Behaviors of Drag and Inertia Coefficients of Circular Cylinders Under Vortex-Induced Vibrations With Forced Oscillation Tests in Still Water

This paper describes the drag coefficient and the inertia coefficient on rigid circular cylinders under oscillating flows. And also VIV behavior of tubing is investigated by using horizontal orbit patterns of test models including effect of VIV. Rigid circular cylinders are used for the model experiment. The test models are suspended into still water through a flat spring, and hence VIV is observed found with hydroelasticity in spite of a rigid circular cylinder. This is a forced oscillation test in still water. The circular cylinders for the model test have drafts of 30 cm, 60 cm and 80 cm, and diameter of 5 cm and 8 cm. The models are oscillated with periods of 0.5 s to 4.6 s and with about 7 cm amplitude of the oscillation. Model tests of forced oscillation are carried out under transverse motion (VIV) fixed conditions because VIV effects are investigated to the drag and the inertia coefficients. It is shown that the drag coefficient increases and the inertia coefficient decreases when larger VIV response occurs under forced oscillation in an inline direction.