Reference: Physical Review Fluids 5,
034802 (2020) 
Abstract:
We report water wave experiments performed in a long tank
where we consider the evolution of nonlinear deep-water surface
gravity waves with the envelope in the form of a large-scale
rectangular barrier. Our experiments reveal that, for a range of
initial parameters, the nonlinear wave packet is not
disintegrated by the Benjamin-Feir instability but exhibits a
specific, strongly nonlinear modulation, which propagates from
the edges of the wavepacket towards the center with finite
speed. Using numerical tools of nonlinear spectral analysis of
experimental data we identify the observed envelope wave
structures with focusing dispersive dam break flows, a peculiar
type of dispersive shock waves recently described in the
framework of the semi-classical limit of the 1D focusing
nonlinear Schrodinger equation (1D-NLSE). Our experimental
results are shown to be in a good quantitative agreement with
the predictions of the semi-classical 1D-NLSE theory. This is
the first observation of the persisting dispersive shock wave
dynamics in a modulationally unstable water wave system.
