西南交通大学学报

Dynamics of Ballastless Track and Its Application

CAI Chengbiao

2007, 20(3): 255-261.

[Abstract](1543)

Abstract:
A coupling dynamic model for train-ballastless track on subgrade was derived based on the vehicle-track coupling dynamics to analyze the dynamic performances of the ballastless tracks and the stiffness of transition tracks.In the model,the tracks are regard as Bernoulli-Euler beams on discrete elastic supports,and the slabs and the RC(reinforced concrete) roadbed as elastic plates on an elastic foundation.The movement equations of ballastless tracks on the subgrade were also derived.The dynamic performances of slab track and the stiffness of the transition tracks on Suiyu(Suining-Chongqing) railway were investigated with the model and movement equations.The results show that the vertical and horizontal wheel-rail forces,derailment coefficient,rate of wheel load reduction,dynamic stresses in CA mortar and subgrade surfaces are less than the permissible values when a high speed passenger train,a heavy freight train or an ordinary freight train passes.On the transition section between the ballastless track(slab track or bi-block track) and ballasted track,the change rate of rail deflection is less than the permissible value,0.300 mm/m when a high speed passenger train passes,indicating that the stiffness design of the transition tracks is rational although the change rate of rail deflection is slightly greater than the permissible value when a heavy freight train passes.

Three-Dimensional Elastic-Plastic Rolling Contact Stresses in Rail

GUO Jun, WEN Zefeng, JIN Xuesong, LIU Qiyue

2007, 20(3): 262-268.

[Abstract](1680)

Abstract:
A three-dimensional elastic-plastic model of wheel-rail rolling contact was established by finite element method to investigate the effect of yield stress of rail material on residual stresses and strains in the rail.In the model,the geometry and boundary conditions of the rail were taken into account.Repeated wheel rolling and sliding were simulated by multiple translations of normal and tangential surface tractions with Hertz form across rail running surface.The results show that the maximum equivalent plastic strain and shear strain occur on the contact surface,where the cracks initiate easily.The plastic flow direction in the rail near the contact surface is consistent with that observed in the field.An increase in yield stress of rail materials leads to a decrease in residual deformation,and drives the location of the absolute values of the maximum residual stresses to the contact surface.

Uniform White Noise Model for Time-Delay Multi-dimensional Rail Irregularity Excitation

JIN Zhibin, QIANG Shizhong, LI Xiaozhen

2007, 20(3): 269-273.

[Abstract](1572)

Abstract:
To obtain rail irregularity samples for train-bridge vibration control and stochastic analyses,a simulation method of irregularities at all axles of a train was investigated.Rail irregularity at the first axle was generated by the white noise filtration method.To achieve wavelength selection of rail irregularity,a wideband identification method was proposed for the design of a shape filter.To take time-delay among different axles into account,a step-wised time delay system based on a high order Pade’s approximation of the short time-delay between adjacent axles was constructed.By combining the shape filter with the time-delay system,a state equation with uniform white noise as input and irregularities at all axles of a train as output was obtained.A numerical example shows that simulated irregularity samples accord well with the target irregularity power spectral density(PSD) and satisfy the time-delay relation among irregularities at different axles.

Vibration Control of Cables by Cable-Type Dynamic Vibration Absorbers

YANG Suqin, ZHANG Keyue

2007, 20(3): 274-277.

[Abstract](1429)

Abstract:
A cable-type dynamic vibration absorber was presented to control cable vibrations of the predominant modes under harmonic excitations.The controlling cable(dynamic absorbing cable)) and the controlled cable(main cable) are under the same boundary condition,and connected by uniformly distributed springs and dampers.Since the both cables have the same eigenfunctions under the same boundary conditions,the equations of motion of the system in the modal coordinates of the main cable are equivalent to those of the two-degree-of-freedom system with two masses.

Damage Constitutive Model of Rock Based on Drucker-Prager Criterion

XU Jiang, LI Shuchun, LIU Yanbao, LI Kegang

2007, 20(3): 278-282.

[Abstract](1669)

Abstract:
To overcome the shortcoming of the existing method to establish the damage constitutive model of rock,i.e.,it seeks parameters in the constitutive model by linear fitting after logarithmic transformation to result in a complex calculation and not to fit for computer programming,formulas of calculating the parameters in the constitutive model were given by introducing the characteristic parameters of the stress-strain curve of rock and taking the extreme conditions for the stress-strain curve of rock into consideration.As a result,a new constitutive damage model of rock can be easily established.Comparison with the result of triaxial compression tests shows that this model can reflect well the relationship between stress and strain of rock.Through a discussion on parameters m and F0 in the constitutive damage model,it is believed that m and F0 represent the brittleness and strength of rock respectively,and elastic modulus of rock is a co-reflection of the two parameters.

Analysis of Longitudinal Seismic Response of Shield Tunnel

GENG Ping, HE Chuan, YAN Qixiang

2007, 20(3): 283-287.

[Abstract](1796)

Abstract:
In order to investigate the characteristics of longitudinal seismic response of shield tunnels,the seismic response of a shield tunnel across the Yangtze River in Wuhan was investigated with a three-dimensional finite element model for ground-tunnel interaction.The investigation mainly concerns the reasonable mechanics model,the interaction between tunnel and ground,and the vibration characteristics of tunnels.The research obtains the distribution of displacement and stress and their time-dependent curves.The numerical results show that the key points in the aseismatic design of tunnels are the tension and compression stresses in the longitudinal direction of tunnels under a compression wave and the torsional displacement of tunnels under a shear wave.

Shell-Spring-Contact Model for Load and Structure Interaction

SU Zongxian, HE Chuan

2007, 20(3): 288-292,304.

[Abstract](1692)

Abstract:
In order to probe into the 3D mechanical behaviors of shield tunnel segmental linings,a shell-spring-contact model for load and structure interaction was set up by using thick shell,spring,solid and contact elements to analyze forces acting on shield tunnel segments.Several special features were considered,including extrusion between segments,occlusion between segments and bolts,subgrade reaction between radial and tangential components,rotational stiffness of ring joints under positive and negative bending,and approximate insertion angle of the key segment.A numerical example shows that there exists a little difference between the calculational results based on the shell-spring-contact model and a beam-spring model,and the distributions of axial and shear forces on the shell have obvious spatiality.

Parametric Investigation of Ultimate Bearing Capacity of Reinforced Concrete Arch Bridges

LI Song, QIANG Shizhong, TANG Ying

2007, 20(3): 293-298.

[Abstract](1611)

Abstract:
Based on the collapse theory and a 3D numerical simulation model,the ultimate bearing capacity of reinforced concrete arch ribs was calculated to accurately determine the ultimate bearing capacity of a long-span reinforced concrete arch bridge.In this research,the effects of geometric nonlinearity,material nonlinearity,geometric imperfection,concrete crush,concrete crack and aggregate interlocking were taken into account.The effects of geometric imperfection,cross-section type,load distribution form and raise-to-span ratio on the ultimate bearing capacity were mainly discussed.The results show that the mechanical characters of reinforced concrete have a great effect on the ultimate bearing capacity,the ultimate bearing capacity varies nonlinearly with the initial geometric imperfection,and the relationship between the ultimate bearing capacity and the length to radius ratio of arch rib is a cube curve.

Shear Lag Effect of Continuous Curved Box Girder with Different Types of Support

LOU Yihong, LUO Qizhi, DU Jiabin, LI Yongkai

2007, 20(3): 299-304.

[Abstract](1359)

Abstract:
Based on the homogeneous solutions of equilibrium differential equations for shear lag as the displacement patterns of finite segment,a finite segment model taking bending,torsion and shear lag into consideration was established.A corresponding program was designed to calculate the shear lag of continuous curved box girders.The shear lag of a two-span continuous curved box girder was investigated experimentally.The numerical result based on the finite segment model accords with the model test and FEM(finite element method) numerical results.An actual example was given to investigate the shear lag effects of a continuous curved box girder respectively under concentrated load and uniformly-distributed load.The research results show that the type of supports and the form of loads have an obvious influence on the shear lag effect of a continuous curved box girder.

Relationship between Distance Headway and Chaos in Traffic Flow on Expressway

LI Song, HE Guoguang, ZHANG Jie

2007, 20(3): 305-309.

[Abstract](1537)

Abstract:
The relationship between distance headway and chaos in traffic flow on expressway was investigated in order to analyze the formation mechanism of chaos in traffic flow.An improved algorithm for largest Lyapunov exponent was put forward for rapid identification of chaos in traffic flow.The chaos in traffic flow on an expressway was investigated with the improved algorithm and the power spectrum method.The power spectrums of the time series of the traffic flow were illustrated.Through the analysis of the power spectrums of the distance headway,it is clear that there are the variations of noise and wide apices.The largest Lyapunov exponents of the time series of the traffic flow were computed and used to identify the chaos in the traffic flow on the expressway.The results prove that chaos exists in traffic flow on an expressway indeed.The research shows that the change in distance headway is the main factor causing chaos in traffic flow.

Stochastic User Equilibrium Assignment Based on Traffic State

WANG Jianling, JIANG Yangsheng, PU Yun

2007, 20(3): 310-314.

[Abstract](1577)

Abstract:
Based on the basic idea of stochastic user equilibrium assignment and the traffic flow theory,the concept of road traffic state was introduced in order to describe the problem of traffic assignment.The road traffic state was defined as the linear weighted sum of travel time and traffic congestion degree.Based on the assumption that under stochastic variations of link capacities,passengers’ standard to choose a route is the minimization of travel time and traffic congestion degree,a stochastic user equilibrium assignment model based on road traffic state was proposed.The equivalence and uniqueness of the solution of the proposed model were demonstrated,and an algorithm for the model was given.The numerical results for a small traffic network show that the proposed model can reflect the passengers’ routing behavior in a stochastic road network.

Optimal Routing Algorithm for Public Traffic Network Based on Matrix Analysis

HE Di, YAN Yusong, GUO Shoujing, HAO Guang

2007, 20(3): 315-319.

[Abstract](1523)

Abstract:
In order to tally with the actual situation further,i.e.,transfer times are a determining factor and travel time is an important factor in passengers’ choice of a route in a public traffic network,the psychological characteristics of passengers were analyzed,a public traffic network model based on GIS(geographical information system) was established,and the path-planning matrix and the least transfer matrix used to the analysis of public traffic were constructed.On the basis of the above works,an optimal routing algorithm for public traffic networks was proposed by considering the link travel time and the time at bus stops.Finally,a simple example was given to show this algorithm.

Revenue Optimization of Capacity Scheme and Allocation of Third Party Warehousing

LIN Chang, HUANG Qing, BU Xiangzhi

2007, 20(3): 320-325.

[Abstract](1605)

Abstract:
Based on the principle of revenue management,capacity scheme and allocation under a stochastic market demand was investigated in order to maximize the revenue of third party warehousing.A stochastic model was established,and robust optimization was used to the stochastic variables so as to turn the stochastic problem into a linear programming one.In addition,the optimal capacity scheme and capacity allocation policy were determined on the basis of numerical examples.The numerical results show that with the help of the model,revenue increases by 2.66%.

Research on Buy-Back Contract Mechanism of Brand Specialization Supply Chain

ZHAO Zhengjia, HE Hui

2007, 20(3): 326-329.

[Abstract](1286)

Abstract:
To obtain the optimal policy of a brand specialization supply chain with a supplier and a retailer,a buy-back policy model under a stochastic price-dependent demand was proposed,and a buy-back contract based on a linear price-discount sharing scheme was analyzed.The analysis shows that under a linear price-discount sharing scheme,there is much combination of wholesale price and buy-back price to coordinate the supply chain with the supplier’s profit not being zero.In addition,the optimal contract parameters were given.Finally,a numerical example was given to deeply analyze the proposed model,and the profits of the supplier,the retailer and the supply chain as a function of the contract parameters were obtained.

Improved Models of Rough Set Decision-Making and Cluster Analysis

LIU Dun, HU Pei, CHEN Zhijie

2007, 20(3): 330-334.

[Abstract](1454)

Abstract:
By analyzing the intrinsic relationship between the rough set theory and the cluster analysis,their syncretized mechanism was investigated and the correlative mathematical demonstrations were given.Owing to the fact that it is difficult to build a decision table in rough set decision-making,a new concept,equivalent cluster,was put forward by expanding an information table by using the cluster analysis as a tool.As a result,a rough set decision-making model based on the cluster analysis was proposed.In view of the unreasonable determination of weight in the cluster analysis,thinking of attribute reduction in the rough set theory was used to solve the problem of weight determination and redundancy,and a cluster analysis model based on the rough set theory was built so as to overcome the disadvantages of the current rough set decision-making and cluster analysis models.

Taxonomy of Replay Attacks on Security Protocols Based on Attack Hierarchy

TAO Hongcai, HE Dake

2007, 20(3): 335-339.

[Abstract](1360)

Abstract:
A taxonomy of replay attacks based on attack hierarchy was defined on four levels of attacks on cryptographic protocols,i.e.message block,inter-block inside step,inter-steps,and inter-protocols.The taxonomy not only contains the Syverson taxonomy of replay attacks,but also extends the replay attack up to the protocol level.Feasible modes to mount replay attacks corresponding to different levels were discussed.It is easy to check if replay attacks exist in a security protocol by applying the proposed taxonomy.

Safety of Facial Images Based on Fragile Digital Watermarking

ZHANG Zutao, ZHANG Jiashu, HE Hongjie

2007, 20(3): 340-344.

[Abstract](1636)

Abstract:
Fragile digital watermarking for facial image authentication was applied to oppose various attacks to facial images,such as tamper,substitution and addition and to improve the security of facial images.The water mark is obtained by converting the 7 most significant bits(MSB) of the low-frequency wavelet coefficients of the original image into a binary sequence.The water mark is scrambled by a chaotic key,and embedded into the least significant bits(LSB) of the original facial image to detect tamper and the tampered zone.Experimental results show that the facial image with fragile digital watermarks formed by the proposed method is highly sensitivity to tamper,substitution and addition.The embedded fragile digital watermarks have a little negative effect on feature extraction,detection rate and detection speed during face recognition.

Fast H.264/AVC Intra-Prediction Using Frequency Domain Features

WANG Zhengning, PENG Qiang, ZHU Changqian

2007, 20(3): 345-351.

[Abstract](1283)

Abstract:
To reduce the intra-prediction complexity in H.264/AVC,a fast intra-prediction mode selection algorithm was proposed.It calculates the DCT(discrete cosine transform) coefficients for each block,and uses frequency domain features of the target block to eliminate the majority of candidate modes.Simulations verify that the proposed method speeds up the intra-prediction process by 67.5% on average without sacrificing the picture quality and compression ratio.

Effect of Dielectric Anisotropy on Optoelectric Characteristics of Ferroelectric Liquid Crystal

WANG Mengyao, PAN Wei, LUO Bin, ZHANG Weili, ZOU Xihua

2007, 20(3): 352-357.

[Abstract](1377)

Abstract:
A circuit model of ferroelectric liquid crystal(FLC) was proposed to study the effects of biaxial anisotropy on switching time,characteristic time,characteristic voltage and polarization reversal current,and those of ferroelectric torque and dielectric torque on light transmittance.The results indicate that the delay time has the minimum value as the drive voltage amplitude varies,and the characteristic time(voltage) increases(decreases) as the biaxial anisotropy increases.When the value of biaxial anisotropy is large enough,the effect of dielectric torque exceeds ferroelectric torque;the corresponding polarization reversal current becomes unipolar rather than bipolar;and the alternating change in light transmittance between "bright" and "dark" vanishes,and the peak value of light transmittance decreases gradually.

Transmission Characteristics of Optical Pulses in LOA Based on XGM

LI Haitao, PAN Wei, LI Xi

2007, 20(3): 358-362.

[Abstract](1377)

Abstract:
A theoretical model describing transmission of optical pulses in a linear optical amplifier(LOA) was derived to verify the performances of a linear optical amplifier(LOA).Under the condition of gain saturation,the effects of cross-gain modulation(XGM) on transmission pulses and the transmission characteristics of optical pulses were analyzed,and the influences of pulse widths on the gain,carrier density and carrier lifetime were discussed.The results show that with the same peak gain of the signal pulse,the peak output power decreases with an increase in the pump power or a decrease in the probe power;the rising time of the output pulse increases(decreases) with an increase in probe power when the pump power is under(over) 0.5 mW;the rising time of the peak power is delayed by a longer wavelength,accompanied by a decrease in the peak power;and the effect of a wide pulse is weaker than that of a narrow one.

Active and Passive Compound Vibration Control Based on Optical-Electric Displacement Detection

ZHANG Daxing, JIA Jianyuan, DUAN Yabo

2007, 20(3): 363-366,372.

[Abstract](1580)

Abstract:
Position sensitive detector(PSD) was adopted as the vibration detection sensor,which,compared with an acceleration transducer,can improve measurement precision,reduce the response time,and minimize the influence of time delay.The dynamic model of active and passive compound vibration control was derived.An experimental apparatus was designed,and the performances of vibration isolation were verified by experiments.Results suggest that the compound control gains the advantages of both active control and passive control.The ratio of vibration transmissibility is less than 20% when the frequencies of input signals are 10 to 1 500 Hz.

Emission Limits to Harmonics of Electrified Railway

XIE Shaofeng, LI Qunzhan

2007, 20(3): 367-372.

[Abstract](1687)

Abstract:
The impact of harmonic impedance on the relationship between harmonic voltage and harmonic current emission limits was discussed based on a comparison between IEC 61000-3-6 and GB/T 14549-93.There exist differences between traction loads and general loads in determination of the agreed power of the consumer and the total available power,harmonic summation exponent and coincidence factors of multiple harmonic sources.Therefore the distributing method of harmonic emission limits for traction loads is different from that for general loads,and application of the 3-stage method in IEC 61000-3-6 is recommended in the cases of traction loads.An example of an electrified railway in China was presented to show the application of the 3-stage method to evaluate the harmonic voltage emission levels of traction loads.

Automatic Classification of Radar Emitter Signals Based on Cascade Feature Extractions

PU Yunwei, JIN Weidong, HU Laizhao

2007, 20(3): 373-379.

[Abstract](1694)

Abstract:
A scheme of automatic classification of radar emitter signals was presented,which is based on cascade feature extractions.First,an improved instantaneous autocorrelation algorithm is performed to extract instantaneous frequencies of typical radar emitter signals.Then,the extracted instantaneous frequencies are normalized twice to obtain the classification characteristic vector.Finally,the hierarchical decision approach is used to classify radar signals automatically.The results of simulation show that the classification characteristics vector has good separation property between clusters,and the proposed approach achieves a correct rate of above 90%,even when the signal-to-noise ratio is as low as 6 dB.

Algorithm for GPS Network Construction Based on Spherical Delaunay Triangulated Irregular Network

ZHOU Letao, HUANG Dingfa, LI Chenggang, ZHOU Dongwei

2007, 20(3): 380-383.

[Abstract](1549)

Abstract:
A fast growth algorithm for GPS(global positioning system) network construction was developed based on the characteristics of maximized dihedral angle of SDTIN(spherical Delaunay triangulated irregular network).The coordinates,as test data,of GPS sites of ITRF(international terrain reference frame) were utilized to construct a global SDTIN in order to prove the reliability of the algorithm.In addition,the directly searching algorithm for SDTIN was compared with the fast growth algorithm.The comparison result shows that the fast growth algorithm is effective.

Weightable and Regular Independent System

LIU Xiufeng, ZHANG Aili

2007, 20(3): 384-388.

[Abstract](1134)

Abstract:
Two combinatorial structures of regular and weightable independent systems were established based on the general cases of multi-key problems.It was proved that a weightable independent system does not contain any inconsistent sets,the independent system without inconsistent sets is the regular independent system,and some regular independent systems contain inconsistent sets.

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2007 Vol. 20, No. 3