3.4.1. Blades

For the simulation of the blades, the tower is considered as a sti ff body. The dynamics are generated from the rotation of the blades in the azimuth direction and the vibrations in the flap-wise and edge-wise directions. Further, the tower is considered to be a sti ff body in the FAST simulation to create a similar simulation environment for comparison. In Figures 10 and 11, bending moments at the blade root in the flap-wise and edge-wise directions are shown with the azimuth position of the blade.

**Figure 10.** Blade-root, flap-wise bending moment.

**Figure 11.** Blade-root, edge-wise bending moment.

The periodic behaviour of the dynamic response of the blade is due to the e ffect of gravity and inertia on the blades while in di fferent azimuth positions, as well as the shear layer of the flow. As the blade rotates, considering the rotor's tilt angle, the mass centred along the blade length moves such that the blade moves towards or away from the plane of rotation.

Figures 12 and 13 show the blade tip deflections.

**Figure 13.** Blade-tip, edge-wise deflection.

There are some discrepancies between the results of the present tool and FAST, especially in the initial runs of the simulation. Those discrepancies are due the difference in the natural frequencies and mode shapes between the present tool and FAST. The aeroelastic model might as well be modeled in a different way in FAST than in the present tool. Other than the initial condition, there is a very good agreemen<sup>t</sup> between the results of the present tool and FAST results in terms of the ranges of values, mean values, and frequencies of each time series. Consequently, the proposed tool has proved its ability to describe the blade dynamics and hence its ability to model the tower.
