Quartier, N.

Stratigaki, V.

Troch, P.

Vervaet, T.

Open Marine Archive

134 
Poster presentation Competition poster 
Comparative study of the hydrodynamics of a heaving wave energy 
converter using linear and non-linear wave theory  
Quartier Nicolas, Vervaet Timothy, Stratigaki Vicky and Troch Peter 
Department of Civil Engineering, Faculty of Engineering and Architecture, Ghent University, 
Technologiepark 60, 9052 Zwijnaarde, Belgium 
E-mail: nicolas.quartier@ugent.be 
 
Wave Energy is a potential source of clean electricity that can make a significant contribution to 
the de-carbonization of the world’s electricity supply, and can be harvested by using wave 
energy converters (WECs). In order to assess the performance and survivability of WECs, the 
hydrodynamic forces and body motions of the floating devices have to be calculated. Most 
investigations concerning WECs apply linear potential flow theory, which has the major 
drawback of assuming small amplitude oscillations of the WECs, resulting in an underestimation 
of the acting forces under extreme sea states [1]. Therefore, it is more appropriate to use fully 
rotational non-linear models, e.g. models based on Smoothed Particle Hydrodynamics (SPH), 
which is a Lagrangian meshless method used within the field of Computational Fluid Dynamics 
(CFD). 
 
The defining characteristic of a WEC, distinguishing it from a simple floating body, is the power 
take-off (PTO) system, which converts the mechanical energy into useful electricity. In most 
cases this PTO system is modelled as a simple linear damper, which is oversimplified compared 
to e.g. a more realistic hydraulic PTO system. These numerical simplifications can result in an 
overestimation of the absorbed wave power by the WEC of up to 150% [2]. 
 
The aim of the present research is to perform numerical SPH simulations and compare the 
obtained results to those from the simplified linear potential flow theory. More specifically, a 
heaving WEC will be simulated using a coupled NEMOH – WEC-Sim model [3,4] and the average 
absorbed power and acting forces will be determined in different sea states. Thereafter, the 
heaving WEC will be simulated using DualSPHysics, a non-linear SPH solver. Again, the average 
absorbed wave power by the WEC and the hydrodynamic forces acting on the WEC will be 
calculated and compared to the results obtained using the linear method. This will allow to 
define in which cases applying linear potential flow theory leads to excessive errors. 
 
DualSPHysics will be coupled to an accurate model of the PTO system, which will clarify its 
impact on the hydrodynamics of the WEC and on its average absorbed power. The WEC will be 
moored to the seabed and thus in order to assess the effect of the mooring lines on the WEC’s 
hydrodynamic behaviour, a DualSPHysics – MoorDyn coupling will be further developed. This 
coupling also allows modelling of moored floating structures in general, such as floating wind 
turbines. 
 
Finally, the obtained numerical results will be validated using the experimental data of the 
‘WECfarm’ project, which will be carried out in the Coastal & Ocean Basin (COB), Belgium. During 
this project, several heaving cylindrical WECs will be installed in a farm configuration and 
subjected to various wave conditions. These experiments will provide data of the WECs’ motion, 
the forces acting on the WECs and the modified wave field surrounding the WEC farm. 
 
Acknowledgement 
The first author is Ph.D. fellow of the Research Foundation – Flanders (FWO), Belgium (Ph.D. 
fellowship 1SC5419N). 
 
  
135 
References 
[1] Windt et al. (2018). “High-fidelity numerical modelling of ocean wave energy systems: A 
review of computational fluid dynamics-based numerical wave tanks”, Renewable and 
Sustainable Energy Reviews, Vol. 93 
[2]  Penalba et al. (2018). “A high-fidelity wave-to-wire simulation platform for wave energy 
converters: Coupled numerical wave tank and power take-off models”, Applied Energies, Vol. 
226. 
[3]  So et al. (2015). “Development of PTO-Sim: A power performance module for the open-source 
wave energy converter code WEC-Sim”, OMAE 2015 
[4]  Balitsky et al. (2018). “Analyzing the near-field effects and the power production of an array 
of heaving cylindrical WECs and OSWECs using a coupled hydrodynamic-PTO model”, 
Energies, Vol. 11. 
 
Keywords: Wave Enercy Converter; Power take-off system; Smoothed particle hydrodynamics; 
WEC-Sim; WEC farm; Mooring 
  


Comparative study of the hydrodynamics of a heaving wave energy converter using linear and non-linear wave theory

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Comparative study of the hydrodynamics of a heaving wave energy converter using linear and non-linear wave theory

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