Displays

Understanding and classification of the global wave energy resource is vital to facilitate wave energy converter technology development and global roll-out of this promising renewable energy technology. To date, many wave energy converters have been developed based on Northern European wave climates; these are not representative of wave climates worldwide and may not be the best for large scale energy extraction. Classification of resources will highlight alternative wave resource types that may prove fruitful for deployment of future technologies; equally it will enable existing technology to define regions worthy of site exploration. Therefore k-means clustering is used here to classify the global resource from a data-driven, device agnostic perspective.

Parameters relevant to energy extraction (significant wave height, peak wave period, extreme wave height, spectral and directional properties) were extracted from the ECMWF ERA5 reanalysis dataset and used to split the global resource into 6 classes. Only areas within 3 degrees of land (feasible energy transport to user) were considered. The 6 classes returned by the analysis consisted of: 1) low energy high variability areas in enclosed seas; 2) low energy moderate variability areas in semi-enclosed seas and sheltered ocean coasts; 3) moderate energy areas, largely on eastern oceanic coastlines and influenced by local storm activity; 4) moderate energy areas primarily influenced by long period swell and largely on western oceanic coastlines; 5) higher energy areas, with variable conditions, primarily in the northern hemisphere; 6) highest energy areas, primarily on the tips of continents in the southern hemisphere. Consideration of device power matrices show that existing devices only perform well in classes 5 and 6, despite these areas having limited global coverage, which suggests devices should be developed for lower energy classes.

To refine global roll-out planning for existing devices, based on a request from a wave energy converter developer, a second classification is currently being developed with two additional constraints on the areas tested. These constraints are excluding any areas with a mean wave power of less than 15 kW/m (an often-used value for the lower power limit for commercial viability) and a maintenance constraint whereby wave heights must drop below 3m for a minimum of 48hrs per month. These newer results will be presented at the annual assembly and contrasted with our more device agnostic classification.

How to cite: Fairley, I., Lewis, M., Robertson, B., Hemer, M., Masters, I., Horrillo-Caraballo, J., Karunarathna, H., and Reeve, D.: Global wave resource classification and application to marine energy deployments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8135, https://doi.org/10.5194/egusphere-egu2020-8135, 2020.

A novel wave-energy device design [1,2] will be presented based on the following features: (i) an electro-magnetic generator based on cylindrical magnets moving through induction wires around a cylindrical tube, like in the IP wave-buoy, (ii) a convergence in a breakwater to amplify the incoming waves, like in the TapChan device, and (iii) a wave-activated buoy with magnets attached, like in the Berkeley wedge, constrained to move in a slight arc or in a rectilinear manner. Its workings will be demonstrated in a first, operating proof-of-principle. A monolithic mathematical model is established by coupling the three variational principles for the hydro-dynamic wave motion, using the potential-flow approximation, the constrained wave-activated buoy motion, and the electro-magnetic generator together into one grand variational principle. The resistive losses in the electrical circuit and the energy harvested in the (parallel LED) loads are subsequently added to the dynamics. After linearisation of the resulting full 3D nonlinear model around a state of rest and application of the shallow-water approximation, we discretize the linear dynamics in a compatible, i.e. geometrically consistent, manner using a finite-element approach in space and symplectic integrators in time. Preliminary numerical modelling and simple optimization will be shown and these are promising. Finally, further optimisation of the device for different geometries and for a given wave-climate as well as alternative designs will be discussed.

References
[1] O. Bokhove, A. Kalogirou, W. Zweers 2019: From bore-soliton-splash to a new wave-to-wire wave-energy model. Water Waves 1.
[2] O. Bokhove, A. Kalgirou, D. Henry, G. Thomas 2019: A novel rogue-wave-energy device with wave amplification and induction actuator. In: 13th European Wave and Tidal Energy Conference 2019, Napoli, Italy.

How to cite: Bokhove, O.: Rogue-wave-energy: wave-to-wire mathematical modelling , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8769, https://doi.org/10.5194/egusphere-egu2020-8769, 2020.

Over the last decade, a lot of work has been performed to develop wind-wave potential prediction techniques that, effectively and within realistic time-frames, map the local climatology of a specific region. The combination of local and satellite climatic data, has been used, for good reason, in many wind-related-projects as it is linking mesoscale meteorology, with microclimatic weather phenomena. This way the driving geostrophic winds are effectively taken into account for the estimation of low altitude wind distribution.

Using dynamical downscaling methodology, a nesting technique with 1/3 ratio is applied to downscale the raw computational grid of the satellite input data to a finer 3 x 3 Km results grid. This way, higher computational accuracy is achieved over the investigated regions, thus revealing finer wind scales phenomena. For the computational simulations, two different models have been used in order to generate meteo-climate parameters suitable for sea-wave results calculation: a dynamical downscaling model (at regional scale), and a wave model. The first model performs the downscaling of the satellite meteorological data in higher resolution grids for a wide area of the Aegean Sea. The produced fine grid output drives the later wave model in order to estimate the significant wave height and period over the areas of interest. The produced results will later be used in conjunction with novel geostatistical techniques to estimate the wave energy potential distribution in the Aegean and Ionian Sea.

Acknowledgements

This project has received funding from the Hellenic Foundation for Research and Innovation (HFRI) and the General Secretariat for Research and Technology (GSRT), under grant agreement No [1237].

How to cite: Kozyrakis, G. V., Spanoudaki, K., and Varouchakis, E. A.: Dynamical Downscaling of Wind Surface Forcing with Application to the Wave Potential Estimation in the Aegean Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4058, https://doi.org/10.5194/egusphere-egu2020-4058, 2020.

Tidal turbine array was optimized to increase the power production in order to improve the commercial competitivity of tidal current energy with other forms of energy generation. Due to duct-effects, the power performance of turbines in the staggered layout was better than that of the aligned layout. However, shear layer with enhanced turbulence occurred between the duct zone and isolated wake zone downstream, which had influence on the performance stability and increased the fatigue failure of tidal turbines. The study conducted a series of laboratory experiments to investigate the duct-effects of tidal turbines located in multi-row array with staggered layout. The turbine rotor was represented by porous disc. The flow thrust and time-varying velocity were measured using micro strain gauge and acoustic doppler velometer, respectively. Results showed that the flow was accelerated between turbines with the increment around 20% behind the first row, while the duct-effects were weakened as distance increased downstream. The shear-induced turbulence was enlarged by the duct-effect when it diffused mainly towards individual wake zone at the initial stage. As the turbulence filled the whole individual wake zones, it diffused rapidly to lateral sides and jointed together, and the turbulence intensity across the array wake was significantly higher than that of the free flow. Correspondingly, the performance of turbine rotor located downstream was improved limitedly by the duct-effects, and the stability was reduced clearly. It indicated that the advantage of the duct-effect induced in the staggered layout was limited in the near wake as the lateral interval between two turbine centres was 2 times of rotor diameter.

Keywords: Turbine rotor array; Staggered layout; Duct-effects; Turbine performance; Shear-induced turbulence

How to cite: Chen, Y., Lin, B., and Guo, J.: Experimental study of the duct-effects of the tidal current turbines in multi-row-staggered layout, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1604, https://doi.org/10.5194/egusphere-egu2020-1604, 2020.

Tidal-stream energy research has often focused on the applicability of the resource to large electricity distribution networks, or reducing costs so it can compete with other renewables (such as offshore wind). Here we explore how tidal electricity may be worth the additional cost, as the quality and predictability of the electricity could be advantageous – especially to remote “off-grid” communities and industry.

The regular motion from astronomical forces allows the tide to be predicted far into the future, and therefore idealised scenarios of phasing tidal electricity supply to demand can be explored. A normalised tidal-stream turbine power curve, developed from published data on 15 devices, was developed. Tidal harmonics of a region, based on ocean model output, were used in conjunction with this normalised tidal-stream power curve, and predictions of yield and the timing of electricity supply were made. Such analysis allows the type and number of turbines needed for a specific community requirement, as well as a resource-led tidal turbine optimisation for a region. For example, with a simple M2 tide (12.42hour period) of 2m/s peak flow, which represents mean flow conditions, a rated turbine speed of 1.8m/s gives the highest yield-density of all likely turbine configurations (i.e. calculated from power density and so ignores turbine diameter), and with a 41% Capacity Factor. Furthermore, as tidal current and power predictions can be made, we explore the battery size needed for a given electricity demand timeseries (e.g. baseload, or offshore aquaculture). Our analysis finds tidal-stream energy could be much more useful than other forms of renewable energy to off-grid communities due to the predictability and persistence of the electricity supply. Moreover, our standardised power curve method will facilitate technical tidal energy resource assessment for any region.

How to cite: Lewis, M., Maskell, J., Coles, D., Ridgill, M., and Neill, S.: The value of tidal-stream energy resource to off-grid communities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2747, https://doi.org/10.5194/egusphere-egu2020-2747, 2020.

Scotland has ambitious decarbonisation and climate change objectives, such as generating 100% of gross annual electricity consumption from renewable sources by 2020. Tidal stream energy is a renewable and predictable source of energy that converts the kinetic energy within tidal currents, into electricity, using a hydrokinetic device such as a horizontal axis turbine. However, economically viable tidal stream development is currently confined to areas of exceptionally high current speeds, and this can severely limit the choice of area. If the speed threshold required for an economically viable tidal site can be lowered then the number of potential sites could increase dramatically.

It is well known that macro-algae (e.g. kelp) grow in perspective tidal energy sites, as they requiring similar water depths and current speeds. Furthermore, kelp is known to grow in dense patches, reaching from the sea-floor to the ocean surface, and can modify tidal current speeds. Indeed, observations have shown that “kelp forests” can locally reduce current speeds by a third (Jackson and Winant, 1983). This local reduction in current speed will cause an increase in speed elsewhere, in order to conserve mass. Therefore, we hypothesise that by adding a kelp forest in the vicinity of a tidal channel, the current speed and tidal stream resource could be increased sufficiently for the site to become economical.

A three dimensional finite volume hydrodynamic model has been used to model an idealised tidal channel. The drag imposed by kelp was theoretically calculated and represented in the model as a sub grid scale momentum sink. The changes to the current speed resulting from this bio-optimisation of the tidal channel were investigated and show that the current speed in the centre of the channel can be increased. Kelp were then added to a previously developed hydrodynamic model of the Pentland Firth and Orkney Waters to investigate how such bio-optimisation could influence an area currently being considered for substantial tidal stream development. The changes on both the areas of suitable tidal stream development and the power yield are investigated.

Acknowledgements

Matthew Lewis wishes to thank Aaron Owen and Ade Fewings at SuperComputingWales, and Fearghal O'Donncha at IBM-research Ireland for fruitful discussions, and the METRIC grant, EP/R034664/1.

References

Jackson, G. A. and Winant, C. D. (1983). Effect of a kelp forest on coastal currents. Continental Shelf Research, 2(1), pp.75-80.

How to cite: O'Hara Murray, R. and Lewis, M.: Bio-optimisation of a tidal channel, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19231, https://doi.org/10.5194/egusphere-egu2020-19231, 2020.

The Rance tidal power station (located on the Brittany coast of Northern France), was opened in 1966 as the world’s first and largest tidal power station, with peak output capacity of 240 Megawatts. It is currently the second world’s largest tidal power installation after the Sihwa Lake Tidal power station (South Korea). The power plant is located at the mouth of a small steep-sided ria, with a maximum perigean spring tidal range of 13.5 m and an average fluvial discharge of 7 m³/s. The dam is 750 m long and the tidal basin measures 22.5 km². Despite a well-known effect of the plant on the damping of estuarine water levels, little attention has been given to the consequences of the dam in the estuarine environment in terms of hydrodynamics, for instance, the propagation of the tidal wave and tidal currents along the estuary are still little understood. Moreover, net siltation has been reported by several observations, but there is no specific knowledge on the role of the plant on sedimentation. In this study, we analyze the impact of the tidal power station on tidal wave patterns and sediment dynamics in this particular man-engineered system. To this goal, a numerical model based on a two-dimensional depth-averaged approach is implemented to predict the tide propagation and tidal currents along the estuary accounting for the presence of the tidal power station. Three modelling scenarios were performed: the first considering the bathymetry of 1957 (before the plant’s construction), a second scenario considering the bathymetry of 2018 without the presence of the power station and a third scenario considering the bathymetry of 2018 with the power station. Preliminary results showed that, with and without the tidal power station, the upper estuary exhibits a flood dominant behavior, with longer duration of falling water than rising water, and conversely the lower estuary is ebb dominant with shorter duration of falling water than rising water. This analysis also revealed that the tidal power station might switch the flood dominance in the central estuary to ebb dominance. These findings imply a net seaward transport of both coarse and fine sediments in the lower estuary. Therefore, the tidal power station might have a considerable role in modulating the estuarine turbidity maximum and channels’ morphology. Finally, these results are compared with preliminary numerical simulations of suspended sediment transport to further quantify the impact of the tidal power plant on the dynamics of the estuarine turbidity maximum.

How to cite: Rtimi, R., Sottolichio, A., and Tassi, P.: The Rance tidal power station: a preliminary study of its impact on tidal patterns and sediments dynamics in the Rance estuary (France) from 1957 to 2018, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20649, https://doi.org/10.5194/egusphere-egu2020-20649, 2020.

The aim of this work is to analyse the potential impacts of tidal energy extraction on the marine environment. We wanted to put them in the broader context of the possibly greater and global ecological threat of climate change. Here, we present how very large (hypothetical) tidal stream arrays and a ''business as usual'' future climate scenario can change the hydrodynamics of a seasonally stratified shelf sea, and consequently modify ecosystem habitats and animals’ behaviour.

The Scottish Shelf Model, an unstructured grid three-dimensional ocean model, has been used to reproduce the present and the future state of the NW European continental shelf. While the marine biogeochemical model ERSEM (European Regional Seas Ecosystem Model) has been used to describe the corresponding biogeochemical conditions. Four scenarios have been modelled: present conditions and projected future climate in 2050, each with and without very large scale tidal stream arrays in Scottish Waters (UK). This allows us to evaluate the potential effect of climate change and large scale energy extraction on the hydrodynamics and biogeochemistry. We found that climate change and tidal energy extraction both act in the same direction, in terms of increasing stratification due to warming and reduced mixing, however, the effect of climate change is ten times larger. Additionally, the ecological costs and benefits of these contrasting pressures on mobile predator and prey marine species are evaluated using ecological statistical models.

How to cite: De Dominicis, M., Wolf, J., Sadykova, D., Scott, B., Sadykov, A., and O’Hara Murray, R.: Effects on hydrodynamics and ecological costs of climate change and tidal stream energy extraction in a shelf sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11619, https://doi.org/10.5194/egusphere-egu2020-11619, 2020.

The implications of climate change are becoming harder to ignore and highlight the need for increased renewable energy production.  Simultaneously, technological developments like larger turbines and floating foundations are improving our ability to harvest offshore wind energy as a renewable resource.  However, despite having an abundant offshore wind energy resource, Ireland is falling behind on its remit to reduce its carbon emissions as part of the European Union’s targets outlined by the 2030 Climate and Energy Framework.  Reducing this inaction is critically important and improvements to Irish renewable energy planning could also be adapted to other locations.  Here we present spatial data rasters created largely from public datasets that have been designed to improve initial planning and opportunities assessments for Irish offshore wind development.  These rasters include information on surficial sediment types, geomorphology, and slope, which are typically not included in preliminary offshore renewable energy assessments despite their importance to turbine foundation designs, scour protection measures, and cable routes.  Furthermore, these rasters allow fundamental predictions on potential benthic habitat changes to be included into site selection models, which could help avoid economically and/or environmentally costly development decisions.  We examine potential uses for these rasters within a multi-criteria decision analysis and discuss the implications of incorporating such geological data during early investigations. 

How to cite: Peters, J., O’Connell, R., Wheeler, A., Cummins, V., and Murphy, J.: Geological data incorporation into an opportunities model for Irish offshore wind energy to inform engineering considerations and habitat change potential, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8658, https://doi.org/10.5194/egusphere-egu2020-8658, 2020.

Cyprus' energy balance today depends to a large extent on imports of petroleum products for energy production. This has an impact on both the economy and the environment of the island. The contribution of renewable energy sources (RES) in Cyprus, although there is considerable potential, still remains limited. Specifically, renewable energy sources today account for less than 9% of the country's total gross energy consumption.

This paper contributes to the study of the off-shore wind power on the island, focusing on the creation of an integrated geospatial database for the study of wind characteristics on the coasts and offshore of Cyprus using measurements from meteorological stations, data from the European database with horizontal analysis 25x25 km, and 24-hour forecasts from the Open Skiron meteorological model in 5x5 km resolution.

The analysis take advantage of both wind measurement from meteorological stations in coastal Cyprus areas, as well as information on wind values from forecasting models and databases to record an initial reference distribution in space and time.

Acknowledgments:

This research is supported by the project  “Cross-Border Cooperation for Implementation of Maritime Spatial Planning” referred as “THAL-CHOR 2” and it is co-funded by the European Regional Development Fund (ERDF) and by national funds of Greece and Cyprus, under the Cooperation Programme “INTERREG V-A Greece-Cyprus 2014-2020”.

How to cite: Akylas, E., Gravanis, E., Nikolaidis, A., Panagiotou, C. F., Mettas, C., Kyriakidis, P., and Hadjimitsis, D.: Off-Shore wind potential in Cyprus: Towards an integrated representative geospatial database., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21656, https://doi.org/10.5194/egusphere-egu2020-21656, 2020.

The consciousness of global warming gradually transforms the energy dependency from fossil fuels to renewable energy resources such as waves, wind, solar, and geothermal heat. The flexible deployment range of floating offshore wind turbines makes this technology more popular in the offshore wind energy sector recently. However, this technique is still under development and the fluid-structure interaction (FSI) needs to be further investigated to improve the design of the floating wind turbine platform. Due to the significant evolvement of computer and numerical methods in recent years, computational fluid dynamics (CFD) has been widely applied to solve FSI problems. Grid morphing technique is commonly used to solve FSI problems, however, using this technique to deal with large body displacement problems will lead to large grid deformation and consequently induce numerical instabilities. In this study, overset grid was used to understand the interaction between fluid and floating structures to avoid calculation divergence due to excessive grid deformation. The open-source CFD solver was developed using OpenFOAM for offshore floating structures and the numerical wave tank was developed by integrating the overset grid Navier-Stokes solver, overInterDyMFoam, with a wave generation library in OpenFOAM. The accuracy of the developed model was validated using a series of benchmark tests including heave decay test, roll decay test, and a floating structure subject to different wave conditions. The influences of the overlapping zone properties on the model accuracy were discussed and the results obtained by the current study and those computed by dynamic grid solver were compared. Overall, the computed results presented in this study show good agreement with the results of the benchmark tests.

How to cite: Li, S.-Y. and Hsiao, S.-C.: Numerical Analysis of Floating Offshore Structures Using Overset Method, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10178, https://doi.org/10.5194/egusphere-egu2020-10178, 2020.

The global wind energy has developed over 30 years. However, as the offshore wind power installed within 50 to 60 meters of water depth is gradually saturated. Offshore wind power installations are progressively shifting from nearshore to offshore. With the increment of water depth, the difficulties and the cost of the offshore wind power installations are also increased, makes the fixed-bottom type of structures less favorable in deep water areas and accelerate the development of the floating type offshore wind platforms. Floating offshore wind platforms can be classified into main three types: spar buoy, semi-submersible, tension-leg platform (TLP) according to reaching stability. In addition to these types, a barge-type floating platform, a new design concept, can reduce the dynamic motion of the platform by its moon pool. In this study, the hydrodynamic performance of a floating barge platform with a moon pool supports an NREL 5MW wind turbine and with a mooring system at a water depth of 50 meters was investigated. This numerical simulation was applied to analyze the hydrodynamic performance of the platform using ANSYS Aqwa software. Experimental tests in a flat water tank were conducted at National Cheng Kung University, Tainan Hydraulics Laboratory (THL). The model is a 1:64 scaled barge platform and the turbine is scaled down from the NREL 5MW. Three tests of the platform were conducted, including the free decay test, regular wave test, irregular wave test with wind operation and parking. The experimental data was analyzed to get the natural period through the free decay test. The numerical simulation results were compared with the 1:64 scaled experiment to observe the motions and Response Amplitude Operator (RAO) of surge, heave and pitch motions on the barge platform with moon pool. The floating barge platform, designed in this study, will be tested in the open sea to ensure it can withstand - extreme wave conditions such as typhoons.

How to cite: Yang, W.-H., Yang, R.-Y., and Chang, T.-C.: Experimental and numerical study of the stability of barge-type floating offshore wind turbine platform, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10179, https://doi.org/10.5194/egusphere-egu2020-10179, 2020.

In this paper, the commercial software Orcaflex is used to simulate the motion behavior of the OC4 floating platform, and the floater stability and mooring line tension after the mooring system failure. In the time domain analysis, the discussion is divided into three phases—the first phase (before the tether failure), the second phase (before the tether failure, before reaching the new steady-state), and the third phase (after reaching the new steady-state). The motion characteristics and tension values at different stages were observed. In this study, only a 50-year return period wave condition is used as an input condition and simulating 11 different incident wind and wave directions. The numerical results are presented in the trajectory map and the table. About the tension of the mooring line, after the mooring system fails, it is notable that the mooring line tension will first decrease and then increase slightly above the initial tension value. In other words, the mooring system may survive after the failure of one mooring line and got a new balance of it. However, the tension amplitude will be higher than the first stage in the new balance and it will likely increase the risk of mooring line fatigue.

How to cite: Chuang, T.-C., Yang, W.-H., Chen, Y.-H., and Yang, R.-Y.: The Dynamic Motion of the OC4 Floating Turbine with Different Incident Wave and Wind Directions in a Mooring System Failure Condition in Numerical Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12098, https://doi.org/10.5194/egusphere-egu2020-12098, 2020.