Energy Engineering - Doctoral Theses

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    Design, modeling, analysis, and characterization of 3-D inductors for PwrSoC/PwrSiP DC-DC converters
    (University College Cork, 2023) Shetty, Chandra; O Mathuna, Cian; Ye, Liang; Duffy, Maeve; Science Foundation Ireland
    Inductors are essential components in power supplies. Increasingly, point-of-load (POL) power delivery is now the primary issue across all market sections, such as battery-powered portable electronic systems, including laptops, smartphones, tablets, etc. With increasing performance and decreasing footprint, there is a rising demand for on-chip three-dimensional (3-D) inductors. Micro inductors are used in on-chip voltage regulators, radio-frequency (RF) circuits, microsensors, microactuators, power MEMS devices, etc. The benefits of 3-D inductors such as high inductance density can be extended to such applications. This work deals with the design, modeling, and characterization of 3-D inductors for power supply applications: Power Supply in Package (PwrSiP) and Power Supply on Chip (PwrSoC) applications. Even though much work has been carried out to fabricate high inductance density 3D inductors on silicon for power applications, little or no attention has been given to (1) develop a closed-form expression for the inductance, (2) introduce novel structures for the improved figures-of-merit, and (3) dc ratio of inductance to resistance Ldc/Rdc (also known as dc quality factor Qdc). The contributions of this thesis are as follows: (1) analytical models for the inductances of 3-D inductors (toroid, solenoid, and spiral) with air-core are developed and validated by fabricating 3-D inductors on PCB, (2) a detailed study of the impact of design parameters on dc ratio of inductance to resistance (Ldc/Rdc) of 3-D micro air-core inductors is carried out and demonstrated by fabricating inductors on PCB, and (3) design, modeling, and analysis for two novel inductor topologies with magnetic thin films are presented. Followed by the introductory and literature review chapters, in the third chapter, analytical expressions for the DC inductance of four types of 3-D inductors with circular cross-section pillars (CCSP) and rectangular cross-section pillars (RCSP) are derived: (1) a toroid with CCSP; (2) a toroid with RCSP; (3) a solenoid with CCSP; and (4) a solenoid with RCSP. The inductance models are validated against numerical solutions (ANSYS Maxwell and ANSYS Q3D) and measurement results of this work as well as previously published works. The fourth chapter of the thesis focuses on the impact of design parameters such as the number of turns, pitch, height, conductor dimensions, etc. on the Qdc of different 3-D micro air-core inductor configurations. Two well-known traditional inductors are considered for the illustration: the toroid and the solenoid. Solenoid and toroid inductors are fabricated on PCB in 5 mm X 5 mm area to validate the results from Finite Element Analysis (FEA) solutions. Subsequent two chapters explore the design, inductance modeling, and analysis of two novel magnetic core inductor topologies: the fifth chapter presents a novel 3-D spiral inductor structure with magnetic thin films and the sixth chapter introduces a novel inductor structure with a coaxial cross-section of copper conductor and a single layer magnetic thin film core surrounding it. Small-signal performance of the proposed inductors compared with the previously published works to demonstrate their potential for power supply applications; the proposed inductors have the potential to achieve higher figures-of-merit (FOM). A closed-form analytical expression for the inductance, including both air-core (winding) and magnetic core (thin-films) contributions, of the novel inductor structures is derived. Finally, the seventh chapter summarises the research findings. The experimental work in this thesis focused on PCB and silicon inductors. In general, the design, analysis, and characterization methods adapted in the thesis are valid for PCB, in-silicon, and on-silicon inductors.
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    Combined wave, wind, and current simulation in laboratory basins with floating offshore wind turbines
    (University College Cork, 2022-09-16) Otter, Aldert; Murphy, Jimmy; Desmond, Cian; Pakrashi, Vikram; Science Foundation Ireland
    Testing scale models of Floating Offshore Wind Turbines (FOWT) under realistic offshore conditions at scale in wave basins is challenging. There exists a strong coupling between the turbine aerodynamics and platform hydrodynamics, and working in the two different fluid domains of air and water causes a scaling mismatch between Reynolds- and Froude scaling. Furthermore, not every test facility with wave basins has the equipment to generate wind and current to simulate combined environmental loadings. To overcome these challenges a hybrid test method to simulate wind and current was developed for this thesis. Hybrid testing is a combination of real-time numerical modelling and scale model testing. The aerodynamic loads of wind and hydrodynamic loads of currents are calculated in real-time and applied to the FOWT scale model via mechanical actuators. To emulate aerodynamic loads a Multi-Propeller Actuator (MPA) was developed using off-the shelve parts from recreational aerial drones on a custom-made frame. By using several propellers with different thrust directions, multiple aerodynamic loads can be emulated simultaneously, and emulating forces rather than viscous loads solves the scaling mismatch. Aerodynamic loads have been emulated by other researchers with propeller actuators, however, only very few examples of using multiple propellers were found in the literature. The study with the MPA adds to this knowledge gap. A winch actuator was developed to simulate sea currents. By emulating the drag force of a current on the platform of the FOWT, and approximating wave-current interactions by adjusting wave spectra, currents can reliably be simulated. No other examples of this method to simulate current were found, representing a clear knowledge gap. The study with the winch actuator fills this gap in the literature. Both actuators are controlled with a Software-in-the-Loop (SIL) application. This control method uses real-time feedback from a load cell and motion tracking system to update the loads calculation with the real-time numerical simulation for each time-step, improving the accuracy of the simulation. Simulating current with the winch actuator is referred to as SIL current. Experimental results throughout this body of work have been validated with offline numerical simulations using FAST and AQWA. Two validation metrics, developed for this study, have been applied to the results. Experiments with SIL current have also been validated by repeating the experiments with physical current, referred to as the full physical method, and comparing the results of both methods. Both actuators were applied to a 1/50 scale model of the INNWIND semisubmersible platform with the NREL 5 MW as the simulated wind turbine. The results have shown the winch actuator can reliably and accurately emulate the drag force of a current on the FOWT platform and the method to approximate wave-current interactions was found adequate. The results also showed that the MPA can reliably and accurately emulate thrust- and torque loads of the NREL 5 MW turbine. The SIL current and aerodynamics emulation with the MPA, in combination with physical waves, were found suitable to replicate realistic offshore conditions at scale in the wave basin.
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    Challenges in the design of tension moored floating wind turbines
    (University College Cork, 2022) Wright, Christopher S.; Murphy, Jimmy; Pakrashi, Vikram; Science Foundation Ireland
    In order to harness the extensive offshore wind resource, both in Ireland and in many parts of the world with deep offshore seas, the deployment of wind turbines on floating structures is required. Tension moored floating wind turbines are one type of platform with potential to be used for such deployments. These highly constrained platforms offer many benefits but also unique challenges compared against other platform stability types. This thesis investigated the use of such platforms through a combination of numerical simulations and experimental wave basin tank testing. Design improvements in an existing platform, HEXWIND, are identified, leading to the design of a novel platform, TWind. As tension moored platforms are highly constrained in heave, pitch and roll motions, a significant coupling and design complexity is introduced between the wind turbines flexible tower and the pitch/roll motions. The effect of this tower flexibility is parametrised in this work. As tension moored platforms rely on the tendon pretension for stability, operations such as installation and maintenance towing without tendons are statically unstable. Additional float for tow stability are designed and analysed in this work. These floats are designed to become wave energy converters once the platform is installed on site. The structural dynamic and hydrodynamic interaction effects of including these WEC are analysed in detail. Novel survival modes for the WEC floats are proposed. Design considerations related to potential tendon anchor misplacement are also analysed. A platform parameter study has led to a greater understanding of the design effects of modifying the floating concept dimensions. The addition of active WEC on the TMFWT is seen to significantly increase the platform forces and dynamics, with the tower root bending moment doubling compared to the standalone TMFWT. With 100's of GW's of proposed floating offshore wind capacity to be developed this century, the results from this thesis help improve the state of the art in tension moored floating wind design, installation and survivability.
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    Digitisation of industrial data with a view to improving decision making leading to increased efficiency
    (University College Cork, 2022-05) Clancy, Rose; Bruton, Ken
    Industry 4.0 is the fourth stage of the industrial revolution which involves the interconnectedness of products and services, brought about by their digitisation. Industry 4.0 has been criticised regarding its definition and steps for implementation. This research proposes that digitalisation initiatives are conducted to pave the way for organisations in their transition to Industry 4.0. The DMAIC and CRISP-DM methodologies were integrated together in a case study with the purpose of digitising a manufacturing process to enable data-driven decision making leading to process improvement. However, upon implementation of these existing methodologies, there was a lack of tools focused on digitisation specifically. Therefore, the HyDAPI framework was developed, integrating CRISP-DM and DMAIC along with specific tools focused on digitisation, to help managers embark on their digital transformation journey. In line with this, quality management practitioners have yet to reach the potential of digitalisation. One of the objectives of this research was to provide a framework to guide quality practitioners with the implementation of digitalisation in their existing practices. Therefore, the Hybrid Digitalisation Approach to Process Improvement (HyDAPI) framework was proposed to address the emergent need for a digital strategy framework providing a versatile, practical approach for practitioners to follow in implementing digitalisation. The implementation of the proposed HyDAPI framework in an industrial case study was shown to increase efficiency, reduce waste, standardise work and enable the root causation of non-conforming products. The case studies as part of this research focused on the foundry value stream which had a scrap rate of approximately 20% across the year 2020. Analysis was conducted to determine if a relationship existed between manufacturing process parameters and the number of defective parts. The findings from this analysis highlighted that the level of metal ingress scrap was reduced from an average of 0.12 units per batch when SiO2 was at the higher level (average 28.63%) in comparison to the mean of 0.03 units of metal ingress scrap per batch when the SiO2 was at the lower level (average 26.28%). Implementing the HyDAPI framework to digitalise a quality review process resulted in the elimination of 1.9 hours to 3.7 hours per week spent manually gathering data. This research also highlights the requirements for digitalisation found in literature, including advanced skills, organisation structure and organisation agility along with the major barriers to the implementation of digitalisation. The HyDAPI framework was demonstrated to aid organisations in overcoming the barriers to digitalisation. This research also demonstrated how Lean Six Sigma practices can effectively be incorporated to aid the successful implementation of digitalisation and adoption of digital technologies as organisations migrate towards Industry 4.0.
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    Understanding future power system challenges with higher renewables and electrification
    (University College Cork, 2022-01) Mehigan, Laura; Deane, Paul; O'Gallachoir, Brian; Bertsch, Valentin; Science Foundation Ireland
    Urgent action to reduce global greenhouse gas emissions is needed to prevent irreversible damage to the world’s climates. An opportunity exists to decarbonise electricity systems and to aid decarbonisation of heat and transport through electrification. This can only be achieved if electricity systems incorporate significantly higher levels of renewables and can cope with higher electrification. However, achieving this is not without its challenges particularly in the decade to 2030. Failure to make meaningful progress in this crucial decade will reduce the likelihood of meeting the commitments under the Paris Climate Agreement. To solve these challenges, they must first be understood. The central focus of this thesis is to improve the understanding of the challenges faced by future electricity systems with higher Renewable Energy Sources (RES) and higher electrification with an emphasis on the European power sector for the year 2030. The thesis investigates the role of Distributed Generation (DG) in future electricity systems and acknowledges that while the role of DG is important it is not the key determinant of the challenges faced in future electricity systems. The challenge of declining rotational inertia from synchronous generators is investigated and the impact of managing rather than solving this challenge is quantified for every synchronous area in the pan European power system. An exploration of how carbon price influences the role of flexibility providers (batteries and interconnection) in decarbonisation of the European power system for a policy relevant scenario reveals new insights. These insights include the importance of a high carbon price to ensure that flexibility providers reduce emissions while fossil fuels remain in the generation mix, batteries reduce solar curtailment more than interconnection, and interconnection reduces wind curtailment more than batteries. The main contributions of the thesis are the methodological contributions and insights gained into the future challenges from both a synchronous area level and a broader European perspective. The work undertaken as part of this thesis has accelerated discussions on the challenges that will be faced to achieve renewable ambitions in 2030. In particular, this research has contributed to a recent policy decision in Ireland on the need for backup generation in 2030 and during the transition to a decarbonised system.