Application of Constrained Stochastic Simulation to Determine the Extreme Response of Wind Turbines

Up to now just deterministic gust shapes are specified in standards; e.g. the Extreme Operating Gust (IEC) is given by a Mexican hat like shape. In this paper gust shapes will be determined by application of so-called constrained stochastic simulation. This method specifies how to efficiently generate time series around some specific event (e.g. a local maximum) in a normal (Gaussian) process. In this way the generated gusts have the correct stochastic properties of turbulence (like generated wind fields for fatigue analysis). In constrained stochastic simulation a random signal can be generated which satisfies some condition, e.g. a maximum value or jump at some time instant. Usually the condition is applied on the external condition, i.e. the wind or waves (for offshore wind turbines). In this paper the condition of a maximum value, at some time instant, will be applied to the response instead (the blade root flapping moment). Assuming a linearised model of the wind turbine, the accompanying wind input leading to the extreme response, can be derived. By performing load simulations the proposed method is validated. In the future a probabilistic approach of extreme loading may replace the present deterministic procedure in standards