UC San Diego

This thesis exhibits the results of a study focused on the seismic behavior of a 900 kW wind turbine. As of the time of this writing, special engineering provisions for such loading events are not adequately defined. In order to accomplish the research objective, the author relies on available experimental data taken in 2009 from accelerometers attached to a wind turbine base and tower along with an eccentric mass shaker placed on the turbine foundation. On this basis, the dynamic properties of the wind turbine, including tower bending modes and natural frequencies were extracted. An attempt was made to quantify the damping ratios found in these bending modes by applying input shaking simulating the experimental excitation using the finite element program OpenSees. In this undertaking, possible sources of error are discussed. The author then describes a numerical study performed on a calibrated wind turbine like structure involving the application of a large range of actual recorded input motions. Adjustments are made to the original fixed-base model, placing the structure on a linearly elastic soil domain by using BridgePBEE, a graphical interface tool that eases simulation and functions as a pre and post processor. Using this code, the numerical study is further extended by varying the supporting ground stiffness. The study then compares the tower maximal shear and moment values for the studied rigid and flexible ground scenarios and explores trends in the lateral force lever-arm of the system