Fatigue life prediction method of fairleads installed on a FPSO

Paper in proceeding, 2017

As the key devices in the mooring system of a Floating Production Storage and Offloading vessel (FPSO), fairleads are used to guide the cables (wire rope or chain) from the vessel towards the anchor and help to change the vessel’s floating condition in a smooth manner. The fatigue strength of fairleads cannot be neglect-ed because the FPSO always suffers from complicated environmental loadings due to wave, current and wind; and induces highly varied loadings in the fairleads. In this paper, fatigue strength analysis is carried out for the fairleads of a FPSO served in the South Sea in China. Hydrodynamic performance of the FPSO cou-pling with its mooring system is firstly obtained, and then the short-term history of cable tension can be ob-tained by wave scatter diagram. The cable tension is regarded as the dynamic loading acted on the fairleads; and the corresponding history of stress range in the fairleads can be obtained by finite element analysis (FEA). At last, fatigue accumulating damage in the fairleads is calculated based on the rain-flow counting method and S-N curves. The estimation framework based on the ship motion and mooring tension coupling analysis in time domain proposed in this work can provide a fast fatigue life prediction of the fairleads when the ship is operated in different conditions.