JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Numerical Simulation and Analysis on Velocity Profiles of Jet Projectile Charge

2009, 18(4): 379-383.

[Abstract](239)

Abstract:
Jet projectile charge (JPC) is a relatively new type of perforating jet mainly used for defeating concrete targets. Velocity profile is an important parameter to investigate the penetration and performance of JPC. Since limited information such as X-ray radiographs and penetration depth can be obtained through the JPC experiment, the numerical simulation and further methodology are needed to depict the mechanism of JPC. This paper describes a mathematical approach based on Matlab to determine JPC velocity profile at various stand offs using three sets of jet data from numerical simulations. X-ray radiographs experimental results have been obtained at two time instants for two selected JPC design to verify the numerical accuracy. The velocity profiles by mathematical approach and simulation show good accordance. The number of experiments can be reduced by numerical simulation and analysis of velocity profiles. This approach can be generalized to any such system where explosive-metal interaction results in formation of jets.

A Study on Damage Rules on Insulators by Conducting Sols

WEI Ji-feng, WANG Shu-shan, LI Na, ZHANG Zhi-wei, MA Feng

2009, 18(4): 384-387.

[Abstract](368)

Abstract:
Insulating parts are easily subjected to pollution which may cause damage to the electric system. A typical disc insulator is chosen as the target to test its flashover voltage by using an artificial pollution system. This test system aims at obtaining characteristic parameters of damage for chosen conducting sols to the selected insulator. Experimental results show that thickness and electric conductivity of pollutant layer over insulators are the main parameters in damage evaluation. The flashover voltage decreases with increase of thickness and/or conductivity. These results provide a better basis on further revealing the damaging nature of conducting sol materials.

Numerical Simulation of Methane Leakage Diffusion in the Space with Multi-buildings

QIAN Xin-ming, LIU Mu, LIU Zhen-yi, SUN Wen-lei

2009, 18(4): 388-394.

[Abstract](351)

Abstract:
Usingk-εturbulent equation and SIMPLE arithmetic, a multi-buildings space model was set up under realistic circumstances. The methane (CH₄) leakage diffusions from 3 gas-transporting pipelines with different pressures under 3 different wind flow conditions in the space with multi-buildings were simulated and the simulation results were contrasted and analyzed. Simulation results indicate that the leakage diffusion of CH₄could be influenced by surrounding buildings, besides the effect of the wind flow. In addition, CH₄gassy columniation will be bended to be adsorbed by surrounding buildings forming a high concentration zone when the pipe pressure is rather low or the wind velocity is rather fast. It will greatly increase the fatalness to the ambience and surrounding buildings.

Coal Dust Explosions in a Large Scale Experimental Tube

LIU Qing-ming, LI Xiao-dong, BAI Chun-hua, JIANG Li

2009, 18(4): 395-401.

[Abstract](168)

Abstract:
Coal dust explosion conducted in a 200?mm diameter, 29.6?m long tube is presented in this paper. 40 dust dispersion system sets were used to disperse coal dust into the tube. A constant temperature hot wire anemometer was used to measure the gas velocity during the dispersion process. Kistler piezoelectric pressure sensors were used to measure the propagation of the pressure wave during the explosion process. The overpressure of coal dust explosion in the tube was 70?kPa and the velocity of pressure wave propagating along the tube was 370?m/s approximately. The minimum concentration for dust explosion propagating along the tube was 100?g/m³. The effects of two kinds of suppressing agents used to suppress the coal dust explosion were studied.

Experimental Investigations on the Influence of Assumptions in Soot Volume Fraction Measurement by TPD Method

LU Jing, ZHOU Huai-chun

2009, 18(4): 402-407.

[Abstract](231)

Abstract:
This paper investigated the influence of assumptions in soot volume fraction measurement by thermocouple particle densitometry (TPD) method in laminar nonpremixed ethylene/air diffusion flame. TPD method is based on an extension of the theoretical treatment of Eisner and Rosner, who assumed that the particle deposition to a cold surface immersed in a flame is dominated by thermophoresis. They developed a formulation for the soot particle mass flux to thermocouple bead to infer soot volume fraction by inserting the thermocouple to flame rapidly. However, in their formulations, some important parameters were neglected, such as the radiation from soot to thermocouple bead. We added the parameter into the formulation and analyzed its impact. The results show that the ignored parameter had significant influence for the calculation of thermocouple bead emissivity and thermophoresis is not the dominant mechanism during the initial stage of soot particles deposition to bead, whose real causes should be studied further.

Algorithm Based on the Gradient-Hamilton Decomposition Theory of Vector Fields

GANG Tie-qiang, CHEN Li-jie, MEI Feng-xiang

2009, 18(4): 408-411.

[Abstract](252)

Abstract:
Based on the gradient-Hamiltonian decomposition (GHD) theory of vector fields, an algorithm (called as GHD algorithm) is proposed in this paper. For the GHD algorithm, visual interpretations of the advantages in stability are given by using the eigenvalue curves. From the numerical results for linear decay systems, it reaches the conclusion that the GHD algorithm proposed in this paper has a better computational accuracy than other algorithms and presents a replication of long time qualitative properties of the underlying system.

Traffic System Reliability Comparison Between Digital Driving and Conventional Driving

WANG Wu-hong, SHENG Zhong-jie, LIU Hao, YAO Li-ya, Katsushi Ikeuchi

2009, 18(4): 412-415.

[Abstract](437)

Abstract:
Driver behavior modeling is becoming increasingly important in the study of traffic safety and development of cognitive vehicles. An algorithm for dealing with reliability for both digital driving and conventional driving has been developed in this paper. Problems of digital driving error classification, digital driving error probability quantification and digital driving reliability simulation have been addressed using a comparison research method. Simulation results show that driving reliability analysis discussed here is capable of identifying digital driving behavior characteristics and achieving safety assessment of intelligent transportation system.

Hardware-in-the-Loop Research on the Electronic Control Unit for Diesel Engines

WANG Yu-ming, ZHANG Fu-jun, WANG Yong-ting, LIU Bo-lan

2009, 18(4): 416-421.

[Abstract](301)

Abstract:
A hardware-in-the-loop simulating platform is developed to avoid designing defects caused by the complicated logical structure and multiple-functional buildup of the electronic control unit(ECU)in modern diesel engines, and to diminish potential damages on components or human exposure to dangers in R&D endeavor. This platform consists of a computer installed with software Matlab/Simulink/RTW and dSPACE/ControlDesk; a diesel engine ECU, and a dSPACE autobox which runs a real-time diesel engine model. A typical model of diesel engine with turbocharger and intercooler is presented. Based on this model our research is carried out with a real ECU to test its software control strategies. Results show that by using the diesel engine model downloaded inside, the hardware-in-the-loop platform can simulate diesel engine's working conditions and generate all kinds of sensor signals which ECU needs on a real-time basis. So the ECU control strategies can be validated and relevant parameters roughly calibrated.

Investigation on Surge in Centrifugal Compressors

ZHU Zhi-fu, MA Chao-chen, CHEN Shan

2009, 18(4): 422-427.

[Abstract](228)

Abstract:
A test bench for conducting compressor surge experiments is set up, and different system configurations formed by changing the length of compressor outlet pipeline are tested for surge. Dynamic pressure signals relating to surges are acquired at different locations of the configurations using unsteady measurement & data acquisition system. The sliding window method is adopted to set up quantitative criterion on the surge. Parameters included in the criterion, such as location of data collection, size and step of sliding window, a mathematical quantity surge-judging and its threshold, etc., are given. Flow chart of surge evaluation is shown, and surge frequency was evaluated based on system configurations. With all these, the problem of judging the existence of surge by human experiences in compressor performance experiments can be solved. Hence this new approach may help to achieve intelligent operations on automatic compressor performance test rig.

3D Simulation Research on Urea-SCR DeNO_xCatalyst for Diesel Engine

JIANG Lei, GE Yun-shan, Asad Naeem Shah, TAN Jian-wei

2009, 18(4): 428-432.

[Abstract](288)

Abstract:
In order to reduce oxides of nitrogen (NO_x) emanated from a diesel engine, a comprehensive urea selective catalyst reduction (SCR) DeNO_xcatalyst was modeled in which numerical simulations were used as a complementary tool for the experimental investigations to make the design decisions, and hence shorten the development process. In this approach, relevant conversion reactions were studied in 1D model, and the parameters obtained in this way were transferred to 3D simulations. According to the results of the study, the conversion of NO and NO₂increased with the increase in monolith solid temperature. With the increase in the ratio of NO₂/NO, the conversion of NO, NO₂and NO_xincreased resulting in maximum reduction of NO_xat the ratio of 1; beyond this ratio, the conversion of NO₂and NO_xdecreased; however, NO continued to be converted till the ratio was 1.8. The conversion of NO_xdecreased with the increase in space velocity.

Trend Prediction Method Based on the Largest Lyapunov Exponent for Large Rotating Machine Equipments

XU Xiao-li, ZHU Chun-mei, ZHANG Jian-min

2009, 18(4): 433-436.

[Abstract](473)

Abstract:
In order to predict electromechanical equipments' nonlinear and non-stationary condition effectively, max Lyapunov exponent is introduced to the fault trend prediction of large rotating mechanical equipments based on chaos theory. The predict method of chaos time series and two methods of proposingAf^GandAF^Uare discussed. The arithmetic of max prediction time of chaos time series is provided. Aiming at the key part of large rotating mechanical equipments-bearing, used this prediction method the simulation experiment is carried out. The result shows that this method has excellent performance for condition trend prediction.

Analysis of Human Joint Forces in Standing Posture

MA Chao, ZHANG Ming, ZHANG Chun-lin, LI Zhi-xiang, YANG Jian-xin

2009, 18(4): 437-442.

[Abstract](347)

Abstract:
Using the software Anybody Modeling System, a human static-standing musculoskeletal model based on inverse dynamics is presented, which are defined as segments, muscles and joints as elements. Simulation is based on data obtained from experiments using motion capture system VICON and force plate AMTI. In the model AnyBody Modeling System is introduced to help solve the redundancy problem and obtain results of muscle activities, muscle forces and joint forces. From the model, hip and knee joint forces could be analyzed under normal standing posture. Also, activities of the musculus rectus femoris and several other muscles of the lower limbs can be obtained. From the results it could be concluded that stresses at joints are much stronger than theoretical reasoning because of the functions of relevant soft tissues such as muscles, tendons and so on. Results show that joint forces from the simulations are in good conformation with previous experimental researches. And this complicated model would be of use for better understanding human body functions.

Research on Biologically Inspired Hexapod Robot's Gait and Path Planning

ZHANG Hui, LUO Qing-sheng, HAN Bao-ling

2009, 18(4): 443-447.

[Abstract](291)

Abstract:
Realistically there are many robot joints in the biologically inspired hexapod robot, so they will generate many complexities in the calculations of the gait and the path planning and the control variables. The software Solidworks and MSC.ADAMS are adopted to simulate and analyze the prototype model of the robot. By the simulations used in our design, the applicability of the tripod gait is validated, and the scheme which uses cubic spline curve as the endpoint of foot's path is feasible. The principles, methods, and processes of the simulation of hexapod robot are illustrated. A methodology is proposed to get the robot inverse solution in ADAMS, and to simplify the theoretical calculation, and further more to improve the efficiency of the design.

Decoupling of BTT Missile Using Rolling Actuator

YU Yu-bin, ZHANG Jing

2009, 18(4): 448-451.

[Abstract](211)

Abstract:
In order to reduce the coupling between pitch, yaw and roll channels of the bank-to-turn (BTT) missile caused due to missile body roll. A new structure actuator for reducing the coupling of BTT missiles is studied. The new structure actuator can roll independently along the longitudinal axis of the missile. The actuator instead of airframe needs to steer when controlling BTT missile roll. So the rolling speed of main airframe and thus the coupling of missile introduced by airframe rolling are reduced. And control logic is designed for the missile using roll actuator. Finally, analysis and simulation results demonstrate the effectiveness of the rolling actuator in decoupling a BTT missile.

Kinetic Optimal Midcourse Guidance Law for Air-to-Air Missiles

CHANG Chao, LIN De-fu, QI Zai-kang, NONG Yu-lin, CHENG Zhen-xuan

2009, 18(4): 452-456.

[Abstract](409)

Abstract:
A new kinetic optimal midcourse guidance law is derived based on optimal control formulation. A new simplified Runge-Kutta grade numerical method is proposed to find the optimal trajectory. Real data of an air-to-air missile is referred to for comparing results using the kinetic optimal midcourse guidance law with those under both the kinematic optimal guidance law and singular perturbation sub-optimal guidance law, wherein the latter two laws are modified in this paper by adding a vertical g-bias command to each law for the sake of trajectory shaping. Simulation results show that using the new kinetic optimal midcourse guidance law can help save energy and maximize terminal velocity effectively.

Method for Obtaining Line-of-Sight Rate with a Strap-down Imaging Guidance

LI Yi, MA Yan-ni, SONG Zhen-duo

2009, 18(4): 457-462.

[Abstract](239)

Abstract:
In the strap-down TV guidance system, the line-of-sight(LOS) rate can not be obtained from the measured information, the math platform to select missile attitude information must be set up. The LOS rate selecting models based on the missile attitude angle and the rate gyro are set up, the influencing factor and the extracting precision of LOS rate are emulated and analyzed.

New Dynamic Algorithm for IRFPA Bad Pixel Detection and Compensation Based on Statistics

LIU Chong-liang, JIN Wei-qi, CAO Yang, LIU Xiu

2009, 18(4): 463-467.

[Abstract](451)

Abstract:
Based on the analysis to the behavior of bad pixels, a statistics-based auto-detecting and compensation algorithm for bad pixels is proposed. The correcting process is divided into two stages: bad pixel detection and bad pixel compensation. The proposed detection algorithm is a combination of median filtering and statistic method. Single frame median filtering is used to locate approximate map, then statistic method and threshold value is used to get the accurate location map of bad pixels. When the bad pixel detection is done, neighboring pixel replacement algorithm is used to compensate them in real-time. The effectiveness of this approach is tested by applying it to HgCdTe infrared video. Experiments on real infrared imaging sequences demonstrate that the proposed algorithm requires only a few frames to obtain high quality corrections. It is easy to combine with traditional static methods, update the pre-defined location map in real-time.

New Acquisition Algorithm for Direct Sequence Spread Spectrum Signals

WANG Yong-qing, WU Si-liang

2009, 18(4): 468-472.

[Abstract](279)

Abstract:
Aiming at improving acquisition performance for direct sequence spread spectrum (DSSS) signals, a new acquisition algorithm based on fast Fourier transform (FFT) is proposed. The code phases are parallel searched throughout the Doppler frequency domain. Since the influence of Doppler frequency errors on peak-to-average ratios of correlation power shows a pattern similar to the sinc function, it is our belief that by judging on peak-to-average ratios for different Doppler frequency errors false alarm probabilities should be lowered. Analyses have supported the underlying principle of this new algorithm. Simulation results have also indicated that the new algorithm can effectively improve the acquisition performance for DSSS signals.

Robust and Low-Complexity Synchronization for Energy Detection UWB Receiver

XU Zhan, AN Jian-ping, YANG Kai, LIU Peng

2009, 18(4): 473-477.

[Abstract](269)

Abstract:
A simple method using aided sliding rectangular windows for synchronization in energy detector (ED) receiver is proposed for impulse-based ultra wideband radios (IR-UWB) under binary pulse position modulation (PPM), therefore grants an attractive solution for gaining low complexity while the accompanying performance loss in terms of UWB signal reception is comparatively low. Also, a method is developed to suppress noise through accumulation of integrated results before synchronization point is reached. This proposed method can effectively reduce the impact of one of the major performance-degrading factors in ED receivers, i.e., noise caused by heightened noise floor due to large bandwidth product. Our theoretic work on this improved synchronization performance and relevant simulations are conducted on IEEE 802.15.4a channel models, and results show that the proposed design scheme can effectively decrease both the probability of false alarm and probability of missed detection.

Feature Extraction of Symmetrical Triangular LFMCW Signal Using Wigner-Hough Transform

LIU Feng, XU Hui-fa, SUN Da-peng, TAO Ran, WANG Yue

2009, 18(4): 478-483.

[Abstract](301)

Abstract:
Feature extraction of symmetrical triangular linear frequency modulation continuous wave (LFMCW) signal is studied. Combined with its peculiar characteristics, a novel algorithm based on Wigner-Hough transform (WHT) is presented for the detection and parameter estimation of this type of waveform. The initial frequency and chirp rate of each segment of this wave are estimated, and the peak-value searching steps in the parameter space is given. Compared with Wigner-Ville distribution (WVD), Pseudo-Wigner-Ville distribution (PWD) and Smoothed-Peseudo-Wigner-Ville distribution (SPWD), WHT has proven itself to be the best method for feature extraction of symmetrical triangular LFMCW signal. In the end, Monte-Carlo simulations under different SNRs are carried out, with validating results on this method.

Information Geometry of Positive Definite Matrices

ZHANG Shi-cheng, SUN Hua-fei, LI Chun-hui

2009, 18(4): 484-487.

[Abstract](353)

Abstract:
A new Riemannian metric for positive definite matrices is defined and its geometric structures are investigated by means of dual connections introduced to statistical analysis by S. Amari. A few interesting results are obtained and some of those obtained by other authors are extended in our research.

Filtration Structure of Finite-Dimensional Special Odd Hamiltonian Superalgebras in Prime Characteristic

HE Ying-hua, LIU Wen-de, LI Bin

2009, 18(4): 488-491.

[Abstract](136)

Abstract:
The filtration structure of finite-dimensional special odd Hamilton superalgebras over a field of prime characteristic was studied. By determining ad-nilpotent elements in the even part, the natural filtration of special odd Hamiltonian superalgebras is proved to be invariant. Using this result, the special odd Hamilton superalgebras is classified. Finally, the automorphism group of the restricted special odd Hamilton superalgebras is determined.

Transportation Reliability Model of Package Products

BAO Zhi-wen, CUI Li-rong

2009, 18(4): 492-496.

[Abstract](224)

Abstract:
A reliability model of packaged products in transportation has been built in terms of a generalized shock assumption. Shocks acting on products are assumed to come from an unexpected source following Poisson stochastic process in which each shock has a standard normal distributed response acceleration, and the transportation package reliability is defined as the probability that within a given time period, the maximal response acceleration on the packaged products does not exceed a specified value, i.e. fragility of the products. A formula of the transportation package reliability is deduced and a numerical example is presented to illustrate the results. If packaging designers could follow the results given in the paper, packaged products could achieve minimum packaging cost while guarantee delivery safety without causing damage or quality loss.

Application Research of Robust LS-SVM Regression Model in Forecasting Patent Application Counts

ZHANG Li-wei, ZHANG Qian, WANG Xue-feng, ZHU Dong-hua

2009, 18(4): 497-501.

[Abstract](190)

Abstract:
A forecasting system of patent application counts is studied in this paper. The optimization model proposed in the research is based on support vector machines (SVM), in which cross-validation algorithm is used for preferences selection. Results of data simulation show that the proposed method has higher forecasting precision power and stronger generalization abi1ity than BP neural network and RBF neural network. In addition, it is feasible and effective in forecasting patent application counts.

Safety-Critical System Reliability Modeling and Their Analyses in Terms of Effects of Component Failure Modes

JIA Xu-jie, CUI Li-rong, GAO Song

2009, 18(4): 502-506.

[Abstract](292)

Abstract:
New models of safety-critical systems are built here. In these systems, when components fail, different defect states have different effects, hence need different ways to measure. In the models, there are two kinds of failure modes of the components: one could be called failed-safe, and the other may be named failed-dangerous. In practice, the so-called failed-dangerous components may lead a system to peril. However, failed-safe components will not. Reliability and safety issues are analyzed using Ion-Channel modeling theory to get count of repairs and time duration before the system becomes dangerous. In the closing section a numerical example is presented to illustrate the results obtained in the paper.

2009 Vol. 18, No. 4