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This paper presents the principles of developing an electromechanical emulator based on an original hybridization concept of a wind and tidal power system. Wind and tidal horizontal axis turbines showcase functional similarities and electromechanical coupling possibility. Tidal concepts are very close to those of wind power. Tidal turbine technology should thus reach maturity more quickly because it is possible for it to rely on a certain number of reliable and proven techniques developed for wind power. The proposed hybrid wind – tidal turbine system is electromechanically coupled on the axis of rotation of a single and common electric generator. An experimental simulation of the hybrid wind-tidal turbine system was carried out, using a developed architecture of an emulator system. The results are both numerical simulations carried out in the MATLAB/Simulink environment and tests obtained employing real-time emulators. [ABSTRACT FROM AUTHOR]

Recommended practice for quantifying the energy resource at a tidal energy site requires the use of multiple instruments deployed across the site. However, the instruments used work by emitting an acoustic pulse and instruments working at the same time have the potential to interfere with each other through a process known as ’cross-talk’. It is important to understand the impact of cross-talk on measurements and how this can be managed and through data processing or suitable positioning of devices. The ReDAPT project conducted a measurement campaign using two Acoustic Doppler Current Profilers (ADCPs) placed upstream of an operational tidal turbine. This aimed to assess the ’in-line’ instrument placement guidelines from IEC 62600-200 for Power Performance Assessment (PPA) in real-world conditions. Consequently, the results within hold potential to support arguments for expanding these zones or adjusting their general dimensions. Despite adhering to industry standards and best practices to eliminate unreliable data in the Quality Control (QC) checks, in both concurrently measuring ADCPs at different time stamps in approximately 15 % of the returned data. This work identified for the first time interference throughout the campaign and quantified subsequent impact on estimates. A method to remove data anomalies caused by interference between closely positioned ADCPs has been developed and demonstrated, resulting in a 7 % variation in estimated Annual Energy Production (AEP). The algorithm effectively removed approximately 90 % of the corrupted measurements. Moving forward, multi-sensor deployments could use the algorithm described to double-check for interference within the data sets, although care should be taken to avoid this by choosing a suitable layout for deployment.

Commercial scale tidal stream turbines (TST) are expected to be deployed in shallow water where the depth varies from 1.5 to 3 turbine diameters. In this study, numerical simulation is conducted at realistic hydrodynamic conditions of potential tidal sites using the stationary actuator disc method at ambient turbulence varying from 5% to 20%, a range of rotor realistic rotor thrust coefficient from 0.64 to 0.98 and a rotor-diameter-to-depth ratio of 20% to 60%. The result shows that the TST wake is affected by the rotor-diameter-to-depth ratio, ambient turbulence, and thrust coefficient. The new empirical model is in accordance with the numerical simulation of a full-scale turbine and is validated with the TST experiment at different rotor-diameter-to-depth ratios with reasonable results in the far wake. This low computational model can benefit the investigation of tidal turbine parks at different configurations where the far wake is pertinent. [ABSTRACT FROM AUTHOR]

The tidal currents of the Gulf of Morbihan reach up to 3.5 m/s within a narrow (200 m large) channel connecting the sea to the inner part of the gulf. In this study, a Telemac2D model validated with a large dataset of field measurements is used to assess the resources of the gulf. The results show that two sites have the potential to host up to 48 turbines (diameter of 8 m). If the entire width of the channel is occupied by turbines, significant increases in current speed are expected to occur on each side of the main channel. Simulations also show that flow changes differ between ebbing and flooding tides. During ebbing tide, the changes are limited in amplitude and remain localised within the channel. During flooding tide, the changes are more significant, especially in the vicinity of one of the two sites where the water passing through the site is flushed into a large and shallow basin. In this area, energy extraction significantly modifies the spatial distribution of the current velocities. We consider different scenarios of tidal energy extraction. The results show that flow perturbation can be significantly reduced using a lower density of turbines, that extracting tidal energy at one site slightly reduces the resource of the other, and that the deployment of two turbines (testing conditions) has a negligible effect on ambient current speeds. [ABSTRACT FROM AUTHOR]

This paper investigates a multi-objective optimal energy planning strategy for a hub, incorporating renewable and non-renewable resources, like PV, tidal turbine, fuel-cell, CHP, boiler, micro-turbine, reactor, reformer, electrolyzer, and energy storage by utilizing the time of use program (TOU). In this strategy, tidal turbine, fuel-cell, and reformer technologies are considered novel technologies that simultaneously reduce the proposed hub’s cost and pollution. The hub’s total cost and pollution are considered objective functions. To make the results more realistic, characteristics of the tidal turbine are investigated by utilizing the manufactory’s company information. The problem is then modeled as real mixed integer programming (RMIP) and is solved in GAMS software using a CPLEX solver. Epsilon constraints method and fuzzy satisfying approach are used to select the optimal solution based on the proposed model. Finally, a sensitivity analysis is performed to assess the effective parameters that affect the planning’s results. The results show that the overall pollution is reduced by about 9% by assuming the proposed planning, and the total profit is increased by about 30%.

The next stage of development of the tidal stream industry will see a focus on the deployment of tidal turbines in arrays of increasing device numbers and rated power. Successful array development requires a thorough understanding of the resource within potential deployment sites. This is predictable in terms of flow speeds, based upon tidal constituents. However, the operating environment for the turbine is more complex than the turbine experiencing a uniform flow, with turbulence, shear and wave conditions all affecting the loading on the turbine components. This study establishes the accuracy with which several alternative modelling tools predict the resource characteristics which define unsteady loading—velocity shear, turbulence and waves—and assesses the impact of the model choice on predicted damage equivalent loads. In addition, the predictions of turbulence are compared to a higher fidelity model and the occurrence of flow speeds to a Delft3D model for currents and waves. These models have been run for a specific tidal site, the Raz Blanchard, one of the major tidal stream sites in European waters. The measured resource and predicted loading are established using data collected in a recent deployment of acoustic Doppler current profilers (ADCPs) as part of the Interreg TIGER project. The conditions are measured at three locations across the site, with transverse spacing of 145.7 m and 59.3 m between each device. Turbine fatigue loading is assessed using measurements and model predictions based on an unsteady blade element momentum model applied to near-surface and near-bed deployment positions. As well as across-site spatial variation of loading, the through life loading over a 5-year period results in an 8% difference to measured loads for a near-surface turbine, using conditions purely defined from a resource model and to within 3% when using a combination of modelled shear with measured turbulence characteristics. [ABSTRACT FROM AUTHOR]

Dual-mode propellers, as propulsion and turbine devices, have found widespread application in renewable energy systems for marine vehicles, particularly in sailing boats and yachts. However, the existing dual-mode propellers in these contexts are typically chosen in an off-the-shelf manner, indicating a lack of hydrodynamic optimisation to enhance both the propulsion and energy generation efficiency in the same rotor. To address this limitation and furnish scientific validation of the design of a dual-mode propeller turbine rotor optimised to achieve a balanced performance in both propulsion and energy generation, rigorous experimentation was conducted using specialised software, Rotorysics 2019, and a case study vessel, the Princess Royale. Utilising prior experimental data for this propeller turbine, code validation was undertaken to ensure accurate prediction of the effects of the pitch, blade count and expanded area ratio on the performance in both modes. With the intention of achieving optimal power generation and propulsion efficiencies in conjunction with a single rotor, the findings reveal that the optimised fixed-pitch propeller exhibits dual functionality. They serve as both propulsion and tidal/current turbines with balanced efficiency. They are particularly suitable for low-speed vessels such as yachts anchored in currents or for sailboats utilising a propeller as a towed turbine. Through thorough testing and analysis, the concept of a dual-mode propeller turbine was feasible. Analysing them separately, in terms of the propulsion, the best geometry found through numerous tests of different expanded area ratios, blade number, pitch and speed was the 3-blade, 0.6 pitch ratio, which achieved a propulsive efficiency of 54.33% (0.5433204) and a power coefficient of 0.291843. Conversely, if the focus was on power generation while maintaining excellent propulsive efficiency, the optimal geometry would be the 5-blade, 0.6 pitch ratio, which offers a power coefficient of 0.348402 and a propulsive efficiency of 48.55% (0.48547). However, when using both power generation and propulsion as the criteria, the 5-blade, 0.6 pitch ratio, with an EAR of 0.387142, is superior, with balanced optimisation, offering a propulsive efficiency of 52.53% (0.52527) and a power coefficient of 0.319718. As expected, this encompasses a higher blade number for increased power generation efficiency and a higher pitch ratio for increased propulsive efficiency.

Commercial scale tidal stream turbines (TST) are expected to be deployed in shallow water where the depth varies from 1.5 to 3 turbine diameters. In this study, numerical simulation is conducted at realistic hydrodynamic conditions of potential tidal sites using the stationary actuator disc method at ambient turbulence varying from 5% to 20%, a range of rotor realistic rotor thrust coefficient from 0.64 to 0.98 and a rotor-diameter-to-depth ratio of 20% to 60%. The result shows that the TST wake is affected by the rotor-diameter-to-depth ratio, ambient turbulence, and thrust coefficient. The new empirical model is in accordance with the numerical simulation of a full-scale turbine and is validated with the TST experiment at different rotor-diameter-to-depth ratios with reasonable results in the far wake. This low computational model can benefit the investigation of tidal turbine parks at different configurations where the far wake is pertinent.

Demonstrating power performance in real conditions is vital for verifying tidal turbine design. The International Electrotechnical Commission's Technical Specification IEC TS 62600-200 provides guidance for tidal developers to evaluate machine performance. This study evaluates the performance of the operational 1 MW DEEP-Gen IV commercial-scale tidal turbine deployed during the ReDAPT project at the European Marine Energy Centre's tidal test site in Orkney, Scotland. IEC TS 62600-200 states that the power performance should be measured relative to two independently located current profilers deployed in one of two orientations; 'in-line' (preferred) or 'adjacent' (least preferred), relative to the turbine. Two measurement campaigns are used to assess the impact of instrument placement on the measured power curve and annual energy production (AEP). The ambient current flow and vertical profile form differed at each current profiler location (due to topography and bathymetry), leading to AEP variability. The results reinforce the IEC TS preferred orientation for instrument placement, with inline measurements showing smaller variation in AEP estimates compared with adjacent measurements. An additional analysis assesses the sensitivity of AEP estimates on the vertical alignment of the flow profiles with rotor positioning. For this we consider three turbine scenarios: the DEEP-Gen IV and two modelled turbine rotors occupying different regions in the water column. Results show that for regions of high vertical shear, AEP estimates can be misrepresented by up to 5.5% under an imposed vertical misalignment of 2 m. This work has quantified, at this site, the variation in AEP estimates from different flow measurement campaigns informed by IEC TS 62600-200 and has shown the need to ensure good vertical alignment between measurements and turbine rotor positioning. • The measured power curve for TEC is sensitive to the flow reference used. • ADCPs placed in-line to the TEC provide a better reference than adjacently placed. • In-line flow measurements varied despite being placed at IEC prescribed distance. • Large flow structures impacted measurements 30 m from the TEC location. • Vertical ADCP misalignment (±2 m) to TEC swept area can impact AEP by up to 5.5%. [ABSTRACT FROM AUTHOR]

This study involves an experimental and numerical analysis of the Hunter turbine, a vertical axis turbine utilized for tidal energy. A laboratory model of the Hunter turbine, featuring an aspect ratio of 1.2, was designed and tested. Numerical equations, including the Reynolds-averaged Navier–Stokes (RANS) constant, were analyzed through computational fluid dynamics (CFD) software using the k-ω turbulence model to forecast turbine performance and other related flow specifications, such as pressure lines, stream velocity, and pressure. This simulation was conducted on the surface of the turbine blade, and the results were obtained accordingly. The experimental data were utilized to verify the numerical results, and the difference between the two was reasonably acceptable. The turbine was studied in six different flow coefficients and four different vertical positions. The results indicated that the power coefficient increased as the submerged depth from a water-free surface increased, and after a specific depth, the output power remained constant. It was also observed that the minimum depth from a water-free surface for maximum power coefficient was three times the diameter of the turbine drum (3D). [ABSTRACT FROM AUTHOR]

In this work, two new profiles at the leading-edge tubercles of the tidal turbine have been proposed to predict the hydrodynamic performance and obtain more power production than the original blade with a smooth leading edge. A computational method based on the Reynolds-Averaged Navier-Stokes (RANS) is employed for predicting the hydrodynamic performance of the tidal turbine. The turbulent model of the k − ω S S T (shear stress transport) has been used. A three-bladed tidal turbine with the NREL's S814 foil section is selected. The numerical results of the power coefficient against tip speed ratio (TSR) show a good agreement in comparison with the experimental data. Then, two new profiles of tubercles, namely zigzag (ZZ) and absolute sinus (AS), at the leading-edge with 0.1 chord length height at each section, are proposed. The results of the power and torque coefficients are significantly increased, especially at higher TSRs. [ABSTRACT FROM AUTHOR]

Tidal energy is one of the world's most predicable renewable energy sources and therefore holds great potential to be a valuable building block for the decarbonisation of electricity production. This paper focuses on a Venturi shaped duct structure (shroud) to accelerate the flow speed at a vertical axis tidal turbine utilising the low static pressure created at the exit of the shroud. This concept is known as a Davidson Hill Venturi (DHV) turbine. By constructing the nozzle and diffusor using hydrofoils, initial demonstrations indicate increased system efficiency. However, owing to the potential number of geometric and structural hydrofoil variations, only a general description of the location of the hydrofoils is provided in order to facilitate modelling while allowing for future geometric variations to be devised. The conducted investigations focus on the influence of the nozzle and diffusor sections as the main geometry variations, identifying the length component in the orthogonal direction as the dominant parameter. By modelling multiple combinations of these variables it is clear that higher fluid velocities result in larger forces which must be supported by the devices structure. Small adjustments to the reference geometries hydrofoil placement and spacing provided improvements to the fluid flow. Thus, taking the slight alteration to the geometry as this papers main outcome, a further in a 3D-simulation study, including turbine interaction and rotation, is to be completed to fully characterise the systems benefits. The insights gained from this work will allow a reduction in computational costs for the detailed optimisation and study into the adaption of the concept for a wide range of (environmental) boundary conditions.

For the tidal energy industry to move forward to commercialisation, understanding the interaction between the environment and tidal energy converters (TEC) is essential. The benthic environment may be particularly vulnerable to development by changing the existing physical and ecological characteristics. To assess measurable changes of the infrastructural and operation activity of the Deep Green subsea TEC known as the kite, developed by Minesto, benthic surveys were carried out in the Narrows, Strangford Lough, Northern Ireland. At the Minesto site and two other locations, scientific divers carried out circular cardinal-direction benthic camera surveys prior to and after five years of operation. A diverse assemblage of sessile, vagile and mobile species associated with substrate types were identified. No significant changes at any of the sites were recorded in the abundance of species, substrate type or species diversity over the five-year period. The results show that no impact on benthic communities was detected as a result of the operation and deployment of the infrastructure associated with the technology. [ABSTRACT FROM AUTHOR]

The unsteady RANS equations for a two-dimensional hydrofoil were solved using ANSYS Fluent to model and simulate the hydrofoil at a constant Reynolds number, Re, of 2 × 105 and a fixed reduced frequency, f*, of 0.14. The simulations were performed by varying parameters, such as the number of deflectors N, tilt angle of the deflectors β, and vertical spacing of the deflectors J* = J/c, to determine the effect of the upstream deflector's position on the hydrofoil's performance. The results demonstrated that the deflector was effective at redirecting the separated flow away from the edges, which was then amplified downstream before colliding with the leading edge of the oscillating hydrofoil to increase power extraction. The performance of the oscillating hydrofoil was highly reliant on all three studied parameters. The hydrofoil with two deflectors (N = 2) displayed marginally superior power extraction capability compared to the hydrofoil with a single deflector (N = 1). Furthermore, the hydrofoil with the rightward inclined deflector at a low tilt angle (−5° ≥ β ≥ −10°) exhibited relatively better power extraction performance than the others. The best deflector design increased the hydrofoil's cycle-averaged power coefficient by approximately 32% compared to a hydrofoil without a deflector. The vortex structures revealed that the flow evolution and power extraction performance were dependent on the size, robustness, and growth rate of the leading edge vortex (LEV) as well as the timing of LEV separation. The power extraction efficiency of an oscillating hydrofoil increased in the mid downstroke and upstroke due to the formation of a more robust LEV when the hydrofoil–deflector interaction was advantageous, but it dropped in the wing reversal due to the early separation of the LEV when the hydrofoil–deflector interaction was counterproductive. [ABSTRACT FROM AUTHOR]

The tidal currents of the Gulf of Morbihan reach up to 3.5 m/s within a narrow (200 m large) channel connecting the sea to the inner part of the gulf. In this study, a Telemac2D model validated with a large dataset of field measurements is used to assess the resources of the gulf. The results show that two sites have the potential to host up to 48 turbines (diameter of 8 m). If the entire width of the channel is occupied by turbines, significant increases in current speed are expected to occur on each side of the main channel. Simulations also show that flow changes differ between ebbing and flooding tides. During ebbing tide, the changes are limited in amplitude and remain localised within the channel. During flooding tide, the changes are more significant, especially in the vicinity of one of the two sites where the water passing through the site is flushed into a large and shallow basin. In this area, energy extraction significantly modifies the spatial distribution of the current velocities. We consider different scenarios of tidal energy extraction. The results show that flow perturbation can be significantly reduced using a lower density of turbines, that extracting tidal energy at one site slightly reduces the resource of the other, and that the deployment of two turbines (testing conditions) has a negligible effect on ambient current speeds.

Tidal currents are renewable and predictable energy sources that could prove fundamental to decrease dependency from fossil fuels. Tidal currents, however, are highly unsteady and non uniform, resulting in undesirable load fluctuations on the blades and the drive train of turbines. A passive morphing blade concept capable to reduce the load fluctuations without affecting the mean loads has recently been formulated and demonstrated with numerical simulations (Pisetta et al., 2022). In this paper, we present the first demonstration of this morphing blade concept, through experimental tests on a 1.2-m diameter turbine. We show that fluctuations in the root-bending moment, thrust and torque are consistently reduced over a broad range of tip-speed ratios. This work also highlights some critical design aspects of morphing blades. For instance, it is showed that the friction resistance can substantially decrease the effectiveness of the system and thus must be minimised by design. Overall this paper demonstrates for the first time the effectiveness of morphing blades for tidal turbines, paving the way to the future development of this technology. • We test a model-scale tidal turbine equipped with a passively pitching blade. • The blade angle of attack decreases with an increase in instantaneous loads. • This does not affect the time-averaged power generated by the tidal turbine. • Torque and thrust fluctuations are reduced by at least 40% at on-design conditions. • Friction on the turbine shaft affects performance and must be minimised. [ABSTRACT FROM AUTHOR]

In this study, we improved the energy acquisition efficiency of tidal turbines with bionic airfoils by optimizing the seagull, long-eared owl, sparrowhawk, and two-dimensional airfoils, thereby obtaining a better lift–drag ratio. We used Isight software to integrate the Integrated Computer Engineering and Manufacturing (ICEM) software and used Fluent simulation software, batch operation file, and multi-island genetic algorithm to maximize the lift–drag ratio as the objective function for optimizing the original airfoil. The optimized upper airfoil profile was distributed upward from the starter wing, and the thickness of the upper wing was the greatest. Meanwhile, the lower airfoil profile was thinner and more curved. The thickness of the three airfoils was distributed backward from the front of the wing, with the maximum thickness at the front, and the maximum camber was distributed backward from the front. The three optimized wings exhibited a maximum lift–drag ratio at an angle of attack of approximately 5°, with the sparrowhawk wing having a maximum lift–drag ratio of 80.87 at an angle of attack of 6°, the seagull wing having a maximum lift–drag ratio of 76.82 at an angle of attack of 4°, and the long-eared owl wing having a maximum lift–drag ratio of 68.43 at an angle of attack of 5°. [ABSTRACT FROM AUTHOR]

The next stage of development of the tidal stream industry will see a focus on the deployment of tidal turbines in arrays of increasing device numbers and rated power. Successful array development requires a thorough understanding of the resource within potential deployment sites. This is predictable in terms of flow speeds, based upon tidal constituents. However, the operating environment for the turbine is more complex than the turbine experiencing a uniform flow, with turbulence, shear and wave conditions all affecting the loading on the turbine components. This study establishes the accuracy with which several alternative modelling tools predict the resource characteristics which define unsteady loading—velocity shear, turbulence and waves—and assesses the impact of the model choice on predicted damage equivalent loads. In addition, the predictions of turbulence are compared to a higher fidelity model and the occurrence of flow speeds to a Delft3D model for currents and waves. These models have been run for a specific tidal site, the Raz Blanchard, one of the major tidal stream sites in European waters. The measured resource and predicted loading are established using data collected in a recent deployment of acoustic Doppler current profilers (ADCPs) as part of the Interreg TIGER project. The conditions are measured at three locations across the site, with transverse spacing of 145.7 m and 59.3 m between each device. Turbine fatigue loading is assessed using measurements and model predictions based on an unsteady blade element momentum model applied to near-surface and near-bed deployment positions. As well as across-site spatial variation of loading, the through life loading over a 5-year period results in an 8% difference to measured loads for a near-surface turbine, using conditions purely defined from a resource model and to within 3% when using a combination of modelled shear with measured turbulence characteristics.

Tidal energy is one of the world's most predicable renewable energy sources and therefore holds great potential to be a valuable building block for the decarbonisation of electricity production. This paper focuses on a Venturi shaped duct structure (shroud) to accelerate the flow speed at a vertical axis tidal turbine utilising the low static pressure created at the exit of the shroud. This concept is known as a Davidson Hill Venturi (DHV) turbine. By constructing the nozzle and diffusor using hydrofoils, initial demonstrations indicate increased system efficiency. However, owing to the potential number of geometric and structural hydrofoil variations, only a general description of the location of the hydrofoils is provided in order to facilitate modelling while allowing for future geometric variations to be devised. The conducted investigations focus on the influence of the nozzle and diffusor sections as the main geometry variations, identifying the length component in the orthogonal direction as the dominant parameter. By modelling multiple combinations of these variables it is clear that higher fluid velocities result in larger forces which must be supported by the devices structure. Small adjustments to the reference geometries hydrofoil placement and spacing provided improvements to the fluid flow. Thus, taking the slight alteration to the geometry as this papers main outcome, a further in a 3D-simulation study, including turbine interaction and rotation, is to be completed to fully characterise the systems benefits. The insights gained from this work will allow a reduction in computational costs for the detailed optimisation and study into the adaption of the concept for a wide range of (environmental) boundary conditions. [ABSTRACT FROM AUTHOR]

Ocean current energy is a promising and reliable resource that offers sustainability and predictability in realizing green future needs. A diffuser-augmented horizontal-axis turbine is utilized to generate ocean current energy. A numerical study on the impact of diffuser angle variations on the power coefficient has been carried out in the previous research. To elucidate the fluid dynamics aspects and further validation of previous computational results, the experimental investigation on the optimal design of tidal turbine with 20.04° diffuser augmentation is presented in this study. The study was conducted in a flowing tank with a current velocity of 0.7 m/s. The maximum power coefficient of 20.04° is 0.436 experimentally, which is a little smaller than the numerical value. Moreover, to reinforce the 20.04° result, a diffuser with an angle of 10.43° was also manufactured and tested experimentally. The maximum power coefficient of 10.43° is 0.303 experimentally, which is 3% smaller than the numerical value. It was concluded that the numerical approach might be considered satisfactory and represent similar phenomena to the experimental investigation in an application for modelling of multi-objective optimization. [ABSTRACT FROM AUTHOR]

Tidal turbines are commonly deployed at sea sites with water depths of up to 50 m to ease their deployment and quick maintenance operations. In these relatively shallow water depth conditions, the vertical expansion of tidal stream turbine wakes is restricted by the proximity of the rotor blades to the bottom bed and free-surface layer. These physical constrains can lead to changes in the flow mechanisms that drive momentum recovery behind the turbines, e.g. limiting the vertical fluxes of velocity. Understanding how the wake recovers depending on the submergence ratio is of utmost importance to designing the future multi-row tidal turbine arrays. Here, we adopt high-fidelity Large-Eddy Simulations (LES) with an Actuator Line Method (ALM) to represent the turbine's rotor to analyse the mean flow and transport equation for mean kinetic energy (MKE) behind a single bottom-fixed tidal turbine for four water depth values. Our results show that the close proximity of the turbine blade tip to the free-surface can notably constrain the wake expansion, with very shallow conditions leading to a limited contribution to the MKE replenishment of the turbulent momentum exchange over the vertical direction. Conversely, under such shallow conditions, the horizontal flux of MKE is enhanced over the lateral boundaries of the downstream wake. Our study evidences that the ratio of water depth to turbine diameter plays a relevant role in future tidal arrays and needs to be correctly accounted for in numerical models to provide reliable results.

Arctic observations are becoming increasingly valuable as researchers investigate climate change and its associated concerns, such as decreasing sea ice and increasing ship traffic. Networks of sensors with frequent sampling capabilities are needed to run forecast models, improve navigation, and inform climate research. Sampling frequency and deployment duration are currently constrained by battery power limitations. In-situ power generation using marine renewable energy sources such as waves and currents can be used to circumvent this constraint. Wave and current resources vary spatially and temporally in the Arctic, with some locations and seasons being better suited for marine renewable energy power generation. Locations and seasons with small resources may still be able to use marine renewable energy because of the low power requirements of the instruments. In this study, we describe the wave and current resources in the Arctic, outline the electricity generation developments that are needed to utilize the resources, and suggest use cases. Wave and current energy converters developed to power observations in the Arctic could also be used to power observations at lower latitudes. Marine renewable energy has the potential to decrease dependence on batteries and improve data collection capabilities in the Arctic; however, this would require the development of new low power technologies that can operate in extreme Arctic environments.

In this paper, a new design scheme for counter-rotating horizontal-axis tidal turbines (CRHATTs) is introduced using blade element momentum (BEM) theory. The coordinated working performance between rotor and generator of the CRHATT are analysed by experimental and CFD methods. The effects of the key parameters on the energy harvesting efficiency of the CRHATT are studied in detail. The study indicates the existence of the optimal rotor solidity (σ) combination and blade installation angle (γ) combination for dual rotors to reduce the power coefficient (Cp) deviation of the dual rotors. The distance between dual rotors (L) is suggested to be set as about 0.225D, which can maximise the Cp of the CRHATT. Finally, the hydrodynamic performance of the flow field is carried out to verify the reliability of the CRHATT design. The results presented in this paper may serve as a reference in the design of CRHATTs in practical engineering. [ABSTRACT FROM AUTHOR]

A 1:20 scaled three-bladed horizontal-axis tidal turbine is positioned in the wake flows of two wall-mounted obstacles: a square cylinder and a combination of a cube in front of a cylinder. The turbine's induction effects are examined with upstream flow measurements without and with the turbine operating at its optimal regime. In front of the turbine (at 0.07 D upstream of the hub extremity, with D the turbine diameter), the mean axial and vertical velocities are modified by induction effects whatever the complexity of the flow is. In the other hand, the normal Reynolds tensor components are less impacted by the turbine's blockage. In the presence of an incoming uniform homogeneous Gaussian flow field, a mean axial velocity deficit of 30% is observed in front of the hub while this velocity deficit is around 10% at the rotor edge. Moreover, the turbine's blockage modifies the intermittency leading to non-Gaussian fluctuations. When low-frequency large-scale flow structures are embedded in the incoming turbulent flow, these large-scale flow structures are affected by the hub whereas the rotating blade's blockage effect is of minor contribution. In this case, the turbine does not affect significantly the intermittency. [ABSTRACT FROM AUTHOR]

This paper explores the maximization of tidal energy conversion by adopting hydraulic transformation and through the design of a robust H∞ control scheme. A hydraulic transformation based tidal turbine applicable to realistic tidal states is presented. In this turbine, a hydraulic transformer is developed to have well-adapted characteristics to turbulent tidal stream flows. The dynamics of the tidal turbine is represented as a state space model based on the equations of its main components. The H∞ control scheme is then synthesized by introducing a new state variable that represents the "filtered" of the turbine rotor speed tracking errors. The control problem is formulated as a convex optimization problem with linear matrix inequality (LMI) that is solved to satisfy H∞ performance and obtain good dynamic characteristics. In addition, a robust H∞ observer for estimating state variables along with the online implementations of the robust controller is also designed by using the LMI approach. A case study of a 150 kW hydraulic transformation based tidal turbine system is conducted and detailed analyses of the dynamic behavior of the tidal turbine are presented. According to the test results, approximately up to 40% total power conversion efficiency can be achieved by the proposed turbine under the typical energetic sea state conditions. • The design, modelling and control of a hydraulic transformation based tidal turbine. • Designing LMI based robust H∞ controller and observer. • Validations of the turbine system and robust H∞ control and H∞ observer. [ABSTRACT FROM AUTHOR]

Up to 6 Schottel Instream Turbines (SIT250) can be mounted on the tidal platform PLAT-I developed by Sustainable Marine Energy. Due to the close proximity of the turbines interactions can occur between them. Two horizontal axis tidal turbines in model scale are investigated experimentally and numerically to analyze these interactions. Experimental data were measured in a towing tank and consist of integral values for torque, thrust and rotational speed. Both a steady state and an unsteady three-dimensional Reynolds Averaged Navier Stokes (RANS) approach are utilized for simulating the turbine flow field. The first part of the paper compares simulation results of a single turbine at different tip speed ratios with measurements to validate the numerical approach and its employed models. The second part analyses the interaction between two turbines. The axial distance in main flow direction between the turbines is half the rotor diameter. The radial distance measured between the hubs of the turbines is varied in steps of 0.2 between 0.0 and 2.0 times the rotor diameter in the experiment and between 0.0 and 1.4 in the simulations. Measurements were conducted for tip speed ratios of 3, 4 and 5. In the simulations the tip speed ratio was fixed at 4. The used simulation domain replicates the actual width and height of the towing tank and a sufficient length up- and downstream of the turbines. The water surface is modeled with a free slip wall. Both thrust and torque are compared between simulation results and experimental data. Furthermore, a detailed analysis of the results and flow field in the numerical simulations is presented and the interaction between the turbines is discussed.

A transfer function determination method is proposed in this study to predict the unsteady fluctuations of the performance of a tidal turbine model. This method is derived from the Response Amplitude Operator (RAO) applied in the offshore industry to predict linear wave-induced loads on large structures. It is based on a spectral approach and requires the acquisition of a turbine parameter (e.g. torque, thrust, power or root-blade force) in synchronization with an upstream flow velocity measurement. On the frequency range where the causality between these two signals is proven, the transfer function is established using the ratio between the cross-spectral density and the spectral density of the incoming velocity. The linearity is verified using the coherence function, which shows validity for the turbine power in the lowest frequencies only. This transfer function is then used to reconstruct the power fluctuations which is compared to the recorded one for a particular flow condition with bathymetry generated turbulence. The result shows the dependence on the accurate location of the velocity measurement point used for the reconstruction. This point must exactly correspond to the expected turbine location, i.e. where the turbine response needs to be processed. Bearing in mind its limits, the method can be used to predict the loadings of extreme events on the turbine structure and the performance variations corresponding to the unsteady characteristics of a turbulent flow, for a better grid integration.

For the tidal energy industry to move forward to commercialisation, understanding the interaction between the environment and tidal energy converters (TEC) is essential. The benthic environment may be particularly vulnerable to development by changing the existing physical and ecological characteristics. To assess measurable changes of the infrastructural and operation activity of the Deep Green subsea TEC known as the kite, developed by Minesto, benthic surveys were carried out in the Narrows, Strangford Lough, Northern Ireland. At the Minesto site and two other locations, scientific divers carried out circular cardinal-direction benthic camera surveys prior to and after five years of operation. A diverse assemblage of sessile, vagile and mobile species associated with substrate types were identified. No significant changes at any of the sites were recorded in the abundance of species, substrate type or species diversity over the five-year period. The results show that no impact on benthic communities was detected as a result of the operation and deployment of the infrastructure associated with the technology.

With tidal energy demonstration projects with one or a small number of turbines having provided very positive results, the technology is moving to the commissioning and operation of tidal energy farms. For this next step, the understanding of the wakes generated downstream of the turbines is crucial to optimize the array performance. To date, the analysis of wakes of MW-scale tidal turbines has been made by numerical methods or experimentally with downscaled rotors. However, no consensus on a methodology to characterize wakes generated by full-scale turbines based on data measured on-site has yet been reached. The present paper introduces a new method to compare current velocity data measured before and during turbine operation that minimizes the impact of the spatial and temporal variability of tidal currents, thus enabling the estimation of the velocity deficit caused downstream of the turbine. Through this method, a characterization of the near wake was possible, with velocity deficits of 0.537, 0.463, 0.469 and 0.431 at 2D, 3D, 4D and 5D from the turbine. Results from this paper present a very valuable tool for the validation of numerical models aiming to estimate the wake losses in tidal energy farms. • Wake from a 0.5 MW bottom-fixed tidal turbine in a tidal site is characterized. • A new method to calculate velocity deficit with vessel-mounted ADCP data is presented. • Velocity deficit at the rotor hub height decreases from the turbine to a 5D distance. • Farther from 5D, the turbine impact on current velocity dissipates. [ABSTRACT FROM AUTHOR]

The operation of tidal turbines is inevitably influenced by waves, and extensive research has undoubtedly been conducted on this topic. However, most investigations of such studies have utilized small-scale turbines, with a primary focus on the load characteristics of the turbines themselves. There is a slight deficiency in attention to the wave characteristics that contribute to these loads. To bridge this gap, this study develops a computational fluid dynamics (CFD) model of a full-scale tidal turbine. The model's accuracy is assessed through flume experiments using a scaled-down version, validating the numerical approach against wave conditions. Employing actual tidal flow velocity and wave data as input, this study specifically examines how variations in wave period and height affect turbine performance. The analysis reveals a nuanced decrease in time-averaged performance with increases in wave period and height. Load fluctuations arise from wave impacts, turbine rotor rotation, and their interaction. With the increase in wave period or height, the fluctuations caused by the wave impacts and the interaction increase, while those induced by rotor rotation exhibit a slow growth trend but essentially remain stable. • Establishment of a full-scale tidal turbine model using the CFD method. • Validation of the numerical method through a scaled-down experiment. • Exploration of the influences of wave period and height on turbine performance. • In-depth study of both time-averaged performance and load fluctuations. [ABSTRACT FROM AUTHOR]

The unsteady RANS equations for a two-dimensional hydrofoil were solved using ANSYS Fluent to model and simulate the hydrofoil at a constant Reynolds number, Re, of 2 × 105 and a fixed reduced frequency, f*, of 0.14. The simulations were performed by varying parameters, such as the number of deflectors N, tilt angle of the deflectors β, and vertical spacing of the deflectors J* = J/c, to determine the effect of the upstream deflector’s position on the hydrofoil’s performance. The results demonstrated that the deflector was effective at redirecting the separated flow away from the edges, which was then amplified downstream before colliding with the leading edge of the oscillating hydrofoil to increase power extraction. The performance of the oscillating hydrofoil was highly reliant on all three studied parameters. The hydrofoil with two deflectors (N = 2) displayed marginally superior power extraction capability compared to the hydrofoil with a single deflector (N = 1). Furthermore, the hydrofoil with the rightward inclined deflector at a low tilt angle (−5° ≥ β ≥ −10°) exhibited relatively better power extraction performance than the others. The best deflector design increased the hydrofoil’s cycle-averaged power coefficient by approximately 32% compared to a hydrofoil without a deflector. The vortex structures revealed that the flow evolution and power extraction performance were dependent on the size, robustness, and growth rate of the leading edge vortex (LEV) as well as the timing of LEV separation. The power extraction efficiency of an oscillating hydrofoil increased in the mid downstroke and upstroke due to the formation of a more robust LEV when the hydrofoil–deflector interaction was advantageous, but it dropped in the wing reversal due to the early separation of the LEV when the hydrofoil–deflector interaction was counterproductive.

Tidal turbine arrays are planed to be installed in areas with strong currents where the flow can often be sheared throughout the water column. To study the shear flow effects on tidal turbine, four vertical velocity profiles are generated in a flume tank and are imposed to a three-bladed horizontal axis turbine model. Results show that the sheared velocity profiles do not impact the turbine average performance but are responsible for an increase of blade root streamwise load variations. Blade root streamwise load is moreover linked to the turbine rotational frequency and its harmonics. The velocity perceived by the blades during their rotation is estimated over the rotor area and is compared to the angular phase average of the streamwise load measured on the blades. The phase average of the load and the velocity perceived by the blades are highly correlated even if a varying phase lag has been noticed between these two quantities. This phase lag is dependent on the rotational speed of the turbine, on the incoming flow shear, and is probably caused by the turbine induction effects. This experimental study is a first step to understand the effect of shear velocity profiles on tidal turbines better. [ABSTRACT FROM AUTHOR]

Analysing the fluid dynamic performance of a bare rotor when succumb to yawed flow conditions has consistently presented a diminishment in mechanical power conversion efficacy. Introducing a duct along the rotor perimeter has been acknowledged to sustain performance, yet the causation behind this phenomenon is uncertain. This study puts forward an investigation into the hydrodynamic performance concerning a true-scale, ducted, high-solidity tidal turbine in yawed free-stream flows by utilising blade-resolved, unsteady computational fluid dynamics. Investigating the performance within an angular bearing range of 0 o to 45 o with the turbine axis, increases in mechanical rotational power and thrust are acknowledged within a limited range at distinct tip-speed ratio values. Through the multiple yaw iterations, the maximum attainment falls at an angle of 23.2 o , resulting in a power increase of 3.44% to a peak power coefficient of 0.35 at a nominal tip-speed ratio of 2.00, together with an extension of power development along higher tip-speed ratios. In verification of the power increase, the outcomes are analysed by means of linear momentum theory; by utilising area-averaged values of static pressure acquired from annular radial surfaces fore and aft of the rotor, an analogous relationship with the blade-integrated outcomes is attained. The analysis concludes that, at higher tip-speed ratios, the pressure drop across the rotor increases at limited flow bearings, enhancing the resultant axial force loading upon the blades, hence providing further performance augmentation of the ducted, high-solidity tidal turbine. [ABSTRACT FROM AUTHOR]

Tidal turbines are located in shallow water depths in comparison to their dimensions (15 m-diameter turbines in 40 m depths, typically). Constrained vertically by the water depth and laterally by neighbouring turbines, the flow within a tidal farm is subjected to blockage effects that influence the performance of individual devices. The Betz limit (which is the maximum power extractable from an unconstrained flow) can, therefore, be exceeded as demonstrated by Garrett and Cummins. Thus, beyond a significant blockage ratio, blockage effects should be considered when assessing the energy production of a tidal farm. The actuator disk method is particularly suited to simulate the flow field within an array of turbines under realistic tidal flow conditions. However, the implementation of actuator disks in coastal numerical models relies on relationships that neglect the blockage effects on the thrust and power of devices. We propose here an actuator disk formulation corrected to integrate these effects. This modified formulation, based on the model of Whelan et al., is integrated into a regional implementation of a three-dimensional model Telemac3D targeted towards the Alderney Race (English Channel). The method is applied to two hypothetical tidal farms with aligned and staggered arrangements, respectively. Blockage corrections of the thrust and power coefficients are found to have counterbalanced effects on the array production. Thrust correction results in a noticeable flow reduction within the array. However, the associated decrease of the array production is counterbalanced by the increase of the turbine power coefficient. Blockage corrections were, therefore, found to result in a slight increase, by 3%, of the array production over a mean spring tidal cycle. [ABSTRACT FROM AUTHOR]

Electricity generation by extraction of tidal energy has many advantages including being highly predictable, low environmental pollution, and unlimited source of renewable energy. Tidal energy is an emerging field and many tidal turbine manufacturers have entered in this field with new advancements in turbine technologies. These turbine companies require the feasibility studies of potential sites where tidal energy can be extracted. Utilizing tidal energy is not a modern manifestation but in subcontinent (including countries Pakistan, India, Bangladesh, Iran, and Sri Lanka), there is not a single tidal power plant installed so far. Therefore, as a case study, this work is carried out for the first time to assess tidal energy resources of Hawke's Bay and Ghizri by developing geostatistical models with the help of available tidal data of five different locations for the duration of 9 years along the coastal belt of Pakistan. This study is conducted for the first time to assess the available tidal energy resources of area of interest (AOI) for the generation of electric power. Models have been developed by incorporating different layers into ArcGIS environment, such as the following: satellite imageries, tidal data, and other socioeconomic and physical data. Digitized maps and layers are developed after processing all data. The best fitted model is selected to predict the tidal data of Hawke's Bay and Ghizri. Results obtained from five different models are compared and cross-validation of each model is performed. Moderate tidal range was found at study area and total theoretical tidal power is estimated to be 153.34 MW. This feasibility study will be beneficial for the turbine companies that are trying to explore new regions for the deployment of tidal turbines that work under low head technology. [ABSTRACT FROM AUTHOR]

Coupled blade element momentum-computational fluid dynamic (BEM-CFD) approaches have been extensively used to study tidal stream turbine performance and wake development. These approaches have shown to be accurate when compared to tests conducted in tow-tanks or in regulated flumes with uniform flows across the turbine. Whilst such studies can be very useful, it is questionable as to what extent the results would differ in a larger scale environment where the flow is more representative of real-world conditions, being either unsteady or non-uniform. In this work, the effectiveness of a generalised actuator disk-computational fluid dynamics (GAD-CFD) approach in accurately capturing fluid-machine interaction for single and multiple tidal energy converters models is further assessed. A unique large-scale experimental facility, FloWave, has been used to conduct physical testing of three instrumented model tidal energy converters of rotor diameter 1.2 m under differing turbine layouts and realistic scaled environmental conditions. These large-scale tests provide a unique dataset against which this work's numerical simulations have been extensively validated. Comparisons between the tank and GAD-CFD approach show good agreement, particularly when comparing modelled to measured thrust, and enabled an evaluation of the effects of turbine spacing and arrangement on turbine performance and flow-field response. [ABSTRACT FROM AUTHOR]

Acoustic emissions from current energy converters remain an environmental concern for regulators because of their potential effects on marine life and uncertainties about their effects stemming from a lack of sufficient observational data. Several recent opportunities to characterize tidal turbine sound emissions have begun to fill knowledge gaps and provide a context for future device deployments. In July 2021, a commercial-off-the-shelf hydrophone was deployed in a free-drifting configuration to measure underwater acoustic emissions and characterize a 25 kW-rated tidal turbine at the University of New Hampshire's Living Bridge Project in Portsmouth, New Hampshire. Sampling methods and analysis were performed in alignment with the recently published IEC 62600-40 Technical Specification for acoustic characterization of marine energy converters. Results from this study indicate acoustic emissions from the turbine were below ambient sound levels and therefore did not have a significant impact on the underwater noise levels of the project site. As a component of Pacific Northwest National Laboratory's Triton Field Trials (TFiT) described in this Special Issue, this effort provides a valuable use case for the IEC 62600-40 Technical Specification framework and further recommendations for cost-effective technologies and methods for measuring underwater noise at future current energy converter project sites. [ABSTRACT FROM AUTHOR]