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Pages from 2004_5

# Pages from 2004_5 - large uncertainty is removed a more...

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Thus, by measuring the response in only a relatively small number of points, then after an output-only modal ID, the corresponding response in any point of the structure can be calculated. A similar relation holds for stresses, because in a linear model, if the displacements are known, so are the stresses. Thus in all the points defined by the FE model – or in the subset of points defined in the beginning [] ) ( ) ( ) 6 ( ... , ) ( ) 5 ( 2 1 t t t N Cq σ σ = = σ The elements of the matrix can be associated with the stress concentration factors. In this formulation they relate the amplitude of the mode shape to the hot spot stress contribution from each of the modes. The matrix is estimated as a part of the Finite Element analysis. C C Doing an analysis like described in this section, the engineer can perform an improved fatigue analysis by- passing all the uncertainty from loading modelling and from relating the loading with the stress history. Since a
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Unformatted text preview: large uncertainty is removed a more accurate fatigue analysis can be performed and a better prognoses for the future damage accumulations can be performed. MONITORING SYSTEM The performance of the Vestas 3 MW wind turbine is monitored online by a surveillance camera. The image is shown in Figure 8. To measure the modal space the foundation and the turbine tower are equipped with a monitoring system complying of 15 Kinemetrics force balance accelerometers, model FBA ES-U. The position of the accelerometers in the tower and bucket are shown in Figure 9, 10 and 11. The on-line monitoring system is seen in Figure 12. Figure 8: Online image of the Vestas 3MW - V90 in operation. Figure 9. The position of the accelerome-ters in the tower and bucket foundation. Figure 10. Accelerometer mount at the connection between the tower and the foundation....
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