الفهرس 
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Abstract
ABSTRACT
Bladeless wind turbines (BWT) based on vortex-induced vibration (VIV) usually consist of a cylindrical body mounted on top of a flexible support. An inherent feature of this kind of turbines is that the power generation is considerable only in a narrow band, when the frequency of shedding vortices is close to the structural natural frequency; the so-called lock-in phenomenon. The present study proposes a novel semi-active approach for tuning the VIV-BWT response to widen the lock-in region over a broad band of wind speeds. Based on numerical modeling of the aeroelasticity interaction phenomenon, a parametric analysis is done and the effective parameters on the turbine performance are highlighted. The proposed tuning technique then works to maintain the effective parameters at the optimum values from the power generation point of view.
In order to realize this, a supporting mechanism is suggested that can change the effective length of the BWT’s supporting stand and consequently the structural natural frequency. However, to avoid phenomenon attenuation due to the damping effect produced by power extraction process, a second level for tuning the structure damping ratio is added. The second tuning is done by controlling the electric damping level of a suggested linear electromagnetic power take-off (PTO). Results of numeric simulations showed that, compared to previous work, the proposed tuning technique is effective in improving the power performance of the VIV-BWT over a broad band of wind speeds. The efficiency of BWT with the proposed tuning system is greater than or equal 15 % over a wind speed range of 3.3 – 6 m/s. The maximum harvested mechanical power is 514 W at a wind speed of 6 m/s. The overall system presented can be applied in small to medium scale BWT and does not assume a certain wind direction.