JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Study on Near Field Dispersal of Fuel Air Explosive

Zhang Qi, Bai Chunhua, Liu Qingming, Wang Zhongqi, Liang Huimin, Xiao Shaoqing

1999, 8(2): 113-118.

[Abstract](283) [PDF 193KB](17)

Abstract:
Aim To study fuel dispersion in fuel air explosive(FAE) and computational ways of fuel dispersion velocity in the near area. Methods The dispersion process of fuel in FAE was analyzed by the use of results measured with KODAK EKTAPRO EM Motion Analyzer and setting up mechanical models. Results Computational methods for fuel dispersion velocity in the acceleration stage is given and taken as a base for the study of fuel dispersion in the intermediate and the far area. Conclusion When the fuel flow velocity is higher than that of the explosion gas in the center cavity, the fuel divides with the explosion gas and its velocity of flow reaches a maximum. The acceleration stage ends at that time. The fuel dispersion velocity at this time is the initial conditions for numeral analyses of dispersion process in the intermediate and far areas.

Experiments and Numerical Calculations on an Ignition System

Chen Lang, Feng Changgen, Zhang Shouqi, Wang Liqiong, Xiang Yong

1999, 8(2): 119-123.

[Abstract](283)

Abstract:
Aim To present a new kind of rapid ignition tube for igniting the propellant of heavy calibre gun uniformly and synchronistically so as to decrease the pressure wave. Methods Firing tests were carried out. Relationships between pressure and time ( p-t curves) at different positions of the tube are measured. The mode of igniter tube of quasi one dimensional two phase flow is given. Results The test results indicate that the speed of ignition front in the ignition tube is very fast and the pressure distribution within the igniter tube is uniform. Results of experiments and numerical calculations of the combustion in the igniter tube are in reasonable agreement. Conclusion The new igniter tubes have a very high velocity of propagation of ignition stimuli and can ignite the propellant bed synchronistically.

Effect of Thermal Treatment on the PA-6 in the Blends

Qiu Wulin, Luo Shanguo, Luo Yunjun, Tan Huimin, Li Zhengjun, Mai Kancheng, Zeng Hanmin

1999, 8(2): 124-129.

[Abstract](180)

Abstract:
Aim To investigate the multiple melting behavior of polyamide 6(PA 6) in polyamide 6/linear low density polyethylene blends crystallized from the crystal amorphous state. Methods The effects of annealing temperature, annealing time, heating rate, and the step wise annealing were measured by DSC. Results and Conclusion There exists a critical heating rate affecting the middle temperature melting peak. When annealed at the temperature close to the melting peak, the main melting peak of PA 6 shifted to a higher temperature. Within a short time, annealing time has much effect on neat PA 6 but little effect on PA 6 in the blends. Addition of PE results in a decreasing in the height of melting peak. These phenomenon show that the melting behavior of PA 6 was affected by PE, compatibilizer, as well as thermal treatment.

AFM Observation of GaN Grown on Different Substrates at Low Temperatures

Cao Chuanbao, Attolini G, Fornari R, Pelosi C

1999, 8(2): 130-137.

[Abstract](203) [PDF 604KB](5)

Abstract:
Aim To study the relationship between the substrate temperature and the morphology and properties of GaN. Methods Applying the hydride chemical vapor deposition method, GaN films were deposited on different kinds of substrates, including sapphire, Si(111),Si(100),GaAs and GaP(111) both on the P face and the Ga face. The growth was performed at low temperatures of below 700℃. XRD, Hall measurement, cathodoluminescence (CL) and atomic force microscopy (AFM) were used to characterise the film properties. Results It was found that the temperature and the nature of substrate materials influence the layer morphology. Conclusion The analysis shows that no apparent relationship exists between the optical properties and layer morphology.

Analysis of the Elastic Plastic Dynamic Finite Element on a Jointed Rock Mass

Guo Wenzhang, Feng Shunshan, Wang Haifu

1999, 8(2): 138-143.

[Abstract](252)

Abstract:
Aim To study the elastic plastic dynamical constitutive relations about a jointed rock mass under explosion load and its computer simulation. Methods Stress history is taken into account and stresses will follow changes in time during a period of explosion load. According to the principle of static force balance, the corresponding nodal concentrated force is calculated and the nodal displacement is counted. The elastic plastic dynamic finite element equations are thus obtained. Results A finite element method is given for a jointed rock mass under explosion load. Conclusion The problem of large plastic deformation for jointed rock mass on blasting was efficiently resolved through dynamic finite element analysis and the range of damages by blasting simulated, and this pushes forward the problem to engineering practice.

Analysis of Mine Ventilation Network

Xie Xianping, Feng Changgen, Wang Hailiang

1999, 8(2): 144-149.

[Abstract](211)

Abstract:
Aim To determine the global optimal solution for a mine ventilation network under given network topology and airway characteristics. Methods The genetic algorithm was used to find the global optimal solution of the network. Results A modified genetic algorithm is presented with its characteristics and principle. Instead of working on the conventional bit by bit operation, both the crossover and mutation operators are handled in real values by the proposed algorithms. To prevent the system from turning into a premature problem, the elitists from two groups of possible solutions are selected to reproduce the new populations. Conclusion The simulation results show that the method outperforms the conventional nonlinear programming approach whether from the viewpoint of the number of iterations required to find the optimum solutions or from the final solutions obtained.

Using Genetic Algorithm

Chen Xin, Xiang Changle

1999, 8(2): 150-153.

[Abstract](161)

Abstract:
Aim To improve the efficiency of fatigue material tests and relevant statistical treatment of test data. Methods Least square approach and other special treatments were used. Results and Conclusion The concepts of each phase in fatigue tests and statistical treatment are clarified. The method proposed leads to three important properties. Reduced number of specimens brings to the advantage of lowering test expenditures. The whole test procedure has more flexibility for there is no need to conduct many tests at the same stress level as in traditional cases.

Rules Governing Pressure Distribution for a Traveling Charge Under the Condition of Lagrange Hypothesis

Luo Yunjun, Tan Huimin, Chen Futai

1999, 8(2): 154-160.

[Abstract](190)

Abstract:
Aim To study the rules governing pressure distribution of traveling charge under the condition of Lagrange hypothesis. Methods The study is based on the laws of conservation of momentum and energy. Results The gas flow velocity distribution formula at the back of a projectile and the momentum equation of a traveling charge are deduced, and rules governing their pressure distribution under the Lagrange hypothesis conditions are established. The pressure distribution of a traveling charge is compared with that of a conventional charge. Conclusion The pressure distribution in the bore of a traveling charge can be accurately predicted. A parabolic pressure distribution type is revealed.

Numerical Algorithm for Polarity Reversal Electric Field and Its Application

Lü Xiaode, Gao Benqing

1999, 8(2): 161-166.

[Abstract](189)

Abstract:
Aim To analyze the transient speciality of nonlinear, anisotropic, AC+DC coupling electric field, and to compare the withstand voltage strength of different insulation structures. Methods The transient process of polarity reversal is analyzed, considering the anisotropic property of oil immersed press board, a new finite element model based on Galerkin method is presented and verified. The model developed is applied to calculate the electric field distribution in four typical winding end structures of the converter transformer. Results The whole ring structure possesses the best insulation characteristics. Conclusion By introducing reasonable insulation components, insulation strength with the same surrounding sizes can be improved more than 30%.

ASIC Design of DA Based 2-D Inverse Discrete Cosine Transform

Chen He, Han Yueqiu

1999, 8(2): 167-174.

[Abstract](192)

Abstract:
Aim To present an ASIC design of DA based 2 D IDCT. Methods In the design of 1 D IDCT is utilized a Chen based fast IDCT algorithm, and multiplier accumulators based on distributed algorithm contributes in reducing the hardware amount and in enhancing the speed performance. Results and Conclusion VHDL simulation, synthesis and layout design of system are implemented. This 2 D IDCT ASIC design owns best timing performance when compared with other better designs internationally. Results of design prove to be excellent.

Analyzing Undersampled Signals Using High Order Ambiguity Function Algorithm

Tao Ran, Shan Tao, Zhou Siyong, Wang Yue

1999, 8(2): 175-180.

[Abstract](231) [PDF 193KB](6)

Abstract:
Aim To find an effective and fast algorithm to analyze undersampled signals. Methods The advantage of high order ambiguity function(HAF) algorithm is that it can analyze polynomial phase signals by phase rank reduction. In this paper, it was first used to analyze the parameters of undersampled signals. When some conditions are satisfied, the problem of frequency confusion can be solved. Results and Conclusion As an example, we analyze undersampled linear frequency modulated signal. The simulation results verify the effectiveness of HAF algorithm. Compared with time frequency distribution, HAF algorithm reduces computation burden to a great extent, needs weak boundary conditions and doesn't have boundary effect.

Application of Radial Basis Function Network in Sensor Failure Detection

Niu Yongsheng, Zhao Xinmin

1999, 8(2): 181-187.

[Abstract](210) [PDF 229KB](2)

Abstract:
Aim To detect sensor failure in control system using a single sensor signal. Methods A neural predictor was designed based on a radial basis function network(RBFN), and the neural predictor learned the sensor signal on line with a hybrid algorithm composed of n means clustering and Kalman filter and then gave the estimation of the sensor signal at the next step. If the difference between the estimation and the actural values of the sensor signal exceeded a threshold, the sensor could be declared to have a failure. The choice of the failure detection threshold depends on the noise variance and the possible prediction error of neural predictor. Results and Conclusion The computer simulation results show the proposed method can detect sensor failure correctly for a gyro in an automotive engine.

Optimal Guaranteed Cost Control via Static Output Feedback for Uncertain Discrete Time Systems

Wu Huaining, Fei Yuanchun

1999, 8(2): 188-195.

[Abstract](227)

Abstract:
Aim To study the optimal guaranteed cost control problem via static output feedback for uncertain linear discrete time systems with norm bounded parameter uncertainty in both the state and the control input matrices of the state space model. Methods An upper bound on a quadratic cost index was found for all admissible parameter uncertainties and minimized by using Lagrange multiplier approach. Results and Conclusion Sufficient conditions are given for the existence of a controller guaranteeing the closed loop system quadratic stability and providing an optimized bound. A numerical algorithm for solving the output feedback gain is also presented.

Adaptive Fuzzy Neural Control of Dynamic System

Zhao Baojun, Han Yueqiu, Mao Erke

1999, 8(2): 196-200.

[Abstract](187)

Abstract:
Aim To build an adaptive fuzzy neural controller and simulate it. Methods Fuzzy logic and back propagation(BP) algorithm are combined to utilize their advantages while avoiding the disadvantages. Results and Conclusion Simulation results of the third order plant with disturbances and dead times show the validity of the presented controller. The presented controller can control cases that preceding controllers were unable to control.

Study of Diesel Spray Particle Velocity Field Using a Particle Image Velocimetry Setup

Hao Lijun, Liu Fushui, Liu Yulin, Sun Jimei

1999, 8(2): 201-206.

[Abstract](214) [PDF 294KB](3)

Abstract:
Aim To investigate the spray particle velocity and its distribution characteristics. Methods A set of PIV (particle image velocimetry) system was developed and used to observe and analyze the spray particle velocity field. Results and Conclusion Double-exposure image of the spray particle within the region of 10-50 mm from the nozzle tip was recorded and analyzed by the IBAS2000 analysis system. Some characteristics of the spray particle velocity and its dis-tribution were obtained.

Simulation of Restraint System Performance upon the Occupant's Response During Impact

Sun Liqing, Lin Yi, Sun Fengchun

1999, 8(2): 207-213.

[Abstract](184)

Abstract:
Aim To study the influence of restraint system performance upon the occupant's response during impact, and provide a scientific base for occupant restraint system design. Methods In the light of basic theory of multibody system dynamics and impact dynamics on the basis of classical theory of impact, R W method is adopted to construct the vehicle occupant system model consisting of fourteen rigid bodies, thirty seven DOFs and slip joints for the simulation. A software named SVC3D(3 dimensional simulation of vehicle crash) is developed in the FORTRAN language. Results The results of simulation have a good coincidence with those of tests and the restraint system with low elongation webbing and equipped with pretensioner provides better restraint effect for the occupant. Conclusion The model of vehicle occupant multibody system and SVC3D are suitable for use. Occupant should be belted with low elongation webbing to a certain degree and occupant restraint system should be equipped with pretensioner.

Human Error Model and Definition of Human Reliability

Jing Guoxun, Feng Changgen, Wang Hailiang

1999, 8(2): 214-218.

[Abstract](219)

Abstract:
Aim A model of human errors is given. His reliability of action is also determined. Safety countermeasures to prevent human errors are put forward. Methods Human system is regarded as a maintainable Markov system. On the basis of Markov method, the deduction and calculation in practice are made. Results Human errors are the chief factors leading to accidents, and may appear in different models. There are two kinds of states the normal and error state in a process of work. The process of state transfer human system is a Markov process. Human action reliability will be decreased with the continuation of time. Conclusion Human errors are described in the quantified form. It will have some significance in terms of theory in the study of the relationship between human action and accidents. Thus helping us in the preven tion of accident occurrence. The safety of a system can be improved in this way.

Cusp Model for Risk Analysis

Qian Xinming, Qiao George

1999, 8(2): 219-224.

[Abstract](210)

Abstract:
Aim To assess simultaneously various risk states of a system. Methods Using the catastrophe and fuzzy theory, the energy and uncertainty in a system are set as two control variables and the function of the system is used as the state variable for analysis. Results and Conclusion A risk analysis model named the cusp model is presented. Various states regarding the safety of the system such as the accident state, no accident state and miss state can be represented at will on the cusp model.

1999 Vol. 8, No. 2