49 / 2021-10-12 10:35:31

Vessel motion influenced in steel catenary riser touchdown zone

SCR; riser-soil interaction model; vessel motion; trench development; fatigue life.

Abstract: This work is focused on the second-order motion of vessel influenced on behavior at touchdown zone (TDZ) of steel catenary riser (SCRs). The complex TDZ dynamic response depends on several factors, such as seabed model, riser characteristics, and vessel motion. The vessel motion as the upper boundary condition of the whole riser system is one of the main causes of cyclic oscillation in the dynamic behavior of SCRs locally at the TDZ, thus causing fatigue damage in TDZ. With first- and second-order wave force the vessel motion response is different, and the second-order motion cause bigger drift motion amplitude. However, previous studies do not completely describe the phenomena resulting from the vessel practical motion, such as the second-order motion of the vessel. To demonstrate the second-order motion's influence, we consider a single SCR hosted by a tension leg platform, fatigue analysis and dynamic response of SCR TDZ are studied based on the time domain for different vessel motion responses. The results obtained as follow: the dynamic response of SCR TDZ is greatly influenced by the second-order motion of vessel; suction amplitude can be range different, because the pull-out velocity varies with different vessel motion, a slightly fatigue life reduction, suction amplitude larger and TDZ length increment can be appeared through a consideration of the practical vessel motion. The results of this study indicate that the second-order motion of the vessel should be considered as a whole in future study.