ABSTRACT
To estimate the annual energy production from a wind turbine at a given site with known wind distribution it is sufficient to apply a steady BEM method as described in Chapter 6 to compute the steady power curve. But due to the unsteadiness of the wind seen by the rotor caused by atmospheric turbulence, wind shear and the presence of the tower it is necessary to use an unsteady BEM method to compute realistically the aeroelastic behaviour of the wind turbine. To do this a complete structural model of the wind turbine is also required; this must be coupled with the unsteady BEM method since, among other things, the velocity of the vibrating blades and the tower change the apparent wind seen by the blades and thus also the aerodynamic loads.
