On the following subject:
"Characterisation of wind wave breaking and concomitant turbulent mixing of surface waters".
Supervisor: Guillemette Caulliez, CNRS Research Fellow
Summary:
This work falls within the general framework of ocean-atmosphere interactions and focuses more specifically on the experimental study of interactions between wind, waves and current in the water surface layer. Two aspects in particular are being studied: the development of the current under the first wind waves, from their generation to the first micro-breaks; and the geometric properties of the breaking waves.
The development of the current is studied using an acoustic Doppler profiling velocimeter. By introducing a frame of reference that moves with the waves, it has been possible to evaluate the evolution with the fetch of the main characteristics of the mean current, orbital movements and turbulence.
Most of the surf measurements carried out previously have focused on point or two-dimensional methods, which ultimately prove insufficient to fully describe the highly three-dimensional aspects of this phenomenon. The originality of the work presented here therefore lies in the development and use of a system for measuring surface slopes using coloured imagery. This technique makes it possible to evaluate the two components of the wave slope over an extended area of the surface and thus to monitor the three-dimensional evolution of breaking wind waves. We were thus able to study the existence of a universal breaking criterion and propose an evaluation of the breaking crest length per unit area Lambda(c), which was compared with models and results in the literature.