Table of Content

31 December 2021, Volume 42 Issue 12

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Contents

Contents

2021, 42(12):  0. 

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Paper

Comprehensive Analysis for Compatibility of Armed Helicopter and Air-to-ground Missile

ZOU Ruping， CHEN Yun， CHEN Shichao

2021, 42(12):  2531-2542.  doi:10.3969/j.issn.1000-1093.2021.12.001

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A comprehensive analysis method, which takes various factors into consideration, is proposed for the compatibility of the armed helicopter and air-to-ground missile (AGM). The influences of the rotor down-wash flow and the flight speed of helicopter on missile trajectory, the relative position relationship between missile trajectory and helicopter during missile launching, and the influence of engine jet flow on the helicopter are comprehensively analyzed. The proposed method perfects the analysis system for the compatibility of armed helicopter and AGM, providing technical support for the compatibility design and the selection of attacking conditions. The analysis results demonstrate that the increased flight speed of helicopter during attack, the reasonable initial ballistic design and the reduced engine jets can improve the compatibility of armed helicopter and AGMs. Simulated and real flight data have verified the effectiveness of the proposed method.

Design and Analysis of Multi-branch Non-circular Gear Continuously Variable Transmission Mechanism

XING Qingkun， LIN Chao， YU Yongquan， HU Yanan

2021, 42(12):  2543-2554.  doi:10.3969/j.issn.1000-1093.2021.12.002

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Continuously variable transmision is an important component of vehicle transmision system. A new type of multi-branch non-circular gear continuously variable transmission mechanism is proposed based on the transmission characteristics of non-circular gear. The continuously variable transmission is realized by the combination of non-circular gear pair，differential mechanism and transmission selection mechanism，and the final transmission ratio depends on the phase angle between two pairs of non-circular gears. The transmission principle of multi-branch non-circular gear continuously variable transmission mechanism is analyzed. The pitch curve，tooth profile and balancing characteristics are designed for non-circular gear pair，and the tooth profile and three-dimensional solid model of non-circular gear are obtained through simulation processing. The overall transmission ratio characteristics of the mechanism are compared and analyzed in theory，simulation and experiment through the ADAMS simulation and transmission experiment，and the maximum simulated and experimental errors of overall transmission ratio are about 4.5% and 5.6%, respectively. The transmission ratio characteristics of single gear pair are compared through the non-circular gear manufacturing and transmission experiment，and the maximum simulated and experimental errors of transmission ratio of gear pair are about 3.5% and 6.3%, respectively. Considering the influences of manufacturing error，assembly error and measurement error， the simulated and transmission experimental errors are all within the reasonable error range，which verifies the correctness of the theoretical analysis method.

Design and Optimization of Occupant Lower Limb Protection Device against Explosion Shock below Military Vehicle

SUN Xiaowang， ZHANG Jincheng， PENG Bing， ZHANG Jinkun， WANG Xianhui

2021, 42(12):  2555-2564.  doi:10.3969/j.issn.1000-1093.2021.12.003

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For severe damage to the lower limbs of vehicle occupant caused by the explosion shock below vehicle，a vehicle occupant lower limb protection device was designed by combining the flexible floor and the explosion-proof foot pad. The protective performance of the lower limb protection device and the influence of design parameters on the protective performance are studied based on vehicle explosive simulation，and a preferable design is determined. Static stiffness analysis of the preferable design is made to determine if it can provide sufficient support in daily use. Multi-objective optimization is performed for the structure of lower limb protection device to obtain the optimal design. The vehicle explosion simulation and test were carried out to verify this design. The results show that the occupant lower limb protection device can effectively reduce the impact to the lower limbs and significantly improve the protection ability of the lower limbs.

A Dual-directional Information Transmission Method for Fuze Wireless Setting System Based on Nonlinear Parity-time-symmetry

LI Changsheng， DONG Wenjie， CAO Juan， ZHU Chuanjun， ZHANG He

2021, 42(12):  2565-2574.  doi:10.3969/j.issn.1000-1093.2021.12.004

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The principle of nonlinear parity-time-symmetric wireless power transfer can be used to improve the flexibility and adaptability of fuze wireless setting system，but the problem of dual-directional information transmission between transmitter and receiver should be solved. The differential equations of the setting system are established to obtain the theoretical relationship between the transient response characteristics of voltage and current and the transmission parameters based on the mutual inductance coupling theory. A power and information synchronous transmission method of non-return-to-zero amplitude modulation is proposed，which can not only transmit power continuously，but also effectively shorten the starting and stopping vibration in the loop. The reverse transmission of information is realized by inducing the resonant frequency jump at the transmitter through the instantaneous detuning at the receiver，which has short detuning time and less negative impact on the power transmission. Finally，a principle prototype was designed based on the proposed theory. The forward information transmission rate is 20 kbit/s, and the reverse transmission rate is 12.8 kbit/s. The experimental results verify the correctness of the proposed model and the feasibility of the dual-directional information transmission method.

Multi-objective Optimization of Aerodynamic Shape of Microspoiler for Spin-stabilized Projectile

QIAN Long， CHANG Sijiang， NI Yi

2021, 42(12):  2575-2585.  doi:10.3969/j.issn.1000-1093.2021.12.005

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In order to improve the shooting accuracy of a spin-stabilized projectile，a microspoiler is used for the spin-stabilized projectile to provide lateral lift for the projectile，thus changing the projectile body attitude and achieving the purpose of changing the flight trajectory. Through the numerical simulation method，the axial force coefficient，normal force coefficient and static moment coefficient of microspoiler are calculated，the change of the aerodynamic coefficient of microspoiler with the shape parameters and Mach number is analyzed，and the influences of shape parameters and Mach number on the equilibrium angle of attack are analyzed. A multi-objective optimization design model is established. In the proposed model, the main shape parameters of microspoiler are used as design variables，the trajectory correction and the terminal remaining speed are taken as the optimiztion targets，and the angle of attack，correction ability，spoiler size and other constraints are considered. The genetic algorithm is used to obtain global optimal solution. The results show that the method of using the microspoiler to adjust the projectile's attitude and trajectory is feasible and effective；there is an optimal solution for the lift-to-drag ratio in the shape parameters of microspoiler in the sub-transonic range，and the lift-to-drag ratio decreases with the increase in Mach number at supersonic speed.

The Factors Affecting the Gap of Common Tail Structure in High-pressure Gun

PENG Jiacheng, JIANG Jianwei, LIAO Wei, LU Yihao

2021, 42(12):  2586-2596.  doi:10.3969/j.issn.1000-1093.2021.12.006

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For the affecting factors and change rules of the gap in open tail seat during the high-pressure gun launch, LS-DYNA software is used to simulate the internal ballistics of a typical extended-range ammunition with a common tail. The dynamic response at every moment in internal ballistics was obtained. The muzzle velocity and rotation speed at the muzzle are in good agreement with the test data. The axial compressions of engine support, engine shell and warhead base, and the change rule of gap between the tail fins and the warhead base under different yield strengths and preloads are analyzed. The results show that the axial compressions of the engine support, shell and warhead base increase first and then decrease, which is consistent with the bore pressure-time variation; the engine shell has a greatest effect on the gap between tail fin and warhead base, and the proportion reaches 78.2% in total compression; when the yield strength of engine shell reduces to 800 MPa, the total compression caused by the elastic deformation of common tail exceeds the gap between tail and warhead base, resulting in collision on the base. When the preloads are abnormal, the gaps between each tail and the base is not synchronized and up to 17.3% of the initial gap, causing the deep and shallow collided marks.

Characteristics of Muzzle Jet Noise Field Including Moving Bullet of a Pistol

YOU Peng， ZHOU Kedong， HE Lei， MIAO Huanju

2021, 42(12):  2597-2605.  doi:10.3969/j.issn.1000-1093.2021.12.007

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In order to study the characteristics of aerodynamic noise at pistol muzzle, the characteristics of jet noise field of a 9 mm pistol is studied through numerical calculation and experiment. The muzzle gas flow field of a pistol with moving bullet is numerically calculated by using the CFD-CAA two-step method and the dynamic mesh technology. The muzzle flow field is calculated to obtain the fluid information on sound source integral surface by the large eddy simulation (LES) method.Then the sound source information and the sound pressure signal at each sound monitoring point are obtained by solving the Ffowcs Williams-Hawkings（FW-H） sound wave equation, and finally the transient sound field is obtained. In order to verify the feasibility of the numerical model, the experimental results are analyzed in comparison with the numerically calculated results. The result shows that the numerical model considering the movement of bullet makes the calculation results more accurate；the errors of the measuring points values between the numerically calculated and experimental results are less than 5%, which proves the validity and availability of the proposed model. The research results and the proposed model can provide better reference value for the muzzle noise prediction and the design of muzzle silencer.

Interior Ballistic Characteristics of Compressed Air Ejection System

LI Boping， LI Guoqing， ZHANG Jiwei， L Hongliang， WU Jun， LI Mengyuan， LI Congrui

2021, 42(12):  2606-2616.  doi:10.3969/j.issn.1000-1093.2021.12.008

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An interior ballistic mathematical model of ejection process was established to investigate the interior ballistic characteristics of compressed air ejection system under different initial conditions.The effects of the full opening time and flow area of launch valve and the initial volume of low-pressure chamber on the interior ballistic characteristics were studied through numerical calculation.The results show that the opening time of launch valve has a significant impact on the internal ballistic characteristics，and with the increase in the opening speed，the ejection time becomes shorter，the initial velocity of projectile increases，and the overload of projectile becomes larger. In a certain range，with the increase in the maximum flow area of launch valve，the ejection time becomes shorter，the initial velocity of projectile increases，and the overload of projectile changes more smoothly.However，the maximum flow area of launch valve has a weak influence on the maximum overload of projectile.The initial volume of low-pressure chamber has a weak influence on the ejection stroke and velocity，but has a great influence on the overload of projectile at the initial ejection stage.

On-line Rapid Planning Method for Interceptor Missile Midcourse Guidance Trajectory

LI Wanli， LI Jiong， LI Mingjie

2021, 42(12):  2617-2625.  doi:10.3969/j.issn.1000-1093.2021.12.009

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An online trajectory planning algorithm based on dynamic inversion in the virtual domain(IDVD) is proposed for the online rapid planning of midcourse guidance trajectory of interceptor missile that meets multiple constraints. The virtual factors are introduced to transfer the discrete state variables from the time domain to the virtual domain. Based on the idea of dynamic inversion，the virtual arc length is used to obtain the high-order derivative of the boundary conditions，which improves the computational efficiency. A penalty function for process constraints is constructed to plan the guidance trajectory with the performance indicators so that the trajectory can meet multiple constraints in the time domain. Finally，an on-line re-planning strategy after updating the target information is presented based on the proposed algorithm.The simulated results show that, although the proposed algorithm can quickly generate a reference trajectory that satisfies multiple constraints，it has good real-time performance and robustness，and is suitable for solving on-line rapid trajectory planning problems.

Tracking Method for Hypersonic Glide Vehicle Based on Adaptive Multi-channel Interacting Multiple Model

ZHANG Junbiao， XIONG Jiajun， LAN Xuhui， LI Fan， CHEN Xin， XI Qiushi

2021, 42(12):  2626-2636.  doi:10.3969/j.issn.1000-1093.2021.12.010

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The near-space hypersonic glide vehicle (HGV) has the high maneuverability，which makes it difficult to track stably by using the single tracking model. To solve this problem，a tracking method based on adaptive multi-channel interacting multiple model is proposed. Based on the analysis of the force and maneuvering characteristics of HGV，the characteristics of strong adaptability of kinematic model and the high matching degree of dynamic model are fully considered in the proposed method. The kinematic model and the dynamic model are taken as a model set. The likelihood function value is used to adjust the transition probability matrix in real-time to enhance the proportion of the matching model. The residual edge distribution is used to describe the matching degree of the filtering model with the target motion in three different dimensions of x，y and z axes. Simulation experiments show that the proposed method has good adaptability in tracking HGV under typical control laws. When the HGV maneuvers，the proposed method has higher accuracy and stability.

Analysis of the Minor Deformation of Imaging Primary Mirror Supporting Platform of Missile at Low Temperature

CHEN Ke， ZHANG Yongfei， WANG Dulin， LIU Zijun， FU Xiaogang

2021, 42(12):  2637-2645.  doi:10.3969/j.issn.1000-1093.2021.12.011

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During the environmental test of a certain type of missile seeker，its imaging primary mirror can always capture the target normally at room temperature，but it often loses the target at low temperatures. The imaging primary mirror fails because of its own surface shape with small deformation. The cause of primary mirror deformation should be determined to avoid the surface shape of primary mirror changing at low temperature in subsequent mass production. A finite element analysis software ANSYS simulation model，including screw pre-tensioning and low-temperature deformation，was established for the low-temperature failure of the imaging primary mirror，and the process of low-temperature environmental test was reproduced in the finite element software to analyze the specific failure reason of the imaging primary mirror. The simulated results show that the influence of the pre-tightening force of screws on the imaging primary mirror is much smaller than that of the uneven deformation of the primary mirror at low temperature due to the limitation of the cover screws on it. The entire process of the imaging primary mirror from assembly to low-temperature failure is recurred through simulation，which provides a sufficient theoretical basis for solving the problem about the low-temperature deformation of the imaging primary mirror，and eliminates the assembly concerns for subsequent mass production.

Distribution Law of Explosion Stress on Hole Wall of Water Interval Charge

LIU Jiangchao， GAO Wenxue， ZHANG Shenghui， LI Xiaoshuai

2021, 42(12):  2646-2654.  doi:10.3969/j.issn.1000-1093.2021.12.012

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The length of water medium has an important influence on the blasting effect when water infusion blasting is used in the process of tunnel excavation. Therefore，in order to get the distribution law of stress on hole wall of water interval charge，the Starfield superposition method is used to deduce the changing situation of stress on the hole wall，in which the attenuation and superposition of stress wave are considered，and ANSYS/LS-DYNA are used to verify the calculated results.The results show that the stress on the hole wall is the largest at the interface of explosive and water medium.With the increase in the distance from the interface，the explosion stress decreases in the form of exponential function.The equivalent interval initiation method is used to simulate the explosion processes of water interval charges with different charge masses.The attenuation law of simulated explosion stress on the hole wall in the water interval section is consistent with that of the theoretical explosion stress，and the error between simulated and theoretical explosion stresses at the same position is about 10%.The total stress on the hole wall of water interval section increases with the increase in charge mass.In conclusion，it is reasonable to use the Starfield superposition method to obtain the explosion stress formula of hole wall in water interval section.

A Deep Deterministic Policy Gradient Optimization Approach for Multi-users Data Offloading in Wireless PoweredCommunication Network

GENG Tianli， GAO Ang， WANG Qi， DUAN Weijun, HU Yansu

2021, 42(12):  2655-2663.  doi:10.3969/j.issn.1000-1093.2021.12.013

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In the wireless powered communication network (WPCN)，the wireless devices can offload data through wireless backscattering and active radio frequency transmission.How to adjust the working mode as well as manage the time allocation of ambient backscattering and active RF transmission properly is a great challenge for reducing the system transmission delay and enhancing the transmission efficiency.A deep deterministic policy gradient(DDPG) algorithm is proposed to search the best time allocation in a continuous domain，in which the data size，the channel conditions and the fairness between wireless devices are considered.The experimental results show that DDPG algorithm achieves the algorithm convergence in finite time step， and all the wireless devices can complete the data offloading at the same time by introducing Jain fairness index.Compared with the traditional Round-Robin and Greedy algorithms，DDPG algorithm can be used to reduce the average transmission delay by 77.7% and 24.2%，respectively，and the energy efficiency is largely improved especially for wireless devices with a small amount of offloading data.

A Lightweight Target Detection Algorithm Based on the Improved Faster-RCNN

MA Yuehong， KONG Mengyao

2021, 42(12):  2664-2674.  doi:10.3969/j.issn.1000-1093.2021.12.014

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The target detection algorithms based on deep learning has become the mainstream of target detection in synthetic aperture radar images. Deep network algorithm often has a large number of parameters and don't run fast enough to meet real-time requirements，making it difficult to deploy on resource-constrained devices such as mobile terminal. Considering the requirements of real-time performance and portability of the model，Faster-RCNN for the two-stage target detection algorithm was improved to compare the influence of different improved methods on the speed and accuracy of algorithm.The lightweight model was optimized in combination with the characteristics of synthetic aperture radar (SAR) images，and finally compared with the single shot multibox detector for one-stage target detection algorithm.The experimental results show that the speed of the improved lightweight model is greatly improved while maintaining the original accuracy level，which can effectively meet the real-time requirements of SAR image target detection.

An Algorithm for Detection of Prohibited Items in X-ray Images Based on Improved YOLOv4

MU Siqi， LIN Jinjian， WANG Haiquan， WEI Xiongzhi

2021, 42(12):  2675-2683.  doi:10.3969/j.issn.1000-1093.2021.12.015

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An improved YOLOv4 algorithm for detecting the prohibited items in X-ray images is proposed to increase the speed of security inspection and realize the automatic detection of prohibited items in X-ray images. The proposed algorithm is used to design a dilated dense convolution module based on the one-stage object detection algorithm YOLOv4. The features after the upsampling link fusion are input into the dilated dense convolution module to enhance the feature expression ability and the convolution field of vision. An attention mechanism is added to the fused feature information to enhance effective features and suppress invalid features. Finally，a feature map representing image information is input to detection head. Mosaic data enhancement method is used to train the network to improve the robustness of the network. The results show that the mean average precision (mAP) of the proposed algorithm on the public SIXray data set reaches 80.16%，and the detection speed is 25 frames per second (FPS). The proposed algorithm can achieve high detection accuracy for multiple types of prohibited items on the public SIXray dataset， and meet the real-time requirements of detection.

Field Distribution of Biconical-wire Grating Antenna for Radiated-wave EMP Simulator

XIAO Jing， WU Gang， WANG Haiyang， XIE Linshen， CHENG Le， GUO Jinghai

2021, 42(12):  2684-2692.  doi:10.3969/j.issn.1000-1093.2021.12.016

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The horizontally polarized radiated-wave antenna with biconical-wire grating structure has less influence on the half-width of radiated E-field，and it is easy to erect and maintain. Mastering the E-field distribution rule is a premise to determine the simulator's uniform area and conduct the EMP effect experiment.The distribution rule of the radiated E-field is studied using the antenna theory，and the analysis results are verified by simulation and practical experiment.It shows that the polarized E-field component below the biconical apex is only inversely proportional to the distance from the observation point to the excitation source if the antenna structure and excitation voltage are determined.On Oxz plane，the polarized E-field amplitudes on a circle centered at the biconical apex are equal. And they reach the peak value at the same time.On Oxz plane，the total E-field amplitudes at the observation points on a horizontal line are equal，and their directions are along the tangent line of an arc where the observation points is located.The E-field components are symmetrical with Oxz and Oyz planes.As for a practical simulator，the ground reflection causes severe decline in the falling edge of the radiated E-field，which reduces the half-width of the radiated field near the ground. Meanwhile，the wire grating plate also affects the radiated field nearby，and the reflections are stronger at four angular points of the plate.The distribution of radiated fields at other points is consistent with theoretically analyzed result.

Prediction of Wave-absorbing Coating Thickness of Airborne Conformal Antenna Based on Orthogonal Experimental Designand Regression Analysis

ZHANG Qingjun， XIE Yin， WU Song

2021, 42(12):  2693-2699.  doi:10.3969/j.issn.1000-1093.2021.12.017

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The wave-absorbing coating thickness has direct effect on the wave-absorbing performance of conformal antenna. 25 groups of spraying process parameter level combinations were designed using the orthogonal experimental design method. The corresponding wave-absorbing coating thickness data were obtained through 25 sets of wave-absorbing coating spraying experiments. The range analysis，variance analysis and nonlinear regression analysis were made for the thickness data of wave-absorbing coating. The result shows that the influences of spraying process parameters on the thickness of wave-absorbing coating are sorted in descending order:spraying speed> stepping distance> spraying distance> paint viscosity> spraying angle> spray gun air pressure. The spraying speed has a significant effect on the thickness of wave-absorbing coating. A regression model for predicting the thickness of wave-absorbing coating was established. It can accurately characterize the quantitative relationship among the wave-absorbing coating thickness and the spraying process parameters.

Joint Multi-station Target Association and Positioning Based on Divide-and-conquer and Greedy Thoughts

WANG Guanqun， ZHANG Chunhua， ZHANG Shuran

2021, 42(12):  2700-2709.  doi:10.3969/j.issn.1000-1093.2021.12.018

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Because the existing target association and positioning method separates association and positioning into two independent processes，the target positioning accuracy is seriously limited by the correct association in this kind of step-by-step processing when taking the local optimal association and positioning method.Therefore，a joint multi-station target association and positioning method based on the divide-and-conquer and greedy thoughts is proposed. The sets of real intersection points on each bearing line are selected according to the divide-and-conquer thought and the minimal distance principle，and all the sets of intersection points are merged according to the greedy thought. In the merging process of sets，the target association and positioning accuracies are guaranteed through repeated verification between the positioning and association processes.The mutually exclusive target measurement sets are combined according to the association relationship，and the multi-target measurement set with the maximum joint association probability is selected as the final output.The simulated results show that the association accuracy of the method remains above 90% when there is clutter，and still above 70% when there is both false alarm and missing detection. The proposed method is to use the greedy thought to reduce the calculation complexity and overhead.The simulated and experimental results both verify that the proposed method has high target association and positioning performance，and is suitable for underwater environments with low detection limit and high false alarms.

Identification Mechanisms for Damage Characteristics of Fully Appendage Submarine Propeller

LIU Zongkai， LIU Manhong， GUO Zhengyang， LI Zhanjiang

2021, 42(12):  2710-2721.  doi:10.3969/j.issn.1000-1093.2021.12.019

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The intelligent fault diagnosis should be based on a perfect sample database，which must contain enough sampled data obtained from different working conditions. But many faults，especially in some special conditions，cannot be gained by experiments or practical samplings，so they need to be accumulated through numerical simulations. Based on the basic fluid principle，the influence of blade damage on the flow field and moments fluctuation of fully appendage underwater vehicle under uniform flow is obtained by solving the three-dimensional unsteady Reynolds average N-S equations and turbulent flow closed equations. The coupling mechanism between blade damage characteristics，propulsion efficiency and hull dynamics characteristics is concluded by field strength analysis. The results show that the pressure plays a leading role on total moment compared with the viscous force. The fluctuation of pressure moment can be divided into a large-amplitude low-frequency oscillation and a small-amplitude high-frequency oscillation. The frequency for the former oscillation mostly depends on the detached vortex frequency，and the frequency for the high frequency oscillation is consistent with the propeller rotation frequency. For the large amplitude oscillation of pressure moment coefficient，the thrust eccentric position of blade determines the offset of the balance line relative to the zero position. The phase difference between pitch and yaw moments reflects the symmetry of blade，and the smaller the phase difference is，the stronger the symmetry of blade will be. The blade damage types are predicted from the change of viscosity moment.

The Four-stage Assisted Technology of Flexible Ankle Exoskeleton Robot Based on Force and Position Hybrid Control

LIU Yali， SONG Qiuzhi， ZHAO Mingsheng， ZHOU Nengbing， LIU Yue

2021, 42(12):  2722-2730.  doi:10.3969/j.issn.1000-1093.2021.12.020

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The assistant strategy for lower extremity joints is a key factor influencing the assistant efficiency of exoskeleton robots. The exoskeleton robots during walking on level ground have been widely explored and proved to be effective. However，the performance of exoskeleton robots during walking on a slope has not been widely analyzed，and even the assistant characteristics of exoskeleton robots during walking on a slope has not been explored.An exoskeleton robot was developed to study the physiological characteristics and joint power characteristics of human during walking on a slope.A four-stage force-position hybrid control method for ankle assisted exoskeleton robot was proposed based on the rationale of human movement. A flexible ankle exoskeleton was deverloped based on the analysis，and the assisting efficiency testing experiment of the assistance torque and energy consumption was made. The results demonstrate that the exoskeleton robot can provide the assisted ankle joint torque of 7% and decrease the oxygen uptake by 3.5% during walking on a slope.

Coupling Effect of Initial Residual Stress-initial Geometric Error on Machining Deformations of Aeronautical MonolithicComponents and Its Control

LIN Feng， YAO Wan， QIN Guohua， YE Haichao， TAO Jiang

2021, 42(12):  2731-2742.  doi:10.3969/j.issn.1000-1093.2021.12.021

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In the process of high-speed milling，the release of initial residual stress will cause the machining deformation of aeronautical monolithic component. The machining deformation caused by the initial residual stress release of blank with initial geometric error should be analyzed to control the machining quality，which is very important for the precision machining process.A mechanical model of machining deformation and a finite element method are established to reveal the influence of the initial geometric error of blank on the workpiece deformation. An optimization model of machining position is established with the minimum deformation as the objective. According to the condition that the increment of two adjacent machining positions does not exceed the threshold，a step decreasing algorithm of the optimization model is proposed. The results show that the model calculated values are in good agreement with both the finite element simulated values and the experimental results whether in deformation trend or amplitude. When the blank has initial geometric error or no initial geometric error，the optimal machining positions of the three-frame integral structure are 22.754 3 mm and 23.265 mm，and the corresponding deformation values are -0.006 mm and -0.007 mm，respectively. When the blank has no initial geometric error，its deformation at the position of 22.754 3 mm is 0.043 mm，and when the blank has initial geometric error，its deformation at the position of 23.265 mm is -0.144 mm.It is further verified that the initial geometric error of the blank has a great influence on its deformation.

Prediction of Contact Fatigue Life of Thermal Sprayed Coating Based on Support Vector Machine

MA Runbo， DONG Lihong， WANG Haidou

2021, 42(12):  2743-2752.  doi:10.3969/j.issn.1000-1093.2021.12.022

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For the contact fatigue life prediction of thermal sprayed coatings，a series of contact fatigue tests of the plasma sprayed Al₂O₃-40wt% TiO₂ composite coating (AT40 coating) were conducted on a multifunctional contact fatigue/wear testing machine (RM-1 tester) developed by National Key Laboratory for Remanufacturing of Army Academy of Armored Forces by using a central composite design scheme under the action of contact stress, rotation speed, coating thickness and slip ratio. The failure morphology of the coatings is observed by scanning electron microscopy. 3σ criterion is used to test the reliability of contact fatigue life test. The training set and test set are divided rationally by the combination of the golden section method and the information entropy theory. A life prediction model considering the contact stress， rotation speed， coating thickness and slip ratio is established based on the principle of support vector machine. The results show the main damage failure of the coatings is delamination failure and surface wear under the joint action of contact stress， rotation speed， coating thickness and slip ratio，the contact fatigue life obtained by using central composite design scheme is reliable， and the prediction model based on the support vector machine theory could be used to characterize the function relationship between the contact fatigue life of AT40 coating with contact stress， rotation speed， coating thickness and slip ratio. These results could provide theory support to the prediction of contact fatigue life of sprayed coatings.

A Method for Taking Values of Equipment Reliability Design Assurance Coefficient

HU Tingchun， SUN Yufeng， ZHAO Guangyan

2021, 42(12):  2753-2761.  doi:10.3969/j.issn.1000-1093.2021.12.023

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For the control of quality risk in a project，the national military standards and model specifications both stipulate that the reliability prediction value of equipment should be at least 1 to 1.5 times the contract value (hereinafter referred to as the design assurance coefficient). However，the selection of design assurance coefficient is lack of theoretical basis，especially the selection basis for precise quantification. In view of this problem， a reference method is established for accurately determining the design assurance coefficient. Based on the discussion of the connotation and interrelationships of related indicators such as the reliability prediction value，the specified value，the minimum acceptable value，and the upper/lower limits of the appraisal test，the selection method and basis for the design assurance coefficients are given for two types of products which their lives are based on Weibull distribution and exponential distribution. Based on this， the upper and lower limit constraints of reliability improvement cost and reliability index are considered，and a general basis is given for the value of design assurance coefficient. The design assurance coefficient selection method and value table proposed in this paper provide theoretical basis and guidance for the determination of reliability prediction index requirements from the perspective of reliability qualification test risk control.

Bayesian Compression and Reconstruction for Rotating Mechanical Vibration Signal Based on Laplace Prior and Sparse BlockCorrelation

MA Yunfei， BAI Huajun， WEN Liang， GUO Chiming， JIA Xisheng

2021, 42(12):  2762-2770.  doi:10.3969/j.issn.1000-1093.2021.12.024

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For the difficult compression and reconstruction of mechanical vibration signal caused by high sampling frequency，an improved Bayesian compressive sensing algorithm is proposed by combining Laplace prior model with periodic sparse block of vibration signal for monitoring the equipment condition in real-time through wireless transmission. A Laplace distribution-based Bayesian priori model is proposed， which has stronger sparse promotion effect compared to Gaussian priori model. The vibration signal period is calculated according to the rotational speed and sampling frequency of mechanical equipment for dividing the signal periodically.The original signal expectation is estimated iteratively by fast correlation vector machine based on the feature of that multiple sparse blocks share the same hyperparameters.A two-stage parallel gearbox is selected as the research object. The compression and reconstruction simulations were carried out. It is found that the proposed method can effectively improve the reconstruction effect of mechanical vibration signals using the same sparse basis.

Operational Task Hierarchical Decomposition

DU Weiwei， CHEN Xiaowei

2021, 42(12):  2771-2782.  doi:10.3969/j.issn.1000-1093.2021.12.025

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Operational task decomposition is a key step for the military operation planning in computer-aided decision-making. To this end，a multi-scheme task decomposition and selection framework is presented. A standard task description method is proposed to realize the quantitative operational task description based on 5W theory. A task decomposition model is established according to task scenario and domain knowledge，which formulates the task decomposition as a multi-constraint optimization problem and alleviates the problem complexity caused by various influential factors and constraints. A hierarchical task decomposition method is presented to generate the multiple solutions and further finalize an optimized solution，which overcomes the unavailability of sufficient task decomposition and optimization means.The proposed method is validated based on a specific battle task decomposition，and the simulated results demonstrate the effectiveness and practicability of the proposed method，achieving over 90% optimum rate.