Comparative Structural Reliability Analysis of Monopile-supported Offshore Wind Turbines ﾖ considering the Effect of Flexible Foundation and Simulation Time on Long-term Extreme Response Extrapolation

Abstract

This paper deals with the development of semi-probabilistic design formats for ultimate strength design of monopile-supported Offshore Wind Turbines. The effect of the flexible foundation and simulation time on long-term extreme response extrapolation on the reliability measures and hence the safety factors, are addressed. A case study based on the benchmarked NREL 5-MW monopile OWT, according to IEC 61400-3-1, is conducted to illustrate the variation in implied reliability for various characteristic wave-to-wind moment ratios. Reliability analyses conducted indicate that the definition of bias in extreme response extrapolation due to simulation length has an important effect on the implied safety level. The effect of flexibility in pile-soil interaction model on the implied safety level is marginal. Analyses indicate that the implied safety levels in codes should properly be harmonized.