Engineering critical assessment (ECA) for monopile foundation of an offshore wind turbine subjected to pitting

Abstract

An engineering critical assessment (ECA) framework for the monopile foundation of offshore wind turbines subjected to pitting is proposed in this paper. In the framework, a finite element (FE) analysis is conducted based on a 3D model of pitting, and the extended finite element method (XFEM) is utilized to predict the propagation behavior of pitting cracks. The critical size of pitting cracks is then assessed by a failure assessment diagram (FAD) in terms of the BS7910. Compared with the traditional ECA, the proposed ECA framework is more effective in assessing the effects of pits on crack propagation and thus the excessive conservatism of fatigue failure assessment for pitting structures is avoided. An engineering application example is conducted to demonstrate the capability of the proposed ECA framework. The influence of the pit depth and the initial location of the pitting crack on the foundation's fatigue life are further investigated. The results show that the fatigue life of a monopile foundation can be significantly decreased by pitting, and fatigue life can be decreased by almost 30% even a pit with a depth of 2.3 mm.