Special Issue "Numerical and Experimental Modelling of Wave Field Variations around Arrays of Wave Energy Converters"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics".

Deadline for manuscript submissions: 1 March 2020.

Special Issue Editors

Prof. Dr. Peter TROCH
E-Mail Website1 Website2 Website3
Guest Editor
Department of Civil Engineering, Ghent University, Technologiepark 904, 9052 Ghent, Belgium
Interests: wave energy; wave–structure interaction; wave tank experiments; numerical modelling of WEC farm wake effects; moored floating structures
Dr. Vicky STRATIGAKI
E-Mail Website1 Website2 Website3
Guest Editor
Department of Civil Engineering, Ghent University, Technologiepark 904, 9052 Ghent, Belgium
Interests: marine renewable energy; wave energy converter arrays; experimental modelling; numerical coupling methodologies; WEC–WEC interactions
Dr. Matt FOLLEY
E-Mail Website
Guest Editor
Marine Renewables Research Group, Queen's University Belfast, Belfast, United Kingdom
Interests: wave energy; spectral-domain modelling; wave energy resource; wave energy arrays; wave-tank modelling
Assist. Prof. Dr. Eva LOUKOGEORGAKI
E-Mail Website
Guest Editor
Division of Hydraulics and Environmental Engineering, Department of Civil Engineering, Aristotle University of Thessaloniki, Thessaloniki, Greece
Interests: Fluid–structure interaction; ocean engineering, moored floating structures; multi-body hydrodynamic interactions; hydroelasticity; wave energy converters; offshore wind turbine

Special Issue Information

Dear Colleagues,

Wave energy has a huge potential to contribute to the required renewable energy supply worldwide. Wave energy converters (WECs) will need to be installed in arrays (or farms) to capture a sufficient amount of energy from the incident waves. Conventionally, the power output, the power take-off system, and (conversion) efficiency of single WECs are investigated in detail during the design phase, aiming at WEC device optimization.

However, the individual WECs in an array configuration interact with each other, which affects the overall power output of the WEC array (“near field” effects). Moreover, large WEC arrays, called WEC farms, have a significant effect on the surrounding wave field. These are “far field” effects or “wake” effects for the WEC farms, featuring reduced wave heights in the shadow zone behind the farm due to the wave absorption in the farm. As a result, an accurate assessment of the environmental impact of WEC arrays and farms due to the wave field variations is also required during the design phase.

Papers are invited which present experimental or numerical methodologies for modelling both near field effects and far field wake effects of WEC farms on the surrounding wave field, on the coastal morphology, or on other users of the sea, as the relevant tools for the environmental impact assessment.

Apart from WECs, other floating devices placed in an array configuration are also targeted, including recent trends such as co-located wave and wind energy farms, offshore floating platforms, arrays of combined energy devices, etc. These topics are directly related to the new “WECANet COST Action CA17105 - A pan-European network for Marine Renewable Energy”.

Prof. Dr. Peter TROCH
Dr. Vicky STRATIGAKI
Dr. Matt FOLLEY
Assist. Prof. Dr. Eva LOUKOGEORGAKI
Guest Editors

Manuscript Submission Information

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Keywords

  • marine renewable energy
  • wave energy converter arrays
  • array wave tank experiments
  • numerical modelling of WEC farm wake effects
  • arrays of moored floating structures, numerical coupling methodologies
  • co-located wave and wind energy farms
  • WEC arrays combined with other marine facilities (e.g., breakwaters, offshore platforms, offshore wind turbines)
  • WEC farm near and far field effects
  • WEC array environmental impact assessment
  • WEC array interactions

Published Papers (6 papers)

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Research

Open AccessArticle
Performance of an Array of Oblate Spheroidal Heaving Wave Energy Converters in Front of a Wall
Water 2020, 12(1), 188; https://doi.org/10.3390/w12010188 - 09 Jan 2020
Abstract
In this paper, we investigate the performance of a linear array of five semi-immersed, oblate spheroidal heaving Wave Energy Converters (WECs) in front of a bottom-mounted, finite-length, vertical wall under perpendicular to the wall regular waves. The diffraction and radiation problems are solved [...] Read more.
In this paper, we investigate the performance of a linear array of five semi-immersed, oblate spheroidal heaving Wave Energy Converters (WECs) in front of a bottom-mounted, finite-length, vertical wall under perpendicular to the wall regular waves. The diffraction and radiation problems are solved in the frequency domain by utilizing the conventional boundary integral equation method. Initially, to demonstrate the enhanced absorption ability of this array, we compare results with the ones corresponding to arrays of cylindrical and hemisphere-shaped WECs. Next, we investigate the effect of the array’s distance from the wall and of the length of the wall on the physical quantities describing the array’s performance. The results illustrate that the array’s placement at successively larger distances from the wall, up to three times the WECs’ radius, induces hydrodynamic interactions that improve the array’s hydrodynamic behavior, and thus its power absorption ability. An increase in the length of the wall does not lead to any significant power absorption improvement. Compared to the isolated array, the presence of the wall affects positively the array’s power absorption ability at specific frequency ranges, depending mainly on the array’s distance from the wall. Finally, characteristic diffracted wave field patterns are presented to interpret physically the occurrence of the local minima of the heave exciting forces. Full article
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Open AccessArticle
The Expected Shoreline Effect of a Marine Energy Farm Operating Close to Sardinia Island
Water 2019, 11(11), 2303; https://doi.org/10.3390/w11112303 - 03 Nov 2019
Abstract
Coastal areas are defined by numerous opportunities and threats. Among them we can mention emerging renewable projects and on the other hand coastal erosion. In the present work, the impact of a generic wind–wave farm on the nearshore waves and currents in the [...] Read more.
Coastal areas are defined by numerous opportunities and threats. Among them we can mention emerging renewable projects and on the other hand coastal erosion. In the present work, the impact of a generic wind–wave farm on the nearshore waves and currents in the vicinity of the Porto Ferro inlet (northwest Sardinia) was assessed. Using a reanalysis wave dataset that covers a 40-year interval (1979–2018), the most relevant wave characteristics in the target area were identified. These can reach during winter a maximum value of 7.35 m for the significant wave height. As a next step, considering a modeling system that combines a wave model (simulating waves nearshore (SWAN)) and a surf model, the coastal impact of some generic marine energy farms defined by a transmission coefficient of 25% was assessed. According to the results corresponding to the reference sites and lines defined close to the shore, it becomes obvious that there is a clear attenuation in terms of significant wave heights, and as regards current velocities, although the general tendency for them to decrease, there are, however, some situations when the values of the nearshore current velocities can also decrease. Finally, we can mention that the presence of a marine energy farm seems to be beneficial for the beach stability in this particular coastal environment, and in some cases the transformation of the breaking waves from plunging to spilling is noticed. Full article
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Open AccessArticle
WECANet: The First Open Pan-European Network for Marine Renewable Energy with a Focus on Wave Energy-COST Action CA17105
Water 2019, 11(6), 1249; https://doi.org/10.3390/w11061249 - 14 Jun 2019
Abstract
Growing energy demand has increased interest in marine renewable energy resources (i.e., wave energy, which is harvested through wave energy converter (WEC) arrays. However, the wave energy industry is currently at a significant juncture in its development, facing a number of challenges which [...] Read more.
Growing energy demand has increased interest in marine renewable energy resources (i.e., wave energy, which is harvested through wave energy converter (WEC) arrays. However, the wave energy industry is currently at a significant juncture in its development, facing a number of challenges which require that research re-focuses on a holistic techno-economic perspective, where the economics considers the full life cycle costs of the technology. It also requires development of WECs suitable for niche markets, because in Europe there are inequalities regarding wave energy resources, wave energy companies, national programs and investments. As a result, in Europe there are leading and non-leading countries in wave energy technology. The sector also needs to increase confidence of potential investors by reducing (non-)technological risks. This can be achieved through an interdisciplinary approach by involving engineers, economists, environmental scientists, lawyers, regulators and policy experts. Consequently, the wave energy sector needs to receive the necessary attention compared to other more advanced and commercial offshore energy technologies (e.g., offshore wind). The formation of the first open pan-European network with an interdisciplinary approach will contribute to large-scale WEC array deployment by dealing with the current bottlenecks. The WECANet (Wave Energy Converter Array Network) European COST Action, introduced in September 2018 and presented in this paper, aims at a collaborative and inclusive approach, as it provides a strong networking and collaboration platform that also creates the space for dialogue between all stakeholders in wave energy. An important characteristic of the Action is that participation is open to all parties interested and active in the development of wave energy. Previous activities organised by WECANet core group members have resulted in a number of joint European projects and scientific publications. WECANet’s main target is the equal research, training, networking, collaboration and funding opportunities for all researchers and professionals, regardless of age, gender and country in order to obtain understanding of the main challenges governing the development of the wave energy sector. Full article
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Open AccessArticle
Analysing the Near-Field Effects and the Power Production of Near-Shore WEC Array Using a New Wave-to-Wire Model
Water 2019, 11(6), 1137; https://doi.org/10.3390/w11061137 - 30 May 2019
Abstract
In this study, a series of modules is integrated into a wave-to-wire (W2W) model that links a Boundary Element Method (BEM) solver to a Wave Energy Converter (WEC) motion solver which are in turn coupled to a wave propagation model. The hydrodynamics of [...] Read more.
In this study, a series of modules is integrated into a wave-to-wire (W2W) model that links a Boundary Element Method (BEM) solver to a Wave Energy Converter (WEC) motion solver which are in turn coupled to a wave propagation model. The hydrodynamics of the WECs are resolved in the wave structure interaction solver NEMOH, the Power Take-off (PTO) is simulated in the WEC simulation tool WEC-Sim, and the resulting perturbed wave field is coupled to the mild-slope propagation model MILDwave. The W2W model is run for verified for a realistic wave energy project consisting of a WEC farm composed of 10 5-WEC arrays of Oscillating Surging Wave Energy Converters (OSWECs). The investigated WEC farm is modelled for a real wave climate and a sloping bathymetry based on a proposed OSWEC array project off the coast of Bretagne, France. Each WEC array is arranged in a power-maximizing 2-row configuration that also minimizes the inter-array separation distance d x and d y and the arrays are located in a staggered energy maximizing configuration that also decreases the along-shore WEC farm extent. The WEC farm power output and the near and far-field effects are simulated for irregular waves with various significant wave heights wave peak periods and mean wave incidence directions β based on the modelled site wave climatology. The PTO system of each WEC in each farm is modelled as a closed-circuit hydraulic PTO system optimized for each set of incident wave conditions, mimicking the proposed site technology, namely the WaveRoller® OSWEC developed by AW Energy Ltd. The investigation in this study provides a proof of concept of the proposed W2W model in investigating potential commercial WEC projects. Full article
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Open AccessArticle
Wake Effect Assessment in Long- and Short-Crested Seas of Heaving-Point Absorber and Oscillating Wave Surge WEC Arrays
Water 2019, 11(6), 1126; https://doi.org/10.3390/w11061126 - 29 May 2019
Abstract
In the recent years, the potential impact of wave energy converter (WEC) arrays on the surrounding wave field has been studied using both phase-averaging and phase-resolving wave propagation models. Obtaining understanding of this impact is important because it may affect other users in [...] Read more.
In the recent years, the potential impact of wave energy converter (WEC) arrays on the surrounding wave field has been studied using both phase-averaging and phase-resolving wave propagation models. Obtaining understanding of this impact is important because it may affect other users in the sea or on the coastline. However, in these models a parametrization of the WEC power absorption is often adopted. This may lead to an overestimation or underestimation of the overall WEC array power absorption, and thus to an unrealistic estimation of the potential WEC array impact. WEC array power absorption is a result of energy extraction from the incoming waves, and thus wave height decrease is generally observed downwave at large distances (the so-called “wake” or “far-field” effects). Moreover, the power absorption depends on the mutual interactions between the WECs of an array (the so-called “near field” effects). To deal with the limitations posed by wave propagation models, coupled models of recent years, which are nesting wave-structure interaction solvers into wave propagation models, have been used. Wave-structure interaction solvers can generally provide detailed hydrodynamic information around the WECs and a more realistic representation of wave power absorption. Coupled models have shown a lower WEC array impact in terms of wake effects compared to wave propagation models. However, all studies to date in which coupled models are employed have been performed using idealized long-crested waves. Ocean waves propagate with a certain directional spreading that affects the redistribution of wave energy in the lee of WEC arrays, and thus gaining insight wake effect for irregular short-crested sea states is crucial. In our research, a new methodology is introduced for the assessment of WEC array wake effects for realistic sea states. A coupled model is developed between the wave-structure interaction solver NEMOH and the wave propagation model MILDwave. A parametric study is performed showing a comparison between WEC array wake effects for regular, long-crested irregular, and short-crested irregular waves. For this investigation, a nine heaving-point absorber array is used for which the wave height reduction is found to be up to 8% lower at 1.0 km downwave the WEC array when changing from long-crested to short-crested irregular waves. Also, an oscillating wave surge WEC array is simulated and the overestimation of the wake effects in this case is up to 5%. These differences in wake effects between different wave types indicates the need to consider short-crested irregular waves to avoid overestimating the WEC array potential impacts. The MILDwave-NEMOH coupled model has proven to be a reliable numerical tool, with an efficient computational effort for simulating the wake effects of two different WEC arrays under the action of a range of different sea states. Full article
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Open AccessArticle
Internal Wave Generation in a Non-Hydrostatic Wave Model
Water 2019, 11(5), 986; https://doi.org/10.3390/w11050986 - 10 May 2019
Abstract
In this work, internal wave generation techniques are developed in an open source non-hydrostatic wave model (Simulating WAves till SHore, SWASH) for accurate generation of regular and irregular long-crested waves. Two different internal wave generation techniques are examined: a source term addition method [...] Read more.
In this work, internal wave generation techniques are developed in an open source non-hydrostatic wave model (Simulating WAves till SHore, SWASH) for accurate generation of regular and irregular long-crested waves. Two different internal wave generation techniques are examined: a source term addition method where additional surface elevation is added to the calculated surface elevation in a specific location in the domain and a spatially distributed source function where a spatially distributed mass is added in the continuity equation. These internal wave generation techniques in combination with numerical wave absorbing sponge layers are proposed as an alternative to the weakly reflective wave generation boundary to avoid re-reflections in case of dispersive and directional waves. The implemented techniques are validated against analytical solutions and experimental data including water surface elevations, orbital velocities, frequency spectra and wave heights. The numerical results show a very good agreement with the analytical solution and the experimental data indicating that SWASH with the addition of the proposed internal wave generation technique can be used to study coastal areas and wave energy converter (WEC) farms even under highly dispersive and directional waves without any spurious reflection from the wave generator. Full article
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