On a Hirota equation in oceanic fluid mechanics: Double-pole breather-to-soliton transitions

In oceanic fluid mechanics, a Hirota equation describing the propagation of the deep ocean broader-banded waves is studied in this paper. With respect to the envelope of the wave field, we simultaneously take the multi-pole phenomena and breather-to-soliton transitions into account to investigate the double-pole breather-to-soliton transitions via the second-order generalized Darboux transformation. Under certain parameter conditions, double-pole anti-dark solitons, periodic waves, W-shaped solitons and multi-peak solitons are derived, analyzed and graphically illustrated. We perform the asymptotic analysis on the double-pole anti-dark solitons to investigate their interaction properties, e.g., amplitudes, characteristic lines, slopes, phase shifts and position differences. Different from the known double-pole solitons of some other models, the double-pole anti-dark solitons, hereby, indicate that the two soliton components own unequal amplitudes.