**4. Design variables**

The definition of wind turbine variables and parameters is of great importance in formulating a design optimization model. Actually, a wind turbine is a complicated network composed of thousands of interconnected elements. However, a breakdown of the system may help identify the most important design variables for each subsystem.

The following list shows the main design variables of wind turbine subsystems, with emphasis on variables related to the blade and tower structures.

#### **4.1 Rotor variables**

a. Main variables

	- General layout (length chord and twist distributions coning angle).
	- Cross section (airfoil type construction).
	- Blade-Hub connection (semi-articulated fully articulated hingeless).
	- Type of hub (fixed teetered)
	- Type of bearings
	- Shaft construction and dimensions

Type of mounting of rotor shaft onto gearbox.
