Numerical investigation of bore hole filling volume in a coastal area

Abstract

Tidal energy is a promising way to reduce the carbon fossil energy. Installing tidal converters remains difficult particularly due to the bore hole filling by drill residuals and ambient sediments. To fix this issue, we perform a coupling between a coastal circulation model and a discrete element model, with an application to Alderney Race, and considering spherical particles. The coupled model is firstly described, validated and then used to investigate the parameters controlling the filling volume of monopile and tripod technologies. The results are analysed for different disposition of residuals and initial current direction and intensity. We show that: the distance between the bore hole centre and the residuals is the key parameter controlling the filling by drill residuals; the current direction plays a negligible role in monopile while this distance remains smaller than 20 m; the filling of tripod is strongly influenced by current effects and seabed morphology. Impacts of bed roughness (modelled by steady spherical particles inlaying in the seabed) and ambient sediments are quantified and discussed. Interactions between moving particles and bottom roughness lead to a slight increase of the filling while the impact of ambient sediments strongly depends on seabed morphology and current effects.