Abstract
Vortex-induced motion is an oscillatory phenomenon which occurs to a floating body with low aspect ratio. The basic phenomenological study about the effects of free surface and end cell on flow around a finite fixed circular cylinder was investigated in this study using particle image velocimetry and hydrodynamic force measurement. It was found from the former experiment that the wake of the cylinder is influenced by the both end cell and free surface. Blowup and back flow are generated from the end cell, and their effects are suspended by free surface. The result of hydrodynamic force measurement showed the effect of Reynolds number, Froude number, and the aspect ratio of the floating body on the hydrodynamic force. Fluctuating components of hydrodynamic coefficients decrease for increasing Reynolds number, Froude number, and the aspect ratio. On the other hand, the mean drag coefficient increases as Froude number increases and decreases as the aspect ratio increases. The interpretation to these results was discussed in comparison with flow structures observed in the experiment. In addition, it was found that the effect of Reynolds number on the mean drag coefficient changes at different aspect ratios. A possible interpretation to this phenomenon was proposed.
Highlights
Offshore wind is recently expected as one of the promising renewable energy sources which may secure domestic energy as well as mitigate greenhouse gas emission
The basic phenomenological study about the effects of free surface and end cell on flow around a finite fixed circular cylinder was investigated in this study using particle image velocimetry and hydrodynamic force measurement
Blowup and back flow are generated from the end cell, and their effects are suspended by free surface
Summary
Offshore wind is recently expected as one of the promising renewable energy sources which may secure domestic energy as well as mitigate greenhouse gas emission. From technical and economical viewpoints, the floating type of wind turbine is considered to be the most feasible in the offshore. Because the motion of floating offshore wind turbines (FOWT) is directly related to the efficiency of power generation, it is necessary to analyze and predict their motions in wind, waves, and currents. FOWT is widely studied experimentally and numerically and the comparison among numerical models is being carried out these days. In most of the numerical models, the motion of FOWT is mainly caused by wind, waves, and moorings. Motions induced by vortex are not considered in those models
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