Tidal Energy Research Articles

Tidal turbine blade design optimization based on coupled deep learning and blade element momentum theory

The practical design optimization of blade structures is crucial for enhancing the power capture capability of tidal turbines. However, the significant computational costs required for directly optimizing turbine blades through numerical simulations limit the practical application of blade structure optimization. This paper proposes a framework for tidal turbine blade design optimization based on deep learning (DL) and blade element momentum (BEM). This framework employs control points to parameterize the three-dimensional geometric shape of the blades, uses convolutional neural networks to predict the hydrodynamic performance of each hydrofoil section, and couples BEM to forecast the performance of tidal turbine blades. The multi-objective non-dominated sorting genetic algorithm II is employed to optimize the geometric parameters of turbine blades to maximize the power coefficient and minimize the thrust coefficient, aiming to obtain the optimal trade-off solution. The results indicate that the prediction of the DL-BEM model agrees well with experimental data, significantly improving optimization efficiency. The optimized tidal turbine blades exhibit excellent power coefficients and reduced thrust coefficients, achieving a more balanced structural solution. The proposed optimization framework based on DL accurately and rapidly predicts the performance of tidal turbines, facilitating the design optimization of high-performance tidal turbine blades.

Eccentric binaries: Periastron events and tidal heating

Context. Binary stars cannot be fully understood without assessing the interaction effects between the two components and the impact of these effects on observational diagnostics. Periastron brightening events, also known as the heartbeat phenomenon, are a clear manifestation of this type of interaction. Aims. We aim to explore the role of tidal shear energy dissipation in stars undergoing periastron brightening events. Methods. We performed a computation from first principles that uses a quasi-hydrodynamic Lagrangian scheme to simultaneously solve the orbital motion and the equations of motion of a 3D grid of volume elements covering the inner, rigidly rotating “core” of a tidally perturbed star. The equations of motion include the gravitational acceleration of both stars, the centrifugal, Coriolis, gas pressure accelerations, and viscous coupling between volume elements. The method is illustrated for a grid of model binary systems with a 10 M⊙ primary that is perturbed by a 6.97 M⊙ companion in eccentric orbits (e = 0 − 0.7). The model is then applied to the heartbeat star MACHO 80.7443.1718. Results. We find an increase by factors ∼10−6–10−3 in tidal shear energy dissipation at periastron, consistent with the majority of observed heartbeat stars. The magnitude of the periastron effect correlates with the degree of departure from synchronicity: stars rotating much faster or much slower than the synchronous rate at periastron present the strongest effect. We confirm that for eccentricities ≤0.3, pseudo-synchronization occurs for 0.8 < ω/Ωave < 1, where Ωave is the average orbital angular velocity. The minimum energy rotation rate (pseudo-synchronism) for e = 0.5 and 0.7 occurs for 1.0 < ω/Ωave < 1.15. The tidal shear energy dissipation model reproduces from first principles the ∼23% maximum brightness enhancement at periastron of MACHO 80.7443.1718. Conclusions. Our results suggest that the magnitude and shape of the heartbeat signal may serve as diagnostics for the internal stellar rotation and turbulent viscosity values.

Localized Tidal Energy Extraction in Puget Sound Can Adjust Estuary Reflection and Friction, Modifying Barotropic Tides System‐Wide

AbstractHarvesting energy via tidal stream turbines is being increasingly considered as a renewable energy resource in estuaries with strong tidal currents. It remains unclear how localized energy extraction changes basic tidal physics throughout real systems. Here, we analyze the influence of an extensive synthetic tidal turbine array on barotropic tides in the Salish Sea, a complex, tidally energetic estuary, using a realistic numerical model. Tidal energy fluxes are calculated at 15 sections throughout the system and decomposed into incident and reflected components, as well as by frequency. Results show the dominant semidiurnal constituent, M2, controls the total tidal energy flux everywhere. When turbines are placed in Tacoma Narrows, the M2 energy flux is enhanced at sections seaward of the array in Puget Sound and reduced landward. The principal diurnal constituent, K1, contributes little to the total energy flux, but behaves similarly. Changes to each constituent are primarily attributed to turbine enhanced frictional dissipation which reduces the estuary's natural resonant period (∼10 hr) amplification. Being close to the semidiurnal frequencies, the resonance adjustment reduces M2 tidal reflection seaward of the turbines and free surface amplitude (particularly landward of the turbines) thereby increasing (decreasing) tidal energy fluxes at seaward (landward) locations. K1 is further from the natural frequency and insensitive to resonance changes. We hypothesize K1 is directly sensitive to increased frictional dissipation which acts to reduce reflection and tidal amplitude, regardless of the estuary natural frequency. Spatial variability in dynamics is discussed, as well as potential environmental implications.

Study on the influence of ship waves on the dynamic response of floating tidal current power generation device

To study the influence of ship traveling waves on the hydrodynamic performance between the carrier platform and the turbine, the computational fluid dynamics method and the DFBI motion module of STAR CCM+ software were adopted. Under the condition of the coupling of the ship traveling wave and wave current generated at different speeds, the overall motion response of the power plant is simulated. What’s more, the influence of different wave conditions on the heave, pitch, and roll of the carrier platform and the energy efficiency of the turbine is analyzed. The results show that the ship speed has little effect on the carrier heave motion, but the maximum value of the carrier pitch motion increases with the increase in the ship speed. The value of turbine energy acquisition efficiency always decreases with decreasing lateral spacing and increases with decreasing speed. This paper has a certain reference value for the engineering application of floating tidal current power generation equipment.

Orca hydrofoil shape optimization using Bezier curve and Artificial Neural Network – Multiple objective Genetic Algorithm for low flow velocity

Tidal energy is a clean and predictable power source that is commonly harnessed by using horizontal axis tidal turbines. The power generating process of tidal turbines is influenced by various elements, one of which is the hydrofoil performance. This includes the lift coefficient, drag coefficient, and lift-to-drag ratio. This study introduces the utilization of the Orcinus Orca hydrofoil for horizontal axis tidal turbines. The Orcinus Orca geometry is obtained by modified the NACA0021 airfoil. Subsequently, Bezier curve parameterization is employed to make a smooth hydrofoil profile. The study further deploy an Artificial Neural Network coupled with a Multi-Objective Genetic Algorithm, specifically targeting optimization of the hydrofoil shape optimization at a low flow velocity, specifically at an inlet velocity of 0.5 m/s. The aim of this optimization is to augment the lift coefficient and diminish the drag coefficient in order to amplify the lift to drag ratio. The findings reveal a significant enhancement in performance, as the optimized Orcinus Orca hydrofoil exhibits a remarkable increase of 42.78 % and 27.93 % compared to the original Orcinus Orca and the Bezier-modified Orcinus Orca hydrofoils, respectively.

Tidal current power in Capalulu strait, North Maluku: A feasibility study

The Indonesian government has set goals for increasing the use of renewable energy in the coming years. Currently, Indonesia relies heavily on non-renewable energy sources, which poses a threat to the environment due to the country's growing energy needs. This study aims to assess the potential for developing a tidal power plant in Capalulu Strait, North Maluku. Using hydrodynamic modelling, the study identified two potential locations at coordinates 1.877°S – 125.328°E (Capa-2) and 1.863°S – 125.323°E (Capa-4) which were selected for having median current speeds exceeding 1.8 m/s and maximum current speeds exceeding 3.5 m/s. The study tested a hypothetical implementation of KHPS Gen5 instrument(s) by Verdant Power, a 5 m diameter turbine with a rated nominal power of 37 kW and a maximum rated power of 56 kW. A power plant layout was designed to be placed at Capa-2 and Capa-4, each location accommodating 45 turbines. The development of this power plant is estimated to produce up to 22 GWh per year. Financial analysis resulted in a LCOE of IDR 5,930/kWh. However, this price is still high compared to the national electricity tariff of IDR 1,027.70/kWh. Variations in the number of turbines also may not result in a lower LCOE than the national tariff. Nevertheless, the estimated cost of generating electricity is still competitive compared to diesel, which is around IDR 5,804/kWh.

Transitory Tidal Heating and Its Impact on Cluster Isochrones

The kinetic energy in tidal flows, when converted into heat, can affect the internal structure of a star and shift its location on a color–magnitude diagram from that of standard models. In this paper we explore the impact of injecting heat into stars with masses near the main-sequence turnoff mass (1.26 M ⊙) of the open cluster M67. The heating rate is obtained from the tidal shear energy dissipation rate, which is calculated from first principles by simultaneously solving the equations that describe orbital motion and the response of a star’s layers to the gravitational, Coriolis, centrifugal, gas pressure, and viscous forces. The stellar structure models are computed with MESA. We focus on the effects of injecting heat in pulses lasting 0.01 Gyr, a time frame consistent with the synchronization timescale in binary systems. We find that the location of the tidally perturbed stars in the M67 color–magnitude diagram is shifted to significantly higher luminosities and effective temperatures than predicted by the standard model isochrone and includes locations corresponding to some of the blue straggler stars. Because tidal heating takes energy from the orbit, causing it to shrink, blue straggler stars could be merger or mass transfer progenitors, as well as products of these processes.

Distributed Optical Fibre Sensing for High Space‐Time Resolution Ocean Velocity Observations: A Case Study From a Macrotidal Channel

AbstractDespite significant recent technological advances, oceanographic observations on horizontal scales of meters to a few kilometres prove challenging. Exploiting legacy seafloor cables presents a disruptive prospect to address this gap, as it may provide low‐cost sustained observations with high space‐time resolution, enabled through novel opto‐electronic interrogation of optical fibers within the cables. Here, we demonstrate this approach in a renewable tidal energy cable embedded within a region with a strong barotropic tide. By making remote measurements continuously over 12 hr, we obtain the distributed differential strain experienced by 2 km of offshore cable from a diverse range of oceanic flow processes, with an along‐cable resolution of 2.04 m. We successfully identify: (a) nearshore wave breaking and its modulation by changes in water depth; (b) along‐cable tidal velocity, shown to be linearly related to the differential strain; and (c) high‐frequency motions consistent with 3‐dimensional turbulent processes, either of natural origin or from flow‐cable interaction. These inferences are supported by nearby conventional measurements of water depth and velocity.

Energy, Society and Sociodemographic Constraints Nexus: Development and Future Prospects

To overcome the challenges faced by the energy sector, policymakers need to prioritize the development of strategic policies that promote the adoption of waste-to-energy technologies, Tidal energy, solar power systems, and wind farms. These policies should emphasize the integration of renewable energy sources into the existing energy infrastructure, ensuring a more sustainable and resilient energy supply for urban areas. The study underscores the importance of collaboration between various stakeholders, including government bodies, private sector entities, and local communities. By fostering partnerships and creating incentives, it becomes possible to mobilize resources and expertise towards the implementation of renewable energy projects. This collaboration would not only address the energy crisis but also contribute to job creation and overall socioeconomic development. Proper utilization of renewable energy resources can resolve the dilemma of energy crises in the country. According to our results, solar stood first in the overall ranking followed by Tidal, waste-to-energy, and wind energies. Solar performed better in indigenous manufacturing and development, resource potential, and technological development. Pakistan has abundant green energy resources which could be utilized by the formation of a proper policy roadmap and mitigation of policy pathways to overcome the hazardous dependence on fossil fuels for energy requirements. The implementation of policies adopted should be assured to achieve energy sustainability

Vanadium redox flow battery: Characteristics and application

Renewable energy such as solar energy and wind energy will enter a new period of development. However, the output power of photovoltaic power generation has great randomness. In order to ensure the normal operation of the whole photovoltaic power generation system, it is particularly important to introduce smooth power dynamics of energy storage system (ESS) to ensure electrical stability. As an energy storage device, flow batteries will develop in the direction of large-scale and modularization in the future. The flow battery system can easily realize computer automatic control and is an ideal smart battery. In addition, the combination of flow batteries with photovoltaic cells, wind power stations, tidal power stations, biogas power stations and other renewable energy systems is an important category and content in developing the application fields of flow batteries. As a new type of green battery, Vanadium Redox Flow Battery (VRFB) has the advantages of flexible scale, good charge and discharge performance and long life. It is suitable for large-scale electric energy storage and has attracted wide attention in recent years. In this paper, the characteristics and applications of liquid flow battery and VRFB are summarized. This paper starts from introducing ESS, analyzing several types of flow batteries, and finally focusing on VRFB to analyze its technical characteristics and application market.

Offshore Renewable Energy

Offshore renewable energy is an abundant clean energy source that includes offshore solar energy, offshore wind power, wave energy, ocean thermal energy conversion (OTEC), and tidal energy [...]

Lagrangian surface drifter observations in the North Sea: an overview of high-resolution tidal dynamics and surface currents

Abstract. A dataset of 85 Lagrangian surface drifter trajectories covering the central North Sea area and the Skagerrak from 2017–2021 of 17 deployments is presented. The data have been quality-controlled, uniformly structured, and assimilated in a standard NetCDF format (https://doi.org/10.1594/PANGAEA.963166, Meyerjürgens et al., 2023a). Using appropriate methods presented in detail here, surface currents were calculated from the drifter position data. Based on a drifter deployment in the Skagerrak, it is demonstrated that the Lagrangian measurements can be converted into an Eulerian representation by calculating mean current velocities. Tidal energy spectra were analyzed separately for the southern and northern areas of the North Sea, and tidal ellipses were calculated to determine the tidal impact on surface currents. Significant differences between the shallow shelf and the deeper areas of the North Sea are evident. While the shallow nearshore areas are dominated by tidal currents, deeper areas such as the Skagerrak record a high mean residual circulation driven by high-density gradients. Measurements using Eulerian approaches and remote sensing methods are restricted in temporal and spatial coverage, in particular, to capture fine-scale dynamics. For this reason, Lagrangian measurements, to a large extent, provide new insights into the complex submesoscale dynamics of the North Sea. Exemplarily, the Skagerrak region is used to demonstrate that high-resolution drifter observations capture both mesoscale and small-scale current patterns. This unique dataset, covering the entire southeastern North Sea and the Skagerrak, offers further analysis possibilities and can be used for the investigation of various hydrodynamic and environmental issues, e.g., the analysis of submesoscale current dynamics at ocean fronts, the determination of the kinetic eddy energy, and the propagation of pollutants in the North Sea.

A Generalized Empirical Model for Velocity Deficit and Turbulent Intensity in Tidal Turbine Wake Accounting for the Effect of Rotor-Diameter-to-Depth Ratio

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.

Assessing the Costs of Commercialising Tidal Energy in the UK

There is a need for increased renewable energy to meet net-zero targets and decarbonise the economy. Harnessing the predictable power of the tides with tidal stream turbines can contribute to this. Tidal energy is a nascent technology with higher costs at present. However, cost reductions have been observed with an increased deployment in other renewable energy technologies that have received financial support, and it is postulated that similar will happen with tidal energy. The first tidal stream projects have been awarded market support in the UK through the Contracts for Difference (CfD) scheme, with almost 100 MW expected to be commissioned by 2028. This work uses learning rates to investigate how much investment in ongoing market support might be needed to achieve cost reductions through subsidised deployment alongside research and innovation. Using a range of informed ‘what if?’ scenarios, it shows sensitivity to key inputs. The results show that the support needed is most sensitive to the learning rate, reducing it from 15% to 12.5% or 10% doubles or more than quadruples the investment required, respectively. The support is also highly dependent on the starting cost from which learning occurs, taken as the CfD Strike Price in 2025. Varying this between 156 and 220 GBP/MWh results in total investment of GBP 6.7 and 22.3 bn, respectively. Most importantly, a balance is needed between subsidising deployment to drive down costs through learning and funding innovation to maintain a high learning rate.

A deep learning approach for hydrofoil optimization of tidal turbines

Hydrofoil optimization plays a crucial role in improving the hydrodynamic performance of tidal turbines. However, the high-dimensional representations in hydrofoil design space require significant Computational Fluid Dynamics (CFD) simulations, increasing computational load and time expenditure. This paper proposes a hydrofoil optimization framework based on deep learning to achieve an effective mapping between design parameters, pressure fields, and hydrodynamic characteristics. The designed hydrofoil represented using the Signed Distance Function (SDF) is input to Convolutional Neural Networks (CNN) for fast prediction of hydrodynamic coefficients and pressure field. Due to the effective integration of the prediction model and genetic optimization algorithm, this framework can generate a large number of smooth hydrofoils and rapidly predict their hydrodynamic performance to achieve efficient optimization of hydrofoils. The optimized hydrofoil shapes obtained based on the above framework exhibit a higher lift-to-drag ratio than common hydrofoils. Furthermore, the optimized hydrofoils are applied to design tidal energy turbine blades. The simulation results demonstrate that the hydrodynamic performance of tidal turbines can be effectively improved through hydrofoil design optimization. The proposed framework enhances the design efficiency of the tidal turbine rotor and provides turbine hydrofoils with higher power coefficients.

Performance evaluation and optimal design for passive turbulence control-based hydrokinetic energy harvester using EWM-based TOPSIS

Passive turbulence control (PTC) in the form of square-shaped rods (SSR) is applied to improve the performance of the flow-induced vibration (FIV)-based energy harvester. The influence of SSR installation positions (θ) on the mechanical power and hydroelastic efficiency of SSR-cylinders is studied experimentally. Vortex-induced vibration (VIV) and VIV-galloping coupling modes are observed in this research. It is found that the SSR-cylinder with θ = 150° (VIV-galloping coupling) achieves the highest mechanical power, while the SSR-cylinder with θ = 180° (VIV) attains the highest hydroelastic efficiency. To evaluate the performance of energy harvesting and find the optimal design of the oscillator, the technique for order of preference by similarity to ideal solution (TOPSIS) is employed. The TOPSIS method considers both the average and maximum values of mechanical power and hydroelastic efficiency, with data-driven and adaptive weights estimated using the entropy weight method (EWM). It is indicated that the SSR installed at 150° obtains the optimal performance in a wide flow velocity range, followed by 140° and 70°. Finally, the effectiveness of the optimal design is validated by comparing it with other harvesters and the rationality of the proposed EWM-based TOPSIS method is analyzed in detail.

Leading-edge tubercles as an alternative to increasing a Francis turbine torque generation

Hydroelectricity accounts for 63.8% of Brazilian electricity, but several of the country’s power plants require modernization. For this, the insertion of leading-edge tubercles is an alternative since this device improves wind and tidal turbines. Surprisingly, no study explored the device’s potential for hydraulic turbine improvement. To address this gap, numerical simulations were conducted in Ansys CFX to assess the tubercles’ effects on the performance of Francis turbines. For this, the current study validated the simulations and tested the impacts of the tubercle structural parameters variation over the benchmarking turbine Francis-99 and applied the device in a non-modernized runner blade to evaluate its effects on equipment performance. The parameters test revealed that variations in tubercle amplitude and waviness ratio improved the torque generation up to 0.34% despite elevating the net head up to 0.43%. In the non-modernized blade, the device increased the torque generation and net head up to 1.77% and 4.13%, respectively, proving that the tubercles are an alternative for hydraulic turbine improvement. Also, the flow field analysis exhibits that the device creates vortices that influence the blade pressure side, delaying boundary layer detachment, agreeing with other results in the literature.

A comprehensive review on scour and scour protections for complex bottom-fixed offshore and marine renewable energy foundations

Due to the marine environment's complexity, optimising offshore foundations' design is still a major focus of the scientific and industrial community, since foundations represent a large portion of the total investment. Scour is one of the main causes that lead to ultimate, and service limit states, impacting design optimization and costs. Scour at monopile foundations has been extensively studied. However, advances in scour protections for hybrid structures, and other bottom-fixed foundations for offshore renewable energy harvesting technologies are often kept confidential by stakeholders, and knowledge gaps must be covered. Thus, the present paper provides a summary of the most recent physical and numerical studies related to scour and riprap scour protections for complex bottom-fixed foundations, such as jackets, tripods, gravity-based foundations (GBF), high-rise structure foundations (HRSF), and suction buckets, while covering other marine energy harvesting technologies as well, including wave energy converters (WEC) and tidal energy converters (TEC). This manuscript presents knowledge gaps, recent improvements, and potential studies on hybrid foundations – offshore wind turbine foundations combined with WECs or TECs. It is shown that offshore scour protection is a study field with a wide margin of development, but crucial for the future of the offshore renewable energy sector, thus pointing out key challenges and major opportunities for future research.

A novel full-process test bench for deep-sea in-situ power generation systems

A novel full-process test bench was developed to replace lengthy and costly deep-water experiments. This platform can accurately simulate the dynamic characteristics of hydrokinetic turbines and can be used to evaluate their power-supply capabilities under various conditions. The hydrokinetic turbine power model was established by obtaining discrete performance data through experimentally validated computational fluid dynamics simulations and building surrogate models using the response surface methodology. This approach offers higher accuracy and broader applicability than empirical models. Moreover, a stepper motor platform based on a speed control scheme is proposed for the first time that can achieve high-precision transient simulation with a simplified control mechanism. This platform was employed to assess the power supply capacity of two hydrokinetic turbines under constant and typical deep-sea flow speeds. The ductless Archimedes screw hydrokinetic turbine was found to be more suitable for the deep water application than the high-solidity horizontal axis turbine due to its high self-start capacity and power coefficient. Furthermore, a case study was conducted on the design of a deep-sea in-situ power generation system at Luzon Undercurrent. Results suggest that a ductless Archimedes screw hydrokinetic turbine with a 1000 mm radius can comfortably cater to the energy demands of miniature AUVs.

Study on the impact of wave characteristics on the performance of full-scale tidal turbine

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.