Abstract
In this paper, we investigate, in the frequency domain, the performance (hydrodynamic behavior and power absorption) of a circular array of four semi-immersed heaving Wave Energy Converters (WECs) around a hybrid wind–wave monopile (circular cylinder). The diffraction/radiation problem is solved by deploying the conventional boundary integral equation method. Oblate-spheroidal and hemispherical-shaped WECs are considered. For each geometry, we assess the effect of the array’s net radial distance from the monopile and of the incident wave direction on the array’s performance under regular waves. The results illustrate that by placing the oblate spheroidal WECs close to the monopile, the array’s power absorption ability is enhanced in the low frequency range, while the opposite occurs for higher wave frequencies. For hemispherical-shaped WECs, the array’s power absorption ability is improved when the devices are situated close to the monopile. The action of oblique waves, with respect to the WECs’ arrangement, increases the absorbed power in the case of oblate spheroidal WECs, while these WECs show the best power absorption ability among the two examined geometries. Finally, for the most efficient array configuration, consisting of oblate spheroidal WECs situated close to the monopile, we utilize an “active” Power Take-Off (PTO) mechanism, facilitating the consideration of a variable with frequency PTO damping coefficient. By deploying this mechanism, the power absorption ability of the array is significantly enhanced under both regular and irregular waves.
Highlights
The increase of energy demand, the rising cost of fossil fuels, and the environmental problems derived from their overexploitation have put a spotlight on renewable energy resources
The effect of the net radial distance of the oblate spheroidal Wave Energy Converters (WECs) from the monopile on the WECs’ non-dimensional heave exciting forces is shown in Figure 5, where the variation of F3 for all WECs of the circular array is presented as a function of ω for all examined dnet values
The symmetry of the array with respect to β = 0o (Figure 4) leads to the same values of F3 for the WECs situated in the seaward side of the monopile (i.e., WEC1 and WEC4, Figure 4) as well as for those situated in the leeward side of the bottom-mounted support structure (i.e., WEC2 and WEC3, Figure 4)
Summary
The increase of energy demand, the rising cost of fossil fuels, and the environmental problems derived from their overexploitation have put a spotlight on renewable energy resources. This integration can be realized in a twofold way by (a) locating OWTs and WECs in the same marine area, leading to the formation of the so-called “co-located parks” [4,5,6,7] and/or (b) combining offshore wind and wave energy technologies into one structure, resulting to the deployment of the so-called “hybrid systems” or “combined systems” The latter systems can be further categorized into bottom-mounted and floating ones, depending upon the type of the support structure utilized (bottom-mounted or floating platform, respectively). The most efficient array configuration (WECs’ geometry and net radial distance) is chosen in order to further enhance its power absorption ability by appropriately adjusting the damping coefficient of the PTO mechanism along the examined frequency range (i.e., utilization of an “active” PTO mechanism) In this case, the power absorbed by the array is assessed for regular waves as well as for various sea states by utilizing the Jonswap spectrum
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