Дисертації: "Pendulum Wave Energy Converter"

1

POZZI, NICOLA. "Numerical Modeling and Experimental Testing of a Pendulum Wave Energy Converter (PeWEC)." Doctoral thesis, Politecnico di Torino, 2018. http://hdl.handle.net/11583/2708896.

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The research activities described in the present work aims to develop a pendulum converter (PeWEC: Pendulum Wave Energy Converter) for the Mediterranean Sea, where waves are shorter, thus with a higher frequency. In particular, the Pantelleria Island site wave climate is assumed as reference. The research activities started from the preliminary investigation of the working principle validity in the case of the Mediterranean Sea wave characteristics, taking into account a 1:45 scale prototype. The numerical model reliability and the success of experimental tests motivated the design and development of a 1:12 scaled device, useful for a deeper investigation of the technology capabilities and performances. Globally, the technology readiness level (TRL) was increased from 1 to 4. Important effort were focused in the development of a reliable model-based design and optimization methodology for the investigation of a full scale configuration. The latter was widely used to identify a preliminary full scale configuration and to assess the economic viability of the PeWEC technology in the Mediterranean Sea context. Results were benchmarked against the ISWEC pilot plant, deployed in 2015, in Pantelleria Island. One of the major outcomes of this analysis is a detailed overview of the advantages and drawbacks of an active (ISWEC) and a passive (PeWEC) technology, together with some guidelines for the improvement of this technology.

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O'Boyle, Louise. "Wave fields around wave energy converter arrays." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602715.

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Wave energy converters, by their nature, extract large amounts of energy from incident waves. If the industry is to progress such that wave energy becomes a significant provider of power in the future, large wave farms will be required. Presently, consenting for these sites is a long and problematic process, mainly due to a lack of knowledge of the potential environmental impacts. Accurate numerical modelling of the effect of wave energy extraction on the wave field and subsequent evaluation of changes to coastal processes is therefore required. Modelling the wave field impact is also necessary to allow optimum wave farm configurations to be determined. This thesis addresses the need for more accurate representation of wave energy converters in numerical models so that the effect on the wave field, and subsequently the coastal processes, may be evaluated. Using a hybrid of physical and numerical modelling (MIKE21 BW and SW models) the effect of energy extraction and operation of a WEC array on the local wave climate has been determined. The main outcomes of the thesis are: an improved wave basin facility, in terms of wave climate homogeneity, reducing the standard deviation of wave amplitude by up to 50%; experimental measurement of the wave field around WEC arrays, showing that radiated waves account for a significant proportion of the wave disturbance; a new representation method of WECs for use with standard numerical modelling tools, validated against experimental results. The methodology and procedures developed here allow subsequent evaluation of changes to coastal processes and sediment transport due to WEC arrays.

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Du, Plessis Jacques. "A hydraulic wave energy converter." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/19950.

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Thesis (MScEng)--Stellenbosch University, 2012.
ENGLISH ABSTRACT: As a renewable energy source, wave energy has the potential to contribute to the increasing global demand for power. In South Africa specifically, the country’s energy needs may easily be satisfied by the abundance of wave energy at the South-West coast of the country. Commercially developing and utilizing wave energy devices is not without its challenges, however. The ability of these devices to survive extreme weather conditions and the need to achieve cost-efficacy while achieving high capacity factors are but some of the concerns. Constant changes in wave heights, lengths and directions as well as high energy levels and large forces during storm conditions often lead to difficulties in keeping the complexity of the device down, avoiding over-dimensioning and reaching high capacity factors. The point absorber device developed as part of this research is based on an innovation addressing the abovementioned issues. An approach is followed whereby standard "offthe- shelf" components of a proven hydraulics technology are used. The size of the device is furthermore adaptable to different wave climates, and the need for a control system is not necessary if the design parameters are chosen correctly. These characteristics enable low complexity of the device, excellent survivability and an exceptionally high capacity factor. This may lead to low capital as well as low operationand maintenance costs. In this paper the working principle of this concept is presented to illustrate how it utilises the available wave energy in oceans. The results obtained from theoretical tests correlate well with the experimental results, and it is proven that the device has the ability to achieve high capacity factors. As the device makes use of existing, "off-the-shelf" components, cost-efficient energy conversion is therefore made feasible through this research.
AFRIKAANSE OPSOMMING: As ’n hernubare/ herwinbare energiebron bied golfenergie die potensiaal om by te dra tot die bevrediging van die stygende globale energie-navraag. In spesifiek Suid-Afrika kan die oorvloed van beskikbare golfenergie aan die Suid-Weskus van die land gebruik word om aan die land se energiebehoeftes te voldoen. Betroubaarheid en oorlewing in erge weerstoestande, koste-effektiwiteit en die behaal van hoë kapasiteitsfaktore is beduidende struikelblokke wat oorkom moet word in die poging om ’n golfenergie-omsetter wat kommersieël vervaardig kan word, te ontwikkel. Daarby dra voortdurende veranderings in golfhoogtes, -lengtes en -rigtings sowel as hoë energievlakke en groot kragte tydens storms by to die feit dat dit moeilik is om die kompleksiteit van die stelsel laag te hou. Dit terwyl daar voorkom moet word dat die toestel oorontwerp en verhoed word dat hoë kapsiteitsfaktore bereik word. Die puntabsorbeerder-toestel wat in hierdie navorsing ontwikkel is, bestaan uit ’n ontwerp wat spesifiek ontwikkel is om die bogenoemde probleme aanspreek. ’n Unieke benadering is gevolg waardeur standaard, maklik-bekombare komponente gebruik is en die komponent-groottes ook aangepas kan word volgens golfgroottes. Indien die ontwerpsdimensies akkuraat gekies word, is die moontlikheid verder goed dat ’n beheerstelsel nie geïmplementeer hoef te word nie. Hierdie eienskappe verseker lae stelselkompleksiteit, uitstekende oorlewingsvermoë en ’n uitstaande kapasiteitsfaktor. Lae kapitaal- sowel as onderhoudskostes is dus moontlik. Die doel van hierdie dokument is om die werking van die konsep voor te stel en teoreties sowel as prakties te evalueer. Die resultate van teoretiese toetse stem goed ooreen met eksperimentele resultate, en dit is duidelik dat die toestel hoë kapasiteitsfaktore kan behaal. Aangesien die toestel verder gebruik maak van bestaande komponente wat alledaags beskikbaar is, word die koste-effektiewe omsetting van golfenergie dus moontlik gemaak deur hierdie navorsing.

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Salar, Dana. "Miniature Wave Energy Converter (WEC)." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-366760.

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Abstract In this project, I present a design of a scale model of a linear generator (LG) similar to a full size Wave Energy Converter (WEC) being developed at Uppsala University since 2002 and commercialized by Seabased AB. The purpose of a WEC is to convert the energy from ocean waves into electrical energy. In order to implement the behaviour of the prototype design, a preliminary study has been done to further build it for use in education, laboratory tests and research. The challenge with this project is to scale down the WEC but maintain the shape, appearance and characteristics of the generator for educational purposes. A miniature version of a WEC, previously developed by Uppsala University in collaboration with Seabased Industry AB, has been designed with scaling rate 1:14 of the linear dimensions. In this case, the value of the output power is not important- it has simply been calculated. The electrical rated parameters of the three phase generator are power 26 W, peak line-line voltage 13 V and rated armature current 2 A. The mechanical parameters utilized in the design are the total length and the diameter of the miniature WEC, 50 cm and 25 cm, respectively. The simulated prototype model (described in Section 5.4) has been validated with an experimental setup comprising translator and stator (described in Section 5.1), where the translator is moved by a programmed industrial robot. The experimental results have shown good agreement with the simulations.

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Xu, Xu. "Nonlinear dynamics of parametric pendulum for wave energy extraction." Thesis, University of Aberdeen, 2005. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=189414.

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A new concept, extracting energy from sea waves by parametric pendulor, has been explored in this project. It is based on the conversion of vertical oscillations to rotational motion by means of a parametrically-excited pendulor, i.e. a pendulum operating in rotational mode. The main advantage of this concept lies in a direct conversion from vertical oscillations to rotations of the pendulum pivot. This thesis, firstly, reviewed a number of well established linear and nonlinear theories of sea waves and Airy’s sea wave model has been used in the modelling of the sea waves and a parametric pendulum excited by sea waves. The third or fifth order Stokes’s models can be potentially implemented in the future studies. The equation of motion obtained for a parametric pendulum excited by sea waves has the same form as for a simple parametrically-excited pendulum. Then, to deepen the fundamental understanding, an extensive theoretical analysis has been conducted on a parametrically-excited pendulum by using both numerical and analytical methods. The numerical investigations focused on the bifurcation scenarios and resonance structures, particularly, for the rotational motions. Analytical analysis of the system has been performed by applying the perturbation techniques. The approximate solutions, resonance boundary and existing boundary of rotations have been obtained with a good correspondence to numerical results. The experimental study has been carried out by exploring oscillations, rotations and chaotic motions of the pendulum.

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6

BRACCO, GIOVANNI. "ISWEC: a Gyroscopic Wave Energy Converter." Doctoral thesis, Politecnico di Torino, 2010. http://hdl.handle.net/11583/2562362.

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ISWEC (Inertial Sea Wave Energy Converter) is a Wave Energy Converter transforming the wave-induced rocking motion of a buoy into electrical power by means of the gyroscopic effects produced from a spinning flywheel carried inside the buoy. A unique feature of ISWEC with respect to most of the existing converters is that externally it is composed only of a floating body without moving parts working into sea water or spray, thus achieving a high reliability and reduced maintenance costs. In this Thesis the analysis of the ISWEC both on the numerical and the experimental levels is performed. The converter dynamics is analyzed in order to obtain a mathematical model and experimental tests are carried out in the wave tank of the University of Edinburgh on a 1:45 model to validate such mathematical model. The validated models are used to design a larger scale prototype (1:8) and to make considerations on the design of a full scale ISWEC system.

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Price, Alexandra A. E. "New perspectives on wave energy converter control." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/3109.

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This work examines some of the fundamental problems behind the control of wave energy converters (WECs). Several new perspectives are presented to aid the understanding of the problem and the interpretation of the literature. The first of these is a group of methods for classifying control of WECs. One way to classify control is to consider the stage of power transfer from the wave to the final energy carrier. Consideration of power transfer can also be used to classify WECs into families. This approach makes it possible to classify all WECs, including those that had previously eluded classification. It also relates the equations of motion of different classes of WECs to a generalised equation of motion. This in turn clarifies why some types of control are suited to some WECs, but not others. These classification systems are used to demarcate the boundary for the theoretical work that follows. The theory applies to WECs with governing equations of motion that are linear, and to control systems that are linear, aim to maximise power, and which regulate the PTO stage of power flow. Another important perspective is the new wet and dry oscillator paradigm, which is used to differentiate between frequency domain modelling and a commonly used technique, monochromatic modelling. This distinction is necessary background for many of the new ideas discussed. It is used to resolve an ongoing debate in wave energy research: whether frequency domain modelling can be applied to cases that are not monochromatic. It is the key to an extension to the theory of capture width, a widely used performance indicator. This distinction is also the rationale behind an improved method of presenting frequency domain results: the frequency responses due to both monochromatic and polychromatic forcing are represented on the same graph. These responses are different because the optimal control problem is acausal, a topic that is also discussed in depth. This visual tool is used to investigate and confirm various ideas about the control of WECs, and to demonstrate how the newly redefined capture width encapsulates the essential control problem of WECs. The optimal control problem is said to be acausal because information about the future is required to achieve optimal control. Another vantage point offered is that of the duration of the prediction interval required for optimal control. This is given by a new parameter emerging from this work, which has been termed the premonition time. The premonition time depends on the amount of knowledge required, which is determined by the geometry of the WEC, and the amount of information available, which is largely determined by the bandwidth of the sea state. The new perspectives introduced are the various systems of classification, the wet and dry oscillator paradigm, the presentation of monochromatic and polychromatic results on the same axes, premonition time, and the revised theory on capture width. These are all used to discuss the interrelationship between WEC geometry, the control strategy and the sea-state. The opportunities for, and limitations of, the use of intelligent control techniques such as artificial neural networks are discussed. The potential contribution of various control strategies and associated design principles is explored. This discussion culminates in a series of recommendations for control strategies that are suited to each class of WEC, and for the areas of research that have the potential to bring about the greatest reductions in the cost of harnessing energy from sea waves.

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Ljungbäck, Jacob. "Characterization of Cascade gearbox for wave energy converter." Thesis, KTH, Maskinkonstruktion (Inst.), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-182811.

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This Master Thesis, written in collaboration with CorPower Ocean, serves as the finalization of the author’s master degree education at KTH (Royal Institute of Technology) Stockholm. The purpose has been to characterize the Cascade gearbox which is used to convert vertical motion induced by waves to rotational motion which powers generators in the company’s future wave energy power plant. The purpose was also to suggest future improvements and shed light on any problems discovered. The method for characterizing the Cascade gearbox was to conduct physical measurements of the load sharing in the inherently overdetermined geometrical design. These data were then used to calibrate a static as well as a dynamic model also developed for this thesis. Focus has been on determining that the novel load sharing method is sufficient and that no gear takes more than the 2,5% overload during max load the gearbox is dimensioned for at any time. Also included in the thesis is an analysis of the tolerances effect on the performance of the Cascade gearbox. Results showed that the current design perform within the expected dimensioning limits. However some unexpected characteristics were discovered after analysis of the results. Because of deliberate geometric decisions half of the gears trail behind initially in one direction causing uneven load sharing and unwanted lateral forces on the rack. Also discovered was the importance of equal stiffness of the flex units, used to divide the load evenly between the gears, since the load sharing factor converges towards values directly proportional to the stiffness ratios in between them. As a conclusion it can be said that although the current design is sufficient, there is still room for improvements which could enhance life expectancy as well as load sharing performance of the Cascade gearbox.
Detta examensarbete utfört i samarbete med CorPower Ocean, är det slutgiltiga steget i författarens utbildning på masternivå på KTH (Kungliga Tekniska Högskolan) Stockholm. Syftet med arbetet är att karakterisera en kaskadväxellåda som används för att omvandla vertikal rörelse från vågor till rotation som driver generatorer i företagets framtida vågkraftverk samt att utifrån resultat föreslå möjliga förbättringar och belysa eventuella problem. Den metod som använts för att karakterisera kaskadväxellådan var att via fysiska mätningar, på den testrigg placerad på KTH (Kungliga Tekniska Högskolan) i Stockholm, erhålla data för lastfördelningen i den geometriskt överbestämda konstruktionen. Dessa data användes sedan för att kalibrera en statisk och en dynamisk modell som också utvecklades för det här projektet. Huvudfokus för arbetet har legat i att ta reda på om den konstruktion som används för att fördela lasten mellan kugghjulen fungerar tillfredställande samt att säkerställa att inget kugghjul tar mer än de 2,5% överlast vid fullast växellådan är dimensionerad för vid något tillfälle. Examensarbetet inkluderar även feltoleransers inverkan på lastfördelningen i kaskadväxeln. Resultaten visade att den nuvarande konstruktionen presterar inom de specificerade dimensioneringsintervallen. Några oväntade karaktärsdrag upptäckdes dock vid analys av resultaten. På grund av en avsiktlig geometrisk oregelbundenhet släpade hälften av kugghjulen efter åt ena hållet vilket i sin tur resulterade i en ojämn lastfördelning och oönskade sidokrafter på kuggracken. Flexenheterna som används för att fördela lasten likvärdigt mellan kugghjulen skilde sig åt i styvhet. Den inverkan spridningen av dessa har på lastfördelningen belystes också eftersom lastfördelningen konvergerar mot värden direkt proportionella mot styvhetsförhållandet mellan dem. Slutsatsen från examensarbetet är att den nuvarande konstruktionen, även om den fungerar tillfredställande, lämnar utrymme för förbättringar som potentiellt kan förbättra både livslängd och lastfördelningsprestanda.

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Gastelum, Zepeda Leonardo. "Life Cycle Assessment of a Wave Energy Converter." Thesis, KTH, Industriell ekologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-206486.

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Renewable energies had accomplish to become part of a new era in the energy development area, making people able to stop relying on fossil fuels. Nevertheless the environmental impacts of these new energy sources also require to be quantified in order to review how many benefits these new technologies have for the environment. In this project the use of a Life Cycle Assessment (LCA) will be implemented in order to quantify the environmental impact of wave energy, an LCA is a technique for assessing various aspects with the development of a product and its potential impact throughout a product’s life (ISO 14040, 1997). Several renewables have been assessed for their environmental impact using this tool (wind power, biofuels, photovoltaic panels, among others). This project will be focused on the study of wave power, specifically devices called point absorbers.At the beginning this thesis offers a description of the Life Cycle Assessment methodology with a brief explanation of each steps and requirements according to the ISO 14000 Standard. Later a description of different wave energy technologies is explained, along with the classification of different devices depending on its location and its form of harvesting energy. After explaining the different types available at the moment, the thesis will focus on the point absorber device and explain an approach that can be taken in order to simplify the complexity of the whole system.Once the device is fully explained the thesis approaches the methodology pursued in order to evaluate the system in terms of environmental impact in the selected category, for this case global warming. After, an evaluation of the different modules from the wave energy converter in terms of its environmental impact and choosing the best conditions in order to reduce it has being done.At the end of the thesis an economical overview of building wave energy converters is considered among its monetized cost to the environment and a comparison of this new technologies among other renewables in the market is done, in order to have an overview of the potential this type of energy can have.The main research question to be answered by this master thesis is how competitive is wave energy among other renewable technologies available at the moment. Since at the moment wave energy is in its early stages a representation of how other renewables had advanced from its early stages until today is presented, and the potential of this type of energy is evaluated in environmental and economic figures showing competitive results that can further be improved.

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10

Magagna, Davide. "Oscillating water column wave pump : a wave energy converter for water delivery." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/349009/.

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The research presented in this dissertation investigates the development and the performances of a new type of Wave Energy Converter (WEC) aimed to provide water delivery and energy storage in the form of potential energy. The Oscillating Water Column Wave Pump (OWCP) concept was proposed and tested through a series of experimental investigations supported by scientific theory. The OWCP was developed after an extensive study of the existing wave energy technology available, from which it emerged that the Oscillating Water Column (OWC) device could be further implemented for water delivery purposes. The existing theory of the OWC was employed to develop a mathematical theory able to describe the system wave response and water removal of the OWCP. In order to understand and validate the mathematical models of the OWCP, experimental investigations were carried out under the influence of incident linear waves in a two-dimensional (2D) and three-dimensional (3D) wave flume. The experimental equipment and methodology are outlined, including the description of wave flumes, models and data acquisition equipment. Experimental tests were used to verify the concept of the OWCP and assess its performances, investigating both the response of the device to the waves with and without water removal. In order to increase the efficiencies of delivery, array configurations of multiple OWCPs were adopted. The research demonstrated that up to 14% of the energy carried by the incoming waves can be converted into useful potential energy for a single device. Moreover a further increase of the efficiencies can be obtained with the array configuration improving the overall capability of the OWCP, for optimal separation distance between the array components. Further model tests are required to extended this research to validate the developed mathematical models as an effective prediction tool of the performances of the OWCP and further increase the efficiency of water removal that can be achieved.

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11

Engström, Jens. "Hydrodynamic Modelling for a Point Absorbing Wave Energy Converter." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-160319.

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Surface gravity waves in the world’s oceans contain a renewable source of free power on the order of terawatts that has to this date not been commercially utilized. The division of Electricity at Uppsala University is developing a technology to harvest this energy. The technology is a point absorber type wave energy converter based on a direct-driven linear generator placed on the sea bed connected via a line to a buoy on the surface. The work in this thesis is focused mainly on the energy transport of ocean waves and on increasing the transfer of energy from the waves to the generator and load. Potential linear wave theory is used to describe the ocean waves and to derive the hydrodynamic forces that are exerted on the buoy. Expressions for the energy transport in polychromatic waves travelling over waters of finite depth are derived and extracted from measured time series of wave elevation collected at the Lysekil test site. The results are compared to existing solutions that uses the simpler deep water approximation. A Two-Body system wave energy converter model tuned to resonance in Swedish west coast sea states is developed based on the Lysekil project concept. The first indicative results are derived by using a linear resistive load. The concept is further extended by a coupled hydrodynamic and electromagnetic model with two more realistic non-linear load conditions. Results show that the use of the deep water approximation gives a too low energy transport in the time averaged as well as in the total instantaneous energy transport. Around the resonance frequency, a Two-Body System gives a power capture ratio of up to 80 percent. For more energetic sea states the power capture ratio decreases rapidly, indicating a smoother power output. The currents in the generator when using the Two-Body system is shown to be more evenly distributed compared to the conventional system, indicating a better utilization of the electrical equipment. Although the resonant nature of the system makes it sensitive to the shape of the wave spectrum, results indicate a threefold increase in annual power production compared to the conventional system.

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Guaraldi, Irene. "Hydraulic evaluation of the gyro electric wave energy converter." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8427/.

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Motivation Thanks for a scholarship offered by ALma Mater Studiorum I could stay in Denmark for six months during which I could do physical tests on the device Gyro PTO at the Departmet of Civil Engineering of Aalborg University. Aim The goal of my thesis is an hydraulic evaluation of the device: Gyro PTO, a gyroscopic device for conversion of mechanical energy in ocean surface waves to electrical energy. The principle of the system is the application of the gyroscopic moment of flywheels equipped on a swing float excited by waves. The laboratory activities were carried out by: Morten Kramer, Jan Olsen, Irene Guaraldi, Morten Thøtt, Nikolaj Holk. The main purpose of the tests was to investigate the power absorption performance in irregular waves, but testing also included performance measures in regular waves and simple tests to get knowledge about characteristics of the device, which could facilitate the possibility of performing numerical simulations and optimizations. Methodology To generate the waves and measure the performance of the device a workstation was created in the laboratory. The workstation consist of four computers in each of wich there was a different program. Programs have been used : Awasys6, LabView, Wave lab, Motive optitrack, Matlab, Autocad Main Results Thanks to the obtained data with the tank testing was possible to make the process of wave analisys. We obtained significant wave height and period through a script Matlab and then the values of power produced, and energy efficiency of the device for two types of waves: regular and irregular. We also got results as: physical size, weight, inertia moments, hydrostatics, eigen periods, mooring stiffness, friction, hydrodynamic coefficients etc. We obtained significant parameters related to the prototype in the laboratory after which we scale up the results obtained for two future applications: one in Nissun Brending and in the North Sea. Conclusions The main conclusion on the testing is that more focus should be put into ensuring a stable and positive power output in a variety of wave conditions. In the irregular waves the power production was negative and therefore it does not make sense to scale up the results directly. The average measured capture width in the regular waves was 0.21 m. As the device width is 0.63 m this corresponds to a capture width ratio of: 0.21/0.63 * 100 = 33 %. Let’s assume that it is possible to get the device to produce as well in irregular waves under any wave conditions, and lets further assume that the yearly absorbed energy can be converted into electricity at a PTO-efficiency of 90 %. Under all those assumptions the results in table are found, i.e. a Nissum Bredning would produce 0.87 MWh/year and a North Sea device 85 MWh/year.

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Gotthardsson, Björn. "Analysis and Evaluation of the Wavebox Wave Energy Converter." Thesis, Uppsala universitet, Elektricitetslära, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-149364.

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Increasing attention to climate change in combination with ever-growing energy consumption worldwide has boosted the demand for new green energy sources. Wave power is developing in many different branches to become part of the new era of electricity production. This thesis deals with a wave power system in its primary stages of development. The system was investigated in order to estimate its potential to produce electric power from sea waves. It is a system consisting of a moored buoy to which the energy is transferred when the wave tilts the buoy in the pitch direction. Due to the increased pitch angle, an amount of liquid contained inside the buoy is allowed to flow via ramps to an upper container, from where it flows down through a hydroelectric turbine. A computer program was used to calculate the properties of the buoy in sea waves. Another program was written in MATLAB to simulate the movements in sea waves and from a set of given parameters calculate the power output. A brief economic study was made to determine if the power output was large enough for the concept to be of financial interest to any future investors. The results show that the wave power system produced 0.9 kW in a wave climate equal to that off the coast of Hanstholm, Denmark, and 1.6 kW in a wave climate off the coast of San Diego, USA. The economic study shows that the power output needed to be improved by a factor of at least five to have a chance of being economically viable. A number of enhancements were suggested to increase the power output of the system, and further investigation could be of use to improve the concept. The created computer simulation model, as well as the results in this thesis could be valuable in any future research on the concept.

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14

Joubert, James Rattray. "Design and development of a novel wave energy converter." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85817.

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Thesis (PhD)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: The design, development and evaluation of a novel wave energy converter (WEC) device, called the ShoreSWEC, in a South African port development is presented. Based on the device requirements, site selection criteria were specified and applied to identify a suitable deployment location. A wave modeling procedure was developed to determine the operational wave conditions and available wave power resource at the selected location. The site was found to have a low mean annual average resource of approximately 2.3 kilowatt per meter wave crest (kW/m) due to its relatively sheltered location. The wave model was further used to determine design storm conditions and a structural stability analysis of the device was conducted. Experimental tests were performed to evaluate the hydrodynamic conversion efficiency of a single chamber of the device at its most conservative orientation, under a variety of wave energy conditions. The effect of a floor incline and an additional chamber on the performance of the system was investigated. The incline improved efficiency for low wave heights, making it ideal for the low wave power resource conditions of the site, whilst the multi-chamber system experienced increased performance at high wave periods. A comparison between the ShoreSWEC and a conventional oscillating water column (OWC) WEC showed that the OWC extracted 72% more energy, highlighting the sensitivity of performance on device orientation. A three-dimensional (3D) numerical model of the experimental setup was developed. The numerical model provided comparable water surface elevations inside the flume and chamber, yet predicted significantly higher internal chamber pressures and overall efficiency. The electricity generation potential of a 10 chamber ShoreSWEC at the specified location, approximated from the experimental results and 11 years of hindcast wave data, was found to be 6 kW on average for a 15 kW capacity system. Results of this study highlighted the need for greater understanding of the hydrodynamic characteristics of a full length device. Experimental tests in a 3D wave basin on a scaled full length ShoreSWEC model are therefore recommended. Once conducted, South Africa will be one step closer to the deployment of the full scale SWEC device.
AFRIKAANSE OPSOMMING: Die ontwerp, ontwikkeling en evaluasie van ‘n unieke golfenergieomsetter (GEO), genaamd die ShoreSWEC, in ‘n Suid-Afrikaanse haweontwikkeling word aangebied. Terrein evaluasie kriteria, gebaseer op die omsettervereistes, is ontwikkel en toegepas om die mees belowende terrein te identifiseer. ‘n Golfmodeleringsprosedure is ontwikkel om die operasionele golfkondisies en beskikbare golfdrywinghulpbron te bepaal. Daar is gevind dat die terrein ‘n lae gemiddelde golfdrywing van bykans 2.3 kilowat per meter golfkruin het as gevolg van die beskutte ligging. Die golfmodel is verder gebruik om ontwerpstormkondisies te bepaal en ‘n stabiliteitsanalise was op die toestel struktuur uitgevoer. Eksperimentele toetse van verskeie golfenergie kondisies is gedoen om die hidrodinamiese omsettingseffektiwiteit van ‘n enkel kamer van die toestel te bepaal teen sy konserwatiefste orientasie. Die effek van ‘n vloerhelling en ‘n addisionele kamer op die uitsette van die sisteem is ondersoek. Die helling het effektiwiteit verbeter vir lae golfhoogtes wat dit ideaal maak vir die lae hulpbron by die terrein, terwyl die veelvoudige-kamer-sisteem beter gevaar het by hoë golfperiodes. ‘n Vergelyking tussen die ShoreSWEC en ‘n konvensionele ossilerende waterkolom (OWK) GEO het gewys dat die OWK 72% meer energie onttrek. Dit beklemtoon die sisteem se sensitiwiteit vir die inkomende golfrigting. ‘n Drie-dimensionele (3D) numeriese model van die eksperimentele opstelling is ontwikkel. Die numeriese model het aansienlik hoër drukke binne die kamer, en gevolglik algehele effektiwiteit, voorspel as die eksperimentele toetse. Die elektriese opwekkingskapasiteit van ‘n 10 kamer ShoreSWEC by die terrein, gebaseer op die eksperimentele resultate en 11 jaar se golfdata, is bereken as 6 kW gemiddeld vir ‘n 15 kW kapasiteit stelsel. Die bevindinge van hierdie studie het die behoefte aan ‘n beter begrip van die hidrodinamiese eienskappe van ‘n vollengte sisteem beklemtoon. Eksperimentele toetse in ‘n 3D golfbak op ‘n geskaleerde vollengte ShoreSWEC model word dus aanbeveel. Sodra dit voltooi is, sal Suid-Afrika een stap nader wees aan die ontplooiing van ‘n volskaalse SWEC toestel.

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15

Cheemakurthy, Harsha. "Load case analysis for a resonant Wave Energy Converter." Thesis, KTH, Marina system, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185261.

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As we progress beyond the information age, there is a growing urgency towards sustainability. This word is synonymous with the way we produce energy and there is an awareness to gradually shift towards green energy production. Corpower Ocean aims at producing energy by utilizing the perpetual motion of ocean waves through the motion of small floating buoys. Unlike previous designs, this buoy utilizes the phenomenon of Resonance thus greatly enhancing the energy output. In the thesis, the simulation model developed by Corpower Ocean to virtually describe the buoy in operation was validated. This was done by comparing forces obtained from buoy scale model experiments, simulation model and ORCAFELXTM software. After satisfactory validation was established, the shortcomings in the simulation model were identified. Next the simulation model was used to generate data for all sea states for a target site with given annual sea state distribution. This information was then used to predict ultimate loads, statistical loads, motions and equivalent load for a given fatigue life and loading cycles. The results obtained are then treated with a statistical tool called Variation Mode and Effect Analysis to quantify the uncertainty in design life prediction and estimate the factor of safety. The information will be used by the design team to develop the buoy design further. Finally the issue of survivability was addressed by checking buoy behavior in extreme waves in ORCAFLEXTM. Different survivability strategies were tested and videos were captured for identifying slack events and studying buoy behavior in Extreme conditions. The work aims at validating a technology that is green from environmental and economic point of view.

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16

Nebel, Paul. "Synthesis of optimal control of a wave energy converter." Thesis, University of Edinburgh, 1994. http://hdl.handle.net/1842/12708.

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The thesis begins by describing the experimental determination of the hydrodynamic coefficients of two test models; an Edinburgh duck and a semi-submerged, horizontal right circular cylinder. The impedance and wave force coefficient matrices are measured for these two models, and in the case of the cylinder are checked against exact analytical results. The radiation and scattering pattern matrices are also measured. Synthesis of optimal (complex-conjugate) control is achieved for the cylinder in one and two degrees-of-freedom, and for the duck in one, two and three degrees-of-freedom. Synthesis is defined as the pre-computation of drive signals to simulate control using prior knowledge of the incident wave and the device hydrodynamics. The concept of complex-conjugate control with amplitude constraint is introduced, and synthesised for the cylinder. This is compared with the results for control without constraint. A discrepancy is found between efficiency calculated at the duck axis and efficiency calculated from the wave amplitudes. This is traced to physical losses in the system. These losses are due to the scale of the test models, and may not be present at full-scale. Having accounted for these losses, the results for the synthesis runs agree well with predictions based on the model coefficients and hydrodynamics. This suggests that the linear model can be used to predict the effect of changes in shape on the forces, displacements and velocities of an optimally controlled device. Full-scale performance is predicted for a 10m diameter duck in unidirectional mixed seas. Two pseudo-optimal control strategies are defined which are based on the impedance measurements. Four different physical configurations are considered. It is found that changing the configuration will roughly determine the effectiveness of the device, and choosing the correct control strategy for that configuration fine tunes performance. The two pseudo-optimal strategies are simple to implement, but are nearly as effective as complex-conjugate control.

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17

Lamont-Kane, Paul. "Physical and numerical modelling of wave energy converter arrays." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.679215.

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This thesis investigates the effects of hydrodynamic interactions within arrays of wave energy converters, provides a significant amount of much needed physical model data to the industry for validation purposes and assesses the relative suitability of various numerical models for use in isolated device and array studies. Experience gained from two large sets of physical experiments undertaken early in the project resulted in the planning, preparation, design and execution of a third set of experiments, the results of which have been reported in this thesis. The physical data obtained allowed for the estimation of the effect of array interaction on device response and performance under a wide range of incident, control and array setup conditions. To undertake these experiments novel testing protocols and procedures were developed to allow for the production of useful data where the quantity of interest was much smaller than any particular measured value, It was found that even small errors and uncertainties may have significant implications for data obtained and that the error and uncertainty inherent within a physical system is capable of misrepresenting array interactions. In outline, it has been found that investigating the effects of array interaction experimentally is difficult and requires significant attention to detail. Two different Frequency Domain Models and a Time Domain Model have been produced for modelling the effects of array interactions in regular sea states. A Spectral Domain Model and Time Domain Model were produced to estimate array interactions in irregular sea states. Results obtained from these models have been compared to those obtained from physical testing and by estimating the error in physical results the validity of a variety of industry standard numerical models has been assessed for the first time. The importance of distinguishing between model accuracy, adequacy and suitability is highlighted. It is also argued that in many cases, Time Domain Models will not provide the most accurate results achievable and that Spectral Domain Models provide a suitable alternative in these cases.

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18

Eriksson, Carolina. "Model Predictive Control of CorPower Ocean Wave Energy Converter." Thesis, KTH, Skolan för elektro- och systemteknik (EES), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-196859.

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Wave power is currently a hot topic of research, and has shown great potential as a renewable energy source. There have been lot of progress made in developing cost eﬀective Wave Energy Converters (WECs) that can compete with other sources of energy in regard to price and electrical power. Theoretical studies has shown that optimal control can increase the generated power for idealized WECs. This thesis is done in collaboration with CorPower Ocean, and investigates the use of economic Model Predictive Control (MPC) to control the generator torque in a light, point-absorbing, heaving WEC that is currently under development. The objective is to optimize the generator torque, such that the average generated power is maximized while maintaining a small ratio between maximum and average generated power. This results in a nonconvex cost function. Due to the highly nonlinear and nonsmooth dynamics of the WEC, two controllers are proposed. The ﬁrst controller consists of a system of linear MPCs, and the second controller is a nonlinear MPC. Relevant forces acting on the WEC are identiﬁed and the system dynamics are modelled from a force perspective. The models are discretized and the controllers are implemented in Simulink. The WEC, together with the controllers, is simulated in an extensive Simulink model developed by CorPower Ocean. Several diﬀerent types of ocean waves are considered, such as its energy content and its regularity. In the majority of cases, the controllers do not increase the performance of the WEC compared to a simple, well tuned controller previously developed by CorPower Ocean. Finally, possible improvements of how to reduce existing model errors are proposed.
Vågkraft har de senaste åren visat stor potential som en ny, förnyelsebar energikälla. Det har skett många framsteg inom området med att ta fram ett robust vågkraftsverk som kan utmana andra energikällor i pris och elektrisk eﬀekt. Teoretiska studier har visat att optimal styrning kan öka den elektriska eﬀekten för idialiserade vågkraftsverk. Denna rapport är skriven i sammarbete med vågkraftföretaget CorPower Ocean, och undersöker hur ekonomisk Model Predictive Control (MPC) kan användas för att styra dämpningen i ett lätt vågkraftverk vars storlek är relativt liten våglängden. Målet är att optimera dämpningen, vridmomentet, i generatorerna så att medeleﬀekten maximeras samtidigt som toppeﬀekten minimeras, detta för att skapa ett stabilare system med mindre ﬂutuationer mellan medel- och toppeﬀekt. För att nå detta mål krävs en icke konvex kostfunktion. På grund av stora olinjäriteter och diskontinuteter i systemets dynamik utvecklas två regulatorer; ett system av linjära MPC, samt en olijär MPC. Relevanta krafter som påverkar systemet identiﬁeras och modelleras från ett kraftperspektiv. Modellerna diskretiseras, och regulatorerna implementeras och simuleras i en detaljerad Simulink modell av systemet, utvecklad av CorPower Ocean. Både regelbundna och oregelbunda vågset med varierande energiinnehåll har simuleras. Regulatorerna ökar inte vågkraftverkets prestanda jämfört med en enkel, väl inställd regulator utveklad av CorPower Ocean. Slutligen föreslås förbättringar för att minska modelfell i modellerna.

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19

Zhou, Tianzhi. "Damping Profile Research for Corpower Ocean's Wave Energy Converter." Thesis, KTH, Optimeringslära och systemteori, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-181315.

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With increasing energy demanding and greenhouse gases from fossil fuel, the need to develop new ways to convert energy in sustainable methods is becoming more and more urgent. Corpower Ocean AB designed a point absorber type wave energy converter to harvest energy from surface wave. To maximize the energy output, phase and amplitude control of the converter are needed. Falnes and Budal proposed latching around 1980s which could deliver almost perfect phase and thusly boost power output, however, the peaky machinery force and power output result from it’s discontinuity remained a problem. A continuous phase control method using a negative spring called WaveSpring which further increased power absorption was recently proposed by Jørgen Hals Todalshaug. Meanwhile, there are more and more promising results indicate it is possible to predict the wave in coming seconds. Corpower Ocean’s wave energy converter implements the WaveSpring approach, further more, flywheels are used in the system to increase damping capacity and in the mean time work as a temporary energy storage. In this thesis project, an optimized damping profile making use of wave estimation applying wave to wave control was researched. Optimal damping during regular waves with certain wave height and wave period were first calculated by approximating the wave energy converter using linear oscillation theories. They were then used in wave to wave control by predicting and discretizing irregular ocean waves. The damping was first implemented using only generator and then with a combination of generator and flywheel making use of flywheel equivalent damping and inertia calculated from Fourier decomposition. Damping profiles were tested in Corpower Ocean’s simulation model, simulation results showed that the specific wave to wave control significantly increased energy output, and using the combination of flywheel and generator was confirmed effectively decrease the maximum torque requirement of the generator while maintain high energy output.

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20

Brandt, Anders, and Piotr Zakrzewski. "Model Predictive Contorol of a Wave Energy Converter -3DOF." Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-21944.

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There is a demand for renewable energy in today’s society. Wave energy is a nearly untapped source of renewable energy. Ocean Harvesting Technologies AB (OHT) is currently developing a device that can be used to convert wave energy into electricity. The device is a Wave Energy Converter of the type point absorber. Their concept is a floating buoy that is connected to the seafloor via a Power Take-Off (PTO) unit. The PTO unit is equipped with generators, which are used to convert kinetic energy of the buoy into electricity. The objective of this thesis is to control the generators to optimize the performance of the system. OHT was interested in knowing how their system performs under the influence of a controller based on MPC. Hence an MPC-controller is constructed in this thesis. The developed controller functions by predicting the states (position and velocity) of the buoy over a finite time (e.g. $5s$). Then the controller uses the predictions to find a control force that makes the system behave optimally for the next $5$ seconds. A requirement from the company is that the controller should find the control force based on how the buoy is predicted to move in 3 Degrees Of Freedom (DOF). Further, the controller should be able to operate in real-time. To meet the company’s requirements, the following is done. A linear 3ODF model of the system is derived. This is used to predict the states of the buoy in the controller. An MPC algorithm is constructed. In this, the linear model and constraints of the system are included. Then, a simulation environment is built. This is including a non-linear model of OHT’s system. The performance of the controller is tested in the simulation environment. Real-time implementation is an important aspect of the controller. The computational time required by the controller is measured in the simulations. The results imply that the controller stands a chance of being real-time implementable. However, make sure that it can be run in real-time it should be tested on the control unit that OHT plans to use in their system. A linear model of the system is used in the controller to predict the future states o the buoy. It is important that the predictions are accurate for the controller to control the system in an optimal way. Hence, the validity of the linear model is investigated. The controller is managing to predict some states better than others. However, the controller is doing a fine job with controlling the system in terms of generated power. Thus the linear model is considered to be valid for the application. An advantage with controllers based on MPC is the simplicity of tuning the controller. Changes of settings in the controller have a predictable effect on the results. For the settings found in this thesis, the system is performing fine in terms of power generation. However, more work is needed to find more optimal settings.

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21

Antar, Robert, and Daniel Gonzalez. "Miniature wave energy converter using dual rotating dynamic axes." Thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-326275.

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22

De, Marichalar Alegre Alexandra. "Overtopping Converter Prototype for Electrical Generation from Wave Energy : Laboratory Test." Thesis, KTH, Energiteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-38883.

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It is not a coincidence that over half the world‟s population live in coastal areas using the sea as a mean to develop its industry, thus the sea is present in most aspects of daily life. Because of the vital relationship with the marine environment, for many years mankind is aware of the high energy potential contained in waves. During the last hundred years, thousands patents of devices for the extraction of the energy from waves have been published. However, the researching still faces the challenge of develop the optimal wave energy converter that matches robustness, to withstand extreme marine conditions, and sensitivity, to respond the different sea states. In this thesis a scale model of a wave overtopping converter has been designed, built and tested. In this type of wave electricity converter the waves ascend a ramp, filling a reservoir located at a certain height above sea level. The stored water in the reservoir is discharged back into the sea, powering a turbine, thus generating electricity. The system is composed of a wave energy converter, at a scale of 1:100 without turbine, a test channel and a plunger type wave maker. Different sea conditions have been simulated, to assess how the different configurations of the device influence the obtained hydraulic power and flow. It has been concluded that there is an appropriate configuration of the wave electricity converter for each wave period and height. The simulated sea conditions were composed of wave periods of around a second and wave heights of about two centimeters. Finally by applying scale transformations, an estimation of the hydraulic power that the wave electricity converter would extract with this configuration in the deep waters of Tenerife South has been calculated. Summarizing, in this thesis the methodology of testing and the comparison with real conditions has been developed.

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23

Ulvin, Johannes Christopher. "Grid Integration of the Wave Energy Converter Bolt2 : Control of the Grid Side Converter with Energy Storage." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19042.

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This thesis is written in cooperation with Fred Olsen's Wave Energy Project Bolt2 which is a Wave Energy Converter (WEC) recently deployed outside of Falmouth Bay in the UK. After the initial phases of testing, the device is to be grid connected to the local distribution network. The purpose of this thesis is to develop a model that can serve as a useful starting point for investigating grid connection issues for Wave Energy Converters or as a part of a complete wave-to-wire modelling of a WEC. The Bolt2 project will be used as a framework for the thesis. Measurements from the testing of Bolt2 have been provided and strengthen the project by applying real life conditions to the model.The work emphasizes on the challenges of grid connecting wave energy devices as motivation for the work. As a first step, the design of the grid side converter and its control system is carried out with the main criterion being a constant DC-link voltage. In addition, the control circuit ensures no reactive power exchange at the converter output that the currents are injected at the grid frequency. The control strategy applied is based on vector control due to its well documented performance in a variety of applications.One of the main barriers for wave energy developers are the large power variations that are inherent to most WECs since the produced wave power goes through zero twice in each wave period. An effective way of reducing the power fluctuations is by disposing several point absorbers in an array configuration which is one of the advantages of Fred Olsen's Bolt2.To further smooth out the power, an Energy Storage System (ESS) is considered. After a short discussion, the energy storage device was chosen to be a supercapacitor (SC) bank. Initially, the possibility to provide a constant power to the grid was investigated but was rejected as being unrealistic for a practical case. Instead, an alternative power management strategy of the ESS was developed. It was decided to chop off only the largest power peaks and to discharge whenever any amount of energy remained in the SCs for the storage system to be completely discharged and prepared for any incoming power peak. A bi-directional DC-DC converter was used to interface the SCs with the DC-link and the described power management strategy was realized through current control of the switching devices. Two similar but separate control schemes were necessary in order to perform both buck charging and boost discharging.Finally, simulations of power data from a design sea state were performed in order to prove the validity of the developed model. The peak-to-average power ratio was demonstrated to be reduced with the integration of the energy storage system. However, the expenses of including a storage would have to be justified by reduced costs for the developer in order for the scenario to be economically viable.

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24

Jansson, Elisabet. "Multi-buoy Wave Energy Converter : Electrical Power Smoothening from Array Configuration." Thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-293689.

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This master thesis is done within the Energy Systems Engineering program at Uppsala University and performed for CorPower Ocean. Wave energy converters (WECs) are devices that utilize ocean waves for generation of electricity. The WEC developed by CorPower Ocean is small and intended to be deployed in an array. Placed in an array the different WECs will interact hydrodynamically and the combined power output is altered. The aim of this thesis is to model and investigate how the array configuration affects the electric power output. The goal is to target an optimal array layout for CorPower Ocean WECs, considering both average power and power smoothness in the optimization. In this thesis multiple buoys have been implemented in the time-domain model at CorPower Ocean. The hydrodynamic interactions are computed using an analytical interactions theory together with a recently developed calibration method able of handling WEC bodies of complicated shapes. The array behavior in regular waves is analyzed and it is identified how the beneficial separation distances vary with wave length. It is observed that the best separation distances for high average power does not exactly correspond to the best for minimizing the peak-to-average power. Simulation results show that it is possible to obtain both high average array power as well as increased power smoothening in a regular wave. A genetic algorithm for optimizing the array configuration is designed and tested for two different array patterns. Initial simulations are conducted in realistic multi-directional irregular waves. The power smoothening capacity of the array remains even in these conditions but the exact extent of it is still uncertain. This thesis delivers a WEC array simulation model as well as an initial view on the array characteristics of the phase controlled CorPower Ocean WEC. Additionally, it demonstrates an optimization algorithm taking both average power and power smoothness into account.

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25

Leijon, Jennifer. "Simulation of a linear wave energy converter with different damping control strategies for improved wave energy extraction." Thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-287369.

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In this project, the wave energy converter (WEC) designed at Seabased AB and Uppsala University was modelled in the program MATLAB. In order to increase the average output power, the WEC should be controlled. Therefore, the simulation tool was used to investigate damping strategies where the damping coefficient was changed at different times of the wave period. The tests showed that a suitable damping strategy, matched to the sea state at the specific location of the site and the overall WEC design, increases the average output power, as well as may protect the WEC from damages. This can lead to a more sustainable WEC system, which may contribute to the increasing demand of renewable energy solutions.

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26

Waters, Rafael. "Energy from Ocean Waves : Full Scale Experimental Verification of a Wave Energy Converter." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9404.

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A wave energy converter has been constructed and its function and operational characteristics have been thoroughly investigated and published. The wave energy converter was installed in March of 2006 approximately two kilometers off the Swedish west coast in the proximity of the town Lysekil. Since then the converter has been submerged at the research site for over two and a half years and in operation during three time periods for a total of 12 months, the latest being during five months of 2008. Throughout this time the generated electricity has been transmitted to shore and operational data has been recorded. The wave energy converter and its connected electrical system has been continually upgraded and each of the three operational periods have investigated more advanced stages in the progression toward grid connection. The wave energy system has faced the challenges of the ocean and initial results and insights have been reached, most important being that the overall wave energy concept has been verified. Experiments have shown that slowly varying power generation from ocean waves is possible. Apart from the wave energy converter, three shorter studies have been performed. A sensor was designed for measuring the air gap width of the linear generator used in the wave energy converter. The sensor consists of an etched coil, a search coil, that functions passively through induction. Theory and experiment showed good agreement. The Swedish west coast wave climate has been studied in detail. The study used eight years of wave data from 13 sites in the Skagerrak and Kattegatt, and data from a wave measurement buoy located at the wave energy research site. The study resulted in scatter diagrams, hundred year extreme wave estimations, and a mapping of the energy flux in the area. The average energy flux was found to be approximately 5.2 kW/m in the offshore Skagerrak, 2.8 kW/m in the near shore Skagerrak, and 2.4 kW/m in the Kattegat. A method for evaluating renewable energy technologies in terms of economy and engineering solutions has been investigated. The match between the technologies and the fundamental physics of renewable energy sources can be given in terms of the technology’s utilization. It is argued that engineers should strive for a high utilization if competitive technologies are to be developed.

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27

Weller, Samuel David. "Wave energy extraction from device arrays : experimental investigation in a large wave facility." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/wave-energy-extraction-from-device-arrays-experimental-investigation-in-a-large-wave-facility(5e43e3e5-4776-42c1-9d4e-22160de8abbe).html.

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Multiple wave energy devices supported by a common structure represent one possible method of efficiently converting ocean wave energy into electricity. In this study, experimental measurements of multiple small-scale wave energy devices are reported to assist the development and validation of numerical models. Through observation and measurement, the response of two float geometries subjected to a range of wave conditions and device settings were determined. A range of regular wave conditions were identified that caused a linear relationship to occur between the heave displacement amplitude of the float and the incident wave amplitude. These test cases will enable comparisons to be made with linear simulations of response. Tests conducted in various wave conditions have highlighted the capability of altering the device response by changing the equilibrium draft of one float geometry. Additional damping on the upper surface of the float, due to wave overtopping, could be exploited as a method of limiting the heave response of the device in large amplitude waves. The influence of hydrodynamic interactions on arrays of closely spaced devices has been experimentally investigated for devices subjected to regular and irregular wave conditions. The magnitude and occurrence of interactions and their affect on the individual device response is demonstrably dependent on the incident wave frequency and device separation distance. Compared to an isolated device, positive interactions result in higher average power outputs for an array of devices at certain wave frequencies. Positive interactions occuring at particular wave frequencies are balanced by negative interactions at other wave frequencies, in agreement with published numerical studies of array performance. Varying the level of mechanical damping applied to the float through the power take-off system results in a frequency shift of the calculated power transfer function and alters the motion path of the float. This finding implies that the level of generator torque could be used as an alternative method to tune the response of the device based on the measured incident wave-field. Several time-averaged and time-varying approaches to simulating the response of a wave energy device subjected to wave-field forcing and undergoing free response have been studied. By comparing the simulated and measured responses, the feasibility of using linear and non-linear force terms in a time-varying model has been assessed. In general, single degree-of-freedom simulations based on linear hydrodynamic parameters tend to over-predict device response amplitudes, requiring the application of additional damping. The simulation approach which resulted in the closest agreement with measured responses required the combination of linear diffraction force and radiation added mass terms with non-linear drag and buoyancy force terms, as well as body inertia and gravity forces. This approach goes part way to simulating the complex time-varying hydrodynamics associated with a wave energy device subjected to wave-field forcing.

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28

Steynor, Jeffrey Robert. "Minimising the lifetime carbon and energy intensities of the Oyster wave energy converter." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/17959.

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Converting energy from ocean waves is an exciting concept aimed at reducing our dependency on fossil fuels. Ocean energy devices must convert the large forces and relatively small movements from ocean waves into electrical power with a minimum carbon and energy intensity in order to be economically viable. The research herein focuses on the Oyster, a flap-type pitching wave energy converter developed by Aquamarine Power. A device that has the minimal carbon or energy intensity is not necessarily the most mechanically efficient. A commercially viable wave energy converter should have a competitive cost of energy and be as carbon negative as possible. In order to expedite the route to commercialisation, successive designs should iterate towards a minimum lifetime cost of energy. The sheer complexity of wave energy converter systems makes for a vast optimisation problem to determine the system parameters that exhibit the minimum carbon and energy intensities. This thesis presents a study of the oscillating flap-type wave energy converter to determine the trends between design parameters, total power output and carbon and energy throughput. The minimum carbon and energy intensities have been shown to be strongly dependent on minimising maintenance requirements. In order to determine the design criterion a range of flap widths and system pressures are investigated and their effect on component service lives assessed. The results are then converted to lifetime carbon and energy intensities for a direct comparison. To achieve this, fundamental research on the maintenance requirements of critical components such as the hinge bearings and hydraulic power system is required. A hydrodynamic model describes the dynamic response and links the system energy inputs to its modelled energy output. This work is intended to help guide developers of flap-type wave energy converters towards commercialisation. It enhances the understanding of the routes to failure and service life predictions, providing avenues to balance service lives to optimise maintenance and maximise uptime. This will assist in the development of more energy efficient wave energy converters over their lifetime. This information will better enable the marine energy sector to offset our fossil fuel dependence, ultimately reducing our impact on the environment and leading to a ‘greener’ future.

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29

Barnabè, Paola. "Analysis of Wells Turbine for a specific wave energy converter." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.

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Vista la crescita della popolazione globale ed il conseguente aumento del fabbisogno di energia è necessaria una transizione verso forme di energie rinnovabili e sostenibili. Gli oceani e le coste del mondo, costituenti fondamentali di quello che è il 'Blue World' sono componenti chiave del capitale ambientale del pianeta e del suo capitale economico. Solo quando si imparerà a sfruttare questo tipo di risorse questa transizione sarà possibile ed efficace per l'intera popolazione globale. Ecco perché l'elaborato finale tratta l'analisi di una turbina di tipo Wells per i convertitori di energia dalle onde del mare e degli oceani.

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Horko, Michael. "CFD optimisation of an oscillating water column wave energy converter." University of Western Australia. School of Mechanical Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0089.

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Although oscillating water column type wave energy devices are nearing the stage of commercial exploitation, there is still much to be learnt about many facets of their hydrodynamic performance. This research uses the commercially available FLUENT computational fluid dynamics flow solver to model a complete OWC system in a two dimensional numerical wave tank. A key feature of the numerical modelling is the focus on the influence of the front wall geometry and in particular the effect of the front wall aperture shape on the hydrodynamic conversion efficiency. In order to validate the numerical modelling, a 1:12.5 scale experimental model has been tested in a wave tank under regular wave conditions. The effects of the front lip shape on the hydrodynamic efficiency are investigated both numerically and experimentally and the results compared. The results obtained show that with careful consideration of key modelling parameters as well as ensuring sufficient data resolution, there is good agreement between the two methods. The results of the testing have also illustrated that simple changes to the front wall aperture shape can provide marked improvements in the efficiency of energy capture for OWC type devices.

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31

Bånkestad, Maria. "Modeling, Simulation and Dynamic control of a Wave Energy Converter." Thesis, KTH, Numerisk analys, NA, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-134104.

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The energy in ocean waves is a renewable energy resource not yet fully exploited. Research in converting ocean energy to useful electricity has been ongoing for about 40 years, but no one has so far succeed to do it at sufficiently low cost. CorPower Ocean has developed a method, which in theory can achieve this. It uses a light buoy and a control strategy called Phase Control. The purpose of this thesis is to develop a mathematical model of this method - using LinearWave Theory to derive the hydrodynamic forces - and from the simulated results analyze the energy output of the method. In the process we create a program that will help realizing and improving the method further. The model is implemented and simulated in the simulation program Simulink. On the basis of the simulated results, we can concludes that the CorPower Ocean method is promising. The outcome shows that the energy output increases - up to five times- compared to conventional methods.
Vågenergi är en förnyelsebar energikälla som ännu inte utnyttjas fullt ut. Forskning inom konvertering av vågenergi till användbar elektricitet har pågått i cirka 40 år, men ingen har hittills lyckas att göra det tillräckligt kostnadseffektivt. CorPower Ocean har utvecklat en metod, som i teorin kan uppnå detta. De använder en lätt boj och en kontrollstrategi kallad Phase Control. Syftet med detta examensarbete är att utveckla en matematisk modell av metoden -genom att använda Linear Wave Theory för att härleda de hydrodynamiska krafterna -och från de simulerade resultaten analysera energiutbytet. Under arbetets gång skapades också ett simuleringsprogram som hjälpmedel till att realisera och förbättra metoden. Modellen implementeras och simuleras i programmet Simulink. Utifrån de simulerade resultaten kan vi dra slutsatsen att CorPower Oceans metod är lovande. Resultatet visar att energiutbytet ökar -upp till fem gånger - jämfört med konventionella metoder.

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Lok, Kane Sing. "Optimisation of the output of a heaving wave energy converter." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/optimisation-of-the-output-of-a-heaving-wave-energy-converter(83a94b70-d75b-4149-98c4-5a120388d583).html.

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This research project is to investigate the control of the wave power device, known as the 'Manchester Bobber' (MB), and to optimise the output by tuning its drive-train parameters. The work starts with building a numerical model and developing a control strategy. The work sequentially progressed to obtain the experimental results from a physical model in order to make a comparison with the numerical results.An assessment of three different control strategies is made. These are reactive control, latching control, and two methods of torque control based on either time-averaged velocity or a pre-defined static characteristic. It is found that reactive control and latching control are not feasibly applicable to the MB wave energy device due to the configuration of the device. It is also found that the historical data approach is able to reduce the problem of high rate of change of electromagnetic torque but with a subdued output performance. A method based on a static characteristic, similar to the approach used to control wind turbines, is shown to significantly enhance the power output performance although this imposes a high rate of change of electromagnetic torque.The findings of the numerical simulation are supported by experimental measurements obtained in the wave tank. The parameters used in the numerical model (i.e. hydrodynamic damping co-efficient, added mass co-efficient and Froude-Krylov force co-efficient) are calibrated by comparing with the experimental measurements.Two drive-train parameters, the number of generator poles and flywheel inertia, are optimised in order to both maximise output power and minimise rate of change of electromagnetic torque. The proportional gain and integral time constant of the PI controller are tuned to further reduce the maximum rate of change of electromagnetic torque, so that the device is protected from the high mechanical stress. It is found that the annual energy production from the device at a range of locations is found to be almost linear with the annual average significant wave height of each site.

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Alexandre, Armando Emanuel Mocho fernandes e. "Wave energy converter strings for electricity generation and coastal protection." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/wave-energy-converter-strings-for-electricity-generation-and-coastal-protection(c7d53691-22f6-4ea8-a7ec-c9850218a1d5).html.

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Generation of electricity from ocean waves has seen increasing research and commercial interest in recent years. The development of projects of several hundred megawatts rated capacity is now being considered. There is a clear need for improved understanding of the environmental impact of large-scale wave energy extraction, particularly in nearshore regions where sediment transport and cliff erosion may be affected. This thesis investigates the change in nearshore wave conditions and sediment transport due to energy extraction by long strings of wave energy devices. The influence of wave energy converter (WEC) arrays has been studied using transmission coefficients implemented within a spectral wave model. It is shown that the breaking wave height nearshore is larger (5%) if transmission is defined as frequency dependent. This is due to the energy dissipation processes associated with different wave frequencies. Linear wave theory is employed to determine frequency dependent transmission and reflection coefficients across a line of wave energy devices based onthe amplitude of scattered and radiated waves. This approach is compared with experimental measurements of the wave field in the vicinity of an array of five heaving floats. The transmitted wave amplitude is predicted with reasonable accuracy but additional numerical damping is required to predict the measured float response amplitude. This comparison indicates that linear analysis is an acceptable approach for predicting float response and wave field in the vicinity of the array for a certain range of conditions. Linear wave analysis is subsequently applied to investigate the variation of transmission coefficients with distance inshore of a long array of heaving WECs undergoing free response and with damping specified to optimise power extraction. A method is presented for identifying representative transmission and reflection coefficients such that change in wave energy is equal to energy extraction by the devices. These coefficients are employed to quantify the change in nearshore conditions due to deployment of a long line of wave devices at a site near the East Anglian coastline. Wave conditions are modelled at 12 points along the shoreline over a 140 year period and significant wave height reductions up to 30% were obtained. Importantly, changes in nearshorewave direction are also observed. Analysis using the sediment transport model SCAPE (Soft Cliff and Platform Erosion model) indicates that the introduction of the array reduces both the sediment transport rate and cliff recession rate by an average of 50%.

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Wilkinson, Laurie Fletcher. "Assessment of a nearshore modular flap-type wave energy converter." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31163.

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This thesis presents an assessment of a modular flap-type wave energy converter. Comparisons are made to an equivalent width rigid device. All quoted relative difference results here use the rigid device as the reference point. The variables that are evaluated are the power capture and surge and yaw foundation loads. The power capture is evaluated at both module and device level, while the foundation loads are assessed just at the device level. The investigation is carried out through testing of a 30th scale physical model in a wave tank. A key output from the work is the development of the physical model. The model consists of six flap modules, mounted on a common base structure. Each module contains a highly controllable and compact power take off system. The devices are tested in a range of conditions, primarily consisting of regular waves of different period and direction. The damping strategy employed is the simplest approach available, setting the achievable damping level on each module to be the same. For the modular device in head-on regular waves, the results show that the power capture increases significantly moving from the outer to the central modules. On average, the central pair of modules produce 68 % of the total mean power, the inner modules 25 % and the outer modules only 7 %. Between the devices, it is shown that the power captures in head-on waves are similar, with a mean relative difference of -3 %, with +/-5 % uncertainty. Thus, no statistically significant change in power capture is shown. In off-angle waves, the mean relative difference is –1 %, with +/-4 % uncertainty. However, for the highest wave direction that was tested in, 27.5 degrees, the modular device outperforms the rigid flap, by 10 %, with uncertainty of +/-1 %. The surge foundation loads are shown to be very similar for the two devices - in head-on waves, the mean relative difference is +2 %. Depending on the level of applied damping, however, significant differences in the yaw foundation loads are shown. Using damping where the power capture is maximised, the yaw loads increase by a mean of 10 %; using damping where the power to load ratio is instead maximised, the modular yaw loads are 26 % lower. Finally, the economics of the power production is estimated through division of the power capture with a cost metric, the foundation loads. While this does not provide a full techno-economic assessment, it effectively captures the interdependency of the power capture and foundation loads for the devices. The mean relative differences in the power per load ratios of the devices are found to be similar across the wave conditions. In the head-on waves, the differences are between –8 and –0.4 %, depending on damping strategy; in the off-angle waves, the differences are between –6 and +10 %. For both sets of wave conditions, the modular flap performs better when the damping is set to maximise the ratio of power capture to foundation loads. The work concludes that the modular and rigid devices produce power and experience foundation loads at similar levels in head-on waves. Given the high power capture efficiency, nearshore location, simple mode of operation and high survivability of the flap-type WEC, this suggests that the modular device is a viable stand-alone concept. The work also finds that in off-angle waves, some benefits can be achieved with an appropriately damped modular system, notably in improved power capture and reduced yaw foundation loads. These could reduce the sensitivity that flap-type devices have in off-angle waves and allow expansion of the width and hence capacity of machines. Further work should extend the wave conditions tested in, by using more irregular and directional waves, and investigate more damping strategies and geometries. Economic assessment should also be carried out.

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Jarocki, Dmitri. "Wave Energy Converter Performance Modeling and Cost of Electricity Assessment." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/278.

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California is experiencing a rapid increase in interest for the potential of converting ocean waves into clean electricity. Numerous applications have been submitted for the permitting of such renewable energy projects; however the profitability, practicability, and survivability have yet to be proven. Wave energy conversion technology has steadily matured since its naissance in the 1970’s, several wave energy power installations currently exist, and numerous plans for commercial power plant are in the works on the shores of multiple continents. This study aims to assess the economic viability of two proposed commercial wave energy power plant projects on the Central California Coast. A theoretical 25 MW capacity wave energy plant located at a site five nautical miles off of Point Arguello, in Santa Barbara County is compared to a site five nautical miles off of Morro Bay, in the County of San Luis Obispo. The Pacific Gas and Electric Company and Green Wave Energy Solutions, LLC have proposed full-scale commercial wave power plants at these sites, and are currently undergoing the federal permitting processes. Historical wave resource statistics from 1980 to 2001 are analyzed with performance specifications for the AquaBuOY, Pelamis P1, and WaveDragon wave energy converters (WECs) to calculate the annual electrical output of each device at each site. Sophisticated computer modeling of the bathymetric influence on the wave resource at each site is presented using the program Simulating Waves Nearshore (SWAN) developed by the Delft University of Technology. The wave energy flux, significant wave height, and peak period are computed at each site for typical summer and winter swell cases, using seafloor depth measurements at a 90 meter rectangular grid resolution. The economic viability of commercial electricity generation is evaluated for each WEC at each site by the calculation of the net present value of an estimated 25-year project life-cycle, the internal rate of return, and the required cost of electricity for a 10-year project simple payback period. The lowest required price of electricity is $0.13/kWh and occurs at the Point Arguello site using the AquaBuOY WEC. The highest annual capacity factor is 18% using the Pelamis WEC. The net present value and internal rate of return calculations suggest that the AquaBuOY WEC is profitable at both sites for electricity prices above $0.14/kWh. Shallow water wave propagation SWAN modeling demonstrated favorable wave energy flux states for WEC operation and power generation at both sites, with typical winter energy fluxes of 30-37 kW/m.

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CAGNINEI, ANDREA. "Hull and mooring design of gyroscopic-based wave energy converter." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2615515.

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Wave energy is one of the less exploited, yet potentially more interesting renewable energy source. In a world where the energy consumption is constantly increasing, but economic and environmental reasons drive the research of alternatives to not-renewable energy sources, it’s just a matter of time before wave energy become an economically sustainable source of renewable energy. The research effort, started in the seventies, was focused on the development of devices for the harvesting of energy from the energetically rich seas of northern Europe. The work presented in this thesis is focused on the development of ISWEC, a wave energy converter based on a gyroscopic conversion of a hull motion, designed specifically to work in the Mediterranean Sea. The device, described in detail in chapter 3, was designed in the Department of Mechanics of the Polytechnic of Turin since 2005, and I worked within the research group responsible for its development. Design of a wave energy converter requires understanding the complex interactions between the device, and its energy-harvesting system, and the waves of the sea. This can be done by the use of numerical models, but experimental validation and testing are always necessary to gain a complete knowledge of such complex phenomena. A substantial part of my work was dedicated to experimental analysis of ISWEC: chapter 4 describes the analysis conducted on the 1:8 scaled model of the device, in order to adjust and validate a numerical model able to describe the device behavior. Results obtained from the experimental campaign on the 1:8 model have been used to design the hull of the full scale prototype of the device, as described in chapter 5. Chapter 6 is dedicated to the study conducted on the mooring system for ISWEC, again performed with the aid of an extensive campaign of tests on a 1:50 scaled model of the device, and of its mooring system.

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ESPING, JONATAN. "Bearings in Wave Energy Converters." Thesis, KTH, Skolan för industriell teknik och management (ITM), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-299281.

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Wave energy and wave energy converters is a fast rapidly developing field of research and energy harvesting. In recent years, more and more designs have seen operational success, and more and more are in development. Wave energy converters face a challenge not properly explored until recently, high loaded, oscillating motion in a highly hostile environment. Which poses a multitude of challenges ranging from contact fatigue to corrosion wear. However, this field is still in early development, seeing little to no research published about it. This work intends to inform about the challenges these wave energy designs pose in tribology and more specifically to bearings, through a literature study and review. The review establishes a rating for different bearing designs based on how applicable a certain bearing selection would be based on available research. Reaching the conclusion that whilst currently inappropriate to employ, seawater lubricated bearings could reach commercial viability in the future for wave energy devices. Additionally, with the help of excellent sealing solutions and well conducted lubrication regimes, both sliding bearings and rolling element bearings have their advantages and disadvantages and can make use of a multitude of different materials.
Vågkraft och vågkraftsgeneratorer är ett område som växer snabbt i intresse för både forskning och produktutveckling. På senare år har fler och fler vågkraftsgeneratorer och designer för dessa sett framgång i prototyptester och flera är på fortsatt utveckling. Vågkraftsgeneratorer står inför flera utmaningar, med de sammansatta faktorerna av en väldigt korrosiv miljö, höga krafter och oscillerande rörelse. Vilket stället flera krav på designers på allt ifrån korrosionsskydd till materialkunskap krig utmattning av maskinkomponenter. Dessvärre finns ytterst lite noga dokumenterad forskning kring området då det är en väldigt ung bransch. Denna rapport söker att utforska och informera kring de utmaningar som kan ställas på vågkraftsgeneratorer inom specifikt tribologi och specifikt för lager och lagerval. Arbetet fokuserar på en litteraturstudie över de möjliga utmaningarna området skapar. Grundat på relevant forskning inom liknande områden betygsattes ett urval av lagerval för vågkraftsgeneratorer. Där slutsatserna pekar på att då det möjligtvis är olämpligt i nuvarande läge att nytta saltvatten som smörjningsmedel, i framtiden kan detta bli en kommersiell verklighet. Där både glidlager och rullningslager har sina fördelar och nackdelar inom applikationen, med noga valda materialkombinationer, smörjningsmedel och tätningar.

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Greenwood, Charles. "The impact of large scale wave energy converter farms on the regional wave climate." Thesis, University of the Highlands and Islands, 2016. https://pure.uhi.ac.uk/portal/en/studentthesis/the-impact-of-large-scale-wave-energy-converter-farms-on-the-regional-wave-climate(e734db00-2108-48f9-b162-a1fc85ef61d6).html.

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39

Bayoumi, Ahmed Seif-Eldine Mohamed. "Development of numerical wave power prediction tool offshore oscillating water column wave energy converter." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18992.

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Marine renewable energy sources are crucial alternatives for a sustainable development. The idea of generating electrical power from water waves has been realized for many years. In fact, waves are now considered as an ideal renewable energy source since a Wave Energy Converter (WEC) has no fuel cost and provides cleanly a high power density that is available most of the time. The third generation of WECs is intended to be installed offshore. This allows the device to harvest the great energy content of waves found in deep water and minimise the environmental impacts of the device. On the other hand, moving WECs to offshore locations will increase the initial and maintenance costs. So many types of device may be suggested for wave power extraction that the task of selecting a particular one is made complicated. Therefore modelling of different WECs allows the comparison between them and the selection of the optimum choice. Recent studies showed that the SparBuoy Oscillat ing Water Column (OWC) has the advantage of being simple, axi-symmetrical, and equally efficient at capturing energy from all directions, but its efficiency (capture factor) is affected significantly by the incident wave periods variation due to the dynamic coupling of the water column and the floating structure. The proper modelling of the device allows the optimization of the geometries and the Power Take-Off (PTO) mechanism in order to maximise the power absorbed. The main objective of this research is to develop experimentally validated numerical wave power prediction tool for offshore SparBuoy OWC WEC. The numerical tool should be able to predict the spar motions and the water column oscillations inside the structure, in addition to the estimation of the pneumatic power absorber and the evaluation of the device performance. Three uncoupled linear second order differential equations have been used to predict the spar surge, heave and pitch motions, where wave forces have been calculated. Three uncoupled linear second order differential equations have been used to predict the spar surge, heave and pitch motions, where wave forces ha ve been calculatedanalytically in frequency domain in inertia and diffraction regimes. Mooring system has been involved in surge motion only using static and quasi-static modelling approaches. Finite element multi-static model have been developed using OrcaFlex to validate the analytical results. Single Degree of Freedom (DOF) mechanical oscillation model has been presented to simulate the water column oscillations inside captive cylindrical OWC where PTO damping and stiffness due to air compressibility inside the pneumatic chamber have been taken into account linearly. Later on, nonlinearity due to large waves has been investigated. Linearized frequency domain model based on classical perturbation theory and nonlinear model where wave forces are calculated in time domain have been proposed. Furthermore, nonlinearity due to damping forces has been considered. First, iterative procedure has been used to optimise the linear and quadratic damping coefficients in frequency domain. Then, another model has been provided where equivalent viscous damping coefficients are calculated in time domain by taking into consideration the instant oscillation amplitude. Finally the nonlinear effects due to air compressibility inside the OWC chamber has been considered in a time domain model which include the water column oscillations amplitudes. Two different dynamic models have been implemented to describe floating OWC and will be referred to in the text as simplified 2DOF model and Szumko model. Both models considered two translational modes of motions in heave direction. Simplified 2DOF model has been solved analytically in frequency domain due to its simplicity, while numerical solutions in time domain have been provided for both models using Matlab. Different approaches have been adopted to modify both models in order to obtain a satisfactory agreement between the predicted and measured results. A floating platform consists of four similar SparBuoy OWC WECs rigidly attached together by trusses where spars are located at the corners have been tested experimentally. Numerical model has been developed to predict the platform motions. Finally the experimentalresults have been compared to those obtained from the modelling of single SparBuoy OWC.

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Rahm, Magnus. "Ocean Wave Energy : Underwater Substation System for Wave Energy Converters." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-112915.

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This thesis deals with a system for operation of directly driven offshore wave energy converters. The work that has been carried out includes laboratory testing of a permanent magnet linear generator, wave energy converter mechanical design and offshore testing, and finally design, implementation, and offshore testing of an underwater collector substation. Long-term testing of a single point absorber, which was installed in March 2006, has been performed in real ocean waves in linear and in non-linear damping mode. The two different damping modes were realized by, first, a resistive load, and second, a rectifier with voltage smoothing capacitors and a resistive load in the DC-link. The loads are placed on land about 2 km east of the Lysekil wave energy research site, where the offshore experiments have been conducted. In the spring of 2009, another two wave energy converter prototypes were installed. Records of array operation were taken with two and three devices in the array. With two units, non-linear damping was used, and with three units, linear damping was employed. The point absorbers in the array are connected to the underwater substation, which is based on a 3 m3 pressure vessel standing on the seabed. In the substation, rectification of the frequency and amplitude modulated voltages from the linear generators is made. The DC voltage is smoothened by capacitors and inverted to 50 Hz electrical frequency, transformed and finally transmitted to the on-shore measuring station. Results show that the absorption is heavily dependent on the damping. It has also been shown that by increasing the damping, the standard deviation of electrical power can be reduced. The standard deviation of electrical power is reduced by array operation compared to single unit operation. Ongoing and future work include the construction and installation of a second underwater substation, which will connect the first substation and seven new WECs.

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Kapell, Jennie. "Analysis of the Inner Flow in the Wave Energy Converter WaveTube." Thesis, KTH, Tillämpad termodynamik och kylteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-102293.

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Wave energy technology is currently growing and gaining popularity. With around 100 separate technologies researched globally in over 25 countries wave energy are believed to soon be able to compete with other renewable sources such as wind energy. One of the new technologies is WaveTube; a wave energy converter currently under development and in need of technical verification. The basic idea of WaveTube is a partially submerged container with an enclosed fresh water volume. The kinetic energy of the ocean waves are transferred onto the floating container, creating an inner flow in the structure and electricity is generated as the fresh water flows through turbines. Previous small-scale model tests have confirmed the basic idea of WaveTube and an inherent continuation is visualizing and evaluating the inner flow using Computational Fluid Dynamics. A simplified 2D simulation where the WaveTube structure is subject to a pure sinusoidal, rotational motion was believed to be able to give useful information about the inner flow field. However, this Master Thesis project shows that a simulation using ANSYS Fluent of this case is not a successful approach. With inner moving parts a so called dynamic mesh was required, which updates the mesh as the boundaries move. In order for this method to be successful the mesh needs to be of high quality. However, for the complex geometry that WaveTube is no mesh was found to meet the requirements and the calculations using the Volume of Fluid method were not able to proceed.

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Ditlefsen, Arne Marius. "Wave Energy Conversion : Simulation Verification and Linearization of Direct Drive Wave Energy Converter with Variable DC-link Voltage Control." Thesis, Norwegian University of Science and Technology, Department of Electrical Power Engineering, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-9912.

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Lowering the cost of wave energy conversion is an essential task for it to succeed as a future energy resource. In this work a converter, assumed cheaper than the regular back to back converter setting, have been investigated for a electric direct drive point absorber. Both experimental work and simulations are used in the analysis. In the experimental work, a permanent magnet generator with a 6-pulse diode rectifier, a DC-link and a DC/DC converter equivalent, was used. Steady state, dynamic and transient measurements were preformed and a simulation model was compared to the measurements. Good results were obtained and deviations were in general small, mostly +-3% for voltage and current measurements and +-8% for torque measurements. Based on transient measurements and simulations a general linearization of the system was made in order to obtain useful information about the system. A step up converter was used in the simulation and it demonstrated stable passive loading control. By using the information obtained by the linearization, the performance of the simulation model was improved by decreasing the DC-link capacitance. The modified simulation model had significant less torque ripple than the initial. The linearization model also can been used to identify time delay represented by the power take off unit in a wave energy converter. This will be done for a commercial size wave energy converter summer 2009.

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Martin, Dillon Minkoff. "Hydrodynamic Design Optimization and Wave Tank Testing of Self-Reacting Two-Body Wave Energy Converter." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/80298.

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As worldwide energy consumption continues to increase, so does the demand for renewable energy sources. The total available wave energy resource for the United States alone is 2,640 TWh/yr; nearly two thirds of the 4,000 TWh of electricity used in the United States each year. It is estimated that nearly half of that available energy is recoverable through wave energy conversion techniques. In this thesis, a two-body 'point absorber' type wave energy converter with a mechanical power-takeoff is investigated. The two-body wave energy converter extracts energy through the relative motion of a floating buoy and a neutrally buoyant submerged body. Using a linear frequency-domain model, analytical solutions of the optimal power and the corresponding power-takeoff components are derived for the two-body wave energy converter. Using these solutions, a case study is conducted to investigate the influence of the submerged body size on the absorbed power of the device in regular and irregular waves. Here it is found that an optimal mass ratio between the submerged body and floating buoy exists where the device will achieve resonance. Furthermore, a case study to investigate the influence of the submerged body shape on the absorbed power is conducted using a time-domain numerical model. Here it is found that the submerged body should be designed to reduce the effects of drag, but to maintain relatively large hydrodynamic added mass and excitation force. To validate the analytical and numerical models, a 1/30th scale model of a two-body wave energy converter is tested in a wave tank. The results of the wave tank tests show that the two-body wave energy converter can absorb nearly twice the energy of a single-body 'point absorber' type wave energy converter.
Master of Science

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44

De, Lauretis Laura. "Optimization of a wave energy converter for the WECwakes II project." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.

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Wave energy has the potential to play a significant role in the future energy system. Estimates show that ocean wave energy can realistically provide about 10% of the world's electricity needs. Exploiting the energy of ocean waves, however, addresses several important challenges that have hitherto prevented the wave energy industry from being blocked. Therefore, several Wave Energy Converter (WEC) projects have been developed in recent years. In most cases, the WEC will not be installed in single units but will be installed in parks to extract an important amount of wave power. In the former WECwakes project, a number of 25 WEC buoys were tested in different geometric configurations and tested in different wave conditions, obtaining essential data on the importance of the effects of the WEC array. However, it is desirable to improve the understanding of the effects of the WEC array by providing high quality experimental data. Therefore, the WECfarm project was established. A first goal in progress is to improve the original WEC design. The developed WEC unit is based on the type of absorption point. The main objective of this thesis was to define a new WEC design with a better radiation effect to maximize WEC wave interactions, WEC-WEC interactions and a reduced peak force on the WEC system. To this end, a numerical study provided by a BEM (Boundary Element Method) model, NEMOH, was performed with the objective to evaluate the performance of the designed WEC unit. Second objective of this dissertation are to provid experimental data for a good choice of the bearings. Air bushings experimental tests were performed on two different layouts.

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45

Bjørnstad, Eiril. "Control of Wave Energy Converter with constrained electric Power Take Off." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12469.

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Because of ocean waves' high energy density and substantial, global technical potential wave energy might become a significant contributor to supply the world's increasing energy demand. The nature of ocean waves is strongly irregular and the power generation from a Wave Energy Converter will have large fluctuations what is a challenge for the electrical system. In the history of wave energy research the focus has been on controlling devices for increasing the absorbed power based on results from mechanical and hydrodynamic mathematical analysis. However, recent work shows that the peak of produced power increases compared to the average absorbed power when traditional control strategies like passive loading and optimal control are applied. The rating and the energy storage requirements of the electrical system will then be increased and the gain due to the increased power production might be lost.In recent work a control strategy that optimizes the torque of the generator with respect to a power saturation level is presented. The work in this report focuses on a practical implementation of this strategy. Further, modifications to meet the torque and speed limitations of the system are made. A control algorithm is presented that utilizes the overrated speed region of the generator to maximize the power production with regards to the power and torque ratings. Simulations for irregular waves and control parameters chosen according to passive loading are then executed and the control algorithm is realized by use of field oriented control of the induction generator. The average absorbed power is changed only to moderate extends compared to the unconstrained case. At the same time the peak to average ratio and the maximum torque is considerably reduced. However, the strategy's reduced torque capability results in a higher maximum speed and pull out speed can be reached. Consequently there will be a trade off between investment costs, produced power and operation range of the system. Therefore the system should be optimized with respect to torque and power limitations, costs, produced power and pullout speed.

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46

Morrison, Iain George. "The hydrodynamic performance of an oscillating water column wave energy converter." Thesis, University of Edinburgh, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493723.

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47

Kluger, Jocelyn Maxine. "Synergistic design of a combined floating wind turbine - wave energy converter." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111692.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 241-251).
Offshore energy machines have great potential: higher capacity factors, more available space, and lower visual impacts than onshore machines. This thesis investigates how combining a wave energy converter (WEC) with a floating wind turbine (FWT) may produce offshore renewable energy cost savings. Attaching the WEC to the FWT greatly reduces the WEC's steel frame, mooring lines, electric transmission lines, and siting/permitting costs, which may comprise 56% of a standalone WEC's cost. A 5 MW FWT currently requires up to 1700 tons of platform steel and 5700 tons of ballast concrete for stabilization in the ocean. This required material may be reduced if the WEC stabilizes the FWT. This thesis addresses several challenges to designing a combined FWT-WEC. First, parameter sweeps for optimizing ocean machine performance are limited by high dimensionalities and nonlinearities, including power takeoff control and wave viscous forcing, which normally require computationally expensive time-domain simulations. This thesis develops a statistical linearization approach to rapidly compute machine dynamics statistics while accounting for nonlinearities in the frequency domain. It is verified that the statistical linearization method may capture significant dynamics effects that are neglected by the traditional Taylor series linearization approach, while computing the results approximately 100 times faster than time domain simulations. Using Morison's equation for wave viscosity and quasi-steady blade-element/momentum theory for rotor aerodynamics, we find that viscous effects and nonlinear aerodynamics may increase the FWT motion and tower stress by up to 15% in some wind-sea states compared the the Taylor series linearized system. Second, the WEC must stabilize rather than destabilize the FWT. This thesis investigates the dynamics statistics of dierent FWT-WEC configurations using a long wavelength, structurally coupled model. It is shown that simultaneous targeted energy transfer from both the FWT and waves to the WEC when the WEC and FWT are linked by a tuned spring is unlikely. That being said, this thesis considers heave-mode oscillating water column WEC's that are linked to the FWT platform by 4-bar linkages, so that the FWT and WEC's are uncoupled for small heave motions and rigidly coupled in all other degrees of freedom. It is shown that this configuration allows the WEC to move with a large amplitude in its energy harvesting degree of freedom, and therefore harvest a significant amount of power without significantly increasing the FWT motion in the same direction. In the rigidly-connected modes, the WEC inertial resistance to motion must be greater than the wave forcing, as these properties are transmitted to the FWT. Third, the WEC requires power robustness in dierent sea states. Typical WEC's require control schemes to maintain good power performance when the ocean wave dominant frequency differs from the WEC resonant frequency. This thesis introduces a nonlinearity into the WEC design that passively increases power adaptability in dierent sea states. While the optimized nonlinear WEC requires 57% more steel than the optimized linear WEC, the nonlinear WEC produces 72% more power on average, resulting in a 3% lower levelized cost of energy. Further optimization of the nonlinear WEC may find improved performance. This thesis determines that attaching a single linear hinged floating spar oscillating water column to the FWT reduces the levelized cost of energy from $0.31/kWh for the standalone system to $0.27/kWh (13%) without changing stress on the FWT tower. Attaching a single nonlinear hinged floating spar oscillating water column to the FWT reduces the levelized cost of energy to $0.26/kWh (16%) and reduces the lifetime equivalent fatigue stress on the FWT tower from 32.4 MPa to 31 MPa (5%). A 6-unit array of the nonlinear WEC's encircling the FWT platform may generate an average of 400 kW while reducing the FWT tower stress by over 50%. In wave tank experiments, the response statistics of four dierent combined FWT-WEC configurations are measured, verifying the FWT-WEC dynamics model.
by Jocelyn Maxine Kluger.
Ph. D.

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48

Seixas, de Medeiros João. "Wave energy converter design via a time-domain Rankine panel method." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/108919.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 111-115).
Efficient design of energy converters heavily depends on the capacity of the designer to accurately predict the device's dynamic, which ultimately leads to the power extraction. This is specially true for wave energy converters (WEC), which usually present a high cost per kWh generated. In this thesis a particular WEC which uses a rotating mass for power extraction is studied. A numerical model for the prediction of its motion and power extraction is presented. The nonlinear dynamic model consists of a time-domain three dimensional Rankine panel method coupled, in the time integration, with a MATLAB algorithm which solves for the equations of the gyroscope and Power Take-Off (PTO). The former acts as a force block, calculating the forces due to the waves on the hull, which is then sent to the latter through TCP/IP, which couples the external dynamics and performs the time-integration using a 4th order Runge-Kutta method. With the proposed code, two case studies are examined. The first consists of two gyroscopes, rotating in opposite directions, to negate undesirable yaw effects on the WEC's hull. The device's optimum PTO damping value and flywheel spin are then shown, which change for different sea states. The second is a comparison against results from experimental testing of a 1:50 model at the Davidson Laboratory during the Wave Energy Prize.
by João Seixas de Medeiros.
S.M.

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49

Minns, Julian. "Comparative performance of a novel oscillating water column wave energy converter." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10042.

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This thesis presents research which shows that a helically configured Oscillating Water Column (OWC) could deliver improved performance compared to a conventional tube OWC, whilst saving a significant amount of draft. It is anticipated that savings in the deployment costs for this compact machine will outweigh any additional manufacturing costs. In order to prove the benefits of the helical concept, its performance relative to a conventional plain tube OWC was investigated in detail using scaled physical models. These models evolved during the course of the study, and refined models were developed. A variable impedance turbine simulator was also developed to test the models at their optimum conditions. The tests themselves were also refined leading to a high degree of confidence in the final result. A mathematical model was also adapted to model the performance of the physical models, and to help understand the physical processes involved in the system. With this series of improving physical models and tests, it has been shown that it is possible to achieve a 27% reduction in draft, with a 24% increase in power output.

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50

Dahl, Becedas Martin. "Linear and Nonlinear Model Predictive Control of a Wave Energy Converter." Thesis, KTH, Skolan för elektroteknik och datavetenskap (EECS), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-284252.

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The topic of this thesis has been to design a regulator that maximizes the energytransfer from kinetic wave energy to electrical energy. The wave energyconverter used, is of the heaving point absorber type, which is developed bythe company CorPower Ocean AB. Two models have been used, a linear modeland a model in which a selection of nonlinear forces have been active. A Linearand Nonlinear Model Predictive Controller have been developed, usingMatlab’s optimizer fmincon. The cost function of these controllers has alsobeen varied in an attempt to take the infinite horizon into account, using aterminal weight. In order to get an idea of the performance, these controllerswere compared with a differently formulated Model Predictive Controller thatused Matlab’s optimizer quadprog. The latter generally performed betterwith respect to extracted energy. It seemed as the choice of optimizer couldhave an impact on the results. When nonlinear drag and net restoring stiffnessforces were introduced to the model, the Nonlinear Model Predictive Controllerincreased the output energy compared to its linear counterpart.
Detta examensarbete har syftat till att utveckla en regulator som maximerarenergiöverföringen från kinetisk vågenergi till elektrisk energi. Vågkraftverketsom använts är av typen punktabsorberande system, som utvecklas av företagetCorPower Ocean AB. Två modeller har använts, en linjär approximationsamt en modell där ett urval av olinjära krafter varit aktiva. En Linjär samtOlinjär Modellprediktiv Regulator har utvecklats, där Matlabs optimeringslösarefmincon användes. Kostnadsfunktionen för dessa regulatorer har ävenvarierats i ett försök att ta hänsyn till oändliga tidshorisonten. För att få enuppfattning av prestandan jämfördes dessa regulatorer med en annorlunda formuleradModellprediktiv Regulator som använde Matlabs optimeringslösarequadprog. Den sistnämnda presterade generellt bättre med avseende på utvunnenenergi. Regulatorerna som togs fram i detta arbete betedde sig interikigt som väntat då de i flera fall minskade i energi med en längre tidshorisont.Att försöka beskriva oändliga horisonten i kostnadsfunktionen resulteradeoftast i något mer utvunnen energi, det skulle dock krävas vidare arbeteför att kunna dra slutsatser kring denna metod. Det fanns indikationer på attfmincon presterade sämre med längre horisont, även här skulle det krävasmer arbete för att kunna fastställa huruvida detta var orsaken eller inte.

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Дисертації з теми "Pendulum Wave Energy Converter"

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