Environmental contours based on imprecise probability distributions

Abstract

Environmental contours are commonly applied in the design of marine structures to identify extreme environmental conditions that can give rise to extreme loads and responses. There are different methods to establish these contours, mainly the one based on the Rosenblatt transformation and the one based on Monte Carlo simulations, and in some cases significant differences can be obtained.In this paper, a method to determine environmental contours using imprecise probability models is proposed. The aim is incorporating the uncertainties that exist in the joint cumulative distribution function of the environmental variables. This is accomplishment through probability boxes defined by confidence intervals of the parameters of the joint cumulative distribution function of the environmental variables, which are proposed to be obtained with the maximum likelihood method. Furthermore, the dependence structure of the environmental variables is modeled using copulas.The proposed method is applied to obtain imprecise environmental contours for a site in the Gulf of Mexico, using extreme sea states defined by significant wave height and peak period. Then, such environmental contours are used to determine the imprecise most probable extreme response of a tension leg platform.