VIV analysis of a riser under top excitation conditions with a numerical method

Abstract

The object of this study is to develop the tool to analyze VIV(vortexinduced vibration) of a slender marine structure which may vibrate in inline and cross-flow directions due to the vortex shedding on the condition of top excitation with a period and an amplitude. KC(Keulegan-Carpenter) numbers distributed along the riser length excited at the top end are calculated and the riser is assumed to be excited with the vortex shedding frequencies corresponding to different KC number along the riser length. In the case studies, vortex-induced lift force with three kinds of vortex shedding frequencies and an exciting frequency excites the riser in the cross-flow direction. The riser, by vortex-induced lift forces with the vortex shedding frequencies corresponding to different KC number along the riser length, vibrates in complex behaviour characteristics. Although the riser is excited with only one vortex shedding frequency at a point of the riser it showed to response in several frequencies component. That is caused by the structural wave propagation along the riser length. This research can contribute the prediction of fatigue and design life for a riser. Copyright ？ 2011 by the International Society of Offshore and Polar Engineers (ISOPE).