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Space-time resolved measurements for water waves: time-reversal and wave turbulence.
Adam Przadka, doctorant - Ph.D student Crédits : ESPCI ParisTech
This thesis presents an experimental investigation on water waves and concentrates on two current challenges. The first, to validate the time-reversal focusing of surface waves, and the second, to characterize the wave turbulence by joint space-time energy spectra analysis.
The common requirement for each study was the measurement of free-surface deformation. Quantitative data was gathered by Fourier Transform Profilometry. Resonance-type wave damping is shown to be present while using this method with water colored by standard paint. A proper investigation of the wave phenomena is enabled by a crucial improvement to this technique which overcomes the damping effect.
This work provides the first experimental evidence of time-reversal focusing of surface waves. One time-reversal channel was sufficient to reconstruct the wave at the point source in a reverberating cavity. It is also demonstrated that the quality of the refocusing increases linearly with the number of re-emitting channels. This thesis also concerns wave turbulence experiments performed for two forcing frequency ranges with varying wave intensity. Depending on the forcing bandwidth two differen regimes were observed. The energy cascade slope was found to be both forcing dependent, as classically observed in laboratory experiments, or forcing independent. In the latter case, the results are in agreement with the theory. The remainder of the thesis focuses on bathymetry. The feasibility of underwater depth reconstruction, by fitting an appropriate Bessel function to the experimental data, is demonstrated using a "circle method".