An investigation on vortex-induced vibration of a flexible riser transporting severe slugging

Abstract

An investigation on the dynamic characteristics of a flexible riser due to the coupling effects of Vortex-Induced Vibration (VIV) and severe slugging is performed in this paper. Firstly, a 2D Computational Fluid Dynamics (CFD) model is developed for capturing the dynamic characteristics of severe slugging. Based on the mass and velocity of internal fluid from the CFD analysis, a classical van der Pol oscillator is employed to simulate the dynamic characteristics of the effect of VIV coupled with severe slugging. The governing equation of the riser with internal flow is discretized by the finite difference method and it is then solved by the Runge-Kutta method. The results show that the effect of severe slugging exhibits quite distinguished dynamics owing to the intermittent feature both in in-line (IL) and cross-flow (CF) directions. The VIV characteristics of the riser with severe slugging, such as frequencies, dominant modes, and root mean square (RMS) displacements, are substantially different from those of the riser without internal flow. In addition, severe slugging may trigger new mode responses of the riser and a multi-frequency vibration phenomenon in IL and CF directions due to severe slugging is observed.