Showing papers in "Journal of Xi'an Jiaotong University in 2008"

A Roberts' Adaptive Edge Detection Method

Abstract: An adaptive edge detection method is proposed for the sensitivity to noise and given threshold of existing Roberts algorithmsThe basic principle of the Roberts algorithm is used and the direction of the detection is expandedThe algorithm generates automatically adaptive threshold according to the mean value of the 3×3 area pixels around the detecting pixel and the property of people's visionIt not only can keep advantages of existing Roberts algorithm such as parallel process,fast calculation speed and the comparatively thin edge,but also can play a certain part in restraining noiseBecause the edge detected by Roberts algorithm is comparatively thick,and the efficiency of the edge-thin algorithm is lower,the edge-thin algorithm is analyzed and improvedThe improved algorithm detects the edge of the image where there exists noise,filters the fake edge,then thins the edge of the image,and finally gets the single pixel edgeBy comparing the test results of the adaptive edge detection algorithm with those of the existing Roberts algorithm,the adaptive edge detection method can generate automatically adaptive threshold,improves the performance in getting detailed-edge and restraining noise

Experiment Study on Performance of Refrigerator Using Nano-Particle Additive

Abstract: An experimental study was conducted on the performances of a refrigerator using the mixture of HFC134a/HC600a,mineral oil and nano-particles of Fe3O4.The cooling speed and the power consumption of the refrigerator,the temperatures at the different selected points in the refrigerator were measured under the different charging amount,with and without adding nano-particles in the system.The experimental results show that there was an optimal cooling speed and an optimal power consumption of the refrigerator but their corresponding charging amounts were different.With nano-particles under the same conditions,the refrigerator performance rose.The temperature of the compressor shell decreased by 2.2 ℃ while the suction temperature changed slightly.Moreover,the discharge temperature decreased by 3.5 ℃ and the average evaporator temperature decreased by 0.3 ℃.The cooling time decreased by 148 seconds and the power consumption decreased slightly.It seems that the nano-particles may be effective to enhance the heat transfer of the refrigerant and improving the property of the mineral oil.

Brake-Force Distribution Strategy for Electric Vehicle Based on Maximum Energy Recovery

Abstract: To heighten electric vehicle(EV)recovery energy,a brake-force distribution strategy based on motor brake torque is proposed from the viewpoint of maximum energy recovery,together with the analysis of the vehicle brake dynamics and related regulations.Motor model and EV power-train model are established,and simulation is carried out with MATLAB/Simulink.The results show that with the adoption of the strategy,the EV meets braking stability and regulations requirement.Compared with the ideal front and rear braking force distribution,the proposed strategy enables to take advantage of motor brake torque,and simulation results show that it can enhance motor regenerative energy by 56.1% for the Japanese 1015 driving cycle.A remarkable motor regenerative energy improvement can be found for the other driving cycles.

Modeling of Large-Scale Wind Farms in the Probabilistic Power Flow Analysis Considering Wake Effects

Abstract: Based on the Jensen model and Lissaman model and combined the frequency distribution model of wind speed and steady-state model of wind turbine generator,an integrated model for large wind farm is proposed which is connected directly to the distribution grid.Considering the energy loss caused by wake effect and impact of topographical factor on wind speed of wind turbine in different location,the output of whole wind farm can be evaluated via the model.Then,the model is applied in the IEEE 14-bus test feeder to analyze the impact of wind farm on nodal voltage of power system and give reference for reducing voltage fluctuation.Moreover,the variable transformation is adopted to estimate the parameters of three-parameter Weibull distribution function.

Fault Line Selection in Non-Solid Earthed Network

Abstract: To improve sensitivity and reliability of fault line selection in non-solid earthed network based on the model identification,a new Π model with unequal capacitances is presented,where the capacitance of bus-side equals to half of the zero sequence capacitance value of the line,and the capacitance of load-side is unknown which depends on the operation mode of the power system.Then the equation of the Π model gets linear which can be solved easily.Integral algorithm is chosen to restrain high-frequency component to lower the performance requirements of filter and the identified parameters become more accurate.Thus the sensitivity and reliability of fault line selection are improved.The validity of this proposed method is verified via EMTP simulator and fault recorded data.

Chaos Small-World Optimal Algorithm Based on Population Entropy

Abstract: To avoid trapping into local minimum and improve searching efficiency of local short-range operator during the function optimization,a chaos small-world optimal algorithm based on population entropy is presented.The individual density,constructed according to the information entropy,and fitness are taken as the evaluation criterion,and the individuals of high density are replaced by new initial individuals,which achieve the self-adjustability and diversity of population.The characteristics of ergodicity and randomness of chaotic variables are considered to produce the initial population with logistic mapping,and the individual local search is performed by chaos disturbance after local short-range search,thus the searching efficiency and accuracy are obviously heightened.The simulation results show that the proposed algorithm remarkably improved the searching capacity and efficiency in small-world algorithm.

Ultracapacitor with Applications to Electric Vehicle

Abstract: The mechanism and characteristic of ultracapacitor are introduced.The ultracapacitor application status in electric vehicle(EV) at home and abroad is outlined.Analyzing the topology and control strategy of ultracapacitor applied in EVs,a novel control system of ultracapacitor-battery hybrid power EV is designed,which comprises a bi-directional DC/DC converter and a three-phase full bridge inverter.The experimental results show that the hybrid power EV enables to combine the advantages of battery and ultracapacitor,enhance the start-up and accelerating performance of EV,improve the energy-regenerative efficiency,and increase the driving range.EVs employing ultracapacitor as the only power may be used as fixed-line buses,but the basic facilities ought to be imprared.

Non-Uniform Rational B-Splines Curve Fitting Based on the Least Control Points

Abstract: Aiming at the optimizing design of vane curve,a novel algorithm of adaptively choosing appropriate nodes is proposed to interpolate non-uniform rational B-splines(NURBS) curve,and the error-bounded curve fitting is carried out and the control points are determined.The dominant points are identified and extracted with the curvature information,and serve as nodes to interpolate NURBS curve,then the control points are evaluated via de Boor iterative equation.Simultaneously,a new node is adaptively added according to the error and curvature properties of fitting curve to iterate procedure until the required accuracy is met.Several experiments are performed to validate this method.

Voltage Fluctuation of a Power System with Wind Farms Integrated by Probabilistic Load Flow

Abstract: A new probabilistic load flow model to investigate voltage fluctuation caused by wind farm integration is presented.Considering wind speed randomness and other stochastic disturbances,such as varying loads,generation unit and branch outages,the probabilistic distributions of constraint violation of node voltages and branch transfer powers can be obtained,then the enduring ability of the integration node for the stochastic wind power generation,the reactive power compensation and the integrating equipment effect on the voltage fluctuation can be analyzed thoroughly,which provide a useful tool for electrical engineers to reveal the voltage quality of the gird and choose the integration node for a wind farm.The three-parameter Weibull distribution model taking location parameter into account is proposed to describe wind speed random fluctuation.Compared with the normal two-parameter Weibull distribution model,the impact of the high speed wind on the power output of the wind turbine is considered in the presented model,thus more satisfied results can be obtained in the evaluation.The calculation of voltage fluctuation has been preceded on IEEE RTS 24 test system integrated with wind farms.

A Technique For Extending Dynamic Range of Medical X-Ray Image

Abstract: A technique for extending the dynamic range of medical X-ray image that uses multi-scale image decomposition is proposed to extend the dynamic range of digital radiology equipment with either image intensifier or charge coupled device.Two images obtained at different tube voltages are decomposed by multi-scale image decomposition,and the resulting components are then recombined to reconstruct an image with extended dynamic range.Experiments show that the image processed by the technique contains 3 or more regions of interest(ROI) regions while the original image contains 2 ROI regions.Total surface dose in two exposures is 2.646×10-4 Gy/cm2 that does not cause any increase in patient dose.The technique can improve the utilization of digital radiology equipment using either image intensifier or charge couple device.

Novel Selective Support Vector Machine Ensemble Learning Algorithm

Abstract: Focusing on the problem that conventional ensemble learning methods may be invalid when support vector machine(SVM) is used as component learner,a new selective SVM ensemble algorithm is proposedξα estimator is used to estimate the generalization performance of the component SVM,and negative learning theory is used to introduce diversity among component SVMsA set of component SVMs with high generalization performance and high diversity is selected during ensemble through recursive elimination algorithmExperimental results on UCI data sets show that compared with single SVM,conventional Bagging ensemble method and negative learning ensemble method,the classification accuracy of selective SVM ensemble is increased on average by 04%,024% and 016%,respectively

An Empirical Analysis on the Regional Discrepancy and Tendency of EKC in China(1981-2004)

Abstract: In this paper, we use the panel data from 1981 to 2004 to carry out an empirical analysis on the existence of the environmental Kuznets curve (EKC), regional discrepancy and the trend of convergence, and finally, the tendency of change. The results of the empirical research show that some pollutants have obvious EKC characteristics, and the income of turning points is lower than the level of developed countries. However, the short-term EKC characteristics and the dependence on the model setting indicate that we must make rational judgment of the problem of Chinese environmental pollution. Meanwhile, China′s economic development gap between regions has an impact on the environment-income relationship, which reflects the regional discrepancy of China′s environmental Kuznets curve from another side.

Two-Dimensional High Precision Positioning Maglev Stage

Abstract: To eliminate the movement and position error caused by gap,friction of motion pair and elastic deformation of driving-part for the traditional mechanical stage,a prototype for two-dimensional movement maglev stage with near-zero-friction motion pair is developed,where the double stage structure with 500 mm movement distant is adopted,each stage is constracted with six pairs of the same electromagnets to achieve magnetic levitation motion,and the stage in the way of foursquare magnetic levitation and translational control in the side direction are located above the lead rail.Designing the magnetic force applied to the one-dimension stage,the decoupling control scheme of the maglev stage for vertical and horizontal directions is established.According to the mathematic model of active magnetic bearing system,the two-dimensional maglev stage and the control system are designed and developed.With the method of dSPACE digital control prototype and analog control,the maglev stage is successfully levitated in 5 degrees of freedom under PID control,and the start-levitation characteristic and shock response of the maglev stage are tested.The suspension accuracy of two-dimensional maglev stage gets to 10 μm,which predicts the further applications for the next-generation of semiconductor manufacturing.

Numerical Simulation of Subcooled Boiling Water in Vertical Concentric Annulus under Low Pressure

Abstract: Adopted a modified bubble departure diameter correlation based on the Unal mechanism model,a numerical simulation of subcooled boiling water under low pressure was performed on the computational fluid dynamics code CFX5.7 with user defined FORTRAN program.The water boiling flow experiments under low pressure in a vertical concentric annulus from reference were adopted to validate the modified model of bubble departure diameter.Moreover,the examination of grid independence was discussed,and the influences of the non-drag force on the radial void fraction distribution force were investigated,including lift force,turbulent dispersion force and wall lubrication force.The simulation results indicate that the models are endowed with a preferable applicability for broad test conditions.Especially,the peak void fraction at near-wall region occurs in low liquid subcooling and low mass flux,contrariwise,the peak void fraction in near-wall region never appears.which is in accordance with the experimental data.The predicted profiles of liquid velocity are close to the experimental data,but obviously differ from the prediction of vapor velocity in the near-wall region.

Sound Absorption Properties of Sintered Fibrous Metals under High Temperature Conditions

Abstract: Focusing the attention on a sintered fibrous metal sample,the sound absorption properties under different temperatures(from 20 ℃ to 500 ℃) and temperature gradients(-24 ℃/mm and 405 ℃/mm) are theoretically evaluatedBy adopting the two-microphone transfer-function method,a set for measuring the uniform high-temperature sound absorption properties of porous metal is developed,and the sound absorption properties of a sintered fibrous metal sample at different temperatures are measured to validate the theoretical resultsIt is found that reference-temperature method can be used to well evaluate the porous metal acoustic properties at relatively low temperaturesAnd the changes of temperature fields exert remarkable effects on the surface acoustic impedance at normal incidence of materialWhen the constant temperature gradient exists across the material cross-section,the effects of temperature gradient on overall sound absorption characteristics of porous metal ought to be regarded considerablyUnder certain conditions,the minus temperature gradient may enhance the sound absorption of porous metal whereas the positive temperature brings an adverse effect

Chinese Stock Market bubble Inevitable or Incidental

Abstract: Three adverse specific psychological factors of Chinese investors,including 'greed','envy' and'speculation',are principal explanations for the development of Chinese stock market bubble which developed so quickly during 2006-07 Excessive valuations and fundamental weakness of listed Chinese companies were ultimately responsible for the stock market crash in the first eight months of 2008 The lack of further investment capital was the needle that pricked this bubble In the long term,as most Chinese investors become more aware of the potential risks and returns,the stock markets will be less volatile,avoiding the dramatic boom-and-bust cycle seen over last two years This means that it will take a rather long time for the market to become bullish again

Contemporary Engineering Values and Engineering Education

Abstract: Contemporary engineering values play an important role in engineering education.This paper has analyzed the essential contents of contemporary engineering values in comparison with the traditional values.Then the problems of overemphasizing scientific and technological rationality in traditional engineering education are studied.At last,the corresponding strategies of engineering education are dealt with based on integrated rationality and contemporary engineering values.

Error Analysis and Compensation of Linear Structured Light Scanning Probes

Abstract: For polynomial fitting measuring model of a linear structured light scanning probe,the extraction and compensation methods for systematic errors of the probe are presented.By measuring fixed lines at different height,the proposed method extracts the measuring errors in positions with different depth of the field.And systematic errors of the probe at different measuring height are separated from the extracted errors,and the first error compensation in the height direction can be implemented.According to the calibrating result and error compensation lattice in the height direction,a comparison is made between the spatial lattice obtained by calibrating image grid lattice and the practical calibrating spatial grid lattice.The remaining errors of measuring results after compensation in the height direction are further extracted.And the second error compensation and correction are implemented simultaneously.The experimental results show that the measuring depth of field can be expanded effectively and reached 150 mm with the presented method.A high accuracy(±50 μm) can be ensured in a large range of depth of field on common mechanical accuracy platforms(single axis positioning accuracy:15 μm) driven by step motor with open-loop style.

Control Algorithm and Parameter Match for an Electromagnetic Coupling Hybrid Electric Bus

Abstract: Based on the knowledge of dynamic servo,a novel research project of electromagnetic coupling hybrid electric bus is proposed to keep the internal combustion engine running at an optimal operation line independent of wheel load.The mechanical clutch and manual transmission fixed in the conventional bus are replaced by double motors to execute the functions of electromagnetic clutch and continuously variable transmission simultaneously.By analyzing the operating principle and determining the control algorithm,the parameter design and match of engine,double motors and power battery are investigated to meet the vehicle dynamic performance and typical driving-cycles for the aim bus.The simulation results from the vehicle backward simulation model indicate that the acceleration period from 0 to 60 km/h decreases by 16.5% and fuel economy of the novel bus improves by 39.6% compared with the conventional bus.

Modeling and Evaluation of Composite Web Services Based on Generalized Stochastic Petri Net

Abstract: To ensure the correctness of composite Web services described by semantic Web services markup language(OWL-S),and to guarantee the high performance of the composite Web services,a generalized stochastic Petri net based method is proposed for modeling,verification and evaluation of the OWL-S process models.The transforming rules from OWL-S process models to generalized stochastic Petri net(GSPN) are given.The analysis of S-invariant,T-invariant and reachability of the Petri net are used to verify the soundness of the process models.Moreover,Markov chains of the models are constructed.Performances of the processes are analyzed in terms of steady state probability distribution of generalized stochastic Petri net.It is verified mathematically that the models are correct and reliable.Also the bottlenecks of composite Web services is found.It is believed that the method will support to the reconstruction,optimization and decision-making of the composite Web services.

Contamination Depositing Characteristics of Suspension Insulators under Sandstorm Circumstance Simulated Artificially

Abstract: The contamination depositing characteristics of suspension insulators under the sandstorm circumstance were investigated by the experiments of insulators running in circumstance of sandstorm simulated in laboratory artificially.Following artificial experiments,the contamination depositing and distributing characteristics were discussed,such as difference of deposition among sheds at different position,difference of deposition between big shed and small shed,relationship between deposition quantity and flow speed,relationship between deposition quantity and experiments duration.The obtained results show that shed position has no evident effect on pollution depositing as only flowing effect gets considered;flow speed and duration affect the dust and salt quantity depositing on shed surface greatly;at certain flow speed and duration,the deposition quantity may get the largest.

Propagation Characteristic of Partial Discharge Ultra High Frequency Signals Outside Transformer

Abstract: It is found in field detection that ultra high frequency(UHF) signals can diffract from the joint of transformer.The feasibility of using external UHF sensor for detecting partial discharge activities is discussed,and the external propagation characteristic of UHF electromagnetic wave is investigated via the lab experiment.The wavelet packet analysis of signals shows that the frequency distribution of external signals and the inside signals is quit difference.The relationship between distance of joint and UHF sensor is also researched and the results show that UHF signals may leak outside the transformer through the joints after multiple refraction and reflection in the transformer tank,and the electromagnetic wave expression varies with difference distance.

Measurement and Analysis for Pulse Current Shapes of Partial Discharge in Oil under DC Voltage

Abstract: A test system with wide frequency response was designed to measure pulse current shape of partial discharge(PD) based on the PD model and ultra-wideband detection method under direct current voltageThe measuring impedance was tested by square wave with very steep trailing edge and the corona in air under DC voltage was detected,which confirms the validity of the whole systemAccording to the defect analysis in oil-paper insulation of converter transformer,six corresponding PD defect models were constructed to gain the PD pulse current shapesThe results show that the PD pulse current shapes of the defects in oil under DC voltage get non-oscillatory without overshoot and the characteristic parameters of the pulse current shapes differ from each other for different defect models,which coincides with the discharge model under DC voltage mentioned above

Component Placement Process 0ptimization for Chip Shooter Machine Based on Genetic Algorithm

Abstract: The component placement sequence and feeder arrangement are the critical factors determining assembly time of chip shooter machine.Based on the engineering analysis,an integrated optimization model of chip shooter machine is formulated,and a two-dimensional coding method is proposed with improved genetic algorithm(IGA).In the individual chromosome,the component number describes the component placement sequence,the feeder number describes the feeder arrangement,and the component type number describes the relation between the component placement sequence and feeder arrangement.The IGA with order-based crossover,adaptive mutation and local search,contains a parallel structure.The component placement sequence and the feeder arrangement are optimized simultaneously to improve the assembly efficiency.

Finite-Difference Extended Kalman Filtering Algorithm for Ballistic Target Tracking

Abstract: In order to overcome the disadvantage of the common used filtering algorithms that can not achieve the tracking accuracy and effectiveness at the same time,a finite-difference extending Kalman filter algorithm was proposed for ballistic target tracking problem in the re-entry phaseThis algorithm uses finite differences to approximate the priori error covariance matrix and the posterior error covariance matrix,and avoids evaluations of derivatives,the Jacobian and Hessian matrices,which enlarge the application areas and improve the filtering convergenceThe Monte Carlo simulations show that,compared with the extended Kalman filter(EKF) and the unsented Kalman filter(UKF),the tracking accuracy of the new algorithm is close to that of UKF,but 20% higher than that of EKF;the computational complexity of the new algorithm is close to that of EKF,but 39% lower than that of UKFAll these results show that the filtering accuracy of the proposed algorithm is improved evidently with a little increasing in computational cost

Energy Finite Element Analysis to High-Frequency Bending Vibration in Cylindrical Shell

Abstract: To obtain detail information of high-frequency vibration in cylindrical shell,the governing equation of energy density about bending vibration in cylindrical shell is developed based on the relationship of an energy balance and thin shell theory.A deduced second order equation models the far field energy distribution.The resulting equation is solved by means of finite element method.A comparison between the results of energy finite element analysis and statistical energy analysis indicates that the energy finite element analysis enables to get more detail information of high-frequency vibration.This governing equation is similar to the beam equation for only high-frequency axisymmetric bending vibration response of cylindrical shell.

Study on a Parallel Test System Based on Multi-Core

Abstract: The efficiency of the parallel test is limited with the traditional test program.Three decomposed methods,which are based on missions,data and data flows,are brought forward to solve the problem of the parallel decomposition in test processes.The multi-core technology is introduced into the field of the parallel test,and it improves the real-time capability of test task with its parallel ability.The schedule strategy based on the task amount is advanced to optimize the test flow and the task schedule of MCP system,and solves the problem that single-core program couldn't utilize MCP technology effectively.The experiment results show that the performance of the plat based on MCP is enhanced about 30%-50% against the single-core plat.

Evaporation Investigation of Single Droplet in High Temperature Fuel Gas

Abstract: To understand the movement and evaporation behavior of single droplet in high temperature fuel gas,a mathematical model was proposed by considering the gas-liquid two-phase coupling.The droplet diameter,velocity and average temperature during its evaporating process and the influence of the fuel gas temperature(1 530 K - 2 130 K) and velocity(30 m/s - 60 m/s) were analyzed.The numerical results show that both higher temperature and higher velocity of fuel gas can accelerate the evaporation of droplet.When the fuel gas temperature decreases continuously along the droplet movement direction,a critical droplet diameter for evaporation exists.The evaporation time shortens with the increasing gas velocity as the droplet diameter gets lower than the critical value.However,the trend is contrary to the droplet diameter beyond that value.In the present condition(the temperature of the fuel gas drops from 2 210 K to 1 090 K along 550 mm length),the critical value is 100 μm.The evaporation investigation of a single droplet provides a foundation for the research of spray evaporation in high temperature gas.

Multiobjective Reactive Power Optimization in Power System

Abstract: Based on the traditional model of reactive power optimization,index of static voltage stability is introduced and a model of multiobjective reactive power optimization is established,where the active power loss minimization,static voltage stability margin maximization and high voltage quality are taken into account,and improved multiobjective particle swarm optimization algorithm based on Pareto conception is chosen to solve multiobjective reactive power optimization problem for IEEE 30 bus system.The simulated results show that the model is able to heighten power system voltage stability during the economical operation,and validity of the established model and effectiveness of the proposed algorithm are verified.

Effects of System Spatial Distribution on Natural Circulation under Rolling Motion Condition

Abstract: The effects of the system spatial distribution including mass distribution,rolling axes and double loops on natural circulation under rolling motion condition were studied theoretically based on the mathematical model of natural circulation flow with rolling motion.The results show that the spatial distribution has important influences on natural circulation flow due to the time-spatial characteristic of additional acceleration caused by the rolling motion,and the effect of rolling axes is significant.For the coolant system,the effect of centripetal force may be counteracted by the symmetrical distribution of the loop;the effect of tangential force may be reduced by locating the rolling axes outside the loop,and the fluctuation of the total coolant mass flow rate may be lowered by using symmetrical double loops.