Quasi-Static Response of Fixed Offshore Platforms to Morison-Type Wave Loadings

Abstract

The stochastic response of a rigid platform is quasi-static and can be represented as a linear combination of nonlinear random wave loadings. In this study two efficient probabilistic approaches are respectively presented to estimate the higher-order statistics of mildly and highly non-Gaussian structural responses. The eigenvalue analysis of structural quasi-static response in the first approach is based on the expansion of the response in terms of independent Gaussian random variables. The second approach extends the earlier quasi-static analysis procedures to obtain the higher moments of response by including current effects and inundation effects. The interested prediction of extreme responses during a short-term storm, by mean upcrossing rates and mean extremes, can then be achieved by applying Winterstein's functional transformation. These quantities are found in good agreement with not only Monte Carlo simulation results but also the extreme values obtained using a recently proposed method by Naess et al. in 2007.