Nonlinear dynamic behavior of a flexible asymmetric aero-engine rotor system in maneuvering flight

Aero-engine rotor systems installed in aircraft are considered to have a base motion. In this paper, a flexible asymmetric rotor system is modeled considering the nonlinear supports of ball bearings and Squeeze Film Dampers (SFDs), and the dynamic characteristics of the rotor system under maneuvering flight are systematically studied. Effects of the translational accelerative motions, the angular motions and the pitching flight with combined translational and angular motions on nonlinear dynamic behavior of the rotor system are investigated. The results show that, due to the nonlinear coupled effects among the rotor, ball bearings and SFDs, within the first bending resonance region, responses of the rotor show obvious nonlinear characteristics such as bistable phenomenon, amplitude jumping phenomenon and non-synchronous vibration. Translational acceleration motion of the aircraft leads to axis offset of the rotor system and thus results in the reduction and the final disappearance of the bistable rotating speed region. The pitching angular motion mainly affects rotational vibration of the rotor system, and thus further induces their transverse vibrations. For the pitching flight with combined translational and angular motions, a critical flight parameter is found to correspond to the conversion of two steady responses of the rotor system, in which one response displays small amplitude and synchronous vibration, and the other shows large amplitude and non-synchronous vibration.     

Erosion degradation characteristics of a linear electro-hydrostatic actuator under a high-frequency turbulent flow field

The paper proposes a performance degradation analysis model based on dynamic erosion wear for a novel Linear Electro-Hydrostatic Actuator (LEHA). Rather than the traditional statistical methods based on degradation data, the method proposed in this paper firstly analyzes the dominant progressive failure mode of the LEHA based on the working principle and working conditions of the LEHA. The Computational Fluid Dynamics (CFD) method, combining the turbulent theory and the micro erosion principle, is used to establish an erosion model of the rectification mechanism. The erosion rates for different port openings, under a time-varying flow field, are obtained. The piecewise linearization method is applied to update the concentration of contaminated particles within the LEHA, in order to gain insight into the erosion degradation process at various stages of degradation. The main contribution of the proposed model is the application of the dynamic concentration of contamination particles in erosion analysis of Electro-Hydraulic Servo Valves (EHSVs), throttle valves, spool valves, and needle valves. The effects of system parameters and working conditions on component wear are analyzed by simulations. The results of the proposed model match the expected degradation process.     

卫星编队飞行相对轨道动力学模型的比较及选用

基于动力学方法推导了几种编队飞行相对轨道动力学模型．分析比较了引力项线性化以及J2摄动引起的模型误差的数量级,给出了模型选取的参考准则以及适用条件,分析了不同模型的适用性．最后选取太阳同步轨道和静止轨道作为数值算例,选取合适的相对轨道动力学模型,验证模型选取准则的有效性．仿真结果表明一定范围内考虑^摄动能提高精度,而超出一定范围J2的引入只会增加复杂性,因此提出的模型选取准则对相对轨道动力学模型的选取有一定的参考价值．     

基于矩阵误差的流动自适应求解

为了构造一个网格沿流场特征方向进行分布,以保证整个流场的误差尽量均匀化的网格系统,本文对可压缩流动的自适应求解进行了研究.研究内容包括基于误差矩阵的流场特征探测方法和网格自适应方法.网格自适应方法包含网格移动、网格加密、网格稀疏以及这3种方法的混合.基于误差矩阵的流场探测方法能找到流场特征的主方向, 通过网格自适应使得网格按主方向进行分布,可以减少该区域的误差而得到高精度的解.以边为单位能使得该流场的误差尽可能均匀化.本文以捕捉激波为例,对该方法的过程及应用进行了描述,结果验证了该方法的可靠性.     

空间机械臂关节动力学建模与分析的研究进展

空间机械臂的机械部分是一个由关节和臂杆等结构、机构部件组成,在空间零重力环境下运行的多体系统。关节是空间机械臂的核心部件,在机械臂动力学特性中起着重要的作用。准确全面地了解关节的动力学特性,是正确分析与模拟机械臂系统空间运动特性的关键,而建立精确的关节动力学模型,是机械臂系统设计、分析和控制的基础。文章结合空间应用的特殊性,对机械臂关节动力学建模方法的发展过程和研究成果进行了总结;并讨论了关节模型的求解算法;最后,对空间机械臂关节动力学建模与分析方面有待进一步研究的问题进行了展望。     

基于模态信息的叶盘结构失谐识别方法鲁棒性研究

为有效运用整体叶盘结构失谐识别技术,针对一种以模态信息作为输入参数的识别方法进行了鲁棒性方面的研究.推导了该方法中识别参数对各输入参数的灵敏度公式,利用灵敏度分析的结果,可以明确各个输入参数的重要程度,为实际运用中获取输入参数信息提供指导;另外也可对识别结果的准确度作进一步的分析评价,为可靠的使用该识别方法提供保障.      

对称交叉激波和湍流边界层相互作用的数值研究

针对两种双尖鳍外形的对称交叉激波与湍流边界层相互作用,采用N-S方程和两种湍流模型进行了计算。研究了网格收敛性、鳍的角度和湍流模型对壁面压强、Stanton数和壁面摩擦力线的影响。弱相互作用的计算结果较好,强相互作用的壁面压强和摩擦力线的计算结果与试验吻合较好,而Stanton数的计算结果较差,峰值高达试验的2.5倍左右。随着鳍的角度的增加,壁面压强和Stanton数的分布从单调分布发展为M型分布,两者的峰值不在相同的位置。湍流模型对壁面压强和壁面摩擦力线影响很小,对Stanton数计算的影响很大,SST模型比BSL模型表现好一些。     

作大范围运动刚柔混合体的动力学建模与仿真

考虑耦合效应的柔性空间结构耦合动力学研究在航空航天领域具有重要的应用价值.用有限元法对柔性结构进行离散化处理,得到了柔性结构的模态阵.以模态展开方法以及Kane方程为理论基础,建立了作大范围运动刚柔混合体的动力学模型,并通过Matlab软件编写程序进行求解.为了检验该动力学模型及其程序的正确性,将Matlab仿真结果与商用软件仿真结果进行对照,进而验证了该仿真的正确性.本研究解决了中心刚体加柔性附件这一类航天器的动力学仿真问题.      

基于虚网格的格心ADT搜索法

针对重叠网格寻点问题,提出了一种直接在格心网格下操作,基于虚网格的ADT(Alternating Digital Tree)搜索方法.通过对计算网格进行扩展,建立虚边界网格,解决了格心网格因覆盖区域不完整而无法直接建立ADT数据结构的问题.搜索结果即为包含解的格心单元集合,可直接对结果列表遍历以得到合理贡献单元,故完全摒弃了可靠性差的Stencil Walk方法.由虚网格的定义,使寻点在边界附近的处理更为灵活,可以准确给出边界附近贡献单元的有效信息,同时简化了虚网格体系的构建.扩展了重叠边界类型,构建的搜索空间能完整覆盖网格范围,解决了对称面重叠问题.算例研究表明:该方法可靠性好,边界处理能力强,有效提高了重叠网格方法对大型复杂网格的解算能力.     

基于多体动力学的旋翼模型与气弹稳定性

针对无轴承等先进旋翼结构特点,建立了基于柔性多体系统动力学方法的旋翼气弹分析模型.旋翼各构件建模相互独立,便于组成不同构型旋翼,适合于新构型旋翼气弹分析.分析模型集成了适合于旋翼气弹分析的隐式大变形桨叶模型,构件动力学方程增加了铰链动力学方程,统一约束方程形式,改进了角运动约束方程,避免连续旋转引起的奇点问题.应用分析模型计算无铰式旋翼和无轴承旋翼的气弹稳定性,分析结构参数对旋翼气弹稳定性的影响.分析结果表明模型能准确计算结构弹性变形的耦合及非线性,提高旋翼气弹稳定性分析精度.