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Experiments by Invited Researchers

 

Large scale experiments on wave energy converter farms to study the near-field effects between the converters and the far-field effects on other users in the coastal area

Project acronym: HyIV-DHI-08
Name of Group Leader: Peter Troch
User-Project Title: Large scale experiments on wave energy converter farms to study the near-field effects between the converters and the far-field effects on other users in the coastal area
Facility: Shallow water basin
Proceedings TA Project: PHYSICAL MODELLING OF WAVE ENERGY CONVERTER ARRAYS IN A LARGE-SCALE WAVE BASIN: THE WECwakes PROJECT
Data Management Report: Report

User-Project Objectives

The shrinking reserves of fossil fuels in combination with the increasing energy demand have enhanced the interest in renewable energy sources, including wave energy. In order to extract a considerable amount of wave power, large numbers of Wave Energy Converters (abbreviated as WECs) will have to be arranged in farms or arrays using a particular geometrical layout. The operational behaviour of a single device may have a positive or negative effect on the power absorption of the neighbouring WECs in the farm (near-field effects). Moreover, as a result of the interaction between the WECs within a farm, the overall power absorption and the wave climate in the lee of the WECs is modified. These wave field changes (far-field effects) can influence neighbouring activities in the sea, other marine energy projects in the area, coastal eco-systems and even the coastline and the coastal defence conditions and parameters. Several numerical studies on large WEC farms have already been performed, but large scale experimental studies on near-field and far-field wake effects of large WEC farms were not available publically in literature. Within the HYDRALAB IV European programme, the research project 'WECwakes' (HyIV-DHI-08) has been introduced, with the objective to perform large scale experiments in the Shallow Water Wave Basin of DHI, in Denmark, on large farms of heaving point absorber WECs (up to 25 WECs) for different layout configurations and spacings between the WECs. The obtained results from these experimental tests will be very useful to validate and extend the recently developed numerical models, as well as to optimize the geometrical layout of WEC farms for real applications.

Short description of the work carried out

The experimental set-up of 25 individual WEC units in a farm layout and placed in a large wave tank is at present the largest set-up of its kind, worldwide, studying the important effects of both WEC interactions and WEC near-field and far-field wake effects. The usual smaller difficulties that come along with experimental testing of new scale model set-ups have been encountered by the User Group. Due to appropriate in advance preparation of the project and the WEC models by the User Group, large number of participants present at the DHI basin and the meetings, and significant support by the local DHI team and the facility manager, no major difficulties (which would delay the progress) have been encountered.

Highlights of important research results

The WECwakes research project has been completed to further develop understanding of how WEC farms interact with the incident wave field and how WECs of a farm affect each other. Importantly, WEC response and wave field modification have been measured simultaneously. Different WEC farm geometric configurations and spacings between the WECs have been tested, in order to study near-field and far-field wake effects of heaving point absorber WECs. Through these WECwakes experiments, the first extensive public database covering several geometrical layouts, wave conditions, surface elevations and surge forces has been established and is available for offering a deeper physical insight, and for validation and extension of numerical models used for WEC-farm modelling and their wake effects. Moreover, the obtained results from these experimental tests are useful to provide insight to optimizing the geometric configurations of WEC farms for real applications. The results of this research are available through the publications made by the consortium, in international coastal engineering and wave energy conferences, as well as in scientific journals.

Publications
Stratigaki Vasiliki and Troch Peter Large scale experiments on farms of heaving wave energy converters , 2012 Babarit A., H. Mouslim, A. Cl?ment and P. Laporte-Weywada. 2009. On the numerical modelling of the non-linear behaviour of a wave energy converter. 28th Int. Conf. Ocean, Offsh. & Arctic Engin., Hawaii. Stallard T., P.K. Stansby and A. Williamson. 2008. An experimental study of closely spaced point absorber arrays. Proc.18th International Offshore & Polar Engineering Conference, Canada. Stratigaki V., P. Troch, L. Baelus and Y. Keppens. 2011. Introducing wave regeneration by wind in a mild-slope wave propagation model, MILDwave, to investigate the wake effects in the lee of a farm of wave energy converters. Proc. of the 30th OMAE 2011, Rotterdam. Troch P. 1998. A numerical model for propagation and transformation of linear water waves. Department of Civil Engineering, Ghent University. Troch P., C. Beels, J. De Rouck and G. De Backer. 2010. Wake effects behind a farm of wave energy converters for irregular long-crested and short-crested waves. 32nd International Conference on Coastal Engineering, Shanghai, China, ASCE.
Stratigaki, V., Troch, P., Stallard, T., Kofoed, J.P., Benoit, M., Mattarollo, G., Babarit, A., Forehand, D., Folley, M. Large scale experiments on farms of heaving buoys for investigation of wake dimensions, near-field and far-field effects , 2012 Babarit A., Mouslim H., Cl?ement A., Laporte-Weywada P., (2009): On the numerical modelling of the non-linear behaviour of a wave energy converter. 28th Int. Conf. Ocean, Offsh. & Arctic Engin., Hawaii. Stallard T., Stansby P.K., Williamson A. (2008): An experimental study of closely spaced point absorber arrays. 18th Intern. Offsh. & Polar Engin. Conf., Canada. Troch, P., Beels, C., De Rouck, J., and De Backer, G., (2010): Wake effects behind a farm of wave energy converters for irregular long-crested and short-crested waves. ICCE2010, No. 32, Shanghai, China.
Stratigaki, V., Troch, P., Vantorre, M., Folley, M. Development of a point absorber Wave Energy Converter for investigation of wake effects and wave energy absorption , 2012 Borgarino, B., Babarit, A. & Ferrant, P., 2012. Impact of wave interactions effects on energy absorption in large arrays of wave energy converters. Ocean Engineering 41, 79-88. Child, B.F.M., 2011. On the configuration of arrays of floating wave energy converters. Ph.D, Edingburgh Univ. Folley, M., Babarit, A., O? Boyle, L., Child, B., Forehand, D., Silverthorne, K., Spinneken, J., Stratigaki, V., Troch, P., 2012. A review of numerical modeling of wave energy converter arrays, 31st OMAE,Rio de Janeiro,Brazil. Stratigaki, V., Troch, P., Stallard, T., Kofoed, J.P., Benoit, M., Mattarollo, G., Babarit, A., Forehand, D. & Folley, M., 2011. Large scale experiments on wave energy converter farms to study the near-field effects between the converters and the far-field effects on other users in the coastal area. HYDRALAB IV, Research report. Stratigaki, V., Troch, P., Stallard, T., Kofoed, J.P., Benoit, M., Mattarollo, G., Babarit, A., Forehand, D., Folley, M., 2012. ?Large scale experiments on farms of heaving buoys for investigation of wake dimensions, near-field and far-field effects?. Proc. of the International Conference on Coastal Engineering 2012, Santander, Spain. Troch, P., Beels, C., De Rouck, J., and De Backer, G., 2010. Wake effects behind a farm of wave energy converters for irregular long-crested and short-crested waves. ICCE 2010, Shanghai, China.
Troch Peterand Stratigaki Vasiliki Dutch title:'Van vijandige golven vrienden maken'; English translation of title: 'Becoming "friends" with hostile waves' , 2012
Vasiliki Stratigaki, Peter Troch, Timothy Stallard, Jens Peter Kofoed, Michel Benoit, Giovanni Mattarollo, Aurelien Babarit, David Forehand, Matthew Folley Large scale experiments on farms of heaving buoys to investigate wake dimensions, near-field and far-field effects , 2012
P. Troch, V. Stratigaki, T. Stallard, D. Forehand, M. Folley, J.P. Kofoed, M. Benoit, A. Babarit, D. Gallach S?nchez, L. De Bosscher, P. Rauwoens, B. Els?sser, P. Lamont-Kane, P. McCallum, C. McNatt, E. Angelelli, A. Percher, E. Carpentero Moreno, S. Bellew, E. Dombre, F. Charrayre, M. Vantorre, J. Kirkegaard, S. Carstensen Physical Modelling of an Array of 25 Heaving Wave Energy Converters to Quantify Variation of Response and Wave Conditions , 2013 [1] Folley, M., A. Babarit, L. O? Boyle, B. Child, D. Forehand, K. Silverthorne, J. Spinneken, V. Stratigaki, and P. Troch. 2012. A review of numerical modeling of wave energy converter arrays, Proceedings of the 31stInternational Conference on Offshore Mechanics & Arctic Engineering, Rio de Janeiro, Brazil. [2] Li,Y.,Y.-H.,Yu.2012.A synthesis of numerical methods for modeling wave energy converter-point absorbers. Renewable & Sustainable Energy Reviews,16.6:4352-4364 [3] Borgarino, B., A. Babarit, and P. Ferrant. 2012. Impact of wave interactions effects on energy absorption in large arrays of wave energy converters. Ocean Engineering, 41, 79 88. [4] Yu,Y.-H.,Y.Li. 2013. Reynolds-Averaged Navier-Stokes simulation of the heave performance of a tow-body floating-point absorber wave energy system. Computers & Fluids,73;104-114 [5] N. Booij, I.J.G. Haagsma, L.H. Holthuijsen, A.T.M.M. Kieftenburg, R.C. Ris, A.J. van der Westhuysen, M. Zijlema, SWAN cycle III version 40.51AB User Manual, 2007. [6] P.A. Madsen, O.R. S?rensen, A new form of the Boussinesq equations with improved linear dispersion characteristics. Part 2: A slowly-varying Bathymetry. Coastal Eng. 18(1992), 183-204. [7] V. Venugopal, G.H. Smith, Wave climate investigation for an array of wave power devices, Proceedings of the 7th European Wave and Tidal Energy Conference (2007), Porto. [8] Alexandre, A., T. Stallard, and P.K.Stansby. 2009. Transformation of Wave Spectra across a Line of Wave Devices. Proceedings of the 8th European Wave and Tidal Energy Conference, Uppsala, Sweden [9] Silverthorne, K. and Folley, M. [2011]. A new numerical representation of wave energy converters in a spectral wave model. 9th European Wave and Tidal Energy Conference, Southampton, UK. [10] P. Troch, MILDwave ? A numerical model for propagation and transformation of linear water waves. Internal Report, Department of Civil Engineering, Ghent University, (1998). [11] Beels, C., P. Troch, G. De Backer, M. Vantorre, and J. De Rouck. 2010. Numerical implementation & sensitivity analysis of a wave energy converter in a time-dependent mild-slope equation model, Coastal Engineering, Vol. 57(5), pp. 471-492. [12] Troch, P., C. Beels, J. De Rouck, and G. De Backer. 2010. Wake effects behind a farm of wave energy converters for irregular long-crested and short-crested waves. Proceedings of the International Conference on Coastal Engineering, No. 32(2010), Shanghai, China. [13] K. Budal, J. Falnes, A. Kyllingstad, G. Oltedal, Experiments with point absorbers in regular waves. Proceedings of the 1st Symposium on Wave Energy Utilization (1979), 253?282, Gothenburg, Sweden. [14] M. Vantorre, Third-order potential theory for determining the hydrodynamic forces on axisymmetric floating and submerged bodies in a forced periodic heave motion, PhD thesis, Ghent University, 1985. [15] L. Marquis, M. Kramer, P. Frigaard, First Power Production figures from the Wave Star Roshage Wave Energy Converter, Proceedings of the 3rd International Conference on Ocean Energy (ICOE-2010), Bilbao. [16] Thomas, S., Weller, S. and Stallard, T.J. Float response within an array: Numerical and experimental comparison. Proc. 2nd International Conference on Ocean Energy (ICOE), Brest, France, Oct 2008. [17] Weller, S.D. Stallard, T.J. and Stansby, P.K. 2010. Interaction factors for a rectangular array of heaving floats in irregular waves. IET Renewable Power Generation. 4(6), 628?637. [18] Ashton, I., L. Johanning, and B.Linfoot. 2009. Measurement of the Effect of Power Absorption in the Lee of a Wave Energy Converter, Proceedings of the 28th International Conference on Offshore Mechanics & Arctic Engineering, Honolulu, Hawaii, OMAE 2009, vol. OMAE2009-79793 [19] M. Folley, T. Whittaker. Preliminary cross-validation of wave energy converter array interactions, submitted for the Proceedings of the OMAE2013 Conference, Nantes, France. [20] V. Stratigaki, P. Troch, T. Stallard, D. Forehand, M. Vantorre, J. P. Kofoed, A. Babarit, M. Folley, M. Benoit, Heaving wave energy converters for large-scale WEC array experiments, submitted for Renewable Energy. [21] T. Bjarte-Larsson, ?Friction for a floating body heaving along a fixed vertical guiding strut,? in Proc. 7th EWTEC, Porto, Portugal, 2007. [22] M.S. Longuet-Higgins, D.E. Cartwright, and N.D. Smith. Observations of the directional spectrum of sea waves using motions of a floating buoy. In Ocean Wave Spectra, pages 111?136.Prentice Hall, New York, 1963. [23] Y. Goda and Y. Suzuki. Computation of refraction and diffraction of sea waves with Mitsuyasu?s directional spectrum. Tech. Note of Port and Harbour Res. Inst., 230, 1975. [24] D. I. M. Forehand, A. P. McCabe, and A. R. Wallace, ?A hydrodynamic, time-domain, wave energy converter array model using state-space techniques,? to be submitted to Ocean Engineering, 2013. [25] (2013) WAMIT version 7.0 user manual. [Online]. Available: http://www.wamit.com/. [26] K. Friedrich. Friction and wear of polymer composites, E , 1986. [27] Aalborg University. (2007): WaveLab 3.33 Manual. homepage: http://www.hydrosoft.civil.auc.dk/
Vasiliki Stratigaki, Peter Troch, Tim Stallard, David Forehand, Jens Peter Kofoed, Matt Folley, Michel Benoit, Aur?lien Babarit and Jens Kirkegaard 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 , 2014
Vasiliki Stratigaki Experimental Study and Numerical Modelling of Intra-Array Interactions and Extra-Array Effects of Wave Energy Converter Arrays , 2014
PETER TROCH, VASILIKI STRATIGAKI, TIM STALLARD, DAVID FOREHAND, MATT FOLLEY, JENS PETER KOFOED, MICHEL BENOIT, AUR?LIEN BABARIT, MARC VANTORRE & JENS KIRKEGAARD AN OVERVIEW OF THE WECwakes PROJECT: PHYSICAL MODELING OF AN ARRAY OF 25 WAVE ENERGY CONVERTERS , 2014
Stratigaki, V., Troch, P., Vantorre, M., Folley, M., Stallard, T., Forehand, D., Kofoed, J.P., Babarit, A., Benoit, M. Development of a Point Absorber Wave Energy Converter for Investigation of Wake Effects and Wave Energy Absorption , 2013
Stratigaki, V. and Troch, P. Wave basin experiments with large wave energy converter arrays , 2014
Vasiliki Stratigaki, Peter Troch, David Forehand, Tim Stallard, Jens Peter Kofoed, Matt Folley, Michel Benoit, Aur?lien Babarit, Jens Kirkegaard, David Gallach S?nchez, [......], Cameron McNatt, Elisa Angelelli, Arthur Pecher, Efrain Carpintero Moreno, Sarah Bellew, Emmanuel Dombre, Fran?ois Charrayre, Stefan Carstensen, Peter Stansby, Marc Vantorre Physical modelling of wave energy converter arrays in a large-scale wave basin: the WECwakes project , 2014
Vasiliki Stratigaki; Peter Troch; Tim Stallard; David Forehand; Jens Peter Kofoed; Matt Folley; Aur?lien Babarit; Michel Benoit MODELLING OF WAVE ATTENUATION INDUCED BY MULTI-PURPOSE FLOATING STRUCTURES , 2014
Peter Troch, Vasiliki Stratigaki, Tim Stallard, David Forehand, Matt Folley, Jens Peter Kofoed, Michel Benoit, Aur?lien Babarit, David Gallach Sanchez, Lieselot De Bosscher, Pieter Rauwoens, Bj?rn Els??er, Paul Lamont-Kane, Peter McCallum, Cameron McNatt, Elisa Angelelli, Arthur Pecher, Efrain Carpintero Moreno, Sarah Bellew, Emmanuel Dombre, Fran?ois Charrayre, Marc Vantorre, Jens Kirkegaard, Stefan Carstensen Physical Modelling of an Array of 25 Heaving Wave Energy Converters to Quantify Variation of Response and Wave Conditions , 2013

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