12 Février – Thesis defense - Florian Desmons

14 h In visio

Numerical study of the breaking process for capillary-gravity waves.

Surface wave breaking, occurring from the ocean to the coastal zone, is a complex and challenging two-phase flow phenomenon which plays an important role in numerous processes, including air–sea transfer of gas, momentum and energy. Recent modelling attempts are struggling with the lack of physical knowledge of the finest details of the breaking processes. Furthermore, no universal scaling laws for physical variables have been found so far. Hence, parameterising and characterising breaking dynamics becomes very difficult.
A numerical momentum preserving method, based on literature, has been developed during the thesis in order reach the finest details of the breaking process for capillary-gravity waves. This method reduces the nonphysical sea-air exchange of momentum during the simulation which allows to perform highly accurate simulations of the breaking process. This method is verified on literature verification cases. And it is validated on laboratory experiments such as drop impact on deep pool and breaking plunging wave on the sloping beach. These verifications and validations confirm the use the method developed during the following study on breaking wave.
The breaking of capillary-gravity waves was investigated with the variation of the wave depth. In the literature, most of the experimental and numerical results were performed for deep water wave. The study is focused on the influence of the depth on the breaking dynamics. The surface geometry, underwater vorticities and total energy are studied for more than 170 simulations of the breaking of a Stokes wave on a flat bottom. The numerous simulations results permit to create a breaking map for three different ratios of water depth over the wavelength. The plunging and spilling breaking types were subdivided following the observations done on the simulations. The studies performed during the thesis lead to a better understanding of the breaking wave of capillary-gravity waves for intermediate depth.

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