Explosive ripple instability due to incipient wave breaking. (25th March 2019)

• Record Type: Journal Article
• Authors: Mailybaev, Alexei A.; Nachbin, André
• Is Part Of: Journal of fluid mechanics. Volume 863(2019)
• Page Start: 876
• Page End: 892
• Publication Date: 2019-03-25
• Subjects: surface gravity waves; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2018.1016
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Considering two-dimensional potential ideal flow with a free surface and finite depth, we study the dynamics of small-amplitude and short-wavelength wavetrains propagating in the background of a steepening nonlinear wave. This can be seen as a model for small ripples developing on the slopes of breaking waves in the surf zone. Using the concept of wave action as an adiabatic invariant, we derive an explicit asymptotic expression for the change of ripple steepness. Through this expression, nonlinear effects are described using the intrinsic frequency and intrinsic gravity along Lagrangian (material) trajectories on a free surface. We show that strong compression near the tip on the wave leads to an explosive ripple instability. This instability may play an important role in the understanding of fragmentation and whitecapping at the surface of breaking waves. Analytical results are confirmed by numerical simulations using a potential theory model.