Final published version
Research output: Contribution to Journal/Magazine › Journal article › peer-review
Research output: Contribution to Journal/Magazine › Journal article › peer-review
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TY - JOUR
T1 - The effect of directionality on Northern North Sea Extreme wave design criteria
AU - Ewans, K.
AU - Jonathan, P.
PY - 2008
Y1 - 2008
N2 - 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 H S 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 H S , estimated using the directional model, differ from those estimated when ignoring the directionality of storms. In particular the extreme right-hand tail of omnidirectional H S100 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 H S 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. Copyright © 2008 by ASME.
AB - 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 H S 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 H S , estimated using the directional model, differ from those estimated when ignoring the directionality of storms. In particular the extreme right-hand tail of omnidirectional H S100 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 H S 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. Copyright © 2008 by ASME.
KW - Ocean currents
KW - Probability distributions
KW - Risk perception
KW - Storms
KW - Automated approaches
KW - Cost criterions
KW - Cross validations
KW - Design costs
KW - Design specifications
KW - Directional models
KW - Extreme values
KW - Extreme waves
KW - Fourier
KW - Generalized Pareto distributions
KW - Hindcast
KW - Nonexceedence probabilities
KW - North seas
KW - Optimal selections
KW - Optimal values
KW - Penalized maximum likelihoods
KW - Storm directions
KW - Design
KW - design
KW - modeling
KW - numerical method
KW - ocean wave
KW - storm
KW - Atlantic Ocean
KW - North Sea
U2 - 10.1115/1.2960859
DO - 10.1115/1.2960859
M3 - Journal article
VL - 130
JO - Journal of Offshore Mechanics and Arctic Engineering
JF - Journal of Offshore Mechanics and Arctic Engineering
SN - 0892-7219
IS - 4
M1 - 041604
ER -