RELIABILITY-BASED PREDICTIONS OF A DESIGN AIR GAP FOR FLOATING OFFSHORE STRUCTURES

The reliability of a floating offshore structure against extreme air gap response levels is studied. A procedure that includes nonlinear diffraction effects under random wave excitation is presented. It permits inclusion of randomness in significant wave height, Hs, in peak spectral period Tp given Hs, and also in the extreme air gap given Hs and Tp. Numerical results are presented by applying these methods to a specific floating structure: a semi-submersible. This semi-submersible is one that is sited in the Northern North Sea. Appropriate joint contours of significant wave height and peak period are developed to establish nominal load levels for use in a load-and-resistance-factor-design (LRFD) procedure.