Energy Dissipation and Transfer in Breaking Waves Generated by Directional and Multi-Frequency Focusing in Deep Water

Abstract

Wave energy dissipation and energy transfer between wave components during the directional wave breaking are investigated experimentally. Directional breaking waves in deep water were simulated by focusing the multi-frequency and multi-directional wave components at a designed location based on constant wave amplitude and constant wave steepness frequdncy spectrum. The incipient and plunging breakers with the same spectral characteristics were generated by applying the different scale factors on wave amplitude. The time series of surface wave elevation were measured at 9 different locations around the wave focusing point using a wave gauge array and the horizontal velocity of gluid motion was also measured to examine the variation of directional spreading function. By comparing the incipient and plunging breaking waves, the characteristics of energy dissipation and energy transfer caused by waves breaking are investigated and their dependences on directionality as well as frequency are analyzed. The breaking in deep water significantly dissipates wave energy in the upper region of peak-frequency band while enhance wave energy in the low-frequency band by energy transfer.