JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Computation of the Matching Performance of Diesel Engine with Variable Geometry Turbocharger

SHI Xin, MA Chao-chen

2006, 15(4): 379-383.

[Abstract](182)

Abstract:
To compute the matching performance of diesel engine with variable geometry turbocharger(VGT), the formerly used program is improved through adjustment of turbine mass flow rate and efficiency characteris-tics. The calculation result is applied to forecast the performance of J6110Z diesel engine with rotary-vaned VGT70, and to guide the improvement of engine fuel supply. The computed engine performance curve coin-cides with the experiment result well: the low-speed torque, fuel economy, exhaust temperature and boost pressure of the VGT engine are all improved.

Electronic Unit Pump Test Bench Development and Pump Properties Research

LIU Bo-lan, HUANG Ying, ZHANG Fu-jun, ZHAO Chang-lu

2006, 15(4): 384-388.

[Abstract](89)

Abstract:
A unit pump test bench is developed on an in-line pump test platform. The bench is composed of pump adapting assembly, fuel supply subsystem, lubricating subsystem and a control unit. A crank angle domain injection control method is given out and the control accuracy can be 0.1° crank degree. The bench can test both mechanical unit pump and electronic unit pump. A test model—PLD12 electronic unit pump is tested. Full pump delivery map and some influence factors test is done. Experimental results show that the injection quantity is linear with the delivery angle. The quantity change rate is 15% when fuel temperature increases 30℃. The delivery quantity per cycle increases 30mg at 28V drive voltage. The average delivery difference for two same type pumps is 5%. Test results show that the bench can be used for unit pump verification.

Calibration of a Parallel Kinematic Machine Tool

HE Xiao-mei, DING Hong-sheng, FU Tie, XIE Dian-huang, XU Jin-zhong, LI Hua-feng, LIU Hui-lin

2006, 15(4): 389-392.

[Abstract](161)

Abstract:
A calibration method is presented to enhance the static accuracy of a parallel kinematic machine tool by using a coordinate measuring machine and a laser tracker. According to the established calibration model and the calibration experiment, the factual 42 kinematic parameters of BKX-I parallel kinematic machine tool are obtained. By circular tests the comparison is made between the calibrated and the uncalibrated parameters and shows that there is 80% improvement in accuracy of this machine tool.

Cavitation Inception in Turbulent Flows Around a Hydrofoil

ZHANG Min-di, WANG Guo-yu, ZHANG Zhen, GAO Yuan-yin

2006, 15(4): 393-396.

[Abstract](126)

Abstract:
The phenomenon of cavitation inception around a hydrofoil is studied experimentally. The flow ve-locities around the foil are measured by a laser doppler velocimetry (LDV). The inception cavitation aspects are observed by using a high-speed video camera. In the experiment, the Reynolds number is fixed at a value of 7.0×10⁵. The boundary layer around the foil undergoes turbulent flow under the experiment condition. The LDV measurement results show that the flow in the boundary layer around the foil doesn't separate from the surface. It is found that the cavitation inception in non-separated turbulent flow is related to the coherent structures in the boundary layer. It is clear that the turbulent bursting and the hairpin-shaped vortex structure accompany the incipient cavitation.

Corrugation Stuffed Shield for Spacecraft and Its Performance

LIU You-ying, WANG Hai-fu

2006, 15(4): 397-400.

[Abstract](77)

Abstract:
A corrugation stuffed shield system protecting spacecrafts against meteoroid and orbital debris (M/OD) is presented. The semi-empirical ballistic limit equations (BLEs)defining the protection capability of the shield system are given, and the shielding performance is also discussed. The corrugation stuffed shield (CSS) is more effective than stuffed Whipple shield for M/OD protection,and its shielding performance will be im-proved significantly as increasing the impact angle. Orbital debris up to 1cm in diameter can be shielded effec-tively as increasing the impact angle to 25° at the corrugated angle of 30°. The results are significant to space-craft design.

Pulse Compression Technique of Radio Fuze

HU Xiu-juan, DENG Jia-hao, SANG Hui-ping

2006, 15(4): 401-405.

[Abstract](193)

Abstract:
The advantages of using phase-coded pulse compression technique for radio fuze systems are evaluated. With building mathematical models a matched filter has been implemented successfully. Various simulations for pulse compression waveform coding were done to evaluate the performance of fuze system under noisy environment. The results of the simulation and the data analysis show that the phase-coded pulse compression gets a good result in the signal identification of the radio fuze with matched filter. Simultaneously, a suitable sidelobe suppression filter is established by simulation, the suppressed sidelobe level is acceptable to radio fuze application.

Study on Ultra-Short Laser Pulse Ablation of Metals by Molecular Dynamics Simulation

LIU Xuan, WANG Yang, ZHAO Li-jie

2006, 15(4): 406-410.

[Abstract](101)

Abstract:
The dynamical progresses involved in ultra-short laser pulse ablation of face-centered cubic metals under stress confinement condition are described completely using molecular dynamics method. The laser beam absorption and thermal energy turning into kinetics energy of atoms are taken into account to give a detailed picture of laser metal interaction. Superheating phenomenon is observed, and the phase change from solid to liquid is characterized by a destroyed atom configuration and a decreased number density. The steep velocity gradients are found in the systems of Cu and Ni after pulse in consequence of located heating and exponential decrease of fluences following the Lambert-Beer expression. The shock wave velocities are predicted to be about 5000m/s in Cu and 7200m/s in Ni. The higher ablation rates are obtained from simulations compared with experimental data as a result of a well-defined crystalline surface irradiated by a single pulse. Simulation results show that the main mechanisms of ablation are evaporation and thermoelastic stress due to located heating.

Accuracy Assignment Study of Tank Fire Control System Based on Value Analysis Method

DOU Li-hua, ZHANG Jia, CHEN Jie

2006, 15(4): 411-415.

[Abstract](171)

Abstract:
A method of accuracy assignment based on value analysis method (VAM) in tank fire control system (TFCS) is proposed. From the analysis of primary error sources and their error transfer relationships, the mathematical model is built on the basis of VAM to solve the accuracy assignment problem. Simulation results show the validation and feasibility of the proposed method. It can help designer of tank fire control system work out an optimal system more efficiently and more economically.

Hybrid Level of Detail Algorithm for Real-Time Rendering of Large-Scale Terrain

DU Jian-xia, LI Feng-xia, ZHAN Shou-yi

2006, 15(4): 416-419.

[Abstract](161)

Abstract:
Hybrid level of detail (LOD) (HLOD) algorithm based on discrete LOD and continuous LOD is presented for real-time rendering of large-scale terrains. There are n HLOD models created off-line, which form a pyramid with n layers. Each of these models contains countless versions of the model at various levels of detail. When rendering, the corresponding models in some layer will be chosen. As the viewer's moves, either the continuous LOD algorithm will be applied to the selected models, or the visible models in another layer will be selected. An experiment on a triangular irregular network(TIN) terrain model was performed respectively using discrete LOD, continuous LOD and HLOD. The experimental results show that the HLOD algorithm exceeds the other two kinds of LOD in frame rate without reduction of terrain's fidelity.

Parallel Expectation-Maximization Algorithm for Large Databases

HUANG Hao, SONG Han-tao, LU Yu-chang

2006, 15(4): 420-424.

[Abstract](159)

Abstract:
A new parallel expectation-maximization (EM) algorithm is proposed for large databases. The purpose of the algorithm is to accelerate the operation of the EM algorithm. As a well-known algorithm for estimation in generic statistical problems, the EM algorithm has been widely used in many domains. But it often requires significant computational resources. So it is needed to develop more elaborate methods to adapt the databases to a large number of records or large dimensionality. The parallel EM algorithm is based on partial E-steps which has the standard convergence guarantee of EM. The algorithm utilizes fully the advantage of parallel computation. It was confirmed that the algorithm obtains about 2.6 speedups in contrast with the standard EM algorithm through its application to large databases. The running time will decrease near linearly when the number of processors increasing.

Occlusion Culling Algorithm Using Prefetching and Adaptive Level of Detail Techni

ZHENG Fu-ren, ZHAN Shou-yi, Yang Bing

2006, 15(4): 425-430.

[Abstract](70)

Abstract:
A novel approach that integrates occlusion culling within the view-dependent rendering framework is proposed. The algorithm uses the prioritized-layered projection(PLP) algorithm to occlude those obscured objects,and uses an approximate visibility technique to accurately and efficiently determine which objects will be visible in the coming future and prefetch those objects from disk before they are rendered. View-dependent rendering technique provides the ability to change level of detail over the surface seamlessly and smoothly in real-time according to cell solidity value.

Real-Time Structure and Motion by Fusion of Inertial and Vision Data for Mobile AR System

CHEN Jing, WANG Yong-tian, LIU Yue, AXEL Pinz

2006, 15(4): 431-436.

[Abstract](185)

Abstract:
The performance of adding additional inertial data to improve the accuracy and robustness of visual tracking is investigated. For this real-time structure and motion algorithm, fusion is based on Kalman filter framework while using an extended Kalman filter to fuse the inertial and vision data, and a bank of Kalman filters to estimate the sparse 3D structure of the real scene. A simple, known target is used for the initial pose estimation. Motion and structure estimation filters can work alternately to recover the sensor motion, scene structure and other parameters. Real image sequences are utilized to test the capability of this algorithm. Experimental results show that the proper use of an additional inertial information can not only effectively improve the accuracy of the pose and structure estimation, but also handle occlusion problem.

Automatic Image Registration Algorithm Based on Wavelet Transform

LIU Qiong, NI Guo-qiang

2006, 15(4): 437-442.

[Abstract](185)

Abstract:
An automatic image registration approach based on wavelet transform is proposed. This proposed method utilizes multiscale wavelet transform to extract feature points. A coarse-to-fine feature matching method is utilized in the feature matching phase. A two-way matching method based on cross-correlation to get candidate point pairs and a fine matching based on support strength combine to form the matching algorithm. At last, based on an affine transformation model, the parameters are iteratively refined by using the least-squares estimation approach. Experimental results have verified that the proposed algorithm can realize automatic registration of various kinds of images rapidly and effectively.

Novel Doppler Frequency Extraction Method Based on Time-Frequency Analysis and Morphological Operation

HOU Shu-juan, WU Si-liang

2006, 15(4): 443-447.

[Abstract](180)

Abstract:
A novel method of Doppler frequency extraction is proposed for Doppler radar scoring systems. The idea is that the time-frequency map can show how the Doppler frequency varies along the time-line, so the Doppler frequency extraction becomes curve detection in the image-view. A set of morphological operations are used to implement curve detection. And a map fusion scheme is presented to eliminate the influence of strong direct current (DC) component of echo signal during curve detection. The radar real-life data are used to illustrate the performance of the new approach. Experimental results show that the proposed method can overcome the shortcomings of piecewise-processing-based FFT method and can improve the measuring precision of miss distance.

Optical Fiber Bragg Grating Michelson Interferometer

JIANG Yi, JIANG Tian-fu, LIU Li

2006, 15(4): 448-450.

[Abstract](151)

Abstract:
A new Michelson interferometer based on fiber Bragg grating(FBG) is demonstrated. FBGs are used as reflectors, and the laser is replaced by a broadband source as input light in this interferometer. To demodulate the signals, a 3×3 coupler is used as a splitter. By combining with software demodulation, the outer interference can be obtained from the outputs of the interferometer. This kind of interferometer can also be wavelength-multiplexed easily by composing a series Michelson interferometer. The experiment results show that the clear interference fringe can be obtained by adjusting the path difference to make it less than interference length of FBG. The signals are also demodulated.

Design of Efficient Tunable Terahertz-Wave Parametric Oscillator

SIDDIQUE Muhammad, ZHANG Wei, LI Zhuo, YANG Su-hui

2006, 15(4): 451-456.

[Abstract](204)

Abstract:
An efficient widely tunable terahertz(THz)-wave parametric oscillator (TPO) has been designed based on the basic principle of optical parametric oscillator. The design of TPO comprises the theoretical calculations for wavelength dependent refractive index dependent wavelength when the frequency is in the far infrared region, the low-loss parametric gain has been discussed as a same form as the parametric gain in the optical region, realized the non-collinear phase-matching conditions of the terahertz optical parametric oscillator and structure of lithium niobate (LiNbO₃) for TPO. The tunable spectrum range of terahertz-wave has been achieved. To increase THz output, a cut exit was made at the corner of the LiNbO₃crystal.

Influences of Atmospheric Turbulence on Image Resolution of Airborne and Space-Borne Optical Remote Sensing System

ZHANG Xiao-fang, YU Xin, YAN Ji-xiang

2006, 15(4): 457-461.

[Abstract](270)

Abstract:
A new way is proposed to evaluate the influence of atmospheric turbulence on image resolution of airborne and space-borne optical remote sensing system, which is called as arrival angle-method. Applying this method, some engineering examples are selected to analyze the turbulence influences on image resolution based on three different atmospheric turbulence models quantificationally, for the airborne remote sensing system, the resolution errors caused by the atmospheric turbulence are less than 1cm, and for the space-borne remote sensing system, the errors are around 1cm. The results are similar to that obtained by the previous Fried-method. Compared with the Fried-method, the arrival angle-method is rather simple and can be easily used in engineering fields.

Performance and Improvement of MCS Selection with Channel Quality Estimation Errors for HSDPA

JIA Min-li, KUANG Jing-ming, WAN Lei, FEI Ze-song

2006, 15(4): 462-466.

[Abstract](180)

Abstract:
The throughput performance of modulation and coding schemes (MCS) selection with channel quality estimation errors (CQEE) is analyzed for high-speed downlink packet access (HSDPA). To reduce the loss of throughput caused by CQEE, the robust MCS selection method and adaptive MCS switching scheme are proposed. In addition, automatic repeat request (ARQ) scheme is used to improve the block error rate (BLER) performance. Simulation results show that the proposed methods decrease the throughput loss resulted from CQEE efficiently and BLER performance gets better with ARQ scheme.

Processing Methods for Conical Scan Hopped-Frequency Signal

WANG Xiao-hong, LONG Teng

2006, 15(4): 467-472.

[Abstract](228)

Abstract:
The new radar system of combination of the hopped-frequency with the conical scan is presented. According to the principle and expression of the conical scan hopped-frequency signal, the angle processing method in which angle information is obtained by taking discrete Fourier transform (DFT) for the conical envelop of each scattering centre by means of high range resolution profile (HRRP) is presented,and the corresponding formula is derived. The influence of non-ideal factors, such as amplitude fluctuation noise and system noise, leakage of time and frequency domain, unstable rotation of antenna, and missile rotation, on angle-measurement precision and the possible solving methods are also focused on. The simulation results show that the combination of the hopped-frequency and conical scan system could get satisfactory angle information, which could ensure good quality when used in practical tracking radar.

Molecular Structure of Aminoguanidine Sulfate Monohydrate

CHEN Hong-yan, ZHANG Tong-lai, QIAO Xiao-jing, YANG Li, SHAO Feng-lei

2006, 15(4): 473-477.

[Abstract](140)

Abstract:
The single crystal of aminoguanidine sulfate monohydrate [(AG)₂SO₄·H₂O] is obtained and its structure is determined by X-ray diffraction analysis. The compound crystallizes in orthorhombic system with space group Pnma and the empirical formula C₂H₁₆N₈O₅S. The unit cell parameters are as follows: a= 0.6759(2)nm, b=1.4131(5)nm, c=1.1650(4)nm, V=1.1128(6)nm³, Z=4, Dc= 1.578g/cm³, F(000)=560, s=1.069, μ(MoKα)=0.318mm^-1. The final R and wR are 0.0312 and 0.0833, re-spectively. The title compound is an ionic compound and its structure unit consists of two aminoguanidium cations, one sulfate anion and one crystal water molecule, which are interconnected by electrostatic forces and hydrogen bonds into net structure, making the title compound very stable. Under a linear heating rate, the thermal decomposition processes of (AG)₂SO₄·H₂O have one endothermal dehydration stage, one melting pr-ocess and one exothermic decomposition stage at 50-400℃, and can evolve abundant gas products.

Application of the Backpropagation Neural Network Method in Designing Tungsten Heavy Alloy

ZHANG Zhao-hui, WANG Wei-jie, WANG Fu-chi, LI Shu-kui

2006, 15(4): 478-482.

[Abstract](257)

Abstract:
The model describing the dependence of the mechanical properties on the chemical composition and as deformation techniques of tungsten heavy alloy is established by the method of improved the backpropagation neural network. The mechanical properties' parameters of tungsten alloy and deformation techniques for tungsten alloy are used as the inputs. The chemical composition and deformation amount of tungsten alloy are used as the outputs. Then they are used for training the neural network. At the same time,the optimal number of the hidden neurons is obtained through the experiential equations,and the varied step learning method is adopted to ensure the stability of the training process. According to the requirements for mechanical properties,the chemical composition and the deformation condition for tungsten heavy alloy can be designed by this artificial neural network system.

Tribological Property of Polyimide Porous Materials

PU Yu-ping, Lv Guang-shu, LI Xiao-jun, XIAO Han-cheng

2006, 15(4): 483-487.

[Abstract](105)

Abstract:
The friction performance of the polyimide (PI) porous composite materials made by moulding method with MoS₂or polytetrafluoroethylene (PTFE) appended are disserted. The result shows that all the PI-based porous composites have the performance of transfer lubrication in the friction process, and the transfer film is built between the counter friction bodies; with the increasing of the MoS₂amount from 0 to 20%, the friction coefficient trends toward decrease, and the transfer lubricate phenomenon become more obvious; when adding PTFE as synergist to the porous PI+MoS₂composite material, the synergistic effect happens, which can improve the friction performance of the material effectively.

Preparation and Performance Study of a New Type Lead Paste

GAO Jun, SHI Peng-fei, YANG Tao

2006, 15(4): 488-491.

[Abstract](107)

Abstract:
A new type lead paste mixed with binders used in thin-plate, spirally wound lead acid batteries is introduced. The utility of positive active material can obtain 54.17% and 37.71% at discharge currents of 0.5C and 5.0C. The investigation was performed by means of X-ray diffraction (XRD), scaning electron microscopy (SEM), infrared spectroscopy (IR), cylic voltammetry (CV), the results revealed more details on the reaction mechanism of paste-mixing. Further conclusion can be obtained that the reaction of paste-mixing is a physical process, and the chemical reactions is local reaction, which is different from traditional mixing process, the binders has some effect on the formation of battery process. The binders can dissolve in electrolyte, which have no disadvantageous effect on the charge-discharge performance.

Development and Electrochemical Testing of Novel Bipolar Nickel Metal Hydride Batteries

DENG Chao, SHI Peng-fei

2006, 15(4): 492-495.

[Abstract](110)

Abstract:
Some aspects in the design and development of bipolar Ni/MH battery are presented. After optimizing sealing technique and modifying capacity ratio of two adjacent electrodes in one sub-cell, some bipolar Ni/MH stacks with 6 sub-cells have been assembled and investigated. Electrochemical testing results show the bipolar battery has excellent high rate discharge capability and fast recharge ability, and satisfactory charging efficiency in different states of charge. Moreover, the battery also displays good stability under pulse cycles in simulating hybrid vehicle working conditions.

Entropy Exchange in Coupled Field-Superconducting Charge Qubit System with Intrinsic Decoherence

SHAO Bin, ZHANG Jian, ZOU Jian

2006, 15(4): 496-499.

[Abstract](64)

Abstract:
Based on the intrinsic decoherence effect, partial entropy properties of a superconducting charge qubit inside a single-mode cavity field is investigated, and entropy exchange which is recently regarded as a kind of anti-correlated behavior of the entropy between subsystems is explored. Our results show that although the intrinsic decoherence leads to an effective irreversible evolution of the interacting system due to a suppression of coherent quantum features through the decay of off-diagonal matrix elements of the density operator and has an apparently influence on the partial entropy of two individual subsystems, it does not effect the entropy exchange between the two subsystems.

Ant Colony System for a Fuzzy Adjacent Multiple-Level Warehouse Layout Problem

ZHANG Qiang, YU Ying-zi, LAI K K

2006, 15(4): 500-504.

[Abstract](115)

Abstract:
A warehouse layout problem where the warehouse has more than one level and both the distance from the cell to the receive/exit bay and demand of item types are fuzzy variables is proposed. The problem is to find a layout with the minimum transportation cost subject to adjacency and other constraints. A fuzzy expected value model is given and an ant colony system is designed to solve the problem. Computational results indicate the efficiency and effectiveness of the method.

2006 Vol. 15, No. 4