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Modelling Structural Damage in FPSO Collisions
Abstract
While the oil operators become more interested in developing oil and gas in deeper and more remote offshore locations, there should be further research and development that focuses on collision assessment of floating structures, especially ship-shaped floating production, storage and offloading units (FPSOs).The focus of this paper is on general methodology and design accident scenarios for FPSOs using more sophisticated tools such as the nonlinear FEM used so that structural responses during and after a collision can be more precisely predicted.The extent of FPSO hull damage due to the different collision scenarios and impact energy levels are determined using the guidelines contained in the NORSOK Standard. The collision scenario is considered for Accidental Limit State (ALS) with 5-years onsite environment in this study. The various collision scenarios are defined such as supply vessel collision bow on, supply vessel collision side on, supply vessel collision stern on, and off take tanker collision bow on. Nonlinear finite element analysis, using large deformation FEM is applied to analyse the damages to FPSO hull structures. Conservatively, the impacting vessel is considered non-deformed during the collision (whole energy absorbed by the FPSO). Damage evaluation to hull parts of FPSO is checked, including flare and flares foundations, aft muster station, offloading reel and piping and green water protections above cargo deck.The reduction of hull girder strength associated to the worst damage resulting from the application of the MARPOL regulation is also evaluated and accounted for, assuming no further escalation of the damage.
Keywords: Collision, accident scenarios, nonlinear FEM, acceptance criteria, oil outflow, residual strength, post accidental loads
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