Analysis of Frequency Nonstationarity via Continuous Wavelet Transform in the Response of Primary-Secondary Systems

An investigation into the frequency nonstationarity in the response of primary-secondary (P-S) systems and the impact it could have in the analysis of such structures has been presented in this note. For this purpose, a torsionally coupled P-S system subjected to nonstationary support motion is considered here. Simulated time history records of relative displacement of the secondary system are used to evaluate the time varying power spectral density functions. This is achieved by using a wavelet-based time-frequency analysis, which shows the temporal variations in the frequency content. The numerical results presented in this study advocate the use of nonstationary analysis of the P-S system for their proper design as conventional methods using cascading approximation may fail to capture this phenomenon, especially in the light of tuning and torsional coupling. System parameters such as mass ratio and radius of gyration are also observed to have a significant impact on the time varying frequency content of the response which is evidenced from the constructed time varying power spectrum.