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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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Medina-López, Encarnación. "Thermodynamic processes involved in wave energy extraction." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31422.
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Wave energy is one of the most promising renewable energy sources for future exploitation. This thesis focuses on thermodynamic effects within Oscillating Water Column (OWC) devices equipped withWells turbines, particularly humidity effects. Previous theoretical studies of the operation of OWCs have resulted in expressions for the oscillation of the water surface in the chamber of an OWC based on linear wave theory, and the air expansion{compression cycle inside the air chamber based on ideal gas theory. Although in practice high humidity levels occur in OWC devices open to the sea, the influence of atmospheric conditions such as temperature and moisture on the performance of Wells turbines has not yet been studied in the field of ocean energy. Researchers have reported substantial differences between predicted and measured power output, and performance rates of OWCs presently coming into operation. The effect of moisture in the air chamber of the OWC causes variations on the atmospheric conditions near the turbine, modifying its performance and efficiency. Discrepancies in available power to the turbine are believed to be due to the humid air conditions, which had not been modelled previously. This thesis presents a study of the influence of humid air on the performance of an idealised Wells turbine in the chamber of an OWC using a real gas model. A new formulation is presented, including a modified adiabatic index, and subsequent modified thermodynamic state variables such as enthalpy, entropy and specific heat. The formulation is validated against experimental data, and found to exhibit better agreement than the ideal approach. The analysis indicates that the real gas behaviour can be explained by a non{dimensional number which depends on the local pressure and temperature in the OWC chamber. A first approach to the OWC formulation through the calculation of real air flow in the OWC is given, which predicts a 6% decrease in efficiency with respect to the ideal case when it is tested with a hypothetical pulse of pressure. This is important because accurate prediction of efficiency is essential for the optimal design and management of OWC converters. A numerical model has also been developed using computational fluid dynamics (CFD) to simulate the OWC characteristics in open sea. The performance of an OWC turbine is studied through the implementation of an actuator disk model in Fluent®. A set of different regular wave tests is developed in a 2D numerical wave flume. The model is tested using information obtained from experimental tests on a Wells{type turbine located in a wind tunnel. Linear response is achieved in terms of pressure drop and air flow in all cases, proving effectively the applicability of the actuator disk model to OWC devices. The numerical model is applied first to an OWC chamber containing dry air, and then to an OWC chamber containing humid air. Results from both cases are compared, and it is found that the results are sensitive to the degree of humidity of the air. Power decreases when humidity increases. Finally, results from the analytical real gas and numerical ideal gas models are compared. Very satisfactory agreement is obtained between the analytical and the numerical models when humidity is inserted in the gaseous phase. Both analytical and numerical models with humid air show considerable differences with the numerical model when dry air is considered. However, at the resonance frequency, results are independent of the gas model used. At every other frequency analysed, the real gas model predicts reduced values of power that can fall to 50% of the ideal power value when coupled to the radiation-diffraction model for regular waves. It is recommended that real gas should be considered in future analyses of Wells turbines in order to calculate accurately the efficiency and expected power of OWC devices.
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Moisel, Christoph, and Thomas Carolus. "A facility for testing the aerodynamic and acoustic performance of bidirectional air turbines for ocean wave energy conversion." Elsevier, 2016. https://publish.fid-move.qucosa.de/id/qucosa%3A36338.
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Bidirectional air turbines are used in oscillating water column (OWC) power plants for harnessing ocean wave energy. This paper describes the bidirectional aerodynamic and aero-acoustic facility at the University of Siegen for model air turbines performance testing. At least nine test facilities are known worldwide, but their layout, the performance testing procedure and the presentation of performance data are not standardized to this day. The layout of the facility at the University of Siegen follows ideas in ISO 5801 for fan performance testing. The pressurized air supply is bidirectional but steady-state. Achievable values of Reynolds and Mach number of the test turbines are 1,000,000 and 0.5, respectively. In addition, the facility is equipped with acoustic attenuators in the air supply for allowing synchronous determination of aerodynamic and acoustic characteristics of a turbine.
A good practice guideline for turbine performance testing and presentation is proposed by showing full sets of non-dimensional aerodynamic and acoustic performance characteristics from two sample model turbines. Eventually, a comparison of in situ data from a full-scale turbine in transient operation with scaled up steady-state model performance measurements underlines the usefulness of steady-state model performance testing.
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Lima, Yuri Theodoro Barbosa de. "Aplicação do método Design Construtal na avaliação numérica da potência hidropneumática de um dispositivo coluna de água oscilante com região de transição trapezoidal ou semicircular e estudo da influência da turbina no formato elíptico." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/153297.
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A conversão da energia das ondas dos oceanos em energia elétrica é uma alternativa para o problema da falta de combustíveis fósseis. Uma das possibilidades de aproveitamento é através de dispositivos cujo princípio de funcionamento é o de Coluna de Água Oscilante (CAO). No presente trabalho o objetivo é, através da modelagem computacional e do emprego do Design Construtal, maximizar a potência hidropneumática de um dispositivo conversor de energia das ondas do mar do tipo CAO. São analisados diferentes eixos da restrição física, no formato elíptico, que representa a turbina, e duas formas geométricas na região de transição entre a câmara hidropneumática e a chaminé do dispositivo CAO: trapezoidal e semicircular. Considerando um domínio bidimensional, as restrições para estes problemas são: Área da restrição elíptica (AR), Área total do dispositivo (AT) e razão entre a área da restrição elíptica e a área total (ϕn). Os graus de liberdade analisados são: a razão entre os comprimentos dos eixos da restrição elíptica (d1/d2) para o caso da restrição física da turbina, o ângulo de inclinação da parede (α) para o caso com região de transição trapezoidal, o raio (r) e H2/l (razão entre altura e comprimento da chaminé de saída da câmara CAO) para o caso com região de transição semicircular. Para a solução numérica é empregado um código de dinâmica dos fluidos computacional, FLUENT®, baseado no Método de Volumes Finitos (MVF). O modelo multifásico Volume of Fluid (VOF) é aplicado no tratamento da interação água-ar. O domínio computacional é representado por um tanque de ondas com um dispositivo CAO acoplado. Os resultados obtidos indicam que, para o estudo da região de transição trapezoidal o desempenho do conversor tem aproximadamente o mesmo desempenho para todas as geometrias estudadas. A região de transição semicircular, apresenta resultados para os quais foi possível otimizar a potência hidropneumática. O estudo da turbina indica que foi possível determinar uma geometria capaz de converter a energia da onda incidente ao dispositivo, sem que ocorresse a obstrução do escoamento de ar na chaminé do dispositivo CAO. Assim, mostra-se a relação entre o método Design Construtal e o clima de ondas na definição das dimensões que maximizam a potência hidropneumática.The conversion of ocean’s wave energy into electrical energy is an alternative for the scarcity of fossil fuels. One of the possibilities of energy use is through devices, whose operating principle is the Oscillating Water Column (OWC). In this work the aim is, through computer modeling and the Constructal Design, to maximize hydropneumatic power of a power converter device type OWC. Different axes of physical constraint with elliptical shape, representing the effect of the turbine , are analyzed. Two geometric shapes in the transition region between the hydropneumatic chamber and the chimney OWC device, trapezoidal and semicircular, are also analyzed. Considering a two-dimensional domain the restrictions for this problem are: Elliptical restriction area (AR), Total area device (AT) and the ratio between the area of the elliptical restraint and the total area (ϕn). The considered degrees of freedom are: the ratio between the lengths of the axes (d1/d2) of the elliptical restraint, for the turbine’s physical constraint case, the inclination angle (α) of the wall for the trapezoidal transition case, and the radius (r) and H2/l (ratio between height and length of output chimney CAO) for the semicircular transition region case. For the numerical solution, a commercial code of computational fluid dynamics, FLUENT®, which is based on the Finite Volume Method (FVM), is employed. The multiphase model Volume of Fluid (VOF) is applied in the treatment of water-air interaction. The computational domain is represented by a wave tank with a fixed OWC device. The obtained results indicate that, for the study of the trapezoidal transition region, the performance of converter don’t seems to be compensatory only by changing the geometry of the trapezoidal area. However, for the semicircular transition region, it was possible to optimize a hydropneumatic power. The study of turbine effect indicates a geometry capable of converting the energy of the incident wave to the device, without obstructing the air flow in the chimney of de OWC, showing the relationship between the Constructal Design method and the wave climate in the definition of the dimensions that maximize the hydropneumatic power.
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Kooverji, Bavesh. "Pneumatic power measurement of an oscillating water column converter." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86662.
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Thesis (MScEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: A measurement device was developed to accurately determine the pneumatic power performance of an Oscillating Water Column (OWC) model in a wave flume. The analysis of the pneumatic power is significant due to the wave-topneumatic energy being the primary energy conversion process and where the most energy losses can be expected. The aim of the research study is to address the accurate pneumatic power measurement of unsteady and bidirectional airflow in OWC model experiments. The two fundamental measurements required for the pneumatic power measurement are the pressure difference over an orifice on the OWC model and the volumetric flow rate of air through the outlet. The designed, constructed and assembled measurement device comprised of a venturi flow meter, containing a hot-film anemometer, which could measure the pressure drop and the volumetric flow rate in one device. The assembled pneumatic power measurement device was calibrated in a vertical wind tunnel at steady state. The results from the calibration tests showed that the volumetric flow rate measurements from the pneumatic power measurement device was accurate to within 3 % of the wind tunnel’s readings. The pneumatic power measurement device was incorporated onto a constructed Perspex physical model of a simple OWC device. This assembled system was used as the test unit in the wave flume at Stellenbosch University (SUN). The results from the experimental tests underwent comparative analysis with three analytical OWC air-flow models which were simulated as three scenarios using Matlab Simulink. These results showed that the measurement device has the ability to measure the pneumatic power but there is difficulty in modelling the complex air-flow system of the OWC device. This results in varying levels of agreement between the experimental and simulated pneumatic power results. The research study has revealed that there is difficulty in designing an accurate device for a wide range of test parameters due to the variance in output values. The unsteady and bidirectional nature of the air flow is also difficult to accurately simulate using a one-dimensional analytical model. Recommendations for further investigation are for CFD systems to be used for the analysis of the air-flow in an OWC system and to be used to validate future pneumatic power measurement devices.
AFRIKAANSE OPSOMMING: ‘n Meetinstrument was ontwikkel om die pneumatiese kraglewering van ‘n model van die Ossillerende Water Kolom (OWK) golfenergie omsetter in ‘n golf tenk akkuraat te meet. Dit is belangrik om die omskakeling van golf na pneumatiese energie te analiseer siende dat die grootste energieverlies in dié proses plaasvind. Die doel van hierdie navorsingsprojek was om die akkurate pneumatiese kragmeting van variërende en twee-rigting vloei van lug in ‘n OWK model na te vors. Die twee fundamentele metings wat benodig word vir die pneumatiese kragbepaling is die drukverskil oor die vloei vernouing en die volumetriese vloeitempo van lug deur die uitlaat van die toetstoestel. Die spesiaal ontwerpte meettoestel wat gebruik is in die eksperiment het bestaan uit ‘n venturi vloeimeter wat ‘n verhitte-film anemometer bevat het wat die drukverandering en die volumetriese vloeitempo kan meet in ‘n enkele instrument. Die pneumatiese kragmeting was gekalibreer in ‘n vertikale windtonnel waarin ‘n konstante vloei tempo geïnduseer was. Die kalibrasieproses het bevestig dat die meettoestel metings lewer met ‘n fout van minder as 3 % wanneer dit vergelyk word met die bekende konstante vloei tempo soos bepaal in die windtonnel. ‘n Fisiese model van ‘n vereenvoudigde OWK golfenergie omsetter was ontwerp en gebou uit Perspex om as toetstoestel te gebruik vir die evaluering van die ontwerpte pneumatiese kraglewering meettoestel. Die toetse was uitgevoer in ‘n golftenk by die Universiteit Stellenbosch (SUN). The toetsresultate was vergelyk met drie ander OWK lugvloei modelle wat gesimuleer was deur om die analitiese modelle op te stel en te simuleer in Matlab Simulink. Die vergelyking van modellering resultate het gewys dat die meettoestel die vermoë het om pneumatiese krag te meet. Daar was wel komplikasies met die modellering van die komplekse lugvloei in die OWK toestel, die resultate het geen definitiewe ooreenstemming gewys tussen die eksperimentele en gesimuleerde pneumatiese krag resultate nie. Die navorsingsprojek het gewys dat daar komplikasies is om ‘n enkel toestel te ontwerp wat oor ‘n wye bereik kan meet weens die variasie van die verskillende parameters. Die variërende en twee-rigting lugvloei is ook moeilik om akkuraat te simuleer met ‘n een-dimensionele analitiese simulasie model. Aanbevelings vir verdere navorsing sluit in om die lugvloei in die OWK stelsel te modelleer en te analiseer in ‘n drie-dimensionele model om die lesings van ‘n pneumatiese krag meettoestel te bevestig.
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Perdigão, José Nuno Bebiano Mesquita de Azeredo. "Reactive-control strategies for an oscillating-water-column device." Phd thesis, Instituições portuguesas -- UTL-Universidade Técnica de Lisboa -- IST-Instituto Superior Técnico -- -Departamento de Engenharia Mecânica, 1998. http://dited.bn.pt:80/29667.
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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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Martins-rivas, Hervé. "Power extraction from an oscillating water column along a coast." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45257.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.Includes bibliographical references (p. 121-123).
For reasons of wave climate, geography, construction, maintenance, energy storage and transmission, some devices for extracting energy from sea waves will likely be installed on the coast. We study here the specific case where an Oscillating Water Column (OWC) is attached to the tip of a long breakwater. A three-dimensional numerical model of a skeletal geometry of the the Foz do Douro breakwater is developed in order to determine the response inside the OWC pneumatic chamber to incident waves and assess the possible effects of the breakwater geometry. The model uses the hybrid element method and linear water wave theory. Then, a more analytical approach for a simplified geometry is presented. Making use of an exact solution for the scattering by a solid cylinder connected to a wedge, we solve for the linearized problems of radiation and scattering for a hollow cylinder with an open bottom. Power-takeoff by Wells turbines above an air chamber is modeled by including the compressibility of air. It is shown for the case of a circular OWC attached to a thin breakwater, that the incidence angle affects only the waves in and outside the column but not the power extraction which depends only on the averaged water-surface displacement inside. Optimization by controlling the turbine characteristics is examined for a wide range of wavelengths. Finally, the same approach is used to solve the case of an OWC positioned along a straight coast line. It is found that in this configuration, the extracted power does depend on the incidence angle. It is also shown that the average efficiency is doubled compared to the thin breakwater geometry.
by Hervé Martins-rivas.
S.M.
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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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Leitch, John Gaston. "Productivity analysis and optimization of oscillating water column wave power devices." Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329360.
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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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Mackinnon, Pauline Anna. "The influence of geometry on turbulent losses in an oscillating water column." Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357453.
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Freeman, Kate. "Numerical modelling and control of an oscillating water column wave energy converter." Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3290.
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An oscillating water column (OWC) wave energy converter (WEC) is a device designed to extract energy from waves at sea by using the water to move trapped air and thus drive an air turbine. Because the incident waves and the force caused by the power take-off (PTO) interact, control of the power take off (PTO) system can increase the total energy converted. A numerical model was developed to study the interaction of an OWC with the water and other structures around it. ANSYS AQWA is used here to find the effects on the water surface in and around the central column of a five-column, breakwater-mounted OWC. For open OWC structures, coupled modes were seen which lead to sensitivity to incident wave period and direction. The frequency-domain displacements of the internal water surface of the central column were turned into a force-displacement, time-domain model in MATLAB Simulink using a state space approximation. The model of the hydrodynamics was then combined with the thermodynamic and turbine equations for a Wells turbine. A baseline situation was tested for fixed turbine speed operation using a wave climate for a region off the north coast of Devon. A linear feedforward controller and a controller based on maximising turbine efficiency were tested for the system. The linear controller was optimised to find the combination of turbine speed offset and proportional constant that gave maximum energy in the most energy abundant sea state. This increased the converted energy by 31% in comparison to the fixed speed case. For the turbine efficiency control method, the increase was 36%. Energy conversion increases are therefore clearly possible using simple controllers. If increased converted energy is the only criterion for controller choice, then the turbine efficiency control is the best method, however the control action involves using very slow turbine speeds which may not be physically desirable.
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Dai, Saishuai. "Assessing the performance of an oscillating water column type wave energy device." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27860.
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To meet the need of clean energy, a variety of renewable energy technologies have been developed. Among those, wave energy stands out for its outstanding merits. For instance, wave energy is clean, renewable, has high energy intensity and long resource available time. However, due to the short development history of wave energy technologies, the cost of wave energy is too high compared with the other renewable energy technologies. As well as lack of cost effective Wave Energy Converters (WECs) scenarios, another reason that keeps the cost of wave energy high is that the performance of a WECs may not be accurately assessed during its design and development stage. This leads to error in estimating the cost of energy produced by the full scale device. Therefore, this study aims to drive the cost of WECs down by investigating several major aspects that will bias the assessing of the performance of a WEC during the design and development stage. Literature review suggested the uncertainty in the measurement, the tank width effect (in tank testing), the performance of the simulated simple Power Take Off (PTO) and the scale effect are major aspects that bias the assessment. By tank testing and Computational Fluid Dynamic (CFD) simulation, the above three aspects were investigated. It is found that the uncertainty in the measurement leads to an uncertainty in the power captured at model scale about 5% around the peak output. The appearance of the tank wall will over estimate the performance of a single unit depending on the width of the tank. A 1 : 150th scaled (of the full scale.) device may under estimate the performance of the device by about 34% compared with a 1 : 16.67th scaled device, while a 1 : 50th scaled device under estimate the performance of a 1 : 16.67th scaled device by 6.6%. The CFD simulation demonstrated its advantage over the tank testing when scaling and tank width effect is concerned. Therefore, to better estimate the performance, the assessment shall be carried out by both experiment and numerical simulation. Based on the study carried out, recommendation and guide line for tank testing of a FSCOWC device was given at the end of the thesis.
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Holzhauer, Eva. "Assessment of the power available in a fixed offshore oscillating water column plant." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/8053.
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The early effects of the global warming can be observed and people around the world are beginning to realize the seriousness of the situation. Reducing the CO2 emissions produced by fossil energy seems to be one of the main worldwide technological challenges at the time of writing. Hence, since the oil crisis in the 70s, a growing interest in renewable energies has been noticed. In Europe, the European Commission fixed a target: to produce 20% of the EU energy from renewable sources by 2020. Similar initiatives, in varying degrees, are being considered around the globe.
Among all the renewable energy technologies currently on the market, the ocean energy industry is still at an early stage, despite investigations that have been carried out on both tidal and wave energy devices over the past 40 years. The subject of this thesis focuses on one of the wave energy devices: the Oscillating Water Column.
The information found in the literature about this type of plants is mainly about onshore and floating offshore OWCs. Very little information about fixed offshore OWC is available. Besides, the availability of large numbers of fixed offshore structures installed in the world oceans suggests that many of these could possibly host an OWC plant. Hence, the present study investigated a fixed offshore OWC.
The aim of this thesis is to assess the power available in a fixed offshore OWC plant. To illustrate the procedure of power assessment, the fictional scenario of a platform located in the Santa Maria sea region, off the coast of Californian, is introduced. This work intends to develop a methodology to study the feasibility of such installation and estimate the power extractable through various complementary approaches. From a theoretical approach based on the wave climate of Santa Maria to wave tank experiments with various geometries and shapes of chamber (cylinder and bent duct buoy in frontward and backward position), the viability of a fixed offshore OWC plant is demonstrated for the chosen location. Results highlight the performance of the Backward Bent Duct Buoy (BBDB) for the Santa Maria characteristic sea conditions. With the intention of completing the study with a Computational Fluid Dynamics (CFD) analysis, numerical investigations about the implementation of an alternative method to generate regular waves demonstrates better results of wave propagation than the common wave generation method based on Linear Wave Theory previously used at Cranfield University. In the conclusion, the work achievements and recommendations for future CFD investigations to reproduce the wave tank experiments are discussed.
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Brendmo, Arne. "An investigation of wave-energy absorption by single and double oscillating water-column converters." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 1995. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14721.
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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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Carolus, Thomas, and Christoph Moisel. "Bidirectional air turbines for oscillating water column systems: Fast selection applying turbomachinery scaling laws." Elsevier, 2017. https://publish.fid-move.qucosa.de/id/qucosa%3A36340.
Full textAbstract:
The collector of an oscillating water column system (OWC) for wave energy utilization requires a bidirectional turbine that copes with pneumatic power while providing specified impedance or, in terms of an OWC designer, “damping”. Damping is realized by keeping to a specific flow rate through the turbine at a given pressure head due to the individual performance characteristic of the turbine. With the number of turbine designs increasing designers of OWC systems are facing more options to select and dimension a bidirectional turbine. Energy yield, size and hence cost of the turbine and electric generator, operational behaviour, envisaged control strategy and noise emitted by the turbine are possible criteria for selection.
The primary objective of this paper is to describe a simple procedure for making a first choice of a turbine for a particular OWC application. Here we confine ourselves to a family of reaction type of turbines (axial-flow Wells and mixed-flow turbines by Moisel) with their approximately linear pressure head/volume flow rate characteristics. Starting point is the set of non-dimensional steady-state characteristics of each turbine in the family. Utilizing standard scaling laws and a very simple time domain model for the cyclic turbine operation (i.e. based one single sea state and turbine operation assumed to be fixed rotational speed), first estimates of turbine size and rotor speed, number for stages or flows, and performance curves can be determined. The resulting turbine may also serve as a starting configuration for a refined analysis, e.g. the optimization of the turbine and the complete OWC system, utilizing more complex stochastic models. Three case studies illustrate the application of the method: selection and scaling of turbines, effect of collector parameters, turbines in series and parallel.
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Stewart, Terence Patrick. "The influence of harbour geometry on the performance of oscillating water column wave power converters." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359126.
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Sparrer, Wendelle Faith. "Implementation and Demonstration of a Time Domain Modeling Tool for Floating Oscillating Water Columns." Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/101889.
Full textAbstract:
Renewable energy is a critical component in combating climate change. Ocean wave energy is a source of renewable energy that can be harvested using Wave Energy Converters
(WECs). One such WEC is the floating Oscillating Water Column (OWC), which has been
successfully field tested and warrants further exploration. This research implements a publicly accessible code in MatLab and SimuLink to simulate the dynamics of a floating OWC
in the time domain. This code, known as the Floating OWC Iterative Time Series Solver
(FlOWCITSS), uses the pressure distribution model paired with state space realization to
capture the internal water column dynamics of the WEC and estimate pneumatic power
generation. Published experimental results of floating moored structures are then used to
validate FlOWCITSS. While FlOWCITSS seemed to capture the period and general nature
of the heave, surge, and internal water column dynamics, the magnitude of the response
sometimes had errors ranging from 1.5% −37%. This error could be caused by the modeling
techniques used, or it could be due to uncertainties in the experiments. The presence of
smaller error values shows potential for FlOWCITSS to achieve consistently higher fidelity
results as the code undergoes further developments. To demonstrate the use of FlOWCITSS,
geometry variations of a Backward Bent Duct Buoy (BBDB) are explored for a wave environment and mooring configuration. The reference model from Sandia National Labs, RM6,
performed significantly better than a BBDB with an altered stern geometry for a 3 second
wave period, indicating that stern geometry can have a significant impact on pneumatic
power performance.Master of Science
Renewable energy is a critical component in combating climate change. Ocean wave energy is a source of renewable energy that can be converted into electricity using Wave Energy Converters (WECs). One such WEC is the floating Oscillating Water Column (OWC), which has been successfully field tested and warrants further exploration. Floating OWCs are partially submerged floating structures that have an internal chamber which water oscillates in. The motions of the water displace air inside this chamber, causing the air to be forced through a high speed turbine, which generates electricity. This research develops a publicly accessible code using MatLab and SimuLink to evaluate the motions and power generation capabilities of floating OWCs. This code is then validated against physical experiments to verify its effectiveness in predicting the device's motions. This publicly accessible code, known as the Floating OWC Iterative Time Series Solver (FlOWCITSS), showed error ranging from 1.5 % - 37% for the most important motions that are relevant to energy harvesting and power generation. These errors could be caused by the numerical models used, or uncertainties in experimental data. The presence of smaller error values shows potential for FlOWCITSS to achieve consistently higher fidelity results as the code undergoes further developments. To demonstrate the use of FlOWCITSS, geometry variations of floating OWCs are explored.
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Simonetti, Irene [Verfasser], and Hocine [Akademischer Betreuer] Oumeraci. "Optimization of oscillating water column wave energy converters - a numerical study / Irene Simonetti ; Betreuer: Hocine Oumeraci." Braunschweig : Technische Universität Braunschweig, 2017. http://d-nb.info/1175816590/34.
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Ahmed, Nisaar. "Thermo-fluid modelling of electrical generator frames under forced convection in an oscillating water column environment." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31363.
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This PhD involved computational fluid dynamic simulations of finned generators cooling under forced convection in an oscillating water column environment. Various design changes to the upstream Wells turbine and its effect on the consequent cooling of the generator were investigated. Simulations were run in steady-state to obtain an initial condition, thereafter, unsteady simulations revealed a steadying of heat transfer over the course of multiple blade rotation cycles. This justified the use of steady-state for the remaining simulations over a range of flow coefficients. The results revealed that the heat transfer from the generator increased for tighter blade tip clearances, thicker blade profiles and greater turbine solidity. The heat transfer was found to increase with rising flow rate coefficient, which was adjusted by increasing the inlet velocity whilst maintaining the angular velocity of the turbine at a constant 2000 RPM. Additionally, the variation of turbine angular velocity at a fixed flow rate coefficient was investigated, the heat transfer was also found to increase with angular velocity, albeit by a far lesser extent. The inclusion of the Wells turbine upstream of the generator was investigated initially and was found to increase heat transfer due to the resulting impingement of airflow across the generator. In all design scenarios in which the heat transfer increases, there is also an observed increase in the mass flow rate of air, radially, towards the generator.
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Crema, Ilaria [Verfasser], and Hocine [Akademischer Betreuer] Oumeraci. "Oscillating water column wave energy converters integrated in very large floating structures / Ilaria Crema ; Betreuer: Hocine Oumeraci." Braunschweig : Technische Universität Braunschweig, 2018. http://d-nb.info/1175815357/34.
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Guo, Lihui. "Applicability and potential of wave power in China." Thesis, University of Gävle, Department of Building, Energy and Environmental Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-7151.
Full textAbstract:
Wave power is renewable energy which is environmentally friendly. Unlike most of renewable energy resources, wave energy can produce power all the year. The wave energy is stored in the ocean worldwide and highly concentrated near the ocean surface. It can be captured by wave power devices. Wave power is considered as a competitive energy resource in future.
Waves are generated by wind blows across the surface of sea. Wave energy is one kind of mechanical energy which will be used for electricity generation. Wave power can’t be used directly to generate electricity; at first the wave energy is converted into the other form of useful mechanical energy and then converted into electricity. Wave power has a high potential to be captured and used for generating electricity in future as the technology develops further.
Wave energy has been used since 1890s. There is a lot of energy stored in waves. 94% energy of the ocean stored in the wave, and the other 6% is tidal energy. Only small a part of the wave power is used for commercial electricity generation today.
The China is a developing country with a very large population which annually consume about 3073TWh electricity of which 496TWh is from renewable energy. The wave power was less than 1GWh in 2007 (reference from International Energy Agency). The World Energy Council has measured the total useful power of the ocean wave energy to be more than 2TW in the world and corresponding to 6000TWh per year. There is about 70GW useful wave power resources in China, equivalent to an annual useful wave power resource of 200TWh.
The lowest capital cost for the wave power system is today around 0.1Euro/kWh. China will in the future focus on the development electricity generation by wave power. There will be hundreds of new wave power plant built in China during the next twenty years, and the total installed capacity will be larger than 1GW at 2030, which delivers 3TWh annually. This corresponds to less than 1 percent of the total use of electricity in China.
This thesis focuses on the functionality, efficiency and economic pay-off of existing ocean wave power systems, as well as how easy the ocean wave power can produce electricity. Firstly it discusses the physical concepts of wave power, and then focus on the existing wave power systems around the world. It is concluded from the Chinese sea characteristics and the designed conditions of different wave power systems, that the Pelamis and Oyster wave power converters are the best suitable systems for China.
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Larsson, Petter, and Gustaf Rudbeck. "Wave Energy Concept Benchmarking." Thesis, KTH, Maskinkonstruktion (Inst.), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-298841.
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Denna rapport ämnar undersöka de vanligast förekommande typerna av teknologier för vågkraftverk (eng. Wave Energy Converter, WEC) teknologier för att jämföra de olika konceptens förmåga att absorbera vågenergi. Koncept som undersöks är punktabsorbatorer och oscillerande vattenkolumner. I denna rapport används de vanligt använda engelska översättningarna point absorber och oscillating water column (OWC). Beräkningar görs för de olika koncepten i liknande vågförhållanden för att kunna jämföra den energi som kan utvinnas. I rapporten sker beräkningar under optimala vågförhållanden. Vågorna antas vara linjära och vågkraftverken antas vara i fas med vågens svängningsrörelse. Den vågdata som använts är uppmätt utanför Belmullet i Irland. Beräkningar görs på vågor med en signifikant våghöjd på 1,25 m och en periodtid på 7,5 s. Det görs även beräkningar på den största uppmätta förekommande vågen. I huvudsak används effektberäkningar enligt en modell som Kjell Budal. Syftet är att grafiskt och numeriskt jämföra den teoretiska och faktiska maxeffekt som kan utvinnas ur respektive våg. Resultatet från undersökningen visar att den största bidragande faktorn till en hög energiutvinning beror på bojens volym. Volymen måste anpassas för de vågförhållanden som finns där bojen ska placeras.Vid beräkningar av en OWC med tvärsnittsarea på 19 m2 visar det sig att den effekt som kan utvinnas av en luftkammare med tillhörande turbin är ungefär 10 kW, 1/30 av de 300kW som kan utvinnas av en point absorber. En OWC består dock sällan utav en ensam luftkammare utan ofta i en array med ett flertal luftkammare med separata turbiner för att öka effekten.This report intends to examine the most common types of wave energy converter technologies to compare the different concepts' ability to absorb wave energy. Concepts being investigated are point absorbers and oscillating water columns (OWC). Calculations are made for the different concepts in the same wave conditions to be able to compare the energy that can be extracted. In the report, calculations are made under optimal wave conditions. The waves are assumed to be linear and the wave energy converter is assumed to be in phase with the oscillating motion of the wave. The wave data used is measured outside Belmullet in Ireland. Calculations are made on waves with a significant wave height of 1.25 m and a period time of 7.5 s. Calculations are also made on the largest measured wave present. In essence, power calculations are used according to a model developed by Kjell Budal and with the help of this be able to graphically and numerically compare the theoretical and actual maximum power that can be extracted from each scale. The results from the survey show that the largest contributing factor to high energy recovery is due to the volume of the buoy. The volume must be adapted to the wave conditions that exist where the buoy is to be placed.When calculating an OWC with a cross sectional area of 19 m2, it turns out that the power that can be extracted from an air chamber with an associated turbine is approximately 10 kW, 1/30 of the 300 kW that can be extracted by one point absorber. However, an OWC rarely consists of a single air chamber but often in a construction with several air chambers with separate turbines to increase the power.
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Lara, Maria Fernanda Espinel. "Estudo numérico bidimensional com aplicação de constructal design para otimização da geometria e da profundidade de submersão de um dispositivo conversor de ondas do mar tipo coluna d'água oscilante." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2015. http://hdl.handle.net/10183/117786.
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O presente trabalho tem como objetivo maximizar a potência hidropneumática convertida num dispositivo do tipo Coluna d'Água Oscilante (CAO). Para fazê-lo, o método Constructal Design é aplicado para aprimorar a geometria e a profundidade de submersão do dispositivo. No desenvolvimento do método Constructal são propostos e analisados três graus de liberdade: H1/L (razão entre a altura e comprimento da câmara do dispositivo CAO), H2/l (razão entre a altura da câmara e o comprimento da chaminé) e H3 (profundidade de submersão do dispositivo CAO). As restrições do problema (parâmetros constantes) são a área da câmara A1 e a área total do dispositivo CAO A2. O domínio computacional consiste de um dispositivo CAO inserido num tanque que é submetido a ondas na escala real. A malha é desenvolvida no software Ansys Icem®. O código de Dinâmica dos Fluidos Computacional Ansys Fluent® é empregado para encontrar a solução numérica a qual é baseada no método dos Volumes Finitos. O modelo multifásico Volume of Fluid (VOF) é usado na interação das fases água-ar. Os resultados indicam que a potência hidropneumática máxima obtida é de 190 W para razões de H1/L, H2/l e H3 iguais a 0,135, 6,0 e 9,5 m respectivamente. Por outro lado, o menor valor obtido da potência hidropneumática é de quase 11 W, o que mostra a utilidade do método Constructal, para fornecer uma relação entre o clima de ondas de um lugar determinado e as dimensões ótimas do dispositivo CAO.The present work aims to maximize the hydropneumatic power converted in an Oscillating Water Column (OWC) device. To do this, Constructal Design is applied to optimize its geometry and submergence. For the development of Constructal method, it has been proposed and analyzed three degrees of freedom: H1/ L (ratio between the height and length of OWC chamber), H2/l (ratio between height and length of chimney), and H3 (submergence). The problem constraints (fixed parameters) are total area of the OWC chamber A1 and total area of OWC device A2. The computational domain consists of an OWC inserted in a tank where waves in a real scale are generated. The mesh is developed in ANSYS ICEM®. The Computational Fluid Dynamics code FLUENT® is used to find the numerical solution which is based on Finite Volume Method (FVM). The multiphasic Volume of Fluid (VOF) model is applied to tackle with the water-air interaction. The results show that the maximum hydropneumatic power obtained was 190 W for H1/L, H2/l e H3 ratios equal to 0.135, 6.0 and 9.5 m respectively. In contrast, the smaller value obtained for the hydropneumatic power is almost 11 W. So, it shows the utility of Constructal Method which provides a relationship between the wave climate of a particular place and the optimal dimensions for the OWC device.
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Gomes, Mateus das Neves. "Constructal design de dispositivos conversores de energia das ondas do mar em energia elétrica do tipo coluna de água oscilante." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/109161.
Full textAbstract:
O presente trabalho apresenta um estudo numérico bidimensional sobre a otimização da geometria de um dispositivo conversor de energia das ondas do mar em energia elétrica. O objetivo principal é, através da modelagem computacional de um dispositivo cujo principio de funcionamento é o de Coluna de Água Oscilante (CAO) e do emprego de Constructal Design, maximizar a conversão da energia das ondas do mar em energia elétrica. Essa técnica é baseada na Teoria Constructal. O aspecto inédito deste trabalho, em relação aos estudos disponíveis na literatura, é o fato de levar em conta o clima de ondas de uma dada região e, a partir disso, dimensionar o dispositivo de modo que ele tenha um desempenho otimizado. Para tanto, foi empregado o método Constructal Design, os graus de liberdade empregados são: H1/L (razão entre a altura e o comprimento da câmara CAO) e H3 (profundidade de submersão do dispositivo CAO). A relação H2/l (razão entre altura e comprimento da chaminé de saída da câmara CAO) é considerada um parâmetro fixo. Foram realizados estudos levando em conta uma onda em escala de laboratório e um espectro de ondas real. Foi também realizado um estudo sobre a influência da perda de carga da turbina através de uma restrição física. Para a solução numérica foi empregado um código comercial de dinâmica dos fluidos computacional, FLUENT®, baseado no Método de Volumes Finitos (MVF). A geometria e a geração a malha foi realizada no software GAMBIT®. O modelo multifásico Volume of Fluid (VOF) é aplicado no tratamento da interação água-ar. O domínio computacional é representado por um tanque de ondas com o dispositivo CAO acoplado. Os resultados obtidos mostram que é possível estabelecer uma razão de H1/L ótimo, conhecendo-se o clima de ondas, ou seja, o recomendável é que esta razão seja igual a quatro vezes a altura da onda dividido pelo comprimento da onda incidente.The present work presents a two-dimensional numerical study about the geometric optimization of an ocean Wave Energy Converter (WEC) into electrical energy. The main goal is, through computational modeling of a device whose operating principle is the Oscillating Water Column (OWC) and from employment Constructal Design, to maximize the conversion of energy of ocean waves into electricity. This technique is based on Constructal Theory. The inedited aspect of this work comparing to the available studies is that it takes into account the wave climate of a given region to design the device so that it achieves optimum performance. Constructal Design is employed varying the degrees of freedom H1/L (ratio between the height and length of OWC chamber) and H3 (lip submergence). While the relation H2/l (ratio between height and length of chimney) is kept fixed. Studies were performed considering a wave on a laboratory scale and a spectrum of real waves. Yet a study of the influence of the turbine pressure losses was performed using a physical constraint. For the numerical solution it is used the Computational Fluid Dynamic (CFD) commercial code FLUENT®, based on the Finite Volume Method (FVM). The geometry and mesh generation was performed in GAMBIT ® software. The multiphasic Volume of Fluid (VOF) model is applied to tackle with the water-air interaction. The computational domain is represented by an OWC device coupled with the wave tank. The results show that it is possible to establish a relationship of H1 / L optimum, if the wave climate is know. It is recommended that this ratio be equal to four times the height of the wave divided by the length of the incident wave.
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Elhanafi, ASSM. "Performance and survivability of offshore oscillating water column wave energy converters." Thesis, 2017. https://eprints.utas.edu.au/23971/2/Elhanafi_whole_thesis_ex_pub_mat.pdf.
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This research was performed with a focus on two key aspects of energy cost–reduction for offshore OWC devices; improving the power extraction efficiency and reducing the excess margin in structural safety factors by a better understanding of wave–induced loads on these devices. This study utilised information from three different resources. First, 2D and 3D numerical results from fully nonlinear Computational Fluid Dynamics (CFD) simulations performed using the commercial code STAR–CCM+ that was validated in good agreement with physical scale model measurements at each stage of increasing complexity during this research. Second, published experiments in the literature for 2D OWC devices subjected to unidirectional regular waves to validate the 2D CFD models of this study. Third, experiments conducted in the towing tank of the Australian Maritime College (AMC) for 3D offshore stationary and floating–moored OWC devices (at a model–scale of 1:50) subjected to unidirectional regular and irregular waves. These experiments were designed to (1) compare the hydrodynamic performance of both devices, (2) estimate wave–induced loads on the fixed device during operating conditions, (3) investigate the survivability of the floating–moored device with intact and damaged mooring systems and (4) validate the 3D CFD models of this study.
Using the combined CFD and experimental approach, it was found that optimizing the underwater geometry of an offshore stationary OWC device could significantly improve the power extraction efficiency up to 0.97. However, this efficiency could be reduced due to air compressibility effects at full–scale. The surge motion of the floating–moored device improved device efficiency in regular and irregular waves. Furthermore, the effectiveness of deploying offshore OWC devices in deep–water where waves are more energetic was proven by increasing the extracted pneumatic energy by a maximum of about 7.7 times when wave height was doubled (incident wave energy increased four times). The instantaneous position of the floating–moored OWC device and its interactions with a certain wave train was more important than the maximum wave height in an irregular sea state when assessing device survivability. Survivability with a damaged mooring system was the key analysis for mooring design. For this analysis, using an equivalent design regular wave condition along with the current safety factors recommended for offshore oil and gas platforms was found to over–design the mooring system of the floating OWC device. The good agreement between CFD experiments for survivability analysis with intact and damaged mooring systems in regular waves highlighted that CFD is a very promising tool a designer can employ to investigate and assess device survivability under different conditions upon further validations in irregular waves.
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Mitchell, Ferguson TG. "An experimental investigation into WEC operation in realistic sea states using PIV." Thesis, 2016. https://eprints.utas.edu.au/23470/7/Mitchell_Ferguson_whole_thesis_ex_pub_mat.pdf.
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The focus of this study is on two key aspects of model scale experimentation when investigating the operation of ocean wave energy converters: the type of wave in which the device is exposed to; and the presence of three dimensional effects within and around the device. Scale model experiments were performed on an oscillating water column (OWC) in different conditions utilising particle image velocimetry (PIV). PIV is an advanced experimental technique which captures full velocity fields without interference with the flow and can be used to provide both qualitative and quantitative flow visualisation.
To investigate the impact of wave type on the operation of an OWC, experiments were performed in three wave types: regular, polychromatic and irregular waves. While regular and irregular waves are often used, polychromatic waves offer an intermediate option which has properties of both. When investigating polychromatic waves phase averaging was shown to be a useful tool to generate averaged results for both PIV velocity fields and other more conventional data sources with a reduction in uncertainty. It was seen that testing in regular waves results in unrealistic harmonic effects which impact on device performance, in particular the formation and size of vortices. For experiments in irregular waves, a linear relationship was identified between the energy within vortices and the total energy within the velocity field.
Identifying the presence of three dimensional effects was achieved by capturing two dimensional (2D) flow velocities at four transverse planes. This showed the transition between inflow and outflow conditions occurs at different times across the device. Velocity field divergence was calculated and large vortices were identified at the inside lip of the sidewall during inflow. It also indicated the device utilises the volume outside of its sidewalls during outflow, allowing an effective width greater than the extents of its sidewalls. This results in the potential for more power to be generated during outflow than inflow.
This study has revealed the importance of performing experiments in realistic sea states and has highlighted the value of experiments in polychromatic and/or irregular waves early in the design process. The use of PIV provided a vast amount of information on the operation and performance of wave energy converters and should be strongly considered when performing quantitative flow visualisation, comparative studies and validation of numerical models.
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Chi-ShengLin and 林啟聖. "Wave Loadings Distribution of Oscillating Water Column Caisson Breakwaters." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/36727018989237630297.
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碩士國立成功大學
水利及海洋工程學系碩博士班
101
Renewable energy generation is currently under active development. Wave power is an example of such energy and could be one of the primarily developed source of energy for our country in the future. Within all the wave energy converter types, the oscillating water column system could be combined with caisson breakwater structures to provide both power supply generation and near shore protection. This study examines the stability and pneumatic reaction of the oscillating water column breakwater, using a Hualien test site. Spatial pressure measurements using surface water pressure on the caisson were used for stability analysis. The result shows that the gate of the oscillating water column breakwater may change the pressure distribution. For relative depths less than 0.2, the horizontal force of the oscillating water column breakwater can be approximated by the Goda formula, but rotating torque, however, is underestimated compared to the measurements. For the pneumatic reaction, the measurement result shows that, under the experimental constraints of this study, the wave conditions which create the best pneumatic reaction are coincident with the field wave conditions in Hualien. This study could be referenced for further development of wave energy in Taiwan.
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Yang, Chung-Ying, and 楊宗穎. "Numerical Simulation of Oscillating Water Column Wave Energy Converters." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/14747013454604375072.
Full textAbstract:
碩士國立臺灣海洋大學
機械與機電工程學系
103
The thesis aims to study oscillating water column (OWC) wave energy converters (WEC) that are suitable for the northeast coast of Taiwan, and to simulate the OWC WEC model referring to the Limpet of Scotland by using computational fluid dynamics software ANSYS Fluent. There are three main topics to be studied: 1. to discuss the effect of chamber’s geometry to the conversion efficiency of the OWC WEC, specifically the inclined angle of the back wall; 2. to investigate the influence of the air duct size to the conversion efficiency without turbine installed; 3. to calculate the capture efficiencies of the Wells turbine by applying the preferred model size which is resulted from the above two investigations. From the previous literature, the relative geometric relation between chamber’s front and back walls has significant influence to the wave energy conversion efficiency. The simulation conditions are by fixing the air duct size and changing the inclined angles of the back wall, then to calculate the sum of kinetic energy, potential energy and pressure power, and used it as the criterion of the wave energy conversion efficiency. The air duct size is regarded closely related to Wells turbine’s capture efficiency. Hence, in order to compare the capture efficiency with different air duct sizes, the sum of kinetic energy and pressure power of different cases are calculated and compared as the criterion of capture efficiency. Finally, by using the preferred chamber geometry and the duct size combination based on the previous results, the overall power and capture efficiency are calculated with Wells turbine added. According to the simulation results, the chamber with 90-degree inclined angle of the back wall has the largest wave energy conversion efficiency, but it also has the largest energy loss. A comprehensive study shows that, the size of OWC has the preferred wave energy conversion efficiency with 60-degree back wall inclined angle and 65(mm) of the air duct radius. A simulation is performed to the above preferred geometry with Wells turbine installed. Under the wave conditions of wave height H= 0.07 (m), wave period T= 1.56 seconds, the result shows that the overall power of the OWC WEC is 0.1566 (W), the wave energy conversion efficiency 13.9%, and the Wells turbine’s capture efficiency 55.37%.
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WeiChen and 陳葳. "Simulation of An Oscillating Water Column Type Wave Energy Conversion Device." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/30399424114803601471.
Full textAbstract:
碩士國立成功大學
航空太空工程學系
102
SUMMARY The purpose of this study is to continue the research of Chun-Wei Mo (2013), “The Study of Converting Wave Energy by Using Air Pressure and Oscillating Water Column”, designing a 6 m-length, 2.3 m-width container with a Savonius vertical axial turbine wave energy device. From the previous study Chun-Wei Mo researched, water was filled in the generator sink. The wave motion will cause the liquid in the generator sink to reciprocate and motivate the turbine to generate. In order to obtain the performance of the blade from simulation, CFD method was employed. The software ANSYS CFX has been used in this study which is a numerical method used to solve 3-D Navier-Stokes equations with the finite volume method. The SST turbulence model was adopted to simulate the turbulent model. The self-adjusted tetrahedral non-structural grid was constructed based on the mesh generation software, ICEM. The major work in this study is to determine the operating condition for this design and discuss the power output in different wave type. Hence, the range of the volume flow from 1 m3/s to 12 m3/s has been simulated and each case is discussed, including the power output and efficiency. To determine the operating rotational speed, the method of predicting rotational speed is proposed in the simulation. Key words: wave energy, Savonius blade, CFD, OWC INTRODUCTION Due to the shortage of nonrenewable energy such as petroleum and coal, development of technology related to renewable energy has accelerated recent decades. A worldwide desire to limit our dependency on fossil fuels as a means to produce power has motivated research in solar, wind and wave energy as well. Wave energy is available in a variety of forms such as marine current, tidal current, geothermal vent and waves. The most commercially viable resources studied so far are ocean current and waves. In this study, a 6 m-length, 2.3 m-width container with a Savonius vertical axial turbine physical model filled with water was set up. This device was established to be an oscillating water column and it would generate power by waves. NUMERICAL METHOD Nowadays, CFD modeling provides a good description of flow field analysis with details usually available through physical modeling. In this study, numerical simulations have been performed. The software ANSYS CFX was used in this study which is a numerical method solved 3-D Navier-Stokes equations with the finite volume method. Grid generation uses ANSYS ICEM CFD to generate the unstructured tetrahedral mesh. Additionally, a few prismatic layers were established near the tip area to increase the precision of the simulation. In order to achieve the accurate result, k-ωSST turbulence model was adopted since k-ωSST turbulence model has been widely used to analyze Savonius type turbine in previous researches. RESULTS and DISCUSSION This study is mainly aimed to analyze the output characteristics of the entire system at different volume flow rates. After the selection of the Savonius type blade, a traditional combination of a semi-cylindrical five-leaf Savonius model, flow field at 1 ~ 4m3/ s has been simulated. Based on the output characteristics and flow channel, the shape of the original blades was modified, improving the performance of the blade. To understand the physical condition of such device, and properties of the output of the modified Savonius rotor, the flow through the inlet section of the housing 1 ~ 12 m3/ s has been simulated. The results of the simulation showed the performance of the modified type blade was higher than that of the original one. In addition, the results indicated the power output is less than 30 kW at 1 ~ 5m3/ s; 30~60 kW at 6 ~ 7m3 / s and 100 ~ 300 kW at 8 ~ 12m3/ s. The value of performance efficiency is located within 0.06 to 0.08. The flow field of the whole system shows that there is a huge low pressure region with some vortex. Furthermore, this research is used to estimate the actual output performance of the wave power device based on this hydraulic turbine. As different environments caused different wave motions, this study only considered the wave period at eight seconds, and the half cycle can lead to eight tons of water flowing through the blade as physical conditions. Based on the physical conditions, 3 different types of waves were plotted to estimate a possible value of power output. The maximum volume flow rate of three different waveforms 3m3/s, 6 m3/s and 12 m3/ s, totaled to a maximum output power of 5.94 kW, 39 kW, 294.45 kW respectively. The corresponding values of the average power output during a period are 0.75 kW, 5.75 kW, and 37 kW.
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Lin, Chi-Chien, and 林繼謙. "Design of a Wave Energy System Using Onshore Oscillating Water Column." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/20868481000012919856.
Full textAbstract:
碩士國立成功大學
系統及船舶機電工程學系碩博士班
97
This thesis investigates the feasibility of applying oscillating water column (OWC) wave energy system to the onshore area in Taitung, Taiwan. A laboratory scale prototype of the OWC wave energy system is built based on the surveyed wave data at the target site. The prototype is scaled down using the Froude number theory for equivalence to the real site condition. The OWC is designed to have two chambers and two cascaded Savonius turbines, each of them being used for one chamber of the OWC. This configuration helps to stabilize the air flow passing the turbines so that the rotational speed the the turbines can be more steady than that with single chamber. Consequently, the cost on power electronics can be reduced and the quality of the power output can be maintained. The designed side-mounted OWC, differing from conventional systems, is structurally parallel to the propagation of the waves and allows the wave to penetrate the OWC. This will enhance the conversion rate for transferring wave energy to the chamber air, and thus the turbine. The OWC and the permanent-magnet generator are designed in a systematic manner for better system efficiency. The prototype is tested for performance validation.
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Fleming, AN. "Phase-averaged analysis of an oscillating water column wave energy converter." Thesis, 2012. https://eprints.utas.edu.au/15913/1/front-flemming-2012.pdf.
Full textAbstract:
The work described in this thesis is concerned with the application of phase-averaging to experimental data obtained for a forward-facing bent-duct oscillating water column (OWC) wave energy converter. Experiments were performed on a three-dimensional model of the OWC in monochromatic waves. The research includes the development of new curve-fitting and ensemble-averaging phase-averaging algorithms designed to phase-average two-dimensional particle-imaging velocimetry (PIV) data. The phase-averaged PIV velocity fields were then used for qualitative and quantitative analysis. Qualitatively - visualisation of the velocity fields as vectors over a wave cycle shows the average flow field phenomena including bulk flow, water column slosh, front wall swash and downwash, vortices and an outflow jet. Quantitatively – two-dimensional kinetic energy and vorticity was calculated from the phase-averaged velocity fields and used in an energy balance analysis.
Experimental and theoretical data were combined in an energy balance analysis of the OWC to map the flow of energy from the incoming waves to intermediate stores and finally to sinks, which importantly permits the inclusion of non-linear phenomena. Using the energy model it was found that for the OWC model tested that the phase-averaged energy dissipated by the power-take-off was greater during water outflow than during water inflow. Phase-averaged experimental analysis of OWCs is an additional tool suitable for the design of underwater geometry of OWCs with potential application to other wave energy converters.
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Chih-YinChung and 鍾智印. "Numerical study on air-water responses of oscillating water column wave energy caisson breakwater." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/g9uc49.
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Chuang, Chia-Yu, and 莊佳于. "Experiments on Hydrodynamic Characteristics of Wave Energy Absorber with Oscillating Water Column." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/39174478439422180628.
Full textAbstract:
碩士國立中興大學
土木工程學系所
104
The study of the wave power capture system has been gone for years around the world. Among the variety types of ocean wave energy absorbed system, the Oscillating Water Column (OWC) system could be considered a major, it has been evaluated for decades with many investigations of. This paper presents a new type of wave energy absorber embodying OWC system from Tsai (2016), and discussing its hydrodynamic characteristics adopted different wave definitions by physical model tests in this study. The experimental tests measured the oscillation of water column and used the high speed camera with laser system to do flow visualization. The study also compare with the U-OWC from Boccotti (2007) and the conventional OWC. When the water column of the air chamber oscillating by the waves, it will compress the air and generate the wind speed at the device. When the water column rise up it will cause the air flow out from the device, and flow in when it comes down. From the stabilization of water column variation, the wind speed caused by the water column will also be stabilize. The study adopted different wave definitions to discuss the relation between the wind speed and the wind power and the relation between the relative width and the wave reflection from OWC, the wave pressure on the OWC. The result shows the smaller of the relative width B/L(B : the width of OWC, L : the wavelength) of OWC and the larger of the Ursell parameter of incident wave induce the larger of the wind speed which it was generated and produced much more wind power in the different incident wave height conditions. On the other hand the result indicates that the wave reflection from OWC and the wave pressure on the OWC is minimal when B/L is about 0.16.The study also compare with the U-OWC and the conventional OWC, the result shows that the present absorber not only capture more wind power than the U-OWC and the conventional OWC but also the wave reflection from OWC and the wave pressure on the OWC is less than the other two.
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Wang, Hao. "Wave Energy Extraction from an Oscillating Water Column in a Truncated Circular Cylinder." Thesis, 2013. http://hdl.handle.net/1969.1/151188.
Full textAbstract:
Oscillating Water Column (OWC) device is a relatively practical and convenient way that converts wave energy to a utilizable form, which is usually electricity. The OWC is kept inside a fixed truncated vertical cylinder, which is a hollow structure with one submerged open end in the water and with an air turbine at the top. The research adopts potential theory and Galerkin methods to solve the motion of the OWC. Based on the air-water interaction model, optimal OWC design for energy extraction from regular wave is explored.
The hydrodynamic coefficients in scattering and radiation potential are solved using Galerkin approximation. The numerical results for the free surface elevation have been verified by a series of experiments conducted in the University of New Orleans Towing Tank. The effect of geometric parameters on the response amplitude operator (RAO) of OWC is studied and amendment of the equation for evaluating the natural frequency of the OWC is made.
Using the model of air-water interaction under certain wave parameters and OWC geometric parameters, a computer program OWC Solution is developed to optimize the energy output from the system. Optimization results by the program OWC Solution lead to an effective method to design the OWC system.
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Chia-YingChang and 張家穎. "Analytical and Experimental Investigation of Chamber Hydrodynamic Performance of Oscillating Water Column System." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/jkdswa.
Full textAbstract:
博士國立成功大學
水利及海洋工程學系
105
Renewable green energy is becoming increasingly important due to the expected limit of fossil energy resources and to reduce pollution. Wave energy generation technology has been significantly developed in recent years among numerous types of renewable energy. Fixed breakwater, used to protect shorelines, marine structures, moored vessels, marinas and harbors from wave attacks, may be considered as a common site for installing oscillating water column (OWC) for exploited wave energy. Wave energy have been considered by many experts as one of the most promising green energy for Taiwan. However, the amount of wave energy presently generated constitutes a minor percentage of Taiwan’s total energy production. This paper presents experimental results of a laboratory water chamber of OWC, wherein the fundamental parameters of geometrical design are individually investigated and optimized, for maximum wave energy. The effects of a variety of back plates angle, fence plates and open wide inlets of OWC chamber are analyzed and tested for catching capability of wave energy. Three experimental models are tested to include an evaluation of the effectiveness of back plate, fence plate and open wide inlet. The operation of OWC qualitatively differs from that predicted by linear theory, identify to critical flow characteristic; front wall down-wash in the water column. The surveys were then expanded to offer general arrangement or a planning material for the geometry optimization of the chamber that could potentially achieve the largest average amplification factor of an OWC system. The wave energy in the OWC significantly varies with different back angles. The results demonstrate that this new OWC could provide more efficient wave energies.
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Howe, DP. "Integration of oscillating water column wave energy converters within multi-use maritime structures." Thesis, 2020. https://eprints.utas.edu.au/35841/1/Howe_whole_thesis_ex_pub_mat.pdf.
Full textAbstract:
Ocean energy presents arguably one of the most rich renewable energy solutions currently under exploration, and consists of a variety of potential resources including tidal barrages, salinity gradients and ocean thermal energy. However two sources, tidal currents and ocean waves, are considered by many as the most promising and have subsequently observed the greatest development in recent decades. Ocean waves offer a predictable, dense and virtually untapped energy resource with potential to significantly contribute towards the rising global energy demands. A number of prototype failures and subsequent lack of long term commercial deployments has consequently impacted the development of Wave Energy Converter (WEC) technologies, such that the technologies are considered immature and currently economically uncompetitive with renewable energy counterparts such as wind and solar. To combat the economic argument, a number of solutions have been devised to reduce the high costs currently associated with ocean wave energy, one of which is integration within maritime structures to create synergistic multi-purpose platforms.
While concepts have been formulated for the integration of various WEC technologies, the Oscillating Water Column (OWC) WEC is favoured as a predominant devices for implementation due to its rigid design, capability for incorporation within solid edifices, and relative ease of maintenance due to all moving parts above water. The OWC device's operational principle, in its most elementary form, utilises incident wave interaction to oscillate a trapped column of water inside the chamber, subsequently operating in a 'piston-type' motion to force air in and out of a turbine. The economic benefits of OWC device integration encompass both the capital and operating expenditure, from costs shared during the construction, through to the reduction in maintenance and grid connection costs, ultimately making the concept more competitive within the renewable energy sector. With some full scale demonstration cases and commercial devices currently operational, the vast majority of maritime structure integrated WECs target bottom-mounted breakwaters, which are typically depth limited due to the economic constraints associated with deep water construction. This type of integration restricts the operational range of the concept to onshore/nearshore regions; however, with the expansion of many blue economy industries into offshore regions, opportunities arise for exploration of wave energy conversion to serve in deeper waters. In order to migrate from the nearshore integrated concepts, integration within floating offshore structures, such as breakwaters and offshore platforms, must be explored for viability from both economic and operational perspectives. Understanding the hydrodynamic performance of OWC devices integrated within maritime structures, both _fixed and floating, is the focus of this research project.
Initial stages of the research project considered a detailed model scale experimental investigation regarding integrated OWC device performance, which was conducted to explore two specific parameters respective impact on OWC device energy absorption; firstly, the cross-sectional geometry, and secondly, breakwater integration. An isolated OWC device of rectangular cross-section was compared to a previously researched device with a circular cross-section of equivalent area to explore the impact on energy absorption, where negligible difference in performance was observed between the geometrically varying devices. Following this realisation, both respective devices were incorporated within a model scale, gravity-based breakwater to compare the extraction efficiency of the devices between both isolated and integrated configurations. The results obtained indicated that the energy absorption capacities of the OWC devices are significantly improved through breakwater integration, with the rectangular OWC device recommended due to its orthogonal construction allowing for less complex incorporation. This research provided a foundation for the performance of OWC device integrated maritime structures, and enhanced the potential for OWC device integration within floating offshore structures.
Development of the project generated a second comprehensive model scale investigation designed to establish a proof-of-concept for a floating breakwater integrated with multiple OWC devices. A generic π-type, soft-moored breakwater was integrated with a modular number of OWC devices and subjected to both regular and irregular sea states to analyse how variations to device configuration, breakwater width, pneumatic damping, wave height and motion constraints impact two overarching parameters; the energy absorption of the integrated OWC devices, and the performance of the floating breakwater. The investigation yielded substantial insights regarding the beneficial impact OWC device integration can have on the motion characteristics of the floating breakwater, while minor reduction was simultaneously observed for wave transmission and reflection. The investigation also highlighted the importance of device spacing with respect to OWC device performance, where insufficient spacing was found to have a detrimental impact on energy absorption where destructive device-device interference was observed. Through specific configuration of the aforementioned design parameters, the WEC/breakwater concept was able to obtain total device conversion efficiencies of up to approximately 80% at resonance in regular waves, and observed equivalent performance in irregular waves. This project reveals that maritime structure integration of OWC WECs provides significant benefits to the hydrodynamic performance of the integrated devices, which in association with the previously established economic benefits, further strengthens the viability of the concept, and provides foundation for future development.
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Chun-WeiMo and 莫鈞維. "The Study of Converted Wave Energy by Using Air Pressure and Oscillating Water Column." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/83796694558994875864.
Full textAbstract:
碩士國立成功大學
航空太空工程學系碩博士班
101
The purpose of this study is to design a wave-energy device to convert wave energy. Oscillating water column type of wave-energy device has a good adaptation for different topographies, and it is easy to design. Due to the loss of energy density, the method of generating power by using oscillating water column to push air would lower the output. In this experiment, a wave nergy device is designed to improve the power generating system. Also, it verifies the feasibility of using air pressure to generate oscillating water column in order to create the difference in the water level that can produce energy to push the water turbine. The device of the experiment is an oscillating water column type of energy device that its air chamber part is connected to a generator-sink. Therefore, the generator-sink and air chamber become an enclosed space. In this way, the oscillating water column changes the air pressure in the air chamber, and the inside air pressure changes the water level in the generator sink. To simplify the mechanism of this experiment, no turbine is installed on the wave-energy device. We can get the maximum potential energy by measuring the wave height on the air chamber wall, the air pressure between the air chamber and the generator sink, and the change of water level in the generator sink. The parameters of the wavemaker in this experiment are the local water depth, the stroke , and the frequency of paddle. The stroke of paddle is 0.2m, 0.3m, and 0.4m. The wave period is in the range of 1.5s to 3.4s. The ratio of the wave height in the generator sink to the wave height on the air chamber wall are 19% to 68%(when the stroke is 0.2m), 30% to 61%( when the stroke is 0.3m) , and 19% to 68%(when the stroke is 0.4m). Obviously, the maximum potential energy of the generator sink is larger than the potential energy when a wind turbine is equipped at the end of the air chamber.
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Luo, Yuan-Ting, and 羅元廷. "Hydrodynamic Characteristics of a New Type of Wave Energy Absorber with Oscillating Water Column." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/99267938082982984562.
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Ko, Chun-Han, and 柯鈞瀚. "Study on Hydrodynamic Performance of a Breakwater-Integrated Oscillating Water Column Wave Energy Converter." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/d4kzs4.
Full textAbstract:
博士國立中興大學
土木工程學系所
107
This study is aimed to investigate the hydrodynamic and aerodynamic performances of an innovative breakwater-integrated oscillating water column (OWC) wave energy converter. This innovative OWC device consists of an extra perforated wall in front of the typical OWC chamber, which can be integrated with a caisson breakwater for capturing efficiently the wave power. The characteristics of the flow behavior in the OWC chamber and the effect of structural geometry on the hydrodynamic efficiency of the device are investigated by adopting both numerical simulations and laboratory experiments. The CFD numerical model for solving this air-water and wave-structure interaction problems is based on the three-dimensional RANS equations and the RNG -ε turbulent closure model, from which the numerical simulations is implemented by the Flow-3D software. The numerical model is first validated by using previous PIV experimental results for a typical OWC chamber and the present experiments for the innovative OWC device. Then the numerical simulations considering full scale OWC model are implemented for exploring the water and air flow characteristics and the geometric effect on the hydrodynamic performance parameters, including the water column surface elevation, the differential air pressure in the chamber, the airflow rate through the orifice and the pneumatic power. Based on the numerical simulations and experimental investigation, it is found that the larger velocity of water flow and the corresponding vortices always occur near the lip of the front submerged wall, and the airflow forms a conical shape due to the circular orifice on the roof centre of chamber. The maximum positive and negative differential air pressures in the chamber occur at the instant as the mean water level of the oscillating water column commences upward and downward, respectively. The positive and negative differential air pressure inside the chamber induce the air to extrude and suck through the orifice. The effects of the chamber geometry including the chamber breadth, the open height of front submerged wall, the orifice size and porosity of the front perforated wall are discussed by simulations considering full scale model of the present OWC device. It is found that the following remarkable effects. (i) The maximum pneumatic efficiency could reach to about 84% under the resonant frequency condition and the optimized geometry. (ii) The resonant frequency condition decreases with the increase of the breadth of the OWC chamber. (iii) The smaller and larger entrances of the open submerged wall could not produce higher pneumatic power, which the optimum value is found as 0.6 times of the water depth. (iv) The smaller orifice area might induce the larger the airflow velocity across the orifice and the larger differential air pressure in the chamber, however it does not produce the larger the pneumatic power due to the lower airflow rate. The max hydrodynamic efficiency happened as the orifice area ratio is 0.7%. (v) The front perforated wall could influents the wave reflection coefficient and the dissipation of turbulent kinetic energy, and reaches the max hydrodynamic efficiency when the porosity is 25%. Finally, by the comparisons the hydrodynamic performance between present and typical OWC, it shows that the present OWC device has better performance for pneumatic power extraction and less wave pressure on the front submerged wall.
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LIU, YUNG-CHING, and 劉永慶. "Experimental Study on the Optimization of an Oscillating Water Column System Considering Real Gas Compressibility." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/q77246.
Full textAbstract:
碩士東南科技大學
營建科技與防災研究所在職專班
105
Renewable energy for the government is currently actively developing the energy, Taiwan surrounded by the sea, the winter has a strong northeast monsoon, so that the eastern and northeastern Taiwan have considerable potential for wave power generation, which oscillates the water column system may become the future wave development type one. In this study, the experiment shows the oscillating water column type power generation system (OWC)corresponding to the water depth ratio acrylic model to observe and record the wave height, pressure and outlet wind speed in the tank with different wave-making conditions. Considering the real gas compressibility and considering the different openings and gates The optimal rate of the average wind speed, the maximum average wind speed and the maximum wind speed is compared with the difference between the open rate and the maximum wind speed. Considering the real gas compressibility and gas tank respectively according to the different opening and the gate opening rate corresponding to different wave conditions the average wind speed, average wind speed and maximum wind speed to find the optimal alignment analysis of the test of the oscillating water column type power system design, according to the test results found that the average wind speed, in the condition of D=50mm the maximum average wind speed and maximum wind speed under the condition of opening height is not much difference in the G=175mm and G=200mm gate, but when G=200mm meets the low trough may have occurred to the cabin air lead to instability, and considering the need to consider the shore type marine high and low tide difference factors, according to the experimental results evaluation of gate opening height of G=175mm (opening rate 175mm/250mm=70%) and the gas tank outlet aperture D=50mm for optimal OWC design.
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Chiu, Chao-Chin, and 丘兆欽. "Development of Flexible PZT Composite Film for Oscillating Water Column Type Wave Energy Converter Application." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/63694348907688346152.
Full textAbstract:
碩士國立中興大學
機械工程學系所
104
The dissertation proposes to develop an oscillating water column(OWC) type wave energy converter(WEC) using flexible lead zirconate titanate(PZT) composite films. An OWC type WEC uses the motion of ocean surface waves to create oscillating water column and generate electricity. The converter with an impacting plate moves by ocean wave energy and generate electric energy. The power generating elements of converter is made by PZT composite films of disk type. Flexible PZT composite films were fabricated by sol-gel pro- cess on the copper/nickel composite substrates.Its thickness is 13.65 μm, the impedance is 3.47 kΩ, the phase is -88.51°, the capacitance is 45.83 nF, the dielectric loss is 2.60% and the relative dielectric constant is 15.69 at the fre- quency of 1kHz. The analytic and finite element models of converters will be studied and analyzed. By the finite element analysis, the resonance fre- quency of first resonance mode is 103.3 Hz. By the measurement, the OWC type WEC generates a maximum voltage of 30.2 mV at the resonance fre- quency of 97.25 Hz.
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Rajapakse, G. "Control and power management of grid connected vented oscillating water column wave energy converter arrays." Thesis, 2021. https://eprints.utas.edu.au/37931/1/Rajapakse_whole_thesis.pdf.
Full textAbstract:
Wave energy is a vast, sustainable, and low environmental impact renewable energy source with a high degree of predictability and availability at large scale. Over the last six decades, numerous studies have been conducted, and various technologies have been developed to convert wave energy into electricity. Nevertheless, Wave Energy Conversion (WEC) is still not a widespread technology, compared to other dominant renewable energy technologies such as wind and solar. One of the contributing factors for this is the large and periodic fluctuations present in the extracted power in WEC systems. Even though intermittencies are present in the extracted power in the wind and solar generation systems, the level of fluctuations present in those systems are much smaller compared to that in wave energy. Therefore, the direct connection of a WEC system to a power grid without any power conditioning could lead to instabilities.
The use of energy storage is a promising solution to absorb fluctuation and thereby ensure smooth power delivery to the grid. Battery energy storage is the most common solution recommended for similar issues in the wind and solar energy systems. Nevertheless, due to the short-term and periodic (10 -15 seconds) nature of the power pulses present in wave energy, a combination of battery and supercapacitor is recommended as the most suitable energy storage solution for WEC systems. Most studies reported in the literature on WEC systems with battery-supercapacitor hybrid energy storage have considered only a single WEC system. The effects of spatial and temporal averaging of extracted power in wave energy converter arrays on the sizing of energy storage systems have not been explored so far. Therefore, this study has attempted to fill this knowledge gap using vented oscillating water column (VOWC) wave energy converter arrays. VOWC is a novel WEC technology developed at the Australian Maritime College in collaboration with the Wave Swell Energy company in Australia. This technology produces energy only during the inhale stage resulting in large discrete power pulses. These characteristics of VOWC make control and power smoothing even more challenging compared to conventional bi-directional WEC technologies such as Wells turbines. As solutions, novel control and power management strategies have been developed to suit the characteristics of the VOWC. The efficacy of the developed control and power management solutions are validated through simulations carried out on the MATLAB/Simulink digital simulation platform. The results verify the efficacy of the proposed control strategy in tracking the setpoints efficiently with minimal overshoots and oscillations. Furthermore, the findings confirm that the proposed PMS can reduce the mismatch between supply and demand, while maintaining smooth delivery of power to the grid in single and array configurations of VOWC WECs. Moreover, further findings reveal that the required ESS capacity drops when WEC systems are placed correctly in array configurations.
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Pestana, Ronaldo Jorge. "The modelling of a squirrel-cage induction generator in an oscillating-water-column wave-energy converter." Thesis, 2015. http://hdl.handle.net/10539/17557.
Full textAbstract:
The research is focused on the modelling of a squirrel-cage induction generator in dynamic
generation involving ocean-wave energy. The chosen application includes an oscillating
water column fitted with a Wells turbine.
The modelling approach is based on the evaluation of existing generator models. These
include the equivalent steady-state and dynamic models which are considered from a timedomain
(differential equation) perspective. Since generation is dynamic in nature, model
stability is an important component of model evaluation.
The evaluated models provide information regarding the electrical and mechanical
operational variables of the generator. Power flow and energy loss between the mechanical
and electrical subsystems are easily calculated from these variables.
The wave-energy converter excluding the induction generator is not explicitly considered.
The generator models are evaluated by considering typical generator inputs which are
representative of the given application. These dynamics are reproduced experimentally and in
simulations with a comparison of generator response allowing for a conclusion on model
performance. Generator inputs include the stator voltage excitation and turbine torque with
the generator response given by the stator currents and rotor velocity. Electrical and
mechanical power are also considered.
Dynamic generation is broken down into two modes of operation: the first mode involves
generation for a constant sea state and the second mode involves generator operation for a
change in sea state. The dynamics for the first mode involve a set generator speed (set voltage
supply) and a sinusoidal prime-mover torque. Dynamics for the second operating mode are
not well-defined owing to system variations. Since only the generator model is considered, an
informative dynamic is tested providing an indication of possible model performance. The
tested dynamic involves a sinusoidally-varying stator frequency and prime-mover torque.
The steady-state model considered from a time-domain perspective is found to be unstable
for all generating slip values and is, therefore, unsuitable for the given generation application.
The dynamic model shows good agreement between experimental and simulated generator
response for the two operating modes identified. In conclusion, the model is applicable for a
constant sea state with a wave period of up to 0.2 s. Furthermore, it is suspected that the
dynamic model is applicable in the case of a change in sea state. Cases involving magnetic
saturation and parameter variation are left for future development.
The dynamic-model evaluation assumes a balanced stator-voltage excitation – strange
electrical transients including electrical faults are not considered. An important simulation consideration involves the quantification of state-variable initial
conditions. Initial rotor currents are problematic as these are not easily measured or defined
in a practical squirrel-cage rotor construction. The initial rotor currents are approximated by a
phasor analysis of the steady-state circuit model at zero time.
The use of an inverter-based generator excitation for the experimental work poses an analysis
problem owing to the pulse-width-modulation-based voltage supply (not truly sinusoidal).
This is solved by considering only the fundamental component of the stator voltage and
current. Second-order low-pass filters are used to facilitate such measurements.
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Ansarifard, N. "CFD analysis and optimisation of unidirectional radial turbine geometry for application with oscillating water column wave energy converters." Thesis, 2019. https://eprints.utas.edu.au/32532/1/Ansarifard_whole_thesis.pdf.
Full textAbstract:
An oscillating-water-column (OWC) is a popular device for harnessing the power of ocean waves. A key component in the system is the air turbine, which operates as the power take-off unit (PTO) converting pneumatic power to mechanical. The turbine is probably the most complicated geometry in the system and is mainly designed in either an axial or radial configuration.
The efficiency of a conventional radial impulse turbine (bidirectional version) rarely reaches more than 40%, which makes it a less efficient choice than axial turbines. However, the radial configuration has some advantageous features compared with the axial turbine, such as lower bearing loads and easier manufacturing. Current research on unidirectional radial impulse turbines shows a higher resistance to backflow and negative torque than the axial turbines, which is particularly useful in a twin-turbine configuration of the OWC system. The work described in this thesis is concerned with efficiency improvement of unidirectional radial air turbines using computational engineering approaches.
In this research, optimisation techniques were used in conjunction with Computational-Fluid-Dynamics (CFD) simulations to maximize efficiency of a unidirectional radial turbine for a vented OWC (where air flows through the turbine in only one direction). A parametric turbine geometry was created by varying geometrical features to control the shape of upstream guide vanes, rotor blades, downstream guide vanes and the duct section. This method led to flexibility in design and adjustment of rotating and stationary elements. The optimised design obtained significantly improved torque production for a single flow direction due to its highly-asymmetric rotor blades and well-adjusted inlet guide vanes. A parameter sensitivity analysis was performed using the response surface method and the optimum geometry of the turbine was obtained from a large design space (containing over 140 design cases for the inflow turbine and around 80 design cases for the outflow turbine).
This research provides a detailed analysis on the impact of each parameter on the turbine performance and is conducted in four steps. First, identifying the design drawbacks and sources of energy loss in the initial geometry of a unidirectional radial turbine and suggesting design modifications. Second, studying the turbine performance in a vented OWC and finding the optimum design of the turbine in the centripetal configuration (inflow mode). Third, studying the turbine performance in the vented OWC and optimising the turbine design for maximized efficiency in centrifugal configuration (outflow mode). Finally, comparing the global efficiency of the optimised inflow and outflow radial turbines considering their application with the vented OWC and twin-turbine OWC configurations.
This study contributed to a significant increase in energy capture of unidirectional radial impulse turbines compared to their bidirectional version, where the optimised centripetal and centrifugal turbine configurations of this research obtain peak steady-state efficiencies of 80% and 74% respectively (almost double the global efficiency of a conventional bidirectional radial turbine).
The integration of the turbine-chamber under an oscillating flow regime was studied by considering the operation of unidirectional turbines in twin-turbine-OWC and vented-OWC configurations. Extrapolated hydrodynamic experimental data of irregular waves in King Island test site, Tasmania, were utilized with the turbine flow resistance simulated by an orifice plate. The flow and damping characteristics of the inflow and outflow turbine geometries were evaluated regarding the given optimum operation of the OWC chamber.
The unsteady performance evaluation of the turbines is made by comparing their power extraction under fixed and controlled RPM schemes. Comparison of the unidirectional turbines of this research concluded that the inflow turbine due to having a higher direct efficiency yields better performance than the outflow turbine in a vented-OWC system. However, it operates less effectively in a twin-turbine-OWC configuration due to the effects of backflow and negative torque in the reverse operational mode. The outflow turbine offers interesting features such as smaller size in full scale, higher backflow prevention and less sensitivity to RPM variations. In addition, it was found that the unidirectional inflow turbine integrated in a vented OWC obtains comparable power extraction to a bidirectional-turbine-OWC system fitted with a state-of-the-art bi-directional turbine.
Finally, this research shows that the concept of unidirectional radial turbine integrated in a vented OWC can be a more economical choice than the twin-turbine concept, due to eliminating the cost associated with the extra turbine (and extra generator). It also encourages a simpler turbine design with lower energy losses compared to the bidirectional turbine-OWC concept for a comparable power extraction.
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Huang, Ching-En, and 黃靖恩. "Studies on Hydrodynamic and Air-flow Characteristics of a New Type of Wave Energy Absorber with Oscillating Water Column." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/89881230929171578420.
Full textAbstract:
碩士國立中興大學
土木工程學系所
103
This paper presents a new type of wave energy absorber embodying OWC system, and discussing its hydrodynamics and air-flow characteristics. Using both computational fluid dynamics (CFD) and physical model tests in this study. A CFD called Flow-3D was employed, which one-fluid model is used to simulate the flow field of the oscillation of water column, and two-fluid model is adopted to simulate the wind field. The experimental tests measured the oscillation of water column and used the high speed camera with laser system to do flow visualization. The results show that the simulations of the flow field, the wind field and the free surface variation of the water column are quite constant and the same with the experimental tests. According to the results, when the water column of the air chamber oscillating by the waves, it will compress the air and generate the wind speed at the device. When the water column rise up it will cause the air flow out from the device, and flow in when it comes down. From the stabilization of water column variation, the wind speed caused by the water column will also be stabilize. The study adopted different wave definitions to discuss the relation between the wind speed and the wind power. The result shows the larger of the wave height induce the larger of the wind speed which it was generated and produced much more wind power in the different incident wave height conditions. In the same wave height but different relative depth conditions,the OWC device will absorber more wind power when the relative depth is decreasing. When the width of the air chamber b over the structure width B from OWC device is increasing,the OWC device will absorber more wind power in the same wave height and relative depth conditions. The study also compare with the conventional OWC,and the result shows that the present one absorber more wind power than the conventional one.
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Rodriguez-Macedo, Julio Cesar. "Design and experimental evaluation of a unidirectional flow collective air pumps wave energy converter." Thesis, 2017. https://dspace.library.uvic.ca//handle/1828/8957.
Full textAbstract:
Commercial viability of Wave Energy Converters (WEC) depends on addressing
not only the energetic effciency, but also in solving the practical issues related to
manufacturing methods, access to technology, handling, transportation and installation,
operation and maintenance, impact on marine life and most importantly the
cost per kW-h. The UFCAP WEC is one concept which has the potential to facilitate
handling, manufacturing, and installation activities as well as to be able to lower the
current wave energy cost per kW-h, however its feasibility had not been properly assessed nor proved. It consists of multiple interconnected Oscillating Water Columns
(OWC) chambers, it is modular, and simple, with no-moving parts in contact with
the water and can use a simpler one-direction turbine which is more economic, and
more effcient than self-rectifying turbines used in most of the OWCs devices. Testing
of the device to fully assess its feasibility required a low pressure check-valve, and
a customized turbine which were developed during the present work. Check-valves
are widely used in the industry for medium or high-pressures, but were not available
at all for large-flows with low-pressure-differences. A novel check-valve was devised
for this application, along with the scaled UFCAP prototypes developed to be tested
in a wave-flume and in the ocean to validate UFCAPs concept feasibility, and identify
critical design parameters and features such as the conduit/air-chamber ratio.
Ocean tests allowed to observe performance at component and assembly levels, learning
new failure-modes and stablishing best-practices for future deployments. Testing
confirmed the UFCAP WEC is not only an idea, but a concept which works
and can generateing electricity at a competitive cost.Graduate