西南交通大学学报

Survey of the Selection of Kernels and Hyper-parameters in Support Vector Regression

XIAO Jian, YU Long, BAI Yifeng

2008, 21(3): 297-303.

[Abstract](2625)

Abstract:
The structure of support vector regression model plays an important role in simultaneously reducing both the empirical risks and confidence intervals.To make a systematical analysis,the existing typical methods for SVR model selection were classified into two major categories: kernel selection and hyper-parameter determination.These selection methods were surveyed and discussed from various aspects.The accuracy and generalization ability of SVR heavily depend on kernel function and hyper-parameters.Future research directions were suggested.

Effects of DC Control Strategies on DC Power Transmission System Stability

WANG Yuhong, LI Qunzhan, HE Xiaoqiong, GAO Shibin

2008, 21(3): 304-308.

[Abstract](1750)

Abstract:
DC(direct current) control strategy and its application in power transmission systems were analyzed,and constant current control(CCC) and constant power control(CPC) were compared in terms of their principles and implementation.Gao-Zhao(Gaopo in Guizhou to Zhaoqing in Guangdong) HVDC(high voltage DC) transmission system in China Southern Power Grid was taken as an example.Current controllers with different transfer functions were designed.Simulations were performed on the system stability of power networks,dynamic responses of current controllers and effects of DC modulation by CCC or CPC under the same parameters.The results show that,with proper parameters,CCC and CPC obtain similar stabilities; a PI controller delivers small current overshooting,fast responses and a good adjustability;and DC modulation increases system damping so as to raise power network stability.

Missile Guidance Law with Terminal Impact Angle Constraint

WU Peng, YANG Ming

2008, 21(3): 309-313.

[Abstract](1068)

Abstract:
The correlation between terminal impact angle and expected angle of sight was analyzed to ensure impact angle of a missile.A guidance law with a terminal impact angle constraint was proposed based on Lyapunov stability theorem and estimation about time-to-go.The proposed guidance law is simple and overcomes the limitation that a passive homing missile does not has a distance-measurement function.Numerical simulation results demonstrate that the proposed guidance law can guide the missile to hit some mobile targets with high maneuverability by stem chase impact or perpendicular impact.

Video Shot Detection Method Based on Wavelet Transform and Wavelet Entropy

DAI Xiaowen, CAI Zhiping, ZHONG Guiying

2008, 21(3): 314-318.

[Abstract](1685)

Abstract:
A detection method for video shot transitions based on wavelet transform and wavelet entropy was presented.The mean and standard deviation of the low frequency components of an image is used to detect cut transitions.To detect gradual transitions,the wavelet entropies of the image in horizontal,vertical and diagonal directions are used as characteristic values,and these values are taken as inputs to calculate the Euclidean distances between neighboring images.A gradual transition is determined if at least two Euclidean distances are larger than a preset threshold in the detection window.Experiment results indicate that using the proposed method the ratio of correct detection is 95% and the detected ratio is 96% respectively for cut transitions,and 87.5% and 83.8% respectively for gradual transitions.

Experimental Research on Shear Behaviors of Specially Shaped RC Columns with Different Lengths of Limbs

HUANG Chengkui, QU Fulai, ZHAO Shunbo

2008, 21(3): 325-329.

[Abstract](1545)

Abstract:
Twelve model columns were tested under low reversed cyclic loading to investigate the shear behaviors of specially shaped RC(reinforced concrete) columns with different lengths of limbs.The effects of different factors,such as the length of limbs,the direction of horizontal force and the spacing of lateral reinforcements,on the shear behaviors were investigated.The experimental results indicate that the two limbs of a specially shaped RC column have an effect to resist shear force,and the shear capacity increases with the increase of flange length.Furthermore,the shear capacity and deformation capacity of a specially shaped RC column vary with changes in the direction of horizontal force.Finally,a modified formula considering the effect of flange length was suggested based on the experimental results to be possible to calculate the shear capacity of specially shaped RC columns with different lengths of limbs.

Local Buckling of Extended End-Plate Connection in Fire

HAO Shuying, YANG Xiuping, YAO Bin

2008, 21(3): 330-334.

[Abstract](1437)

Abstract:
In order to reveal the effects of the thicknesses of end-plate and stiffener on the failure modes of extended end-plate connection in a fire,the formation conditions of one or two groups of plastic hinges in the tension zone of end-plates were investigated based on the elastic-plastic theory and validated by using nonlinear FEM(finite element method).The research result shows that with the increase of temperature,two groups of plastic hinges will be formed in the tension zone of an end-plate with a thin thickness,and large plastic bending deformation occurs to lead to a large rotation of the beam and severe local buckling of its bottom flange in compression.Under the condition of a thin stiffener and a thick end-plate,only one group of plastic hinges will be formed,and stiffener buckling will result in the failure of the connection.The conditions to form the plastic hinges in the connection in a fire are nearly the same as those at room temperature,but the most common failure mode in a fire is severe local buckling.Therefore,the thicknesses of end-plate and stiffener should be increased properly to avoid the buckling of stiffener and beam flange and improve the fire resistance of the connection significantly.

Centrifuge Model Test of Earthquake Countermeasures for Deposit-on-Slope

YANG Ming, YAO Lingkan, WANG Jian, YANG Qinghua

2008, 21(3): 335-340.

[Abstract](1762)

Abstract:
Based on the pseudo-static method,the reinforcement measures of anti-slide piles and their combination with anchor bolt frames were investigated with centrifuge model tests and numerical simulation in order to probe into the failure mechanism of deposit-on-slope reinforcement under an earthquake.The experimental results show that overtopping collapse possibly occurs when only anti-slide piles are used to reinforce the bottom of deposit-on-slope.Anti-slide piles combining with anchor bolt frames can improve the distributions of stresses and strains in deposit-on-slope,and decrease its deformation and force acting on anti-slide piles greatly.Based on the above results,it is suggested that the principle of "slope bottom reinforcement and mountainside strengthening" should be emphasized in the design of deposit-onslope in high earthquake intensity regions.

Effects of Expansive Agents on Deformation Property of CA Mortar

HU Shuguang, WANG Tao, WANG Fazhou

2008, 21(3): 341-345.

[Abstract](1672)

Abstract:
In order to maintain the volume stability of CA(cement asphalt) mortar,the effects of the type and dosage of expansive agents and curing humidity on the volume stability of CA mortar were investigated experimentally.The investigation results indicat that the expansion effect of aluminum powder occurs within 12 h after casting,and volume shrinkage occurs after 16 h.U-type expansive agent has a little shrinkage compensating effect within 12 h,but the volume of CA mortar expands obviously after 20 h and reaches the maximum at 7 d after casting,and volume shrinkage is followed immediately.Furthermore,the shrinkage ratio reduces with increasing the dosage of U-type expansive agent.The volume of CA mortar including aluminum powder and U-type expansive agent expands persistently within 7 d,and volume shrinkage follows and decreases with the increase of curing humidity,from 0.035‰ to 0.100‰.M-type expansive agent can reduce remarkably volume shrinkage at the later stage,and the shrinkage ratio decreases by more than 0.160‰ at 180 d after casting.

Non-linear Creep Model Based on Plasticity Strengthening and Viscosity Weakening of Rock

LUO Runlin, RUAN Huaining, ZHU Changxing

2008, 21(3): 346-351.

[Abstract](1449)

Abstract:
To more reasonably describe the creep behavior of rock,especially the 2nd and 3rd stages of rock creep,a non-linear creep model of rock was established based on the creep mechanism of rock and introducing a plasticity strengthening function and a viscosity weakening function into the visco-plasticity model.The result of a creep experiment on cylindrical sandstone specimens under uniaxial compression shows that the established model can fits the experimental result well,the correlation coefficients being greater than 0.98.The non-linear creep model can describe the whole process of rock creep exactly.

Fracture Controlled Blasting of Different Coupling Mediums in Bore Hole

ZHU Zhiwu, LI Yi, SONG Shuncheng

2008, 21(3): 352-355.

[Abstract](1431)

Abstract:
Based on the different physical and energy transfer characteristics of water and air,coupling blasting of different mediums (water and air) in the same bore hole was presented to control the release process and action direction of energy to control the generation and development of cracks.The effect of water and air coupling blasting on surrounding medium was analyzed,and strain and damage induced by coupling blasting of water and air were investigated experimentally.The research results show that water coupling blasting can generate great strain and damage than air coupling blasting,as a result,it is possible to destroy one side of surrounding rock and protect the other side.

Surface Crack Problem of Half Space under Rolling Load

ZHU Chengjiu, CHEN Mengcheng, YU Huiqin

2008, 21(3): 356-360.

[Abstract](1566)

Abstract:
To simplify the calculations of wheel-rail contact force and governing equations,a surface crack problem in a semi-infinite space was reduced to solving a set of hyper-singular integral equations with displacement jumps as unknown functions.The boundary element method was used in numerical analyses to disperse the integral equations,and a special numerical treatment for the hyper-singular integrals was proposed.Finally,the surface crack problem in a semi-infinite space with or without internal oil infiltration between crack surfaces under rolling load was discussed.The research result shows that oil infiltration will accelerate the propagation of surface cracks.

Coupling Dynamic Analysis of Vehicle and Turnout on Bridge

CHEN Rong, WANG Ping, CHEN Xiaoping

2008, 21(3): 361-366.

[Abstract](2317)

Abstract:
To research the vehicle-turnout-bridge dynamical interaction under a high-speed running condition,a dynamic model for a vehicle-turnout-bridge coupling system was established,and the numerical simulation method was applied to analyze the dynamic characteristics of turnout and bridge structures,the running safety and the ride comfort.By taking the vertical and horizontal ratios of deflection to span as the index of bridge rigidity,an analysis and calculation were conducted on six standard spans of continuous girder bridges used most commonly in high-speed railway.Dynamic responses,such as vehicle-bridge vibration acceleration,load reduction rate,derailment coefficient,bridge vibration amplitude and acceleration,were acquired,and the reasonable rigidity of a continuous girder bridge with a span of 24,32,40 or 48 m was determined to be 1/20 000,1/9 000,1/5 000 and 1/3 000 respectively.The research shows that except static analyses should meet the relevant criterions,a dynamic analysis is necessary to specific turnout structures,running conditions and bridge structures.

Virtual Prototyping-Based Feedback Model of Product Design Process

DING Guofu, HE Yong, ZOU Yisheng, WANG Jue, ZHANG Weihua

2008, 21(3): 367-372.

[Abstract](1700)

Abstract:
In order to accelerate the convergence of a product design process towards the design object,a feedback model for product design processes was proposed.This model includes a product design model,an analysis model and a simulation model,and they are syncretized in a product design process.The proposed model is based on a digital prototype built in the CAD environment,so it can guarantee the entirety of the design object and the consistency of the design process.By taking the virtual prototyping of a locomotive based on the multi-body system as an example,the concrete forms of the product design model,the analysis model and the simulation model were given to testify the validity of the proposed model.

Super-high Speed Curve Passing Performances of Vehicle with MRF Coupled Wheelsets

NI Pingtao, ZHANG Hong, WANG Kaiwen

2008, 21(3): 373-376,391.

[Abstract](1839)

Abstract:
In order to research the dynamic performances and running feasibility of a vehicle with MRF(magnetorheological fluid) coupled wheelsets at super-high speed,a spatial curve passing model for a holonomic vehicle with MRF coupled wheelsets and anti-hunting dampers was established based on the MRF biviscous constitutive relation.The simulation result shows that under the condition of a small MRF yield stress,the vehicle will hold higher critical velocity,but wheel/rail two-point contact appears easily.Vehicles with MRF coupled wheelsets and anti-hunting dampers may possess a good super-high speed curve passing performance under the conditions of given suspension parameters,a suitable MRF yield stress and anti-hunting damp.

Influence of Primary Spring Stiffness on Strength of C0 Bogie Frame

ZHANG Kailin, LUO Huajun, ZHANG Hongjun

2008, 21(3): 377-380.

[Abstract](1513)

Abstract:
In order to determine the reasonalbe stiffness of middle-axle primary spring,the distribution of stresses in C0 bogie frame was investigated with FEM(finite element method) based on two kinds of boundary conditions,i.e.,spring constraint and force constraint.The influence of middle-axle primary spring on stresses of partial key nodes was analyzed under different vertical curves and vertical stiffness.In addition,the re-distribution of stresses in C0 bogie frame was discussed.The numerical result shows that the constraint conditions in a finite element model for C0 bogie frame must ensure that the three axles have the same mass,and a reasonable distribution of stresses in C0 bogie frame can be obtained when the vertical stiffness of middle-axle primary spring is smaller than that of the two end-axles.

Global Stability Analysis of Cohen-Grossberg Neural Networks with Unbounded Time Delays

LONG Lan, XU Xiaohui, ZHANG Jiye

2008, 21(3): 381-386.

[Abstract](2008)

Abstract:
In order to apply the neural networks to optimization problems,the conditions ensuring the existence,uniqueness and global asymptotical stability of the equilibrium point of Cohen-Grossberg neural networks(CGNN)with unbounded time delays were investigated.Without assuming the boundedness,monotone and differentiability of the activation functions,the existence condition of the equilibrium point of CGNN was obtained.Using the vector Liapunov function method,the intero-differential inequalities with unbounded time delays were constructed,and the stability of the intero-differential inequalities were analyzed to obtain the criteria for the global asymptotical stability of the equilibrium point.Based on the criteria,the global asymptotic stability of CGNN can be get by judging whether the matrix constructed by the weighed coefficients,self-feedback functions and activation functions of CGNN is an M-matrix.Finally,an example was given to testify the validity of the criteria.

Design of Direct-Connect Impulse Combustion Wind Tunnel

YANG Yang, LIU Weixiong, LE Jialing, WANG Jinnuo

2008, 21(3): 387-391.

[Abstract](1846)

Abstract:
To effectively and economically investigate the performance of supersonic combustors,a new kind of direct-connect impulse combustion wind tunnel was designed and constructed.It provides a high-enthalpy flow by combusting oxygen/nitrogen and hydrogen/nitrogen provided by a Ludwieg tube and a fuel-providing device,respectively.The fuel-providing device was elaborately designed to eliminate insecurity result from residual hydrogen after a run,and maintain nearly a constant pressure in a test.Specially-designed pneumatic high-speed valves were used to control the rapid synchronized-injection of oxygen/nitrogen and hydrogen/nitrogen into a combustion heater.The operation results show that the combustion heater can provide a wide operation range with a total temperature of 1 100 to 2 200 K,a total pressure of 1.0 to 4.0 MPa and a duration of 100 to 150 ms.

Multi-attribute Decision-Making Method Based on Design Axioms

WANG Xiaoyong, TANG Dunbing, LOU Peihuang

2008, 21(3): 392-397.

[Abstract](1542)

Abstract:
To overcome the objective conflicts of multi-attribute decision-making and reduce the complicacy of repetitive decision-making,a directed hierarchy model of multiple criteria analysis based on the independence axiom and an evaluation method based on the improved information axiom were presented through investigating the decision-making process based on the axiomatic design theory.Owe to the attention to the hierarchy and independence of criteria in this model,impacts among the criteria can be analyzed distinctly and objective conflicts be reduced. The formula of calculating the information contents in the information axiom was improved by adding a term reflecting the satisfaction degree of decision-makers to remedy the shortcoming,i.e.,the original formula reflects only the ability of a system through the success probability.In addition,computation methods for the information contents of the fuzzy attribute and the crisp attribute were described.With the evaluation method,solutions can be ranked from the magnitude of system information content.Finally,a case was given to show the validity and feasibility of the proposed method.

Optimization of Passenger Station Layout in Railway Junction Terminal for High Speed Passenger Railway

WANG Nan, ZHU Zhiguo, HU Yan

2008, 21(3): 398-403.

[Abstract](3696)

Abstract:
Allocation of passenger stations in a railway junction terminal was categorize into centralized and distributed forms based on an analysis of the limitations to construction of new railway passenger stations.The allocation forms to be adopted depend on city scales,layout plan of existing railway terminal,number and grade of railway lines connecting with the terminal,composition of the urban transit network,city planning,and so on.The optimization models and solution algorithms for the two allocation forms were proposed according to the optimization principles of passenger station allocation.The proposed optimization method was verified by taking the railway junction terminals in Haikou and Chengdu as examples.

Fast Optimization of Final Approach Sequence of Aircrafts

MOU Qifeng, WANG Ciguang

2008, 21(3): 404-408.

[Abstract](2096)

Abstract:
Dynamic programming method was used to solve the problem of optimal sequencing of aircrafts in final approaching.Criteria for fast judgment of priority between any two aircrafts in a queue were proposed.Based on these criteria and following the regulations of air traffic control(ATC),the parameters of aircrafts were simplified,and a method for fast optimization of a final approach sequence was presented.A case study result indicates that the proposed method meets the ATC regulations,and is suitable for fast optimization by ATC personnel without any help from a tool.

Reverse Gravity Model Based on OD Traffic Flow of Air Passengers

LIU Xiaoming, XIA Hongshan

2008, 21(3): 409-414.

[Abstract](1692)

Abstract:
To estimate passenger traffic at airports based on air passenger OD(origin-destination) traffic flows and air route distances,a simplified algebraic algorithm was proposed with the help of Hamiltonian graphs.The parameters in the reverse gravity model were calibrated with the statistic data of 15 major airports in China.The simplified algebraic algorithm and conventional algebraic algorithm were used to calculate the passenger traffic of 15 airports.Their results are reasonably consistent.Compared with the conventional algebraic algorithm,the simplified one needs only a smaller number of data,and it is especially suitable for large-scale OD matrix analyses without compete inter-airport data.

Dynamic Location Assignment of AS/RS Based on Genetic Algorithm

MA Yongjie, JIANG Zhaoyuan, YANG Zhimin

2008, 21(3): 415-421.

[Abstract](1817)

Abstract:
Optimal control objectives based on a stochastic storage strategy for an automated storage/retrieval system(AS/RS),in which some spaces are occupied,were defined as the assignment optimizations for the whole warehouse and locations in it,and that for travel time of storage/retrieval machines(SRMs).Constraints in the optimization model include the capacity and the travel speed,and the rules such as storage first and retrieval last,storage from near to far,and retrieval from far to near for the SRMs in a multi-command cycle.The optimal Pareto solution of the dynamic location assignment and picking up path optimization was obtained using a genetic algorithm.An experiment was presented to show the feasibility of the proposed method.

Extraction Method for Traffic Information of Regional Road Network

JI Xiaofeng, LIU Lan, WU Qigang

2008, 21(3): 422-426.

[Abstract](1535)

Abstract:
To extract the traffic information of regional road networks,a method was proposed to identify traffic states using the matter-element analysis theory.In the method,traffic states are taken as decision attributes,a characteristic information table of traffic flows is constructed based on road grades,time and traffic parameters,and the traffic flow characteristics are extracted using the rough set theory.Numerical results of a case study verifies the effectiveness of the proposed method.The proposed mothod applys to traffic state analysis on-line and to extraction of traffic information from historical databases.

Extraction and Counting of Partial Discharges under Pulse Voltage

ZHOU Kai, WU Guangning, HE Jingyan, LIU Jun, TONG Laisheng

2008, 21(3): 319-324.

[Abstract](1497)

Abstract:
The extraction and counting method for partial discharge(PD) under pulse voltage was proposed.dB6 and dB2 wavelet packages were used to filter high and low frequency interferences respectively based on an analysis on correlation coefficient between simulation signals and extracted signals.A phase window was used to remove oscillating signals of PDs generated by sensors according to the characteristics of PDs under pulse voltage.PD phases were defined based on sampling rate,sampling length and zero-crossing of pulse voltage to analyze phase resolved patters(e.g.,-n and -q-n plots) under pulse voltage.Experiment results indicate that the proposed methods are effective for extraction and counting of PDs.

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2008 Vol. 21, No. 3