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Shock and Vibration
Volume 2014, Article ID 325839, 11 pages
Research Article

Some Elements of Operational Modal Analysis

Department of Engineering, Aarhus University, Edison Building, Finlandsgade 22, 8200 Aarhus N, Denmark

Received 27 June 2013; Accepted 26 February 2014; Published 6 July 2014

Academic Editor: Nuno Maia

Copyright © 2014 Rune Brincker. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


This paper gives an overview of the main components of operational modal analysis (OMA) and can serve as a tutorial for research oriented OMA applications. The paper gives a short introduction to the modeling of random responses and to the transforms often used in OMA such as the Fourier series, the Fourier integral, the Laplace transform, and the Z-transform. Then the paper introduces the spectral density matrix of the random responses and presents the theoretical solutions for correlation function and spectral density matrix under white noise loading. Some important guidelines for testing are mentioned and the most common techniques for signal processing of the operating signals are presented. The algorithms of some of the commonly used time domain and frequency domain identification techniques are presented and finally some issues are discussed such as mode shape scaling, and mode shape expansion. The different techniques are illustrated on the difficult case of identifying the three first closely spaced modes of the Heritage Court Tower building.