Operational Modal Analysis (OMA) is used to derive an experimental dynamics model from vibration measurements on a structure in operational conditions (as opposed to dedicated laboratory testing). The successful application of OMA to various industrial cases provided the motivation to also consider it as a valuable tool for in-flight helicopter data analysis. However, some specific challenges arise in this case: the measurement data contains multiple harmonic components originating from the main rotor and tail rotor and the data "between" the harmonics is prone to measurement noise since the range of the data acquisition system has to be set quite large as to properly sample the high-amplitude harmonic components. In Operational Modal Analysis applications, it is assumed that the structure is excited by white noise. However, in some cases, the operational vibration data are acquired while rotating equipment is active in the background or while it is even the main source of excitation. The structural responses will then consists of a broadband response from which the structural modes can be determined and additional harmonic response at discrete frequencies, which are disturbing the parameter identification process. Sometimes, the harmonic response is dominating and the Operational Modal Analysis methods only find poles at these harmonic frequencies. Therefore, it is desired to try to remove the disturbing harmonics from the data before applying Operational Modal Analysis. In this paper, a cepstrum-based method will be discussed to remove selected discrete frequency components from a time signal. After this pre-processing, the new "PolyMAX Plus" modal parameter estimation method will be applied. This method belonging to the class of Maximum Likelihood Estimators is able to deal with very noisy datasets and provides confidence bounds on the modal parameter estimates. Real in-flight helicopter data will be used to illustrate the approaches. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering. All rights reserved.

Helicopter in-flight modal analysis: Solutions for dealing with harmonics and noise / B., Peeters; R. B., Randall; S., Manzato; F., Marra; Coppotelli, Giuliano. - ELETTRONICO. - 3:(2012), p. 2045. (Intervento presentato al convegno 25th International Conference on Noise and Vibration engineering, ISMA2012 in conjunction with the 4th International Conference on Uncertainty in Structural Dynamics, USD 2012 tenutosi a Leuven nel 17 September 2012 through 19 September 2012).

Helicopter in-flight modal analysis: Solutions for dealing with harmonics and noise

COPPOTELLI, Giuliano
2012

Abstract

Operational Modal Analysis (OMA) is used to derive an experimental dynamics model from vibration measurements on a structure in operational conditions (as opposed to dedicated laboratory testing). The successful application of OMA to various industrial cases provided the motivation to also consider it as a valuable tool for in-flight helicopter data analysis. However, some specific challenges arise in this case: the measurement data contains multiple harmonic components originating from the main rotor and tail rotor and the data "between" the harmonics is prone to measurement noise since the range of the data acquisition system has to be set quite large as to properly sample the high-amplitude harmonic components. In Operational Modal Analysis applications, it is assumed that the structure is excited by white noise. However, in some cases, the operational vibration data are acquired while rotating equipment is active in the background or while it is even the main source of excitation. The structural responses will then consists of a broadband response from which the structural modes can be determined and additional harmonic response at discrete frequencies, which are disturbing the parameter identification process. Sometimes, the harmonic response is dominating and the Operational Modal Analysis methods only find poles at these harmonic frequencies. Therefore, it is desired to try to remove the disturbing harmonics from the data before applying Operational Modal Analysis. In this paper, a cepstrum-based method will be discussed to remove selected discrete frequency components from a time signal. After this pre-processing, the new "PolyMAX Plus" modal parameter estimation method will be applied. This method belonging to the class of Maximum Likelihood Estimators is able to deal with very noisy datasets and provides confidence bounds on the modal parameter estimates. Real in-flight helicopter data will be used to illustrate the approaches. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering. All rights reserved.
2012
25th International Conference on Noise and Vibration engineering, ISMA2012 in conjunction with the 4th International Conference on Uncertainty in Structural Dynamics, USD 2012
experimental modal analysis; harmonic excitation; helicopter structure; operational modal analysis
04 Pubblicazione in atti di convegno::04b Atto di convegno in volume
Helicopter in-flight modal analysis: Solutions for dealing with harmonics and noise / B., Peeters; R. B., Randall; S., Manzato; F., Marra; Coppotelli, Giuliano. - ELETTRONICO. - 3:(2012), p. 2045. (Intervento presentato al convegno 25th International Conference on Noise and Vibration engineering, ISMA2012 in conjunction with the 4th International Conference on Uncertainty in Structural Dynamics, USD 2012 tenutosi a Leuven nel 17 September 2012 through 19 September 2012).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/499696
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