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Offshore wind with high energy density and low turbulence has attracted the global scientific community towards the development of the Offshore Wind Turbines (OWTs). Today, most of the shallow water sites are already occupied, and the industry is looking to install turbines at the deep water sites (water depth > 50m). However, an OWT support structure designed with the conventional concepts becomes massive and expensive in deeper waters. In contrast, floating OWTs are more expansive than the bottom supported ones, and considered suitable for a water depth of 60 m or more. A novel support structure concept termed a ‘bottom supported tension leg tower’ (BSTLT) has been proposed recently and the possibility of using bottom supported structures in deeper waters is shown. In this paper, an extension of the BSTLT concept has been achieved using inclined tethers with a monopile. The preliminary technical feasibility including the sensitivity of the natural frequencies and dynamic analyses considering the in-place operating and the extreme design conditions has been studied for 50 m water depth. The results show that the proposed concept can be utilized to make the monopile based support structures more cost-efficient for the water depth stated above.

Assessing the evolution of the performance of water supply and sanitation services is essential to monitor progress towards the universalization of water services, as specified by the Sustainable Development Goal 6 of Agenda 2030, adopted by United Nations member countries. Brazil, a developing country with a continental size and geographical diversity, will face significant challenges to achieve this goal. The main objective of this paper is to evaluate the evolution of productivity of water supply and sanitation services in Brazilian municipalities in the period 2012-2019. The analysis also explores whether water services' performance is balanced across the country, with a specific analysis of performance at the macroregion level. From a methodological perspective, this research evaluates productivity change over time using a Malmquist Productivity Index estimated with a metafrontier, satisfying the circularity property. It also develops a pseudo Malmquist index that compares productivity levels across macro-regions. The results revealed a productivity loss of approximately 4% at the national level, with an unequal profile across the macro-regions. The Southeast municipalities stand out for exhibiting, on average, higher productivity levels than the South and Northeast municipalities.

Wave climate and associated energy characterization is essential for an assessment of a country’s renewable energy potential. A wave model was validated against satellite data with good performance in terms of error metrics. The hindcast data, covering the period 1979–2018, was used to describe the spatial, seasonal and interannual variability and trend of wave energy flux along the United Arab Emirates coastline. The annual mean wave energy flux along the study area is higher at the central region reducing towards the south and north. The wave energy shows a clear seasonality and interannual variability for all locations with higher and lower energy during winter and autumn, respectively. A trend analysis of the historical data indicates an increase in annual mean energy flux along the coast. Alongshore, seasonal and interannual variability of wave energy flux and direction should be considered in the initial stages of marine renewable energy projects. A detailed analysis of historical wave energy trends and influence of large-scale climate indices will be particularly relevant for longer-term projects.

The combined exploitation of wave and offshore wind energy resources is expected to improve the cost competitiveness of the wave energy industry as a result of shared capital and operational costs. In this context, the objective of this work is to explore the potential benefits of co-locating CECO, an innovative wave energy converter, with the commercial WindFloat Atlantic wind farm, located on the northern coast of Portugal. For this purpose, the performance of the combined farm was assessed in terms of energy production, power smoothing and levelised cost of energy (LCoE). Overall, the co-located farm would increase the annual energy production by approximately 19% in comparison with the stand-alone wind farm. However, the benefits in terms of power output smoothing would be negligible due to the strong seasonal behaviour of the wave resource in the area of study. Finally, the LCoE of the co-located farm would be drastically reduced in comparison with the stand-alone wave farm, presenting a value of 0.115 per USD/kWh, which is similar to the levels of the offshore wind industry as of five years ago. Consequently, it becomes apparent that CECO could progress more rapidly towards commercialisation when combined with offshore wind farms.

In this study, the simultaneous application of sacrificial piles and cable was experimentally examined as a pier scour countermeasure. The experiments were carried out for a single pier, a group of two and three piers using a clear-water regime. It is believed that applying the sacrificial piles and cable at the same time decreases the scour depth at a single pier and a group of two piers efficiently. In a group of three piers, the sacrificial piles with triangular configuration were able to decrease the scour depth considerably with a value of 69% reduction at the first pier. Nevertheless, the cable affects the scour depth reduction negatively at the group of three piers. This research highlights that the combination of cable and sacrificial piles is a suitable method to decrease the local scour at a single and a group of two piers, while sacrificial piles alone can be highly recommended for the group of three piers.

The R&D project Oracle – offshore risk analysis for climate change adaptation and lifetime extension – is focused on optimising the design of scour protection schemes for the extended lifetime of offshore foundations. This project proposes an optimisation of scour protections by combining reliability-based techniques with the novel concepts of dynamic and wide-graded armour layers. The ultimate goal is to develop a decision support system (DSS) for scour protection design and risk and reliability analysis to be used by professionals and researchers dealing with fixed foundations applied to marine renewable energy projects (e.g. wind, wave and tidal). However, a meaningful implementation of such a DSS implies prior analysis of several knowledge gaps related to scour protection in the offshore environment, which are yet to be fully addressed in the literature. This paper provides a brief review of the scientific and technical challenges in the research field of reliability of offshore scour protection. On the basis of identified challenges, the discussion of future research lines is performed with a particular focus on the aim of the Oracle project. The recent findings related to risk and reliability analysis of offshore scour protection are addressed and framed within the existing knowledge gaps in the literature.

CECO is a wave energy converter (WEC) of the oscillating body type equipped with an inclined PTO system and being developed at the Faculty of Engineering of the University of Porto. In the last years, several research studies have been performed to assess and to improve the performance of this WEC, using both physical model tests and numerical simulations. The main objective of this paper is reviewing the most significant findings of past research works, so as to provide a detailed overview about the present status of knowledge, but also presenting recent outcomes on the development of CECO and the next research steps. It discusses the influence of the PTO slope angle and damping on the efficiency of CECO harvesting wave energy and describes its energy conversion stages. Furthermore, the intra-annual variability of the wave resource (i.e., on a monthly basis) is considered in the analysis of the influence of the PTO inclination and local water depth at the deployment site on CECO captured energy and captured energy efficiency, along the North Atlantic coast of the Iberian Peninsula. The results have shown significant differences between the summer and winter months and also highlighted the fact that the initial geometry of this WEC is more suitable for the less energetic wave climates, characteristic of the southern locations of the case study area and of shallow waters. The conclusions obtained supported the design of an enhanced version of CECO, prepared for the more energetic stretches of the study area, which presents a hydrodynamic efficiency of more than twice the original one, for the target wave conditions.

Offshore oil and gas platforms have very high-power demands, being the electric power supply usually provided by gas turbines operating with natural gas extracted from the field. Since fields are ageing, the amount of gas available for electric power production is declining. One common alternative is to feed those gas turbines with fuel diesel, which is an expensive solution at remote locations and has a high carbon footprint. Since oil and gas platforms often operate in deep waters and are exposed to energetic wave climates, ocean wave energy can be used in their electrification. Even though wave energy is not yet cost competitive for suppling onshore grids, power supplying remote oil and gas platforms might be the niche market enabler to launch commercially the sector, due to the high cost of the electricity produced in those offshore facilities and the abundance of wave resource at most of their locations. This paper proposes a new techno-economic model to assess and scale wave energy converters to match the local wave climate at their deployment site, while maximizing the income of the wave farm and accounting for their life cycle costs. At the same time, the economic feasibility of providing electricity from ocean waves to remote offshore oil and gas facilities is analysed using as case study an oil and gas platform in operation at the North Sea. Seven wave energy converters were assessed at the case study site and it was proved that its hydrodynamic performance is not directly linked to its economics attractiveness. The values of the levelized cost of energy ranged from 188 to 471 €/MWh and were benchmarked against reference values. The feasibility of providing electricity from waves to offshore oil and gas facilities is also demonstrated and the exploration of this untapped market advocated.

The damping coefficient of the power take-off (PTO) system is a key parameter in the performance assessment of a wave energy converter (WEC). However, since in most WEC studies the focus is mainly on the absorbed power, damping estimation is generally overlooked on the assumption that a single constant coefficient can properly characterize the WEC's damping of a given configuration for all wave conditions. Recently, while analyzing the experimental tests of CECO, a floating-point absorber WEC, significant discrepancies were found among their experimental responses under different incident waves. Instead of attributing those differences to nonlinear hydrostatic or Froude-Krylov effects, it was hypothesized that variations in the PTO damping associated to incident waves was the main cause. This study presents the experimental evidences of that behavior for regular and irregular waves. Furthermore, a hybrid approach for the assessment of damping coefficients is proposed and applied to CECO's experimental responses. The results demonstrated that: a) damping coefficients were significantly affected by wave conditions; b) higher PTO damping coefficients were obtained for milder irregular waves than for rougher regular waves; c) the hybrid approach reliably and efficiently estimated the WEC power in regular and irregular waves.

The design of a wave energy converter (WEC) is a many-sided and important assignment that determines its future technical and economic viability. Presently, there is a lack of structured design methodologies that take into account both the hydrodynamic performance, structural reliability and economic data from early development stages. Therefore, a new methodology is proposed, aiming for a viable predesign solution for avoiding major setbacks at later stages. It includes a series of steps related to the initial design definition, hydrodynamic analysis, yield strength investigation and early-stage economic assessment. For demonstration, the methodology is applied to progress a sloped motion WEC for near-shore locations. The original WEC configuration is also assessed and the novel design, which allows reducing the mass of floating elements by 70%, is developed. It is found that: for recurrent sea states, the capture width ratio of the new design (20-40%) is similar to the one of the original design (20-50%), the estimated cost of the device is reduced by 28.6% and the payback period is reduced by 2.4 years. Overall, the results obtained for the case study demonstrated the interest in the proposed methodology that can assist in the development and analysis of early-stage WEC concepts. (c) 2022 Elsevier Ltd

The design of appurtenant structures for dams, such as spillways, is a complex task because of the turbulent high-velocity aerated nature of the flowing water. In previous years, physical m...

The worldwide river and tidal hydrokinetic power potential is considerable. Harnessing such potential could allow the generation of a significant amount of sustainable electricity for local uses. To the present, most studies on hydrokinetic power have focused on large-scale commercial technology development, large tidal farms planning, and high-intensity resources assessment. Reduced attention was oriented towards investigating possibilities for small to medium-size hydrokinetic plants. However, given the characteristics of rivers and estuaries, in most cases, relevant hydrokinetic power exploitation possibilities exist regardless of the dimensions of the region considered. The planning of small to medium-size hydrokinetic plants for various aspects differs from larger developments. In the present work, a method for assessing the hydrokinetic resource is proposed and applied to the case study of the Douro waterway, which is characterized by moderate flow speeds and limited water depths. A high-resolution shallow-water numerical model is set up using ocean and river inflow boundary conditions. The flow velocities are estimated for the neap-spring period for different freshwater discharges. The spots presenting the highest annual hydrokinetic power average were identified, maximum flow speeds of about 1 m/s were found, and an annual mean power of 0.4 kW/m2 was estimated, indicating that prospects for hydrokinetic energy harvesting exist. (c) 2022 by the authors. Licensee MDPI, Basel, Switzerland.

This study proposes a benchmarking approach to assess water supply and sanitation services’ performance in Brazilian municipalities from an integrated perspective of efficiency and access. The regional differences and the impact of the governance models adopted by different municipalities (local public entities, regional public entities, and private entities) on efficiency levels are also explored. The results revealed significant heterogeneity in the efficiency levels of Brazilian municipalities, as the average efficiency score is relatively low (45%). The Southeast and Center-west regions stand out both in terms of efficiency and access dimensions. There is evidence that municipalities with services provided by local public entities have higher efficiency than those with regional providers. On the other hand, efficiency differences between municipalities with public and private providers are statistically significant. Finally, regulatory strategies are suggested based on the outcome of the integrated analysis.

This article presents a methodology to assess the reliability of dynamic scour protections used to protect offshore wind turbine foundations. The computed probabilities of failure are based on a dataset of 124 months of hindcast data from the Horns Rev 3 offshore wind farm. Copula-based models are used to obtain the joint distribution function of the significant wave height and spectral peak period and to obtain the probability of failure of scour protections. The sensitivity of the probability of failure to each model is addressed. The influence of the duration of the waves’ time series is also studied. A sensitivity analysis of the probability of failure to physical constraints, such as the water depth, current’s velocity or the mean diameter of the armour units, is performed. The results show that probability of failure is dependent on the copula used to model the spectral parameters and the associated value of Kendall’s τ. It is shown that the copula presenting the best values of Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) did not lead to the probabilities of failure that are closer to the non-parametric estimation, obtained by means of the bivariate version of the Kernel density estimation method. The application to the case study led to annual probabilities of failure, which are comparable with the values applied for other offshore components, according to the current offshore wind industry standards.

Power estimation is the most important task in the performance assessment of wave energy converters (WEC). Depending on the type of WEC, power take-off (PTO) system, and available instrumentation, different approaches are usually applied to assess power from experimental tests. Since neither for tests execution nor for the analyses exist standard methodologies, the estimated power can significantly differ among the approaches, thus, introducing inaccuracies in the assessment of the WEC’s performance. This study analyzed an extensive set of experimental results of a WEC and applied different power estimation approaches to compare and validate the obtained results. The strengths and weaknesses of those methodologies were analyzed and discussed. The major outcomes were: (a) PTO damping characterization based on bench tests can lead to unrealistic values of the WEC’s absorbed power; (b) the hybrid (experimental plus numerical) approach provide more reliable results than the traditional ones; (c) the kinetic energy harvester approach underestimates power but can be useful for preliminary qualitative performance assessments; (d) the new proposed gross efficiency index allows the definition of upper boundaries for wave power conversion as well as the identification of the wave conditions for which WEC performance can be improved.

In offshore wind turbines, the need for scour protection may represent a considerable part of the total investment required. Its optimisation is therefore a key aspect in offshore wind energy investments. The protection is commonly designed to be statically stable. An economically attractive possibility is to adopt a dynamic stability criterion that enables some degree of movement of the armour layer stones without allowing the filter placed beneath to be exposed at any time. This criterion is based on the acceptable damage number used to specify the mean diameter of the stones used in the armour layer. Little guidance exists on how to define the acceptable limits for this damage number. This paper elaborates on the effect of different hydrodynamic conditions on the damage number of scour protections. The behaviour of the damage number is studied by means of physical model testing of an offshore monopile foundation. The results show that dynamically stable profiles are developed for damage numbers ranging from 0·40 to 3·53. The accuracy of a predictive formula for the damage number is influenced by the water depth. This parameter described the stability of dynamic scour protections more accurately than the stability parameter used in former projects.

Single-layer cube (SLC) armoured breakwaters with a regular placement pattern are a relatively recent concept despite the cube being one of the oldest concrete units available. Limited investigation on the performance and hydraulic stability of this armour type is available to date. This work presents a quantitative assessment of the damage evolution for SLC armoured breakwaters with a regular placement pattern based on 2D physical modelling tests carried out at the University of Porto, Portugal. Tests were carried out for different armour porosities, wave steepnesses, and armour crest levels. A new method for automatically determining cube positions for each test was developed with image-processing techniques using advanced machine-learning tools. This method greatly reduces processing time since several images can be processed in batch mode. Innovative parameters to describe armour layer behaviour were derived and proposed for assessment and quantification of the damage evolution: exceedance probability of cube movements, mean grid orthogonality, and relative damage number for SLC. New damage level classification and criteria for initiation of damage are proposed for each of the parameters assessed. This analysis is focused on the initial stages of the damage, which are critical in designing new structures.

E-Motions wave energy converter is a promising device capable of harnessing energy from wave/wind induced roll oscillations onto a generic floating platform, whose development was initiated with an experimental proof of-concept study that, despite demonstrating the potentialities of the device, also highlighted the need for further developments, aimed at improving its performance and efficiency. This justified a new phase of numerical modelling, where E-Motions was reproduced within the ANSYS (R) AQWATM environment, a potential theory based numerical model widely used in the field of wave energy converter development. The model was setup (first stage) and calibrated (second stage) with experimental data from a proof-of-concept study, carried out on a 1:40 geometric scale, with a good agreement being obtained for the hydrostatic properties (difference below 5%) and hydrodynamic roll response (minimum average error of 2.83 degrees). From a follow-up third stage, focused on comparing eight different hull solutions with similar natural roll periods, it was determined that the half-sphere and trapezoidal prism geometries produced the highest power outputs for the studied conditions (maximum average outputs of nearly 5 kW/m and 8 kW/m, respectively). These two designs were then adapted to a 1:20 geometric scale alongside an updated version of the half-cylinder, which served as a "control" case, and subjected to a final stage of numerical modelling centered on assessing the Power Take-Off's influence (namely through variable damping and mass) in their performance. Outcomes from this stage denote the necessity of a careful selection of Power Take-Off mass/damping combinations, as a disproportionate relationship could lead to scenarios where the conversion system would stall on one of the superstructure's sides, moving within a very limited range of the available sliding amplitude. Maximum average power output values reach nearly 24 kW, 30 kW and 18 kW for the half-cylinder, half-sphere and trapezoidal prism, respectively, with a follow-up experimental study being planned for the near future, in order to evaluate the validity of these results.

Seaports’ breakwaters serve as important infrastructures capable of sheltering ships, facilities, and harbour personnel from severe wave climate. Given their exposure to ocean waves and port authorities’ increasing awareness towards sustainability, it is important to develop and assess wave energy conversion technologies suitable of being integrated into seaport breakwaters. To fulfil this goal whilst ensuring adequate sheltering conditions, this paper describes the performance and stability analysis of the armour layer and toe berm of a 1/50 geometric scale model of the north breakwater extension project, intended for the Port of Leixões, with an integrated hybrid wave energy converter. This novel hybrid concept combines an oscillating water column and an overtopping device. The breakwater was also studied without the hybrid wave energy device as to enable a thorough comparison between both solutions regarding structural stability, safety, and overtopping performance. The results point towards a considerable reduction in the overtopping volumes through the integration of the hybrid technology by an average value of 50%, while the stability analysis suggests that the toe berm of the breakwater is not significantly affected by the hybrid device, leading to acceptable safety levels. Even so, some block displacements were observed, and the attained stability numbers were slightly above the recommended thresholds from the literature. It is also shown that traditional damage assessment parameters should be applied with care when non-conventional structures are analysed, such as rubble-mound breakwaters with integrated wave energy converters.

This work aims to get a better insight into the behaviour of CECO, an oscillating-body wave energy converter that presents a singular feature: the motion of its oscillating part is restricted to translations along an inclined axis. In order to study in the time domain the response of CECO for a wide range of wave conditions, a hybrid numerical approach based on the Boundary Element Method (BEM) and the Morison’s equation was used. The effects of the power take-off system were included in the numerical model and calibrated with the results from previous wave basin experiments. The results show that CECO is able to capture up to 40% of the incident wave energy when the direction of translation is 45°. However, if the direction of translation is vertical, the amount of captured wave energy decreases almost three times. This investigation demonstrates the advantage of limiting the oscillation of the CECO floating part to an inclined direction and reaffirms the concept as a promising technology for wave energy conversion.

CECO is a novel Wave Energy Converter (WEC) concept, which has shown promising results in previous studies. The present work focuses on assessing the performance of CECO for a 11-year horizon in relation to the characteristics of the wave climate (intra and inter-annual seasonal variations) by means of two performance indicators defined ad hoc: Captured Energy (CE) and Captured Energy Efficiency (CEEff ). For this purpose, the CECO matrix of absorbed wave power was constructed for an operating water depth of 30 m using the panel-based model ANSYS®-AQWA(r). The Atlantic coast of the Iberian Peninsula, which presents a highly seasonal and energetic wave climate, was used as case study. Overall, it was found that CECO is able to capture large amounts of wave energy, especially for milder wave conditions, with values of CEEff exceeding 40%. However, for harsher wave conditions the results of CEEff decrease considerably ranging from 10% to 20%, which may result from the current design of CECO. In this context, the results obtained offer some valuable insight into the future evolution of CECO with the purpose of addressing the limitations of the current design and to optimise its performance according to the wave conditions for specific locations.

A novel perforated-wall caisson concept, the so-called LOW REflection Breakwater (LOWREB), based on a three-chamber perforated-wall and inner weirs, is under development in the University of Porto – Faculty of Engineering, Portugal. Physical model tests, carried out in the wave basin of the Hydraulics Laboratory of the Hydraulics, Water Resources and Environment Division, Civil Engineering Department, have been used to study the hydraulic processes related to wave reflection. The physical model was built to a Froude scale of 1:50. Test conditions covered two water levels and irregular waves at three significant wave heights (3.0, 4.0 and 5.0 m) and three peak wave periods (10, 14 and 18s). Three models of varying porosity, and vertical slots' arrangements were tested under the same hydrodynamic conditions to study how these affect the LOWREB performance, namely how these affect the wave reflection from the structure, as compared to a plain caisson tested under the same conditions. The experimental study demonstrates that the LOWREB caisson is a valid concept for marine structures, namely harbour breakwaters, because of its wave energy dissipation capacity, for which the inner weirs were found to play a major role. Results indicate that the hydraulic efficiency of the LOWREB caisson increases with wave height for the lower water level, and decreases with it for the highest. Greater efficiency with respect to wave reflection was accomplished with the highest water level.

No presente trabalho descreve-se a aplicação de uma metodologia para avaliação das consequências do galgamento no porto de Ponta Delgada, S. Miguel, Açores, recorrendo a uma análise multicritério (Processo de Análise Hierárquica, AHP) do impacto da ocorrência de galgamentos superiores aos limites admissíveis. Esta metodologia permite obter resultados baseados numa análise espacial dos indicadores que caraterizam a zona portuária em estudo, no que diz respeito à sua importância relativa. https://doi.org/10.14195/1647-7723_24_9

Previous experimental works proved the ability of CECO to harness wave energy. This wave energy converter (WEC) is presently at Technology Readiness Level (TRL) three, where characterizing the energy conversion stages and evaluating the energy conversion efficiency is crucial. Therefore, in this work Ansys® Aqwa™ was applied to study a CECO unit and to obtain a detailed knowledge of its performance throughout the different energy conversion stages. The numerical model was initially calibrated with results from experimental tests and then used to simulate different configurations of the power take-off (PTO) system under a wide range of regular and irregular wave conditions. For most of the irregular wave conditions tested, CECO can absorb between 10 and 40% of the incident wave power and transmit to the electric generator up to 18%. Although the results reveal a high energy conversion efficiency, there is still scope for improvement of the device by optimizing the PTO. On these grounds, the ideal values of the electric generator damping coefficient are presented for different wave conditions, which allow to define an adequate control strategy in future works.

Marine Renewable Energy (MRE) sources, such as offshore wind, waves, tides, ocean currents, thermal and salinity gradients, appear as promising low-carbon forms of energy. However, with the sole exception of offshore wind, MRE exploitation is far from being commercially feasible. Among the obstacles faced by the sector, the complex legal framework that applies to MRE projects stands out. In this context, the objective of this work is to assess the main aspects of the MRE legal framework, and when necessary, propose corrective measures for further development of the sector. For this purpose, the countries of the Atlantic region of Europe (France, Ireland, Portugal, Spain, and the UK), which present one of the world's largest MRE resource, were used as a benchmark. Overall, the adoption of marine planning policies contributes positively to the development of the sector, defining priority areas for MRE exploitation and establishing clear preference criteria with other maritime activities. Furthermore, streamlining licensing procedures and periods, ideally adopting a one-stop-shop approach like the case of Scotland, becomes essential to attract new developers and investors to the MRE sector. Finally, the examples of Ireland, Portugal and especially the UK, show that the adoption of MRE sectoral plans, including actions for financial support, technology progress and supply chain development, is essential to achieve a fully-fledged MRE industry.

As the world strives to remove its reliance on fossil fuels, wave energy presents a reliable source of renewable energy with a very high potential. Numerical simulations offer an inexpensive alternative, in comparison to physical modelling, for the development of wave energy converters. In this paper, a computational fluid dynamics model of the CECO wave energy converter (WEC) has been developed using the commercial software ANSYS CFX. In order to reduce on the computational resources required, a 2-dimensional model of this sloped (combination of heave and surge) motion WEC has been developed and then successfully validated with experimental results from physical model tests, demonstrating the capability of such models to accurately describe the response of WECs. The validated numerical model was then used to investigate the non-linear effects on the motions of CECO and to obtain more insights in relation to wave loading during a wave cycle and the viscous effects associated to the dissipation of energy in the flow around its floaters. The water particle velocity and vorticity around CECO and the heave and surge loadings on CECO, while it is in operation, are analysed and discussed. The numerical model, not only aid in the development of a new and enhanced geometry for CECO but, also, it can be used to model and analyse similar WECs. (c) 2020 The Authors

Mooring systems are required to keep floating wave energy converters (WECs) on station. The mooring concept chosen for this has an impact on the performance of the WEC, on its cost and on its integrity. To clarify the pros and cons of different mooring designs, we present the results of experiments on physical models of three different mooring concepts in regular and irregular waves, including operational and survival conditions. The parameters evaluated are the tension in the cables, the motions of the device in the different degrees of freedom and the seabed footprint in each case. We can see that the mooring system affects the wave energy converters, but the magnitude of the impact depends on the parameter analysed, on the mode of motion studied and on the conditions of the sea. Moreover, different configurations have similar performances in some situations and the choice of one over another might come down to factors such as the type of soil of the seabed, the spacing desired between devices, or environmental impacts. The results of our experiments provide information for a better selection of the mooring system for a wave energy converter when several constraints are taken into account (power production, maximum displacements, extreme tensions, etc).

The Sea-wave Slot-cone Generator (SSG) is a multi-level overtopping based wave energy converter that can be installed either nearshore or offshore. The installation in harbor breakwaters and in the shoreline presents several advantages despite the usual exposure to smaller waves than at offshore locations. This work analyzes the effect of wave focusing walls ( i.e ., wave concentrators) on the performance of isolated SSG units using a physical model built on a geometric scale of 1/40. Seven configurations were defined by changing the opening angle and the crest level of those elements. The use of wave concentrators proved to be advantageous since a wider wave front is captured and the run-up and overtopping phenomena are enhanced on the SSG ramp owing to the wave energy concentration (walls tapering effect). In fact, the total mean power captured increased for all SSG configurations with concentrators in comparison to the base configuration (without concentrators), regardless of the sea state considered. In terms of hydraulic performance, the gain associated to the use of wave concentrators depends on the characteristics of incident waves, being higher for the smaller significant wave heights and the shorter peak wave periods. The hydraulic efficiency, defined as the ratio between the total mean power captured per meter of SSG width and the wave power per meter width of the incident waves, increases with the significant wave height and reduces with the peak wave period in all tested SSG configurations. In addition, in comparison to the base configuration, the hydraulic efficiencies with concentrators were higher for the smaller significant wave heights, but smaller for the other sea conditions. The use of wave concentrators increased the annual energy production approximately to the double. Overall, the application of the SSG technology in breakwaters presents itself as promising considering the characteristics of the wave resource nearshore or even in onshore locations.

Obtaining information about the motion of mooring cables in small scale models in laboratories can be difficult. To help mend this limitation we present a proof of concept of an experimental technique to track mooring cables. Our technique records underwater videos of cables and then applies image processing to extract the coordinates of the complete medial axis of the cables. Using video acquisition has little interference in the experiments and the processing algorithm performs well even under sub-optimal contrast conditions. All the experimental steps are executed underwater, avoiding the need to simplify complex physical models due to visibility or access constraints. Since the whole length of the cable is fully captured on video, any singularity or quick motion (such as those caused by wave energy converters) is adequately detected. Also, the technique yields an acceptable error when compared to directly measured values. With this technique it is possible to acquire important information about the dynamics of mooring cables.

Breakwater concrete armour units have been continuously evolving since the 1950s. Lower concrete consumption, increased hydraulic stability, reduced wave run-up, and easier placement techniques are the main drivers of this development. A recent innovative solution for breakwater armour, based on one of the oldest type of units available, consists of a configuration adopting a single-layer of concrete cubes placed in a regular pattern and a porosity of 0.25–0.30. This paper presents a summary of the laboratory test results available from literature in terms of hydraulic stability and wave overtopping. Studies indicate that this is a feasible solution with several advantages over other armour configurations related to the simplicity of the cube unit and placement pattern. However, there is still some degree of uncertainty in both hydraulic stability and wave overtopping estimates for a structure with this configuration where few laboratory tests have been conducted in comparison to other armour units. Furthermore, the available methods for quantification of damage are not considered adequate for use in single-layer cube armour with a regular placement pattern. This paper discusses current knowledge gaps and provides guidelines for future research.

Wave measuring equipment are subject to malfunction that can be caused by various reasons such as maintenance, navigation accidents, errors in communications and biofouling of sensors. This can eventually result in loss of valuable data before the equipment is fixed. A continuous data set is often critical for modelling and/or analysis of wave conditions. Data gaps in wave records can be filled using numerical modelling. This study presents an alternative method for filling missing data based on publicly available wind and wave information and artificial neural networks (ANN). The ANN developed in this study uses offshore hindcast wave and wind information (significant wave height, peak wave period and direction, wind speed and direction) from a data set publicly available for any region of the globe. The results of the application of this method to two one-week gaps in wave measurements are compared against a spectral wave model developed and implemented to estimate wave conditions at the measurement location. The ANN results for the validation period show slightly better statistical performance when compared to the wave model results in terms of the correlation coefficient, root mean square error, bias and scatter index. ANN are viable alternative methods to wave modelling for filling gaps in data and have several advantages since specific knowledge of wave models is not required, input data to feed the neural network is available for any region of the globe and the processing time is highly reduced when compared to numerical modelling.

This work reviews the advances in the development of CECO, a wave energy converter (WEC) of the floating oscillating bodies subgroup that has its motions and power take-off system (PTO) restricted to an inclined direction. For this purpose, the review is conducted on the basis of the Technology Readiness Levels (TRLs), the most frequently used metric to assess the maturity of a technology. The main conclusions and milestones of each stage are also presented along with an introduction to the ongoing works and a general picture of future research lines.

The design of certain seawalls / breakwaters has often been required to achieve very low targetovertopping discharges when these structures protect vulnerable infrastructure or activities. Thebalance between economically viable protection and performance requirements is often difficult toachieve without good knowledge on low overtopping. The paucity of data in this space and the highuncertainties associated with existing methods, increase the challenge. The occurrence of a lownumber of overtopping waves has the consequence that any test results are substantially moreaffected by the inherent variation of random waves, therefore more uncertain. The physical model testresults presented hereafter were successful in obtaining low to very low overtopping discharge data.For low / very low overtopping, these test data present considerable scatter relative to the latestempirical prediction. A number of repetitions was performed for conditions giving very low overtoppingdischarges, which illustrated the inherent uncertainty associated with low overtopping.

A new concept of wave energy device (CECO) has been proposed and developed at the Hydraulics, Water Resources and Environment Division of the Faculty of Engineering of the University of Porto (FEUP). In a first stage, the proof of concept was performed through physical model tests at the wave basin (Rosa-Santos et al., 2015). These experimental results demonstrated the feasibility of the concept to harness wave energy and provided a preliminary assessment of its performance. Later, an extensive experimental campaign was conducted with an enhanced 1:20 scale model of CECO under regular and irregular long and short-crested waves (Marinheiro et al., 2015). An electric PTO system with adjustable damping levels was also installed on CECO as a mechanism of quantification of the WEC power. The results of regular waves tests have been used to validate a numerical model to gain insight into different potential configurations of CECO and its performance (López et al., 2017a,b). This paper presents the results and analyses of the model tests in irregular waves. A simplified approach based on spectral analyses of the WEC motions is presented as a means of experimental assessment of the damping level of the PTO mechanism and its effect on the WEC power absorption. Transfer functions are also computed to identify nonlinear effects associated to higher waves and to characterize the range of periods where wave absorption is maximized. Furthermore, based on the comparison of the present experimental results with those corresponding to a linear numerical potential model, some discussions are addressed regarding viscous and other nonlinear effects on CECO performance.