Observations of gravity–capillary lump interactions. (8th February 2017)

• Record Type: Journal Article
• Authors: Masnadi, Naeem; Duncan, James H.
• Is Part Of: Journal of fluid mechanics. Volume 814(2017)
• Publication Date: 2017-02-08
• Subjects: bifurcation, -- solitary waves, -- waves/free-surface flows; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2017.50
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : In this experimental study, we investigate the interaction of gravity–capillary solitary waves generated by two surface pressure sources moving side by side at constant speed. The nonlinear response of a water surface to a single source moving at a speed just below the minimum phase speed of linear gravity–capillary waves in deep water ( $c_{min}\approx 23~\text{cm}~\text{s}^{-1}$ ) consists of periodic generation of pairs of three-dimensional solitary waves (or lumps) in a V-shaped pattern downstream of the source. In the reference frame of the laboratory, these unsteady lumps propagate in a direction oblique to the motion of the source. In the present experiments, the strengths of the two sources are adjusted to produce nearly identical responses and the free-surface deformations are visualized using photography-based techniques. The first lumps generated by the two sources move in intersecting directions that make a half-angle of approximately $15^{\circ }$ and collide in the centreplane between the sources. A steep depression is formed during the collision, but this depression quickly decreases in amplitude while radiating small-amplitude radial waves. After the collision, a quasi-stable pattern is formed with several rows of localized depressions that are qualitatively similar to lumps but exhibit periodic amplitude oscillations, similar to a breather. The shape of the wave pattern and the period of oscillations depend strongly on the distance between the sources.