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Accueil > Équipes > Equipe MEIGE : Modélisation, Expériences et Instrumentation pour la Géophysique et l’Environnement > Diffusion scientifique > Séminaires internes

Modelling the multiscale interactions of the coupled atmosphere-ocean-sediment system, induced by Marine Renewable Energy Devices

Tim Nagel, 02/07/2014

While the world assist to an increasing development of offshore wind energy, the environmental impact of offshore wind farms remains still unknown. If some recent studies have recently light up the impact of offshore wind farms piles on the seabed morphodynamic or the slight influence of wind farm presence on regional climate, no one has, as far as we know, ever considered the turbine wake impact upon both ocean and sediment layers. The purpose of this internship was to study this phenomenon an a local scale with an idealized 2D numerical model. A large part of the work has consisted in the building and testing of the numerical model. Starting from nothing, the model consists in two modules, one for the ocean which solves the Shallow Water equation and one other for the sediment transport, solving the sediment mass conservation equation. The two modules are coupled with a quadratic friction law. Tests undertaken in one and two dimensions and comparisons with analytical solutions show the model accuracy and robustness.

The results highlight the fact that Kelvin-Helmholtz instabilities generated in the ocean by the wake presence seems to be controlled by the bottom friction. Sufficiently low friction induces a homogeneous turbulence state. Increasing the water depth leads to that turbulence state. Due to the turbulence, the morphological impact is thus lower. In the short time (days) main effects on the seabed are linked to the mean wake when in the long term, changes in the seabed could be dominated by turbulent or laminar nature of the wake. Nevertheless, more computations are necessary to ensure these first conclusions.