Vortex excited vibration of a vertical circular cylinder in waves

This study deals with some of the nonlinear phenomena of the vortex-excited vibration of a circular cylinder in waves. Laboratory experiments have been performed to study the dynamic transverse response of a vertical circular cylinder in regular waves. The test cylinder was pivoted at its base and supported flexibly by springs at its top. The movement of the test cylinder in the inline direction was restricted. The most remarkable result is the appearance of two types of peak in the amplitude of the vortex-excited vibration of the cylinder produced by perfect resonance coupled with waves and by vortex coupling. In the case of steady flow, perfect resonance appears in the locked-in range, but in waves, it appears only close to ratios of wave frequency fw to the natural frequency fnw of the cylinder in still water in the sequence of fw/fnw = 1/2, 1/3, 1/4,…; elsewhere vortex coupling may occur for light damping in which the oscillation frequency is not a simple multiple of wave frequency.