Floating Wind Turbine Modeling

The FLORIS wind turbine description includes a definition of the performance curves (power and thrust_coefficient) as a function of wind speed, and this lookup table is used directly in the calculation of power production for a steady-state atmospheric condition (wind speed and wind direction). The power curve definition typically assumes a fixed-bottom wind turbine with no active or controllable tilt. However, floating wind turbines have additional rotational degrees of freedom including pitch which adds a tilt angle to the rotor. As the turbine tilts, its performance is affected similar to a yawed condition. The turbine is no longer operating on its defined performance curve, and corrections must be included to accurately predict the power production.

Support for modeling this impact on a floating wind turbine were added in PR#518 and allow for correcting the user-supplied performance curve for the average tilt. This is accomplished by including an additional input, floating_tilt_table, in the turbine definition which sets the steady tilt angle of the turbine based on wind speed. An interpolation is created and the tilt angle is computed for each turbine based on effective velocity. Taking into account the turbine rotor's built-in tilt, the absolute tilt change can then be used to correct the power and thrust coefficient. This tilt angle is then used directly in the selected wake models.