Assessment of Scale Effects, Viscous Forces and Induced Drag on a Point-AbsorbingWave Energy Converter by CFD Simulations
Journal article, 2018

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.

scale effects

computational fluid dynamics

viscous drag

induced drag

wave energy

point absorber


Johannes Palm

Chalmers, Mechanics and Maritime Sciences (M2), Marine Technology

Claes Eskilsson

Aalborg University

Lars Bergdahl

Chalmers, Mechanics and Maritime Sciences (M2)

Rickard Bensow

Chalmers, Mechanics and Maritime Sciences (M2), Marine Technology

Journal of Marine Science and Technology

20771312 (eISSN)

Vol. 2018 6 124-146

Including Nonlinear and Viscous Effects when Modelling the Performance of Wave Energy Converters

Swedish Energy Agency (40428-1), 2015-08-01 -- 2017-02-28.

Driving Forces

Sustainable development

Subject Categories

Applied Mechanics

Vehicle Engineering

Fluid Mechanics and Acoustics

Areas of Advance



Basic sciences


C3SE (Chalmers Centre for Computational Science and Engineering)



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