Dynamics of flexible tower-blade and rigid nacelle system: dynamic instability due to their interactions in wind turbine

The dynamic stability of a coupled tower-blade wind turbine system is investigated analytically and experimentally. Coupled equations of motion and associated boundary conditions for the wind tower and a rotating blade are derived by considering the lateral acceleration of the nacelle at the tip of the tower, which is the base of the flexible blade. The coupled eigenvalues are computed for various blade rotational speeds and densities of the tower material by using Galerkin's method in spatial coordinates. The results indicate that the coupled tower-blade system becomes unstable when certain vibrational modes of the tower and blade coalesce. Additionally, the vibration of the rotating blades is measured using a wireless telemetry system attached to the small-scale tower-blade wind power system, and the results are compared with those of the analytical study. The experiment shows that instability is observed in the same ranges of the blade rotational speed as those predicted by our analytical study.