Open Research Exeter - University of Exeter
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Modelling flow dynamics and suspended sediment deposition patterns around patches of rigid emergent vegetation using a porosity-based two-dimensional hydromorphodynamic numerical model
No full textRivers and floodplains are complex, dynamic environments characterised by pronounced spatial heterogeneity, with the exchange of water and sediment controlling the construction, preservation, and destruction of fluvial landforms over time. These environments support a wide range of dead and living vegetation, including rigid emergent vegetation which is characterised by its inflexible stems which grow above the water surface. Vegetation such as this both responds to the prevailing environmental conditions, and modifies and modulates geomorphic processes, thus exerting significant control over landform dynamics. Over the past several decades, significant advances in computing power have enabled researchers to investigate the interactions between rigid emergent vegetation and hydrogeomorphic processes at scales ranging from individual stems, through to the reach-scale morphological evolution of vegetated river-floodplain systems over thousands of years.
In this study, an existing two-dimensional physics-based hydromorphodynamic numerical model is modified using a porosity-based approach to represent the blockage and roughness effects of rigid emergent vegetation patches in open channel flow. The performance of this model, and its sensitivity to parameterisation, is comprehensively evaluated using results obtained from laboratory-scale experiments conducted by other researchers, in which simple spatial distributions of vegetation patches were considered. The evaluated model is then used to simulate the flow field and suspended sediment deposition patterns around complex spatial distributions of vegetation patches typically not investigated in laboratory experiments or numerical modelling studies.
In the first chapter, the state of current scientific knowledge and understanding of the relationships between rigid emergent vegetation and hydrogeomorphic processes is discussed, and opportunities for improving our knowledge and understanding in this field are identified. The research objectives and questions of this study are then outlined.
In the second chapter, the model development process is first outlined, detailing how the numerical model was modified to represent the blockage and roughness effects of rigid emergent vegetation. Further modifications which enabled the model to simulate laboratory-scale experiments conducted in a recirculating flume, in order to evaluate its performance and sensitivity, are then outlined. The approaches used to analyse the model simulations performed in this study are subsequently discussed.
In the third chapter, the performance of the model, and its sensitivity to the parameterisation of the streamwise and cross-stream grid cell resolution, is evaluated. The regular structured grid was found to be highly sensitive to refinement in the cross-stream direction due to the importance of representing the flow acceleration between pairs of vegetation patches, and the associated impacts on the development of the wake zones downstream. The model performed optimally on finer resolution grids, but was unable to accurately simulate the flow field around pairs of small diameter patches separated by small interpatch distances.
In the fourth chapter, the performance of the revised model, and its sensitivity to the parameterisation of the bulk vegetation drag coefficient used in the surface roughness law, is evaluated. The modelled flow field was found to be highly sensitive to this coefficient, with the model performance significantly improving when this parameter was calculated dynamically at each timestep according to the solid vegetated fraction of each grid cell and its associated instantaneous flow velocity. It was suggested that a more sophisticated turbulence closure may improve the model performance further in those regions of the channel where significant flow velocity gradients exist.
In the fifth chapter, the performance of the revised model, and its sensitivity to the parameterisation of the critical velocity threshold for deposition and the deposition efficiency constant, is evaluated. The modelled suspended sediment deposition patterns were highly sensitive to parameterisation, particularly in respect of the deposition efficiency constant because this controlled the deposition rate independently of the flow velocity. The model performed optimally when simulating pairs of dense patches separated by large interpatch distances, and it was suggested that an alternative deposition function, such as one based on turbulence, may improve the model performance further.
In the sixth chapter, the revised model is parameterised with the optimal grid cell resolution, bulk vegetation drag coefficient equation, critical velocity threshold for deposition, and the deposition efficiency constant, to simulate the flow field and suspended sediment deposition patterns around complex spatial distributions of vegetation patches. An increase in the number of patches led to a reduction in the mean flow velocity in the channel due to development of low velocity wake zones downstream of each patch. Increasing the patch density did not significantly affect the overall mean flow velocity, although at the patch-scale, lower density patches exhibited higher patch interior and exit velocities. In addition, as the fraction of the channel width occupied by vegetation decreased, the variability in mean flow velocity was also found to diminish because patches were more frequently located within the wake zones of their upstream neighbours. The total suspended sediment deposition also decreased with increasing patch abundance, with considerably greater variability when the channel was occupied by a large number of patches, which may have implications on the way in which deposition is calculated in coarse resolution models.
This study demonstrates that an optimally parameterised two-dimensional physics-based hydromorphodynamic numerical, with a fine resolution regular structured grid and a porosity-based approach to representing the blockage and roughness effects of vegetation, is able to represent the key responses of the flow field and suspended sediment deposition patterns to the presence of rigid emergent vegetation patches. Ultimately, the model was found to be sensitive to parameterisation, but was able to simulate a wide range of complex spatial distributions of vegetation patches typically not investigated in laboratory experiments or numerical modelling studies
Numerical Investigation of Thermal Management Strategies for Lithium-Ion Batteries Using Phase Change Materials and Hybrid Cooling Systems
No full textThis thesis provides an extensive numerical analysis of thermal management systems (BTMS) for lithium-ion (Li-ion) batteries, with the goal of enhancing thermal performance and safety in electric vehicles. The study investigates a variety of cooling approaches, including air-cooling, liquid-cooling, PCM-cooling, and thermoelectric cooling, to analyse their effectiveness and efficiency using extensive simulations and analyses.
In this study, a thorough examination of current BTMS designs has been conducted, emphasising the need for novel methods to overcome the thermal issues associated with Li-ion batteries. Using the Lattice Boltzmann Method (LBM), the study models the PCM melting process under magnetohydrodynamic (MHD) forces. The findings show that MHD forces greatly improve heat transfer control within battery packs, resulting in better overall thermal management.
In the next chapter of thesis, the incorporation of boundary detection techniques into LBM simulations, which addresses the issues provided by complicated geometries. This approach allows for more accurate and reliable modelling of honeycomb-inspired designs, indicating that hexagonal PCM containers with thermally conductive fins greatly improve heat transmission and shorten phase shift durations.
The study also investigates the use of graphite in hybrid BTMS, which combines cold plate and air-cooling systems. The results show that graphite's strong thermal conductivity provides uniform temperature distribution within the battery pack, improving its performance, safety, and longevity. The examination into thermoelectric cooling (TEC) systems coupled with PCM and porous media reveals significant efficiency increases, indicating that optimal TEC placement can further improve cooling performance and energy efficiency.
This thesis contributes significantly to the field of battery thermal management by:
•Providing a comprehensive review of recent BTMS advancements.
•Introducing novel computational methods for optimising PCM and MHD effects.
•Demonstrating the effectiveness of biomimetic honeycomb-inspired designs.
•Highlighting the benefits of high-conductivity materials like graphite.
•Highlighting the potential of thermoelectric cooling in hybrid BTMS.
The findings provide important insights for designing enhanced BTMS for Li-ion batteries, overcoming present constraints, and optimising thermal performance under a variety of operating circumstances. Future research directions include investigating hybrid cooling strategies, assessing long-term performance in real-world conditions, and developing sustainable BTMS materials.
Keywords: battery thermal management system, Computational Fluid Dynamics (CFD), Lattice Boltzmann Method (LBM), phase change materials (PCM), magnetohydrodynamic forces, graphite integration, thermoelectric cooling.</p
Pupils’ perceptions and experiences of ‘fundamental British values’: maintaining, (re)producing and challenging hierarchies of citizenship
No full textSchools are conceived as critical sites in preparing children for citizenship, equipping them with the knowledge, skills and values required to contribute to society. This focus on preparation for citizenship means that childhood is viewed as an interim and inferior stage in the journey to adulthood.
Within education, if a primary goal is to develop ‘future’ citizens of the nation, the duty on schools to promote ‘fundamental British values’ speaks to this goal in its stated aim to prepare pupils for life in modern Britain. However, this duty has been met with substantial criticisms including its consequences for rendering schools sites that exclude and silence pupils.
This thesis explores pupils’ perceptions and experiences of FBV across three primary schools in the South West of England. As a qualitative study, employing ethnographic and participatory methods, it presents the views of children and adults on and school practices of FBV and its respective values: democracy, rule of law, individual liberty, and mutual respect and tolerance of those with different faiths and beliefs. This study addresses the concerns regarding FBV by attending to the limited empirical knowledge in this area, particularly in pupils’ conceptions of the values.
Its findings highlight FBV’s role in maintaining, (re)producing and potentially challenging inequalities, marginalisations and domination in schools and wider society. In discourses and practices of FBV collectively and individually pupils’ participation as citizens is currently limited. These limitations largely result from the status of children in society; however, across childhood, there are further hierarchies of citizenship. These hierarchies result from intersecting classed and racialised framings in relation to spatial belonging, mobilities and attachments. Understanding and engaging with these hierarchies is achieved through the combined application of Pierre Bourdieu’s analytical tools on the reproduction of inequalities alongside Frantz Fanon’s theory of the internalisation of (racial) inferiority. These theories are applied within an overarching postcolonial approach to highlight and counter the ongoing role of colonial logics in the structured and psychosocial dimensions shaping citizenship practice
Life stories of people with post-stroke aphasia: A narrative study
No full textBackground
People are natural storytellers and the narratives we tell ourselves and other people are how we construct our identities and make meaning from the events in our lives. Serious illness, and other challenging experiences, call for a particular need to tell stories to make sense of what has happened and adapt our future trajectories and plans. The onset of aphasia is associated with high levels of psychological distress whilst also impeding an individual’s ability to use language to process trauma. Clinicians need to know more about the successful adjustment to living with aphasia and how best to support this process.
Method
Narrative analysis was used to examine biographic interviews elicited from 15 participants with mild/moderate aphasia, initially based on the Listening Guide approach: listening for plot, the voice of I and contrapuntal voices. Additional analysis examined broad themes, attending to talk and adaptation to aphasia.
Key findings
Storylines were recapitulated and plot types were categorised: Comedy (10); Romance (2) and Tragedy (3). Broad themes relevant to identity were: Loss of/ changing identity, Agency and competence, Masculine identity and the Assimilation of aphasia as part of self. Types of positive talk and indicators of both positive and negative adjustment were also identified.
Discussion
People with aphasia use narrative to reshape their identity and repair the damage that has been done to their sense of self. Clinicians can assist psychosocial adjustment by supporting people with aphasia to tell their story, nurturing their sense of agency and encouraging positive framing
From linear to circular: Capabilities, defensive reasoning, and supply chain collaborations in manufacturers' circular economy transition
No full textManufacturers in developing countries face challenges during their transition to the circular economy (CE) due to rapid industrialisation, resource constraints, and the need to balance economic development with sustainability. These conditions provide valuable context for understanding the complexities of CE adoption. This study investigates the critical capabilities required, the impact of defensive reasoning, and the role of supply chain collaboration in overcoming challenges to CE adoption. Using a multiple-case research design and insights from 38 interviews with six manufacturers, the study examines their transition through organisational learning theory. Initially, manufacturers engage in 'single-loop learning,' focusing on circular design, risk monitoring, and resource optimisation strategies. However, defensive reasoning— stemming from concerns over costs and disruptions—emerges as a major obstacle. In response, manufacturers shift to 'double-loop learning,' which re-evaluates their value propositions and business models. This shift is essential in overcoming resistance and enabling sustainable practices. The research highlights the pivotal role of supply chain collaboration, illustrating how it catalyses overcoming challenges to CE adoption. By emphasising organisational learning, this study contributes to the broader discourse on CE adoption in developing countries, showcasing how learning processes enable sustainable practices that align with global goals despite local challenges.</p
Urban herring gull behaviour and its development
No full textAlthough herring gulls are well known for urban-living, their behaviour within urban environments has not been as well researched as their behaviour in more rural areas. In this thesis, I investigate whether wild herring gulls show differing levels of object neophilia in experimental presentations of a common and novel anthropogenic object across urban-rural gradient (Chapter 2). I did not find clear evidence of object neophilia as the environmental context was influential, in which increasing human presence increased vigilance and non-participation. I considered whether early-life experience could influence later-life behaviour and urban use in the formation of dietary preferences in captive-reared herring gull chicks (Chapter 3). I demonstrate that despite contrary experimental diets of terrestrial and marine-sourced foods, herring gull chicks predominantly prefer fish. Next, I investigated individual variations in urban-facilitating behaviours within and among captive reared chicks over their development (Chapter 4). I tested whether behavioural responses to novel objects and people were consistent over time and found that individuals were still flexible in their behavioural responses, with only aggression towards human handlers considered a consistent behavioural trait. In Chapter 5, I GPS-tracked captive-reared and wild juvenile herring gulls' movement and behaviour as a first for the UK. I tested whether differences in early-life experience would affect the dispersal and ecology of juveniles’ behaviour, particularly with regard to the use of (sub)urban areas. I demonstrate that GPS-tracking of juvenile herring gulls is possible with no apparent effect on survival or sighting likelihood. Over the 12-month study period, we found that rescued and wild juveniles do show differences in their behavioural ecology, although all juveniles visited and avoided the same habitats. Rescue juveniles showed larger home ranges and a preference for more rural habitat use than wild juveniles, but they did show more active classified behaviours within urban areas than wild juveniles. Interestingly, all juveniles did not venture far out to sea and would remain coastal or inland, with rescued juveniles showing less use of inland saltwater areas. These juveniles’ behaviour contrasts with previous studies of adult herring gulls. Collectively, my findings highlight the importance of increasing our understanding of individual behavioural responses, and the need to research the impact of escalating anthropogenic change within all animal life history stages in order to conserve biodiversity and continue our coexistence
The m-step Solvable Mono-anabelian Geometry of Number Fields
No full textIn 1970’s, it was proven by Neukirch and Uchida that number fields are determined up to isomorphism by their absolute Galois groups which is known
as the Neukirch-Uchida theorem. A pro-solvable version of the Neukirch-Uchida theorem was proven by Uchida in 1976. However, the structures of
the Galois groups considered in both cases are unknown. In 2019, Saïdi
and Tamagawa proved an m-step (for suitable positive integer m) solvable
version of the Neukirch-Uchida theorem. In particular, they proved that number fields are determined up to isomorphism by the maximal 3-step solvable
quotients of their absolute Galois groups.
However, all results above do not provide a group-theoretic algorithm to
reconstruct a number field from their (various quotients of) absolute Galois
groups. In 2021, Hoshi established a group-theoretic algorithm, to reconstruct a number field (together with its maximal pro-solvable extension) from
the maximal pro-solvable quotient of its absolute Galois group.
The goal of this thesis is to develop a group-theoretic algorithm, to reconstruct a number field (together with its maximal m-step solvable extension)
from the maximal m+6-step solvable quotient of its absolute Galois group.
If K is an imaginary quadratic field or Q, we establish a group-theoretic reconstruction of K from the maximal 3-step solvable quotient of its absolute
Galois group.
Furthermore, we proved that an open continuous homomorphism between
the maximal m+3-step solvable quotients of absolute Galois groups of number fields determines an open continuous homomorphism between the corresponding maximal m-step solvable quotients that arises from field embedding
if and only if it is compatible with the cyclotomic characters
Cracks Beneath the Surface: The Intersection of Mild Traumatic Brain Injury and PTSD in the UK Police Force and General Population
No full textThis doctoral thesis examines the co-occurrence of Persistent Post-Concussion Symptoms (PPCS),, PTSD and
complex PTSD (C-PTSD) following mTBI. We explore how “dosage” of injury may
influence outcomes by comparing individuals with a history of multiple mTBIs, a
single mTBI, and no TBI. The research begins with a systematic review and meta-
analysis to estimate the pooled prevalence of PTSD in civilian TBI samples and
identifies key correlates of PTSD after TBI. This was followed by a large cross-
sectional study in a community-based sample of the general population, examining
the relationship between mTBI, PPCS and PTSD/C-PTSD. A second cross-sectional study exploring PPCS and PTSD/C-PTSD was then
conducted in a national sample of UK police officers, a population with a high risk of
both TBI and psychological trauma. A final study employing machine learning
techniques was then conducted to identify a subgroup of police officers endorsing
more severe symptomatology and explore symptom patterns that may contribute
towards such outcomes. The research is presented across four studies, each
structured for publication</p
Promoting and advertising tourism resorts in the UK 1914–1918: A re-appraisal
No full textModern day resort advertising can be traced to the Edwardian period but its role in the First World War remains terra incognita, with most studies of tourism overlooking the 1914-18 period citing a lack of data or its cessation due to war. This paper represents a shift in thinking by demonstrating that resort promotion and advertising and visitation continued. The study has international significance, illustrating how modern day sources of tourist information (e.g. Official Destination Guides) were created and popularised in the pre- and wartime period. The study also offers lessons for policymakers, reconstructing how destination stakeholders responded to an extreme crisis, through collaboration, cooperation and political lobbying to ensure locales with a dependence on tourism remained resilient destinations. The responses evident in this study are also observed in subsequent studies as the First World War was the first major crisis at a global scale that the expanding tourism sector faced.</p