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- Ekweoba, Chisom Miriam, 1992-
(författare)
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Geometry optimisation of a floating platform with an integrated system of wave energy converters using a genetic algorithm
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This study investigates the feasibility of optimising the geometry of a multi-purpose floating platform using a genetic algorithm (GA). The platform provides a foundation for a floating wind turbine while housing pitching wave absorbers. A frequency-domain analysis is performed on the integrated wave absorbers to estimate the annual energy production for varied geometries of the platform. For ease of modification of the platform geometry, an analytical model of the platform-wave absorber system is made using personalised WAMIT GEOMXACT subroutines for efficient updating of the geometries in-between optimisation searches. WAMIT is a linear potential theory-based, boundary element method programme. To accommodate corresponding changes in the mass properties of the platform for every unique solution tested, a beam model of the platform is created and used for the platform mass properties evaluation. Extended degrees of freedom are also introduced and used in this paper to account for the relative motion between the optimized platform and the wave absorbers. A parameter sweep is done to observe how closely the optimisation algorithm comes to the global optimum. Several simulations are used to test for speed and accuracy of convergence, simulation time and repeatability. Results show that the number of iterations to convergence increases with an increased number of optimized variables. It is also shown that computation time is independent of the number of optimized variables but rather depends on the complexity of the objective function and computational power of the machine use. More results suggest that no global optimum exists for the studied platform geometry, but different combinations of the characteristic features can result in a similar performance of the integrated wave absorber. Finally, it is observed that the GA optimum tends towards platform geometries for which the wave absorber's resonance frequency coincides with the wave climate and wider absorption range.
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| 2. |
- Ekweoba, Chisom Miriam, 1992-
(författare)
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Hydro-mechanical optimization of a wave energy converter
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wave energy conversion technology has gained popularity due to its potential to be-come one of the most preferred energy sources. Its high energy density and low car-bon footprint have inspired the development of many wave energy converter (WEC) technologies, few of which have made their way to commercialisation, and many are progressing.The Floating Power Plant (FPP) device is a combined floating wind and wave converter. The company, Floating Power Plant, was established in 2004 and has developed and patented a floating device that consists of a semi-submersible that serves as a foundation for a single wind turbine and hosts four wave energy converters (WECs). Each WEC consists of a partially submerged wave absorber whose pitching motion generates energy from incoming waves. The wave absorbers are connected to an oil hydraulic power take-off system located in a dry “engine room” above the free water surface, where the mechanical energy in the absorber is converted to electricity. When undergoing pitching movements, there are interactions between individual wave absorbers and the surrounding platform. This thesis focuses on developing methods to improve the FPP WEC’s hydrodynamic interactions.The first part of this thesis optimises the wave absorber (WA) ballast. An ana-lytical model is developed to enable systematic selection of WA ballast combination with significantly less computational effort when compared with the more conven-tional means, such as using CAD software. The study suggests an algorithm with which the absorbed power and resonance frequency can be improved and adjusted by manipulating the ballasts’ mass, the position of its centre of gravity, placement and inclination of the WA. The proposed method is generic and can be applied to other WEC concepts or submerged bodies in general. The results show the feasibility of designing the absorber ballast to offer passive control for increased wave absorption. It demonstrates the effect of ballast on the WA inclination, resonance frequency and response amplitude operator (RAO).The second part focuses on the optimisation of the FPP platform geometry. The genetic algorithm optimisation technique is implemented to maximise the annual en-ergy produced by the relative pitch motion of the WA to the floating platform. The optimised variables are characteristic lengths of the floating platform, most of which are part of the immediate surrounding walls of the absorber. The objective function is a function of the WA’s annual energy production (AEP) and RAO. Results show the feasibility of improving the hydrodynamic interaction between the floating platform and its integrated wave absorbers for a given wave climate by using a heuristic search technique. The number of iterations to convergence tends towards increased values when considering more optimised variables. It is also observed that the computational time appears to be independent of the number of variables but is significantly impacted by the computational power of the machine used.
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