电静液作动器自调节积分鲁棒运动控制

针对电静液作动器系统中存在的匹配干扰及不匹配干扰,基于扩张状态观测器,设计了一种自调节积分鲁棒控制方法。首先设计扩张状态观测器估计系统的匹配不确定性并且进行前馈补偿;然后设计自调节积分鲁棒控制器分别处理系统的不匹配干扰和状态估计误差,实现了电静液作动器的渐近跟踪控制;最后通过仿真验证了该控制方案的有效性。结果表明：相较于传统的PID控制器,该控制器的跟踪误差约为0.2mm,控制精度达到0.4%左右。     

Whistler waves in plasmas with time-varying magnetic field: Laboratory investigation

Modulation of whistler waves in a plasma with time-dependant magnetic field perturbations was investigated experimentally. The experiments were performed on large “Krot” device, which was specially designed to study space plasma physics phenomena. It is shown that magnetic field variations on the wave propagation path can lead to splitting of initially continuous whistler wave into the sequence of bursts, whose repetition rate corresponds to magnetic field perturbation period. The frequency inside each burst is changing from its front edge to the back edge. Relative shift of the wave frequency can be as large as the relative magnetic disturbance. Distortion of whistler wave frequency spectrum after its passing through magnetically disturbed areas can be used as a diagnostics for low-frequency magnetic field variations. The applicability of our laboratory results to space plasma is discussed.     

Automatic orbital docking with tumbling target using sliding mode control

The present study aimed to propose translational and rotational control of a chaser spacecraft in the close vicinity docking phase with a target subjected to external disturbances. For this purpose, two sliding mode controls (SMC) are developed to coordinate the relative position and attitude of two spacecraft. The chaser is guided to the tumbling target by the relative position control, approaching in the direction of the target docking port. At the same moment, the relative attitude control coordinates the chaser attitude so that it can be aligned with the target orientation. These control systems regulate the relative translational and rotational velocities to be zero when two spacecraft are docking. The robustness of the closed-loop system in the presence of external disturbances, measurement noises and uncertainties is guaranteed by analyzing and calculating the control gains via the Lyapunov function. The simulations in different scenarios indicated the effectiveness of the controller scheme and precise maneuver regarding the accuracy of docking conditions.     

基于ADRC迭代学习控制的四旋翼无人机姿态控制

针对农用无人机超低空表型遥感和喷药精准悬停易受地效扰动问题，提出了一种自适应ADRC姿态控制器。首先设计了基于ADRC的姿态控制器，结合四旋翼无人机平台在0.9~1.1、1.1~1.3、1.4~1.6、2.0~2.4、2.5~2.9、3.3~3.6 m/s侧向水平风、0.9~1.1 m/s （11°）、1.1~1.3 m/s （13°）、1.4~1.6 m/s （18°）、1.8~2.0 m/s （18°）、2.1~2.5 m/s （18°）前俯向风和侧俯向风下进行干扰的预测和控制量的补偿实验。实验结果显示使用ADRC姿态控制器后无人机抗风性能有较大提升。然而在存在初始误差时，ADRC固定带宽无法满足要求，进一步设计了自适应ADRC姿态控制器（ILC-ADRC）。通过迭代学习控制在线优化自抗扰控制器带宽，实现了不同增益观测器的自适应整定。实验结合四旋翼无人机平台分别进行了机头实际方向与期望方向偏离55°、90°、180°，水平风速1.1~1.3、1.4~1.6、2.0~2.4、2.5~2.9 m/s下使用ADRC和ILC-ADRC的对比。实验结果显示采用ILC-ADRC姿态控制器，在150次控制周期内，偏航角误差均在-15°~15°之间，满足四旋翼无人机偏航角控制精度要求，同时调节时间分别缩短了40%，16.67%，12.5%，53.33%，10.34%，13.95%，27.27%，58.66%，11.86%。     

Longitudinal variations of geomagnetic and ionospheric parameters in the Northern Hemisphere during magnetic storms according to multi-instrument observations

We present a joint analysis of longitude-temporal variations of ionospheric and geomagnetic parameters at middle and high latitudes in the Northern Hemisphere during the two severe magnetic storms in March and June 2015 by using data from the chains of magnetometers, ionosondes and GPS/GLONASS receivers. We identify the fixed longitudinal zones where the variability of the magnetic field is consistently high or low under quiet and disturbed geomagnetic conditions. The revealed longitudinal structure of the geomagnetic field variability in quiet geomagnetic conditions is caused by the discrepancy of the geographic and magnetic poles and by the spatial anomalies of different scales in the main magnetic field of the Earth. Variations of ionospheric parameters are shown to exhibit a pronounced longitudinal inhomogeneity with changing geomagnetic conditions. This inhomogeneity is associated with the longitudinal features of background and disturbed structure of the geomagnetic field. During the recovery phase of a storm, important role in dynamics of the mid-latitude ionosphere may belong to wave-like thermospheric disturbances of molecular gas, propagating westward for several days. Therefore, it is necessary to extend the time interval for studying the ionospheric effects of strong magnetic storms by a few days after the end of the magnetospheric source influence, while the disturbed regions in the thermosphere continues moving westward and causes the electron density decrease along the trajectories of propagation.     

地球物理导航中位场下延的迭代正则化方法研究

地磁、重力数据下延是制备地球物理导航基准图的重要内容,而它通常是一个不适定问题,采用常规代数方法求解并不奏效;对此,结合航空地球物理测量和地球物理导航的特点,研究了迭代正则化方法(包括迭代Tikhonov法、Landweber迭代法和截断奇异值分解(TSVD)法)在位场下延中的应用.首先给出了位场下延和迭代正则化的基本理论,然后采用理论位场模型验证了迭代正则化方法在位场下延中的应用可行性,最后分析了迭代正则化方法的下延精度、计算时间和边界效应等性能.由分析结果可知,迭代Tikhonov方法具有最好的综合下延性能,应优先在实际的位场下延中使用.     

刚体卫星姿态的有限时间控制

针对刚体卫星的姿态控制问题,设计了不存在和存在扰动力矩两种条件下的有限时间状态反馈控制律.对于无扰动力矩情形,基于非线性齐次系统性质,设计了一种便于工程实践性的连续、非奇异的比例微分形式控制算法,保证姿态闭环系统有限时间收敛到零点,而且此算法能直接推广到卫星姿态跟踪问题.对于存在扰动力矩的情形,基于有限时间Lyapunov定理设计的连续、非奇异的控制力矩保证卫星姿态和角速度在有限时间内收敛到原点附近的邻域.当外扰力矩为零时,此控制律使闭环系统状态有限时间收敛到平衡点.数学仿真结果说明了提出的控制算法有效.     

Ionospheric F-region response to geomagnetic disturbances

The F2-region reaction to geomagnetic storms usually called as an ionospheric storm is a rather complicated event. It consists of so called positive and negative phases, which have very complicated spatial and temporal behavior. The main morphological features of ionospheric storms and the main processes governing their behavior were understood at the end of the 1900s and described in a series of review papers. During the recent decade there were many publications dedicated to the problem of ionospheric storms. In this paper a concept of ionospheric storm morphology and physics formulated at the end of the 1990s is briefly summarized and the most interesting results obtained in the 2000s are described. It is shown that the main features of the studies of the previous decade were: the use of GPS TEC data for analyzing the ionospheric storm morphology, attraction of sophisticated theoretical models for studying the processes governing ionospheric behavior in disturbed conditions, and accent to analysis of ionospheric behavior during prominent events (very strong and great geomagnetic storms). Also a special attention was paid to the pre-storm enhancements in foF2 and TEC.     

The impact of large solar events on the total electron content of the ionosphere at mid latitudes

Ionospheric disturbances associated with solar activity may occur via two basic mechanisms. The first is related to the direct impact on the ionosphere of EUV photons from a flare, and the second by prompt electric field penetration into the magnetosphere during geomagnetic storms. In this paper we examine the possibility that these two mechanisms may have an impact at mid latitudes by calculating the total electron content (TEC) from GPS stations in Mexico during several large X-ray flares. We have found that indeed large, complex flares, which are well located, may affect the mid latitude ionosphere. In fact, in the solar events of July 14, 2000 and April 2001 storms, ionospheric disturbances were observed to increase up to 138 and 150 TECu, respectively, due to the influence of EUV photons. Also, during the solar events of July 2000, April 2001, Halloween 2003, January 2005 and December 2006, there are large ionospheric disturbances (up to 393 TECu in the Halloween Storms), due to prompt penetration electric field, associated with CME producing geomagnetic storm.     

交互式棱柱网格生成中翘曲现象形成机制及消除算法

在基于径向基函数插值的交互式棱柱网格生成中,当物面网格单元空间法矢变化范围较大或变化剧烈时,棱柱网格生成会发生翘曲问题,降低棱柱网格质量。针对该问题,首先采用DLR-F6机翼外形算例对翘曲现象进行了介绍和初步分析,并结合平板外形棱柱网格生成,通过不同波长推进位移扰动模拟法矢变化对推进位移的影响,研究棱柱网格翘曲现象的形成机制。不同位移扰动下平板棱柱网格生成结果证实边界棱线网格点推进位移不光滑会通过空间插值放大,引起棱柱网格发生翘曲,且网格翘曲的表现形式与推进位移的分布有关。从而间接表明棱柱网格生成中翘曲现象是由法矢变化带来推进位移分布不光滑引起的。然后从翘曲现象的形成机制出发,基于拉普拉斯方法发展了推进位移光顺技术,并通过DLR-F6机翼算例进行了验证。测试结果表明,光顺技术能够完全消除棱柱网格的翘曲,获得光顺的高质量棱柱网格。最后通过DLR-F6翼身组合体外形棱柱网格生成,展示了添加光顺技术的棱柱网格生成算法的应用潜力。