In the wind farm, there's an important rule regarding the hoisting of wind turbines. Once the top tower segment is successfully raised, the cabin must be hoisted on the same day. Why is this necessary? Let me break it down for you.
When constructing a wind turbine, there are several methods used to suppress vortex-induced vibrations that can affect the tower and other components. These vibrations occur when air flows around non-streamlined objects, like the tower, creating alternating vortices. These vortices generate fluctuating pressures, leading to periodic oscillations in the tower if it’s flexible enough. If the natural frequency of the tower aligns with the vortex shedding frequency, it could result in catastrophic resonance. To avoid this, various techniques have been developed.
One approach involves installing spoilers on the tower to disrupt the airflow and prevent stable vortices from forming. Spoilers are often made of lightweight materials like plastic foam, arranged in triangular sections around the upper part of the tower and secured to the ground with strings.
Another method uses dampers to reduce vibration. A pendulum-based system can counteract the tower's movement by applying reverse inertial forces. However, the effectiveness depends heavily on the tower's mass and stiffness. Incorrect design might worsen the situation rather than improve it.
Cable stays offer another way to control these vibrations. By applying tension through cables, they interfere with the aerodynamic forces acting on the tower, limiting its initial sway and preventing vortex formation. This stops the tower from accumulating vibration energy during the vortex shedding process.
Installing the nacelle, generator, and rotor blades also helps mitigate vortex-induced vibrations. With the nacelle and generator in place, the airflow becomes less predictable, making it harder for stable vortices to form that could resonate with the tower. Similarly, once the rotor blades are attached, their surface interacts with the wind, causing rapid changes in airflow that disrupt stable vortex generation.
Lastly, keeping the tower door closed during hoisting enhances internal damping within the structure. This reduces the tower's vibration amplitude since the airflow inside acts as a natural buffer. Conversely, leaving the base open eliminates this damping effect, allowing external eddies to interact with internal airflow, amplifying the tower's vibrations.
By following these practices, engineers ensure the safety and longevity of wind turbines while minimizing maintenance costs. Proper execution of these measures is critical for long-term success in wind energy projects.
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