挠性支承对飞轮隔振系统性能的影响分析

飞轮的高速转子在运转过程中会激发微幅多频振动,对航天器的高精度姿态稳定控制产生不利影响.本文基于飞轮隔振系统结构,建立其动力学模型,并通过实验验证该被动隔振装置的固有模态.对增加挠性支承的飞轮隔振系统的数学模型,通过仿真分析隔振装置在挠性支承条件下对飞轮扰动的抑制效果,实验测试了不同挠性支承条件对飞轮隔振系统微振动特性的影响.结果表明,隔振装置在悬臂挠性支承条件下依然具有优异的隔振性能,挠性支承刚度的适当减弱有利于飞轮隔振系统抑制扰动;挠性支承刚度会降低飞轮隔振系统的二阶结构固有振动频率,但基本不影响其涡动特性.     

三层铝板结构高速撞击损伤与极限特性

利用二级轻气炮发射铝球弹丸,在真空环境下高速撞击双层铝板和三层铝板结构,研究撞击速度、板间距、铝板厚度对结构撞击损伤的影响。然后分析三层铝板结构的撞击极限速度,并与相同面密度的双层铝板结构的试验结果进行比较。结果表明,当面密度相同时,三层铝板结构比双层铝板结构具有更强的高速撞击防护能力,增加首层铝板厚度有助于提高三层铝板结构高速撞击防护性能,当第二层铝板位于首层铝板与舱壁中间位置时,三层铝板结构的高速撞击防护性能趋于最佳。     

基于2种中介轴承的对转双转子系统耦合碰摩动力学模型

以2种不同支承形式的中介轴承双转子结构系统为研究对象,建立了对转双转子系统轴向一径向耦合碰摩有限元动力学模型。基于陀螺效应引起轮盘偏转产生轴向位移,导致轴向碰摩的假设,给出了轴向碰摩力与节点坐标之间的表达式,考虑了不同支承形式的中介轴承耦合力处理方式,并以此为基础详细推导了系统的振动微分方程。模型既能描述转静间的轴向碰摩和径向碰摩,又允许轴向碰摩和径向碰摩独立发生,亦可共同发生。     

Influences of milling and grinding on machined surface roughness and fatigue behavior of GH4169 superalloy workpieces

Surface topography of superalloy GH4169 workpieces machined by milling and grinding is different significantly. Meanwhile, surface roughness, as one of the main indicators of machined surface integrity, has a great influence on the fatigue behavior of workpieces. Based on analyzing the formation mechanism and characteristics of surface roughness utilizing different machining processes and parameters, the machined surface roughness curve can be decoupled into two parts utilizing frequency spectrum analysis, which are kinematic surface roughness curve and stochastic surface roughness curve. The kinematic surface roughness curve is influenced by machining process,parameters, geometry of the cutting tool or wheel, the maximum height of which is expressed as R'_z.By subtracting the kinematic part from the measurement curve, the stochastic surface roughness curve and its maximum height R'_zcan be obtained, which is influenced by the defects of cutting tool edge or abrasive grains, built-up edges(BUE), cracks, high frequency vibration and so on. On the other hand, the results of decoupling analysis of surface roughness curves indicate that Raand Rz values of milling GH4169 are 2–5 times and 1–3 times as high as those of grinding, while R'_zvalue of milling is 13.85%–37.7% as high as that of grinding. According to the results of fatigue life tests of specimens machined by milling and grinding, it can be concluded that fatigue behavior of GH4169 decreases with the increase of R'_zmonotonically, even utilizing different machining processes.     

A brief overview of the School of Aerospace Engineering of Tsinghua University

This article provides a brief overview of the teaching and research at the School of Aerospace Engineering (SAE) to celebrate the 80th anniversary of the establishment of aeronautics as a discipline at Tsinghua University. The evolution of the school, undergraduate/graduate students and faculty members, and research activities and achievements have been described. The research input including research funding and research projects are summarized, showing a diversity of funding sources and a significant growth in either sum total or spending per researcher. The achievements including publications and inter/national academic awards are also introduced. It can be seen that the level of academic publications has been growing over the past decades. In addition, four representative research achievements have been briefly described to show the scientific contributions of the school.     

一种基于航迹特征的无人机与飞鸟目标雷达识别方法

对于现代雷达探测系统而言,无人机与飞鸟同属于具有“低慢小”特征的一类典型目标,而面对比较复杂的作战环境,其对功能的要求已经不仅局限于对两者目标实现稳定探测跟踪,如何有效区分两者类型并完成识别更是当下急迫且重要的难题。常规方法是从目标的微动特征差异进行区分,但由于两者回波微弱,很难通过时频分析方法提取目标特征。针对该问题,从航迹特征出发,提出一种无人机与飞鸟目标雷达识别方法。首先对比两者目标在运动轨迹上的差异性,进行特征分析,提出时间相关的航向震荡频率与速度震荡频率特征量描述方法,并在离线状态下,利用实测雷达系统记录的航迹数据,提取两者的有效特征量;然后利用支持向量机算法对样本进行训练,并在获得最优模型参数后,通过测试样本进行测试,测试分类结果显示准确识别率能够达87%;最后在线状态下跟飞实验,其结果既表明该方法的正确性,也体现了在工程实现角度上的轻量性、实用性、适用性,具有较高价值。     

HYBRID POSITION/FORCE MANIPULATION OF MULTIFINGERED HAND

ＨＹＢＲＩＤＰＯＳＩＴＩＯＮ／ＦＯＲＣＥＭＡＮＩＰＵＬＡＴＩＯＮＯＦＭＵＬＴＩＦＩＮＧＥＲＥＤＨＡＮＤＧＵＡＮＹｉｓｈｅｎｇ（管贻生）,ＺＨＡＮＧＱｉｘｉａｎ（张启先）（ＲｏｂｏｔｉｃｓＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅ,ＢｅｉｊｉｎｇＵｎｉｖｅｒｓ...     

基于区间电流的SRM功率变换器短路故障诊断

功率变换器是开关磁阻电机（SRM）调速系统的核心部件之一,也是系统可靠性最弱的环节。针对传统功率变换器短路故障诊断需增加额外硬件、控制器负担大、诊断范围有限等问题,以非对称半桥式功率变换器为研究对象,在深入分析短路故障模式的基础上,为提取明显的故障特征,对电流传感器进行了重新排布,提出了基于特定转子位置区间内电流的功率变换器故障诊断方法。在某相单独励磁区间内,通过另外两相电流传感器输出值之差与前一相输出值的比值,即可快速定位故障器件。所提方法不受电机相数和控制方式限制,控制器负担小,且无需增加额外硬件。仿真和实验验证了方法的有效性。      

复合材料层压板低速冲击行为及剩余拉伸强度

通过实验研究了复合材料层压板的低速冲击行为和剩余拉伸强度。首先,通过冲击实验研究了冲头类型和铺层形式对层压板冲击响应的影响,并通过凹坑深度、损伤投影面积、冲击力和冲击能量转化等对冲击损伤特性进行评估。其次,通过准静态拉伸实验调查了层压板的冲击后拉伸响应和剩余拉伸强度。最后,分析了冲头类型和铺层形式对层压板冲击行为和剩余拉伸强度的影响机理。结果表明:冲头类型对层压板冲击损伤的影响与冲击接触面投影面积和凹坑深度的函数关系密切相关;在较高的冲击能量下,条刃形冲头是造成损伤的关键冲击威胁,而立方角形冲头造成的损伤相对不严重;铺层形式对层压板的冲击损伤阻抗性能和拉伸断裂形貌有明显的影响。      

非线性移动路径跟踪及着舰控制应用

针对传统路径跟踪方法不能有效解决移动路径跟踪（MPF）问题, 通过改进时变向量场方法提出一种新型移动路径跟踪控制方法, 并应用到舰载机自主着舰控制问题中。基于舰载机非线性模型, 以反步法为主体框架, 在时变向量场中定义轨迹误差, 同时为定义的虚拟控制量设计Lyapunov函数, 实现航向角和爬升角的快速准确跟踪, 保证舰载机航迹跟踪期望移动路径。稳定性分析证明跟踪误差收敛, 仿真结果表明控制方法具有良好的着舰性能。