Civil and Environmental Engineering - Doctoral Theses
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Item Improved modelling of pumped hydro energy storage(University College Cork, 2012) Deane, John Paul; O'Gallachoir, Brian; McKeogh, Eamon; Eirgrid Plc.Rising greenhouse gas emissions, diminishing fossil fuel reserves and concerns over energy security have led to renewable energy targets that have spurred the growth of variable renewable generation sources such as wind and wave in many countries. The introduction of variable sources of electrical generation makes the operation and modelling of the power system more challenging. Pumped hydro energy storage is a flexible, fast acting generating source with the ability to store large amounts of electricity, and to facilitate the technical integration of variable renewable sources of generation. Recently, there has been resurgence in pumped hydro energy storage as many European countries strive for greater integration of renewables; however, the software tools and techniques used to traditionally model the power system need to be improved in order to capture the operation and role of flexible enabling technologies such as pumped hydro storage. Traditionally deterministic models that simulate the power system at hourly resolution are employed to assess the role and usefulness of pumped hydro storage. In this thesis, techniques are developed and presented to improve the current representation of pumped hydro energy storage, eliminating the weakness of perfect foresight assumption in model simulations. It is also demonstrated that higher temporal resolution simulations of the power system have the ability to capture important aspects of power system operation such as binding ramp rates. New techniques are also put forward for the improved modelling of large pumped storage in the context of wind forecast uncertainty, and it is shown that energy system models can benefit in the modelling of pumped hydro storage by soft-linking with power system models. Overall, this works shows that existing pumped hydro energy storage will play an ever more important role in Ireland as levels of installed wind capacity increase.Item Experimental testing and finite element analysis of segmented water pipeline(University College Cork, 2024) Zhang, Qinglai; Li, Zili; Soga, KenichiUnderground pipeline networks are crucial for the serviceability of sustainable water distribution in contemporary society. Nonetheless, thousands of miles of segmented pipeline infrastructure are susceptible to substantial damage from natural disasters, such as earthquakes and landslides, particularly at the vulnerable joint sections. To enhance the resilience of the segmented pipelines, many previous studies have already investigated various types of pipeline joints and materials in both academia and industry. Over the years, Ductile Iron (DI) Pipes have already been widely used in buried underground infrastructure, owing to their durability and reliability under various soil and loading conditions. On the other hand, Polyvinyl Chloride-Oriented (PVCO) pipelines have emerged as a novel alternative in recent years due to its cost-effectiveness, environmental friendliness and easy installation. Both are valued for their adaptability to different local ground conditions. Continued advancements in both DI and PVCO pipeline technologies have led to significant improvements in the design and functionality of segmented pipelines. To evaluate the effectiveness of their recent innovations, it is crucial to conduct the corresponding experimental testing and develop computational models. Hence, this PhD study aims to comprehensively investigate the mechanical responses of modified jointed DI and newly designed segmented PVCO pipelines to earthquake-induced forces through a series of full-scale laboratory tests utilizing distributed fiber optic sensing (DFOS) technology for continuous strain measurement and conducting advanced three-dimensional (3D) finite element (FE) analyses. A series of laboratory tests were conducted on the 203-mm (8-in) diameter DI pipeline with a restrained axial joint, three critical states have been identified: axial tension, deflection and biaxial tension (combined tension and bending). The behavior in each state is influenced by the orientation, quantity, and installation of locking segments in bell-spigot joints, leading to variations in joint stiffness, flexibility, and capacity. The analysis was then further extended to an innovative surrogate model using bushing connectors to replace the complex bell-spigot joint configurations, aligning well with expected outcomes while significantly reducing simulation time. This is particularly beneficial for future soil-pipeline interaction studies at the system level. Similar to DI pipelines, a series of bending tests was also conducted on the 160-mm (6-in) diameter PVCO pipeline. The pipeline employs a 'Fittom-Coupler' fitting, sealed with an Ethylene Propylene Diene Monomer (EPDM) rubber and polypropylene ring gasket to connect two spigots securely and ensure water tightness. The results highlighted that performance is primarily influenced by bending stresses, leading to deflection and axial sliding. Validated models incorporating anisotropic properties and seal materials helped in conducting sensitivity analyses on varying wall thicknesses and fitting designs. Pipeline failure modes are shown typically involve mechanical disconnection at the joints and also local buckling related to variations in wall thickness. Such buckling can be reduced by altering the length or local shape of the fitting. Both segmented restrained DI pipes and PVCO pipes present unique advantages for seismic water infrastructure. DI pipes provide exceptional strength for high-load environments, whereas PVCO pipes, with thinner walls and enhanced circumferential strength allow greater deflection capability, suitable for areas requiring resilience to large deformations.Item Experimental and numerical investigation of towing operations for large floating offshore wind farms(University College Cork, 2024) Chitteth Ramachandran, Rahul; Murphy, JimmyFloating Offshore Wind Turbines (FOWTs) represent a pivotal advancement in renewable energy technology, extending the reach of wind power to previously inaccessible waters. Their importance lies in their ability to exploit the stronger and more consistent winds in deep waters. Installing these floating platforms in sites where the weather is harsh invites significant challenges. A major challenge lies in towing these platforms from the fabrication site to the farm location. The commercialisation of floating wind aims at farm-scale deployments and installation of large wind turbines. For planning fast, cost-effective and safe towing operations, the understanding of its physics is paramount. It is also important to develop numerical methods and simulation approaches to understand and predict the motions and towing loads while towing these significant floating structures. This thesis constitutes a deep exploration of the towing operations associated with floating wind turbines, integrating a multifaceted analysis encompassing case studies, experimental tests and numerical methodologies. Semi-submersible floaters, being one of the early movers, are the main focus of this thesis. The presented thesis has followed an ‘industry-ready’ approach and aims at minimising the gap between academia and industry by attempting an equilibrium between them. The thesis is split into four research papers and starts with a literature review examining marine operations integral to floating wind turbines, identifying specific challenges and finding opportunities for synergy with other well-established and developed offshore industries such as Oil and Gas (O & G) and fixed-bottom wind industries. Towing operations, being required for installation, major repairs and decommissioning are then analysed and two numerical approaches for the hydrodynamic analysis of semi-submersible floating wind turbines are developed and implemented in two different commercial hydrodynamic analysis tools. The first method is a potential flow-based forward speed approach with corrections for viscous effects implemented in the in-house tool SEACAL. The second method is a hybrid approach utilising a potential flow method combined with the Morison equation and implemented in the commercial tool Orcaflex. The hybrid approach is also implemented in a free open-source numerical tool OpenFAST for the further development of the research work. To validate the numerical results, a detailed experimental campaign was conducted and validation data for towing in various sea conditions, towing configurations and towing speeds were generated. A comparative study of both approaches is presented and the advantages and disadvantages of the developed methods are summarised. The findings indicate that both developed numerical models possess the capability to analyse and predict towing characteristics contingent upon towing speed and prevailing wave conditions. The first method is better suited to considering low speeds (0.514 m/s–1.542 m/s) and low wave heights (1m – 2m) whilst the second method is better suited for higher speeds (0.514 m/s – 3.084 m/s) and higher wave heights (1m – 6m). Depending on the weather conditions, towing requirements and availability of the numerical tools, the suitable analysis method can be chosen.Item Economic, environmental, and technical assessment of on-farm anaerobic digestion systems in Ireland(University College Cork, 2024) Diaz Huerta, Jorge; O'Shea, Richard; Wall, David; Murphy, Jerry; Sustainable Energy Authority of Ireland; Gas Network IrelandIreland's pursuit of producing 5.7 TWh of biomethane from anaerobic digestion (AD) plants, to reduce reliance on fossil-derived natural gas, necessitates a thorough examination of viable system configurations. The implementation of AD in Ireland is seen as a targeted approach to achieving emissions reduction of 25% in the agricultural sector. On-farm AD unlocks the opportunity to generate biomethane from indigenous feedstock and curtail emissions from livestock farming. Previous assessments of the mitigation potential of AD systems in agriculture have been undertaken through Marginal Abatement Cost Curves in an Irish context. Although this initial assessment deemed AD as a high-cost of abatement solution, recent uncertainty in energy prices, due to recent geopolitical events, might provide new opportunities for the development of biomethane from on-farm AD. Furthermore, using single values for abatement costs may not encompass or describe the impact of the varying system boundary of an AD system, which can have consequences for the financial and environmental performance. Such variables include the scale of the on-farm AD system, the feedstock used, and the biogas energy end-use. AD systems can vary significantly in terms of scale, design, technology, feedstock, and function. This thesis delves into the financial and environmental viability of on-farm AD systems, emphasising the need to consider additional inputs and outputs beyond energy sales that lie within the system boundary. The work evaluates different biogas end-use options and varying farm sizes for on-farm AD systems, revealing a wide range of abatement costs, whilst accounting for the uncertainty of external factors. The findings indicate that, when income from co-products such as biofertilisers are factored into the analysis, as well as the emissions reductions from digestate use, a more optimistic evaluation of AD system viability is attained. Analysis across different scales and process configurations reveals varying mitigation potential, with abatement costs ranging from -7 € tCO2eq-1 to +816 € tCO2eq-1. A key result of the analysis shows that, if a single input variable is changed within the system boundary, the financial and environmental performance of a system can be significantly changed. The efficiency of the AD process emerges as a key determinant, alongside farm conditions such as grass silage yield and synthetic fertiliser use. While heat and electricity production exhibit lower uncertainty, biomethane production faces challenges, necessitating additional incentives for small-scale AD uptake. Novel approaches, such as the integration of microbial electrolysis cell (MEC) technologies, could present an opportunity to enhance small-scale upgrading feasibility, though capital constraints remain Connecting on-farm AD systems through pipelines to centralised upgrading facilities offers a promising alternative to the transportation of materials to a large centralised AD plant, or upgrading biogas at small individual plants, reducing investment requirements. Overall, this research provides insights into enhancing the economic and environmental feasibility of on-farm AD systems, crucial for sustainable agricultural practices and emission reduction goals. Through strategic integration and policy support, on-farm AD holds promise as a key contributor to decarbonisation efforts, offering diversified revenue streams for farmers and addressing emissions from the agricultural sector. Further research and policy development are essential to realise the full potential of on-farm AD in contributing to sustainable development and mitigating climate change impacts.Item Quantitative risk assessment of pesticides in drinking water under current and future climates(University College Cork, 2024) Harmon O'Driscoll, Jenny; Ryan, Paraic; Healy, Mark; Environmental Protection AgencyRisk assessment approaches have become critical for pesticide risk management and mitigation. Despite this, scientists and pesticide regulators have acknowledged the need to improve representation of variability in input data, and uncertainty in pesticide fate processes in existing approaches. Additionally, current methods are limited in their ability to represent the inherent uncertainty and variability associated with climate change, and therefore cannot inform future planning under changing climates. This thesis presents the development of a novel, practical risk assessment framework to assess the risks posed by pesticide contamination in drinking water under current and future climates, incorporating novel risk scoring systems, probabilistic risk modelling frameworks, and climate change projections. The main body of the thesis discusses the different stages involved in the development of the risk assessment framework. Firstly, a novel risk screening tool was developed to rank pesticide risks to human health, considering pesticide use, chronic health effects, environmental fate, and site-specific soil conditions. This approach incorporated both pesticide properties and site conditions in the scoring of pesticide mobility to enable more a realistic representation of the effects of location on pesticide transport; metabolite data was also used to inform overall risk scores based on EU recommendations. This method aids in identifying high-risk pesticides from a wide range of pesticides to better inform monitoring programs and further detailed risk assessments. Secondly, an existing deterministic simulation model was modified to better represent both site scenarios and transport processes involved in pesticide runoff to drinking water supplies. Additionally, a Monte-Carlo approach was utilised to enable probabilistic assessment and account for variability in pesticide properties, population characteristics, site conditions, and climatic factors. This framework enables farm advisors and catchment managers to predict concentrations of pesticides in drinking water supplies, quantify potential risks to human health arising from pesticide exposure, and implement risk mitigation measures using a practical and accessible probabilistic model. An Irish case study was used to illustrate the implementation of the framework to predict pesticide concentrations in surface water and assess health risks to adults and children at a grassland site typical of Irish agriculture. The results found pesticide concentrations exceeding EU drinking water limits for several pesticides, including MCPA, mecoprop, and 2,4-D, but indicated that health risks were low under current conditions despite these exceedances. Finally, this thesis investigates the impact of climate change on pesticide transport and health risks, integrating high-resolution climate model projections into the proposed probabilistic risk model. Standardised climate projections for Ireland were used to demonstrate how the probabilistic risk model developed in this thesis can be adapted for future climates. A risk assessment of pesticides for three timeframes (current, 2050, 2100), under two climate scenarios (RCP4.5 and RCP8.5) showed that pesticide risks will increase with future climate conditions. The study found significant regional variations, with higher risks in the south-west compared to the north-east of Ireland, and projected overall risk increases ranging from 18% to 85%, depending on the scenario and timeframe. Despite the projected increases in pesticide risk, the impact to human health remained below EU regulatory health thresholds even under worst-case climate conditions. This approach can be adapted to account for indirect impacts of climate change e.g. land-use, pest prevalence and agricultural policy, to better represent overall changes to pesticide risks under a changing climatic and legislative landscape. Overall, this research highlights the importance of incorporating site-specific conditions, variability in environmental and climatic factors, and future climate change projections into pesticide risk assessments. The methodologies developed provide robust tools for managing pesticide risks and can be adapted for various locations and conditions, thus informing future pesticide management, climate adaptation approaches, and public health protection strategies.