An Experimental Analysis of Second-Order Roll Motions of New Generation FPSOs

Abstract Floating Production, Storage and Offloading (FPSO) units represent the main type of platform adopted nowadays for oil & gas production offshore Brazil. Since the first versions in the early 1990s, the FPSOs designed to operate in deep water fields underwent several modifications, and, more recently, those of the new generations are characterized by a significant increase of hull size and topside weight. One of the consequences of this increase in the FPSOs size are the higher values of their natural periods of roll motions, making them more susceptible to (low-frequency) resonant motions induced by waves. The present work brings more details on a set of experimental results designed to evaluate the difference-frequency roll motions of a small-scale model with geometry and mass distribution within the range representative of the new FPSO units. The main objective of the tests was to provide the basis for the verification of the predictions obtained by numerical models that are often used for the units’ seakeeping analysis. Besides identifying the resonant roll motions induced by second-order wave effects in the experimental records, some preliminary comparisons are presented with computational predictions. Results show that a reasonable level of adherence may be obtained, notwithstanding the well-known limitations of the numerical procedure.