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J. Mar. Sci. Eng. 2018, 6(4), 124; https://doi.org/10.3390/jmse6040124

Assessment of Scale Effects, Viscous Forces and Induced Drag on a Point-Absorbing Wave Energy Converter by CFD Simulations

1
Department of Mechanics and Maritime Sciences, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
2
Department of Civil Engineering, Aalborg University, Thomas Manns vej 23, DK-9220 Aalborg ø, Denmark
*
Author to whom correspondence should be addressed.
Received: 26 September 2018 / Revised: 17 October 2018 / Accepted: 19 October 2018 / Published: 22 October 2018
(This article belongs to the Special Issue Nonlinear Numerical Modelling of Wave Energy Converters)
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Abstract

This paper analyses the nonlinear forces on a moored point-absorbing wave energy converter (WEC) in resonance at prototype scale (1:1) and at model scale (1:16). Three simulation types were used: Reynolds Averaged Navier–Stokes (RANS), Euler and the linear radiation-diffraction method (linear). Results show that when the wave steepness is doubled, the response reduction is: (i) 3% due to the nonlinear mooring response and the Froude–Krylov force; (ii) 1–4% due to viscous forces; and (iii) 18–19% due to induced drag and non-linear added mass and radiation forces. The effect of the induced drag is shown to be largely scale-independent. It is caused by local pressure variations due to vortex generation below the body, which reduce the total pressure force on the hull. Euler simulations are shown to be scale-independent and the scale effects of the WEC are limited by the purely viscous contribution (1–4%) for the two waves studied. We recommend that experimental model scale test campaigns of WECs should be accompanied by RANS simulations, and the analysis complemented by scale-independent Euler simulations to quantify the scale-dependent part of the nonlinear effects. View Full-Text
Keywords: wave energy; point absorber; scale effects; viscous drag; induced drag; computational fluid dynamics wave energy; point absorber; scale effects; viscous drag; induced drag; computational fluid dynamics
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Palm, J.; Eskilsson, C.; Bergdahl, L.; Bensow, R.E. Assessment of Scale Effects, Viscous Forces and Induced Drag on a Point-Absorbing Wave Energy Converter by CFD Simulations. J. Mar. Sci. Eng. 2018, 6, 124.

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