西南交通大学学报

Evaluation Theory and Method of High-Speed Train Diagrams

PENG Qiyuan, BAO Jingjing, WEN Chao, FENG Liping

2013, 26(6): 969-974. doi: 10.3969/j.issn.0258-2724.2013.06.001

[Abstract](1442)

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Abstract:
In order to improve the quality of high-speed train diagram, a complete evaluation index system for high-speed train diagrams was established. In the system, the evaluation indexes are extracted from three aspects, i.e., the train diagram production efficiency, passenger service quality, and dynamic performance; and their quantification methods are provided. As an example, the train diagram of the north section of Zhengzhou-Xi'an high-speed railway was evaluated using the proposed method. The result shows that the proposed evaluation index system is convenient and feasible for a single train diagram evaluation, and it is also can be used for comparison of multiple train diagrams. The grey evaluation result of Zhengzhou-Xi'an north section is 3.294, indicating the good quality of the train diagram.

Numerical Simulation of Stochastic Characteristics of Fluctuating Lift on a Fixed Circular Cylinder

ZHU Zhiwen

2013, 26(6): 975-982. doi: 10.3969/j.issn.0258-2724.2013.06.002

[Abstract](1082)

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Abstract:
In order to investigate the applicability of large eddy simulation (LES) in wind engineering research, numerical simulation was carried out for flow field around a circular cylinder at Re=4.11104. The obtained mean and root mean square (RMS) component of fluctuating pressure and the vortex shedding Strouhal number are in good agreement with the results from available reports. An equation, based on the correlation coefficients between 90 and 270 position and RMS of the fluctuating pressure at those two points, was presented to estimate the sectional fluctuating lift on the cylinder. Coherent analysis was carried out between fluctuating pressures on circular surface, and the flow mechanism of aerodynamic forces was discussed in view of the coherence function of the fluctuating pressures on cylinder surface. It is found that the vortex shedding is not in-phases along the span-wise direction, and the vortex shedding frequency varies with the flow time. In particular, the vortex shedding energy is concentrated on a narrow band of frequency, while the pressure fluctuating energy is concentrated on the vortex shedding frequency; the fluctuating pressure time series at 90 and 270 on the opposite shoulder of the circular share the same statistical features.

Aerodynamic Stability of Long-Span Bridges in Post Flutter

WANG Qi, LIAO Haili, LI Mingshui, MA Cunming

2013, 26(6): 983-988. doi: 10.3969/j.issn.0258-2724.2013.06.003

[Abstract](1090)

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Abstract:
To provide reasonable explanations for the motion types of girder in post flutter status of long-span bridges, the nonlinear aerodynamic stability of bridge girder was analyzed based on an existing nonlinear motion-induced aerodynamic force (MIAF) model and the nonlinear vibration differential equation, by using the 4th Runge-Kutta algorithm. Four typical MIAF cases of streamline box girder with large vibration amplitudes were taken into account in the analysis. The results show that different types of motions would occur to the girder of long-span bridge in post flutter under conditions of different amplitudes and reduced velocities. The vibration of bridge girder will converge when the aerodynamic work is negative only or the negative work is larger than the positive one. The divergent motion will occur when the aerodynamic work is positive only or the positive work is larger than the negative one. If the aerodynamic positive and negative work are well matched to each other, the girder vibration will converge slowly because of the structural damping. If the aerodynamic positive energy is equal to that consumed by structure in the same period, an equal-amplitude vibration will occur. The motion of bridge girder could diverge if ignoring the nonlinear items of the motion-induced aerodynamic force.

Influence of Track Regularity and Soil Dynamic Characteristics on Vibration of Subway Tunnel

WEI Kai, ZHAI Wanming, XIAO Junhua

2013, 26(6): 989-995. doi: 10.3969/j.issn.0258-2724.2013.06.004

[Abstract](1187)

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In order to accurately calculate the frequency-domain vibration response of a subway shield tunnel due to dynamic loading of trains, a vertical coupling dynamic model of subway shield tunnel is established to study the influence of the nonlinear variation of soft-soil dynamic stiffness on the random vibration of subway shield tunnel at different levels of track irregularity. In this model, the dynamic stiffness of soft soil varies nonlinearly with the frequency-domain response of soft soil strain. The results show that along with the deterioration of track regularity, the nonlinear dynamic stiffness of soft soil causes obvious heterogeneous variations to the vibration accelerations in frequency domains of the subway shield tunnel. In addition, the nonlinear dynamic stiffness of soft soil not only alters the frequency-domain vibration amplitude of subway shield tunnel after the deterioration of track irregularity, but also makes the corresponding frequencies appear to shift, and the biggest deviation is about 0.2 Hz, which leads to a redistribution of the vibration energy of the subway shield tunnel in frequency domain.

Influence of Stochastic Cracks on Sulfate Diffusion in Concrete of Underground Structure

LIU Weiqing, LIU Xin, WANG Shuguang, DU Dongsheng

2013, 26(6): 996-1001. doi: 10.3969/j.issn.0258-2724.2013.06.005

[Abstract](1114)

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The influence of the stochastic crack width on sulfate diffusion coefficient and concentration in underground concrete was investigated. It is assumed that the crack is composed of crack elements, and the probability density function of crack element location along longitudinal direction of the crack follows the normal distribution. The rule of sulfate diffusion coefficient in cracking concrete varying with the cracks width was deduced. Based on Fick's second law, a modified diffusion equation was presented, and the numerical simulation was conducted with two crack shape parameters. The results showed that in both cases the sulfate ion concentration reached a steady state within 50 h. The small crack shape parameter and irregular crack shape slowed down the diffusion rate and the time for steady concentration.

Parameter Optimization of Fluid Viscous Damper Based on Stochastic Vibration

ZHAO Guohui, LIU Jianxin, LI Yu

2013, 26(6): 1002-1007. doi: 10.3969/j.issn.0258-2724.2013.06.006

[Abstract](1112)

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In order to avoid the large computational cost and low efficiency of parametric-sensitivity methods in the parameter optimization of fluid viscous dampers, the theoretical optimum damping ratio of the bridge superstructure vibration system was derived by stochastic vibration method, and an analytical expression for the optimum damping coefficient of linear fluid viscous damper for bridge was then obtained. Meanwhile, the optimum damping coefficient of nonlinear fluid viscous damper for bridge was also derived based on the principle of energy equivalence. In order to verify the reliability of the analytical expression, taking a continuous bridge as an example, the parametric sensitivity on the damping coefficient was analyzed by dynamic time history method. The results show that the theoretical optimum damping ratio of the bridge linear fluid viscous damper is 0.5, which enables the damper to reach its maximum frequency. Compared with the linear fluid viscous damper, the optimum damping coefficient and damping force of the nonlinear fluid viscous damper is decreased by 55% -67% and 16% -22%, respectively.

Optimal Selection Model of Railway Location Designs Based on Utility Theory

LUO Yuan, YAO Lingkan, ZHU Ying, YANG Ming

2013, 26(6): 1008-1015,1023. doi: 10.3969/j.issn.0258-2724.2013.06.007

[Abstract](1160)

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Traditional scheme comparison methods for railway route selection have not taken into account the impact of different macroeconomic situations on the optimal selection of railway locations. Besides, there still exist operational difficulties in qualification of indicators that cannot be measured by money. To overcome these defects, the utility theory and projection method were introduced into optimal selection of railway location designs in this work. Firstly, interval numbers were introduced to quantify qualitative indicators after experts evaluated alternatives using linguistic variables. Then, by defining utility functions to quantify the impact of macroeconomic situation, a model of route scheme evaluation in different macroeconomic situations was established. From this model, the optimum scheme could be selected by using different economic environmental factor k. Finally, an example of local alignment scheme comparison was used to illustrate the operation procedure of the model. This work provided a new and synthetic evaluating model for optimal railway route scheme selection in railway location design.

Stochastic Ultimate Bearing Capacity Analysis Based on Elastic Modulus Reduction Method

YANG Lufeng, WU Wenlong, YU Bo

2013, 26(6): 1016-1023. doi: 10.3969/j.issn.0258-2724.2013.06.008

[Abstract](1138)

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Abstract:
To determine the stochastic ultimate bearing capacity of engineering structures, a novel method for stochastic ultimate bearing capacity analysis based on the elastic modulus reduction method (EMRM) was proposed by combining the elastic modulus adjustment procedure (EMAP) and the perturbation stochastic finite element method (PSFEM). The stochastic responses and reliability indices of structural elements were calculated by the PSFEM to define the uniformity of reliability indices and the reference reliability index. Meanwhile, the proportional loading conditions of stochastic limit analysis as well as the proportional relationship between the stochastic responses and the external loads were demonstrated theoretically. Finally, by adjusting the elastic moduli of elements with low reliability index the failure evolution was simulated to form a set of statically admissible stress fields, and further the structural failure mode and the corresponding stochastic ultimate bearing capacity were determined based on the plastic limit analysis theory. Numerical examples demonstrate that the proposed method is converged after 15 iterative steps or so, and compared with the Monte Carlo method for 500 000 samples, it has a relative error of less than 0.5%.

Distinguishing between Sensor Deterioration and Structural Damage

MA Shenglan, WENG Liuqing, JIANG Shaofei

2013, 26(6): 1024-1030. doi: 10.3969/j.issn.0258-2724.2013.06.009

[Abstract](1053)

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Current detection methods for structural damage only consider environmental or operational effects on damage detection, but neglect the problem that sensor performance degradation can be caused by environmental changes, and thus seriously affects the damage detection accuracy. In this paper, a method for distinguishing between sensor performance degradation and structural damage is proposed, which is based on the fact that the sensor performance degradation is local, while structural damage is global. In this method, the minimum mean square error and the generalized likelihood ratio test (GLRT) are used to detect and locate the abnormal response in a structural system. Besides, the modes of the control index fluctuation out of the limit of the statistical quality control chart are used to judge the source of abnormal responses. A numerical study is performed to validate the proposed method via a simple-supported beam. The results show that the GLRT can effectively detect the abnormal responses, and the statistical quality control chart is capable of distinguishing between the degradation sensor and damage accurately. If the control index fluctuation out of the limit of the statistic control chart shows a stable mode, the abnormal response comes from structural damage; otherwise, it comes from sensor performance degradation.

Experimental Study on Damage Identification of Pipeline Based on Operational Strain Modal Shape

XU Chengxiang, JIA Shanpo, TU Jinzhao, DU Guofeng

2013, 26(6): 1031-1037. doi: 10.3969/j.issn.0258-2724.2013.06.010

[Abstract](1390)

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Abstract:
In order to make damage detection, real-time safety evaluation and life prediction of pipelines, and hence prevent pipeline accidents, difference formulas of strain mode for damaged pipelines are derived based on vibration tests and the character of one-dimensional continuum of pipelines, and a mathematical model of direct indexes for damage location and degree identification was built. Then, physical model tests for three pipelines in different damage status are carried out to identify their damage. The results show that when using the natural frequency as an identifying global indicator for damage identification, the maximal change rate of pipeline natural frequency is only 6.71% and the damage cannot be identified effectively due to the limitation of less information; the difference value of strain sensitivity, however, has more obvious mutations in damage area and can identify the pipeline damage correctly.

A Filtering Method for LiDAR Cloud Points in Urban Areas Based on Serial Morphological Operators

SUN Meiling, LI Yongshu, CHEN Qiang, CAI Guolin

2013, 26(6): 1038-1044. doi: 10.3969/j.issn.0258-2724.2013.06.011

[Abstract](990)

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To improve the accuracy of single morphological operator and automatic classification in LiDAR filtering, a new LiDAR filtering method based on serial morphological operators was presented. In view of the characteristics of morphological operators and the features of different objects in LiDAR point data, first morphological opening operator and white top-hat transformation were applied to LiDAR points with small window size for filtering low outliers and small objects (such as tree, car and electric-power line etc). Then morphological gradient was used to detect building edges. Finally, connectivity analysis and binary morphological reconstruction were applied for removing large buildings. As a result, ground points were retained and non-ground points were removed. The experimental results for nine different complexity urban data provided by ISPRS show that the average values of type Ⅰ, type Ⅱ and total errors are 6.90%, 3.33% and 5.44%. Compared with traditional filter methods, this method improves the effects of classification and automatic recognition.

Automatic Train Control Algorithm for Train Tracking

WANG Pengling, WANG Qingyuan, CUI Hengbin, MA Lei, FENG Xiaoyun

2013, 26(6): 1045-1051. doi: 10.3969/j.issn.0258-2724.2013.06.012

[Abstract](1033)

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To build a safe and stable operation strategy for train tracking, a train tracking model was established by the train longitudinal dynamics. In the model, control objectives of the train operation differ between single-and multi-train operation: In the single train operation, the train runs on a curve at the optimal speed; in the train-tracking operation, a safe headway between trains should be guaranteed. A hierarchical model-predictive controller together with quadratic optimization was applied to determine the optimal speed regulation process. A simulation was conducted based on the CRH2 EMU and the Wuhan-Guangzhou railway line to verify the model's validity. The results show that the train tracking security is significantly improved by the proposed method, and the riding comfort is guaranteed while the acceleration is at -0.75-0.5 m/s2 and the jerk is at -0.5-0.5 m/s3.

Characteristics of Cathode System in Fuel Cells for Electric Vehicles

GUO Ai, LI Qi, CHEN Weirong, LIU Zhixiang

2013, 26(6): 1052-1058. doi: 10.3969/j.issn.0258-2724.2013.06.013

[Abstract](1045)

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To improve the efficiency of fuel cells for vehicles, a cathode system model with a twin screw compressor was built by mass conservation, ideal gas law, and two-dimensional interpolation method. The methods to compute the air flow rate and the power of the compressor were discussed according to its rotational speed and pressure ratio. Based on the cathode system model, the influences of ambient factors on the cathode flow property and oxygen excess ratio (OER) were studied. Simulation results show that the output power and the efficiency change with the change of OER in the same way under the set conditions, and the optimal value of OER is 2.5, while the electrical efficiency decreases with OER increasing. In addition, elevated stack temperature will result in an increase in output power and a slight decrease in electrical efficiency. When the temperature elevates from 60 ℃ to 80 ℃, the output power increases by 5.03% and the electrical efficiency decreases by 0.57%.

Inductance Characteristics of Bearingless Permanent Magnet Synchronous Motor

SUN Xiaodong, CHEN Long, YANG Zebin, LI Feng, ZHU Huangqiu

2013, 26(6): 1059-1065. doi: 10.3969/j.issn.0258-2724.2013.06.014

[Abstract](1151)

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In order to solve the problem that the inductance parameters of the bearingless permanent magnet synchronous motor (BPMSM) can not be measured accurately by experiments, the inductance characteristics of a two-pole surface-mounted BPMSM with four-pole suspension system was investigated using finite element analysis. According to the operation principle of the BPMSM, the static and incremental inductances were defined. On this basis, the static inductances of torque windings and suspension force windings in stator frame were studied, and the dq-axis static inductances in rotor synchronous reference frame were obtained by 3/2 transformation. Taking the torque windings as an example, its incremental inductance was studied and compared with the static one. Finite element simulation results show that the incremental inductance value is 6% lower than the static one, which confirms the validity of the theory analysis.

Power System Design and Integral Modeling of Fuel Cell Electric Bicycles

CHEN Weirong, LI Xiaoyan, PENG Fei

2013, 26(6): 1066-1071. doi: 10.3969/j.issn.0258-2724.2013.06.015

[Abstract](1154)

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In order to solve the problem of output voltage ripple that is harmful to stable operation of fuel cell electrical bicycles, a two-phase interleaved DC/DC converter for fuel cell electric bicycles was designed and constructed. Based on the design, an integral model of the fuel cell electrical bicycle was set up and simulated in SIMULINK, and a prototype bicycle with a PhyX-220 type fuel cell was tested experimentally. The results show that the model could reflect the dynamic characteristics well and meet the power requirement of dynamic load; the system output voltage ripple could be controlled within 2%, and the system efficiency was larger than 94%. This verifies the feasibility of the electric bicycle driven by fuel cell.

Experimental Research of Heat-Transfer Measurements on Stagnation Points

QIN Feng, HE Chuan, ZENG Lei, KONG Rongzong, LIU Jichun

2013, 26(6): 1072-1077. doi: 10.3969/j.issn.0258-2724.2013.06.016

[Abstract](957)

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In order to improve the measurement precision of stagnation point heat transfer in shock tunnel tests, a research on developing a coaxial thermal-couple of 1 mm diameter and improving the endurance of thin-film heat-transfer sensors was carried out. Data processing methods of the two sensors were established based on the theoretical model for the inverse problem of heat conduction. Five heat transfer sensors of different types and dimensions were tested in a shock tunnel of 2 m diameter. The test results were compared to those calculated by F-R formula, and the influences of factors such as sensor shape, hot wall, sensing elements, and film thickness on the test results were analyzed. The results show that the response time of the coaxial thermal couple satisfies the test requirement, and the repeatability error of the thin film heat transfer sensor was is less than 8%.

Origin-Destination Matrix Estimation Model for Freeway Oriented Internet of Vehicles

WANG Chengliang, ZHANG Chen, HUANG Wenlong

2013, 26(6): 1078-1083. doi: 10.3969/j.issn.0258-2724.2013.06.017

[Abstract](1152)

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The internet of vehicles with radio frequency identification technology (RFID) was applied to capturing an OD matrix with missing data. In the OD matrix estimation model, Lagrange multiplier method was used to solve the maximum likelihood estimation for the probability of OD matrix elements. The algorithm of estimating OD matrix based on the expectation maximization algorithm was developed. Experimental results with 912 nodes shows that the proposed algorithm is more accurate than the simulation acquisition, and the root mean square error of real data is reduced by 77.7%,which validates the flow of the algorithm and the effectiveness of the models.

Source Number Estimation of Underdetermined Blind Mixing Signals Based on Spatial Time-Frequency Distribution and Parallel Factor Analysis

XIA Jianghua, GUO Jin, WANG Xiaomin

2013, 26(6): 1084-1089. doi: 10.3969/j.issn.0258-2724.2013.06.018

[Abstract](934)

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To estimate the number of sources of underdetermined blind mixing signals, a novel algorithm based on spatial time-frequency distribution (STFD) and parallel factor analysis (PARAFAC) was proposed. The time-frequency distribution matrices corresponding to the single auto-terms time-frequency (TF) points were stacked in a three-order tensor, and the core consistency diagnostic (CORCONDIA) was performed to estimate the number of sources. Then the uniqueness of the three order tensor low rank decomposition was analyzed. This algorithm does not need to assume that source signal must satisfy the sparse and independence conditions, and does not require that the signal meets Gaussian distribution. In simulation the recognition accuracy rate is increased by 18 dB when the signal-to-noise ratio is -5 dB, which demonstrates the proposed recognition algorithm is effective.

Joint Precoding Design and Power Control in MIMO Two-Way Relay Network

YANG Dingcheng, XIAO Lin, LIU Sheng'en

2013, 26(6): 1090-1096,1128. doi: 10.3969/j.issn.0258-2724.2013.06.019

[Abstract](966)

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In order to enhance spatial multiplexing gain of multiple input multiple output (MIMO) two-way relay networks, the transceiver precoding matrixes for all nodes with low complexity were investigated. Using subspace alignment scheme, the bi-directional MIMO channel can be decoupled into several single input single output (SISO) sub-channels. It is accessible for source nodes to use network coding to obtain better spatial multiplexing gain. By calculating and transforming the matrices, an optimal power control method for MIMO two-way relay network was presented. This method can independently optimize each sub-channel power allocation with the fixed precoding matrix. Moreover, a closed-form solution for power allocation among relay nodes and users is derived which considerable decreases the complexity from O(n3) to O(n). Simulation results show that the performance of the proposed approach is close to the iterative gradient descent solution and outperform the traditional pure amplify-and-forward (AF) two-way mode 2.99 bit/(sHz) gains with less computational load in typical scenarios.

A Face Recognition Method Based on Kernel Locality Preserving Projection

QI Yongfeng, HUO Yuanlian

2013, 26(6): 1097-1103. doi: 10.3969/j.issn.0258-2724.2013.06.020

[Abstract](1058)

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To effectively extract non-linear structure information of face images, a novel method based on maximum scatter difference rule was proposed in this paper. Firstly, the kernel function was used to map original sample data into high dimensional feature space and the scatter matrices were obtained. Secondly, the nearest graphs of original sample data were embedded into scatter matrices; then the maximum scatter difference was used to extract the feature of samples. Experimental results on Pie and Yale face databases demonstrate that the proposed face recognition method is efficient and its top recognition rate can reach 99%.

Friction Power Loss of Swing Movable Teeth Transmission under Elastohydrodynamic Lubrication

LIANG Shangming, ZHANG Jie, YAO Jin

2013, 26(6): 1104-1109. doi: 10.3969/j.issn.0258-2724.2013.06.021

[Abstract](918)

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To obtain the sliding friction power loss of swing movable teeth transmission under elastohydrodynamic lubrication accurately, the calculation method of the sliding friction coefficient between movable teeth and the internal gear under elastohydrodynamic lubrication was discussed, and the time-varying law of the sliding friction coefficient in the transmission process was analyzed, according to the meshing principle of swing movable teeth transmission. Then, a calculation model for the instantaneous sliding friction power loss of each point in a meshing period of the transmission under elastohydrodynamic lubrication was built, which is based on the analysis of the normal contact pressure and the sliding velocities between movable teeth and the internal gear. In this model, the function of instantaneous sliding friction power loss in a meshing period was established by the least square fitting method; by integrating the function, the calculation formulae of the average sliding friction power loss were derived. The results of a case study show that the calculation model of frictional power loss is feasible, and the instantaneous sliding friction power loss at the inflection point of internal gear profile curve reaches the maximum value of 118.4 W.

Energy-Saving System for Hybrid Hydraulic Excavators

WU Wenhai, KE Jian, LIU Huanlong, WANG Guozhi

2013, 26(6): 1110-1115. doi: 10.3969/j.issn.0258-2724.2013.06.022

[Abstract](1033)

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To reduce energy consumption and carbon emissions of medium-sized hydraulic excavators, a hydraulic-electric hybrid power system and a hydraulic-hybrid power system, both with energy recovery equipment, were devised in combination with the current energy-saving method after the energy-consumption characteristics of the traditional hydraulic excavator system were analyzed. According to the parameter configuration of the 23 t hydraulic excavator from a company, three kinds of mathematic models of slewing mechanism were set up, i.e., the traditional hydraulic excavator system, the hydraulic-electric hybrid system, and the hydraulic hybrid system. The AMEsim software was used to calculate the models in the condition of the same load, and the characteristic curves of the angular displacement, angular speed, power and energy-consumption were analyzed. The results indicate that in terms of the dynamic response of angular displacement and speed, the two hybrid slewing systems are more rapid and accurate than the traditional hydraulic system, and the hydraulic-electric hybrid system is faster than the hydraulic hybrid system. Compared with the traditional hydraulic power system, the hydraulic-electric and hydraulic hybrid power systems obtain an energy-saving index of 42% and 28%, respectively.

Train Routing Optimization Model for Urban Rail Transit

CHENG Jie, PENG Qiyuan, ZHAO Jun

2013, 26(6): 1116-1121. doi: 10.3969/j.issn.0258-2724.2013.06.023

[Abstract](1131)

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In order to determine operation sections and turning-back stations of urban rail trains, a multi-objective 0-1 mixed integer train routing model was built based on the practical experience of transportation organization by pursuing the best match between space distribution of train capacity and passenger flow. This model aims to obtain a rapid train turnover and a minimum passenger transfer within the facility capacity limit, and comprehensively takes into account the operation and passenger convenience. After treatment of decision variables, object functions, and constraints, this model was simplified to be solvable by optimization software. Finally, taking Chongqing urban rail line 1 as an example, the proposed method was tested for different route limits, which worked out 4 routing plans in 2 s, and provided a decision support for operators.

Relation and Risk in Owner and Contractors of Tunnel Projects Based on Probability and Logic Theories

HU Lan, HU Pei

2013, 26(6): 1122-1128. doi: 10.3969/j.issn.0258-2724.2013.06.024

[Abstract](1030)

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Based on classic probability and logic theories, a probability evaluation method was presented to assess relation and risk in owner and contractors of tunnel and underground projects. By analyzing real project cases, several logic probability tree models were built from the perspective of the logic relationship between owner and contractors. By comparison, risk probability of the OR gate model was larger than the maximum probability value of owner and contractors; risk probability of AND gate model was less than the minimum probability value of owner and contractors; risk probability of hybrid gate model was between the maximum probability value and the minimum probability value of owner and contractors. Therefore, in tunnel construction, the cooperative relationship between all project parties should be adjusted to form a relation of AND gate model and avoid a relation of OR gate model.

Lead-Time Based Multi-agent Policies Synergy and Optimization between Quay and Supply Chains

ZHOU Jianpin

2013, 26(6): 1129-1135. doi: 10.3969/j.issn.0258-2724.2013.06.025

[Abstract](1441)

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Targeting the great uncertainty of the process lead time in the international supply and distribution networks, the paper proposed a coordination framework of mixed multi-agent policies between the quay system and supply chains, and built a loop optimization decision-making model based on the tactical lead time. According to the different requirements for the supply chain responsiveness, suitable policies were chosen to control the mean flow time of the quay front operating system in an international supply chain node, to regulate the lead time fluctuation of the international supply chains, and to drive the goal optimization of the supply chain performance between time and cost. The research adopted a combination of multi-objective optimization genetic algorithm and neural network and used an example of simulating the planning decision process of supply chain oriented policies adopted by a container quay. The results demonstrated that the proposed policies could enhance the synergy effects between the quay tactical planning and the goals of time-sensitive supply chains. Although more operational equilibrium cost was needed to regulate the lead time fluctuation, the obtained certainties of the time goal can evidently improve the overall performance of the supply chain network.

Analysis of Collusion between Contractors and Supervisors in Constructions

ZHAO Lei, ZHONG Sheng

2013, 26(6): 1136-1141. doi: 10.3969/j.issn.0258-2724.2013.06.026

[Abstract](1003)

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In order to avoid collusions between supervisors and contractors due to benefit drive and asymmetrical information in constructions, a moral hazard model with a single principal and multiple agents was set up by using regulation theory and introducing a hierarchical principal-supervisor-agent structure, for quantitative research of engineering management. The result shows that under the bidding evaluation mode with bill of quantities, the profit value of bidding contracts, the effort cost of contractors, the penalty imposed by owners on contractors, and the bribery proportion of supervisors are all positively correlated to the agent cost; but the detection probability of collusions by owners and the intensity of punishment are negatively correlated to the agent cost. In addition, owners should devise the reward and punishment mechanism according to their own capacity of punishment. When owners' capacity of punishment is lower than a certain value, they should increase the rewards to supervisors in order to encourage the efforts of contractors and supervisors and prevent the collusions to the maximum extent.

Evaluation Model of Critical Thermal Shock Resistance Temperature Difference for Engineering Ceramics

ZHOU Zehua, WANG Guowei

2013, 26(6): 1142-1146. doi: 10.3969/j.issn.0258-2724.2013.06.027

[Abstract](956)

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Traditional thermal shock resistance theories cannot be used for quantitative evaluation of thermal shock property of ceramics. To solve this problem, a novel model of thermal shock resistance for engineering ceramics was developed on the basis of traditional theories and previous research achievements. In this model, the critical thermal shock resistance temperature difference Tc was calculated using mechanical and thermal parameters of ceramics, and the effect of fracture toughness on thermal properties was discussed for the first time. The model can be used for qualitative and even half quantitative evaluation of the thermal shock property of ceramics. To verify the proposed model, thermal shock resistance experiments were performed on different series of ceramics, including those with different characteristics (dense and porous ceramics) and those with different typical structures (bulk and laminated ceramics). The results indicate that the experimental Tc was close to the calculated value, with an average error rate of about 5%.

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2013 Vol. 26, No. 6