0.45时减阻效果最好;对于梯形沟槽,当h/d为0.30、0.36时表现为增阻,h/d为0.45、0.60、0.75时表现为减阻,其中当h/d为0.60时的减阻效果最好。为了验证模拟计算的规律,进行了阻力冲刷实验,实验结果与模拟计算结果的对比分析表明模拟计算与实验结论一致。     

Numerical analysis of surface piercing propeller in unsteady conditions and cupped effect on ventilation pattern of blade cross-section

The aim of this study is to calculate hydrodynamic performance and ventilation flow around wedge, 2D blade and 3D surface piercing propeller (SPP), using computational fluid dynamic based on Reynolds-averaged Navier–Stokes method. First, numerical analyses for two-phase fluid flow around the wedge and 2D blade section (cupped and non-cupped) are presented. Flow ventilation, pressure distribution and forces are determined and compared with experimental data. Then, the method is extended to predict the hydrodynamic performance of propeller SPP-841B. The propeller exhibits a cupped blade. In the simulated configuration, SPP is one-third submerged (I = h/D = 0.33) and is working at various loadings with full ventilation occurring at low advance coefficient (J). The open water performance, pressure distribution, forces/moments and ventilation pattern on the SPP-841B model are obtained and compared with experimental data. The numerical results are in good agreement with experimental measurements, especially at high advance coefficient.     

Hydrodynamic optimization of ship hull forms in shallow water

A computational method for improving hull form in shallow water with respect to wave resistance is presented. The method involves coupling ideas from two distinct research fields: numerical ship hydrodynamics and nonlinear programming techniques. The wave resistance is estimated by means of Morinos panel method, which is extended to free surface flow and considers the influence of finite depth on the wave resistance of ships. This is linked to the optimization procedure of the sequential quadratic programming (SQP) technique, and an optimum hull form can be obtained through a series of iterations giving some design constraints. Sinkage is an important factor in shallow water, and this method considers sinkage as a hydrodynamic design constraint. The optimization procedure developed is demonstrated by selecting a Wigley (C _B = 0.444) hull and the Series 60 (C _B = 0.60) hull, and new hull forms are obtained at Froude number 0.316. The Froude number specified corresponds to a lower than critical speed since most of the ships operating in shallow water move below their critical speed. The numerical results of the optimization procedure indicate that the optimized hull forms yields a reduction in wave resistance.     

Hydrodynamic performance of multiple-row slotted breakwaters

This study examines the hydrodynamic performance of multiple-row vertical slotted breakwaters. We developed a mathematical model based on an eigenfunction expansion method and a least squares technique for Stokes second-order waves. The numerical results obtained for limiting cases of double-row and triple-row walls are in good agreement with results of previous studies and experimental results. Comparisons with experimental measurements of the reflection, transmission, and dissipation coefficients (C _R , C _T , and C _E ) for double-row walls show that the proposed mathematical model adequately reproduces most of the important features. We found that for double-row walls, the C _R increases with increasing wave number, kd, and with a decreasing permeable wall part, dm. The C _T follows the opposite trend. The C _E slowly increases with an increasing kd for lower kd values, reaches a maximum, and then decreases again. In addition, an increasing porosity of dm would significantly decrease the C _R , while increasing the C _T . At lower values of kd, a decreasing porosity increases the C _E , but for high values of kd, a decreasing porosity reduces the C _E . The numerical results indicate that, for triple-row walls, the effect of the arrangement of the chamber widths on hydrodynamic characteristics is not significant, except when kd<0.5. Double-row slotted breakwaters may exhibit a good wave-absorbing performance at kd>0.5, where by the horizontal wave force may be smaller than that of a single wall. On the other hand, the difference between double-row and triple-row vertical slotted breakwaters is marginal.