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The Effects of Hurricane Wind Field Characteristics on Wind Blade Loads

Abstract
Over recent years, offshore wind energy has been growing around the world. This necessitates placing wind turbines directly in or near the oceans where hurricanes can be. Previous research has suggested that hurricane wind veer and direction change can have adverse loading effects on the turbine. Such effects can create damage to the blade or worsen existing ones. Currently, there is no known design standard for addressing wind veer and direction change specifically from hurricanes. Quantifying the loading contribution from these phenomena is not abundant either. This thesis seeks to demonstrate a proposed procedure for defining design veer profiles and direction changes from hurricanes using statistical averages and percentiles of veer and direction change magnitudes. Using simulated wind field data that describes a stationary Category 5 hurricane, the maximum veer profiles and direction changes will first be determined. Methods for statistically characterizing these wind field phenomena will be applied to provide design veer profiles and direction changes. These maximum and design veer profiles and direction changes will be applied to a feathered IEA-15MW turbine blade at 0 and 180 degrees azimuth, and the effects on the static blade loadings will be examined using blade element theory. Baseline scale factors describing the loading increase from veer or direction change will be established for the maximum and design veer profiles and direction changes. Rated scale factors describing the loading increase from veer and wind speed or direction change and wind speed relative to the rated condition loadings will also be established. The purpose of these scale factors is to estimate increases in loads from these wind field characteristics and not be directly used in any serious wind blade design. This thesis will show that hurricane wind veer and direction change can each, individually, increase the blade loading greater than the wind velocity can on a feathered blade. The wind speed/wind veer loadings can induce resultant moments up to 2.5 times rated with veer contributing 87.5% of the increased loading while the wind speed / direction change loadings can induce resultant moments up to 2.8 times rated with direction change contributing 88.8%.
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http://creativecommons.org/licenses/by/4.0/
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