Dynamic numerical analysis of typical monopile foundations for offshore wind turbine applications

Offshore wind energy has become an important source of renewable energy in recent years, with large-diameter monopile foundations serving as the primary support structures for offshore wind turbines. The design of these monopiles requires an understanding of their structural behavior and interaction with the surrounding soil. Within this study, a 7.5m diameter monopile embedded in a dense sand soil was analysed using finite element method and the simplified design procedures available in the literature. The effect of structural and soil parameters on the monopile behavior was examined, and results indicated that the stiffness of the soil and internal friction angle have a nonlinear and negative relationship with the monopile's lateral displacement and rotation. The simplified design procedure and elastic solution in combination with the Winkler model underestimated the pile displacement and rotation, while the finite element analysis accurately predicted the behavior of the monopile. Based on the results obtained from the finite element simulations, regression equations that can be used for the initial design of monopiles embedded in dense sand soil conditions were presented. In conclusion, this study provides insight into the behavior of large-diameter monopiles embedded in granular soils which is quite common in offshore wind energy applications and offers recommendations for their design. The regression equations generated within this study can be used as a preliminary design tool for large-diameter monopiles in dense sand soil conditions.