Influence of varying bathymetry in rogue wave occurrence within unidirectional and directional sea-states

Recent experimental and numerical studies have demonstrated an increased rogue wave activity during the propagation of a wave field over a sloping bottom, from a deeper to a shallower domain. These studies have shown the influence of several parameters (wave steepness, amplitude of depth variation, slope profile, etc.) but were limited to unidirectional sea-states. In this work, we focus on the effect of the directional spreading on the wave statistics. A highly nonlinear potential flow solver based on the High-Order Spectral method is used. We demonstrate that the enhancement of the extreme wave occurrence observed close to the shallower side of the slope is reduced when considering the directionality of the sea-state. We can state that the underlying physics is different between a real configuration and simplified unidirectional simulations. It is consequently essential to include directional effects in the context of rogue waves to have an accurate estimation of their probabilities of occurrence. © 2017, Springer International Publishing AG.