On the Operational Modal Analysis applied to linear time periodical systems

In this paper, an approach for the identification of the dynamic properties of linear time periodical (LTP) systems is proposed. Such a novel approach is based on an already developed operational modal analysis (OMA) method, called the Hilbert Transform Method (HTM), used to characterize linear time-independent (LTI) systems. It is shown that the approach is capable to identify both the non-periodical (basis) and the periodical (parametric) modal properties of LTP systems. Both numerical analysis and experimental investigations on a rotor-blade structure, considered as representative of a time-periodical system, are shown to assess the developed methodology in terms of accuracy and robustness of the identification. Finally, the paper reports an improvement of the HTM estimating technique aimed at increasing the accuracy of the modal parameters identification when dealing with (very) close-poles systems.