复杂动力学模型下星载天线跟瞄控制技术研究

针对星载天线动力学复杂这一问题,从天线系统刚柔耦合动力学建模、指向跟踪控制以及振动抑制等方面研究了柔性星载运动部件的指向控制方法。首先,通过描述系统几何拓扑关系建立系统运动学方程,从而简化动力学建模过程;之后,利用假设模态法,对天线反射面挠性进行建模;最后,将拉格朗日方程与挠性关节模型相结合,从而建立了星载天线非线性刚柔耦合动力学模型。在以上复杂动力学建模的基础上,采用分层设计的思路进行了控制策略设计：先运用基于计算力矩法的滑模控制器得到不考虑挠性关节的耦合控制律,从而保证卫星基体的稳定性以及天线挠性反射面的振动抑制;再使用反步法对挠性关节进行控制,实现对天线反射面的指向精度控制。最后,讨论了动力学参数不确定性对系统跟踪指向控制的影响并采用数学仿真的方式验证了相关动力学模型与控制算法。仿真结果表明该方法能较好地实现对星载天线的指向跟踪控制以及振动抑制,提高星载天线的动态指向精度。     

基于压电纤维复合材料的航天器动力学建模与振动抑制

压电纤维复合材料(MFC)在柔性航天器的振动主动抑制中具有很好的应用前景。利用哈密顿原理和压电驱动的载荷比拟方法,建立了带MFC压电驱动的离散形式的刚柔耦合动力学方程,采用线性二次型最优控制(LQR)算法进行主动控制。结果表明：在航天器的柔性体受到脉冲载荷激励条件下,使用MFC驱动器可以实现航天器挠性振动的快速抑制,并且同时保持中心刚体姿态的稳定性,即能够实现挠性振动与姿态运动的协同控制。基于MFC的主动控制方法对于高频响应也具有较好的控制效果。对于柔性占优的航天器,采用MFC的主动控制优于被动控制。本文方法在处理具有复杂柔性体的航天器时更具优势,更适合于工程应用。     

Investigation on nonlinear lateral-torsional coupled vibration of a rotor system with substantial unbalance

Substantial unbalance may be caused by fan blade off during the operation period of gas turbine engines, and related dynamic problems are very critical to the safety design of rotor system in aero-engine. This article aims to understand lateral-torsional coupled vibration of the rotor system with substantial unbalance. The governing equation of a modified unbalanced rotor system is established based on Lagrangian approach. Then, a mathematical analytical method is proposed in which a linear approximation is derived and the Floquet theory and Hill’s method are incorporated, from which the modal characteristics of the unbalanced rotor are obtained. The modal characteristics of the unbalanced rotor system are revealed comprehensively for the first time. Furthermore, the relation between the modes and responses of the unbalanced rotor is discussed in detail. The results show that the lateral vibration and torsional vibration of the unbalanced rotor are coupled through the inertial terms in the governing equations. Due to the coupling, veering and lock-in phenomena occur between the frequencies of the forward whirl mode and the torsional mode. Furthermore, lock-in can lead to a kind of principal instability. With regard to the response of the unbalanced rotor, both natural vibration components and enforced vibration components appear in the lateral response, while only natural vibration components appear during torsional vibration. Moreover, natural vibration components play a crucial role in the response within the principal instability region and cause divergence of the vibration amplitudes in the lateral and torsional directions.     

椭圆振动切削加工的同步控制研究

利用椭圆振动切削加工的回转体表面微织构是在机床主轴旋转、平台进给和装置椭圆振动的联合运动下得到的,机床主轴转动与装置位移输出如果不能保持完全的实时同步,会造成微织构加工的偏差。为了解决这一问题,提出了一种新的基于转角的同步控制方法,该方法在主轴的对位基准处实现装置正弦信号的复位,以修正转速漂移造成的加工位置误差,并通过判断主轴角度信号实时输出对应幅值电压来实时同步信号输出和机床旋转运动。基于LabVIEW FPGA搭建同步控制模块,经试验验证,利用该方法加工的矩形阵列微织构轴向排列与中轴线平行,与周向排列的夹角和仿真结果的偏差不超过0.1°,织构深度随转角的不同发生预设的变化,因此,同步控制方法具有实时同步控制椭圆振动切削装置的能力。     

Near-wall topological patterns and flow structures over a simplified Danaus plexippus model

Studies on the high-lift mechanisms of butterfly gliding flights shed light on the design of the micro air vehicles. The flow field around a simplified Danaus plexippus model is investigated using the hydrogen bubble visualization and the Particle Image Velocimetry (PIV) techniques. There are three near-wall topological patterns with different Angles of Attack (AoAs): the separation bubble, the Leading-Edge Vortex (LEV) and the high AoAs flow. For the separation bubble pattern, two saddles and two foci form in the middle of the model. The features of the LEV pattern are the leading-edge separation lines. The topological characteristics of the separation lines are changed by the interaction between the LEV and the Wing-Tip Vortex (WTV). For the high AoAs flow pattern, four unstable foci are found at the forewing and the hindwing respectively. The angle between the trajectory of the WTV and the model increases with increasing AoA even though the slope of the WTV angle versus AoA curve declines at the moderate AoAs.     

Analysis on Output Power for Multi-direction Piezoelectric Vibration Energy Harvester

To predict the performance of multi-direction piezoelectric vibration energy harvester,an equation for calculating its output power is obtained based on elastic mechanics theory and piezoelectricity theory.Experiments are performed to verify theoretical analysis.When the excitation direction is along Y direction,a maximal output power about 0.139 mW can be harvested at a resistive load of 65kΩ and an excitation frequency of 136 Hz.Theoretical analysis agrees well with experimental results.Furthermore,the performance of multi-direction vibration energy harvester is experimentally tested.The results show that the multi-direction vibration energy harvester can harvest perfect energy as the excitation direction changes in XY plane,YZ plane,XZ plane and body diagonal plane of the harvester.     

改革开放以来我国社会管理思想的发展脉络及评述

改革开放以来,市场经济使国家和社会的关系发生了深刻变化,中国共产党在治国理政的过程中,不断探索和调整适合我国国情和发展需要的社会管理理念、方式和决策机制。从十一届三中全会至今,历次党代会上中国共产党都对社会管理都有新的认识、新的提法和新的部署,反映了党在不断探索和调试的过程中,在理论和实践的互动中社会管理思想的逐步形成。     

旋转机械轴系不对中故障的建模及其理论分析

轴系不对中是旋转机械常见的故障,通过对该故障建立理论模型,并采用 Ｒａｃｃａｔｉ传递矩阵法对之进行数值计算和理论分析,重点计算了角度不对中时的振动特性。为旋转机械的故障诊断提供理论参考。     

Plane wave spectrum and boresight error of radome-enclosed antennas

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终端区域理想速度剖面的生成

本文着重探讨了飞机进入终端区域后理想速度剖面的生成问题,目的是通过执行理想剖面生成算法,达到对飞机进行精确的时间控制,消除等待时间,提高机场利用率,达到节省燃料减少延误的目的。