Wind load response of offshore wind turbine towers with fixed monopile platform

Abstract

Wind turbine towers are continuously subjected to wind force as their major dynamic load. Dynamic response of the wind turbine tower subjected to wind forces is usually estimated by numerical methods such as finite element method (FEM). In this paper, the analytical transfer matrix method (TMM) is used to determine wind load response of wind turbine. Therefore, various and general models including coupled springs (CS), distributed springs (DS) and apparent fixity length (AF) models are employed for modeling of wind turbine foundation and axial force is modeled as a variable force along the tower, as well. Wind force is divided into two parts containing thrust and distributed force. The transfer matrix is derived based on Euler-Bernoulli's beam differential equation. The global transfer matrix is obtained by applying boundary conditions of the tower and constructing the point matrix. Then, the factors affecting the tower dynamic response such as foundation models, axial induction factor, terrain factor, wind shear and gust condition are examined in several case studies. Finally, the TMM results are compared with the available results in the literature such as of the FEM which show good agreement. The comparisons can be concluded that the TMM can be used instead of the conventional numerical methods maintaining high accuracy for wind induced vibration analysis of wind turbine towers.