Measured wind turbine loads and their dependence on inflow parameters

The Long-Term Inflow and Structural Test (LIST) program is gathering inflow and structural response data on a Westinghouse 600-kW wind turbine located at a test site near Boulder, Colorado. Data from 1043 ten-minute time segments are analyzed here to determine the dependency of fatigue and extreme loads on inflow parameters. Flap and edge bending moment ranges at the blade root are studied as the structural response variable of interest. Various parameters related to the inflow (including primary parameters such as the mean and standard deviation of the hub-height horizontal wind speed as well as secondary parameters such as Reynolds stresses, vertical shear exponent, etc.) are each considered in an inflow parameter vector. Time series for the structural response are processed in order to obtain a structural response parameter, which in separate statistical studies, is taken to be either an equivalent fatigue load or an extreme load. We describe a procedure by which the important “dependencies” of response on the various variables contained in the inflow parameter vector may be determined considering all the available data. The procedure employed is similar to other previous studies, but we do not bin the data sets by wind speed since dependencies in one wind speed bin may be different from those in other bins. Also, our procedure, in sharp contrast to previous studies, examines each inflow parameter in the vector in a sequential analysis, rather than by using multivariate regression.