微重力条件下热管吸热器瞬态热分析

基于微重力条件下的导热控制微分方程,采用焓法对热管吸热器相变材料容器进行了二维数值建模与仿真,在同时考虑空穴和相变的情况下,对微重力条件下蓄热单元相变传热进行了模拟计算,分析了空穴率对蓄热容器内部的温度场和热性能的影响,并将计算结果同美国航空航天局（NASA）方案热管吸热器蓄热单元相变传热计算结果进行了比较,验证了文中微重力条件下计算模型的合理性与准确性。研究结果表明：空穴影响着蓄热单元相变的进程,空穴的存在增加了容器内部的温度梯度,使得容器的蓄热能力降低;由于热管径向温差较小,热管壁温在相变材料熔点附近变化较小,从而在一定程度上能缓解热斑和热松脱现象。     

航天器薄壳柔性附件展开耦合行为特性研究

为研究大范围运动柔性附件几何非线性和耦合效应与中心刚体的精确动力学行为,以薄壳结构柔性附件为研究对象,引入非线性应变和位移关系,利用虚功原理推导了做大范围运动带柔性附件航天机构的完整非线性动力学模型,所构建的模型包含了非线性几何变形及附加非线性项。针对线性和非线性模型,相应开展了大范围运动航天机构刚柔耦合数值分析。结果表明,随着转速增大,线性与非线性模型动力学特性产生根本差异,指出线性模型忽略了非线性耦合项的不足,而非线性模型可精确地预测大范围运动带柔性附件航天机构动力学行为。结论对航天机构定向和跟踪操作的动力学与控制具有重要的理论价值及工程实际意义。     

Enhanced electrothermal effect of carbon fibrous composites decorated with high conductive carbon nanotube webs

Literature has demonstrated that Carbon Nanotubes (CNTs) can greatly enhance the electrical conductivity and matrix-dominated mechanical properties of fibrous composites. However, electrothermal coupling effect of CNTs on Carbon Fiber Reinforced Plastics (CFRPs) has scarcely been considered. This work prepared and introduced thin and porous CNT webs to the surface or/and interface of a CFRP to enhance its electrothermal properties. The results show that CNT webs can enhance the transverse electrical conductivities of the CFRP by 231%−519% in a current range of 50–150 mA, when compared to the base-CFRP. Also, the surface temperature of CNT webs decorated CFRP can be improved by 20.5–32.3 °C within 3 min showing a self-heating rate of 6.8–10.8 °C/min just with an applied voltage of 20–30 V, increased by 152%−177% when compared to the base-CFRP (2.7–3.9 °C/min). Also, deicing can be finished within 4–10 min with a voltage of 18 V and an input power of 246 W/m². Moreover, the electrothermal processes nearly have no negative effect on the mechanical properties of the CFRP. The relatively low input power and short response time for deicing make the CNT webs decorated CFRP may be a potential new generation for aeronautical deicing structure.     

航天器新型非奇异饱和终端滑模姿态控制

针对刚体航天器姿态机动过程中存在的控制饱和与外部干扰问题,提出一类基于新型非奇异饱和终端滑模面的有限时间控制器设计方法。该控制方案不仅保证姿态机动过程的快速性,而且避免了传统的终端滑模面所带来的奇异性问题。此外,本文建议的控制器不仅显式考虑执行器输出力矩的饱和幅值要求,使航天器在饱和幅值的约束下完成姿态控制任务,而且控制器的设计对外部干扰的上界没有任何要求,也无需作任何小角度的假设。进一步的稳定性分析表明,通过引入新型非奇异饱和终端滑模,该控制器使得闭环系统能够快速收敛到滑模面的微小邻域内,继而收敛到平衡点的微小邻域内,并且系统对外部干扰具有较强的鲁棒性。数值仿真校验了该控制器在姿态机动过程中的性能。     

Real-time spacecraft intercept strategy on J2-perturbed orbits

A real-time intercept strategy for spacecraft under the non-uniform gravitational perturbation of Earth is addressed in this paper. To intercept a target spacecraft on general conic sections, an interceptor considered in this work makes use of a thruster propelling the constant thrust which is comparable to unrealistic impulse-type thrust. The $J_2$ perturbation introduces critical dynamic variations of spacecraft orbiting the Earth, which results in a considerable amount of position error of the interceptor at the final intercept point. In order to release the burden of $J_2$ disturbance and make the miss distance between the target and interceptor small, a real-time intercept technique with an optimal intercept algorithm is suggested. The strategy proposed is to obtain an optimized output iteratively for a given time interval with previously obtained optimal values. These parameters are evaluated by the optimal intercept algorithm suggested. Once the optimal velocity change is obtained to satisfy intercept requirements, although the orbital system is perturbed, it is easy to regenerate a new solution by setting the previous solution as new initial guesses. This strategy is employed iteratively until the interceptor meets the target. Several numerical simulations are performed to highlight the proposed real-time strategy for spacecraft intercept missions.     

Traverses for the ISECG-GER design reference mission for humans on the lunar surface

This study explores the Design Reference Mission (DRM) architecture developed by Hufenbach et al. (2015) as a prelude to the release of the 2018 Global Exploration Roadmap (GER) developed by the International Space Exploration Coordination Group (ISECG). The focus of this study is the exploration of the south polar region of the Moon, a region that has not been visited by any human missions, yet exhibits a multitude of scientifically important locations – the investigation of which will address long standing questions in lunar research. This DRM architecture involves five landing sites (Malapert massif, South Pole/Shackleton crater, Schrödinger basin, Antoniadi crater, and the South Pole-Aitken basin center), to be visited in sequential years by crew, beginning in 2028. Two Lunar Electric Rovers (LER) are proposed to be tele-robotically operated between sites to rendez-vous with crew at the time of the next landing. With engineering parameters in mind we explore the feasibility of tele-robotic operation of these LERs between lunar landing sites, and identify potential high interest sampling locations en-route. Additionally, in-depth sample collection and return traverses are identified for each individual landing site across key geologic terrains that also detail crew Extra-Vehicular Activity (EVA). Exploration at and between landing sites is designed to address a suite of National Research Council (2007) scientific concepts.     

挠性空间结构振动的独立模态空间最优控制方法

针对大型挠性空间结构的特性,考虑在独立模态空间内进行控制,设计模态滤波器,对从物理空间采集到的模态信息进行预滤波处理;设计模态观测器,从模态加速度中获取模态位移和模态速度;其次,利用独立模态空间理论中各阶模态相互独立解耦的特性,设计了基于最优控制的独立模态空间控制器;在此基础上,考虑外部干扰信号作用下,设计了基于模态滤波器的 次优控制器,构成了一个完整的挠性空间结构闭环主动振动控制系统。对简化的桁架和单翼帆板结构振动控制进行了仿真验证,结果表明：两种控制器均能使振动得到有效抑制,相比传统比例积分微分控制器最大振幅减小约一半,且具有一定的抗干扰能力。     

电学前沿计量技术在航天型号保障中的应用

针对航天器中电学基准的长期稳定性、多种传感器输出电信号的线性度、电脉冲测量的时延等多个航天电测领域的难题,提出采用电学量子计量技术和计算基准技术的解决方案,可以10^-9量级的不确定度测量航天器中电阻基准短期变化量,从而推算出长期变化量,对航天器的稳定控制具有重要作用;可以极小的不确定度校准多种传感器输出的毫伏、微伏量级电压的线性度,对航天传感器测量准确度具有重要意义;可在10^-9秒量级确定电脉冲测量中电阻引入的时延,对航天器电推进系统的控制具有重要作用。     

“嫦娥4号”月球背面着陆区月壳及深部结构特征

深部月壳和月幔物质结构是月球科学探测的关键问题之一。“嫦娥4号”初步将月球背面南极—艾肯（South Pole-Aitken,SPA）盆地内的冯·卡门（Von Kármán）撞击坑作为着陆点,具有重要的科学研究价值。结合月球重力、地形、布格重力、月壳厚度等地球物理数据,综合对冯·卡门撞击坑的月壳及其深部结构特征进行了分析。结果显示：冯·卡门撞击坑重复撞击到南部的冯·卡门M撞击坑上,后者的中央峰具有明显的布格正重力异常和线性的布格重力梯度特征,显示出高密度的幔部物质向上涌起;冯·卡门撞击坑极有可能穿透了该区域的整个月壳,并挖掘出了深部月幔的物质;该区域南部月壳厚度较薄小于5 km,北部平均月壳厚度在15～20 km,月壳平均密度为2 630 kg·m^-3,比背面高地月壳密度高,且平均孔隙度为9%,低于月球的平均孔隙度12%。     

超声速空腔流动波系演化及噪声控制研究进展

空腔结构在先进飞行器和动力装置中应用十分广泛,如飞机内埋武器舱、起落架舱、导弹光学头罩、超燃冲压发动机燃烧室、推力矢量发动机喷口等。这些空腔结构在实际应用中普遍面临严峻的气动噪声问题。研究表明,空腔噪声的产生与腔内非定常流动和复杂波系结构关系密切。对超声速空腔流致噪声已开展的研究进行综述,从而为系统地认识波系结构的演化规律、噪声产生机理和噪声控制机理提供参考。首先,介绍了闭式、过渡式和开式3种不同类型超声速空腔流动的主要特点,针对气动噪声最为严重的开式空腔流动,分析了7种典型波系结构形成、传播和相互作用等规律。然后,从空腔压力振荡反馈回路的4个关键环节出发,分析了当前广泛应用的3种压力反馈模型的异同。最后,总结梳理了超声速空腔噪声控制的5条路径,指出在第5条控制路径"干扰反馈激波的传播"研究方面存在的不足。并指出了当前研究存在的部分问题,就未来研究方向提出了建议。