西南交通大学学报

Industrial Frequency Single-Phase AC Traction Power Supply System and Its Key Technologies for Urban Rail Transit

LI Qunzhan

2015, 28(2): 199-207. doi: 10.3969/j.issn.0258-2724.2015.02.001

[Abstract](1369)

Abstract:
To avoid stray current and maintain the benefit of no phase-split in the DC traction power supply system, an AC traction power supply system was proposed for the urban public transport such as metro and light rail transit. The proposed system consists of main substation (MSS) and cable traction network (CTN). MSS includes a single-phase main traction transformer (MTT) and a negative sequence compensation device (NCD), while CTN includes double-core cables (DCC), traction transformers (TT), overhead catenary system (OCS), rails (R), etc. Three key techniques of the proposed system were discussed. First, power supply principle, equivalent circuit and transmission ability of CNT were introduced and cable-catenary matching technique, catenary voltage level selection were discussed. Second, the segmentation technology, status identification method for traction power supply network, distributed and centralized protection schemes, etc. were discussed. Third, single-line main substation supply scheme, and two or more lines shared main substation scheme were presented. Given that the excellent technical performance, good economy and high reliability of the proposed system, it provides a new alternative for metro and urban rail transit power supply system.

Solution to Track Section Occupation Using Multi-sensor

HUA Zexi, CHEN Xiangdong

2015, 28(2): 208-217. doi: 10.3969/j.issn.0258-2724.2015.02.002

[Abstract](840)

Abstract:
To handle the bad shunting of track circuit, a solution using multi-sensors was proposed to solve the track section occupancy. Different layouts of three types of sensors, i.e., the infrared sensor, proximity switch and distance measurement sensor, were used in data collection. Based on D-S evidence theory, track occupancy detection model was constructed. The Petri net model of detecting track section occupation operating at the lower computer was used to realize axis counting and examine track occupancy at upper monitor, which provides a basis for railway traffic control. Analysis shows that the wrong side failure rate of the proposed solution is 10-7, and that the MTBF (mean time between failure) reaches up to 105 h, which could meet the reliability and safety requirement of railway application. Compared with conventional track circuit, the correct rate of this solution dealing with track section occupancy is increased by 20%.

Frequency-Domain and Time-Domain Characteristics of Valley V2 Controlled Boost Converter

HE Shengzhong, ZHOU Guohua, XU Jianping, WU Songrong, XU Yinglei, CHEN Li

2015, 28(2): 218-225. doi: 10.3969/j.issn.0258-2724.2015.02.003

[Abstract](1064)

Abstract:
Based on the analysis of the output voltage ripple characteristics of boost converter, the V2 control technique was applied to Boost converter. The principle of operation of valley V2 controlled Boost converter was analyzed in detail and a small-signal model was established. Based on this model, the control-to-output, input-to-output, and output impedance transfer functions were deduced. The characteristics of valley V2 controlled Boost converter in time-domain and frequency-domain was analyzed, and it was also compared with valley current mode (VCM) controlled Boost converter. The results show that valley V2 controlled Boost converter has faster input and load transient response speed than VCM controlled Boost converter. The time domain simulation results show that, compared with the valley current control, when the input voltage increases and decreases, transient response time of valley V2 control is reduced by about 530 s and 800 s respectively, and when the load increases and decreases, it is reduced about 650 s and 1 330 s respectively. Experimental results are in agreement with simulation ones, demonstrating that the theoretical analysis is correct.

Inter-tripping Protection Scheme for Feeding Sections of High-Speed Railway Based on Impedance Features

LIU Shuping, HAN Zhengqing, GAO Shibin

2015, 28(2): 226-232. doi: 10.3969/j.issn.0258-2724.2015.02.004

[Abstract](982)

Abstract:
In order to achieve a rapid and selective protection of cross-coupling AT feeding systems for high-speed railways, an inter-tripping protection scheme for feeding system based on impedance features was proposed. According to loop voltage equations and Kirchhoff's current law, the short-circuit impedance in substation, AT station, and section station was derived;and the relation between short-circuit impedances and fault position was analyzed. In the novel protection scheme, protection elements of distance zone Ⅰ are respectively installed in substation, AT station, and section station, and integrated via inter-tripping signals. When any protection element detects a fault, it will trip the related circuit breaker in the station and send an inter-tripping signal to the other protection elements for the same feeding section to complete fast fault isolation. Simulation results show that the proposed scheme can isolate the fault feeding section within 100 ms after fault, while at the same time not interrupting the power supply of the parallel feeding section. Therefore, the requirement of selectivity and speediness for protection are both satisfied.

Applicability of Active Control Algorithms for Pantographs of High-Speed Railway

LU Xiaobing, LIU Zhigang

2015, 28(2): 233-240. doi: 10.3969/j.issn.0258-2724.2015.02.005

[Abstract](997)

Abstract:
In order to seek the best active control algorithms for different pantographs, an efficient pantograph-catenary model was established, based on which an optimal controller, a variable structure controller, and a fuzzy controller were designed. A simulation was then conducted by applying the control algorithms to the widely used pantographs SBS81, DSA250, DSA380 and SSS400+ in high-speed railway, and the control algorithms were compared in terms of the maximum, minimum, mean and standard deviation of the contact force before and after controllers applied to the pantographs. The results show that, when the locomotive speed is operated with a simple stitched catenary at 250 km/h, the contact force standard deviation is reduced by 34.4% and 18.6% respectively for the SBS81 and DSA380 equipped with variable structure control. However, the standard deviation is just reduced by 12.7% and 10.0% if the optimal control is applied to them. For DSA250, the standard deviation of contact force is reduced by 25.7% under the optimal control, but only 14.8% under the variable structure control. For SSS400+, the contact force standard deviation is reduced by 38.1% when it is equipped with fuzzy control. Therefore, the variable structure control is more suitable for SBS81and DSA380, the optimal control is more suitable for DSA250, and the fuzzy control is more suitable for SSS400+.

Improved Incomplete Derivative PID Control of Axial Active Magnetic Bearing

JIANG Qilong, HU Zhenqiu

2015, 28(2): 241-246. doi: 10.3969/j.issn.0258-2724.2015.02.006

[Abstract](903)

Abstract:
In order to reduce the interference of measurement noise and improve the steady-state precision of magnetic bearing control, the active magnetic bearing of a vertical motor was adopted to analyze the influence of measurement noise on the traditional PID control. Considering that the incomplete derivative PID controller with the first-order filter and the traditional PID controller cannot meet the requirement in performance of controlling the measurement noises, an improved algorithm for the incomplete derivative PID control with the second-order filter was proposed. A simulation platform was then built in Simulink of MATLAB, and the improved algorithm was verified experimentally on the active magnetic bearing platform using C programming language. Results of simulation and experiments show that the improved algorithm can improve the static performance of the magnetic bearing. Using the incomplete derivative PID controller with the second-order filter, the steady-state error of the air gap of the magnetic bearing was about 20 m, reduced by nearly 50% (i.e., 30 m in magnitude) compared to the traditional PID controller and the incomplete derivative PID controller with the first-order filter. This proves the effectiveness of the improved algorithm.

Matching between Free Angle of Round-Pin Coupler and Carbody Structure Parameters

QU Tianwei, XU Ziqiang, MA Weihua

2015, 28(2): 247-255. doi: 10.3969/j.issn.0258-2724.2015.02.007

[Abstract](877)

Abstract:
To explicate the matching relation between main structure parameters of carbody and round-pin coupler, theoretical analysis and dynamic simulation method were used to analyze the relation between main structure parameters of carbody and rotation angle of the coupler in the cases of curve passing and pressure bearing on straight line. Control system simulation method was adopted to establish the model of aligning shoulders taking into account the nonlinear hysteresis characteristics of buffer, which can reflect real-time characteristics of aligning shoulders force. Coupler head profile were discretized to obtain the profile data, which were fitted through the spline interpolating function and reverted to coupler head curve surfaces;then the contact models between curve surfaces of coupler head were established, further considering the interaction between coupler heads, which can accurately simulate the relative movement between coupler heads. Force analysis of carbody at different free angles was conducted, and the equation for designing optimal coupler free angle was presented and validated. The results indicate that actual coupler angles were larger than that of the calculated ones by 0.5~1.0owning to the changes of track curvature. Relative angles between coupler heads can offset that of couplers so as to negotiate curves. To ensure the running safety of locomotive when bearing compressive strength, the coupler free-angle and the carbody structure parameters should match each other, and the design value of the locomotive's coupler free-angle should be less than 8. Overall, the results agree well with the calculated results.

Railway Fastener Detection Algorithm Integrating PHOG and MSLBP Features

LIU Jiajia, LI Bailin, LUO Jianqiao

2015, 28(2): 256-263. doi: 10.3969/j.issn.0258-2724.2015.02.008

[Abstract](929)

Abstract:
In order to improve the recognition rate and robustness of railway fasteners detection, and to increase the effectiveness of PHOG (pyramid histogram of oriented gradients) feature, a simple and effective sleeper shoulder locating algorithm was proposed. In this algorithm, the redundant information in fastener images was removed before extraction of PHOG feature, according to the positional relationships among the sleeper shoulder, fasteners, and background. Then, an MSLBP (macroscopic local binary pattern) sampling method was designed and applied to extract the macroscopic texture feature of the fastener images, which could well simulate human visual attention mechanism. Finally, the two different categories of features were integrated by the hierarchical weighted fusion method;using the SVM classifier to classify and detect fastener defects, a defect recognition algorithm based on computer vision and PHOG-MSLBP fusion feature was presented. The algorithm was applied to experiments, and the results show that the average recognition rate based on PHOG-MSLBP feature is 6.3% higher than that based on PHOG feature, and 4.5% higher than that based on MSLBP feature. In addition, the proposed algorithm is more robust than several mainstream methods, and can meet the need of automatic inspection of fastener defects.

1 Bit Compressed Sensing Reconstruction Algorithm Based on Blind Operation

YAN Bin, CHEN Hao, WANG Wendong, ZHOU Xiaojia

2015, 28(2): 264-269. doi: 10.3969/j.issn.0258-2724.2015.02.009

[Abstract](913)

Abstract:
To solve the problem that the matching sign pursuit (MSP) algorithm can not adaptively reconstruct signals when the sparsity is unknown, we proposed a forward-backward matching sign pursuit (FBMSP) algorithm. Based on successive approximation theory, by gradually expanding the support set to expand search scope, FBMSP algorithm takes a difference between adjacent iterations as a termination criterion and conducts blind operations to reconstruct the signals under the model of the MSP algorithm. The numerical experiments show that compared with the traditional MSP algorithm, the precision of FBMSP is increased by 3 dB, and the calculation time is reduced by 40% when the control iterative coefficient =8 and =1.

A Novel Clutch Actuator Control Algorithm Based on Lipschitz Observer

WU Haikang, ZHONG Zaimin, YU Zhuoping

2015, 28(2): 270-278. doi: 10.3969/j.issn.0258-2724.2015.02.010

[Abstract](854)

Abstract:
For parallel hybrid vehicles, a nonlinear observer based novel position servo control algorithm was designed without the need of speed sensors. This algorithm, according to the feedback of system states, can implement high-quality servo control of friction torque through the position control of release bearing in diaphragm spring clutch. It can also obtain actuator moving velocity without differentiating position signal with noise. Based on the elastic properties of diaphragm spring, wave spring and release finger, release bearing side load feature were analyzed, nonlinear actuator state space equations were derived in order to design feedforward compensation. Meanwhile, Lipschitz nonlinear observer theory was applied to observe actuator position, motor speed and release bearing force. Simulation results demonstrate that the control algorithm is feasible and has satisfactory observation robustness: In the presence of deviation between the worm gear efficiency and actual one, although there are steady errors in position and speed observation, the former error is negligible, and the latter is no more than 10 r/min, both of which are acceptable;Noise is visible in the observed values of position and force observations, but does not affect speed observation;When the driven plate is worn, although position and speed observations are still desirable, there is steady error in force observation, which is no more than 25 N.

Helix Error Testing and Tracing on Planar Enveloping Hourglass Worm Tooth Surface

LUO Wenjun, CHEN Yonghong, ZHANG Guanghui

2015, 28(2): 279-285. doi: 10.3969/j.issn.0258-2724.2015.02.011

[Abstract](771)

Abstract:
In order to improve the manufacture precision of planar enveloping hourglass worm tooth surface, a method for the helix error testing, tracing, and correction was proposed. Based on the theory of differential geometry and gear meshing, mathematical models for the tooth surface, the hourglass helix, and the hourglass helix with manufacturing errors were established for the planar enveloping hourglass worm. The principle of probe radius compensation and the method of error assessment were analyzed. In addition, the helix error of the prototype tooth surface was tested using the developed hourglass worm detector, and the error tracing was analyzed by the genetic algorithm. The prototype tooth surface was then amended and manufactured based on the results of error tracing. The results show that through the error tracing and error correction, the helix error of the prototype tooth surface was reduced from 0.140 to 0.025 mm.

Hazard Mechanism Analysis of Taoguan Giant Debris Flow in Wenchuan Earthquake Area on July 10th, 2013

HU Xiewen, HAN Mei, LIANG Jingxuan, PAN Cong, FANG Li, WU Jianli

2015, 28(2): 286-293. doi: 10.3969/j.issn.0258-2724.2015.02.012

[Abstract](934)

Abstract:
For the giant debris flow caused by heavy rainfall in Taoguan gully, in Wenchuan earthquake area on July 10th, 2013. Field investigation and experiments were made to analyze the loose materials, rainfall, and terrain conditions of the Taoguan gully, and study the process of startup flow and deposition of the debris flow. The result shows that the damage of the rock mass triggered by earthquake in the gully is the root cause of such frequent debris flow after the earthquake. Its mechanism is actually the startup and superposition of loose materials from collapse and landslides, and deposits on slopes and in the gully. From the development trend, the Taoguan debris flow is now on a high-frequency developmental stage, and the possibility of breakout of large scale debris flows still exists.

Fatigue Life Estimation of Corroded Bridge Wires Based on Theory of Critical Distances

YE Huawen, HUANG Yun, WANG Yiqiang, QIANG Shizhong

2015, 28(2): 294-299. doi: 10.3969/j.issn.0258-2724.2015.02.013

[Abstract](834)

Abstract:
Based on the theory of critical distances, critical distance to influence fatigue damage zone determining was solved in light of the notch stress gradient of corroded wires so as to estimate the fatigue performance of bridge wires in service. FEM (finite element method) was used to propose a fatigue assessment to predict the life of corroded wires. The fatigue lives were obtained by fatigue tests for corroded galvanized steel wires on three corrosion levels as well as wire specimens with an artificial pit, including to round pit, triangle pit or triangle pit with a notch, and compared with the predicted lives. The research results show that the axial stress distribution has a significant effect on the fatigue strength of corroded bridge wires. The critical distance decreases when stress concentration raises. Stress concentration factor (SCF) is recommended to be an estimation indicator of residual life of wires, and the corroded wires with an SCF of above 3 should be replaced.

Optimal Design of Concrete Tied Arch Bridge

QIAO Jiandong, WU Huishan, YANG Wei

2015, 28(2): 300-305. doi: 10.3969/j.issn.0258-2724.2015.02.014

[Abstract](954)

Abstract:
In order to investigate the multi-parameter optimal design method of concrete tied arch bridges, an optimal model was established. In this model, rise, cross section dimensions of arch ribs and tied beams, area of each suspender and number of pre-stressed steel bars in each hole are selected as the design variables, code values as the constraint conditions, and total cost of whole bridge as the objective function. A plane analysis program for bridge structure, the software ANSYS and the mix-integer sequence quadratic program method were used together to program and solve the optimal model. The optimal model was solved by taking an arch bridge as engineering background, the optimal results were compared with the design values. The comparison results show that the concrete consumptions of tied beams and arch ribs is respectively reduced by 40.98% and 23.81%, the number of pre-stressed steel bars is decreased by 28.23%, and the total material cost is cut by 28.63%.

Fluid-Solid Interaction-Based Mechanical Characteristics of Underwater Shield Tunnel

QI Chun, HE Chuan, FENG Kun

2015, 28(2): 306-311,330. doi: 10.3969/j.issn.0258-2724.2015.02.015

[Abstract](917)

Abstract:
In order to investigate the mechanical characteristics of a underwater shield tunnel under fluid-solid interaction during construction stage, a numerical simulation model was established to calculate water pressure on segment lining by taking Shiziyang shield tunnel as an example. Field tests were carried out to measure external and internal loads acting on segment lining structure. The calculated water pressure was acted on the spring-beam model to analyze structural internal forces, and mechanical characteristics of a segment structure under fluid-solid interaction during construction stage were obtained. The research result shows that water pressure fluctuates obviously to the first 3 to 5 rings after the target segment ring lefts the shield tail owing to grouting pressure. When the number of left-shield-tail rings comes to 10 or more, the water pressure gets close to hydrostatic pressure with the dissertation of grouting pressure and the vanishing of fluid-solid interaction.

Model Test on Bearing Capacity Characteristics of Steel Tubular Composite Piles

ZHANG Min, MA Jianlin, SU Quanke, WU Weisheng

2015, 28(2): 312-318. doi: 10.3969/j.issn.0258-2724.2015.02.016

[Abstract](859)

Abstract:
In order to investigate the bearing capacity of steel tubular composite (STC) piles, two groups of piles, including a group of STC piles with shear ring, drilling mud skin and anticorrosion coating and a group of reinforced concrete piles, were used to conduct comparative model tests. The load-deformation curves and steel tube deformations of specimens in the two groups were compared, and the confinement effect of STC piles was analyzed by decomposition analysis method. The test and calculation results show that the bearing capacity of the STC pile was larger than that of the reinforced concrete pile significantly. Due to the confinement effect, the bearing capacity of the STC pile was increased by 9.8%even compared with the sum of the bearing capacity of a hollow steel tube and a reinforced concrete pile;at the same time, the shear strength of the core concrete was increased by 1.2 times. The confining stress of the STC pile increases with load and pile depth. The maximum confining stress of the STC pile with anticorrosion coating, drilling mud skin, and shear ring could reach 2.32 MPa. In addition, the specification ACI (2005) could apply to the ultimate bearing capacity calculation of STC piles with anticorrosion coating, drilling mud skin, and shear ring, in a way to calculate the internal strength.

Decoupling of Evolutionary Power Spectral Density and Its Engineering Applications

PENG Liuliu, HUANG Guoqing, MA Cunming, SU Yanwen

2015, 28(2): 319-324,330. doi: 10.3969/j.issn.0258-2724.2015.02.017

[Abstract](918)

Abstract:
In order to improve the simulation efficiency of nonstationary processes and simplify the structural response analysis under nonstationary excitations, evolutionary power spectral density (EPSD) was approximately decoupled into the linear summation of products of the squared modulus of Fourier transform of wavelet function at different scales and associated time coefficients, i.e., a generally modulated nonstationary process was transformed into the summation of a number of uniformly modulated nonstationary processes. The decoupled EPSD was applied to engineering fields, including the simulation of nonstationary processes and the stochastic response analysis of structures. The research results show that the decoupled EPSD has a satisfactory accuracy. The simulation efficiency of nonstationary stochastic processes is generally improved for dozens of times by using the fast Fourier transform (FFT). The estimated autocorrelation function of simulated samples agrees very well with the target function. The stochastic response analysis of structures is simplified, and the calculated responses using the proposed method have small errors compared with the targets.

Weights of Slope Stability Evaluation Indexes Based on Factor Analysis Method

ZHAO Jianjun, HE Yuhang, HUANG Runqiu, JU Nengpan

2015, 28(2): 325-330. doi: 10.3969/j.issn.0258-2724.2015.02.018

[Abstract](957)

Abstract:
For rapid evaluation of slope stability, 44 typical slopes along Tangtun highway were investigated. The factor analysis method was adopted to analyze 7 evaluation indicators of slope stability, i.e., slope gradient, slope height, lithology, slope structure, structural plane cementation, main discontinuity and rock mass integrity. These indexes were sorted in light of their effects on slope stability, and evaluation indexes' grades after normalization were taken as evaluation indexes' weights. The research shows that from their importance, main factors are listed as slope shape, slope structure and structural plane characteristics in proper order, and sorting of evaluation indexes is in turn rock mass integrity, lithology, slope structure, main discontinuity, structural plane cementation, slope gradient and slope height.

Comparative Research of Probabilistic Stability Analysis Methods of Embankment Based on Limit Equilibrium Method

JIANG Xin, ZHU Qijiong, CHEN Tao, GAO Xiaofeng, QIU Yanjun

2015, 28(2): 331-335,341. doi: 10.3969/j.issn.0258-2724.2015.02.019

[Abstract](925)

Abstract:
In order to reasonably select probabilistic slope stability analysis methods, a comparison research on the global minimum method and the overall slope method was carried out based on vertical slice limit equilibrium method software SLIDE and geotechnical centrifuge model test of embankment on sloped weak ground. The overall slope method was used to get the influence rule of anti-slide pile reinforcement on the stability of embankment on sloped weak ground. The research result shows that compared with the global minimum method, the overall slope method has a strict algorithm, more and conservative results, but more time consumption. The selection and application of the two probabilistic slope stability methods should depend on the model complexity and the analysis goals. The overall slope method can prove the effectiveness of anti-slide piles for embankment reinforcement on sloped weak ground well.

Hyperspectral Image Classification Based on Structured Dictionary Learning

QIN Zhentao, YANG Wunian, YANG Ru, PAN Peifen, DENG Cong

2015, 28(2): 336-341. doi: 10.3969/j.issn.0258-2724.2015.02.020

[Abstract](891)

Abstract:
In order to improve the classification accuracy of hyperspectral images, a new structured dictionary-based method for hyperspectral image classification was proposed. This method incorporates both spatial and spectral characteristics of hyperspectral images to obtain a dictionary of each pixel, the pixels in an identical pixel group have a common sparsity pattern;image sparsity representation coefficients are calculated in light of the dictionary to gain sparse representation features of hyperspectral images;the classification of hyperspectral images is determined using a linear support vector machine. Experiments on AVIRIS and ROSIS hyperspectral images were carried out. The experimental results show that compared with the common dictionary learning, the classification accuracy is respectively raised by 0.041 1 and 0.046 6, the Kappa coefficient is improved by 0.179 3 and 0.056 3, respectively.

Effect of Dosage of Fly Ash and Blast Furnace Slag on Performance of Concrete Prepared with Poorly Graded Sand

LI Maohong, ZHANG Yujie, CHEN Hang, ZHAO Jumei

2015, 28(2): 342-346,353. doi: 10.3969/j.issn.0258-2724.2015.02.021

[Abstract](967)

Abstract:
In order to fabricate high quality concrete using poorly graded sand, six groups of concrete with poor sand gradation were prepared with different dosages of fly ash (FA) and blast furnace slag (BFS). The sand and stone compactness of the concrete was evaluated using the Andreasen equation, and the slump and compressive strength of the concrete were tested to study the effect of the dosage of fly ash and blast furnace slag on the workability and compressive strength of the concrete prepared with poor sand gradation. The results showed that the poorly graded sand and crushed stones had an adequately dense packing;both the concrete groups with 40% FA+BFS replacement and 30% FA replacement satisfied the pumping requirement;the concrete compressive strength in each group at 56 d satisfied the requirement of the strength grade, and decreased with the increasing of the dosage of fly ash. Therefore, the effect of the FA and BFS dosage on the workability and compressive strength of the concrete with poor sand gradation and dense packing is similar to that on the concrete with normal sand gradation.

Flow Field Characteristics of Exhaust Flow Assisted with a Jet

YANG Yang, WANG Yi, LI Yanbin

2015, 28(2): 347-353. doi: 10.3969/j.issn.0258-2724.2015.02.022

[Abstract](832)

Abstract:
To decrease the jet flow rate in contaminants control for a purpose of energy conservation, the flow field characteristics of exhaust flow assisted with a jet was focused. When the angle between the jet and the exhaust flow ranges from 90to 60 , utilizing the numerical simulation, the conditions to form steady flow was determined and the changes of the centerline velocity and control region of the exhaust flow were studied. Meanwhile, based on simulation results and the analysis of the factors that affect centerline velocity and control region, two calculation methods for the decay of centerline velocity and control region of the exhaust flow with different were obtained. The results show that when is less than 70, the steady exhaust flow can not form;when ranges from 90to 70, the increase rate of the centerline velocity drops with the momentum ratio of the jet and the exhaust flow increasing, while the increase rate of the centerline velocity increases when decreases. Thus, the exhaust flow can be enhanced by decreasing , which effectively control contaminants.

Stair-Like Control Strategies of Variable Speed Limit for Bottleneck Regions on Freeway

YANG Qingfang, MA Minghui, LIANG Shidong, LI Zhilin

2015, 28(2): 354-360. doi: 10.3969/j.issn.0258-2724.2015.02.023

[Abstract](884)

Abstract:
The traffic flow operation at bottleneck sections on freeway mainlines is usually deteriorated by heavy traffic load, resulting in an increase in travel time and a decrease in traffic efficiency. By analyzing the space-time characteristics of the traffic flow at bottleneck sections on freeway mainlines, the cell transmission model was expanded to describe the traffic flow in the bottleneck area under variable speed limit (VSL) control. On this basis, a VSL control model for bottleneck region was established, and stair-like strategies were proposed to prevent the long queue from interrupting the vehicles operation at upstream on-and off-ramps. The proposed methods were tested through a case study, and the results demonstrate that the proposed stair-like strategies for VSLs can effectively reduce the travel time and decrease the average delay. Compared with no control and the strategy of using mainline control on single sections, the proposed strategies can reduce the average delay by about 13.78% and 1.60%, respectively.

Link Travel Time Estimation for Urban Roads Using Low Frequency GPS Data and Intersection Delay

WANG Zhijian, MA Chaofeng, LI Liang

2015, 28(2): 361-367. doi: 10.3969/j.issn.0258-2724.2015.02.024

[Abstract](958)

Abstract:
In order to solve the problem of large error in link travel time estimation with low-frequency GPS data, vehicle delay features in road intersection-affected areas were analyzed. According to whether two adjacent GPS points stride over multiple intersection-affected areas and whether there are GPS points in the intersection-affected areas, GPS distribution types were divided into four types and a difference algorithm for travel time estimation was designed based on calculation of intersection delay time. This travel time estimation algorithm was then verified using the vehicle GPS data in the Bajiao area of Beijing in a case study. The results show that the average absolute errors of link travel time estimates by the algorithm are within 14% in non-peak and rush hours. Compared with an improved interpolation method, the proposed algorithm improves the average estimate accuracy by 7.9%, and the effect is more obvious in the link with a larger intersection delay time.

Modeling and Simulation Analysis of Microscopic Traffic Flow in Multi-airport Terminal Airspace

ZHANG Honghai, HU Yong, YANG Lei, XU Yan

2015, 28(2): 368-374. doi: 10.3969/j.issn.0258-2724.2015.02.025

[Abstract](886)

Abstract:
In order to study the microscopic spatial and temporal characteristics and evolution law of air traffic flow in multi-airport terminal airspace, considering the operation characteristic of single, converging, and crossed traffic flow flying to the target point, a local sorting model, a aircraft-following model, and a maneuverable model for air traffic flow were established using the first-come-first-service principle and the stimulus-response aircraft-following theory. A multi-agent simulation platform based on the above models was then set up with NetLogo to simulate the traffic flow. The correlativity and sensitivity of basic traffic flow parameters as well as the interaction between arrival and departure traffic flow were analyzed through simulation experiments. The result indicates that notable phase transitions and hysteresis characteristic exist in the evolution process of the arrival traffic flow. The fundamental phase states can be divided into free, unconstrained, pseudo-congestion, and synchronization phases. There is a linear relationship between the traffic flow rate and the product of velocity and density. The control interval has a great influence on the traffic flow. There is an optimal control interval, and its value at the arrival intersection point is 8 km.

Robust Optimization Model for Integrated Aircraft Scheduling Based on Delay Propagation

ZHU Xinghui, WU Weiwei, QI Yanlong

2015, 28(2): 375-381. doi: 10.3969/j.issn.0258-2724.2015.02.026

[Abstract](957)

Abstract:
In order to alleviate the impact of flight delays on the flight operation, a double objective network flow robust optimization model for integrated aircraft scheduling was presented based on analysis of the delay propagation characteristics and its distribution. The first objective was to minimize the propagated delay, and the second was to minimize the airline operation cost. Then, the model was verified using the actual operation data from a major domestic airline, and a branch-and-price solution and a column generation algorithm were used to solve the problem. Computational results show that our approach can reduce delay propagation by 41%. Compared with the airline actual flight schedule and the non-robust integrated aircraft scheduling model, the total cost was decreased by 11.33% and 9.93%, respectively.

Phase Field Modeling on Effects of Static Magnetic Field on Oscillatory Deformation of Molten Droplet

SHI Wanyuan, ZHANG Fengchao, TIAN Xiaohong, SHEN Jun

2015, 28(2): 382-387. doi: 10.3969/j.issn.0258-2724.2015.02.027

[Abstract](702)

Abstract:
In order to study the characteristics of oscillatory process of a molten silicon droplet under static magnetic field, the phase field method was adopted to numerically simulate the interface oscillation and internal fluid convection of a molten silicon droplet. The influence of an axial static magnetic field on the internal convection and interface oscillation of a molten silicon droplet with an initial shape of the second-order Legendre function was analyzed. The numerical result exhibits that the shrink of the droplet under static magnetic field is faster than that without magnetic field. The static magnetic field suppresses the fluid convection inside the droplet. As the imposed magnetic field intensity increases from 0 to 0.9 T, the maximum values of stream function reduce from 0.57 to 0.08, and the internal convection and interface oscillation are weakened gradually. Under magnetic field, the ratio of long-axis to short-axis of droplet quickly tends to 1. However, the magnetic field has almost no influence on oscillation frequency of droplet. The investigation indicates that the phase-field modeling can effectively simulate the interface oscillation and internal convection of the molten droplet even with high density.

Nonlinear Flutter of a Two-Dimensional Viscoelastic Plate with Motion Constraints in Subsonic Flow

TANG Huaiping, LI Peng, YANG Yiren

2015, 28(2): 388-392. doi: 10.3969/j.issn.0258-2724.2015.02.028

[Abstract](807)

Abstract:
In order to study the stability and nonlinear flutter of a cantilevered viscoelastic plate with nonlinear motion constraints in subsonic flow, the motion equation of the cantilevered plate is established by Hamilton theory. The equation is then transformed to a series of ordinary differential equations using the Galerkin method;the flutter and divergence is addressed and their boundaries are presented in a two-parameter space. The complex nonlinear behavior in the region of flutter instability is investigated using numerical simulations. The flutter region is divided into three subregions according to different types of plate motions. Results show that the plate loses it stability by flutter;the plate undergoes limit cycle motions due to the nonlinearity after flutter instability;period-3 and period-5 motions appear along with chaotic motions;and, with the dynamic pressure increasing, divergent motions occur finally.

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2015 Vol. 28, No. 2