Fatigue life analysis of monopile-supported offshore wind turbines based on hyperplastic ratcheting model

Abstract

Fatigue life is an important factor to be considered in foundation design of offshore wind turbines (OWTs), and accurate prediction of fatigue damage is dependent on an appropriate foundation model. Currently, the rigid foundation is widely used to model the monopile foundation in most aero-hydro-servo-elastic simulation tools, and soil stiffness and damping are not considered. This will lead to an inaccurate estimation of fatigue damage of monopile-supported OWTs. Given this limitation, hyperplastic ratcheting model is incorporated into FAST v7, the variations of stiffness, damping and accumulated displacement for monopile-supported OWTs subjected to cyclic loadings are well considered. The validity of the implementation is demonstrated by presentation of non-linear soil resistance-displacement curves, and a series of hysteresis loops can be observed. Based on this integrated tool, extensive simulations and analyses for monopile-supported OWTs under different environmental states are performed. Furthermore, the effect of pile-soil interaction on fatigue life of monopile is quantified. The aim of this paper is to provide an accurate model to estimate fatigue life of monopile-supported OWTs.