Fatigue and fracture mechanics of offshore wind turbine support structures

摘要

Wind power, especially offshore, is considered to be one of the most promisingsources of ‘clean’ energy towards meeting the EU targets for 2020 and 2050.However, its popularity has always fluctuated with the price of fossil fuels sincenowadays wind electricity production cannot compete with nuclear or coalelectricity production. Support structures are thought to be one of the main driversfor reducing costs in order to make the wind industry more economically efficient.Foundations and towers should be fit for purpose, extending their effectiveservice life but avoiding costs of oversizing.An exhaustive review of the background and state of the art of the Fatigue-Lifeassessment approaches has been carried out, combining analysis of thegathered experimental data and the development of Finite Element models basedon contemporary 3D solid models with diverse Regression Analyses, in order toidentify their weakness and evaluate their accuracy. This research shows that theguides and practices currently employed in the design and during the operationof the offshore wind turbine support structures are obsolete and not useful foroptimisation, which generally leads to conservationism and an unnecessaryincrease in costs.The basis for a comprehensive update of the Girth Weld and Tubular Joint S-Ncurves and the Stress Concentration Factors of Tubular Joints has been set out.Furthermore, a reliable methodology for deriving the Stress Intensity Factor at thedeepest point of a semi-elliptical surface saddle crack in a tubular welded T-jointhas been proposed.