Evaluation of vortex-induced vibration of a steel catenary riser in steady current and vessel motion-induced oscillatory current

A large-scale model test of a truncated steel catenary riser (SCR) was performed in an ocean basin to investigate the riser responses under pure steady uniform current and pure vessel motions separately. Out-of-plane vortex-induced vibration (VIV) was confirmed to have occurred under both test conditions. A comparative analysis and discussion were carried out on selected cases in terms of out-of-plane VIV responses, VIV developing mechanisms and the fatigue damage contribution. Results indicate that both steady current-induced and vessel motion-induced VIV responses are dominated by strong travelling waves, but vessel motion-induced VIV responses are more 'intermittent' with respect to the response amplitude and frequency owing to its space- and time-varying shedding frequency. 'Power-in' regions are further estimated to understand the VIV developing mechanisms for both test conditions. Finally, fatigue damages are evaluated showing the damage by vessel motion-induced VIV is comparable and at the same level as uniform current-induced VIV, which highlights the great importance of vessel motion-induced VIV, which cannot be neglected in the design and analysis for SCR systems.