Table of Content

31 July 2020, Volume 41 Issue 7

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Contents

2020, 41(7):  0. 

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Paper

A Simulation Method for Inflatable Floating of Underwater Vehicle

ZHANG Xiaoguang， LI Bin， DANG Huixue， WEN Jinpeng， SUN Pan

2020, 41(7):  1249-1261.  doi:10.3969/j.issn.1000-1093.2020.07.001

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A multidisciplinary co-simulation method is proposed to study the influence of airbag deployment on the attitude and trajectory of underwater vehicle during the inflatable floating. A dynamic model of underwater airbag deployment is established, and the volume expansion curve is obtained based on the control volume algorithm. A hydrodynamic model that can simultaneously couple the six-degrees-of-freedom rigid body motion of vehicle and the local deformation of airbag is established under the condition that the volume expansion rate of airbag is equivalent. The calculation is carried out based on the Navier-Stokes equation. Through the simulation calculation, the refinement process of underwater vehicle's floating is obtained, and the resultant force component-time history curves and the attitude data of underwater vehicle during floating are obtained. The results show that the buoyancy of airbag can effectively make the vehicle float; during floating, the vehicle is subjected to a certain lateral force because of the asymmetry of the vortex structure, and it is in a ‘spiral' upward process when it floats; and the vehicle is subjected to the vertical force provided by the current. In order to speed up, the angle of attack of vehicle should be adjusted to be positive before it goes up. Key

Low-cycle Fatigue Life Prediction and Validation of Main Shaft of Power-shift Steering Transmission Based on Dynamic Torque Measurement

WANG Cheng, MAO Feihong, HOU Wei, ZHANG Jinle, ZOU Tiangang

2020, 41(7):  1262-1269.  doi:10.3969/j.issn.1000-1093.2020.07.002

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In order to solve the low-cycle fatigue failure of main shaft of power-shift steering transmission, the dynamic torque of main shaft was measured during pavement testing, and the fatigue sample was analyzed. An elastoplastic finite element model of main shaft is established to predict the low-cycle fatigue life of main shaft. The low-cycle fatigue test of main shaft was made to verify the low-cycle fatigue life prediction method. The results show that the impulsive torque of tracked vehicle in starting stage is the main cause of low-cycle fatigue of main shaft. For the asymmetric structure, the impulsive torque on the right side of main shaft is about 1.54 times of that on the left side. The maximum stress of main shaft is 1 510 MPa, and the maximum strain is 0.008 692 3, both occur at the root of boundary between output spline and transition arc on the right side, which is consistent with the fatigue fracture location of fatigue sample. The number of main shaft withstanding the starting impact torque is 17 082, the number of main shafts withstanding the starting impact torque obtained by bench tests is 5 000, and the number of main shafts withstanding the starting impact torque obtained by low-cycle fatigue life prediction is 5 843. The simulated results are basically consistent with test results, which verifies the feasibility of the low-cycle fatigue life prediction method. Key

Rub-impact Characteristics and Drag Torque at High Circumferential Velocities in No-load Multi-plate Wet Clutch for Vehicles

ZHANG Lin, WEI Chao, HU Jibin, HU Qi

2020, 41(7):  1270-1279.  doi:10.3969/j.issn.1000-1093.2020.07.003

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It is found in experiments that the rub-impact between friction plate and steel plate is easy to appear in the high-speed no-load wet clutch, which results in the sharp increase in drag torque. The high-speed drag torque has significant negative influence on the efficiency and reliability of transmissions. So it is necessary to establish a reliable rub-impact model of friction pair to explore the change law of high-speed drag torque. The fluid stiffness and damping are derived to obtain the fluid forces by small perturbation method. The elastic deformations and energy loss in the process of rub-impact between friction plate and steel plate are analyzed to establish the rubbing function of friction pairs. On this basis, the fluid force, rub-impact force, friction, and coupling motion between the friction plate and steel plate in three degrees of freedom are taken into consideration to establish a fluid-solid coupling rub-impact dynamic model for multi-plate wet clutch, which is solved by fourth-order Runge-Kutta method. Then the bifurcation and chaos characteristics of non-linear motion of friction pairs are analyzed. The research results indicate that, when the friction pair does not contact, the friction/steel plates move stably and show periodic movement rule; when the friction pair impacts, the friction/steel plates lose stability and show chaotic motion under the action of axial rub-impact force; and with the increase in the flow rate of lubricating oil, the critical rub-impact speed of friction pair climbs, but the rub-impact frequency also grows, resulting in the increase in the drag torque. Key

Analysis of Sliding Electric Contact Characteristics of Series-augmented Railgun Based on Breech Voltage

ZHU Chunyan, WANG Jun, MA Fuqiang, NI Yanjie, TANG Bo, LI Baoming

2020, 41(7):  1280-1287.  doi:10.3969/j.issn.1000-1093.2020.07.004

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An analysis method based on the breech voltage is proposed to study the sliding contact resistance characteristics of the partially augmented electromagnetic railgun. A mathematical model of contact resistance, breech voltage, breech inducted voltage and rail current is constructed. The proposed model is used to quantitatively characterize the sliding contact resistance. Through the analysis of the characteristics of the contact resistance waveform, the state of contact between armature and rail is divided into four stages: start-up stage, resistance steady decline stage, resistance growth stage, and single rail stage. The launch efficiency of launching system and the energy consumption rate of contact resistance Joule heat are calculated. The results show that the contact resistance is high as the interface between the armature and rails is in a solid-solid contact state at the initial startup stage; the gradually formed aluminum melt film increases the actual contact area and improves the contact state; the contact pressure is negatively correlated with contact resistance; the contact resistance is an important factor affecting launching efficiency. Therefore, the analysis of the sliding electric contact characteristics of the partially angmented railgun plays a positive role in the mechanism research and design of the railgun. Key

Identification of Thread Connection Parameters of Projectile-fuze System Based on Thin-layer Element Method

YAN A'min， WANG Xiaofeng， WANG Jian, PI Aiguo， HUANG Fenglei

2020, 41(7):  1288-1298.  doi:10.3969/j.issn.1000-1093.2020.07.005

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Thread connection is one of the main forms of connection between penetrating projectile and fuze body. To address the problem that thread connection can not be represented accurately by way of the existing dynamic numerical analysis, a method of simulating the thread connection using thin-layer elements is proposed, and a method for identifying the material parameters of thin-layer element based on test results is established. Modal test of pipe threads was carried out. The influences of the amplitude of excitation force and the loose and tight connection of threads on the modal frequency and frequency response curve are discussed, and the thin-layer element method is used for the simulation calculation of pipe threads. Results show that the state of loose thread connection is much more affected by non-linear factors compeared with tight connection; the magnitude of excitation force exerts greater influence on the measured result of loosely connected threads; the maximum error of modal frequency is reduced from 26.66% to 1.35% by comparing the simulated results of thin-layer element with the fixed nodes. Key

Simulation Study of Screening Efficiency of Explosive Smoke Bomb

XU Lucheng， HAO Xueying， XIAO Kaitao， SONG Weiwei， CHEN Chunsheng

2020, 41(7):  1299-1306.  doi:10.3969/j.issn.1000-1093.2020.07.006

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Gauss model or Rachtman diffusion theory that assumes uniform and stable wind field is usually involved in traditional methods of smoke simulation. However, these methods neglect the complex characteristics of the actual atmosphere. To solve this problem, a screening efficiency simulation model for smoke bomb is established based on computational fluid dynamics (CFD) in this paper. The model uses Lagrange method to construct the initial smoke cloud by randomly generating particles. The thermal effect of combustion heat release is analyzed, and the dispersion of smoke is simulated to obtain the temporal and spatial distribution of smoke mass concentration based on CFD method and discrete phase model. Furthermore, the effective shading region of smoke to visible light is obtained by means of calculation of smoke surface density. Lastly, compared with the experimental and Rachtman model results, the validity of the model is confirmed. It is shown that the proposed model well reflects the variation of smoke shape, length and height in the early diffusion stage of explosive smoke bomb. Key

Research on Reentry Trajectory of Powered Hypersonic Vehicle with Discontinuous Ignition

LIN Jun, HE Yingzi, HUANG Panxing

2020, 41(7):  1307-1316.  doi:10.3969/j.issn.1000-1093.2020.07.007

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Discontinuous ignition boost for powered hypersonic vehicle could effectively improve the flexibility and maneuverability of reentry vehicle. To analyze the influences of ignition time and boost time on the reentry trajectory, the modified Gaussian pseudo-spectral method was used to optimize the reentry trajectory with different ignition time and boost duration. When the engine is off, the Gauss pseudospectral method is used to generate the optimal reentry trajectory that meets multi-constraints. After the engine is ignited, the reentry trajectory is calculated and generated by numerical integration according to the given control input. Additional constraint conditions are added to ensure the continuity of vehicle states between each pair of phases. Four typical moments (A, B, C, D) in the reentry process were selected to perform the first and second ignitions of the engine, and the simulations were designed with the target of maximum lateral range. The results show that the improved Gauss pseudospectral method could effectively solve the reentry trajectory optimization for powered hypersonic vehicle with discontinuous ignition. When the total impulse of the engine is given, the ignition timing has a significant effect on the reentry trajectory. Key

Preparation of Nano-SrCO₃/AP Composite Particles and Study of Their Impact Sensitivities and Thermal DecompositionPerformances

LI Kuankuan, GUO Xiaode, LIANG Li, ZHANG Zhengjin, XIA Liang, CHANG Zhipeng

2020, 41(7):  1317-1322.  doi:10.3969/j.issn.1000-1093.2020.07.008

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Nano-SrCO₃ was prepared by ultrasonic-assisted co-precipitation, and nano-SrCO₃/AP composite particles were prepared by solvent-nonsolvent method. The morphology, particle size, crystal type and composite effect of nano-SrCO₃/AP composite particles were characterized by transmissive electron microscope (TEM), scanning electron microscope (SEM) and X-ray powder diffractometer (XRD). The impact sensitivities of SrCO₃/AP composites with pure AP and different contents were tested. Thermal decomposition properties of nano-SrCO₃/AP composite particles and a simple mixture of nano-SrCO₃ and AP were analyzed by using DSC. The nano-SrCO₃/AP composite particles were calcined in a muffle furnace at 350 ℃ and 500 ℃, respectively, for 1 h. The calcined products were characterized by XRD, and the action mechanism of nano-SrCO₃ was studied. The results show that nano-SrCO₃ prepared by ultrasonic-assisted co-precipitation is spherical with a particle size of about 60 nm, and its crystalline form is orthorhombic. In the nano-SrCO₃/AP composite particles prepared by solvent-nonsolvent method, nano-SrCO₃ is uniformly distributed on the surface of AP. The impact sensitivity of AP increases with the addition of nano-SrCO₃. Nano-SrCO₃ added in two different ways can increase the decomposition peak temperature of AP at high temperature, but has no effect on the decomposition of AP at low temperature. Compared with the simple mixture of nano-SrCO₃ and AP, the peak decomposition temperature of AP in nano-SrCO₃/AP composite particles is increased by 6.02 ℃. It is proved that the negative catalytic effect of nano-SrCO₃ on AP decomposition at high temperature can be improved by compounding nano-SrCO₃ with AP. Key

Synthesis of Nitrified Graphene Oxide and Its Catalytic Activity for Ammonium Perchlorate Decomposition

GUAN Fayang, YU Lan, REN Hui, JIAO Qingjie, LIU Jie

2020, 41(7):  1323-1329.  doi:10.3969/j.issn.1000-1093.2020.07.009

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In order to improve the energy release and catalytic effects of graphene in energetic materials, a nitrified graphene oxide (NGO) was obtained by nitrifying a graphite oxide prepared by Hummers method. The prepared samples were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy, organic element analyzer, Fourier transform infrared spectroscopy and TG-DSC synchronous thermal analysis for strctural and performance analysis. Constant volume combustion test was used to probe the burning behavior of NGO in energetic system. The experimental results show that the prepared NGO is lamellar with wrinkles as a novel energetic catalyst. The nitrate group and the nitro group are suspended at the oxygen-containing functional group sites of graphene oxide, and the mass ratio of nitrate element is 8%. Exothermic enthalpy of NGO is around 659 J/g, and the thermal total weight loss is 47%. When 5% NGO is added into ammonium perchlorate (AP), the peak temperature in each decomposition step is lower, and the activation energy of AP in the first decomposition step decreases from 123.7 kJ/mol to 99.4 kJ/mol. Meanwhile the critical thermal explosion temperature decreases from 431 ℃ to 366 ℃. NGO is added to increase the reaction heat of AP-coated Al system and the peak pressure by 13% and 56%, respectively. Key

Two-stage Real-time Track Correlation Algorithm Based on Gray Correlation

JIN Bingyang, LIU Zheng, QIN Jikai

2020, 41(7):  1330-1338.  doi:10.3969/j.issn.1000-1093.2020.07.010

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For the multi-mode composite seeker, the track correlation mistakes tend to happen using the traditional track correlation algorithms when the tracks of multiple targets cross. A novel two-stage real-time track correlation algorithm is proposed based on the gray correlation degree. A gray correlation coefficient matrix is formed by the gray correlation degree between tracks, and the calculation of gray correclation is modified according to the characteristic of track correlation. The gray correlation coefficient matrix is modified by a two-stage track correlation discrimination using the similarity of the overall motions of target tracks and the local property during the latest period of current time. Finally, the maximum criterion of gray correlation degree is exploited to obtain the track correlation pair. The simulated results show that the proposed algorithm can be used to correctly correlate the tracks when the sensors obtain wrong track data due to track crossing or target jamming. Key

Experimental Research on Initiation and Propagation Characteristics of Kerosene Fuel Rotating Detonation Wave

LI Baoxing, WANG Zhong, XU Guiyang, WENG Chunsheng, ZHAO Fengqi

2020, 41(7):  1339-1346.  doi:10.3969/j.issn.1000-1093.2020.07.011

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A rotating detonation engine（RDE） was test to study the initiation and propagation characteristics of kerosene fuel rotating detonation wave. The inner diameter, outer diameter and length of RDE annular combustor are 120 mm, 153 mm and 240 mm, respectively. It is ignited by a hydrogen/oxygen micro-pulse detonation engine with kerosene and oxygen-rich air used as fuel and oxidant, respectively. The initiation process and propagation of gas-liquid two-phase rotating detonation wave, and the operation characteristics of engine are analyzed from high-frequency pressure signals in combustor. The test results indicate that the reactivity of mixtures plays an important role on the initiation of detonation wave. When the content of oxygen in the oxidant is low, the reactivity of the mixture is low, and the rotating detonation wave fails to be initiated. It is until the oxygen content increases to 39.2% that the rotating detonation wave can be formed. The rotating detonation wave always propagates in two-wave collision mode with the wave velocity range of 815-920 m/s after successful initiation. The velocity of detonation wave tends to rise with the increase in equivalence ratio under lean fuel condition. The engine mainly works in a deflagration mode when the mass flow rate of air is more than 822 g/s. Key

A SAR Image Building Detection Algorithm Based on Improved YOLOv3

LI Xiang， SU Juan， YANG Long

2020, 41(7):  1347-1359.  doi:10.3969/j.issn.1000-1093.2020.07.012

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Since the traditional synthetic aperture radar （SAR）image building detection algorithm is mainly to detect the specific buildings by manually extracting the features in specific scenarios, it always has low average detection accuracy and low detection efficiency. A SAR image building detection algorithm based on improved YOLOv3 is proposed to realize the automatic detection of buildings through deep learning. The SAR image building dataset is produced, and the sizes of priori anchors are re-set by the improved K-means clustering algorithm according to the size characteristics of the buildings. Then the structure of the aggregated residual transformations for deep neural networks is used to construct the feature layer of YOLOv3 skeleton network. The single-channel convolution residual module is improved into a multi-channel convolution residual module to increase the channel information utilization and reduce the computation load. And a shallow feature fusion module is added to increase the contour shape characteristics of buildings in the feature map. The feature layer is upsampled to add detail features before the feature fusion layer through the transposed convolution. The improved YOLOv3 algorithm is used to train the building detection model which is tested on the test dataset. Experimental results show that the improved YOLOv3 algorithm improves the average detection accuracy on SAR image building dataset by 9.2% and the recall rate by 6.3% compared with the original YOLOv3 algorithm, while maintaining a fast detection speed. Key

A Communication Method Based on Time Division Modulation Weighted Fractional Fourier Transform

ZHANG Xiaoyu， FENG Yongxin

2020, 41(7):  1360-1367.  doi:10.3969/j.issn.1000-1093.2020.07.013

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The weighted fractional Fourier transform (4-WFRFT) is a new physical layer secret communication method, which can greatly improve the anti-modulation identification of the communication system. For the deficiencies of single-parameter weighted fractional Fourier transform, a time division modulation weighted fractional Fourier transform (TM-WFRFT) communication method is proposed. The proposed method adopts the strategy of different parity modulation and makes full use of the rotation factor to encrypt dynamically, so the security of the 4-WFRFT signal can be improved by time-division data weighted fractional Fourier modulation. The simulated results show that TM-WFRFT can significantly improve the 4-WFRFT reliability and significantly reduce the ability of the eavesdropper to decipher, thus improving the effectiveness of signal transmission and further enhancing the confidentiality of information transmission. Key

Performance Analysis of DCO-OFDM in Modulated Retro-reflector Optical Communication over Weak Turbulence

TANG Fang, XU Zhiyong, WANG Jingyuan, ZHAO Jiyong, LI Jianhua

2020, 41(7):  1368-1374.  doi:10.3969/j.issn.1000-1093.2020.07.014

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The retro-reflect modulator of micro-electro-mechanical system has low modulation rate and limited linear region. To improve the transmission rate effectively, a symmetry clipped DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) is proposed in the light of DCO-OFDM characteristic. The nonlinear distortion caused by double clipping is modeled as clipping noise, and the effective signal-to-noise ratio function is derived. the theoretical average bit error rate of the double clipping DCO-OFDM of modulated retro-reflector optical communication system in weak turbulence under special communication conditions like ground-ground and air-air is studied and simulated using Monte Carlo method, and the effect of direct current (DC) bias on the performance of symmetric clipping is analyzed. The simulated results show that the effective signal-to-noise ratio increases first and then decreases as the DC bias increases at better optical power. Small DC bias will cause severe clipping noise, thus limiting the change of effective signal-to-noise ratio with optical power. Key

Experimental Reaserch on Cavitation and Motion Characteristics of Low-speed Water Entry of Rotary Bodies in Tandem

YU Delei, CAO Wei, WEI Yingjie

2020, 41(7):  1375-1383.  doi:10.3969/j.issn.1000-1093.2020.07.015

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In order to study the evolutions and motion characteristics of cavitations in the process of water entry in tandem, the high-speed camera and time release system are used in testing the low-speed tandem water entry of rotary bodies at different initial spacing. The motion characteristics of rotary bodies are identified and extracted using image processing technology, and the influence of the initial spacing of water entry on cavitation evolution, longitudinal displacement and deflection angle of rotary body was obtained through test. The test results show that the cavitation structures and sizes of two rotary bodies are affected during the water entry in tandem at the small initial spacing. With the increase in the initial spacing of water entry, four motion modes, including colliding disturbance, closed cavity disturbance, transition disturbance and weak disturbance, arise in the process of tandem water entry of rotary bodies. In different motion modes, the vacuolizations and motion characteristics of two rotary bodies are quite different. The colliding disturbance mode has the greatest influence on the motion characteristics of rotary body. Key

A Multi-beam Sonar-based Graph SLAM Method

DAI Tian， MIAO Lingjuan， SHAO Haijun

2020, 41(7):  1384-1392.  doi:10.3969/j.issn.1000-1093.2020.07.016

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Database-referenced navigation systems(DBRNSs) are commonly used in autonomous underwater vehicles as underwater auxiliary navigation systems to correct the cumulative errors of inertial navigation systems. However, the DBRNS cannot run if a high resolution database cannot be obtained. A multi-beam sonar-based graph simultaneous localization and mapping (SLAM) method is proposed. A mismatch detection module is added to the front end to reduce the negative impact caused by the false closed-loop detection results. In the proposed method, the local gray value coding algorithm is used for the closed-loop detection module in order to improve the detection accuracy. Simulations based on the actual seabed terrain base map show that, compared with the general graph SLAM method, the proposed method can achieve higher positioning accuracy. Key

Robust Adaptive Position Tracking Control of Underactuated Unmanned Surface Vehicle

ZHANG Chengju， WANG Cong, WANG Jinqiang, LI Conghui

2020, 41(7):  1393-1400.  doi:10.3969/j.issn.1000-1093.2020.07.017

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An neural network adaptive position tracking control strategy for underactuated unmanned surface vehicle (USV) is proposed to solve the problem of horizontal position tracking of underactuated USV with unknown uncertainties. A nonlinear controller is designed by using the backstepping method. The dynamic surface method is used to obtain the derivative of dummy variable, which reduces the complexity of direct derivation of dummy variables. The uncertain function of USV system is approximated by employing the neural network adaptive method, which overcomes parameter uncertainty problem. An exponentially convergent current observer is designed to effectively estimate the constant current velocity. The stability of the closed-loop control system is proved by using Lyapunov stability theory. Finally, the effectiveness and robustness of control strategy are verified by simulation experiments. Key

Dynamic Observation of Fracture Microstructure of Ti6321 Titanium Alloy in TaylorBar Impact Test

XU Xuefeng， WANG Lin， CHENG Xingwang， LIU Anjin， TAYYEB Ali, ZHOU Zhe， NING Zixuan， ZHANG Binbin， ZHAO Denghui

2020, 41(7):  1401-1407.  doi:10.3969/j.issn.1000-1093.2020.07.018

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The duplex and lamellar structures were obtained by heat treatment of near α-Ti6321 alloy. The influences of different microstructures on the dynamic damage and fracture behavior of material are investigated under Taylor bar impact test. The Taylor bar is used to test the cylindrical samples under dynamic compression loading, with impact velocity ranging from 146 m/s to 228 m/s. The microstructure evolution is observed and analyzed by using optical microscope, scanning electronic microscopy and quantitative metallography. The experimental results show that Ti6321 alloy with duplex structure exhibits better impact resistance property. All samples deform significantly after dynamic compression loading. With increase in impact velocity, the primary α grain size of the duplex structure decreases from 25.3 μm to 16.7 μm, and the secondary α phase and β phase are deformed and crushed under dynamic loading. The secondary α phase of lamellar structure samples is significantly elongated along the direction of the loading. The smooth melting areas and dimple areas can be observed from the impact fracture morphologies, and the boundary between two areas is not obvious. The failure mode of titanium alloy with both the structures is adiabatic shear banding. Compared to lamellar structure samples, Ti6321 alloy with duplex structure exhibits a better capability to resist an adiabatic shear damage. Key

Multi-stage Manufacturing Quality Modeling Based on Process Factors Statistics and Quantization

LI Yi, ZHANG Faping, YAN Yan, ZHANG Tianhui, ZHOU Jianhua, GUO Feiyan

2020, 41(7):  1408-1416.  doi:10.3969/j.issn.1000-1093.2020.07.019

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For the incomplete description and inaccurate analysis results of existing multi-stage manufacturing system (MSMS) model for complex weapon equipment, a quality transfer comprehensive model (QTCM) is proposed based on the characteristics of MSMS, which gives a strict mathematical expression of multi-stage quality transfer process. In the framework of QTCM, the operator capability and the manufacturing equipment state are quantified for the influencing factors of product quality with the help of psychological and statistical knowledge, which were often ignored in the past. For the transfer process of the quality, the mapping relationship between influencing factors and quality output is constructed by using historical data of the manufacturing process. For the improvement of product quality, the main error sources affecting the quality are determined by analyzing the contribution of each factor, which guides the improvement of product manufacturing quality. The analysis of rotor system of a missile engine shows that the final quality distribution can be easily calculated according to the quality of raw materials or process quality, and the analyzed results are in agreement with the measured results. Key

Processing and Inspection Method for Parts with Small Angle

ZHAI Yan, JIANG Huilin, MEI Gui

2020, 41(7):  1417-1422.  doi:10.3969/j.issn.1000-1093.2020.07.020

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A set of processing and testing methods for optical elements with small angles are proposed for the assembly process of a large-scale infrared camera. 6 mirrors are added in processing and inspection, and the heights of the four feature points, the reverse sides and the initial angles of the machined element with 4 silicon carbide lenses are monitored. 6 mirrors are inspected using an interferometer. The angle between the processed surface and the initial surface of element and the height difference between the high point and the low point of element are calculated from the obtained interference fringes for guiding the amount of finish and machining angle of further processing. The value of the angle between the mirror surface of back surface and the back surface of element is calculated by the difference between their interference fringes. By processing, on the 80 mm-wide adjustable pad, an angle between the top and bottom surfaces finally is 0.21″, and the height difference between the upper edge and lower edge of adjustable pad is 0.100λ (λ=632.8 nm), that is, 63.28 nm, which is within the error range. The adjustable pad is mounted in an optical system, which meets the design requirements through mechanical and thermo-optical tests. The results show that it is feasible to use optical machining method to obtain the plane with the required small angle for small-sized mechanical parts. An interferometer is used to perform interference detection on the surface of auxiliary mirror, and the amount of finish on the surface of element is calculated. The surface height difference of the processed parts calculated from the interferogram of auxiliary mirror can meet the needs of the optical system installation and adjustment. Key

Reliability Model of Competing Failure System with Dependent Degradation

YANG Zhiyuan, ZHAO Jianmin, CHENG Zhonghua, LI Liying, CHI Kuo

2020, 41(7):  1423-1433.  doi:10.3969/j.issn.1000-1093.2020.07.021

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Failure of complex systems is often affected by multiple degradation processes and external shocks, and is a competing failure process. To analyze the reliability of such systems, the influence of shock process on the degradation process, the dependency of different degradation processes, and the dependency of the sudden increments of degradation caused by shock are considered simultaneously, and the system reliability model with competing failure is derived based on Gamma process and Copula function, and then an approximate reliability model is proposed to simplify the calculation. On this basis, the parameter estimation and Copula function selection methods are presented. The approximate model of system reliability is tested by taking micro-engine as an example, and the influence of dependency parameters on system reliability is analyzed. The result verifies the accuracy of the approximate reliability model, and illustrates that the dependent degradation has direct influence on the system reliability. Thus, for the system that degradation failure is the dominant failure mode, the dependent degradation should be considered seriously in reliability analysis. Key

Sampling Method of High Value Ammunition Based on Weibull Life Distribution

NIU Yueting ， ZHAO Hui， LI Yan， MU Xihui， ZHANG Guozhi

2020, 41(7):  1434-1440.  doi:10.3969/j.issn.1000-1093.2020.07.022

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A sampling method for life evaluation of high-value ammunitions is proposed. The sampling problem of high-value ammunition with high reliability and long life is studied. The intrinsic relationship among sample size, storage time, reliability evaluation accuracy of high-value ammunition when its life-span obeys Weibull distribution is studied, and the mathematical formulas to reveal the relationship among them are given. High-value ammunition has the following characteristics: high single-shot value, fewer samples for experimental study, and different storage years (productive year). These bring a series of difficulties to its sampling. This paper solves the problem of minimum sample size of high-value ammunition in reliability test, and provides theoretical support for scientific evaluation of its storage life. The method is used to sample a certain type of high-value ammunitions stored for 8 years. The minimum sample size of this batch of high-value ammuitions stored for 8 years is 9 with the confidence of 0.9 and the reliability evaluation accuracy index of 0.15. Key

Two-dimensional Small Displacement Measurement Method Based on Capacitive Grating Sensor

WANG Rui， LI Xin'e， MA Tiehua， DU Hongmian， LU Yangyang

2020, 41(7):  1441-1448.  doi:10.3969/j.issn.1000-1093.2020.07.023

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A two-dimensional small-displacement measurement method based on capacitive grating sensor and a binary parameter model of displacement in any direction on a plane are proposed, and a dual-channel test system with capacitive grating sensor for small displacement is designed for the difficult discrimination of direction of small displacement of object.The small displacement (mm) of simulated object on the plane is measured on a simulation test bench with 2 micrometers. The two channels of the test system output the differential voltages corresponding to the change in small displacement. The magnitude and direction of small displacement can be obtained by analyzing the differential voltage outputs of two channels. The feasibility of the test method and the correctness of the parameter model were verified through experiment. The experimental results show that the direction and magnitude of displacement can be clearly determined according to the change in the differential voltage outputs of two channels when an object produces a relative displacement in one direction on x-axis or y-axis of the plane coordinate; and the direction and magnitude of displacement can be determined from the computed results of the parameter model by the analyzing the change in the differential voltage outputs of two channels when an object produces a relative displacement at any location on the plane. Key

Importance Evaluation of Equipment Support Network Node Based on Fuzzy Local Dimension

ZHANG Qiang， CAO Junhai， SONG Tailiang， YAN Xu， ZHANG Chuang

2020, 41(7):  1449-1456.  doi:10.3969/j.issn.1000-1093.2020.07.024

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Under the background of information and intelligent warfare, all kinds of support organizations at all levels interweave into a network structure, and the effective protection of important support nodes has become an important concern for improving the overall invulnerability of equipment support network. In view of that the node deletion method, the importance contribution method and the efficiency matrix method cannot effectively distinguish the node importance in the local scope, the membership function expression of nodes is constructed based on the fractal and similarity principle of complex networks, and the influences of different nodes at the shortest distance on the central node in a given radius are analyzed. The importance of nodes is described by using the fuzzy local dimension, and the specific algorithm is described in detail. The example shows that the proposed method can be used to quickly and accurately identify the important nodes in the equipment support network, and provide decision support for targeted implementation of node attack immunity.Key

Research on Sensitivity and Resolution of Superfluid Gyroscope

ZHENG Rui, LI Fangdong, ZHAO Chuanchao

2020, 41(7):  1457-1463.  doi:10.3969/j.issn.1000-1093.2020.07.025

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Sensitivity and resolution are the important performance indexes of novel high accuracy superfluid gyroscope. Based on the operating principle of superfluid gyroscope, the relation between sensitivity and working curve is researched, the diaphragm vibration amplitude of displacement detecting system is analyzed, the equation of detecting element noise is deduced, and a mathematic model of resolution is established. Then the phase fluctuation of superfluid which is caused by thermal energy is researched, the equation of thermal noise is deduced, and a mathematic model of limiting resolution is established. Research results show that the resolution of superfluid gyroscope is determined by detecting element noise, and its limiting resolution is determined by thermal noise. The sensitivity and resolution of gyroscope change periodically, and its limiting resolution is constant. A phase shift control system is used to lock the working point of gyroscope at a position where there is the highest sensitivity, the resolution of gyroscope is 10^-8 (rad·s^-1）/Hz and its limiting resolution is 10^-9 (rad·s^-1）/Hz. Key

Research Notes

Emitter Signal Modulation Recognition Based on Joint Projection Dictionary Learning

LI Dongjin， YANG Ruijuan， DONG Ruijie

2020, 41(7):  1464-1472.  doi:10.3969/j.issn.1000-1093.2020.07.026

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An emitter signal recognition method based on joint projection dictionary learning (JPDL) is proposed for the limited atomic representation ability and the insufficient adaptability of complex environment for dictionary learning. The initial features of emitter signal are extracted by time-frequency transform, and the feature preprocessing is realized by dimensionality reduction and noise reduction. Then the atomic structure of the dictionary is optimized by using the methods of kernel space projection and dimensionality reduction projection, and a joint projection dictionary is obtained through data set training. The validity verification is completed by the classification test. The simulated results show that the extracted dictionary atoms have strong representation ability and can adapt to the complex environment with variable parameters. Compared with the conventional supervised dictionary learning method, the proposed method can better distinguish the multi-type and high-similarity signals. The overall recognition rate of 10 types of emitter signals, such as single carrier frequency modulation (SCFM) signal, linear frequency modulation (LFM) signal, nonlinear frequency modulation (NLFM) signal, binary phase shift keying (BPSK) signal, quadrature phase shift keying (QPSK) signal, Frank signal, binary frequency shift keying (BFSK） signal, quadrature frequency shift keying (QFSK) signal, LFM-BPSK modulation signal and BFSK-BPSK modulation signal, at -6 dB is 94.4%. Key