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About Wind-wave misalignment and a combination method for direction-dependent extreme incidents

"An oblique misalignment of wind and waves with respect to ± 15° appear for 10% of the time, while wind and waves are aligned 25% of the time. If the threshold value is increased to ± 30°, the alignment amounts 47% of the time."

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Link to the Paper

Highlights

 

An oblique misalignment of wind and waves with respect to ± 15° appear for 10% of the time, while wind and waves are aligned 25% of the time. If the threshold value is increased to ± 30°, the alignment amounts 47% of the time.

The wind and wave misalignment for storm incidents varies with regard to the mean approaching wind direction of the storm. The observed misalignment of predominantly Northern storms amounts up to 30° and increases more or less gradually until 60° for southerly storm directions.

The directional load misalignment of the design wind speed and the significant wave height Hs50differs between 45° and 60°.

For the shown statistical approach large sectors lead to increasingly conservative results, since few extreme measurement values in a subsector are able to influence the result of the sector significantly.

Combination factors are determined for aligned extreme wind speeds and significant wave heights based on direction dependent extreme value analyses. The maximum wind appears with an aligned Hs = 0.77 Hs50, and Hs50 aligns with a wind speed of 0.92 of the maximum wind speed.