Table of Content

01 September 2012, Volume 33 Issue 9

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Paper

Molecular Dynamic Simulation of Cyclotetramethylene Tetranitramine/11-Diamino-2.2-DinitroethyleneCo-crystal Explosive

LIN He, ZHANG Lin, ZHU Shun-guan, LI Hong-zhen, PENG Xin-hua

2012, 33(9):  1025-1030.  doi:10.3969/j.issn.1000-1093.2012.09.001

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Six models of cyclotetramethylene tetranitramine (HMX)/1,1-diamino-2.2-dinitroethylene(FOX-7) co-crystal were constructed based on the main growth faces of HMX crystal and the hydrogen bond rules of co-crystal formation. The probability of HMX/FOX-7 co-crystal formation was investigated using the molecular dynamics (MD) method. The distributions of bond length, angle, and dihedral angle were calculated during MD. As a result, a serious distortion was observed. The radical distribution function (RDF) was used to study the acting force between oxygen atoms in HMX and hydrogen atoms in FOX-7 or hydrogen atoms in HMX and oxygen atoms in FOX-7, which indicates that there are strong hydrogen bonds and Van Der Waals forces between HMX and FOX-7. Binding energies and X-ray powder diffraction (XRD) were calculated on the basis of the final HMX/FOX-7 co-crystal structure. The results show that the orders of binding energies of the six co-crystal models are E_b(020)>E_b(100)>E_b(randomness)>E_b(111 )>E_b (102 )>E_b(011), and the XRD peaks of six co-crystal models are quite different from pure HMX or FOX-7. In view of the research on crystal growth morphology, binding energy and RDF, the model of HMX molecular substituted by FOX-7 on the surface (111 ) of HMX is more liable to form.

Study on Time-delay Inter-pulse Jitter Repeater Jamming Style to Interfere Synthetic Aperture Radar

HUANG Hong-xu, ZHOU Yi-yu

2012, 33(9):  1031-1035.  doi:10.3969/j.issn.1000-1093.2012.09.002

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Aimed at the contradiction between interference regional coverage and interference power loss in partly coherent jamming styles, a new partly coherent jamming style against synthetic aperture radar (SAR), time-delay inter-pulse jitter repeater jamming is proposed. In the synthetic aperture time, the inter-pulse time delay of this repeater jamming varies randomly in a small time range. The research shows that this repeater jamming can obtain the whole matched processing gains in range dimension and its SAR imaging output is a similar noise swath, covering a part of fast time domain as well as the whole slow time domain. Thus, it is superior to both noise jamming and other interferences which have dismatched jamming parameters. And it can be implemented easily. The theoretic analysis is given and its performance is verified by simulation.

Background Suppression for Dim and Small Target Based on Pyramidal Dual-tree Directional Filter Bank

QIN Han-lin, YAO Ke-ke, ZHOU Hui-xin, LIU Shang-qian, LAI Rui

2012, 33(9):  1036-1040.  doi:10.3969/j.issn.1000-1093.2012.09.003

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The complex background suppression is difficult for infrared warning system detecting long- distance target. A background suppression method based on pyramidal dual-tree directional filter bank was proposed for some dim and small targets and retina theory was introduced to improve its ability. Firstly, the filter bank was adopted to decompose the input infrared image into multiple scales and directions and extract the image's features. Then, according to the difference between target and background clutter signal, the decomposed sub-band's coefficients were adjusted by using improved retina theory equations to suppress the background details and enhance target information. Several groups of experiment results demonstrate that the proposed method can detect the target with SCR>1.6 effectively, compared with several classical background suppression method, such as two-dimensional least means square (TDLMS) and max median (MMed) filters.

Research on Electronic Image Stabilization Technique for Vehicle-borne Low-light-level Telescope

ZONG Yan-tao₁, JIANG Xiao-yu₁, WANG Xi₁, JI Hong-xia₂, ZHAO Kai₁

2012, 33(9):  1041-1047.  doi:10.3969/j.issn.1000-1093.2012.09.004

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Aimed at the stabilization problem of low-light-level image in bottom-reflecting fire control system, a novel real-time high-precision electronic image stabilization system based on gyroscope and block matching algorithm was proposed. Its overall structure was designed; the transformation equations between the carrier movement and image movement were derived on the basis of perspective imaging model; the image motion model and the gyroscope signal calibration method were given also. Based on the initial estimation for the image motion vector and combined the block matching algorithm, the motion vector was estimated accurately. The traditional diamond search method was modified to avoid local minimum in high noise and low contrast and improve the accuracy of the algorithm.

Detection and Parameter Estimation of Polyphase Code Signals Based on Fractional Fourier Transform

XU Hui-fa, HU Xiao-feng, ZHANG Ming-zhi₁

2012, 33(9):  1048-1054.  doi:10.3969/j.issn.1000-1093.2012.09.005

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The polyphase code (Frank, P1, P2, P3 and P4 code) signals are a kind of typical low probability of intercept (LPI) radar signals. For the detection and parameter estimation of this kind of signals, the time-frequency distribution characteristics of the polyphase code signals were analyzed; the fractional spectrum characteristics of the polyphase code signals were also analyzed and the parameter estimation expressions of the polyphase code signals were deduced, taking Frank code signal for example. An algorithm for detection and parameters estimation of the polyphase code signals was proposed based on fractional Fourier transform (FRFT). And the algorithm first presents a method to estimate the carrier frequency of the polyphase code signals. Finally, simulations verifying the algorithm still has better signal detection and parameter estimation effect in low signal-to-noise ratios (SNR) condition.

Research on UWB Signal’s Path Loss Characteristic in Minefield

YANG Li， FANG Xiang， LIU Qiang, ZHANG Wei-ping

2012, 33(9):  1055-1061.  doi:10.3969/j.issn.1000-1093.2012.09.006

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The application of ultra wide band (UWB) technology in the minefield has good prospects and great significance. The existent path loss models of UWB can not satisfy the requirements in minefield environment. In order to make it practicable, a minefield model was established and the UWB signal's propagation features and laws were analyzed. Based on the theoretical analysis, a feasible UWB path loss model was put forward and the numerical simulations and experiments were also carried out. The results show that the new model can exactly reflect the UWB signal's propagation characteristic in the minefield and it is flexible and can be used in different conditions. The results can provide a basis for the application of the UWB technology in the mine weapons and equipment.

Design of Optimal Search Operation Parameters for Phased Array Radar

ZHANG Hua-rui, YANG Hong-wen, YU Wen-xian

2012, 33(9):  1062-1065.  doi:10.3969/j.issn.1000-1093.2012.09.007

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The existing methods for optimizing search performance of phased array radar are mainly referred to two parameters, the dwell time of a search beam and the scan time. But for alert-confirm operation mode, the expending time resulting in false alarm is also a factor which affects search performance. The influence on search performance caused by the dwell time of a search beam, scan time and false alarm probability was analyzed, then the optimal operation parameters for search performance was designed. Compared with other methods, the simulation results show the validity of this method.

Study on Influence of Micro-vibration During the Optical Aspheric Surface Ultra-precision Grinding on Forming Accuracy

ZHANG Xue-chen， CAO Guo-hua， NIE Feng-ming， WU Qing-tang

2012, 33(9):  1066-1069.  doi:10.3969/j.issn.1000-1093.2012.09.008

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In ultra-precision grinding process of the axial symmetric aspheric optical element, both imbalance of grinding wheel and micro-vibration of spindle would directly affect the forming accuracy and roughness. Analyzed the phenomenon of micro-vibration in grinding, a mathematical model of the aspheric surface's spherical radius deviation caused by the micro-vibration was established, and a dynamic high-precision micro-vibration measurement device with accuracy of 0.02 μm was developed. For the developed large-diameter ultra-precision aspheric grinding machine, the influence of the rotation speed of grinding wheel and spindle and the oil pressure of hydrostatic bearing on the radial and axial micro-vibration of grinding wheel and spindle was measured and analyzed. The parameters of the rotation speed of grinding wheel and the oil pressure of hydrostatic bearing and the rotation speed of spindle were determined to make the micro-vibrations of grinding wheel and spindle minimum. The machining results show that the error of aspheric surface of 500 mm in diameter can be less than 4 μm.

Study on Aerial Vehicle Attitude Estimation Based on Quaternion Particle Filter Algorithm

QIAO Xiang-wei， ZHOU Wei-dong， JI Yu-ren

2012, 33(9):  1070-1075.  doi:10.3969/j.issn.1000-1093.2012.09.009

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A quaternion particle filter algorithm was proposed to solve the aerial vehicle nonlinear attitude determination problem. To reduce computational burden, the state vector was divided into linear part and nonlinear part. Aiming at quaternion weighting sum normalization problem, a Lagrange cost function was derived to compute the predicted quaternion by minimizing the cost function, and the normalization of disturbed quaternion was ensured by calculating the square root of diagonal elements of the quaternion error covariance matrix, the multiplicative quaternion error was used for predicted covariance computation of the quaternion, since it represented the distance between quaternion points and the predicted mean quaternion. The simulation results show that, compared to traditional extended Kalman filter（EKF） and unscented Kalman filter（UKF）algorithms, the proposed algorithm has higher estimation precision and better stability.

Study on the Calculation Method of Penetration Process of Projectile with Booster into Concrete Targets

GUO Jin-yan, RUAN Wen-jun, WANG Hao, ZHANG Ding-shan

2012, 33(9):  1076-1080.  doi:10.3969/j.issn.1000-1093.2012.09.010

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The penetration process of the earth penetration weapon (EPW) with booster into concrete targets was studied to have a deeper cognition for it, and an appropriate boosting scheme was chosen in the design of EPW. Referred to the modified Forrestal resistance model given by Ref.［7］, based on the cavity-expansion theory and considered the influences of projectile acceleration on the penetration resistance, an semi-empirical calculation formula of penetration resistance which could be used for EPW with booster was proposed. Then, in the study on EPW with booster, the penetration process into concrete targets was calculated. Compared with the experiment results, the calculation results show that the new semi-empirical formula can reflect the penetration resistance better. The research in this paper has some practicability; moreover, it can be used to guide the study of the EPW with booster.

Research on Anti-explosion Capability of Nonmetallic Composite Material

MA Hai-yang， LONG Yuan₁, LIU Hao-quan₁， ZHOU Xiang₁, YANG Li₁，

2012, 33(9):  1081-1087.  doi:10.3969/j.issn.1000-1093.2012.09.011

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In order to study the anti-explosion capacity of nonmetallic material, explosion of shelled explosive was analyzed theoretically, and a method to determine the protective radius was proposed. The protective radius of damage and protective radius of expansion were both considered. The explosion experiments were carried out to validate the anti-explosion capability of new type safety equipment. Both overpressure of the explosion shock and noise were measured. The experiment results demonstrate that the new type safety equipment has better performances in attenuating shock and noise.

A New Estimation Method for Critical Gap Thickness

WANG Dian-peng, TIAN Yu-bin, LIU Liu

2012, 33(9):  1088-1094.  doi:10.3969/j.issn.1000-1093.2012.09.012

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The critical gap thickness is an important parameter to characterize the shock wave sensitivity of energetic materials. Now, the up-and-down and Neyer methods are most popular. However, they need larger amount of samples and many invalid tests may exist when the step length becomes larger. In this paper, a new optimization method to estimate the critical thickness was proposed. Based on the idea of optimal stochastic approximation, it needs not to estimate the parameters by using maximum likelihood, improves the limitation for overlap intervals and avoids the invalid tests effectively. Its performance was compared with those of up-and-down and Neyer methods. The results show that the new method needs only small amount of samples and can estimate the critical gap thickness accurately and reliably.

Simulation of Viod Coalescence in Ductile Metals Under High Strain Rate

WANG Yong-gang， XU Dong-ming

2012, 33(9):  1095-1100.  doi:10.3969/j.issn.1000-1093.2012.09.013

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The void coalescence and interaction in dynamic tensile fracture of ductile metals were investigated by using axial symmetric finite element analysis. The influences of initial ligament distance between voids and loading strain rate on the void coalescence process were discussed. The start time of void coalescence was estimated quantitatively through correlated shape evolution of the voids. The measurement results show that the critical ligament distance at the start time of coalescence is approximately a half of void diameter, which is independent of initial separation distance between voids and strain rate. In reality, the voids may interact through their plastic fields. However, a critical plastic strain threshold in the ligament zones is needed to drive the void coalescence. Assuming that the voids are uniformly distributed within the damaged material, the critical ligament distance are consistent to the critical porosity in physical essence, and can be transformed each other.

Numerical Simulation of Ignition of Explosives in Spigot Test

ZHANG Han-yu, DUAN Zhuo-ping, SUN Wen-sui, HUANG Feng-lei

2012, 33(9):  1101-1106.  doi:10.3969/j.issn.1000-1093.2012.09.014

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To investigate the ignition mechanism of explosives under impact, the node tie-breaking method combined with the thermo-elastic-plastic material constitution and chemical kinetics equations was used to simulate ignition for explosives of PBX-2. The influence of mesh size on the explosive's temperature rising was discussed. The explosive's mechanical damage image in the spigot test and local temperature rising curve were obtained. The critical drop velocity of ignition was calculated. The results are consistent with the experiment data better. It indicates that the approach can effectively describe the explosive's damage and ignition reaction under thermal-mechanical-chemical coupled effect.

A Passive Locating Method for Underwater Target Based on Three-element-array

JIANG Ke-yu， YAO Zhi-xiang， YIN Jing-xiang

2012, 33(9):  1107-1111.  doi:10.3969/j.issn.1000-1093.2012.09.015

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A new passive detection and location method for underwater targets based on the correlation metric of three signals received by three elements was proposed, and its advantages compared with two-element- correlation in detection performances were analyzed. The simulation was performed to verify the detection performances and time delay estimation accuracy. The simulation results show that, compared with two-element-correlation method, the modified method can improve the detection performance by 2 dB and the time delay estimation accuracy in a certain extent.

Correction Algorithm of Acoustic Vector Sensor Array and DOA Estimation Based on Subspace Fitting

LIANG Guo-long， ZHANG Kai， WU Wen-feng

2012, 33(9):  1112-1117.  doi:10.3969/j.issn.1000-1093.2012.09.016

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Considered the advantage of combined processing by using pressure and particle velocity, a method for high resolution DOA estimation based on subspace fitting (vector sensor array subspace fitting, VSF) was proposed. The proposed method offered not only a lower complexity of calculation, but also an acceptable estimation and resolution performance. Aimed at the performance depravation of the method when the array element location error exists, an array correction method based on iterative optimization was proposed. The simulation results demonstrate that the correction method combining DOA estimation technology can effectively estimate the elements' location error by using single vector hydrophone and two disjoint sources, and the performance of the proposed correction method can be improved with the increase of signal-noise ratio of disjoint sources.

Trust Region Optimization Method for Single Hydrophone Passive Ranging

LIU Jun-xing， ZHANG Xin-hua， QI Dun-hao， ZHANG Ben-hui

2012, 33(9):  1118-1123.  doi:10.3969/j.issn.1000-1093.2012.09.017

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In order to solve the problem of single hydrophone passive ranging, a method of Doppler passive ranging based on trust region optimization method was proposed. Compared with the existing method that has to detect the time and frequency when the target arrives to the course shortcut, the new method can detect the target in real-time detecting before it arrives to the course shortcut. This approach can obtain not only the kinetic parameters but also the current and predicted distances of the target. It makes full use of the target's Doppler information, and realizes real-time ranging for moving target by single hydrophone. It can also be suitable for the uniformly accelerated target model and has better practice value. Simulation results show its correctness.

Numerical Study on Unsteady Characteristics of Cavitation Flow Generated from Hemispherical Model

WANG Bai-qiu, WANG Cong, HUANG Hai-long, DONG Lei, ZHANG Jia-zhong

2012, 33(9):  1124-1130.  doi:10.3969/j.issn.1000-1093.2012.09.018

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To further study the unsteady characteristics of cavitation flow, a new mathematical cavitation model based on Rayleigh-Plesset equation was given out. Both steady and unsteady cavitation flow generated from hemispherical cylinder were simulated numerically by using the new model in 2D axial symmetrical coordinates. The successful application and validation of the new model show that the condensation occurs when the bubble expands and evaporation happens when the bubble collapses. It can be seen from the analysis of the experiments and the numerical simulations that, according to the cavitation number, the cavitation flow is divided into three types, i.e. supercavitation flow, secondary cavitation flow and weak cavitation flow. Due to the unsteadiness, each type of cavitation flow corresponds to different model coefficients. The new cavitation model can successfully capture the unsteady details of the cavitation flow, and it is helpful to further study the mechanism of cavitation.

Impulsive Source Localization in Shallow Water Using Single Hydrophone

WANG Jin-jin₁, WANG Da-cheng₁, FAN Jun₂, CAI Ping₁, HU Jun₃

2012, 33(9):  1131-1137.  doi:10.3969/j.issn.1000-1093.2012.09.019

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Aimed at coherent multipath structure of the underwater acoustic channel in shallow water, a method of impulsive source localization using a single hydrophone was proposed. The phase change properties of reflected wave at different acoustic interfaces were studied. The difference between surface reflection and bottom reflection was used to solve position ambiguity in the location equation. The estimated resolutions of amplitude attenuation and phase change of the underwater acoustic channel were improved by using projection onto convex sets, compared with match filter. The localization error using single hydrophone was estimated with the error propagation equation. The experiment results show that this method is feasible in shallow water environment, and has the advantages of simple structure and low cost.

Research on Two Array Processing Methods for Vector Sensor Array

YAO Zhi-xiang, HU Jin-hua, JIANG Ke-yu

2012, 33(9):  1138-1142.  doi:10.3969/j.issn.1000-1093.2012.09.020

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For signal processing of an acoustic vector sensor array (AVSA), the extended method which keeps the coherence of AVSA and acoustic pressure sensor array can not show the particle velocity information obviously. Aimed at this problem, the AVSA datum covariance matrix of extended method was analyzed. The Bartlett bearing spectrum was derived. By using block matrix, the AVSA extended method can be coherent with combined method. The numerical simulation and lake experiment verify the theoretical results.

Study on Efficiency and Mathematical Modal for Grinding Convex Curvilinear Revolving Workpiece Based onLinear Envelop Methode

LIN Bin， ZHU Yong-kui， DU Fan， YUAN Qi-hai

2012, 33(9):  1143-1147.  doi:10.3969/j.issn.1000-1093.2012.09.021

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The convex curvilinear revolving workpieces with higher accuracy and better surface quality are applied extensively in the area of aerospace as well as others. The traditional locus method for grinding can not meet the demands of highly efficient precision process due to low accuracy and efficiency. A new linear envelop method to process convex curvilinear revolving workpiece and its implementation were introduced. Based on the analysis on the forming mechanism, a computational model of cc points suitable for this forming method and keeping the same scallop height was proposed. Compared the efficiencies of linear envelop method and locus method under the same scallop height, it can be concluded that the processing efficiency of linear envelop method is about four times higher than that of locus method when the radius of curvature on contour lines outside the workpiece is comparatively large.

Research Notes

Experimental Research on Igniting the Aviation Kerosene by Reactive Fragment

WANG Hai-fu， ZHENG Yuan-feng，YU Qing-bo，LIU Zong-wei，YU Wei-min

2012, 33(9):  1148-1152.  doi:10.3969/j.issn.1000-1093.2012.09.022

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The damage effects of reactive fragment on full-filled fuel tank, including tank rupture and aviation kerosene ignition, was studied through ballistic experiment, and compared with the damage of the fuel tank subjected to a tungsten alloy fragment mass matched. The results show that the reactive fragment is able to perforate a 10 mm thick LY12 aluminium wall at 1 080 m/s and ignites the aviation kerosenes, but the tungsten alloy fragment penetrating into the tank at 1 643 m/s fails to ignite the fuel. The reactive fragment results in more damage on the fuel tank than the tungsten alloy fragment and improves the ignition ability to the aviation kerosene at normal temperature, mainly by its explosion effects and chemical energy release.