Larsen, Gunner Chr.6; Bierbooms, W.7; Hansen, Kurt Schaldemose6
1 Risø National Laboratory for Sustainable Energy, Technical University of Denmark2 Wind Energy Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark3 Aeroelastic Design, Wind Energy Division, Risø National Laboratory for Sustainable Energy, Technical University of Denmark4 Fluid Mechanics, Department of Mechanical Engineering, Technical University of Denmark5 Department of Mechanical Engineering, Technical University of Denmark6 Department of Wind Energy, Technical University of Denmark7 unknown
The gust events described in the IEC-standard are formulated as coherent gusts of an inherent deterministic character, whereas the gusts experienced in real situation are of a stochastic nature with a limited spatial extension. This conceptual differencemay cause substantial differences in the load patterns of a wind turbine when a gust event is imposed. The Newgust method is a rational way of taking wind speed gust situations into account in a design process. A corner stone in the method is a cogentalgorithm to embed a wind speed gust of a prescribed appearance in a stochastic wind field [Dragt, 1996]. However, dealing with wind turbine design, not only detailed knowledge on the spatial/time structure of the gust event is required. The probabilityof occurrence of a gust event with a given wind speed amplitude/magnitude is equally important. This theme is addressed in the present report. A theoretical expression for the probability density function associated with local extremes of a stochasticprocess is presented. The expression is basically based on the lower four statistical moments and a bandwidth parameter. The theoretical expression is subsequently verified by comparison with simulated synthetic wave/wind fields as well as with measuredwind fields covering a broad range of mean wind speed situations and terrain conditions. The simulated wave fields represents narrow band processes, whereas the wind fields represent broad-banded processes. The work reported makes part of the project"Modelling of Extreme Gusts for Design Calculations " (NEWGUST), which is co-funded through JOULEIII on contract no. JOR3-CT98-0239.