Operational modal analysis (OMA) allows modal parameters, such as natural frequencies and damping, to be estimated solely from data collected during operation. However, a main shortcoming of these methods resides in the evaluation of the accuracy of the results. This paper will explore the uncertainty and possible variations in the estimates of modal parameters for different operating conditions. Two algorithms based on the Least Square Complex Exponential (LSCE) method will be used to estimate the modal parameters. The uncertainties will be calculated using a Monte-Carlo approach with the hypothesis of constant modal parameters at a given operating condition. In collaboration with Andritz-Hydro Ltd, data collected on two different stay vanes from an Andritz-Hydro Ltd Francis turbine will be used. This paper will present an overview of the procedure and the results obtained.
[1]
R. Vogel,et al.
The moving blocks bootstrap versus parametric time series models
,
1996
.
[2]
P. Bühlmann,et al.
Block length selection in the bootstrap for time series
,
1999
.
[3]
Prasenjit Mohanty,et al.
Operational modal analysis in the presence of harmonic excitation
,
2004
.
[4]
D. Politis.
The Impact of Bootstrap Methods on Time Series Analysis
,
2003
.
[5]
R. Blevins,et al.
Flow-Induced Vibration
,
1977
.
[6]
Thomas G. Carne,et al.
The Natural Excitation Technique (NExT) for modal parameter extraction from operating wind turbines
,
1993
.
[7]
Palle Andersen,et al.
Comparison of System Identification Methods using Ambient Bridge Test Data
,
1999
.