Vessel relocation solution for steel catenary riser touch down fatigue management

Abstract

This work is focused on developing a formal optimisation approach to the vessel relocation program for steel catenary riser (SCR) touch down zone (TDZ) fatigue management. Vessel relocation is the planned repositioning of the vessel within the acceptable limit of the riser design to help spread and reduce the fatigue damage over the SCR TDZ. There is a need to obtain an optimum vessel relocation program that best reduces the SCR TDZ fatigue damage. Hence, the facility operator will need to know the optimum combination of the following: the number of stations along the relocation axis, the distance limits for the relocation, and the relocation axis direction. The constraints on the problem are imposed by the stress utilisation, TDZ compression and top tension. The index-matching optimisation technique is applied to solve the optimisation problem. To demonstrate the approach's suitability, we consider a single SCR hosted by a production platform. The fatigue damage responses of the SCR with the optimum vessel relocation programs are compared with those without vessel relocation. The results obtained indicate that a considerable fatigue reduction can be achieved through a well-planned and optimum vessel relocation program.