西南交通大学学报

Stochastic Seismic Response Analysis of Large-Span Cable-Stayed Bridge Subjected to Multi-dimensional and Multi-support Excitations

ZHENG Shixiong, ZHANG Jin, JIA Hongyu, ZHANG Keyue, KANG Rui

2014, 27(5): 747-753. doi: 10.3969/j.issn.0258-2724.2014.05.001

[Abstract](1071)

Abstract:
In order to investigate the stationary random response of large-span cable-stayed bridge under seismic excitations, a large-span cable-stayed bridge was employed for numerical simulation, and a three-dimensional finite element model in ANSYS software was used to study the response of large-span cable-stayed bridge subjected to multi-dimensional and multi-support seismic excitations (MDMSSE). The spatial variations of earthquake action including traveling wave effect (TWE), coherent effect (CE), and local site effect (LSE) were taken into account to analyze their effect on displacement and internal force responses of the main beam and the main tower. Results show that the structural seismic response increased remarkably under MDMSSE in comparison with uniform excitation: the main beam longitudinal displacement increased about 2.3 times; the top longitudinal displacement and bottom traverse moment of main tower ① increased about 2.2 and 2.3 times, respectively. Therefore, only considering uniform excitation is unsafe to a large-span cable-stayed bridge. In addition, the structural response will reduce when considering TWE and CE influence, and hence can be ignored. A soft site has a great influence on structural seismic response.

Determination of Fabrication Dimensions of Steel Box Girders in Cantilever Construction

ZHAO Lei, JIA Shaomin, YANG Xingwang

2014, 27(5): 754-759. doi: 10.3969/j.issn.0258-2724.2014.05.002

[Abstract](853)

Abstract:
In order to effectively determine the fabrication dimensions of steel box girders to ensure the smooth erection of main beam and make the profile upon completion state meet design requirements, a new method to calculate fabrication dimensions was established by using the calculation results of construction phase. This method is based on the geometry control method, and commences from the unstressed relationship between a new lifting beam segment and its adjacent installed beam segment in cantilever construction. In addition, the fabrication dimensions of steel box girders of the main channel bridge of Jiashao bridge, as the research subject, were determined. The construction practice shown that the main channel bridge construction of Jiashao bridge was going well. The measured data indicated that the profile of the main beam of the bridge upon completion state was smooth, and the maximum elevation error was far less than the prescribed limit values to verify the correctness of the established method.

Vortex-Induced Vibration of Continuous Steel Box-Girder Bridge with Variable Cross-Sections at Typical Erection Stages

QIN Hao, LIAO Haili, LI Mingshui

2014, 27(5): 760-765,786. doi: 10.3969/j.issn.0258-2724.2014.05.003

[Abstract](1072)

Abstract:
In order to investigate the vortex-induced vibration performances of a long-span continuous steel box-girder bridge during erection to propose effective mitigation measures, the erection of a six-span continuous variable cross-section steel box-girder bridge was regarded as an engineering example. Its vortex-induced vibration at typical erection stages was investigated through aeroelastic model wind tunnel tests with a geometric ratio of 1 to 45, and additional damping ratio was applied to mitigate vortex-induced vibration. The mechanism of the vortex-induced vibration was discussed based on the test phenomenon. The research results show that the bridge may suffer serious vortex-induced vibration after the 2nd span is completed, and the vortex-induced vibration will exceed the specification limit. If the damping ratio is up to 1.2%, vortex-induced vibration amplitude can meet the specification requirement, and if the damping ratio is up to 2.1%, the vortex-induced vibration will be suppressed effectively.

Analytical Method for Calculating Dynamic Response of Coupled Train-Bridge System Based on Duhamel Integral

QIAO Hong, XIA He, DU Xianting

2014, 27(5): 766-771. doi: 10.3969/j.issn.0258-2724.2014.05.004

[Abstract](940)

Abstract:
In order to shorten the computation time of solving the dynamic response of a coupled train-bridge system, the modal decomposition method is used to decompose the train subsystem and bridge subsystem in the coupled system. Assuming that the vehicle-bridge interaction forces change linearly within each time step, the dynamic response of the system during this period is obtained by Duhamel integral. Based on this theory, a new method is proposed to analyze the dynamic response of the coupled train-bridge system. The proposed method is then used to analyze a 4-axle train passing through a 32 m simply-supported beam at a constant speed. The results show that the dynamic responses obtained by the proposed method for the coupled train-bridge system are very close to those obtained by the Newmark-β method, and the relative error at every extreme points is less than 1%. Compared with the Newmark-β method, the proposed method can increase the time interval of integration by at least 5-10 times while ensuring the precision.

Aerodynamic Characteristics of Tapered Tall Buildings with Square Section

ZHANG Zhengwei, QUAN Yong, GU Ming, XIONG Yong

2014, 27(5): 772-778. doi: 10.3969/j.issn.0258-2724.2014.05.005

[Abstract](988)

Abstract:
Square tall buildings with different taper ratios were tested using the high frequency force balance (HFFB) technique in two different simulated wind fields. The effects of taper ratio, turbulence intensity and wind direction on aerodynamic base moment and torque coefficients, the power spectrum densities (PSD) of along- and across-wind base moments and torques, and the correlation between base moment and torque were analyzed systematically. The test results indicate that tapering of square tall buildings can reduce the amplitudes of the aerodynamic base moment and torque coefficients by 25% or more, but can not change the law of aerodynamic wind loads varying with wind directions. The tapering measure can reduce the PSDs of along-wind base moment and torque within all the reduced frequencies, but it can only reduce the spectral peak value of the PSD of across-wind base moment in low frequency region, and increase the frequency of the vortex shedding and the PSD value in high frequency region. With the turbulence intensity increasing, the effect of the tapering measure becomes weak. The coherence between across-wind base moment and torque is increased by the tapering measure when the reduced frequency is between 0.10 and 0.15.

Fire Resistance Performance of Concrete-Filled Steel Tube RC Square Columns under Axial Loading

XIANG Kai, WANG Guohui

2014, 27(5): 779-786. doi: 10.3969/j.issn.0258-2724.2014.05.006

[Abstract](1052)

Abstract:
In order to research the fire resistance performance of concrete-filled steel tube reinforced concrete (CFSTRC) square columns under axial loading, fire resistance tests of four CFSTRC square columns subjected to axial load were conducted. The effects of axial loading level, steel tube area ratio and side length of cross section on the fire resistance performance were discussed by numerical simulations. The research results show that axial expansion deformations of CFSTRC square columns increase and their axial compression deformations decrease with minishing of axial loading level and raisings of steel tube area ratio and side length of cross section under fire exposure. Under the same elevated temperature curve and fire exposure time, a large side length of cross section will result in low temperature inside the square columns, and steel tube area ratio has a slight influence on the temperature distribution of CFSTRC square columns. Axial loading level, side length of cross section and slenderness ratio have great effects on the fire resistance performance of CFSTRC square columns under axial loading, while steel tube area ratio, reinforcement ratio and material strength have a slight influence on the fire resistance performance.

Design Method for Multi-frame Beams with Anchor Bolts Used to Stabilize High Soft-Rock Slope

XIAO Shiguo, ZHANG Tengfei, CAO Xingsong, ZHOU Depei, LIU Shixiong

2014, 27(5): 787-792. doi: 10.3969/j.issn.0258-2724.2014.05.007

[Abstract](836)

Abstract:
In order to avoid the disadvantages of the existing design methods for multi-frame beams with anchor bolts used to stabilize high soft-rock slopes, a novel design method was proposed on the basis of interaction mechanism between a structure and a slope. With the proposed method, tensile forces of anchor bolts are determined by analyzing slope stability in terms of design safety factor and failure mode of a slope, and then internal forces of frame beams are calculated from static equilibrium and deformation compatibility conditions between anchor bolts and frame beams and the Winkler foundation model used to interpret interaction between frame beams and a slope. The method was verified by a laboratory model test. The research results show that the distribution mode of slope pressure on every frame beam is a parabola in the direction of the longitudinal axis.

Model Experiment Study of Continuous Track Slab Tension Cracks

ZHAO Pingrui, YAN Jianhua, WANG Kejiang, WANG Dong, LI Wei, WANG Jiawei

2014, 27(5): 793-798. doi: 10.3969/j.issn.0258-2724.2014.05.008

[Abstract](950)

Abstract:
To investigate the thermal cracking patterns in continuous ballastless track and verify the rationality of its thermal force determination method, several reinforced concrete specimens were built to model the continuous track slab and base plate which was widely used in China's high-speed railways. Taking into account the key design factors of the continuous track slab, such as concrete grade, reinforcement ratio, rebar diameter, etc., all the specimens were designed as 450 mm long, with an 80 mm×80 mm cross section; and a ribbed rebar of 10 mm diameter was deployed at the center of the cross section. The test specimens were tensioned using the universal testing machine to simulate the development of cracks under the tensile thermal force in the process of temperature drop. The axial force of the specimens and the stress distribution in concrete and reinforcement were recorded before and after cracking. The results show that cracks in specimens during the tensile process were in two states: unstable and stable. Reinforcement and concrete stress was extremely uneven distributed after cracks appear, and reinforcement stress increased to more than 300 MPa at the crack position. The axial force of the specimen would drop suddenly when cracks occurred to the whole section, and the axial force just before and after cracking was higher than or equal to the theoretical cracking axial force of the concrete. For continuous track slab using C40 concrete, more than 0.9% reinforcement should be configured to ensure the safety of the structure. Cracks in track slab should be controlled in unstable stage. As one of the design loads of the continuous track slab, the maximum thermal force load should be calculated using the axial tensile force after cracking.

Least Squares Adjustment and Accuracy Estimation in Multiplicative Error Models

SHI Yun

2014, 27(5): 799-803. doi: 10.3969/j.issn.0258-2724.2014.05.009

[Abstract](854)

Abstract:
To probe into the parameter estimation in multiplicative error models, three least squares (LS) adjustment methods, i.e., the LS method, the weighted LS method and the bias-corrected weighted LS method, in multiplicative error models were discussed based on the existing researches and using the least squares theory. Their accuracy estimation expressions were derived, the parameter estimations and the variance-covariance matrices were obtained, and the variances of unit weight were constructed for the three LS adjustment methods. A simulated example demonstrates that the bias-corrected weighted LS method is optimal and unbiased because in the example the estimations of unit weight variance are respectively 1.964 8, 0.999 8 and 0.980 7 to the LS method, the weighted LS method and the bias-corrected weighted LS method.

Analysis of Dynamic Damage of Airport Rigid Pavement under Pickaxe Machine Breaking Load

YUAN Jie, WANG Long, LUO Yong, YAN Qikun, TAN Yue

2014, 27(5): 804-810. doi: 10.3969/j.issn.0258-2724.2014.05.010

[Abstract](1086)

Abstract:
In order to determine the technical parameters for airport rigid pavement demolition reasonably, a finite element model of rigid pavement was established using the ABAQUS software, and a half-sine impact load was imposed on the rigid pavement to analyze its dynamic responses under pickaxe machine breaking load. The dynamic responses including vertical displacement and tensile stress were calculated by systematically considering load parameters and pavement structure parameters. The simulation results show that the magnitude and position of load have a significant influence on the dynamic responses of rigid pavement. The thickness of slab has a great influence on the tensile stress and little effect on the vertical displacement. Under the example condition, the dynamic responses become prominent only when joint load transfer capacity is below 80%. The location of impact load should not be within 30 cm away from the edge of slab so as to mitigate the dynamic damage of reserved slab.

Travel Time Computation and Optimal Path Selection Algorithm of Urban Expressway Network

YAN Maode, CHANG Nannan, ZHANG Changli

2014, 27(5): 811-816. doi: 10.3969/j.issn.0258-2724.2014.05.011

[Abstract](1030)

Abstract:
In order to improve the overall functionalities and utilities of urban expressway network, a travel time computation and optimal path selection algorithm was proposed for urban expressway network by utilizing the dynamic traffic data acquired along expressway segments in real time. According to the influential patterns of dynamic traffic factors on travel time, this algorithm classifies the urban expressway network into non-jammed and jammed segments, and computes their travel time using safe stop distance and residual traffic capacity, respectively. The minimum overall travel time is taken as optimization criteria for optimal path selection of urban expressway network. As a case study, this algorithm was applied to Xi'an urban expressway network. The analysis results show that the optimal paths selected are in good agreement with the practical cases. The coincidence rate error is kept within 15%, and the distance of optimal path is about 1.84 times that of the shortest path.

Driver's Trajectory Tracking Model in Curves of Two-Lane Highway

WANG Wanqiu, QIAN Yubin, LIN Yu

2014, 27(5): 817-823. doi: 10.3969/j.issn.0258-2724.2014.05.012

[Abstract](837)

Abstract:
Considering the complexity of horizontal alignment in curves, and the uncertainty of steering behavior resulting from drivers' fuzzy perception and subjective tendency, the control factors of steering behavior were introduced by analyzing drivers' driving characteristics which are influenced by road alignments ahead. The multi-objective fuzzy optimization decision theory was used to study the influence of fuzziness and subjectivity on steering behavior. Then a mathematical method for modeling driver's trajectory tracking behavior was established using the weight determination method that is based on the gray theory and combines subjectivity with objectivity together. In addition, field experiments in five curves were carried out, and the modeling method was verified to be feasible by comparison of experimental and simulation values in trajectory curves. The results show that the length of trajectory, lateral force coefficient, trajectory's lateral offset are control factors of trajectory tracking behavior; and driver's subjective characteristics in fuzzy optimal decision making trajectory tracking behavior can be reflected by the weight determination method combing subjectivity and objectivity.

Method for Analyzing Characteristics of Travel Behavior Based on Minimum Determinant of Asymptotic Variance-Covariance

REN Ting, CHEN Lin, YANG Fei, YAN Qipeng

2014, 27(5): 824-830. doi: 10.3969/j.issn.0258-2724.2014.05.013

[Abstract](893)

Abstract:
In order to overcome the low precision of the model estimation results in the existing stated preference (SP) experimental designs, a new experimental design method for SP survey was proposed. This method aims to minimize the determinant of asymptotic variance-covariance (AVC) matrix to compute iteratively the alternative attribute level combinations and then obtain the corresponding alternative attribute level combinations. A new metro connecting a city and its satellite cities was taken as the research case. Comparisons between the new design and the orthogonal design are made about the precision of model results by the goodness of fit and standard deviation of parameter estimations. The results indicate that based on the new design, the standard deviation of parameter estimations is less and the goodness of fit is 0.145, which is improved about 0.05 compared to the orthogonal design. In addition, the new design improves the precision of Logit model parameter estimation and has the advantage of the flexibility in choosing the number of combinations.

Simulation Method for Couplers and Buffers in Train Collision Calculations

XIAO Shoune, ZHANG Zhixin, YANG Guangwu, ZHU Tao

2014, 27(5): 831-836. doi: 10.3969/j.issn.0258-2724.2014.05.014

[Abstract](999)

Abstract:
In order to study the behaviors of couplers and buffers (CABs) accurately in the process of train collision, a new simulation method for analyzing the characteristics of CABs was proposed based on the discrete beam in LS-DYNA. This method was then verified through a case study where a head to head collision between two identical subway trains marshaled by 6 cars occurred under a scenario with a relative speed of 36 km/h. The CABs' loading and unloading conditions, as well as their failure and falling-off behaviors under the ultimate load were simulated, and the contribution of CABs in the total energy absorption of the train collision was analyzed. The results show that the proposed method can simulate effectively the mechanical properties of CABs and couplers' failure and falling-off behaviors in the train collision. In addition, it can be used to obtain the indexes such as output characteristics and energy absorption of CABs in different positions. During the train collision, the energy adsorbed by the CABs accounts for 27% of the total energy.

Reliability Optimization Design of Vehicle Variable Stiffness Spring Assembly by Fuzzy Theory

WANG Hong, TANG Jinsong, LIU Wanxuan

2014, 27(5): 837-841. doi: 10.3969/j.issn.0258-2724.2014.05.015

[Abstract](891)

Abstract:
In order to improve the design quality of spring assembly, a fuzzy reliability optimization design model of variable stiffness spring assembly was established using the fuzzy and the reliability design theory based on traditional optimization design method. In this model, the spring stress and strength were used as a random variable and a fuzzy variable, respectively; and the static strength, fatigue strength, stability, and quality factors were synthetically considered. In addition, taking a new type of variable stiffness spring assembly of a freight car as the object, an optimization analysis was carried out by used of the proposed model. The calculation results show that compared with the original design program, the model increases the static deflection of vehicle in empty and heavy load 5.4 and 3.2 mm, respectively; and in the mean time decreases the total quality of the spring assembly by about 15.8%. Therefore, the fuzzy reliability optimization design model can meet the design requirements.

Small Fault Detection and Classification Method for Complex Production Process

ZHANG Min, CHENG Wenming, LIU Juan

2014, 27(5): 842-847. doi: 10.3969/j.issn.0258-2724.2014.05.016

[Abstract](789)

Abstract:
In order to monitor the condition of a complex production process, based on the multivariate statistical process control and support vector machine theory, the cumulative control chart principle was extended to multivariate form for data preprocessing, and the principal component analysis (PCA) was utilized to extract significant information from the complex production process. The effective data of small fault was obtained. Then, the statistical threshold values of normal data, statistic T2, and squared prediction error (SPE) of corresponding fault data were constructed to realize the small fault detection of the complex production process, and the support vector machine (SVM) multi-classification method was used to classify the detected fault modes. The simulation results of a hot mix asphalt production process show that in cases of small fluctuation, cyclical rise and fall respectively, the small fault detection recognition rate is about 95%, with an average improvement of 75% over the PCA method; the classification accuracy rate reaches 92.5%, improved 19.3% compared with the BP neural networks method.

Microstructure and Fatigue Performance of Electron Beam Welded Joints of AZ31B Magnesium Alloy

WANG Wenxian, MA Zhengzheng, ZUO Congjin, XU Haiying, FU Pengfei, CUI Zeqin, YAN Zhifeng

2014, 27(5): 848-854. doi: 10.3969/j.issn.0258-2724.2014.05.017

[Abstract](774)

Abstract:
In order to improve the microstructure and mechanical properties of magnesium alloy welded joints, a 10 mm thick AZ31B magnesium alloy plate was welded by the electron beam welding (EBW). The microstructure, element distribution, and phase composition of the EBW joints were then analyzed, and their static tensile properties and fatigue performance were measured. The results show that the microstructure and mechanical properties of the EBW butt joints all get improved. The crystal grains of the welding seam of are refined obviously. The mass fraction of Mg and Zn elements in the weld zone is decreased by 0.12% and 0.28%, respectively; while that of Al and Mn elements is increased by 0.24% and 0.14%, respectively. The fusion zone consists of single-phase α-Mg, and contains no obvious Mg17Al12 phase which has a low melting point and causes brittleness. The tensile strength of the EBW joints is 242 MPa, reaching the tensile strength of the base metals. Under 2×106 cycles and R=0.1, the fatigue strength of the EBW joints is 91 MPa, nearly 78.4% of the fatigue strength of the base metal.

Simulation of Interactions between Pores and Cracks inside Fusion Welded Aluminum Alloys

WU Shengchuan, YU Cheng, ZHANG Weihua, XUE Biyi

2014, 27(5): 855-861. doi: 10.3969/j.issn.0258-2724.2014.05.018

[Abstract](888)

Abstract:
In order to investigate the influence of interactions between cracks and pores within fusion welded aluminum alloys on the performance of the joints, polygonal elements each embedded with a single elliptical hole or multi cracks were constructed based on the hybrid polygonal element (HPE). Then, a plane stress model was formulated for a fusion welded aluminum alloy joint, which consisted of both a main crack and arbitrarily distributed pores, and the influences of the distribution of these pores on the cracks initiated from the weld root were studied. The result shows that errors between the HPE method solutions and the theoretical ones can be limited to the level of 0.5%, even if sparse meshes are used. Smaller-sized pores in the bottom of the welding joint can increase the stress intensity factor (SIF)Ⅰand SIFⅡby 2.15% and 324%, respectively, showing a significant enhancement effect on the stress field of the crack tip; what's more, the smaller the distance between pores and cracks, the greater the coupling effect.

Metallurgical Structure and Mechanical Properties Test of Weld-Joint of Industrial Pure Zirconium

HU Xiaodong, JIANG Di, LI Yajiang

2014, 27(5): 862-868. doi: 10.3969/j.issn.0258-2724.2014.05.019

[Abstract](878)

Abstract:
The element distribution, metallurgical structure and mechanical properties in different parts as base-zone, heat-treatment zone, and welded seam in butt-jointed seam of industrial pure zirconium R60702 welded with TIG was analyzed using optical microscope, electron probe and micro-hardness tester to study the relationship of microstructure and mechanical properties. The results show that different zones of the butt-jointed seam have different metallurgical structures: the crystalline grains in the base metal are equiaxed and surface textured; smaller and equiaxed grains in incomplete recrystallization zone create better mechanical properties in strength and plasticity; coarse grains are found in over-heated zone; and the casting organization with fibre structure is obtained in welded seam zone. The elements distribute uniformly in the butt-welded seam without obvious segregation. The hardness distribution in the butt-jointed seam between the base metal to the welded seam zone is depicted as W-shape: the maximum micro-hardness reaches 290 HV50 g at the position of welded seam, the minimum harness is located in the overheated zone with a value of 162 HV50 g, and the hardness of over-heated zone fall in between.

Analysis of Temperature Field of Resin Matrix Composite Patches during Curing Process

CHEN Shuxian, WANG Yuantao, YANG Wenfeng, LI Meng, QIN Wenfeng, TANG Qingru

2014, 27(5): 869-874. doi: 10.3969/j.issn.0258-2724.2014.05.020

[Abstract](966)

Abstract:
In order to optimize the curing parameter of resin matrix composite patches, a physical model and a mathematical model for composite laminate patches during thermal curing process were established by finite element method. Based on these models, numerical simulations were made to study the variation rules of temperature and curing degree during the curing process of the composite prepreg patches. The internal temperature distributions in prepreg repair patches were analyzed for different curing stages, and the curing processes at different points inside the patches were compared. The influences of heating rate, the patch thickness, and patch shape on the temperature and curing degree during curing process were also studied. The simulation results show that a faster heating rate can shorten the time for completing the curing process, and result in a higher temperature gradient within the patch; a more thick patch needs a shorter curing time and has a lower internal temperature gradient; and, the effect of the patch shape on the temperature and curing degree can be ignored for the non-penetrating repair.

Vector Control of Seven-Phase Induction Motor with Harmonic Currents Elimination

GUO Jiling, XIAO Jian, QIU Zhongcai, LUO Peng

2014, 27(5): 875-881. doi: 10.3969/j.issn.0258-2724.2014.05.021

[Abstract](824)

Abstract:
In order to control the flux and torque and eliminate harmonic status currents of seven-phase induction motors simultaneously, three methods were proposed according to the principle of reducing the harmonic subspace composite voltage vectors in the space decomposition model. These methods included the space vector pulse width module (SVPWM) A where the composite voltage vector of the 3rd harmonic subspace is zero, the SVPWM B where the composite voltage vector of the 3rd or the 5th harmonic subspace is zero, and the unified voltage module (UVM) C that adopts a closed-loop motor control strategy. Speed-regulating experiments were then performed to verify the efficiency of the three methods in control of the flux and torque. The results show that the performance on harmonic currents elimination using SVPWM A or SVPWM B is not satisfying, since only the action time and sequence of voltage vectors are adjusted while the modulation depth and motor speed are changing continuously. However, a closed loop control of motor is realized under the constraint that harmonic space voltage is zero; therefore, the harmonic currents were eliminated remarkably using UVM C. Compared with the fundamental content (52.5 dB), the 3rd and 5th harmonic contents are very small, only 17.8 and 9.8 dB, respectively.

A Novel Method for Fast Smoothing Transition of Arterial Coordination Control Plans

GUO Haifeng, PENG Qitao, CHENG Jun, ZHANG Jue

2014, 27(5): 882-887. doi: 10.3969/j.issn.0258-2724.2014.05.022

[Abstract](815)

Abstract:
In order to eliminate disturbances caused by traffic signal transition and ensure smooth traffic flow in dynamic coordination control system, in view of transition time and smoothing characteristics, a fast smoothing transition method was proposed based on the optimization of offset adjustment. This method intends to minimize offset difference for each intersection, calculates the optimal offset adjustments, and further computes signal interval during the transition of coordination control plans. The simulation analysis shows that when the amount of offset adjustment is 40 s, the proposed method, in contrast to Add and Subtract methods, can decrease average vehicle delay by 23% and 11%, and average number of stops by 9% and 8%. Furthermore, the proposed method can ensure transition time no more than 3 signal intervals, and its control performance is better than those of Add and Subtract methods.

3D Pavement Crack Image Detection Based on Anisotropy Measure

PENG Bo, WANG Kelvin C.P., CHEN Cheng, JIANG Yangsheng

2014, 27(5): 888-895. doi: 10.3969/j.issn.0258-2724.2014.05.023

[Abstract](1023)

Abstract:
In order to detect cracks precisely and completely, a novel automatic cracking detection algorithm based on 1 mm/pixel 3D pavement images was proposed with three core parts: anisotropy measure calculation and self-adaptive threshold optimization, depth verification and multi-resolution denoising processing. First of all, considering pixel features of a pavement image, anisotropy measure was calculated for each pixel based on mean values and standard errors of four linear neighborhoods at 0 degrees, 45 degrees, 90 degrees and 135 degrees to represent significance of orientation, and an optimal anisotropy threshold was determined by the OTSU method to segment the pavement image into two parts, that is, strong orientation and weak orientation pixels. Then, a depth threshold was set based on mean depth value in a square neighborhood with a radius of d, thus a potential crack image was formed by pixels with strong orientation and depth not bigger than the depth threshold. At last, the crack image was divided into several blocks and denoised by a moving window denoising method based on newly designed templates, from which final crack image was obtained. Algorithm tests were conducted based on 166 three dimensions pavement images(2 048×2 048) with various types of cracks. The result shows that the proposed algorithm achieves relatively high precision (averaging 91.57%) and recall (averaging 81.29%), leading to an mean F1 score of 84.26%, thus outperforming seeds based approach(mean F1 score: 69.19%), Canny edge detection(mean F1 score: 8.15%) and OTSU segmentation(mean F1 score: 5.11%).

Analysis of Conflict Characteristic between Early Right-Turning Vehicles and Pedestrians at Signalized Intersections

CHEN Yongheng, ZHANG Hu, QU Zhaowei, CAO Ningbo

2014, 27(5): 896-903. doi: 10.3969/j.issn.0258-2724.2014.05.024

[Abstract](1142)

Abstract:
Vehicles turning right early at signalized intersection was prone to be blocked by the vehicles that go straight when they travel in a mixed lane shared by both right-turning and straight-going vehicles and are not directed by a signal. Based on traffic flow characteristics in the mixed lane and the effect of signal control on the upstream of pedestrian flow, the blocking time of right-turn vehicles was considered to analyze the conflict process between vehicles and bidirectional pedestrian flow. The vehicles and pedestrians crossing time were calculated, and the delay model of right-turn vehicles and pedestrians was established. The case study shows that the relative error between the calculated results and the real data is less than 20%; and when the vehicle volume is less than 350 pcu/h, vehicles have little impact on pedestrian crossing, and when the vehicle volume is more than 350 pcu/h, the conflict between pedestrians and vehicles was obvious.

Intelligent Monitoring Technologies for Railway Signaling Systems in China

LIU Dawei, GUO Jin, WANG Xiaomin, CHEN Jianyi, YANG Yang

2014, 27(5): 904-912. doi: 10.3969/j.issn.0258-2724.2014.05.025

[Abstract](1823)

Abstract:
The state of the art in the monitoring technologies for railway signaling systems in China was introduced. By analyzing the drawbacks of these technologies in interconnection, data sharing, intelligent analysis and prediction, as well as their development trend and maintenance requirement, a scheme of an integrated intelligent monitoring and maintenance system for railway signaling systems was presented. The system structure, functionality and key technologies involved such as shared data selection, data integration mechanism, intelligent analysis and interface specifications were also elaborated, which provide the feasible alternatives for the condition-based maintenance of signaling equipments. Moreover, the layered implementation principle based on current monitoring situation, and the security isolation between the monitoring system and signaling systems were discussed.

Fast Method for 2D Threshold Segmentation Algorithm Based on Inter-class and Intra-class Variances

LIU Jin, JIN Weidong

2014, 27(5): 913-919. doi: 10.3969/j.issn.0258-2724.2014.05.026

[Abstract](1048)

Abstract:
In order to shorten the running time of 2D threshold segmentation algorithm, a fast implementation of 2D Otsu was developed. First, a two-dimensional optimal threshold (s*,t*) was split into two one-dimensional optimal thresholds, s* and t*. The intra-class variance was defined to propose a new optimal discriminant D(s*,t*). Then the original 2D histogram was divided into M×M regions, and each region was combined as a point to form a new 2D histogram. Based on this new 2D histogram, the discriminant D(s*,t*) was solved to determine the region that corresponds to the optimal threshold, and last the optimal threshold was calculated using D(s*,t*). The theoretical analysis and experimental results of some images with different signal-to-noise ratios (SNRs) show that the segmentation error rate of the proposed algorithm is lower than the original two-dimensional Otsu method. The time complexity of the proposed method is reduced from O(L4) to O(L1/2), and space complexity is reduced from S(L2) to S(2L).

Novel PV/Li-Ion Energy Storage System Based on Non-balancing Cell Management

PENG Fei, LIU Zhixiang, CHEN Weirong

2014, 27(5): 920-927. doi: 10.3969/j.issn.0258-2724.2014.05.027

[Abstract](814)

Abstract:
A novel topology of an energy storage system composed of PV panels and lithium-ion batteries was presented. For the individual module of the proposed system, the energy coupling between the photovoltaic panel and lithium-ion cell is achieved with the designed control unit. Besides, with the structural coupling of the photovoltaic panel and lithium-ion cell of the PV/Li-ion module, the non-balancing cell management (NBCM) for the lithium-ion cell is realized. The proposed system was verified by simulation and experiments. It is shown that, in the proposed PV/Li-ion module, with the low-voltage floating charging criteria, the approximate MPPT (maximum power point tracking) control was accomplished with the charge-discharge of the lithium-ion cell. In comparison with the schottky diode connection, the operation efficiency of the PV/Li-ion module is increased by about 8% when there is a nearly direct connection between the lithium-ion cell and the 30 W PV panel with nearly no intervening electronics (just MOSFETs, metallic oxide semiconductor field effect transistor). The novel topology of the NBCM PV/Li-ion system can be applied both in stand-alone photovoltaic-battery systems and in grid-connected photovoltaic power plants.

Effect Mechanism of Multi-scenarios Terminal Capacity Based on Flow Decomposition Barrier

LI Yinfeng, HU Minghua, PENG Ying, WANG Hongwei

2014, 27(5): 928-934. doi: 10.3969/j.issn.0258-2724.2014.05.028

[Abstract](846)

Abstract:
In order to investigate the influence factors and variation trends of terminal capacity, a capacity network model for terminal area was built using the flow decomposition barrier theory according to the terminal area characteristics, in which the length of routes, flight speed, control separation, and other factors were considered. Taking Hangzhou terminal area as an example, multi-scenarios were built about location of bad weather, dual-runway operation pattern, etc., and the effect mechanism and relationship of different influence factors on the terminal capacity was investigated. The results indicate that terminal capacity has a uneven step-like decline due to bad weather, and the descent gradient is closely related to the route substitutability. When the bad weather affect the single route of AND direction, the capacity decreases 10-20 vehicles per hour; the dual-runway capacity differs significantly with different operating patterns, and the capacity ranges from 33 to 108 vehicles per hour.

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2014 Vol. 27, No. 5