Modeling of the interaction of swell with a varying current – MORHOC'H

The present research project aims to study the physical processes governing the wave propagation in vertically sheared current. Such currents can frequently be found in coastal areas where the associated effects of wind and bathymetry easily modify the vertical current profile.

Most of the classical wave propagation models assume the currents to vertically uniform. However, recent experiments have demonstrated the crucial need to account for the vertical structure of the current when modelling the wave dynamics. Significant differences are observed between models and experiments when neglecting the vertical shear of the current.

The physical processes which control the wave dynamics and are expected to explain the gap between models and experiments are mainly the diffration, the refraction and the reflection. These processes act on the wave propagation direction and then on the geometrical focusing. The instability mechanisms, which are related to the non-linearity of the wave field, are also expected to play an important rôle in modifying the wave envelope modulations during the propagation.

This set of physical processes are widely studied when waves propagate in a vertically uniform current, but are still poorly understood in the presence of a vertically sheared current. The present project aims precisely to tackle this issue. Classical models of wave refraction, diffraction and reflection are mostly restricted to linear waves propagating over weakly variable bathymetry in the presence of vertically uniform current. The non-linear models, which are able to describe longitudinal and transverse instabilities, generally consider a fluid at rest, i.e. the total absence of current. Aiming to overcome such limitations in our knowledge of wave propagation, the objective of the present research project is to develop an ensemble of physical models allowing to understand and to predict the influence of the vertical structure of sheared currents.