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.
Environmental Contour Lines: A Method for Estimating Long Term Extremes by a Short Term Analysis
Haver, S., and S. R. Winterstein. "Environmental Contour Lines: A Method for Estimating Long Term Extremes by a Short Term Analysis." Paper presented at the SNAME Maritime Convention, Houston, Texas, USA, October 2008. doi: https://doi.org/10.5957/SMC-2008-067
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