Study On Time Domain Modal Identification Methods And System Development Based On Structural Vibration Response

Identification of structural modal parameters via analysis and processing the structural dynamic response signals is an important way for structural health monitoring and damage diagnosis.In recent decades,it has been widely studied and applied in many fields involving vibration engineering,such as structure,water conservancy,transportation,machinery,aerospace,etc.At the same time,with the development of information technology,the health monitoring system developed by Delphi,LabVIEW,MATLAB and other software platforms,as a compreh ensive platform integrating monitoring response,modal analysis,model updating,damage detection and other key health monitoring technologies,has widely received the attention from domestic and international researcher.Based on the basic theory of vibration modal analysis,the identification method of modal damping ratio and the development and design of time domain modal parameter identification system were studied in this paper.The main works are as follows:(1)Reviewing of the research and application of time-frequency domain parameter identification methods based on structural vibration response at home and abroad,summarizing their commonalities,deficiencies and applicable conditions in practical engineering applications,and briefly expound the basic vibration theories such as parametric models,non parametric models and their interrelationship.(2)Aiming at the problem of insufficient accuracy of parameter damping ratio identification,a modal damping ratio identification method based on natural excitation technology and time-shift characteristics of Fourier transform is derived theoretically and it is compared with the traditional ITD method and the state-of-the-art SSI-DATA method through simulation examples and response data of field bridge dynamic test.Comparison of the identification results indicates that the proposed approach can provide a convenient and reliable way to identify the damping ratios of large-scale engineering structures.(3)Based on the advanced time-domain modal identification theory and the powerful and efficient human-computer interaction programming environment of Matlab_GUI platform,a structural modal parameter identification system including multiple time-domain parameter identification methods was developed.The requirements analysis,overall layout design and function realization of the system are systematically introduced.At the same time,the feasibility and practicability of the parameter identification of the integrated system was verified by structural monitoring data.(4)Based on the structural response data measured by the shaking table test model under white noise base excitations condition,combined with the developed time-domain modal parameter identification system,five output-only system identification methods(SSI-DATA,NExT-ERA,SSI-COV,RDT-ITD and NExT-FT)were applied to estimate the modal parameters of the structure at various damage states.The feasibility of using structural parameters to identify damage was studied by comparing the identification results.The results show that the natural frequencies identified by the five system identification methods are basic ally the same,while the damping ratio identified shows great variability;With the increase of structural damage degree,the natural frequency of the structure gradually decreases.The trend of increasing the first-order damping ratio identified is the most obvious,followed by the second-order,and the third-order damping ratio has no obvious trend with damage.