Transmissibility Based Operational Modal Analysis in Presence of Harmonics

Abstract

A modal model comprising natural frequencies, damping ratios and mode shapes called modal parameters, is always appreciated due to its appropriate interpretation for physical phenomenon. For real structures, the modal parameters can be obtained from an operational modal analysis that offers several advantages: simple equipment thus low cost, continuous use, real boundary conditions. However, the excitation not controlled and not measured is always assumed as white noise in the operational modal analysis. In presence of harmonics on excitation, the white noise assumption is not verified and that makes the modal identification process difficult, even leading to biased results. A transmissibility function defined by ratio in frequency domain between two responses, is known as independent of excitation nature. This study proposes therefore to apply the transmissibly functions for modal identification in presence of harmonics. The proposition is validated by numerical examples and an experimental test.