基于有限元理论的螺栓联接结构振动特性时频分析方法研究

	基于有限元理论的螺栓联接结构振动特性时频分析方法研究
其他题名	Finite Element Analysis of Vibration Characteristics of Structure with Bolt Connections Using the Method of Transient Response and Frequency Transformation
	王强龙
学位类型	硕士
导师	刘震宇
	2015
学位授予单位	中国科学院大学
学位专业	机械工程
关键词	时频计算方法振动模态接触非线性时频积分频域处理
摘要	光电经纬仪用于自动捕捉与跟踪远距离运动物体的运行轨迹、空间姿态等运动特性。由于光电经纬仪要求高精度的快速捕获跟踪与瞄准能力，其支撑结构的固有频率应避免接近或者落入伺服系统的带宽范围之内从而避免引起由于伺服系统或者外界激励载荷引起的结构共振，因此光机支撑结构动态特性的精确仿真是结构设计阶段非常重要的组成部分。光电经纬仪中支撑结构的联接主要是由螺栓联接实现，螺栓联接需考虑相关联接件的接触状态。接触状态分析主要引入了非线性接触边界条件，并根据螺栓预紧力的大小确定局部的结构非线性变形甚至材料蠕变等非线性特性。在结构振动特性分析中，接触区域面积、相互空间位置、以及接触力法的幅值等随结构的变形而发生改变，从而使得接触区域的局部刚度和阻尼特性表现为依赖外部振动载荷和时间的非定值常量。因此通常结构设计采用的线性模态仿真方法与实验获得的结构振动特性相差较大。本论文通过引入时域和频域结合的数值计算方法仿真具有螺栓联接的结构振动特性。仿照振动模态实验的思路，首先通过构造脉冲和指定频域范围的步进正弦扫频等外加载荷计算结构的时间-位移响应，然后利用傅立叶分析方法获得了位移曲线的频域特性，最后借助信号滤波方法获得结构的各阶谐振频率。在数值计算方面，首先利用固结结构替代螺栓联接，根据采样定理合理选取时间-位移计算中的时间计算间隔和计算时长，验证了时域和频域结合计算结构共振频率的正确性。通过引入非线性接触有限元分析和时间步的隐式积分算法，对考虑接触和预紧力的单螺栓悬臂梁模型进行了计算和仿真。与试验模态结果对比表明，此数值方法的计算误差控制在7%以内。通过计算单螺栓结构的时域响应，指出此类结构存在次频响应等非线性振动的特征。通过对比具有不同接触面积螺栓联接模型的计算结果，证实了螺栓联接条件下接触面积越小，利用线性模态分析获得的共振模态值与实际振动特性误差越小、结构次超频响应特性越不明显。另外利用具有挡块的悬臂梁模型分析了自由碰撞下结构的受迫振动，指出在该类强非线性接触振动条件下，基于线性模态的振动理论已完全不适用于结构的受迫振动分析。在实际工程应用中，本文采用的时频分析方法耗费资源过大，计算时间过长。因此，本文研究了利用子结构方法结合时频分析方法用以提升计算效率和节省计算时间的问题。本文针对单螺栓联接悬臂梁模型利用子结构方法进行了数值计算时间的验证计算。数值计算结果在满足计算精度要求的前提下，计算时间可缩减一倍以上。最后总结和展望了利用此方法计算结构谐振频率的优缺点，并指出需要进一步完善的研究内容。
其他摘要	Photoelectric theodolite is widely used to capture and track the orientation, trajec-tory and the other objective characteristic of moving objects in the distance automati-cally. Because the photoelectric theodolites needs the capability of rapid search of high moving objects with high precision, the natural vibration frequencies of the support structure of the tracking system are required not fall into the servo bandwidth range or close to the servo systems frequency so as to avoid resonance due to the servo system or the external excitation. Therefore, it is important in the design stage to simulate the dynamic characteristic of optical and mechanical support structure accurately. The structural connection of theodolite is mainly implemented by the bolt connec-tion. During the simulation analysis of the contact state, nonlinear contact boundary condition needs to be considered. Because of the contact area, location of contact region are changed with the structural deformation, the contact stiffness, contact area, damping characteristic of contact interface and the contact force normal to the deformation area are also changed. Therefore, the method used in the linear mode simulation cannot be directly used in structure with bold connection. And results are quite different between simulation and experiment. In this thesis, a new numerical method is proposed by combining time-domain and frequency-domain analysis to calculate the vibration characteristic of structure with bolt connection. According to method of the mode experiment, pulse and step sine sweep loading excitation of specified frequency range are constructed and time-displacement response are calculated by applying constructed excitation to the structure. The fre-quency characteristic about calculated time-displacement response curve are obtained by using Fast Fourier Analysis (FFT) method. Finally, the resonant frequency of struc-tural are obtained via signal filtering method. The method that combined time-domain and frequency-domain is proved to be an effective method to model with contact effect. The time intervals and calculating time are analyzed according to the sampling theorem during calculating the time-displacement curve of consolidated structure. The beam model connected by a single bolt which pre-tightening force and contact nonlinearity is simulated through new algorithm using implicit integration method and nonlinear finite element analysis. By comparing the experimental model results and simulation results of proposed numerical method, the calculations error is less than 7%. By calculating the time-domain response of structure of single bolt, the nonlinear-ity vibration characteristic and secondary frequency response characteristic of beam model are pointed out. The results are compared between the model with large and small contact area. Numerical results illustrate that the smaller contact between two beams, the harmonics response characteristics are less and the difference are much less between the response frequency simulated through linear model analysis and experi-ment. The forced vibration of beam model with block is calculated and the result noting that under such strongly nonlinear conditions the vibration theory based on linear vi-bration modes cannot applied to analyze forced vibrations. In order to decrease the computational cost of time-domain analysis of structural vibration with nonlinear bolt connection, the substructure method is reseated for the cantilever beam with single bolt connection. At last, the potential improvement of the proposed numerical method are discussed for the further research on multiple-bolt connection.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/49297
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	王强龙. 基于有限元理论的螺栓联接结构振动特性时频分析方法研究[D]. 中国科学院大学,2015.

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