无人机复杂环境中跟踪运动目标的实时航路规划

在复杂地形环境中,无人机在跟踪运动目标时,现有的航路规划方法在实时性和可行性上存在一定缺陷.提出了一种新的滚动窗口启发方向计算方法,使其能够跟踪运动目标,同时在滚动窗口内采用流函数法进行避障.根据无人机约束,滚动窗口为三角形,并设计了基于行为的伸缩功能.在流函数中,利用水势能方法克服了陷阱地形并进行了航路平滑.仿真结果表明:这种混合算法对于复杂地形条件下跟踪运动目标的航路规划,能够减小规划算法的时间和空间复杂度,使规划出的航路适于无人机飞行.     

湿热环境下复合材料层合板本构模型研究及其应用

近年来复合材料被广泛地应用于航空航天等工程领域。在实际的使用中,复合材料在不同的湿热环境下其力学性能会发生显著变化,针对这一问题,国内外已有大量的试验研究,而对湿热环境下复合材料的本构模型理论的研究则较少。在经典层合板理论基础上引入湿热膨胀系数的概念,通过定义一个无量纲的温度,建立材料弹性常数与湿热参数之间的函数关系,推导出复合材料单层板在湿热力耦合作用下的本构关系,同时加入三维Hashin失效判定准则对层合板的损伤演化及失效模式进行模拟。结果表明:该模型较好地预测了复合材料层合板在不同湿热环境下的弹性响应,为分析实际工程中复合材料结构模型在湿热环境下的力学行为提供了重要参考。     

不同重力环境下间隙铰链关节磨损分析

为研究不同重力环境对空间机构间隙铰链关节磨损的影响,将机械系统摩擦学行为和动力学行为相耦合,建立了磨损与动力学耦合分析模型和数值计算框架。首先采用非线性弹簧阻尼模型作为间隙处接触碰撞力的计算模型,同时采用Coulomb 法来计算运动副间隙处的摩擦力,进而建立了含间隙的机构动力学模型;然后通过基于Archard磨损模型二次开发的ANSYS程序来计算磨损,其中运用节点位移的方法来描述磨损过程。结果表明：当间隙关节转速较低时,重力对于关节轴承的磨损分布和磨损程度的影响很大,轴承出现集中磨损现象,磨损间隙急剧增加,严重影响机构的性能和精度;随着关节转速升高,重力对间隙关节磨损的影响逐渐减弱,轴承的磨损分布、磨损程度和关节最大磨损间隙的增长率将逐渐与微重力环境下趋同。     

航天器材料空间环境适应性评价与认定准则研究

航天器材料空间环境适应性是指航天器材料适应空间环境的能力,同时又是航天器系统级空间环境适应性的基础。确保航天器材料空间环境适应性是航天器研制初期重要环节。文章首先介绍了航天器材料的空间环境适应性类型;其次列举了材料空间环境适应性评价试验标准体系;然后分析了空间环境适应性评价手段与认定准则,包括选材阶段的评价试验、采购和使用阶段的验收试验以及空间环境适应性的认定。文章对我国航天器材料空间环境适应性评价与认定工作提出若干建议,为航天器材料选择和空间环境适应性控制提供参考。     

深空辐射环境及其效应的分析与比较

深空辐射环境对深空探测活动将带来严重的威胁。文章首先对深空辐射环境及效应进行了分析,接着对月球、火星、木星和土星等不同星体的辐射环境及效应进行了详细的探讨及比较。文章得到的结论可为深空探测器的设计和航天员的防护设计提供重要的指导与帮助。     

未来太空气象预报系统一瞥

文章从几个方面对太空气象预报系统进行了简单的介绍,包括:当前太空气象预报系统的水平;模板预报方案实施细则;实施模板方案的难度与可行性。作者关心我国对太空气象预报系统的研究,为进一步降低航天器发射风险、提高航天器运行可靠性而献计献策。     

Interface Familiarity Restores Active Advantage in a Virtual Exploration and Reconstruction Task in Children

Abstract

Active exploration is reportedly better than passive observation of spatial displacements in real environments, for the acquisition of relational spatial information, especially by children. However, a previous study using a virtual environment (VE) showed that children in a passive observation condition performed better than actives when asked to reconstruct in reality the environment explored virtually. Active children were unpractised in using the input device, which may have detracted from any active advantage, since input device operation may be regarded as a concurrent task, increasing cognitive load and spatial working memory demands. To examine this possibility, 7–8-year-old children in the present study were given 5 minutes of training with the joystick input device. When compared with passive participants for spatial learning, active participants gave a better performance than passives, placing objects significantly more accurately. The importance of interface training when using VEs for assessment and training was discussed.     

Environmental reference systems for large-scale spaces

Human navigation in well-known environments is guided by stored memory representations of spatial information. In three experiments (N = 43) we investigated the role of different spatial reference systems when accessing information about familiar objects at different locations in the city in which the participants lived. Our results indicate that two independent reference systems underly the retrieval of spatial knowledge. Environmental characteristics, e.g., the streets at an intersection, determine which headings are easier to imagine at a given location and lead to differences in accessibility of spatial information (orientation-specific behavior). In addition, access to spatial information depends on the relative direction of a location with respect to the imagined heading, such that information about locations imagined in front of oneself is easier to access than about locations towards the back. This influence of an egocentric reference system was found for environmental knowledge as well as map-based knowledge. In light of these reference system effects, position-dependent models of spatial memory for large-scale environments are discussed. To account for the simultaneous effect of an environmental and an egocentric reference system, we present a 2-level model of spatial memory access.     

空间辐射器热分析

在航天飞机温控系统中,空间辐射器是最主要部件。对以航天飞机蒙皮为辐射表面的,单面翼—管式空间辐射器进行了详细的热分析,把平均翼效率代替局部翼效率,利用有限差分的方法对单面翼—管式辐射器进行了性能计算。     

A distributed approach for lidar-based relative state estimation of multi-UAV in GPS-denied environments

In this paper, we present a distributed framework for the lidar-based relative state estimator which achieves highly accurate, real-time trajectory estimation of multiple Unmanned Aerial Vehicles(UAVs) in GPS-denied environments. The system builds atop a factor graph, and only onboard sensors and computing power are utilized. Benefiting from the keyframe strategy, each UAV performs relative state estimation individually and broadcasts very partial information without exchanging raw data. The com...