Renewable energy is constantly being developed to reduce the dependency on fossil fuels. Energy from ocean waves can be utilized by installing Wave Energy Converters (abbreviated as WECs) in the sea, which are devices that convert the kinetic and/or potential energy of waves into electricity. Many concepts of WECs have already been developed, mainly distinguished based on the conversion principle, in (i) oscillating water columns and wave-activated bodies, which oscillate under incident waves, and (ii) overtopping devices, which capture the overtopped waves in a basin above sea level that creates a hydraulic head. In order to extract a considerable amount of energy at a specific site location, the installation of large numbers of WECs will be required, arranged using specific geometric configuration. In this chapter, an overview of typically performed research on waveactivated bodies and WEC arrays is provided, since this PhD dissertation deals with arrays of this WEC type. In contrast to the large body of numerical simulations of WEC arrays and the physical modelling of individual WECs or pairs of WECs, very few experimental studies are publically available which deal with only small WEC arrays. There is, therefore, a lack of physical modelling studies on large WEC arrays and a clear need to perform such experiments, which has been dealt with within the main objective of this PhD research.

https://biblio.ugent.be/publication/5934441/file/5934450.pdf

Experimental study and numerical modelling of intra-array interactions and extra-array effects of wave energy converter arrays

Numerical modeling of vegetation-induced dissipation using an extended mild-slope equation

This chapter describes the use of a phase-resolving wave propagation model, MILDwave (based on the mild-slope equations), for assessing the park effect in arrays of wave energy converters (WECs) and the far-field wake effects of the arrays. The implementation of the WEC (array) is carried out using the numerical techniques of so-called sponge layers and wave generation along a circle, to simulate the physical process of energy absorption by the WEC, and the resulting wave transformation processes of reflection, diffraction, and radiation. A generic coupling methodology is presented for modelling accurately both the wave energy absorption by the WEC and the propagation of the perturbed wave field over larger distances, allowing the study of the coastal impact of arrays. The approach is applied in a practical situation to study the wave height reduction behind a single WEC and a farm of WECs, and advantages and limitations are discussed.

Phase-Resolving Wave Propagation Array Models

Irish Research Council for Science Engineering and Technology (EMBARK Initiative); Science Foundation Ireland (Charles Parsons Research Award)

Characteristics of the wave energy resource at the Atlantic marine energy test site

https://biblio.ugent.be/publication/8617445/file/8617448.pdf

A fundamental coupling methodology for modeling near-field and far-field wave effects of floating structures and wave energy devices

The increasing energy demand, the need to reduce greenhouse gas emissions and the shrinking reserves of fossil fuels have all enhanced the interest in sustainable and renewable energy sources, including wave energy. Many concepts for wave power conversion have been invented. In order to extract a considerable amount of wave power, single Wave Energy Converters (abbreviated as WECs) will have to be arranged in arrays or ‘farms’ using a particular geometrical layout, comprising large numbers of devices. As a result of the interaction between the WECs within a farm, the overall power absorption is affected. In general, the incident waves are partly reflected, transmitted and absorbed by a single WEC. Also, the wave height behind a large farm of WECs is reduced and this reduction may influence neighbouring farms, other users in the sea or even the coastline (wake effects of a WEC farm). The numerical wave propagation model MILDwave has been recently used to study wake effects and energy absorption of farms of WECs, though without taking into account wave regeneration by wind in the lee of the WEC-farm which can be significant in large distances downwave the WECs. In this paper, the implementation of wave growth due to wind in the hyperbolic mild-slope equations of the wave propagation model, MILDwave is described. Several formulations for the energy input from wind found in literature are considered and implemented. The performance of these formulations in MILDwave is investigated and validated. The modified model MILDwave is then applied for the investigation of the influence of the wind on the wakes in the lee of a farm of wave energy converters.Copyright © 2011 by ASME

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

The increasing energy demand, the need to reduce the greenhouse gasses, and the shrinking reserves of conventional energy have enhanced the interest in sustainable and renewable energy sources, a.o. wave energy. Many concepts for wave power conversion have been invented, a.o. Wave Energy Converters (abbreviated as WECs). In order to extract a considerable amount of wave power, single WECs will have to be arranged in arrays or ‘farms’, using a particular layout. As a result of the interaction between the WECs of a farm (near-field effects), the overall power absorption is affected. Moreover, the wave height behind a large farm of WECs is reduced, possibly influencing neighboring farms or other users in the sea or even the coastline (far-field effects). In general, the incident waves are partly reflected, transmitted and absorbed by a single WEC. Those devices can be distinguished in two main types: type (i) (different cases of floating bodies) and type (ii) (fixed or slack moored overtopping devices that capture the overtopped waves). The present study refers to the development of the numerical modeling of the above mentioned wake effects of a WEC farm in a mild-slope wave propagation model, MILDwave. Here, the effect of wind input is introduced in order to investigate the effect of wave growth by wind on the reduced wave heights in the lee of single WECs and WEC farm layouts. The numerical wave propagation model MILDwave has been recently used to study wake effects and energy absorption of farms of WECs (Beels et al., 2010a; 2010b; Troch et al., 2010; Baelus and Keppens, 2010) by using a sponge layer technique. MILDwave is a mild-slope wave propagation model based on the equations of Radder and Dingemans (1985) and developed by Troch (1998). This phase resolving model is able to generate linear water waves over a mildly varying bathymetry and to calculate instantaneous surface elevations throughout the domain. Wave transformation processes such as refraction, shoaling, reflection, transmission, diffraction and wave breaking can be simulated intrinsically. Other typical applications of the model are the study of wave penetration in harbours, e.g. Zeebrugge and Ostend in Belgium (e.g. Stratigaki and Troch, 2010; Stratigaki et al., 2010), the harbour of Hanstholm in Denmark (Margheritini et al., 2010), wave transformation studies, e.g. in the Norwegian coast (Kofoed et al., 2008) and in the Belgian coast for the Thorntonbank, etc. The physical process of wave regeneration by wind in a phase resolving model has been developed. The wakes behind single WECs and WEC farms are investigated for various wave conditions under the effect of wind. The evolved technique is applied on farms composed by hypothetical WECs with basic dimensions 36mx36m exhibiting a certain amount of absorption and on WECs known as Wave Dragons. Results in the lee of WEC farms when the wind effect is incorporated confirm that the available wave power increases when wind is applied. Moreover, taking into account wave regeneration by wind represents in a better way the actual wave and wind conditions in the field.

/pdf/study-of-wave-regeneration-by-wind-in-the-lee-of-farm-of-3bkbous567.pdf

Study of wave regeneration by wind in the lee of farm of wave energy converters using the Mild-Slope wave propagation model, MILDwave

Begin 2008 stelde Europa haar ambitieuze 20-20-20 klimaatdoelstellingen voor, die intens gekoppeld zijn aan hernieuwbare energie. Eén veelbelovende en duurzame technologie is het opwekken van energie uit golven. Numerieke modellering van de golfenergie-convertoren is een belangrijk aspect in de verdere ontwikkeling van deze technologie. Dit artikel [1] beschrijft de implementatie van de golfgroei door wind in de hyperbolische mild-slope vergelijkingen die door het numerieke golfvoortplantingsmodel MILDwave gebruikt worden. Verschillende uitdrukkingen voor de energie-overdracht van de wind naar de golven, beschikbaar in de literatuur, worden beschouwd. De toepasbaarheid van deze uitdrukkingen voor MILDwave wordt onderzocht en gevalideerd, en de uitdrukking die de meest bevredigende resultaten levert, wordt weerhouden om de invloed van de wind op de zogzone van een park van golfenergie-convertoren te onderzoeken.

Yannick Keppens

Papers

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

Study of wave regeneration by wind in the lee of farm of wave energy converters using the Mild-Slope wave propagation model, MILDwave

Numerieke modellering van de golfgroei door wind in de zogzone van een park van golfenergieconvertoren m.b.v. het golfvoortplantingsmodel MILDwave