Table of Content

30 June 2017, Volume 38 Issue 6

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Contents

2017, 38(6):  0. 

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Paper

Experiments and Numerical Simulation of Penetration Resistance of Steel Fiber Reinforced Concrete Target Backed by Steel Plate

FENG Jun， SUN Wei-wei， LIU Zhi-lin， WANG Xiao-ming

2017, 38(6):  1041-1051.  doi:10.3969/j.issn.1000-1093.2017.06.001

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In order to investigate the penetration resistance of steel fiber reinforced concrete (SFRC), 12.7 mm armor-piercing projectiles and long rod projectiles are used to penetrate a high strength fiber reinforced concrete backed by armor steel in high speed impact test. The penetration resistance of composite target is evaluated using protection factor according to the penetration depth of rear target. The lattice discrete particle model (LDPM) is introduced to model fiber reinforced concrete, and the elastic-plastic model and Johnson-Cook criterion are used to describe the projectile and armor steel. A numerical simulation model for penetration into concrete target is established. The feasibility of numerical model for simulation of penetration into fiber reinforced concrete is validated in terms of penetration depth and concrete target damage mode. The effects of internal gap and fiber content of composite target on penetration response in 3 typical penetration tests are simulated and analyzed. The numerical results show that, for the composite target without gap, the residual penetration depth of rear target can be effectively reduced, and the fiber reinforcement has no effect on the penetration depth but affects the concrete damage mode significantly. Further numerical analyses of fiber reinforced concrete target perforated by 12.7 mm armor-piercing projectiles indicate that the perforation velocity of projectile tends to converge if the diameter of cylindrical target is 30 times larger than projectile diameter, and the residual velocity approximates a linear relationship with impact velocity with the decrease in target thickness. Key

Research on Feeding Position of Armature in Railgun

WU Jin-guo, LI Hai-yuan, CHENG Nian-kai, LI Long, LI Bao-ming

2017, 38(6):  1052-1058.  doi:10.3969/j.issn.1000-1093.2017.06.002

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The armature of railgun relies on the electromagnetic thrust generated by pulse current to drive a projectile. The appropriate feeding position of armature helps to reduce the startup delay of armature, and reduce the redundant length of rails. The influence of feeding position of armature on electromagnetic thrust at startup position is studied. Theoretical analysis and numerical simulations of hybrid finite element and boundary element method show that the electromagnetic thrust on the armature gradually approaches a saturation, with the increase in length of the rails in circuit by changing the feeding position of armature. For a square caliber railgun, the armature acquires 99% electromagnetic thrust at the four caliber position. However, with the increase in the distance between rails, the feeding position should be far more from the breech for the armature to get the most thrust. The influence of breech buss-bar on the feeding position of armature is also analyzed. Compared with the lateral layout, the longitudinal layout is more conducive to shorten the feeding length of armature. Key

Analysis of In-bore Magnetic and Electric Fields in Electromagnetic Railgun under Dynamic Condition

YIN Qiang， ZHANG He， LI Hao-jie

2017, 38(6):  1059-1066.  doi:10.3969/j.issn.1000-1093.2017.06.003

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A numerical computation method is presented for the distribution characteristics of in-bore magnetic and electric fields in electromagnetic railgun under dynamic condition. The measured dynamic test data and the magnetic flux density at the breech end of the railgun are used to calculate the current densities in the armature and rails based on the magnetic diffusion equation and Ampere's law. The distribution characteristics of magnetic field and electric field of the investigated points along the central axes of the armature front end and back end are calculated. The results show that the peak magnetic flux densities of each investigated point decrease gradually with the increase in the distance from point to armature, the decay rate of the investigated point in front of the armature is much larger than that the point behind the armature. The electric field intensity of the investigated point at the muzzle is about several times of that in in-bore launching process. The proposed method can effectively calculate the induced electric field and magnetic field of railgun intelligent ammunition. The calculated results can be used in the electromagnetic shielding design of intelligent ammunition. Key

Research on the Rocket Consumption Reduction in Multiple Launch Rocket System Test

YU Cun-gui，LIANG Xiao-yang，ZHU Zhi-min

2017, 38(6):  1067-1074.  doi:10.3969/j.issn.1000-1093.2017.06.004

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The test method and simulation technology about the non-full loading firing dispersion for multiple launch rocket system (MLRS) are studied. A new method for reducing the rocket consumption in dispersion test of MLRS is presented. A parameterized simulation model of MLRS is established by use of the virtual-prototype-based dynamics simulation technology and multi-island genetic algorithm. The proposed model is integrated in the multidisciplinary optimization software ISIGHT. Based on the idea of equal initial disturbance deviation, a firing dispersion test method of a non-full loading MLRS is presented by using the multi island genetic algorithm as the optimization control strategy. The initial disturbance and firing dispersion are calculated via simulation in the case of full loading salvo and non-full loading continuous fire. The simulated results show that the two schemes have the same initial disturbance, and the system firing dispersion is satisfied with F test, which proves that the proposed firing dispersion test method with the non-full loading for MLRS is completely feasible. The rocket consumption in firing dispersion test of a MLRS can be decreased by 41.7% using the proposed non-full loading scheme. Key

Experimental Study of Distribution of Chaff Cloud Launched at High-speed

WANG Zheng-wei, WANG Hao, ZHANG Cheng, XIE Da-yong, JIN He-long

2017, 38(6):  1075-1081.  doi:10.3969/j.issn.1000-1093.2017.06.005

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In order to study the separation and dispersion of chaff cloud launched at high-speed, the chaffs were packed and launched by the adjustable speed rocket at different speeds, which utilize the throwing system structure of airborne dispenser. The chaffs were launched from a piston, separated and dispersed in the high speed airflow, and the detailed motion of chaff cloud was clearly recorded using several high speed cameras. After statistical analysis of the test results, the separation mechanism and dispersion parameter of chaff cloud are concluded. In comparison with the experimental results launched at different speeds, it is clearly concluded that the radial distribution of chaff cloud and the onset time increases with the increment of the velocity of carrier. However, the radial distribution of chaff cloud will not linearly increases with the increment of velocity of carrier.Key

Inertia Force Analysis for Fuzein Motion of a Dynamic Imbalance Rotating Projectile around Mass Center in Exterior Ballistics

DONG Sheng-peng， WANG Yu-shi， WEN Quan， ZHANG Zhi-biao， LU Feng-sheng， LIU jin-chun

2017, 38(6):  1082-1089.  doi:10.3969/j.issn.1000-1093.2017.06.006

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In order to provide an accurate mechanical environment of exterior ballistics for the safety and reliability design of fuze, a mathematical model of the motion of rotating projectile, which has dynamic unbalance angle and the axis of rotation of fuze being umparallel to the axis of projectile, around the center of mess in exterior ballistics is established based on the rigid body dynamics. The formulas of the axial, radial and tangential components of inertial force acting on fuze parts, which is caused by the motion of rotating projectile around the center of mess, are derived. The credibility of the theoretical analysis is verified by the simulation of ADAMS software. It can be known from force analysis that, when the center of axial moving parts of fuze and the centroid of bullet and axis are on the same plane, and the distance between the centroid of axial moving parts of fuze and the inertia principal axis of projectile is maximum, the axial force and radial inertia force of fuze are greatly increased compared with the traditional calculation results (the inertia force of 155 mm caliber projectile achieves several times). The fuze axial moving parts can not be prevented from moving forward under the action of axial force even if the radial and tangential forces are far greater than axial force in the condition of periodic fluctuation and large fluctuation amplitude. Key

Numerical Simulation and Analysis of 3D Flow Field for High Spinning Base Bleed Projectile

SHI Jin-guang, XIE Li-ping

2017, 38(6):  1090-1096.  doi:10.3969/j.issn.1000-1093.2017.06.007

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3D flow field of high spinning base bleed projectile is simulated using sliding mesh technology. Drag reduction characteristics of base bleed projectile at different spinning speed are studied, and the influence of rotating effect on drag reduction is also analyzed. The constraint relation between bleed parameter and spining speed under the condition of a given drag coefficient is discussed. Research results show that the drag coefficientl decreases when spinning speed increases for a same bleed parameter; the drag coefficient fisrt decreases and then increases when the bleed parameter increases at a same spinning speed; the drag reduction effect is better when the projectile spins at a high speed; the bleed parameter is an inverse relationship with the spinning speed for a given drag reduction; there is a best bleed parameter for the base bleed projectile with a certain spinning speed. These results offer reference for the research and engineering application of spinning base bleed projectile. Key

Simulation of Non-penetrating Damage of Head due to Bullet Impact to Helmet

CAI Zhi-hua, BAO Zheng, WANG Wei, MAO Zheng-yu

2017, 38(6):  1097-1105.  doi:10.3969/j.issn.1000-1093.2017.06.008

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New ballistic helmet can provide good protection for human head. The head injury caused by ballistic impact has not been well understood. There is a lack of relevant test procedure to evaluate the efficiency of a ballistic helmet. The head model is validated against several impact tests on cadavers, and the helmet model is validated against data from shooting tests. The mechanical response of the helmet to the human head under non-penetration of helmet is obtained through the simulation of the ballistic helmet with 386 m/s impact speed of bullet. The simulated results show that the deformation of the back of helmet can lead to skull fracture and high intracranial pressure. The influences of helmets with and without foam pad, as well as foam pad thickness on the head injury are compared and analyzed. The results show that, by using the helmet with foam pad, the intracranial pressure of head wearing a helmet with foam poad is reduced by 20.6%, and the deformation of helmet with foam poad is reduced by 10%. The skull was still under high-risk of skull fracture with 6 mm foam pad. With 12 mm foam pad, the intracranial pressure is decreased by 50%, and the deformation of the back of helmet is decreased by 10%. Key

Comparison of Effective Moduli of Polymer Bonded Explosive Predicted by Different Micromechanical Methods

WANG Jing-cheng, LUO Jing-run

2017, 38(6):  1106-1112.  doi:10.3969/j.issn.1000-1093.2017.06.009

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Polymer bonded explosives (PBXs) are different from conventional particle reinforced composites. PBXs possess over 85% of particle volume fraction, and the elastic modulus of particle can be three or four orders of magnitude higher than that of binder. Large deviations are observed on the effective moduli predicted by micromechanical methods. The predicted results of several micromechanical methods for the effective moduli of PBX are analyzed based on finite element method. Results indicate that both Voigt-Reuss bounds and Hashin-Shtrikman bounds give rather large estimated regions; when particle fraction is less than 10%, the differences among the effective moduli estimated by the different methods are not obvious since the particle interaction is negligible; when particle fraction exceeds 20%, the estimated results of three analytic methods are different from each other gradually due to the enhancement in particle interactions, and the estimated results of differential method agree with those of finite element method. For the particle fraction of 94.9%, Young’s modulus calculated by differential method is only 3.7% higher than the experimental value of PBX, while a huge error occurs using Mori-Tanaka method or self-consistent method. For the composites that possess high particle fraction and strong contrast in their ingredient properties, the differential method provides better estimates of effective modulus owing to its relatively favorable evaluation on particle interactions. Key

Study of the Double Longitudinal Mode Operation and the Self-biasing Phenomenon in Prism Laser Gyro

LIU Jian-ning, JIAO Ming-xing, MA Jia-jun, LIAN Tian-hong， REN Li-na

2017, 38(6):  1113-1119.  doi:10.3969/j.issn.1000-1093.2017.06.010

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When laser gyro with prisms operates in a specific double longitudinal modes and four frequency oscillation state. it can detect the normal component of the earth’s rotation angular velocity without offset frequency, the locking disappears, and the gyro is at the self-biasing state. A mode state control system of the prism ring laser cavity is designed based on the gas density and the refractive index controlling. On this basis, a self-biasing experimental platform is established. The characteristics of self-biasing are obtained from experiments: the two longitudinal modes oscillate in both sides of gain curve, the oscillation intensity ratio of the strength and weak modes is about 1.4 to 1.0. According to the laser semiclassical Lamb theory, a physical model of laser gyro operating in double longitudinal modes and self-biasing is established to derive that the main factor inducing the self-biasing effect is the frequency repulsion of the weak modes. This analytic study provides a reference for developing a new type of self-biasing laser gyro. Key

Effect of Bay Door on Separation Characteristics of Internal Store

YAN Pan-pan， ZHANG Qun-feng， JIN Ming

2017, 38(6):  1120-1130.  doi:10.3969/j.issn.1000-1093.2017.06.011

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To study the effects of bay door and door opening states on the separation characteristics of internal store, a simplified buried weapon bay-door-missile model is simulated using SST k-ω IDDES method, six degrees of freedom rigid body dynamics equations and overset mesh method under the condition of supersonic inflow. The separation trajectories of missile bodies in different cases were obtained. The results show that, in supersonic flow, shock intersection and shock shear layer reflection are present in the flow field. Considering that the bay door may make the wave structure changed, the trajectory of missile is also changed. The upward pitch angle of missile increases from 0.5° to 6.5°, the right yaw angle of missile increases from 0.3° to 2.5°, and the growth rate of falling speed decreases in later period. Change in door opening state has little impact on dropping displacement and pitch angle, but has greater impact on the yaw angle of missile. It shows that keeping the door away from missile as far as possible can effectively reduce the influence of the door, decrease the yaw angle and improve the separation quality. Key

Numerical Research on Blast-resistant Performance of Graded Corrugated Sandwich Plates under Air Blast Loading

LI Yong， CHENG Yuan-sheng， ZHANG Pan， LIU Jun

2017, 38(6):  1131-1139.  doi:10.3969/j.issn.1000-1093.2017.06.012

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The dynamic response of graded corrugated sandwich plates under air blast loading is investigated using Autodyn software. The effect of core arrangement on the response modes and blast-resistant performances of graded corrugated plates is analyzed. The graded corrugated sandwich plate with a certain core configuration is selected, which is filled with polyvinyl chloride foam. Furthermore, the influence of filling strategy on blast-resistant performances of sandwich structures is studied. The energy absorption property of sandwich structures is discussed. The results reveal that the sandwich plate, of which core web thickness gradually decreases from front face to back face, has the optimal blast-resistant performance. The deflection of bottom face sheet of sandwich plate is minimal, in which the first core layer was filled with foam. As polyvinyl chloride foam is filled into one of the layers of the sandwich plate from front face to back face, the energy absorption proportion of polyvinyl chloride foam continuously declines. The deflection of back face, and the energy absorption of polyvinyl chloride foam and bottom face sheet increase with the increase in the number of filling layers. Key

Multi-feature Compressive Sensing Target Tracking Algorithm Based on Redundant Dictionary

ZHU Su, BO Yu-ming, HE Liang

2017, 38(6):  1140-1146.  doi:10.3969/j.issn.1000-1093.2017.06.013

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In consideration that the basis of signal sparse representation is an orthogonal matrix in the multi-feature compressed sensing algorithm, the multi-features of infrared and visible images are extracted to construct a sparse representation in a subspace of redundant dictionary, and the selection of sensing matrix and the reconstruction of sparse signal in the algorithm are analyzed. A redundant dictionary-based target tracking algorithm of multi-feature compressed sensing in the framework of particle filter is proposed by reconstructing the signal sparse representation, which can automatically detect dynamic targets in complex environment. Experimental results show that, compared with other classical algorithms, the proposed algorithm has better robustness and real-time in complex environment like illumination change and interference object occlusion. Key

Horizontal Trajectory Tracking Control of Autonomous Underwater Vehicle Based on Seabed Optical Detection Mission

MA Yan-tong， ZHENG Rong， HAN Xiao-jun

2017, 38(6):  1147-1153.  doi:10.3969/j.issn.1000-1093.2017.06.014

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Autonomous underwater vehicles (AUVs) need to be provided with more accurate navigation control due to the limited operating range of optical detection device for detecting the seabed. An improved bilayer PID control algorithm which is independent of the object model is proposed. By controlling the channel propellers which are retrofitted to flanks around AUV, the controller can achieve AUV precise navigation control at low speed. The controller consists of two layers: the inner layer is a PID controller for distance deviation computation, which converts the output to desired deflection angle; the outer layer is a PID controller which computes the desired thrust and torque by inputting the output value of inner layer. The horizontal navigation precision can be reflected by tracking the planned detection route. The precise tracking path was obtained in lake trial. The mean value of course angular deviation is 0.09 °, and the mean square errors of deviation from the course is 0.29 m, which verifies the feasibility of the control scheme. Key

Analysis of Propeller Thrust Performance in the Process of Autonomous Underwater Vehicle Recovery

DU Xiao-xu, ZHANG Zheng-dong

2017, 38(6):  1154-1160.  doi:10.3969/j.issn.1000-1093.2017.06.015

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The influence of propeller thrust performance on the stability control and safety performance of autonomous underwater vehicle (AUV) during the process of AUV recovery is very obvious. Based on CFD method, the multi-block meshes method combined with RNG k-ε turbulent model is used for the simulation of propeller thrust performance of AUV in different recovery cases. The three-dimensional geometric models of AUV and propeller are built. The calculation domain is dispersed by multi-blocks meshes, and the dynamic mesh technique is used to simulate the motion of AUV and propeller. The numerical simulations are performed based on the finite volume method. The comparison of numerical and experimental results，as well as numerical independence test show that the proposed numerical method can be used to calculate the propeller thrust performance during the process of AUV underwater recovery accurately, and the numerical results can provide theoretical reference to the stability control and safety performance of underwater AUV recovery. Key

Adaptive Frequency-change Sampling Strategy of Multi-channel Transient Signal Test

WANG Xiao， HAN Tai-lin， ZHANG Yong-li， LIU Xuan， WANG Yi-jun， GONG Yu-lin

2017, 38(6):  1161-1167.  doi:10.3969/j.issn.1000-1093.2017.06.016

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In the multi-channel transient signal test, the redundant data test by the conventional test system at long time and high sampling rate causes the storage and transmission problems. An adaptive frequency-change sampling strategy is presented to solve these problems. The algorithm lets the test system acquire the primary data at the same sample rate as the traditional test systems can, and divides the data in time. According to the frequency domain characteristics of signal in each segment, the occurring time and duration of transient signal are determined. The non-transient signals are resampled to reduce the redundant data, and the transient segments can be saved completely. The data compression ratio is more than 33 after the data is processed by the algorithm, while the duration data of transient signal is fully retained, and the maximum error of the non-transient segments are less than 0.5FS. The experimental results show that the algorithm can effectively reduce the redundant data in transient test. Key

Evaluation Method for Equipment Important Degree Based on Multidimensional Relationship Complex Networks

CHEN Chun-liang, ZAN Xiang, ZHANG Shi-xin, CAO Yan-hua, CHEN Wei-long

2017, 38(6):  1168-1177.  doi:10.3969/j.issn.1000-1093.2017.06.017

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A new equipment important degree evaluation method based on multidimensional complex networks is designed in consideration of equipment architecture. Command and control relationship, spatial relationship and cooperative relationship are considered and introduced into an equipment architecture model based on complex networks. Appropriate parameters are chosen to establish the node importance evaluation index by analyzing the features of different relationship networks. An improved analytic hierarchy process is applied in node architecture importance comprehensive evaluation by considering both node architecture importance and node attribute importance. An example is used to validate the retionality and effectuality of the proposed method. Key

Configuration and Optimization Method of Carrying Spares of Mission-oriented Combat Unit

RUAN Min-zhi， FU Jian， ZHOU Liang， WANG Jun-long

2017, 38(6):  1178-1185.  doi:10.3969/j.issn.1000-1093.2017.06.018

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Spare parts are important guaranty and basic material for a combat unit to ensure that the failure equipment can be put into combat and resumed to fight immediately. A calculation method for spares demand rate of redundant system based on equivalent life transformation is proposed. According to repairable spares inventory control theory, a carrying spares dynamic configuration model for multi-phase mission is established by taking with system mission success probability as objective function. Through the introduction of Lagrange constraint factors, a multi-constraint oriented spares optimization method is proposed. In a given example, the calculated result is analyzed, which meets all constraint conditions. The deviation between the calculated result and the ExtendSim simulation results is less than 3%. The correctness of the model is verified. Key

Research on Multi-objective Optimization of Multi-item Maintenance Material Distribution Problem

YANG Fan， WANG Tie-ning

2017, 38(6):  1186-1191.  doi:10.3969/j.issn.1000-1093.2017.06.019

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A multi-objective optimization model is established for multi-item maintenance material distribution to help the supply centers satisfy the maintenance material demands of troops. In the proposed model, the priority, fairness and efficiency are taken as the multi-objects. An improved genetic algorithm is combined with grey correlation degree method, which can transfer multi-objective problem to single-objective problem. The example verification shows that the best and mean fitness values are reduced by 31.538 5% and 37.371 1%, respectively. The proposed model can be used to reduce the unfairness of multi-item maintenance material distribution, and improve the efficiency of materials supply. Key

Comprehensive Review

Research on the Overall Design of Integrated Electronic Information System for Tanks and Armored Vehicles

MAO Ming， LIU Yong， HU Jian-jun

2017, 38(6):  1192-1202.  doi:10.3969/j.issn.1000-1093.2017.06.020

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Integrated electronic information system, which is the basis and core to fulfill the informatization of tanks and armed vehicles, has direct impacts on the platform informatization level and tactical capabilities. The development of integrated electronic information system has been constrained to some extent due to lack of clear understanding on its double role as general informatization unit and vetronics function system. The essential meaning of vetronics system is illustrated, and it is concluded that the electronic information system of tanks and armored vehicles relies on system integration. The history and development process of vetronics technology are reviewed and analyzed, and the important technique points of sensor integration, display and control integration, seat role integration, processing and information integration are discussed and summarized. The key technology, as well as the general design process and modeling simulation method of vetronics system are proposed, which could be considered to provide some useful directions for the evolution of the integrated electronic information system of tanks and armored vehicles. Key

A Review on the Research of Lateral Control for Intelligent Vehicles

CHEN Hui-yan, CHEN Shu-ping, GONG Jian-wei

2017, 38(6):  1203-1214.  doi:10.3969/j.issn.1000-1093.2017.06.021

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Intelligent vehicle, which has great advantages in enhancing the driving safety and diminishing road accidents, has become an emerging research focus worldwide. The development and research current status of lateral control for intelligent vehicles at home and abroad are reviewed. The research process and modeling of vehicle lateral dynamics and tire dynamics, the theory and methods of lateral control, and the automatic steering actuator design are discussed and summarized. Several research issues and development trends of lateral control of intelligent vehicles are presented, in which the modeling of vehicle lateral dynamics and the lateral controller design concerning the nonlinearity, uncertainties and time-varying characteristics, particularly in high speed lateral control, and the integrated design combining sensing, perception and decision-making systems with vehicle system dynamics will be research focuses in the future. Key

Research Notes

Cognitive Modeling for Crew's Information Processing Based on Multi-resource Theory

LIU Wei-ping， NIE Jun-feng， LIU Xi-xia

2017, 38(6):  1215-1222.  doi:10.3969/j.issn.1000-1093.2017.06.022

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The effective cognitive model is a key technology to study the information processing work state of armored vehicle crew and enhances the combat effectiveness of man-machine system. In view of the basic trend of transforming the physical operating task to information processing task，the operatal units are systematically analyzed，the cognitive elements are extracted based on multi-resource theory(MRT), a cognitive model is established based on task-network，and the objective-subjective verification process for crew's cognitive model is proposed. The model is verified through example, with an aim to solve the problem of cognitive modeling. The results indicate that the proposed model could be used to describe the whole cognitive process of crew's information processing task, and predict the reaction times of operatal units accurately. It has high prediction accuracy and reusability preferable. It is an effective and feasible approach for crew's cognitive modeling. Key

Measurement of Ray Radiation and Electromagnetic Scattering from Hypersonic Sphere Models and Their Flow Fields in Ballistic Range

MA Ping, SHI An-hua, YANG Yi-jian, YU Zhe-feng, SUN Liang-kui, HUANG Jie

2017, 38(6):  1223-1230.  doi:10.3969/j.issn.1000-1093.2017.06.023

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The ray radiation and electromagnetic scattering of the sphere models in the ballistic range are measured to investigate the effects of hypervelocity vehicle and flow field on the target detection and recognition. The models are launched from a two-stage light gas gun. The models are the spheres with the diameter of 15 mm, which are made of Al₂O₃. The velocity ranges from 4.2 km/s to 6.1 km/s, and the target chamber pressure ranges from 2.0 kPa to 15.4 kPa. The intensities of ultraviolet radiation (254 nm and 365 nm) and visible radiation (430 nm) of the models are measured by the photomultiplier detectors, respectively. The intensities of infrared radiation (3-5 μm and 8-12 μm) of the models are measured by using InSb detectors. The radar cross section (RCS) of the full targets is measured by the monostatic radar system working at X waveband, of which the visual angle between the main beam and the flight direction is 40°. The results show that the ray radiation intensities of the models and flow field and the electromagnetic scattering characteristics depend on the flight speeds of the models and the chamber pressure. The ultraviolet radiation intensity is the same as their visible light radiation intensity. The difference of radiation intensity between 3-5 μm and 8-12 μm is within one order of magnitude. The ultraviolet radiation and visible radiation mainly come from the shock wave radiation, which do not present in the wake radiation at all. The intensity of infrared radiation of the wake in the range of 3-5 μm is higher and its duration is longer compared to that of 8-12 μm. The electromagnetic scattering energy mainly comes from the regions of the models surrounded by the flow field when the flight speed is lower, and the electromagnetic scattering energy of the wake is markedly strengthened when the flight speed is higher. The electromagnetic scattering energy mainly comes from the regions of the models surrounded by flow fields and wakes when the flight speed is high. The total RCS of wake is about one order of magnitude larger than that of the model surrounded by flow fields under certain conditions. Key

Interaction Effects of Processing Parameters on Surface Quality of Two-dimensional Ultrasonically Extruded 7075 Aluminum Alloy

ZHENG Jian-xin, LIU Wei-cheng, DUAN Yu-tao

2017, 38(6):  1231-1238.  doi:10.3969/j.issn.1000-1093.2017.06.024

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The orthogonal test was carried out to study the interaction effects of processing parameters on the surface quality of two-dimensional ultrasonically extruded 7075 aluminum alloy. The optimal parameters, including static pressure F_s, extrusion speed v and feed rate f_r, were studied. The influence order and significance of processing parameters which have the interaction effects on the surface roughness and hardness are determined through range analysis and variance analysis. The prediction models for surface roughness and hardness are constructed using regression analysis based on data-driven method. The interaction effects of processing parameters on surface roughness and hardness are analyzed based on response surface method. The optimal processing parameters are determined by constrained multi-objective programming model. The study found that the surface roughness of 7075 aluminum alloy decreases obviously after two-dimensional ultrasonic vibration, while the surface hardness increases greatly. The surface roughness mainly depends on the interaction of v and f_r, v and f_r, while the surface hardness mainly depends on F_s, v, and the interaction effects of v and f_r as well as F_s and v. The surface roughness and surface hardness obtained by the prediction models are close to the measured values, and the optimal parameters with the lowest surface roughness and the highest hardness agree with the experimental results. The results show that the interaction effects of the processing parameters on the surface quality are important, and the prediction models for surface roughness and hardness are effective. Key

Stiffness Analysis of Asymmetric Double-row Four-point-contact Ball Slewing Bearing

NIU Rong-jun， XU Jin-chao， SHAO Xiu-hua， DENG Si-er

2017, 38(6):  1239-1248.  doi:10.3969/j.issn.1000-1093.2017.06.025

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Owing to the bearing space constraints and high load carrying capacity requirements, the traditional symmetric double-row four-point contact ball slewing bearing with negative clearance （α₀₁=α₀₂=45°）is improved, and a new asymmetric contact angle design（α₀₁=35°-60°，α₀₂=90°-α₀₁） with negative clearance is proposed. A calculation model of double-row four-point-contact bearing with asymmetric contact angle is established based on the Hertz contact theory and rolling bearing design method. The influences of asymmetric contact angle and negative clearance on bearing stiffness are analyzed. The results show that,with the increase in unidirectional loads F_a, F_r and M, the main stiffness decreases first and then increases nonlinearly, and a critical inflection point exists on bearing stiffness curve due to the negative clearance. In the initial stage, the initial preload stiffness of bearing is obviously improved, however, the effect of negative clearance on bearing stiffness is gradually weakened and eventually tend to be consistent with the increase in negative clearance. Under unidirectional loading condition, the integrated bearing stiffness is the best for the negative clearance being -0.03 mm and α₀₁=55° and α₀₂=35°. Under the combined loading condition, the bearing stiffness is optimum for the negative clearance being -0.03 mm and α₀₁=60°, α₀₂=30° or α₀₁=35°, α₀₂=55°. Asymmetric contact angle and negative clearance design have a significant effect to improve the overall stiffness of bearing. Key