Observations of gravity-capillary lump interactions

TL;DR

This experimental study explores how gravity-capillary lumps generated by side-by-side moving sources interact, collide, and form complex, oscillating patterns on a water surface, revealing insights into nonlinear wave dynamics.

Contribution

It provides new experimental observations of lump interactions, including collision dynamics and pattern formation, under controlled conditions.

Findings

Lumps collide and form steep depressions that radiate waves.

Post-collision, a quasi-stable oscillating pattern emerges.

Wave pattern characteristics depend on source separation.

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 ($c_{min}\approx23$ cm 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 degrees and collide in the centerplane 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.