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Table of Content

    29 November 2019, Volume 40 Issue 11
    Contents
    Contents
    2019, 40(11):  0. 
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    Paper
    Experimental Study of Underwater Explosion Performance of RDX-based Aluminized Explosive
    RONG Jili, ZHAO Zitong, FENG Zhiwei, WEI Huiyang, PAN Hao, XU Hongtao, XIN Pengfei
    2019, 40(11):  2177-2183.  doi:10.3969/j.issn.1000-1093.2019.11.001
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    To investigate the underwater explosion performance of RDX-based aluminized explosive, the underwater explosion experiments for RDX-based aluminized explosives with different charge masses and aluminum contents were carried out in outdoor pools. The process of generation, expansion and contraction of underwater explosion bubbles was observed through the high-speed camera placed in water, and the pressure history of shock wave was measured by a pressure sensor. Under the experimental conditions, the secondary reaction process of powdered aluminum for RDX-based aluminized explosive during underwater explosion was captured by the high-speed camera firstly, which indicates that secondary reaction process of powdered aluminum is in the order of milliseconds. According to the experimental data, the pressure in flow field and the bubble pulsation were analyzed. The experimental results indicate that the secondary reaction of powdered aluminium occurs in both the initial stage of bubble expansion and the end of bubble contraction. The secondary reaction of powdered aluminium significantly increases the pulsation ability of bubble. The secondary reaction of powdered aluminium has little effect on the peak value of shock wave and great influence on the peak value of bubble pulsation. The secondary reaction of powdered aluminium obviously affects the energy structure distribution of underwater explosion. Key

    Optimal Control of Posture Adjustment for Articulated Suspension Vehicle
    HAN Ziyong, YUAN Shihua, PEI Weiya, LI Xueyuan, ZHOU Junjie
    2019, 40(11):  2184-2194.  doi:10.3969/j.issn.1000-1093.2019.11.002
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    The motion control method mainly based on kinematics equations cannot accurately describe the relationship between the driving joint torque and the vehicle body trajectory and attitude because of the many degrees of freedom of motion and complex posture adjustment of articulated suspension vehicle. A general dynamic optimal control framework suitable for the overall posture adjustment of the leg-wheeled robot vehicle is established based on the centroidal dynamics model and the quadratic programming method. In the controller, the wheel-ground reaction force is directly controlled by using the quadratic programming method based on dynamic model and the inverse kinematics control. The above control method is used to simulate the posture adjustment of roll, pitch and composite attitude of articulated suspension vehicle and its application on bumpy road. The results show that the dynamic optimal control method of dynamic posture adjustment can meet the requirements of the real-time performance and control precision. Key
    Wavelet Analysis and Numerical Simulation of Jet Noise induced by a Large Caliber Small Arms
    ZHAO Xinyi, ZHOU Kedong, HE Lei, LU Ye, LI Junsong
    2019, 40(11):  2195-2203.  doi:10.3969/j.issn.1000-1093.2019.11.003
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    The aerodynamic characteristics of muzzle noise are studied based on experimental and numerical research on jet noise induced by complex flows discharging from a large caliber small arms with a muzzle brake. The measured noise data are analyzed to distinguish the muzzle shock wave from muzzle impulse noise by the wavelet transform method. The muzzle noise is numerically simulated by a CFD-CAA hybrid method. The feasibility of the proposed method is proven by comparing the simulated results with the test results. In addition, the distribution of shock wave in muzzle brake and the directivity of muzzle noise field are analyzed based on the numerical simulation. The results indicate that the muzzle noise has a wide spectrum with high sound energy and complex components. It is found that the muzzle brake causes the lateral diversion of flow field around the muzzle, thus affecting the distribution of muzzle flow noise. Key
    Research on a Novel Magnetic Sensitive Layer-counting Method for Penetration
    ZHANG Xiongxing, ZOU Jinlong, WANG Wei, SU Siyou
    2019, 40(11):  2204-2211.  doi:10.3969/j.issn.1000-1093.2019.11.004
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    A magnetic sensitive penetrating layer counting method is proposed to solve the problem of signal sticking when the penetration fuze is penetrated at high speed. Magnetic steel and magnetic sensors are installed in the penetration fuze. When the warhead penetrates into the finite thick reinforced concrete target, the magnetic field strength in the fuze changes significantly with the change of the relative position of the target and the warhead, and can be used as a response signals of penetrated layers. The response signal of the penetrated layer is detected to count the layers by using the magnetic sensor. According to the proposed method, the penetrating warhead and reinforced concrete models were established by finite element method, and the penetration process was simulated. A magnetic sensitive simulation fuze was designed and fabricated. The reinforced concrete target was simulated by steel mesh, and the static semi-physical test was carried out to verify the feasibility of the magnetic susceptibility layer method. The proposed method has the advantages of being less susceptible to speed and vibration, and can realize the accurate metering when the penetrating warhead with large aspect ratio penetrates the multi-layer concrete target at high speed. Key
    Service Life Prediction of Solid Motor during Vertical Storage Based on Accelerated Aging and Actual Loadings
    WANG Xin, ZHAO Ruyan, LU Hongyi, LIU Lei, WU Peng
    2019, 40(11):  2212-2219.  doi:10.3969/j.issn.1000-1093.2019.11.005
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    The influences of accelerated aging and actual loadings are both considered in predicting the storage life of solid motor grain during vertical storage. The variation law of the extensibility of propellant was obtained by high temperature accelerated aging test. The variation of von Mises strain of grain dangerous point and the fatigue damage of grain under vibration were obtained by the finite element simulation of motor under two loadings of curing/static vertical storage/blast-off and curing/ dynamic vertical storage. Service life of motor was predicted according to the variation law of von Mises strain and extensibility with storage time. Test results show that the extensibility of propellant decreases with time; the creep effect appears in the grain under a long-term action of gravitational load, and the periodic stresses are generated at the points in the grain under actual loadings. The fatigue damage of grain storaged for half a year is 0.017 12. The storage time has a negative exponent relation with vertical storage frequency, and the allowable vertical storage is 15 times. Its storage life during vertical storage is between 8.24 and 11.75 years, and its storage life under horizontal storage is 17.81 years. Key
    Preparation of Ultrafine Lead Ferrocyanide/ammonium Perchlorate Composite Particles and Study of Their Thermal Decompositionand Anti-agglomeration Performance
    ZHANG Zhengjin, GUO Xiaode, LIU Jie, LIANG Li, LI Kuankuan, CHANG Zhipeng, XIA Liang, TIAN Shubao, HUANG Dongyan, YANG Xueqin
    2019, 40(11):  2220-2228.  doi:10.3969/j.issn.1000-1093.2019.11.006
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    In order to improve the decomposition performance and dispersibility of ammonium perchlorate (AP), the crude lead ferrocyanide (Pb2Fe(CN)6) was synthesized by using the coordination precipitation method, and the nanometer-scale particles were pulverized by using a vertical stirring ball mill. Ultrafine Pb2Fe(CN)6/AP composite particles were prepared by using direct grinding method, ultrasonic assisted method and solvent-nonsolvent method. The morphology, particle size, crystal structure and thermal decomposition performance of the prepared composite particles are characterized by using scanning electron microscope, dry laser granulometer, X-ray diffractometer, infrared spectrometer and differential scanning calorimetry. The morphology of composite particles synthesized by solvent-nonsolvent method is quasi-spherical, the particle size is about 8 μm, the dispersion is relatively uniform, and the coating effect is better. Compared with pure AP, the pyrolysis temperatures of the composite particles prepared by direct grinding method, the ultrasonic assisted method and the solvent non-solvent method are reduced from 446.3 ℃ to 390.4 ℃,391.2 ℃and 379.1 ℃, respectively. The activation energy of pyrolysis is reduced by 14.2%, and the rate constant k is increased by 28.6 times. The combination of AP and Pb2Fe(CN)6 can effectively prevent AP agglomeration, meanwhile, the apparent bulk density is increased by 6.16%,and the tap density is increased by 10.4%. Key
    Robust Multi-objective Linear Parameter-varying Control for Hypersonic Vehicle
    CAI Guangbin, ZHAO Yang, ZHANG Shengxiu, YANG Xiaogang
    2019, 40(11):  2229-2240.  doi:10.3969/j.issn.1000-1093.2019.11.007
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    A robust multi-objective linear parameter-varying (LPV) control method based on pole assignment in specified region is proposed for longitudinal flight control of air-breathing hypersonic vehicle with wave-rider configuration. A longitudinal nonlinear mechanism model of air-breathing hypersonic vehicle is presented, which is used for obtaining its rigid LPV model. A design method of LPV state feedback control system based on pole assignment in specified region is proposed. The robust stability, disturbance rejection and tracking performance of the system are constrained to realize the multi-objective robust tracking control of LPV system by extended linear matrix inequality. The conservatism of this method is reduced by introducing the slack variables to decouple the Lyapunov function matrix and system matrix. The designed controller is applied to the nonlinear mechanism model of hypersonic vehicle for simulation proof. The simulated results show that the designed controller can be used to make the closed-loop feedback control system effectively track the change of command signals, and the system has good dynamic performance and strong anti-interference ability. Key
    A Vision Aided MEMS-SINS/GPS Ultra-tight Coupled Navigation System Suitable for High Dynamic and Strong Interference Environment
    LI Qunsheng, ZHAO Yan, WANG Jinda
    2019, 40(11):  2241-2249.  doi:10.3969/j.issn.1000-1093.2019.11.008
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    MEMS-SINS/GPS ultra-tight integrated navigation system has poor anti-jamming ability in high dynamic and harsh GPS environment. A vision aided MEMS-SINS/GPS ultra-tight coupled navigation system suitable for high dynamic and strong interference environment is proposed. The observability of the platform's misalignment angle is improved by introducing the attitude information provided by binocular vision into the MEMS-SINS/GPS ultra-tight coupled navigation system. The state equation and measurement equation of the system are derived, and a fuzzy control method is proposed to integrate the navigation results of two sub-filters. The feasibility of the system scheme design is verified through digital simulation. When the GPS signal results in decreased tracking precision under strong noise and multipath interference, the vision aided MEMS-SINS/GPS ultra-tight coupled navigation system can effectively reduce the navigation error. The system position and velocity errors can be kept within 5.0 m and 0.5 m/s, respectively, which effectively solves the navigation problem of low altitude aircrafts when the GPS signal is occluded or disturbed. Key
    Research on Dynamic Response of Pre-cracked Target Plate Subjected to Underwater Shock Wave
    WEI Huiyang, RONG Jili, WEI Zhenqian, XIANG Dalin, HE Xuan, ZHAO Zitong
    2019, 40(11):  2250-2258.  doi:10.3969/j.issn.1000-1093.2019.11.009
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    The ship structure is inevitable to be scratched, grooved or damaged in the processes of manufacturing and use, which may reduce the damage-resistant capability of ship structure to some extend. An equivalent underwater explosion impact loading device was used for the impact experiments on the pre-cracked target plate, and the deformation of target plate was recorded by using high-speed camera. The dynamic response mechanism of the pre-cracked plate under underwater impact load was studied through experiment and ABAQUS simulations, and the “three-stage” dynamic response result was acquired. The results show that the dynamic responses of target plates which have pre-cracks with different shapes are different in the final failure stage. The target plates tend to release all the energy with fewest cracks. The crack parameters are studied. The displacement of pre-cracked target plate has approximately linear relationship with the loading impulse. With the increase in the crack depth or length, the residual impact resistance of target plate decreases.Key
    Interior Ballistic Modeling and Test of a Push-pull Cylinder Type Torpedo Launcher
    XU Qinchao, PAN Haibing, LIAN Yongqing, LI Chunlai, LI Zongji
    2019, 40(11):  2259-2265.  doi:10.3969/j.issn.1000-1093.2019.11.010
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    A design scheme of push-pull cylinder type torpedo launcher for warship is proposed to solve the problems about long launch preparation time and poor support capability of ship-launched torpedo. Simulink and Adams co-simulation method is used to establish a dynamic model of high pressure air launching process of the launcher for simulation analysis. The simulated results were verified by the scaled prototype experiments. The simulated and experimental results show that, when the gas pressure in cylinder is 25 MPa, the peak pressure of push-pull cylinder is 9.3 MPa, the maximum contact force between the parts in the launcher is 66.6 kN, the muzzle velocity of torpedo is 14.7 m/s, the maximum acceleration is 236 m/s2, and the time of launching is 0.14 s. Key
    Experimental Investigation on Hydrodynamic Characteristics of Supercavitating Vehicle during Its Motion
    SHI Suguo, WANG Yadong, YANG Xiaoguang, LIU Lehua
    2019, 40(11):  2266-2271.  doi:10.3969/j.issn.1000-1093.2019.11.011
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    The free-running process of supercavitating vehicle is experimentally studied to investigate the hydrodynamic characteristics of supercavitating vehicle during its motion. The evolutionary process of supercavitation in a pool is observed by using a high-speed video camera, the surface pressure of the vehicle is measured by using the pressure sensors, and the hydrodynamic characteristics of supercavitating vehicle are measured by using a built-in measuring device. The experimental results show that the axial force coefficient is not a steady value which is fluctuated around an average value of about 0.1, the average axial force coefficient increases with running time, and the normal force coefficient fluctuates 0 due to the linear movement. The normal force coefficient fluctuates periodically with time, and the fluctuation cycle is about 0.055 s. It is found that the pose of supercavitating vehicle varies due to the gravity and other impact factors, the one rear side of the vehicle impacts the cavity, a peak pressure occurs, which causes the normal force to be increasing, and then the rear of the vehicle moves to the other side due to the restoring moments. A phenomenon of the trailing cycle oscillation on the vehicle impacting to the cavity occurs, and the periodic evolution of flow field leads to the periodic change in the normal force coefficient. Key
    Experimental Research on the Effect of Anisotropic Properties of Composite Material on Bubble Shape
    CHANG Qing, ZHANG Mindi, MA Xiaojian, HUANG Biao, HUANG Guohao
    2019, 40(11):  2272-2282.  doi:10.3969/j.issn.1000-1093.2019.11.012
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    In order to study the effect of anistropic properties of composite material on bubble shape, the shapes of bubbles near the carbon fiber composite material boundaries and the deformation of the carbon fiber composite material boundaries were recorded and observed by using high-speed camera. The shapes of bubbles near the composite material boundaries with different ply angles are studied. The changing processes of bubble shape and the deformation modes of the composite material boundaries at the same initial distance of bubble from the boundary are compared for the carbon fiber composite plates with the ply angles of 0°,90° and 0°+90°. The results show that the high-speed jet and shock wave generated by the collapse of bubble near the boundaries are the important factors for the damage of boundaries, and the different ply angles of carbon fiber composite material lead to different deformation modes, which has an important impact on the shapes of bubbles. Key
    Sound Speed Profile Inversion Based on Mode Signal and Polynomial Fitting
    LIU Fuchen, JI Tuo, ZHANG Qiaoli
    2019, 40(11):  2283-2295.  doi:10.3969/j.issn.1000-1093.2019.11.013
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    A sound speed profile inversion method based on mode signal and polynomial fitting is proposed for the limitation of using the empirical orthogonal function to represent the sound speed profile in unknown environment. A concept of mode signal and the distribution characteristics of deep sea are given. It is proven through theoretical analysis and simulation that the low-order polynomial fitting can be used for presenting the sound speed profile in seabed.The five-order polynomial fitting can be used for accurately presenting the sound speed profile in 2 000 m-depth sea water. And in the inversion process, the copy mode signal vector is obtained by polynomial fitting of different parameters, and the mode signal is obtained from the test data by using the pulse acoustic signal, of which the parameters are optimized by genetic algorithm. The inversion performances of vertical array, single hydrophone and non-SRBR signal are simulated and analyzed by taking typical Munk profile as an example. It is concluded that the higher the order of polynomial is, the better the fitting effect of sound speed profile is. When a certain error is allowed, the lower order can be used for fitting the sound speed profile. The simulated results show that the performance of sound speed profile inversion using a single hydrophone is close to that of the vertical array, and the inversion performance under the condition of unknown seabed parameters can be improved by using the non-SRBR mode signal inversion. And finally, the performance of the proposed method is verified by using the pulse signal received by the single hydrophone in 4 000 m-depth sea water (distance: 180 km, and receiving and transmitting depth: 100 m). The results show that the inversion error of sound speed profile is less than 0.2 m/s. Key
    A Digital Pattern Design Method Based on Equipment Three-dimensional Model
    CAI Yunxiang, SHI Lei, TIAN Zhenxi
    2019, 40(11):  2296-2303.  doi:10.3969/j.issn.1000-1093.2019.11.014
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    Digital pattern design is a key to achieve camouflage effect. Pattern design for automatic painting operation is the development trend and research hotspots. A three-dimensional quadrilateral mesh model of military equipment is constructed by using the object modeling method.The five-sided unfold digital camouflage pattern of the minimum enclosing rectangular body from target is obtained by using the camouflage generation method based on fractal Brownian model, the transformation between two-dimensional and three-dimensional camouflage patterns is realized by using the texture mapping method based on the minimum normal angle, and the pattern optimization and modification are completed by using the artificial interactive function module based on OpenGL and MFC. The simulated and painting experimental results show that the three-dimensional digital camouflage pattern conforms to the background characteristics and meets the input requirements of automatic painting operation. Key
    Research on Dynamic Compression Properties of TiB2-B4C Composite
    GAO Yubo, QIN Guohua, ZHANG Wei, YI Chenhong, DENG Yongjun
    2019, 40(11):  2304-2310.  doi:10.3969/j.issn.1000-1093.2019.11.015
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    In order to study the dynamic mechanical properties of TiB2-B4C composite and the effect of additive TiB2 on the mechanical properties, a series of static/dynamic compression experiments and plate impact experiments were designed to evaluate the dynamic compression property of the composite at different strain rates. Experimental results show that the TiB2-B4C composite is a brittle material as ceramic. The stress-strain relations of the composite show a typical linear characteristic. The Hugoniot elastic limit of the composite is increased from 14.98 to 16.91 GPa with the increass in loading strain rate. When the loading rate is lower than 103 s-1, the dynamic compression strength of TiB2-B4C composite is higher than those of the pure B4C and pure TiB2 ceramic, and it has a positive strain rate sensitivity under one-dimensional stress wave loading. The increase in compression strength of the composite benefits from the improvement of the microstructure. The strain rate sensitivity is mainly controlled by the additive TiB2 which serves as a strengthening and toughening agent. However, when the loading rate is higher than 104 s-1, the Hugoniot elastic limit of TiB2-B4C composite is close to that of the matrix B4C, and is little affected by the additive TiB2. Key
    Research on Control Method of Nitrogen Content and Porosity in Hybrid Welding Joint of High Nitrogen Steel
    CUI Bo, ZHANG Hong, LIU Shuangyu, LIU Fengde
    2019, 40(11):  2311-2318.  doi:10.3969/j.issn.1000-1093.2019.11.016
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    The laser-arc hybrid welding test of high nitrogen steel was carried out to solve the porosity and nitrogen loss of high nitrogen steel during welding. The effects of shielding gas composition, welding wire composition and ultrasonic vibration on the porosity and nitrogen content of welded joint were investigated. The results show that, when the shielding gas is Ar+N2, the nitrogen content of welded point increases with the proportion of nitrogen in the shielding gas, and the porosity decreases first and then increases. When 2% O2 is added to Ar+N2, the nitrogen content and porosity increase obviously. With the increase in the proportion of nitrogen, the nitrogen content in welded joint increases, but the porosity changes irregularly. With the increase in nitrogen content in the welding wire, the nitrogen content of welded joint increases first and then decreases, and the porosity decreases first and then increases. With the increase in ultrasonic power, the nitrogen content of welded joint decreases slightly, and the porosity decreases first and then increases. Appropriate shielding gas and welding wire composition can be used to improve the nitrogen content of welded joint, and inhibit the formation of weld porosity. The porosity is suppressed in the best effect when the ultrasonic power is 180 W. Key
    Design of BSST-SMT-based Weaponry Testability Verification Test Scheme
    WANG Kang, SHI Xianjun, QIN Liang, NIE Xinhua, LONG Yufeng
    2019, 40(11):  2319-2328.  doi:10.3969/j.issn.1000-1093.2019.11.017
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    The current sequential probability ratio test method leads to the uncontrollable sample size of testability verification, and the sequential mesh test method can make the determined sample size be still large without using the prior information. A method for determining the sample size of testability verification is proposed, which is based on Bayes small sample theory and sequential mesh test. According to the prior distribution of testability indicators and the related parameter constraint values, the parameter space of indicators is divided based on the sequential mesh test method, and the Bayes factor and its threshold calculation method are given.Once the insertion position of a checkpoint is determined, the maximum sample size required for testability verification could be given. At the same time, a censoring strategy of sequential mesh test based on Bayesian small sample theory was designed, in which the consumer’s and producer’s risks are considered. The proposed method was validated by an example, and compared with classical testability verification method, sequential probability ratio test method, traditional sequential mesh test method and sequential posterior odds test method. The results show that the censored sample size and average sample size determined by the proposed method are better than those of other methods, and the consumer’s and producer’s risks can be effectively reduced. Key
    Internal Defect Detection of Metal Three-dimensional Multi-layer Lattice Structure Based on Faster R-CNN
    ZHANG Yuyan, LI Yongbao, WEN Yintang, ZHANG Zhiwei
    2019, 40(11):  2329-2335.  doi:10.3969/j.issn.1000-1093.2019.11.018
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    The cracks, incomplete fusion, faults and other defects may exist in the metal three-dimensional lattice structure prepared by additive manufacturing technology, which lead to the decline of structure-functional performance of metal lattice structure. A Faster R-CNN-based internal defect detection method is proposed for metal three-dimensional multi-layer lattice structure. A feature extraction network is designed on the basis of the Faster R-CNN network architecture. It makes the defects in the obtained gray-scale image and the CT scanning image be detected and positioned quickly, accurately and intelligently. The experimental results show that the recognition rate of the typical internal defects of metal three-dimensional multi-layer lattice structure sample is 99.5%. Key
    Path Tracking for Intelligent Vehicles Based on Frenet Coordinates and Delayed Control
    WANG Wei, CHEN Huiyan, MA Jianhao, LIU Kai, GONG Jianwei
    2019, 40(11):  2336-2351.  doi:10.3969/j.issn.1000-1093.2019.11.019
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    The path tracking problem for intelligent vehicle with delayed control inputs is studied. The cramping angle is expressed as a series structure model with pure lag and first-order inertial delay, and a steering control delay model is established using Matlab/Simulink. The collected steering control data of an actual vehicle is analyzed for parameter identification of the proposed delay model.The equivalent delay performance in simulation environment based on V-REP and ROS is implemented. The model predictive control (MPC)-based path tracking controllers without or with considering delay control are designed based on Frenet coordinates, and the kinematic and dynamics models, which can also be used for marching vehicle formation. A curvature-variant reference paths collected at 5, 10 and 20 m/s are set in V-REP simulation environment. Three curvature-variant reference paths are presented. For the MPC path tracking controller without delay modeling, the average tracking error is less than 0.22 m for a vehicle platform without control delay. The MPC controllers with and without delay modeling are tested to compare their tracking performances for the vehicle system with long control delay. Simulated results indicate that the average and maximum tracking errors of MPC controller with delay modeling are 83.7% and 74.4% less than those of MPC controller without delay modeling when they are used on a vehicle with delayed control inputs. The kinematics-based MPC controller performs better at low speed, whereas the dynamics-based MPC controller performs better at high speed. Only dynamics-based MPC controller with delay modeling completed the whole test safely at 20 m/s on the vehicle with delayed control. Key
    Design and Kinematic Modeling of Cable-driven 4-SPS/U Rigid-flexible Parallel Trunk Joint Mechanism with Spring
    PAN Yitao, CHEN Yuan, WANG Lidong, LU Hao
    2019, 40(11):  2352-2362.  doi:10.3969/j.issn.1000-1093.2019.11.020
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    A two-degrees-of-freedom cable-driven 4-SPS/U rigid-flexible parallel trunk joint mechanism is proposed by using the construction method of over-constrained parallel mechanism, which has the advantages of wire-driven mechanism and rigid parallel mechanism. A mobile hexapod robot which is composed by the trunk joint mechanisms is established. The trunk joint mechanism can enable the hexapod mobile robot to flexibly realize various motion modes, such as walking, underwater propulsion, climbing and rolling. The degree of freedom of cable-driven 4SPS/U rigid-flexible parallel trunk joint mechanism is calculated by using screw theory. An inverse kinematics model of the mechanism is constructed by using the closed vector method and the decoupling method for eigenstructure assignment. The velocity and acceleration models of the mechanism are derived, and the singularity of the mechanism is analyzed by Jacobian matrix. The theoretically simulated datum of displacement, velocity and acceleration of trunk joint mechanism are calculated through theoretical numerical examples, and the theoretically simulated datum are compared with the simulated results of Adams software, which verifies the correctness of the theoretical model. Key
    Guiding Signal Iterative Learning Control Method with Parameter Learning
    HUANG Jing, ZHENG Huayi, LI Hong, LI Guoxiu, QIU Cheng
    2019, 40(11):  2363-2369.  doi:10.3969/j.issn.1000-1093.2019.11.021
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    An iterative learning control method for guiding signals is proposed to solve the control divergence in using the traditional iterative learning control method in the loading system of air rudder load simulator. The proposed method is improved for improving its intelligence and adaptability and having a faster convergence speed. The control parameters are learned while the iterative learning of the pilot signal is performed, so the proposed control method has dual learning capabilities. Under the actual situation that the initial state of each iteration cycle of the system is inconsistent, the convergence characteristics of the control method are mathematically analyzed and proven, and the sufficient conditions for convergence are finally given. The improved control method is applied to the simulation model of air rudder load simulator loading system for simulation and verification. Compared with the traditional iterative learning control method and the control method without parameter learning, the proposed iterative learning control method with parameter learning has faster convergence speed and better control effect. Key
    Fault Feature Enhancement Method for Rolling Bearing Fault Diagnosis Based on Wavelet Packet Energy Spectrum and Principal Component Analysis
    GUO Weichao, ZHAO Huaishan, LI Cheng, LI Yan, TANG Aofei
    2019, 40(11):  2370-2377.  doi:10.3969/j.issn.1000-1093.2019.11.022
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    The acquired vibration signal is usually unstable once rolling bearing damage occurs, which results in inaccurately detecting the fault features of rolling bearing by time-domain or frequency-domain analysis. A fault diagnosis method which uses the wavelet packet energy spectrum and principal component analysis (PCA) to diagnose the faults of rolling bearing is presented. The wavelet packet decomposition algorithm is used to decompose and refine the vibration signals in different frequency ranges. The energy spectra in the focused frequency ranges are calculated after the vibration signal is decomposed by wavelet packet decomposition. PCA is performed to decrease the dimension of the energy spectrum and reduce the noise interference, thus enhancing the extracted fault feature without the noise interference. And then the different fault types of rolling bearing are classified by two types of clustering algorithms, i.e., hierarchical clustering analysis (HCA) and fuzzy c-means (FCM). The results show that the fault types can be correctly identified by both cluster algorithms. The example verification indicates that the proposed method can be used to effectively extract the useful fault features in the vibration signal and identify the fault types exactly. This provides a feasible method for diagnosing a machine with some similar faults. Key
    Research Notes
    Experimental Investigation on the Damage Characteristics of Typical Body Armor by the After-effect Fragments of Bullet
    YAN Wenmin, WANG Guanghua, JIN Yongxi, WANG Shu, XU Xiao, TIAN Ye
    2019, 40(11):  2378-2384.  doi:10.3969/j.issn.1000-1093.2019.11.023
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    In order to explore the killing ability of the after-effect fragments of bullet, an after-effect experimental was carried out based on an armor-piercing bullet with tungsten alloy penetrator, 10 mm-thick homogeneous steel plate and a typical polyethylene composite body armor. The mass distribution and dispersion law of after-effect fragments and the penetration effects of after-effect fragments penetrating into body armor at different velocities are analyzed. The results show that the mass distribution range of after-effect fragments is larger; the dispersion radius of after-effect fragments at 1.4 m from the protective steel plate is 21.3 cm; the failure mode of body armor is dominated by shear failure, and at the same time, it is accompanied by the melting and burning damages. The boundary between penetration holes is torn due to the boundary intersection, and a large open gap is formed to develop tear propagation and exacerbate the damage. Key