Occurrence of extreme waves in three-dimensional mechanically generated wave fields propagating over an oblique current

Abstract

Abstract.Laboratory experiments were performed to study the dynamics of three-dimensional mechanically generated waves propagating over an oblique current in partial opposition. The flow velocity varied along the mean wave direction of propagation with an increasing trend between the wave-maker and the centre of the tank. Tests with regular wave packets traversing the area of positive current gradient showed that the concurrent increase of wave steepness triggered modulational instability on otherwise stable wave trains and hence induced the development of very large amplitude waves. In random directional wave fields, the presence of the oblique current resulted in a weak reinforcement of wave instability with a subsequent increase of the probability of occurrence of extreme events. This seems to partially compensate the suppression of strongly non-Gaussian properties due to directional energy distribution.

Rogue wave occurrence and dynamics by direct simulations of nonlinear wave-field evolution

“…For all the BMNLS simulations, the energy is verified to be conserved to within ∼0.5 %. The present BMNLS solver has been systematically validated through convergence tests (see figure 8) and direct comparisons with various existing results in the literature (Lo & Mei 1985;Dysthe et al 2003;Socquet-Juglard et al 2005;Toffoli et al 2011) and the HOS simulations.…”

Rogue waves in opposing currents: an experimental study on deterministic and stochastic wave trains

“…This may consequently trigger the formation of breathers in the presence of a current, because of a shift of the modulational instability band. This conjecture has been foreshadowed in a number of theoretical, numerical and experimental studies over recent decades (see, for example , Gerber 1987;Lai et al 1989;Stocker & Peregrine 1999;Chawla 2000;Chawla & Kirby 2002;Suastika 2004;Ma et al 2010;Toffoli et al 2011;Moreira & Peregrine 2012, among others). Only recently, however, has the amplification of wave instability induced by adverse current gradients and the concurrent generation of extremes been confirmed theoretically (Hjelmervik & Trulsen 2009;Onorato, Proment & Toffoli 2011;Ruban 2012) and experimentally (Ma et al 2013;Toffoli et al 2013).…”

Outcomes of the Special Issue on Extreme and Rogue Waves

“…4 Laboratory experiments with large-amplitude water waves Toffoli et al (2011) discussed laboratory experiments performed to study the dynamics of three-dimensional mechanically generated waves propagating over an oblique current in partial opposition. The flow velocity varied along the mean wave direction of propagation, with an increasing trend between the wave-maker and the centre of the tank.…”