Reduction of vibration by periodically stitched sandwich panel

This work reveals that the addition of periodically distributed stitches to sandwich structure enables a significant reduction of vibration in stop-band and this new functionality is systematically investigated. Firstly, a finite element model which is capable of taking into consideration the three layers of the sandwich as well as the stitches is developed. The diagram of dispersion is calculated by applying Floquet-Bloch theorem to the boundaries of unit cell. With properly chosen properties of stitches, a stop-band for flexural wave is observed. This stop-band is further confirmed by the forced response of a large stitched sandwich panel under point excitation. The level of vibration in the stop-band is significantly reduced. The influence of the stitch rigidity and density on upper and lower limits of stop-band is also examined, which confirms that stitched sandwich can be tuned to mitigate vibration in a certain frequency band with appropriate stitch properties. These investigations have demonstrated the potential application of stitched sandwich in the area of vibration reduction.     

FASTMast伸展机构屈曲模式的理论分析与试验

针对空间站盘绞式（FASTMast）伸展机构在轨工作的承载与变形特点,从理论角度对以伸展机构后屈曲柔性条作为弹性支承的屈曲模式进行了分析。结果表明：在后屈曲柔性条达到临界刚度之前,伸展机构屈曲模式表现为肘关节运动,与伸展机构对角拉索无关;达到临界刚度之后,屈曲模式表现为欧拉屈曲,而后屈曲柔性条的刚度与其截面惯性矩成正比。通过与试验结果的对比,验证了理论分析的正确性,同时也为其它同类机构的设计和试验提供了参考依据。     

Multi-layered plate finite element models with node-dependent kinematics for smart structures with piezoelectric components

This article presents a type of plate Finite Element (FE) models with adaptive mathematical refinement capabilities for modeling laminated smart structures with piezoelectric layers or distributed patches. The p-version shape functions are used in combination with the higher-order Layer-Wise (LW) kinematics adopting hierarchical Legendre polynomials. Node-Dependent Kinematics (NDK) is employed to implement local LW models in the regions with piezoelectric components and simulate the global substrate structure with the Equivalent Single-Layer (ESL) approach. Through the proposed NDK FE models, the electro-mechanical behavior of smart structures can be predicted with high fidelity and numerical efficiency, and various patch configurations can be conveniently modeled through one set of mesh grids. Moreover, the effectiveness and efficiency of the NDK FE approach are assessed through numerical examples and its application is demonstrated.     

充气式再入航天器总体方案及关键技术初探

充气式再入航天器是一种新型的再入航天器,可实现载人航天和行星探测任务中的行星大气再入,具有系统简单、质量小、气动加热低和可适应不同外形的再入载荷等优点。文章介绍了充气式再入航天器的国际发展现状,并对充气式再入航天器的总体方案进行了初步分析。参考俄罗斯的充气再入与降落技术(inflatable re-entry and descent technology,IRDT)设计先例,提出了充气式再入航天器的构型方案,并针对该构型进行了基于计算流体力学(computational fluid dynamics,CFD)的气动力和热仿真分析。计算采用了迎风格式的层流模型,基于密度进行求解。文章还基于国际空间站的运行轨道,开展了再入轨道的设计,最后对再入气动特性分析、柔性热防护材料、布局与折叠包装和充气机构设计等关键技术提出了初步建议。     

Initial phase of mid-latitude aurora during strong geomagnetic storms

Analysing the initial mid-latitude aurora phase during strong geomagnetic storms we found that the initial phase of the mid-latitude aurorae observed at 630 nm emission during the strong geomagnetic storms on March 24, 1991, April 6, 2000, October 30 and November 20, 2003 is characterized by a short (∼1 h) wave-like disturbance. This disturbance corresponds to the beginning of main phase of the magnetic storms. The marked effect of the mid-latitude aurorae is analyzed using data on magnetosphere and ionosphere conditions in observation periods. The features of the dynamics of the 630 nm emission intensity and its connection with the dynamics of magnetospheric–ionospheric structures are considered. Possible excitation mechanisms of the atomic oxygen emission (630 nm) during these disturbances are discussed.     

曲面复合材料胶接修补参数优化

随着复合材料在航空结构上的应用越来越广泛,国内外对受损复合材料结构的修补问题开展了较多的研究,但目前所开展的研究基本上是针对平板结构的修补,曲板结构修补的研究开展很少,所以迫切需要开展这方面的研究。本文针对曲板复合材料孔洞型穿透性损伤,采用方形复合材料补片胶接贴补方式,对影响修补效率的多个胶接参数进行了分析计算。在有限元分析中,考虑到曲面复合材料的外形特殊性,及胶接修补的特点,建立了修补结构的力学分析模型:“三实体模型”。有限元分析采用ANSYS软件,所得结论对工程应用具有实用价值。     

考虑摩擦的周边桁架式可展天线展开动力学分析

结合一种周边桁架式可展天线的模型制作,介绍了该类天线的总体布局、展开收纳机理和设计要点;然后提出了切实有效的数学算法,有效地构造了约束方程及其Jacobi矩阵,实时地模拟了结构收纳过程的约束条件,采用广义逆矩阵的方法分析了周边可展桁架运动过程;研究了摩擦这一非线性因素在其展开过程中的作用机理,建立其展开动力学模型,实现了考虑摩擦的周边桁架式可展天线结构展开动力学分析.编制了仿真程序进行算例分析,验证了分析方法的有效性.      

杆-梁和梁-梁组合结构中的波动现象

杆-梁结构和梁-梁结构都是典型的组合结构.用间接模态叠加法分析杆-Timoshenko梁之间以及两根Timoshenko梁之间的碰撞问题.在间接模态叠加法中,首先分别独立求得杆和梁的固有频率和模态函数,然后建立碰撞体和靶体之间的位移协调方程,并用逐步积分方法求解该方程.分析了纵波和剪切波在杆和梁中的传播特性.      

不同相位壁面局部微振动诱导边界层大涡结构

以平板边界层Blasius解为基本流,利用直接数值模拟的方法求解三维不可压缩N-S方程,研究了边界层中不同初始相位壁面局部微振动诱导大涡结构的过程。计算结果表明:壁面扰动初始相位为0或π,大涡结构的初始扰动速度场完全相反,初始相位为0时,大涡结构演化时无论其扰动速度幅值、高低速条纹结构,流向涡量均随时间的增加而增长,壁面平均切应力明显大于平板边界层流动,近壁平均速度剖面变得饱满;初始相位为π时,诱导形成的大涡结构较弱。壁面局部微振动可诱导边界层内形成大涡结构,大涡结构演化特性与局部微振动初始相位密切相关。     

基于神经网络的风洞尾支杆减振系统

风洞试验时,由于气流的影响,测试用悬臂式尾支杆容易产生大幅度低频振动,这会严重影响测试精度,甚至损坏自身结构。为了有效抑制尾支杆的振动,本文设计了基于压电组件的主动减振系统,并将人工神经网络应用于PID控制,提出了神经网络PID智能控制算法。对尾支杆进行有限元分析,获取其模态参数。然后设计试验测试减振系统的性能,将神经网络PID与经典PID的控制效果进行对比。试验结果表明:在连续载荷的作用下,采用经典PID控制算法与神经网络PID均可达到有效控制(减振幅度70%以上),且神经网络PID在保证减振效果的情况下实现控制参数自整定,具有良好的鲁棒性。