Structural dynamic modeling and stability of a rotating blade under gravitational force

Turbine blade lengths have been increasing in recent wind energy system designs in order to enhance power generation capacity. A longer blade length makes the structural system more flexible and often results in an undesirable, large dynamic response, which should be avoided in the design of the system. In the present study, the equations of motion of a rotating wind turbine blade undergoing gravitational force are derived, while considering tilt and pitch angles. Since the gravitational force acting on the rotating blade creates an oscillating axial force, this results in oscillating stiffness terms in the governing equations. The validity of the derived rotating blade model is evaluated by comparing its transient responses to those obtained by using a commercial finite element code. Effects of rotating speed, tilt angle, and pitch angle of the wind turbine blade on its dynamic stability characteristics are investigated.