Rogue waves associated with resonant slow sloshing waves spontaneously excited in wind-driven water wave turbulence

Abstract

Rogue wave events (RWEs), rare uncertainly emerging localized events with extreme amplitudes, widely exist in various nonlinear wave media. Past laboratory studies on RWEs of water surface waves have mainly focused on mechanically excited waves but to a lesser extent on waves solely excited by wind, which also have a large number of degrees of freedom. In this work, we experimentally demonstrate the laboratory observation of RWEs in a wind-driven water surface wave system after the transition to the steady wave turbulent state by increasing averaged wind speed. The spatiotemporal water surface height evolution is measured using diffusive light photography. It is found that RWEs uncertainly emerge in traveling bursts with high frequency large-amplitude fluctuations and irregular burst amplitude. The associated spontaneous slow periodic wave is identified as the resonant slow sloshing wave selected by the water tank with a finite length and spontaneously excited under turbulence. The surface wind speed modulation by the oscillating surface height of the sloshing wave in the small fetch region is proposed as the source for the excitations of sequential large amplitude bursts. The burst envelope shape deterioration through further turbulent wind and water wave interactions as bursts propagate downstream causes the non-Gaussian water surface height histogram with a highly stretched tail, contributed by the uncertain generation of RWEs in irregular bursts in the middle fetch region.