Soliton and breather solutions of the nonlinear Schrödinger equation (NLSE) are known to model localized structures in nonlinear dispersive media such as on the water surface. One of the conditions for an accurate propagation of such exact solutions is the proper generation of the exact initial phase-shift profile in the carrier wave, as defined by the NLSE envelope at a specific time or location. Here, we show experimentally the significance of such initial exact phase excitation during the hydrodynamic propagation of localized envelope solitons and breathers, which modulate a plane wave of constant amplitude (finite background). Using the example of stationary black solitons in intermediate water depth and pulsating Peregrine breathers in deep water, we show how these localized envelopes disintegrate while they evolve over a significant long distance when the initial phase shift is zero. By setting the envelope phases to zero, the dark solitons will disintegrate into two gray-type solitons and dispersive elements. In the case of the doubly localized Peregrine breather the maximal amplification is considerably retarded; however, locally, the shape of the maximal focused wave measured together with the respective signature phase-shift are almost identical to the exact analytical Peregrine characterization at its maximal compression location. The experiments, conducted in large-scaled shallow-water as well as deep-water wave facilities, are in very good agreement with NLSE simulations for all cases.

• Received 3 July 2020
• Accepted 30 September 2020

DOI:https://doi.org/10.1103/PhysRevFluids.5.114801