Determination of damping of blade and tower vibrations

A method for experimental determination of damping of edgewise blade vibrations has been developed in a previous project. With an excitation mechanism, the wind turbine nacelle is subjected to a periodic force and this enables the identification of the blade damping. The method has been verified with measurements on a 600 kW turbine. It is expected that a similar method can be used for identification of damping of other vibrational mode shapes. Furthermore, other parameters of importance for wind turbine design basis can be identified. The potential of the method is clarified through teoretical investigations. The mode shapes in focus are flapwise blade bending, tilt and yaw bending and tower bending. Based on the theoretical work, an excitation mechanism is developed. The method is verified with mesurements on a Bonus wind turbine. Measurements are carried out with focus on the following: 1) Identification of mode shapes and frequencies for stand still and operation. 2) Identification of damping for tower, flapwise, tilt and yaw mode shapes. 3) Identification of dynamic response of the loads in order to verify dynamic airfoil characteristics. It is expected that the method can be used in general to verify important parts of wind turbine design basis