#### Table of Content

28 June 2018, Volume 52 Issue 6
 Numerical Simulation of Cavitating Flow Around an Under-Loading Propeller FU Huiping，LI Jie 2018, 52 (6):  631-635.  doi: 10.16183/j.cnki.jsjtu.2018.06.001 Abstract ( 1103 )   Numerical simulation of under-loading propeller cavitation and hydrodynamic thrust and torque coefficients were carried out by calculating the Case 2.3.3 of propeller model of Potsdam Propeller Test Case 2011. The research was done through discussion on different meshing patterns, meshing densities, cavitation parameters based on the homogeneous mixture flow model and the ZGB and Sauer cavitation models. It is shown that the correct calculation of thrust and torque coefficients on the under-loading condition needs finer meshing; the methods put forward here can predict correctly KT and KQ, tip vortex, cavities on both suction side and pressure side; the spiral mesh is a promising gridding method to succeed in capturing tip vortex cavitation; the nucleation site volume fraction and the bubble number density are two parameters which have important effects on the computed results.
 Numerical Analysis of Hydrodynamic Characteristics of Surface Piercing Propeller Under Naturally Ventilated Condition REN Zhen,WANG Chao,WAN Decheng,YUAN Yuming 2018, 52 (6):  636-642.  doi: 10.16183/j.cnki.jsjtu.2018.06.002 Abstract ( 40 )   To study the hydrodynamic characteristics of surface piercing propeller under natural ventilation condition, the numerical simulation on the unsteady gas-liquid two-phase flow field of the standard model 841B was performed by solving RANS equation and combining it with the VOF method and using sliding mesh technique. The results show that the calculated values of thrust coefficient KT and torque coefficient 10KQ are in good agreement with the experimental data; especially near the design point, the errors of both are within 5%. The air cavity develops downstream in spirals in the wake field; the diameter of the spiral first increases and then decreases; finally, the spiral cavity gradually disappears. The forces/moments acting on the surface piercing propeller under small immersion condition are very large in horizontal and vertical directions. The wake flow field of surface piercing propeller is bounded by the free surface. The velocity in the wake field mutates in the free surface. In front of the disk, surface piercing propeller affects the flow field by suction effect; whereas the slipstream effect dominates the flow field behind the disk.
 Optimization of Ship Structure for the Crashworthiness Based on Critical Velocity CHEN Luyun,LI Leixin 2018, 52 (6):  643-649.  doi: 10.16183/j.cnki.jsjtu.2018.06.003 Abstract ( 44 )   By analyzing the relationship among structural collision damage, collision energy transformation and collision force of ship structure, the critical collision velocity was defined as an crashworthiness index, and the crashworthiness optimization formulation was established. The fishing vessels-vessels collision was taken as an example, numerical calculation of ship right collision was carried out. The influences of striking velocity on the collision characteristic such as deformation, energy transformation and collision force of the broadside structure of the struck ship were compared, the critical velocity of struck ship structure was determined, aiming at improving the critical collision speed of struck ship structure a proposal was given. The results of numerical calculation show that it is feasible to evaluate the crashworthiness index based on the safety critical velocity.
 Estimation of Vertical Concentrations of Fine Particulates Alongside an Elevated Expressway GAO Ya,WANG Zhanyong,LU Qingchang,PENG Zhongren 2018, 52 (6):  650-657.  doi: 10.16183/j.cnki.jsjtu.2018.06.004 Abstract ( 49 )   A study on vertical variation of PM2.5 concentrations was carried out in this paper. Field measurements were conducted at eight different floor heights outside a building alongside a typical elevated expressway in downtown Shanghai, China. A back propagation neural network based on principal component analysis (PCA-BPNN), was applied to predict the vertical PM2.5 concentration and examined with the field measurement dataset. Experimental results indicated that the PCA-BPNN model provides reliable and accurate predictions as it can reduce the complexity and eliminate data co-linearity. Furthermore, this paper investigated the vertical distribution of PM2.5 and their relationship with traffic volume, weather and height by generalized additive model (GAM). These findings reveal the vertical distribution of PM2.5 concentration and the potential of the proposed model that will be applicable to predict the vertical trends of air pollution in similar situations.
 Optimal Control Strategy of Two Speed Automatic Mechanical Transmission in Shift Process CHAI Benben1,WU Shaofang1,ZHANG Jianwu1,LIN Lianhua2,XU Haigang2 2018, 52 (6):  658-665.  doi: 10.16183/j.cnki.jsjtu.2018.06.005 Abstract ( 49 )   In order to validate the shift strategy of 2-speed automatic mechanical transmissions (2AMT) for electric vehicles, the powertrain test rig including high performance electric dynamometer is built up and experiments under different conditions are made. Then, a compound optimal control strategy is presented to improve the shift performance. In other words, a linear quadratic regulator is employed to actively compensate the drive motor torque and a nonlinear time-optimal control is used to track the actuator rotor position. The experiment results show that this optimal control strategy can not only reduce the driveline vibration, but also cut down period of the shift time. The coupled dynamic model of the driveline and shift actuator is precise enough for the analysis of shift process, and the compound optimal control strategy is effective to improve the shift quality.
 Fast Collaborative Multi-Objective Optimization for Hydrodynamic Based on Kriging Surrogate Model WANG Gangcheng，MA Ning，GU Xiechong 2018, 52 (6):  666-673.  doi: 10.16183/j.cnki.jsjtu.2018.06.006 Abstract ( 53 )   The wave drag, heave and pitch performance of the ship at design speed are optimized by introducing Kriging surrogate model. During the optimizing process, hull lines are optimized by utilizing the non-dominated sorting genetic algorithm and surface modification functions based on Rankine source method and 3-D Green function method. In addition, the high-precision Kriging surrogate model is applied to approximate optimization objectives in order to solve the time-consuming problem in the iterative process. Numerical results show that the present optimization approach can be used to optimize ship hull forms for reducing drag and improving seakeeping performance, and Kriging surrogate model can improve optimization efficiency considerably. Finally, the drag optimization results at model scale λ=31.599 are validated via CFD method based on Reynolds-averaged Navier-Stokes (RANS) equations.
 Detached Eddy Simulation of Near Wake Field and Vortex Characteristics for a Ducted Propeller GONG Jie,GUO Chunyu,WU Tiecheng,SONG Kewei,LIN Jianfeng 2018, 52 (6):  674-680.  doi: 10.16183/j.cnki.jsjtu.2018.06.007 Abstract ( 44 )   Detached eddy simulation (DES) is employed to simulate the near wake field and vortical characteristics for a ducted propeller under design condition. Spalart & Allmaras model is selected to satisfy the Navier-Stokes equations. Unsteady sliding mesh technique and hybird-grid have been used in the hydrodynamic performance simulation. Based on the analysis of the transient wake field and wake vortex structure, it is found that in the near wake flow field, continuous vortex structures are distributed near the propeller radius region, and the axial velocity is larger in the wake field than that in freestream. The vortex system is composed of shear-layer vortex of the duct, blade vortex system and hub vortex. The blade vortex system contains the tip vortex, root vortex, hub vortex and the S shape secondary vortex, which are induced between two adjacent tip vorteces. There exists complex interference between multiple vortices, which lead to the merging, distortions and breakdown of wake vortex morphology, and gradually diffuse in the downstream.
 Alignment Calculation for Ship Propulsion Shaft Based on Segmentation Elastic Contact Theory of After Stern Tube Bearing YANG Hongjun1,LU Fei1,CHE Chidong2 2018, 52 (6):  681-686.  doi: 10.16183/j.cnki.jsjtu.2018.06.008 Abstract ( 41 )   In order to investigate the contact status between after stern tube bearing and propeller shaft of large merchant ships in static condition, the FE model of shaft alignment for propulsion shaft was built by beam element, where the stern tube bearing was divided into several sections. As non-linear support boundary condition of beam element, both Hertz and Winkler elastic contact model were used to simulate contact status between each shaft bearing and shaft. The FE model was solved by iterative method. In accordance with the calculation results, it was revealed that two methods had similar outcomes in the contact area of after stern tube bearing, but the contact stiffness of Winkler contact model, with smaller contact area and more concentrative force, was higher than Hertz contact model. And the contact area of Hertz contact model was larger, and could not fulfil the prerequisite of Hertz contact model, so it might result in limitation in after stern tube bearing contact calculation.
 An Improved Monte Carlo Reliability Analysis Method Based on Neural Network CHEN Songkun,WANG Deyu 2018, 52 (6):  687-692.  doi: 10.16183/j.cnki.jsjtu.2018.06.009 Abstract ( 40 )   Monte Carlo (MC) is a very accurate method in the structure reliability calculation, however, its application is limited due to a large number of computation when it comes to complex engineering structures. It is time-consuming even in a single analysis. To reduce the calculation, the neural network approach is adopted to construct the BP-MC method. The back propagation (BP) neural network is built through design of experiments (DOE), then the weighting factors and the distance to failure surface are used as filters to pick up the design points out of the MC points. Those picked points are prone to cause the structure failure, and transferred into the training set to update the BP model. The filter-update process continues until the convergence of the BP, and then reliability index is calculated with the BP model on the MC points. The efficiency and usability are elucidated with a mathematic model and a stiffened panel model at the end of this paper.
 Evaluation Technology of Design Scheme for Liquified Natural Gas Bunker Vessel WANG Yunlong，SHEN Jiaqi，WANG Qingpeng，WU Dehua,JIN Chaoguang 2018, 52 (6):  693-697.  doi: 10.16183/j.cnki.jsjtu.2018.06.010 Abstract ( 53 )   With the increase of the ship that uses liquified natural gas (LNG) as main fuel, the technology, methods, facilities and equipment for the filling of LNG fuel have been a prominent issue in shipbuilding and shipping industry. LNG bunker vessel is an important development direction of LNG offshore filling technology because of its advantages of self-navigation ability, safety and reliability, flexible scheduling and so on. Considering the research work of the design of the LNG bunker vessel and experts advice in recent years, a set of evaluation index system for LNG bunker vessel is established and its evaluation method is studied. On the basis of establishing the evaluation index system, the optimization of design scheme is made by using the improved fuzzy analytic hierarchy process. Preliminary analysis and calculation examples show that the evaluation index system and evaluation method are applicable and reliable.
 Frequency Domain Computation Study on the Seakeeping Performance of Small-Waterplane-Area Twin Hull Based on the Translating-Pulsating Source Green Function SUN Xiaoshuai,YAO Chaobang,XIONG Ying,YE Qing 2018, 52 (6):  698-707.  doi: 10.16183/j.cnki.jsjtu.2018.06.011 Abstract ( 47 )   The seakeeping performance of a small-waterplane-area twin hull (SWATH) installed with stabilizing fins was investigated on the basis of the three-dimensional translating-pulsating (3DTP) source Green function. The effects of the hydrodynamic interaction between twin hulls, the viscous damping and the lift generated by the stabilizing fins were included. The numerical method was validated by comparison with the test results of a SWATH vehicle called SWATH-M. Then the influences of the forward speed on the seakeeping characteristic of SWATH-M were studied, and the effects of the viscosity and stabilizing fins on the hydrodynamic forces of the total hull were analyzed. The results obtained from the present method based on the 3DTP source Green function show good agreement with those of the test. The transfer functions of both heave and pitch modes depict two peak values with the wavelength increase. With the increase of the forward speed, the peak value in the relatively short wave zone increases while the peak value in the long wave zone decreases. The effects of the viscosity and stabilizing fins have obvious contribution to the heave-heave damping, the pitch-pitch damping, the imaginary part of heave force and the real part of pitch moment.
 Structural Deformation Mechanism Analysis of Web Girders Subjected to In-Plane Load LIU Kun1,2,FU Jie2,WANG Zili2,TANG Wenyong1 2018, 52 (6):  708-714.  doi: 10.16183/j.cnki.jsjtu.2018.06.012 Abstract ( 43 )   Stiffened web girders are widely used in ship hull structures. They are often damaged due to the in-plane loads during ship collision and grounding accidents, certainly affecting the safety of the ship structure. In this paper, the longitudinal stiffened web girder is selected as the research object, the quasi-static impact test and related numerical simulations are conducted to investigate the structural deformation mechanism of web girder subjected to in-plane load. Then, a new deformation model for web girders subjected to in-plane load is proposed in accordance with the features found in the test and simulation analysis. Based on the new model, the analytical formulae for energy dissipation, instantaneous force and mean resistance of web girders are obtained in the light of the plastic analysis. Finally, the new analytical method is verified by the results of model test. It turned out that the proposed analytical method can be a reference to the preliminary structural design and assessment for ship crashworthiness.
 Liquid Film Thickness Design of Cam-Rotor Vane Motor Based on Efficiency Analysis ZHU Yannan1，ZHANG Qiang1，CHEN Lifeng2，TAO Jianfeng1，WANG Xuyong1 2018, 52 (6):  715-721.  doi: 10.16183/j.cnki.jsjtu.2018.06.013 Abstract ( 48 )   A new kind of cam-rotor vane motor is introduced with its working principles and features. Motor’s leakage models are established based on the clearance flow model between parallel flats and parallel plates. Therefore, the relationship between motor’s liquid film thickness and volumetric efficiency is obtained. The relationship between motor’s thickness of liquid film and mechanical efficiency is obtained by the analysis and calculation of the friction torque between motor’s two critical friction pairs based on the absolute viscosity model. Based on analysis on the motor of a three-axis non-magnetic turntable system, the optimal liquid film thickness leading to motor’s maximum total efficiency is obtained by synthesizing the effect of volumetric efficiency and mechanical efficiency. The significance of the study is to provide the theoretical basis for the subsequent optimization of liquid film thickness of vane motor’s critical friction pairs. Furthermore, the dimensional precision, geometric precision and surface roughness of the key components such as cam rotor, stator and clapboard can be put forward in the process of design and manufacture of cam-rotor vane motor.
 A Piecewise Calculation Model for Fractal Rough Surface Contact Deformation CHEN Hongxu,DONG Guanhua,XIE Luofeng,YIN Ming,YIN Guofu 2018, 52 (6):  722-728.  doi: 10.16183/j.cnki.jsjtu.2018.06.014 Abstract ( 48 )   To address the existing problems of fractal theory, a piecewise calculation model was proposed. This new model was calculated by different functions with the corresponding parameters set by the wavelength. The fractal detail and deformation process of asperity were considered in this model. The contact deformation process of rough surface was studied and the relationship between real contact area and load was given. The analysis results showed that contact deformation process of rough surface is a transition from plastic to elastic contact model, where elastic deformation and plastic deformation model alternately take place. The top radius of curvature of the asperity is a fixed value which is independent of the deformation under a certain scale. When the fractal dimension is close to 1, the rough surface is dominated by the plastic deformation, and the surface contact property is only affected by the material. An optimal value of fractal dimension is existed when the rough surface contact property is the best.
 Review of the Kinematic Compatibility Design of Hand Exoskeletons LI Jianfeng1，ZHANG Zhaojing1，ZHANG Leiyu1，TAO Chunjing2，JI Run2，FAN Jinhong1 2018, 52 (6):  729-742.  doi: 10.16183/j.cnki.jsjtu.2018.06.015 Abstract ( 50 )   The design arts and status of hand exoskeletons are analyzed and reviewed from the perspective of human-robot kinematic compatibility. Firstly, the main existing hand kinematic models are introduced on the basis of the analyses of the hand anatomical structure and hand joint kinematics. Secondly, according to the design methods to realize the human-robot kinematic compatibility, the hand exoskeletons are divided into three classifies including the joint axis-alignment hand exoskeletons, the joint axis self-adaptive hand exoskeletons, and the compliance glove hand exoskeletons. Moreover, the design characteristics of the typical hand exoskeletons are also briefly analyzed. Finally, the influences of the kinematic difference between human and robot joints, the individual difference and wearing offset on the human-robot kinematic compatibility are analyzed, on which the main issues in the design of hand exoskeletons and the future research are discussed and prospected.
 Influence of Aerodynamic Load on Fatigue Life of Mooring Lines of Floating Wind Turbines DENG Lu1,HU Binfen1,WU Songxiong1,HUANG Minxi2,SONG Xiaoping3 2018, 52 (6):  743-749.  doi: 10.16183/j.cnki.jsjtu.2018.06.016 Abstract ( 46 )   Based on a coupled analytical model of floating wind turbine, an investigation into the influences of aerodynamic load and wind turbulence intensity on the fatigue life of mooring lines was performed by using the Miner’s cumulative damage theory, the rain flow method and the T-N curves. The results of the fatigue analyses of mooring lines show that the including of the turbulent wind loads causes an 80% decrease in the fatigue life of mooring lines, indicating the importance of choosing a reasonable turbulent wind model; in sea states with wind speed which is close to the rated wind speed of the wind turbine, aerodynamic loads can greatly amplify the horizontal displacement of the platform, thus increase the tension of mooring lines, and decrease the fatigue life of mooring lines; the interaction among the responses can worsen the fatigue damage of mooring lines. This study can guide the fatigue design of mooring lines.
 Adaptive Fuzzy Sliding Mode Control for a Chain Driving Shell Magazine Based on an Exponential Reaching Law YUE Caicheng1,QIAN Linfang1,XU Yadong1,LI Ying2 2018, 52 (6):  750-756.  doi: 10.16183/j.cnki.jsjtu.2018.06.017 Abstract ( 57 )   A control scheme based on exponential reaching law is proposed for a class of nonlinear systems with wide variations of parameters, chattering and nonlinear friction problems. An adaptive fuzzy sliding mode control (AFSMC) scheme is employed to realize the precision position control, to adjust the unknown external disturbance, to adjust the reaching law parameters online, to guarantee the tracking performance and enhance the robustness. The traditional sign function is replaced by a saturation function. This improved saturation function ensures that the switching process is more continuous. Chattering of the chain driving shell magazine is also restrained. The stability and convergence of the overall system are proved by the Lyapunov method. Experimental results show that the performance of the chain driving shell magazine by using this AFSMC scheme is better than using equivalent sliding mode control (SMC) scheme. The system has a good position tracking performance, a strong anti-interference capability and a desired positioning accuracy.