Nonlinear Numerical Analysis of Vortex-Induced Vibration of A Three-Dimensional Deepwater Steep Wave Riser with Large Deformation Features.

The cross-flow (CF) vortex-induced vibration (VIV) of a deepwater steep wave riser (SWR) subjected to uniform or shear flow loads is investigated numerically. The model is based on a three-dimensional (3D) nonlinear elastic rod theory coupled with a wake oscillator model. In this numerical simulation, the nonlinear motion equations of the riser with large deformation features are established in a global coordinate system to avoid the transformation between global and local coordinate systems, and are discretized with the time-domain finite element method (FEM). A wake-oscillator model is employed to study the vortex shedding, and the lift force generated by the wake flow is described in a van der Pol equation. A Newmark-β iterative scheme is used to solve their coupling equation for the VIV response of the SWR. The developed model is validated against the existing experimental results for the VIV response of the top-tension riser (TTR). Then, the numerical simulations are executed to determine VIV characteristics of the SWR. The effects of both flow velocity and the spanwise length of the flow field on the drag coefficient in the inline (IL) direction and the lift coefficient in the CF direction are investigated systematically. The results indicate that compared with TTR, the low frequency and multi-modal vibration are the main components of the SWR due to the large deformation and flexible characteristics. For shear flow, the multi-frequency resonance dominates the VIV response of the SWR, especially at the hang-off segment. [ABSTRACT FROM AUTHOR]