Reliability analysis for monopile foundation of offshore wind turbine considering correlated wind and waves and spatially varying soils

Abstract

The monopile-supported offshore wind turbines (OWTs) are increasingly installed in more challenging seabed environments, resulting that the reliability of the monopile foundation attracts more attention. The reliability of the monopile foundation is largely uncertain due to uncertainties in correlated wind and waves and spatially varying soils. To address this issue, a reliability analysis framework is suggested to assess the annual probability of failure of the monopile foundation, that considers the correlated wind and waves, and spatial variability of soil properties. In this framework, a two-stage fragility surface of the monopile foundation is constructed. A joint probability distribution is calibrated using copulas to describe the correlation between wind and wave conditions. Spatially varying soils are modeled by the random field method. An example is provided to illustrate the application of the framework. The results suggest that the reliability of the monopile foundation may be overestimated if the spatial variability of soil properties is ignored. Additionally, the assumption that wind and waves are fully correlated may lead to an over-conservative reliability analysis.