基于星上实时信号处理机的Chirp Scaling算法实现方法

基于改进的Chirp Scaling算法,提出了一种适用于星上实时信号处理机的高效成像处理实现方法,其核心思想也可应用于其它高分辨率星载SAR的精确成像算法.首先介绍了实时信号处理机的结构,分析了数据处理粒度及其并行流水处理结构.在此基础上,针对单个粒度的成像处理重新设计了算法流程,提出了一种高效的实现方法.利用实时信号处理机,对仿真的回波数据进行了成像处理实验,结果表明:在41?s内能够完成成像处理,成像处理速度和图像质量满足系统设计要求,从而验证了该方法的有效性.     

Occurrence features of simultaneous H+- and He+-band EMIC emissions in the outer radiation belt

As an important loss mechanism of radiation belt electrons, electromagnetic ion cyclotron (EMIC) waves show up as three distinct frequency bands below the hydrogen (H⁺), helium (He⁺), and oxygen (O⁺) ion gyrofrequencies. Compared to O⁺-band EMIC waves, H⁺- and He⁺-band emissions generally occur more frequently and result in more efficient scattering removal of <～5?MeV relativistic electrons. Therefore, knowledge about the occurrence of these two bands is important for understanding the evolution of the relativistic electron population. To evaluate the occurrence pattern and wave properties of H⁺- and He⁺-band EMIC waves when they occur concurrently, we investigate 64 events of multi-band EMIC emissions identified from high quality Van Allen Probes wave data. Our quantitative results demonstrate a strong occurrence dependence of the multi-band EMIC emissions on magnetic local time (MLT) and L-shell to mainly concentrate on the dayside region of L?=?～4–6. We also find that the average magnetic field amplitude of H⁺-band waves is larger than that of He⁺-band waves only when L?<?4.5 and AE¹?<?300?nT, and He⁺-band emissions are more intense under all other conditions. In contrast to 5 events that have average H⁺-band amplitude over 2 nT, 19 events exhibit >2 nT He⁺-band amplitude, indicating that the He⁺-band waves can be more easily amplified than the H⁺-band waves under the same circumstances. For simultaneous occurrences of the two EMIC wave bands, their frequencies vary with L-shell and geomagnetic activity: the peak wave frequency of H⁺-band emissions varies between 0.25 and 0.8 f_cp with the average between 0.25 and 0.6 f_cp, while that of He⁺-band emissions varies between 0.03 and 0.23 f_cp with the average between 0.05 and 0.15 f_cp. These newly observed occurrence features of simultaneous H⁺- and He⁺-band EMIC emissions provide improved information to quantify the overall contribution of multi-band EMIC waves to the loss processes of radiation belt electrons.     

Start-up current adaptive control for sensorless high-speed brushless DC motors based on inverse system method and internal mode controller

The start-up current control of the high-speed brushless DC (HS-BLDC) motor is a chal-lenging research topic. To effectively control the start-up current of the sensorless HS-BLDC motor, an adaptive control method is proposed based on the adaptive neural network (ANN) inverse system and the two degrees of freedom (2-DOF) internal model controller (IMC). The HS-BLDC motor is identified by the online least squares support vector machine (OLS-SVM) algo-rithm to regulate the ANN inverse controller parameters in real time. A pseudo linear system is developed by introducing the constructed real-time inverse system into the original HS-BLDC motor system. Based on the characteristics of the pseudo linear system, an extra closed-loop feed-back control strategy based on the 2-DOF IMC is proposed to improve the transient response per-formance and enhance the stability of the control system. The simulation and experimental results show that the proposed control method is effective and perfect start-up current tracking perfor-mance is achieved.     

Tribological evaluation of surface modified H13 tool steel in warm forming of Ti–6Al–4V titanium alloy sheet

The H13 hot-working tool steel is widely used as die material in the warm forming of Ti–6Al–4V titanium alloy sheet. However, under the heating condition, severe friction and lubricating conditions between the H13 tools and Ti–6Al–4V titanium alloy sheet would cause difficulty in guaranteeing forming quality. Surface modification may be used to control the level of friction force, reduce the friction wear and extend the service life of dies. In this paper, four surface modification methods(chromium plating, TiAlN coating, surface polishing and nitriding treatment)were applied to the H13 surfaces. Taking the coefficient of friction(CoF) and the wear degree as evaluation indicators, the high-temperature tribological behavior of the surface modified H13 steel was experimentally investigated under different tribological conditions. The results of this study indicate that the tribological properties of the TiAlN coating under dry friction condition are better than the others for a wide range of temperature(from room temperature to 500 C), while there is little difference of tribological properties between different surface modifications under graphite lubricated condition, and the variation law of CoF with temperature under graphite lubricated is opposite to that under the dry friction.     

Modeling and Simulation of Pipeline Security Monitoring System Based on Line-Structure Sagnac Interferometer with 3×3Coupler

The third damage action,human disruption behavior,is one of the major threats to pipeline operation.It is necessary to monitor and locate the perturbation behavior that may threat pipeline safety in real-time.Therefore,a new pipeline security monitoring system is designed by using line-structure Sagnac optic fiber interferemeter with the characteristic of 3×3coupler that can modulate the phase of optic signal,with no need for phase modulation and demodulation.The optic structure of the new system is simplified,the signal processing accuracy is improved,and the polarization effect is reduced.The working principle of the monitoring in ideal condition is described,the phase demodulation is analyzed and the location of the possible damage action point is formulated.By using simulink,the optic signal propagation and interference is simulated and interference signals in different frequencies are obtained.The results validate the feasibility of the monitoring system and indicate that the low frequency signal less than 1kHz resulting from the human damage action can be detected.The disturbance set at 10 km can be located by calculating the demodulation signal accurately over a long monitoring distance.     

直升机线路老龄化引发故障探讨

贝尔206是美国贝尔公司在OH-4A轻型观察直升机的基础上发展的轻型多用途直升机,随着使用年限的增长,线路老化问题引发故障逐步增多,线路的检查与处理显得非常重要.本文从直升机维护实际出发,对线路老化引发的故障进行分析,总结出按照线路维修规范操作,定检维修中重视导线检查的方法,这将对提高直升机维护质量、保障飞行安全起到积极作用.     

雷达/红外复合制导模拟方法研究

雷达/红外双模复合制导是精确制导武器的重要制导方式.通过分析雷达/红外复合制导机理,提出了基于单模导引头单机的雷达/红外复合制导模拟方法,解决了两部导引头如何时空配准、数据关联、融合识别和融合跟踪等问题.     

Mechanical study on initial profile solution for inflatable reflector made of orthotropic material

The woven fabric membrane materials are widely used in space and terrestrial inflatable reflectors. However the material?s anisotropy makes the design analysis more complex. The deviation from the desired shape, so-called “W-profile error”, influences the precision of the membrane surface significantly. In this study, a model of an axisymmetric paraboloid surface using membrane theory is established for the purpose of facilitating the surface precision optimization. Analytical solutions for displacements of the reflector are derived. An iteration method of initial reflector profile solution is stated and a finite element (FE) software employed in the solution is presented. A case study is illustrated to make a comparison between numerical and theoretical analyses. Finally, the conclusions are drawn that the analytical method and the FE iterative method for initial profile solution are feasible and efficient.     

网络融合的接入网技术

本文从电信网、广播电视网和因特网三种网络的不同特点入手，说明了三网合一的必要性和可行性，重点探讨了三网合一中关键的接入网技术。     

双内胆热处理井式电炉的技术改造

双内胆热处理井式空气循环电炉存在容积小、控温热电偶不在工作室、仪表控制温度与工作室温度相差较大等缺点。对该类电炉采取扩容、引偶入室等技术改造措施取得了良好的技术经济效果。