Issues in Tracking Instantaneous Modal Parameters for Structural HealthMonitoring Using Wavelet Approach

摘要

Viewing a structure with damage as a time varying system, the concept of instantaneous vibration modes hasbeen introduced and the instantaneous modal parameters, I.e. the instantaneous natural frequency and thenormalized instantaneous mode shape, can be effectively used to monitor the structural health condition. Theinstantaneous modal parameters have been successfully identified for both of sudden stiffness loss andprogressive stiffness degradation by using wavelet based approaches in the authors' previous work. The paperaddresses some important issues in identification of the instantaneous modal parameters, particularly the effect ofthe system nonlinearity. A multi-degree of freedom system with bilinear components, subjected to both impulseand harmonic excitation, is considered in this study. The simulated response data are analyzed by wavelet basedapproaches, I.e. the continuous wavelet transform (CWT) in conjunction with the Hilbert Transform (HT), toidentify the instantaneous modal parameters of the system. It is illustrated that change in the identifiedinstantaneous modal parameters may have different patterns for the linear system, the system with slow stiffnessdegradation, and the system with bilinear behavior. The results may help to distinguish change in theinstantaneous modal parameters caused by structural damage or by structural nonlinear behavior and thereforeto improve the accuracy of structural health monitoring.