Performance-based assessment of the monopile foundation of offshore wind turbines

Abstract

Due to uncertainties in metocean conditions and soil properties at the offshore wind farm, the performance of the monopile foundation of offshore wind turbines (OWTs) is also uncertain. In this study, a performance-based assessment method is suggested to calculate the annual probability of exceedance of a performance measure of monopile foundations of OWTs. In the suggested method, a finite element model is constructed to analyze the responses of the monopile foundation when the OWT system is subjected to aerodynamic and hydrodynamic loadings. A procedure is suggested to develop the fragility function of the monopile foundation considering both uncertainties in metocean conditions and soil properties. The annual probability of exceedance of the performance measure is then calculated by integrating the fragility function with respect to the occurrence rate of the metocean conditions. An example is provided to demonstrate the application of the suggested method. It is found that the annual probability of exceedance of the allowable lateral displacement of the monopile foundation at mudline is affected by both uncertainties in metocean conditions and soil properties. Specifically, it is unconservative to ignore the uncertainties in soil properties.