oads are generated on the revolving rotor blades due to wind shear. The loads alter every now and then as the blades of the turbine experience periodically changing wind speeds during each full rotation. A similar periodically altering load is induced on the blades and turbine by consistent off axis winds. The tower of the wind turbine creates a stagnation point and forms a boundary layer as it acts as an obstacle for the incoming airflow, as a result the flow in front of the tower decelerates. Due to this phenomenon, the aerodynamic forces acting on the blades decline each time they individually pass the tower. This induces an oscillation to occur which in turn excites each blades frequency to an intense 1P (and multiples 2P, 3P…) and also excites the tower and the nacelles frequency to 3P (and multiples 6P, 9P…). The following abbreviations refer to the rotor frequency and multiples thereof. Wind turbines are designed in a way that the major natural frequency of the tower and the platform are above or below these 1p and 3p frequencies to avoid inducing resonances that can affect the lifetime of the structure 8.

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