Operational modal analysis of mechanical systems using transmissibility functions in the presence of harmonics

Ambient vibration testing is a preferred technique for heath monitoring of civil engineering structures because of several advantages such as simple equipment, low cost, continuous use and real boundary conditions. However, the excitation not controlled and not measured, is always assumed as Gaussian white noise in the processing of ambient responses called operational modal analysis. In presence of harmonics due to rotating parts of machines or equipment inside the structures, e.g., fans or air-conditioners…, the white noise assumption is not verified and the response analysis becomes difficult and it can even lead to biased results. Recently, transmissibility function has been proposed for the operational modal analysis. Known as independent of excitation nature in the neighborhood of a system's pole, the transmissibility function is thus applicable in presence of harmonics. This study proposes therefore to apply the transmissibility functions for modal identification of ambient vibration testing and investigates its performance in presence of harmonics. Numerical examples and an experimental test are used for illustration and validation. Keywords: operational modal analysis; transmissibility function; harmonic component; ambient vibration testing.