Abstract
ABSTRACT The design of monopile foundations for offshore wind farms, the estimate of wave loads, and the effect of the structures on the environment usually consider one single vertical cylinder. This choice is based on the size of the ratio cylinder diameter to wavelength, and on the large distances between turbines. However, for large arrays of monopiles, the ensemble effect must be investigated. This study addresses monochromatic wave propagation through a rectangular array of four cylinders 800 m and 300 m apart, considered here as the fundamental geometry for an arbitrary array of monopiles turbines. Results for bottom velocities, mean water level, mass transport, and radiation stress tensor in the presence of the array are compared with those for a single cylinder. The numerical model WAMIT® is used to compute the potential velocity solution. Relevant spatial variations were found, especially for radiation stresses, for different periods and directions of propagation. Diffraction effects on the wave field by the array are significantly stronger than the superposition of individual effects of isolated cylinders under the same conditions. Impacts of the entire wind farm on bottom morphodynamics near the foundations, on the design loads, and on the wave climate past the wind farm are discussed.
Highlights
Policies to reduce carbon emission have changed the world energy matrix, gradually substituting fossil fuel sources by renewable ones: the use of offshore wind energy has rapidly grown during the last two decades as being a viable option (Breton & Moe, 2009)
This paper presents the results of wave-cylinder interaction for bottom velocities, mean water level, depth averaged mass transport, and radiation stress field for an array of four cylinders separated by distances of the order of 16 > dx / L > 7 and 6 > dy / L > 2.6, where dx and dy are the distances between turbines along the x and y axes, respectively, and compares these results with those obtained for one isolated cylinder
Results for the bottom velocity field, mass transport, mean water level, and radiation stress components are shown
Summary
Policies to reduce carbon emission have changed the world energy matrix, gradually substituting fossil fuel sources by renewable ones: the use of offshore wind energy has rapidly grown during the last two decades as being a viable option (Breton & Moe, 2009). By the end of 2018, the total offshore wind power capacity installed worldwide was 23.14 GW (Global Wind Energy Council, 2019). Most of the offshore wind energy has been installed in the northern European waters, currently representing 79% of the total installed capacity. A broader distribution among other areas of the world is expected to happen in the years. As offshore wind energy plays an important role in energy supply, it is necessary to improve the methodologies for environmental impact assessment and monitoring. This is important as the number of turbines installed in wind farms has significantly increased
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