西南交通大学学报

Maximum Acceleration Recording from Lushan Earthquake on April 20, 2013

WEN Ruizhi, REN Yefei, QI Wenhao, LU Tao, YANG Zhenyu, SHAN Zhendong, WANG Yunlong

2013, 26(5): 783-791. doi: 10.3969/j.issn.0258-2724.2013.05.001

[Abstract](1281)

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Abstract:
The Lushan earthquake on April 20, 2013 is another destructive event after the Wenchuan earthquake in 2008. More than 100 strong motion stations were triggered in the main shock. The 51BXD station located in Baoxing Country recorded a peak ground acceleration (PGA) of more than 1g, that is 1.026g (-1 005.3 gal) in the EW direction. It has been the first time that more than 1g is recorded at free field site in China and it should be a milestone event in Chinese strong motion observation history. However, in the released official Lushan intensity map, the around area was classified to intensity Ⅶ, which raises an interesting question why such a great PGA leads to a low intensity. During the post-earthquake field survey, it was found that this station was located on a steep slope, not a real "free-field" station, so the recording could be affected by the topography. By comparing with 3 other nearby stations with the next generation attenuation models, it is shown that the earthquake response spectrum less than 0.2 s was amplified significantly. To support this evidence, a background noise test was performed around this area, and predominant period and horizontal acceleration amplification factor were calculated with the traditional spectral ratio method. The calculation results clearly show that from the bottom of the valley to the top, the predominant frequency increases and the amplification factors also raise with the predominant frequency increasing. In addition, the response spectrum of 51BXD recording was calculated and compared with some others from the Wenchuan earthquake to interpret why there were so slight damages to its around buildings. The preliminary conclusion is that the topography is the root cause for 1g peak ground acceleration recording in the Lushan earthquake.

Influence of Metro Tunneling Methods on Environment and Its Control

QI Taiyue, WU Zhanrui, LUO Chi, WANG Rui

2013, 26(5): 792-797,817. doi: 10.3969/j.issn.0258-2724.2013.05.002

[Abstract](1113)

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In order to probe into the effects of the drilling-blasting method for metro tunnel with complicated sections on city environment, based on the principles that the influences of city metro tunnel construction on surface ground and buildings must satisfy the vibration, deformation and stress control standards, software FLAC3D was used to the numerical simulation of an practical project, as an example, and the blasting effects of different excavation methods were investigated. And a comparison between a numerical simulation result and field measured vibration velocity was made. The research result shows that the combination of the mechanical and drilling-blasting excavation methods is a satisfying selection to the practical project.

H∞ Norm Based Optimal Design of Vibration Control for Structural Perturbation Using Tuned Liquid Damper

HUO Linsheng, SHEN Wenhe, LI Hongnan

2013, 26(5): 798-802. doi: 10.3969/j.issn.0258-2724.2013.05.003

[Abstract](1030)

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In order to reduce the vibration of building structures excited by earthquakes, the mass ratio, frequency ratio, and damping ratio of a tuned liquid column damper (TLCD) are optimized. A five-story reinforced concrete structure building is selected for the numerical example with the consideration of parameter perturbation. The optimization objective is set to be the H∞ norm of the transfer function from the ground motion to the structural responses. The acquired optimal mass ratio, frequency ratio, and damping ratio of TLCD are 0.022 801, 0.909 070, and 0.098 655, respectively. With these optimal values, the robustness of the control system is verified. The results show that the control system has good robustness for structural parameter perturbation under seismic action in both frequency and time domain. The seismic reduction ratio is still kept above 7% even if the maximum system perturbation of mass, damping, and stiffness reach 30%.

Dynamic Model for Train-Track-Bridge Coupling System Subjected to Non-uniform Seismic Excitation

LEI Hujun, LI Xiaozhen

2013, 26(5): 803-809. doi: 10.3969/j.issn.0258-2724.2013.05.004

[Abstract](1250)

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In order to analyze the effects of traveling wave effect on the running safety of a train running over a high-speed railway bridge subjected to earthquake action, a dynamic model for train-track-bridge system subjected to non-uniform seismic excitation was set up based on the train-track-bridge dynamic interaction theory and by introducing a seismic multi-support excitation mode. This dynamic model consists of a vehicle model with 35 degrees-of-freedom, a slab track model and an FEM (finite element method) bridge model. A simulated analysis program was compiled. As an example, a simply-supported beam bridge with a span of 32 m was modeled, and the dynamic responses of vehicle and bridge system under uniform and non-uniform El Centro seismic excitations were calculated. The analysis results show that the traveling wave effect has a great influence on the dynamic responses' amplitudes of the coupling system. When the train speed is 350 km/h and traveling wave speed is 300 m/s, the derailment coefficient, the wheel unloading rate and the wheel-rail lateral force reduce by 84.1%, 19.5% and 87.8% respectively compared with uniform seismic excitation. So, when the traveling wave effect is ignored, the judgment of the running safety of a train passing a bridge under earthquake action may be wrong.

Stiffness Transition Analysis of a Steel-Concrete Joint Section Based on Vehicle-Bridge Interaction

LIU Quanmin, LI Xiaozhen, ZHANG Xun, ZHANG Zhijun, LI Yadong

2013, 26(5): 810-817. doi: 10.3969/j.issn.0258-2724.2013.05.005

[Abstract](1100)

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In order to study the dynamic stiffness transition issue of hybrid girder bridges, a vertical vehicle-bridge coupled vibration model was built for a cable-stayed bridge with single tower. In the coupled vibration model, a finite element model for the bridge was established by converting the joint section to the same material according to the equivalent stiffness law, a tri-axial vehicle model with 9 degrees of freedom (DOFs) was adopted, the sample of class B road roughness was simulated from the roughness spectrum in the national code by the trigonometric series method, and the motion equations of the coupled vehicle-bridge system were solved by Newmark-β method. According to the vehicle-bridge coupled vibration model, the dynamic analysis codes of the vehicle-bridge interaction were programmed to solve the system's dynamic responses under different conditions. The results show that the vertical acceleration of joint section will double if the road roughness decreases a grade; in dynamic behavior, the dynamic transition of the fully filled joint section is slightly smoother than that of the half filled.

Structure Damage Detection Method Based on Adaptive Stochastic Resonance Technology and Response Sensitivity Method

LIU Liu, YAN Yunju, CHANG Xiaotong, XI Zhuyou

2013, 26(5): 818-824. doi: 10.3969/j.issn.0258-2724.2013.05.006

[Abstract](1127)

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In order to solve the structural damage identification problem in strong noise environment, a two-step approach based on nonlinear denoising and damage location was proposed. In the first step, structural excitation response and background noise are processed through the nonlinear stochastic resonance system for enhancing the response signal. In the second step, local minor damage is defined as Young's modulus reduction, and the sensitivity of responses to the unit Young's modulus is worked out. Then the Young's modulus is revised to locate the damage in the structure. Numerical examples show that this method can well realize structural damage location under 50% background noise level, with the identification error rate being less than 0.2% for single damage and less than 0.5% for multiple damage.

New Method for Move Distance Calculation with Coordinate Method for Existing Railway Curve

LIU Yongxiao, LIU Xueyi, YANG Junbin, DAI Feng

2013, 26(5): 825-830. doi: 10.3969/j.issn.0258-2724.2013.05.007

[Abstract](1149)

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To overcome the error resulted from substituting chord length for arc length in the traditional method to calculate the move distance of a transition curve, based on the theories related to existing railway curve realignment by the coordinate method, a new method to calculate move distance was put forward by using the distance from the existing measurement points to the points on the moved curve in the radial direction. The analytical method was utilized to derive the calculation formulas of move distance and moved coordinates of measure points. The calculation results were compared to those calculated by the traditional method. The results indicate that the traditional coordinate method to calculate move distance has errors, and the errors of the move distance and moved versine increase with increasing of transition curve length and decreasing of its radius. With the traditional method, the maximum errors of the move distance and moved versine reach 1.3 and 1.0 mm, respectively.

Intelligent Railway Aignment Optimization Based on Stepwise Encoding Genetic Algorithm

LI Wei, PU Hao, ZHAO Haifeng, HU Jianping, MENG Cunxi

2013, 26(5): 831-838. doi: 10.3969/j.issn.0258-2724.2013.05.008

[Abstract](1361)

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In order to achieve the optimization of railway 3D alignments, an optimization model was built, in which comprehensive factors including construction, operation, environment, and constraints were embedded. Different distributions for horizontal and vertical control points were presented. A genetic series that consists of offsets of intersection points, the radii of the circular curve, and the elevations of grade change points was designed. Then a stepwise horizontal-vertical-integral genetic encoding method was put forward, and the genetic operators for crossover and mutation were also designed to achieve the optimization of railway alignments. The results of application examples indicate that this method can overcome the shortcoming of the overlapping of horizontal curves and vertical curves, and yield a group of alignments with low comprehensive costs and meanwhile conforming to railway constraints. The optimal alignment obtained by this optimization method can reduce the overall comprehensive cost by 6.5% than the alignment obtained by human work.

Experiment Study on Engineering Property Indexes of Expansive Soil for Railway Subgrade and Its Improvement Measures

JIANG Zezhong

2013, 26(5): 839-844,850. doi: 10.3969/j.issn.0258-2724.2013.05.009

[Abstract](1415)

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In order to improve the engineering properties of undisturbed subgrade soil, systematic indoor experiments were made to study the expansive soil for the railway subgrade filling in Xi'an-Nanjing railway subgrade project. Physical and mechanical parameters of the expansive soil were measured by the basic tests of geotechnical properties, such as the direct shear test and tri-axial test. According to the actual engineering properties of the expansive soil, a soil improvement measure using lime was put forward. Parameters such as the particle size distribution, physical properties, water-physical properties, strength, and expansibility of the expansive soil were tested and compared before and after improvement. The test results show that the weak-middle expansive soil gets an obvious improvement in particle composition, physical properties, and swelling behavior; and the mechanical strength and water stability are also enhanced greatly. According to the test results of mechanical and physical properties, the optimal ash mixing rate for the expansive soil is determined to about 5%.

Wind-Resistant Optimization of Portal Frames Based on Quantum-Behaved Particle Swarm Algorithm

FU Jiyang, ZHONG Liang, HUANG Youqin, WANG Yanping, XU An

2013, 26(5): 845-850. doi: 10.3969/j.issn.0258-2724.2013.05.010

[Abstract](1163)

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In order to make up for the insufficiency of researches on the structural wind-resistant optimization of large span roofs, the quantum-behaved particle swarm algorithm was adopted to optimize a large-span roof under wind loads. Equivalent static wind loads on the structure were obtained from the database of wind tunnel tests, and the search space of discrete variables was formed according to the shape steel table. An improved fitness function was proposed by defining a coordinate factor for constraint violation, and the over-flow dealing technique was constructed to guarantee the feasibility and convergence of the optimization. Ten runs of computation were carried out to determine the optimal design of the portal frame, and the validity of the optimal solution was checked in all wind directions. The research results show that the objective function decreases monotonically with respect to iterations, standard deviation for total mass is only 4% of its mean value, and the mean iteration number for every run is 24. Therefore, the quantum-behaved particle swarm algorithm displays strong robustness and high efficiency in the wind-resistant optimization of portal frames.

Numerical Simulation of Wind-Induced Roof Snow Distributions Based on Time Variable Boundary

WANG Weihua, LIAO Haili, LI Mingshui

2013, 26(5): 851-856,967. doi: 10.3969/j.issn.0258-2724.2013.05.011

[Abstract](1040)

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In order to predict snow deposition on a building roof under wind action, a numerical method based on the Euler-Euler two-phase mixture model was employed to simulate wind-induced roof snow distributions. In the method, the latest improved k-ω turbulence model is used to turbulence closure, and the computational domain boundaries uses the adaptive deformation technique based on snow depth changes. An example of numerical calculation was given to verify the validity of this method, and then snow distribution on a stepped roof was simulated. The time histories of roof snow distributions in some different states were gained. The simulation results show that along with the time development, the snow distribution on the roof has a great influence on air flow, and the snow deposition rate will change. The simulation results after 22 h are in good agreement with the field observation ones, and without considering snow effect on air flow, large errors will be result in. The simulation results for different velocity ratios are basically consistent. As the velocity ratio is smaller, the snow-depth coefficient gets larger, and the simulation time of reaching similar distribution becomes shorter.

Equilibrium Equation Derivation of Structures Formed by Stages Based on Plane Shell Element

XU Leiping, QIN Shunquan, MA Runping

2013, 26(5): 857-862. doi: 10.3969/j.issn.0258-2724.2013.05.012

[Abstract](1025)

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In order to research the influence factor of the final state of structures formed by stages based on plane shell element, the structural equilibrium equation including the unstressed state amounts was established. The relationship between unstressed state amounts at any point within the isoparametric plane shell element and at Gaussian integral points was founded. The total potential energy of structure was calculated from the zero state when the isoparametric plane shell element is unstressed. From the principle of minimum potential energy, the structural equilibrium equation including unstressed state amounts was derived to make clear the relationship between the final state and unstressed state amounts of plane shell element. The analysis results show that when a structure system, external loads and boundary conditions are given, the final state of a structure formed by stages is definite if the unstressed state amounts of plane shell element are certain.

Nonlinear Target Tracking Algorithm Based on Block Ensemble Kalman Filter

CUI Bo, ZHANG Jiashu, YANG Yu

2013, 26(5): 863-869. doi: 10.3969/j.issn.0258-2724.2013.05.013

[Abstract](1008)

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As target tracking performance depends on correlated tracks and the selection of filter initial states, ensemble Kalman filter was introduced to nonlinear target tracking system, and the feasibility and validity of the system were verified. A new target tracking algorithm based on block ensemble Kalman filter was proposed, where initial ensemble was produced by the block method, and covariance matrix weighting was used for all the blocks in the target tracking process. The simulation results show that the algorithm based on block ensemble Kalman filter has the same computational complexity as previous ensemble Kalman filter while offers higher estimation accuracy for motion parameters, and can fulfill real-time tracking in contrast to high computational complexity of particle filter.

Forest Fire-Point Location Based on Bundle Adjustment of Double Images

DUAN Zhugeng, XIAO Huashun

2013, 26(5): 870-877. doi: 10.3969/j.issn.0258-2724.2013.05.014

[Abstract](949)

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Using a camera to obtain the stereo pair of digital photographs of forest area, and a three-dimensional electronic compass to measure the three-dimensional attitude angles at each instant shooting as the initial values, three dimensional coordinates of the forest fire-point was determined with bundle adjustment of double images. The experiments showed that the accuracy of locating fire-point reached 100 m, which meets the requirement of the forest fire prevention regulation. As this method does not require a known point to be a control point, the location accuracy is dependent on parallax error of corresponding image points, photographic baseline length, corner and photographic distance, etc. The coordinate positioning error increases with the photographic distance, and the error in the shooting direction is significantly greater than that in the other two directions. Fire point positioning accuracy will improve with the increase of photographic baseline length, and the influence of corner on the positioning accuracy of fire point is not evident. In the selection of photo station, photographic baseline length should be within 30-200 m, which ensures that the overlap between the left and right images falls in the interval of 60% to 80% and the images can correctly match each other.

Dynamic Traction Load of a Multi-mass EMU Braking Model

HE Xiaoqiong, PENG Xu, ZHOU Yingying, XIAO Jian

2013, 26(5): 878-884. doi: 10.3969/j.issn.0258-2724.2013.05.015

[Abstract](1136)

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As single-mass model of an EMU (electrical multiple units) model can not exactly describe vehicle braking performance, a multi-mass EMU model was established according to braking force distribution. Basic resistance, additional resistance and the time-varying power of traction network were deduced, and the EMU braking situations with common rail, ramp and curve were simulated. In contrast to the measured data,the distance error of the multi-mass model is less than 50 meters, which demonstrates the accuracy of this model.

Multi-objective Optimal Control of Micro-grid Based on Event-Driven Method

CHEN Weirong, LU Wenting, DAI Chaohua

2013, 26(5): 885-891. doi: 10.3969/j.issn.0258-2724.2013.05.016

[Abstract](970)

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The multi-objective optimal control problem of micro-grid is usually described by high dimensional nonlinear differential equations, which cannot be solved satisfactorily by current mathematics method. Hybrid control method is proposed to achieve multi-objective optimal control of micro-grid. A Stateflow model was estabilished, which can output control quantity according to the input data and the control objects, schedule various micro power supply in the micro-grid and achieve the multi-objective optimal control of the micro-grid. In a case of a specific DC micro-grid, the dispatching strategy of micro sources in the micro-grid was discussed, the related events were defined and the event-driven control system was designed. Finally, simulation by MATLAB/Simulink/Stateflow shows that with given values of fuel cell operation cost, battery voltage and power shortage, this model can output control signals in agreement with theoretical analysis.

A 2FSK-Based High-speed Signal Transmission Method for ICPT System

DAI Xin, DU Renjie, TANG Chunsen, WANG Zhihui, SUN Yue

2013, 26(5): 892-897. doi: 10.3969/j.issn.0258-2724.2013.05.017

[Abstract](772)

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In view of magnitude attenuation and electromagnetic interference in the signal transmission of the inductively power transfer (ICPT) system, a new high-speed signal transmission method based on 2FSK is proposed. This method can achieve high-speed signal transmission without increasing the number of coupled coils in main circuit and affecting normal system operation. Firstly the characteristics of channel impedances and frequency responses under different main circuit structures were analyzed; then the modulation and demodulation mode were determined. Finally a circuit experiment system was built. With carrier frequencies of 2.5 MHz and 1.7 MHz, a 100 kHz pulse signal transmission was achieved. The agreement of simulation and experimental results verifies the feasibility of this method.

Analysis of Characteristics of Wheel/Rail Rolling Contact Based on Mixed Lagrangian/Eulerian Method

XIAO Qian, XU Hongxia, WANG Chengguo, ZHANG Hai

2013, 26(5): 898-903. doi: 10.3969/j.issn.0258-2724.2013.05.018

[Abstract](1006)

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To overcome the long time consumption of the explicit finite element calculation of wheel/rail rolling contact, the mixed Lagrangian/Eulerian method is used to establish a wheel/rail rolling contact finite element model. Through this model, the elements of the wheel/rail contact region are refined, and the wheel/rail contact characteristics are investigated in trains' starting, running, and braking conditions. The results show that under the different conditions, the maximum Mises stress, and the maximum contact stress, and the area of wheel/rail contact patches vary in the range of 2%, but the Mises stress distribution of the longitudinal section in the contact region and the longitudinal shear stress distribution vary greatly. Positions of the maximum Mises stress and the maximum longitudinal shear stress in starting and braking conditions are closer to the surfaces of wheel/rail than in free rolling. Especially it can be found that the size and direction of friction within the contact patch vary with different conditions, and pure sliding occurs when the friction reaches the limit between wheel and rail in the train traction and braking. In addition, the longitudinal friction force also varies within 2%when the train is in different speed grades.

Causes Analysis of Tread Spalling Defects on Solid Rolled Wheels of SS3B and DF8B Locomotives

WANG Yuhui, HE Guoqi

2013, 26(5): 904-908. doi: 10.3969/j.issn.0258-2724.2013.05.019

[Abstract](856)

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In order to find out the causes of locomotive wheel tread spalling defects, the tread spalling of solid rolled wheels were sampled for routine examinations, including the SS3B31024047 wheels of the SS3B locomotive, the DF8B31644017 wheels and the DF8B32774060 wheels of the DF8B locomotive. The macroscopic feature and microstructure of the tread spalling area were analyzed in terms of the TJZJ-01-98, with light micro-scope observation and electronic scanning. The test results show that the surface metal of DF8B32774060 wheels mainly underwent plastic deformation under contact stress, and the spalling was caused by the rolling contact fatigue. However, SS3B31024047 and DF8B31644017 wheels' tread spalling was attributed to the plastic deformation layer in the tread spalling area caused by thermal fatigue. Therefore, reduction of the wheel tread spalling caused by the rolling contact fatigue could be achieved by adjustment of the chemical composition of steel, improvement of the heat treatment and tread processing technologies of wheels; and the thermal fatigue spalling can be alleviated by changing the braking mode and optimizing the traction operation.

Effect of Wheel Material on Rolling Friction and Wear Behaviors of Wheel/Rail Rollers

WANG Wenjian, WANG Hong, LIU Qiyue

2013, 26(5): 909-914. doi: 10.3969/j.issn.0258-2724.2013.05.020

[Abstract](950)

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In order to find a desired match and alleviate the wear and damage between wheel and rail materials, the rolling friction, wear, and damage behaviors between three kinds of wheel materials and U71Mn rail were investigated under dry conditions using the MMS-2A testing apparatus. The results indicate that the wheel material has no obvious effect on the rolling friction coefficient of wheel/rail, and the steady value of friction coefficient is about 0.4. With the increase of carbon content of wheel material, the wear volume of wheel specimen has a linear drop, while the wear volume of rail specimen has a linear increase; consequently the total wear volume of wheel/rail presents a decrease trend. In addition, the surface damage and morphologies of wheel specimens are obviously different for different wheel materials. When the carbon content of the wheel material is 0.57, the spalling damage is serious and the plastic deformation is slight. With the hardness of wheel specimens decreasing (carbon content 0.51), the spalling damage of wheel specimens becomes slight; however, the plastic deformation of wheel specimens is serious. For rail specimens, adhesion and spalling wear dominates the rolling wear process.

3D Model Reconstruction and Its Feature Parameters Extraction of a Turbine Blade

LAI Xide, LI Guangfu, ZHANG Weibin, CHEN Xiaoming, SONG Wei, JIANG Hai

2013, 26(5): 915-920. doi: 10.3969/j.issn.0258-2724.2013.05.021

[Abstract](1034)

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In order to achieve an innovation design of turbine blades, the point cloud data of an existing turbine blade was digitally acquired by a handy laser scanner, and then a reverse design methodology was proposed to accurately reconstruct a 3D digital model and extract the geometric and aerodynamic feature parameters from the point cloud data. In order to obtain the blade section profiles and extract the geometric and aerodynamic feature parameters accurately, using the point cloud data of the turbine blade, the pressure side and suction side were fitted with quintic polynomial curves, and the trailing and leading edges were approximated with the arc. The results show that using the methodology, the curve equation of blade section profiles can be approximated with a deviation in the range of with Matlab software, and the geometric and aerodynamic feature parameters can be extracted from these curve equations accurately.

Response Analysis of Wing-Mounted Engine Rotor System under Atmospheric Turbulence

LIU Xiaobo, TU Junchao, DENG Beibei

2013, 26(5): 921-927. doi: 10.3969/j.issn.0258-2724.2013.05.022

[Abstract](1047)

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In order to study the phenomenon that wing-mounted engines working at high altitudes could be affected by the atmospheric turbulence, a dynamic model of wing-mounted engine rotor system under atmospheric turbulence was established using the theories of wing aeroelastics and rotor dynamics and adopting the Dryden turbulence model as the atmospheric speed model. To solve the dynamic model, the pseudo-excitation method was used for numerical calculation. The results show that the power spectral density (PSD) of the displacement response at each turntables station in the rotor system has almost a similar variation trend to the PSD of the atmospheric turbulence speed, but the displacement response intensity peak occurs at the natural frequency. The displacement response intensity caused by atmospheric turbulence decreases with the angular frequency increasing when the angular frequency is larger than 100 rad/s, and the effect of rotor system characteristics on the displacement response intensity cannot be neglected.

Analysis of Route Travel Time Variation of Road Network Suffering Traffic Incidents

ZHANG Xi, LIU Haixu, PU Yun

2013, 26(5): 928-933. doi: 10.3969/j.issn.0258-2724.2013.05.023

[Abstract](934)

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Analyzing route travel time variation of road network suffering traffic incidents can provide reliable decision supports for the incident management of advanced traffic management systems. Taking into consideration the randomness of travelers' daily route choice when incidents with a duration of several days occurs, a random dynamical assignment model was proposed to describe the route travel time variation of the road network system under such occasion based on the dynamical adjustment process with route flows subjecting to a joint probability distribution. Then, the model was applied to an example network to confirm its feasibility. The results show that when the traffic incident duration prolongs 10 more days, the average route travel time increases 0.24%. Compared with normal links, the critical link that suffers the traffic incident causes the average travel time to increase 3.07%: When the link capacity degrades 10%, the average travel time increases 2.53%. The necessary time for the network system recovering to equilibrium after the clearance of incident is greatly affected by the link with traffic incident. The recovery time of the critical link suffering incident is about 4 times longer than that of normal links.

General Model and Simulation Research on Passenger-Dedicated Line Station Based on TPr/T-S

LI Wang, NI Shaoquan

2013, 26(5): 934-941. doi: 10.3969/j.issn.0258-2724.2013.05.024

[Abstract](1090)

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In order to construct a general passenger-dedicated line station model, which is irrelevant to the stations' structure and scale, the station model can be treated as a set of routes and tracks. Predicate/transition-system (Pr/T-S) has been extended to timed predicate/transition-system (TPr/T-S) with the consideration of time parameter. TPr/T-S can be used to track the trace of individuals in the simulation while describing the relationship between individual state change and time. Considering that the general passenger-dedicated line station model is irrelevant to the station's topology and scale, the paper models the relationship between TPr/T-S and individual entities including trains, routes, and tracks. The simulation results of Xuzhou East station show that the occupation and utilization rate of station routes is averagely 34% and there is proper route available for each train during the simulation. The results demonstrate the safety and feasibility features of the adopted train operation diagram and the effectiveness of the general TPr/T-S model.

Simulating Impacts of Variable Speed Limits on Traffic Safety on Freeways

LI Zhibin, LIU Pan, SHAN Xiaonian, WANG Wei

2013, 26(5): 942-948. doi: 10.3969/j.issn.0258-2724.2013.05.025

[Abstract](1044)

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To reduce the occurrence of rear-end collisions during the propagation of kinematic waves in freeway section upstream of a recurrent bottleneck, a simulation platform for variable speed limits (VSLs) was developed using the PARAMICS microscopic simulation model. The simulation network is a freeway section containing an on-ramp bottleneck. A crash prediction model was adopted to quantify the real-time rear-end collision risks accompanying the propagation of kinematic waves in the section upstream of the on-ramp bottleneck. Control strategies for VSLs were proposed to reduce the collision potential. Results show that the optimal strategy to reduce collision risk is that the startup threshold of collision probability is set to 0.25, time step for VSL change to 120 s, speed step for reduction to 20 km/h, speed step for recovery to 10 km/h, and difference between adjacent speed limit signs to 20 km/h. Using the optimal control strategy for VSLs, the rear-end collision risk in the freeway section upstream of the recurrent bottleneck is reduced by 20%.

Design and Implementation of Path Planning System Based on Improved Highway-Hierarchical Algorithm

ZHANG Guanxiang, ZHOU Xing, CAI Wenxue, ZHONG Huiling, XU Jing

2013, 26(5): 949-954. doi: 10.3969/j.issn.0258-2724.2013.05.026

[Abstract](991)

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Highway-Hierarchical algorithm is a highly efficient path planning approach in the recent years. In the preliminary data manipulation process, there are problems of compressed ring road in the network, the strategies of multi-layer data storage, and the calculation of the optimal route. To resolve these issues, the paper proposes to use the no-cycle compressing strategy, the tiered storage strategy, and the local shortest path storage strategy to improve the efficiency of the algorithm. Under the internet settings, the paper designs the highly efficient route planning system by improving the Highway-Hierarchical algorithm with the WCF technology. The results show that the improved system is 5.03 and 4 times of temporal and spatial efficiency, respectively, as opposed to the original algorithm. The route planning system can meet the high users' demand and also provides the general information on the travel time, mileage, travel expenses, critical sections, text description, etc.

Short-Term Traffic Flow Forecasting and Reliability Analysis of Urban Road

NIE Qinghui, XIA Jingxin, QIAN Zhendong

2013, 26(5): 955-960. doi: 10.3969/j.issn.0258-2724.2013.05.027

[Abstract](1098)

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In order to capture the uncertainty of short-term traffic forecasting caused by the random fluctuation of traffic flow, the heteroscedasticity which can reflect the fluctuation is used to quantify the reliability of traffic forecasting. On the basis of time series and its heteroscedastic theory, a generalized autoregressive conditional heteroscedasticity (GARCH(1,1)) model was developed, in which an autoregressive integrated moving average (ARIMA(0,1,1)) model was used as the mean equation. The ARCH LM test results show that the heteroscedasticity of the ARIMA(0,1,1) model can be effectively captured and eliminated by the proposed GARCH(1,1) model. Performance evaluation illustrates that based on the GARCH(1,1) model, the traffic volume forecasting of urban expressway has a mean absolute percentage error (MAPE) of less than 10%, and the speed forecasting of urban expressway and arterial roads has a MAPE between 7.86% and 10.24%. Compared with the fixed confidence intervals predicted by ARIMA(0,1,1) model, the GARCH(1,1) model can produce narrower forecasting confidence intervals on the premise of effective prediction of free flow traffic conditions; while in congested traffic conditions, the GARCH(1,1) model can produce wider forecasting confidence intervals to improve the forecasting reliability by reducing the invalid prediction.

Preparation of La0.7Sr0.3MnO3 Single-Crystal Epitaxial Films and Their Magnetoresistance Properties

ZHANG Xin, YANG Xinsheng, CHENG Cuihua, ZHANG Yong, LV Li, ZHANG Min, ZHAO Yong

2013, 26(5): 961-967. doi: 10.3969/j.issn.0258-2724.2013.05.028

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Abstract:
In oder to obtain high quality single La0.7Sr0.3MnO3 (LSMO) buffer layers and study their low-field magnetoresistance (MR), a series of epitaxial films of perovskite manganites La0.7Sr0.3MnO3 (LSMO) deposited on the LaAlO3 (LAO) single crystal substrates were fabricated by the polymer-assisted chemical solution deposition method. Taking into account the influences of argon and oxygen annealing atmosphere on the LSMO phase formation, investigations were conducted on the surface morphology and texture of the specimens annealed in argon and the transport properties and colossal magnetoresistance (CMR) effect of the specimens annealed in oxygen. The results show that thick and high quality single LSMO buffer layers can be produced at low costs by the polymer-assisted chemical solution deposition method and annealing in argon atmosphere. The films fabricated in oxygen are found with good c-axis textured, and the MR measurements of the films shows a peak, corresponding to the insulator-metal (I-M) transition. The MR value does not change with the temperature between 200 to 300 K, and is about-26.0 % at room temperature in 1 T magnetic field.

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2013 Vol. 26, No. 5