JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Investigating Jet Appearance in Different Background Lights with High-Speed Frame Photography

WANG Cheng, YUN Shou rong, HUANG Feng lei, ZHANG Han ping

2002, 11(2): 113-116.

[Abstract](216) [PDF 175KB](27)

Abstract:
Shaped charge jet formation process is studied under the conditions of different background lights by means of high speed frame photography. In order to shoot true jet appearance, the glass tube in which jet moves is vacuumized. The experiment results show that observing jet appearance with the double reflecting mirrors system is feasible as long as the vacuum of the glass tube can meet the requirement of experiment.

Error Analysis and Compensation of Strapdown Inertial Navigation System

LIU Qin, LIU Li, QI Zai kang

2002, 11(2): 117-120.

[Abstract](372) [PDF 251KB](46)

Abstract:
Based on error analysis, the influence of error sources on strapdown inertial navigation systems is discussed. And the maximum permissible component tolerances are established. In order to achieve the desired accuracy (defined by circular error probability), the types of appropriate sensors are chosen. The inertial measurement unit (IMU) is composed of those sensors. It is necessary to calibrate the sensors to obtain their error model coefficients of IMU. After calibration tests, the accuracy is calculated by uniform design method and it is proved that the accuracy of IMU is satisfied for the desired goal.

Mid-Course Guidance Law for Long Range Multi-Purpose Missiles

LUO Xi-shuang, ZHANG Tian qiao

2002, 11(2): 121-124.

[Abstract](197) [PDF 148KB](23)

Abstract:
A useful mid course guidance law for long range multi purpose missiles is proposed. The law consists of two parts. One is used in the horizontal guidance plane, and the other in the vertical guidance plane. The mid course is combined with variable structure proportional navigation in the homing phase. Simulation results show that the proposed guidance law can meet the demands for starting up the homing phase and so the handing over between mid course guidance and terminal guidance can be carried out successfully.

Methods of Validating Simulation Model and Program Design

CHEN Li, ZHANG Qing ming, WANG Xiao ying, WANG Yu li

2002, 11(2): 125-128.

[Abstract](279) [PDF 147KB](22)

Abstract:
Validating simulation model is one of the important aspects for modeling and simulation. Some methods of validating model are compared and analyzed. Several typical methods, such as TIC's inequality coefficient, gray interconnected analysis, direct spectrum estimation, maximum entropy spectral estimation based on Burg or Marple, are chosen and programmed in C language. Some examples by using the program are given. The results show that the program is available and it is best to adopt multi methods for validating models.

Modeling and Simulation of the Characteristics of Pneumatic Cushion Cylinders

JIANG Ze min, ZHANG Bai hai, WANG Tao, PENG Guang zheng, WANG Hai tao

2002, 11(2): 129-132.

[Abstract](301) [PDF 140KB](33)

Abstract:
The analysis of the characteristics of the cushion process of the pneumatic cushion cylinder is presented, and the nonlinear model of pneumatic cushion cylinders is built in the form of nonlinear differential equations. Besides, through the simulation of the pressure in the cushion chamber, the characteristics of the pneumatic cushion cylinder are obtained, which helps to understand the performance of the pneumatic cushion cylinder and improve or design the better cushion structure.

Applying Multibody System Dynamics to the Improvement of Valve Train's Cam Profiles

QIN Wen jie, LIAO Ri dong, ZUO Zheng xing, LIANG Li wei

2002, 11(2): 133-136.

[Abstract](245) [PDF 151KB](25)

Abstract:
The method of applying multibody system dynamics to the simulation of valve trains' kinematics and dynamics properties is presented, and used in the analysis of 4102QB engine's side mounted valve train. The results show that it is needed to optimize its cam profile. Thus four style Ⅰ multiple cam profiles with different parameters, two polynomial profiles and one multi cycloid profile are designed and applied to the valve train's multibody system dynamics model. By comparing the analysis results, a reasonable cam profile is obtained.

New Method to Restrain Pumping Voltage of Braking Procedure for Brushless DC Motor of Electric Armored Vehicle

ZHENG Mu qiao, SONG Xiao qing, SUN De fu, ZANG Ke mao

2002, 11(2): 137-141.

[Abstract](244) [PDF 298KB](27)

Abstract:
In order to restrain the high pumping voltage of braking procedure which is harmful to the system of electric armored vehicle. Based on the analysis of pumping voltage of the braking procedure, the relation between pumping voltage and PWM ratio is derived and a new digital control method to restrain the pumping voltage by changing PWM ratio is put forward. Because the capacitance is decreased effectively, the volume of controller is reduced and the performance to price ratio is improved. The results of computer simulation and experiment proved that this method is feasible and valid.

Oil-Film Clutch in Soft-Start of Belt Conveyor

ZHOU Man shan, WEI Chen guan, YU Yan, ZHANG Yuan

2002, 11(2): 142-145.

[Abstract](283) [PDF 192KB](26)

Abstract:
The oil film clutch, which is superior in speed adjustment, is capable of being used in the belt conveyor to carry out soft start operation. According to running properties of both belt conveyor and oil film clutch, equations that are used to decide the lubricating oil flow and the number of oil films (i.e. the number of rotating and stationary plates) are deduced theoretically. Also key parameters are provided for the design of the hydraulic system. All these together provide the theoretical basis for the soft start design of the belt conveyor and references for the application of the oil film clutch in similar fields.

Development of Turbocharger for Improving Diesel Engine Matching Performance

ZHANG Hong, MA Chao chen

2002, 11(2): 146-149.

[Abstract](283) [PDF 207KB](26)

Abstract:
The two development ways of turbocharger technology to solve the problem of matching performance with diesel were presented. The ways of waste valve gate turbocharger and variable geometry turbocharger can solve the problem of engine's low speed torque and achieve lower smoke level. Especially for variable geometry turbocharger, it covers all conditions of engine. It can not only improve the low engine's speed torque and keep the power performance at high engine speed, but also cover wide engine speed performance that keeps lower fuel consumption and exhaust gas temperature in full load and part load matching. The results of theory analysis and experiment research showed that it's the ideal solution to solve the matching problem of diesel engines.

Analysis and Experimental Identification of Torsional Dynamic Characteristics of Hydrodynamic Torque Converter

CHEN Dong sheng, XIANG Chang le, LIU Hui

2002, 11(2): 150-154.

[Abstract](267) [PDF 217KB](26)

Abstract:
The subsection linear torsional model of hydrodynamic torque converter was established and further simplified. According to the identification theory, the frequency characteristic was achieved with the Matlab/ Ident toolbox. Then parametric model was established by adopting the subsection linearization method, and the damp value was estimated. The curve and function of damp changing with speed ratio was also established by fitting. In order to validate the identification results, the experimental output was compared with the output of the model in which torque was chosen as input signal and speed as output signal in Matlab/Ident toolbox. It was shown that model output is in good agreement with experimental output.

Finite Element Simulation of the Vibratory Characteristics for Quartz Tuning Fork Gyroscope

WANG Ying, SUN Yu nan, QIN Bing kun

2002, 11(2): 155-158.

[Abstract](323) [PDF 112KB](27)

Abstract:
The micro quartz crystal tuning fork gyroscope is a new type of vibratory gyroscope. The gyroscope should be analyzed and simulated early in the design stage in order to offer reliable basis for design and to shorten the period of development. Thus the vibratory characteristics of the gyroscope is simulated with the finite element method of coupled field. The optimum exciting frequency and the factors which influence the gyroscope sensitivity are determined. The method for adjusting the frequency deviation between driving and detecting modes is also proposed.

Computations on the Earth Terrain Return of Pulse Doppler Radar Altimeter

ZENG Chao, LI You ping, LI Hong qi

2002, 11(2): 159-163.

[Abstract](270) [PDF 177KB](28)

Abstract:
Concerning the PDRA (pulse doppler radar altimeter) designing and evaluation, owing to that the specifications of PDRA should be adaptively fixed according to the ETR (earth terrain return), and that in certain stages of product evaluation of PDRA which means the designations of PDRA are successful or not, the usage of ETR are indispensable, so the terrain return from spherical earth is critically important. A complete analytic derivation of the antenna shot section model of PDRA and the bright section model constrained by pulse emitted from antenna are given. Furthermore, the doppler effect mode and the earth terrain RCF (radar crossing factor) model are constructively analyzed. Then, the computing methodology on PDRA, which are used to compute the scattering power, scattering doppler spectrum, and the scattering signal, is studied. Besides, in order to check the correctness and efficiency of the algorithm, computing examples of ETR (earth terrain return) under the supposing premises are furnished. Finally, the conclusion is drawn that the models and algorithm are rational, the computational precise is satisfactory, the cost of computing time is low.

Technique of Error Concealment for Block-Based Image Coding Using Genetic Algorithm

YANG Shou yi, LUO Wei xiong

2002, 11(2): 164-168.

[Abstract](329) [PDF 198KB](29)

Abstract:
Since real world communication channels are not error free, the coded data transmitted on them may be corrupted, and block based image coding systems are vulnerable to transmission impairment. So the best neighborhood match method using genetic algorithm is used to conceal the error blocks. Experimental results show that the searching space can be greatly reduced by using genetic algorithm compared with exhaustive searching method, and good image quality is achieved. The peak signal noise ratios(PSNRs) of the restored images are increased greatly.

Coding Scheme for Ka-Band Fixed Satellite Communication System

WANG Ai hua, LUO Wei xiong

2002, 11(2): 169-173.

[Abstract](254) [PDF 274KB](28)

Abstract:
The performance analysis and simulation of coding schemes based on the modeling Ka band fixed satellite channel have been presented. The results indicate that concatenated codes with large inner interleaving depth have good performance and high spectrum efficiency. The studies also show that simple block interleaving is very effective in combating the slow frequency nonselective fading of Ka band.

Performance Analysis of AMR Voice Activity Detection Algorithm for Mandarin Based on Objective Test Method

CHEN Dong, ZHANG Yan, KUANG Jing ming

2002, 11(2): 174-179.

[Abstract](260) [PDF 200KB](21)

Abstract:
To evaluate the performance of adaptive multi rate (AMR) voice activity detection (VAD) algorithm standardized by 3GPP applied to Mandarin, the formal objective test method is adopted as the performance metric, this kind of method is based on statistics of clipping probability, voice activity factor, noise detected as speech probability and speech input level. With different background noises and different signal to noise ratios, the AMR VAD algorithm is simulated and compared with both reference VADs including enhanced full rate (EFR) and ITU G.729B. The results show that the AMR VAD performs better than G.729B VAD and worse than EFR VAD in most of cases.

Optimization of Linear Antenna Arrays Based on Genetic Algorithms

WANG Hong jian, GAO Ben qing, LIU Rui xiang

2002, 11(2): 180-183.

[Abstract](280) [PDF 193KB](23)

Abstract:
The methods of moment and genetic algorithm (GA) are combined to optimize the Yagi Uda antenna array and Log periodic dipole antenna (LPDA) array. The element lengths and spacing are optimized for the Yagi Uda array; while the ratio factor of spacing to length as well as the ratio of length to diameter of the elements are optimized for LPDA array. The results show that the main parameters, such as gain and pattern, have been improved apparently; and the high back lobe level of LPDA can be reduced greatly, therefore, GA is a very competent method for optimizing the linear array as well as in other fields.

Two-Dimensional Entropy Method Based on Genetic Algorithm

WANG Lei, SHEN Ting zhi

2002, 11(2): 184-188.

[Abstract](256) [PDF 176KB](24)

Abstract:
Two dimensional(2 D) entropy method has to pay the price of time when applied to image segmentation. So the genetic algorithm is introduced to improve the computational efficiency of the 2 D entropy method. The proposed method uses both the gray value of a pixel and the local average gray value of an image. At the same time, the simple genetic algorithm is improved by using better reproduction and crossover operators. Thus the proposed method makes up the 2 D entropy method's drawback of being time consuming, and yields satisfactory segmentation results. Experimental results show that the proposed method can save computational time when it provides good quality segmentation.

Numerical Simulations of Polymer Melt Conveying in Co-Rotating Twin Screw Extruder

PENG Jiong, CHEN Jin nan

2002, 11(2): 189-192.

[Abstract](213) [PDF 178KB](31)

Abstract:
The 3 D non isothermal flow of non Newtonian viscous polymer melt in a co rotating twin screw extruder is modeled. The distributions of the velocity, temperature, pressure and the viscous dissipation in the flow domain are presented by using a fluid dynamics analysis package (Polyflow). The numerical results show that the temperatures are high in the intermeshing region and on the screw surface, the maximum pressure and the minimum pressure occur in the intermeshing region, and the flow rate is almost proportional to the screw speed.

Product Data Management Implementation

LU Ji ping, TANG Shui yuan

2002, 11(2): 193-197.

[Abstract](257) [PDF 177KB](31)

Abstract:
On the basis of PDM(product data management) definition and its connotation, the factors to ensure implementation success are analyzed. The definition phase, analysis phase, design phase, build and test phase, and post production phase during PDM implementation are described. The implementation is divided into ten processes, which consist of the above different phases. The relationships between phases and processes are illustrated. Finally, a workflow is proposed to guide the implementing at a fixed price.

Security of Application System

LI Xiao ping, ZHONG Hong, DING Yan, XIANG Zhi, HU Hai sheng, WU Xue lin, ZHANG Qi, ZHU Jian xue

2002, 11(2): 198-202.

[Abstract](328) [PDF 176KB](24)

Abstract:
A safe and reliable application system frame based on Internet and Intranet for Stock Supervision and Administration Council of China is built up. An all sided, multi tier and multi technical security method has been adopted, which includes identity recognition, data encryption, digital signature, Domino and WWW servers, access control list, directory service, certificate authorization server, IC card and so on. The recognition system based on CA server is a high efficient, convenient and reliable system. The encryption technology and security method are proved to be reliable. The recognition system is of high security and is worthy of being popularized in some places where some special security requirements need meeting. Multi tier technology can improve the security of database. Double keys method is a useful data encryption method.

Real-Time Face Tracking and Recognition in Video Sequence

XU Yi hua, JIA Yun de, LIU Wan chun, YANG Cong

2002, 11(2): 203-207.

[Abstract](292) [PDF 253KB](27)

Abstract:
A framework of real time face tracking and recognition is presented, which integrates skin color based tracking and PCA/BPNN (principle component analysis/back propagation neural network) hybrid recognition techniques. The algorithm is able to track the human face against a complex background and also works well when temporary occlusion occurs. We also obtain a very high recognition rate by averaging a number of samples over a long image sequence. The proposed approach has been successfully tested by many experiments, and can operate at 20 frames/s on an 800 MHz PC.

Simple Path Planning for Mobile Robots in the Present of Obstacles

JIA Yan hua, MEI Feng xiang

2002, 11(2): 208-211.

[Abstract](249) [PDF 190KB](23)

Abstract:
To obtain the near optimal path for the mobile robots in the present of the obstacles, where the robots are subject to both the nonholonomic constraints and the bound to the curvature of the path, a simple planning is applied by the heuristic searching method in which Reeds and Shepp's shortest paths are chosen as heuristic functions. It has performed well in simulation of mobile robots moving in a cluttered environment.

Existence of Multiple Positive Solutions for Higher-Order p-Laplacian Boundary Value Problems

HE Xiao ming, GE Wei gao

2002, 11(2): 212-216.

[Abstract](271) [PDF 184KB](31)

Abstract:
The existence of multiple positive solutions for a class of higher order p Laplacian boundary value problem is studied. By means of the Leggett Williams fixed point theorem in cones, existence criteria which ensure the existence of at least three positive solutions of the boundary value problem are established.

On the Total Domination Number of Graphs with Minimum Degree at Least Three

LIU Hai long, SUN Liang

2002, 11(2): 217-219.

[Abstract](251) [PDF 121KB](29)

Abstract:
Let G be a simple graph with no isolated vertices. A set S of vertices of G is a total dominating set if every vertex of G is adjacent to some vertex in S. The total domination number of G, denoted by γ t (G), is the minimum cardinality of a total dominating set of G. It is shown that if G is a graph of order n with minimum degree at least 3, then γ t (G)≤n/2. Thus a conjecture of Favaron, Henning, Mynhart and Puech is settled in the affirmative.

Existence of Solutions for S-L Singular Boundary Value Problems with p-Laplacian Operators

GUO Yan ping, GE Wei gao, SHAN Wen rui

2002, 11(2): 220-224.

[Abstract](268) [PDF 172KB](28)

Abstract:
The existence of solutions for singular nonlinear two point boundary value problems subject to Sturm Liouville boundary conditions with p Laplacian operators is studied by the method of upper and lower solutions. The proof is based on an application of Schauder's fixed point theorem to a modified problem whose solutions are that of the original one. At the same time, Arzela Ascoli theorem is used to prove that the defined operator N is a compact map.

2002 Vol. 11, No. 2