Centre for Marine and Renewable Energy (MaREI) - Masters by Research Theses
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- ItemFeasibility 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 FundTidal 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.
- ItemPerformance 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 FundWave 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.
- ItemGEOBIM, BIM integrated geohazard monitoring of at risk slopes and historical retaining structures(University College Cork, 2022-06-30) Pantoja Porro, Roberto; O'Shea, Michael; Murphy, Jimmy; Geological Survey of IrelandOver time, structures such as slopes and retaining walls are increasingly deteriorating, resulting in a risk of collapse. Factors such as climate change, human activities, societal development, rapid growth of cities, increasing population and economy make geological disasters occur more frequently than usual. Geological hazards of nature, slope collapse, slope fractures or slope movements have become a problem to be solved by civil engineering. With the advent of low-cost sensors, optical topographic surveying and BIM (Building Information Modelling), such risk could be mitigated and, in some cases, eliminated. The main aim of this research was to use wireless sensors to monitor slopes that are potentially at risk and to incorporate all the information obtained in BIM (Building Information Modelling), in order to make a digitalized vision of the structures in real time. High precision and innovative tools, such as drone flights and slope scanners were utilized for a detailed analysis of the risk of change in the geohazards including soil slopes and historic retaining walls. Through the combination of data from sensors with point clouds generated from drone flights, an early warning system was developed. This early warning system was clearly able to display when there was surface changes therefore highlighting the areas of high risk of collapse. This thesis shows how continuous real-time surveillance of soil slopes and retaining walls can be achieved clearly and concisely, in a cost-effective manner.
- ItemAn experimental investigation into the most prominent sources of uncertainty in wave tank testing of floating offshore wind turbines(University College Cork, 2022-08-30) Lyden, Eoin; Murphy, Jimmy; Judge, FrancesThere is an urgent need to replace carbon-based energy sources with renewable energy sources, and floating offshore wind is seen as a critical component in the drive towards energy diversification. Floating offshore wind facilitates accessing a far vaster wind resource that exists in deeper waters, further offshore. Floating offshore wind platforms must undergo wave tank testing in the early stages of development to assess model responses to different wave and wind conditions. Wave tank testing, while highly beneficial, is liable to errors arising throughout the testing campaign. Errors can arise during wave tank setup, testing, and analysis of results. Some of the primary sources of error include errors in the model location within the tank, errors in model parameters like mass, inertia and CoG, and errors due to incorrect replication of mooring forces and aerodynamic forces from the turbine. Scaling wind turbine blade properties can be challenging; this is because aerodynamic forces are scaled using Reynolds scaling, but all hydrodynamic forces are scaled using Froude scaling. For this reason, wind emulation systems are used to replicate the aerodynamic forces from the turbine only. Testing was completed using two very different floating offshore wind concepts. A sensitivity analysis was completed by conducting variations to the wind emulation system used, the model inertia and centre of gravity, and the mooring stiffness of the model. The magnitudes of the variations to the inertia, centre of gravity and mooring stiffness were based on the uncertainty in the values of each of the parameters. Three wind emulation systems of varying complexity were used for this comparison, a simple weighted pulley system, a constant thruster and the software in the loop system developed by CENER. The comparison was conducted to assess the influence of wind emulation systems on the uncertainty of platform response It was found that the effects of each variation conducted were magnified at resonance, and the magnitude of platform response was affected to a greater extent than the period of resonance response. Of all the variations to the model properties conducted, the inertia about the y-axis and location of the centre of gravity along the x-axis affected pitch response to the greatest extent. A 7% change in the inertia about the y-axis coupled with an 8.57% resulted in a 10% change in the period of resonance response for pitch, Tr, and 52% decrease in the magnitude of resonance respsonse for pitch, Tr, mag. Changes in the wind emulation system affected the pitch response most significantly, while the period of resonance response Tr, was mostly unaffected , the magnitude of resonance response Tr, mag, was reduced by nearly 90% when a pulley system was used in lieu of a conventional thruster for a semi-submersible model. Changes in mooring stiffness did not influence the period of resonance response but did affect the magnitude of resonance response, particularly in surge. For a linear horizontal mooring system applied to a semi-submersible model, a 1% decrease in the spring stiffness resulted in a 9% decrease in the magnitude of resonance response for surge, Tr, mag.
- ItemHigh resolution wave and tidal energy resource assessment in the Irish and western UK waters(University College Cork, 2021-10-19) Furlong, Rebecca; O’Connell, Ross; Murphy, Jimmy; European Regional Development FundAs island countries, both Ireland and the UK have long and extensive coastlines, making offshore renewable energy easily accessible. Previous studies in the area have shown that there is resource availability for both wave and tidal energy in UK and Irish waters, with an abundant wave resource off the west coast of Ireland and a well-known tidal resource within the Irish and Celtic Seas. The Irish Climate Action Plan 2019 set out that 70% of electricity would come from renewable sources by 2030, meaning that research and development that is ongoing in the offshore industry is key to reaching that target. This study aims to create new, updated GIS layers showing both the wave and tidal energy resource as well as the parameters needed to compute them, including significant wave heights, wave energy periods and tidal current speeds. The Copernicus Marine Service recently updated two models that now contain wave spectrum data at high resolutions, both less than 5 kilometres, and long hindcasts of greater than 20 years. The accessibility of this data means that the wave energy resource can be modelled very accurately at high resolutions, a parameter that is hugely important for marine renewable energy developers to gain an understanding of potential deployment site characteristics. Data for tidal resource analysis is available through the Irish Marine Institute and is based on a ROMS model. This study has shown that the Copernicus models correlate very well with each other, and it is possible to create resource layers for use in GIS with the data. This information is imperative for marine renewable energy developers at a first stage so they can have a thorough understanding of the resource availability and conditions available at a proposed site. Having resource information available within a GIS tool can give developers a spatial overview of where the best resource is available, while the GIS can also provide valuable information such as the location of the closest grid connections and the nature of the underlying bedrock, all factors that can influence the location of a wave or tidal farm.