Session: 08-06-02: VIV of Flexible Risers and Cables

Paper Number: 78236

78236 - Influence of Internal Slug Flow on Vortex-Induced Vibration of Flexible Riser With Variable Curvature 

Flexible risers carrying multiphase gas-liquid flows may experience vortex-induced vibration (VIV) due to the external current flow. Previous studies have mostly focused on either VIV of flexible risers or multiphase flows in static straight pipes, whereas the understanding of combined external-internal (VIV-multiphase) flow effects on flexible risers with variable inclinations and curvatures is still limited. The present study aims to model and numerically investigate the dynamics of a slug flow-carrying catenary riser subject to VIV and to evaluate the internal nonuniform slug gas-liquid flow effects on the overall flow-induced vibration behaviors. A steadily time-varying slug flow model, based on a series of traveling slug gas-liquid unit cells, is applied to approximate the slug flow-induced vibration (SIV) caused by the variation of internal flow weight, momenta, and pressure change along the inclined and sagged riser. Cross-flow and in-line VIV responses of the flexible catenary riser under the perpendicular uniform flow are modeled by using the inclination-dependent, distributed van der Pol wake oscillators leading to 3-D responses with out-of-plane and in-plane (horizontal and vertical) displacements. Validation of the VIV model is conducted by comparing numerical results with experimental results in the literature. Some experimentally observed VIV and SIV features of flexible cylinders are numerically predicted. Through comparing the cases under various internal-external flow conditions, riser responses are assessed in terms of dynamic responses, resonant frequencies, vibration modes, and stresses for the VIV-only versus combined VIV-SIV scenarios. The slug flow results in greater dynamic and mean stresses in the catenary riser owing to the amplified curvatures, mean drifts, and multimode oscillations. This observation should be recognized in the practical design of production risers transporting multiphase flows.

Presenting Author: Narakorn Srinil Newcastle University

Authors:

Bowen Ma Shanghai Ship and Shipping Research Institute
Narakorn Srinil Newcastle University