The 21st century is recognised as the era of the ocean, where the global agreement on achieving net-zero emissions, together with the energy crisis caused by geopolitical factors, has led to substantial growth in the development of Offshore Renewable Energy (ORE). In this rapidly expanding field, this thesis specifically concentrates on offshore wave and wind energy. A high-fidelity numerical tool with Computational Fluid Dynamics (CFD) method is further developed based on the open-source CFD toolbox OpenFOAM. With high numerical accuracy, it enables the simulation of fluid-structure interaction (FSI) problems associated with wave energy converter (WEC) and floating offshore wind turbine (FOWT) in the time domain, offering a cost-effective alternative to physical testing in wave tanks or basins.
The aim of this study is to broaden the applicability of the present tool for the FSI analysis of WEC and FOWT. The main challenge in the present FSI study is the requirement for supplementary solvers for multiphysics simulations. Different structural solvers and aerodynamic models are needed for various scenarios. Therefore, an integrated multiphysics simulation framework is further developed by integrating an aerodynamic model for wind turbine analysis, different structural models for flexible and multi-body structures analysis, and mooring system models. This framework accounts for the complexities of various environmental conditions and operational contexts. With this tool, various scenarios of WECs and FOWTs are studied.
The thesis first studies two innovative WECs. The first configuration features a multi-body WEC system comprising multiple floats and interconnected sub-structures. It is numerically analysed using the current CFD tool coupled with an external multi-body solver. The interaction force among sub-structures can be accurately captured, and the results indicate that the response mode of the individual float is strongly affected by the mechanical linking arms and the incident wave conditions, which is difficult to achieve with only the CFD solver itself. The predicted peak output is found to increase with the decreasing of wave period and an optimal device’s damping to reach a maximum power capture exists, which varies with wave period and wave height.
The second configuration involves a flexible WEC constructed of hyper-elastic material, which is analysed by coupling a Finite Element Analysis (FEA) code into the current CFD solver. A strongly nonlinear hyper-elastic material is used for the WEC, and its dynamic response under regular waves is studied. Results show that adopting hyper-elastic material has improved performance in power generation compared to linear-elastic material. Additionally, compared to conventional rigid-body WECs, the fWEC can harvest considerable wave energy within a much wider range of wave periods.
Another part of the FSI study is on FOWT, which first examines the motion response of individual supporting platforms under wave-current conditions. When considering the ocean current interaction of blunt structures, a low-frequency sway motion of the FOWT platform exists, the so-called Vortex-Induced Motion (VIM), that cannot be solved with potential flow theory and other low-fidelity methods. The dynamic response of FOWT platforms to waves and currents from different directions is studied, revealing that non-colinear interactions can intensify VIM. Present findings suggest that smaller waves may also induce significant platform motions in the presence of current.
Subsequently, it explores the performance of a fully coupled wind turbine array in the presence of waves by coupling the Actuator Line Model (ALM). This significantly reduces the time cost and complexity compared to the blade resolved method, making the simulation of FOWT farm simulation possible. The three FOWTs with different staggered layouts are simulated, and their dynamic response and wake interactions are analysed. The results indicate that the periodic motion caused by waves introduces an oscillation in the power output and thrust. It is also found that the pitch and surge motion have an opposite influence on the power output
| Date of Award | 26 Sept 2024 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Sponsors | University of Strathclyde |
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| Supervisor | Qing Xiao (Supervisor) & Atilla Incecik (Supervisor) |
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