ABSTRACT:

Flow control that attached different sized control rods to the rearward stagnation point of a circular cylinder was carried out in a circulating water channel by PIV technique. Reynolds numbers varied from Re≒5,000, 10,000, 15,000, 20,000 to 25,000 based on the main circular cylinder diameter(D=50mm). Wake velocity distributions were measured with varied control rods and Reynolds numbers. The measured results were compared with each other. The results indicated that the flow control by rods has different effects according to the change of inflow. Strong time mean turbulence intensity appeared within X/D=3.5. The control rod, d/D=0.3 has an outstanding effect to reduce the turbulence intensity around the circular cylinder.

INTRODUCTION

The quantity of goods transported at sea has been increasing at the rate of 67% over the last decade due to faster transportation systems and the free trade agreement between countries. There is also a growing potential for marine accidents due to the high density traffic, strong currents and scattered littoral islands. Thus the steady demands on marine buoys also have been increased with the need for improvement of safety at sea. For the sake of safety, the buoy system must be accuracy and have stable performance and position stability. To meet these demands, hydrodynamic research has been conducted in various areas to develop safe and trustworthy systems. Within the IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) Buoyage System, there are five types of navigational marks; lateral, cardinal, isolated danger, safe water and special marks, which may be used in different combinations. Its two-dimensional formation under the free surface looks upon a circular cylinder. The flow around the circular cylinder is closely related to many practical applications, such as offshore risers, bridges, piers, and buoys.

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