基于整体式初始位移的柔性结构低频模态试验方法

Low frequency modal test method for flexible structure based on integral initial displacement

大型柔性结构由于刚度较低、结构庞大,采用传统测试方法难以获取结构的整体模态。提出了一种基于整体式初始位移的大型柔性结构低频模态试验方法。推导了任意初始位移条件下结构响应,以及初始位移条件下特征系统实现算法;在柔性结构上施加整体式初始位移来获取结构的整体振动响应,基于特征系统实现算法识别了大型柔性结构的低频整体模态。以长度为30 m的三棱柱型桁架为研究对象,验证整体式初始位移激励下结构模态参数辨识的可行性,并讨论结构在白噪声工况下的辨识精度。采用具有理论解的集中质量柔性梁模态试验进一步验证所提方法,锤击法难以激发该柔性梁的基频模态,而该方法能够准确识别柔性梁的模态。结果表明,通过在柔性结构施加整体式激励可以有效辨识出结构的低频模态参数。

Due to lower stiffness and huge size of large flexible structure, it is difficult to obtain its overall modes using traditional testing methods. Here, a low frequency modal test method for large flexible structure based on integral initial displacement was proposed. The structural responses under arbitrary initial displacements and the eigen-system realization algorithm under the condition of initial displacements were derived. Integral initial displacement was exerted on flexible structure to obtain its overall vibration response, and then the eigen-system realization algorithm was used to identify its low-frequency integral modes. Taking a triangular prism truss with length of 30 m as the study object, the feasibility of structural modal parametric identification under integral initial displacement excitation was verified. The identification accuracy of the structure under white noise condition was also discussed. Modal tests of a lumped mass flexible beam having theoretical solution were used to further verify the proposed method, the hammering method was difficult to excite the fundamental frequency mode of the flexible beam, while the proposed method can be used to correctly identify it. The results showed that low-frequency modal parameters of flexible structure can be effectively identified by using the proposed method.