西南交通大学学报

Geometrical Nonlinear Analysis of Thin-Walled Box Girder with Variable Height

LUO Qizhi, CHEN Yuji

2007, 20(5): 521-525.

[Abstract](1422)

Abstract:
Based on the variation principle of potential energy and considering the shear lag effect of stresses on flanges and the geometrical nonlinearity of vertical deflection of structures,the nonlinear governing differential equation was derived and solved by using the spline least square collocation method for thin-walled box girder with a variable height.The numerical simulation results are in good agreement with those obtained from experiments.The research shows that the distribution of stresses at the inner support is more uneven than that in the middle section of the middle span for a three-span continuous thin-walled box girder with a variable height under uniform distributed loads,and the nonlinear effectiveness becomes more obvious with the increase of load.

Model Test of Cantilever Casting Construction of Reinforced Concrete Arch Bridge

LI Xiaobin, YANG Yongqing, PU Qianhui, LIU Zusheng

2007, 20(5): 526-530.

[Abstract](1881)

Abstract:
In order to demonstrate the feasibility of the construction technique of cantilever casting of a reinforced concrete arch bridge and the rationality of cable force adjustment and construction control,a model test of cantilever casting construction was made by taking the No.1 Baishagou bridge as project background.The displacement of model arch,the stress of control sections and the force of cables were tested.In addition,the test results were compared with calculated results based on the FEM(finite element method),showing reasonable agreement.The research results show that the model arch is safe during the construction,the construction technique of cantilever casting of reinforced concrete arch bridges is feasible,and the method of cable force optimization and adjustment is reasonable.

Vibration Analysis of Noise Barrier Structures Subjected to Train-Induced Impulsive Wind Pressure

JIAO Changzhou, GAO Bo, WANG Guangdi

2007, 20(5): 531-536.

[Abstract](1579)

Abstract:
A numerical analysis of the dynamic response,induced by the impulsive wind pressure of trains,of noise barrier structures with stop plank was conducted by using ANSYS software and considering the interaction of pile,soil and structure.The dynamic characteristics of noise barrier structures were investigated by analyzing the effects of the type and speed of trains and the length and height of the structures.The reasonable parameters were provided for the design of the structures for a high-speed railway.The research shows that compared with a CRH3 train,a CRH2 train will result in a greater displacement and bending moment of props of a noise barrier structure,respectively with a increase of 18.6% and 8.5%.The displacement and the bending moment increase significantly with a nonlinear relationship with the increases of train speed and structure height.Under the condition that the length of a noise barrier structure is smaller than 120 m,the displacement and the bending moment increase with the increasing of the length,and then decrease and trend toward stable values.

Calculation of Tunnel Blasting Parameters Based on Prior Knowledge and BP Neural Network

XIAO Qinghua, ZHANG Jichun, XIA Zhenrong

2007, 20(5): 537-541.

[Abstract](1716)

Abstract:
To overcome the shortcoming of the parameter design of tunnel blasting,i.e.,they are selected empirically by designers,a three-layer neural network model with an input layer,an output layer and a hidden layer was constructed.The Protodikonov’s hardness coefficient,tunnel cross-section area,practical advance per round,blast-hole diameter and others are considered as the input parameters of a BP network,and the designed advance per round,powder factor,contour hole spacing,reliever-hole spacing and excavated-hole spacing as the output parameters.A algorithm for the neural network model was given,and the restrain conditions of network study were proposed on the basis of blasting prior knowledge,so solving of the model can be accelerated.The calculating results for a practical example of tunnel blasting design show that with the help of the neural network model and the algorithm,the parameters of tunnel blasting may be calculated accurately and quickly by using the existed blasting data,so an optimal blasting effect can be obtained.

Basic Study on Method of Karst Geology Forecasting Based on Fractal Theory

LI Cangsong, GAO Bo, MEI Zhirong

2007, 20(5): 542-547.

[Abstract](1342)

Abstract:
To improve the accuracy of karst geology forecasting,the fractal theory was applied.Through the analyses of macroscopic and microcosmic laws of karst,a concept,karst unit,was drawn out,and the fractal growing law of karst was described.Fractal dimension and fractal assessment index of karst were calculated,and they were used to evaluate karst development degree.Five classes of karst were suggested on the basis of the karst development degree.In addition,karst geology forecasting for two tunnels,as examples,were given,and a satisfied result was obtained.The research provides a theoretical basis for karst geology forecasting with the fractal method.

Image Texture Segmentation Based on Cloud Fuzzy Theory

WANG Zuocheng, LI Yongshu, XUE Lixia, Wang Linlin

2007, 20(5): 548-552.

[Abstract](1341)

Abstract:
To deal with the fuzziness and randomness of image textures,a vector cloud model for texture features was proposed on the basis of the cloud fuzzy theory and was successfully used to the segmentation of textural images.With this method,texture feature vector cloud is generated backward after fuzzily processing the statistical descriptor of textures.The fuzziness and randomness of textures can be represented perfectly by the digital characteristics of the vector cloud model,and as a result,image segmentation can be accomplished by cloud distance calculating and texture feature vector cloud growing.The research result shows that the segmentation accuracy is higher and the convergence speed is quicker using the proposed model than using the iterative self-organizing data analysis techniques algorithm(SODATA) and the K-means cluster algorithm.

Research on Algorithm of Quadric Surface Fitting in Reverse Modeling for Mechanical Parts

TIAN Huaiwen, GUO Shizhang

2007, 20(5): 553-557.

[Abstract](1464)

Abstract:
To solve the problem of quadric surface reconstruction in reverse modeling for mechanical parts,a two-step fitting algorithm was presented.With this fitting algorithm,the objective function is built based on the coordinates of measuring points,the normal vector of each point and the geometrical features of mechanical part surfaces,and as a result,the nonlinear calculation of quadric fitting can be changed into a linear least square problem.Furthermore,the geometrical parameters of mechanical part surfaces can be gained through fitting calculation to provide a basis for building solid model and feature model in the reverse engineering for mechanical parts.

Object-Oriented Modeling and Manufacturing Simulation of Virtual Flexible Manufacturing Systems

HE Yong, DING Guofu, ZHAO Shujun, ZHANG Jihui, XU Mingheng

2007, 20(5): 558-562.

[Abstract](1524)

Abstract:
In order to solve the problem of facility layout induced by resource recombination in flexible manufacturing systems,an object-oriented modeling method was proposed to construct the virtual prototype system of a flexible manufacturing system.By modeling of the geometry and behavior of each facility in a manufacturing system,virtual facility models are formed,and by adopting the production schedule flow,a facility layout scheme and dispatch model are constructed.The accuracy of NC(numerical code) can be validated,the rationality and feasibility of a layout scheme can be analyzed,and the layout scheme may be optimized by the simulation of a virtual prototype system.Finally,two different layouts were simulated.The simulation results show the effectiveness of the proposed method.

Decoupling Method of Multidisciplinary Design Optimization Based on Sensitivity Analysis

ZHANG Jing, LI Bailin, LIU Yongjun

2007, 20(5): 563-567.

[Abstract](1708)

Abstract:
To solve the coupling complexity of MDO(multidisciplinary design optimization),coupling factors of a complex system were investigated based on the sensitivity analysis.The conception of coupling strength was presented,the membership degree function of coupling factors was defined with the method of fuzzy mathematics,and the judgment criteria of the coupling degree of coupling factors was given.Based on the conception and the judgment criteria,a decoupling method of MDO was proposed.Finally,a six-bar mechanism was given as an example to demonstrate the validity of the proposed method.

Numerical Simulation of Face Flow Field for Dry Gas Seal

WANG Heshun, CHEN Cichang, WANG Jinnuo

2007, 20(5): 568-573.

[Abstract](1679)

Abstract:
Based on the Navier-Stokes equation,the laminar model and the SIMPLEC algorithm,the numerical simulation of face flow filed under different face clearances and rotational speeds was carried out to obtain more details about the fluid field and high stability of dry gas seal.The distribution of film pressure and the variety of opening force were investigated emphatically.The numerical result shows that there is a clear change in film pressure at the intersection of groove and dam.Hydrodynamic pressure produces at the outlet,and a negative pressure zone is formed at the inlet.Hydrodynamic pressure decreases rapidly with the increase of face clearance and changes acutely when the clearance is less than 3 μm.The difference pressure of inlet and outlet will raise opening force and film stiffness.Opening force and film stiffness can be raised through enlarging the positive pressure zone and reducing the negative zone,and as a result,the stability of dry gas seal is increased.

Rail Grinding Technique and Its Application in High-Speed Railway

WANG Wenjian, CHEN Mingtao, GUO Jun, LIU Qiyue

2007, 20(5): 574-577.

[Abstract](1598)

Abstract:
On the basis of formation and development characteristics of oblique rail cracks in Guangzhou-Shenzhen railway line,the rail asymmetrical grinding was used to prevent and decrease the appearance of oblique cracks.A field grinding test and numerical calculation were carried out.The calculated results show that the rail asymmetrical grinding has an effect on wheel-rail contact parameters,makes the wheel-rail contact point move from the shoulder of rail to the center of rail top surface,and decreases wheel-rail contact stress.The field grinding test has proven the above calculated results.The field test results indicate that the rail asymmetrical grinding can change the contact zone of wheel and rail and make the contact point move toward the center of rail tread.

Flutter of Airfoil with Structural Nonlinearity in Supersonic and Hypersonic Flow

ZHENG Guoyong, YANG Yiren

2007, 20(5): 578-582.

[Abstract](1368)

Abstract:
In order to investigate the aeroelastic characteristics of a two-dimensional airfoil in supersonic and hypersonic flow,aerodynamic force on an airfoil was calculated based on the piston theory,and the governing equations were established by using the energy method.The critical flutter velocity was obtained by using the Hopf bifurcation theory,and the effects of system parameters on the critical flutter velocity were discussed.In addition,limit cycle responses were investigated using the equivalent linearity method and the numerical integration algorithm,the same results being obtained.The research results show that the limit cycle response occurs when non-dimensional flow velocity ranges from 9.48 to 43.2,and the amplitude of limit cycle increases with increasing of flow velocity.

Absolute Exponential Stability of Generalized Hopfield Neural Networks

WEN Haixia, HUANG Lixiang, ZHANG Jiye

2007, 20(5): 583-588.

[Abstract](1597)

Abstract:
The existence and uniqueness of the equilibrium point of a class of generalized Hopfield neural networks(GHNN),altogether with its absolute exponential stability,were investigated.GHNN includes Hopfield neural networks and cellular neural networks,and it is not necessary for its activation functions to be differential and bounded functions.By applying the topology theory,the necessary and sufficient condition for the existence and uniqueness of the equilibrium point of GHNN was obtained.Based on matrix properties,the sufficient conditions for the absolute exponential stability of GHNN were given by constructing Lurie-type Liapunov functions.In some special cases,the necessary and sufficient conditions of the absolute exponential stability of neural networks were determined.

Performance Evaluation of Multi-channel Stop-and-Wait ARQ with Packet Combining

CHEN Hong, FAN Pingzhi

2007, 20(5): 589-594.

[Abstract](1316)

Abstract:
Detailed performance evaluation was presented with respect to the channel number,combining mode,packet loss ratio and transmission delay of multi-channel stop-and-wait ARQ associated with packet combining over a Rayleigh fading channel.The analysis results show that,to achieve optimal system performance,the number of parallel ARQ channels should be planned according to the packet transmission time and round trip feedback delay etc.;the processing delay in the receiver could be decreased by choosing an appropriate combining scheme according to channel quality;and steady transmission delay and throughput could be achieved by adjusting the maximum number of ARQ retransmissions according to the packet loss ratio and channel quality.

E-Cash System for Multiple Banks Based on Restrictive Proxy Blind Signature

LU Rongbo, HE Dake, WANG Changji

2007, 20(5): 595-599.

[Abstract](1371)

Abstract:
To overcome the shortcomings of a multi-bank system based on group signature and improve efficiency,a concept called restrictive proxy blind signature was proposed,in which the restrictive assumption in blind signature was added to proxy blind signature.A fair off-line e-cash system for multiple banks can be implemented based on the restrictive proxy blind signature.The user’s anonymity is protected under normal conditions,and it can be revoked by the issuing bank under the supervision of the central bank if anything abnormal happens(such as requirement by law).

Performance Comparison of Modulation Schemes for Atmospheric Optical Communication

ZHONG Xiaochun, HAN Jiajia

2007, 20(5): 600-603.

[Abstract](1405)

Abstract:
The performances of modulation schemes,OOK(on off key),PPM(pulse position modulation),DPPM(differential pulse position modulation) and DPIM(digital pulse interval modulation),used in optical communication over the atmospheric turbulence channel were analyzed and compared in terms of packet error rate(PER) and bandwidth efficiency.In terms of PER,DPIM is the best followed by PPM and DPPM,and OOK is the worst.With regard to bandwidth efficiency,PPM is desirable with a small modulation parameter,and DPPM and DPIM are good with a large modulation parameter.All these schemes,except OOK,require a small laser power.

Post-IDFT Multidimensional Beamforming for STC-OFDM Systems

LIU Hongwu, FENG Quanyuan

2007, 20(5): 604-610.

[Abstract](1326)

Abstract:
A post-inverse discrete Fourier transform(post-IDFT) multidimensional beamforming scheme was proposed for space-time coded-orthogonal frequency division multiplexing(STC-OFDM) systems.This scheme obtains multiple eigen mode by decomposing cross-matrix of space-frequency channels,and forms multidimensional post-IDFT beamformings for STC-OFDM systems based on the orthogonality of the STBC transmission matrix.The space-diversity gain achieved by the scheme is the sum of the multiple eigen values,and is the same as that of the sub-carrier beamforming,with a lower symbol error rate(SER) than a STC-OFDM does.The proposed scheme reduces the complexity to 1/S(S is the number of subcarriers of an OFDM system) compared with the sub-carrier beamforming;moreover,when the dimension of the post-IDFT beamforming(m) is less than the number of the transmit antennas(M),the system reduces M-m IDFT blocks.

Modification of Reflection and Transmission Coefficients of Frequency Selective Surfaces

MENG Fanji, YANG Rugui, ZHANG Shuangwen

2007, 20(5): 611-614.

[Abstract](1348)

Abstract:
The existing reflection and transmission coefficients of a frequency selective surface(FSS) do not apply to calculation of reflection and transmission under normal incidence of waves,and need to be modified.The incident field was decomposed into two components,parallel and perpendicular to the incidence plane,respectively.Consequently,reflection and transmission coefficients were defined by tangential components of the scatter field.The modified coefficients are simple in structure and applicable to incidence at any angle.A numerical result shows that the modified reflection and transmission coefficients agree with those obtained with the commonly used simulator HFSS.

Filtering Performances of Cascaded Mach-Zehnder Interferometer with Chirped Path Differences

ZHOU Zhi, PAN Wei, LUO Bin, ZOU Xihua

2007, 20(5): 615-619.

[Abstract](1632)

Abstract:
To enlarge the FSR and improve the band-pass filtering performances of cascaded Mach-Zehnder interferometers(MZIs),chirped path differences,rather than fixed path differences,were used based on the similarity between the principles of a cascaded MZIs and a ladder type filter.A theoretical model for cascaded MZIs with chirped path differences was established by transfer matrix method.The variations of 3dB bandwidth and FSR were analyzed.The analysis results show that wider FSR and narrower 3dB bandwidth of cascaded MZIs with chirped path differences can be obtained with an optimized chirp coefficient,and that the optimal chirp coefficient increases with an increase in diffraction order.

Multirate Extended Kalman Filter and Its Application to Speed Estimation of Induction Motors

LU Ke, XIAO Jian

2007, 20(5): 620-625.

[Abstract](1470)

Abstract:
Based on an analysis on algorithm of extended Kalman filters(EKFs) and multirate digital control systems,a multirate EKF algorithm was proposed,including the input and output algorithms.The algorithms were applied to speed estimation for induction motors.Simulation results reveal that the proposed algorithms have better abilities in information access,state estimation and noise reduction than a singlerate algorithm does,and that the decrease in error is 41.4% to 87.6% compared with the singlerate algorithm.

Block-Wise Kernel Partial Least-Squares Method

BAI Yifeng, XIAO Jian, YU long

2007, 20(5): 626-630.

[Abstract](1293)

Abstract:
A method of block-wise kernel partial least-squares(BKPLS) was proposed to solve the problem of dimensional explosion of kernel matrix in batch-wise kernel partial least-squares(KPLS).In the BKPLS,the batch-wise method in the KPLS is transformed into a block-wise method based on the symmetric character of kernel matrix,so that it relaxes the requirement on computer hardware and decreases calculation time.Simulation result verifies that the BKPLS reduces calculation time effectively,and can implement the identification algorithm for the sample with a great size while KPLS fails.

Self-Organized Evolutionary Mechanism of Transportation Corridor

MAO Min

2007, 20(5): 631-635.

[Abstract](1325)

Abstract:
A transportation corridor was defined in terms of transportation and regional economy,and its basic structure was analyzed based on the social-technical theory.A transportation corridor was regarded as a biome,and its evolutionary process was elaborated.A 4-phase life cycle model was proposed to describe the ontogenetic process of a transportation corridor on a microscopic scale,and the main phases of its self-organization evolution were discussed on a macroscopic scale.The evolutionary mechanism of a transportation corridor is the coordinated development resulting from the mutual coupling hypercycles between the transportation corridor and the geographical system where it locates,and between the transportation corridor and the transportation system.

Overbooking Model of Ocean Shipping Container under CVaR

YANG Chenghu, DU Wen, WANG Cuihong

2007, 20(5): 636-640.

[Abstract](1418)

Abstract:
Conditional value-at-risk(CVaR) was applied to a study on overbooking problem of ocean shipping containers.An overbooking model of ocean shipping containers was proposed in the CVaR framework,and a set of equations for optimal overbooking levels were obtained by solving the model.The effects of risk aversion and empty container pick-up on optimal overbooking levels were analyzed.The analysis results show that the optimal overbooking level for a risk averse company depends on demand distribution and degree of risk aversion,and may not be less than that for a risk neutral one;and optimal overbooking levels decline if empty container pick-up is considered.

Model and Algorithm for Shortest Path of Multiple Objectives

HAO Guang, ZHANG Dianye, FENG Xunsheng

2007, 20(5): 641-646.

[Abstract](1896)

Abstract:
To obtain acceptable shortest paths,which meet the decision-maker’s requirements,for a multi-objective shortest path problem,a model and a polynomial algorithm were presented.The algorithm is a combination of a k-shortest path algorithm and a multi-objective lattice-order decision-making method.In the algorithm,a set of feasible paths for each objective is determined using the k-shortest path algorithm according to the acceptable upper limit for the objective,and the intersection of all the sets is obtained.Then efficient paths in the intersection are compared with each other by the method of multi-objective lattice-order decision-making,and the best one in the set is finally selected as the acceptable path.

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2007 Vol. 20, No. 5