The rising fossil energy prices and global warming phenomenon is driving researchers to look for alternative renewable and clean energy. Wind energy is considered as one of the most important alternative resources. Considering the space and other public requirements, offshore wind turbine could be larger. Technically, deepwater wind turbines are feasible since long-term viability of floating platforms has already been successfully demonstrated by the offshore oil and gas industries over decades. However, there are certain vibration issues which require critical attention for designing floating wind turbines. Flow-induced vibrations is the most important design criteria for most offshore structures and will also be important for floating wind turbines. Both the main structural elements as well as supporting structural members must be designed to withstand such oscillations. In addition to inline vibrations, the flow induced vibrations are known to initiate oscillations in a direction transverse to the general direction of motion. Most of the previous research has been concentrated on flap-wise vibration of wind turbine. This paper investigates the use of semi-active tuned mass dampers (STMDs) in controlling the edgewise vibration and the stability of floating wind turbines modeled as discrete dynamical systems in the blade rotation plane. Morison's equation is used to represent the interaction between the flow field and the offshore platform supporting the wind turbine. Numerical simulations prove that STMD has higher vibration reduction efficiency than TMD in the edge-wise blade direction under either steady or turbulent wind load, even with parameter changes such as rotation speed, nacelle stiffness loss and blade stiffness loss.
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