Semi Analytical Model for the Dynamic Behavior of Offshore Wind Turbine with Flexible Foundation

A new semi analytical formulation is developed which models the dynamic behavior of offshore wind turbine with variable cross section and flexible foundation. The wind turbine tower is modeled using Euler-Bernoulli beam model while the soil-tower interaction is modeled by rotational and lateral springs at the lower end of the tower. Recursive differential method is used to calculate natural frequencies which is found to be efficient in terms of accuracy as well as the computational cost. The predicted natural frequencies of the current proposed mathematical technique were validated and compared with those of two other analytical and experimental techniques, for four selected offshore wind turbines, and results were found to be in very good agreement. Furthermore, the results of the current model, which accurately models the variation of the cross section properties, were found to be in a better agreement with the experimental results compared to those of the constant cross-section approximation. (paper)