Table of Content

30 June 2015, Volume 36 Issue 6

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Paper

Robust Optimization of Hydraulic Pump Stroking Mechanism Based on Monte Carlo Method

WANG Hu-jiang，MAO Ming，TANG Shou-sheng，JI Hai

2015, 36(6):  961-967.  doi:10.3969/j.issn.1000-1093.2015.06.001

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In order to ensure the robustness of stroking mechanism, the mean and standard deviation of dynamic tracking accuracy and stability index are taken as the optimization targets according to the special demand on stroking mechanism of tracked vehicle. A system dynamic model is established, and a new robust optimization method is built based on Monte Carlo method. Research shows that the dynamic tracking accuracy and stability of system can be guaranteed and the ability of system resistant to the change of structure parameters and fluid parameters can be enhanced by optimizing the nominal values of the feedback fork length, valve port gradient and piston area. The system robustness can be significantly improved.

Analysis and Experiment of Tracked Vehicle Steering Torque Based on Shear Stress Model

RUI Qiang, WANG Hong-yan, WANG Qin-long, GUO Jing, ZOU Tian-gang, WAN Li

2015, 36(6):  968-977.  doi:10.3969/j.issn.1000-1093.2015.06.002

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For the study of steering performance of tracked vehicles under skidding, a steady-state steering model of tracked vehicle, which takes the skid and slippage of tracks and centrifugal force into consideration, is established to improve the simulating accuracy of the tracked vehicle steering model. Expressions of driving force and braking force of outside track and inside track, and steering resistance torque of tracked vehicles are derived using shear stress-shear displacement relationship model, respectively. According to force and torque equilibrium theory, the steering dynamic equations of tracked vehicle are established and solved by iterative algorithm. Taking a certain type of tracked vehicle with the integrated transmission device as the object,the accuracy of steering model of tracked vehicles is verified by comparing the experimental and calculated results. The rules of changing the kinematics and dynamic steering performance of tracked vehicles with turning radius and running velocity are deeply studied based on the steady-state steering model of tracked vehicle. The results show that the influence of the steering centrifugal force on steering performance increases significantly with the increase in running velocity and the decrease in turning radius.

Research on Test and Evaluation of Unmanned Ground Vehicles

SUN Yang， CHEN Hui-yan

2015, 36(6):  978-986.  doi:10.3969/j.issn.1000-1093.2015.06.003

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A pre-established test and evaluation system will benefit the development of unmanned ground vehicles. A design method is proposed for a scientific and comprehensive test and evaluation system for unmanned ground vehicles. The test and evaluation system includes the test contents, the test environment, the test methods and the evaluation methods. A hierarchical design approach is used to design the test content stage by stage, moving from simplicity to complexity and from individual modules to the entire vehicle. The hierarchical test environment is established according to the levels of test content. The test method based on multilevel platforms and sensors is put forward to ensure the test accuracy. The fuzzy extension analytic hierarchy process (fuzzy-EAHP) method is used for the comprehensive evaluation, which can quantitatively evaluate the individual module and the overall technical performance of unmanned ground vehicles. The proposed test and evaluation system has been successfully applied to the test and evaluation of unmanned ground vehicle.

Linear Active Disturbance Rejection Control for Two-axis Coupling Position Servo System of Rocket Launcher

ZHENG Ying， MA Da-wei， YAO Jian-yong， HU Jian

2015, 36(6):  987-993.  doi:10.3969/j.issn.1000-1093.2015.06.004

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In order to study the performance of the position servo system of rocket launcher with the azimuth axis and pitch axis coupling, a model of two-axis coupling position servo system is established based on real servo system with velocity closed loop. The second-order approximate models of azimuth axis and pitch axis are proposed through frequency domain analysis. The linear extended state observer and active disturbance rejection controller of the two-axis system are designed to estimate and compensate uncertain dynamics. The simulation results show that the proposed observer estimates the total system disturbances satisfactorily, and the controller compensates the strong disturbance of combustion gas flow impact moment and the coupling effect. The proposed controller could restrain the vibration of the coupling system to maintain launching accuracy in condition of servo tracking and launching, of which control performance is superior to that of PID controller.

Simulation and Analysis of Plates Cluster Distribution of Surface-type Infrared Decoy

WANG Zheng-wei， NING Hui-jun， WANG Jin-long， RUAN Wen-jun， WANG Hao

2015, 36(6):  994-1000.  doi:10.3969/j.issn.1000-1093.2015.06.005

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A rigid body model and a database including 220 kinds of aerodynamic conditions are established to study the separation and dispersion of cylindrical plates of surface-type IR decoy launched at high-speed. The dispersion process of thousands of plates in surface-type IR decoy launched at 0.8 Mach is numerically simulated based on the flow field numerical simulation of plates’ multi-body separation process. Research results show that the rigid body motion model can be to use to simulate the dispersion process of cylindrical plates. The new distributing characteristics of plate cluster are presented. The surface-type infrared decoy filled with cylindrical plates is validated to quickly spread within 0.5s with a large dispersion area, and the hang time lasts more than 3.0 s with a uniform distribution.

Anti-active Noise Jamming Performance of Pulse Doppler Fuze

LI Ze, LI Ping, HAO Xin-hong, YAN Xiao-peng, WANG Jian-tao

2015, 36(6):  1001-1008.  doi:10.3969/j.issn.1000-1093.2015.06.006

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The anti-active noise jamming performance of pulse Doppler (PD) fuze is quantitatively studied based on the characterization parameters of processing gain and power spectrum in order to reveal the jamming mechanism and improve the anti-jamming performance of PD fuze. The input signal-to-jamming ratio, output signal-to-jamming ratio and processing gain of the procedure from the echo reception to the correlation detection under the radio frequency noise jamming, noise amplitude modulation jamming and noise frequency modulation jamming are deduced. The signal feature parameters affecting the anti-active noise jamming performance of PD fuze are obtained, and the simulation verification is carried out. The quantitative analysis and simulation results indicate that the PD fuze has the strong performance of anti-active noise jamming, and its performance of anti-active noise jamming is mainly determined by the pulse duty cycle and the bandwidth of Doppler filter.

Two-dimensional Interior Ballistics Model of High Pressure Ejection Apparatus and Analysis on the Characteristics ofFlow Field in Launching Chamber

JIANG Shu-yuan， WANG Hao, RUAN Wen-jun

2015, 36(6):  1009-1014.  doi:10.3969/j.issn.1000-1093.2015.06.007

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High pressure accumulated by propellant burning in high pressure ejecting apparatus makes the chamber open instantly and eject a projectile to a target. In order to grasp the complex change of gas flow in the launching chamber, a two-dimensional interior ballistics model is established and simulated by Runger-Kutta and MacCormark schemes. The calculated pressure results are reliable by comparison with the experimental ones. The flow field characteristics are got through the analysis of the calculated results, such as gas pressure, velocity, etc. The results show that the size and distribution of high pressure gas accumulated at the bottom of the projectile have the direct effects on the ejection performance.

Iterative Method to Solving Re-entry Trajectory Optimization with Complex Constraints

ZHANG Meng-ying， TANG Qian-gang， HAN Xiao-jun， ZHANG Qing-bin， GE Jian-quan

2015, 36(6):  1015-1023.  doi:10.3969/j.issn.1000-1093.2015.06.008

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Re-entry trajectory optimization with complex constraints for hypersonic vehicles is a strong nonlinear optimal control problem with multiple phases and constraints. A trajectory optimization framework which adds the constraints successively based on Gauss pseudo-spectral method is proposed. The framework is used to build more accurate models of typical regular no-fly zone to provide multiple choices for mission plan, and then a successive approximation solving method is proposed to simplify the complexity of constraint model. In each iteration, the previous solutions to simpler problems are used as initial guesses to approach the solution of the original problem. Numerical examples for minimizing time of trajectory with multiple constraints including heat flux of stagnation point, overload, dynamic pressure and no-fly zone constraints are simulated to demonstrate the proposed method. The simulation results show that the phased adding constraints trajectory optimization framework has better robustness.

The Influence of Annular Cavity on Secondary Combustion of Gas-ejection Initial Cavity

HU Xiao-lei， LE Gui-gao， MA Da-wei， REN Jie， ZHOU Xiao-he

2015, 36(6):  1024-1032.  doi:10.3969/j.issn.1000-1093.2015.06.009

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To study the influence of annular cavity of gas-ejection launcher on secondary combustion, RNG k-ε turbulence model, finite-rate/dissipation model and dynamic mesh update method are adopted to establish a secondary combustion model of initial cavity, in which the movement of rear cover is considered. Compared with experimental result of ejection launcher without annular cavity, the variation in fluid structure, ejection interior ballistics and variation in load are studied for the initial cavity with/without annular cavity and the initial cavity with different opening directions. The mechanism of that annular cavity reduces the secondary combustion impact is analyzed. Results show that, from the point view of fluid structure, an annular cavity can is added to change the direction of gas diffusion and decrease the area between gas and air. The backflow region with annular cavity can decrease the pressure peak caused by secondary combustion. From the point view of interior ballistics, the acceleration of missile in which the annular cavity opening is formed upwardly changes gently, the velocity out of tube is reduced by 5.9%, and the time out of tube is delayed by 4.5%.

A Novel Image Registration Based on Cultural Particle Swarm Optimization Algorithm

ZHU Xia, CHEN Ren-wen, XIA Hua-kang, ZHANG Piao-yan

2015, 36(6):  1033-1039.  doi:10.3969/j.issn.1000-1093.2015.06.010

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Some problems, such as registration inaccuracy and slow convergence, exist in image registration when the mutual information of images is used as similarity function. A measure function based on maximized mutual information is constructed according to the image gray and spatial structure information. The cultural particle swarm optimization, which is suitable for automatic image registration, is combined to present a novel image registration algorithm. Two kinds of search spaces, i.e., population space and belief space, are set in the algorithm. The population space is evolved with adaptive PSO strategy, and the belief space is evolved with update function. The particle swarms of population space not only track individual extremum and global extremum to update themselves, but also interact with best individuals in belief space to speed up the convergence speed, which overcomes the problems, such as the large amount of computation in image registration, slow search speed and so on. Experiments show that the proposed algorithm has stronger robustness and better registration accuracy compared with the existing PSO registration algorithm.

Study of Reconnaissance Reception Algorithm of Wide-band Channelization in the Fractional Fourier Domain

DENG Bing, LUAN Jun-bao

2015, 36(6):  1040-1045.  doi:10.3969/j.issn.1000-1093.2015.06.011

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Digital channelized receiver is currently the main stream of reconnaissance receivers. In order to reduce the equipment demand of band-folded channelized receiver, and remedy the shortages of output channel fuzzy, decrease in sensitivity, and reduction in interception probability, a receiving method of digital channelization is proposed based on fractional Fourier spectrum enfoldment, using the discrete fractional Fourier transform as the digital signal processing tool. The basic principle about the proposed method and the setting condition of some parameters are analyzed. The detail steps are provided. Finally, the simulation is made to prove the above-mentioned theories. The results show that the proposed method is used to eliminate the channel fuzzy if the recieved signal is divided into K simpling frequencies. The total power of output noise is only 1/K of tranditional band-folded channelized receiver.

Study of the Measuring Area in the Proving of Magnetic Field of Magnetic Decoy in Air

LIU Zhong-le, SHI Jian, WEN Wu-di

2015, 36(6):  1046-1051.  doi:10.3969/j.issn.1000-1093.2015.06.012

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In the proving of magnetic field of magnetic decoy discharged from a submarine in air, the magnetic field at low altitude is measured on account of the difficulty in proving the magnetic field at high altitude. However, the distribution characteristics of magnetic field of magnetic decoy are different in the different areas at the same altitude. In order to find the most suitable area to be measured, the distribution of magnetic field of magnetic decoy at a certain altitude is analyzed based on the change characteristic parameters in terrain feature statistics, such as standard deviation and roughness, and the terrain entropy in underwater terrain matching field, and a method of choosing the measuring area is studied. The choosing process of measuring area is simulated. And the sea trial is made to verify the proposed method. The results show that the relative measuring error of area chosen by this method is smaller than that of other area. 〓〓

Numerical Simulation and Analysis of Non-cavitation Noise Line-spectrum Frequency of Underwater Counter-rotation Propeller

ZENG Sai, DU Xuan-min，FAN Wei

2015, 36(6):  1052-1060.  doi:10.3969/j.issn.1000-1093.2015.06.013

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The generation mechanism of non-cavitation noise line-spectrum frequency of counter-rotation propeller is analyzed. The mechanism is the interference effects of front and rear propellers and the circumferential harmonic field effect. According to the generalized acoustic analogy equation, the lift and drag which are caused by the mechanism are the sources of noise. The far field sound pressure expression is presented. The line-spectrum frequency and the directionality of sound pressure are analyzed. The results show that the predicated line-spectrum frequency could be written as f=sAPF+pBPF₁+hBPF₂; sound pressure radiation is distributed as“8”-shape, and the peak condition of Bessel function is a necessary condition for line-spectrum generation. The non-cavitation of counter-rotation propeller is numerically simulated using RNG k-ε turbulence model, sliding mesh model and FW-H equation. The results shows that RNG k-ε turbulent model has the better accuracy than Realizable k-ε turbulent model. The non-cavitation line-spectrum frequency of counter-rotation propeller and the directionality of sound pressure are got by using the proposed method, which agree well with the theoretical results.

Application of Pareto Optimality in Protective Structure Design of Vehicle Underbody

WEI Ran, WANG Xian-hui, ZHOU Yun-bo, WANG Liang-mo, ZHENG Ya-li

2015, 36(6):  1061-1066.  doi:10.3969/j.issn.1000-1093.2015.06.014

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The multi-objective optimization of vehicle bottom structure under landmine explosion is a mass computation, strong-nonlinearity and high dimension multi-objective optimization problem. The protective vehicle structure response is simulated based on combination of LAE and FSI methods. The thickness and geometry parameters of vehicle bottom structure are screened with sensitivity analysis. A response surface is built by employing the experimental design and regression analysis. Eventually, the Pareto optimality, normal boundary intersection and multi-objective optimization genetic algorithms are applied to get the Pareto optimal front and an ideal solution which could give a comprehensive consideration of the contradiction between lightweight and protection capability.

A Simulation Investigation on Grinding Forces in Ultrasonic Assisted Grinding of Ceramics with Single Abrasive Grain byUsing SPH Method

MI Zhao-yang， LIANG Zhi-qiang， WANG Xi-bin， ZHOU Tian-feng， ZHAO Wen-xiang， TIAN Meng

2015, 36(6):  1067-1073.  doi:10.3969/j.issn.1000-1093.2015.06.015

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In order to investigate the influence of axial ultrasonic vibration on the grinding force during ultrasonic assisted grinding (UAG) of SiC and Al₂O₃ ceramics, the grinding forces of UAG SiC and Al₂O₃ ceramics with single diamond abrasive grain are simulated by using smoothed particle hydrodynamic (SPH) method. In the simulation，the average undeformed chip thickness is set as the depth of cut. It is found that the average undeformed chip thickness decreases with the increase in ultrasonic amplitude and the decrease in abrasive velocity. The simulation results of grinding forces show that the assistance of axial ultrasonic vibration can effectively reduce the grinding forces，and the higher ultrasonic amplitude has a positive effect on the decrease in grinding forces compared with that during conventional grinding. Under the same grinding parameters，the grinding forces in the grinding of SiC ceramics are larger than those in the grinding of Al₂O₃ ceramics.

Research on Control Strategy and Fault Diagnosis Method of Multi-system for Electrochemical Machining

WANG Fu-yuan, ZHAO Jian-she, TANG Lin

2015, 36(6):  1074-1081.  doi:10.3969/j.issn.1000-1093.2015.06.016

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In order to improve the electrochemical machining precision, reliability and efficiency of the work pieces such as aero-engine blisk, automobile engine nozzle, etc, a new control system for electrochemical machining(ECM), which integrates machine motion, electrolyte conveying, temperature control, power supply and electrode vibration into one, is set up. A new multi-system control strategy and a fault diagnosis method are proposed. The integrated control system is composed of a main controller and several sub-controllers. The distributed architecture and modularized design are adopted in hardware structure. The collaborative control method based on multi-system is used in control strategy. The subsystems are controlled by the respective controller, and the sub-controllers are managed by the main controller; therefore, the whole system can be effectively controlled. In the failure diagnosis, a prefect machining information acquisition system is created, and the status of electrochemical machining is diagnosed by the procedures of feature extraction, processing and pattern recognition. The experiments prove that the control system has the high integration, fast response, convenient operation and high work efficiency. The multi-system can be used to avoid successfully the damage to work-piece and machining system caused by failures and improve the processing reliability.

Study of Method of Sphericity Evaluation and Error On-line Compensation for Large Spherical Precision Grinding

HU De-jin

2015, 36(6):  1082-1088.  doi:10.3969/j.issn.1000-1093.2015.06.017

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A new method based on image recognition is presented for the sphericity evaluation and error on-line compensation for large spherical precision grinding, The main principle of the proposed method is to determine the spherical shape error according to the spherical grinding trace morphology，and discriminate the geometric position deviation of grinding spindle rotation center line and the ball rotation center line according to the spherical shape error. The geometrical errors of machine tool are analyzed and mathematically modeled. On this basis, an on-line compensation device is designed, and an automatic compensation method of sphericity error is proposed. Experiments show that the proposed method can effectively improve the shape precision of large spherical grinding.

Multi-objective Decision of Preventive Maintenance Intervals of Weapon Systems

DU Ye-hong, YU Hao, ZHAO Jing, ZHANG Yang, YANG Chun-lai

2015, 36(6):  1089-1095.  doi:10.3969/j.issn.1000-1093.2015.06.018

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To solve the problem of that the failure rate of the weapon system is difficult to be described with time as an independent variable, a model is established by using the amount of intervally fired projectiles as the independent variable to describe the failure rate of the weapon system. Since the failures of weapon systems are closely related to the the amount of intervally fired projectiles, the preventive maintenance opportunity determined by the amount of intervally fired projectiles is easy to operate in practice, and the statistical data of the amount of intervally fired projectiles are retained easily. Based on the failure data of a weapon system, Ao (Operational availability) and EMC (Expected maintenance cost), which are two important objectives, are analytically expressed by the proposed failure rate model. For these two objectives, the optimized decision is made with MOPSO, and the satisfactory solutions meeting the requirements are obtained.

Fault Diagnosis Method of Rotor System with Multi-crack Based on Nonlinear Output Frequency Response Function

LI Zhi-nong, DU Yi-guang, XIAO Yao-xian

2015, 36(6):  1096-1103.  doi:10.3969/j.issn.1000-1093.2015.06.019

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The fault diagnosis of rotor system with multi-crack is more complex and more difficult than the fault diagnosis of rotor system with single crack. The nonlinear output frequency response function (NOFRF) is introduced to fault diagnosis of rotor system with two cracks, and a fault diagnosis method of rotor system with two cracks based on the NOFRF is proposed. The NOFRF values of two cracks with different crack angles and crack depths are compared. The experimental results show that the NOFRF values are very sensitive to different crack angles and different crack depths, and the existence of rotor crack fault and the variation of crack angle and crack depth can be reflected by the NOFRF values. Therefore, the sensitivity of the NOFRF values to the crack fault can be effectively used for the detection of a rotor system with multi-cracks.

Reliability Assessment Based on Physical Parameters

GAI Jing-bo， KONG Yao

2015, 36(6):  1104-1109.  doi:10.3969/j.issn.1000-1093.2015.06.020

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A scientific evaluation method used to evaluate mission reliability is difficult to get enough failure data in limited testing time for the large mechanical equipment, or even get no failure data. Reliability assessment based on physical parameters has become an effective way. The reliability assessment process based on physical parameters is briefly described. The system nonlinear correlation analysis method based on the Kendall correlation coefficient and the relation between input and output variables based on kernel regression modeling method are discussed. The output parameters of the conditional probability distribution theory based on kernel regression and device reliability evaluation methods are given. A large complex mechanical hydraulic equipment is evaluated, which monitors the performance parameters in order to use the reliability calculation method to achieve the mission reliability assessment.

Application of Multi-scale Line Fitting Method in Change Point Detection in Time Series

HUANG Jing, LI Chang-chun, YAN Hao, ZHAO Xu-chang, YANG Xue-song

2015, 36(6):  1110-1116.  doi:10.3969/j.issn.1000-1093.2015.06.021

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In test and selection processes of electro-hydraulic servo valve, the change point of time series should be checked to measure the dead zone and the resolution ratio. The main detection methods are Mann-Kendall method, cumulative sum charts (CUSUM) method, least mean square error (MSE) method, and wavelet transform method. The methods all have some limitations. A multi-scale line fitting method is proposed, which can be used to detect the change point step-by-step by changing the scale of line fitting. The time series are divided into many segments according to the initial scale calculation method, and every single segment is replaced by a fitting line using least square method. Then the slopes of every neighbor segment are compared to find out the maximum change of the slope, and the change point should be included in these two segments. The scale is changed in the range of the two neighbor segments, and the change points are continously detected using the method until the length of segment is reduced to 1. The final point found out by the method is the change point of original time series.The proposed method is compared with other methods. The proposed method is used for the electro-hydraulic servo testing system and the fault signal detection to verify its accuracy and effectiveness.

Research Notes

Parameter Optimization of a Shell Elevating Device with Interval Uncertainties

JIANG Qing-shan, QIAN Lin-fang, XU Ya-dong, ZOU Quan

2015, 36(6):  1117-1122.  doi:10.3969/j.issn.1000-1093.2015.06.022

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An optimization method for shell elevating device with interval uncertainties is proposed to solve the problem of performance degradation during operating. A multidisciplinary model based on ADAMS is established. The parameters of hydraulic system and the friction coefficient are regarded as the interval uncertainties, and the minimal loading and fluctuation on the mechanism are set as the objectives by using the interval theory. Simulations are carried out on Latin hypercube sampling (LHS) points. An approximate model of shell elevating device is constructed based on radial basis function (RBF) neural networks to improve the efficiency. The nested optimization method based on multi-island GA and NLPQL is used to obtain the robust solutions. The simulation and experimental results demonstrate the efficiency and adaptability of the proposed method for solving the complex problems in automatic loading system.

Study of Novel Screw Extruded High Energy Composite Double-base Propellant

LIU Suo-en, CHEN Jin-fang, PAN Bao, ZHOU Wei-liang, ZHAO Mei-ling,

2015, 36(6):  1123-1127.  doi:10.3969/j.issn.1000-1093.2015.06.023

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A novel five unit (NC-NG-DNTF-HMX-Al) high energy composite propellant suitable for screw extrusion process is developed. The main properties and key technology of the propellant are discussed in detail. The results show that the energy property of the propellant is improved by using 3,4-dinitrofurzananofuroxan(DNTF), spherical Al powder and HMX. Chemical stability and output energy of the propellant are further enhanced by adding energetic stabilizer P-Nitro-N-Methylamine (PNMA). Application of an energetic catalyst which guarantees good burning rate contributes additional energy to the propellant. The new propellant formulation has excellent comprehensive property.

Study of Target Threat Assessment for Ground Surveillance Radar

SHI Xiao-bin, GU Hong, SU Wei-min, DONG Tian-qi, CHEN Xu-long

2015, 36(6):  1128-1135.  doi:10.3969/j.issn.1000-1093.2015.06.024

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The target threat assessment for ground surveillance radar based on the target state parameters and the identification results is an issue urgently to be solved. Based on the attribute set of targets, a dynamic Bayesian model of target threat assessment for ground surveillance radar is constructed by using membership function, expert knowledge and Bayesian network. Simulation results show that the variation characteristics of the target threat assessment data conform to the reasoning process of human. The dynamic Bayesian model of target threat assessment can be applied practically in the ground surveillance radars. Multifunction phased array radar can track the target in virtue of adaptive scheduling beam with target threat assessment.

Stabbing Effect Target and Its Assessment Model

GUO Shi-gui， ZHANG Zhong-ying， WANG De-wen， LIU Yun-jian， PENG Rui-yun

2015, 36(6):  1136-1139.  doi:10.3969/j.issn.1000-1093.2015.06.025

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The barbed nail characteristics, combat boot characteristics, biological contrastive test and hominine foot equivalent research are carried out for stabbing effect test and assessment. An equivalent hominine foot target is developed, of which soft tissues and bone structure are made of silicone rubber and epoxy. The target is made according to the "standard man"dimension and booted with a pair of special homebred combat boots. A stabbing effect evaluation model was established by using the stabbing position, depth, quantity and remaining things of the barbed nails stabbing into hominine foot as the input data based on the biological test, equivalent test and war injuries data. In the model, the degree of impact on operations is divided into levels 1-4 from low to high.The effect of the barbed nail on personnel mobility could be assessed by using the effect assessment model and the test data of the equivalent targets.

Analysis of Dynamic Stiffness Characteristics of Double-row Angular Contact Ball Bearings

DENG Si-er, DONG Xiao, CUI Yong-cun, HU Guang-cun

2015, 36(6):  1140-1146.  doi:10.3969/j.issn.1000-1093.2015.06.026

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A simulation and analysis model is established to describe the dynamic stiffness of double-row angular contact ball bearings based on the dynamics analysis. Fine integral method and predict-correct Adams-Bashforth-Moulton multi-step method are used to solve the dynamic stiffness model. The influences of bearing structural parameters and operating conditions on the dynamic stiffness are investigated. The research provides theoretical basis to analyze the dynamic stiffness and optimize the geometry parameters of double-row angular contact ball bearings. The results show that the groove radius of curvature has a small effect on the bearing dynamic stiffness. With the increase in inner and outer groove radii of curvature, the radial stiffness increases slightly, while the axial stiffness and angular stiffness decrease. The dynamic stiffness can be improved by increasing the number of balls. A big axial preload contributes to higher dynamic stiffness, while excess preload makes the bearing life decrease, so the axial preload should be selected properly. With the increase in rotating speed, the dynamic stiffness decreases first and then increases. The bearing dynamic stiffness can be replaced by the contact stiffness approximately when the bearing works at a low speed, while at a high speed, the bearing dynamic stiffness should be calculated by combining the contact stiffness with the film stiffness. External loads have an obvious effect on the dynamic stiffness, which gains greatly with the increase in radial and axial loads. The dynamic stiffness changes complexly with the increase in tilting moment, and decreases first and then increases trend on the whole.

Heat Transfer Characteristics of Micro-channel Condenser and Copper Pipe Condenser in Heat Pump Water Heater

WU Jiang-hong， LI Hui-xi， YOU Shao-fang

2015, 36(6):  1147-1152.  doi:10.3969/j.issn.1000-1093.2015.06.027

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For the small heat transfer contact area and low heat transfer efficiency between traditional outer-coil condenser and water tank, a micro-channel heat transfer technology is considered a prospect alternative to outer-coil condenser. The heat transfer characteristics and performances of two heat exchangers are compared experimentally. The results show that, for same heat pump system (except condenser), the average pressure drop of micro-channel condenser is 87% lower than that of copper pipe condenser in normal condition. The heating capacity of outer-coil micro-channel is relatively larger than those of outer-coil copper pipes, which is up to 37.5% in summer condition, 8.7% in normal condition and 19.6% in minimum condition. Exergy analytical calculation results show that the micro-channel condenser has better exergy efficiency than the other one, which is up to 20%.