高超声速边界层转捩机理及应用的若干进展回顾

高超声速边界层转捩对飞行器的热传递、表面摩阻和流动分离等有重要影响,尤其是再入飞行器和吸气式巡航飞行器。然而,人们对边界层转捩机理中的很多问题认识还不清楚,或存在争议。本文从扰动波演化的角度回顾了高超声速边界层感受性、线性稳定性和非线性作用的国内若干研究进展,并以基于谐波共振的人工转捩技术为例示范了这些机理认识在转捩控制上的应用。扰动的产生和发展是认识边界层转捩机理的核心。通过研究扰动波来认识边界层转捩机理,开展应用创新研究对提升飞行器性能具有重要意义。     

Ionospheric TEC disturbances over China during the strong geomagnetic storm in September 2017

From September 7 to 8, 2017, a G4-level strong geomagnetic storm occurred, which seriously impacted on the Earth’s ionosphere. In this work, the global ionospheric maps released by Chinese Academy of Sciences are used to investigate the ionospheric responses over China and its adjacent regions during the strong storm. The prominent TEC enhancements, which mainly associated with the neutral wind and eastward prompt penetration electric field, are observed at equatorial ionization anomaly crests during the main phase of the storm on 8 September 2017. Compared with those on 8 September, the TEC enhancements move to lower-latitude regions during the recovery phase on 9 September. A moderate storm occurred well before the start of the strong storm causes similar middle-latitude TEC enhancements on 7 September. However, the weak TEC depletion is observed at middle and low latitude on 9–10 September, which could be associated with the prevailing westward disturbance electric field or storm-time neural composition changes. In addition, the storm-time RMS and STD values of the ionospheric TEC grids over China increase significantly due to the major geomagnetic storm. The maximum of the RMS reaches 12.0 TECU, while the maximum of the STD reaches 8.3 TECU at ~04UT on 8 September.     

Neural adaptive control for a ground experiment of the space proximity operation in a six-degree-of-freedom micro-gravity simulation system

In this study, a neural adaptive controller is developed for a ground experiment with a spacecraft proximity operation. As the water resistance in the experiment is highly nonlinear and can significantly affect the fidelity of the ground experiment, the water resistance must be estimated accurately and compensated using an active force online. For this problem, a novel control algorithm combined with Chebyshev Neural Networks (CNN) and an Active Disturbance Rejection Control (ADRC) is proposed. Specifically, the CNN algorithm is used to estimate the water resistance. The advantage of the CNN estimation is that the coefficients of the approximation can be adaptively changed to minimize the estimation error. Combined with the ADRC algorithm, the total disturbance is compensated in the experiment to improve the fidelity. The dynamic model of the spacecraft proximity maneuver in the experiment is established. The ground experiment of the proximity maneuver that considers an obstacle is provided to verify the efficiency of the proposed controller. The results demonstrate that the proposed method outperforms the pure ADRC method and can achieve close-to-real-time performance for the spacecraft proximity maneuver.     

面向空间天线的TWF复合材料性能研究

利用碳纤维三向编织物（triaxial woven fabric，TWF）作为增强材料，与柔性基体材料硅橡胶复合，制成兼具一定柔性和刚性的复合材料壳膜结构，用于卫星天线反射器，是一种新型的高精度可展开天线实现方案。采用复合材料细观方法，对碳纤维增强硅橡胶TWF复合材料进行了力学性能的研究。首先由纤维和基体的材料特性得到均质纤维束的材料特性；接下来考虑纤维束交织情况（起伏波动）建立由纤维束组成的单胞实体有限元模型；然后对单胞实体有限元模型进行均匀化分析，施加周期性边界条件，最终得到等效的均质材料特性；为满足天线反射器高性能需求，分析了碳纤维种类、纤维体积分数对单胞等效性能的影响规律。对该材料力学性能的研究，可以为其未来应用于大型高精度可展开天线反射器提供一定的理论依据。     

Identification of seismic activity sources on the subsatellite track by ionospheric plasma disturbances detected with the Sich-2 onboard probes

Using a cylindrical Langmuir probe and the authors’ proprietary two-channel pressure transducer, ionospheric plasma parameter distributions along the orbit of the Sich-2 satellite (Ukraine, 2011–2012) were measured. This paper is concerned with identifying the space–time location of ionospheric plasma disturbance sources, including the epicenters of actual earthquakes (before or during the satellite flyover) and incipient earthquakes on the subsatellite track, from the measured distributions of the electron density and temperature and the neutral particle temperature along the satellite orbit. To do this, the measured ionospheric plasma parameter distributions are connected to the coordinates on the subsatellite track.It is shown that local disturbances in the electron density and temperature and neutral particle temperature distributions in the satellite orbit in the ionosphere may serve as indicators of seismic activity on the subsatellite track. The epicenters of incipient earthquakes may be set off from other plasma parameter disturbance sources associated with seismic activity using information provided by special monitoring and survey centers that monitor the current seismic situation.     

Backstepping sliding-mode control of stratospheric airships using disturbance-observer

In the presence of unknown disturbances and model parameter uncertainties, this paper develop a nonlinear backstepping sliding-mode controller (BSMC) for trajectory tracking control of a stratospheric airship using a disturbance-observer (DO). Compared with the conventional sliding mode surface (SMS) constructed by a linear combination of the errors, the new SMS manifold is selected as the last back-step error to improve independence of the adjustment of the controller gains. Furthermore, a nonlinear disturbance-observer is designed to process unknown disturbance inputs and improve the BSMC performances. The closed-loop system of trajectory tracking control plant is proved to be globally asymptotically stable by using Lyapunov theory. By comparing with traditional backstepping control and SMC design, the results obtained demonstrate the capacity of the airship to execute a realistic trajectory tracking mission, even in the presence of unknown disturbances, and aerodynamic coefficient uncertainties.     

新型航空发动机空气冷却器流动传热性能试验

空气冷却器是航空发动机中空气热量交换的重要场所,针对传统扰动结构强化换热不足问题,重点研究了空气冷却器 中扰动结构的结构形貌特征与流动换热的关系。以三周期极小曲面结构为基础,设计制造了D型极小曲面扰动结构、P型极小曲 面扰动结构和基于Sigmoid函数杂化方法的D-P型（P-D型）结构。并利用纳米CT重构出样品的3维数字特征,试验研究了不同结 构来流速度与压降、换热性能和综合换热性能的关系。结果表明：D型极小曲面结构具有最优的压降、换热性能和综合换热性能： D-P型杂化极小曲面结构的阻力系数f最大,比D型结构的高56.81%;D型的平均努塞尔数Nu比P型的高18.49%,P-D和D-P杂 化结构的换热性能比P型结构的有效提高;P-D型D-P型杂化结构的Nu分别比P型结构的高2%和8.27%。在4种结构中,D型结 构的综合换热性能最优,分别比P型、P-D型、D-P型结构的高40.35%、57.2%、71.02%。     

强磁场扰动对宇宙线调制的统计研究

对1978─1982太阳活动高年时发生的激波、强磁场扰动及激波与强磁场扰动共存这三类事件引起的宇宙线变化进行了统计研究,得到如下结果:(1)激波与强磁场扰动共存时引起的宇宙线强度下降最为显着;只有激波或强磁场扰动时,宇宙线的强度变化相对较小;(2)标志速度间断的激波是产生宇宙线Forbush下降的重要因素;(3)速度间断在强磁场扰动对宇宙线的调制中可能起一个触发的作用。      

基于LADRC的无人机高精度定高控制

针对复杂气流扰动对无人机（UAV）航迹高度控制的影响,对存在复杂气流扰动下的定高控制策略、控制结构和控制器参数优化展开研究,实现高精度高度控制。基于线性自抗扰控制（LADRC）确定总体控制架构,设计扩张状态观测器（ESO）观测估计纵向高度通道和速度通道中存在的总扰动,在控制中引入扰动补偿,减小扰动对系统输出造成的影响。对UAV在飞行过程中存在的大气紊流扰动或离散突风等风干扰分析其功率谱密度,构造考虑风扰动对高度影响、时域响应特性和稳定裕度的综合目标函数,通过粒子群优化算法得到具有高精度、高抗干扰性能的控制器参数,优化中考虑风干扰的功率谱密度分布,减小了控制器参数设计的保守性。通过与常规比例-积分-微分（PID）控制器控制效果进行对比,说明基于线性自抗扰控制器的纵向高度控制的优异性能。      

一种适用于大幅值Quasi周期轨道的数值构造方法

针对现有方法在构造大幅值quasi周期轨道时收敛性和通用性不足等问题,提出一种适用于大幅值quasi周期轨道的数值构造方法。首先针对2维不变环面的计算问题,设计了映射间隔约束的环面多步微分修正算法。在此基础上,采用自然参数延拓法和伪弧长延拓法两种不同的思路构造等映射间隔的quasi周期轨道族。接着以quasi-Vertical为对象分析了两种思路各自的特点。最后以quasi-Axial, quasi-DRO等为对象验证了方法对三角平动点及多对复特征值情况的适用性。仿真结果表明,所提出的方法能够简单有效地解决多种类型幅值比超过1.2的大幅值quasi周期轨道的数值计算问题。