Table of Content

30 January 2015, Volume 36 Issue 1

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Paper

Research on Evaluation Method for Launch Safety of Propellant Charge

RUI Xiao-ting, FENG Bin-bin, WANG Yan, LI Chao, CHEN Tao

2015, 36(1):  1-11.  doi:10.3969/j.issn.1000-1093.2015.01.001

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The launch safety problem of gun propellant charge has severely restricted the development of modern gun, and has already become major theoretical and technical problems which has attracted considerable attention. A new concept, namely the initial dynamic vivacity ratio of propellant charge is presented based on 17 years of profound research on theoretical analysis, computation and test which reveals the mechanism of bore premature caused by propellant charge. The industry standard and military standard of launch safety evaluation method were set up. The evaluation principle of launch safety for propellant charge, the evaluation process of launch safety for propellant charge, the mechanics environment test method of propellant charge in chamber, the test method of dynamic stress and fracture of propellant charge, the test method of initial dynamic vivacity ratio of propellant charge, the approach to determine the criterion of launch safety for propellant charge, and the evaluation method of launch safety for propellant charge are introduced. The methods have been in the engineering practice successfully. The theoretical basis, technical approaches and technical standards are provided for the scientific evaluation of launch safety of propellant charge.

Research on Timing Method of Two Shifting Actuators Filling and Draining Hydraulic Oil During Shifting

LI Chun-fu， CHEN Hui-yan

2015, 36(1):  12-18.  doi:10.3969/j.issn.1000-1093.2015.01.002

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The shifting process of automatic transmission is an alternating process of two actuators filling and draining the hydraulic oil. The improper oil filling and draining of two shifting actuators may cause power interruption or too much overlap, power lose, impact of shifting and aggravated wear of shift actuator. Lagrange equation is used to establish the dynamic equation of the shifting process by taking Allison automatic transmission (HD4070PR) as the study subject. The timing method of two shifting actuators filling and draining hydraulic oil during shifting process is analyzed on the basis of the equation, and verified by real vehicle test. The research results show that, for the upshifting process, the power shifting can be realized, and the impact of shifting can be reduced through the rational power lap;and for the downshift process, since the emergence of power interruption is inevitable, only the loss of the power should be reduced as far as possible.

Analysis of the Effect of Trim Angle on the Resistance Characteristics for Wheeled Amphibious Vehicle

JU Dong-mei， XIANG Chang-le， ZHOU Peng-fei， XIAO Nan-xi， LIU Jing

2015, 36(1):  19-26.  doi:10.3969/j.issn.1000-1093.2015.01.003

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One of the effective ways to increase the speed of amphibious vehicle is to reduce the overall resistance. In order to research the influence of trim angle on the resistance characteristics, a numerical calculation method is used to research the resistance characteristics of high speed wheeled amphibious vehicle. The numerical results are in good agreement with the experimental results. The research results show that the resistance increases with the increase in speed when the vehicle trim angle is small; it increases first and then tends to be stable with the increase in speed when the vehicle trim angle is bigger. When the speed is low, the trim angle has a small influence on longitudinal resistance; when the speed is higher, the resistance decreases first and then increases with the increase in trim angle. As speed increases, the vehicle trim angle becomes smaller, but the resistance increases.

Design of Al-alloyed Cylinder Head for Automobile Diesel Engine under High Loads

ZHANG Quan-zhong, WEI Zhi-ming, MA Jun-hua, REN Gui-feng, LIU Chang-zhen, BAI Jun-ai

2015, 36(1):  27-32.  doi:10.3969/j.issn.1000-1093.2015.01.004

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With the increase in thermal and mechanical loads of engine, the higher standard is required for materials, and the more serious challenges had been taken for the design technique of engine. A new frame cylinder head is obtained by simulating 5 strengthened cylinder-heads. The load carrying structures, which are interdependent, are included by the stud bolts, the mounting support of fuel injector, the stiffeners of top ceiling and the fire face. The reliability test results of mechanical fatigue and thermal fatigue show that the structure of the cylinder head under peak pressure (20 MPa) is reasonable.

Research on Effect of Nozzle Hole Distribution on Performance of Combustion System with Double ω CombustionChamber for Diesel Engine

WEI Sheng-li, WANG Fei-hu, CHEN Huan ， LENG Xian-yin

2015, 36(1):  33-39.  doi:10.3969/j.issn.1000-1093.2015.01.005

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A double ω-combustion chamber matched with a double-row nozzle hole combustion system is proposed to improve the spray spatial distribution and the mixture formation quality for diesel engines. The in-cylinder spray, mixture formation and combustion process of the new combustion system are simulated and investigated by using AVL FIRE software. The effects of nozzle hole distribution on the fuel/air equivalence ratio, temperature field and emission characteristics in the chamber are analyzed by changing the spatial distribution of nozzle hole. The results show that the mixture formation quality can be effectively improved by increasing the number of nozzle holes in the upper row, and moreover, the combustion process can be improved. With the spatial distribution of 5 nozzle holes in the upper row and 3 nozzle holes in the lower row, NOx and Soot emissions can be reduced.

Effects of H₂ Addition on Exhaust Emissions of COCO₂ and HC in Cummins ISM370 Diesel Engine

YANG Zhen-zhong， Hailin Li

2015, 36(1):  40-45.  doi:10.3969/j.issn.1000-1093.2015.01.006

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In order to reduce the emissions of diesel engine, the investigation into the effect of H₂ addition on the emissions of heavy-duty diesel engines is attracting attention from researchers in recent years. The effects of H₂ addition at different proportions (the highest volume proportion of hydrogen is 7% of hydrogen air mixture in inlet pipe) on the emissions of CO, CO₂ and HC in Cummins ISM370 diesel engine are researched. Research shows that the addition of hydrogen can benefit the reduction in the emissions of CO, CO₂ and THC in various loads, and has little effect on the emissions of THC. Moreover, with the increase in amount of hydrogen, the emission characteristics of CO, CO₂ and THC varies with the change of load. The amount of hydrogen added should be appropriate to load operation to reduce the emission in maximum extent.

Experimental Investigation on Penetration of Grooved Projectiles into Concrete Targets

PANG Chun-xu， HE Yong， SHEN Xiao-jun， ZHANG Xian-feng， LI Wen-bin， GUO Lei， PAN Xu-chao

2015, 36(1):  46-52.  doi:10.3969/j.issn.1000-1093.2015.01.007

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In order to study the performance of grooved projectiles rotarily penetrating into concrete target, the penetration experiments of non-rotating oral projectiles and non-rotating grooved projectiles against the mortar concrete targets were conducted with the use of 14.5 mm smooth-bore gun. And the penetration experiments of rotating oral projectiles and rotating grooved projectiles against the mortar and limestone concrete targets were conducted with the use of 14.5 mm rifled bore gun. The results show that the grooved projectile and rotating penetration can be used to change the concrete failure from a single axial compression to the combined effects of axial compression and circumferential shear. The axial resis-tance of projectile becomes lower and the penetration power of the projectile gets stronger. The anti-penetration capability of limestone concrete target is stronger than that of mortar concrete target.

Force Analysis for the Fuze on the Motion of a Unrotating Projectile Around the Center of Mass in Exterior Ballistics

WANG Xiao-peng， WANG Yu-shi， WEN Quan， FENG Yan-zhe， SU Hong-wei

2015, 36(1):  53-57.  doi:10.3969/j.issn.1000-1093.2015.01.008

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In order to provide an accurate mechanical environment of exterior ballistics for fuze safety design, a mathematical model of the motion of unrotating projectile around the center of mess in exterior ballistics is established based on the rigid body dynamics. The formulas of the radial and axial components of the inertial force acting on fuze parts, which is caused by the motion of non-rotating projectile around the center of mess, are derived. The results show that the ratio of the maximum radial component of the inertial force to its maximum axial one is the largest nutation angle. And the radial component closes to zero when the axial component reaches to the maximum, and vice versa. So the frictional force caused by this inertial force can be ignored during the analysis for motion of fuze parts caused by the same inertial force.

Two-dimensional Numerical Simulation on Two-phase Flow Interior Ballistic Performance of a Guided Projectile

CHENG Cheng， ZHANG Xiao-bing

2015, 36(1):  58-63.  doi:10.3969/j.issn.1000-1093.2015.01.009

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To simplify the complexity of moving boundary treatment in the two-phase flow numerical simulation and improve the computational accuracy of moving boundary treatment, a two-dimensional two-phase flow model based on ALE method is established. The governing equations are discretized with the TVD-type MUSCL scheme to obtain a second order accuracy in finite volume form. A two-step and fourth-order Runge-Kutta method is used to solve the source terms．The dynamic mesh update method and numerical method are verified by a standard test with the exact solution. The numerical application on a large caliber guided projectile shows the complete development and the two-phase flow characteristics of the interior ballistic process. The calculated results are in good agreement with the experimental results. The effects of different ignition conditions on interior ballistic performance are investigated. The study lays a theoretical foundation for deep optimization of the interior ballistic performance and firing safety.

Preparation and Characterization of Submicron Hexanitrohexaazaisowurtzitane

OUYANG Gang, GUO Xiao-de, XI Hai-jun, LIU Jie, HAN Hua, LI Feng-sheng

2015, 36(1):  64-69.  doi:10.3969/j.issn.1000-1093.2015.01.010

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Submicron hexanitrohexaazaisowurtzitane (CL-20) is prepared using HLG-50 pulverized machine. The laser particle size analyzer and SEM are used to characterize the particle size, size distribution and morphology of sample. The polymorph and purity of CL-20 particles are characterized by Fourier transform infrared spectrometer, laser Raman spectrometer, XRD and HPLC, respectively. The TG/DSC simultaneous thermal analyzer is used to study the thermal decomposition of CL-20. The shock sensitivity of samples are studied. The results show that CL-20 particles are pseudo-spherical with an average particle size (d₅₀) of 210 nm. The polymorph of submicron CL-20 is consistent with that of the raw ε-CL-20. Compared with the raw CL-20, the thermal decomposition peak temperature of the submicron CL-20 is decreased slightly, and the shock sensitivity of the submicron CL-20 is considerably reduced by 53.1%. That implies the obvious reduction in the shock sensitivity of CL-20.

Determination of 14 Nitrophenol Products by SPE-Ultra Performance Liquid Chromatography

LIU Yu， ZHANG Tong-lai, YANG Li, LIU Rui, LIU Ying

2015, 36(1):  70-77.  doi:10.3969/j.issn.1000-1093.2015.01.011

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A simple ultra performance liquid chromatography (UPLC) method for the determination of fourteen nitrophenol residues in environmental waste water is proposed. A Bond Elut Plexa solid phase extraction( SPE) is used for the extraction and purification of the compounds in environmental waste water. The water sample with sampling amount of 5.0 mL is purified using a solid phase extraction column, and then eluted with 3.0 mL tetrahydrofuran. The elution is introduced into the instrument and determined by HPLC with photodiode array detector with detection wavelength of 220 nm. A good base line separation of target compounds is achieved within 22 minutes under the optimal condition. The calibration curves of 3 amides are linear in the concentration range of 0.1~20 mg/L with the correlation coefficients of 0.997 3~0.998 7. The recoveries are 82.5%~104.8%, and the relative standard deviations range from 3.2% to 5.7% for the target compounds. The minimum detectable concentrations are 0.02~0.04 mg/L. This proposed method is convenient to use, sensitive and accurate, and is suitable for the routine detection of trace amide contaminants in environmental waste water.

Integrated Guidance and Control Backstepping Design of Blended Control Missile Based on Adaptive Fuzzy Sliding Mode Control

WANG Zhao-lei, WANG Qing, RAN Mao-peng, DONG Chao-yang

2015, 36(1):  78-86.  doi:10.3969/j.issn.1000-1093.2015.01.012

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An integrated guidance and control law is proposed for dual-control missiles based on the backstepping sliding mode design approach. A command filter is introduced to eliminate the computation explosion problem of conventional backstepping design method. An adaptive fuzzy approximator is employed to approximate the system uncertain functions, and a sliding mode surface is constructed to compensate the effects of approximate error and bounded disturbances. The controller parameters are adjusted adaptively on-line to guarantee the robustness of the system. A numerical example is provided. The simulation results show that the integrated guidance and control approach has robustness to disturbances and improves the control performance while ensuring the operating stability of system when a target maneuvers with high acceleration.

Numerical Analysis of Fragile Back Cover Opening Process Coupling with Jet Flow

NIU Yu-sen， JIANG Yi， SHI Shao-yan， LI Jing

2015, 36(1):  87-93.  doi:10.3969/j.issn.1000-1093.2015.01.013

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The motion process of fragile back cover interacts with the flow field of gas jet. The dynamic mesh technology based on smoothing method and remeshing method is used to study the opening process of back cover, The opening process is simulated by coupling the motion process of back cover with the gas jet flow field. The initial shock wave is observed, and the pressure curves of monitoring points are plotted. The effect of jet flow on the motion of cover debris is analyzed. Compared to the results of uncoupled case, the results of coupled case are closer to the experimental data. The driving moment is getting small with the increase in rotation angle of cover debris. The rotation speed rises fast at first and then goes down slowly.

Analysis on Stability of a Slender Missile under Axial Loads

QUAN Jing-ge, YE Zheng-yin, ZHANG Wei-wei

2015, 36(1):  94-102.  doi:10.3969/j.issn.1000-1093.2015.01.014

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For slender missile, there is a potential coupling effect between rigid mode and elastic mode, which makes the system unstable. As the axial loads have a negative effect on the structural stiffness property, the stability of the system gets worse further. A finite element method is used to study the influence of the axial loads on the structural stiffness property of missile. The local piston theory coupled with the structural motion equations is developed to analyze the stability of a slender missile in state-space. It is shown that the rigid mode and elastic mode of the slender missile couple together under high axial loads，resulting in the system instability. Moreover, as the axial acceleration loads increase, the structural stiffness of the missile reduces, and the critical instable speed falls.

Sensor Fault Estimation Method for Flight Control Systems Based on Aerodynamic Parameter Identification

WANG Jian-chen， QI Xiao-hui

2015, 36(1):  103-110.  doi:10.3969/j.issn.1000-1093.2015.01.015

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The aircraft model shows obvious time-varying characteristic due to the uncertainty of aerodynamic parameters. The fault diagnosis of the flight control systems is a difficult issue. A sensor fault estimation approach based on aerodynamic parameter identification and iterative learning is proposed by taking the longitudinal motion model of some unmanned aerial vehicle as the study subject. The augmented cubature Kalman filter (ACKF) is used for the aerodynamic parameter estimation so that the system model can be identified online. Once a fault comes up, the currently identified aerodynamic parameters are applied to system modeling in the local flight envelope, and a fault estimator is constructed using the iterative learning algorithm. Furthermore,a novel iterative learning algorithm based on the essence of extended state observer (ESO) is designed to improve the fault estimation speed. The fault simulation experiments are conducted to verify the feasibility and effectiveness of the proposed approach.

A New Imaging Algorithm for Synthetic Aperture Radar Mosaic Mode

LI Cai-pin， HE Ming-yi

2015, 36(1):  111-116.  doi:10.3969/j.issn.1000-1093.2015.01.016

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An imaging processing algorithm is proposed for the issues of squint imaging at the edge of imaging module and inconsistent pixel interval at different imaging blocks of mosaic mode. The signal azimuth spectrum aliasing in azimuth direction is eliminated effectively by using an improved de-ramping processing technology. On this basis, the range Doppler algorithm is used for range compression and range migration correction. Then the spectral algorithm based on CZT transform is used to eliminate the difference between the pixel intervals of sub-blocks. The simulation result shows that the proposed algorithm can be used for the imaging of mosaic mode.

Research on Dynamic Compensation Algorithm of Acquisition Process of Laser Communication Between Aircrafts

ZHAO Yi-wu, LOU Yan, HAN Cheng, JIANG Hui-lin, TONG Shou-feng

2015, 36(1):  117-121.  doi:10.3969/j.issn.1000-1093.2015.01.017

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In order to effectively eliminate the influence of relative velocity between aircrafts on acquisition performance, the mechanism of influence of relative velocity on acquisition process is described. According to the measured data of aircraft motion and vibration, the dynamic compensation formulas are derived, an acquisition algorithm based on dynamic compensation in space laser communication is proposed, and the acquisition performance of the algorithm is analyzed. The results show that the relative velocity has a seriouse influence on the statistical coverage of acquisition. In order to meet the statistical coverage of acquisition, the maximum acquisition time and average acquisition time of common algorithms are significantly increased. The acquisition algorithm could greatly improve the performance of acquisition system by increasing the acquisition probability and reducing the acquisition time.

Study of Underwater Target Recognition for Torpedo Electromagnetic Fuse with High Detecting Precision

CHEN Bin-qiang， LYU Shu, YAO Bin, ZHANG Zhou-suo, BAI Zhi-ke

2015, 36(1):  122-129.  doi:10.3969/j.issn.1000-1093.2015.01.018

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Characteristic information is hidden in the received signal of active torpedo electromagnetic fuse. The conventional burst controlling strategies based on energy-comparison are affected by ambient and electromechanical noises. The improved algorithms based on digital signal processing techniques are proposed. The received signals are first processed by all-phase compensation method to eliminate the direct coupling component, and then the residual signal is demodulated using STFT. An improved polynomial least mean square approximation method, which reduces the computation time, is presented for eliminating the side-effects brought by noise. A parametric estimation model base on bell-shape impulse is used to estimate the maximum of echo envelope. Simulation and trial data show that the proposed algorithm is effective and practical.

Image Morphological Characteristics of Geometrical Structure of Target Echo Time-frequency Distribution

LI Xiu-kun, XIA Zhi, ZHU Xu

2015, 36(1):  130-137.  doi:10.3969/j.issn.1000-1093.2015.01.019

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The key of underwater bottom target recognition is to extract the stable target echo signal feature from reverberation background. The edge scattering of target carries its geometrical information, and it has regular distribution on the time-frequency plane. But the path difference of edge scattering is little, and it’s always drowned out by reverberation. Because of the limited time-frequency resolution and the limited anti-reverberation ability of existing time-frequency analysis method, there hasn’t been any effective feature extraction method of target geometrical characteristics. The geometrical distribution feature of target echo on the time-frequency plane is extracted as an image feature. The morphological characteristics of geometrical highlight and reverberation on the time-frequency plane are researched. The structural element matched with the time-frequency distribution is constructed, and the time-frequency distribution image is morphologically filtered. The experimental data processing result shows that, compared with existing method, the proposed method can be used to recognize the geometrical highlight structure of target and suppress the reverberation at the same time.

Observability Analysis of Cooperative Localization System for MAUV Based on Condition Number

MA Peng， ZHANG Fu-bin， XU De-min， LIU Shu-qiang

2015, 36(1):  138-143.  doi:10.3969/j.issn.1000-1093.2015.01.020

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For the multiple autonomous underwater vehicle (MAUV) cooperative localization system based on the moving long baseline, the 2D kinematic models and range measurement equations of MAUV are established.The observability theory of nonlinear system based on Lie derivatives is used to derive the observability matrix of the cooperative localization system and describe the unobservable trajectories of MAUV system. The evaluation function for the observability metric of the localization system is given using the condition number of observability matrix obtained from singular value decomposition(SVD) theory. Finally, a series of simulation experiments are designed to analyze the system observability under the different MAUV formations. The results show that the system observability change with the MAUV formation, which provides an effective reference to improve the performance of cooperative localization system by transforming the MAUV formation.

Investigation on the Relationship among Tool WearCutting Force and Vibration in Milling of TC4

JIANG Zhen-xi, SUN Jie, LI Guo-chao, JIA Xing-min, LI Jian-feng

2015, 36(1):  144-150.  doi:10.3969/j.issn.1000-1093.2015.01.021

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Experiments of milling TC4 titanium alloys with solid cemented carbide milling cutters coated with AlCrN are carried out. The tool wear of circumferential cutting edge, cutting force and vibration are measured. The tool wear morphology is observed by using scanning electron microscope ( SEM) , and the element distribution of the worn tool surface is detected by using energy dispersive spectrometer (EDS). The influence of tool wear on cutting force and vibration is further discussed based on the wear mechanism in order to provide a theoretical and technical support for the realization of online check of tool wear state. The experimental results indicate that the mechanical crack, thermal crack, adhesion and oxidation wear exist on the rake face, and the mechanical crack, adhesion and oxidation exist on the flank face. The cutting force and vibration increase with wear loss. The different states of wear have the different effects on cutting force and vibration.

Design and Analysis of Flow Field in Electrochemical Machining of Cochlear Channel of Closed Integral Structure

KANG Bao-yin, FAN Zhi-jian, TANG Lin

2015, 36(1):  151-156.  doi:10.3969/j.issn.1000-1093.2015.01.022

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The design of flow field is an important part of preparing the cathode and device in the electrochemical machining of cochlear channel of closed integral structure. The models of the forward feed device and reverse feed device are established based on UG , of which inlet area is about twice as much as outlet area，respectively, and their gap flow fields are simulated based on COMSOL Multiphysics. The difference between these gap flow fields formed by the forward feed and reverse feed at the same electrolyte inlet pressure is analyzed from its streamline pattern, velocity and pressure nephograms. The results show that the flow velocity of the end gap and the side gap in the reverse feed is higher than that in the forward feed, and the flow field of the reverse feed is more uniform. The reverse feed devices are used in the experiment, the machining process is smooth without spark and short circuit.

Inspection of Base separation of Charge by Industrial CT Imaging

LYU Ning, XU Geng-guang

2015, 36(1):  157-162.  doi:10.3969/j.issn.1000-1093.2015.01.023

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A volume effect of industrial computed tomography(CT) imaging and a contrast method for density inspection are used to build an algebraic model for base separation inspection, which improves the base separation inspection method in theoretical and practical ways. The size information is qualitatively and quantitatively analyzed with high precision by the fluctuation of inspected CT values. The experimental results of base separation inspection show that the density contrast model is suitable for the inspection of 0.20~0.50 mm base separation, and the relative error is less than 3.5%.

Flow Nonlinear Analysis and Compensation Control Validation for High-speed On-off Valve

LIU Zhi-hao, GAO Qin-he, GUAN Wen-liang

2015, 36(1):  163-174.  doi:10.3969/j.issn.1000-1093.2015.01.024

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The nonlinear control methods of compensated pulse width modulation(PWM) control based on the dead and saturated zones and PWM-PFM(pulse frequency modulation) control are presented for the dead, saturated and non-linear zones in the flow control of high-speed on-off valve, which are compared with the PWM control and the traditional PWM control. The flow characteristic of HSV with the nonlinear control is analyzed and simulated, and a hydraulic loop controlled by HSV is set up to verify the nonlinear control by simulation and experiment. The result shows that the nonlinear control method compensates the dead, saturated and nonlinear zones in the terms of duty ratio and frequency and can linearizes the flow with the duty ratio of 0%~100%; the large tracking error resulting from the dead zone and saturated zone is avoided effectively in simulation and experiment.

The Influence of Magnetic Fluid Yield Stress on the Performance of Magnetic Fluid Seal

HE Xin-zhi， LI De-cai， HAO Rui-can

2015, 36(1):  175-181.  doi:10.3969/j.issn.1000-1093.2015.01.025

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Magnetic fluid seal is one of the most mature applications of magnetic fluid. It is found that the anti-pressure capacity of the static or dynamic magnetic fluid seal may rise over time. If it is a dynamic seal, the starting torque will increase. These phenomena are investigated through experiment. Then the concept of yield stress of magnetic fluid is introduced to explain qualitatively the phenomena. And the formulas of anti-pressure capacity and torque are improved. The results show that the yield stress of magnetic fluid is the main factor inducing the increase in the anti-pressure capacity and torque of magnetic fluid seal. The greater the yield stress is, the higher the anti-pressure capacity is, and the larger the starting torque is. The results provide a design basis to reduce the starting torque and improve the anti-pressure capacity of magnetic fluid seal.

Research Notes

An Automatic Direct Aiming Control Method of Self-propelled Artillery

ZHANG Wei-min, LIANG Jian-qi, MA Hong-wei, WANG Tong, WU Zhi-hui

2015, 36(1):  182-186.  doi:10.3969/j.issn.1000-1093.2015.01.026

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An automatic direct aiming control method is proposed for self-propelled indirect aiming artillery. The proposed method can be used to make a self-propelled artillery directly aim at the fixed and moving targets without the addition of any hardware configuration of fire control system. The control model and the rapid calculation method of trajectory are studied. The aiming error and system response time are analyzed. The method can significantly improve the rapid reaction ability and firing accuracy of artillery and the automation level of weapon system.

Imaging Method for SAR with Low Height and Large Squint Angle Based on Optimized Golomb Sequence and ω-k Algorithm

OU Jian-ping, LI Wei, WU Hao-tian, ZHANG Jun, YAN Jia-bing

2015, 36(1):  187-192.  doi:10.3969/j.issn.1000-1093.2015.01.027

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Higher requirement of pulse repetition frequency will be faced when synthetic aperture radar (SAR) is at a very low height. Doppler centroid will deviate from zero when the squint angle is too large,resulting in defocusing the final image. For imaging of low-height and squint-looking SAR, a pulse repetition frequency is designed properly in order to get a high resolution image and avoid the range and azimuth ambiguities and the interference of the transmitted pulses, and the problem of overlaying the azimuth spectrais solved. Golomb sequence is optimized with cyclic algorithm, and a good autocorrelation is used to get high range resolution. After STOLT interpolation mapping, the raw data is properly processed using ω-k algorithm to get agood imaging result. Simulation results show that the algorithm can solve the problem of low height and large squint SARimaging.