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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.
Xingxian Bao; Zhichao Wang; Gregorio Iglesias. Damage detection for offshore structures using long and short-term memory networks and random decrement technique. Ocean Engineering 2021, 235, 109388 .
AMA StyleXingxian Bao, Zhichao Wang, Gregorio Iglesias. Damage detection for offshore structures using long and short-term memory networks and random decrement technique. Ocean Engineering. 2021; 235 ():109388.
Chicago/Turabian StyleXingxian Bao; Zhichao Wang; Gregorio Iglesias. 2021. "Damage detection for offshore structures using long and short-term memory networks and random decrement technique." Ocean Engineering 235, no. : 109388.
Floating offshore wind, far less constrained by water depths than bottom-fixed, has great potential in the Mediterranean Basin. The levelised cost of energy (LCOE) is arguably the single most reliable metric to measure the viability of energy projects. In this work, the levelised cost of energy for floating offshore wind is mapped for the first time in the European and Eastern Mediterranean with a detailed cost breakdown and a focus on semi-submersible platforms. A multi-parameter analysis is conducted in a case study to discern the effects of specific elements on the LCOE. Expressions are formulated as functions of site-specific variables: distance to shore, water depth and annual energy production. The latter is estimated accurately by combining the power curve of an exemplar wind turbine with hindcast, site-specific wind data. The mapping shows the paramount importance of the wind climate, i.e., the resource, for the LCOE. The lowest values (~95 €/MWh) occur where the wind resource is most abundant, i.e., the Gulf of Lion and the Aegean Sea. The highest values (>250 €/MWh) are found where the resource is scarce, i.e., around the Balearic Islands and in the North Adriatic, Tyrrhenian and Levantine Seas. Moderate values of the LCOE (130–180 €/MWh) occur off South Spain (Alboran Sea), Sardinia, Sicily and Malta, and in the South Adriatic. In addition to the local wind resource, other parameters that play a relevant role in the LCOE are those related to the production of energy (number of turbines in the wind farm and installed power), on the one hand, and to substantial sources of costs (cost of turbines and substructure), on the other, as well as the project lifetime and discount rate. These results identify hotspots for the deployment of floating offshore wind in the Mediterranean and opportunities for cost reductions, and contribute to decision-making in a region much in need of renewable energy.
A. Martinez; G. Iglesias. Multi-parameter analysis and mapping of the levelised cost of energy from floating offshore wind in the Mediterranean Sea. Energy Conversion and Management 2021, 243, 114416 .
AMA StyleA. Martinez, G. Iglesias. Multi-parameter analysis and mapping of the levelised cost of energy from floating offshore wind in the Mediterranean Sea. Energy Conversion and Management. 2021; 243 ():114416.
Chicago/Turabian StyleA. Martinez; G. Iglesias. 2021. "Multi-parameter analysis and mapping of the levelised cost of energy from floating offshore wind in the Mediterranean Sea." Energy Conversion and Management 243, no. : 114416.
New large-scale laboratory data are presented on a physical model of a spar buoy wind turbine with angular motion of control surfaces implemented (pitch control). The peculiarity of this type of rotating blade represents an essential aspect when studying floating offshore wind structures. Experiments were designed specifically to compare different operational environmental conditions in terms of wave steepness and wind speed. Results discussed here were derived from an analysis of only a part of the whole dataset. Consistent with recent small-scale experiments, data clearly show that the waves contributed to most of the model motions and mooring loads. A significant nonlinear behavior for sway, roll and yaw has been detected, whereas an increase in the wave period makes the wind speed less influential for surge, heave and pitch. In general, as the steepness increases, the oscillations decrease. However, higher wind speed does not mean greater platform motions. Data also indicate a significant role of the blade rotation in the turbine thrust, nacelle dynamic forces and power in six degrees of freedom. Certain pairs of wind speed-wave steepness are particularly unfavorable, since the first harmonic of the rotor (coupled to the first wave harmonic) causes the thrust force to be larger than that in more energetic sea states. The experiments suggest that the inclusion of pitch-controlled, variable-speed blades in physical (and numerical) tests on such types of structures is crucial, highlighting the importance of pitch motion as an important design factor.
Sara Russo; Pasquale Contestabile; Andrea Bardazzi; Elisa Leone; Gregorio Iglesias; Giuseppe Tomasicchio; Diego Vicinanza. Dynamic Loads and Response of a Spar Buoy Wind Turbine with Pitch-Controlled Rotating Blades: An Experimental Study. Energies 2021, 14, 3598 .
AMA StyleSara Russo, Pasquale Contestabile, Andrea Bardazzi, Elisa Leone, Gregorio Iglesias, Giuseppe Tomasicchio, Diego Vicinanza. Dynamic Loads and Response of a Spar Buoy Wind Turbine with Pitch-Controlled Rotating Blades: An Experimental Study. Energies. 2021; 14 (12):3598.
Chicago/Turabian StyleSara Russo; Pasquale Contestabile; Andrea Bardazzi; Elisa Leone; Gregorio Iglesias; Giuseppe Tomasicchio; Diego Vicinanza. 2021. "Dynamic Loads and Response of a Spar Buoy Wind Turbine with Pitch-Controlled Rotating Blades: An Experimental Study." Energies 14, no. 12: 3598.
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.
Gabriel Ibarra-Berastegi; Alain Ulazia; Jon Sáenz; Paula Serras; Santos J. González Rojí; Ganix Esnaola; Gregorio Iglesias. The power flow and the wave energy flux at an operational wave farm: Findings from Mutriku, Bay of Biscay. Ocean Engineering 2021, 227, 108654 .
AMA StyleGabriel Ibarra-Berastegi, Alain Ulazia, Jon Sáenz, Paula Serras, Santos J. González Rojí, Ganix Esnaola, Gregorio Iglesias. The power flow and the wave energy flux at an operational wave farm: Findings from Mutriku, Bay of Biscay. Ocean Engineering. 2021; 227 ():108654.
Chicago/Turabian StyleGabriel Ibarra-Berastegi; Alain Ulazia; Jon Sáenz; Paula Serras; Santos J. González Rojí; Ganix Esnaola; Gregorio Iglesias. 2021. "The power flow and the wave energy flux at an operational wave farm: Findings from Mutriku, Bay of Biscay." Ocean Engineering 227, no. : 108654.
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.
Yu Zhou; Dezhi Ning; Lifen Chen; Gregorio Iglesias. Nonlinear hydrodynamic modeling of an offshore stationary multi-oscillating water column platform. Ocean Engineering 2021, 227, 108919 .
AMA StyleYu Zhou, Dezhi Ning, Lifen Chen, Gregorio Iglesias. Nonlinear hydrodynamic modeling of an offshore stationary multi-oscillating water column platform. Ocean Engineering. 2021; 227 ():108919.
Chicago/Turabian StyleYu Zhou; Dezhi Ning; Lifen Chen; Gregorio Iglesias. 2021. "Nonlinear hydrodynamic modeling of an offshore stationary multi-oscillating water column platform." Ocean Engineering 227, no. : 108919.
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.
Iván López; Rodrigo Carballo; David Fouz; Gregorio Iglesias. Design Selection and Geometry in OWC Wave Energy Converters for Performance. Energies 2021, 14, 1707 .
AMA StyleIván López, Rodrigo Carballo, David Fouz, Gregorio Iglesias. Design Selection and Geometry in OWC Wave Energy Converters for Performance. Energies. 2021; 14 (6):1707.
Chicago/Turabian StyleIván López; Rodrigo Carballo; David Fouz; Gregorio Iglesias. 2021. "Design Selection and Geometry in OWC Wave Energy Converters for Performance." Energies 14, no. 6: 1707.
In this study, based on 55 years’ worth of high-resolution simulated wave data using numerical modeling off the southern coasts of China, intra-annual and decadal variations of the wave climate and wave energy were evaluated. The results show that it is important to consider a sufficiently long time period for wave energy assessment to take into account the changing climate. The high-resolution wave dataset enabled the quantitative analysis in both nearshore and offshore, and the quantitative analysis was performed in two phases: First, using two different approaches. i.e., “Climate-dependent Sustainability Index” and “Wave Exploitability Index”, the wave power and its short and long-term changes were considered to prioritize the candidate stations for further assessment. Then, a modified “Multi-Criteria Approach” consisting of both sea state and Wave Energy Converters (WECs) was applied to determine the most suitable combination of WEC and location in the domain, which is Wave Dragon in the eastern parts of the domain with the energy production of around 92,000 MWh for a single device. The results provide the quantitative analysis for different scenarios of development plans in the study area on the selection of appropriate location and technology.
Bahareh Kamranzad; Pengzhi Lin; Gregorio Iglesias. Combining methodologies on the impact of inter and intra-annual variation of wave energy on selection of suitable location and technology. Renewable Energy 2021, 172, 697 -713.
AMA StyleBahareh Kamranzad, Pengzhi Lin, Gregorio Iglesias. Combining methodologies on the impact of inter and intra-annual variation of wave energy on selection of suitable location and technology. Renewable Energy. 2021; 172 ():697-713.
Chicago/Turabian StyleBahareh Kamranzad; Pengzhi Lin; Gregorio Iglesias. 2021. "Combining methodologies on the impact of inter and intra-annual variation of wave energy on selection of suitable location and technology." Renewable Energy 172, no. : 697-713.
The WaveCat is a moored Wave Energy Converter design which uses wave overtopping discharge into a variable v-shaped hull, to generate electricity through low head turbines. Physical model tests of WaveCat WEC were carried out to determine the device reflection, transmission, absorption and capture coefficients based on selected wave conditions. The model scale was 1:30, with hulls of 3 m in length, 0.4 m in height and a freeboard of 0.2 m. Wave gauges monitored the surface elevation at discrete points around the experimental area, and level sensors and flowmeters recorded the amount of water captured and released by the model. Random waves of significant wave height between 0.03 m and 0.12 m and peak wave periods of 0.91 s to 2.37 s at model scale were tested. The wedge angle of the device was set to 60°. A reflection analysis was carried out using a revised three probe method and spectral analysis of the surface elevation to determine the incident, reflected and transmitted energy. The results show that the reflection coefficient is highest (0.79) at low significant wave height and low peak wave period, the transmission coefficient is highest (0.98) at low significant wave height and high peak wave period, and absorption coefficient is highest (0.78) when significant wave height is high and peak wave period is low. The model also shows the highest Capture Width Ratio (0.015) at wavelengths on the order of model length. The results have particular implications for wave energy conversion prediction potential using this design of device.
James Allen; Gregorio Iglesias; Deborah Greaves; Jon Miles. Physical Modelling of the Effect on the Wave Field of the WaveCat Wave Energy Converter. Journal of Marine Science and Engineering 2021, 9, 309 .
AMA StyleJames Allen, Gregorio Iglesias, Deborah Greaves, Jon Miles. Physical Modelling of the Effect on the Wave Field of the WaveCat Wave Energy Converter. Journal of Marine Science and Engineering. 2021; 9 (3):309.
Chicago/Turabian StyleJames Allen; Gregorio Iglesias; Deborah Greaves; Jon Miles. 2021. "Physical Modelling of the Effect on the Wave Field of the WaveCat Wave Energy Converter." Journal of Marine Science and Engineering 9, no. 3: 309.
Wind energy is a fundamental pillar of the energy mix in Europe – hence the need for understanding the evolution of the wind energy resource under climate change. For this purpose, near-, mid- and long-term wind speed projections from 18 global climate models are considered and a multi-model ensemble is constructed with the ones found to best reproduce past-present conditions. The evolution and temporal variability of wind power is investigated considering different climate change scenarios through the novel Shared Socioeconomic Pathways (SSPs). More specifically, two SSPs are considered, each corresponding to its own socio-economic and political environment and, therefore, its own level of greenhouse emissions: SSP5-8.5 (highest emissions scenario) and SSP2-4.5 (intermediate emissions scenario). Both scenarios lead to a significant reduction (up to 35%) in wind power density in northern Continental Europe and the Central Mediterranean, and an increase of similar magnitude in West Finland. Over the Atlantic Ocean, Ireland and Britain the resource is also projected to decrease significantly. In other regions, however, the general trend (positive or negative) depends on the SSP scenario. This is the case, notably, of Central Europe, with considerable growth in SSP2-4.5 but some reduction in SSP5-8.5. Thus, in the intermediate emissions scenario (SSP2-4.5) both growth and decline in wind power density are forecast, depending on the region. By contrast, in the highest emissions scenario (SSP5-8.5) the forecast is a general decrease, of the order of 15% overall, with an annual rate of change of approximately –0.2% and an increase in seasonal variability. These trends will affect the energy production of wind farms and, therefore, need to be accounted for in assessing wind power projects in Europe.
A. Martinez; G. Iglesias. Wind resource evolution in Europe under different scenarios of climate change characterised by the novel Shared Socioeconomic Pathways. Energy Conversion and Management 2021, 234, 113961 .
AMA StyleA. Martinez, G. Iglesias. Wind resource evolution in Europe under different scenarios of climate change characterised by the novel Shared Socioeconomic Pathways. Energy Conversion and Management. 2021; 234 ():113961.
Chicago/Turabian StyleA. Martinez; G. Iglesias. 2021. "Wind resource evolution in Europe under different scenarios of climate change characterised by the novel Shared Socioeconomic Pathways." Energy Conversion and Management 234, no. : 113961.
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.
AjabGul Majidi; Bilal Bingölbali; Adem Akpınar; Gregorio Iglesias; Halid Jafali. Downscaling wave energy converters for optimum performance in low-energy seas. Renewable Energy 2020, 168, 705 -722.
AMA StyleAjabGul Majidi, Bilal Bingölbali, Adem Akpınar, Gregorio Iglesias, Halid Jafali. Downscaling wave energy converters for optimum performance in low-energy seas. Renewable Energy. 2020; 168 ():705-722.
Chicago/Turabian StyleAjabGul Majidi; Bilal Bingölbali; Adem Akpınar; Gregorio Iglesias; Halid Jafali. 2020. "Downscaling wave energy converters for optimum performance in low-energy seas." Renewable Energy 168, no. : 705-722.
Coastal cliffs cover about 75% of the world's coastlines. Many of these cliffs suffer severe erosion problems, which are mainly caused by wave action and lead to important damages. The main objective of this work is to propose and apply a methodology to characterize and map wave exposure levels for the management of cliff coasts. The methodology proposed consists of a number of steps. First, a statistical characterization of the wave climate in deep water is performed. Second, relevant sea states are propagated towards the cliff by means of a numerical model. Then, the results are used to assess the distribution of significant wave heights and wave power along the cliff toe. Finally, four exposure levels are defined based on the wave power values at the cliff, and exposure zones are mapped accordingly along the cliff. This approach is illustrated with a case study – the Catedrales Cliffs and Beach, a tourism hotspot in Galicia (NW Spain) where erosion caused loss of human life. We find that exposure levels are primarily influenced by the nearshore bed morphology, which controls wave refraction, shoaling and breaking, as well as by the geometry and orientation of the cliff, with some parts more exposed than others to the prevailing wave direction. On the islets off the cliff the windward faces have a greater level of exposure, since the leeward faces are protected by the islets themselves and lower water depths. The rocky outcrops that occur at the cliff toe in some sections act as emerged (submerged) breakwaters under low (high) tide conditions, dissipating wave power and thus reducing wave exposure. The methodology proposed in this work enables coastal managers to prevent the personal and material damages derived from cliff erosion by focusing remedial measures where they are most needed.
Rafael J. Bergillos; Cristobal Rodriguez-Delgado; Luis Medina; Gregorio Iglesias. Coastal cliff exposure and management. Ocean & Coastal Management 2020, 198, 105387 .
AMA StyleRafael J. Bergillos, Cristobal Rodriguez-Delgado, Luis Medina, Gregorio Iglesias. Coastal cliff exposure and management. Ocean & Coastal Management. 2020; 198 ():105387.
Chicago/Turabian StyleRafael J. Bergillos; Cristobal Rodriguez-Delgado; Luis Medina; Gregorio Iglesias. 2020. "Coastal cliff exposure and management." Ocean & Coastal Management 198, no. : 105387.
The selection of areas for wave energy development requires a thorough characterisation of the resource. For all its importance, wave power should not be the only criterion, and overly emphasising its role to the detriment of other aspects may mislead developers to the wrong areas. In this work, a new approach is presented based on a combination of two elements: the Wave Exploitability Index (WEI), defined ad hoc, and a classification of the resource based on mean wave power. These elements are applied at a global scale using the ERA-5 database, which spans the period 1979–2019. The highest WEI values (0.14–0.22) are found to occur in the Tropics and mid-latitudes, which highlights their potential for wave energy exploitation. The lowest WEI values (below 0.06) are located in (semi)-enclosed seas, such as the Mediterranean Sea or the Gulf of Mexico. As regards the classification of the resource, Classes IV and V, with mean wave power over 40 kWm−1, occur in areas which have aroused great interest but which often do not have high WEI values due to the resource variability (e.g., Western Europe); these areas are hardly ideal from the resource standpoint. Class I (below 10 kWm−1), typical of enclosed seas, is of little interest. Finally, Classes II and III (10–40 kWm−1) occur in areas open to the ocean in the lower and lower-middle latitudes (e.g., Chile, SW Australia); they present the highest WEI values, thus showing great potential, and have received scant attention so far.
A. Martinez; G. Iglesias. Wave exploitability index and wave resource classification. Renewable and Sustainable Energy Reviews 2020, 134, 110393 .
AMA StyleA. Martinez, G. Iglesias. Wave exploitability index and wave resource classification. Renewable and Sustainable Energy Reviews. 2020; 134 ():110393.
Chicago/Turabian StyleA. Martinez; G. Iglesias. 2020. "Wave exploitability index and wave resource classification." Renewable and Sustainable Energy Reviews 134, no. : 110393.
Oscillating water column (OWC) devices and oscillating buoys (OBs) are two of the main types of wave energy converters (WECs). In this paper a hybrid oscillating water column-oscillating buoy wave energy converter is proposed, which we have named OWCOB. The oscillating buoy is hinged at the outer wall of the oscillating water column. As waves propagate through the OWCOB, the water column within the OWC chamber moves up and down, producing air flow to propel a turbine. Meanwhile, the oscillation of the OB drives a separate hydraulic system. To solve the wave diffraction and radiation problems of the OWCOB and investigate its energy capture performance, an analytical model is developed based on linear potential flow theory and the eigenfunction matching method. Assuming that the PTOs of the OWC and OB are both linear, the wave power extraction of the OWCOB is evaluated in the frequency domain. Of the two configurations considered, the OWCOB with the OWC opening waveward and the OB hinged leeward is found to have a broader primary frequency band of wave power capture compared to the OWCOB with the OWC opening and the OB on the same side. Further, a thorough sensitivity analysis of power capture is carried out considering the main design parameters (size and submergence of the OWC opening, distance between the OWC and the OB, OB hinge elevation, OB radius), which can form the basis of an optimization study for a particular wave climate. Importantly, we find that the OWCOB performs generally better than stand-alone OWCs and OBs, not least in terms of frequency bandwidth.
Lin Cui; Siming Zheng; Yongliang Zhang; Jon Miles; Gregorio Iglesias. Wave power extraction from a hybrid oscillating water column-oscillating buoy wave energy converter. Renewable and Sustainable Energy Reviews 2020, 135, 110234 .
AMA StyleLin Cui, Siming Zheng, Yongliang Zhang, Jon Miles, Gregorio Iglesias. Wave power extraction from a hybrid oscillating water column-oscillating buoy wave energy converter. Renewable and Sustainable Energy Reviews. 2020; 135 ():110234.
Chicago/Turabian StyleLin Cui; Siming Zheng; Yongliang Zhang; Jon Miles; Gregorio Iglesias. 2020. "Wave power extraction from a hybrid oscillating water column-oscillating buoy wave energy converter." Renewable and Sustainable Energy Reviews 135, no. : 110234.
To mitigate the effects of wind variability on power output, hybrid systems that combine offshore wind with other renewables are a promising option. In this work we explore the potential of combining offshore wind and solar power through a case study in Asturias (Spain)—a region where floating solutions are the only option for marine renewables due to the lack of shallow water areas, which renders bottom-fixed wind turbines inviable. Offshore wind and solar power resources and production are assessed based on high-resolution data and the technical specifications of commercial wind turbines and solar photovoltaic (PV) panels. Relative to a typical offshore wind farm, a combined offshore wind–solar farm is found to increase the capacity and the energy production per unit surface area by factors of ten and seven, respectively. In this manner, the utilization of the marine space is optimized. Moreover, the power output is significantly smoother. To quantify this benefit, a novel Power Smoothing (PS) index is introduced in this work. The PS index achieved by combining floating offshore wind and solar PV is found to be of up to 63%. Beyond the interest of hybrid systems in the case study, the advantages of combining floating wind and solar PV are extensible to other regions where marine renewable energies are being considered.
Mario López; Noel Rodríguez; Gregorio Iglesias. Combined Floating Offshore Wind and Solar PV. Journal of Marine Science and Engineering 2020, 8, 576 .
AMA StyleMario López, Noel Rodríguez, Gregorio Iglesias. Combined Floating Offshore Wind and Solar PV. Journal of Marine Science and Engineering. 2020; 8 (8):576.
Chicago/Turabian StyleMario López; Noel Rodríguez; Gregorio Iglesias. 2020. "Combined Floating Offshore Wind and Solar PV." Journal of Marine Science and Engineering 8, no. 8: 576.
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.
Rafael J. Bergillos; Cristobal Rodriguez-Delgado; Javier Cremades; Luis Medina; Gregorio Iglesias. Multi-criteria characterization and mapping of coastal cliff environments: A case study in NW Spain. Science of The Total Environment 2020, 746, 140942 .
AMA StyleRafael J. Bergillos, Cristobal Rodriguez-Delgado, Javier Cremades, Luis Medina, Gregorio Iglesias. Multi-criteria characterization and mapping of coastal cliff environments: A case study in NW Spain. Science of The Total Environment. 2020; 746 ():140942.
Chicago/Turabian StyleRafael J. Bergillos; Cristobal Rodriguez-Delgado; Javier Cremades; Luis Medina; Gregorio Iglesias. 2020. "Multi-criteria characterization and mapping of coastal cliff environments: A case study in NW Spain." Science of The Total Environment 746, no. : 140942.
Shipping water, the flow washing over and impacting the upper decks of ships and offshore structures, occurs frequently during their service life and often causes structural problems. For engineers to design safe floating structures subjected to shipping water it is essential to gain an in-depth understanding of its depth and flow field, and the resulting impact forces. In this work, Computational Fluid Dynamics (CFD) is applied to understand the physics of shipping water washing over a stepped platform. We find that the most accurate solutions are obtained with the k−ε turbulence closure. The hydrodynamic load generated by the shipping water is found to strongly depends on the kinematic energy of the water hitting the step. It is shown that with smaller values of the freeboard a more dynamic flow ensues, with a stronger vortex and larger velocity gradient resulting in deeper shipping water and a larger impact force.
Danial Khojasteh; Sasan Tavakoli; Abbas Dashtimanesh; Azam Dolatshah; Luofeng Huang; William Glamore; Mahmood Sadat-Noori; Gregorio Iglesias. Numerical analysis of shipping water impacting a step structure. Ocean Engineering 2020, 209, 107517 .
AMA StyleDanial Khojasteh, Sasan Tavakoli, Abbas Dashtimanesh, Azam Dolatshah, Luofeng Huang, William Glamore, Mahmood Sadat-Noori, Gregorio Iglesias. Numerical analysis of shipping water impacting a step structure. Ocean Engineering. 2020; 209 ():107517.
Chicago/Turabian StyleDanial Khojasteh; Sasan Tavakoli; Abbas Dashtimanesh; Azam Dolatshah; Luofeng Huang; William Glamore; Mahmood Sadat-Noori; Gregorio Iglesias. 2020. "Numerical analysis of shipping water impacting a step structure." Ocean Engineering 209, no. : 107517.
In this paper we consider hybrid wave farms, in which different types of WEC are combined, through a case study involving oscillating water columns (OWCs) and point-absorbers (PAs). A new parameter, called “H-factor”, is introduced to compare hybrid (multi-type) and conventional (single-type) wave farms in terms of wave power capture. We develop an ad hoc semi-analytical model to calculate the H-factor in a computationally efficient manner, and apply it to investigate how the H-factor and, consequently, the power capture, depend on: (i) the spacing and layout of the WECs, (ii) the type of WEC technology, and (iii) the wave conditions. We discuss the influence of these factors and, in the process, show that the H-factor is a valuable decision-aid tool. For specified wave conditions and layout limitations, a conventional wave farm may not be the most efficient option as a result of a destructive array effect, whereas a hybrid farm can be more efficient if a constructive hybrid effect occurs (if the H-factor value is above unity). This constructive hybrid effect can even overcome the destructive array effect for specified cases, demonstrating the potential advantage of hybrid wave farms relative to conventional wave farms.
Siming Zheng; Yongliang Zhang; Gregorio Iglesias. Power capture performance of hybrid wave farms combining different wave energy conversion technologies: The H-factor. Energy 2020, 204, 117920 .
AMA StyleSiming Zheng, Yongliang Zhang, Gregorio Iglesias. Power capture performance of hybrid wave farms combining different wave energy conversion technologies: The H-factor. Energy. 2020; 204 ():117920.
Chicago/Turabian StyleSiming Zheng; Yongliang Zhang; Gregorio Iglesias. 2020. "Power capture performance of hybrid wave farms combining different wave energy conversion technologies: The H-factor." Energy 204, no. : 117920.
The operativity of the transport infrastructures and urban developments protected by coastal structures is conditioned by flooding events and the resulting wave overtopping. This work presents a methodology to assess the operational conditions of infrastructures located in coastal areas based on the combination of advanced statistical techniques, laboratory experiments and state-of-the-art numerical models properly validated. It is applied to a case study in the SW coast of England, the railway seawall at Dawlish, which was subjected to recurrent wave overtopping until its dramatic collapse in February 2014. To quantify the increase in overtopping discharges with wave height and water level, we define an ad hoc variable, the effective overtopping forcing, which explains 98% of the variability of the overtopping discharge. The return periods associated to the operational thresholds for coastal structures protecting people and railways are also obtained. The proposed methodology enables the assessment of the overtopping discharge induced by a given sea state and, thus, check if a coastal infrastructure will be or not operational under any expected marine condition. This innovative methodology can also be used to analyse the flooding event consequences on urban areas protected by coastal infrastructures.
Cristobal Rodriguez-Delgado; Rafael J. Bergillos; Gregorio Iglesias. Coastal infrastructure operativity against flooding – A methodology. Science of The Total Environment 2020, 719, 137452 .
AMA StyleCristobal Rodriguez-Delgado, Rafael J. Bergillos, Gregorio Iglesias. Coastal infrastructure operativity against flooding – A methodology. Science of The Total Environment. 2020; 719 ():137452.
Chicago/Turabian StyleCristobal Rodriguez-Delgado; Rafael J. Bergillos; Gregorio Iglesias. 2020. "Coastal infrastructure operativity against flooding – A methodology." Science of The Total Environment 719, no. : 137452.
The intra-annual variability in the wave resource is often disregarded when analysing the performance of wave energy converters (WECs), despite the fact that this variability is substantial in the majority of the areas of interest for the development of wave energy. The objective of this work is to analyse and quantify the intra-annual variability in the performance of oscillating water column (OWC) WECs through a case study in Galicia (NW Spain). To this end a three-step methodology which combines numerical and experimental modelling is followed: (i) intra-annual wave energy resource matrices are determined numerically through a high-resolution procedure; (ii) efficiency matrices of the device are determined by means of physical modelling, considering the influence of air compressibility and different turbine specifications represented through different values of turbine-induced damping; and (iii) finally, intra-annual energy capture matrices are calculated by combining the resource and efficiency matrices. It is found that the intra-annual variability in the energy capture of an OWC converter is significant, over 20% in the case study considered, albeit slightly smaller than that of the wave energy resource itself. The turbine-induced damping exerts a modulating effect over the variability in the intra-annual captured energy. Furthermore, the optimum damping which maximises the performance of the OWC converter varies from month to month.
I. López; R. Carballo; G. Iglesias. Intra-annual variability in the performance of an oscillating water column wave energy converter. Energy Conversion and Management 2020, 207, 112536 .
AMA StyleI. López, R. Carballo, G. Iglesias. Intra-annual variability in the performance of an oscillating water column wave energy converter. Energy Conversion and Management. 2020; 207 ():112536.
Chicago/Turabian StyleI. López; R. Carballo; G. Iglesias. 2020. "Intra-annual variability in the performance of an oscillating water column wave energy converter." Energy Conversion and Management 207, no. : 112536.
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.
Siming Zheng; Yongliang Zhang; Gregorio Iglesias. Concept and performance of a novel wave energy converter: Variable Aperture Point-Absorber (VAPA). Renewable Energy 2020, 153, 681 -700.
AMA StyleSiming Zheng, Yongliang Zhang, Gregorio Iglesias. Concept and performance of a novel wave energy converter: Variable Aperture Point-Absorber (VAPA). Renewable Energy. 2020; 153 ():681-700.
Chicago/Turabian StyleSiming Zheng; Yongliang Zhang; Gregorio Iglesias. 2020. "Concept and performance of a novel wave energy converter: Variable Aperture Point-Absorber (VAPA)." Renewable Energy 153, no. : 681-700.