Since most offshore platforms have comparable length and breadth, the transverse stability is not sufficient to estimate safety of floating platform. The current solution is to follow conventional transverse stability methodology to any orientation, then take the weakest one as a key consideration. However, the analysis ignores trim in all process of heeling. Longitudinal balance at each heel angle reduce the righting arm of platform, which is more reasonable.
In this study, the Euler angles are used as floating parameters of platform, and three kinds of longitudinal balance cases are divided. The oblique free trim method and the free twist method, two of the three cases mentioned, are chosen to establish floating equations of platform. The potential energy surface and the longitudinal coefficient of stiffness are applied to the analysis from standpoints of energy balance and moment balance separately, the former is used to get the most critical axis for a given heel angle, and the latter can be used as the stability criterion of floating condition. Following this idea, a numerical tool has been developed.
This paper describes the method used to estimate the stability of offshore platform, and validation work is presented for simple geometries. Then, results from two operational stability studies are discussed. Finally, possible further work is discussed.