Modulation depth and breaking strength for deep-water wave groups

Progression of nonlinear wave groups to breaking was studied numerically and experimentally. Evolution of such wave group parameters as distance to breaking and modulation depth was described. The wave modulation depth R is a height ratio of the highest Hh and the lowest Hl waves in the group: R = Hh=Hl. This parameter, together with distance to breaking, was studied by means of the fully-nonlinear Chalikov-Sheinin (CS) model. Subsequent experiment demonstrated a good qualitative agreement with the numerical results. In the present study, both in numerical simulations and laboratory experiments, a wave group was initially generated as a superposition of two waves with primary and secondary wave steepnesses and close wave numbers, and allowed to evolve. It was shown that the modulation depth decreases as a function of the primary wave steepness, that distance to breaking also decreases with primary wave steepness, but grows as a function of the ratio of the primary and secondary wave steepnesses.