| dc.description.abstract | Rogue wave events (RWEs), the unpredictable, spatiotemporal localized, and suddenly appeared rare extreme events, extensively appear in several nonlinear wave systems. Although RWEs are firstly observed on wind-driven ocean surfaces, in water surface wave systems, the previous laboratory studies are mainly focused on mechanically generated waves.
In this work, using diffusive light photography, we experimentally investigate the spatiotemporal dynamics of RWEs formation on the system of water surface wave solitary driven by wind. After the transition to steady wave turbulent state by increasing averaged wind speed, it is found that RWEs uncertainly emerge in the traveling burst with intermittent large irregular envelopes and high-frequency fluctuations. The bursts are associated with the stochastic resonant slow periodic wave, called sloshing wave or seiche, selected by the finite tank length under noisy driving. We propose that the emergence of the sequential large-amplitude bursts is caused by the modulated surface wind speed through the slow oscillated surface level of the sloshing wave in the small fetch region. As the bursts propagate downstream, their envelope shapes deteriorate through further turbulent wind and water wave interactions, which cause the non-Gaussian water surface height histogram with a highly stretched tail, and the generation of the uncertain RWEs in the middle fetch region.
To study the interactions between different modes in turbulence and the following formation process of the RWEs, Hilbert-Huang transformation is used to decompose wave turbulence with multiscale. It is found that the propagating crests are 2+1D spatiotemporally modulated, and the rogue waves mostly appear on the crossing tail of two crescent wind-generated wave crests. By decomposing the continuous power spectrum into empirical mode functions with specific scales, the strong phase-amplitude couplings among the different modes are identified on the high crests. That manifests the slow modes crests excite the fast modes, because of robust wind-wave interactions according to the wind profile. This mechanism may be one of the generic routes to excite the multiscale wave turbulent on the wind-driven water surface. Together with Huygens principle, the synchronized focusing structure with concave crest fronts of different modes is the key to RWE generation. | en_US |