ESTIMATION OF MODAL DAMPING OF AN OFFSHORE WIND TURBINE ON A GRAVITY FOUNDATION

抄録

The structural damping is an important parameter in the seismic resistant design of wind turbine. In this study, the effect of soil properties on modal damping is studied. Firstly, a sway-rocking model is built to simulate soil-structure interaction, and results show that sway-rocking model simulates second mode shape better than fixed-foundation model. Secondly, the method to evaluate second mode damping ratio is proposed, and results show that the higher value of second mode damping ratio comparing to the guidelines is caused by soil-structure interaction and modal damping is evaluated accurately by using sway-rocking model. Thirdly, the effect of soil properties on modal damping ratios is systematically studied, and results show that for gravity foundation supported wind turbine, first mode damping ratio is close to structural damping ratio while second mode damping ratio is dominated by soil properties. These findings in this study can help to improve design of gravity foundation supported wind turbine.