Combined Long-Term and Short-Term Description of Extreme Ocean Wave Conditions by 3-Dimensional Environmental Contours
- Erik Vanem (Group Technology and Research) | Arne Bang Huseby (University of Oslo)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- Environmental loads, Structural reliability, Ocean Engineering, Environmental contours, Ocean waves, Marine structures
- 1 in the last 30 days
- 14 since 2007
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In this paper, 3-dimensional contours are developed and applied to the joint distribution of sea states and individual wave heights to obtain a combined long-term and short-term description of extreme ocean waves associated with a certain return period. The 3-dimensional environmental contours utilizes the direct sampling approach that has recently been proposed as an alternative to the traditional IFORM-approach for estimating environmental contours. The paper outlines the extension of the direct sampling approach to environmental contours to 3-dimensional problems and presents an algorithm for constructing such contours in a 3-dimensional space. Moreover, the contours will be applied to the trivariate problem of jointly extreme significant wave height, wave period and individual wave height. Contours corresponding to different quantiles of the individual wave height in a sea state will be established, i.e. the median individual wave height, the upper quartile individual wave height, the upper decile individual wave height and the maximum individual wave height in a sea state. This will illustrate the usefulness of 3-dimensional environmental contours and demonstrate that the direct sampling approach to environmental contours can be extended to higher dimensions.
Environmental contours are often used in marine design and ocean engineering applications for identification of extreme environmental conditions that may result in extreme loads and responses. Most often, environmental contours are applied to two-dimensional problems and a typical application is to establish contours for wave parameters such as significant wave height and wave period. These are sea state parameters and such contours describe the long-term variability of sea states. The short-term variability of individual wave heights can then be described conditioned on a particular sea state, and it may be of interest to provide a joint description of extreme ocean waves taking both the long-term variability of sea states and the short-term variability of individual wave heights into account. Other examples of trivariate problems that may benefit from 3-dimensional environmental contours are the joint description of significant wave height, wave period and wind speed, and the joint distribution of wave heights, currents and sea water level.
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