On Wave Deformation after Breaking

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Abstract
Waves will dissipate their energy rapidly after breaking. In this paper, the three factors, (i) formation of a horizontal roller, (ii) bottom friction, and (iii) turbulence with air entertainment, which will contribute to the energy dissipation, are dealt with experimentally and theoretically The horizontal roller formed by a plunging breaker is approximated as a Rankine-type vortex by experiments, and it is calculated that 15%-30%of wave energy is dissipated due to the formation of horizontal roller alone from a breaking point to a point of the roller disappearance. A bottom shear stress due to a breaker is measured by the shear meter deviced by the authors and it is clarified that the energy dissipation due to bottom friction is a little Main part of the energy dissipation is taken to be caused by the turbulence with air entrainment. It is indicated that an incident monocromatic wave is transformed into a higher frequency wave due to the turbulence. Furthermore, a new basic equation for breaking waves with a turbulence term expressed by a Reynolds stress is presented The theoretical curves computed numerically have a consistent agreement with the experimental results

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