Wind Wave and Swell Separation from Directional Wave Spectrum – The Duration-Limited Method

Abstract

The coexistence of wind wave and swell often occurs in the sea It is necessary to separate wind wave and swell components for engineering design and hazard warnings Swell separation using a frequency spectrum (1D) was originally proposed and useful However the separation of wind wave and swell should consider the misalignment between wave and wind directions A separation approach based on a directional spectrum (2D) is essential Hanson and Phillips (2001) proposed a 2D separation method that has been widely applied such as being adopted in the WaveWatch III model and most of the separation results are correct However this study found that this may overestimate wind sea energy under strong wind conditions because their method essentially assumed unlimited wind fetch and duration This study proposed a modification to reflect wind duration when separating wind wave and swell We used 12 typical directional wave spectra in various marine weather conditions for validation The wind wave and swell separation by our proposed method obtained reasonable results The wind wave component is verified to satisfy the wind-generated wave growth function In addition the results were re-verified when studying their steepness distribution and spectrum time series

Date of Award	2017 Sept 4
Original language	English
Supervisor	Dong-Jiing Doong (Supervisor)