Vortex-induced vibration of a flexible fluid-conveying riser due to vessel motion

Abstract

As vessel motion and internal flow can exert impact on vortex-induced vibration (VIV) of flexible risers, it is of great significance to take these two factors into consideration while VIV is investigated. Therefore, crossflow (CF) VIV of a flexible fluid-conveying riser is studied when vessel motion is considered. The governing equation is firstly discretized based on finite element method and solved by Newmark-β method. Then, validation is conducted by comparing with experimental data. Subsequently, CF VIV response of a flexible riser is explored with consideration of both vessel motion and internal flow. The results show that regardless of low and high Keulegan-Carpenter (KC) numbers, vessel motion can have a notable effect on top tension and CF VIV characteristics. Variations of CF VIV amplitude, vibration frequency as well as top tension frequency are affected by both vessel motion and internal flow. With the increase of internal flow velocity, CF VIV amplitude is changed while mode jump occurs concomitant with frequency transition. Besides, both vessel motion and internal flow velocity can have an impact on energy allocation along the flexible fluid-conveying riser. Noteworthy is that although both vessel motion and internal flow can exert an impact on top tension and VIV response, the effect induced by vessel motion still plays a dominated role.