Dominant parameters for vortex-induced vibration of a steel catenary riser under vessel motion

Abstract

Recent research has confirmed a new type of vortex-induced vibration (VIV) in steel catenary risers (SCRs), purely caused by vessel motion. Vessel motion-induced VIV occurs because the SCR is exposed to the equivalent oscillating current due to its own motions relative to the still water. Preliminary results indicate that vessel motion-induced VIV is quite different from ocean current-induced VIV and is characterized with distinct time-varying features. In the present study, we aim at further summarizing the dominant parameters that govern the general vessel motion-induced VIV responses. Throughout the comparative studies on the instantaneous and statistical VIV responses including strain, displacement, response frequency, fatigue damage and top tension variation, the maximum Keulegan-Carpenter number KCmax and the maximum equivalent current velocity Vn_max are found to be the two dominant parameters that govern the vessel motion-induced VIV responses. Generally speaking, when KCmax is sufficiently large (larger than 39 according to the present study), the general vessel motion-induced VIV response is dominated by Vn_max. However, when KCmax is small, the VIV response is less time-varying and shows strong correlation with both KCmax and the local KC number distribution along the SCR. Vessel motion-induced VIV response frequency models are also reviewed and discussed considering different KCmax and Vn_max ranges. Hopefully, these results can provide some general guidelines for future vessel motion-induced VIV prediction and for industrial references.