Identifying mode shapes and modal frequencies by operational modal analysis in the presence of harmonic excitation

Operational modal analysis techniques allow us to extract the modal properties of structures based on their response to non-measured stationary white noise, i.e., by considering only the system response to operational excitations. In this paper we outline a procedure to deduce modal parameters from operational response measurements. In particular, we discuss a novel approach to analyze operational responses due to unknown harmonic excitation in addition to noise. Structural eigenfrequencies and modal damping are computed using a modified least-squares complex exponential method. Once the poles of the system are identified, mode shapes are obtained by post-processing. The robustness and accuracy of the approach are illustrated by performing tests on a plate structure.