Design of monopiles supporting offshore wind turbines using finite element analysis

Abstract

Offshore wind turbines are subjected to loads from wind, waves, and current. These repeatable loads are transferred to the soil through the monopile foundation. For optimal design of these monopiles, detailed analyses of the response are needed. This chapter presents a design approach using 3D finite element analysis (FEA) and spring calibration. The FEA program can be used to calculate the permanent rotation of the monopile at the end of the lifetime (serviceability limit state), the capacity under maximum loads (ultimate limit state), and the pile response during operation (fatigue limit state). Based on the detailed FE analyses, simpler spring models can then be calibrated to mimic the response of the more advanced analyses. This provides a proper modelling of the monopile when simpler models are used by other disciplines, for example, load or fatigue analyses. This chapter presents the general design philosophy for offshore monopiles supporting wind turbines, the time-efficient 3D FEA program, a simplified cyclic accumulation methodology, and the optimization methodology to calibrate soil-reaction springs.