Numerical simulation of 3D fluid-structure interaction in floating wave energy converter devices

• Autor(a) principal: Lopes, João Miguel Correia dos Santos
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/152867
• topic: Fluid-structure interaction (FSI); OpenFOAM; Floating WECs; Numerical modelling; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Mecânica

Global energy consumption and, consequently, energy related carbon dioxide (CO2) emissions have been increasing in the last few decades. Currently, the large majority of countries cover most of their energy needs with fossil fuels, contributing for CO2 emissions to the atmosphere, which have a strong impact on global warming. Recently, there has been growing concern about the significant increase in energy demands and environmental pollutants emissions by worldwide governments and organizations, resulting in the implementation of policies that promote the investment in non-polluting natural resources. The need to diversify the available renewable energy sources intensified the interest in ocean renewable energy. Research and development (R&D) of devices capable of extracting energy from the oceans (waves, wind, currents, tides) and transform it into electrical energy has, therefore, been one of the main focus of ocean engineering in recent years. Wave energy technology is not recent but, as opposed to wind and solar energy, it is still lacking a design convergence, contributing for a higher levelized cost of energy (LCOE), when compared to other sources. Wave energy technology has a strong potential of development and may have a fundamental contribution on achieving carbon neutrality and satisfying the increasing global energy demand. One of the main challenges of offshore renewable energies is to reduce costs, common to both wave and wind energy. Consequently, the incentive to couple semisubmersible platforms (SSPs), for the support of offshore wind turbines, and wave energy converters (WECs) emerges, allowing the reduction of installation costs. Although there are many advantages, the coupling of WECs with offshore wind turbines also introduces the influence of the interaction between both, resulting in a complex hydrodynamic system. Therefore, this work consists in studying a WEC which can be coupled with a floating SSP. The study is performed using the OpenFOAM software, augmenting its functionalities using olaFlow’s library for the generation and propagation of waves. In this context, the objectives of this thesis are: i) validation of the numerical model using experimental data from literature; ii) analysis of large amplitudes of motion effects of the device; iii) study of regular wave interaction with the wave energy hyperbaric converter (WEHC) device; iv) study of irregular wave interaction with the WEHC device; and v) study of the influence of the WEHC power take-off (PTO) damping characteristics. In the first part of this study the validation of wave generation and propagation is executed, comparing the wave parameters of simulated regular waves with analytical values. After the validation, a mesh convergence study is done. Afterwards, regular wave interaction with the WEC device is studied. First, a free heave and pitch decay tests are carried out to calculate the WEC’s natural period. Then, simulations without the PTO system are performed, enabling the characterization of the WEC’s behaviour for the different maritime conditions considered. The obtained results allow to conclude that the WEC is in resonance with the waves for frequencies around 0.20 Hz. It is also observed that both the heave amplitude and the pitch angle present small variations for shorter period waves. The influence of the pitch angle on the WEC’s heave amplitude is also studied. After, simulations with the PTO system are carried out, with results about the extracted power and optimal PTO’s linear damping coefficient being obtained. A power curve in function of the PTO’s linear damping coefficient, for each case considered, is presented. Finally, irregular wave interaction with the WEC device is studied. The influence of the PTO system when the WEC is under irregular waves is characterized.