西南交通大学学报

New Method for Infrared Dim Target Detection Based on Wavelet and SVR

RONG Jian, SHEN Jine, ZHONG Xiaochun

2008, 21(5): 555-560.

[Abstract](1461)

Abstract:
By analyzing dim target and background characteristics from infrared images,a new detection method based on the wavelet transform and the support vector regression adaptive filter(WTSVRAF) was presented.With this method,the wavelet transform is used to inhibit the majority of background clutter.Then the SVR-based adaptive filter(SVRBAF) is adopted to treat high-frequency wavelet coefficients.As a result,the image signal-to-noise ratio(SNR) is greatly improved.Furthermore,based on the continuity of the target and the coherence of trajectory,the image sequence processing method is utilized to further improve the detection performance.The simulation results show that the detection method can significantly increase the probability of infrared target detection to achieve long-range target detection.

Successive Interference Cancellation Algorithm Based on Gram-Schmidt Orthogonalization Algorithm

ZHANG Donghong, LIAO Guisheng

2008, 21(5): 561-565.

[Abstract](1545)

Abstract:
A new SIC(successive interference cancellation) algorithm based on the Gram-Schmidt orthogonalization algorithm was presented.Unlike the conventional SIC algorithm,this algorithm uses an optimal despreading sequence,locally generated by the Gram-Schmidt orthogonalization of spreading sequences,to demodulate a received signal in each stage.The despreading code of the strongest user in each stage is orthogonal to the subspace spanned by the spreading code of other users,so that the multiple access interference(MAI) is fully suppressed.An approximate bit error rate(BER) formula with the amplitude mismatch was proposed,and the effect of the amplitude mismatch on the BER performance of CDMA systems was discussed.Simulations show that the new algorithm can effectively cancel MAI and improve the BER performance.

SVPWM Control of Three Level Inverter for Traction Drive in EMUs

GE Xinglai, FENG Xiaoyun

2008, 21(5): 566-572.

[Abstract](1486)

Abstract:
Space vector pulse-width modulation(SVPWM) control strategies were proposed for three level inverters of traction drives in high-speed EMUs(electrical multiple units).A constant-maximum-switching-frequency asynchronous modulation control strategy is applied during starting and low-speed periods of the EMU’s motor because low torque ripples are required during these periods.At high-speed,because low-switching-frequency and low-harmonic component are required,a variable-switching-frequency synchronous modulation control strategy is used with a 4-pulse modulation at mid-high speed and a 2-pulse modulation at top-high speed respectively.The effectiveness of the proposed strategies were verified by comparing the simulation voltage waveforms with the measured data of the EMU’s motor.

Transient Stability Assessment Based on Random Forest Algorithm

YE Shengyong, WANG Xiaoru, LIU Zhigang, QIAN Qingquan

2008, 21(5): 573-577.

[Abstract](1804)

Abstract:
A model for the power system transient stability assessment based on random forest algorithm was presented.This model combines decision trees which depend on the values of a random vector sampled independently and with the same distribution.Simulation results on the IEEE 16-generator and IEEE 50-generator test systems show the validity of the proposed method.Its assessment performance is better than decision tree,artificial neural networks,support vector machine and K nearest neighbor.

Theoretical Analysis of Autocorrelation Function of Image as Sharpness Evaluation Function

SONG Kang, ZHANG Tao, LIAO Junbi

2008, 21(5): 578-581,659.

[Abstract](1725)

Abstract:
The effectiveness and feasibility to take an autocorrelation function as the evaluation function of images were proved theoretically according to the Wiener-Khintchine theorem.The autocorrelation function of an image has the same physical meaning with grey variation,grade and grey entropy functions.The proportion of high frequency components of an image is correlated with the sharpness of the autocorrelation curve by an image sharpness index that indicates sharpness of the image.An experiment verifies that the image sharpness index is positively proportional to the width of the autocorrelation curve.

Variable Precision Fuzzy Rough Model for Data Analysis

FENG Lin, WANG Guoyin

2008, 21(5): 582-587.

[Abstract](1544)

Abstract:
A variable precision fuzzy rough data model(VPFRDM) that is an extension of Ziarko’s variable precision rough set(VPRS) model was proposed based on fuzzy set.A method for attribute reduction from a fuzzy decision information system was developed,in which the attribute importance is taken as the heuristic information.Fuzzy knowledge is extracted through calculating classification ability of each fuzzy pattern class to the decision categories.Simulation results show that the VPFRDM is effective and has better data generalization ability compared with Ziarko’s VPRS.

Propagation Characteristics of Metal Circular Waveguide Filled with Multilayer Reciprocal Chiral Media

XIONG Tianxin, YANG Rugui

2008, 21(5): 588-594.

[Abstract](1341)

Abstract:
With the method of separation of variables,the general mode eigenequation of the metal circular waveguide filled with multilayer reciprocal chiral media was given.From the general eigenequation,the mode eigenequation of metal circular waveguide filled with an ordinary medium can be obtained.To reveal the propagation characteristics,numerical results for some modes in the metal circular waveguide filled with one or two layers of reciprocal chiral media were presented.The research results show that the main factor influencing the propagation characteristics is the refractive index of the reciprocal chiral media filled in it.When the permeability of the reciprocal chiral media filled in it is changed but the refractive index,chiral parameters and the ratio of the outer radii of the first and the second layers are given,the normalized cut-off frequency will obviously change.When the parameters of the reciprocal chiral media filled in it are given but the ratio of the outer radii of the two layers is changed,the normalized cut-off frequency of low-order modes changes slightly.Therefore,changing the ratio of the outer radii of the two layers is not a good approach to change the normalized cut-off frequency of low-order modes and normalized bandwidth of the metal circular waveguide.

Analyzing Method for Vehicle Collision Based on Dent Superposition

ZHANG Jian, ZHANG Xin

2008, 21(5): 595-599.

[Abstract](1758)

Abstract:
The traditional method is not applicable to analyzing some vehicle collision accidents without the definite colliding positions.To solve this problem,a dent superposition method was proposed,in which the dents on involved vehicles are superposed to represent their meshing state at the colliding moment based on basic site investigation information such as dents on the vehicles and their stop positions.The trajectories of vehicle centroids are inferred from their stop positions,and the colliding position is determined by the optimization theory.The analysis result of a vehicle collision case shows that the error in calculated speed is less than 2% obtained by the proposed method compared with that obtained by the two-dimensional collision theory.

Grey Analysis of Airport Apron Safety

LIU Gang, ZHU Jinfu

2008, 21(5): 600-604.

[Abstract](1577)

Abstract:
A weighting method combining subjective and objective weighting,the former being G1 method and the latter being mean-square error method,was proposed to determine weights of indices of airport apron safety.A grey evaluation model for airport apron safety was presented using grey analysis and analytic hierarchy process.In the model,there is a two-level evaluation index system,with the first level indices being the safety of apron facilities,airport public security,management of apron operation personnel,management of vehicles in the apron,field management and coordinating ability,and other safety factors.An example shows that the proposed method can take full use of available information about the evaluation indices to evaluate the airport apron safety.

Combined Evolution of Self-organization and Hetero-organization of Urban Traffic System

JIANG Kejin, ZHANG Dianye, LIU Fanxiao

2008, 21(5): 605-609.

[Abstract](1699)

Abstract:
The evolution of an urban traffic system is a combined processes of self-organization and hetero-organization,and the non-linear effects(cooperation and competition) between the subsystems are the essential driving forces for the evolution of the urban traffic system.A combined evolution model for self-organization and hetero-organization of urban traffic systems was proposed,in which the capacity of road network and traffic volumes were taken as parameters.Simulation results show that different control degrees cause different evolution results: private car,public transportation and mixed traffic structures,and different development speeds of traffic demand and supply result in different development models of traffic supplies: following,guiding and over-demand models.

Simulation of Rain and Snow in Visual Simulation of Train Operation

HE Hongyun, SU Hu

2008, 21(5): 610-615.

[Abstract](1646)

Abstract:
A simulation method for rain and snow in visual simulation of train operation was proposed.A real-time rain and snow particle system was designed based on the physical model of raining and snowing.The implement of the particle system was discussed,including the definition of particles,control of particle lifecycles,and so on.In the system,a visual area is defined to simulate the obstructing effect on the rain and snow particles by a tunnel or a railway station.Particle positions are calculated by a simplified dynamic model,and the billboard technique is employed to render particles.Application of the proposed method shows that the rain and snow particle system performs well for real-time rendering of complicated raining and snowing in visual simulation of train operation.

Local Stability of Balancing Speed of Train under Condition of Air Brake

L? Hongxia, LIAO Yong

2008, 21(5): 616-620.

[Abstract](1569)

Abstract:
In order to probe into the stability of train’s balancing speed under the condition of air brake,the relationship between its balancing speed and the monotonicity of the function of train unit resultant force was investigated.When the function of train unit resultant force is monotonously decreasing,the balancing speed is stable,otherwise it is instable.Therefore,under the condition of air brake the function of train unit resultant force is monotonously decreasing in some speed range,and the balancing speed is stable locally.The speed range in which the balancing speed is stable was calculated by using the dichotomy.To an empty freight train with an initial brake speed of 100 km/h equal to its limit running speed,drawn by an SS4 locomotive with medium phosphor cast iron brake shoes,its critical speed is 53.5 km/h.So when its running speed is between 53.5 and 100 km/h,the balancing speed is stable under the condition of air brake.

Influence of Shape Misalignment of Wheelsets on Stability of Vehicle System

CHI Maoru, ZHANG Weihua, JIN Xuesong, ZHU Minhao

2008, 21(5): 621-625.

[Abstract](1693)

Abstract:
A dynamics model for a vehicle with the shape misalignment of wheelsets was set up,and the influence of the shape misalignment on the critical vehicle speed was analyzed by a numerical simulation.The simulation result shows that the stability of vehicle systems can be parted into easy-stable region,sub-stable region and defective-stable region in light of the value of wheelsets’ misalignment angle.In the easy-stable region,a vehicle system has better stability and wheelsets have few abrasion.In the defective-stable region,the system has worse stability and wheel treads have heavy abrasion.In the sub-stable region,the system has better stability but wheel flanges have heavy abrasion.Therefore,in order to improve the stability of a vehicle system and decrease the abrasion of wheelsets,the shape misalignment of wheelsets should be decreased as possibly as,so that the vehicle can run frequently in the easy-stable region.

Optimization of Comprehensive Performance of Planar Redundant Parallel Manipulator

LIU Xin, QIU Yuanying, SHENG Ying, LI Junhua

2008, 21(5): 626-632.

[Abstract](1676)

Abstract:
The optimization of comprehensive performance of a planar 2-DOF(degree-of-freedom) redundant parallel manipulator was investigated.Based on the kinematics model of the manipulator,its Jacobian matrix and optimal topologies were given.The influences of structural parameters of the manipulator on its workspace and singularity were discussed.A comprehensive performance criterion was proposed to evaluate kinematics accuracy,force transmissibility,structural stiffness and workspace utilization rate.An optimization model with the proposed criterion as the objective function and task-space and nonsingular configuration as the constrains was constructed,and an adaptive genetic algorithm was utilized to obtain the optimal solution.The research provides a reference for the optimal design of similar manipulators.

Formation and Strengthening Mechanisms of Plasma Sprayed Nanostructured WC-Co Coating

CHEN Hui, GOU Guoqing, LIU Yan, TU Mingjing

2008, 21(5): 633-637.

[Abstract](1327)

Abstract:
Nanostructured and conventional WC-Co coatings were prepared by plasma spray to investigate the formation and strengthening mechanisms of the nanostructured coatings.The results indicate that typical nanostructures exist in the nanostructured coating.The sub-particles of 2-5 nm in size dispersing in the WC grains act as crystallization nuclei,which is beneficial to the formation of nanostructured coating.The hardness,elastic module,fracture toughness and bonding strength of the nanostructured coatings are higher than those of the conventional coatings,with the grain-refining being the main strengthening mechanism.

Dynamic Tensile Properties of High Strength Fiber Bundles

WANG Tinghui, SONG Shuncheng, WANG Mingchao, SUN Zhijie, ZHANG Zuoguang

2008, 21(5): 638-642.

[Abstract](1344)

Abstract:
The dynamic tensile properties of 5 types of high strength fiber bundles(PBO,UHMWPE,Kevlar,Glass fiber S-2,and Basalt) were measured using a dynamic tensile test device and a combination clamp with thin-walled bars.The comparison between the dynamic tensile and the static properties shows obvious strain rate effects.The dynamic tensile strengths of all the fiber bundles are higher than those of the static ones,and the dynamic tensile fracture strains of all the fiber bundles except UHMWPE are also larger than those of the static ones.There is no an identical strain rate effect on dynamic failure strains for the 5 types of fiber bundles.

Integrated Framework of Collaborative Commercial Platform for Manufacturing Industrial Chain

WANG Shuying

2008, 21(5): 643-647.

[Abstract](1476)

Abstract:
An integrated framework of collaborative commercial platform for manufacturing industrial chains was proposed based on an analysis on the collaborative characteristic of enterprises in manufacturing industrial chains.A software bus was designed based on common basic components following aspect oriented ideology to support dynamic registration,authorization,and maintenance.The proposed platform realizes loosely-coupled integration of different business subsystems in a collaborative commercial system,and it can adjust cooperative partners and change service functions on demand in a dynamic business environment.

Model Test of Corbel Cracking and Reinforcement of Urban Overpass

PU Qianhui, GOU Hongye, ZHANG Junhua

2008, 21(5): 648-653.

[Abstract](1664)

Abstract:
In order to ensure the safe operation of urban overpasses,model tests of corbel cracking and reinforcement of the main bridge and ramp bridge of Niulong road overpass in Chengdu City were carried out respectively.By controlling the region,shape and size of cracks,corbel cracking of the overpass was simulated,and the factors to cause corbel cracking were analyzed.In addition,a comparative analysis of stresses in the corbel before and after strengthening prestressed reinforcement was made.Stresses under the anchorage of prestressed reinforcement were analyzed to investigate the effect of the reinforcement measure.The research shows that the reasons of corbel cracking are the great loss of prestress,the effect of loaded vehicles and the eccentric loading of vehicles,and the strengthening prestressed reinforcement measure is feasible.

Topology Optimization of Structure Based on Modified Balanjin Theory

ZHANG Jinfang, ZHAO Renda, XIANG Tianyu

2008, 21(5): 654-659.

[Abstract](1737)

Abstract:
In order to seek a new structural optimization method with engineering practicability,the evolutionary structural optimization(ESO) was applied to the topology optimization of structures based on a stress level.Through modifying the Balanjin theory,the stress level of elements was measured by the ratio of ultimate uniaxial tension to compression stresses and the principal stresses of elements.As a result,an evolutionary structural optimization method based on the modified Balanjin theory was proposed.The numerical results show that the proposed method can be used for the topology optimization of 2-D and 3-D structures effectively.

Fatigue Load for Semi-rigid Connection of Rail Floor Beam of Long-Span Steel Truss Arch Bridges

WEI Xing, LI Jun, QIANG Shizhong, LIU Dejun

2008, 21(5): 660-665.

[Abstract](1600)

Abstract:
In order to estimate the fatigue damage accumulation of semi-rigid connection between the rail floor beam and truss of a steel truss arch bridge bearing light rail transit and highway vehicle loads,fatigue load spectrum,produced due to traffic loads in the designed service life of the bridge,for the semi-rigid connection was investigated.Based on the analysis of traffic loads and the AASHTO specification,a fatigue load model to reflect the actual running state of the bridge during the designed service life was established.A 3-D finite element analysis was made to simulate the load history for the semi-rigid connection.Based on the fatigue damage accumulation theory,fatigue test load for the semi-rigid connection was determined.

Analysis of Factors Influencing Longitudinal Force of Welded Turnout on Simply Supported Beam Bridge

YANG Rongshan, LIU Xueyi, WANG Ping

2008, 21(5): 666-672.

[Abstract](1565)

Abstract:
Based on the characteristic of longitudinal interaction of welded turnout on a bridge,a finite element model for welded turnout-bridge-platform was established.By taking No.18 welded turnout on a simply supported beam bridge as an example,factors influencing its longitudinal force and displacement were analyzed.These factors are the temperature of rail,the temperature of bridge,the length of beam,the layout of support,the stiffness of pier,the structure of frog heel,and the resistance of fastening and ballast.Calculational results show that the influence range of welded turnout on a simply supported beam bridge was within two spans.The arrangement of welded turnout on simply supported beam bridges should make the expansion displacement directions of the turnout lead rail and the beam be opposite.The longitudinal stiffness of piers under welded turnout should be increased,and spacer block should not be adopted as the frog heel of welded turnout on a simply supported beam bridge.The No.18 welded turnout is suitable for laying on a simply supported beam bridge with a span of 32 or 48 m.

Sensitivity Analysis of Geoelectric Parameters in Transient Electromagnetic Method for Tunnels

TAN Daiming, QI Taiyue

2008, 21(5): 679-684.

[Abstract](1845)

Abstract:
In order to investigate the characteristics of a transient electromagnetic field in tunnels using the transient electromagnetic method for advanced detection,the propagation characteristics of transient electromagnetic fields in an underground whole-space and in a layered half-space were respectively simulated using the ANSYS software.The sensitivity characteristics of transient electromagnetic fields were investigated by changing the depth,radius,resistivity of an anomalous body and the resistivity of surrounding rock,and the eigenfunctions of response curves for the field were obtained by fitting the data of time response spectrum.The numerical simulation results show that the propagation of the transient eddy current field in surrounding rock indicates a "water wave effect" in the whole-space other than a "smoking ring effect" in the half-space.The time-domain characteristics of the secondary field are greatly changed due to changing the geoelectric parameters of a conductive body,so the transient electromagnetic field in tunnels is sensitive to the geoelectric parameters of the conductive body.The time-domain characteristics of the secondary field are slightly changed duo to changing the geoelectric parameters of surrounding rock,so the transient electromagnetic field are lowly sensitive to the geoelectric parameters of surrounding rock.

Compressive Stability of Continuous-Slab-Track on Long-Span Bridge

LIN Hongsong, LIU Xueyi, YANG Rongshan

2008, 21(5): 673-678.

[Abstract](1129)

Abstract:
To research the compressive stability measures of continuous-slab-track on a long-span bridge,based on its structural and longitudinal mechanical features a finite element model for slab-bridge-pier was established by taking a prestressed concrete continuous rigid frame bridge with a span of 94 m+168 m+84 m as an example,and the most unstable segment of continuous-slab and bed-plate was determined.By taking the upward deflection of continuous-slab and bed-plate under a train load as the initial bending defects,the nonlinear compressive stability of continuous-slab-track was analyzed.The research results show that continuous-slab and bed-plate on a long-span bridge are unstable under train and temperature loads,setting a bi-directional block like converse-L can enhance their stabilities,and the suggested distance between two adjacent bi-directional blocks should be less than 16.7 m for the example bridge when the maximum allowable temperature rising is 30℃.

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2008 Vol. 21, No. 5