基于预实验分析的箱梁模型模态测试

以箱梁模型为实验对象,使用一种基于预实验分析的方法对箱梁模型进行模态识别。首先,在有限元模型模态分析结果的基础上,利用预实验分析确定合理的布点方案及最优激励点;再由预实验分析结果,采用激振器法对自由支撑的箱梁模型进行模态识别;最后,将实验模态与有限元模态进行相关性分析,以验证实验模态数据的可信性。实验结果表明,识别的四阶模态频率值与有限元分析结果在10%以内,前三阶在5%以内;与有限元模态相关性分析表明,实验测得的模态数据与有限元结果相似度高,尤其是对应前两阶模态振型相关性高达90%以上。

ModalTestoftheBox-girderModelBasedonPre-testAnalysis

In engineering, the sound absorption material is usually laid on the boundary of the sound field to reduce the noise. Generally speaking, the impedance of the acoustic material varies with the frequency. This is especially true at low frequencies. Thus, the acoustic model analysis problem becomes a nonlinear eigenvalue problem. Modern finite element analysis software cannot carry out the acoustic modal analysis of this frequency dependent impedance boundary. The impedance of the absorption material is usually set to constant in engineer to avoid the solving of nonlinear eigenvalue problem. However, this will bring large error in modal frequency results. This paper aims to extend the application of a newly-developed resolvent sampling based Rayleigh-Ritz projection method (RSRR) to the solution of this kind of problem. The algorithm is implemented in the commercial finite element software ANSYS. Representative numerical examples aregiven to show the high precision and good numerical stability of this method. It is proven to be a general method for the modal analysis of large-scale sound field.