Showing papers on "Wave power published in 2019"

A recent increase in global wave power as a consequence of oceanic warming.

Abstract: Wind-generated ocean waves drive important coastal processes that determine flooding and erosion. Ocean warming has been one factor affecting waves globally. Most studies have focused on studying parameters such as wave heights, but a systematic, global and long-term signal of climate change in global wave behavior remains undetermined. Here we show that the global wave power, which is the transport of the energy transferred from the wind into sea-surface motion, has increased globally (0.4% per year) and by ocean basins since 1948. We also find long-term correlations and statistical dependency with sea surface temperatures, globally and by ocean sub-basins, particularly between the tropical Atlantic temperatures and the wave power in high south latitudes, the most energetic region globally. Results indicate the upper-ocean warming, a consequence of anthropogenic global warming, is changing the global wave climate, making waves stronger. This identifies wave power as a potentially valuable climate change indicator. The upper-ocean warming, a consequence of anthropogenic global warming, is changing the global wave climate, making waves stronger. Here the author show that global wave power has been increasing and can represent a climate change indicator.

Wave power extraction from multiple oscillating water columns along a straight coast

Abstract: The integration of oscillating water column (OWC) wave energy converters into a coastal structure (breakwater, jetty, pier, etc.) or, more generally, their installation along the coast is an effective way to increase the accessibility of wave power exploitation. In this paper, a theoretical model is developed based on the linear potential flow theory and eigenfunction matching method to evaluate the hydrodynamic performance of an array of OWCs installed along a vertical straight coast. The chamber of each OWC consists of a hollow vertical circular cylinder, which is half embedded in the wall. The OWC chambers in the theoretical model may have different sizes, i.e. different values of the radius, wall thickness and submergence. At the top of each chamber, a Wells turbine is installed to extract power. The effects of the Wells turbine together with the air compressibility are taken into account as a linear power take-off system. The hydrodynamic and wave power extraction performance of the multiple coast-integrated OWCs is compared with that of a single offshore/coast-integrated OWC and of multiple offshore OWCs. More specifically, we analyse the role of the incident wave direction, chamber size (i.e. radius, wall thickness and submergence), spacing between OWCs and number of OWCs by means of the present theoretical model. It is shown that wave power extraction from the coast-integrated OWCs for a certain range of wave conditions can be significantly enhanced due to both the constructive array effect and the constructive coast effect.

Experimental investigation of a land-based dual-chamber OWC wave energy converter

Abstract: Extensive investigation on wave energy converters (WEC) that convert wave power into electricity is required to improve competitiveness of wave energy, one of the most promising renewable energy resources. Better hydrodynamic performance should enable wave devices to compete favorably with conventional power plants in the near future. In this study the hydrodynamic performance of a land-based dual-chamber Oscillating Water Column (OWC) device is investigated experimentally, with emphasis on its overall performance and respective performance of the two sub-chambers of the system. The effects of the chamber breadth and the barrier wall draft on the hydrodynamic efficiency, the free surface elevation and the air pressure inside the chambers are investigated over a wide range of wave periods with a constant wave amplitude. Numerical simulations using fully nonlinear numerical wave tanks (NWTs) within the framework of potential flow theory are also carried out to cross-check the results, and help to further understand the experimental observations. It is found that both the maximum efficiency and the range of wave frequencies that leads to a higher rate of wave energy absorption, i.e. the effective frequency bandwidth, increase in the dual-chamber OWC system when compared to an equivalent typical single-chamber OWC device. The overall efficiency of the system is found to be insensitive to the variation of the sub-chamber breadth, while the efficiency of the two sub-chamber increases with its breadth when the total chamber breadth is kept the same. Additionally, the hydrodynamic efficiency is found to decrease with increasing barrier wall draft. The rear chamber (i.e., on the landward side) outperforms the front chamber (i.e., on the seaward side) for most of the wave frequencies investigated in this study, especially for the wave frequency that is at or close to the resonance frequency of the system.

State of the Art and Perspectives of Wave Energy in the Mediterranean Sea: Backstage of ISWEC

Abstract: According to the European Commission, sea waves have a great potential as renewable energy source. Despite wave energy technology is a field in continuous development, it is not yet competitive with the other renewables, due to the small quantities of devices sold, most of them being prototypal solutions at level. So far, various Wave Energy Converter concepts have been developed and some of them tested in full scale. The most recurrent test environment is the North Atlantic Ocean, which possesses high energy potential. The Mediterranean Sea on the other hand is less energetic, but also possesses less dangerous extreme conditions. It represents a favourable starting point to develop technologies that later will be scaled up to more powerful sites. This article illustrates the wave energy potential of the Mediterranean and analyses the wave energy converters engineered according to sea states characteristic of the Mediterranean Sea. Focus is brought to the Inertial Sea Wave Energy Converter (ISWEC) technology, which is one of the few Mediterranean concept to have reached Technology Readiness Level (TRL) 7. The article will document the deployment and the following open sea test campaign of a full scale prototype off the shore of Pantelleria Island, Italy.

Dynamics and control of air turbines in oscillating-water-column wave energy converters: Analyses and case study

Abstract: The paper presents a detailed analysis of the dynamics and control of air turbines and electrical generators in oscillating-water-columns (OWCs). The aim is to explain the performance of an OWC device based on the physical behaviour of each system component. The Mutriku wave power plant was chosen as the test case. The power plant is a breakwater located in the Bay of Biscay, in Basque Country, Spain. The contributions of the work are: i) development of a hydrodynamic model of the power plant in the frequency domain; ii) implementation of a non-linear time-domain wave-to-wire model; iii) real-valued implementation of the Prony method for the computation of the wave-radiation force; iv) a detailed generator model based on experimental data to assess the influence of the generator efficiency on the power take-off performance; v) a critical performance comparison of the Wells and biradial turbines; vi) a sensitivity analysis of the control parameters of the turbine/generator set; and vii) an explanation of the comparative performance of both turbines based on statistical data. The turbine performance curves were taken from developers’ published experimental data. The results were obtained with a simplified model of the wave climate off the Mutriku test site comprising 14 sea states.

Wave energy resource classification system for US coastal waters

Abstract: Energy resource classification systems are useful assessment tools that support energy planning and project development, e.g., siting and feasibility studies. They typically establish standard classes of power, a measure of the opportunity for energy resource capture. In this study, we develop wave energy resource classification systems for the US based on wave power (J, kW/m) and its distribution with peak period ( T p , s ). These metrics are calculated for 70,386 sites from partitioned bulk wave parameters generated from a validated 30-year WaveWatch III model hindcast. As the operating resonant period bandwidth of a wave energy converter (WEC) technology is an important design characteristic, the dominant period band containing the largest energy content is identified among three peak period band classes. These classification systems, comprised of four power classes and three peak period band classes, are based on the total wave power or the partitioned wave power in the dominant peak period band. They discriminate distinct trends in wave energy resource among five regions within the US, and provide useful information for energy planners, project developers, and technology designers. They also establish a framework for investigating the feasibility of a compatible wave climate (design load) conditions and WEC technology classification system to reduce design and manufacturing costs.

Trend analysis of significant wave height and energy period in southern Italy

Abstract: The Mediterranean Sea is subject to significant and variable climatic changes. In this work, an analysis of a 39-year-long wave time series was performed in order to identify ongoing trends of two synthetic parameters, significant wave height and energy period, along the coasts of the Calabria region (southern Italy). First, wave data were acquired from the global atmospheric reanalysis data set European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-Interim) and were processed in order to check their quality. Then, the data were subject to a geographical transposition method in order to transfer the wave parameters at a representative water depth of 100 m. Finally, trend analyses have been performed using the nonparametric Mann–Kendall (MK) test and a graphical technique, the Innovative Trend Analysis (ITA), which allows to identify trends in the several values of a series. At annual and seasonal scale, the results deduced from MK test mainly evidenced a slight or null increase of the significant wave height and a relevant increase of the energy period, influencing the magnitude of the wave power by the occurrence of longer waves. Moreover, the ITA method highlights a general increase in the highest values of the involved wave parameters. For the studied area, these aspects have a significant impact on the retreating of the beaches and on the future field installations of wave energy converters (WECs) for electricity purposes.

A Linear-Generator-Based Wave Power Plant Model Using Reliable Multilevel Inverter

Abstract: The huge untapped energy from ocean waves is one of the ideal solutions for world energy crisis. This paper proposes a linear-generator-based direct power conversion plant model to generate the electrical energy from ocean waves. The linear generator output is of variable magnitude and variable frequency in nature. In this paper, this variable output is converted to fixed dc voltage by using a diode bridge rectifier and a dc-link capacitor. The linear generator along with a diode bridge and a capacitor forms a wave power unit. These wave power units can be connected in series and parallel to meet the power ratings. A reliable multilevel inverter is fed from the wave power units to ensure uninterrupted tapping of power from this abundant renewable energy source. The reliable inverter operation is analyzed under open- and short-circuit faults in switches by reconfiguring the carrier waves of sine pulsewidth modulation during fault conditions. A fault detection algorithm using a single sensor at the output is also proposed to detect the faults in the switches of the proposed reliable inverter. The proposed plant model with a linear generator and a reliable inverter is simulated using ANSYS MAXWELL and MATLAB/Simulink. The plant model is tested using a programmable ac source for emulating the linear generator and the developed prototype of the diode bridge rectifier and the reliable multilevel inverter.

CMIP5-Based Wave Energy Projection: Case Studies of the South China Sea and the East China Sea

Abstract: Wave energy development will help ease resource crises. The projection of wave energy has practical value for the long-term planning of energy development (implementation of power generation, trading strategies, and so on). This paper proposed a wave energy projection program. South China Sea (SCS) and the East China Sea (ECS) in 2019 were carried out as case studies using the Coupled Model Intercomparison Project Phase 5 (CMIP5) dataset to drive the WAVEWATCH-III (WW3) wave model. The multiyear average wave energy of the SCS and ECS was presented. A comparison of the projected values with multiyear averages of the wave energy could positively contribute to the planning of the wave energy development. The results show that the SCS possessed relatively rich energy for both the past and future and that January and October possessed the highest wave power density (WPD). The projected annual average WPD in 2019 was similar to the multiyear average WPD in the north and middle of the ECS, slightly higher than the multiyear average in the south of the ECS, and considerably greater than that in the SCS. The projected WPDs in January, April, and October 2019 were higher than the multiyear averages in the corresponding months. In July, the projected WPD in the SCS was smaller than the multiyear average, while the opposite was observed in the south of the ECS. The projected effective wave height occurrence (EWHO) and the occurrence of WPD >2 kW/m in 2019 were also superior to the multiyear average values.

Resonant absorption in expanding coronal magnetic flux tubes with uniform density

Abstract: Aims. We investigate the transfer of energy between a fundamental standing kink mode and azimuthal Alfven waves within an expanding coronal magnetic flux tube. We consider the process of resonant absorption in a loop with a non-uniform Alfven frequency profile but in the absence of a radial density gradient.Methods. Using the three dimensional magnetohydrodynamic (MHD) code, Lare3d, we modelled a transversely oscillating magnetic flux tube that expands radially with height. An initially straight loop structure with a magnetic field enhancement was allowed to relax numerically towards a force-free state before a standing kink mode was introduced. The subsequent dynamics, rate of wave damping and formation of small length scales are considered.Results. We demonstrate that the transverse gradient in Alfven frequency required for the existence of resonant field lines can be associated with the expansion of a high field-strength flux tube from concentrated flux patches in the lower solar atmosphere. This allows for the conversion of energy between wave modes even in the absence of the transverse density profile typically assumed in wave heating models. As with standing modes in straight flux tubes, small scales are dominated by the vorticity at the loop apex and by currents close to the loop foot points. The azimuthal Alfven wave exhibits the structure of the expanded flux tube and is therefore associated with smaller length scales close to the foot points of the flux tube than at the loop apex.Conclusions. Resonant absorption can proceed throughout the coronal volume, even in the absence of visible, dense, loop structures. The flux tube and MHD waves considered are difficult to observe and our model highlights how estimating hidden wave power within the Sun’s atmosphere can be problematic. We highlight that, for standing modes, the global properties of field lines are important for resonant absorption and coronal conditions at a single altitude will not fully determine the nature of MHD resonances. In addition, we provide a new model in partial response to the criticism that wave heating models cannot self-consistently generate or sustain the density profile upon which they typically rely.

Resonant absorption in expanding coronal magnetic flux tubes with uniform density

Abstract: Aims. We investigate the transfer of energy between a standing kink mode and azimuthal Alfven waves within an expanding flux tube. We consider the process of resonant absorption in a loop with a non-uniform Alfven frequency profile but in the absence of a radial density gradient. Methods. Using the MHD code, Lare3d, we model an oscillating magnetic flux tube that expands radially with height. An initially straight loop structure with a magnetic field enhancement is relaxed towards a force-free state before a standing kink mode is introduced. Results. We demonstrate that the transverse gradient in Alfven frequency required for the existence of resonant field lines can be associated with the expansion of a high field-strength flux tube from concentrated flux patches. This allows for the conversion of energy between wave modes even in the absence of the density profile typically assumed in wave heating models. As with standing modes in straight flux tubes, small scales are dominated by the vorticity at the loop apex and by currents at the foot points. The azimuthal wave exhibits the structure of the expanded flux tube and is therefore associated with smaller length scales close to the foot points of the flux tube. Conclusions. Resonant absorption can proceed throughout the corona, even in the absence of dense loop structures. The flux tube and MHD waves considered are difficult to observe and our model highlights how estimating hidden wave power within the solar atmosphere can be problematic. We highlight that, for standing modes, the global properties of field lines are important for resonant absorption and coronal conditions at a single altitude will not fully determine the nature of MHD resonances. We provide a new model in partial response to the criticism that wave heating models cannot self-consistently generate or sustain the density profile upon which they typically rely.

Temporal Variation of the Wave Energy Flux in Hotspot Areas of the Black Sea

Abstract: This paper aims to examine the temporal variation of wave energy flux in the hotspot areas of the Black Sea. For this purpose, a 31-year long-term wave dataset produced by using a three-layered nested modelling system was used. Temporal variations of wave energy were determined at hourly, monthly, seasonal, and yearly basis at seventeen stations. Based on the results obtained, it can be concluded that the stations have very low fluctuations in mean wave power during the day. Mean wave power in the summer months shows a low difference between the stations, but in the winter months, there is a higher difference in wave power between the stations. This difference is more at the stations in the southwestern part of the Black Sea and much lower in the eastern Black Sea stations around Sinop, being in the middle of the southern coast of the Black Sea. In addition, it is concluded that mean wave energy flux presents a decreasing trend at all stations, but maximum wave power offers an increasing trend at most of the stations.

Design of Permanent-Magnet Linear Generators with Constant-Torque-Angle Control for Wave Power

Abstract: This paper presents a simulation method for direct-drive permanent-magnet linear generators designed for wave power. Analytical derivations of power and maximum damping force are performed based on Faraday’s law of induction and circuit equations for constant-torque-angle control. Knowledge of the machine reactance or the load angle is not needed. An aim of the simulation method is to simplify comparison of the maximum damping force, losses, and cost between different generator designs at an early design stage. A parameter study in MATLAB based on the derived equations is performed and the effect of changing different generator parameters is studied. The analytical calculations are verified with finite element method (FEM) simulations and experiments. An important conclusion is that the copper losses and the maximum damping force are mainly dependent on the rated current density and end winding length. The copper losses are inherently large in a slow-moving machine so special consideration should be taken to decrease the end winding length. It is concluded that the design of the generator becomes a trade-off between material cost versus high efficiency and high maximum damping force.

Characterization of Wave Energy Potential for the Baltic Sea with Focus on the Swedish Exclusive Economic Zone

Abstract: In this study, a third-generation wave model is used to examine the wave power resource for the Baltic Sea region at an unprecedented one-kilometer-scale resolution for the years 1998 to 2013. Special focus is given to the evaluation and description of wave field characteristics for the Swedish Exclusive Economic Zone (SEEZ). It is carried out to provide a more detailed assessment of the potential of waves as a renewable energy resource for the region. The wave energy potential is largely controlled by the distance from the coast and the fetch associated with the prevailing dominant wave direction. The ice cover is also shown to significantly influence the wave power resource, especially in the most northern basins of the SEEZ. For the areas in focus here, the potential annual average wave energy flux reaches 45 MWh/m/year in the two sub-basins with the highest wave energies, but local variations are up to 65 MWh/m/year. The assessment provides the basis for a further detailed identification of potential sites for wave energy converters. An outlook is given for additional aspects studied within a broad multi-disciplinary project to assess the conditions for offshore wave energy conversion within the SEEZ.