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    29 July 2022, Volume 43 Issue 7
    Electronic edition of this issue
    Electronic edition of this issue
    2022, 43(7):  0. 
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    2022, 43(7):  0. 
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    Broadband Electromagnetic Compatibility Modeling for Three-Phase Synchronous Motor of Armored Vehicle
    XIONG Ying, LI Xiaojian, ZHOU Wei, LI Nan, JIAO Mei, LI Yan, DU Xiaolin, NIE Xiuli, JI Xiangpu
    2022, 43(7):  1467-1477.  doi:10.12382/bgxb.2021.0387
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    Broadband and high-amplitude electromagnetic interference exists in the working process of an electric drive system,posing a significant threat to the system itself and other electronic and electrical equipment. This paper proposes an innovative method for modeling the three-phase synchronous motor while taking the parasitic effect of interference into consideration. The method can help researchers analyze EMI risks and improve the system.First,the frequency domain characteristics of the common-mode and differential-mode impedance of the motor's three-phase port are obtained upon tests.Then,the characteristics of the single-phase common-mode and differential-mode impedance of the motor are obtained upon mathematical derivation,and high-frequency equivalent circuit models of the single-phase port of the motor are developed through vector fitting. Finally,a complete three-phase circuit model of the motor is constructed based on star connection of single-phase equivalent circuits. Based on this method,an equivalent model of a 140 kW permanent magnet synchronous motor is built,and the accuracy of the model is validated by tests.Results show that this method is compatible with a wide frequency range and has good convergence and high accuracy,and can be cascaded with other electronic and electrical modules to form a complete electric drive system model.The innovative and practical approach can effectively support fast analysis and prediction of system-level EMI and electromagnetic sensitivity.
    A Gap Control Method for Electromechanical Brakes
    LIU Zhiqiang, CHEN Yujin, CHEN Lin
    2022, 43(7):  1478-1487.  doi:10.12382/bgxb.2021.0395
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    A novel electromechanical brakes (EMB) design is proposed to address current problems in gap control, such as greater size due to the integration of additional mechanical structures and sensors for automatic adjustment, complex structures, and increased costs. A gap control strategy is proposed to use motor speed and current change signals to identify the critical points of contact and separation between the brake pad and brake disc. Furthermore, a mathematical model is established. The designed EMB brake is simulated and analyzed using MATLAB/Simulink. Based on the pressure loop, speed loop, and current loop, the EMB adopts PID type-Ⅲ control loop as the control system. Simulation and experimental results demonstrate that the EMB and gap control strategy can effectively ensure the brake gap and reduce the target clamping force as well as the time required to eliminate the brake gap, validating the feasibility and effect of the design.
    Rapid Erection Technology and Verification of Special Vehicles Based on High-Voltage Energy Storage
    ZHOU Bojun, YU Chuanqiang, LIU Zhihao, KE Bing
    2022, 43(7):  1488-1497.  doi:10.12382/bgxb.2021.0461
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    Focusing on the rapid erection requirements of special vehicles under heavy loads, and to solve the problem that the gas-liquid hybrid driving method is difficult to achieve erection within 15 s, the optimization of the traditional gas-liquid driving method and the erection structure is studied. The scheme of using high-pressure accumulator to drive the erection of a three-stage cylinder is adopted, and the three-hinge point erection structure and buffer device are optimized according to actual needs. The rapid erection scheme is simulated and verified by the simulation software AMESim, and an experimental prototype is built for rapid erection experiments. The experimental results show that in the scheme, the erecting mechanism is driven through the high-pressure accumulator by quickly releasing the high-pressure gas stored in the device which pushes the piston in the accumulator, so that the hydraulic oil quickly flows into the hydraulic cylinder. Then through stage change and the final buffering by means of throttling, the erection to 95.3° in 12.7 s under heavy loads is realized, and subsequently it takes 1.8 s to reach the amplitude of less than 1° with a stable erection angle of 95°. The total rapid erection time is 14.5 s. Compared with traditional hydraulic pump driving method, the erection by the proposed method is increased by 71.5%. Due to the large span of the experimental prototype, and affected by the impact induced by stage change, the elastic deformation of the experimental prototype causes larger amplitude during stage change, so the buffer structure of the experimental prototype needs to be further optimized to ensure the stability of the erection process.
    Design of an Intermittent High Power Density Permanent Magnet Motor for External Energy Gatling Machine Gun
    ZHANG Pengjun, WANG Ziyong, LU Weiqiang, WANG Jianbo, QIN Qiwei
    2022, 43(7):  1498-1509.  doi:10.12382/bgxb.2021.0378
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    External energy Gatling machine guns are equipped with a type of special motor with a short startup time and high overload, and its improved power density is beneficial to the minimization and mechatronics design of weapon systems. The key characteristics of the electric motor, including fast starting speed, high torque, and short working time, are considered in the motor design. By analyzing the test data of the resistance torque and supply resistance torque of the automata under different radio frequencies, the motor design requirements are determined. Using Maxwell software, a 12-slot 10-pole electric motor model is developed. Results shows that the torque ripple can be reduced by optimizing the magnetic circuit structure, stator slot parameters, and the permanent magnet structure. The overload capacity and power density of the electric motor are improved by optimizing the core flux density at the working point and the saturation flux density of the stator core. Simulation results agree well with the experimental data. The maximum output power of the electric motor is 16.3 kW at 5 000 r/min, and the peak power density is 5.8 kW/kg. Experiments are conducted at a firing rate of 1 000-3 000 rounds/min. The automatic acceleration of the electric motor is completed within 200 ms. Upon reaching the rated firing frequency, the speed fluctuation of the electric motor is less than 10%, meeting the design requirements.
    Active Disturbance Rejection Control of the Roll-isolated System of a Spinning Guided Rocket
    SONG Jinchao, ZHAO Liangyu
    2022, 43(7):  1510-1518.  doi:10.12382/bgxb.2021.0415
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    Under large pitch angles, slope or sine interference disturbances can result in control failures of the roll-isolated system and saturation of the roll gyro. A roll-isolated active disturbance rejection controller (ADRC) is proposed for spinning rockets. Mathematical simulation and theoretical analysis of the PI roll-isolated system are used to reveal the mechanism of saturation of the roll gyro and the control failure. ADRC is designed for the roll-isolated system of the spinning rocket. Based on the numerical simulation results, the improved system is able to effectively handle slope or sine disturbances and ensure the effectiveness of roll isolation. The roll angular velocity can be controlled within a small range of 1°/s. The roll angle can be controlled at about 0°.
    Performance of Solid Fuel Ramjet with Central Bluff Body for Projectile
    ZHANG Ning, SHI Jinguang, WANG Zhongyuan, MA Yexuan
    2022, 43(7):  1519-1526.  doi:10.12382/bgxb.2021.0428
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    To develop a high-performance ramjet for projectiles, a scheme of using bluff bodies in the combustion chamber of the solid fuel ramjet is proposed. The turbulent combustion model is established based on equations for Reynolds transition and eddy dissipation, and the internal flow field, combustion efficiency, thrust, specific impulse and total pressure loss of the combustion chamber with or without the bluff body are compared and analyzed by numerical calculation. The findings show that there are two vortices outside the pore behind the central bluff body. The high-speed airflow in the pore and small-scale vortices below has maintained some wake stability, which can ensure the smooth operation of the ramjet. Compared with the reference solid fuel ramjet (without bluff body structure), adding a bluff body in the afterburning chamber can improve the mixing effect and temperature of fuel and air at the downstream of this chamber, which can increase the combustion efficiency. When the intake air mass flow rate was 0.3 kg/s, the ramjet thrust and specific impulse was increased by about 16.21%, and the combustion efficiency improved by about 20.50%, but the enhancement effects would decrease with the increase of air-fuel ratio. Under the same combustion efficiency, adding a bluff body in the combustion chamber can effectively reduce the length of the ramjet and thus leaving installation space for other parts.
    Initial Velocity Distribution of Fragments from Cylindrical Charge Shells with Different Thick End Caps
    GAO Yueguang, FENG Shunshan, LIU Yunhui, HUANG Qi
    2022, 43(7):  1527-1536.  doi:10.12382/bgxb.2021.0443
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    The end cap thickness is an important factor to be considered in the accurate design of fragmentation warheads, so this study focues on the initial velocity distribution of fragments from cylindrical charge shell with different thick end caps, which is detonated at the center of one end. Based on theoretical analysis and SPH numerical simulation, the models of cylindrical shells are established, and then the theoretical formula of axial distribution of the initial fragment velocity is proposed. The results show that, with the increase in thicknesses of two end caps, the effect of axial rarefaction waves decreases, and the fragment velocity near the two ends increases accordingly. The acceleration effect of detonation products is the main cause of the velocity increase of fragments near the detonation end, while the acceleration effect of detonation waves is the main cause of the velocity increase of fragments near the non-detonation end. Compared with the fragments near the detonation end, the acceleration of the fragments near the non-detonation end is more apparent. The proposed formula is more suitable for end caps and materials in engineering and the relative error can be significantly reduced. The findings of this study can provide reference for the accurate design of warheads.
    Attitude Deflection Mechanism of Projectiles with Variable Elliptical Cross-sections Obliquely Perforating Thin Targets
    TIAN Ze, WANG Hao, WU Haijun, DENG Ximin, PI Aiguo, LI Jinzhu, HUANG Fenglei
    2022, 43(7):  1537-1552.  doi:10.12382/bgxb.2021.0367
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    With the development of new weapon platforms, warheads with novel cross-sections (elliptical and variable elliptical cross-sections) have drawn wide attention due to high platform adaptability, lift-drag ratio, and stealth performance. This study investigates the oblique penetration mechanism and the attitude deflection of projectiles with variable elliptical cross-sections by examining projectiles with three types of cross-sections (circle,elliptic,and tapered elliptic) obliquely penetrating a double-layer thin steel plate through experiments. Based on the failure mode of the target plate and the mechanic characteristics of the projectile body, the penetration process is divided into four stages, namely press-in of the projectile nose, penetration of the nose, transition, and penetration of the projectile body. The mechanic characteristics of each projectile at each stage are also analyzed based on the law of energy conservation and virtual work principle. A theoretical model is constructed for the projectile's attitude deflection. The theoretical model is validated through comparing the experimental and simulation results. The model is used to study how the attitude deflection of projectiles with variable elliptical cross-sections is affected by different parameters, including impact velocity, initial oblique angle, centroid position, roll angle, and the long to short axis ratio of the elliptical cross-sections. The results show that as the impact velocity of the projectile increases, the attitude deflection angle decreases exponentially; the deflection increases as the initial oblique angle increases; the deflection increases as the centroid moves away from the projectile nose; the deflection angles vary when the projectile hits the target from different rolling angles; the deflection at γpt=0° is greater than that when γpt=90°; as the long to short axis ratio increases, the deflection increases when γpt=0°, yet it decreases when γpt=90°.
    Research on Interior Ballistics of Catapult using High-Pressure working medium
    ZHAO Zixi, JIANG Yi, JIA Qiming, NIU Yusen
    2022, 43(7):  1553-1564.  doi:10.12382/bgxb.2021.0370
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    To analyze the feasibility of high pressure working medium-based catapults,an interior ballistic model is constructed based on the Soave-Redlich-Kwong equation of state,and an one-dimensional isentropic nozzle model considering real gas effect is introduced.Using experimental data of nozzle mass flow rate and calculation results from relevant literature,the interior ballistic model is validated.Based on validation and simulation,a multi-objective optimization model is developed and solved by using a genetic algorithm.The results show that the missile catapult based on high pressure working medium can meet the given launch requirements.The interior ballistic model is less sensitive to time step,and the ideal gas and real gas models yield significantly different results.Compared with specific reference conditions,the optimized mass of working medium is reduced by 32. 2% ,and the energy utilization rate is increased by 49. 52%.The research results can provide theoretical reference for designing high pressure working medium-based catapults.
    Damage Behaviors and Mechanisms of Reactive Fragments Impacting Fuel Tanks
    XIE Jianwen, LI Peiyu, WANG Haifu, ZHENG Yuanfeng
    2022, 43(7):  1565-1577.  doi:10.12382/bgxb.2021.0384
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    The ignition and damage behaviors of reactive fragments impacting fuel tanks under the coupling effect of kinetic energy and chemical energy are studied. On the basis of theoretical and experimental analysis, typical damage modes and mechanisms of reactive fragments impacting fuel tanks with different levels of fuel content are investigated. The experimental results show that reactive fragments impacting a partially-filled fuel tank at 806-1 331 m/s cause flash-ignition of the fuel/air layer, but the liquid fuel does not burn continuously. When the fragments hit a full-filled fuel tank at a velocity ranging from 855 m/s to 1 225 m/s, the typical damage modes are perforation, weld-seam cracking, leakage combustion, and disintegration combustion. An analysis of the experimental results and the impact response features of reactive materials reveals the damage mechanism. Based on the energy release characteristics of reactive materials, a structural failure analysis model of a full-filled fuel tank is developed. The calculation results agree well with the experimental results.
    Experiment and Calculation of Critical Velocity of Long-rod Projectile Penetrating Mortar Target at Hypervelocity
    YAO Zhiyan, LI Jinzhu, QI Kaili, XU Yang, HUANG Fenglei
    2022, 43(7):  1578-1588.  doi:10.12382/bgxb.2021.0403
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    A high-strength alloy steel long-rod projectile of 30CrMnSini2A was tested at speeds of 1 381 m/s~1 879 m/s into a semi-infinite mortar concrete target to determine the critical velocity for reverse decrement of penetration depth. The results show an approximate linear relationship between the penetration velocity and crater diameter, crater depth, crater volume, and ballistic aperture. When the penetration velocity is lower than 1 724 m/s, penetration depth increases with increasedvelocity;when it is higher than 1 724 m/s, penetration depth decreases with increased velocity. Penetration depth reaches its maximum when the velocity reaches 1 724 m/s.Target dissection results show that when the long-rod projectile penetrates the target at hypervelocity, the smallhitting attitude of the projectile leads to a serious deflection in the penetration trajectory, which is a “J” shape.Based on the experimental results, the modified A-T model is used to determinethe critical velocity at which the penetration depth of the long-rod projectile decreases when the long-rod projectile penetrates the mortar target at hypervelocity, to analyze the influence of different projectile and target parameters on the critical velocity, and to verify the validity of the theoretical model based on experimental data.
    Trajectory Planning for Exoatmospheric Midcourse Ballistic Missile Interception
    ZHAO Meng, DUAN Junhong, WANG Mingyu, YIN Shuangbin
    2022, 43(7):  1589-1595.  doi:10.12382/bgxb.2021.0410
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    Using the elliptical trajectory and two-body theory, a trajectory planning model of ballistic missile midcourse interception is established to solve the problem of fast trajectory planning for anti-missile interception. First, we obtain information about the initial flight position and velocity on the target trajectory at a given time. The relationship between the flight position and flight time is established based on elliptical trajectory theory, which predicts the point of impact. Second, the motion parameters of the interceptor missile are computed using Lambert equation under the flight time constraint, based on the launch point position of the interceptor and the predicted impact point position. Finally, the effectiveness of the interceptor planning model is verified by using MATLAB simulation. This model provides a method for the planning of midcourse interception trajectory. Under the corresponding constraints, the planned interception trajectory can meet the requirements of midcourse anti-missile interception theoretically.
    A New Type of Controllable Thrust Vertical Launcher and its Interior Ballistic Law
    JIA Qiming, JIANG Yi, YANG Ying, ZHAO Zixi, WANG Zhihao
    2022, 43(7):  1596-1605.  doi:10.12382/bgxb.2021.0433
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    To improve the generality of launchers, this paper proposes a new type of ejection device, wihch is a controllable thrust vertical launcher similar to the concentric canister. Through the numerical calculation of zero-dimensional interior ballistics and simulation of three-dimensional interior ballistics, the influence of the gas outlet area of the low-pressure chamber on the internal ballistic performance of the launcher is analyzed. By means of polynomial fitting, the relationship between the gas outlet area of the low-pressure chamber and the maximum ejection acceleration, the ejection velocity, and the ejection time are obtained, and the fitted formulas are verified. The findings are as follows. It is feasible to change the gas outlet area of the low-pressure chamber to control the thrust of the launcher; the maximum ejection acceleration, ejection velocity, and ejection time change approximately linearly with the gas outlet area, so as the area of the gas outlet of the low-pressure chamber decreases, the maximum ejection acceleration increases, the ejection velocity increases, and the ejection time decreases; the error of maximum ejection acceleration obtained by the relational expression is within 8%, and the errors of the ejection velocity and the ejection time are both within 4%.
    Adhesion Enhancement of Electrophoretic Deposition Driven Energetic Film via KCl Inorganic Crystal Network
    DING Rui, LIU Xu, DONG Yue, XU Na, YIN Yanjun
    2022, 43(7):  1606-1613.  doi:10.12382/bgxb.2021.0379
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    Electrophoretic deposition is a film forming technology that is highly compatible with different electrode shapes, highly controllable, and low-cost. Yet, its adhesion and hardness are relatively low, which limits its use in energetic materials. To improve the adhesion of electrodeposited energetic films, a convenient post-processing strategy is proposed. The target films are impregnated with different concentrations (0.1 mol/L, 0.2 mol/L, 0.5 mol/L) of an inert inorganic salt solution (KCl solution). The morphology, composition, heat release, and adhesion of the Al/CuO films are examined by scanning electron microscopy, X-ray diffraction, simultaneous thermal analyzer, high-speed camera, and American national by tape standard ATSM D 3359—17 standard test methods for rating adhesion by tape tests. The results show that the treated Al/CuO energetic film surface is loaded with KCl, and that the inorganic salt solution is recrystallized during the drying process, thus filling the gaps between the energetic particles and forming a network structure, bonding the scattered particles and boosting the film adhesion from Level 1 to Level 3. Furthermore, the heat released by Al/KCl (0.2 mol/L)/CuO film after treatment is 1 781 J/g, 164 J/g higher than that of the Al/CuO film (1 617 J/g) before treatment. Due to the filling of KCI inorganic salt, the heat release of the Al/KCl/CuO system is improved, increasing the contact between nanoparticles and enhancing the density of the energetic film.
    Hygroscopic Properties of Ammonium Dinitroamide-based High Energy Propellant
    LI Lei, WANG Yanwei, DANG Li, WANG Huisi, DU Fang, TAO Bowen, HU Xiang, ZHOU Shuiping, GU Jian
    2022, 43(7):  1614-1619.  doi:10.12382/bgxb.2021.0536
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    The hygroscopicity and sensitivity of Ammonium Dinitroamide (ADN) and ADN-based solid propellants were comparatively investigated through the use of balancer, high performance liquid chromatography, and analysis of contact angle for water and mechanical sensitivity. The results showed that the ADN-based high-energy solid propellant samples had strong hygroscopicity. At 25°C and a relative humidity of 75%, a large number of ADN-containing droplets appeared on the surface of the propellant sample, after 72 hours of moisture absorption, and the percentage of weight gain was 9%. The hygroscopicity of the modified ADN-based propellant was significantly reduced with a weight gain of only 0.3%, and no droplets appeared. The analysis indicated that the contact angle of the modified ADN with water increased significantly, from 8° before modification to 78° after modification, resulting in the remarkable reduction of the adsorption of the modified ADN with water molecules in the air. The impact sensitivity of the propellant before and after ADN modification was increased from 8.1 J to 14.3 J, and its friction sensitivity before and after ADN modification was reduced from 60% to 32%. The impact sensitivity and friction sensitivity of the propellant were both apparently improved. The findings of this work is of great referential significance for the application of ADN in solid propellants.
    Refined Design of Electricity Consumption for the Electromechanical Actuation System of Tactical Weapons
    LIU Hongzheng, ZOU Huaian, HU Dengjie, LIU Yuanfeng, ZHOU Yuliang, LONG Qiang, WU Zhang
    2022, 43(7):  1620-1627.  doi:10.12382/bgxb.2021.0289
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    To address the problem of large electricity consumption margins, a new method is proposed based on the analysis of control data to optimize the energy use of actuator systems. Firstly, analyze the torque, angular velocity, and angular acceleration of the actuator based on guidance and attitude control data. Then, calculate the current change of the actuator using the power and torque balance equation. Finally, determine the working current and peak current range by accurate analysis of the current change. Compared with traditional analysis methods, the working current is reduced by 70%, and the peak current by 33.3%, preliminarily verifying the effectiveness of the refined method.
    A Collaborative Method for Measuring the Triaxial Moment of Inertia Using the Vertical Vibration Compound Pendulum andCircular Torsion Pendulum
    LU Zhihui, SUN Haozhi, WANG He, YANG Hongtao, WU Yiyong
    2022, 43(7):  1628-1635.  doi:10.12382/bgxb.2021.0383
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    A missile warhead in the horizontal posture is supposed to rotate 90 degrees during a moment of inertia measurement. To simplify the measuring process for mass property parameters, a coordinative triaxial measuring method for moment of inertia is proposed based on the use of both a vertical vibration compound pendulum and a circular torsion pendulum. The structure of the measuring device and the calculation principle are also introduced. The difference relation between the components of the two moments of inertia along the y and z directions of the missile warhead in the vertical posture is obtained by measuring swing periods along the two axes. The method is more convenient than using the proportional relation, and it is equal to the difference relation between the components of the two moments of inertia based on the vertical vibration compound pendulum axis. The results show that the other moment of inertia can only be calculated by measuring a moment of inertia in the horizontal posture, with a maximum measuring error of 0.35 kg·m2 which meets the accuracy requirement of 1 kg·m2 for the finalized measuring device. The new method combines the advantages of both vibration pendulum and torsion pendulum, and improves the convenience and accuracy for measuring the triaxial moment of inertia.
    Adaptive Exponential Time-varying Sliding Mode Control based on Disturbance Observer for Photoelectric Stabilized AirbornePlatform
    MIAO Shuangquan, ZHANG Baoquan, WANG Mingchao, WANG Xinwei, SHEN Yu
    2022, 43(7):  1636-1645.  doi:10.12382/bgxb.2021.0229
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    An adaptive exponential time-varying sliding mode control method based on a non-linear disturbance observer is proposed for a photoelectric stabilized airborne platform, taking aircraft torque fluctuations, nonlinear friction, and parameter uncertainty into consideration. The non-linear disturbance observer in the method is used to observe the composite uncertainty. The adaptive exponential time-varying sliding mode control module is integrated to realize global robust control of the angle rotation of the photoelectric stabilized platform impacted by residual disturbances not visible to the disturbance observer. The sliding mode controller is designed without the upper bound information of the composite uncertainty by the adaptive law. The exponential time-varying sliding mode function solves the problem of excessive adaptive for switch gain and improves the system response. According to Lyapunov's theory, the global asymptotically stable performance of the system is proved, and the angle position of system is asymptotically converged to the desired one. The simulation and prototype test results show that the method can achieve high-precision angle control despite external disturbances and parameter uncertainty.
    An Estimation Method for Rotation Factors of Weighted Fractional Fourier Transform Signals Based on Cyclic Correlation
    ZHANG Xiaoyu, SONG Bixue, WANG Yang, FENG Yongxin, QIAN Bo
    2022, 43(7):  1646-1654.  doi:10.12382/bgxb.2021.0412
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    Weighted fractional Fourier transform (WFRFT) has been widely used in secure communication systems due to its strong anti-interception and anti-modulation recognition capabilities. Accurate estimation of rotation factors of WFRFT signals will facilitate signal processing. In this study, the characteristics of WFRFT signals are analyzed, and an estimation method for rotation factors of WFRFT signals is proposed. To shorten the estimation time, the peak value and position of normalized correlation values of different rotation factors are statistically analyzed, and the cyclic correlation method was introduced to accurately estimate the rotation factor of WFRFT signals under unknown signal parameters. According to the simulation results, the parameter estimation method based on cyclic cross-correlation can accurately estimate the rotation factor of WFRFT signals, which provides an important basis for WFRFT communication countermeasures.
    Parameterized Time-frequency Analysis in Continuous-wave Active Detection
    XUE Cheng, GU Yiming, GONG Zaixiao, LI Zhenglin
    2022, 43(7):  1655-1666.  doi:10.12382/bgxb.2021.0420
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    Acontinuous wave signal processing algorithm is proposed based on parameterized time-frequency analysis to address the problems of target echo detection and direct wave interference suppression of hyperbolic frequency modulation signal in continuous-wave active detection. First, based on the analysis of the time-frequency characteristics of the hyperbolic frequency modulated continuous wave signal andthe idea of parameterized time-frequency analysis, we propose afrequency-domain parameterized time-frequency transform suitable for active detection and the kernel function design for hyperbolic frequency modulated signal. Then, to suppress the direct wave interference in the received signal, the parameterized rotating time-frequency transform is used, along with the time-frequency domain filtering in order to separate the signal components, and then the echo signal is reconstructed via the inverse transform. Numerical simulation and marine experimental results show that the proposed algorithm not only can accurately estimate the time-frequency characteristics of the signal, effectively obtain the time-frequency gain of the hyperbolic frequency modulated continuous wave signal, and improve the detection performance, but also can effectively suppress direct wave interference.
    Building Detection Algorithm in SAR Images Based on Ghost Convolution and Attention Mechanisms
    YAN Jiwei, SU Juan, LI Yihong
    2022, 43(7):  1667-1675.  doi:10.12382/bgxb.2021.0425
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    A building detection algorithm in SAR images based on a lightweight network is proposed to address the problems caused by the large quantity of model parameters and memory resources involved in deep convolutional neural networks. First, the algorithm is based on the rotating detector R-centernet, and the traditional convolution in backbone network is replaced by Ghost convolution. Then, the Ghost-ResNet is constructed to reduce the number of model parameters. Second, a channel attention module that fuses width and height information is developed to enhance the network's ability to locate significant regions in the images accurately. An up-sampling method named CARAFE is used to replace the DCN module in the network, and the feature map information is fully combined in the up-sampling process to improve target detection. Finally, the improved R-centernet is used to train and test the SAR rotating building dataset. Based on the experimental results, compared with the R-centernet, the improved algorithm has increased detection accuracy by 3.8%, recall by 1.2%, and detection speed by 12 frames per second.
    Three-dimensional Global Path Planning for UUV Based on Artificial Fish Swarm and Ant Colony Algorithm
    HU Zhiyuan, WANG Zheng, YANG Yang, YIN Yang
    2022, 43(7):  1676-1684.  doi:10.12382/bgxb.2021.0215
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    To solve the problem of global path planning of underwater unmanned vehicles (UUVs) in a three-dimensional environment, this study examines a fusion algorithm for fish swarm and ant colony that optimizes the initial pheromone distribution and transfer probability of UUVs. The fusion algorithm improves the state expression and moving step of the artificial fish swarm algorithm. The heuristic value and pheromone of the ant colony algorithm are also optimized. Using the congestion factor, the transfer probability of traditional ant colony algorithms is improved, and the new algorithm is capable of global optimization. Based on grid modeling of the actual marine environment data, we take the path length as the measurement index to simulate and verify the algorithm through MATLAB. The experimental results indicate that the initial convergence speed of the fusion algorithm is faster, the optimal fitness value is higher, and the executed time is shortened, verifying the effectiveness of the algorithm.
    Flow Field Characteristics of the Early-stage Coupling Interaction between Supersonic Jet and Tail Cavity of Underwater Vehicles
    ZHANG Chun, WANG Baoshou
    2022, 43(7):  1685-1694.  doi:10.12382/bgxb.2021.0360
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    For the vertical launch of underwater vehicles, igniting the solid rocket engine in the tail cavity to control movements is an essential approach to stabilize the trajectory under the interference of complex factors. Based on the fluid volume model, standard k-ε turbulence model and dynamic mesh method, and by solving Reynolds-averaged Navier-Stokes equations, the flow field characteristics and evolution law of the coupling effect between supersonic jet and tail cavity in the early stage are studied. The results show that the semi-ellipsoidal appendage tail cavity formed after an underwater vehicle leaves the launch tube gradually evolves into a gourd-shaped cavity due to the supersonic jet effect. The internal flow is reconstructed after damage without forming a reentrant jet flow. The supersonic jet flow is completely limited in the tail cavity, and the radial size of the jet flow is basically equal to the diameter of the nozzle outlet. Primary and secondary vortex rings appear successively in the tail cavity due to jet cogging and the effect of the cavity surface, while pressures at the tail of the underwater vehicle and the center of the launch tube exit show wide-amplitude oscillations. The maximum amplitude is about 1.2 times of the water pressure at the launching spot, causing significant variance in the jet structure and engine thrust.
    Preventive Maintenance Optimization and Spare Parts Prediction Method for Aircraft Group Oriented to Operational Readiness
    LI Ting, LIU Lin, PENG Yuncheng, CUI Chaoxiong, XUE Fei
    2022, 43(7):  1695-1705.  doi:10.12382/bgxb.2021.0437
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    As the operational environment is increasingly complex and the training intensity keeps growing for operational readiness in the new era, aircraft equipment are required to be able to provide comprehensive support capabilities. Operational readiness (availability) is one of the core technical indicators of aircraft combat capability for successful combat tasks, which reflects the maintenance and spare parts management levels. To this end, simultaneous analysis is done for the typical failure law of aircraft components, the life model, and the levels of aircraft maintenance and spare parts management (such as inspection time, spare parts replacement time, etc.). First, the component-level maintenance policy is optimized to formulate the time-based system-level group maintenance scheduling method. Second, the system-level group maintenance policy is optimized and an availability model built based on the delay time and Markov process is studied. On this basis of the maintenance policy, spare parts prediction approach is developed. The results of the numerical study show that, compared with the traditional corrective maintenance and scheduled maintenance, the proposed approach can effectively improve the operational readiness of the aircraft within the precise and controllable range of demand for spare parts.
    Simulation of the Dynamic Response of Cement Concrete Pavement under Multiple Cold Launch Loads
    ZHANG Zhendong, GAO Yuan, MA Dawei, ZHU Zhongling, WANG Xi
    2022, 43(7):  1706-1717.  doi:10.12382/bgxb.2021.0380
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    As the road structure is coupled dynamically with the launching system, the impact mechanical behaviors of pavements will directly affect missile launching safety. A loading device for simulating cold launching loads is developed with compressed air as a power source. Then, an asphalt concrete pavement is paved in a three-dimensional test slot fitted with strain and soil pressure sensors. The variation laws of surface layer displacement is obtained by analyzing the response of the pavement under multiple impact loads, and the relationship between the internal pressure stress of the soil subgrade and the depth and distance from the load center is studied. The failure modes and mechanisms of the surface layer under multiple simulated cold launching loads are observed. The experimental results show a linear relationship between the impact pressure and the peak compressive stress of the soil subgrade. The peak compressive stress of the soil subgrade at different depths under different impact loads is very small at 3 300 mm away from the center of load. The surface layer is elastically deformed when the impact load is small, and radial penetrating cracks are generated on the concrete surface layer when the impact load is increased to 0.77 MPa. The cold launching load cause an integral settlement in the pavement.
    Comprehensive Review
    Current Status and Trends in Shock-absorbing and Anti-explosion Technologies for Military Vehicle SeatsResearch on Design Technology of Shock Absorbing and Anti-explosion for Military Vehicle Seats(Series I)
    WANG Guosheng, LEI Qiangshun, CAO Yu, ZHANG Weijie, LI Guibing
    2022, 43(7):  1718-1732.  doi:10.12382/bgxb.2021.0402
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    If the shock absorption and antiknock performance of military vehicle seats are poor, it will greatly affect the physical health and combat effectiveness of combat vehicle passengers. Tank seats are important due to their influence on occupant health, operation and maneuvering efficiency, and life security. The research status on shock absorption and anti-explosion of occupant seat in armored vehicles as well as the development gap between China and foreign countries are analyzed. The disadvantages of occupant seats in Chinese military vehicles are evaluated based on the ride comfort, shock absorption, and anti-explosion requirements, especially in step-less height adjustment, synchronous vibration damping and buffering, self-adapting weight damping, and multiple reuse of anti-explosion structures. A summary regarding the development trend, research direction, and key technologies of occupant seats is presented. The study further reveals the necessity and urgency of speeding up research in armored vehicle seats.