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The parametric study and optimization of a two‐body wave energy converter (WEC) for the wave and current conditions in the region of Zhaitang Island (China) is presented. Nine parameters are considered, and their influence on the power captured by the two‐body WEC is investigated following both single‐parameter and multi‐parameter approaches. A backpropagation neural network model is developed and applied to predict the captured power for any given values of the nine parameters and the wave frequency. Then the robust design method, also known as the Taguchi method, is implemented to study the comprehensive effects of the parameters on the power output of the device. Moreover, scale model experiments are conducted to verify and confirm the influence of the principal parameters on the power output. Combining numerical simulations, a neural network model and experimental work, this study provides an optimization programme for the main parameters of the device in the target sea region and, at a more general level, references for two‐body WEC designs based on specific sea states.

Offshore wind energy is widely regarded as one of the most credible sources for increasing renewable energy production towards a resilient and decarbonised energy supply. However, current expectations for the expansion of energy production from offshore wind may lead to significant environmental impacts. Assessing ecological risks to marine ecosystems from electricity production from wind is both timely and vital. It will support the adoption of management measures that minimize impacts and the environmental sustainability of the offshore wind energy sector.

As wave energy converters (WECs) are typically designed and optimized for ocean wave conditions, they struggle to perform in low-energy seas or bays, where wave conditions are very different. This work investigates the hypothesis that downscaled versions of WECs may well be more suited for such conditions. More specifically, fifteen downscaled WECs are considered for deployment in the Black Sea. The resizing (downscaling) of the WECs is based on Froude scaling law. Ten values are considered for the scaling factor (λL = 1.0, 0.9, 0.8 … 0.1), and the value that yields the highest capacity factor is selected for downscaling the WEC. The downscaled WEC is then compared with the original (full-scale) WEC in terms of performance (capacity factor, full-load hours, and rated capacity). This analysis is carried out for fifteen WECs and 62 locations at different water depths (5, 25, 50, 75, and 100 m), distributed on 13 lines perpendicular to the shoreline along the south-western coast of the Black Sea. The highest capacity factor was obtained by Oyster, whereas the highest energy output was achieved by SSG and WaveDragon for the locations with 4–16 m depths. For deeper waters (25, 50, 75, and 100 m), the highest capacity factor was obtained by Oceantec. In terms of energy output, the best performers were WaveDragon (at 25 m water depth) and Pontoon (at 50, 75, and 100 m water depths). The interest of this approach, however, lies not only in that it enables a scaling factor to be determined for downscaling a WEC for a given site, but also – and more generally – in that it proves the initial hypothesis that downscaled WECs may provide a better alternative for low-energy seas than their full-scale counterparts.

Currently, worldwide attention to clean energy and sustainable energy has been expedited because of its many environmental benefits. In fact, wind and solar energies play a prime role in decarbonizing the energy market. However, finding the most suitable locations for wind/solar power plants is difficult because of the non-homogeneous distribution of these sources. This paper presents a novel method for selecting the optimal locations for wind and solar farms by mapping the space of the decision criteria to the site score. In addition, the multiple linear regression model was used, with the help of the combination of GIS and AHP methods, to model the siting of wind and solar power plants. The site scoring method used in this study is reliable and globally evaluated; therefore, the scores are accurate and effective. To reveal the ability of the proposed method, two study areas were investigated and researched. The results achieved based on the introduced method showed that, in case study 1, areas with an area of about 9, 4 and 7 km2 are suitable for the construction of wind, solar and wind/solar power plants, respectively. This paper also used fourteen existing wind/solar, wind and solar farms from five continents around the world. The results showed that the suggested model acts the same as the real data. In addition to the interest these results hold for the development of renewable energy in the study area, this novel approach may be applied elsewhere to select optimum sites for wind, solar, and combined wind and solar farms.

The demand for tailored climate data by different users is growing worldwide together with the awareness of the challenges posed to society and the environment by climate change. The extreme weather events intensification, sea-level rise, and coastal erosion are urgent challenges to be addressed by European coastal cities. The overreaching scope of the H2020 SCORE (Smart Control of the Climate Resilience in European Coastal Cities) project is to develop a framework for the definition and uptake of integrated Ecosystem-Based Approaches (EBA) and smart digital tools by establishing a network of 10 coastal city' living labs' (CCLLs) to increase the climate resilience of European coastal cities. To achieve this, the first steps are focused on i) the identification and selection of reference datasets for the historical baseline characterization and the projections for the next decades, ii) the downscaling of climate projections in order to produce a dataset of environmental parameters with the suitable temporal and spatial resolution for the project CCLLs' application needs, and iii) the development of statistical tools for data analysis, modeling and testing to assess the occurrence of major coastal hazards and the future evolution trends of the coastline. For this purpose, open, free, and reliable climate data are needed.Based on some essential requirements, a procedure to select, from the main European climate services, fit-for-purpose climate and marine data of interest for SCORE users has been set up. Moreover, a step-by-step procedure on how to access and handle these data has been provided. One of the main issues encountered while exploring the vast range of different climate services and datasets available consists in the articulation of the users' needs. In particular, the best coverage in terms of variables of interest for modeling and Spatio-temporal resolution must be ensured, while guaranteeing a good users' experience in terms of easy accessibility and the provision of information on (meta)data quality, standards, and conventions. The fragmentation of marine data repositories during the previous decades, along with their limited historical temporal coverage are other main challenges encountered. In addition, notwithstanding the availability of datasets downscaled from global to regional models, the spatio-temporal resolution of most part of datasets requires undertaking some statistical or physical downscaling procedures for their use in local impact studies.We thus construct our analysis on those databases and services which are officially available through and/or supported by EU institutions like, e.g., the Copernicus Climate Change Service (C3S) and the Climate Data Store (CDS), the Copernicus Marine Environment Monitoring Service (CMEMS) portal or the European Marine Observation and Data Network (EMODnet) initiative. The various criteria defined to select the most appropriate climate services and related datasets for the SCORE activities will be presented as well as a few case studies as examples of possible climate information communication strategies, to help the end-user practically understand and tackle the challenges when interacting with the dataset-interface and in data handling procedures.

The complexity corresponding to the industrial projects and their management are concepts whose interest is increasing. The structural complexity derives directly from the main characteristics of c...

Ocean waves are a huge and largely untapped resource of green energy. In order to extract energy from waves, a novel wave energy converter (WEC) consisting of a floating, hollow cylinder capped by a roof with a variable aperture is presented in this paper. The power take-off (PTO) system is composed of a linear generator attached to the seabed, driven by the heave motion of the floating cylinder through a tether line. The air pressure within the cylinder can be modified by adjusting the roof aperture. The hydrodynamic characteristics of this WEC are investigated through an analytical model based on potential flow theory, in which the wave diffraction/radiation problems are coupled with the air pressure fluctuation and PTO system. Analytical expressions are derived for the maximum power absorbed by the WEC under different optimization principles, revolving around the PTO damping, roof aperture damping and non-negative mooring stiffness. We find that the best power absorption is obtained when the aperture is either completely open or entirely closed, depending on the wave conditions. Intermediate values of the aperture are useful to minimize the heave motion and thus ensure survivability under extreme sea states.

Integrating wave energy converters with marine structures such as breakwaters, piles, and offshore wind turbines offers benefits in terms of wave power extraction, construction costs, and survivability. In this paper, the integration of an oscillating water column(OWC) into a vertical tubular structure is considered. The OWC chamber is enclosed by the tubular-structure with its submerged side partially open to the sea. As ocean waves propagate through the device, an air turbine installed at the top of the chamber can be driven to extract wave power. An analytical model based on potential flow theory and the eigen-function matching method is developed to solve the wave scattering and radiation problems of the device in finite water depths. Wave excitation volume flux, hydrodynamic coefficients, optimal turbine damping and power capture factor are evaluated. Upon successful validation, the model is applied to investigate the effect of the radius and finite wall thickness of the tubular-structure, the size and position of the opening on wave power extraction. We find that a thinner chamber wall thickness offers benefits to wave power extraction in terms of a broader primary band of power capture factor response, and that a broader and higher capture factor band can be achieved by increasing the height of the vertical opening.

Development of third generation of Tidal Energy Converters (TECs) may boost the exploitation of the tidal stream energy resource in depth-limited regions. The hydrodynamic conditions of depth-limited tidal sites are highly influenced by changes in the bathymetric conditions, such as sedimentation and/or dredging operations, which are typical of these regions. Consequently, significant variations in terms of magnitude and predominant flow direction can be present during the operating life of tidal farms, which may compromise their viability. The objective of this work is to explore the potential effects caused by dredging operations on the performance of tidal farms and to propose initial threshold values for key variables (flow magnitude and direction, operating hours of TECs), to ensure the techno-economic viability of tidal farms. For this purpose, three potential tidal sites in a shallow water estuary (Ribadeo, NW Spain), were used as case study. Significant variations were found between the pre- and post-dredging scenarios in terms of energy production, with annual variations exceeding 38%, for the tidal sites present in the region. In sum, the present study highlights the importance of considering the potential bathymetric changes in the decision-making process, when planning the installation of tidal farms in depth-limited regions.

Coastal urbanisation, energy extraction, food production, shipping and transportation have led to the global proliferation of artificial structures within the coastal and marine environments (sensu “ocean sprawl”), with subsequent loss of natural habitats and biodiversity. To mitigate and compensate impacts of ocean sprawl, the practice of eco-engineering of artificial structures has been developed over the past decade. Eco-engineering aims to create sustainable ecosystems that integrate human society with the natural environment for the benefit of both. The science of eco-engineering has grown markedly, yet synthesis of research into a user-friendly and practitioner-focused format is lacking. Feedback from stakeholders has repeatedly stated that a “photo user guide” or “manual” covering the range of eco-engineering options available for artificial structures would be beneficial. However, a detailed and structured “user guide” for eco-engineering in coastal and marine environments is not yet possible; therefore we present an accessible review and catalogue of trialled eco-engineering options and a summary of guidance for a range of different structures tailored for stakeholders and end-users as the first step towards a structured manual. This work can thus serve as a potential template for future eco-engineering guides. Here we provide suggestions for potential eco-engineering designs to enhance biodiversity and ecosystem functioning and services of coastal artificial structures with the following structures covered: (1) rock revetment, breakwaters and groynes composed of armour stones or concrete units; (2) vertical and sloping seawalls; (3) over-water structures (i.e., piers) and associated support structures; and (4) tidal river walls.

Hydrokinetic energy has been mainly studied in areas where the principal driver of the current is the tide. However, in certain areas river discharges play also a principal role. The exploitation of the hydrokinetic resource in such areas has its own peculiarities, dictated by the combined influence of the two driving agents. The objective of this paper is to investigate the exploitation of hydrokinetic energy in the Miño Estuary, the largest estuary in NW Spain and N Portugal, with a focus on the site-specific performance of hydrokinetic energy converters (HECs) and its intra-annual variability. A state-of-the-art hydrodynamics numerical model is implemented and successfully validated based on field data. A third-generation HEC—to be more specific, the new Smart Freestream Turbine (SFT)—is considered, and its performance at the location with the greatest potential is assessed by means of: (i) site-specific efficiency, (ii) availability factor, and (iii) capacity factor. We find that, whereas the site-specific efficiency does not vary significantly, the availability and capacity factors do experience substantial intra-annual (seasonal) variability. In summer and autumn, river discharges are low, and the tide dominates the hydrokinetic resource. In contrast, during winter and spring, the river discharges significantly contribute to the resource, leading to a considerable increase in the availability and capacity factors. More generally, the results imply that in areas subject to combined fluvial and tidal influences the performance of HECs may depart significantly from that in tide-dominated areas, and this departure must be carefully weighed in assessing a project.

Residual flows are of major importance in coastal areas, driving environmental processes such as sediment transport or nutrient dispersion. Consequently, in those areas where a large tidal stream energy resource is available, prior to the installation of a tidal farm, it is imperative to assess how energy extraction affects the residual flows and, in particular, upwelling events. In this paper, the potential effects of different configurations of tidal stream farms on the residual circulation and its seasonality are analysed by means of a case study: Ria de Ortigueira, the westernmost of the Galician Rias Altas (NW Spain). For this purpose, a 3D numerical model was implemented and validated against field measurements. Next, a total of eight case studies, including the operation of bottom-fixed and floating converters under typical summer and winter scenarios, considering upwelling favourable winds, were studied. Overall, when a tidal farm operates, regardless of its configuration and the forcings considered, the resulting general residual flow pattern does not experience significant modifications. This pattern is characterized by a 2D circulation in the inner ria and a positive estuarine circulation in the middle and outer ria. The largest modifications of the residual flow are apparent in the vicinities of the plant, with maximum values of about 0.05 ms−1. Outside this area, the alteration is lower than 0.01 ms−1 and virtually negligible at some distance from the farm where upwelling events develop.

In this work, a novel approach based on artificial intelligence (AI) to assess the efficiency of wave energy converter (WEC) farms in coastal protection isdeveloped. We consider as a case study a beach subjected to severe erosion: Playa Granada (S Spain). More specifically, we analyse the changes in the dry beach area (quantified through the Pelnard-Considere equation) with and without wave farm protection by means of an Artificial Neural Network (ANN) model. The model is selected after a thorough comparative study involving forty ANN architectures, with one and two hidden layers, and two training algorithms (Levenberg-Marquadt and Bayesian regression). The best results are obtained with a [5-10-1] architecture trained with the Bayesian regression algorithm. Once validated, this ANN model is applied to optimize the design and position of the wave farm. The results confirm that ANN models are a useful design tool for hybrid wave farms.

Resumen En este texto presentamos un trabajo de investigación realizado con jóvenes universitarios de la Universidad Autónoma de Querétaro (México), con el objetivo de conocer sus formas de sociabilidad. Preguntar por las formas de sociabilidad nos permite comprender los espacios, actividades y dinámicas desplegados por las/los jóvenes y el valor que dichas relaciones cobran en un contexto de desafiliación acelerada. Así, recuperamos el papel que juega la sociabilidad en términos de las posibilidades de relación y vínculo entre las juventudes y como espacio de encuentro y creación de sentidos.

Climate change is poised to exacerbate coastal erosion. Recent research has presented a novel strategy to tackle this issue: dual wave farms, i.e., arrays of wave energy converters with the dual function of carbon-free energy generation and coastal erosion mitigation. However, the implications of sea level rise – another consequence of climate change – for the effectiveness of wave farms as coastal defence elements against shoreline erosion have not been studied so far. The objective of this work is to investigate how the coastal defence performance of a dual wave farm is affected by sea level rise through a case study (Playa Granada, southern Iberian Peninsula). To this end, a spectral wave propagation model, a longshore sediment transport formulation and a one-line model are combined to obtain the final subaerial beach areas for three sea level rise scenarios: the present situation, an optimistic and a pessimistic projection. These scenarios were modelled with and without the wave farm to assess its effects. We find that the dual wave farm reduces erosion and promotes accretion regardless of the sea level rise scenario considered. In the case of westerly storms, the dual wave farm is particularly effective: erosion is transformed into accretion. In general, and importantly, sea level rise strengthens the effectiveness of the dual wave farm as a coastal protection mechanism. This fact enhances the competitiveness of wave farms as coastal defence elements.

Wave farm planning in a coastal region should lead to the selection of: i) the type of technology of wave energy converter (WEC) providing the highest performance at specific sites and ii) the sites for wave farm operation allowing an integrated coastal zone management (ICZM). On these bases, the deployment of a wave farm should be based on an accurate analysis of the performance of different WECs at coastal locations where wave energy exploitation does not interfere with other coastal uses, and the environmental impact is minimised (or positive, e.g. allowing coastal protection). With this in view, in this piece of research the intra-annual performance of various WECs of the same type (buoy-type) is computed at different locations in NW Spain allowing an ICZM perspective. For this purpose, the intra-annual version of WEDGE-p® (Wave Energy Diagram Generator – performance) tool is implemented. The results show that, as opposed to previous analysis on WECs with different principle of operation, the level of performance of buoy-type WECs at specific locations may present strong similarities. In this case, an accurate computation of different performance parameters along with their joint analysis emerge as a prerequisite for an informed decision-making.

In this paper, a semi-analytical model for solving wave radiation from a truncated cylinder of arbitrary cross section is presented based on linear potential flow theory. The water domain is divided into the interior domain beneath the cylinder and the exterior domain outside the vertical cylinder column. Radiated spatial potentials in these subdomains are expressed as a series expansion of eigen-functions using the method of separation of variables. The continuity conditions for pressure and velocity are satisfied at the interface of the two domains, where the Fourier series expansion method is employed to deal with the radius function associated terms. Therefore, the unknown coefficients in the radiated potential expressions are determined by means of the eigen-function matching method. Hydrodynamic coefficients of the truncated cylinder are evaluated directly based on the radiated spatial potentials. Case studies on wave radiation from a truncated cylinder with “cosine” and “circular” cross sections show a good agreement between the semi-analytical results of added-mass/radiation damping and numerical ones/published data. The validated semi-analytical model is then adopted to study the hydrodynamic characteristics of truncated cylinders with “circular”, “cosine”, “elliptical” and “quasi-elliptical” sections. For the latter case, the influence of draft on wave radiation is also investigated.

Wind energy resources will be impacted by climate change. A novel hybrid ensemble technique is presented to improve long-term wind speed projections using Coupled Model Intercomparison Project Phase 6 (CMIP6) data from global climate models. The technique constructs an optimized system, which relies on a Genetic Algorithm and an Enhanced Colliding Bodies Optimization technique. Next, the performance of the proposed method over a target area (United Kingdom) is evaluated between 1950 and 2014. Finally, to avoid single-valued deterministic projections and mitigate the uncertainties, the improved wind speed data series are investigated considering different climate-change scenarios - the Shared Socioeconomic Pathways (SSPs) - for the period 2015-2050. The performance of different CMIP6 models is found to differ over time and space. In the target area the data derived from the Hybrid model confirm that extreme wind events will occur more frequently. The monthly mean wind speed is expected to increase from 3.41 m/s during 1950-2014 to 3.60, 3.63, 3.48, 3.59 and 3.61 m/s during the study period in the SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP4-6.0 and SSP5-8.5 climate-change scenarios, respectively. More generally, the results prove that the Hybrid model is highly effective in improving the accuracy, direction and geographical patterns of the data, and this novel method can narrow the potential uncertainties of numerical simulations.

Climate change can bring about destructive effects (e.g., rising temperatures, heavy rains and droughts) to countries worldwide, severely influencing future growth and degrading the quality of life. Asia, which is home to the majority of the world's population, is particularly vulnerable to these impacts. Asian countries are responsible for more than half of the global CO2 output and renewable energy production is limited. Unabated climate change may endanger previous economic developments and place the region's future at serious risk. Therefore, there is a clear need to increase the share of renewable energy via various sources. Importantly, the continent has extensive coastlines, with abundant wave energy in many areas. The main objectives of this study are to review the current status of wave energy in Asia and to provide an overview of the areas that may be considered for future development. For this purpose, Asia is divided into four regions: East, Southeast, South and West. Active wave energy projects are highlighted, and the wave energy potential is discussed country by country based on the data available in the literature, including suggested sites for development.

A detailed study is undertaken of the computational modelling of a sub-platform for floating offshore wind using the software Star-CCM+ with the application of the RANS approach. First, a mathematical introduction to the governing equations is carried out. Then, the computational grid is defined, and the grid-independence of the solution is verified. A time-dependent study is performed with the selected time-step. Finally, two examples of 3D decay tests in heave of the sub-platform without and with moorings are presented, accompanied by a damping factor study, with the aim of providing a better understanding of the hydrodynamic damping of the platform. Throughout the process, three degrees of freedom (DoFs) are locked due to the limitations imposed by the use of a symmetry plane; this implementation allowed us to reduce the computational cost of each simulation by 50%. Therefore, three DoFs (heave, surge and pitch) are considered. The coupling study, adding a mooring system in the decay tests and the regular wave tests, shows good agreement between the experimental and computational results. The first half-period of the simulations presents a greater discrepancy due to the fact that the damping of the platform is lower in the computational simulation. However, this does not imply that the hydrodynamic damping is underestimated but may be directly related to the lock of various DoFs associated with the hydrodynamic damping. The current investigation was developed under the framework of the European Regional Development Fund through the “Interreg Atlantic Area Programme” under contract EAPA 344/2016, providing experimental inputs to complete this study.

Climate change induced sea level rise (SLR) is likely to impact estuarine hydrodynamics and associated processes, including tidal energy. In this study, a hierarchy of factors influencing the future of estuarine tidal energy resources is proposed based on their relevance to SLR. These include primary factors (e.g., tidal prism, tidal range, tidal current, tidal asymmetry), secondary factors (e.g., sediment transport), and tertiary factors (e.g., shifts in estuarine shape/landform). The existing uncertainty regarding SLR impacts on tidal energy resource is high, given the spatial variability of estuaries. SLR may cause tidal ranges or currents to strengthen or weaken, depending on estuarine shape and boundary conditions (e.g., presence or absence of levees and adjacent low-lying areas). To date, local site studies have not resulted in an overarching assessment of SLR effects on tidal energy resources and comparative studies encompassing different regions and estuary types are recommended in order to address the existing knowledge gaps and provide insights for policymakers and stakeholders. SLR implications to estuarine tidal energy resources may be particularly important as SLR-induced changes can alter the available resource within a renewable energy development's operational lifetime (-20-30 years for tidal stream devices and-120 years for tidal barrages). In this regard, broader environmental impacts, as well as technoeconomic assessments, are difficult to predict and long-term management decisions associated with harnessing the potential of tidal energy schemes within estuaries should be made with caution.

[Abstract] This paper presents a novel approach to characterize cliff exposure to marine action that combines wave power and biology. This multidisciplinary approach is illustrated through a case study on a coastal stretch in NW Spain – the Catedrales Natural Monument. The engineering perspective is based on quantifying the wave power acting on the cliff. To this end, a statistical characterization of the wave climate in deep water is carried out, and relevant sea states are propagated numerically from deep water to the cliff. Four levels of cliff exposure, from sheltered to exposed, are defined based on wave power and mapped onto the study area. As for the biological perspective, ecological factors, bioindicated variables and biological indicators characterized through field observations are considered and, on this basis, also four levels of cliff exposure are established and mapped. In general, there is good agreement between the exposure patterns obtained through the engineering and biological perspectives; however, there are some differences in certain areas. The upshot is that the engineering and biological points of view should be regarded as complementary. The multi-criteria characterization performed in this paper may be used as a management tool to establish different degrees of exposure to marine action on cliff coasts elsewhere. Ministerio de Ciencia, Innovación y Universidades; FJCI-2017-31781

In this work, a combined multidisciplinary method to characterize coastal cliff environments is presented. It combined two complementary approaches – engineering and geomorphological. The first one is represented by the wave power values along the cliff face. For that purpose, the deep-water wave climate is statistically characterized, and high-energy sea states are numerically propagated to the cliff with a state-of-the-art model. The variations in wave power at the cliff face are controlled by the varying cliff orientation and by the irregular morphology, which influences wave propagation through refraction and shoaling processes. Based on wave power, four engineering exposure levels, from low to extreme, are defined and mapped onto the cliff. The geomorphological approach is based on an index developed ad hoc for this work, the Cliff Stability (CS) index, which takes into account the cliff geometry, lithology, structure and degradation state, as well as the hydrological conditions. Based on the CS index, four geomorphological exposure levels are defined and mapped, from low to extreme. The combined approach is shown through the application to a study site in NW Spain. The two perspectives, engineering and geomorphological, are found to yield similar results in some sections of the study area, but not all. It may be inferred that, despite the importance of wave action in shaping the cliff, the additional elements included in the CS index also play a significant role. In practical terms, the significance of these results is that the two approaches, engineering and geomorphological, should be combined to properly characterize coastal cliffs. This combined approach represents a multidisciplinary tool to define and characterize the exposure levels and, thus, prevent damages in cliff environments across the world.

Understanding the spatial variation of the levelised cost of energy (LCOE) of offshore wind is fundamental for identifying potential areas for the development of this technology. With this in view, this paper presents a large-scale mapping of the LCOE of floating offshore wind over the European Atlantic, with a focus on floating semi-submersible platforms. The energy production is estimated accurately at every site using hindcast wind data combined with the power curve of an exemplar wind turbine. Furthermore, this work presents an analysis of the different costs incurred in the lifetime of the project using expressions depending on site-specific variables, i.e., water depth and distance to shore. The results highlight the paramount influence of the energy production and, therefore, the wind resource on the final cost of energy. The lowest LCOE values (∼95 €/MWh) correspond to the areas where the wind resource is most abundant: off Great Britain and Ireland, in the North Sea and off NW Spain. The influence of the resource leads inevitably to LCOE values somewhat higher off Portugal and Norway (∼125 €/MWh), and much higher in the Gulf of Biscay and south of the Iberian Peninsula (>160 €/MWh). Within regions with a similar resource, e.g., the North Sea (LCOE in the range 95–135 €/MWh), the distance to shore is found to be the main variable affecting the LCOE. By comparison, the costs related to water depth (primarily, mooring costs) are of little significance – unlike with bottom-fixed technologies.

Worldwide, many estuaries have the potential to harness tidal stream energy via the conversion of current velocities into a consumable energy source. However, the effects of future sea level rise on the tidal stream energy resource within different estuary types are largely unknown. To address this knowledge gap, 978 idealised hydrodynamic simulations were carried out to first identify estuary types and the location of hotspots within them that are promising for tidal energy exploitation in present-day conditions, and then provide insights into the altered tidal stream energy of different estuary types under various future sea level rise and river inflow scenarios. The results indicate that, under sea level rise, the tidal stream energy of prismatic estuaries reduces more than that of converging estuaries. This implies that estuaries that are currently worth exploiting for tidal power may cease to be in the future due to accelerating sea level rise. Further, as sea level rise may bring about geomorphic adjustments, the spatial energy patterns within an estuary may shift and optimal energy sites may be eliminated or displaced. These climate change effects pose a serious challenge for the management of tidal energy generation in future. In this context, the findings of this study are of practical significance for decision-makers in designing long-term strategies for the development of tidal energy installations in estuaries under rising mean sea levels.

The impacts of wave farms (arrays of wave energy converters, or WECs) on the nearshore must be fully understood for wave technology to develop and thus contribute to a sustainable, carbon-free energy mix in the near future. The objective of this work is to investigate the role played by the farm layout on the wave propagation patterns leewards and the implications for longshore sediment transport (LST) and shoreline evolution on a gravel-dominated deltaic coast. Changes in wave propagation in four scenarios, corresponding to as many wave farm layouts, are computed by means of a spectral numerical model (Delft3D-WAVE) under (i) low-energy and storm conditions, and (ii) westerly and easterly waves - the two prevailing wave directions. On this basis, sediment transport rates are computed and changes in the shoreline position assessed using a one-line model. To quantify the impact of the wave farm on the nearshore wave conditions, sediment transport and shoreline, we define three ad hoc indicators: the non-dimensional wave height reduction, the non-dimensional LST rate reduction and the non-dimensional shoreline advance. Significant wave heights decrease in the lee of the wave farm, with the consequent reduction in LST rates. As a result, the dry beach area increases in every scenario under both westerly and easterly waves. We find that case studies with the WECs arranged on fewer rows but covering a greater stretch of coastline provide better coastal protection. These results confirm that wave farms can be used not only to generate carbon-free energy but also to protect gravel-dominated coasts.

School of Engineering of the University of Plymouth Hydraulic Engineering research area of the University of Santiago de Compostela

Characterisations of the tidal stream resource and its variability over various timescales are crucial for the development of the tidal stream energy industry. To date, no research has compared resource sensitivity in standing wave (when peak currents occur midway between high and low water) and progressive wave (where peak currents occur at high and low water) tidal systems. Here, we compare the flow regimes of standing wave versus progressive wave systems and the associated variations in tidal stream power with applications to device deployment options (floating-platform turbines versus bottom-mounted turbines). We use a validated 3D numerical model (ROMS) of a globally-significant tidal energy shelf sea region (Irish Sea), to test the hypotheses that the influence on potential extractable energy, and suitability for different devices, may be markedly different between these contrasting systems. Power density was also calculated and compared for floating versus bottom-mounted devices using in-situ current data (ADCPs) obtained from a standing wave site and a progressive wave site. We show that progressive wave systems are characterised by velocity-asymmetry over a tidal cycle (i.e. stronger peak flows at high water than at low water), leading to power-asymmetry. Such power asymmetry was shown to have more of an effect on floating device technology, where an assumed turbine depth tracks the sea surface, in contrast to bottom-mounted technology, where the hub height is fixed at a certain position above the sea bed. Shallow, high-flow regions where tidal range is large contained up to 2.5% more power density from bottom-mounted compared with floating turbines; however, there were areas where floating devices were exposed to higher mean currents over a tidal cycle. Standing wave systems, where flow asymmetry is minimised, did not particularly favour either technology. The results highlight the requirement for detailed resource assessments to consider the vertical plane, and are applicable to all potential tidal stream energy sites.

Achieving cost reduction in wave energy conversion is seen as essential to enabling the progress of the sector. At utility scale in a wave farm, multiple devices are likely to be deployed in array configurations. Closely spaced, compact wave energy converter (WEC) arrays are a promising option for cost reduction, realising synergies in operation and maintenance tasks and auxiliary installations, whilst achieving economies of scale. Mooring and anchorage systems are known to be a major component of the structural costs, and the use of interconnecting lines between neighbouring devices can reduce the number of anchors and minimise total line length. In this paper, we present the experimental study of different configurations of a five-device array of spar-buoy oscillating-water-column wave energy converters in a wave basin, focusing on the analysis of the power production performance. The study compares the performance of a single isolated device, an array with independently-moored devices and three arrays with inter-body connections, with different levels of connectivity in the mooring arrangement. Results show considerable performance implications linked to the interconnecting of devices, with the interconnected array configurations yielding a 75% increase in the annual energy extracted compared to the baseline (non-interconnected) arrangement. The performance enhancements are primarily attributed to the interconnecting moorings resulting in greater heave motion at higher frequencies for which the phase relationship between the water column and heave motion is more beneficial. Evidence is also presented that positive intra-array effects occur within interconnected arrays when the wavelength is equal to the array spacing.

A damage detection method is presented which combines the random decrement technique (RDT) with long and short-term memory (LSTM) networks. The method uses the measured vibration response of offshore structures subjected to random excitation and is able to locate and assess the damage with accuracy, even in noisy conditions. The applicability of the proposed RDT-LSTM method is verified through a numerical example and laboratory tests. The numerical example consists of a jacket platform subjected to random wave excitation. The simulated damage cases encompass single and multiple damage locations not only on whole segments but also on local elements (one-fifth of the whole segment) of the numerical structure, with minor (1%–5%) severity, and different noise levels. RDT is applied first to process the noisy random data, and then the damage detection is carried out using LSTM. After the numerical example, the proposed method is applied to laboratory tests of a jacket platform model under random loading produced by a shaking table. Minor and major damages and their combination at different locations are discussed. Both the numerical simulation and laboratory test show that the proposed RDT-LSTM method has an outstanding performance in structural damage detection.

publisher: Elsevier articletitle: An integrated approach for the installation of a wave farm journaltitle: Energy articlelink: http://dx.doi.org/10.1016/j.energy.2017.07.114 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved.

Ports are often located in naturally sheltered areas such as estuaries. The strong tidal currents that occur in many of these areas drive a dynamic morphodynamic regime, with the result that the approach channels to these ports are gradually infilled. Periodic dredging is therefore necessary to maintain the operativity of the port. A case in point is Ribadeo (NW Spain), an important port for the economy of the area. In this work, the sediment transport patterns of the estuary (Ria de Ribadeo) are investigated through high-resolution numerical modelling and field measurements covering a 4-year period. On this basis, a decision-aid tool is developed that enables to predict the time evolution of the approach channel and thus contributes to the planning of dredging operations and, more generally, the maintenance of adequate operativity levels in a cost-effective way.

Marine energy is one of the most promising solutions to attempt the ambitious renewable energy target of 20% by 2020 due to its very substantial energy resource. However, it is often considered uneconomical and difficult, and this may hinder its development. Combined energy systems, such as co-located offshore wind turbines and wave energy converters, have recently emerged as a solution to increase the competitiveness of marine energy by taking advantage of the synergies between renewables; which would lead to reductions in the energy cost and improvements in the power output variability and security. On this basis, finding viable locations for combined offshore renewable energies is fundamental to boosting their development. The objective of this paper is to determine suitable locations for deploying a co-located wind and wave energy farm in the North Sea - an area with several characteristics that make large-scale integration of renewable energy sources attractive. In this assessment we investigate not only the existing resource but also other parameters such as its variability and the correlation between waves and winds by means of the CLF index. In addition, inter- and intra-national user conflicts are considered, while balancing environmental conservation and economic development.

This paper summarizes the assessment of the structural analysis and design of a floating foundation for offshore floating wind turbine (FWT) based on DNVGL standard and Eurocode in terms of economy and reliability. The wind loads are calculated using empirical equations. The wave loads are obtained and verified using various methods including hand calculation, AQWA and Flow-3D. It is found that the shell thickness could be reduced significantly by introducing the stiffeners (stringer or ring), which can decrease the weight of the hull and lower the cost. While DNVGL and Eurocode yield similar design solutions if using plane shell structures, Eurocode significantly underestimates the buckling resistance of stiffened cylindrical shells.

In this chapter, a new methodology to manage coastal protection by means of wave farms is proposed. Artificial intelligence tools, more specifically artificial neural networks (ANNs), were used to assess dry beach surface differences between the no wave farm situation and different wave farm project scenarios. A number of alongshore locations and layouts—represented as the number of rows and the spacing between devices—formed the wave farm scenarios and the influence of the wave climate—significant wave height and mean wave direction—was also taken into account. The selected study site was Playa Granada (southern Iberian Peninsula), a beach with important erosion problems. The datasets used for training and testing the ANN were obtained by means of a suite of numerical models including a third generation wave propagation model, a sediment transport formulation and a shoreline response equation. In order to obtain the ANN which provides the best fit to the data, a comparative study involving more than forty different architectures formed by one and two hidden layers and trained by means of two training algorithm was carried out. The [5-10-1] architecture obtained the best results with a correlation coefficient and RMSE of 0.9489 and 4.22 m\(^2\), respectively. Once the best architecture was found, the ANN was applied to the study site in order to obtain the optimum location and layout for a wave farm project and the results indicate that dry beach surface could increase up to 5400.18 m\(^2\) per year. These results show that ANNs can be useful for managers to optimize the design of wave farms for coastal protection.

In this chapter, the efficiency of wave farms in coastal protection under sea-level rise is investigated. A wave farm formed by 11 wave energy converters was modelled off Playa Granada, a gravel-dominated coast in Southern Spain, under three sea-level rise scenarios: the current water level and the water level in 2100 according to a low- and high-emission scenario. In order to explore the effects produced by the wave farm, the natural scenario without wave farm was also studied. Waves were propagated through the wave farm by means of Delft3D-Wave and breaking parameters were obtained in order to apply a longshore sediment transport (LST) formulation. The results obtained with the LST formulation were used in a one-line model to compute the changes in the position of the shoreline at the study site. The results highlight that wave farms are able to decrease beach erosion (shoreline retreat) even under sea-level rise scenarios. That makes wave farms attractive management strategies, as they contribute to the decarbonisation of the energy mix and more efficient in terms of coastal protection under sea-level rise than traditional hard-engineering structures.

In this chapter, the effects of wave energy converter geometry on coastal flooding are explored. In particular, it is assessed the efficiency of two angles between hulls of the WaveCat devices (30\(^\circ \) and 60\(^\circ \)) for the mitigation of coastal inundation. The case study consists of a wave farm composed by 11 devices deployed off a deltaic beach is southern Spain (Playa Granada). First, laboratory tests were performed to determine the reflection and transmission coefficients under low-, mid- and high-energy conditions. Then, these coefficients were used to jointly apply Delft3D-Wave and XBeach-G in Playa Granada considering wave farms with both wedge angles. The results highlight that devices with wedge angles of \(60^\circ \) are more efficient than those with \(30^\circ \) to reduce nearshore wave heights, run-up values and flooded dry beach areas for long wave periods and high-energy conditions. Thus, since coastal flooding commonly occurs under storm conditions, the devices with wedge angles of \(60^\circ \) are more efficient as coastal defence elements against flooding.

This work analyses the effects of sea-level rise on flooding events for 3 different scenarios: present situation (S0), optimistic projection (RCP4.5) and pessimistic projection (RCP8.5). The study area is a gravel-dominated beach in southern Spain (Playa Granada), where the SWAN and XBeach-G models are applied to assess wave propagation patterns, total run-up and flooded dry beach area. The results indicate that sea-level rise modifies wave propagation patterns, with alongshore-averaged increases in breaking wave height equal to 1.2% (1.9%) un-der westerly (easterly) storms in the optimistic scenario and 2.6% (2.4%) in the pessimistic scenario. These increments lead to maximum increases in total run-up greater than 13% (14%) for westerly (easterly) storms in the optimistic scenario and 16% (20%) in the pessimistic scenario. Finally, the increases in flooded dry beach area induced by sea-level rise under westerly (easterly) storms are equal to 1.6% (5.9%) and 1.8% (7.7%) in scenarios RCP4.5 and RCP8.5, respectively, and the maximum increments in flooded cross-shore distances exceed 8% in all cases. The methodology proposed in the present work can be extended to other coasts worldwide for assessing the influence of sea-level rise on coastal flooding events.

The hydrodynamics of an offshore stationary platform consisting of four cylindrical Oscillating Water Column (OWC) Wave Energy Converters (WECs) are considered in this paper. Based on the potential flow theory, a second-order Higher-Order Boundary Element Method (HOBEM) model is developed to simulate the wave interaction with the multi-OWC platform in time domain. Laboratory tests of a carefully instrumented scale model are also conducted, and the results from the two methods are compared for the validation. It is found that the linear model overestimates the relative capture width of the OWC device by approximately 10% around the resonant frequency. Subsequently, the hydrodynamic properties of the multi-OWC platform are investigated systematically in terms of the air pressure and free surface oscillations in the chamber, as well as the relative capture width. The isolated cylindrical OWC device is also considered for the comparison. The effects of the incident wave direction, the column and row spacing between the OWC devices are explored. The surface elevation distribution inside and around the OWC device is discussed. The occurrence of the maximum free surface elevation inside the chambers is found to lag behind the crest of the incident wave. The optimum angle of wave incidence in terms of energy capture is β = 0, i.e. multi-OWC platform aligned with the incoming waves. A strategic design of the column and row spacing can lead to a significant improvement for capturing wave energy.

Mutriku is a wave farm on the Spanish coast of the Bay of Biscay that has now been continuously supplying electricity for more than nine years. Since 1979, there has been a growing trend in wave energy flux for the whole Bay of Biscay. ERA5 data at the grid point nearest to Mutriku indicate an increase of 0.146 kW/m per decade for the 1979–2019 period. In this paper, a Self-Organizing Map (SOM) with a 2X5 architecture has been fitted to identify ten major sea-state types, each with a distinctive electricity generation pattern at a daily scale. This rendered it possible to reconstruct the daily electric power that would have been generated if the Mutriku wave farm had been operational over the entire 1979–2019 period and, accordingly, evaluate the impact that the observed changes in the wave climate and associated wave energy flux would have had on the electricity production. The results indicate that the electricity production or power flow would have remained constant during that period despite the increasing trend in wave energy flux. This is due to the regulation procedures and mechanisms used in the operation of Mutriku's Oscillating Water Column (OWC) wave energy converters, which dampen the effect of the increasing trend observed. The main conclusion is that the power flow levels off above a given threshold, making it more stable than the wave energy flux.

Although oscillating water column (OWC) wave energy converters are arguably one of the most studied technologies, it is not clear which chamber geometry, among all of the available alternatives, would provide the best performance at a site of interest. In this work, a numerical model based on the Navier-Stokes equations for two compressible fluids, using a volume-of-fluid interface-capturing approach, is implemented to determine the best performing OWC geometry in a case study off the Port of Vigo (NW Spain). Four general shapes of OWC are analyzed: classic, stepped-bottom, U-shaped and L-shaped, and geometrical variants are investigated. In total, 18 chamber geometries are studied, considering the same turbine geometry in all of them. It was found that the U-shaped and L-shaped designs are the most easily tuned to resonate at a period of interest. Of these two, the L-shaped performs better. The best performance is achieved for an L-shaped OWC design with a shallow entrance, a high horizontal chamber duct and a wide vertical duct, for which a maximum capture-width ratio of 71.6% was achieved.

Co-located wave and wind energy farms can serve to tackle one of the downsides of offshore wind energy relative to its onshore counterpart: the longer non-operational periods. These are partly caused by delays to maintenance tasks due to energetic sea states preventing access. By co-locating Wave Energy Converters (WECs) in an appropriate configuration it may be possible to reduce the wave heights within the wind farm area (shielding effect) and thereby increase the weather windows for maintenance. Previous works analysed the improvements in accessibility obtained by configuring the co-located WECs as a peripheral barrier or interspersed within the farm. However, the former led to an insufficient wave height reduction as the distance to the barrier increased and the latter presented other handicaps, notably in respect of the submarine cable installation and the navigation of workboats. The objectives of this work are: (i) to analyse whether a uniformly distributed array may be more convenient in these respects and (ii) to carry out a comparative economic assessment. This investigation is carried out through a case study at the Horns Rev 1 wind farm by means of a high-resolution spectral wave model. Annual cost savings of up to 900,000 € are found.