Dynamic Behavior of Variable Cross-Section Offshore Wind Turbine with Flexible Foundation Using Finite Element Method

Abstract

A Finite Element model for variable cross section offshore wind turbine with flexible foundation is developed to accurately determine the fundamental frequency of the tower-nacelle system. The tower is modeled using two-noded Euler beam element with two degrees of freedom, namely transverse displacement and rotation, and Hermite polynomial shape function. The governing equations are obtained using Euler-Lagrangian energy-based approach, including the effect of variable tower cross section and the nacelle mass. The soil-tower interaction is modeled by rotational and lateral springs at the lower end of the tower. Four offshore wind turbines were selected as case studies in terms of validation and comparison. The results of the current model, compared to those of an experimental, clearly show that it better simulates the dynamic behavior of the tower-nacelle system compared to those of the constant cross-section approximated models.