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Performance Evaluation of a Combined Floating Offshore Energy System (CFOES) in Operational and Extreme Conditions

Cutler, J (2024) Performance Evaluation of a Combined Floating Offshore Energy System (CFOES) in Operational and Extreme Conditions. Doctoral thesis, Liverpool John Moores University (LJMU).

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The holistic aim of this thesis is to broaden knowledge on the coupled behaviour of a combined floating offshore energy system (CFOES) that supports three different offshore renewable energy (ORE) systems. In this work, a CFOES concept is innovated and tested using numerical simulation under typical design load cases. The three systems include a catamaran type floating wind turbine, a wave energy converter system, and a tidal turbine system. Currently, no numerical tools exist explicitly for the design and analysis of such a system. Thus, numerical tools used purposed for pure ORE systems are integrated together in order to create a sophisticated numerical model of the CFOES. The numerical model is built within FAST2AQWA (F2A). F2A is an aero-hydro-servo-elastic tool used for the design and analysis of floating wind turbines. The tool is based on the integration of a commercial wind turbine simulator, FAST, into a commercial hydrodynamic analysis software tool, ANSYS AQWA. AQWA is effective at studying multibody hydrodynamics and has modelling features such as fenders and joints which allow the simulation of linear WEC PTO systems. AQWA also provides a built-in DLL capability which is used for external force calculations. This function permits the calculation of the aerodynamic forces of the wind turbine and hydrodynamic forces of the tidal turbines. Together, the combination of these capabilities enables the construction of an integrated numerical model of a triple CFOES. The numerical model is used to perform integrated loads analysis for operational and extreme conditions. It was found in rated and above rated conditions, the performance of the wind turbine in the CFOES improves compared to a floating wind turbine. The power output is greater and smoother and there is less variability in aerodynamic thrust, rotor torque and blade pitch. The WEC system significantly reduces platform rolling and pitching in more energetic sea states. For certain conditions, the WEC system reduces the roll motion of the platform by 66%. Consequently, the side-side tower-base bending moment of the wind turbine is reduced. A reduction of 35% and 40% in the maximum and minimum was observed. When the tidal turbines are in operation a hydrodynamic thrust is produced. As a result of this, the global surge response is increased and so is mooring line tension. However, the variability about the mean surge is reduced because of added hydrodynamic damping. Finally, the mean additional power that could be generated by the tidal and wave energy systems was up to 30%. The numerical results demonstrated several important advantages in ORE hybridization including increased energy yield, reduced structural loading, nd improved floating platform stability. This work provides a solid basis for future study involving advanced design and analysis of CFOESs that are comprised of three or more ORE systems.

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Wind turbine; Wave energy converter; Tidal turbine; Floating wind; Energy system; Renewable energy; Offshore renewable energy
Subjects: G Geography. Anthropology. Recreation > GE Environmental Sciences
T Technology > TA Engineering (General). Civil engineering (General)
Divisions: Engineering
SWORD Depositor: A Symplectic
Date Deposited: 11 Mar 2024 14:36
Last Modified: 11 Mar 2024 14:37
DOI or ID number: 10.24377/LJMU.t.00022761
Supervisors: Bashir, M, Wang, J and Loughney, S
URI: https://researchonline.ljmu.ac.uk/id/eprint/22761
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