Control co-design of heterogeneous arrays of wave energy converters
Date
2023-12
Authors
Abdulkadir, Habeebullah
Major Professor
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Abdelkhalik, Ossama
Sarkar, Partha
Ren, Juan
Ward, Thomas
He, Ping
Committee Member
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Abstract
As the world population continues to grow, so does the energy need. There is also a need to shift the world economy’s dependency on fossil to cleaner sources. Ocean waves have high power density, with the theoretical global ocean reserves of wave energy ranging between 8000–80000 TWh annually. However, the current uncompetitive cost of harvesting ocean power is a drawback that hinders the wide deployment of wave energy converters (WECs). Using the mathematical model of the devices, innovative control methods are developed aiming at improving the efficiency of the devices. In several studies, this control design step often comes in as the last stage of the design process, after the mechanical, electrical, and other subsystems are completely defined. In this work, we present an approach to the WEC device design process that ensures the integration of all relevant engineering at the start of the design process; this is referred to as the control co-design (CCD) approach. Control co-design formulation is developed for multiple WEC devices deployed in an array to reduce energy costs. Geometric optimization for WEC devices is a core aspect of WEC design to achieve constructive interaction between the device structure and the waves. To improve the performance of a WEC array, this study investigates how optimizing the dimensions of individual devices in the array can affect the overall performance; the resulting array contains devices of differing sizes and is referred to as a heterogeneous array. The optimization variables were the radii, submerged draughts of cylindrical buoys, and control parameters. The performance of the heterogeneous array is assessed against an optimized traditional array containing the same number of devices in an identical layout while assuming the same total submerged volume. To reduce the computational time of this rather complex optimization problem, an optimal and computationally efficient time-domain controller is developed using Pontryagin’s minimum principle to compute the performances of the arrays. This optimal control formulation accounts for the limitations of the WECs’ PTO properties, improving the accuracy of our simulations. A computationally efficient semi-analytic method based on eigenfunction expansion is developed for computing the hydrodynamic coefficients of the devices. The optimization was performed using a genetic algorithm. For the chosen test sites, it was found that a heterogeneous array can achieve a performance improvement of up to 40% over the corresponding homogeneous array.
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dissertation