基于激光多普勒测振的结构工作模态分析

Operational modal analysis of structure based on laser Doppler vibration measurement

为验证激光多普勒测振仪快速识别高层建筑结构模态参数的适用性,提出一种采用两台远距离激光多普勒测振仪进行环境振动测试的方法。以一悬臂灯杆为例进行实测,获得振动速度响应。该方法实施便捷,测量精度能够满足要求。本文采用频域分解法(FDD)及随机子空间算法(SSI)对其模态参数进行了识别,为进一步应用于环境激励下的高层建筑等大型结构提供试验基础。结果表明,两种算法均可较好地获取结构自振频率及模态振型,自振频率差异很小,振型则几乎一致。并对灯杆进行简化的有限元分析,将模态识别结果与数值模拟结果相比,二者振型吻合较好,但自振频率略有差别。为避免模态遗漏和虚假模态,应结合多种模态识别算法进行模态分析。最后采用该方法对一超高层建筑进行环境激励下的振动实测与模态参数识别。

To verify the applicability of laser Doppler vibrometer(LDV) for quick modal parameters identification for high-rise buildings,an ambient vibration test method using two LDVs remotely positioned was proposed.The vibration test of a cantilever lamp pole was performed to measure the velocity response.This method is convenient to conduct,and the accuracy of measurement can meet the requirement of applications.The modal parameters of this structure were identified based on frequency domain decomposition(FDD) and stochastic subspace identification(SSI) in this paper,providing an experimental basis for further application to large-scale structures like high-rise buildings under environmental excitation.The results show that both methods can effectively extract natural frequencies and mode shapes of the structure,of which the difference between the identified natural frequencies of the two methods is very little,while the identified mode shapes are nearly the same.Besides,finite element analysis of the lamp pole with a simplified model was carried out.By comparing with numerical modal results,the identified mode shapes agreed well,but the natural frequencies presented some difference between the modal identification results and the numerical results.To avoid mode absence and false modes,multi modal identification methods should be combined for modal analysis.At last,this method was used for vibration measurement of a super high-rise building under environmental excitation,and its modal parameter was identified.