The fluid resistance of shrouded and unshrouded circular cylinders in the oscillatory flow



Journal Title

Journal ISSN

Volume Title



This investigation concerns itself with the measurement of a strain-gage signal responding to a sinusoidal variation of tension and compression brought about by a circular cylinder oscillating with simple harmonic motion in a tank of water, otherwise at rest. The strain-gage signal is transformed into the fluid resistance acting on circular cylinders. A series of plots of force coefficient versus Reynolds Number were developed to gain a better understanding of the phenomenon. The experimental apparatus is analogous to the distribution of wave forces present on a single fixed leg of an offshore structure. The fundamental variables involved were the diameter of the cylinder (O.625-, 1.0, and 1.5-inch) and amplitude and speed of oscillation, one- to six-inches and 10 to 60 rpm, respectively. The effects on the fluid resistance acting on the two smaller cylinders enclosed in a concentric perforated shroud of the same outside diameter as the largest cylinder were determined relative to the fluid resistance acting on the largest unshrouded cylinder. The effects of the shroud were investigated to ascertain the feasibility of reducing wave forces on the structural members of an offshore platform.