BREAKING WAVES IN LABORATORY-GENERATED JONSWAP SEAS

Results from a laboratory study of wave breaking in deep-water random seas are presented for approximate JONSWAP sea states. Waves generated at one end of a 116-meter wave tank are observed for breaking at a se ction of the tank approximately 30 meters from the wavemaker and in re gions spanning three and six meters about the section. Emphasis is on the relative number of breaking waves observed at the section and in t he regions about it, and on the relative number of crest amplitudes ex ceeding specified levels at the section. Measurements at the section a re shown to be in good agreement with predictions formed using idealiz ed assumptions about the breaking waves and a modified Rayleigh distri bution of crest amplitudes that accounts approximately for nonlinear e ffects in seas with narrow-banded wave frequencies. Results indicate t hat the average downward crest acceleration of breaking waves in these sea states is equal approximately to one-third the acceleration of gr avity. Experimental measurements of breaking in regions about the sect ion are shown to be in good agreement with theoretical predictions rel ating breaking events over a region to those at a fixed location.