The Nonlinear Roll Damping of a FPSO Hull

Abstract

The ship-rolling problem is a subject that has been studied for a long time. Since Eroude's time (in the 19th century) to nowadays, this subject was revisited several times in order to adjust the theory to changes in ship hulls, dimensions, materials, appendages, etc. On the other hand, ship analysis technological resources, including both experimental techniques and computational capacity (that did not exist in Froude's time), have also amazingly improved. But despite all those technological developments, the assessment of the nonlinear roll damping of some types of hulls still is a challenging problem. The floating production storage and offioading (FPSO) hull fitted with larger bilge keels, for instance, has behaved in such a way that it is impossible to obtain results from nowadays industry standards via decaying tests. This paper discusses an alternative way to assess the nonlinear damping behavior of FPSO hulls with large bilge keels. Since it is fairly easy to perform decaying tests, the paper also proposes an alternative way to analyze the FPSO properties through this kind of testing by grouping multiple results instead of using only a single test. This artifice brought improvements, such as an increased agreement between the alternative model and the experimental data. The paper also compares the more traditional approaches with the alternative method and finally shows the latter's applicability.

Numerical and Experimental Calculation of Roll Amplitude Effect on Roll Damping

“…Avalos et al [15] carried out CFD simulations with their own two-dimensional Navier-Stokes solver for free roll decay of FPSO. They performed simulations with and without bilge keels and compared results with the experiments carried out by Oliviera and Fernandes [16]. They presented that vortex size and roll damping depends on the amplitude of roll motion and the width of bilge keel.…”