**3. Structural design**

After determining the wind turbine geometry, a structure design should be accomplished to create the wind turbine. The structure design includes several analyses, such as static analysis, modal analysis, dynamic analysis, and aeroelastic analysis. There are two schools in wind turbine structure analysis and design. The first school suggests the design of the wind turbine structure by approximating the wind turbine blade into a beam model [2]. This method is very efficient in computational time and cost, but it cannot provide a detailed solution for deformation, strain, and


**Table 1.**

*Comparison between 1D beam and 3D numerical solutions.*

stress distribution. The second school prefers to analyze the wind turbine blade as a full 3D model using numerical software. The most popular method to conduct these analyses is the finite-element method. However, the 3D simulation can provide a detailed solution to the wind turbine blade structure; it costs lots of time and money in comparison to the 1D beam analysis. **Table 1** provides a detailed comparison between the beam and numerical solutions.

Usually, four solutions should be studied to make sure that the wind turbine structure is safe and stiff enough:

