西南交通大学学报

Effect of Distributions of Static Suspension Deflection on Ride Comfort of High-Speed Passenger Cars

LIU Pengfei, WANG Kaiyun, ZHAI Wanming

2013, 26(2): 193-198. doi: 10.3969/j.issn.0258-2724.2013.02.001

[Abstract](1148)

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Abstract:
In order to improve the ride comfort of high-speed passenger cars, a study was made on the static deflection of suspension system, and the relationship between the total static deflection and the static deflection ratio of the secondary to primary suspension was discussed. According to the vibration theory and the principle of multi-body system dynamics, the forced oscillation characteristics of 2-DOF wheel load system were studied for different static deflection ratios, and a high-speed vehicle model was established to investigate the influence of static deflection distributions on ride quality at various speeds. The results show that as the deflection ratio of the wheel load system increases, the carbody acceleration reduces when the vertical vibration frequency of the carbody is within 4 Hz, but it is comparatively small for deflection ratios of 1.0 and 2.0 when the vibration frequency is above 4 Hz. By increasing the deflection ratio, bogie vibrates more violently, the carbody lateral stability worsens slightly, and the vertical vibration accelerations within the frequency range from 2 to 10 Hz become larger significantly. The vertical ride comfort index values of static deflection ratios 0.5 and 8.0 are 1.5% and 6.0% higher than that of static deflection ratio 2.0.

A Novel Fatigue Analysis Method of Welded Frames

XIAO Shoune, YANG Chao, YANG Guangwu

2013, 26(2): 199-204. doi: 10.3969/j.issn.0258-2724.2013.02.002

[Abstract](1105)

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In order to evaluate the fatigue strength of welded bogie frames under multi-axial stress in load cases, a tensor method based on the direct method and projection method was proposed by applying coordinate transformation property of the second-order tensor. This method, by transforming multi-axial stress to the same coordinate system and the same section, uses the obtained maximum stress and minimum stress for the fatigue evaluation. The finite element model was then built based on a certain welded bogie frame. The stresses in several static conditions were calculated. For comparison purpose, the direct method, projection method, and tensor method were used to evaluate the fatigue strength of this bogie frame, respectively. The rationality of the three methods was verified by critical plane approach and Ncode. The results show that the tensor method, which took the direction of multi-axial stress into consideration, is obviously better than the other two methods, with the smallest error of 4.42% compared with the Ncode result.

Lifting Dynamic Characteristics of Crane with Frequency Control

PU Hanjun, XIE Xiaopeng, LIANG Guangchi

2013, 26(2): 205-210. doi: 10.3969/j.issn.0258-2724.2013.02.003

[Abstract](1216)

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For purpose of calculating the lifting dynamic load in a crane accurately, a generalized precise direct integration method was proposed to analyze dynamic characteristics of the load-lifting system of the crane. Using this method, the dynamic responses of the system during the load-lifting process of the frequency conversion crane were studied, and the dynamic characteristics of the crane system under various accelerating modes were obtained. The results show that the dynamic lifting coefficient is linear with the lifting speed and exponential with the acceleration time. Compared with the step speed regulation, the frequency conversion speed regulation can reduce the hoisting dynamic load of the crane system by 10% to 60%.

Experimental Investigations of Three-Dimensional Flow Field around the Head of Gas-Liquid Slug Flow in Microchannels

WANG Ling, LUO Rui, WANG Buxuan

2013, 26(2): 223-229. doi: 10.3969/j.issn.0258-2724.2013.02.006

[Abstract](870)

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The three-dimensional micro-particle image velocimetry (PIV) technique was used for experimentally studying three-dimensional flow field properties of slug flow in microchannels. By processing images of slug flow, three-dimensional fluorescent particles distribution and velocity flow field of the liquid around the head of slug bubble was obtained. The results show that there was two symmetrical and reverse vortices near the head of the bubble. The fluid near the bubble head had a larger velocity and flowed along the bubble surface. In the flow field far away from the bubble, the distribution of liquid velocity was parabolic in the radial direction, which was similar to a single-phase pressure driven flow. The fluid between the bubble surface and the microchannel walls had a complex motion: it might be pushed to the bubble tip if closer to the bubble surface or might be passed if closer to the walls. In addition, the gas-liquid interface was approximately rigid.

Temperature Field of Catenary for Electrified Railway during Online Anti-icing

GUO Lei, LI Qunzhan, XIE Shaofeng, SHU Zeliang

2013, 26(2): 230-235,242. doi: 10.3969/j.issn.0258-2724.2013.02.007

[Abstract](1295)

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Accidents of icing on catenary have great impacts on normal operation of electrical railway. In order to guarantee traction power supply, an online anti-icing technology for catenary was proposed based on the static var generator (SVG). Heat balance equations for catenary were built, and solved results were compared with test results and data provided by the TB/T 2809-2005 to prove the correctness of the technology. The temperature fields of catenary during running of the online anti-icing system were calculated, and the factors influencing temperature distribution, such as train velocity and load current, were analyzed. The analyzed result shows that when ambient temperature is -4 ℃ and target temperature is 2 ℃, maximum temperature difference of droppers and clamps will reach to 5.3 ℃, so droppers and clamps may be weakest.

High-Efficiency Power Distribution Scheme for Online Powered System of Electric Vehicles

SUN Yue, TIAN Yong, SU Yugang, WANG Zhihui

2013, 26(2): 236-242. doi: 10.3969/j.issn.0258-2724.2013.02.008

[Abstract](1013)

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In order to reduce the serious transmission loss in the online powered system for electric vehicles, a power distribution scheme based on high-voltage transfer and low-voltage stimulation was proposed. In this scheme, a high-voltage track is used to reduce the transmission loss, and a low-voltage track is utilized to enhance the ability of power transmission. The basic framework of the distribution scheme was given out, and its operating principle was expounded. In addition, the generation mechanism of the transmission loss was analyzed, the calculation formula for the transmission loss was derived, and a continuous powered approach in the tracks-switching course was investigated. Finally, simulation analysis and experiment investigation were carried out to verify the feasibility and validity of the proposed power distribution scheme and the continuous powered approach. The analysis result shows that when the transmission distance is approximately larger than 70 m, the proposed power distribution scheme can effectively improve the efficiency of remote power transmission.

Influence of Frequency of Impulsive Square Wave Voltage on Partial Discharge Characteristics and Its Mechanism

WANG Peng, WU Guangning, LUO Yang, ZHANG Yiqiang, XU Huihui

2013, 26(2): 243-249,270. doi: 10.3969/j.issn.0258-2724.2013.02.009

[Abstract](963)

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To probe into the influence of frequency of (impulsive) square wave voltage on partial discharge (PD) characteristics, a system for PD detection specially used at square wave voltage was designed by resorting to the ultra-high frequency (UHF) detection method and the IEEE 488.2 protocol. By utilizing this system, PD features of corona resistance enameled wires, i.e., magnitude, occurring phase and time/frequency characteristics, were investigated. The research results show that high-frequency (above 200 Hz) square wave voltage will make space charge decaying rate reduce to increase the probability of initial electrons for PD, decrease instantaneous voltage when PD occurs and result in PD events with voltage magnitudes below 200 mV. Under high-frequency square wave voltage, when PD occurs at the rise time of voltage, PD features will be changed to make energy components with 1 to 2 GHz frequency increase. So when PD of inverter-fed motors is detected on the basis of related standards, low-frequency (below 200 Hz) square wave voltage should be used to induce the PD of insulation weak points easily. Furthermore, to increase the signal-to-noise ratio, UHF sensor should have a better performance in the frequency range equal to and higher than 1.2 GHz, and 500 MHz high-pass filter ought to be adopted.

Method of Identifying Volterra Frequency-Domain Kernels Based on Stimulus of Multi-tone Signal

HAN Haitao, MA Hongguang, YU Ningyu, ZHANG Jialiang

2013, 26(2): 250-256. doi: 10.3969/j.issn.0258-2724.2013.02.010

[Abstract](1049)

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In order to solve the problem of difficultly identifying Volterra frequency-domain kernels, the output properties of Volterra frequency-domain kernels stimulated by multi-tone signal were investigated, and a novel non-parametric method to identify Volterra frequency-domain kernels was proposed based on multi-tone stimulus. With this method, a multi-tone signal with a proper frequency basis is selected as the test stimulus signal to make each kernel put out unique frequency components, further the output of each kernel is separated by the Vandermode method. The formula to identify Volterra frequency-domain kernels was derived, and theoretical and simulation analyses were carried out. The results indicate that any order Volterra frequency-domain kernel can be precisely identified by the proposed method, and the order of magnitude of the absolute error is 10-4 V. The proposed method overcomes the defects of the conventional methods, i.e., they are unable to correctly identify Volterra frequency-domain kernels and the identification results are limited to the first three orders, and it has a high precision and is easy to operate.

Universal Data Organization Method of LED Display Screen Based on Multi-scanning-beam

JIN Wei, ZHU Yunfang, WU Zhiquan, LI Qi

2013, 26(2): 257-263. doi: 10.3969/j.issn.0258-2724.2013.02. 011

[Abstract](702)

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In order to overcome the shortcoming of the current data organization methods with a lack of the versatility for different unit circuit boards, by analyzing the existing unit circuit boards of LED display screens a universal data organization method of LED display screens was proposed based on multi-scanning-beam. On the basis of the internal 74HC595 connection forms, a commonly-used unit circuit board is divided into two classes, i.e., direct connection and bypass connection. To the two connection forms, output display data is continuously arranged in memory based on the multi-scanning-beam and the data field to make the output display data have a maximum rate from the control systems to the display screens. Finally, a control card for the proposed method was developed. The experiment results show that with the developed control card, the data output rate is up to 4 Mbit/s.

3 GHz Thermoacoustic Tomography System

HUANG Lin, LIU Lixin, LU Kui, ZHONG Xiaochun, LI Tingting, CHEN Bingzhang, RONG Jian, JIANG Huabei

2013, 26(2): 264-270. doi: 10.3969/j.issn.0258-2724.2013.02.012

[Abstract](900)

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To evaluate the performance of a 3 GHz thermoacoustic tomography (TAT) system, absorbers with different shapes and contrasts were investigated using the circular scanning method, the imaging depth was probed into by adding porcine fat to the top of an absorber. Tissue-mimicking phantom experiment results show that the absorbers with different contrasts and shapes, i.e., 10 mm by 20 mm rectangle, 8 mm square and 8 mm diameter circular absorbers, can be imaged, and spatial resolution and imaging depth of the system are 2 and 5 cm, respectively.

Empirical Mathematical Model for Nonlinear Motion-Induced Aerodynamic Force of Bridge Girder

WANG Qi, LIAO Haili, LI Mingshui, MA Cunming

2013, 26(2): 271-277. doi: 10.3969/j.issn.0258-2724.2013.02.013

[Abstract](1216)

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In order to probe into the nonlinear motion-induced aerodynamic force (MIAF) of bridge girder, based on Taylor expansion of the equilibrium position, a nonlinear MIAF mathematical model for bridge girder under harmonic motions was established, and the plural and real expressions were deduced. The identification method of nonlinear aerodynamic parameters in the expressions was introduced. This mathematical model includes the properties of nonlinear MIAF composing of multiple harmonic components, and can be applied to the analysis of nonlinear aerodynamic stability of bridges. An application shows that the maximal error between the wind tunnel test results of a streamline box girder and fitting ones based on the model is less than 3%to verify the validity of the mathematical model.

Pier Linear Stiffness Optimization of Large-Span Simply-Supported Beam Bridge for Continually Welded Rail

QIAO Jiandong, LI Zhihui, YANG Qing

2013, 26(2): 278-282. doi: 10.3969/j.issn.0258-2724.2013.02.014

[Abstract](1403)

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In order to obtain the key factor of the overall design of a large-span high-pier long-league bridge, the reasonable value of pier longitudinal stiffness was discussed. Based on stress transfer mechanism of continually welded rail on bridge, a rail-beam-pier-foundation integration model was established. A parameterized optimization model was built, and a pier line stiffness optimizer was compiled by the means of ANSYS re-developing with APDL parameter design language. By combining with an actual project, the pier longitudinal stiffness limitation of a 64 m simply-supported beam bridge with continually welded rails was analyzed. The analysis results show that the rapid relative displacement between beam and rail and the additional stress of rail are key factors of the overall design of a large-span high-pier long-league bridge with continually welded rails, and the pier longitudinal stiffness limitation of the 64 m simply-supported beam bridge with continually welded rails ought to be greater than 750 kN/cm.

Destructive Field Test on Properties of Uplift and Compression Piles

MA Jie, ZHAO Jian, ZHAO Yanlin

2013, 26(2): 283-289,296. doi: 10.3969/j.issn.0258-2724.2013.02.015

[Abstract](1033)

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To clarify the similarities and differences of properties of uplift and compression piles, the mobilizations of skin friction and tip resistance were analyzed based on destructive filed tests on two uplift piles and two compression piles. The destructive field test results showed that under a destructive load, there was a softening relationship between pile tip displacement and load. The average limit skin frictions of the uplift piles were about 0.373 to 0.763 times those of the compression piles, and larger values were found in deep soils. The skin friction degradation along the pile depth was observed. The failure ratio of skin friction was from 0.87 to 0.97 and 0.83 to 0.94 for the uplift and compression piles, respectively. The relative pile-soil displacements for fully mobilizing the skin frictions in different soils were 0.6% to 1.5% and 0.9% to 2.0% of pile diameter for the uplift and compression piles, respectively.

Theoretical Analysis and Experimental Investigation on Cross-Legged Silent Rail

ZHAO Caiyou, WANG Ping

2013, 26(2): 290-296. doi: 10.3969/j.issn.0258-2724.2013.02.016

[Abstract](1199)

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In order to reduce wheel-rail noises, a cross-legged silent rail was designed. Unlike the traditional silent rail, an extension layer is added between rail and the damping layer, moreover, the extension layer and the constraining layer are interlaced mutually. The structure was optimized using the finite element method. Based on the optimized results that aluminum material with a thickness of 1 mm should be taken as the expansion layer, IPN damping material as the damping layer and 2 mm thick steel as the constraining layer, a prototype of the cross-legged silent rail was made and tested in laboratory. The tested results show that vibration duration time of the cross-legged silent rail is only 1/5 of the standard rail, and compared with the standard rail, its radiation sound pressure level decreases by 10.4 and 13.2 dB respectively at vertical excitation and lateral excitation.

Length Determination of Track Concrete Plate for Unit Double-Block Ballastless Track

WEI Youxin, QIN Chaohong, LI Chenghui, YANG Bin

2013, 26(2): 297-302,309. doi: 10.3969/j.issn.0258-2724.2013.02.017

[Abstract](1114)

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In order to determine the rational length of unit track concrete plate, the numerical simulation method was applied to analyze the stress and strain responses of unit double-block ballastless track with different lengths under train load, transversal and longitudinal loads, temperature force and temperature gradient. On the above basis, minimum reinforcement ratio needed for track concrete plate and crack widths were calculated. A contrast analysis was conducted by combining site observation. The research result shows that a long unit track concrete plate will result in high internal stresses, big plate end displacement and large crack width, as a result, the minimum reinforcement ratio needed will increase. The reasonable length of track concrete plate for unit double-block ballastless track should be less than 8.0 m, while it should be 6.5 m to subgrade sections along the new Lanzhou-Urumchi railway.

Influence of Weak Layer Properties on Deformation of Embankment over Sloped Weak Ground

LIU Jinnan, JIANG Xin, QIU Yanjun

2013, 26(2): 303-309. doi: 10.3969/j.issn.0258-2724.2013.02.018

[Abstract](1002)

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In order to get the deformation characteristics of embankment over sloped weak ground with different weak layer properties, a numerical model was established based on the nonlinear finite element method. The orthogonal design was applied to evaluate the significances of influencing factors. The research results show that the elastic modulus and thickness of a weak layer are the decisive factors affecting vertical settlement and lateral deformation; the lateral slope of ground is an important factor aggravating embankment deformations; when the weaker layer locates on ground top, embankment deformations are significantly affected, especially on lateral deformation. Engineering measures based on weak layer properties, such as foundation treatment and lateral restraint should be adopted to eliminate the deformations.

Engineering Geological Division of Geological Hazards along Dali-Ruili Railway in Gaoligong Mountain Section

ZHAO Zhiming, WU Guang, KOU Chuan

2013, 26(2): 310-316. doi: 10.3969/j.issn.0258-2724.2013.02.019

[Abstract](1126)

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The Gaoligong Mountain section of Dali-Ruili railway line is characterized by complicated topography and terrain, diverse rock and soil mass, and frequently active faults. In order to evaluate the impact of geological hazards such as rock falls, landslides, and debris flows on the railway project in this section, a field investigation was made into the geological materials to analyze the development of geological hazards and engineering risks. The grades of geological hazards were divided into four grades: (Ⅰ) safe, (Ⅱ) moderately safe, (Ⅲ) relatively dangerous and (Ⅳ) dangerous. Using the analytic hierarchy process (AHP) theory, a evaluation model was then established, and used for engineering division of this section of railway line, by evaluating the risk of the geological hazards. The results show that the grades belong to Ⅱ and Ⅲ from Xiaozhaizi to Mangshi, and the present route plan can avoid the impact of dangerous geological hazards.

Kalman Filter Algorithm for Medium-Range Real-Time Kinematic Positioning with One Reference Station

XU Yantian, CHENG Pengfei, CAI Yanhui

2013, 26(2): 317-322,356. doi: 10.3969/j.issn.0258-2724.2013.02.020

[Abstract](897)

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In order to achieve real-time kinematic (RTK) accurate positioning for medium-range baselines and weaken the effects of double-difference tropospheric delay and ionospheric delay between stations and satellites, dry tropospheric delay was computed with the Hopfield model, while double-difference tropospheric wet delay was estimated with a relative tropospheric zenith delay (RTZD) parameter. The double-difference ionospheric delay was estimated with relative ionospheric zenith delay (RIZD) between two stations. A Kalman filter algorithm was proposed by taking position parameters, relative tropospheric zenith delay, relative ionospheric zenith delay and double-difference ambiguities as state variables to be estimated. The experimental results show that the proposed algorithm only needs a few of epochs to initialize, and the mean square error of one epoch is less than 2 and 5 cm in the horizontal and vertical directions, respectively.

Compatibility of Polycarboxylate Superplasticizer with Cements of Different Freshness

ZHAO Jumei, LI Maohong, DENG Siyuan, YU Hongquan, LI Yun, QUAN Ming

2013, 26(2): 323-327. doi: 10.3969/j.issn.0258-2724.2013.02.021

[Abstract](1023)

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In order to study the factors influencing the compatibility of polycarboxylate superplasticizer with cements, cement paste fluidity methods were used to evaluate the compatibility between the superplasticizer and cements with different freshness at different temperatures and moistures. The Zeta potential of cements was measured by Zeta potential analyzer, the mean particle sizes were measured by laser particle analyzer, and the cement clinker phases were investigated by X-ray diffraction. The results show that lower cement freshness, lower temperature and higher moisture would lead to lower saturation point of polycarboxylate superplasticizer in cement, higher initial fluidity and lower flow loss, namely, higher compatibility. Compared with the stale cement, the fresh cement was 1.86 mV higher in Zeta potential, 2.63 μm larger in particle size, and higher content of C3A and C4AF that would absorb more superplasticizer. It can be concluded that the possible factors that influence the compatibility of cements with the superplasticizer include temperature, moisture, Zeta potential and the clinker phases of cement.

Influence of Vehicle Length and Velocity on Mixed Traffic Flow in Two-Lane Traffic Flow

PAN Weijun, YANG Kai

2013, 26(2): 335-342. doi: 10.3969/j.issn.0258-2724.2013.02.023

[Abstract](1406)

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In order to study the influence of large vehicles' lane-changing and sensitive driving behaviors on the highway traffic flow, a two-lane mixed traffic cellular automate (CA) model was built by introducing the lane-changing rule into the sensitive driving Nash (SDNS) model, on the assumption that the vehicles with different lengths and maximum velocities appear on the two lanes simultaneously. Under the periodic boundary condition, the fundamental diagrams of the mixed traffic velocity, flow, and density were obtained through numerical simulation by setting different values for parameters such as the lane-changing probability, mixing ratio, braking probability, vehicle length, and maximum velocity. The results show that the system critical density, the maximum average velocity, and the traffic flow decreases with the braking probability increasing. When the proportion of long and slow vehicles is more than 50%, the mixed traffic is more prone to congestion, and the lane-changing rate is less than 5%; when the proportion of long vehicles reaches 50%, the traffic flow peak is merely 0.42, which is 20% less than that of all small/short vehicles. The major factor causing lane changing difficult is the proportion of long vehicles. When the lane-changing probability is 50% and the proportion of long vehicles in the system increases from 25% to 75%, the maximum lane-changing rate decreases from 6.32% to 2.78%.

Travel Time Estimation Method Using SCATS Traffic Data Based on k-NN Algorithm

JIANG Guiyan, LI Qi, DONG Shuo

2013, 26(2): 343-349. doi: 10.3969/j.issn.0258-2724.2013.02.024

[Abstract](1133)

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A new method was designed to improve the effect of travel time estimation using SCATS traffic data. In this method, by analyzing the characteristics of SCATS traffic data that their acquisition intervals are not strictly consistent, the virtual time series of SCATS traffic data was constructed first. Then, factors of cumulative squared loading over 85% extracted by factor analysis were included in the traffic state feature vector, and the Euclidean distance was used to measure the closeness between current traffic state and historical traffic state. Finally, the number of nearest neighbors that correspond to the minimum error of travel time estimation was selected, and the weights of k-nearest neighbors were identified by normalizing the reciprocal of the distance between traffic states, based on which the travel time estimation method was established. The results indicate that compared with the multiple linear regression (MLR) method, the proposed method can reduce the mean absolute error (MAE), mean absolute percentage error (MAPE) and root-mean-square error (RMSE) of travel time estimation by an average of 9.68 s, 8.07% and 4.5 s, respectively.

Video-Based Vehicle Tracking and Capturing System for Expressway Tollgates

XIA Chuangwen, XU Jianmin, LU Yijie, WANG Qionghua

2013, 26(2): 350-356. doi: 10.3969/j.issn.0258-2724.2013.02.025

[Abstract](990)

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In order to reduce the noise impacts in front of the camera and improve the vehicle capturing precision in expressway tollgate scenes, an efficient and flexible judgment framework for vehicle capture was proposed. Specifically, through the analyses of the common motion detection methods, an improved frame difference approach based on motion history images was applied to the framework to increase the motion detection sensitivity. To relieve the calculation complexity, a fast detection algorithm for searching vehicle rectangular region was given. Furthermore, the spatio-temporal rules for vehicle capture judgment were defined, as a result, the judgment framework was formed. In addition, parallel vehicle capturing experiments were conducted on multiple lanes under varied illumination in real time. The experiment result shows that using the proposed framework, the average precision for a 5.5 h test sequence is up to 87.8%, and it is able to resist vehicle and bar movement noises and luminance variation to improve the vehicle capturing precision.

Signal Coordination Algorithm Considering Vehicle Platoon Movement Characteristics on Arterial Streets

BIE Yiming, LI Yishun, WANG Linhong, WANG Dianhai, SONG Xianmin

2013, 26(2): 357-367. doi: 10.3969/j.issn.0258-2724.2013.02.026

[Abstract](1075)

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To develop a signal coordination algorithm and determine its application conditions, a new prediction model of vehicle arrival pattern of intersection coordinated phase was brought forward, which is based on Robertson's dispersion model and take into account three contributing factors such as platoon dispersion, turning vehicles and downstream queue length. According to the relationship between platoon arrival time and the green starting and ending time of coordinated phase, the calculation method for total vehicle delay of coordinated phase was established. Then, an optimization algorithm of signal coordination plan was developed by taking total vehicle delays of coordinated phases of intersections in the traffic control subarea as optimization objective, and offsets as optimization variables. Simulation results shows that compared with the improved numeric method, the proposed algorithm can reduce the vehicle delay of coordinated phases by 7.4%. With the increase of link length, turning vehicles and downstream queue length, the coordinated control benefit decreases gradually.

Modeling the Dynamic Impacts of Multi-modal Guidance Information on Commuters' Trip Chain

ZHAO Dan, SHAO Chunfu, YUE Hao

2013, 26(2): 368-375. doi: 10.3969/j.issn.0258-2724.2013.02.027

[Abstract](1059)

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To study commuters' dynamic choice behavior under the multi-modal guidance information, based on utility theory and multi-stage decision method, a dynamic model was proposed to describe the choice behavior of the daily trip chain that starts and ends at home with the objective of maximizing the perceived utility of a trip chain, and a Dijkstra algorithm was used to solve the model. In the model, the trip chain was divided into some single but sequential trips, and each trip contained pre-trip and en-route decision nodes, on which the travel information was loaded dynamically. Commuters' reliance on information and the learning process were also taken into account to describe the actual decision process more accurately. Computational results show that multimodal guidance information contributes to increase the actual utility of the trip chain by an average of 0.88% for each commuter; in addition, as the reliance increases, commuters will benefit more and tend to shorten the length of trip chain as well as to choose metro or park-and-ride, in order to avoid the utility loss from traffic congestion.

Travel Time Reliability during Incident Duration Time

CHEN Lingjuan, LIU Haixu, PU Yun

2013, 26(2): 376-382. doi: 10.3969/j.issn.0258-2724.2013.02.028

[Abstract](1210)

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In order to describe the stochasticity in road network performance under the influence of an incident, the travel time reliability of the road network was defined as the probability that the mean travel time during incident is smaller than a prespecified threshold. The incident duration was assumed to be a stochastic variable with normal distribution, and is divided into several equal sub-sections. Then, a Monte-Carlo based simulation methodology was put forward to compute the travel time reliability, in which the logit principle and link transmission model are incorporated. A test network was used to illustrate the methodology, in which the mean value of incident duration varies between 8 and 20 min, and variances between 0.5 and 5.0 min, the travel demand of each sub-sections is 4.0 and 4.5 vehicles, and the threshold is 2.0 and 2.2 times the travel time before incident. The results show that the network travel time reliability decreases with the mean incident duration in all cases. In addition, when the travel demand of each sub-section is 4.5 vehicles and the threshold is 2.0 times the travel time before incident, the network travel time reliability increases with the incident duration variance; however, when the demand is smaller than 4.5 vehicles and the threshold is larger than 2.2, the network travel time reliability decreases with the incident duration variance.

Bionics Design of Transverse Stiffener in the Upright Rail Box Girder Based on Bamboo Strucure

FU Weigang, CHENG Wenming, YU Lanfeng, PU Dezhang

2013, 26(2): 211-216. doi: 10.3969/j.issn.0258-2724.2013.02.004

[Abstract](1351)

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In order to find a lightweight solution for the box girders of cranes, taking bamboo as the bionics objective, a structure optimization was made for the transverse stiffeners of the upright rail box girder. A study on the relationship between the nature distribution of bamboo structural parameters and its mechanical behaviors reflects that different cross sections correspond to different equivalent distances between two adjacent nodes of stems. The effect of distances between two adjacent stiffeners on the structure rigidity and strength index was then analyzed to set the maximum distances between two adjacent stiffeners, and the optimization strategy was built to make the stiffener be of the changeable distance and same stability. Finally, the iterative optimization of the elastic buckling analysis was done by the finite element method to complete the solution for stiffeners with changeable distances and the same stability. The results show that the optimization speed increases with the deviation rate increasing. As compared with the traditional box girder, the number of stiffeners in the bionics box girder decreases from 15 to 10, which makes the mass of two main girders decrease 136.12 kg. Besides, the bionics box girder has a more uniform critical buckling load on each section, and meets the design requirements in rigidity and strength index.

Chaotic Motion of Two-Dimensional Viscoelastic Panel with External Excitation in Subsonic Flow

LI Peng, YANG Yiren, LU Li

2013, 26(2): 217-222. doi: 10.3969/j.issn.0258-2724.2013.02.005

[Abstract](1118)

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In order to study the nonlinear dynamics of a panel subjected to external excitation in subsonic flow, the nonlinear governing motion equations of a two-dimensional forced subsonic viscoelastic panel were established by Hamilton theory, and discretized to a series of ordinary differential equations using the Galerkin method. Then, the system equilibrium points and their stability were analyzed, and Melnikov's method was used to obtain the critical values of system parameters for chaos appearance. The critical relations between the external excitation amplitude, frequency, and flow velocity were discussed and compared with the results of chaotic motions by numerical simulation. The results show that the number of equilibrium points and their stability will change after the dimensionless dynamic pressure exceeds 64.42, and the critical parameters determined by Melnikov's method match up to those obtained by numerical simulation. Therefore, the proposed method can be used to judge whether the chaotic motion happens or not.

Post-Disaster Safety Analysis of Construction Site of Scenic Region

FU Fei, DONG Liang, ZHANG Jian, WANG Gang

2013, 26(2): 328-334. doi: 10.3969/j.issn.0258-2724.2013.02.022

[Abstract](1206)

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Abstract:
A 3D virtual model for high gradient zones and flow path regions was built by quantitative analysis methods of the digital elevation model, to guide the safety monitoring and ecological restoration of a regional environment after disaster. Using the virtual model, the site environment in the geological disaster region of Shenxigou was analyzed with a landscape scale of 5 000 unitary granularity. The result shows that the relevant influencing factors that can trigger disasters include slope and confluence cumulant, and regions with a slope of greater than 50 and a large ecological environment change are susceptible to mud-rock flow and other geological disasters. Combination of the cumulant outlet diagram with the hazard maps for mud-rock flow shows that many sites of geological hazards are in the water outlet area or along the flow path. Therefore, the security monitoring and ecological restoration of sensitive slope areas should be strengthened after disasters. In addition, the soil reinforcement and vegetation planning for geological disaster regions and the land utilization adjustment planning for landscape ecological security were proposed.

Collision Risk Model around Intersection of Airways

HAN Songchen, QU Yuling, SUN Fanrong, ZHU Xinping

2013, 26(2): 383-389. doi: 10.3969/j.issn.0258-2724.2013.02.029

[Abstract](1078)

PDF 750KB(382)

Abstract:
In order to estimate the collision risk caused by variable nominal separation when two aircraft on intersecting airways are flying around the intersection, a collision risk model around the airway intersection was proposed by introducing a variable of arrival time interval. A method was given to estimate the collision risk around the intersection where the nominal separation changes with time. The results of a case study show the number of increased collision risk is 1.14710-7 when aircraft are flying on airways with one intersection; as the angle between flight paths increases, the collision risk decreases gradually at first, and then increases slowly; for three different combinations of speeds, the minimal values of the collision risk are all achieved in the interval (70, 75) of angle between flight paths. The proposed collision risk model can be used to calculate the increased collision risk caused by airway intersections and analyze the influence of the angle between flight paths on the collision risk.

Trajectory Optimization Method for Spacecraft Orbit Transfer with Finite Thrust

WANG Changhong, QU Yaobin, LU Zhijun, AN Hao, XIA Hongwei, MA Guangcheng

2013, 26(2): 390-394. doi: 10.3969/j.issn.0258-2724.2013.02.030

[Abstract](1437)

PDF 560KB(461)

Abstract:
In order to achieve the rapid maneuver and effective fuel saving of the spacecraft with finite thrust in flight, trajectory planning based on psedospectral method was studied. Orbit transfer was modeled mathematically with Gauss dynamics equations by using improved equatorial orbital elements. The model could overcome the singularity problems when the orbital eccentricity was 0? or the orbit inclination was 0 or 90. Then, the fuel optimal performance index function, terminal constraint, and path constraint conditions were given; and the original continuous optimization problem was converted to the equivalent finite nonlinear planning problem by psedospectral method. Finally, the sparse nonlinear optimizer (SNOPT) algorithm was utilized to solve the trajectory planning problem, and the specific design steps and methods were given. Compared with the optimization method using fmincon function, the proposed method can reduce the optimization time by 61% and save the fuel consumption by 18% when the maximum thrust is 20 N.

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2013 Vol. 26, No. 2