敏捷成像卫星自主调度技术综述

针对现代卫星载荷能力与机动能力不断提升以及卫星任务需求多样化与复杂化程度持续增加的现状,阐述了敏捷成像卫星调度问题的基本特征,给出了敏捷成像卫星调度问题的一般化描述方法。在此基础上,分别从自主感知、自主决策和自主协同三个方面梳理了国内外敏捷卫星自主调度关键技术的研究进展。最后,面向未来卫星技术发展需求,指出了敏捷成像卫星自主调度技术进一步的研究方向。     

Numerical investigation on flow mechanism in a supersonic fluidic oscillator

A type of supersonic fluidic oscillator is proposed and its ability to generate pulsating supersonic jet is proved in this paper. Unsteady two-dimensional numerical simulations reveal that the fluid transforms from subsonic to supersonic condition in the mixing chamber of oscillator after the supplied flow pressure increases from 1.1 × 10⁵ Pa to 5.0 × 10⁵ Pa. When the supersonic flow is formed inside the oscillator, the wall-attached flow represents expansion wave and compression wave alternately. The oscillating frequency will saturate to a certain value with the increase of supplied pressure. Examination of the internal fluid dynamics indicates that the flow direction inside the FeedBack Channel (FBC) is related to the change of the local pressure at the inlet and the outlet of the feedback channel. The vortices produced in the mixing chamber present different distribution characteristics with the change of the fluid’s direction in the FBC. The sweeping jet is divided into two jets with varying flow rate over time by the splitter. In the end of two channels, two jets are accelerated above sound speed by convergent-divergent nozzle. Therefore, pulsating supersonic jets are produced at two outlets for this type of fluidic oscillator.     

火箭上升段滚动时域制导控制一体化设计

针对传统火箭上升段制导与姿态控制系统分离设计无法最大程度优化控制精度、控制量需求等系统整体控制性能的问题，提出一种基于凸优化的滚动时域制导控制一体化(IGC)设计方法。首先建立反映质心运动和绕质心运动耦合关系的IGC模型并对其进行反馈线性化获得面向控制的线性模型。然后考虑控制约束，将上升段IGC问题建模为最优控制问题，基于凸优化理论设计滚动时域控制器。该方法基于滚动时域控制(RHC)策略中反馈校正和滚动优化的思想，可以及时弥补模型误差和外部干扰等造成的不确定性；同时利用凸优化算法计算复杂度低、求解简单的优势，有效解决了含控制约束的复杂优化问题的求解。基于李雅普诺夫稳定性理论证明了闭环系统的稳定性。数值仿真校验了该滚动时域控制方法的有效性和鲁棒性；并且仿真结果表明，火箭上升段IGC设计比传统分离设计制导精度更高、控制量需求更小且姿态变化更加平缓。     

Glacier mapping based on rough set theory in the Manas River watershed

Precise glacier information is important for assessing climate change in remote mountain areas. To obtain more accurate glacier mapping, rough set theory, which can deal with vague and uncertainty information, was introduced to obtain optimal knowledge rules for glacier mapping. Optical images, thermal infrared band data, texture information and morphometric parameters were combined to build a decision table used in our proposed rough set theory method. After discretizing the real value attributes, decision rules were calculated through the decision rule generation algorithm for glacier mapping. A decision classifier based on the generated rules classified the multispectral image into glacier and non-glacier areas. The result of maximum likelihood classification (MLC) was used to compare with the result of the classification based on the rough set theory. Confusion matrix and visual interpretation were used to evaluate the overall accuracy of the results of the two methods. The accuracies of the rough set method and maximum likelihood classification were compared, yielding overall accuracies of 94.15% and 93.88%, respectively. It showed the area difference based on rough set was smaller by comparing the glacier areas of the rough set method and MLC with visual interpreter, respectively. The high accuracy for glacier mapping and the small area difference for glacier based on rough set theory demonstrated that this method was effective and promising for glacier mapping.     

A comparative study of decision tree,random forest,and convolutional neural network for spread-F identification

Ionospheric spread-F (SF) is a commonly observed phenomenon of electron density perturbation in the F-layer. The ionospheric irregularities structure has an adverse effect on the propagation of electromagnetic waves in the ionosphere. The automatic identification of ionospheric spread-F and statistical study of the formation of spread-F are of great significance to the study of the physical mechanism of ionospheric inhomogeneity and for prediction of ionospheric irregularities. In this paper, we describe and implement three automatic identification methods of spread-F based on machine learning: decision tree, random forest, and convolutional neural network (CNN). The performance of these automatic identification methods was verified using a large set of test data. Results show that the accuracy of all three methods on identifying ionograms with spread-F exceeded 90%. After comparing the results of the three methods, we found that the decision tree method was the simplest and with the structure easiest to be understood, and it required the shortest interpretation time. In terms of the identification results, the random forest method provided better results than the decision tree method, and the CNN method was the best at accurately identifying ionograms with spread-F.     

Dynamics modeling and control of a transport aircraft for ultra-low altitude airdrop

The nonlinear aircraft model with heavy cargo moving inside is derived by using the separation body method, which can describe the influence of the moving cargo on the aircraft attitude and altitude accurately. Furthermore, the nonlinear system is decoupled and linearized through the input–output feedback linearization method. On this basis, an iterative quasi-sliding mode(SM)flight controller for speed and pitch angle control is proposed. At the first-level SM, a global dynamic switching function is introduced thus eliminating the reaching phase of the sliding motion.At the second-level SM, a nonlinear function with the property of ‘‘smaller errors correspond to bigger gains and bigger errors correspond to saturated gains' ' is designed to form an integral sliding manifold, and the overcompensation of the integral term to big errors is weakened. Lyapunovbased analysis shows that the controller with strong robustness can reject both constant and time-varying model uncertainties. The performance of the proposed control strategy is verified in a maximum load airdrop mission.     

应用UBET优化开式模锻中连皮厚度参数

连皮厚度是开式模锻工艺参数中的一个重要参量，它对模锻变形力和材料的消耗有很大的影响。本文应用上限单元法（ＵＢＥＴ）对连皮厚度进行了优化设计。基于连皮厚度和飞边高度间的相对大小关系，建立了三种不同的变形流动模式和动可容速度场，根据上限原理和黄金分割法，利用ＴｕｒｂｏＣ语言编程求解，获得了最大锻造力的最佳上限解，并和实验相比较，两者吻合得较好，表明建立的动可容速度场是合理可行的。以最大锻造力和连皮体积的乘积作为优化准则，更好地得到了最佳连皮厚度值。     

耀斑后环珥系速度场的定量研究

本文研究了在太阳重力、偶极磁压强梯度和气体压力梯度联合作用下环珥系内物质的下落运动,并在等温、定常假设下用数值方法计算了该环系的二维视向速度场。通过将速度场的理论计算跟文[1]中给出的观测速度场拟合,导出了该环系的有关参数及分布。计算表明环系内物质密度和磁场强度对物质下落运动影响较显著。     

关于探测器定点在共线平动点附近的控制问题

对探测器定点在共线平动点附近的轨道控制提出了一种小推力方案,针对日-地（月）系的具体背景给出了数值模拟结果,并对其进行了相应的分析.