1 Introduction

The 20,000DWT river-sea bulk carrier has been required to reduce its delivered power while maintaining its service speed.A variety of different energy-saving devices(ESDs)have been developed in recent years,although most ESDs have been designed for single-screw ships.For example,Kumagaiet al.(2015)used a hydrofoil combined with air bubble generation to reduce ship drag,although this method is relatively complicated and costly.Being simple,robust,and efficient,the pre-swirl stator is one of the most at tractive hydrodynamic ESDs.As reported by de Jong(2011)and Dang et al.(2011,2012),pre-and post-swirl stators(rudder fins included)focus on recovering rotational energy losses.Lee et al.(1992)devised a pre-swirl stator(PSS)that increases propulsive efficiency by decreasing the propeller slipstream’s swirl energy by generating or improving the rotational flow in advance.Mew is and Guiard(2011)developed a series of ESDs that have both a PSS and a duct to improve efficiency and Guiard et al.(2013)used computational fluid dynamics(CFD)simulations in their design process.Shin et al.(2013)designed conventional and unconventional pre-swirl ducts for very large crude carriers(VLCCs).Kawakita et al.(2012)developed reaction fins which has similar mechanism comparing with PSS.ESDs for 317-K VLCCs were recently developed by Kim et al.(2015),who designed two ESD candidates using computational tools and validated the speed performances in model tests.Park et al.(2015)and Shin et al.(2013)used CFD to predict wake fields and numerically simulate ESDs.However,river-sea vessels differ from single-screw vessels in their limitations with respect to river water depth,which has led to different stern designs.Huang et al.(2015)studied the angle of attack of the stators of a twin-screw ship.In this paper,our main focus is the development of ESDs for river-sea bulk carriers,the circumferential arrangements of the ESDs,and different numbers of ESD stators.

In this study,we designed and tested ESDs that improve the performance of the 20,000DWT river-sea bulk carrier.Table 1 shows the principle dimensions of the 20,000DWT river-sea bulk carrier.

2 ESD Design Concep t

We conducted a wake survey of the bare hull with five whole pitot tubes to demonstrate the typical asymmetric wake of a twin-skeg ship;the propellers are in absence during the test.

Table 1 Dimensions of the vessel

Length between PPs(LPP)(m) 156.8 Breadth,B(m) 24.4 Draft,T(m) 8 Deadweight tonnage(DWT)(t) 20,000 Service speed,V s(kn) 12 No.of propellers 2 Sense of rotation Outward

In the test,the skeg was inclined and the sense of propeller rotation was outward,i.e.,the right propeller rotated clockwise.From Fig.1,we can see that the wake fraction at 340 degree is relatively strong.As shown in Fig.2,between 170 and 330 degrees,the direction of the propeller rotation accords with the direction of the wake flow,which is adverse for achieving high propulsion efficiency.

As suggested by Dang et al.(2011),reducing the transverse(rotational)kinetic energy losses in the wake of the ship by the use of ESDs is a key task that can lead to significant power savings in the ship propulsion system.

Hence,the design task can be summarized as follows:design an upstream device,use a PSS to reduce the adverse transverse flow of the wake,and generate pre-swirl flow.

When evaluating the effectiveness of the stators,the variation in the ship resistance must be taken into account.Table 4 shows the calculated total resistance results.The circumferential arrangement of the blades affected the resistance and the ESD Stator 3 has one more blade than Stator 2,although the resistance of the ESD Stator 3 is relatively low.Stator 2 and Stator 1 are both three-stator designs,and the circumferential arrangement resulted in different increases in resistance.For Stator 3,with the blade at 10 degrees,a blade located in the high-wake area makes a major contribution to the effectiveness of the PSS as compared with Stator 2.

一致性即为英文单词“Alignment”，韦伯将其界定为：教育系统中各构成要素能够互相匹配至期待目标的程度，一致性分析范式是指判断、分析某一体系中各个要素之间吻合程度的理念、程序与方法的总和[2].我国学者借鉴过程中也提出对一致性的理解，一般认为是教育系统各要素之间的有效匹配或吻合程度.本文中一致性即指在国家教师考试评价系统中试题与大纲标准的匹配程度.

The arrangements of proposed ESDs are shown in Figs.3,4,and 5.Based on our wake survey results,we propose the use of ESDs with the codenames Duct 1,Duct 2,and Duct 3,which are ducts located in front of the propeller to improve the wake fraction,as shown in Fig.5.Additional ESDs with the codenames Stator 1,Stator 2,and Stator 3 consist of three to four PSSs,which are located according to the velocity vectors,as shown in Fig.4,wherein the red line indicates a stator blade.

Fig.1 Wake distribution contour(1-Vx/V)of the right propeller disk

Fig.2 Transverse velocity field of the right propeller(rear view)

Each blade is inclined 12 degrees toward the inflow direction.Huang et al.(2015)tested 8-degree,10-degree,and 12-degree blade angles of attack on similar hull forms and at similar service speeds,and found the 12-degreeangle of attack to be preferable with respect to service speed.As such,we chose a 12-degree angle of attack for this study.The geometrical designs of the stators consisted of NACA-series foils,and we chose a profile section with a large lift-to-drag ratio for the stator blade.Like trapezoid wings,the chord length of the stator blade varied along its span,the blade roots near the ship hull had a longer chord length,the tips had a relatively short chord length,and Stators 1,2,3 and Ducts 1,2,and 3 all had same blade geometries(Table 2).

Fig.3 Arrangement of the ESD

Fig.4 Stator circum ferential distributions

The proposed radius of the device had almost the same span length as the initial propeller radius R.By referencing previous model tests results,the final arrangements were for the stators to have a 0.9R span and the ducts to have a 0.7R inside radius.

In the ducted ESDs,Duct 3 increased the quasi-propulsive coefficient by 6.48%compared with bare hull,but its benefit did not overcome its corresponding resistance change of 6.68%(Table 5).

(3)围岩蚀变标志：矿体及其围岩普遍具较强的蚀变，主要为硅化、黄铁矿化、钾长石化、绢云母化、碳酸盐化等，这些蚀变控制着金矿化的分布范围，其中硅化、钾长石化、黄铁矿化这三者与成矿关系最为密切，为找矿的重要标志。

Fig.5 Circumferential distributions of ducts

Table 2 Details of stators and ducts

Proposals Name No.of blade Circumferential distributions θ(°)(angle of attack Φ =12°)No.1 No.2 No.3 No.4 1 Stator 1 3 30 90 260 -2 Stator 2 3 140 180 310 -3 Stator 3 4 10 120 180 320 4 Duct 1 3 30 90 260 -5 Duct 2 3 140 180 310 -6 Duct 3 4 10 120 180 320

3 CFD Calculations

We performed numerical simulations of the six proposed ESDs at model scale to evaluate the resulting resistance and self-propulsion performances.Although we ultimately tested the ESDs by towing tank tests,the CFD method provided the potential to identify better designs more rapidly than is possible by conventional design cycles.

We used the Reynolds-averaged Navier-Stokes(RANS)method in our simulations.Ship flows are governed by general conservation laws for mass,momentum,and energy,which are referred to as Navier-Stokes equations.As reported by Wilcox(2006),the flow is considered to be incompressible,which simplifies the conservation equations for mass and momentum and removes the need to solve the energy equation.As reported by Moll and et al.(2011),the Reynolds averaging process assumes that the three velocity components can be represented as rapidly fluctuating turbulent velocity around a slowly varying mean velocity.

We conducted a free-surface bare-hull simulation to evaluate the resistance,with the ESDs located below the free surface.We also considered double-model simulations which neglected the free surface.We performed all other simulations for assessing the ESDs without a free surface.Using a STAR CCM+segregated solver with second-order upwind scheme convection,we applied a steady model for the double-model calculations and applied an implicit unsteady model with a first-order temporal scheme for the free-surface simulation and self-propulsion cases.Table 3 lists the other CFD simulation settings.Figure 6 demonstrates two of the six 3D modelsused in the simulation;double-model simulation domain layout is shown in Fig.7.

Table 3 CFD settings

Turbulent model Realizable k-epsilon Free surface VOF Fluid Fresh water Mesh Unstructured trimmed mesh Ship speed(kn) 12 Domain Half(resistance)

Fig.6 3D model(Stator 3,left and Duct 3,right)

Fig.7 Domain layout(double model)

The results demonstrate that Stator 1 and Duct 1 tend to have a maximum increase in resistance.

In the SSSRI towing tank,the Fd is determined as follows:

3.5.2 拔管时机 对于泌尿系统手术的患者，推荐在夜间拔除导尿管(B级推荐)［5］。多项研究表明，与早晨(6:00～8:00)相比，夜间(22:00～0:00)拔除导尿管有利于增加患者导尿管拔出后的第1次排尿量，且缩短了患者从拔管到第1次排尿之间的时间间隔。

除了情感色彩的差异之外，部分英语单词还由于在联想上存在不同，导致对单词的理解存在差异。比如说dog是狗的意思，在东方文化中，狗在造词中经常用于消极的、批评的词汇，比如狗尾续貂、蝇营狗苟、狗头军师、鸡飞狗跳、狗急跳墙、狼心狗肺等单词都是贬义词，看到这些带有狗字的成语，容易让人联想到不好的含义。然而，在西方文化中，dog却让人联想到好的意思，比如Love me,love my dog就代表着爱屋及乌的意思，狗代表能为主人带来幸运的含义。

The ESDs with the codenames Duct 1,Duct 2,and Duct 3 are composed of shorter PSSs and ducts connected to stator tips.By this process,the hull wake is expected to be accelerated by the proposed ducts while also straightening the flow.

As demonstrated in Fig.8,the stator arrangement affected the pressure distribution of each blade and the pressure on the ship hull.Comparing Duct3 and Stator 3,the duct significantly changed the pressure distribution on the blade.As demonstrated in Fig.9,propellers were absent from the stream line simulations and the flow is pre-swirled by the stators in front of the propeller disks.The vectors of the tangential velocities are changed by the stators,the area with high tangential velocity in the same direction of the propeller rotation is reduced,and the magnitude of the detrimental tangential velocity is reduced.Figures 10 and 11 show the simulated CFD transverse velocities and axial wake.As demonstrated by Figs.10and 11,the ducts straightened the flow and did not obviously accelerate the wake.

Table 4 Resistance result comparisons%

Design Resistance comparisons without free surface(double-model)Bare hull 100.00 Stator 1 103.05 Stator 2 102.70 Stator 3 102.29 Duct 1 107.45 Duct 2 106.71 Duct 3 106.68

Table 5 Self-propulsion change%

Design Quasi-propulsive coefficient comparisons Bare hull 100.00 Stator 3 104.88 Duct 3 106.48

Fig.8 Pressure distribution

Fig.9 Stream lines

Fig.10 CFD transverse velocities(right propeller disk,rear view)

4 Model Test Validations

We conducted model tests to evaluate the four ESDs,Stator 2,Stator 3,Duct 2,and Duct 3,in the Shanghai Ship and Shipping Research Institute(SSSRI)towing tank,which is 192 m long,10 m wide,and has a water depth of 4.2 m.The ESD models installed during the tests are shown in Fig.12.

Fig.11 CFD axial wake(right propeller disk,rear view)

In the resistance test in the SSSRI towing tank,the ship model is towed by the carriage and we measured the total longitudinal force acting on the model at various speeds.During the measuring run,the ship model was free to heave and pitch.

The scale-effect correction on viscous resistance is denoted as Fd,the self-propulsion towing force is denoted as Z,and the self-propulsion point of the ship is defined as being when Z is equal to Fd(Carlton 2012).

Fig.12 ESD models

In the model self-propulsion tests,we used four propeller revolution rates for each ship speed.We recorded the propeller thrust,the propeller torque,and the longitudinal towing force acting on the model for each tested combination of ship speed and propeller rotation rate.Figure 13 demonstrates the test set up.

By interpolating the measured data,we determined the required propeller thrust,torque,and rotation rate at the self propulsion point of the ship.

在“十二五”规划中曾提出不断促进第三产业的发展，优化产业结构，提高第三产业比重的期许，而不断促进第三产业的发展有利于促进我国经济的发展，对于实现我国的可持续发展具有重要的意义。扩大增值税征收范围对于不断促进我国产业结构优化具有重要的意义，也符合经济发展的规律。

二是建档制度。在制度制约下，内容丰富详实的土地质量档案资料，可在土地利用规划编制、耕地保护及土地交易、土地流转、耕地占补平衡、土地整治、土地质量等级变更、农产品安全源头追溯等方面，发挥重要作用。

本研究病理确诊椎间盘变形22例（35.5%），硬膜囊受压37例（59.7%），钙化32例（51.6%），神经根受压24例（38.7%）。CT检查的检出率分别为27.3%、59.5%、78.1%、79.2%，MRI检查的检出率分别为77.3%、94.6%、31.3%、83.3%。椎间盘变形、硬膜囊受压的检出方面，MRI检查的检出率高（P＜0.05）；钙化的检出方面，CT检查的检出率高（P＜0.05）；神经根受压的检出方面，CT和MRI检查的对比无统计学差异（P＞0.05）。见表2。

Similarly,we conducted self-propulsion simulations for Stator 3 and Duct 3.The quasi-propulsive coefficient of Stator 3 increased 4.88%and the quasi-propulsive coefficient of Duct 3 increased 6.48%.We considered Stator 2,Stator 3,Duct 2,and Duct 3 in the towing tank test.

The approximation of Fd is as follows:

where R tm is the model’s total resistance,ρm is the density of the fresh water in the towing tank,ρs is the density of sea water,R ts is the total ship resistance,λ is the scale ratio,vm is the model speed,S m is the model wetted surface area,C fm is the model skin Friction coefficient,and C fs is the ship skin friction coefficient.

The resistance test results agree with the CFD simulations,whereby Stator 3 has the minimum resistance increase at around 12 kn(Table 6).For Duct2 and Duct3,we found a relatively large resistance increase in the experiment(Table 7).

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Stator 3 performed better than Stator 2,which validated the CFD calculation results.

In the model to full-scale extrapolation process,we used the ITTC 1957 model-ship correlation line for the resistance and extrapolated the propulsion test results using the 1978 ITTC(2014)method.We used thrust deduction,wake fraction,and R ts to calculate the full-scale K t/J2,where K t is the thrust coefficient and J is the advance coefficient.Using K t/J2 as the input value,we obtained the full-scale advance coefficient J,read the torque coefficient K q from the full-scale propeller characteristics,and then calculated the rate of revolutions and delivered power from J and K q.We used Ei=(1-w s)/(1-w m)for wake correction instead of the ITTC’s ws,w m correlation,for which the thrust deduction has no scale effect.

根据本文研究结果显示138例患者中有128例患者经手术验证，128例患者中有125例患者术前核磁共振检查，诊断患者为膝关节前交叉韧带断裂，膝关节前交叉韧带断裂总检出率为97.66%。因此，核磁共振成像技术是现代化的诊断技术，在诊断中需要关注患者膝关节前交叉韧带损伤情况，因人而异进行诊断，从而有利于提高患者的诊断准确率。

In this study,we discuss the extrapolation of Pe(power effect)using the ESDs as appendages and the ITTC’s proposed factor β for scaling the appendages.We did not use the R tm values of the hull with ESDs to directly extrapolate the full-scale Pe.According to the ITTC,the 1-β value ranges from 0.6 to 1.We used the following fixed fraction:

Fig.13 Test set up

Table 6 Experimental resistance values

V s/kn Bare hull N Stator 2 N Stator 3 N Duct 2 N Duct 3 N 11 21.50 21.86 21.77 22.98 22.91 12 25.47 25.93 25.85 27.25 27.22 13 30.34 30.88 30.96 32.32 32.31 14 36.83 37.52 37.78 39.26 39.20

We ruled out the method suggested by the ITTC for determining C App S due to the requirement for the frictional resistance coefficient and form factor of the appendage.From tests of the Lucy Ashton(Moll and et al.2011),the 1-β value tends to increase with large-scale models,tending to 1 as the model length approaches that of the ship length.We finally selected the 1-β value of 0.75 for this ship,located the ESDs in the wake,and,unlike appendages possibly partially in the laminar flow due to a thin full-scale boundary layer,found the 1-β value of the ESDs of this river-sea bulk carrier to be relatively large.

In the self-propulsion tests,all the ESDs proved capable of improving the efficiency ηD,but the ESD itself increased the resistance,which led to an increase in the Pe value.

Comparing the CFD and experimental results,we see that the tendencies are consistent(Table 8).As shown in Table 9,the numbers are not directly comparable,the CFD double model calculations exhibit no wave pattern,and the resistance compositions differ.As such,the experimental results prevail in our evaluation.

Duct 2 and Duct 3 failed to reduce the delivered power Pd value at service speed,so their efficiency performance could not overcome their resistance change.We consider Stator 2 and Stator 3 to be successful designs.They exhibited 2.7%and 5.4%improvements,respectively,when compared with the Pd value in bare hull conditions(Table 10).

5 Conclusions

In this study,we used CFD simulations and towing tank tests to successfully design ESDs for the 20,000DWT river-seabulk carrier by considering the hull wake distribution.This ESD design is available for vessels of similar geometry and size to those of the 20,000 DWT.We also demonstrated the design and development process of EDSs in this study,as well as the fact that the stator blades in the high-wake area have great impact on their effectiveness.We found a well-designed four-blade stator ESD with one more blade near the skeg to generate less resistance than a similar three-blade design.Due to differences in their arrangements,the designs of Stator 1 and Stator 2 had the same blade geometries and number of stators but exhibited different resistance and propulsion values.The circumferential arrangement of PSS should be considered based on the wake field.

Table 7 Resistance change at 12 kn(%)

Bare hull Stator 2 Stator 3 Duct 2 Duct 3 ΔR 100 101.81 101.49 106.99 106.87

Table 8 Comparison of CFD and experimental results

Design Resistance CFD(free surface) Resistance experiments N N Bare hull 26.29 25.47

The pre-swirl ESD design is simple,mature,and robust,with an energy-saving effect from moderate to good.We consider this design to be evolutionary rather than revolutionary with respect to energy saving.This study contributes to the river-sea bulk carrier’s Energy Efficiency Design Index and global environment protection by reducing the Pd value at service speed.

Table 9 Tendency of resistance change by CFD and experiments(%)

Design Resistance change(CFD double model)Resistance change(experiments)Bare hull 100.00 100.00 Stator 1 103.05 -Stator 2 102.70 101.81 Stator 3 102.29 101.49 Duct 1 107.45 -Duct 2 106.71 106.99 Duct 3 106.68 106.87

Table 10 Full-scale performance

At 12 kn Delivered power/kW Comparing with bare hull/%Energy savings/%Bare hull 2503.5 100 -Stator 2 2436.9 97.3 2.70 Stator 3 2367.3 94.6 5.40 Duct 2 2558.2 102.2 -2.20 Duct 3 2539.4 101.4 -1.40

Funding Information This study is supported by Ministry of Science and Technology of the People’s Republic of China No.2014BAG04B01.

首先，缺乏合格的翻译人员。西方的文化与中国背景差别很大，存在很大的语言障碍，我们需要中国人翻译成不同的语言给不同的外国人看。因此，图书出版企业需要保持出口品牌的高品质的书籍，要求中国人一个简单的翻译成外文，也是这本书的精神内涵的翻译不丢失，就需要翻译人员拥有对外语有较高的知识，还要很好的语言学，文学，社会学素养，还要精通每个国家的阅读习惯，宗教等。从事实中证明了一点，缺乏合格的翻译人员是造成图书出口现状的重要原因之一。

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