Abstract
Offshore wind turbine monopile foundations are subjected to complex wind, wave, and flow coupling effects, which result in seabed scouring around the monopile. The consequent scour pits threaten the reliability, safety, and load-carrying capacity of the monopile. In order to develop a cost-effective measure to mitigate such an issue, a new countermeasure device, named “fishnet”, is studied in this paper using a combined approach of numerical simulations and experimental tests. In the research, the size of the fishnet, diameter of the fishnet thread, and the installation height of the fishnet were optimized in order to achieve the best protection to the monopile foundation. In the paper, both numerical simulations and laboratory tests proved the effectiveness of the proposed “fishnet” in reducing the scour around the wind turbine monopile foundations. Moreover, its contribution to erosion reduction can be further enhanced via optimization. It was found that, after optimization, the maximum shear force on the seabed could be reduced by 14% in the numerical study, and the maximum depth of the scour pit could be reduced by 38.2% in laboratory tests.
Highlights
Offshore wind was rapidly developed across the world in recent years [1]
Most offshore wind turbines are installed in shallow waters, and more than 70% of them are supported by large-diameter monopiles [3]
Scour pits around the offshore wind turbine foundations were first observed at the Egmond aan Zee Wind Farm in the Netherlands
Summary
Offshore wind was rapidly developed across the world in recent years [1]. The global installed capacity of offshore wind is predicted to reach 46.4 GW by the end of 2022, of which 33.9 GW will be installed in Europe, 11.3 GW in Asia, and 1.2 GW in North America [2]. Hard engineering materials, such as blocks, rack ripraps [17,18,19], and gravel bags [20], are applied on the seabed around the pier to prevent excessive scouring These protective measures have limitations, and not all of them are suited for application to protecting offshore wind turbines. Much effort was made to reduce the scouring around bridge piers, few of the achieved techniques are applicable to protecting offshore wind turbine foundations. This motivated scholars to develop erosion reduction techniques dedicated to offshore wind turbine foundations. As compared to the existing erosion reduction measures, “fishnet” is more cost-effective and easier to be applied to monopile foundations of offshore wind turbines
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