Abstract
Scouring has long been considered to be a major issue affecting the reliability of the monopile foundations of offshore wind turbines (OWTs) on sandy seabeds. To reduce the impact of scouring, several tons of rock/stone are usually placed around the foundations shortly after the installation of them. Such a measure is costly. Moreover, rock and stone may spread widely on the seabed during the long-term service period of OWTs. It has no doubt that recycling these rock and stone on the seabed is quite difficult in future decommission. For this reason, a new scour-countermeasure device (SEMCD) is proposed and studied in this paper. Considering that the major driver of scouring is horseshoe vortices around the monopile foundation, a hollow horn-like SEMCD with an arc surface profile is designed for weakening the horseshoe vortices. The SEMCD is made of either cement or other kinds of corrosion resistant materials. It is light in weight, and easy to install and decommission. In the paper, the working mechanism of the SEMCD is first explained. Then, its scouring mitigation effect (SME), i.e., its contribution to the reduction of horseshoe vortices and the mitigation of seabed erosion around the foundation, is studied through investigating its influences on down/up-flow and seabed shear stress. Finally, the optimal size of the SEMCD is discussed through investigating the impact of its size on the speeds of up and down flows and the shear stress on seabed surface. The calculation results have shown that the proposed SEMCD has great potential to prevent scouring and seabed erosion, so that it is of significance to improve the reliability of the monopile foundations of OWTs.
Highlights
Despite the economic recession, the wind industry continues to grow worldwide
The calculation results have shown that the proposed SEMCD has great potential to prevent scouring and seabed erosion, so that it is of significance to improve the reliability of the monopile foundations of offshore wind turbines (OWTs)
In order to investigate the scouring mitigation effect (SME) of the proposed SEMCD, the southern North Sea site (UK sector) sector) is selected for calculations, where the water is about 31 m deep that is ideal for deploying is selected for calculations, where the water is about 31 m deep that is ideal for deploying monopolemonopole-supported OWTs
Summary
The wind industry continues to grow worldwide. the offshore wind industry is rapidly growing in recent years [1]. Early practice has shown that the reliability of monopile foundations, those placed on sand and soft clay seabed, are significantly affected by scouring This issue was first discovered at the Egmond aan Zee wind farm in the Netherlands. In order to address this issue, much effort has been spent in the past decades [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24], most of which is concerned with the protection of bridge piers, and only a few are for protecting OWT foundations The achievements of these studies can be roughly classified into two groups; one is through bed-armoring, and another is by flow-altering. Further validation research on the proposed device will be conducted at the step, and relevant achievements will be reported in a separate paper
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