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Table of Content

    25 November 2009, Volume 37 Issue 11
    Traffic & Transportation Engineering
    Wu Jia-ming Yu Miao Zhu Liang-sheng
    2009, 37(11):  1-6. 
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    :The calculation and analysis of the integral wave load acting on offshore structures is an important step in the design Of the structures. In this paper, a truss-type offshore structure, which consists of cylindrical underwater members with different diameters, orientations and lengths, is taken as the research object, and the wave forces acting on the cylinders are calculated one by one based on the Morison equation and then superimposed to obtain a comprehensive wave load acting on the integral structure. Numerical results show that the integral response of the structure to waves depends mainly on the relative relations between structure dimension and such wave environment parameters as wave height, period and wave direction.

    Wang Duan-yi Liu Jing-hui Liu Yu
    2009, 37(11):  7-11,21. 
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    Based on the semi-circular bending test, the delayed cracking properties of asphalt mixture, a typical viscoelastic-plastic material, are evaluated using the J-integral theory and the delayed-cracking initiation time. The delayed-cracking initiation time in different loading and temperature conditions as well as the fracture toughness at different testing temperatures is also measured to reveal the rules of crack initiation. The results show that the crack initiation displays obvious viscoelastic-plastic characteristics, and that a simple rheological constitutive model is applicable enough for the evaluation of fracture performance of asphalt mixture using the J-integral theory and the delayed-cracking initiation time.

    Zhang Li-juan Chen Ye-kai
    2009, 37(11):  12-16. 
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    Asphalt mixture is a typical viscoelastic material, whose deformation law can be well described using the generalized Maxwell viscoelastic model. In this paper, the Prony series coefficients of the generalized Maxwell model are obtained by fitting the results of static creep test of AC-13C unmodified and modified asphalt mixtures. Then, a half-sinusoids load with 0.1 s loading duration and 0. 9 s unloading duration is used to simulate the dynamic vehicle load on the pavement. Moreover, the asphalt mixtures under repeated loads are analyzed by means of the viscoelastic finite element method, and the corresponding deformation consisting of both elastic strain and creep strain are predicted, with the results according well with the measured ones. As the creep strain leads directly to permanent deformation of asphalt mixtures, it is feasible to determine the elastic resilience of asphalt mixtures according to the creep strain.

    Zhang Xiao-ning Li Hong-jie Shou Yan-fang
    2009, 37(11):  17-21. 
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    Proposed in this paper is an index system of highway landscape evaluation based on the satisfaction theo—ry in economics,including such indexes as the quality perception,the value perception and the satisfaction of thepublic.The rationality of the selected indexes is verified by the principal component analysis,and a satisfactionmodel of highway landscape evaluation is established by means of the structural equation modeling(SEM).Moreover,a landscape road in Guangzhou is selected to conduct a questionnaire survey.The results show that the pro—posed satisfaction model helps to analyze the perception of public for highway landscape systematically,scientifically and quantitatively

    Hu Chi-chun Wang Duan-yi Kejin Wang Jim Cable
    2009, 37(11):  22-26. 
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    In order to reasonably determine the input parameters in pavement structure design, a self-organized feature mapping neural network is introduced and its weight is trained with Matlab. Then, by taking the convergence of the training as the classification rule, a seasonal roadway classification is made according to such important parameters as temperature, traffic and rainfall. Moreover, pavement structure analysis and material design are performed according to the classification results. The proposed classification method is proved effective in determining reasonable design parameters of pavement. Thus, it greatly prolongs the service life of pavement and improves the economic benefit of road investment.

    Wu Wen-liang Zhang Xiao-ning Li Zhi
    2009, 37(11):  27-30,49. 
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    The rutting of asphalt pavement is always one of the research focuses in road engineering. In this paper, the original image of AC-13C asphalt mixture during the APA rutting test and the corresponding sectional images after the loading respectively for 500, 1000, 2000, 4000 and 6000 times were acquired, and the movement track of coarse particles was analyzed according to the images. The results show that the digital image processing technology has great capability in movement tracking of coarse particles, and that, by defining the rotation angle θ, the displacement L and the statistics △ and α, the complicated particle movement in different loading stages during the APA rutting test can be well described and quantified.

    Chen Da-wei Xu Zhong Li Xu-hong
    2009, 37(11):  31-36. 
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    The layout optimization of regional comprehensive freight regional comprehensive transportation system. In this paper, first, hubs is one of important parts of the planning of a layout optimization model of regional comprehensive freight hubs is established to minimize the total cost of the freight transportation system. Next, a method based on intermodal transport is proposed to describe the regional comprehensive freight transportation network. Then, with the concept of normal intermodal transport route, three constraints, namely reasonable mode sequence, reasonable transport distance and reasonable transfer number, are presented to search for an optimal route. Moreover, a solving method of the proposed model is given based on the super network and the genetic algorithm, and a virtual special route is introduced in the hubs. The proposed model and its solving method are finally verified by a hypothetical analytical example. The results indicate that the model coincides with practical situation, and that it is an effective path of the layout optimization of regional comprehensive freight hubs.

    Lu Kai Xu Jian-min Zheng Shu-jian
    2009, 37(11):  37-42. 
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    By analyzing the influences of the intersection distance, the traffic section volume and the signal timing parameters on the correlation between two neighboring intersections, a new traffic parameter, neighboring intersection correlation degree, is put forward to quantitatively describe the correlation between two neighboring intersections, and the corresponding calculation method is proposed. Then, the rationality of the parameter is analyzed and the definition and calculation formula of the multi-intersections combinatorial correlation degree are presented. Some new principles for the coordinative division of traffic control subareas are given based on the correlation degree analysis.

    Zhan Jian-yun Li Zhi-hen Zhang Yi Duan Hou-li
    2009, 37(11):  43-49. 
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    According to the traffic flow characteristics,the short passageway distance and the serious interweaving of Beijing ring freeway,the node and road section models of the basic model METANET are both improved.Accordingly,a nonlinear optimal control model is established,and a solution to the coordinated control system of passageway is obtained with optimal discreteness.Afterwards,by taking Beijing ring freeway for example,a comparison is made between the simulated results based on the improved AMOC strategies and the actual trafic status.The results show that the improved AMOC strategies help to maintain the traffic density in a desired range with relatively short queue length.and reduce the total travelling time of all vehicles in the road network by 18.4%

    Power & Electrical Engineering
    Zhang Yong-jun Yuan De-fu
    2009, 37(11):  50-55. 
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    As insufficient original reliability parameters greatly reduce the authenticity and effectiveness of the reliability assessment results of power systems, an optimized GM ( 1,1 ) model is used to predict original reliability parameters for the purpose of exploiting some small sample systems. In the optimized GM ( 1,1 ) model, the fitting series of the original parameter series within different time is obtained based on the optimization of the initial value using the least square method, and the fuzzy nearnesses between the original series and the fitting series are used as weight coefficients to treat the prediction values with weighted optimization. This model reflects not only the latest changes but also the overall development trend of data. Therefore, it fully exploits the information contained in original parameters and solves the problem existing the conventional GM ( 1,1 ) model, namely the rapid decline of prediction precision with the prediction point. The proposed model is applicable to the multi-point prediction of original reliability parameters of new electricity components.

    Wang Xiao-gang Xie Yun-xiang Shuai Ding-xin Huang Shao-hui
    2009, 37(11):  56-63. 
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    As the existing digital control methods for active power filters are highly dependent on the adoptea models, this paper proposes a model predictive control (MPC) method for a three-phase four-leg active power filter based on the decoupling control of the positive-negative-order and the zero-order systems. By taking the difference equation as the predictive model, the feedback correction and dynamic optimization in the conventional MPC methods are reserved, and the optimal control law is deduced. The proposed method is then compared with common predictive current control methods, drawing a conclusion that the predictive current control with supply voltage observer is only a special case of MPC. Moreover, the influences of system parameters on the system stability are analyzed, and a larger modeling error allowance of connection reactor and a stronger robustness of the controller are ob- tained by modifying MPC parameters, with the bandpass filter being omitted. The combination of MPC and a repetitive controller eliminates the inherent steady-state error of MPC. Simulated results indicate that the proposed method is effective and valid.

    Liu Ming-bo Xie Hao-nan
    2009, 37(11):  64-70,82. 
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    Based on the quasi-steady-state assumption, an optimal coordinated voltage control model consisting of the constraint of continuous and discrete time differential-algebraic equations is established, and a direct method from the modern optimal control theory is applied to solving this dynamic optimization problem. Then, according to Radau collocation method, the dynamic optimization problem is converted to a nonlinear programming one that contains continuous and discrete variables. Moreover, in order to consider the discrete characteristics of the turn ratio of on-load regulating transformer, the switchable capacitor bank and the shedding load, a nonlinear primal-dual interior-point algorithm incorporating the penalty function mechanism for discrete variables is used during the solving of this problem. Simulated results on New England 10-machine 39-bus system demonstrate that the proposed method improves the long-term voltage stability of power systems because it effectively coordinates the actions of different control devices

    Zhang Zhi Xie Yun-xiang Le Jiang-yuan Chen lin Chen Hao-yong
    2009, 37(11):  71-75. 
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    In this paper, first, a nonlinear mathematical model of three-phase voltage source rectifier (VSR) with pulse-width modulation (PWM) is established in the synchronous rotating reference frame. Next, by considering the high coupling of active and reactive currents, a double closed-loop control algorithm of voltage and current is proposed, in which a sliding-mode control algorithm for the outer voltage loop and an exact feedback linearization method for the inner current loop are adopted. The whole system is then simulated, and the results are finally compared with those obtained by the traditional PI control. It is found that the proposed scheme integrates the advantages of sliding-mode control and feedback linearization method, which makes VSR to be robust and realizes decoupling control of active and reactive currents, and that, with the proposed scheme, the system is of high power factor, constant output voltage, good static and dynamic performance, and robustness to the disturbance and nonlinear variation of the load.

    Zeng Jiang Ye Xiao-jun Liu Yan OuYang Sen
    2009, 37(11):  76-82. 
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    Proposed in this paper is a new method to reduce the switching loss of active power filter (APF) through adjusting the hysteresis band width. In this method, the hysteresis band width of each phase of APF is adjusted according to the output reference current, and the switching number of the phase with high switching loss is reduced while that of the phase with low loss is increased. Thus, the total switching loss is decreased without reducing the overall control precision. Only an adjusting circuit may significantly decrease the switching loss. Computer simulation with the electromagnetic transient program shows that, by using the proposed method, the switching loss of APF decreases by more than 10%, the temperature rise of each phase switch becomes smoother, while the control precision and switching frequency are almost unchanged.

    Wang Wan-wei Yin Hua-jie Guan Lin
    2009, 37(11):  83-87,106. 
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    Proposed in this paper is a direct power control scheme for three-phase PWM rectifiers based on the sliding-mode variable-structure control theory. In this scheme, the slide-mode variable-structure control system with strong robustness, excellent dynamic performance and simple parameter tuning is employed to remedy the shortcomings of the conventional direct power control system based on PI algorithms, namely high sensitivity to external disturbances and PI parameters and large total harmonic distortion (THD) of line current. Then, both the proposed and the conventional PI-based control schemes for three-phase PWM rectifiers are modeled and compared in Matlab/Simulink simulation environment. The results show that the proposed scheme is superior to the conventional one.

    Lin Shun-jiang Liu Ming-bo
    2009, 37(11):  88-94. 
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    This paper proposes a mathematical model for analyzing the transient voltage stability of power systems whose load is presented by a three-order induction motor paralleling constant impedance model, and gives a practical scheme to choose the initial point when the Newton method is used to compute the control'ling unstable equilibrium point (CUEP) corresponding to the instability mode of system voltage. In this scheme, the controlling load bus of a given fault is identified, the Thevenin equivalent circuit is used to represent the rest of. the system in the state of post-disturbance stable equilibrium point, the steady equivalent circuit is adopted to describe the induction motor in a composite load, and a point near the CUEP is obtained based on the torque characteristics of the induction motor and is then taken as the initial iteration point. Moreover, a method to obtain the initial iteration point closer to the CUEP is proposed, by which the CUEP can be computed more reliably. Computation results of the IEEE 9-bus and the 39-bus systems show that the proposed method is reliable and effective.

    Liu Wen-ze Cai Ze-xiang Feng Shun-ping Li Xiao-hua
    2009, 37(11):  95-99. 
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    Fuse is a protection device which directly connects with a capacitor in series. In practice, the abnormal fusing of fuse is of the highest fault ratio among the accessories of capacitor bank. Shunt capacitor bank is the compensation equipment generally used in power systems. It, commonly with framed structure, consists of several capacitors in a double-star structure linking to the power system. This paper analyzes the abnormal-fusing electrical characteristics of fuse, deduces an equivalent electrical model describing the fusing, and presents the phase rules of the voltage and the current of each branch in the capacitor bank with fault. The correctness of the investigation is then proved by the real-time fault data recorded by a monitoring equipment of shunt capacitor bank. Some suggestions for reducing the fault ratio of the capacitor bank are proposed in the end

    Chen Min-wu Li Qun-zhan Xie Shao-feng
    2009, 37(11):  100-106. 
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    The maintenance scheduling of a traction power supply system should give consideration to both system reliability and maintenance economy. In this paper, the method to analyze system reliability, namely GO methodology, is applied to the reliability assessment of the traction power supply system of a high-speed railway, and a quantitative calculation equation of system reliability is deduced. Then, by considering the economic dependency among the maintenance of various electrical equipments and the imperfectness of preventive maintenance, an optimal model of maintenance plan to satisfy the reliability constraints is proposed to minimize the maintenance cost in a finite time interval. The corresponding simulation program with good convergence is also presented based on an improved discrete particle swarm optimization algorithm. Simulated results indicate that the proposed model is objective and effective and is suitable for scheduling the maintenance plan of traction power supply svstems.

    Yang Ping Xiao Ying Jian Qi-fei Luo Xue-wei Liu Wen-fei
    2009, 37(11):  107-111,117. 
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    In order to reduce the air-condition energy consumption and the local heat island effect in communication rooms, the CFD (Computational Fluid Dynamics) method is employed to reveal the airflow organization characteristics, and a sample room is used to make some experimental tests and verification analyses. Experimental and calculated results are basically consistent with each other, meaning that the proposed model is correct and the numerical solution is credible. Moreover, an optimal deployment scheme of the incoming/back wind for communication rooms is designed to optimize the operation environment of the equipment, reduce the cold waste and exploit energy-saving potentialities.

    Mechanical Engineering
    Cui Xiao Dong Yan-liang Zhao Ke-ding
    2009, 37(11):  112-117. 
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    In order to avoid the unbalanced gravity load during the simulation of large-scale aircrafts, a hollow electro-hydraulic servomotor for the simulation turntable is designed and manufactured. Then, the friction torque to affect the ultra-low-speed tracking performance is analyzed, and a mathematical model of the servomotor with large friction torque is established. Moreover, an adaptive controller with friction compensation is devised based on the LuGre model. Finally, simulations and experiments with different inputs are carried out to verify the effectiveness of the controller. The results show that, as compared with the conventional PID controller, the proposed adaptive controller helps to implement the low-speed performance of the servomotor better.

    Huang Zan Zhang Xian-min
    2009, 37(11):  118-122. 
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    The motion estimation based on image is a basic task in many applications of computer vision. The main goal of it is to estimate the motion of scenes and objects as accurate as possible. In the optical flow estimation, outliers may lead to undesirable results and greatly reduce the motion estimation precision. In order to solve these problems, an improved robust multi-scale algorithm of hierarchical motion estimation is proposed. In this algorithm, Tukey's bi-weight function is used to automatically adjust the weights of data with different residual errors and to remove the data with excessive residual errors, and a multi-scale pyramid is employed to accurately estimate the motion vector by an iteration gradually from coarseness to fine. Experimental results show that the proposed algorithm with strong robustness effectively solves the problem of outliers caused by occlusive background and discontinuous motion and greatly improves the precision of motion estimation.

    Hu Jun-feng Zhang Xian-min
    2009, 37(11):  123-128. 
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    In this paper, first, the finite element method is vel planar parallel manipulator with two degrees of freedom. employed to construct an elastodynamic model of a no- Next, on the basis of the proposed model, the distribution of the first four-order natural frequency of the manipulator in the workspace is analyzed. Then, the displacement error of the moving platform under the excitations of external forces and rigid inertial force is investigated. Finally, the maximum dynamic stress and its position at each time point are presented. The results show that the natural frequency of the manipulator is relevant to the configuration, that the displacement error of the moving platform is mainly caused by the rigid inertial force during a high-speed movement, and that the dynamic stress spectra of the flexible components of the manipulator are all amplitude variable.

    Zhou Wei Tang Yong Wei Xiao-ling Pan Min-qiang Wan Zhen-ping
    2009, 37(11):  129-133,150. 
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    Stable-quality fine metal fibers with a length of 10 -22 mm and a diameter of less than 100 μm were fabricated by planning on a common planer with a multi-tooth tool. Then, by comprehensively analyzing the planing process and by investigating the effects of cutting parameters on the planing process, reasonable processing parameters were determined. The results show that both the tool parameters and the cutting parameters greatly influence the quality of metal fibers in the planing process, that a larger rake angle and an appropriate clearance angle of the tool are both favourable to the fabrication of metal fibers, that the back engagement has the greatest influence on the forming process, while the cutting speed and the feed rate have no obvious effect on the forming process, and that, at a back engagement of 0. 04 - 0.06 mm, a cutting speed of 30 - 60 m/min and a feed rate of 0. 72 - 1.44 mm/r, fine copper fibers with stable quality can be fabricated using the muhi-tooth tool with a rake angle of 30°, a clearance angle of 8°, a tooth pitch of 0. 3 mm and a tooth height of 0. 2 mm.

    Wang Bo Zhou Chi Ruan Feng Huang Zhen-yuan
    2009, 37(11):  134-139. 
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    The oxidation of blanking sections of IT products may weaken the contact conductibility and eventually lead to the function failure of products. In order to solve these problems, a plane-strain rigid-plastic finite element analysis (FEA) model is established to numerically simulate the deformation and flow of coating metal in the blanking process. Moreover, a method to estimate the distribution of coating metal in the blanking section is presented and is then verified by experiments using the tin-phosphorus-bronze band with Sn coating. The results show that the coating metal mainly disperses in the roll-over and the euphoric zones of blanking section during the blanking, and that the numerically-simulated content of coating metal in the euphotic zone of blanking section accords well with the experimental result. The proposed method can be applied to the die design for the purpose of estimating the content of coating metal on the blanking section at different blanking parameters, optimizing the parameters to increase the metal content and to further improve the antioxidant ability of the blanking section.

    Wu Rui Xu Jia-wen Zhao Jian-she Wu Jian-min
    2009, 37(11):  140-144. 
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    In order to improve the machining precision of vane surface of integral impeller and the efficiency of cathode movement planning during the electrochemical contour evolution machining, by taking a ruled-surface impeller for example, the effect of twist angle of vane surface on the machining is analyzed, and a movement planning method of contour evolution is proposed. In this method, normal offset curves are obtained from the fitting curve of vane data points, the feature points generated from the offset curves are used to design the movement trajectory of contour evolution, and the results of process experiments are employed to determine the cathode movement parameters. Thus, the negative effect of twist angle on the machining precision is effectively eliminated. It is shown that the proposed movement planning method makes rapid and efficient designs and improves the machining precision for the vane surface of integral impeller.

    Zhou Zhao-yao Pan Jtan-yi Wang Yao Tan Chi-dong Chen He-ai
    2009, 37(11):  145-150. 
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    Two models to analyze the aluminium alloy extrusion in the pocket and the porthole dies are respectively established, and the distributions of stress and velocity field of the billet respectively in the two dies during the extrusion are then compared and analyzed using the finite volume method (FVM). The results indicate that the stress distribution of the billet is not directly related to the height of the die bearing and the flow equilibrium of the material, while the adjustment of the die bearing plays a certain role in the improvement of metal flow. Aiming at the flow equilibrium of the material at the outlet, a criterion is then proposed to judge whether stable qualified products can be obtained by the extrusion. Moreover, the standard deviation of the velocity field (SDV) at the outlet is calculated. The results show that, when the SDV decreases with the increase in time to less than a critical convergence value, stable qualified products can be obtained.

    Zhang Zu-jun Ruan Feng Liu Yi Liu Cheng-jun
    2009, 37(11):  151-156. 
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    In order to improve the numerical stability during the solving of convection-dominated convection-diffusion problems, an upwinding local radial point interpolation method (ULRPIM) is proposed based on the local radial point interpolation method (LRPIM) and the local upwinding weight function. The proposed method is then compared with the LRPIM through some numerical calculations, finding that ULRPIM achieves better results. Mo- reover, the influences of different parameters on the stability of calculation results are investigated by comparing the relative errors of ULRPIM results at different parameters. It is found that the offset of weight function should change with the Peclet number, and that both the parameter q of radial basis functions (RBF) and the size of the support domain have a greater influence on the calculation results than the RBF parameter ac and the quantity of Gauss integral points.

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