Engineering Science - Masters by Research Theses

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    Feasibility study of reusing concrete gravity-based foundations designed for tidal energy converters
    (University College Cork, 2022) Dineen, Kate; Li, Zili; Ryan, Paraic; European Regional Development Fund
    Tidal energy converter devices have been developed to capture the enormous energy potential of the tides. These devices rely on robust mooring and foundation systems to ensure efficient energy extraction in operational conditions, and stability in extreme environmental conditions. Gravity-based foundations (GBF) are currently the most commonly used foundation type within the tidal energy industry. While tidal turbines are typically supported using bespoke carbon-steel tripod structures, concrete gravity-based foundations have been put forward by a number of studies as an alternative support solution. Several novel concrete GBF concepts exist and the developers of such concrete structures state that these foundations may be reused or relocated following decommissioning. Reuse of these massive concrete structures would greatly reduce construction and demolition (C&D) waste, and the need for new concrete GBFs for future devices, thus contributing significantly to the sustainability of the tidal energy industry. However, the concept of reusing concrete gravity-based foundations following long periods of deployment underwater has not been tested in real-world scenarios due to the nascent nature of the industry and long commissioning time periods. As highlighted from a related concept in the oil and gas industry, several safety issues may arise from reusing and relocating concrete GBFs, including geotechnical hazards and concrete degradation due to corrosion. Therefore, this study assessed the practicalities of reusing concrete foundations following decommissioning by designing a concrete GBF from first principles to be used for further analysis. This representative GBF was then extensively tested using Plaxis geotechnical software to investigate soil subsidence and differential settlement, assessing their impact on GBF relocation feasibility. Subsequently, the risk of corrosion to the steel reinforcement in the GBF was examined by, firstly, modelling the chloride concentration profile of the concrete, and secondly, investigating the interrelationship between oxygen availability and water saturation level. Thorough investigation into these study considerations can significantly contribute to the determination of whether it is practicable to reuse or relocate concrete gravity-based foundations in the tidal industry. The findings from the geotechnical analysis supports the possibility of reusing and relocating concrete GBFs for tidal turbines as both the total settlement and the tilt were significantly less than the allowable total settlement and tilt tolerance in a deployment site for which the GBF was designed and a contrasting site for which it was not. However, the findings from the concrete degradation analysis does not support the feasibility of reusing concrete GBFs. A chloride ingress analysis encapsulating three datasets indicated that the critical chloride threshold would be surpassed during a GBFs deployment period, meaning that the protective passive layer on the steel would be compromised leaving it vulnerable to corrosion should sufficient oxygen and water be present.
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    Performance and hull pressure analysis of scaled physical testing of a wave energy converter
    (University College Cork, 2022-06) Bevin, Anne; Murphy, Jimmy; O'Shea, Michael; European Regional Development Fund
    Wave energy conversion is an emerging field with the potential to capture a significant amount of a globally abundant energy resource to lower reliance on fossil fuels. At present, many designs for wave energy converters are being developed which show great promise for efficiently capturing wave energy. One of the most common barriers to the commercial development and deployment of these devices, however, is the high cost of manufacturing and design validation. The ocean is a harsh environment in which to place infrastructure, and there is a high risk of a wave energy converter being critically damaged at sea after going through a long and costly development process. For this reason, small-scale tank tests and computer modelling of concepts are vital to develop wave energy converter technologies to the highest possible degree before being put into an open-water operational environment. This study describes a physical tank testing campaign of one such model, the Ocean Energy (OE) Buoy, a floating oscillating water column wave energy converter. The walls of the OE Buoy are open to allow water to freely flow through it, and this study seeks to determine whether this might allow for the device to be made with a thinner hull than “closed-container” marine devices. If the water pressure that the hull walls will experience during operation is overestimated in the OE Buoy’s current design, this could have the potential to significantly lower costs of materials and production. This testing was conducted at University College Cork’s Lir NOTF tank facility in November and December of 2021, and the OE Buoy model used is designed at 1:15 scale.