JOURNAL OF BEIJING INSTITUTE OF TECHNOLOGY

Internal Energy Losses and Contact Duration About a Circular Plate Colliding to a Half-Plane Target

LV Zhong-jie

2009, 18(3): 253-257.

[Abstract](187)

Abstract:
Collisions between multibody systems are irreversible processes which cause loss of internal energy by a stress wave that propagates in the impacting bodies away from the region of impact. A coefficient of restitution relating to approach velocity is introduced to denote the losses of translational kinetic energy. A parameterβinvolved in internal energy losses has been obtained to calculate the coefficient of restitution. As a result, the internal energy losses caused by elastic stress waves and the contact duration in metals can be calculated numerically for the collision between circular cylinder and half plane. The metals include aluminum alloys, steel-mild 1020, steel-stainless austenitic 304, tungsten alloys, copper alloys, nickel alloys and titanium alloys. By introducing a coefficient of velocity-frequency, an exponential aggression equation related the normalized oscillating frequency and normalized approach velocity has been obtained by the numerical method.

Numerical Simulation Research of Loitering Munitions Aerodynamics

HE Guang-lin, JI Xiu-ling, ZHANG Tai-heng

2009, 18(3): 258-261.

[Abstract](725)

Abstract:
Aerodynamics of loitering munition is studied in this paper. The aerodynamic characteristics of loitering munition with non-circular body and body-airfoil-empennage combination are calculated numerically atMa0.4 based on multi-griddings patching technology, in the range of angle of attack -4°-10°, and the analytical results were compared with those from wind tunnel experiments, they show a good consistency. Analysis of the results showed that the normal force generated by non-circular cross-section missile increases with the angle of attack. Atα≥6°, normal force achieved by missile body can take up to 10% of the total lift. Together with the lifting surface, the loitering munitions can provide a better lift to drag ratio, an improved weapon range and a good longitudinal stability.

Interior Performances of an Impulse Thruster by Numerical Calculation

YANG Qing, WANG Li-qiong, WANG Pei-lan, HUANG Ge-de

2009, 18(3): 262-267.

[Abstract](202)

Abstract:
Impulse thruster is a kind of actuator used for trajectory correction or attitude control of some in-flight munitions and vehicles. A simple mathematical model was set up to model interior characteristics of an impulse thruster. With this model, effects of some key parameters on interior performances of the impulse thruster were studied. Results show that action time is affected significantly by nozzle throat diameter and volume of combustion chamber, while output impulse is sensitive to charge particle diameter and nozzle throat diameter. Through numerical calculation, the ranges of the optimized values for some key parameters were obtained.

Research on Co-simulation with ADAMS and MATLAB for Servo Tracking System Mounted with a Small Arm

WANG Hong-ru, WANG Jian-zhong

2009, 18(3): 268-272.

[Abstract](312)

Abstract:
Research on a servo tracking system mounted with a small arm for robot fighting platform based on multi-body system dynamics and intelligent control theory is presented. A multi-body dynamic model which can accurately express dynamic performances of the system is built in ADAMS. In addition, an intelligent PID control model is built with MATLAB/Simulink, and the two models are integrated and co-simulated by the interface of ADAMS/Controls. Simulation experiments indicate that co-simulation technique used for design of the servo tracking system mounted with a small arm can effectively improve its design efficiency, and can also provide theoretical bases for the motion control and performance improvement of the servo tracking system mounted with a small arm.

Finite Element Modeling and Modal Analysis of Complicated Structure with Bolted Joints

PU Da-yu, LIAO Ri-dong, ZUO Zheng-xing, FENG Hui-hua

2009, 18(3): 273-277.

[Abstract](294)

Abstract:
A contact bolt model is proposed as a new modeling technique to investigate the complex structure with bolted joints for modal analysis and compared with the coupled bolt model, and the test results are given. Among these models, the coupled bolt model provides the best accurate responses compared with the experimental results. The contact bolt model shows the best effectiveness and usefulness in view of operational time. The bolt models proposed in this study are adopted for a dynamic characteristic analysis of a large diesel engine consisting of several parts which are connected by many bolts. The dynamic behavior of the entire engine structure was investigated by experiment. The coupled bolt model and the contact bolt model were applied to model the assembly of engine with high preload. The experimental results are in good agreement with the finite element method (FEM) results. Compared with the other models, the contact bolt model presented in this paper is more effective and useful in view of operational time and experience of analysts.

Genetic Algorithm Based Production Planning for Alternative Process Production

ZHANG Fa-ping, SUN Hou-fang

2009, 18(3): 278-282.

[Abstract](272)

Abstract:
Production planning under flexible job shop environment is studied. A mathematic model is formulated to help improve alternative process production. This model, in which genetic algorithm is used, is expected to result in better production planning, hence towards the aim of minimizing production cost under the constraints of delivery time and other scheduling conditions. By means of this algorithm, all planning schemes which could meet all requirements of the constraints within the whole solution space are exhaustively searched so as to find the optimal one. Also, a case study is given in the end to support and validate this model. Our results show that genetic algorithm is capable of locating feasible process routes to reduce production cost for certain tasks.

Numerical Simulation of a Spark Ignited Two-Stroke Free-Piston Engine Generator

MAO Jin-long, ZUO Zheng-xing, LIU Dong

2009, 18(3): 283-287.

[Abstract](364)

Abstract:
A numerical program is built to simulate the performance of a spark ignited two-stroke free-piston engine coupled with a linear generator. The computational model combines a series of dynamic and thermodynamic equations that are solved simultaneously to predict the performances of the engines. The dynamic analysis performed consists of an evaluation of the frictional force and load force introduced by the generator. The thermodynamic analysis used a single zone model to describe the engine’s working cycle which includes intake, scavenging, compression, combustion and expansion, and to evaluate the effect of heat transfer based on the first law of thermodynamics and the ideal gas state equation. Because there is no crankshaft, a time based Wiebe equation was used to express the fraction of fuel burned in the combustion. The calculated results were validated by using the experimental data from another research group. The results indicate that the free-piston generator has some advantages over conventional engines.

Study on Calibrating of Electronic Governors

HUANG Qian, HUANG Ying, ZHANG Fu-jun

2009, 18(3): 288-292.

[Abstract](180)

Abstract:
The control parameters of electronic governor that influence the transient characteristics of the engine are analyzed. An electric control unit was developed and the control parameters were calibrated on the test bench. The initial value of integral term and the maximum output of rack position proportion, integration and derivation (PID) controller affect the step and triangle response drastically. Through correcting the proportional term and integral term of speed PID controller, the dynamic speed drop and speed overshoot are improved. A property control strategy for cold starting an engine is set, and the calibration process indicates that the fuel injected into the cylinder per cycle and the desired speed ascend rate drastically affect the start transient process.

A New Method for Computing Radiation Heat Flow of In-Cylinder Soot of Diesel Engines

XIANG Chang-hu, ZHANG Wei-zheng, YUAN Yan-peng

2009, 18(3): 293-297.

[Abstract](222)

Abstract:
A concise formula for computing radiation heat flow of in-cylinder soot is presented,based on the assumptions that in-cylinder heat transfer of diesel engines is a quasi-equilibrium process and in-cylinder soot particles are spherical. That in this formula there consist neither constants needing adjustments nor variables related to engine types or operating conditions makes it universal and easy to use. Also it can be seen from the formula that radiation heat transfer is proportional to the quotient of in-cylinder soot mass over the average radius of primary particles. Besides, with the help of different algorithms it can be used for predicting cylinders' global as well as local radiation heat flows. As a demonstrative application on its global facet, a three-dimension simulation study about the soot-radiation-related heat flow in the combustion chamber of a diesel engine is carried out. Results show that the range of the soot-radiation-related heat flow computed by this formula agrees well with other researcher's earlier theoretic reasoning and experimental measurements.

Research on the Critical Speed of a Mixed-Flow Turbocharger with Hybrid Ceramic Ball Bearing

HUANG Ruo, GE Xin-bin, MA Chao-chen

2009, 18(3): 298-303.

[Abstract](216)

Abstract:
The critical speeds for a vehicle turbocharger with hybrid ceramic ball bearing are researched. The ball bearing-rotor system produces resonance when it working in critical speed and that makes the turbocharger injury working for a long time. The calculation and analysis methods of the critical speed for the vehicle turbocharger are described. The critical speed is computed by two methods including Riccati transfer matrix and DyRoBeS finite element method for a vehicle turbocharger with hybrid ceramic ball bearing. The vibration experiment had been taken to validate the calculating result. Comparison between the results by two calculation methods and the test results show that the first critical speed differences are 6.47% and 5.66%, the second critical speed differences are 2.87% and 2.94% respectively. And then, the primary factors which influence the critical speed are analyzed, the conclusions will be helpful for the vehicle turbocharger bearing-rotor system design.

Proportional Navigation Guidance Law with Variable Coefficient Gravity Compensation

YANG Chun-lei, TANG Sheng-jing, SHI Jiao

2009, 18(3): 304-308.

[Abstract](268)

Abstract:
Based upon a discussion on the merits and limitations of proportional navigation (PN) guidance law in which constant gravity compensation is included as a part, a counterpart having varying compensations, which changes with pitching angle and line-of-sight angle, is substituted. Flight trajectory simulation over a submissile model is conducted, resulting in increased impact angle, shorter miss distance, smaller maximum normal overload and narrower terminal angle of attack.

Modeling and Simulation of MOEMS Gyroscope Based on TE-TM Mode Converter

ZHAO Yi, CHEN Shu-fen

2009, 18(3): 309-312.

[Abstract](288)

Abstract:
A novel structure design of micro optic electro mechanical system (MOEMS) gyroscope is presented in this paper. The structure combining surface acoustic wave (SAW) sensor, optical waveguide diffractive component, electro-optical modulator etc. is integrated on a LiNbO₃substrate as the gyroscope for sensing rotating angular velocity, and an optical readout device is added on the traditional SAW typed TE-TM mode converter as the detecting device. The principles of the MOEMS are discussed in the paper, and simulation result shows that there would be apparent advantages of higher precision and stronger anti-vibration capacity.

Fast Intra Downsizing Based on Direction for H.264/AVC Transcoding

ZHANG Jian, SHEN Ting-zhi, JIANG Wei, ZHANG Ying

2009, 18(3): 313-317.

[Abstract](190)

Abstract:
A fast algorithm based on direction in intra frame downsizing in H.264 is proposed, which used modes information of macroblocks before transcoding and the direction relation of modes between decoding and re-encoding in transcoding. This algorithm also made use of statistics between decoded modes and re-encoded modes, which came from a lot of sequences data experiments. Without full modes encoding, it can improve the speed of reducing intra-prediction frame resolution obviously. Comparing to traditional transcoding, it only needs to compute one of thirteen modes in re-encoding. The experiments show that this algorithm can significantly speed up 92 percent transcoding time in intra-prediction frame of H.264 with slight PSNR degradation. It also can support an improvement in real-time for transcoding and ability of bandwidths changing.

Intermittent Clutter Removal Approach for Wind Profiler Data Based on Fractional Fourier Transform

YUAN Lei, AN Jian-ping, BU Xiang-yuan

2009, 18(3): 318-322.

[Abstract](279)

Abstract:
Through the analysis of the target characteristics and according to the intermittent clutter bursting and short duration characteristics, a new method for the clutter recognition based on the fractional Fourier transform (FRFT) is proposed. This method is predicated on the fact that the FRFT perfectly localizes a chirp signal as an impulse when the angle parameter of the transform matches the chirp rate of the chirp signal. The method involves detecting the presence of the intermittent clutter and correctly estimating its orientation in the time-frequency plane, removing the intermittent clutter in the fractional domain, and completing wind estimation by the power spectrum. By testing the artificial WPR-like signal and data measured from the field, we verify that the FRFT-based method is very effective.

Crystal Structure of 3-Allyl-5,5-Dimethylhydantoin

ZHANG Li-na, YANG Rong-jie

2009, 18(3): 323-326.

[Abstract](227)

Abstract:
In this paper single crystals of 3-allyl-5,5-dimethylhydantoin (ADMH) have successfully extracted through recrystallization from a mixture solvents of dichloromethane and petroleum ether. By using single-crystal X-ray diffraction technique, its crystal structure has been determined to belong to monoclinic system, with space groupP2(1)/n,a0.599?53(12),b0.983?7(2),c1.529?0(3)?nm,β100.43(3)°,V0.886?9(3)?nm3,Z4,D_c1.260?g/cm³,F(000)360,μ(MoK_α)0.092?mm^-1,M_r168.20,R0.042?2 andwR0.108?5 for 1?755 observed reflections (I>2σ(I)). Also, its chemical formula has been confirmed as C₈H₁₂N₂O₂. Results of crystal structures determination for the compound show that the bond of N(1)-C(2) has a double-bond characteristic and there are intermolecular hydrogen bonds. This crystal exists in the form of dimers, in which the two constituent ADMH molecules build into an H-bond-centered symmetric pattern.

A Facile Synthesis ofN-alkyl-4'-methyl-1,1'-biphenyl-2-sulfona-mide via Linking DoM Reaction with Suzuki Reaction

ZHANG Jun, ZHOU Zhi-ming, XUE Wei-zhe, LI Zhi-huai

2009, 18(3): 327-332.

[Abstract](236)

Abstract:
SixN-alkyl-4'-methyl-1,1'-biphenyl-2-sulfonamides were synthesized facilely and efficiently from low cost and readily available benzenesulfonyl chloride andC₁-C₄fatty amines via linking DoM reaction with Suzuki reaction. The structures of the new compounds synthesized were confirmed by elemental analysis,IR,1H NMR and MS. This new method makes a feature of low cost and readily available starting material, fewer steps, mild condition, easiness to operate and higher yield.

Structures, Electron Affinities and Vibrational Frequencies of SF₅OX/SF₅OX^-(XF,Cl,Br)

CHENG Su-zhen, XU Wen-guo, LU Shi-xiang

2009, 18(3): 333-338.

[Abstract](234)

Abstract:
The molecular structures, electron affinities, vibrational frequencies and IR intensities of the SF₅OX/SF₅OX^-(XF, Cl, Br) species have been determined by four different density functional theory (DFT) methods (B3LYP, BHLYP, BP86, BLYP) in conjunction with DZP++ basis set. The BHLYP method predicts the best geometry parameters. The adiabatic electron affinities (EA_ad) predicted by the B3LYP/DZP++ method are 4.36?eV (SF₅OF), 4.13?eV (SF₅OCl), 4.12?eV (SF₅OBr), respectively. Large electron affinity implies the corresponding anions are stable. The total intensities in the near IR "window" of the anions SF₅OX^-(XF, Cl, Br) at B3LYP level are 1?602?km/mol (SF₅OF^-), 1?868?km/mol (SF₅OCl^-) and 1?916?km/mol (SF₅OBr^-), respectively, larger than those of the corresponding neutrals. It suggests that SF₅OX/SF₅OX^-(XF, Cl, Br) may be used to "warm" Mars.

Fabrication of Stable Superhydrophobic Cupric Hydroxide Surface with Hierarchical Structure on Copper Substrate

LIU Hong-qin, XU Wen-guo, LU Shi-xiang

2009, 18(3): 339-344.

[Abstract](266)

Abstract:
Cupric hydroxide films with a new hierarchical architecture consisting of beautiful nanotubes and nanoflowers were directly fabricated on copper substrate via a solution-immersion process at a constant temperature of 23?℃. Stable superhydrophobic Cu(OH)₂surface was obtained after Cu(OH)₂films were modified with hydrolyzed 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (C₈H₄Cl₃F₁₃Si, FOTMS). The surface morphology and composition of the film were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. Result shows that the surface of Cu(OH)₂films directly grown on copper substrate was hydrophilic, whereas the modified Cu(OH)₂films exhibited the superhydrophobicity with a water contact angle (CA) of about 160.8°, as well as a small sliding angle (SA) of about 1°. The special hierarchical structure, along with the slow surface energy leads to the high superhydrophobicity of the surface.

Synthesis of γ-AlOOH Nanoparticle and Its Tribological Properties as Additives in Liquid Paraffin

XUAN Yu, LIU Ying, ZHAO Xiu-chen, WANG Fu-chi, LI Jiang-guo, LI Ya-jun

2009, 18(3): 345-350.

[Abstract](167)

Abstract:
An experiment procedure was presented for the synthesis of γ-AlOOH nanoparticles by a dehydration process which employed the solution of H₂O₂as dehydrator. The phase and morphology of the product were investigated by XRD and TEM. The tribological properties of γ-AlOOH nanoparticles with the average diameter of 15?nm as additives in liquid paraffin were investigated by a four-ball tester, and the worn surfaces were analyzed by SEM and EDS. Results show that the average size of synthesized γ-AlOOH nanoparticles increases with the increase of the pH value and temperature of the reactant. The γ-AlOOH nanoparticles as additives could exhibit good tribological properties due to their covering effect, which prevents the direct contact of asperities and reduces the adhesion. As the real area of contact decreases with the decrease of applied load, the optimum concentration varies from 0.4% to 0.1% when the applied load decreases from 294?N to 200?N.

Learning-Memory Function and Swimming Capability of Rat and Ergonomic Evaluation Under Hypoxic Condition

HU Ding-yu, DAI Rong-ji, LI Bo, MAO Jian, GENG Li-na, DENG Yu-lin

2009, 18(3): 351-355.

[Abstract](191)

Abstract:
Effects of hypoxia on learning-memory function and swimming capability of rat were studied and the ergonomics under hypoxic condition was also evaluated from the biological point of view. Three modes of hypoxia were designed and plots of oxygen concentration versus time for each group in hypoxic environment were produced. Results showed that the effects of hypoxia on learning-memory function and swimming capability were related with the time and strength of hypoxia. It had nothing to do with the individual difference of rat models. 10% O₂long-term intermittent anamorphosis hypoxia could improve the swimming capability of rat model significantly. Stimulating with proper level of hypoxia, carbon dioxide could improve ergonomics in airtight hypoxia environment. Under hypoxia condition, from the ergonomic point of view, 6% O₂is the important threshold and might belong in critical region.

Information Geometry for Random Walk

WU Li-ping, SUN Hua-fei, CAO Li-mei

2009, 18(3): 356-360.

[Abstract](348)

Abstract:
The random walk (RW) is investigated from the viewpoint of information geometry and shown to be an exponential family distribution. It has a dual coordinate system and a dual geometric structure. Then submanifolds of RW manifold is studied, and thee-flat hierarchical structure and the orthogonal foliations of RW manifold are obtained. Finally, using the Kullback-Leibler divergence, the projections are given from the RW manifold to its submanifolds.

Information Geometry and Low Density Parity Check Codes

HAN Dong, SUN Hua-fei, YAN Da-yuan

2009, 18(3): 361-364.

[Abstract](252)

Abstract:
The application of information geometry in the low density parity check (LDPC) codes based on the work of Ikeda and Amari is considered. The method is to turn the decoding process into the change of the parameter. When the LDPC decoding procedure converges, both the convergent probability distribution and the true probability distribution belong to the same submanifold, but this does not mean they are equimarginal, that points out the origin of the decoding error.

Market Risk Evaluation on Single Futures Contract: SV-CVaR Model and Its Application on Cu00 Data

ZHOU Ying, ZHANG Hong-xi, WU Hui-shuo

2009, 18(3): 365-369.

[Abstract](292)

Abstract:
A new stochastic volatility (SV) method to estimate the conditional value at risk (CVaR) is put forward. Firstly, it makes use of SV model to forecast the volatility of return. Secondly, the Markov chain Monte Carlo (MCMC) simulation and Gibbs sampling have been used to estimate the parameters in the SV model. Thirdly, in this model, CVaR calculation is immediate. In this way, the SV-CVaR model overcomes the drawbacks of the generalized autoregressive conditional heteroscedasticity value at risk (GARCH-VaR) model. Empirical study suggests that this model is better than GARCH-VaR model in this field.

Bi-matrix Games with Fuzzy Strategies and Fuzzy Payoffs and Their Mathematical Programming Equivalents

GAO Jing, ZHANG Qiang

2009, 18(3): 370-374.

[Abstract](213)

Abstract:
A fuzzy bi-matrix game (FBG), namely a two-person non-zero-sum game with fuzzy strategies and fuzzy payoffs is proposed. We have defined and analyzed the optimal strategies of this FBG, and shown that it can be transformed into a corresponding fuzzy mathematical programming issue, for which a ranking function approach can be applied. In addition, optimal strategies of FBG for both Player I and Player II can be gotten.

Variations and Absolute Continuity of Set Functions onT_∞-tribe

WANG Feng-ye, ZHANG Qiang

2009, 18(3): 375-378.

[Abstract](312)

Abstract:
some properties of the inclusion variation and the disjoint variation of set functions onT_∞-tribe are studied in detail. The absolute continuity and singularity of set functions onT_∞-tribe are discussed. The triangular normsT_∞andS_∞are considered as the operators of intersection and union between the fuzzy sets. As a result, some important conclusions about the variations and absolute continuity of set functions onT_∞-tribe are obtained such as the superadditivity of inclusion variation, the relation between the variations and the equivalence proposition of absolute continuity of set functions onT_∞-tribe. In addition, two small mistakes aboutT_∞-measure are pointed out by the counterexamples and are revised.

2009 Vol. 18, No. 3