Optimization of a design code for wind-turbine rotor blades in fatigue

A reliability-based calibration of a design code for wind-turbine rotor blades is presented. Design against fatigue failure in flapwise bending is considered. The calibration is performed by means of a numerical optimization technique in conjunction with probabilistic and deterministic models for load and resistance. The probabilistic models allow for predictions of the reliability against fatigue failure. The deterministic models express design load and design resistance in terms of characteristic values and partial safety factors. The code calibration consists of determination of the partial safety factors such that — over a specified scope of code — designs with reliabilities with minimum deviations from some prescribed target reliability result when the deterministic models are applied with this particular set of partial safety factors. The scope of code consists of a number of representative design cases, each defined as a particular combination of wind turbine, location and blade material. Emphasis is placed on demonstration of the code calibration principles and a proper formulation of the code format.