Reliability analysis and Response Based Design of a moored FPSO in West Africa

ABSTRACTThe present study is an attempt to re-assess the level of reliability of the mooring system of an existing Floating Production Storage and Offloading (FPSO) unit in West Africa. The study made use of field data for the environment including wind, waves and current together with simultaneous measurements of the FPSO offset and of the mooring line tensions. Three different approaches to predict the extreme response are compared. More specifically, the traditional design method is compared with Response Based Design (RBD) and First Order Reliability Method (FORM) analysis associated with Response Surface Models (RSM) of the moored FPSO. The results of this case study allow assessing the level of conservatism that is currently embedded in classical design rules.

▸ A reliability analysis of an FPSO mooring system is proposed. ▸ Field data including wind, waves and current are used. ▸ Models for FPSO offset and the mooring line tensions were benchmarked. ▸ The traditional design method is compared with Response Based Design (RBD) and First Order Reliability Method (FORM) analysis associated with Response Surface Models (RSM). ▸ The level of conservatism currently embedded in design rules for moored structures is assessed.