Modal identification of output-only systems using frequency domain decomposition

TLDR

The technique addresses modal identification of output‑only systems where the input is unknown, and its user‑friendly nature relates it to classical peak‑picking approaches. The paper introduces a new frequency‑domain technique for modal identification of output‑only systems. The method decomposes the spectral density matrix so that response spectra are separated into single‑degree‑of‑freedom systems, each representing an individual mode. The decomposition enables accurate identification of closely spaced modes even under strong noise and clearly reveals harmonic components in the response signals.

Abstract

In this paper a new frequency domain technique is introduced for the modal identification of output-only systems, i.e. in the case where the modal parameters must be estimated without knowing the input exciting the system. By its user friendliness the technique is closely related to the classical approach where the modal parameters are estimated by simple peak picking. However, by introducing a decomposition of the spectral density function matrix, the response spectra can be separated into a set of single degree of freedom systems, each corresponding to an individual mode. By using this decomposition technique close modes can be identified with high accuracy even in the case of strong noise contamination of the signals. Also, the technique clearly indicates harmonic components in the response signals.