Vortex-excited vibration of a vertical circular cylinder in waves

This study deals with some of the non-linear 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 spring at its top. The movement of the test cylinder in the direction of the inline force 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 now, perfect resonance appears in the range of locked-in, but in the case of wave, it appears only near to the ratio of wave frequency f(w) to the natural frequency f(nw) of the cylinder in still water f(w)/f(nw)=1/2,1/3,1/4,----(multi-appearance), elsewhere vortex coupling may occur for light damping in which the oscillation frequency is not simple a multiple of wave frequency.