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Advisor(s)
Abstract(s)
Este trabalho trata do desenvolvimento de um sistema de recuperação de energia
das ondas que seja capaz de fornecer electricidade a pequenas comunidades insulares, como
as do arquipélago dos Açores. O tema do trabalho enquadra-se dentro das metas definidas
pelas directivas estabelecidas pela União Europeia, complementadas com as directivas
Nacionais para o sector energético. Numa primeira fase é analisado o potencial energético
das ondas, dedicando especial atenção ao grupo Ocidental do arquipélago. Após uma
revisão das principais tecnologias de recuperação de energia das ondas actualmente
existentes, o dispositivo atenuador de tubo distensível faz objecto do nosso estudo. Baseado
no conceito Anaconda, o atenuador de tubo distensível é constituído por um tubo de
borracha flutuante cheio de água, cuja proa é fechada por um nariz alinhado segundo a
direcção das ondas incidentes. A parte traseira do tubo está acoplada a uma chaminé
vertical, de secção circular, através de um cotovelo de 90°. A interacção das ondas com o
tubo pressurizado dá origem a pulsos de pressão no seu interior que se deslocam em
direcção à chaminé vertical, fazendo oscilar uma coluna de água (OWC) dentro desta. As
oscilações são convertidas em energia de pressão numa câmara pneumática, em cujo topo
pode ser instalada uma turbina de ar que acciona um gerador eléctrico. A investigação
realizada é essencialmente experimental, com base no ensaio em tanque de ondas de dois
modelos do dispositivo às escalas 1:50 e 1:20. As condições geradas no tanque de ondas
reproduzem aproximadamente o clima de ondas na Ilha do Corvo, Açores. O desempenho
deste dispositivo é analisado nestas condições e validado com resultados padrão para outros
dispositivos, disponíveis na literatura. O desempenho do sistema com e sem o tubo
instalado é também comparado, por forma a avaliar as vantagens introduzidas pelo tubo
distensível. Os efeitos não-lineares e de escala são posteriormente discutidos. Dando
seguimento às estratégias para melhorar o desempenho do sistema, que vêm sendo
introduzidas desde 2014, foram ainda modeladas três situações reais: um sistema deste tipo
fixo a uma estrutura em treliças assente no fundo do mar, o mesmo sistema equipado com
uma parede reflectora junto à boca da OWC ou equipado com um canal de focagem de fundo
inclinado. O estudo realizado permite demonstrar que o tubo distensível acoplado a um
sistema OWC é viável e apresenta vantagens substanciais relativamente a muitos dos
sistemas que se encontram actualmente numa fase de desenvolvimento pré-comercial.
This work deals with the development of a wave energy device that is capable of supplying electricity to small island communities like the ones of the Azores archipelago. This subject is in line with the goals defined by the European Union’s directives, complemented by the National directives for the energy sector. Firstly the energetic potential of ocean waves is analysed, with special interest in the Occidental group of the Azorean archipelago. A review of the main wave energy technologies is then accomplished, and the distensible tube wave attenuator device becomes the focus of our study. Based on the Anaconda concept, this device makes use of a long rubber tube, filled with water, whose nose is closed and aligned head to the incident waves. Its stern is coupled to a vertical circular shaft by means of a 90° elbow. The interaction of the waves with the tube induces pressure bulges inside it that travel along its length towards the vertical shaft, giving rise to oscillations of a water column (OWC) in the shaft. These oscillations are converted into pressure variations in a pneumatic chamber, on top of which an air turbine driving an electric generator can be installed. Given the robustness of the rubber tube and the development stage of the energy conversion technologies used, this system has the potential to reduce the investment and operational costs of wave energy utilization. The present investigation is mainly experimental and is based on the testing of a model of this device in wave-tank, at 1:50 and 1:20 model scales. The wave conditions generated in the tank approximately reproduce the wave climate at Corvo island, which is part of the Occidental group of the Azores. The device performance is analysed under these conditions and later validated against benchmark results that are available in the literature, obtained with other devices. To assess the advantages of using a distensible tube, a comparison between the performance of the device with and without the tube in place is also accomplished. Nonlinear and scale effects are then discussed. In addition, following the performance enhancement strategies that have been studied since 2014, three real situations where considered: the system fixed to a bottom-standing jacket structure, the same system equipped with a reflecting wall at the OWC mouth, or equipped with a focusing channel of slopped bottom profile. This study demonstrates that the distensible tube system coupled with an OWC is viable and presents significant advantages relative to several systems that have currently achieved a pre-commercial stage of development.
This work deals with the development of a wave energy device that is capable of supplying electricity to small island communities like the ones of the Azores archipelago. This subject is in line with the goals defined by the European Union’s directives, complemented by the National directives for the energy sector. Firstly the energetic potential of ocean waves is analysed, with special interest in the Occidental group of the Azorean archipelago. A review of the main wave energy technologies is then accomplished, and the distensible tube wave attenuator device becomes the focus of our study. Based on the Anaconda concept, this device makes use of a long rubber tube, filled with water, whose nose is closed and aligned head to the incident waves. Its stern is coupled to a vertical circular shaft by means of a 90° elbow. The interaction of the waves with the tube induces pressure bulges inside it that travel along its length towards the vertical shaft, giving rise to oscillations of a water column (OWC) in the shaft. These oscillations are converted into pressure variations in a pneumatic chamber, on top of which an air turbine driving an electric generator can be installed. Given the robustness of the rubber tube and the development stage of the energy conversion technologies used, this system has the potential to reduce the investment and operational costs of wave energy utilization. The present investigation is mainly experimental and is based on the testing of a model of this device in wave-tank, at 1:50 and 1:20 model scales. The wave conditions generated in the tank approximately reproduce the wave climate at Corvo island, which is part of the Occidental group of the Azores. The device performance is analysed under these conditions and later validated against benchmark results that are available in the literature, obtained with other devices. To assess the advantages of using a distensible tube, a comparison between the performance of the device with and without the tube in place is also accomplished. Nonlinear and scale effects are then discussed. In addition, following the performance enhancement strategies that have been studied since 2014, three real situations where considered: the system fixed to a bottom-standing jacket structure, the same system equipped with a reflecting wall at the OWC mouth, or equipped with a focusing channel of slopped bottom profile. This study demonstrates that the distensible tube system coupled with an OWC is viable and presents significant advantages relative to several systems that have currently achieved a pre-commercial stage of development.
Description
Keywords
Energia das ondas Arquipélago dos Açores Atenuador de tubo distensível Ensaio em tanque de ondas