Reference monopile designs for US East Coast sites supporting the IEA 15 MW reference turbine using a novel conceptual design methodology

Abstract

A novel conceptual design methodology was developed and implemented to design twelve reference monopile foundations, compatible with the IEA 15 MW reference turbine. The designs are position-specific, corresponding to planned, US East Coast, wind energy development areas. The monopiles were designed considering the fatigue limit state (FLS), ultimate limit state (ULS), serviceability limit state (SLS), and natural frequency analysis (NFA), following an intentionally reduced subset of design load cases (DLCs) in IEC 61400-3-1. In 11 of 12 cases, the diameter and wall thicknesses of the monopile foundations were found to be determined by FLS criteria. The exception was one position subjected to a combination of breaking waves and a large significant wave height. For the 11 positions governed entirely by FLS, the maximum ULS utilization ratios varied between 0.63 and 0.81, indicating significant reserve capacity for the ultimate limit state. Fatigue damage during turbine idling was found to be an important contributor to lifetime fatigue damage, despite having a relatively small probability of occurrence. The novel design methodology described herein includes a preliminary FLS assessment step, which was found to be an efficient way to select an initial foundation geometry, while providing a 92% improvement in computational efficiency.