Technische Neu- und Weiterentwicklungen sowie eine Änderung der Marktverhältnisse sind maßgebliche Motive für Investitionen. Im Bereich der Kleinwasserkraft sind Investitionen – quantitativ betrachtet – bedingt durch die aktuelle Konjunkturflaute nach der Finanzkrise gesunken. Auf der anderen Seite setzt die Politik verstärkt auf die Nutzung erneuerbarer Energien, um das Konzept der Nachhaltigkeit auf diesem Gebiet zu forcieren.

The amount of energy enclosed in ocean waves has been classified as one of the most promising renewable energy sources. Nowadays, different wave energy conversion (WEC) systems are being investigated, but only a few concepts have been operated in a sea environment. One of the largest challenges is to guarantee the offshore survivability of the devices in extreme wave conditions. However, there are large uncertainties related to the prediction of extreme wave loads on WECs.  Highfidelity computational fluid dynamics (CFD) simulations can resolve nonlinear hydrodynamic effects associated with wave-structure interaction (WSI). This thesis explores the point-absorbing WEC developed by Uppsala University in extreme wave conditions. The dynamic response and the forces on key components (mooring line, buoy, generator's end-stop spring) of the device are studied and compared. The high nonlinear phenomena accompany the steep and high waves, i.e., breaking behavior, slamming loads can be well-captured by the highfidelity CFD simulations. A commonly used methodology for extreme waves selection, recommended by technical specifications and guidelines, is the environmental contour approach. The 100-year contour in Hamboldt Bay site in California and the 50-year contour in the Dowsing site, outside the UK, are utilized to extract the extreme waves examined in the present thesis. Popular methodologies and data from different sources (observational and hindcast data) are examined for the environmental contour generation providing useful insights. Moreover, two popular approaches for the numerical representation of the extreme sea states, either as focused wave or as equivalent regular wave, were examined and compared. A midfidelity model of the WEC is successfully verified, as the utilization of lower fidelity tools in the design stage would reduce the computational cost. Last but not least, in CFD simulations the computational grid is sensitive in large motions, something often occurs during extreme-WSI. The solution of this issue for the open source CFD software OpenFOAM is provided here.

Made available in DSpace on 2014-10-09T12:26:43Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:18Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:26:43Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:18Z (GMT). No. of bitstreams: 0 / A avaliação dos sistemas de fornecimento de energia para o futuro é da maior importância para se obter informações sobre o potencial de impacto ambiental dos vários estágios do ciclo de vida das tecnologias inovadoras, determinando as vantagens competitivas sobre as tecnologias convencionais e para o desenvolvimento de cenários futuros. Este trabalho apresenta e caracteriza os tipos de pilhas combustíveis de média e baixa temperatura mais pesquisadas e comercializadas nos últimos anos. Realiza-se também a apresentação da avaliação do impacto ambiental dos principais materiais utilizados nas pilhas a combustível, considerando as fases de fabricação, operação e disposição final após o término da vida útil. São apresentados vários dados de LCA (Life Cycle Assessment) efetuados para alguns tipos de pilhas. O trabalho efetuou uma contribuição ao estudo da avaliação de impacto ambiental das pilhas a combustível de média e baixa temperatura utilizando a metodologia Delphi. Foi construído um questionário e um banco de dados para formação do conjunto de respondentes que participaram da pesquisa. Eles receberam o questionário na primeira rodada e o responderam. Depois receberam novamente o questionário em conjunto com as respostas obtidas na primeira etapa, para nova rodada de respostas. Ao final o estudo verifica se ocorreu aumento de consenso e a influência dos respondentes mais qualificados sobre os menos qualificados. Os resultados mostraram que os respondentes acreditam numa redução do impacto ambiental das pilhas. O mais surpreendente é que os respondentes acreditam que os catalisadores do grupo PGM Podem ser substituídos. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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%.

Several alternative ways of producing energy came up as the world took conscience of the finite availability of fossil fuels and the environmental consequences of its use and processing. Wave and tidal energy are among the so called green energies. Wave energy converters have been under research for the past two decades and yet there hasn’t been one technology that gathered everyone’s acceptance as being the most suitable one. The present work is focused on a self-rectifying turbine for wave energy harnessing. It’s a self-rectifying biplane Wells with an intermediate stator. The main goal is to evaluate the performance of such a turbine. Two different analyses were performed: experimental and computational. The experimental tests were made so that efficiency, velocity profiles and loss coefficients could be calculated. To do so scaled-down prototypes were built from scratch and tested experimentally. The 3D numerical analysis was possible by using a CFD commercial code: Fluent 6.3. Several simulations were performed for different flow coefficients. Three different degrees of mesh refinement were applied and k-ε turbulence model was the one chosen to simulate the viscous behavior of the flow through the turbine. A steady-state analysis is due and two mixing planes were used at the interfaces between the rotors and the stator. In the end comparisons are made between the experimental and numerical results

La qualité de la puissance injectée au réseau électrique est une problématique importante pour le développement des énergies marines renouvelables, et en particulier de l'énergie des vagues, ou énergie houlomotrice. En effet la puissance produite par les systèmes houlomoteurs à entrainement direct est très fluctuante (fluctuations de l'ordre de la seconde) à cause de la nature oscillante de la ressource. Afin d'étudier l'impact de l'intégration des ces systèmes sur les réseaux électriques, un modèle permettant de représenter la chaîne depuis la vague jusqu'au réseau électrique a été développé. Les simulations effectuées à l'aide de ce modèle pour différents types de réseau électrique et différents états de mer ont montré que la mise en place de solutions pour améliorer la qualité de la puissance produite était nécessaire. Ainsi l'effet du regroupement et de la dispersion spatiale des systèmes houlomoteurs sur la qualité de la puissance a été étudiée. L'insertion d'un système de stockage dans la chaîne wave-to-wire afin de lisser la puissance a aussi été considérée. Enfin, une partie du modèle a pu être validée à l'aide d'un banc de test Hardware-in-the-loop comprenant un banc moteur, des armoires de puissance pour émuler électronique de puissance et le réseau électrique et un module de supercondensateurs. / Power quality is an important issue for the development of marine renewable energies, in particular wave energy. Due to the oscillatory nature of the oceans waves, the wave energy converters output power profile can present fluctuations in the range of seconds. The impact of these devices on the electric grid therefore needs to be investigated for wave farms to be connected to the grid. In order to emulate an operating direct drive wave energy converter, study power quality improvement and test different control strategies, a wave-to-wiremodel has been developed.Simulations carried out with this model for different grid strengths and different levels of sea-state showed that it is necessary to foster solutions to improve power quality. Thus, the wave energy converters aggregating and dispersion effects on power quality have been investigated. As it does not seem sufficient to meet the grid codes requirements, another solution have been considered, consisting of the insertion of an energy storage system into the chain. Finally, a part of the model has been validated using a hardware-in-the-Loop test bench including a motorbench, power modules to emulate the grid and power electronic's control and super capacitors module.

Wave ocean energy is a source of renewable energy which is gaining interest in the modern world. In contrast to other well-researched renewable energy sources such as wind energy, wave ocean energy is under the development phase. Governments around the world are encouraging the research of harnessing wave energy. As of now, there are different concepts to harness energy from waves. Tribological components are one of the main aspects that need attention in these wave energy converters. The moving components such as bearings can be the life-determining component of the entire device. This thesis provides conceptual solutions to adapt an existing start-stop bearing test rig to the conditions of wave energy converters. The test rig can test different bearing sused in the wave energy converters. The new design intends to provide scaled wave energy conditions. These conditions are mainly influenced by the oscillating movement of the bearings, the complex load condition and the salty environment. Since the testing of bearings in wave energy converters is in the initial stage, modular designs are implemented to test different types of bearings. / Se filen