(5) Numerical study of vibrations of a vertical tension riser excited at the top end

Bowen Fu, Decheng Wan ∗
State Key Laboratory of Ocean Engineering, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China

Received 15 May 2017; received in revised form 11 August 2017; accepted 6 September 2017
Available online 14 September 2017

Abstract
This paper presents numerical simulations of vortex-induced vibrations of a vertical riser which is sinusoidally excited at its top end in both one and two directions in still water. A computational fluid dynamics method based on the strip theory is used. The riser’s responses to both top-end and two-end excitations are carefully examined. In low reduced velocity cases, the in-line vibrations consist of three components, the low-frequency oscillation, the first-natural-frequency vibration during the riser reversal, and the second-natural-frequency vibration due to vortex shedding. The sheared oscillatory flow along the span causes low-frequency oscillations in higher modes in the in-line direction, thus forming ‘X’ shaped, ‘II’ shaped, and ‘O’ shaped trajectories at various positions along the span when the riser is excited at its top end in one direction. In the presence of excitations in the other direction, more complex trajectories appear.
© 2017 Shanghai Jiaotong University. Published by Elsevier B.V.
This is an open access article under the CC BY-NC-ND license. ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )

Keywords: Vortex-induced vibration; Oscillatory flow; Riser; Platform motion; Viv-FOAM-SJTU solver.