Influence of pile length on dynamic performance of monopile wind turbine

The influence of pile configuration on safety of wind turbines has been attracting large amounts of attention recently. On the one side, the cost for the foundation accounts for 35 % of the total cost of monopile supported wind turbines (MWTs). On the other side, the working environment of wind turbines brings complex loads to monopiles. In this paper, a series of wind tunnel tests are performed with scaled model under different ground and operation conditions. The test results show that pile length factor (PLF) affect nacelle displacement and maximum pile moment negatively. Top acceleration confirmed a stationary random vibration. The natural frequency of model MWTs increases 11.6 % (dense ground) and 10.1 % (loose ground) when PLF increase from 0.264 to 0.362. While damping ratio decreases 1.447 % (dense ground) and 1.493 % (loose ground). These test results can be up scaled to estimate prototype's dynamic properties. According to test results, some numerical fitting surfaces including d-Ω-PLF, f-Ω-PLF and ξ-Ω-PLF have been established to check unfavorable working conditions, which can be used to guide the design of piles to support MWTs.