Beaches are eroded and accrete under the effect of storms and calm marine conditions, respectively. Normally, beaches reach their narrower state in spring, after the action of winter storms. Accretion processes are slow, and maximum beach recovery doesn't occur until late summer. Sometimes this recovery is not enough to reach the width the beach had the previous year, producing a progressive shoreline retreat and an increased risk of dune erosion and inland flooding during the following winter seasons. The need for wider beaches in early summer for touristic purposes and social support to soft-engineering measures, have increased the interest in Nature-Assisted Beach Enhancement (NABE) techniques. In this study, reduced-scale laboratory experiments on beach ploughing and scraping allowed the comparison of various of these techniques and their effectiveness in controlled conditions for the first time. The beach widening and accretion achieved for five different NABE geometries were analysed and contrasted with natural (control) conditions. Our results show that the best technique is goal-dependent. For dry beach widening, ploughing is recommended as an effective and easy-to-design technique. Scraping the lower intertidal area and placing the sand on an intertidal bar or the beachfront are also effective alternatives if adequately designed. For dune nourishment, the best option is scraping the upper intertidal area and using the borrowed sand for dune regeneration. In general, all the analysed techniques enhance natural beach accretion, in collaboration with natural processes, thus reducing the human action required to achieve the desired objectives from a Building with Nature perspective.

Progressive coastal retreat has been an issue exacerbated in recent years due to climate change. Sand is eroded from beaches during the winter and partially recovered during summer by slow accretion processes. The development of new working with nature techniques that produce enhanced beach accretion could help recover most of the sand lost during winter and thus reduce the impact of climate change on beaches. The presence of bedforms contribute to increasing onshore sediment transport, but few studies have been performed to quantify their effect. In this study, the evolution and effect of artificially created bedforms on onshore sediment transport were analysed in prototype-scale laboratory experiments. The tested bedforms mimicked a beach ploughing of the intertidal area, with a wavelength of 1.6 m and height of 0.25 m, corresponding to the ploughing dimensions that a tractor can perform. Two tests were performed with the same initial morphology, medium sand (D50 = 0.318 mm), sea state conditions (Hs = 0.3 m, Tp = 7 s) that produced accretion, and different water levels that represent two tidal states. The experimental flume was longitudinally split into two equal channels of 1 m wide, allowing the simultaneous simulation of a natural control geometry and a ploughed geometry, facilitating the comparison and assuring the very same sea conditions. The presence of ploughed bedforms produced two effects: (1) an acceleration of natural accretion rates reaching 40%, and (2) onshore sediment transport due to the migration of the bedforms. The acceleration of natural accretion was explained by the extra bottom roughness induced by the bedforms, which produced more wave dissipation through bottom friction and thus more accretive conditions. The ploughed height decreased exponentially as waves broke over the crest of the ridges, which almost disappeared after 2–3 h of wave action. As a result, the extra bottom roughness also decreased as time passed. Consequently, the nature-assisted beach enhancement technique of ploughing should be applied at each low tide to produce a cumulative effect. Plough bedforms migrated onshore at a rate of approximately 0.2 m/h during the first hour, mobilizing onshore up to 61 kg m-1 h-1 of sediment. Ripples appeared on the tops of the ridge crests and migrated faster onshore, contributing to the migration of the ploughed bedforms. These results demonstrated the importance of considering bedforms while studying accretion processes and the potential of ploughing as an innovative strategy of working with nature to enhance beach recovery.

Beach accretion is the natural mechanism that allows dry beaches to recover. Human response to climate change produces hardening of the coasts and the incident marine climate, which increases beach erosion produced during winter and prevents a full recovery during summer. Beach nourishments are performed all around the world to fight coastal erosion with a nature-friendly philosophy. Softer techniques as beach scraping are also widely applied. A kind of beach scraping is proposed here as an innovative nature-assisted beach enhancement technique, that aims to accelerate naturally produced sand accretion on the beach profile. It consists of mechanically ploughing the intertidal area of a beach to create ridges and furrows. Prototype-scale laboratory experiments were performed to analyse its effectiveness under controlled conditions. Seven 1 h tests having different water levels and the same initial bottom geometry and sea state conditions (Hs = 0.3 m, Tp = 7 s) were performed. Sea state, sand, and initial slope characteristics assured accretive conditions. Ploughed and flatbed initial slope geometries were simultaneously tested into two sub-channels of the wave flume. The results indicate that the bottom roughness is 3.57 times larger for the ploughed geometry. Consequently, wave energy dissipation is larger for the ploughed geometry, and therefore, the significant wave height at the shoreward end of the study area is 11% smaller for the ploughed geometry. This smaller wave height under the ploughed morphology leads to more accretive conditions, as observed from the measured onshore sediment transport, which is 2.9 times larger than the natural transport, and the larger accreted sediment volume in all seven test cases. These results demonstrate the effectiveness of ploughing to enhance natural beach accretion under highly probable accretion conditions. Further research is required to define the thresholds of marine conditions in which the potential of beach ploughing can be exploded.

<p>Plastic debris is currently a significant threat to marine and coastal ecosystems. Most previous research focused on the behavior of drifting macro and mesoplastics on global and regional ocean scales. Furthermore, a few more recent studies provide some first insights into the microplastic dispersion in coastal areas. These studies found that waves and wind, as well as the density, size, and shape of microplastics, drive their transport and dispersion in coastal areas; however, they point to the need for a more extensive characterization. This laboratory study assesses the effect of waves and wave-induced currents on the input rate from land to sea and on the cross-shore transport and dispersion of different types of plastic debris, including the macro and mesosizes, in addition to microplastics. A total of 15 types of plastic debris characterized by different sizes, shapes, and densities, including face masks, were analyzed under regular and irregular wave conditions. The results show that the input rates and transport of plastic debris in the marine environment depend on the position they acquire in the water column, which is related to the terminal velocities and the wave steepness. A higher input rate from the beach was found for plastic materials moving closer to the sea bottom and under less steep wave conditions, as these conditions allow items to escape from coastal entrapment. Furthermore, greater onshore transport was observed for plastic debris that showed greater buoyancy under steeper wave conditions. Regarding the cross-shore distribution, the heaviest plastic debris that managed to be transported accumulated in the breaking zone, while the buoyant elements showed a predominant accumulation closer to the shoreline.</p>

Most offshore wind farms are bottom-fixed at sites with less than 50 m of water depth. For deeper waters, floating platforms are economically viable and, for many countries that have steep continental shelves, this is the only option for developing offshore wind farms. If wind energy is being harvested far offshore in deep waters (more than 200 m depth and hundreds of km from the coast), one possible alternative is the use of Floating Production and Storage (FPS) sailing ships that navigate through the ocean using wind force and utilize part of the harvested wind power to produce and store fuel. These ships are called "energy ships". The objective of this paper is to carry out a qualitative determination of the global marine areas suitable for the operation of energy ships. To that purpose, wind and wave ship operation ranges have been defined and global databases of wind and waves have been used to obtain statistics of operational parameters. From the global analysis carried out the most promising areas and seasons for energy ship operation have been identified and qualified in terms of the aforementioned operational parameters.

A numerical model to study the towing maneuver for floating and submerged bodies has been developed. The proposed model is based on the dynamic study of a catenary line moving between two bodies, one body with imposed motion, and the other free to move. The model improves previous models used to study the behavior of mooring systems based on a finite element method by reducing the noise of the numerical results considering the Rayleigh springs model for the tension of the line. The code was successfully validated using experimental results for experimental data from different authors and experiments found in the literature. Sensitivity analysis on the internal damping coefficient and the number of elements has been included in the present work, showing the importance of the internal damping coefficient. As an example of the application of the developed tool, simulations of towing systems on a real scale were analyzed for different setups. The variation of the loads at the towed body and the position of the body were analyzed for the studied configurations. The reasonable results allow us to say that the proposed model is a useful tool with several applications to towing system design, study or optimization.

Rubble mound-breakwaters are commonly constructed with a parapet or crown-wall at the crest. The design of these superstructures depends on the expected storm wave load history throughout the service life cycle. In tsunami-prone areas, this design must include tsunami actions since their loads can definitely exceed those of storm waves. However, tsunami loads are rarely accounted for. This study aimed at incorporating tsunami actions in the design of crown-walls of rubble-mound breakwaters for the first time. Within this scope, laboratory experiments on a scaled model of a typical Mediterranean rubble-mound breakwater typology under tsunami actions were conducted. This paper is the continuation of our previous paper, Aniel-Quiroga et al. (2018) [1], in which experiments were presented and a stability analysis of the armor units was conducted. This research paper presents the second part of the analysis focused on understanding the pressures that crown-walls of rubble-mound breakwaters must support due to tsunami-like actions. These pressures were measured and analyzed, providing the horizontal and uplift pressure time series and laws. The magnitude and timing of the maximum pressure peaks were identified. The maximum horizontal pressure is caused by the first impact of the tsunami. By contrast, the maximum uplift pressure is prompted by a pressure wave generated by the overtopped water falling into the leeside. This pressure wave penetrates the structure from the rear slope. As a result of this analysis, pressures were characterized, allowing the presentation of a new complete methodology that provides, for the tested structure, the design procedure of the crown-wall under tsunami actions. A new formulation to calculate the run-up of solitary waves on the tested rubble-mound breakwater slope is presented here.

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 603839 (Project ASTARTE - Assessment, Strategy and Risk Reduction for Tsunamis in Europe).

Recent tragic tsunami events, like those that occurred in the Indian Ocean in 2004, and in Japan in 2011, have revealed the need of further work to reduce tsunami risk in coastal areas. An important aspect towards risk reduction is the study of the interaction between tsunami waves and coastal structures as these are the first to receive the tsunami's energy. Dikes and breakwaters must have an adequate structural behavior and maintain some functionality and operability under tsunami attacks to be able to contribute to the reduction of its consequences. Within this scope, laboratory experiments on scaled models of two typical Mediterranean rubble-mound breakwater typologies under tsunami waves were conducted for the first time. The tsunami's action was split into 2 parts: (1) the first impact of solitons was tested by means of large solitary waves and, (2) the subsequent overflow was approached by applying a pump-driven wave maker. The damage on the breakwaters due to these actions was measured and assessed. The result is an in-deep analysis of the relationships among Stability Number, Damage Level and Number of tsunami waves. The outcome of this analysis includes the development of a set of formulae that provide, in the range of the conducted tests, the value of the Damage Parameter, so that tsunami actions can be taken into account in the design of rubble mound structures. Finally, based on the results of these experiments, the threshold values of the Damage Parameter used to characterize damage in armors (Initiation of damage, initiation of destruction, destruction) was particularized for tsunami actions.

Focused on offshore wind energy operation and maintenance applications, this work presents a detailed accessibility analysis of the North Sea. After a review of existing normative dedicated to inspection and access of offshore wind turbines, a rigorous mathematical formulation of relevant accessibility parameters is given by means of the set theory. Long-term and high-resolution metocean data are extracted from reanalysis databases and used to evaluate spatial and temporal variability of such parameters. Respectively restricted by significant wave height and mean wind speed, access by workboat and helicopter is evaluated. Being affected by both wave height and wind speed. Access by offshore crane is also analyzed. It resulted that the UK coast and the southern region of the North Sea are highly accessible, while the coast of Denmark and Norway undergoes more severe metocean conditions. This is, however, balanced by a higher wind resource. Moreover, a strong seasonality is ascertained, together with a drastic reduction of accessibility during daytime in a vast part of the basin. Accessibility during daytime in winter and autumn is very difficult for the whole North Sea. Among the studied farms, Dogger Bank is by far the one with the highest resource and lowest accessibility, while Thorntonbank III the one with the lowest resource and highest accessibility. In addition, accessibility is non-linearly related to wind speed and wave height limits chosen for the access strategies covered. Copyright (c) 2016 John Wiley & Sons, Ltd.

Offshore wind energy is moving towards a future where the main challenge is to cope with the increasing water depth needed to access more and better wind resources. One of the first steps to be undertaken is the development of floating structures to support either wind turbines or measurement devices for the proper characterization of wind energy resources. The use of floating devices for measuring wind speed involves a number of uncertainties not presented by seabed fixed systems. These sources of uncertainty or error are present both in instantaneous wind measurements and averaged (10min or hourly) values because of (i) variability in the measurement height, (ii) the tilt of the anemometer and (iii) the relative velocity between the anemometer and the wind, among others. In this paper, a methodology for assessing the error in the wind measurement characterization because of the movement of a floating meteorological mast is presented. By the numerical simulation of a floating mast, the short- and long-term error in the characterization of the wind at different heights has been evaluated. In general, the error because of the tilt can reach up to 80% of the total error; the error because of the variation of the vertical position of the anemometer reaches values of up to 15% in some cases; moreover, the error associated with the relative velocity between the anemometer and the wind, for averaged values, is significantly less. Finally, it can be concluded that the total error is lower than 0.5% for 10min averaged wind speed of up to 24m/s. Copyright (c) 2016 John Wiley & Sons, Ltd.

The hybrid experimental and numerical design process of a floating platform aimed at combined wind and wave energy production is described in this paper. The floating concept developed in this work is motivated by the current challenge of designing energy converters for deep water and harsh conditions. Consequently, a floating platform is designed for an offshore site in the Cantabrian Sea (North of Spain). The paper includes the climate conditions analysis in order to select the suitable resources to be harvested, following with the design process, including numerical modeling and experimental testing in a wave basin. As a preliminary paper, the results included in the present work are mainly focused on the wave energy conversion system.

Tsunamis are relatively infrequent phenomena, but they have caused more than 420,000 casualties since 1850, due to the devastating consequences of the massive flooding they prompt. Marine structures are crucial to mitigate the risk of tsunami flooding on coastal areas as they provide protection to the potentially affected areas. In order to improve the current knowledge and experience on the interaction between marine structures and tsunamis, physical experiments on rubble-mound breakwaters (RMB) under tsunami attack have been carried out. In this laboratory experiments, 2 typologies of RMB have been tested: (1) with crown-wall, and (2) without crown-wall. The action of a tsunami has been physically modeled in two different parts or approaches. Firstly, the first impact of the wave has been modeled with solitary waves, using several different wave heights. And secondly, the overtopping has been modelled by utilizing wave currents, using several flow discharges. Water level, core and crown-wall pressures, and overtopping velocities were measured. Geometry of RMBs was measured before and after each test using a laser profiler. From these profiles, the damage parameter after each test was computed. KEWORDS: tsunami, structure, rubble-mound, breakwater, experiments.

Met-ocean conditions may affect the performance of a floating wind turbine, since a harsh climate could lead the system to exceed its operating thresholds and thus to force the machine shutdown. In this paper, it is a proposed methodology to evaluate the effect of met-ocean conditions on the long-term dynamic behaviour, and energy production, of a floating wind farm. For a sample of 500MW farm located off the coast of Aberdeen (Scotland), 20years of met-ocean data are generated by means of meteorological reanalysis techniques. A subset of 1000 hourly conditions is selected, by means of a maximum dissimilarity algorithm, and input to a dynamic floating wind turbine model. Numerical results are then interpolated for the whole set of met-ocean data, using radial basis functions. This approach allows to dramatically reduce the global computation time. Tower inclination and hub acceleration are chosen as relevant operating parameters: the former mainly depends on mean wind speed and direction, being largest at rated wind speed. The latter is also affected by significant wave height, and reaches its highest values when wind and waves are aligned. For each simulation, any machine exceeding the selected safety threshold is considered to be shut down. Assuming continuous operation, the average lifespan capacity factor of the farm is 50.2%; more restrictive tolerances result in a non-linear reduction of the energy production. This approach may help both at the design and the operational stage, in determining the best trade-off between energy production and safe operation. Copyright (c) 2015 John Wiley & Sons, Ltd.

When looking for a location for a wave energy converter (WEC) installation, developers usually look for sites with high or very high wave energy resource. From this perspective, countries like Scotland or Ireland have made great effort to include this energy source in their energy mix due to their expected high untapped potential. However, higher resource carries marine operation restrictions. Because of that, the selection of a site for a WEC deployment, the installation, operation and maintenance factors have to be considered from the beginning. In this work an analysis of the suitable locations for the development of wave energy is performed based on the operation and maintenance (O&M) parameters. This study is performed across the globe coastlines taking the met-ocean climate data from Reguero et al (2011) global reanalysis database (GOW) developed at IH Cantabria. Firstly, an analysis of the global availability and accessibility levels is performed all around the globe taking different wave height thresholds into account. Seven specific locations (North-West Denmark, West of Ireland, Chile, North of Spain, West Portugal, South-West Australia and North of Scotland) with high interest on wave energy have been further analyzed and compared. Secondly, the O&M access limits are quantified in terms of the weather windows and the waiting period between available weather windows. A statistical analysis of these parameters is performed within different weather windows lengths (6 h, 12 h and 24 h). The seasonality of these parameters is also analyzed. Finally, a failure analysis will be carried out, simulating the repair operation along the lifecycle of the device for different failure rates and waiting times. The affection of this failure and repair scheme over the power production of a device analyzed previously in Andres et al (2014) will be presented. In this study, some locations with high resource (Spain, Nova Scotia) lead to medium to high accessibilities/availabilities due to the balance between resource and persistence of the weather conditions. Some locations with high resource such as Chile or Australia resulted inaccessible during very long periods of time due to the persistence of severe conditions and then not very recommended for novel converters with uncertain failure rates.

In this work an analysis of suitable locations for the development of wave energy farms is carried out based on representative operation and maintenance parameters. The analysis is applied globally on the basis of long-term global climate data set. Availability and accessibility levels are assessed first by considering different wave height thresholds. Secondly, the O&M access limits are quantified in terms of the weather windows and waiting period between them considering different windows lengths and scenarios. Finally, the O&M cost per kW h is calculated for a wave energy converter based on a point absorber concept. O&M costs has been calculated following the methodology proposed on Guanche et al. (2014). As expected, results show that locations with mild wave climate have very low O&M costs per kW h. Some areas with high wave resource, such as Scotland, Spain or Nova Scotia present reasonable O&M costs compared to the power production in these areas. However, other locations with high resource like Chile or Australia resulted in extremely high O&M costs due to the inaccessibility of these sites during long periods of time. (C) 2015 Elsevier Ltd. All rights reserved.

A new solver for wave and structure interaction is used for three-dimensional simulation of an Oscillating Water Column (OWC). The CFD model solves the Reynolds Averaged Navier–Stokes equations for two incompressible phases (water and air). Laboratory experiments are conducted on a small scale to validate the numerical results. Air and water pressures and velocities as well as the free surface evolution inside and outside the chamber are modeled with notably good agreement. The model is further used to improve understanding of relevant processes and shows potential for use detailed analysis. Even if the experimental problem analyzed had a two-dimensional behavior, the three dimensional domain of the wave flume was numerically simulated in order to prove the capabilities of OpenFOAM®.

This study evaluates the influence of wave climate tunability on the performance of a generic Wave Energy Converter (WEC) for different climate scenarios. The generic WEC is assumed to be composed of an array of heaving, floating cylinders. In this study, two natural periods for the cylinders of 4 s and 8 s (typical of enclosed seas and the mean Atlantic swell, respectively) and a location-tunable cylinder are considered to evaluate the influence of tuning on the power performance of the cylinder. The WEC power matrix is computed using a frequency domain model, and the performance of the WEC is evaluated along the global coasts; the met-ocean data originated from the global reanalysis database (GOW) from Reguero et al. (2012). The performance of the WEC is evaluated using two parameters: the capture width ratio (CWR), which evaluates the efficiency of the converter at each location, and the kW/Ton (KWT) parameter, which evaluates the efficiency of the converter using "economic" terms. Tuning a converter for each location displayed a positive CWR; however, the MT was low after WEC tuning because of the weight of the structures required to tune the converter that experiences high peak periods. (C) 2015 Elsevier Ltd. All rights reserved.