Table of Content

31 March 2017, Volume 38 Issue 3

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Contents

2017, 38(3):  0. 

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Paper

Numerical Simulation and Mechanism Analysis of EFP’s Fracture in Forming Process

DING Li, JIANG Jian-wei, MEN Jian-bing, WANG Shu-you

2017, 38(3):  417-423.  doi:10.3969/j.issn.1000-1093.2017.03.001

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In order to study the fracture mechanism of explosively-formed projectile （EFP） in axial direction, the forming and fracturing processes of OFHC EFP with typical charge structure are simulated by using LS-DYNA software, in which Johnson-Cook failure model and adaptive algorithm are introduced. Hemispherical liners with different extrinsic curvatures are simulated, and the simulated results of fracture are validated through experiment. The stress wave theory is used to analyze the fracture mechanism of long rod EFP, and confirm the critical velocity gradient. The results show that the fracture phenomenon of EFP can be well simulated by using LS-DYNA software based on Johnson-Cook failure model and adaptive algorithm. For certain EFP charge structure with hemispherical liner, a critical liner curvature which makes the long rod EFP fracture in forming process exists. The critical value of 60~83 m/s calculated from stress wave theory agrees well with the critical velocity gradient (76 m/s) of EFP fracture. The theoretical analysis method can be used to confirm the critical velocity gradient of long rod EFP fracture. Key

Research on Lubrication Mechanism of Retaining Spherical Pair of Variable Displacement Axial Piston Pump

WANG Tao, MAO Ming, TANG Shou-sheng, GAI Jiang-tao, JI Hai

2017, 38(3):  424-432.  doi:10.3969/j.issn.1000-1093.2017.03.002

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Retaining spherical pair is widely used in variable displacement axial piston pump with the feature of complex spatial relative motions. According to the kinematic relation and geometric feature of retaining spherical pair, a physical model based on the cylinder feature is proposed to study the process of oil lubrication between ball guide and retaining plate. And the lubricating film within retaining spherical pair is numerically investigated based on the modified Jakobsson-Floberg-Olsson (JFO) cavitation algorithm to consider the influence of shearing velocity. The relations among the distributions of shearing velocity, clearance shape, cavitation index and pressure under the conditions of three different tilting angles of swash plate are discussed. The research results show that the pressure distribution has the characteristics of double peak and double valley, which is depended on the hydrodynamic effect resulted from the clearance shape and the hydrostrictive effect due to shearing velocity. The hydrostrictive effect is positively correlated with the tilting angle of swash plate which plays an important role in eliminating the amount of load support. Key

Research on the Reliability Growth of Closed Blots for Automobile Diesel Engine Body

WANG Zeng-quan, WANG Zheng, LAN Yin-zai, CHEN Ze-zhong, HOU Xin-rong

2017, 38(3):  433-439.  doi:10.3969/j.issn.1000-1093.2017.03.003

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For the reliability of closed blots for automobile diesel engine body, the failure mode and its failure mechanism of closed blot is studied. A test equipment of closed blots is designed. The vibration experiment is done for closed blot for diesel engine body, and the fault recovery of closed blot with the fatigue mode is completed. The measures for improving the reliability of closed blots are studied. The improved closed blot is assembled on the diesel engine body, and its reliability is validated through application. The result shows that the failure mode of closed blot for diesel engine body is a vibration fatigue, and the resonance is the reason for the failure of closed blot. After the measures for improving the reliability are adopted, the vibration frequency of closed blot is improved obviously, and it can avoid the resonance effectively. Key

Applied Research on the Life Prolonged and Restored Materials in Gun Tube Weapon

WEI Hua-zhen, GAO Shou-zhen, LI Da-yong, MA Kai-bao, WANG Xiao-li, LUO Chang-hong, QI Feng-jie, XU Xiao-yuan

2017, 38(3):  440-446.  doi:10.3969/j.issn.1000-1093.2017.03.004

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In order to study the effect of life prolonged and restored materials on gun barrel, the life prolonged and restored materials are studied. The morphology, phase structure, ablative resistance, corrosion resistance, friction and wear properties of the life prolonged and restored materials are characterized by scanning electron microscope (SEM),transmission electron microscope (TEM),energy disperse spectroscope(EDS),ablation test machine and friction wear test machine. The firing tests of gun and smoothbore cannon made of the life prolonged and restored materials were completed. The results show that a layer of coating material is attached to the metal surface after restoring. The barrel surface is filled with pits and cracks, and the surface is smoothed. The restored material can significantly reduce the barrel temperature, which will not affect the accuracy of the gun . For the small caliber gun, the restored material can not only increase the initial velocity, but also reduce the wear of gun barrel.Key

Experimental Research on Eccentric Initiation MEFP Warhead

LI Peng, YUAN Bao-hui, SUN Xing-yun, LI Gang, LI Ji-zhen

2017, 38(3):  447-453.  doi:10.3969/j.issn.1000-1093.2017.03.005

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A new asymmetrical initiation multiple explosively formed penetrator（MEFP） warhead is designed to improve the damage efficiency of MEFP warhead. Two principle prototypes with central initiation and eccentric initiation were made for static detonation experiment. The forming and dispersing processes of MEFP with hemispherical liners under different ways of initiation are analyzed through numerical simulation. The numerically simulated results illustrate that the length-diameter ratio of EFP is larger, and the EFP is more dense in two-point eccentric initiation mode. The static detonation experimental results of MEFP warheads in two different initiation modes are compared. The comparative results show that the ecentric initiation can is used to improve the velocity, density distribution and penetration power of EFP. The two-point eccentric initiation can effectively improve the comprehensive damage effectiveness of MEFP warhead. Key

Target Track Prediction Method Based on Grey Residual Modification Theory

DI Yi， GU Xiao-hui， LONG Fei

2017, 38(3):  454-459.  doi:10.3969/j.issn.1000-1093.2017.03.006

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Two grey residual modification models are proposed for the track prediction precision of brainpower antitank (BAT) submunition based on grey theory, which are grey residual modification model (GRMM) and grey Verhulst residual modification model (GVRMM). A grey model of target track prediction is established, and the limitations of this model are analyzed. GRMM and GVRMM are used to correct the grey forecast model on line, respectively. It shows that the proposed method based on real-time residual modification mechanism can be used to reduce the prediction error effectively, and GVRMM has better efficiency in improving track prediction precision. Key

Study of Design and Performance of Micro Initiation Train

XIE Rui-zhen, LI Li-ming, LIU Lan, REN Xiao-ming, XUE Yan

2017, 38(3):  460-465.  doi:10.3969/j.issn.1000-1093.2017.03.007

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A micro initiation train is designed to meet the requirement of MEMS fuze. The micro initiation train integrates all the functions of a conventional mechanical safety and arm （S&A）fire system, and integrates them within 3 cm³. The architecture of the micro initiation train consists of bottom, intermediary and top layers. The bottom layer contributes to the mechanical arming and detonation transfer function. The intermediary layer is Si-based initiator and micro-pyrotechnical actuator. The top layer is the electronics and power supply. The test results show that the safe, arming and firing functions of micro initiation train are achieved, and the output pressure is about 10.85 GPa. Key

Interior Ballistics Modeling and Optimization of One-side Ejection Device with Two-step Cylinder

YAO Lin, MA Da-wei, MA Wu-ning, REN Jie, ZHONG Jian-lin, WANG Ze-lin

2017, 38(3):  466-475.  doi:10.3969/j.issn.1000-1093.2017.03.008

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A kind of one-side ejection device with two-step cylinder is proposed to increase the effective thrust travel of missile pneumatic launching system. The real gas state equation, Peng-Robinson equation, is used as theoretical basis. The mathematical expressions of pneumatic interior ballistics model are deduced on the basis of 'P-R' state equation for the two-step cylinder. The interior ballistics equation is solved by using Simulink software, and the one-side launching ejection is built by means of ADAMS. The co-simulation model of device is achieved. The results show that the pressure of first-order lower-chamber rises first and then falls. It can be seen from the calculated result that both the thermodynamic parameters and the missile acceleration obviously fluctuate in the process of cylinder changing, but their influences on missile speed and displacement are very small. To reduce the equipment volume, the air source volume is selected as the objective function. The air source volume optimized by genetic algorithm is decreased by 64.5%, thus improving greatly the mobility of launcher. Key

Numerical Investigation on the Effect of NOx on Ignition Delay of Mathane

DENG Tong-ye, XU Qing-yao, SHEN Shuang-yan

2017, 38(3):  476-482.  doi:10.3969/j.issn.1000-1093.2017.03.009

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Ignition delay time is an important parameter in the design of scramjet engine. Three reactions are added to the GRI-Mech 3.0 mechanism to investigate the effect of NOx on ignition delay of methane. The ignition process of CH₄/O₂/NOx/Ar mixtures is numerically calculated using the CHEMKIN chemical kinetics software, and the numerical calculation data were compared with the experimental data in Ref.\[6\]. It is found that the GRI-Mech 3.0 mechanism could well simulate the ignition process of methane with NOx when the reactions R326,R327 and R328 are added. Numerically calculated result shows that the addition of NO₂, to a lesser extent of N₂O, leads to the reduction in the ignition delay time of CH₄/O₂/Ar mixtures, which is in good agreement with the experimental result of Mathieu, and the ignition delay time of CH₄/O₂/NOx/Ar mixtures under the oxygen poor condition (fuel-air equivalence ratio of 0.5) is shorter than that under the fuel rich condition (fuel-air equivalence ratio of 2.0). Key

Research on Command Correction Midcourse Guidance Law with Zero Effort Handover in Near Space

ZHANG Hao-qiang， TANG Sheng-jing， GUO Jie， LIU Xiao， XU Qian

2017, 38(3):  483-493.  doi:10.3969/j.issn.1000-1093.2017.03.010

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A space-based cruise phase defense strategy is proposed for near-space hypersonic vehicles. Considering the properties of near-space defense, a valid zero effort interception handover (ZEH) region and its performance criterions are presented by analyzing the handover region, which connects the midcourse and terminal guidance phases. Based on the model predictive static programming (MPSP) theory and the terminal constraints of midcourse phase, a close-formed solution is derived as the command correction guidance law. The proposed guidance law is used for simulation. The simulated results show that a small velocity-ratio condition for terminal engagement is satisfied by ZEH. The proposed method can improve the computational efficiency significantly, and also meet the requirement of ZEH constraint. A large number of Monte Carlo simulations show the robustness of the guidance law against initial disturbances. Key

Test of Parasitic Loop Quality of Strapdown Seeker

BAI Rui, XIA Qun-li, DU Xiao, LU Tian-yu

2017, 38(3):  494-500.  doi:10.3969/j.issn.1000-1093.2017.03.011

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In order to analyze the effect of disturbance rejection rate parasitic loop on strapdown imaging seeker, a model of disturbance rejection rate parasitic loop of strap-down seeker is established. Nondimensionalized method is used to obtain dimensionless characteristic equation, the effects of the guidance parameter and the scale factors and dynamic errors of gyro and seeker on the stability region of parasitical loop as well as the effect of parasitic loop on the dynamics of guidance system are studied by using Routh criteria, and the nonlinear models are established. Monte Carlo method is used to study the change of miss distance with scale factor and dynamics errors. A semi-physical open loop test system is established to appraise the quality of disturbance rejection rate parasitic loop. The research result shows that the scale error and the mismatch between the rate gyro and the detector are the main factors that cause the DRE parasitic loop. The numerical value of the error and mismatch decides whether the parasitic loop is positive or negative feedback. The stable domain of positive feedback is far less than that of negative feedback, while the miss distance is more sensitive to guidance system deviation. To improve the guidance precision, five axis turntable semi-physical simulation test system was used to test and calibrate the damping characteristics of parasitic loop, by which the parasitic effect can be eliminated by eliminating the scale error and the mismatch, or at least be reduced by constructing a negative feedback parasitic loop. Key

Prescribed Performance Fine Attitude Control for Aeroelastic Hypersonic Vehicle

ZHAO He-wei, YANG Xiu-xia, SHEN Ru-song, HU Yun-an

2017, 38(3):  501-511.  doi:10.3969/j.issn.1000-1093.2017.03.012

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A fine attitude controller for hypersonic cruise vehicle is designed by combining the backstepping technique, prescribed performance control and neural network. The influence of elastic deformation of hypersonic vehicle on angle of attack is taken into consideration. The effect of aeroelasticity on hypersonic vehicle is described by using the induced angle of attack. The index of fine attitude control is satisfied by the design of prescribed performance in consideration of aeroelasticity, and the transient performance of hypersonic vehicle is assured. The unknown terms of the induced angle-of-attack equations are approximated online by using the fully tuned dynamic neural networks, and the adaptive laws of weight, core and scope of influence of the neural networks are designed by Lyapunov theory. The robust term is induced to solve the approximate errors of the neural networks. A fine attitude controller with prescribed performance for hypersonic vehicle in considering the aeroelasticity is designed. The stability of system and all the signals in the closed-loop system bounded are proved by Lyapunov theory. The simulated results show that the controller can make the tracking errors satisfy the prescribed performance, and the fine attitude control can be implemented. Key

Space Dynamic Modelling and Analysis of Offshore HUS Flexible Parallel Platform

XIE Ke-feng, ZHANG He, LIU Shan-zeng, LI Hao-jie

2017, 38(3):  512-519.  doi:10.3969/j.issn.1000-1093.2017.03.013

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The space elastic dynamic modelling of parallel platform is created for the elastic deformation and the load pointing displacement error of support link due to the rapid stabilization and large load of offshore HUS flexible parallel platform. Space elastic link is modelled by modal function and space equal section beam element model. The link based on hook joint and ball joint has two degrees of freedom space movement. The transformation matrix of two degrees of freedom between space element coordinate and system coordinate is derived. The kinematic and dynamic constraints of platform are used to establish the space elastic dynamic equations of HUS flexible parallel platform. The elastic dynamic equations are discretely solved by Newmark method. The elastic dynamic response of platform and the maximum dynamic stress of support link are analyzed. And the dynamic test experiment is conducted. The results show that the maximum displacement of support point by elastic deformation is 2.45 mm, and the error of axis x is significantly greater than those of axes y and z. Experimental results are consistent with the simulated results, thereby validating the effectiveness of the numerical model. The influence of elastic deformation on load pointing accuracy is analyzed, and the maximum position error due to elastic angular displacement is 1.35 m. Key

Research on the Positioning of Underwater Vehicle Based on Convex Optimization

CAO Jun， ZHENG Cui-e， SUN Da-jun， ZHANG Dian-lun

2017, 38(3):  520-526.  doi:10.3969/j.issn.1000-1093.2017.03.014

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The localization method based on single beacon ranging is a new research direction of underwater acoustic positioning technology. A method based on convex optimization is proposed for the first time to solve the least square structure for the single beacon ranging and locating. An inequality constraint condition is added to the ranging equation with errors, and the ranging equation is reformulated as a constrained solution equation. The objective function and constraint condition are approximated by radiation, and the convex processing is carried out. The slack variable and penalty function are introduced to reduce the sensitivity of iteration initial value. Simulated results show that the difference of positioning results is in centimeter order of magnitude for different magnitudes of initial errors. The proposed algorithm can be iterated convergence to get high accuracy of the positioning results without reliable initial value. When the beacon is close the center distance of circular track, the positioning accuracy is higher. The effectiveness of the proposed algorithm is verified by experiments on the lake.Key

Research on Material Removal Model of Optical Elements Based on Fast Polishing Technology

LIN Tao, YANG Wei, WANG Jian

2017, 38(3):  527-533.  doi:10.3969/j.issn.1000-1093.2017.03.015

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In order to accurately control the material removal in polishing stage, and achieve the deterministic polishing processing of toptical element, the quantitative mean volume removed by a single particles per unit time and the number of the active particles on the wafer-pad interface are obtained from the force applied on an abrasive particle and the number of all particles on the wafer-pad contact area. An optical element fast polishing material removal model is established based on the analysis of fast polishing principle and fast polishing material removal mechanism. Research shows that, under the experimental conditions of different polishing liquids, polishing pads and optical elements, the theoretically predicted results of the material removal model are well coincident with the experimental results, and the error of material removal can be controlled within 9%. The proposed model is verified to be suitable for the optical element fast polishing technology, thus deterministically controling the fast polishing time and efficiency.Key

Microstructure and Plastic Instability of Mg-4.3Li-1.08Y-5.83Zn Alloy

SHA Gui-ying， YIN Miao， HAN En-hou ， XU Dao-kui， XU Yong-bo， YU Shuang

2017, 38(3):  534-539.  doi:10.3969/j.issn.1000-1093.2017.03.016

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Mg-4.3Li-1.08Y-5.83Zn deforming alloy is prepared using conventional casting and hot extrusion processing. The microstructure, deformation behavior and mechanical properties of the alloy are investigated by optical microscope, scanning electron microscope, energy density spectrum and X-ray diffraction analyses, and tensile tests. The results show that the quasi-crystalline phase I-Mg₃YZn₆, and the secondary phase W-Mg₃Y₂Zn₃ and Mg_0.97Zn_0.03 are generated in the microstructure of Mg-4.3Li-1.08Y-5.83Zn alloy, thus enhancing the yield strength and ultimate tensile strength significantly. The tensile tests at different strain rates show that the plastic instability occurs in the strain rate range from 1×10^-5 s^-1 to 1×10^-2 s^-1 and the yield and ultimate strengths of the alloy exhibit negative strain rate sensitivity with the increase in strain rate. A reasonable mechanism for this is attributed to the dynamic strain aging (DSA) occurring during tensile deformation. Key

Establishment of Thermo-metallurgical-mechanical Coupling Constitutive Model for Armour Steel and ItsApplication in Welding Numerical Simulation

SUN Yu-jie， CUI Qing-chun， HAN Xuan-xuan， SHI Chun-ming

2017, 38(3):  540-548.  doi:10.3969/j.issn.1000-1093.2017.03.017

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Solid-state phase transformation has significant effect on the evolution and magnitude of welding residual stress for armour steel during welding thermal cycle, while the current constitutive model can not take solid-state phase transformation into account. Based on heat transfer theory, solid-state phase transformation theory and continuum mechanics, a thermo-metallurgical-mechanical coupling constitutive model in which the effects of volumetric change, yield strength change and transformation induced plasticity(TRIP) on residual stresses due to solid-state phase transformation on welding residual stress are considered is established. The constitutive model is inserted into a general purpose implicit finite element program via user material subroutine UMAT. The change rules of temperature, microstructure and residual stresses are obtained for a butt welding of armour steel plates. The research results show that longitudinal residual stresses obtained from the coupling constitutive model are in good agreement with experimental results measured by X-ray diffraction perpendicular to weld centerline on the upper surface of the weldment. The correctness of developed computational method is confirmed, and TRIP has certain effects on the evolution of longitudinal residual stresses. For the magnitude of longitudinal residual stresses in the vicinity of weld zone, the fully-transformed region is less than partially-transformed region, and the partially-transformed region is less than untransformed region. Key

Research on Mechanical Properties of High-strength Steel Laser-arc Hybrid Welded Joints

YANG Zhen， ZHANG Ping， CAI Zhi-hai， QIN Hang

2017, 38(3):  549-554.  doi:10.3969/j.issn.1000-1093.2017.03.018

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6 kW fiber laser-MAG hybrid welding is used for 6 mm-thick 30CrNiMo high-strength steel plate. The microstructure and mechanical properties of the steel plate which were welded with ER50-6 and ER308 wires in the same welding process are studied. The result shows that the ER50-6 weld seam is an acicular martensite, and the ER308 weld seam is a coarse columnar austenite. The welded joints of diverse welding wires have significantly different hardness distributions. The low hardness distribution along the fusion line appears in the ER50-6 weld seam, and the low hardness of ER308 weld seam is concentrated in the lower part of the weld seam center. The corresponding tensile fracture positions are found in the fusion line and the weld seam center, respectively. The energy spectrum shows that the high content of Cr in ER308 weld seam is concentrated in the upper part of the weld seam center, which leads to the increase of hardenability and hardness, and sharp decline in toughness on this part, and finally leads to the weakness of the mechanical properties of the weld seam. The hybrid welding method and ER50-6 wire can be used to weld 6 mm-thick 30CrNiMo steel plate without distortion, and the weld strength is up to 1 197 MPa. Key

Improved Design and Experiment for Preparing Uniform Optical DLC Film by Large Area PLD

LU Yi-min, HUANG Guo-jun, GUO Yan-long, DING Fang-zheng, CHEN Xia, WEI Shang-fang, MI Chao-wei

2017, 38(3):  555-560.  doi:10.3969/j.issn.1000-1093.2017.03.019

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The former coating setup for uniform film is improved by considering the effect of the peripheral particles of plasma on the diamond-like carbon (DLC) film prepared by pulsed laser deposition (PLD). A shield with an aperture is inserted between the substrate and the target to remove the peripheral particles and only allow the centric particles pass the aperture. A corresponding module is added in the mathematical model for thickness distribution of film. The uniform diamond-like carbon film with 200 mm in diameter is prepared after simulation and optimization of model. The test results show that thickness variation of film is ±4.5%, and the thickness distribution characteristics are the same as the optimized results. Moreover, the nanohardness and infrared transmittance of film are apparently increased compared with those of the film prepared before improvement. Key

Research on Contact Fatigue Life Prediction of Thermally Sprayed Coating Based on Central Composite Design

MA Run-bo, DONG Li-hong, WANG Hai-dou, XING Zhi-guo

2017, 38(3):  561-567.  doi:10.3969/j.issn.1000-1093.2017.03.020

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The effect of service condition on contact fatigue life of supersonic plasma sprayed AT40 coating is studied by central composite design method. A multi-factor life prediction model with rotation speed, contact stress, and slip ratio is established by using response surface method based on the regression analysis principle, and the comprehension effects of the three factors on contact fatigue life are analyzed. The results show that the rolling contact fatigue life of AT40 coating has same life distribution under different service conditions. Slip ratio has the main effect on the life, and the contact stress has the secondary main effect on it,and the rotation speed has the minimum effect on it. The interactive effect between contact stress and slip ratio and the interactive effect between rotation speed and slip ratio both significantly influence the rolling contact fatigue life.The significance test results show that the response surface model can be used to characterize the relationship among the load conditions (rotation speed, contact stress, and slip ratio) and the rolling contact fatigue life of AT40 coating. Key

Optimal Condition-based Maintenance Decision-making Method of Multi-component System Based on Simulation

WANG Shao-hua, ZHANG Yao-hui, XU Long-yang, LIU Hong-xiang

2017, 38(3):  568-575.  doi:10.3969/j.issn.1000-1093.2017.03.021

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To promote the maintenance benefit by combined maintenance, for multi-component systems subjected to condition-based maintenance each component is supposed to endure independent gradual deterioration, and a stochastic deteriorate model is established. The exponential function is applied to set up the reliability functions taking condition parameters as variables. In consideration of imperfect maintenance and probability distribution of maintenance time, a Monte Carlo-based condition deteriorating simulation model of multi-component system is proposed. TA preventive maintenance threshold optimization model is constructed by taking the expected expenses per unit time as the optimization objective, and is verified by a case study. Key

Research on Miss Distance Test Based on Projectile Shock Wave and Its Inversion

GU Guo-hua, ZHANG Liang, WU Hai-bing, CUI Xun-xue, YU Bo

2017, 38(3):  576-584.  doi:10.3969/j.issn.1000-1093.2017.03.022

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Since the shock wave of supersonic projectile is difficult to be captured due to its complexity and susceptible interference, the miss distance test is a difficult problem. The testing scene of miss distance is described, the formation mechanism of shock wave is analyzed, and the parameter relations before and after shock wave forming are identified. The test model of miss distance and the linear and nonlinear interference models based on simplified shock wave environment are established. The time duration test principle is used for field experiment, and the cumulative effect of pressure of shock wave field is used for simulating inversion in order to verify the accuracy and effectiveness of test methods and engineering test. Key

Analysis of the Influencing Factors and Mechanism of Gas Draining Rate of Mobile Pipeline

JIANG Jun-ze, ZHANG Wei-ming， YONG Qi-wei, JIANG Ming

2017, 38(3):  585-592.  doi:10.3969/j.issn.1000-1093.2017.03.023

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In order to promote the emptying efficiency of mobile pipeline, a dynamic model of emptying is established, which is solved by the method of characteristics (MOC), and the velocity of spherical pig and the variation of pressure drop are obtained. The model was verified by experiments. The emptying rate is related to the critical length of pipeline, the gas flow rate and max pressure of compressor. If the length of pipeline is longer than its critical length, the gas flow rate plays a dominant role in the emptying rate, and a high-flow-rate compressor should be used. On the contrary, if the length of pipeline is shorter than its critical length, the gas pressure plays a dominant role, and a high-pressure compressor should be used. The critical length increases with the development of pipe length, while the critical length decreases with the development of gas flow rate and pressure. Hence, in order to promote the emptying efficiency, the critical length should be determined in the design, and then an appropriate compressor is chosen in terms of the overall length and critical length of pipeline or the length of emptying segment is partitioned according the compressor performance. Key

Research on Mechanical Fault Diagnosis Method Based on Variational Mode Decomposition

LI Zhi-nong, ZHU Ming

2017, 38(3):  593-599.  doi:10.3969/j.issn.1000-1093.2017.03.024

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Variational mode decomposition (VMD) is a new adaptive signal decomposition method. The idea of this method is that most of each mode is assumed to be tightly around a center frequency, the solving problem of mode bandwidth is converted into an optimization problem with the constrain conditions, and finally each modal is solved. VMD is introduced into the mechanical fault diagnosis, and a fault diagnosis method based on VMD is proposed. The proposed method is compared with the ensemble empirical mode decomposition (EEMD). The simulated result shows VMD method is superior to EEMD method, the intrinsic mode of signal can be effectively decomposed by the VMD method. Compared with the EEMD method, the proposed method has some distinct advantages, such as weak mode mixing phenomenon, high calculation efficiency and sufficient theory. The proposed method has been successfully applied to the rub-impact fault diagnosis of rotor system. The experimental results show that the proposed method is effective, and can effectively reveal the frequency structure in rubbing fault and discern the severity of rub-impact fault. Key

Research Notes

Research on Trajectory Prediction of Tracked Vehicles Based on Real Time Slip Estimation

XIONG Guang-ming， LU Hao， GUO Kong-hui， CHEN Hui-yan

2017, 38(3):  600-607.  doi:10.3969/j.issn.1000-1093.2017.03.025

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In order to realize the unmanned driving of tracked vehicle, its future motion trajectory within a period of time should be accurately predicted in trajectory planning. It is difficult to predict the future motion trajectory of vehicle due to the slippage between tracks and ground. A kinematics model based on the instantaneous steering center is developed by studying the interaction of track and ground. The relative pose of vehicle is a function of the slippage parameters, and the Jacobi matrix is difficult to solve. For this problem, the analytical solutions of Jacobi matrix are deduced by linearizoffing the functional differential equations. Slippage parameters are solved iteratively using Levenberg-Marquardt method according to the calculated and measured pose errors, and a set of input commands is given to predict the future motion trajectory within a period of time. The proposed method is used to update the slip parameters in real time without prior knowledge of terrain parameters. The real vehicle tests show that the position errors predicted using this method are reduced by more than 30% compared to the traditional trajectory prediction method. Key

Simulation and Optimization of Hydraulic Spool Valve Opening Process Based on Fluid-structure Interaction

ZHANG Sheng, WANG Qiang, HE Xiao-hui, GAO Ya-ming， WANG Xin-wen

2017, 38(3):  608-615.  doi:10.3969/j.issn.1000-1093.2017.03.026

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To improve the working capability of the spool during the opening process of hydraulic spool valve, a three-dimensional numerical model is established based on fluid-structure interaction theory and dynamic mesh technology, and the movement of spool under the action of driving force, spring force and flow force is simulated. The internal flow channel structure is improved in view of stress on spool. The objective functions of peak value of the maximum von Mises stress and flow force are set up through least squares fit and BP neural network, with four structural parameters of improved spool notches and convex being taken as the optimization object. The optimal values of four structure parameters of notches and convex platform are determined by using genetic algorithm. After optimization, the maximum von Mises stress is decreased by 22.0%, and the maximum flow force is decreased by 16.3%. Results show that the spool valve opening performance is obviously improved through the study of the optimization design of structural parameters of spool. Key

Adaptive Backstepping Sliding Mode Control of Passive Electro-hydraulic Force Servo System

LI Ge-qiang， GU Yong-sheng， LI Jian， LI Yue-song， GUO Bing-jing

2017, 38(3):  616-624.  doi:10.3969/j.issn.1000-1093.2017.03.027

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An adaptive backstepping sliding mode control strategy is proposed for passive electro-hydraulic force servo system, which contains inherent extra torque, nonlinearity of servo valve and time-varying parameters. A nonlinear state space equation of the system is established. A backstepping controller is designed based on the backstepping control theory and three-step recursive method. A nonlinear adaptive backstepping sliding mode controller is designed by using the sliding mode control method in the third step of the backstepping method, selecting a proper Lyapunov function and gving the adaptive law of uncertain parameters. The stability of the controller is tested by the Lyapunov stability theory. Both the simulated and test results show that the controller can effectively restrain the extra torque and possesses a strong robustness to both parameter perturbation and external disturbance. Key