Table of Content

30 July 2021, Volume 42 Issue 7

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Contents

2021, 42(7):  0. 

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Paper

Action Mechanism of Magnetic Field Enhancing the SCJ Stability

MA Bin, YU Xianfeng, HUANG Zhengxiang, JIA Xin, ZU Xudong, XIAO Qiangqiang

2021, 42(7):  1345-1352.  doi:10.3969/j.issn.1000-1093.2021.07.001

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The craters penetrated by the the shaped charge jet (SCJ) coupling with the magnetic field are measured and analyzed to obtain the different stabilizing mechanisms of magnetic field enhancing SCJ stability at different stages. The characteristics of the craters penetrated by SCJ coupling with the magnetic field are analyzed through the static depth-of-penetration experiment and X-ray photograph, and then the coupling mechanisms of SCJ and magnetic field are researched based on the experimental results. The experimental results show that the coupling effect of magnetic field loaded at different timing could increase the SCJ stability under certain conditions, but the stabilization mechanisms are different, which mainly includes two aspects: the delayed breakage of continuous SCJ and the inhibited rotation of fractured jet particles.

Countermeasure to Reduce the Large Scanning Blind Area of Terminal Sensitive Projectile Caused by Interval Sampling

YANG Jie, ZHANG Qi, HE Yuanji, GAO Hongquan, DENG Bin

2021, 42(7):  1353-1362.  doi:10.3969/j.issn.1000-1093.2021.07.002

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For reducing the phenomenon of large searching blind area of terminal sensitive projectile in interval sampling mode, the reason of this phenomenon is analyzed through establishing a scanning point distribution model in interval sampling mode and example demonstrating, which is caused by the periodic repetition or small increment of discrete normalized polar angle. Based on this rule, the geometric features and forming conditions of large blind area phenomena of terminal sensitive projectile without parachute and wing and terminal sensitive projectile with parachute or wings, respectively, are studied and analyzed through theoretical derivation, and the engineering significance of this phenomenon is verified by using experimental data. The small sampling time interval/large sensing device’s field of view countermeasure and the random sampling time interval countermeasure to reduce the scanning blind area are presented based on the forming condition of this phenomenon. They were simulated and evaluated. The result shows that the countermeasure of random sampling can reduces the blind area radius effectively in the precondition of maintaining original hardware scheme, and has technical feasibility and high cost-effectiveness.

Relation among Important Structural ParametersFlyer Velocity and Energy of Flyer Driven by Micro-size Lead Azide

HE Xiang, YAN Nan, ZENG Xiangtao, XIE Ruizhen, BAO Bingliang, ZHANG Liang, WU Weiming

2021, 42(7):  1363-1371.  doi:10.3969/j.issn.1000-1093.2021.07.003

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In order to obtain the relationship among the important structural parameters and the velocity and energy of flyer driven by micro-size lead azide, the simulation study of flyer driven by micro charge was carried out. The parameters of Jones-Wilkins-Lee equation of state of lead azide based on the γ law equation are fitted from the relationship between the detonation velocity and density of lead azide. A simulation model of the flyer driven by lead azide is established by using the finite element analysis software AUTODYN, and the velocity-distance curve of the flyer is measured by using photonic Doppler velocimetry system. The simulated curve is in well consistence with the test curve. The relationship among the diameter and height of charge, the aperture of accelerating chamber, the flyer thickness and the velocity and energy of flyer is analyzed by using the established simulation model. The results show that the velocity and energy growth rates of flyer decrease with the increase in the diameter and height of charge, and the influence of charge diameter on the velocity and energy of flyer is more obvious. With the increase in the flyer thickness, the flyer velocity decreases exponentially; the flyer energy first increases and then decreases, and there is a flyer thickness that makes the flyer energy maximum. When the aperture of accelerating chamber is smaller than the charge diameter, the velocity and energy of flyer decrease slightly; when the aperture of accelerating chamber is larger than the charge diameter, the velocity and energy of flyer decrease sharply.

Extending-time Trajectory Characteristics of Reciprocating Glide of Flying Vehicle

YANG Changzhi， JIANG Yi， NIU Yusen， WANG Jinghui

2021, 42(7):  1372-1380.  doi:10.3969/j.issn.1000-1093.2021.07.004

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A subsonic “reciprocating gliding-hovering” trajectory scheme is proposed to further extend the flight time of reconnaissance cruise missiles. The extending-time efficiency and characteristics of trajectory scheme are studied. The aerodynamic parameters of flying vehicle are obtained through CFD numerical wind tunnel test, and the fourth-order Adams Moulton algorithm is used to solve the equations of trajectory control of flying vehicle. The difference between the the flight times of fliying vehicles in “horizontal-circling” trajectory and “reciprocating gliding-circling” trajectory schemes is compared and analyzed, and the influences of initial velocity and initial trajectory angle on the flight time of “reciprocating gliding-circling” vehicl are further studied. The results show that the reciprocating glide extending-time trajectory scheme of flying vehicle can extend the flight time, and the extending-time efficiency can reach 14.79% relative to the optimal working condition of “horizontal-circling” trajectory. On the premise of the realization of the “reciprocating gliding-circling” trajectory, the initial velocity and initial trajectory angle of flying vehicle have little effect on the flight time of flying vehicle in the “reciprocating gliding-circling” trajectory scheme.

An Approximate Calculation Method for Ejection of Propellant Gas during After-effect Period of Artillery

MIAO Wei, YIN Qiang, QIAN Linfang

2021, 42(7):  1381-1391.  doi:10.3969/j.issn.1000-1093.2021.07.005

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The resultant force in the bore during after-effect period of artillery becomes significant in analyzing the motion of artillery. As the spatial distribution of propellant gas flow properties in the conventional theoretical assumption of after-effect period does not strictly conform to the numerical solutions, a set of differential-integral equations describing the gas flow distribution are derived from the governing equations of in-bore gas. A numerical method is then proposed for solving the equations. Formulas for evaluating the gas flow properties, the resultant force in the bore, and the after-effect coefficient are obtained based on the gas flow distribution. The calculated results of the formulas in this paper and the conventional theories were compared with the numerically simulated results.The results suggest that the gas flow distribution and the resultant force in the bore calculated by the proposed formulas are in fantastic agreement with the numerically simulated ones. The error between the analytical and computational after-effect coefficients ranges from 0.38% to 1.80%.

Application of PCE Method in Parafoil-flight Uncertainty Analysis

LIU Anmin, GAO Feng , ZHANG Qingbin, YUAN Tianbao, ZHANG Guobin

2021, 42(7):  1392-1399.  doi:10.3969/j.issn.1000-1093.2021.07.006

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A parameter uncertainty analysis method is proposed based on polynomial chaos expansions (PCE) method for the uncertainty quantification problem of parafoil flight performance. A nine-degrees-of-freedom multibody dynamics model of parafoil system with random parameters is established, and a proxy model is established to approximate the nonlinear dynamics model of parafoil system by using the PCE method. The influences of different PCE orders and sample sizes on the calculation results are analyzed. Considering the calculation accuracy and efficiency, a PCE model suitable for parafoil-flight uncertainty analysis is proposed. The simulated results show that the PCE method can achieve the same calculation accuracy and has higher efficiency compared with the Monte Carlo method, which verifies the effectiveness of the PCE method for the flight uncertainty analysis of parafoil system. For a small parafoil system, the PCE method is used to study the influence of aerodynamic parameters uncertainty on the distribution and deviation of landing points.

Cooperative Reentry Guidance for Intelligent Lateral Maneuver of Hypersonic Vehicle Based on Downrange Analytical Solution

ZHANG Wanqing, YU Wenbin, LI Jinglin, CHEN Wanchun

2021, 42(7):  1400-1411.  doi:10.3969/j.issn.1000-1093.2021.07.007

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A cooperative guidance law based on deep Q-learning network (DQN) algorithm for lateral maneuver of hypersonic vehicles is proposed to meet the requirement of cooperative saturation attack. The longitudinal and lateral guidance laws are deigned. The longitudinal lift-to-drag ratio is calculated to obtain the modulus of bank angle based on the high-precision longitudinal analytical solution. The lateral bank reversal logic is abstracted as a Markov decision process (MDP), and the reinforcement learning method can be used. A lateral intelligent maneuver decision-making device based on DQN algorithm is designed. The intelligent agent can be generated by offline training according to the mission requirements, and is called online to generate the sign of bank angle. Simulated results show that the proposed guidance law can autonomously generate bank angle reversals on-line, strictly meets the requirements of flight time constraints and energy management, and has high guidance accuracy and good mission adaptability. Compared with the coordinative reentry guidance law based on three-dimensional analytical solutions, the proposed guidance law is used to fully achieve the lateral maneuverability of vehicle and make it have higher penetration potential.

Numerical Simulation of Aerodynamic Interference of Close-coupled Highly Swept-back Wings at Transonic Velocity

LIU Qingyang, LEI Juanmian

2021, 42(7):  1412-1423.  doi:10.3969/j.issn.1000-1093.2021.07.008

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The paper investigates the aerodynamic interference of close-coupled highly swept-back wings to the tail wings at transonic velocity which is from subsonic velocity to hypersonic velocity. The numerical method is based on the Reynolds-averaged Navier-Stokes equations and finite volume method. The Spalart-Allmaras turbulence model is used to simulate the flow field around an air vehicle with close-coupled highly swept-back wings. The distributions of aerodynamic coefficients of tail at different Mach numbers and angles of attack under the influence of the front wing are given. The variation of surface pressure coefficient and the flow structure of tail are analyzed to figure out the aerodynamic interference mechanism. The results indicate that the flow field around tail is influenced greatly by the vortex from the highly swept-back wing under both subsonic and transonic flow conditions. The decrease in the pressure difference of upper and lower tail surfaces results in decreasing the lift coefficient and drag coefficient of tail. Besides, the greater the angle of attack is, the greater the vortex intensity is, and the greater the reductions of lift coefficient and drag coefficient of tail are. The influence of wing on tail decreases with the increase in Mach number.

Cylinder Test and Equation of State for DNAN-based Aluminized Melt-cast Explosive

LI Shurui， DUAN Zhuoping， ZHENG Baohui， LUO Guan， HUANG Fenglei

2021, 42(7):  1424-1430.  doi:10.3969/j.issn.1000-1093.2021.07.009

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To determine the parameters of equation of state (EOS) for detonation products in the shock initiation of aluminized explosives, a series of 50 mm standard cylinder tests was performed for the DNAN-based aluminized RA1 melt-cast explosive (HMX/DNAN/Al) and its corresponding explosive RF1 (HMX/DNAN/LiF) that contains the lithium fluoride (LiF). The detonation velocities of two kinds of explosives and the expanding velocities of cylinders were measured by using the electric probes and the photonic Doppler velocimetry (PDV). The EOS parameters for detonation products of RA1 and RF1 are both determined by genetic algorithm and numerical simulation. It is found that the wall velocity histories of RA1 and RF1 are almost consistent within 0-4.6 μs, but separate obviously after 4.6 μs due to the increasing reaction degree of aluminum powder. This indicates that the aluminum powder mainly reacts in the expansion process of detonation products, and hardly participates in chemical reaction during the detonation as well as the shock initiation. Therefore, in the numerical simulation of shock initiation, the detonation products of the aluminized explosives can be described by the EOS for the detonation products of their corresponding explosives that contain the lithium fluoride.

Multi-branch Continuous Phase Modulation and Demodulation Method Based on PSWFs Signal

YANG Dawei， LIU Chuanhui， ZHANG Lei， KANG Jiafang

2021, 42(7):  1431-1439.  doi:10.3969/j.issn.1000-1093.2021.07.010

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A multi-branch continuous phase modulation and demodulation method based on prolate spheroidal wave functions (PSWFs) signal is studied for the problems of low communication rate and low spectral efficiency in the existing very low frequency (VLF) communication mode. Through introducing the PSWFs signal with high energy aggregation in the time-frequency domain into continuous phase modulation and using the complete orthogonal characteristics of the PSWFs signal, the PSWFs signal with different orders are simultaneously used as the continuous-phase modulated baseband frequency-modulated pulse signals, thereby generating a modulated signal. At the signal receiving end, the traditional differential coherent detection method is used to demodulate the mapping information of information symbol sequence. And then the method of obtaining the sum of cross-correlation values of the signals during multiple bit periods is used to detect and demodulate the PSWFs waveform mapping information. The experimental results show that, compared with the minimum frequency shift keying modulation mode currently used in VLF underwater communication, the spectral efficiency can be effectively improved by about 9.43%, but it can be reduced by about 1.24% under the condition of 99.0% power bandwidth of modulated signal.

Impact Load Characteristics of a Trans-media Vehicle during High-speed Water-entry

YUAN Xulong, LI Min, DING Xutuo, REN Wei, ZHOU Fangxu

2021, 42(7):  1440-1449.  doi:10.3969/j.issn.1000-1093.2021.07.011

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The trans-media vehicle conbines the advantages of missiles and supercavitating weapons, which has higher terminal penetration capability compared to missile and makes up for the shortcoming of short range of supercavitating weapon. The impact load characteristics of a trans-media vehicle during high-speed water-entry and the load-reduction method are the main key technologies for the development of trans-media vehicles. A coupled simulation model for multi-phase flow and trajectory of trans-media vehicle entering into water at high speed was established and verified.The impact load characteristics of trans-media vehicle during high-speed water entry under typical conditions were simulated, and the ballistic parameters of trans-media vehicle in the high-speed water-entry process were compared. The results show that the periodical normal overload is generated during the tail-slapping, which is about 2.7 times as high as the axial overload, and the normal force is mainly composed of the positional force caused by the oscillating angle of attack, and the inertial force is very small and could be ignored. The increase in the water-entry speed speeds up the tail-slapping frequency and decreases the angle of attack oscillation amplitude, and the water-entry speed has little effect on the normal impact force coefficient.

Improved Adaptive Phase-difference Estimator for Ultra-short Baseline System

YU Min， DING Xianjun， ZHANG Xiaoliang， ZHU Mingsi

2021, 42(7):  1450-1456.  doi:10.3969/j.issn.1000-1093.2021.07.012

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In view of the contradiction between convergence speed and steady-state accuracy of the traditional adaptive phase difference estimator due to the use of the least mean square (LMS) algorithm, an improved method is proposed for the adaptive estimator based on the LMS algorithm. And the recursive least square (RLS) algorithm is proposed to be applied to the adaptive phase difference estimator to further improve the stability of adaptive estimator.Through numerical simulation and experimental data verification, the results show that the two improved adaptive phase-difference estimators of LMS and RLS algorithms can both improve the calculation accuracy and convergence speed, and the latter has a higher steady-state accuracy.

Deconvolved Beamforming with Spatial Windowing and Incoherent Noise Reduction

WANG Hao, MA Qiming

2021, 42(7):  1457-1462.  doi:10.3969/j.issn.1000-1093.2021.07.013

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A denconvolved beamforming with spatial windowing and incoherent noise reduction is proposed for multi-target resolution and weak target detection under the influence of strong interference and incoherent noise. The noise reduction capacity is estimated based on the number of snapshots.The noise reduction capacity under different conditions of snapshots is obtained by solving the semi-definite programming problem or estimating the eigenvalue of covariance matrix. Then the covariance matrix after reduction is used to perform spatial windowed beamforming to obtain the spatial energy spectrum，and the point spread function of spatial windowed beamformer is proposed to deconvolve the spatial spectrum for the spatial spectrum estimate in the proposed algorithm. Simulation and sea trial data processing show that the proposed algorithm can effectively suppress the effects of strong interference and incoherent noise on the desired signal，and obtain a detection capability that is superior to those of traditional deconvolution algorithms.

Partition Enhancement Method for NSCT Domain of Side-scan Sonar Image

WU Helong， QIU Zheng, ZHANG Weiquan

2021, 42(7):  1463-1470.  doi:10.3969/j.issn.1000-1093.2021.07.014

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The serious noise pollution, low contrast of gray values of target and background areas, and weak edges in the side-scan sonar image are due to the limitations of side-scan sonar imaging mechanism and the abundant noise sources in the ocean. In response to the above problems, a partition enhancement method for the non-subsampled contourlet transform (NSCT) domain of side-scan sonar images is proposed. For the low-frequency part of sonar image, a nonlinear function enhancement method is used to improve the contrast of low-frequency image. For the high-frequency part of sonar image, the noise and texture edges are partitioned and the corresponding processing is made by analyzing the distribution rule of the difference between the maximum and minimum values of sub-band coefficients in different directions on the same scale. The proposed method was compared with the gamma enhancement method and the wavelet threshold enhancement method through experiment. The results show that the proposed method not only denoises noise well, but also can suppresses trivial textures and enhances weak edges.The enhancement effect for side-scan sonar image is more prominent.

Effect of TiB₂ Addition on Ballistic Properties of Graphene Modified B₄C Ceramic Matrix Composites

YE Tengke， XU Yuxin， WU Yue， REN Yunyan

2021, 42(7):  1471-1481.  doi:10.3969/j.issn.1000-1093.2021.07.015

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The failure mechanisms of graphene modified B₄C composites with and without TiB₂ under the penetration of 12.7 mm armor-piercing projectiles were studied for the development and optimization of new lightweight materials for bulletproof armor. The Vickers hardness, bending strength and fracture toughness of the two ceramic matrix composites were obtained by using Vickers hardness tester, three-point bending method and single edge notched beam method. The anti-penetration performances of the two composites penetrated by 12.7 mm armor-piercing projectiles are studied through the residual penetration depth experiment, which are quantitatively characterized by the protection coefficient. A scanning electron microscope (SEM) was used to analyze the macroscopic damage morphologies of 7075 aluminum alloy back-plates and ceramic fragments to study the failure mechanism of ceramic and the strengthening mechanisms of TiB₂ and graphene. Experimental results show that the addition of TiB₂ can enhance the properties of graphene modified boron carbide ceramics. Compared with the material without TiB₂, the Vickers hardness, bending strength and fracture toughness of the material containing 14wt.% TiB₂ are increased by 19.66%, 24.06% and 19.70%, respectively, and its anti-penetration performance is increased by 15.11% under the penetration of 12.7 mm armor-piercing projectiles at 750 m/s. It is shown that the B₄C ceramic matrix composite exhibits a variety of energy absorption modes and a better crushing resistance due to the addition of TiB₂ and the strengthening effect of graphene, which is the main reason for the improvement of anti-penetration performance.

Task Allocation and Trajectory Optimization of UAV for Multi-target Time-space Synchronization Cooperative Attack

ZHANG Yunfei, LIN Defu, ZHENG Duo, CHENG Ziheng, TANG Pan

2021, 42(7):  1482-1495.  doi:10.3969/j.issn.1000-1093.2021.07.016

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A task allocation and trajectory optimization algorithm for multi-target attack is proposed for the coordinated attack task of distributed UAVs attacking multiple targets in a complex battlefield environment. The typical multi-target strike mission scenarios and UAV models are established. A search map with no-fly zones as nodes is constructed based on Delaunay triangle theory. A^* algorithm is used to achieve the least threatening single-aircraft path search. In terms of UAV dynamics constraints and minimum energy loss, the time adjustment factor is introduced and the distributed UAV time-space synchronization trajectory optimization method based on Bezier curve is adopted to obtain the optimized trajectory for simultaneous attack on multiple targets. A trajectory tracking controller was designed for simulation track of pre-planned trajectory. The simulated results show that the proposed multi-target attack task allocation and trajectory optimization method can achieve multi-angle, time-space synchronization, and distributed coordinated attack on multiple targets, and it has strong robustness against interference such as noise and wind gusts.

Probabilistic Roadmap Method for Path Planning of Intelligent Vehicle Based on Artificial Potential Field Model in Off-roadEnvironment

TIAN Hongqing, WANG Jianqiang, HUANG Heye, DING Feng

2021, 42(7):  1496-1505.  doi:10.3969/j.issn.1000-1093.2021.07.017

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Path planning in complex off-road environment is a key technology to realize the autonomous driving of intelligent vehicle. There are obstacles, environmental threats and terrains that affect vehicle movement in off-road environment. In the traditional path planning methods, the shortest path length and time cost are usually taken as the optimization goal, which makes it difficult to plan a feasible and safe driving path in complex off-road environment. An artificial potential field based probabilistic roadmap (APF-PRM) algorithm is proposed to solve the problem. The potential field algorithm is used to model the off-road environment and evaluate the vehicle traffic risk, and then the probabilistic roadmap method is used to conduct the path planning with multi-dimensional traffic cost between path nodes as the goal. Considering the dynamic characteristic of the vehicle, a dynamic curvature smoothing method is used to optimize the vehicle trajectory. Finally, the APF-PRM algorithm is used to conduct the path planning in a simulated off-road environment. The simulated results show that the APF-PRM algorithm utilizes the artificial potential field algorithm to integrate the obstacles, environmental threats and road conditions in the off-road environment in the process of path planning; the probabilistic roadmap method is used to establish a multi-dimensional traffic cost evaluation matrix among the sampling points; and a feasible, safe and efficient path is generated under complex off-road conditions, which provides a multi-objective optimization path planning method for intelligent vehicles.

Effect of Microstructure on Explosion Failure of Ti6321 Titanium Alloy Target Plate

NING Zixuan, WANG Lin, CHENG Xingwang, CHENG Huanwu, ZHOU Zhe, ZHANG Binbin， WANG Fang, CHEN Dongping

2021, 42(7):  1506-1515.  doi:10.3969/j.issn.1000-1093.2021.07.018

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Ti6321 titanium alloy target plates with different microstructures were obtained through different heat treatments. The effect of microstructure on the deformation and fracture behavior of Ti6321 titanium alloy target plate during explosive loading was studied. The fracture and micro-failure analysis of target plate after explosion were carried out by using optical microscope and scanning electron microscope. The results show that the equiaxed target plate has a higher resistance to deformation, the Widmansttten target plate has a higher resistance to spallation failure and a lower thickness reduction rate. The fracture modes include plastic deformation and central necking ring, partial break along the necking ring, complete break along the necking ring and complete tear in the center. The tensile and shear fracture occur in the bimodal target plate under the explosive loading of 200 g TNT. Under the explosive loading of 300 g TNT, the tensile, shear fracture and spallation occur in the equiaxed target plate, and the shear fracture and spallation occur in the bimodal target plate, the fractures of which are both ductile fracture. Only shear fracture occurs in the Widmansttten target plate under the explosive loading of both TNTs, and the fracture is a mixed ductile and brittle fracture. The spallation and shear fracture of target plates are adiabatic shear failure.

Prediction of Warp Tensile Elasticity of 2.5D Woven Composites

LI Juying, LI Ying, WANG Ronghui, WEI Huazhen, KONG Guoqiang

2021, 42(7):  1516-1523.  doi:10.3969/j.issn.1000-1093.2021.07.019

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A prediction method is proposed for investigating the warp tensile elastic properties of 2.5D woven composites with different structures. Through the design and analysis of nonlinear multiscale materials, the warp tensile elastic properties of the typical volume element（RVE） models of curved and straight linking 2.5D woven composites were simulated, and the warp tensile elastic moduli and warp tensile failure forms of RVE models were obtained. The warp tensile properties of two 2.5D woven composites were characterized to verify the accuracy and rationality of the simulated results. The characterized results are compared with the simulated results.The results show that the design and analysis methods of nonlinear multiscale materials can be used to predict the warp tensile elastic modulus of straight linking 2.5D woven composite, and accurately predict the warp tensile failure forms of two 2.5D woven composites. This provides an effective method for designing and optimizing the warp tensile elastic properties of 2.5D woven composites.

Effect of Laser Process Parameters on Microstructures and Properties of NiCoCrAlYSi Laser Cladding Coating

SHEN Hao, CAI Jie, L Peng, ZHANG Conglin, LI Yuxin, GUAN Qingfeng

2021, 42(7):  1524-1534.  doi:10.3969/j.issn.1000-1093.2021.07.020

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NiCoCrAlYSi coating was fabricated on Ni625 superalloy by laser cladding technique, and the influences of laser power and scanning speed on the metallurgical quality and microstructure of NiCoCrAlYSi cladding coating were researched. The relationship among the laser cladding process parameters, and the microstructures and properties of cladding coating was analyzed by testing its micro-hardness, and friction and wear properties. The results show that, with the increase in laser input energy from 36 J/mm² to 73.3 J/mm², the thickness of cladding layer increases from 534 μm to 1 535 μm, the surface porosity increases from 0.07% to 0.65%, and the pore size increases from 0.23 μm to 1.33 μm. In addition, the grain size of cladding layer increases. The microhardness and wear resistance of the cladding layer decrease gradually with the increase in porosity and grain size. When the laser input energy ratio is 36 J/mm², a cladding coating with high compactness, supper refined grains and high density of dislocations is obtained, which has optimal microhardness and wear resistance.

Calibration of Sensitivity Coefficient of Three-dimensional High-g Accelerometer Based on Vector Decomposition

WU Qian， GUO Weiguo

2021, 42(7):  1535-1543.  doi:10.3969/j.issn.1000-1093.2021.07.021

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In order to generate synchronous measurable tri-axial acceleration overload pulse and calibrate the sensitivity coefficient of three-dimensional high-g accelerometer, Hopkinson bar system is designed to a cylindrical bar with one bevel end on which the accelerometer is placed. The Hopkinson bar system was theoretically analyzed, and simulated and tested by using Abaqus finite element software. The results show that the Hopkinson bar system is used easily to realize the sensitivity coeficient calibration of three-dimensional high-g accelerometer, the synchronization of three-axis loading pulse and the decoupling between axes; according to the optimization design, the different amplitudes of the three-axis high-g accelerometer can be calibrated by analyzing the relationship between the three-axis accelerometer and the standard rod; and different slope angles and accelerator installation angles will cause the changes in vector decomposition, which will affect the pulse configuration. The slope angle with the minimum error is 45° in numerical simulation. Finally, the sensitivity coefficient of three-dimensional high-g accelerometer can be calibrated by loading the standard uniaxial bar and decomposing the vector on inclined plane.

Engineering Equivalent Conductivity Measurement and Inversion Method for Field Environmental Assessment of SREMP

ZHANG Yaohui, HE Wei, LI Yuebo, XIE Yanzhao,YANG Jie

2021, 42(7):  1544-1552.  doi:10.3969/j.issn.1000-1093.2021.07.022

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The source region electromagnetic pulse (SREMP) can penetrate the engineering geotechnical medium, which has a serious impact on the electronic information equipment in the underground engineering. A test scheme of near-field region of SREMP is proposed based on the equivalent test of continuous wave in order to evaluate the environment of underground engineering. An equivalent test system is built, and the near-field characteristics of antenna are studied. The magnetic induction intensity of line antenna near the earth is test, and the feasibility of the test system is verified. On this foundation, the inversion study of equivalent conductivity of the earth is made by the finite-difference time-domain (FDTD) algorithm, and the field environment at typical frequency points in underground engineering at a certain depth is calculated. The proposed method can be used to evaluate the environment of SREMP in underground engineering for different earth media, which provides a reference for studying the SREMP effect and engineering protection design.

Air Combat Situation Assessment Based on Dynamic Variable Weight

YANG Aiwu, LI Zhanwu, LI Bao, XI Zhifei, GAO Chunqing

2021, 42(7):  1553-1563.  doi:10.3969/j.issn.1000-1093.2021.07.023

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In air combat situation assessment, the situation assessment model does not adequately describe the high dynamics and game process of air combat, and the constant weight assessment situation leads to "state imbalance". A situation assessment method based on dynamic variable weight is proposed. First, based on the characteristics of air combat, the maneuver strength and maneuver potential models are established to quantify the tactical intent and enrich the situation assessment model, and solve the problem of deviation between the situation assessment result and the actual air combat situation due to the fixed value of tactical intent. The objective constant weight vector is calculated based on the criteria importance through intercrieria correlation method, and the equilibrium function is constructed from the analysis of the air combat evaluation index influencing factors, and the indicator state variable weight vector is obtained. The variable weight of the indicator is calculated by the Hadamard product of the constant weight vector and the state variable weight vector, and solve the problem of "state imbalance" in the evaluation situation with constant weight. The simulated results show that the proposed method is more objective in situation assessment and conforms to the characteristics of actual air combat.

Research Notes

Measurement of the Wind Drag Coefficient of Tracked Armored Vehicles

DU Minggang， ZHANG Jinle, ZHANG Ximing, SUN Yadong, MAO Feihong

2021, 42(7):  1564-1568.  doi:10.3969/j.issn.1000-1093.2021.07.024

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A test research on the wind drag coefficient of tracked armored vehicles is carried out for the problem about the inaccurate wind drag coefficient of high-speed tracked vehicles affecting the calculation of maneuverability. Based on the similarity theory, a series of wind tunnel tests were made for the miniature scale models of armored vehicles. The wind drag coefficient values of different types of tracked armored vehicles were obtained by processing the test data. The results show that, in the aerodynamic design, the wind drag coefficient of 0.92 can be selected for the main battle tank, 0.99 can be selected for self-propelled artillery vehicles, and 0.83 can be selected for infantry fighting vehicles. The test results provide engineering guidance for the precise calculation of vehicle maneuverability.