## Example three bladed wind turbine

For the purpose of illustration, Fig. 3.20 shows a superelement approximation of a three bladed wind turbine. Observe that both the tower and rotor blades are approximated by one superelement. Each superelement consists of three rigid bodies connected by two joints (marked o). Each joint (i.e. a universal joint since both blade and tower torsion is not considered in this thesis) has two degrees of freedom. This implies that this system has 18-DOF (exclusive pitch and azimuth). Obviously, the total number of degrees of freedom required for proper modeling depends on both the wind turbine and site under investigation.

Three bladed wind turbine

Figure 3.20: Superelement approximation of a three bladed wind turbine, with universal joints (2-DOF rotational joints). Both the tower and rotor blades are approximated by one superelement consisting of 3 rigid bodies connected by ideal torsional springs. The flexibility of the foundation is approximated by a torsional spring.

Please remember that the resulting model accuracy strongly depends on the quality of the input data (i.e. garbage-in is by definition garbage-out). For example, in case of a wind turbine the uncertain (mechanical) parameters are particularly found in the area of foundation stiffness and damping. Obviously, when the correlation with the test data is not satisfactory, there is a need to modify the model by tuning/updating the model parameters. Since ad hoc procedures (trial and error) become impractical for more than three or four parameters, a systematic procedure has to be developed. This subject is treated in Chapter 5.

## Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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