2008 · 149 citations · 4 references
EngineeringCivil EngineeringMarine EngineeringEnvironmental ModelingOffshore EngineeringOffshore StructuresNonlinear Structural AnalysisStructural Response AnalysisDynamic Response Of StructuresEnvironmental Load AssessmentEnvironmental Load ModelingExtreme Load AnalysisSea State CharacterizationSea State Dependence
Design of offshore structures requires reliable estimates for loads and responses at annual exceedance probabilities of 10⁻² and 10⁻⁴, accounting for short‑term variability of extreme values and long‑term variability of sea‑state characteristics, which necessitates a long‑term analysis that is straightforward for linear problems but more complex for strongly nonlinear responses and on‑off load components. The study proposes the environmental contour line method to estimate long‑term extremes from short‑term analysis. The method constructs environmental contour lines based on short‑term variability to approximate long‑term extreme loads. Examples are also included.
Design of offshore structures involves the calculation of reliable estimates for loads and responses corresponding to annual exceedance probabilities of 10-2 and 10-4. In order to do so, all sources of inherent randomness must be accounted for, i.e. the short term variability of say the 3-hour extreme value in a given sea state should be combined with the long term variability of the sea state characteristics. This calls for some sort of a long term analysis. For linear or nearly linear problems this can easily be done, while such an analysis becomes more complicated and time consuming for strongly non-linear response problems. The difficulties are greater if a major part of the environmental load is of an on-off nature. This paper illustrates an approximate approach, the environmental contour line method, for obtaining proper estimates of long term extremes utilizing a short term analysis. Examples are also included.
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