Balitsky, P.

Stratigaki, V.

Troch, P.

Verao Fernandez, G.

Open Marine Archive

 124 
Validation of a coupling methodology for numerical modelling of 
near and far field effects of Wave Energy Converter arrays using the 
MILDwave and NEMOH models, based on the WECwakes experimental 
database 
Verao Fernandez Gael, Balitsky Philip, Stratigaki Vasiliki and Troch Peter 
Department of Civil Engineering, Ghent University, Technologiepark 904, 9052 Zwijnaarde (Ghent), 
Belgium 
E-mail: gael.veraofernandez@ugent.be  
 
Wave energy is a promising resource for the renewable energy sector. However, in order to be able 
to produce large amounts of electricity at a reasonable cost, large farms of Wave Energy Converters 
(WECs) will have to be deployed in the ocean. Due to the hydrodynamic interactions between the 
WECs, the surrounding wave field will be affected, both close to the WECs (near field effects) and at 
large distances from their location (far field effects). However, the accurate simulation of both near 
and far field effects at a reasonable computational cost using a single numerical model is still a 
challenge. 
 
In the past years, a one way coupling methodology has been developed to combine the advantages 
of a wave structure interaction solver (e.g. NEMOH [1], used for the near field effects) and a wave 
propagation model (e.g. MILDwave [2,3], used for the far field effects). NEMOH is a Boundary Element 
Method (BEM) that can accurately model the hydrodynamic interactions of the WECs by solving the 
body motions. MILDwave is a mild-slope wave propagation model than can solve wave transformations 
in large domains. The coupling methodology consists of the superposition of two different wave field 
simulations: an incident wave field and a radiated/diffracted wave field. The incident wave field is 
calculated intrinsically in MILDwave. The diffracted/radiated wave field is calculated around the array 
in NEMOH and then propagated in MILDwave by imposing it on a wave generation boundary along a 
circle.  
 
One of the key factors when developing a new numerical methodology or tool is to validate it against 
available experimental data. For this purpose, the model has been validated using experimental data 
available from the WECwakes project [4]. In this project, arrays of up to 25 heaving point absorber 
WECs have been tested in the DHI wave basin using different geometric WEC array configurations. By 
testing the different WEC array configurations under a wide range of sea states a large experimental 
dataset has been generated and is publically available for numerical validation purposes. 
 
In the present research, numerical results are presented for different WEC array configurations from 
WECwakes (e.g. starting from 1 WEC and up to 5 and 9 under a set of regular wave conditions). Firstly, 
the experimental wave field around the WECs has been compared to numerical results from NEMOH, 
in order to assess the accuracy of modelling the wave field around the WEC. Then, the coupled 
numerical model has been run for the different cases and compared to the experimental data in order 
to validate the model. A good agreement has been found between the experiments and the numerical 
results from the coupling methodology. 
 
References 
 
- LHEEA. Nemoh, open-source BEM linear wave solver. http://lheea.ec-
nantes.fr/doku.php/emo/nemoh/start. 2014. [Accessed 21-12-2016] 
- Troch, P., MILDwave – A numerical model for propagation and transformation of linear water 
waves. Internal Report, Dept. of Civil Engineering, Ghent University, 1998. 
- Troch, P. and Stratigaki, V., “Phase-resolving wave propagation array models”. In Numerical 
Modelling of Wave Energy Converters, M. Folley, ed. Elsevier, ch. 10, pp. 191-216, 2016. 
- Stratigaki, V.; Troch, P.; Stallard, T.; Forehand, D.; Kofoed, J.P.; Folley, M.; Benoit, M.; Babarit, A.; 
Kirkegaard, J. “Wave basin experiments with large wave energy converter arrays to study 
interactions between the converters and effects on other users in the sea and the coastal area,” 
Energies, vol. 7, no. 2, pp. 701–734, 2014. 
 
 
 
 
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Acknowledgement 
 
This research is being supported by the Research Foundation Flanders (FWO), Belgium - Contract 
Number of research project: 3G029114. 
 
Keywords: wave energy converters; WEC arrays; hydrodynamic interaction; wave propagation; 
coupling; MILDwave; Boundary Elements Method; NEMOH; experimental modelling; validation  


Validation of a coupling methodology for numerical modelling of near and far field effects of Wave Energy Converter arrays using the MILDwave and NEMOH models, based on the WECwakes experimental database

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Validation of a coupling methodology for numerical modelling of near and far field effects of Wave Energy Converter arrays using the MILDwave and NEMOH models, based on the WECwakes experimental database

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