In-situ Ambient Vibration Study of a 900-kw Wind Turbine

Abstract

ABSTRACT Dynamic measurements are undertaken on a utility scale wind turbine (900 kW rated power, 55 m hub height, and a 53.6 m rotor diameter) located at Oak Creek Energy Systems near Mojave, California, USA. The acceleration response to wind and other ambient sources is recorded by as many as 81 channels at locations along the height of the tower, on the foundation, and on the surface of the surrounding soil. This extensive dataset is accessible for further studies at https://www.designsafe-ci.org/data/browser/public/nees.public//NEES-2008-0661.groups. In this paper, modal parameters (natural frequencies, damping ratios, and mode shapes) are estimated with the Multiple-Reference Natural Excitation technique combined with the Eigensystem Realization Algorithm based on 19 h of data while the turbine is parked and 1.5 h when it is operating under normal conditions. Structural characteristics are identified from the parked and operational state recordings. These dynamic test series provides a unique opportunity to observe variability in modal parameters of the turbine and is the first to be published for a megawatt scale turbine. The experimentally observed properties are compared to results from a beam-column model, the most common approach for simulating global turbine dynamics. Agreement between the experimentally identified and numerically predicted modal parameters confirms that this modeling approach is representative of modern wind turbine dynamics and provides a basis for seismic response evaluations.