| dc.description.abstract | With increasing driving, the transition from ordered to the turbulence with fluctuating high and low amplitude events ubiquitously occurs in various nonlinear extended media ranging from hydrodynamics flows to nonlinear wave media. Counterintuitively, turbulence is not completely disordered. In hydrodynamics turbulence, multi-scale interacting vortices surrounding filament-like singular cores, are basic coherent excitations.
Previous studies in dust acoustic waves demonstrated, for the weakly disordered single scale wave state before the transition to the wave turbulence state, the spontaneous pair-generation and pair-annihilation of single-scale acoustic vortices (AVs) with opposite helicities winding around low-amplitude hole filament (LAH filament) pairs, are the basic coherent excitation surrounding the low amplitude extreme events. Large-amplitude rogue wave events (RWEs) through 3D particle focusing by the preceding surrounding distorted waveforms were also observed.
Nevertheless in three-dimensional (3D) traveling wave turbulence, whether multi-scale coherent excitations also exist, how they are formed, and how they are correlated with high and low amplitude singular events are unexplored fundamental issues. Moreover, the absence of spectral gaps in the continuous turbulent spectrum disabling the decomposition of turbulent field into multiscale modes though Fourier band-pass filtering, makes the studies of above issues even more challenging.
In this work, the above unexplored issues are experimentally investigated using 3D dust acoustic wave turbulence as a platform, though multi-dimensional complementary ensemble empirical mode decomposition (MCEEMD). It is found, for the first time, the dust acoustic wave turbulence can be viewed as a zoo of self-similar interacting multi-scale AVs. In addition to the AV intra-mode interaction (e.g. pair generation/propagation/annihilation), the inter-mode interactions of AVs with same/opposite helicity, their entanglement and synchronization, are found to be the fundamental dynamical processes in acoustic wave turbulence, akin to the interacting multi-scale vortices around worm-like singular cores observed in hydrodynamic turbulence.
For RWEs in the acoustic wave turbulence, it is found that multiscale waveform focusing and the phase synchronization of multiscale wave crests as well as their envelopes are the keys for the generation of RWEs. In the 2+1D spatiotemporal space, RWEs are located at the intersection of distorted multiscale crest surfaces with large amplitudes and preceded by higher probability of finding LAHs in each mode. The synchronized multiscale distorted crests nearby multiscale LAHs assist 3D particle focusing for the generation of RWE in wave turbulence.
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