Table of Content

30 March 2018, Volume 39 Issue 3

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Contents

2018, 39(3):  0. 

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Paper

Event-triggered Cubature Kalman Filtering Algorithm and Its Application in the Detection Network for Fire Control

LIANG Yuan， SHENG An-dong， WU Zhao-bin， ZHANG Jiao， QI Guo-qing， LI Yin-ya

2018, 39(3):  417-427.  doi:10.3969/j.issn.1000-1093.2018.03.001

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An event-triggered mechanism based on dual-criterion is designed to reduce the amount of data transfer between each detection unit and the data fusion center in a sensor network. The proposed event-triggered mechanism has been utilized to schedule the data transfer between each detection unit and the data fusion center. And a nonlinear fusion estimator based on the aforementioned event-triggered mechanism and the square-root cubature Kalman filter is proposed to obtain better estimation performance than those of existing event-triggered fusion estimation algorithms. The simulated results and experimental results show that the proposed event-triggered fusion estimator can reduce the data transfer amount compared with the fusion estimator based on periodic transmission mechanism and offer better estimation performance than those of existing event-triggered fusion estimators. Key

Research on Completion Ratios of Scavenging in Scavenging Sub-phases of Opposed-piston Two-stroke Diesel Engine

LIU Yu-hang, ZHANG Fu-jun, MU Lian-hao, GAO Hong-li, WANG Su-fei

2018, 39(3):  428-435.  doi:10.3969/j.issn.1000-1093.2018.03.002

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The influences of the free exhaust, discharge and additional scavenging phases of opposed-piston two-stroke (OP2S) diesel engine on the scavenging process are studied. To understand the completion of different scavenging phases in the whole scavenging process is very significant in investigating the OP2S's scavenging process and the influences of scavenging parameters on scavenging process. A 1-D simulation model is established for an OP2S diesel engine, and the accuracy of the proposed model is validated. The completed proportions of different scavenging phases in whole scavenging process are studied from the quality change of carbon dioxide in cylinder. The results illustrate that the completed proportions of free exhaust, discharge and additional scavenging phases are 64.42%, 35.57% and 0.01%, respectively, under the simulation conditions of 1200 r/min, 0.013 MPa pressure difference and 0.18 MPa back exhaust pressure. If the engine speed increases, the free exhaust period decreases and the discharge period increases. The influencing effect of scavenging difference is similar with that of engine speed. The influence of exhaust pressure on the completed proportions of different scavenging periods is not significant but the carbon dioxide mass in cylinder varies significantly when exhaust pressure changes. Key

Performance Optimization of Heavy-duty Diesel Engine in Plateau Environment

TAN Pi-qiang, WANG De-yuan, WANG Cheng-guan, LI Yuan, LOU Di-ming, LI Yun-guang, LIU Sheng, YANG Zhen-huan

2018, 39(3):  436-443.  doi:10.3969/j.issn.1000-1093.2018.03.003

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The performances of different fuel-air-chamber matching schemes at different altitudes are optimized for a heavy-duty diesel engine. The results show that, with the increase in altitude, the actual operating conditions of diesel engine are shifted from low speed and low load to high speed and high load. The five schemes are presented, such as Scheme A (swirl ratio of 2.2, 10 × 0.32 mm injector, and compression ratio of 13.3), Scheme B (swirl ratio of 2.2, 10 × 0.32 mm injector, and compression ratio of 14.1), Scheme C (swirl ratio of 1.5, injector 10 × 0.32 mm, and compression ratio of 13.3), Scheme D (swirl ratio of 1.5, 10 × 0.32 mm injector, and compression ratio of 14.1), and Scheme E (swirl ratio of 1.5, 10 × 0.30 mm injector, and compression ratio of 14.1). Simulated and experimental results show that the fuel-air-chamber matching condition of diesel engine in plateau environment can be improved by appropriately increasing the compression ratio, reducing the swirl ratio and selecting the appropriate nozzle diameter. The difference between the internal and external equivalent ratios of the best scheme is smaller. The fuel-air-chamber optimization of the best scheme is optimal, and the power, economy and emission performance of diesel engine are improved. Key

Influence of Camber Angle on Stiffness and Grounding Characteristics of Non-pneumatic Mechanical Elastic Wheel

ZHAO You-qun, DU Xian-bin, LIN Fen, WANG Qiang, FU Hong-xun

2018, 39(3):  444-450.  doi:10.3969/j.issn.1000-1093.2018.03.004

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The vertical stiffness and grounding characteristics of a non-pneumatic mechanical elastic wheel under the conditions of different camber angle were studied to improve the vehicle driving safety. In considering the laminated structure of flexible tire body, a three-dimensional finite element model (FEM) of mechanical elastic wheel was established, which includes the incompressibility of rubber material, large deformation and contact nonlinearity. Static loading tests were conducted to validate the accuracy and reliability of the FEM. The simulated results of the influence of camber angle on vertical stiffness, contact patch and pressure distribution are compared with experimental results and discussed in detail. The results show that the vertical stiffness decreases with the increase in camber angle; the pressure is mainly concentrated in the shoulder of flexible tire body; and the uniformity of the pressure distribution becomes worse as the camber angle increases. The research provides a theoretical reference for the study on the camber performance, the uneven wear of tread and the structure optimization. Key

Research on Contact Characteristics of Armature and Rail in Augmented Electromagnetic Railgun

WANG Zhen-chun， BAO Zhi-yong， CAO Hai-yao， LIU Fu-cai， ZHAN Zai-ji， WANG Da-zheng

2018, 39(3):  451-456.  doi:10.3969/j.issn.1000-1093.2018.03.005

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In order to explore the contact characteristics of armature and rail in augmented electromagnetic railgun, the muzzle voltage, rail current, armature velocity and displacement are obtained by actual launching test. Taking the mechanical structure parameters of launcher into account, a mathematical model among contact resistance, muzzle voltage, rail current, armature speed and displacement is established based on the analysis of the motion process of armature in the bore. The change law of contact resistance under the condition of different mutual inductance coefficients is analyzed. The change curve of contact resistance is compared with the 3D model of the test track and the damage image of rail after the actual launching test, respectively. The comparative results show that the ablation and friction damage of rail show several typical characteristics, such as burning, sliding and abrasion, due to the changes of armature displacement and contact resistance. Key

Crack Fault Diagnosis of Gun Automatic Mechanism Based on Multifractal Features

REN Hai-feng, PAN Hong-xia

2018, 39(3):  457-462.  doi:10.3969/j.issn.1000-1093.2018.03.006

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In order to make better use of vibration signals to diagnose the crack faults of gun automatic mechanism, a fault diagnosis method based on multifractal features of vibration signals is proposed. The proposed method uses Wavelet Leader to estimate the multifractal spectrum of vibration signals. 6 feature quantities are used to describe the morphological features of multifractal spectrum,and the dimensionality reduction of multifractal spectrum is realized. A classifier based on Mahalanobis distance is used to classify different crack faults. This method is applied to diagnose the crack faults of locking mechanism in a 12.7 mm antiaircraft machine gun, and the diagnostic accuracy is up to 82.5%, which verifies the feasibility of applying the multifractal features of vibration signals to the crack fault diagnosis of gun automatic mechanism. Key

New Approach for Evaluating the Stability Period of Propellant Based on Near-infrared Spectroscopy

ZHOU Jing, DING Li, ZHANG Jun-lin, AN Jing, ZHU Yan-long, LIANG Yi

2018, 39(3):  463-467.  doi:10.3969/j.issn.1000-1093.2018.03.007

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A new approach to evaluate the stability period of propellant is presented to solve the problems of poor safety, fussy operation and time-consuming of the existing methods for evaluating the stability of propellants. The propellant samples with different stabilizer contents were prepared by thermal accelerated aging test, and the kinetic equation of propellant aging was studied. A quantitative model for the determination of stabilizer content in propellant is established using near-infrared spectroscopy and chemometrics algorithm. The best quantitative model is obtained by analyzing and optimizing the proposed model. Applied results show that the determination coefficient (R²) of the model is 0.999 6, and the maximum predicted error is no larger than 0.04%. It proves that the proposed model can be used for the nondestructive, rapid and real-time evaluation of the stability period of propellant. Key

Effect of Slight Density Change on Short-duration Shock Initiation Characteristics of TATB-based Polymer Bonded Explosive

TAN Kai-yuan, HAN Yong, CAO Luo-xia, WEN Shang-gang, WANG Xiang, YE Hui

2018, 39(3):  468-473.  doi:10.3969/j.issn.1000-1093.2018.03.008

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The aim of this study is to examine the effect of slight density change on the short-duration shock initiation characteristics of triaminotrinitrobenzene (TATB)-based polymer bonded explosive (PBX). The PBX samples with different density are initiated by high speed Mylar flyer plates which are accelerated by an electric gun, and the displacement interferometer system for any reflector (DISAR) is used to determine the velocities of flyer plates. And then the shock initiation thresholds (50% probability of initiation) for the samples are calculated. The results show that a slight change in density leads to a substantial change of the shock initiation threshold: as the densities of the samples change from 1.885 g/cm³ to 1.905 g/cm³, the shock-initiation threshold increases from 5.38 GPa²·μs to 8.20 GPa²·μs correspondingly, and the samples become less sensitive to the shock. This indicates that the effect of slight density change on the shock initiation behavior of PBXs cannot be ignored, and suggests that it is necessary to keep the explosive density uniform (at least on the percentile order of magnitude). Key

Cooperative Guidance of Multi-missile with Unsustainable Connected Communication Topology

YE Peng-peng, SHENG An-dong, ZHANG Jiao， WU Zhao-bin， QI Guo-qing， LI Yin-ya

2018, 39(3):  474-484.  doi:10.3969/j.issn.1000-1093.2018.03.009

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Multiple missiles in the cooperative guidance may communicate via a random network in virtue of packet loss and communication delay, resulting in an unsustainable connected or even interrupted communication topology. Hence, a distributed cooperative guidance strategy is proposed. Based on sampled data, a distributed linear consensus protocol is designed, and a deviation system is constructed, which can be stabilized such that all the coordination variables of missiles asymptotically achieve a common state. Multiple missiles disconnect to the communication network and are guided to a target independently when they approach the target. Theoretical analysis reveals that the proposed consensus protocol doesn’t make any requirements on the communication topology at any time, in other words, the communication topology may be disconnected or even be interrupted. Finally, two simulation examples with regard to cooperative guidance with unsustainable connected communication topology are given. The presented guidance strategy can be used to ensure the impact times of all the missiles being the same.

Finite-time H_∞ Tracking Control for Switched Morphing Aircraft

XIA Chuan, DONG Chao-yang, CHENG Hao-yu, WANG Qing, WANG Zhao-lei

2018, 39(3):  485-493.  doi:10.3969/j.issn.1000-1093.2018.03.010

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Considering the tracking control problem in the process of configuration transformation of morphing aircraft, a morfing aircraft model is developed based on switched linear parameter-varying (LPV) theory. In order to suppress the influence of cotroller switching and uncertainties and ensure that the closed-loop system is finite-time bounded with the given performance index, a finite-time tracking controller design method with switching is developed based on mode-dependent average dwell time (MDADT) method and multiple Lyapunov function method. The finite-time robust stability of the system is analyzed. The sufficient existing conditions of controller can be obtained by solving the linear matrix inequality (LMI). Simulated results show that the aircraft system is able to track command signal accurately by using the proposed method, and is robust to controller switching and uncertainties, thus reducing the conservativeness of controller design. Key

Design of Robust Backstepping Controller for Bank-to-turn of Low-speed Cruise Vehicles

WANG Na， SUN Rui-sheng， YANG Zhi-gang， FU Jian

2018, 39(3):  494-501.  doi:10.3969/j.issn.1000-1093.2018.03.011

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In view of coupling and uncertain characteristics of nonlinear control system for bank-to-turn(BTT) low-speed cruise vehicles, a robust backstepping controller is designed to follow the control command. The dynamic model of cruise vehicles is transformed into a block form which is suitable for backstepping algorithm. The block form is assumed to be composed of a nominal model and uncertain terms. The uncertain terms are derived and described by using the Leibniz rule in infinitesimal calculus. On this basis, the basic form of the control law is derived by exploiting backstepping algorithm. The modification of robust function, i.e., a new symbolic function, is conducted to compensate the unmatched uncertainties. Lyapunov redesign technique is introduced to control the matched uncertainties. Comparative simulation cases are implemented to validate the improved robust backstepping algorithm. The results indicate that the presented control response can quickly track the commands of angle of attack, sideslip angle and bank angle, which shows the strong robustness of the system. Key

Analysis of Error Characteristics of Laser Gyro SINS Based on Analytic Alignment Method

CHEN He, ZHANG Zhi-li, ZHOU Zhao-fa, LIU Peng-peng, ZHAO Xiao-feng

2018, 39(3):  502-510.  doi:10.3969/j.issn.1000-1093.2018.03.012

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Error characteristics of initial alignment of laser gyro SINS are analyzed for selection of inertial sensors. Based on the incremental formula of analytic alignment method, the misalignment angle due to the measurement errors of inertial sensors is derived using the parameter perturbation technique, and its random characteristics are analyzed. The attitude angle errors caused by the alignment angle are worked out based on the relationship between attitude angle and attitude matrix. Finally, the theoretically analyzed results are verified through simulation and experiment. The studied results show that the means values of alignment errors depend on the constant errors of inertial sensors and the attitude of vehicle rather than alignment time, while the standard deviation of alignment errors is not only affected by the random walk errors of inertial sensors and the attitude of vehicle, but also is inversely proportional to the square root of alignment time.Key

A New Calculation Method of Quaternion Differential Equation for Attitude of Strapdown Inertial Navigation System

ZHOU Zhao-fa, HU Wen, ZHANG Zhi-li, XU Zi-hao, CHEN He

2018, 39(3):  511-518.  doi:10.3969/j.issn.1000-1093.2018.03.013

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A new calculation method of quaternion differential equation, which is called three-subsample quaternion algorithm, is presented to solve the problem of low calculation accuracy of traditional quaternion algorithm by using the calculation process of three-subsample rotation vector algorithm for reference. In the calculation process, the higher derivative of rotation quaternion is calculated on the basis of quaternion differential equation, the angular velocity of carrier is fitted by the parabola, the expression is given for angular increment, and then a model for calculating quaternion differential equation is established by means of the Taylor expansion of rotation quaternion. The simulated result indicates that the three-subsample quaternion algorithm is better than three-subsample rotation vector algorithm. Key

Research on Flow Field Structure of Slender Spinning Missile under Coupling of Conical and Spinning Motions

PENG Cheng， GUO Yang

2018, 39(3):  519-527.  doi:10.3969/j.issn.1000-1093.2018.03.014

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The aerodynamic characteristics of slender spinning missile with canard rudders under the coupling of conical and rotational motions are studied by using CFD numerical simulation and rigid moving grid technique. The aerodynamic coefficients of slender spinning missile are analyzed,and the changing curves of aerodynamic coefficients with spinning angle are given. The evolutionary trend of rudder-induced vortex is studied, and the tail flow fields at different times are compared. The result shows that the characteristics of conical and spinning motions are taken into account in the flow field structure of slender spinning missile, and these two kinds of motions not only interfere but also blend with each other. The evolution of vortices is more complex, and the aerodynamic curves are periodically and regularly oscillating. The destructiveness of vortex structure is aggravated with the increase in angle of attack, and the pressure around the fins is also changed. Key

Research on Aero Thermodynamics and Influencing Factors for HIFiRE-1

MAO Hong-xia， JIA Ju-hong， FU De-bin， JIANG Yi

2018, 39(3):  528-536.  doi:10.3969/j.issn.1000-1093.2018.03.015

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To investigate the aerodynamic heating and the shock wave-boundary layer interaction (SWBLI) for hypersonic vehicles with cylinder flare, three-dimensional (3D) numerical simulation of flow field around HIFiRE-1 is carried out based on the finite volume method and Reynolds average Navier-Stokes equations. The performance of code and the mesh independence are evaluated by using pressure and heat transfer data from ground test. Simulated results show that the flow conditions and vehicle configurations have effect on the flow states and heat transfer significantly. The increase or decrease in the Reynolds numbers brings about the rapid altering of heat transfer only. The variation of Mach number results in the changes of both the flow structure and the heat transfer. Expanding or narrowing the angle of the flare leads to the diversification of separation bubbles, as well as the heat flux. The reattachment of separated shock wave on the flare is influenced by enlarging or shortening the length of flare, then resulting in the fluctuation of heat transfer.Key

Novel Electronic Cluster-based Embryonics Array

LI Dan-yang, CAI Jin-yan, MENG Ya-feng, ZHU Sai

2018, 39(3):  537-552.  doi:10.3969/j.issn.1000-1093.2018.03.016

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Embryonics array is limited by the poor self-repairing ability, low resource utilization and high hardware resource consumption. In order to solve these problems, a novel kind of electronic cluster composed of inner switch, inner cells and control unit is proposed. Based on the cluster architecture, a gene shifting self-repairing method is proposed. In the simulation, the electronic cluster is configured as an accumulative adder, and the functions of the electronic cluster are verified. Hardware resource consumption of electronic cluster and the reliability of array are analyzed. Simulated and analyzed results show that the gene shifting self-repairing method can be used to repair the faults effectively, and the intermediate states of sequence circuit can be saved. And as the array size increases, the mean time to failures of the array based on electronic clusters is longer, and the hardware resource consumption is lower. Key

Emitter Signal Modulation Feature Recognition Based on Fisher Discrimination Dictionary Learning

WU Xiao-tian, WANG Xing， WANG Zhi-peng， ZHOU Yi-peng, CHEN You

2018, 39(3):  553-559.  doi:10.3969/j.issn.1000-1093.2018.03.017

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The limited forms of atoms in analytical dictionary lead to sub-optimal matching of atoms and complex emitter signal, resulting in low recognition rate of signal modulation. A dictionary learning method based on Fisher discrimination criterion is proposed to improve the recognition efficiency. The time-frequency transformation of emitter signal is made. The feature vectors are extracted from time-frequency graph using image processing method, which are added class labels. In the dictionary training, the Fisher criterion with small within-class scatter and big between-class scatter is introduced, by which the dictionary not only represents signal more suitably, but also owns better classification performance. The simulated result proves that, compared to analytical dictionary and non-supervision dictionary, the proposed method can obtain a better recognition rate, especially under low SNR. For the atom number N_s=20, Fisher discrimination dictionary can achieve a pretty good balance in recognition rate and calculation amount. Key

Fluid-solid Coupling Numerical Simulation on Vertical Water Entry of Projectile at Low Subsonic Speed

HU Ming-yong， ZHANG Zhi-hong， LIU Ju-bin， MENG Qing-chang

2018, 39(3):  560-568.  doi:10.3969/j.issn.1000-1093.2018.03.018

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A fluid-solid coupling calculation model of vertical water-entry of projectile at low subsonic speed is established based on multi-material arbitrary Lagrangian-Eulerian-Lagrangian coupling method. Compressibility effects in fluid mechanics are considered in the proposed model. The multi-medium coupling numerical calculation technology of cavity-fluid-projectile is used to simulate the vertical water entry of projectile. The curves of underwater depth and projectile velocity, and the times of cavity surface closure and cavity deep closure at different velocities of water entry are obtained. The evolutionary process of cavity and the phenomenon during high-speed water entry of projectile are stimulated. The acceleration, stress and strain responses of projectile are obtained, and the influence laws of velocity of water entry on the times of cavity surface closure and cavity deep closure are also obtained. The numerical results show good agreement with the calculated results of empirical formulas. The calculated results show that the proposed numerical method is reliable. Key

Research on Systemic Modeling and Simulation Platform of Warship Vulnerability

WANG Kang-bo， HOU Yue， PU Jin-yun， CHAI Zhuo-ye

2018, 39(3):  569-576.  doi:10.3969/j.issn.1000-1093.2018.03.019

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Current vulnerability modeling and calculation are only for partial system and equipment, rather than the logical relationships among mission capability and various warship's systems. An interactive simulation platform is lacking for the simulation of warship vulnerability. For realizing the improvement of vulnerability assessment from system to mission level, the systemic logical modeling and simulation algorithm of warship vulnerability are developed. In addition, an universal simulation platform for user-defined logical relation and design scheme is designed and developed. Application tests indicate that the research result can be used to analyze warship vulnerability for different design schemes, direct warship vulnerability optimization design effectively, and is used for improving warship survivability design. Key

Effect of Inclination Angle of Cutter Shaft on Machining Deformation of Thin-walled Blade

HUANG Tao, LIU Zhi-bing, WANG Xi-bin, PAN Lin, YAN Zheng-hu, LENG Shou-yang

2018, 39(3):  577-583.  doi:10.3969/j.issn.1000-1093.2018.03.020

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Machining deformation is the main factor to determine the machining quality and efficiency. For the machining deformation of thin-walled blade, the inclination angle of cutter in milling is analyzed. A deformation model of cutter-workpiece cutting force system is proposed, which can be used to predict the deformation of thin-walled blade. The appropriate tool paths and processing technics are planned to control the machining deformation of thin-walled blade. Contrast experiments of machining aluminium alloy 7075 at different inclination angles are carried out, and the cutting force, residual stress and machining deformation are measured and analyzed. The result shows that the actual deformation law of thin-walled blade is consistent with the predicted results, and the optimal inclination angle of cutter is 15°-20°. Key

Dynamic Strain Aging of 316L Stainless Steel under Circular Loading

JIN Dan， ZHANG Jiang-yu， LI Jiang-hua

2018, 39(3):  584-589.  doi:10.3969/j.issn.1000-1093.2018.03.021

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Low cycle fatigue tests in different strain ranges were conducted for 316L stainless steel at 873 K under circular loading. The effects of number of cycles, strain range, and loaded state on the dynamic strain aging (DSA) are discussed. DSA is more obvious in the initial several cycles, followed by weak serrated yielding. The DSA is evident before failure in larger strain range, which can be attributed to the formation of the Snoek solute atom atmospheres. The results of the effect of strain range on DSA show that the stress drop value and the serrated yielding degree increase with the increase in strain range. The increase in serrated number in larger strain range is due to the dislocation multiplication. The thermomechanical analysis shows that the serrated yielding phenomenon is more significant due to the hold-up of vacancy diffusivity when the compression changes to unloading. Scanning electron microscope（SEM）results show that the material failures are attributed to fatigue, DSA, and oxidation in two strain ranges. Key

Hierarchical Response Surface Modeling and Reliability Analysis of Complex Mechanical System Based on Composite Function

WANG Qian， ZHANG Jian-guo， PENG Wen-sheng， YANG Le-chang

2018, 39(3):  590-597.  doi:10.3969/j.issn.1000-1093.2018.03.022

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A hierarchical response surface method (HRSM) based on composite functions is proposed for the reliability assessment of complex mechanical systems. According to the structure and composition of the system and the physical relationship, the proposed method is used to establish the basic variables and the response functions of the parts as the middle-level nodes. For the system performance affected by some basic variables and the above middle-level response functions, HRSM is used to construct the response surface model of the limit state as the top-level node. The first-order second-moment method and Monte Carlo method are used for solving the system failure probability. Taking a two-axis-position mechanism as an example, HRSM is successfully applied to model and analyze the motion accuracy reliability on the basis of error propagation. The maximum failure probability of HRSM is almost the same as the output of Monte Carlo simulation, and does not fluctuate with the sample coefficient, which fully verifies the validity and robustness of HRSM.Key

Dynamic Modeling and Characteristics Investigation of Jet Deflector Servo Valve

WANG Shu-ming, ZUO Zhe-qing, YAN Hao, XU Ling-ling, DONG Li-jing

2018, 39(3):  598-607.  doi:10.3969/j.issn.1000-1093.2018.03.023

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The analytical mathematical models for torque motor, prestage and power stage hydraulic amplifiers are established to investigate the relationship between the internal structure of jet deflector hydraulic amplifier and the dynamic characteristics of servo valve. A simplified calculation method of prestage hydraulic force is presented by analyzing the complex flow of the receiving ports. On this basis, a complete model of jet deflector servo valve is constructed, and the mechanisms of action of jet orifice width, jet disk thickness and nozzle width on the dynamic characteristics of servo valve are presented. For the dynamic drift of the whole valve, the nonlinearity of prestage flow gain and its influence on the dynamic characteristics are presented. The simulated and experimental results show that the proposed model can effectively reproduce the actual dynamic characteristics of servo valve, and the analytical modeling method is reasonable, which provides a theoretical basis for the design and optimization of jet deflector servo valve. Key

Simulation and Analysis on the Ground Separation Test of a Flexible Fairing and Its Flying Mode Prediction

CHENG Xiu-yan, FAN Bo-chao, RONG Ji-li, ZHANG Tao, XIANG Da-lin

2018, 39(3):  608-617.  doi:10.3969/j.issn.1000-1093.2018.03.024

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It is difficult to conduct the ground separation test of large-scale rocket fairings under vacuum condition. To predict the fairing separation during extra-atmospheric flight, the established finite element (FE) model should be corrected by using the ground separation test data. The ground separation test of a large-scale flexible fairing is simulated by the coupled Eulerian-Lagrangian method. The motion characteristics and breathing deformation data of fairing separating under air resistance are obtained and agree well with the test data, which verifies the correctness of the model and the method. The separation of rocket fairing during extra-atmosphere flight is simulated with the same FE model, and the effects of air resistance and axial overload on fairing separation and deformation characteristics are analyzed. The results show that the air resistance attenuates the velocity and breathing vibration frequency of rocket fairing, but increases the amplitude of the breathing motion; the amplitude of breathing motion increases with the increasing in axial overload, meanwhile, the breathing motion of fairing is related to the first-order vibration mode. Key

Research Notes

Analysis of Force Load on the Rail in Rapid-fire Mode of Electromagnetic Rail Launcher

ZHANG Yong-sheng, LU Jun-yong, TAN Sai, LI Bai, WU Xiao-kang, LOU Jian-yong

2018, 39(3):  618-624.  doi:10.3969/j.issn.1000-1093.2018.03.025

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Acquisition of force load distribution of rail in electromagnetic rail launcher is the precondition for analyzing the material failure mechanism and rapid firing application boundary. A field coupling model of electromagnetic force, temperature and stress is established to obtain the temporal and spatial distribution characteristics of force load on the rail under the action of electromagnetic force, temperature stress and preload. Analysis results show that the electromagnetic force load on the rail is nearly always a peak value in the flat period of pulse current; the thermal energy is mainly distributed in the initial period of armature motion, and the thermal energy density reaches to the maximum value in armature position at the end of the pulse current rising; rails bear the most severe force load in armature's position at the end of the pulse current rising; spray cooling can effectively reduce the temperature stress in the rail; optimal pretightening load is to keep the rails not separating from the insulation supports during dynamic launching. Key