With the increasing need for more power production by wind turbines and thus increasing in their sizes, importance of accurate designing of wind turbines has substantially increased. One of the major aspects related to the reliability of operation of wind turbines concerns the safe and adequate performance of the blades. It is important that damage to blades is detected before they fail or cause the turbine to fail. Root joints are located in blade root and join blades to the hub. They are significantly affected by fatigue and extreme loads, so damage detection in root joints is vital. In this article a 100 kW wind turbine model was developed and damages in root joints were modeled by reducing their stiffness and the possibility of damage detection in blade root joint was investigated by tracking the dominant frequencies in nacelle and blades. The model considers structural dynamics of the turbine and includes dynamic coupling between the blades and the tower and consists of 11 degree of freedom (two in each of the blades, two for tower and one for each root joint). Finally, numerical simulations were carried out to evaluate the effectiveness of the method for damage detection. Simulation results showed the dominant frequency tracking method has an appropriate capability of detecting damages in the root joints of the wind turbine.

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