Effect of uncertainty sources on the reliability level of wind turbine rotor blades

Abstract

AbstractWind turbine rotor blades are large composite structures performing most of their design life under random cycle loading patterns. Concurrently, material properties of the constituent plies exhibit inherent variability. In order to ensure a safe and cost‐effective design, uncertainty related to the basic variables (material properties, loads etc.) should be quantified and taken into account in the design calculations. Recently, the blade design standard DNVGL‐ST‐0376 was released, showing the trend of using dedicated probabilistic analysis for wind turbine blade design. A critical evaluation of the new edition of the standard is performed herein, particularly in terms of the ability of the suggested safety factors to satisfy the target failure probability level of 1E‐04. To this end, probabilistic analysis methodology is employed, starting with the measurement uncertainty for the static and fatigue properties of the composite material and going all the way up to the blade failure probability on a layer by layer basis. The application is performed on the INNWIND.EU reference 10MW rotor blade of 90‐m length. Furthermore, the current reliability level of the specific blade design, following the new standard DNVGL‐ST‐0376, is estimated considering the various failure modes, ie, fibre failure (short term and fatigue strength), buckling, and inter fibre failure of the composite laminates, while taking into account sources of variability that contribute to the physical, statistical, measurement, and model uncertainty. Results indicate that while for the static (extreme) analysis deterministic results are conservative, the opposite is observed for fatigue analysis.