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

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.

KEYWORDS:

• Wind turbine
• seismic
• earthquake
• vibration
• modal parameters
• system identification
• natural excitation technique
• damping

Acknowledgments

The authors extend their gratitude to the National Science Foundation (NSF) for funding this work as part of a George E. Brown Jr. NEES Research project (NSF NEESR-II grant No. CMMI 0830422), and OISE 1445712. Contributions, in the form of making the testing site available, guidance, and man-hours, from Oak Creek Energy Systems (Hal Romanowitz, J. Edward Duggan, Vaughn Johnson, Michael Burns, and many others) are most appreciated. In-situ instrumentation would not have been possible without the oversight of Dr. Robert Nigbor of UCLA and the hard work of the NEES@UCLA team (Ben Ferrero, Steve Kang, Steve Keowen, and Alberto Salamanca). Thanks are also due to Dr. Paul Veers and the Sandia National Laboratories Wind Energy Technology Department for providing Mr. Ian Prowell with a summer internship.

Additional information

Funding

This work was supported by the Division of Civil, Mechanical and Manufacturing Innovation [0830422]; Office of International Science and Engineering [1445712].