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In 2019 a Scientific Research & Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China. It is a simplified small model of a two-module semi-submersible-type VLFS. The test on site has continued for more than one and half years since then for long-term observations to validate the developed key technologies for design and behavior predictions of floating structures deployed near islands and reefs. An integrated information system was set up to continuously collect and inspect the data of the encountered waves, structure responses, connector forces, mooring line forces, anti-corrosion status of the platform, the performance efficiencies of a floating breakwater nearby and a wave energy converter attached on the breakwater. In this paper, the status of the on-site measurements and validations of the key technologies are briefly described.

This paper examines the response of a heaving plate wave energy converter integrated with a chambered breakwater system through experimental and numerical simulations. A porous seaside wall with 20% porosity and an impermeable back wall constitutes a chambered breakwater under investigation. The time-domain response of the wave energy converter before and after integration with the chambered breakwater is evaluated using an open-source code WEC-Sim implemented in MATLAB and Simulink. The performance of WEC subjected to regular wave conditions and the wave elevations measured from the experiments are examined in the present investigation. The reflection characteristics of the chambered breakwater system after integrating with the wave energy converter have been found to decrease. The heave RAO of the wave energy converter installed at a location toward the porous wall is observed to have improved by 22% after integrating with the chambered breakwater than the stand-alone wave energy converter. A similar increase in the power generation performance of the wave energy converter is also observed. The proposed system can improve the economic competitiveness of the wave energy converter by serving dual purposes.

With the continuous development of society and economy, people’s demand for electric energy is increasing. The low-carbon and energy-saving technologies of renewable energy especially wave energy have become the focus of current researches. Considering the increasingly serious energy problems, a wave energy converter (WEC) is proposed based on Halbach permanent magnetic array, which increases the output performance. The equivalent magnetic circuit model of the WEC is established. The static magnetic field modeling and structural parameters optimal permanent of the WEC are performed on this theoretical. Theoretical studies have found that the optimal permanent magnet thickness ratios for Halbach permanent magnet array structures is 0.6, and the ratio of permanent magnet to coil radial ratio is 0.7. The coil winding form and rectifying circuit of the WEC were designed. The WEC equivalent magnetic circuit model was verified by COMSOL Multiphysics finite element software, and the open circuit voltages of WEC was obtained. If the WEC moves at a speed of 0.1 m/s, the coil voltage can reach about 113 V after simulation. According to the testing requirements of the WEC, a test platform was built. The Halbach permanent magnet array structures greatly enhances the wave energy collection of WEC.

The hydraulic power take-off (HPTO) is considered as the most promising method to convert wave power to electrical power. This paper presents an experimental assessment of the power conversion of a wave energy converter using HPTO. Based on the experimental results, a modification of accumulator pre-charged pressure and a control strategy were proposed to improve the system performance. System design, the working principle and mathematical model of all components were described. The proposed method was verified based on both simulation and experimental tests. The results showed that the system always works at an optimal condition under different input wave conditions.

System level optimization is used to design an innovative ocean–wind energy converter to meet the “as good as it can be done” design objective. This general design procedure is then applied to the design of a 20 kW energy system and it is demonstrated that a combined energetic and economical design procedure is required for an optimal solution.

Since the hydraulic power take-off (PTO) is a widely-utilized transmission device for oscillating-body wave energy converters, its parameter configurations need to be optimized with an accurate dynamic model. To accurately describe the cylinder friction force, the motor loss and the accumulator working patterns, this paper establishes a novel nonlinear state space model for a hydraulic PTO. The model contains a stiction-involved Stribeck curve for the hydraulic cylinder, an improved Jeong's theory for the hydraulic motor and a pressure-bound-related formula for the high-pressure accumulator. The proposed model is simulated in irregular waves and verified via the comparison with the WEC models based on Yang's theory [1]. Furthermore, the research focuses on obtaining optimal PTO parameter configurations with the suitable piston area and resistance, according to the generating ability, energy conversion efficiency and pressure stability. The results show that the piston area has a more significant impact on the generating ability and pressure stability than the resistance but the same influence on the energy conversion efficiency. In general, a small piston area and a minor resistance are the superior configurations at the fixed capacity.

We consider the hydrodynamics of wave energy converter (WEC) arrays consisting of periodically repeated single bodies or sub-arrays. Of special interest is the array gain due to wave interactions as a function of the spatial configuration of the array. For simplicity, we assume identical WECs oscillating in heave only, although the results should extend to general motions. We find that array gains can be as high as $O(10)$ compared to the same WECs operating in isolation. We show that prominent decreases in array gain are associated with Laue resonances, involving the incident and scattered wave modes, for which we obtain an explicit condition. We also show theoretically that Bragg resonances can result in large decreases in gain with as few as two rows of strong absorbers. For general WEC geometries, we develop a multiple-scattering method of wave–body interactions applicable to generally spaced periodic arrays. For arrays of truncated vertical cylinders, we perform numerical investigations confirming our theoretical predictions for Laue and Bragg resonances. For a special class of multiple-row rectangular WEC arrays, our numerical results show that motion-trapped Rayleigh–Bloch waves can exist and be excited by an incident wave, resulting in sharp, narrow-banded spikes in the array gain.

Today, the importance of using vernier machines in wave energy converters has increased because of its simple structure and ability to generate a lot of thrust force at low speeds due to the magnetic gear effect. The linear vernier permanent magnet machine has been designed in various structures. Proper design and selection of the main parameters of the machine will improve performance and increase the efficiency of the linear vernier machine. One of these parameters is the shape of the permanent magnets and how they are magnetically oriented. The novelty of this paper is the reduction of leakage flux, achieved by changing the shape and orientation of the permanent magnet. Three types of linear permanent magnet vernier machines with different permanent magnet structures and orientation, including V-shape, Halbach array and consequent-pole are presented. The considered machines have been compared to each other and to the existing machine in terms of airgap flux density, back EMF, PM flux, Inductance, thrust force, detent force, loss, efficiency, power factor, flux density and flux line, using the finite element method in the same conditions and with the same volume of permanent magnets. The results show that the magnetic orientation and shape of the permanent magnet have a considerable effect on the leakage flux, and all the proposed models have a lower leakage flux and better performance compared to the existing model.

Wave energy has the potential to play an important role in the UK's electricity mix in the coming years and it is important to understand the interactions of wave energy converters with the environment before considering them viable alternatives for other technologies. The aim of this study was to identify the environmental impacts of the deployment of the Oyster wave energy converter to the EMEC test site at Orkney, UK over its lifetime across three general categories: resource use, human health and ecological consequences. A full life cycle assessment was performed on two different models of the Oyster wave energy converter: Oyster 1 and Oyster 800. It was found that the latter is a fitting upgrade for its predecessor as it has lower environmental impacts in all categories; however, the high infrastructural needs of the Oyster technology makes its environmental performance worse than most other wave energy converters. Key sustainability indicators for energy converters include carbon footprint and energy payback period, and these were found to be 79 and 57 gCO2 eq/kWh and 45 and 42 months for the Oyster 1 and Oyster 800, respectively. Although these are significantly higher than most estimates for other types of renewable energy converter, the carbon impacts are still significantly lower than for conventional fossil-fuelled power generation.

This paper aims to investigate electric dynamics and improve electric power generation of an isolated wave energy converter that uses a linear permanent magnet generator as the power take-off system, excited by regular or irregular waves. This is of significant concern when considering actual operating conditions of an offshore wave energy converter, where the device will encounter different sea states and its electric load needs to be tuned on a sea-state-to-sea-state basis. To that end, a fully coupled fluid-mechanical-electric-magnetic-electronic mathematical model and an optimization routine are developed. This proposed time-domain wave-to-wire model is used to simulate the hydrodynamic and electric response of a wave energy converter connected to specific electric loads and also used in an optimization routine that searches optimal resistive load value for a wave energy converter under specific sea states. Sample results are presented for a point-absorber type wave energy converter, showing that the electric power generation of a device under irregular waves can be significantly improved. Keywords: wave energy converter, wave power system, wave-to-wire model, linear permanent magnet generator, electric load optimization., Comment: Accepted by Energy

The analysis of electromechanical energy converters based on metal-thin film ferroelectric (with a large specific capacitance)-nanogap-moving electrode structures was performed. It was shown that the density of the energy being converted and its absolute value increase with the decreasing gap value between the surfaces of the ferroelectric and the metallic moving electrode up to nanometer values. The effects limiting the growth of this energy were established, and the limiting value of the energy density transformed in the nanogap of these structures was determined to be about 1.6 &times, 1010 J/m3, which is 4 orders of magnitude higher than the energy density in inductive converters. The experimental verification of this model based on the data for micromotors fabricated on these structures is given.

The potential of wave power as an alternative energy resource is being studied to address problems associated with fossil fuel exhaustion and environmental pollution. In this paper, to improve the power generation efficiency of a floating-type wave-energy converter that has an activating body, the effects of the positions of a connecting bridge and different connecting methods between a main body and the activating body of the wave-energy converter were studied. In order to research the activating body’s motion characteristics that are caused by the changes of connecting bridge’s position and connecting methods; hinged or fixed connector, the wave-energy converter was modeled and simulated by using a commercial software. The moment and angular velocity of the axis of power generation were measured from the results of simulations and then the power outputs were calculated based on the moment and angular velocity. The outputs, which were analyzed under several regular wave conditions, were compared to each other.

The information of the wave loads on a wave energy device in operational waves is required for designing an efficient wave energy system with high survivability. It is also required as a reference for numerical modeling. In this paper, a novel system, which integrates an oscillating wave energy converter with a pile-restrained floating breakwater, is experimentally investigated in a 2-D wave flume. The measurements of the wave pressure on the wet-surface of the device are made as the function of the power take-off (PTO) damping force. It is shown that the wave pressure is significantly affected by the PTO system, in particular, at the edges, and the wave pressure varies under different wave conditions. From the results, conclusions can be drawn on how the PTO damping force and wave conditions affect the loads on the device, which is of engineering concern for constructing safe and reliable devices.

In the present paper, the development of a model scale Wave Energy Converter (WEC) and an experimental WEC test rig are presented, and results of numerical simulations and experimental measurements are shown. The presented point absorber WEC is coupled to a generic power take-off (PTO) and is restricted to pure heave motion in regular waves. Experiments were carried out at the Universidad Austral de Chile (UACh) Wave Tank and results from responses and efficiencies were compared with data from the BEM (boundary element method) code WAMIT. Numerical and experimental results showed good agreement. Finally, results were extrapolated and superposed with typical wave energy spectra found in different Chilean regions, providing a first performance estimation for a wave energy converter in Chile. Results are discussed and compared with an existing technology and give an insight of the potential for wave energy technologies in Chile. Further investigation is proposed for an analysis in irregular waves and the use of a more advanced PTO (power take-off) in the future.

The Tupperwave device is a wave energy converter based on the Oscillating Water Column (OWC) concept. Unlike conventional OWC devices, which are opened to the atmosphere, the Tupperwave device works in closed-circuit and uses non-return valves and accumulator chambers to create a smooth unidirectional flow across a unidirectional turbine. The EU-funded OceanEraNet project called Tupperwave was undertaken by a consortium of academic and industrial partners, aimed at designing and modelling the Tupperwave device. The device was numerically modelled using two different methods. It was also physically modelled at the laboratory scale. The various modelling methods are discussed and compared. An analysis of the dependence of the device efficiency on the valves and turbine aerodynamic damping is carried out, using both physical and numerical approaches.

The exploitation of sea wave represents an important frontier for the energy sustainability in the next future. Despite the proposal of several techniques and solutions, commercial devices are not available. In this context, the Department of Engineering is investigating an innovative solution based on linear energy generators. This machine can be adopted as the main component in a wave energy converter, that is the device for the energy extraction of sea wave. Starting from an existing prototype, the paper examines the replacement of the iron stator with a non-magnetic material, in order to solve several common problems of linear generators, such as the cogging force. Results are reported, considering the no-load voltages and the cogging force produced by the generator in both cases.

This paper presents a mathematical model of layered thermoelectric energy Converter, designed for high current power supply. The obtained thermal fields and fields of thermo-mechanical stresses in it. Advantages of high-current layered design elements before the classic U-shaped.

It has long been recognized that a need for practical methods for maintaining optimum cesium pressure within a thermionic energy converter has been pursued for space applications. An attractive solution to the problem is the use of a sorption type reservoir where cesium absorbed into a lattice. Four graphite materials were initially investigated for the potential usage as cesium storage media. Primary research focusing on the characteristics of loading ability, structural integrity, and dimensional change of these materials was performed by synthesizing proper cesium-graphite lamellar compounds with a two zone vapor transport method. Graphite foams show promising prospect for thermionic application as integral cesium reservoir material.

Energy from ocean waves remains largely an untapped resource. This is also highly consistent in comparison to other alternate sources of energy such as wind and solar. Present study deals with the design and development of innovative wave energy converter (WEC) that uses a buoy-type point absorber. The device is proposed to be mounted on an offshore platform and be used to produce electric output for meeting the operational energy demands, partially. The device employs lever arm and gear boxes to obtain the mechanical work from the heave energy of the floating buoy. Subsequently, electric energy is generated from the mechanical work harnessed from the waves by deploying a generator. Design Failure Mode and Effect Analysis is carried out on system to identify effects of failure modes.

A tubular yokeless linear permanent-magnet (PM) machine is proposed for free-piston energy converter (FPEC), where high mass and volume power density are required. Topology, operating principle, design, and optimization of the tubular yokeless linear PM machine are studied. With the quasi-sinusoidal speed characteristic of the resonant piston considered, a single-phase yokeless linear PM machine is designed for FPEC by finite-element method. Some main design parameters, which include air-gap diameter, PM thickness, axial lengths of the radially magnetized magnets at center and two ends of the mover, pole pitch, and tooth pitch, are optimized to achieve higher power density. Compared with the conventional linear PM machines, the yokeless linear PM machine has the advantages of higher efficiency, higher mass, and volume power density. The utilization of space and machine material is also improved by adopting the yokeless machine topology.

Accurate prediction of long-term extreme loads is essential for the design of wave energy converters (WECs), but it is also computationally demanding due to the low probabilities associated with their occurrence. Although a full long-term probabilistic analysis using integration over all sea states or Monte Carlo simulation (MCS) may be used, these methods can be prohibitively expensive when individual response simulations are complex and time-consuming. The application of polynomial chaos expansion (PCE) schemes to allow the propagation of uncertainty from the environment through the stochastic sea surface elevation process and ultimately to WEC extreme load response prediction is the focus in this study. A novel approach that recognizes the role of long-term ocean climate uncertainty (in sea state variables such as significant wave height and spectral peak period) as well as short-term response uncertainty arising from the unique random phasing in irregular wave trains is presented and applied to a single-body point-absorber WEC device model. Stochastic simulation results in time series realizations of various response processes for the case-study WEC. We employ environmental data from a possible deployment site in Northern California (NDBC 46022) to assess long-term loads. MCS computations are also performed and represent the “truth” system against which the efficiency and accuracy of the PCE surrogate model are assessed. Results suggest that the PCE approach requires significantly less effort to obtain comparable estimates to MCS.

Energy harvesting in uniflow fluid environment aims at ambient energy that can be used in water environment for monitor equipment. In this paper, we focus on coupling both bending vibration and torsional vibration to gain better power generation. A novel structure of energy converter(arc-shaped) was designed and manufactured. Meanwhile the influence of vibrator with and without a pelvic fin was tested. Mathematical analyse due to vibration phenomenon and experimental result are reported. The 270-degree arc-shaped ring size piezoelectric ceramic is verified capable of producing an effective voltage over 10 V with the power of 0.5 mW.

Features of physical processes in the electromechanical energy converter of a valve engine are described, and a general procedure of studying the electromagnetic processes in normal and emergency operational modes is developed that is based on them. As a result, the energy parameters and instantaneous values of output engine coordinates are obtained for these modes. © 2012 Allerton Press, Inc.

The last couple of decades have observed an increasing interest in development of wave energy conversion technology for both research and commercial purposes. Though slow due to several reasons, the technology shows an evident progress. Because of the oil crisis facing the energy sector in particular, wave energy is currently seen as a good alternative to fossil fuel based power generation. This has marked its footprints on rising industrial ventures in wave energy based power generation and the search for new devices is gearing up. Among the latest invented models, point wave energy converters are attractive and low investment options. These devices are much smaller than the traditional oscillating water column devices and have good performance when combined in arrays of devices, thus placing the technology in the center of industrial and academic research. This article reports the study conducted to understand the mechanics of the energy exchange in a single-body point wave energy converter device model Cape Verde, patented by the Norwegian company Euro Wave Energy. Furthermore, the article intends to give a practical solution for the design of the anchoring problem in the device. In general, the article attempts to present two completely different objectives: an academic part focusing on understanding the wave energy conversion mechanics, and the industrial development part that attempts to find a practical solution for a particular part of the device. The first step involves establishing a model that describes the motion and potential of absorbance of a conic single-body absorber. The anchor system was designed in accordance with standards provided by Det Norske Veritas, the Norwegian regulatory framework. A quasi-static method is used to calculate the load that the absorber would suffer and a pulley and cable system is proposed to drive these loads to the anchor system. After a review of the different solutions offered for offshore facilities at the present time, the model of a suction anchor is chosen. As design verification through physical testing of prototypes of conversion devices is demanding and costly, various simulation tools are appearing in the field. The application range of some of these different simulation tools has been evaluated and reported in this article.

Free-piston energy converter, composed of a free-piston engine and a permanent-magnet (PM) linear machine, is a promising generator concept for series hybrid electric vehicles (HEVs). In this paper, a novel transverse-flux PM linear machine is investigated for such applications. Unlike conventional transverse-flux machines, the proposed machine features simple mechanical structure. Flux leakage of the proposed machine is analyzed, and parameters of the machine are optimized by finite-element method (FEM). Compared with conventional flux configurations, such as radial flux, axial flux and Halbach, the proposed transverse-flux topology showed advantages in low cogging force, low thrust fluctuation, and high efficiency. A prototype was designed and manufactured. Further experiments indicated satisfactory load characteristic of the machine.

Floating devices, such as a cavity resonance device, take advantage of both the water motion and the wave induced motions of the floating body itself. In the design of a wave energy converter (WEC), the most significant factor is that an optimum length of the internal water column should exists, that is, a length in which maximum power is converted near the heaving resonance. A theoretical analysis of this power generated by a pneumatic-type WEC is performed, and the results obtained from the analysis are used for a real WEC for a buoy. The length of the internal water column corresponds to that of the water mass in the water column. If designed properly, a WEC can take advantage not only of the cavity resonance but also of the heaving motion of the buoy. This paper presents the test results of the generation characteristic of a WEC and the harmful effect of fouling in the internal water column. The results are then applied to the design of a WEC for a buoy.

Two new ideas on the electrohydraulic actuation of blood pumps have been combined. The first idea was to put the energy converters that propel the hydraulic fluid inside the compliance reservoir instead of having them separate. Compactness of the device and better cooling of the energy converter by the surrounding fluid are two major advanages of this approach. Secondly, we put the pumping membrane inside a clamshell that fits over a soft ventricle (I). The ventricle can be implanted first, after which the shell is slid over it. These two ideas have resulted in devices described in this paper. Preliminary in vitro and in vivo data are presented.

Former renewable technologies, which did not prosper at that time due to engineering and material limitations, emerge once again, as in the case of the Alkali Metal Thermal to Electric Converter (AMTEC). This energy converter transforms heat to electricity through an electrochemical process at high temperature (700 – 1000 °C). At Karlsruhe Institute of Technology (KIT) an AMTEC test cell and an AMTEC TEst FAcility (ATEFA) have been designed and are under construction. The paper gives an overview of the history of AMTEC converter and its development; and presents the ATEFA facility included its latest progress in design and construction. In addition, a scoping study on the stability of PEEK polymer compound in liquid sodium environment was started and is reported.

Over the past few years, due to the introduction of Tier 4 emission legislations, new developments for non-road mobile machinery (NRMM) applications to meet these stringent targets have been introduced. This paper presents a design concept for self-cooling of integrated electro- hydraulic machinery for NRMM application. The applicability of this concept is shown for an integrated electro-hydraulic energy converter (IEHEC). Two cooling schematics (passive and active) are proposed. In the passive cooling scheme the coolant flow is obtained from the case drain leakage flow of the hydraulic machine. In the active cooling scheme a boost pump can be used for providing optimal coolant flow. We show that in an NRMM environment such an IEHEC can be utilized using a passive cooling scheme. V zadnjih letih so se zaradi uvedbe zakonodaje o izpustih Tier 4 pojavile novosti na področju necestne mobilne mehanizacije (NRMM), ki omogočajo doseganje teh strogih ciljev. V članku je predstavljen koncept zasnove samohlajenja integriranih elektrohidravličnih strojev za uporabo v NRMM. Uporabnost koncepta je prikazana na primeru integriranega elektrohidravličnega pretvornika energije (IEHEC). V članku sta predstavljena dva pristopa k hlajenju (pasivni in aktivni) električnih strojev za necestno mobilno mehanizacijo. Prvi pristop dodatno moč, ki je potrebna za hlajenje, zmanjšuje z uporabo lekažnega toka iz ohišja hidravlične opreme pod obremenitvijo, drugi pristop pa za vzdrževanje optimalnega toplotnega režima strojev uporablja krmiljeno ojačevalno črpalko. Prvi pristop je podrobneje analiziran za preverjanje, ali je pasivno hlajenje sposobno vzdrževanja temperaturnih omejitev stroja.

Numerical analyses with the one-dimensional approximation have been carried out for a small-scale experimental device of TWDEC. The following results have been obtained. Numerical results agree well with experimental results on the conversion efficiency and the energy distribution when the phase difference between voltages of the modulator and the decelerator is the same as the experiment. It has been found that the phase difference should be determined properly in order to obtain a high efficiency. The position of electrodes in the decelerator has been optimized to obtain higher efficiency. The optimization is carried out for ions to move with the travelling electric field. It has been shown that the optimization can make the efficiency more than 58% when the number of electrodes is 16 even with the present small device.

Considered as a source of renewable energy, wave is a resource featuring high variability at all time scales. Furthermore wave climate also changes significantly from place to place. Wave energy converters are very often tuned to suit the more frequent significant wave period at the project site. In this paper we show that optimizing the device necessitates accounting for all possible wave conditions weighted by their annual occurrence frequency, as generally given by the classical wave climate scatter diagrams. A generic and very simple wave energy converter is considered here. It is shown how the optimal parameters can be different considering whether all wave conditions are accounted for or not, whether the device is controlled or not, whether the productive motion is limited or not. We also show how they depend on the area where the device is to be deployed, by applying the same method to three sites with very different wave climate.

The operating characteristics of traveling wave direct energy converter, which is expected to be used in an advanced fusion, are discussed in the case of broad energy band flux based on the deceler...

As for charge separation capability of cusp-type direct energy converter (CuspDEC), which is expected to be used in an advanced fusion, high density plasma production has been studied with keeping a collision-less condition of the cusp region. Using a pulsed feeding technique, high density plasma production has been achieved and low gas pressure enough to keep collision-less condition has been evaluated by a simple gas dynamics calculation.

Certain properties of ice are reviewed. The phenomenon of freezing of water is discussed, with special emphasis on the blockage and bursting of water pipes. Several concepts are discussed that are related to achieving the freezing of water, the design of the container where freezing occurs and the conversion into mechanical energy. A conceptual design is presented for one type of ice energy converter. Certain design details for this machine are provided. Initial test results are furnished for this device, which was manufactured and tested. Conclusions are drawn and recommendations are made.

Bidirectional flow air turbines are used in association with oscillating water columns to convert wave energy available in the oceans into mechanical power. Radial turbines, among others, were studied for such an application. The efficiency of radial turbines using reaction blading was found to be extremely low. On the other hand, the efficiency of impulse-type radial turbines was found to be higher. However, detailed performance studies on impulse-type radial turbines are not found in the literature. This paper presents detailed performance characteristics as well as some parametric studies based on laboratory experiments.

Concerning an application of a cusp type direct energy converter (CUSPDEC) to high density plasma, subjects on charge separation and deceleration have been experimentally investigated, assuming tha...

In a recent paper by Orazov et al. [On the dynamics of a novel ocean wave energy converter. Journal of Sound and Vibration329 (24) (2010) 5058-5069], a wave energy converter (WEC) was proposed. The converter features a mass modulation scheme and a simple model was used to examine its efficacy. The simple model did not adequately account for the momentum transfer which takes place during the mass modulation. The purpose of the present paper is to account for this transfer and to show that the WEC equipped with a novel and more general mass modulation scheme has the potential to improve its energy harvesting capabilities. © 2013 Elsevier Ltd. All rights reserved.

The effects of non-axisymmetric magnetic field on characteristics of a direct energy converter (DEC) with an axisymmetric cusp configuration are studied. The axisymmetric Cusp DEC (Kobe Cusp) is installed at the end of the GAMMA 10 device, which breaks the axisymmetry of the DEC. It is clarified that the non-axisymmetric magnetic field changes the Stormer potential at the stagnation and the equilibrium electric field by the order of the perturbation field to the equilibrium magnetic field.

A wave energy converter (WEC) based on a linear generator and a point-absorbing buoy has been developed at Uppsala University. Interconnecting an array of WECs in parallel requires a point of common coupling, such as a common dc-bus. The dc voltage level seen by the generator is directly linked to the electromagnetic damping of the generator. A lower dc-level results in a higher damping factor and is important for increased absorption of the wave power. The drawback is increased losses in generator windings and cable resistance. There will be an optimal dc-level for maximum power output. This is a function of not only generator and buoy characteristics, but the current sea state. Experimental results of the full-scale system have been carried out, and used as validation of a simulation model of the system. The model is then used to evaluate how the dc-level seen by the generator influence the power output. The results indicate that higher dc-levels should be used at higher sea states, and power output may vary by up to a factor five depending on which dc-level is chosen.

Abstract This paper presents the initial simulations and model tests into the ‘Green Water Concept’ for wave energy conversion. Instead of reducing the motions and green water as is done in normal offshore hydrodynamics, the ‘Green Water Concept’ tries to maximise the motions and green water through ‘inverse engineering’ to generate electric energy from the waves. First, results are presented of frequency domain calculations for the motion (de-) optimisation. Second, pilot model tests on the ‘Green Water Concept’ are presented. These tests also included the initial modelling of an electric and hydraulic Power Take Off (PTO). The accurate modelling of a PTO is an important aspect in testing of wave energy conversion concepts numerically and in a wave tank: at the moment that energy is converted into electricity in the PTO, the hydrodynamic behaviour of the structure is changing. The tests confirmed the high motions and large amount of green water of the Green Water Concept as predicted in simulations. The application of a real PTO gave important insight in the possibilities and challenges of PTO modelling at model scale. For the present concept a mean Power (at full-scale) close to 1MW was generated in a regular wave of H=3.0m for the maximum possible setting in the chosen test set-up. This setting was limited by the chosen mechanical and electronic motor set-up in this pilot test series, not the actual maximum of the Green Water Concept itself. Considering the test results, it is clear that the potential of the system is significantly larger. Figure 1 Background Wave energy is a concentrated form of wind energy: the wind transfers energy into the waves over a long fetch. Cruz [1] has estimated that Europe has an average wave power of 50kW per metre width of wave front [1]. Others [2] indicate that worldwide the economically exploitable amount of wave energy is estimated at 2,000 TWh/year, an average power of 200GW over a year. This is equivalent of 200 large power stations. The challenge is to generate a predictable amount of energy, in a reliable way, at a reasonable cost.

A novel transverse-flux PM linear machine is proposed in this paper. Flux leakage analysis and parameter optimization are accomplished by finite-element method (FEM). Thrust characteristics, efficiency and power density are compared between comparable radial, axial, halbach and transverse-flux machines. Simulation results indicate the advantage of the transverse-flux machine in thrust characteristics and efficiency. A prototype was manufactured and further experiments showed good agreement with the theoretical results.

This thesis presents how experimental results, from wave power research performed offshore at the Lysekil research site, were obtained. The data were used to verify theoretical models as well as evaluate the feasibility of wave power as a future sustainable energy source.The first experiments carried out at the research site was the measurement of the force in a line where one end was connected to a buoy with a diameter of 3 m and the other end to a set of springs with limited stroke length. The system is exposed to high peak forces compared to average forces. The maximum measured force in the line, when the buoy motion is limited by a stiff stopper rope is ten times the average force in that particular sea state.The experiment performed on the first wave energy converter tested at the Lysekil Research Site is described. The infrastructure of the site is presented where the central connection point is the measuring station. The key finding is that it is possible to transform the motions of ocean waves into electrical energy and distribute it to land.Many wave energy converters must be interconnected if large amounts of energy are to be harvested from the waves. The first submerged substation intended for aggregation of energy from wave power converters is described, with focus on the measurement and control system placed inside the substation. During this experiment period the generators were equipped with many different sensors; these measurements are explained in the thesis.The system that aggregates power from the studied wave energy converter is regularly exposed to peak power of up to 20 times the maximum average output from the converter.Vertical and horizontal movement of the buoy has been measured in different ways. The result is that the vertical displacement of the buoy can be measured with a simple accelerometer circuit but it is much more complicated to measure the horizontal displacement. A special method for measuring the horizontal displacement has been implemented by measuring the strain in the enclosure and the force in the line.