Abstract
Positive and negative short-term extreme wind shear distributions (conditioned on the mean wind speed) are determined and compared for a number of offshore sites. The analysis is based on rapidly sampled field measurements (1–8 Hz) extracted from the “Database on Wind Characteristics” (www.winddata.com).
Three different averaging periods (2, 5 and 10 seconds) are considered, and for each averaging period a relation between the resulting extreme shear distributions and the averaging time are presented. The short-term extreme shear analysis is based on different spatial distances, and extrapolation to a spatial distance of 100 m has been investigated. Such distances are appropriate for the next generation of offshore wind turbines.
The paper concludes with an estimation of the short-term extreme shear values, which are compared to the values specified in the IEC-61400 code. The extreme IEC shear values seems to be rather conservative for an offshore location, compared to the estimated values based on measurements.