| dc.description.abstract | The weakly disordered intermediate state, changed from the ordered wave by increasing the excitation before entering the wave turbulence with power-law spectrum, is a ubiquitous phenomenon in many nonlinear open dissipative systems. Through amplitude and phase modulations, the waveforms are distorted associated with the uncertain generation of defects, located at points with null amplitudes and undefined phases. However, defect dynamics of 3D traveling waves had only been demonstrated recently, without showing the surrounding 3D waveforms and explaining the generation mechanism. In addition to the low amplitude singular objects (defects), the generations of the uncertain and highly localized large amplitude events, rogue waves, is also a ubiquitous fundamental excitation in various nonlinear wave systems. Whether rogue waves exist in the nonlinear acoustic type traveling waves and their generation mechanism still remain elusive, especially from the Eulerian-Lagrangian view of wave-particle interaction.
Dust acoustic wave (DAW) is a density wave with longitudinal oscillations of negatively charged dust particles suspended in weakly ionized discharges. In this work, using the undulated DAW as a platform, the above unexplored issues are experimentally addressed by direct imaging the large area dust density evolutions and tracking the individual dust particle motions. For the first time, we demonstrate the observations of acoustic vortex (AV) and rogue wave event (RWE), and construct pictures explaining their generation mechanisms. AVs with helical waveforms winding around the low amplitude hole (LAH) filaments, generated from the spontaneous symmetry breaking are identified as the basic excitations. Under the modulation instability induced stretching of crest surfaces, the sequential rupturing of crest surfaces, followed by the reconnections between two adjacent crest surfaces, leads to the pair generation of AVs carrying opposite chirality. The above processes are reversed when AVs are pairwise annihilated.
On the other hand, the identification of RWEs is confirmed by observing the tail beyond two significant wave heights in the probability distribution function. It is found that, RWEs tend to be led by the slow growth of wave envelope in a few leading cycles and the higher probability of LAHs before RWE emergences. For a traveling DAW, the particle compression and rarefaction in the crest front and rare control waveform evolution. The presences of AVs tend to be associated with distorted waveforms. The particle focusing and defocusing induced by the additional transverse forces of the distorted waveforms are the key factors for emergences of RWEs and motions of AVs, respectively. | en_US |