A Study on Effect of Mooring Line Failure on a Floating Body and Mooring Stability

Abstract

The depth of operating water is getting deeper due to the expansion of the sea area where floating offshore structures are installed to develop oil under the sea. The mooring tension is greatly affected due to the motion response of floating offshore structure is increased by the external force of the rough marine environment in the deep-sea area. In addition to increasing marine environmental loads, a significant number of offshore structures already installed and in operation are approaching their design life time. Floating offshore structures are exposed to the marine environment for a long time because of their long operation period. The mooring system and offshore structures are more likely to perform less than they did in the initial design phase due to the fatigue load of the marine environment. Also, Corrosion of the mooring line may cause the mooring line failure. Therefore, mooring line failure and the impact of corrosion of it in the design of mooring systems are an important factor to consider. In this paper, the study was conducted to understand the effects of the mooring line failure on floating bodies and the mooring tension. A numerical analysis program was developed for the analysis of floating body motion and mooring systems, reflecting the effects of mooring corrosion in the program. The mooring line failure analysis was carried out assuming taut mooring system with an FPSO model. Various scenarios of mooring line failure were set, and motion of floating bodies and mooring tension are confirmed for each case. According to the result of the mooring line failure simulation, the influence on the remaining mooring tension and the maximum mooring tension is different depending on the mooring line failure point. A result of 8-point mooring system of little resilience of mooring line shows a phenomenon that adjacent mooring lines are failed first, and other remaining mooring lines are also failed by chain action, which makes mooring system collapse.