A method for the prediction of extreme wave loads on a fixed platform

Abstract

Design of offshore platforms requires accurate prediction of the maximum wave loads due to slamming on the structure. The physical processes that influence the load include the propagation of irregular short-crested wind-driven storm seas, wave breaking, and wave-structure interaction. Furthermore, the ocean is a stochastic environment, so the load and its maximum can be considered as random variables. Ideally, the designer would like to know not only the most probable extreme load, but also the extreme load distribution.In this paper we use a novel technique to prescribe wave environments that lead to extreme responses so that high-fidelity simulations can be used to investigate highly-nonlinear processes in detail. Specifically, the dynamics of the relative motion of the sea surface and the platform is specified in terms of a sea spectrum, and the extreme-value probability distribution function (PDF) is calculated for a given exposure window in a storm. The novel aspect of the work is that a set of deterministic sea environments can be generated that are amenable for simulation with a state-of-the-art computational-fluid dynamics software. As an example to demonstrate the method, a set of 500 two-dimensional wave environments are simulated to estimate the extreme-value PDF of the vertical and horizontal loads on a fixed platform.