A Practical Procedure for the Evaluation of the Roll Motions of FPSO’s Including the Non potential Damping

摘要

Nowadays, deep-waters are the new frontier of the latest hugernoil discovers. The most common technology for oilrnexploration in deep waters is based on the FPSO concept.rnTherefore, a key element for a successful exploration of deepwaterrnoil fields is the accurate prediction of the unit motions inrnorder to minimize the stop production due to excessivernmotions and maximum accelerations to which the processrnplant equipment and supports are subjected.rnThe excessive motions of a FPSO can be caused not only duernto rough weather but also due to mild weather at beam searnconditions. Beam sea conditions are faced by FPSOs in arnspreading mooring configuration or even in single pointrnmooring configuration but moored in regions where the swellrnsea is important, for instance, in Campos Basin offshorernBrazil. In such cases, the accurate evaluation of roll motions isrnof prime importance. Moreover, in order to reach valuablernresults, a critical step is the proper evaluation of the differentrndamping effects in particular viscous damping induced by thernbilge keel, or those of risers.rnThe state of the art assumption is that the roll damping isrncomposed of two parts: the linear one and the quadratic one.rnThe former accounts for the potential wave radiation andrnpartly to some frictional effects, while the latter accounts forrndrag forces, flow separation, and other non-linear effects. Inrnpractice, the linear part can usually be neglected and the onlyrnremaining damping is the quadratic part. These fact strengthsrnthe role played by the non-potential damping in a reliablernevaluation of the roll motion amplitude.rnIn this paper, we will show the implementation of a practicalrnprocedure for the evaluation of the roll motions including thernnon-potential damping of a FPSO moored in a spreadingrnconfiguration at Campos Basin and its validation through therncomparison of the numerical results to the model tests.