Abstract

This paper investigates the potential feasibility of SCRs hosted on FPSOs in offshore Brazilian ultra-deepwater regarding to fatigue life at the Touch-Down Zone (TDZ) when the riser system is hanged off from a centered moonpool instead of from the unit's side. A case study is presented here in order to provide a suitable starting point for the study a 2 MMbbl FPSO has been preliminary dimensioned and the focus has been set on wave induced motions fatigue loading. Wave induced motions at two porch locations, one connected to the hull outer shell and another connected at the moonpool of the FPSO, are calculated and used as forced-displacement boundary conditions in a detailed riser FEM analysis whose stress cycle time series are eventually calculated to provide an estimation of the fatigue damage at the TDZ between the two locations. Despite the conservatism that this approach might introduce regarding the estimation of the fatigue life of the SCR due to the fact that the damage is concentrated in quite a few elements, the results from the calculations show a significant decrease in the wave fatigue damage at the TDZ when the risers are installed inside the moonpool.

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