Showing papers on "Wave power published in 2020"

Wave Energy Resource Assessment for Exploitation—A Review

Abstract: Over recent decades, the exploitation of wave energy resources has sparked a wide range of technologies dedicated to capturing the available power with maximum efficiency, reduced costs, and minimum environmental impacts. These different objectives are fundamental to guarantee the development of the marine wave energy sector, but require also refined assessments of available resource and expected generated power to optimize devices designs and locations. We reviewed here the most recent resource characterizations starting from (i) investigations based on available observations (in situ and satellite) and hindcast databases to (ii) refined numerical simulations specifically dedicated to wave power assessments. After an overall description of formulations and energy metrics adopted in resource characterization, we exhibited the benefits, limitations and potential of the different methods discussing results obtained in the most energetic locations around the world. Particular attention was dedicated to uncertainties in the assessment of the available and expected powers associated with wave–climate temporal variability, physical processes (such as wave–current interactions), model implementation and energy extraction. This up-to-date review provided original methods complementing the standard technical specifications liable to feed advanced wave energy resource assessment.

Plasma Waves near the Electron Cyclotron Frequency in the Near-Sun Solar Wind

Abstract: Data from the first two orbits of the Sun by Parker Solar Probe reveal that the solar wind sunward of 50 solar radii is replete with plasma waves and instabilities. One of the most prominent plasma wave power enhancements in this region appears near the electron cyclotron frequency (f_ce). Most of this wave power is concentrated in electric field fluctuations near 0.7 f_ce and f_ce, with strong harmonics of both frequencies extending above f_ce. At least two distinct, often concurrent, wave modes are observed, preliminarily identified as electrostatic whistler-mode waves and electron Bernstein waves. Wave intervals range in duration from a few seconds to hours. Both the amplitudes and number of detections of these near-f_ce waves increase significantly with decreasing distance to the Sun, suggesting that they play an important role in the evolution of electron populations in the near-Sun solar wind. Correlations are found between the detection of these waves and properties of solar wind electron populations, including electron core drift, implying that these waves play a role in regulating the heat flux carried by solar wind electrons. Observation of these near-f_ce waves is found to be strongly correlated with near-radial solar wind magnetic field configurations with low levels of magnetic turbulence. A scenario for the growth of these waves is presented which implies that regions of low-turbulence near-radial magnetic field are a prominent feature of solar wind structure near the Sun.

Recent Progress in Electrical Generators for Oceanic Wave Energy Conversion

Abstract: Oceanic wave energy extraction through electrical generator is one of the most interesting topics in the field of power engineering. Almost all the existing relevant review paper focus on electrical generator with the working principle of electromagnetic induction or piezoelectric or triboelectric effect. In this paper, all the existing types (based on principle of operation) of electrical generator used for wave power harvesting are discussed. This paper not only covers recent progress in electrical power generation by electro-magnetic induction, piezoelectric generator, and electrostatic induction, but also presents critical comparative review as well where suitable use and weakness of each type of generators are discussed. Moreover, the application of advanced magnetic core, winding, and permanent magnets are discussed with extensive explanation which are not focused in the existing reviews. Various new constructional features of the electrical generators such as split translator flux switching, two-point absorber, triangular coil, dual port linear generator, piezoelectric, triboelectric nanogenerator, etc. are highlighted with principles of operation. It also includes emerging human intervened optimization method for determining optimum shape of generator and cooling system which is necessary to prevent demagnetization of the permanent magnet. Finally, the way of supply the generated electrical power form the generator to load/grid is thoroughly described in a separate section that would be obvious for successful operation. The comparison among all types of generators in terms of output voltage, current, scale of power production, power-frequency characteristics, power density, cascading, and approaches are tabulated in this paper.

Water-wave interaction with submerged porous elastic disks

Abstract: Hydroelastic interaction between water waves and submerged porous elastic disks of negligible thickness in water of finite depth is investigated under the assumption of small amplitude water-wave motion and structural response. The disks are either simply supported or clamped at their edges. Wave power can be absorbed/dissipated by the disks due to their porosity. A theoretical model based on the linear potential flow theory and eigenfunction matching method is developed to solve the wave scattering problem of the submerged disks. An indirect method, employing Kochin functions, is derived based on Green's theorem to evaluate the wave power absorption/dissipation, and it produces accurate results at a lower computational cost than the conventional method. This theoretical model is applied to perform a multi-parameter study on the performance of a single submerged porous elastic disk, and an array of disks as well, particularly, in terms of near-field wave motion, disk deflection, far-field scattering coefficient, and wave power absorption/dissipation. Deploying multiple disks in an array is found to be a more promising approach for wave power absorption/dissipation compared to enlarging the area of a single disk.

A systematic approach for selecting suitable wave energy converters for potential wave energy farm sites

Abstract: The ocean covers approximately 70% of the earth's surface and contains an immense source of renewable energy, in terms of ocean waves. However, this resource is unevenly distributed throughout the world, and so, therefore, converting waves into a useful form of energy will require the identification of potential Wave Energy Farm (WEF) locations. This should be undertaken in tandem with selecting an appropriate Wave Energy Converter (WEC), as the characteristics of these devices are critical in capturing the available wave power. Therefore, this paper describes a three-stage systematic approach that was developed and implemented in order to select the most suitable WEC(s) for marine areas identified as optimal for WEFs. As this sector is evolving rapidly, the first stage identified all WECs currently in development and proposed classifying these devices in a practical and meaningful manner. The second stage developed a procedure for identifying generic WEF locations by integrating the multiple dimensions of sustainable development and the technical limitations of the sector, within a geographic information systems framework. Lastly, the third stage incorporates the results from the previous two stages. The devices considered for further analysis were reduced based on commercial viability, whilst the available power was quantified and characterised at each of the optimal WEF sites. Thereafter, appropriate techno-economic performance indicators were identified to rank and determine the optimal device for a specific location.

Hydrodynamic Response of a Combined Wind–Wave Marine Energy Structure

Abstract: Due to the energy crisis and greenhouse effect, offshore renewable energy is attracting increasing attention worldwide. Various offshore renewable energy systems, such as floating offshore wind turbines (FOWTs), and wave energy converters (WECs), have been proposed and developed so far. To increase power output and reduce related costs, a combined marine energy structure using FOWT and WEC technologies has been designed, analyzed and presented in the present paper. The energy structure combines a 5-MW braceless semisubmersible FOWT and a heave-type WEC which is installed on the central column of the semisubmersible. Wave power is absorbed by a power take-off (PTO) system through the relative heave motion between the central column of the FOWT and the WEC. A numerical model has been developed and is used to determine rational size and draft of the combined structure. The effects of different PTO system parameters on the hydrodynamic performance and wave energy production of the WEC under typical wave conditions are investigated and a preliminary best value for the PTO’s damping coefficient is obtained. Additionally, the effects of viscous modeling used during the analysis and the hydrodynamic coupling on the response of the combined structure are studied.

Comparison of wave–structure interaction dynamics of a submerged cylindrical point absorber with three degrees of freedom using potential flow and computational fluid dynamics models

Abstract: In this paper, we compare the heave, surge, and pitch dynamics of a submerged cylindrical point absorber, simulated using potential flow and fully resolved computational fluid dynamics (CFD) models. The potential flow model is based on the time-domain Cummins equation, whereas the CFD model uses the fictitious domain Brinkman penalization technique. The submerged cylinder is tethered to the seabed using a power take-off (PTO) unit, which restrains the heave, surge, and pitch motions of the converter and absorbs energy from all three modes. It is demonstrated that the potential theory overpredicts the amplitudes of heave and surge motions, whereas it results in an insignificant pitch for a fully submerged axisymmetric converter. It also underestimates the slow drift of the buoy, which the CFD model is able to capture reliably. Furthermore, we use fully resolved CFD simulations to study the performance of a three degrees of freedom cylindrical buoy under varying PTO coefficients, mass density of the buoy, and incoming wave heights. It is demonstrated that the PTO coefficients predicted by the linear potential theory are sub-optimal for waves of moderate and high steepness. The wave absorption efficiency improves significantly when a value higher than the predicted value of the PTO damping is selected. Simulations with different mass densities of the buoy show that converters with low mass densities have an increased tension in their PTO and mooring lines. Moreover, the mass density also influences the range of resonance periods of the device. Finally, simulations with different wave heights show that at higher heights, the wave absorption efficiency of the converter decreases and a large portion of available wave power remains unabsorbed.

Wave Energy Converter Power Take-Off System Scaling and Physical Modelling

Abstract: Absorbing wave power from oceans for producing a usable form of energy represents an attractive challenge, which for the most part concerns the development and integration, in a wave energy device, of a reliable, efficient and cost-effective power take-off mechanism. During the various stages of progress, for assessing a wave energy device, it is convenient to carry out experimental testing that, opportunely, takes into account the realistic behaviour of the power take-off mechanism at a small scale. To successfully replicate and assess the power take-off, good practices need to be implemented aiming to correctly scale and evaluate the power take-off mechanism and its behaviour. The present paper aims to explore and propose solutions that can be applied for reproducing and assessing the power take-off element during experimental studies, namely experimental set-ups enhancements, calibration practices, and error estimation methods. A series of recommendations on how to practically organize and carry out experiments were identified and three case studies are briefly covered. It was found that, despite specific options that can be strictly technology-dependent, various recommendations could be universally applicable.

Wave Power Absorption by Arrays of Wave Energy Converters in Front of a Vertical Breakwater: A Theoretical Study

Abstract: The present paper deals with the theoretical evaluation of the efficiency of an array of cylindrical Wave Energy Converters (WECs) having a vertical symmetry axis and placed in front of a reflecting vertical breakwater. Linear potential theory is assumed, and the associated diffraction and motion radiation problems are solved in the frequency domain. Axisymmetric eigenfunction expansions of the velocity potential are introduced into properly defined ring-shaped fluid regions surrounding each body of the array. The potential solutions are matched at the boundaries of adjacent fluid regions by enforcing continuity of the hydrodynamic pressures and redial velocities. A theoretical model for the evaluation of the WECs’ performance is developed. The model properly accounts for the effect of the breakwater on each body’s hydrodynamic characteristics and the coupling between the bodies’ motions and the power take-off mechanism. Numerical results are presented and discussed in terms of the expected power absorption. The results show how the efficiency of the array is affected by (a) the distance between the devices and the wall, (b) the shape of the WEC array configuration, as well as (c) the angle of the incoming incident wave.

Evaluating the future efficiency of wave energy converters along the NW coast of the Iberian Peninsula

Abstract: The efficiency of wave energy converters (WECs) is generally evaluated in terms of historical wave conditions that do not necessarily represent the conditions that those devices will encounter when put into operation. The main objective of the study is to assess the historical and near future efficiency and energy cost of two WECs (Aqua Buoy and Pelamis). A SWAN model was used to downscale the wave parameters along the NW coast of the Iberian Peninsula both for a historical period (1979–2005) and the near future (2026–2045) under the RCP 8.5 greenhouse scenario. The past and future efficiency of both WECs were computed in terms of two parameters that capture the relationship between sea states and the WEC power matrices: the load factor and the capture width. The wave power resource and the electric power capacity of both the WECs will decrease in the near future. The load factor for Aqua Buoy will decrease in the entire area, while it will remain unchanged for Pelamis in most of the area, except north of 43.5° N. The capture width and cost of energy will increase for both devices. The methodology here applied can be easily applied to any device and coastal domain under different climate change scenarios.