Out-of-plane vortex-induced vibration of a steel catenary riser caused by vessel motions

Abstract

A large-scale model test of a truncated steel catenary riser (SCR) was performed in an ocean basin to investigate the riser responses under top vessel motion. Top end of the model was forced to oscillate at given motion trajectories, corresponded with the motion at the truncation point of a full-length SCR under vessel motion. Out-of-plane vortex-induced vibration (VIV) was confirmed under pure top vessel motions, characterized with distinctive time-varying features. Results further indicate that vessel motion-induced VIV was strongly dependent on the KC number and the instantaneous equivalent flow profile. Meanwhile, tension variation was found to be another key factor causing response discrepancy between the ‘lift-up’ and ‘push-down’ phase for the large top vessel motion case. Finally, the relationship between the out-of-plane VIV dominant response frequency, maximum equivalent flow velocity and KC number were unveiled, which provides references for future vessel motion-induced VIV predictions.