In the Output-Only analysis the system is considered excited, in a limited frequency band, with a white noise. Because it is not possible to find directly the spectra, it is necessary to pass through the correlation functions. Therefore, Output-Only analysis is based on the evaluation of the correlation functions applied to the different output responses. The modal parameters may be derived by the correlation functions in the time domain, or by the power spectral densities in the frequency domain. In this paper, the second item is considered with particular reference to the problems connected to the damping ratio overestimation. This effect, due to the limited time window in the correlation function estimate, is highly present in the low frequency modes and can bring to large errors. In the paper some experimental investigations, carried out on two cantilever beams and one helicopter blade, are presented, with a comparison among different techniques, and analyzed showing some possible suggestions to overcome the overestimation of the damping factors due to the biasing problems.

Use of Correlation Techniques in Output-Only Analysis / Agneni, Alessandro; BALIS CREMA, Luigi; Coppotelli, Giuliano. - 1:(2009), pp. 155-161. (Intervento presentato al convegno 3rd International Operational Modal Analysis Conference, IOMAC 2009 tenutosi a Portonovo; Italy nel 4-6 Maggio 2009).

Use of Correlation Techniques in Output-Only Analysis

AGNENI, Alessandro;BALIS CREMA, Luigi;COPPOTELLI, Giuliano
2009

Abstract

In the Output-Only analysis the system is considered excited, in a limited frequency band, with a white noise. Because it is not possible to find directly the spectra, it is necessary to pass through the correlation functions. Therefore, Output-Only analysis is based on the evaluation of the correlation functions applied to the different output responses. The modal parameters may be derived by the correlation functions in the time domain, or by the power spectral densities in the frequency domain. In this paper, the second item is considered with particular reference to the problems connected to the damping ratio overestimation. This effect, due to the limited time window in the correlation function estimate, is highly present in the low frequency modes and can bring to large errors. In the paper some experimental investigations, carried out on two cantilever beams and one helicopter blade, are presented, with a comparison among different techniques, and analyzed showing some possible suggestions to overcome the overestimation of the damping factors due to the biasing problems.
2009
3rd International Operational Modal Analysis Conference, IOMAC 2009
Structural Dynamics; Operational Modal Analysis; Estimating Techniques
04 Pubblicazione in atti di convegno::04b Atto di convegno in volume
Use of Correlation Techniques in Output-Only Analysis / Agneni, Alessandro; BALIS CREMA, Luigi; Coppotelli, Giuliano. - 1:(2009), pp. 155-161. (Intervento presentato al convegno 3rd International Operational Modal Analysis Conference, IOMAC 2009 tenutosi a Portonovo; Italy nel 4-6 Maggio 2009).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/225506
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