Combined use of FRFs and transmissibility functions in an OMAX framework

Abstract

During the recent years several new tools have been introduced in the field of Operational Modal Analysis (OMA) such as the transmissibility-based approach and the OMAX concept. Most OMA estimators assume that the ambient forces are random noise sources with a flat amplitude spectrum. The transmissibility-based approach does not require this assumption: it works for almost any kind of ambient forces. The main advantage of the OMAX concept is the fact that it combines the advantages of Operational and Experimental Modal Analysis: ambient (unknown) forces as well as artificial (known) forces are processed simultaneously resulting in improved modal parameters. The main drawback of the existing OMAX estimators is related to the assumption that the ambient forces are white noise. In this paper, the transmissibility-based output-only approach will be combined with the input/output OMAX concept. This should result in a new methodology in the field of operational modal analysis allowing the estimation of (scaled) modal parameters in presence of arbitrary ambient (unknown) forces and artificial (known) forces. One important application is aeroelastic flutter. Flight flutter tests are necessary to assure that newly developed aircraft are free from flutter throughout the entire flight envelope. The airplane is excited by externally applied forces, but also due to turbulence. This turbulence excitation is not white at all, and can vary a lot between two flight phases. The transmissibility OMA approach benefits from changing operational loading conditions, and this enhances the accuracy of the estimated modal parameters. Our approach is tested on simulations and real-life measurements.

Publication
Proceedings of the International Noise and Vibration Engineering Conference ISMA

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