Reliability of Floating Structures: Extreme Response and Load Factor Design

Abstract

The reliability of a floating offshore platform against extreme offsets is studied. Methods are illustrated to perform more refined analyses of extreme loads and load effects. These include the effect of nonlinear diffraction under random wave excitation. They permit inclusion of randomness in significant wave height Hs, in peak spectral period, Tp given Hs, and also in the extreme load effect given both Hs and Tp. Numerical effects are demonstrated by applying these methods to a specific floating structure: a deep-draft spar buoy. Design of the spar has been considered in two deep-water sites, one in the Gulf of Mexico and another in the Northern North Sea. Appropriate joint contours of significant wave height and peak period are developed, and these are used to develop load and resistance factors for each of the two sites.