Herpelinck, Michiel

Stockman, Kurt

Stratigaki, Vicky

Troch, Peter

Vervaet, Timothy

Ghent University Academic Bibliography

EXPERIMENTAL STUDY OF COMBINED NEAR-FIELD INTERACTIONS AND FAR-FIELD EFFECTS OF WAVE ENERGY CONVERTER FARMS: DEVELOPMENT OF A SINGLE ENERGY DEVICEDEPARTMENT OF CIVIL ENGINEERING1, DEPARTMENT OF INDUSTRIAL SYSTEM AND PRODUCT DESIGN2Timothy Vervaet1, Michiel Herpelinck2, Vicky Stratigaki1, Peter Troch1 and Kurt Stockman2Contact: timothy.vervaet@ugent.beawww.ugent.beReferences[1] Stratigaki, V., 2014. “Experimental study and numerical modelling of intra-array interactions and extra-array effects of wave energy converter arrays”, PhD Thesis, Ghent University. Ghent, Belgium[2] Verbrugghe, T., 2018. “Coupling Methodologies for Numerical Modelling of Floating Wave Energy Converters”, PhD Thesis, Ghent university. Ghent, BelgiumFig. 1: Visual representation of incident, reflected, radiated and diffracted waves around an array of three floating structures. The combination results in the total wave field. [2]Fig. 2: Experimental array set-up of the ‘WECwakes’ project. [1]Fig. 3: Artist impression of the Coastal and Ocean Basin (COB)WECs placed in a farm are responsible for the occurrence of two general phenomena: near-fieldinteractions between the WECs, and far-field effects of the WEC farm on the surrounding wavefield, illustrated in Fig. 1.The motion of a single WEC will positively or negatively affect the power absorption ofneighbouring WECs. These near-field interactions are dependent on the incoming waveconditions, the WEC farm layout and the WEC inter-distance. On the other hand, the powerabsorption of the entire WEC farm reduces the wave height behind the farm. The possibleinfluence of WEC farms on neighbouring farms, offshore activities, marine ecology and thecoastline is expressed by the far-field effects.In the framework of the EU Hydralab IV ‘WECwakes’ project coordinated by Ghent University(UGent), the above phenomena have been investigated for an experimental layout of up to 25heaving WECs, illustrated in Fig. 2 [1]. The obtained unique database served for validationpurposes of numerical models, such as for numerical coupling methodologies for studying wave-WEC interactions (near-field effects) and wave propagation through WEC farms (far-fieldeffects) [2].IntroductionTo make wave energy converters (WECs) economically attractive as an alternative energy source,the levelized cost of energy (LCOE) needs to be competitive with other renewable energysources. Increasing the power output can be achieved by placing a large number of WECs at thesame site in an array geometrical layout, which is called a WEC farm. Since an efficient waveabsorber is also an efficient wave generator, one can theoretically benefit from placing the WECsin an well-considered geometrical layout.Scientific backgroundMain objective is to experimentally investigate near-field interactions and far-field effects fordifferent WEC farm layouts and WEC inter-distances. These tests aim to cover the gap ofavailable experimental data which can be used for validation of recently developed (non-linear)numerical models. As such, the new WEC farms will be also tested under (extreme) waveconditions that induce non-linear effects.Experiments with WEC farms will be conducted in the Coastal and Ocean Basin (COB) (see Fig. 3)in Ostend in 2020, while in 2019 a single ‘Master WEC’ will be developed, tested and fine-tunedprior to the ‘WECfarm’ tests.MethodologyFig. 4 shows a sketch of the design of the ‘Master WEC’. The hydrodynamic part of the designconstitutes the floating buoy. Regarding the geometry, a cylindrical float is designed with arelative large diameter compared to the draft, which aims at maximizing wave radiation andthus inducing positive near-field interactions. The small draft is to limit the surge force, sincethe WEC will operate according to the heave mode only.The mechanical part of the WEC design constitutes:(i) the power take-off (PTO) for which a rack and pinion system is chosen.(ii) air bushings to exclude friction effects in the power absorption measurements. A permanentlayer of pressurized air between the interface of the bushing’s guide with the exterior frameresults in a situation where the contribution of friction to the total power absorption isnegligible.The constructed ‘Master WEC’ is a first step towards the final objectives of the ‘WECfarm’ project.AcknowledgementsThe first author would like to acknowledge his PhD Aspirant Research Fellowship by the ResearchFoundation Flanders, Belgium (FWO) (application number 11A6919N). Funding for constructing theexperimental set-up has been awarded by an ‘FWO Research Grant’ application (Reference code:FWO-KAN-DPA376).Research objectivesHowever, since the completion of the ‘WECwakes’ project, many numerical models haveprogressively advanced. To allow validating these new advanced models, the new ‘WECfarm’project has been introduced by UGent and its partners.Fig. 4: Sketch of the design of the ‘Master WEC’

Experimental study of combined near-field interactions and far-field effects of wave energy converter farms : development of a single energy device

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Experimental study of combined near-field interactions and far-field effects of wave energy converter farms : development of a single energy device

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