Seismic Analysis of Onshore Wind Turbine Including Soil-Structure Interaction Effects

The structural behavior of modern wind turbines has reached a very high complexity and many factors are involved: slenderness of the structure, excitation environment and operational controls. Moreover, if a project is located at sites with relevant seismic hazard, the wind unit must be designed considering a reasonable likelihood of earthquake occurrence during the operational state or an emergency shutdown. The influence of the subsoil on the seismic response of a wind turbine can be crucial during the seismic design phase and need to be properly included into the computational model. Norms and guidelines need to keep up with technological developments and structural peculiarities. However the dynamic soilstructure interaction is often neglected or roughly mentioned. It is usually suggested to represent the soil through springs. The proposed investigation estimates the seismic response of a soil-turbine system and involves a 1.5-MW, 3- blade wind turbine, grounded on a layered half space. The wind turbine system is modeled by means of Finite Element Method (FEM). The effects of the layering are investigated. The soil is simply idealized as a generalized spring, according to the majority of standard codes. In parallel, the same investigation is performed with a more accurate method, a coupling between finite element and Boundary Element Method (BEM). This allows assessing the applicability and accuracy of the simplified soil representation.