13432 Inertial loading Inertial loading can occur in various situations When

13432 inertial loading inertial loading can occur in

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1.3.4.3.2 Inertial loading Inertial loading can occur in various situations. When the turbine is accelerated or decelerated is one of those situations. Braking of the rotor will cause that a small section of the blade will feel a force dF in the direction of the rotation as shown in Figure 32. Figure 32: Loading caused by Braking the Rotor [10] This force can be found with the expression 𝑑𝐹 = 𝜔̇ 𝑟𝑚𝑑𝑟 (83) where m is the mass per length of the blade, r the radius from the rotational axis to the section and dr the size of the small section; 𝜔̇ = 𝑑𝜔 / 𝑑𝑡 can be found from 𝐼 𝑑𝜔 𝑑𝑡 = 𝑇 (84) where I is the moment of inertia of the rotor and T is the torque. Another common type of inertial loading is due to the centrifugal force acting on the blades. This type of loading causes a flapwise bending moment which can be reduced by coning the rotor backwards with a cone angle of θ cone as shown in Figure 33.
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Design Optimization of Winglets for Wind Turbine Rotor Blades R.G. Galdamez, D. Moreno, J. Rodriguez Page | 43 Figure 33: Effect of coning the rotor [10] 1.3.4.3.3 Aerodynamic loading This is the most important type of loading on a wind turbine. Aerodynamic loading is caused by the air flow past the whole stricter, blades and tower. The wind speeds of this airflow increases as the height is larger and causes shear forces on the blades. Wind shear causes a sinusoidal variation of wind speeds seen by the blade. Also, the turbulent fluctuations superimposed on the mean wind speed also produces a variation in the wind speed and thus in the angle of attack. This constant change of the angle of attack causes fatigue on the blades and should be carefully studied using the most realistic wind field as possible. The turbine tower also has an influence in how the wind affects the structure. The tower is changing the flow pattern thus the velocity and the pressure of the wind is altered. Since wind fields in reality, are hard to predict, wind turbines commonly operate in yaw conditions, this means that the direction of the wind is not in the right angle for the blade design. This condition increment the loads on the blade due to increased drag, therefore it will contribute to the fatigue loads that will reduce the expected lifetime of the rotor. It can be concluded that the change of the angle of attack on the blades can highly increase the loading in the structure. These changes can be mainly produced by turbulence, wind shear, turbine tower and yaw/tilt [10].
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Design Optimization of Winglets for Wind Turbine Rotor Blades R.G. Galdamez, D. Moreno, J. Rodriguez Page | 44 2 Conceptual design 2.1 Winglet design The geometry of a winglet is defined by six parameters: Height Sweep angle Cant angle Curvature radius Toe angle Twist angle The geometry of winglets has been extensively investigated for the aeronautical industry and specifically for high performance sailplanes [21]. Since it has been shown that winglets decrease
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