利用计算机视觉识别人行桥时变模态参数

Identification of time-varying modal parameters of pedestrian bridges using computer vision

人行桥健康监测及状态评估需解决的关键性问题是如何根据实测响应信号准确估计桥梁阻尼比及自振频率等时变模态参数。为此提出了一套方案,采用基于HS光流法的分段光流法获取桥梁振动全场位移响应,通过重新定义目标函数,利用自适应遗传算法优化变分模态分解(VMD),对各个位移时程进行分解,结合希尔伯特变换(HT)曲线拟合VMD分解得到的单模态信号求出瞬时频率和阻尼比。在人行桥模型上利用此方案测试不同行人在控制步频、自由行走下的结构响应,得到多组有效的结构位移响应并与激光位移计作对比验证,VMD⁃HT分解得到的行人⁃结构相互作用下的瞬时频率和阻尼比与941B传感器作对比验证。结果表明:采用分段光流法的视觉非接触式测量方法对结构响应具有较高的测量精度,与激光位移计的对比误差为0.85%。根据实测信号,利用VMD⁃HT可有效估计结构的时变模态参数。在行人⁃结构相互作用下,结构自振频率随人数和位移的增加而减小,最大减幅为14.12%,阻尼比随人数和位移的增加而增大,最大增幅为398.33%,控制步频行走相比于自由行走对时变模态参数的影响更大。

The key problem in footbridge health monitoring and condition assessment is to accurately estimate time-varying modal parameters such as damping ratio and natural frequency of the bridge based on measured response signals.Thus,a new set of solu⁃tions is proposed.First of all,based on the HS optical flow method of segmented optical flow method for bridge vibration to the dis⁃placement response,Then,by redefining the objective function,the adaptive genetic algorithm was used to optimize the variation⁃al mode decomposition(VMD),and then each displacement time history was decomposed,Hilbert transform(HT)curve was used to fit the single mode signal obtained from VMD decomposition to get the instantaneous frequency and damping ratio.Through the pedestrian bridge model,this solution is used to test the structural responses of controlled frequency and free walking performed by different pedestrians are tested,multiple sets of effective structural displacement responses are obtained and it is com⁃pared with the laser displacement meter,and the instantaneous frequency and damping ratio of pedestrian structure interaction ob⁃tained by VMD-HT decomposition are compared with the 941B sensor for verification.The results show that the visual non-con⁃tact measurement method adopting the segmented optical flow method shows high measurement accuracy for the structure re⁃sponse,and the error is 0.85%compared with the laser displacement meter.According to the measured signal,the VMD-HT is able to effectively estimate the time-varying modal parameters of the structure.By pedestrian-structure interaction,the natural fre⁃quency of the structure decreases with the increase of the number of people and the displacement,the maximum reduction is 14.12%,and the damping ratio increases with the increase of the number of people and the displacement,the maximum increase is 398.33%.Controlled frequency walking has a greater impact on time-varying modal parameters than free walking.