Development of Environmental Contours for Circular and Linear Metocean Variables

Abstract

Probabilistic structural analysis of offshore structures is a demanding task due to high number of environmental variables and their uncertainties. Thus methods that reduce the computational effort are always welcomed and the environmental contours method is one of these favorite methods. But almost all the developed environmental contours method are limited to combination of linear metocean variables. Because of importance of design wave and wind direction especially in coastal and nearshore areas, this research is concentrated on development of environmental contours for combinations of circular and linear variables. These contours are derived from the Nataf transformation based approach and conditional modelling approach (CMA). In this paper the CMA was modified to be suitable for circular-linear variables. The circular variable is assumed to be the independent one and a mixture of von-Mises distributions was fitted to it. Linear variables were distributed conditionally on the circular variable. The regression between the distribution parameters and circular variable was set by Fourier series. Then, the Nataf- based model was applied to compare the results. The comparison shows that environmental contours based on the CMA illustrate the wave directionality effect much better than the Nataf-based model.