As energias renováveis vêm ocupando parcelas cada vez maiores das matrizes energéticas dos principais países do mundo, devido aos custos e impactos da exploração de combustíveis fósseis, e à necessidade de ampliação dos suprimentos de energia. Atualmente, as energias hidrelétrica, eólica e solar apresentam viabilidade técnica e econômica para uma grande quantidade de aplicações, com desenvolvimento tecnológico em alto nível de maturidade. A energia de ondas oceânicas ainda exige investimentos razoáveis para se tornar uma alternativa viável para fornecimento de energia elétrica, e vem sendo alvo de projetos para prospecção de potenciais e para desenvolvimento de tecnologias para conversão de energia. Neste estudo, chegou-se ao valor médio anual de 12 kW por metro de frente de onda como estimativa do potencial energético das ondas oceânicas do litoral norte do Rio Grande do Sul (RS). Esse valor é considerado razoável se comparado a potenciais em outros locais do mundo, e pode representar um acréscimo interessante de suprimentos de energia ao sistema energético local, que se mostra bastante receptivo aos recursos renováveis. Este trabalho tem como objetivo avaliar, em nível de pré-viabilidade, a inserção de suprimentos de energia de ondas no sistema interligado do litoral norte do RS, com base em simulações computacionais realizadas com o software HOMER, desenvolvido especialmente para otimização de sistemas de geração de energia baseados em recursos renováveis. Os resultados obtidos sugerem que empreendimentos para aproveitamento de energia de ondas atinjam viabilidade econômica quando seus custos específicos se tornarem pelo menos iguais ao dobro dos custos específicos associados aos aproveitamentos eólicos. / Renewable energies are increasingly occupying larger areas of the power generation matrices in major countries in the world, because of the costs and impacts of the fossil fuels exploitation, and because of the need to increase energy supplies. Currently, hydro, wind and solar energies present technical and economic feasibility for a lot of applications, with technological development at a high level of maturity. The wave energy still requires reasonable investment to become a viable alternative for electric energy supply, and has been the target for research projects about locations of potential energy and for development of power conversion technologies. The potential of the coast of Rio Grande do Sul (RS) has already been estimated and presents an annual average around 12 kW per meter of wave front. This value is considered reasonable compared to other potential sites in the world, and may represent an interesting addition to the energy supply of the local energy system, which shows a great receptivity to renewable resources. This study aims to assess, in pre-feasibility level, the insertion of wave energy supplies in the interconnected system of the northern coast of RS, based on computer simulations performed with the software HOMER, specially developed for optimization of power generation systems based on renewable resources. The results suggest that projects for harnessing wave energy reach economic feasibility when their specific costs become at least twice the specific costs associated with wind farms.

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.

Mediante a crescente necessidade de aumento na oferta de energia elétrica devido à constante elevação na demanda mundial, esta dissertação avalia o desempenho de um sistema conversor de energia de ondas marítimas em energia elétrica. O sistema em análise é o de coluna de água oscilante com turbina de dupla ação instalado na costa. Utiliza-se um modelo regular de ondas como perturbação à dinâmica de uma câmara semi-submersa gerando fluxo de ar através de uma turbina à ar de dupla ação. O sistema final é não linear e com parâmetros variantes no tempo. A dissertação investiga possibilidades para o aumento do rendimento da turbina em diferentes condições de mar através do método de simulação numérica. Após a modelagem física e matemática do sistema escolhido, inicia-se a síntese de um controlador proporcional derivativo para controle da pressão de ar na turbina em torno da pressão ideal de trabalho da mesma. A análise inclui o comparativo entre os resultados do sistema com e sem controlador e a avaliação de robustez utilizando ondas com amplitude variável. O trabalho apresenta ainda propostas de otimização do sistema para trabalhar em condições similares a região de Pecém no Brasil. Pelos resultados obtidos nas simulações, conclui-se que o rendimento e a robustez do sistema podem melhorar utilizando um sistema controlado. O rendimento do sistema poderá ainda ser otimizado para a região de instalação. / Facing the growing necessity in increasing the electrical energy offer due to the constant rise in worldwide demand, this work evaluates the performance of an ocean wave energy converter into electrical energy. The system under analysis is an oscillating water column with dual action turbine installed in a shore. A regular wave model is used as disturbance to the semi-submerged air chamber dynamic generating an air flow through the dual action air turbine. The final system is nonlinear and contains time varying parameters. This work investigates, through numerical simulation, possibilities to increase the turbine efficiency under different ocean conditions. After the physical and mathematical modeling, it is synthesized a proportional derivative controller to control the air pressure in the turbine around its ideal working pressure. The analysis of results includes a comparison between results obtained for the system with and without controller and a robustness evaluation with amplitude variation in ocean waves. The work also presents optimization proposals for the system working in conditions similar to the Pecém region in Brazil. By the results obtained with simulation, it is concluded that the efficiency and robustness were improved for the controlled system. It is observed that the efficiency can be optimized for the installation area.

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.

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.

As energias renováveis vêm ocupando parcelas cada vez maiores das matrizes energéticas dos principais países do mundo, devido aos custos e impactos da exploração de combustíveis fósseis, e à necessidade de ampliação dos suprimentos de energia. Atualmente, as energias hidrelétrica, eólica e solar apresentam viabilidade técnica e econômica para uma grande quantidade de aplicações, com desenvolvimento tecnológico em alto nível de maturidade. A energia de ondas oceânicas ainda exige investimentos razoáveis para se tornar uma alternativa viável para fornecimento de energia elétrica, e vem sendo alvo de projetos para prospecção de potenciais e para desenvolvimento de tecnologias para conversão de energia. Neste estudo, chegou-se ao valor médio anual de 12 kW por metro de frente de onda como estimativa do potencial energético das ondas oceânicas do litoral norte do Rio Grande do Sul (RS). Esse valor é considerado razoável se comparado a potenciais em outros locais do mundo, e pode representar um acréscimo interessante de suprimentos de energia ao sistema energético local, que se mostra bastante receptivo aos recursos renováveis. Este trabalho tem como objetivo avaliar, em nível de pré-viabilidade, a inserção de suprimentos de energia de ondas no sistema interligado do litoral norte do RS, com base em simulações computacionais realizadas com o software HOMER, desenvolvido especialmente para otimização de sistemas de geração de energia baseados em recursos renováveis. Os resultados obtidos sugerem que empreendimentos para aproveitamento de energia de ondas atinjam viabilidade econômica quando seus custos específicos se tornarem pelo menos iguais ao dobro dos custos específicos associados aos aproveitamentos eólicos. / Renewable energies are increasingly occupying larger areas of the power generation matrices in major countries in the world, because of the costs and impacts of the fossil fuels exploitation, and because of the need to increase energy supplies. Currently, hydro, wind and solar energies present technical and economic feasibility for a lot of applications, with technological development at a high level of maturity. The wave energy still requires reasonable investment to become a viable alternative for electric energy supply, and has been the target for research projects about locations of potential energy and for development of power conversion technologies. The potential of the coast of Rio Grande do Sul (RS) has already been estimated and presents an annual average around 12 kW per meter of wave front. This value is considered reasonable compared to other potential sites in the world, and may represent an interesting addition to the energy supply of the local energy system, which shows a great receptivity to renewable resources. This study aims to assess, in pre-feasibility level, the insertion of wave energy supplies in the interconnected system of the northern coast of RS, based on computer simulations performed with the software HOMER, specially developed for optimization of power generation systems based on renewable resources. The results suggest that projects for harnessing wave energy reach economic feasibility when their specific costs become at least twice the specific costs associated with wind farms.

European Commission (2011) aims to reduce the greenhouse gas emission sby 85-95% by 2050 in comparison to 1990’s levels. Wave energy could be an important step to archiving this goal. This report aims to develop a quantitative risk assessment for the Uppsala University's wave energy converter. Failure rates have been collected from various databases and reports and have been processed accordingly in order to implement them in the risk analysis. CAPEX, OPEX and possible downtime windows have been estimated. A fault tree analysis (FTA) has estimated the total unavailability, unreliability and downtime. Furthermore an economical assessment model using Monte Carlo and the unreliability data from the FTA has been developed, estimating the expected LCOE and OPEX/WEC for parks consisting of 20, 100, and 200 WECs (wave energy converters). The result show that the O-ring seal has the largest impact on both the unavailability, and the economy of the OPEX/WEC. Second biggest contributor is the translator bearing failure. The study also shows that the CAPEX cost has to be reduced to make the LCOE competitive in comparison to other renewable sources. A comparison between the system unavailability and unreliability has also been done in terms of different component parameters.

This work is divided in to two distinct parts. In the first part a model is developed to assess the redistribution of wave energy about an offshore array of overtopping type wave energy converters. The model is based on a classical analytical solution for diffraction about a breakwater which is modified to consider an array of dissipating, reflecting and transmitting breakwater segments, which are used to approximate an overtopping type WEC array. The model is computationally efficient and phase resolving which allows the effect of wave scattering to be investigated for large domains with high resolution irregular wave distributions. It was found that the radial waves generated by the diffraction effect spreads and defocus wave energy away from the geometrical shadow of the array. This counteracts the rate of recovery of wave energy deficit from wave directional spreading. In the second part, short-term wave forecasting for pneumatic power regulation through relief valve control is investigated at the Pico oscillating water column power plant, located in the Azores. Operational data from the Pico OWC is used to develop and critically assess a number of univariate and multivariate short-term wave forecast modelling approaches. A number of relief valve control strategies, which utilise a short-term wave forecast, are also developed and assessed using a numerical time-domain wave to wire system model. A system model for the Pico OWC is developed and validated using operational data from the Pico plant. The absolute performance potential resulting from control utilising a perfect forecast is considered, in addition to the realistic potential where a forecast, realisable in real-time, is used to drive control actions. One of the proposed relief valve control strategies is within the mechanical limitations of the existing relief valve adjustment system at Pico and this strategy was deployed in real field tests. Field test results of the plant’s performance under this strategy closely matched the simulated performance and power enhancements of up to 29% were achieved in certain sea states and the expected annual power enhancement was projected to be around 10%. Simulations of the long term plant performance under the more advanced relief valve control strategies project far greater potential for enhanced power production although these could not be tested in the field due to the project limitations.

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

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.