Tadashi Kumakiri

Drag forces on oscillating cylinders in a uniform flow

This paper describes the drag coefficients of cylinders oscillated in both in-line and transverse directions to a uniform flow. The drag coefficients C/SUB D/ have been obtained experimentally over a wide range of oscillating frequencies, amplitude and flow velocities for the cylinders of various diameters under simulated practical offshore conditions. The boundary between the regions, where C/SUB D/ approx. =1 and C/SUB D/ <1, are clearly established by employing the Keulegan-Carpenter number and the Reduced Velocity as dimensionless numbers. These numbers also describe C/SUB D/ variation within the region of rapid C/SUB D/ value decrease. Recommendations are offered for determining C/SUB D/ values in order to predict the dynamic response of risers under actual offshore conditions.