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You are here : eLibrary : IAHR World Congress Proceedings : 36th Congress - The Hague (2015) ALL CONTENT : Hydro-environment : Investigation of the multi-scale interactions between an offshore wind turbine wakeand the ocean-sed...
Investigation of the multi-scale interactions between an offshore wind turbine wakeand the ocean-sediment dynamics in a indealized framework
Author : Tim Nagel1, Julien Chauchat2, Achim Wirth3
ABSTRACT
A coupled two dimensional idealized numerical model of the ocean and sediment layers, forced by an offshore wind turbine wake
is used to investigate the complex interactions between the wake, the ocean and the sediment layers, together with the retroaction
on the wind energy. Results show that the turbine wake has an impact on both, the ocean and the sediment layers. The
turbine wake impacts the ocean surface and generates instabilities or vortex streets for some parameter values. Shallow ocean
layers (typically below 15m) are laminar. When water depth is higher, large scale instabilities are generated, leading to a turbulent
dynamic in the ocean layer. The size of the generated vortices in the ocean increases with water depth and decreases with the
quadratic-law bottom friction coefficient. Considering the morphodynamics three cases are observed, depending on whether the
ocean dynamics is laminar (i), has a localized (ii) or domain wide (iii) turbulent behavior. In the first case, changes in seabed
elevation are around a few millimeters per month. Results are similar for the localized turbulence case with small spatial variations.
For the domain wide turbulence case (iii), instantaneous seabed changes are of the order of a few millimeters per month, whereas
the transport averaged over several days decreases to a few tenths of millimeter per month. This behavior is easily explained
by the oscillating local velocity which transports sediments back and forth. The above emphasizes that the water depth is a key
parameter for the coupled atmosphere-ocean-sediment system around wind turbines. Furthermore, considering the ocean velocity
in the atmospheric forcing at the ocean surface leads to a decrease of 4 % of the power lost by friction at the atmosphere-ocean
interface. Ocean dynamics could thus have a non-negligible feedback on the wind power available for the turbines and its variability.
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Chapter : IAHR World Congress Proceedings
Category : 36th Congress - The Hague (2015) ALL CONTENT
Article : Hydro-environment
Date Published : 20/08/2015
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