JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Mercer Kernel Based Fuzzy Clustering Self-Adaptive Algorithm

LI Kan, LIU Yu-shu

2004, 13(4): 351-354.

[Abstract](159)

Abstract:
A novel mercer kernel based fuzzy clustering self-adaptive algorithm is presented. The mercer kernel method is introduced to the fuzzy c-means clustering. It may map implicitly the input data into the high-dimensional feature space through the nonlinear transformation. Among other fuzzy c-means and its variants, the number of clusters is first determined. A self-adaptive algorithm is proposed. The number of clusters, which is not given in advance, can be gotten automatically by a validity measure function. Finally, experiments are given to show better performance with the method of kernel based fuzzy c-means self-adaptive algorithm.

Architecture of Multimedia Proxy Caching over the Internet

PAN Hao, PAN Tian-quan, SONG Han-tao, WANG Da-zhen

2004, 13(4): 355-359.

[Abstract](176)

Abstract:
Streaming media data have strict delay and loss requirements, which cannot be adequately supported by the current Internet. Proxy caching technology is introduced to alleviate the effect of the bottleneck bandwidth on the transporting quality. A new architecture of multimedia proxy caching is given to solve the problem of the traditional Web caching technology for the multimedia streaming. The mixed media management module and the (resource) management module are added to this architecture, the prefetching and replacement method is studied considering the characteristics of streaming media data, the concept of weighed popularity is given to enhance the (exactness) of the replacement algorithm.

Formalized Description of Distributed Denial of Service Attack

DU Yan-hui, MA Rui, LIU Yu-shu

2004, 13(4): 360-364.

[Abstract](120)

Abstract:
The distributed denial of service (DDoS) attack is one of the dangers in intrusion modes. It's difficult to defense and can cause serious damage to the system. Based on a careful study of the attack principles and characteristics, an object-oriented formalized description is presented, which contains a three-level framework and offers full specifications of all kinds of DDoS modes and their features and the relations between one another. Its greatest merit lies in that it contributes to analyzing, checking and judging DDoS. Now this formalized description has been used in a special IDS and it works very effectively.

Study on Virtual Human Skeleton System

GUO Qiao, LI Yi

2004, 13(4): 365-368.

[Abstract](162)

Abstract:
A solution of virtual human skeleton system is proposed. Some issues on integration of anatomical geometry, biodynamics and computer animation are studied. The detailed skeleton system model that incorporates the biodynamic and geometric characteristics of a human skeleton system allows some performance studies in greater detail than that performed before. It may provide an effective and convenient way to analyze and evaluate the movement performance of a human body when the personalized anatomical data are used in the models. An example shows that the proposed solution is effective for the stated problems.

Optimal Observability Analysis of Gimbled Inertial Navigation System on the Moving Base

YU Jia-cheng, CHEN Jia-bin

2004, 13(4): 369-372.

[Abstract](171)

Abstract:
To investigate the observability of gimbled inertial navigation system when the base moves on the basis of piece-wise constant system's observability theory and singular value decomposition, the variation of the singular value in the observability matrix with time is discussed. The simulation results reveal that only if orientation angle is 60° and the flight route is S-figure in initial alignment, the optimal observability is obtained, thus a theoretical foundation for fast and accurate alignment of GINS is provided.

FDTD Analysis of Nonuniform Lossy Cascade Multiconductor Transmission Lines

FU Ji-wei, HOU Chao-zhen, DOU Li-hua

2004, 13(4): 373-377.

[Abstract](67)

Abstract:
A hybrid algorithm is presented for nonuniform lossy multiconductor transmission lines (MTL) connected by arbitrary linear load networks. The networks are characterized by a state-variable equation which allows a general characterization of dynamic elements in the cascade networks. The method is achieved by the finite difference-time domain (FDTD) algorithm for the MTL, and the skin effect is taken into account, the more accurate method is used to compute the skin effect. And this method is combined with the computation of the nonuniform transmission lines. Finally, several numerical examples are given, these results indicate that: the current of the lossy MTL is smaller than the lossless of the MTL; and when the load networks contain the dynamic element, the transition time of the current is longer than the MTL connected by resistance only.

Radiation Characteristics of the Reflector Antenna with Random Perforated Holes

DONG Tao, XU Xiao-wen, XIAO Jiang

2004, 13(4): 378-380.

[Abstract](159) [PDF 124KB](3)

Abstract:
The radiation characteristics of a doubly curved shaped reflector antenna with random holes is analyzed by physical optics (PO) method, and the probability model of the random holes and its numerical realization method are presented. The radiation patterns show that in the azimuth plane the peak sidelobe level becomes much higher as the reflector surface with random holes. The simulation results can provide a theoretical guidance for the radar attackers.

Research for the Dynamic Range and Its Extension of Digital Intermediate Frequency Receiver

CAO Peng, QI Wei, FEI Yuan-chun

2004, 13(4): 381-384.

[Abstract](178)

Abstract:
For the optimization of dynamic range and bandwidth of digital intermediate frequency receiver(DIFR), main factors affecting them and their relationships are studied. Firstly, the DIFR sensitivity, bandwidth, noise factor of radio frequency (RF) analog front-end (RFAF), and processing gain of intermediate frequency(IF) sampling are analyzed. Secondly, the constraint relationship of the noise factor of RFAF, the signal-to-noise ratio of ADC and the dynamic range of DIFR are studied. The relationship between the dynamic range and the RFAF gain, and that of the extended dynamic range and the RF AGC(automatic gain control) step are educed and simulated. These results can be used as theory foundations and design references for the implementation and optimization of the large dynamic range and wideband DIFR.

Linear Discriminant Analysis and Kernel Vector Quantization for Mandarin Digits Recognition

ZHAO Jun-hui, XIE Xiang, KUANG Jing-ming

2004, 13(4): 385-388.

[Abstract](179)

Abstract:
Linear discriminant analysis and kernel vector quantization are integrated into vector quantization based speech recognition system for improving the recognition accuracy of Mandarin digits. These techniques increase the class separability and optimize the clustering procedure. Speaker-dependent (SD) and speaker-independent (SI) experiments are performed to evaluate the performance of the proposed method. The experiment results show that the proposed method is capable of reaching the word error rate of 3.76% in SD case and 6.60 % in SI case. Such a system can be suitable for being embedded in personal digital assistant(PDA), mobile phone and so on to perform voice controlling such as digit dialing, calculating, etc.

ASIC Design of Floating-Point FFT Processor

CHEN He, ZHAO Zhong-wu

2004, 13(4): 389-393.

[Abstract](98)

Abstract:
An application specific integrated circuit (ASIC) design of a 1024 points floating-point fast Fourier transform(FFT) processor is presented. It can satisfy the requirement of high accuracy FFT result in related fields. Several novel design techniques for floating-point adder and multiplier are introduced in detail to enhance the speed of the system. At the same time, the power consumption is decreased. The hardware area is effectively reduced as an improved butterfly processor is developed. There is a substantial increase in the performance of the design since a pipelined architecture is adopted, and very large scale integrated (VLSI) is easy to realize due to the regularity. A result of validation using field programmable gate array (FPGA) is shown at the end. When the system clock is set to 50 MHz, 204.8 μs is needed to complete the operation of FFT computation.

Flame Propagation Characteristics of Propane-Air Mixture in Ducts with Obstacles

LU Jie, WANG Cheng, NING Jian-guo

2004, 13(4): 394-397.

[Abstract](203)

Abstract:
An experimental study on acceleration mechanism of flame propagation of propane-air mixture in ducts with obstacles was conducted. The acceleration mechanism of flame propagation is mainly due to the positive feedback of the turbulence region induced by obstacles for combustion process. It can be seen from the experimental results that the maximum explosion pressure can increase by 20%, the maximum rate of pressure rise can increase by 10 times and the flame propagation velocity can increase by 20 times when obstacles are present.

Building and Analysis of Computer Aided Fuze Fault Tree

WANG Ya-bin, LIU Ming-jie, TAN Hui-min

2004, 13(4): 398-401.

[Abstract](182)

Abstract:
A common software to analyze fuze fault tree is developed to simplify the trivialness in generating the fuze fault tree and reduce the manual calculation work. The overall structure, function and implementation of the system are introduced. The software based on Windows platform is used to generate the fuze fault tree in graphics mode. A quantitative analysis of fuze fault tree can be obtained by the method of minimum cut sets. A calculation example is used to verify the function of the software. Consequently, the expected requirements of this software system are achieved to a certain level.

Simplified Approach to Velocities of Axial Forward Projection Fragments from the End of a Warhead

JIANG Jian-wei, FENG Shun-shan, MEN Jian-bing, YU Quan

2004, 13(4): 402-405.

[Abstract](134)

Abstract:
A warhead with axial forward projection fragments is one of the most important forms of aimable warheads. For such warheads the axial forward projection fragments are placed at the end of the explosive charge and form a fragment beam with high fragment density and high speed by the blast, which will obviously increase the damage to the targets. Experimental data showed that the velocities of the forward projection fragments on the convex end of a warhead which was initiated at the opposite end do not match that predicted by the Gurney equation for cylindrical warheads. A new approach for addressing the velocities of fragments of this kind of warhead is proposed. Two limiting conditions are defined, i.e. for fragment on the circumference of a cylindrical charge and fragments on the end of cylindrical charge, respectively.

Rapid Optimal Generation Algorithm for Terrain Following Trajectory Based on Optimal Control

YANG Jian-ying, ZHANG Hai, XIE Bang-rong, YIN Jian

2004, 13(4): 406-409.

[Abstract](170)

Abstract:
Based on the optimal control theory, a 3-dimensionnal direct generation algorithm is proposed for anti-ground low altitude penetration tasks under complex terrain. By optimizing the terrain following(TF) objective function,terrain coordinate system, missile dynamic model and control vector, the TF issue is turning into the improved optimal control problem whose mathmatical model is simple and need not solve the second order terrain derivative. Simulation results prove that this method is reasonable and feasible. The TF precision is in the scope from 0.3 m to 3.0 m,and the planning time is less than 30 min. This method have the strongpionts such as rapidness, precision and has great application value.

Analysis of Controlled Trajectory Optimization for Canard Trajectory Correction Fuze

GUO Ze-rong, LI Shi-yi, SHEN Qiang

2004, 13(4): 410-413.

[Abstract](171)

Abstract:
The optimization method of the canard trajectory correction fuze's controlled trajectory phase is researched by using the aerodynamics of aerocraft and the optimal control theory, the trajectory parameters of the controlled trajectory phase based on the least energy cost are determined. On the basis of determining the control starting point and the target point, the optimal trajectory and the variation rule of the normal overload with the least energy cost are provided, when there is no time restriction in the simulation process. The results provide a theoretical basis for the structure design of the canard mechanism.

Design of Engine-Generator Work Mode for Hybrid Electric Vehicle

HE Hong-wen, YU Xiao-jiang, SUN Feng-chun

2004, 13(4): 414-417.

[Abstract](169) [PDF 192KB](4)

Abstract:
From electric circuit theory view, a system model of series hybrid electric vehicle was built which uses engine-generator and battery pack as its on-board energy source in this paper. Based on the analysis for the constant power work mode and constant bus voltage work mode of engine-generator, a third work mode was put forward which combined the advantages of constant power and constant bus voltage work modes. The new work mode is reasonable to keep the battery in good working conditions and to extend its life. Also the working conditions of engine can be bettered to get low pollution and high efficiency.

Adaptive FEM Analysis of the Temperature Field of Pistons in Diesel Engines and Their Thermal Stress and Deformation Calculation

QIN Wen-jie, ZHANG Ru-hua, ZUO Zheng-xing

2004, 13(4): 418-421.

[Abstract](140)

Abstract:
The adaptive FEM analysis of the temperature field of the piston in one diesel engine is given by using the ANSYS software. By making full use of the post results provided by the software, the posteriori error estimation and adaptive accuracy meshing algorithm is developed. So the blindness of the mesh design through experiences can be avoided, and the accuracy requirement is adapted to the relative temperature gradient distribution across the entire domain. Therefore the meshes and solutions can be obtained at the same time. Based on the temperature field analysis, the thermal stress and deformation fields are calculated as well. The results show that the stress concentrates on the edge of the piston pin boss and the inside surface of the first ring groove, and the deformation of the head of the piston is greatest. But the difference between the long and short axes of the bottom cross section is greatest.

Test Analysis of Traction Battery Peak Power

LI Hong-lin, ZHANG Cheng-ning, SUN Feng-chun, HE Shi-juan

2004, 13(4): 422-425.

[Abstract](160)

Abstract:
The test process of electric vehicles （EVs） traction battery peak power is analyzed in detail. Aimed at a special “traction” design of versatile battery—HORIZON^C²M Battery, the features are introduced. According to the peak power test schedule, the test parameters of HORIZON^C²M Battery are calculated and the charging and discharging experiments are carried out. The sustained （30 s） discharge power capability of battery at 2/3 of its open circuit voltage at each of various depths of discharge is determined. The dynamic internal resistance under peak power test is established. Considering the temperature impact during discharging, the peak power capability at each of various depths of discharge is corrected. The correctness of peak power test is validated by combining theory analysis with test results.

Control and Simulation of Continuously Variable Transmission for Electric Transmission System

ZHANG Yu-nan, GE Yun-shan, MA Xiao-jun, ZANG Ke-mao

2004, 13(4): 426-429.

[Abstract](150)

Abstract:
According to the study of electric transmission, the concept of the fore and the aft power chain is presented. The control method of continuously variable transmission is established in the aft chain of electric transmission based on brushless DC motor. A fuzzy controller is designed with continuous fuzzy variables and the simulation module of the aft power chain is proved by test. The fuzzy controller controls the process of continuously variable transmission steadily and the acceleration of vehicle is quick according to simulation results. The elementary performance exhibited in the simulation is a foundation for the further study of the electric transmission track vehicle.

New P3D Hydraulic Fracturing Model Based on the Radial Flow

LU Lian-jun, SUN Feng-chun, XIAO Hai-hua, AN Shen-fa

2004, 13(4): 430-435.

[Abstract](159)

Abstract:
Pseudo three-dimension (P3D) hydraulic fracturing models often overpredict the fracture height for a poorly contained fracture. To solve this problem, a new method is presented in shaping the P3D fracture geometry on the basis of the fundamental theory and the original 1D fluid flow is replaced with a more representatively radial flow. The distribution of the fluid in the modified fluid field is analyzed and a sound explanation to the problem is given. Due to the consideration of the fluid flow in the vertical direction, the modified model can predict the fracture height much better. To validate the rationality of the radial fluid flow assumption, the distribution of the fluid in the modified fluid field is simulated with the plane potential flow by using finite element method. And the results agree effectively with those from the assumption. Through comparing with the full 3D model, the results show that this new P3D model can be used to aid the fracturing design and predict the fracture height under poorly contained situation.

Statistical Analysis for the Driving Cycle of Beijing's Bus

WANG Zhen-po, SUN Feng-chun, WANG Jun, SUN Li-qing

2004, 13(4): 436-440.

[Abstract](182)

Abstract:
According to the test data of the driving model for Beijing's bus routes, 9 parameters and the actual values of Beijing bus are confirmed to evaluate the driving cycle, 2 ways of establishing driving cycle model are analyzed, the formula of calculating driving cycle is acquired, and the calculating driving cycle model and the statistical driving cycle model for the buses in Beijing urban areas are set up. This study provides scientific basis for selecting the bus type and confirming the design parameters and the running method in Beijing.

Electric Vehicle IM Controller Based on Voltage-Fed Inverter

SONG Jian-guo, ZHANG Cheng-ning, YUAN Xue, TAN Jian

2004, 13(4): 441-444.

[Abstract](160)

Abstract:
A novel electric vehicle (EV) induction motor (IM) controller based on voltage-fed inverter is presented. It is shown that the proposed adaptive control algorithm effectively both simplifies the structure and expands the capacity of controller. The relationship between stator's voltage and that of current under rotor's flux-oriented-coordinates is first introduced, and then the structure of vector control is analyzed, in which voltage compensation is inducted as the core feedback procedure. Experiments prove that, together with a facility for realization, a smooth transition, a prompt torque response and small concussion are gained. Extensive research conducted by varying parameters that result in practical ripple is proposed in conclusion.

Determination of Stereoisomers of Epalrestat by Liquid Chromatography

QI Mei-ling, WANG Peng, YANG Jian-jun

2004, 13(4): 445-448.

[Abstract](119) [PDF 151KB](5)

Abstract:
An isocratic reversed-phase liquid chromatographic (LC) method is described for the determination of epalrestat and its three stereoisomers (degradation impurities) in drug substance. The LC separation system consisted of a Hypersil C18 column (250 mm×4.6 mm, 5 μm) with a mobile phase comprising methanol, acetonitrile and water (volume ratio 60∶1∶50, pH 4.5) delivered at a flow rate of 1.6 mL/min and UV detection at 280 nm. The proposed LC method is simple and selective for the determination of the stereoisomers of epalrestat in the drug substance with a limit of detection and quantification of 3.9 μg/mL and 4.9 μg/mL, respectively. The stereoisomers were identified by liquid chromatography-mass spectrometry (LC-MS).

Boundedness of Fractional Maximal Operators on Some of Homogeneous Groups

WANG Jie, CHEN Bing-kang, ZHANG Jian-lin

2004, 13(4): 449-453.

[Abstract](62)

Abstract:
Let M α be the fractional maximal operators （0 <α≤1） and （u,v） a pair of weight functions, u∈d ∞, σ="v ^{^{^{^{-1/（p-1）∈A ∞. The boundedness of M α on some homogenous groups （G, ‖·‖, dx） and the covering Lemma of Calderon-Zygmund type are studied. Not only an adequate covering Lemma of Calderon-Zygmund type is shown, but also the boundedness of fractional maximal operators M α（0
<α≤1） on some of homogeneous groups with respect to a given pair weight functions （u,v） as above is proved. moreover, sufficient and necessary condition for m α∈b（u^{qdx, v
^<sup>pdx）, 0
<α<1, 1}}}}}

Novel Method of Predicting Network Bandwidth Based on Support Vector Machines

SHEN Wei, FENG Rui, SHAO Hui-he

2004, 13(4): 454-457.

[Abstract](169)

Abstract:
In order to solve the problems of small sample over-fitting and local minima when neural networks learn online, a novel method of predicting network bandwidth based on support vector machines(SVM) is proposed. The prediction and learning online will be completed by the proposed moving window learning algorithm(MWLA). The simulation research is done to validate the proposed method, which is compared with the method based on neural networks.

Improved Nonlinear Friction Compensation Method for Robot Joint Driving

MEI Zhi-qian, YANG Ru-qing, ZHANG Guang-li, MAO Tai-xiang

2004, 13(4): 458-462.

[Abstract](163)

Abstract:
In order to alleviate the steady-state position error and the destabilizing effect of the nonlinear friction, a novel compensation method is presented, which modified the traditional Southward's compensation method. Estimated the nonlinear friction model using an identification method, the effect caused by its nonlinear component can be compensated, and an enhanced tracking performance is verified on a selectively compliant articulated robot arm(SCARA) robot.

2004 Vol. 13, No. 4