基于佘度和容错技术的高可靠机载智能配电系统设计

针对大型无人机(UAV)用常规配电系统占用航空总线资源多和可靠性低的问题,通过研究多电/全电飞机技术发展趋势和大型无人机供电系统技术特点,提出一种适用于大型无人机体系结构和指标要求的机载智能配电系统;建立系统的马尔可夫模型,计算和分析不同余度结构的供电处理机(PSP)和电气负载管理中心(ELMC)对系统可靠性的影响,进...     

基于全知熵的模式集成不确定性度量模型

不确定性是模式集成的一个固有性质,不确定性度量对模式集成具有重大影响。本文提出一种度量模型,在该模型中模式对象及其属性清洗模块使该模型免受规模影响。根据模式集成多属性分阶段决策的特点,本文基于粗糙集理论的全知熵不确定率进行各阶段的不确定性度量,并把过程模型的不确定性度量引入到总体不确定性的度量中,最后给出了合成多不确定率的方法。实例分析证实所设计模型是可行、有效的。     

加工工艺对C/ SiC 复合材料性能的影响

采用普通磨削和超声辅助磨削工艺对C/Si C复合材料进行加工,对不同加工工艺参数获得的C/Si C复合材料进行表面状态表征及力学性能的测试。结果显示在磨削深度0.05 mm,进给速度600 mm/h,转速1 600 r/min,超声频率14 k Hz的工艺参数匹配条件下,所得到的C/Si C复合材料的表面粗糙度最小,弯曲强度最大。表明超声辅助磨削加工工艺对材料力学性能损伤较小。     

降落伞充气过程中伞衣外形及流场变化研究

根据降落伞的结构和其在充气过程中的受力特性,以某平面圆形伞为原型,建立了伞衣充气过程中的计算流体力学与结构动力学耦合模型。并采用七孔探针对充满状态的绕流流场进行了定量测量,将该状态的试验结果和计算结果进行对比分析,二者的拓扑结构非常相似,压差系数也相差不大,因此所采用的数学模型是可靠的。在此基础上,对整个充气阶段的流场进行了数值模拟和分析,以详细了解降落伞整个开伞过程中伞衣外形变化及伞衣内外流场的变化情况。研究结果表明:①在初始充气阶段,伞衣展开部分外形基本保持较光滑的直筒形状,而非喇叭形。在主充气阶段:空气首先在伞衣顶部聚集,使伞衣顶部膨胀,然后膨胀部分向伞衣底边扩展,直到伞衣完全张满。②当伞顶孔被气流冲开后,伞衣的结构透气性对流场会产生显著影响。但从内外压力系数的变化来看,透气性对伞衣内滞止压力的影响较小,对伞衣外流场结构的影响较大,从而对伞衣外表面的压力影响较大。③对于此类有伞顶孔的平面圆形伞,当伞衣充气张开后,伞衣尾部出现气流分离,在一个漩涡区内形成两个相反旋转方向的漩涡。且随着伞衣直径扩张,分离区扩大,主流对漩涡区的剪切面积增大,因此漩涡区两个漩涡中外侧的一个漩涡增大,内侧漩涡被挤压至离伞顶更近的区...     

激光软钎焊技术及其在高精度惯性仪表中的应用探索

目前,绝缘子引线均采用传统电烙铁加热方式来焊接,存在焊接工作量大、易破坏玻璃和胶接面、质量一致性差等问题。介绍了激光软钎焊技术,包括其工作原理和技术特点,并在高精度惯性仪表外壳绝缘子引线焊接方面进行了应用探索。采用自主设计的激光软钎焊系统来进行焊接试验,得到的焊点外观质量与人工焊接相当,抗拉强度高于20MPa(引线本征抗拉强度）,绝缘电阻为7250MΩ,金属间化合物层(IMC层）平均厚度为0.558μm。试验结果表明,激光软钎焊的绝缘子引线抗拉强度高、绝缘良好、质量可靠,是有望实现惯性仪表自动化焊接的有效途径。     

Separation process of multi-spheres in hypersonic flow

The separation process of multi-spheres in hypersonic flow has been experimentally investigated. The experiments were conducted in a shock tunnel at a nominal freestream Mach number of 6. Iron or acetal small light spheres with different sizes, varying from 2.38 to 6 mm, were considered. They were mounted by a thin wire. The trajectory of the spheres was analyzed using optical images. By varying the radius and the number of spheres from a single to multiple spheres, the lateral velocity and the separation behavior including the phenomenon known as ‘shock wave surfing’ were measured and analyzed. A new equation to account for the lateral velocity of the multi-spheres was proposed by extending the well-known Passey and Melosh’s theory based on two bodies. The theoretical results were compared with the presented experimental data and a good agreement was found. Using the derived equation, the re-entry trajectory analysis of multi-spheres, that is regarded as the hypothetical break-up, was performed. The ground footprint and downrange due to the separation of the multi-spheres were compared with that of single- and two-spheres. The results showed that as the number of spheres increased, the lateral velocity increased while the ballistic coefficient decreased. This led to a large discrepancy in the ground footprint as well as the downrange when compared to the single sphere. Caution should therefore be exercised in the trajectory analysis when the effect of separation induced due to fragmentation is not considered.     

相控阵雷达长时跟踪波束调度与波形优化策略

针对相控阵雷达多目标跟踪波束调度和波形参数优化控制的问题，本文提出了一种基于马尔可夫决策过程（MDP）的相控阵雷达跟踪波束调度与波形参数优化策略，该方法以无迹卡尔曼滤波（UKF）算法为基础来估计目标的状态。首先将本文的序列决策问题建模为马尔可夫决策过程，定义了资源的效费比和长期回报率，然后与当前实际跟踪误差综合考虑作为MDP的回报函数，进而给出了调度的优化模型，最后将长时决策问题转化为动态规划算法结构进行求解，并且提出了一种并行混合遗传粒子群优化算法来求解各决策时刻的最优策略。仿真结果表明了长时策略的先进性以及寻优算法的优越性，与传统的短时策略相比，跟踪精度可提高11.17%。     

Adaptive flow control of low-Reynolds number aerodynamics using dielectric barrier discharge actuator

Aerodynamic performance of low-Reynolds number flyers, for a chord-based Reynolds number of 10⁵ or below, is sensitive to wind gusts and flow separation. Active flow control offers insight into fluid physics as well as possible improvements in vehicle performance. While facilitating flow control by introducing feedback control and fluidic devices, major challenges of achieving a target aerodynamic performance under unsteady flow conditions lie on the high-dimensional nonlinear dynamics of the flow system. Therefore, a successful flow control framework requires a viable as well as accessible control scheme and understanding of underlying flow dynamics as key information of the flow system. On the other hand, promising devices have been developed recently to facilitate flow control in this flow regime. The dielectric barrier discharge (DBD) actuator is such an example; it does not have moving parts and provides fast impact on the flow field locally. In this paper, recent feedback flow control studies, especially those focusing on unsteady low-Reynolds number aerodynamics, are reviewed. As an example of an effective flow control framework, it is demonstrated that aerodynamic lift of a high angle-of-attack wing under fluctuating free-stream conditions can be stabilized using the DBD actuator and an adaptive algorithm based on general input–output models. System nonlinearities and control challenges are discussed by assessing control performance and the variation of the system parameters under various flow and actuation conditions. Other fundamental issues from the flow dynamics view point, such as the lift stabilization mechanism and the influence on drag fluctuation are also explored. Both potentiality and limitation of the linear modeling approach are discussed. In addition, guidelines on system identification and the controller and actuator setups are suggested.     

基于Markov的察打无人机数据链时延建模与补偿研究

为了改善在数据链时延情况下察打无人机的性能,对造成时延的因素及影响进行了分析,在此基础上对数据链时延进行了合理的假设和简化。并对无人机整个控制回路的各个节点的响应方式,提出了一种时间-事件-事件-时间驱动方式,使得无人机数据链的时延序列具有Markov性,同时给出了状态转移矩阵的求取方法。为了改善无人机的响应特性,采用最优控制的方法对时延进行了补偿,并基于某无人机平台验证了补偿方法的有效性。仿真结果表明,该方法的引入使得无人机的动态响应特性有了显著提高。     

不同热处理工艺下激光增材制造TC4钛合金组织与性能研究进展

由于激光增材制造(Laser Additive Manufacturing,LAM)TC4钛合金加工成形过程的特殊性,导致该合金在力学性能上存在明显的各向异性,同时韧性、疲劳性能不能很好地满足使用要求。从材料组织与力学性能之间的关系出发,介绍了不同热处理工艺对激光增材制造TC4钛合金组织与力学性能的影响,指出了当前激光增材制造TC4钛合金热处理研究中存在的问题,并为后续激光增材制造TC4钛合金的热处理研究提供思路与方向。