低速冲击下裂纹成核的位错模型

从理论上研究低速冲击下金属材料中微裂纹的成核,建立了裂纹成核的位错模型,并在其中考虑温度与晶粒尺寸的影响;给出了在低速冲击载荷作用下脆性裂纹成核与延性裂纹成核的速度判据;定义了体现材料抗低速冲击能力的速度阻抗,确立了脆性裂纹成核与延性裂纹成核的速度阻抗的计算表达式;分析了在裂纹成核过程中的尺寸效应和脆性-延性转变。结果表明,裂纹成核的速度阻抗都随着晶粒的粗化而减小;脆性裂纹成核的速度阻抗随温度增加而增加,而延性裂纹成核的速度阻抗随温度增加而减小,两者的交点确定了脆性-延性转变温度。     

Optimal spacecraft formation establishment and reconfiguration propelled by the geomagnetic Lorentz force

The Lorentz force acting on an electrostatically charged spacecraft as it moves through the planetary magnetic field could be utilized as propellantless electromagnetic propulsion for orbital maneuvering, such as spacecraft formation establishment and formation reconfiguration. By assuming that the Earth’s magnetic field could be modeled as a tilted dipole located at the center of Earth that corotates with Earth, a dynamical model that describes the relative orbital motion of Lorentz spacecraft is developed. Based on the proposed dynamical model, the energy-optimal open-loop trajectories of control inputs, namely, the required specific charges of Lorentz spacecraft, for Lorentz-propelled spacecraft formation establishment or reconfiguration problems with both fixed and free final conditions constraints are derived via Gauss pseudospectral method. The effect of the magnetic dipole tilt angle on the optimal control inputs and the relative transfer trajectories for formation establishment or reconfiguration is also investigated by comparisons with the results derived from a nontilted dipole model. Furthermore, a closed-loop integral sliding mode controller is designed to guarantee the trajectory tracking in the presence of external disturbances and modeling errors. The stability of the closed-loop system is proved by a Lyapunov-based approach. Numerical simulations are presented to verify the validity of the proposed open-loop control methods and demonstrate the performance of the closed-loop controller. Also, the results indicate the dipole tilt angle should be considered when designing control strategies for Lorentz-propelled spacecraft formation establishment or reconfiguration.     

A preliminary study of the single crest phenomenon in total electron content (TEC) in the equatorial anomaly region around 120°E longitude between 1999 and 2012

The diurnal variations in total electron content (TEC) in the equatorial ionisation anomaly (EIA) region are not always represented by two crests on both sides of the magnetic equator. Sometimes, only an obvious single crest is evident at equatorial and low latitudes. In this paper, we focus on analysis of the morphological features of the single crest phenomenon in TEC around 120°E longitude during geomagnetic quiet days (Kp < 4₋). The variations in TEC are also compared with morphological parameters (foF2 and hmF2) derived from the International Reference Ionosphere extended to Plasmasphere (IRI–Plas) model. Our results show that the single crest phenomenon occurs mainly on days with extremely low solar activity, while the corresponding F2 layer critical frequency showed obvious asymmetry, or even only a single peak.     

Ionospheric perturbations in plasma parameters before global strong earthquakes

Based on the electron density (Ne) and temperature (Te) data from DEMETER, the ionospheric perturbations before 82 Ms ? 7.0 earthquakes (EQs) during 2005–2010 were studied, using moving median and space difference methods within 10 days before and 2 days after these events in local nighttime. It was found that the plasma parameters disturbances appeared before 49 EQs, in which more disturbances were detected before shallow-focus earthquakes than deep ones, and there was little difference between continental and oceanic ones, both exceeding 1/2 percentage. For the disturbed time, more perturbations were seen in 1, 3, 5, 6, 8 days before EQs and 1 day after EQs. For the spatial distribution, the anomalies before EQs were not just above the epicenters, but shifted equatorward with several degrees to almost twenty degrees. Most of the abnormities were positive ones, which demonstrate that Ne increases before EQs at the altitude of 670 km of DEMETER. Perturbations of Ne were more than that of Te, which illustrates that Ne is much more sensitive to seismic activity than Te.     

利用WW3模式实现中国海击水概率数值预报

海浪对掠海飞行有着重要影响,以T639预报风场驱动WW3（WAVEWATCH-Ⅲ）海浪模式,对2013年3月发生在中国海的一次冷空气海浪场进行数值模拟.结合飞行高度探测的标准差、海浪浪高的标准差,进一步实现了击水概率的数值预报,为低空飞行器的航迹规划提供科学依据.主要计算了5 m高度、10 m高度、15 m高度的击水概率,并对比不同飞行高度击水概率的差异.结果表明,以T639预报风场驱动WW3海浪模式,可以较好地预报中国海海浪场、击水概率场.在冷空气影响下,中国海的击水概率出现明显增幅.飞行高度低于10 m时,海浪会对掠海飞行器的安全造成很大威胁.      

TDC-GP1器件单粒子锁定效应的脉冲激光模拟试验研究

文章介绍了单粒子锁定效应脉冲激光模拟试验的工作原理。以时间测量芯片TDC-GP1为试验对象,利用单粒子锁定模拟试验设备开展了无限流保护电阻和有限流保护电阻的单粒子锁定效应脉冲激光模拟试验研究。结果发现:TCD-GP1芯片在20 nJ脉冲激光辐照下发生了单粒子锁定现象。在对照试验中发现,有限流保护电阻的情况下,在发生锁定时不仅能降低锁定大电流和供电电压,而且还能有效地避免器件的功能损伤。     

高温高声强行波管的传热动态建模方法

文章针对热声疲劳测试中的传热问题提出了一种基于控制框图的新型建模分析方法,并用此方法分析了高温行波管内的多物理场耦合问题,同时针对模型的可靠性进行了试验和高精度数值仿真计算验证。研究表明,该方法可以针对多种工况快速有效地分析和仿真行波管内测试段的动态传热过程,满足工程设计快速预测的需求。     

柔性收集室检漏技术可靠性分析与验证

柔性收集室检漏技术是一种航天器总漏率检测技术,其工作原理是利用柔性材料制成的罩子作为示漏气体的收集容器,以氦质谱检漏技术为基础进行航天器的总漏率检测。文章针对柔性收集室检漏技术中关键环节的可靠性进行了分析研究和试验验证。结果表明:柔性收集室检漏技术可满足航天器总漏率检测任务需要。     

舰船及其海面背景SAR成像模拟研究综述

舰船及其海面背景SAR成像模拟是发展海洋遥感的重要途径。针对舰船及其海面背景不同于陆地目标的特性,从SAR成像模拟的方法及优缺点出发,对其研究现状进行了综述。介绍了舰船隐身的主要技术途径,并对今后进一步的研究方向进行展望。     

国外自主交会测量敏感器技术发展趋势

基于空间任务的高可靠性要求,在传统传感器通过技术改进等方式提升性能的同时,新型探测传感器逐渐进入人们的视野。结合国外自主交会任务,通过介绍自主交会敏感器的发展历程,分析了未来交会对接敏感器的发展方向。