Skip to main content
Research article - Peer-reviewed, 2021

Comparative Analysis of Environmental Contour Approaches to Estimating Extreme Waves for Offshore Installations for the Baltic Sea and the North Sea

Wrang, Linus; Katsidoniotaki, Eirini; Nilsson, Erik; Rutgersson, Anna; Ryden, Jesper; Goteman, Malin


At the stage of design load analysis for offshore installations such as wave energy systems, a critical step is the determination of environmental cases to be evaluated for the definition of the characteristic design load. A commonly used methodology for load case selection, applied in multiple studies and recommended by technical specifications and guidelines, is the environmental contour approach. Here, 50-year environmental contours were generated for four study sites located in the North Sea, Skagerrak and the Baltic Sea by considering both observations and hindcast (model) data. For the construction of the contours, the well-established inverse first-order method (I-FORM) and a modified version using principal component analysis (PCA) were both examined. Furthermore, a 2-dimensional peaks-over-threshold (2D POT) method was evaluated. It was found that a version of the regular I-FORM was able to produce satisfactory contours which properly accounted for the highest waves. When using PCA, the dependency in the data was not properly captured by the probability functions under consideration. The 2D POT method, where applicable, was found to underestimate the extreme sea states. Comparisons between contours obtained from observations and hindcast data showed that the contours may differ substantially depending on the site and method, and thus care must be exercised when using hindcast data for such purposes.


WEC design; wave hindcast; Baltic Sea; North Sea; environmental contours; peaks-over-threshold

Published in

Journal of Marine Science and Engineering
2021, volume: 9, number: 1, article number: 96

Authors' information

Wrang, Linus
Uppsala University
Katsidoniotaki, Eirini
Uppsala University
Nilsson, Erik
Uppsala University
Rutgersson, Anna
Uppsala University
Swedish University of Agricultural Sciences, Department of Energy and Technology
Göteman, Malin
Uppsala University

UKÄ Subject classification

Ocean and River Engineering

Publication Identifiers


URI (permanent link to this page)