The characteristics of hindcast data for extreme storms at a Northern North Sea location are shown to depend on storm direction, reflecting storm strength and fetch variability. Storm peak HS over threshold is modeled using a generalized Pareto distribution, the parameters of which are allowed to vary smoothly with direction using a Fourier form. A directionally varying extreme value threshold is incorporated. The degree of smoothness of extreme value shape and scale with direction is regulated by roughness-penalized maximum likelihood, the optimal value of roughness selected by cross-validation. The characteristics of a 100-year storm peak HS, estimated using the directional model, differ from those estimated when ignoring the directionality of storms. In particular the extreme right-hand tail of omnidirectional HS100 is longer using the directional model, indicating in this case that ignoring directionality causes underestimation of design criteria. Although storm peak data alone are used for extreme value modeling, the influence of a storm, in directional design sectors other than that containing its storm peak direction, is incorporated by estimating the storm's directional dissipation directly from the data. An automated approach to selection of directional design sectors is described. Directional design criteria are developed using three different approaches, all consistent with an omnidirectional storm peak HS nonexceedence probability of 0.5. We suggest a risk-cost criterion, which minimizes design cost for a given omnidirectional design specification, as an objective basis for optimal selection of directional criteria.


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    Title :

    The effect of directionality on Northern North Sea Extreme wave design criteria


    Additional title:

    Der Einfluss der Einwirkungsrichtung von extremen Seegang in der nördlichen Nordsee auf die Entwurfskriterien von Offsshore-Anlagen


    Contributors:


    Publication date :

    2008


    Size :

    1 Seite, 20 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English





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