Parameterization of wind turbine impacts on hydrodynamics and sediment transport

Abstract

International audienceMonopile foundations of offshore wind turbines modify the hydrodynamics and sediment transport at local and regional scales. The aim of this work is to assess these modifications and to parameterize them in a regional model. In the present study, this is achieved through a regional circulation model, coupled with a sediment transport module, using two approaches. One approach is to explicitly model the monopiles in the mesh as dry cells, and the other is to parameterize them by adding a drag force term to the momentum and turbulence equations. Idealised cases are run using hydrodynamical conditions and sediment grain sizes typical from the area located off Courseulles-sur-Mer (Normandy, France), where an offshore windfarm is under planning, to assess the capacity of the model to reproduce the effect of the monopile on the environment. Then, the model is applied to a real configuration on an area including the future offshore windfarm of Courseulles-sur-Mer. Four monopiles are represented in the model using both approaches, and modifications of the hydrodynamics and sediment transport are assessed over a tidal cycle. In relation Responsible Editor: Bruno Castelle Aurélie Rivier to local hydrodynamic effects, it is observed that currents increase at the side of the monopile and decrease in front of and downstream of the monopile. In relation to sediment transport effect, the results show that resuspension and erosion occur around the monopile in locations where the current speed increases due to the monopile presence, and sediments deposit downstream where the bed shear stress is lower. During the tidal cycle, wakes downstream of the monopile reach the following monopile and modify the velocity magnitude and suspended sediment concentration patterns around the second monopile

Localised anthropogenic wake generates a predictable foraging hotspot for top predators

“…In the expanding renewable energy sector (e.g., > 4000 offshore wind turbines in Europe 53 ), monopile foundations similar to the SeaGen design present the most common substructure (66% 53 ) and lead to comparable wake vortices 25,27,54 . However, even submerged tidal turbines, and more so arrays, placed in unsteady flows will change the local hydrodynamic regime, including wake effects 26,55 and more empirical data are required to predict changes in hydrodynamics and foraging habitat.…”

Current and wave effects around windfarm monopile foundations

“…Flow velocity has been shown in numerical models to be modified further downstream than is indicated by the size of the scour hole (Rivier et al, 2014;Rivier et al, 2016). Rogan et al (2014) and Rogan et al (2016) give a detailed study of the downstream impacts of turbulence, indicating that pile induced turbulence can remain for up to 80 pile diameters downstream of the pile.…”

“…However, the local modification of flow, as a result of the inclusion of the pile in the system, means that these velocity predictions do not necessarily accurately represent the velocity near the pile. Numerical models (Rivier et al, 2016) and laboratory experiments (Rogan et al, 2016) have illustrated that the monopile leads to considerable modification of parameters such as the near-pile velocity and bed shear stress. This paper documents new laboratory measurements of currents and wave orbital velocities in the vicinity of a model monopile and downstream of the pile, with the aim of offering guidance parameters describing flow modifications.…”

Experimental study on bed pressure around geotextile mattress with sloping plate

“…The scour on the river banks could shape the bank slope much steeper, which would cause bank collapses [1, 2]. Underwater scours may also endanger the structures installed on the seabed like bridge piers [3, 4], pipelines [5–7] and wind turbine foundations [8–10]. For example, degradation of river channel and scour around bridge piers may cause the exposure of the pier foundations, including the footings and the piles (see Fig 1).…”