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Modelling and analysis of gyroid-based compact heat exchangers
Full text linkThermal management is a growing challenge for modern aircraft. Onboard Thermal Management Systems (TMS) must content with both external heating and internal heat loads. To meet these challenges, TMS rely heavily on Compact Heat Exchangers (CHEs). This thesis explores the design and performance of gyroid-based CHEs. Enabled by advances in Additive Manufacturing (AM), gyroid structures--classified as Triply Periodic Minimal Surfaces (TPMS)--offer high surface area-to-volume ratios and a continuous, interwoven geometry well-suited for dual-stream devices. Using Computational Fluid Dynamics (CFD), this work models such devices across a wide range of operating conditions, providing insight into the viability of gyroid-based designs for TMS.
To establish a foundation, a validated CFD framework is developed using a two-dimensional representation of a traditional wavy-fin plate-fin CHE to assess the impact of various numerical modelling assumptions. It is found that representative hydraulic and thermal performance of a full-scale wavy-fin HE can be recovered, with significantly reduced computational cost, by simulating periodic flow and heat transfer in a 2D wavy-fin test section, as validated against experimental correlations from the literature across a wide range of Reynolds numbers (20 < Re < 5500).
A practical model for evaluating the performance of gyroid-based CHEs was developed by simulating a three-dimensional gyroid test section defined by periodic length (L) and offset parameter (R), which control unit cell size and wall thickness, respectively. The model captures both steady and unsteady effects and is validated against larger-domain simulations, transient solutions, and published data. Based on this framework, two parametric studies were performed, yielding original empirical correlations for the Fanning friction factor (f) and Chilton-Colburn J-factor (j) over 5 < L < 40 mm, 0 < R < 0.6 mm, and 20 < Re < 8000. These correlations quantify sensitivity to geometric variation and offer a predictive tool for integrating gyroid-based CHEs into TMS.
A conjugate cross-flow heat exchanger model was developed to more realistically represent a gyroid-based CHE. This approach captures key physical effects such as transverse mixing and inter-stream thermal interaction, which were absent in the previous approach.
To investigate novel solutions for flow maldistribution--a core challenge in CHE design--this thesis evaluates the gyroid’s ability to self-correct under asymmetry conditions and benchmarks it against a sinusoidal-channel HE. The gyroid’s interconnected structure redistributes non-uniform inflow within 2–3 unit cells, improving outlet uniformity by 16.5% and maintaining thermal-hydraulic performance within 4% across 150 < Re < 8000. In contrast, the sinusoidal geometry, characterised by disconnected flow paths, exhibited significant performance variability under the same conditions. This previously unreported behaviour highlights the gyroid’s suitability for systems where flow maldistribution is unavoidable and active correction impractical.
Finally, the potential of multi-directional geometric grading in gyroid-based heat exchangers was explored through two warp-based strategies, contracting and expanding the core center. While grading altered local flow and pressure due to changes in density and path tortuosity, thermal performance remained largely unchanged (< 0.6% variation). Both strategies increased pressure drop (7.3% contracted, 4.6% expanded), reducing overall thermo-hydraulic efficiency. Although these strategies did not improve performance, they demonstrate the potential of geometric grading as a tool for targeted flow control in gyroid-based CHEs.
Overall, this thesis advances the understanding of gyroid-based CHEs. Empirical correlations for performance are developed in relation to the geometric parameters. In addition, gyroid-specific behaviours relevant to real-world challenges have been investigated. Collectively, these findings offer valuable insight into the viability of gyroid-based designs for integration into TMS
Neanderthal Growth and Development: A Survey
Full text linkThis thesis examines growth in size and morphological change with age in Neanderthal
subadults. A catalogue and extended descriptions of the most informative individuals are
provided. Some of the thesis is purely descriptive, but the subject is also approached from a life-history perspective and further draws upon brain and neurocranial development as well as the essential field of dental development.
Dental and skeletal attainment of Neanderthal subadults must be evaluated against
chronological age, in some cases available from counts of dental microstriae. Growth studies of modern humans are referenced as a guide to growth processes, likely to apply to closely related species, and modern standards allow comparisons with Neanderthals.
Information from the physiological and dental fields and neuroscience is brought to
bear on the question whether Neanderthals grew to adulthood more rapidly than living Homo sapiens, and main conclusions are as follows.
Brain growth affects timing of stages of ontogeny. Neanderthal endocranial volume
range coincides with modern human range, which implies similar effects for both.
From infancy Neanderthals exhibited skeletal apomorphies which became more
pronounced with age. By modern schedules subadults were dentally advanced but postcranially were small and grew slowly. By modern standards of percentage of adult size, using Neanderthal values, subadults were not skeletally advanced for their ages.
There is therefore an apparent dissociation between dental and skeletal/somatic growth
rates in Neanderthals, in contrast to Homo ergaster, in which both systems are accelerated. Hypotheses regarding the dissociation are explored.
Rapid growth in recent humans is found to result principally from adequate or abundant
nutrition and is therefore not always a sign of “live fast die young” life history. Ethnographical research suggests that even if adulthood were attained in fewer years the acquisition of subsistence and social skills would not be constrained
An Acoustic Velocity Vector Based Approach to Robotic Pipeline Inspection
Full text linkWater loss due to damaged, pressurised pipelines is a significant and ongoing problem in the UK and across most of the world. As of 2022, over 20% of treated water in the UK was lost due to leaks, barely improving on loss rates in 1995. This thesis aims to diagnose some of the causes of current issues with leak detection and suggest an improved methodology.
A comprehensive review identified several areas within the leak detection sphere worth investigation: acoustic propagation and attenuation in plastic pipes, the variability in leak-generated noise, and moving beyond monoaxial sensing, given that this captures only a fraction of the available acoustic information. Motivated by these findings, experimental and numerical studies were undertaken considering the propagation and attenuation of sound in plastic pipes and examining the influence of features such as joints, corners, and burial conditions. Results showed that attenuation was strongly frequency dependent, with higher frequencies attenuating considerably over short distances, limiting the viability of traditional correlation-based leak localisation methods for plastic networks.
To address these challenges, this work explores the novel use of acoustic velocity vector sensors (AVVSs) on an in-pipe platform for defect detection. Numerical models demonstrated that radial components of the acoustic velocity are particularly sensitive to small wall defects, while the pressure and axial velocity showed no deviation from background levels close to the defects. This prediction was confirmed experimentally using an AVVS on a test pipe. A robotic platform carrying multiple AVVSs further validated the feasibility of this approach.
This research establishes acoustic vector sensing as a promising new diagnostic method for pressurised water pipes, allowing smaller and incipient leaks to be detected and laying the groundwork for intelligent, mobile in-pipe monitoring systems that can enhance predictive and preventative maintenance of critical infrastructure
Characterisation of Near-field Blast Loading
No full textThe near-field is the period of contact between the explosively generated fireball and shock-wave, prior to detaching. Loading is of extreme pressures, short timescales and subject to variability of specific impulse in terms of both spatial distribution and magnitude. Assessment of near-field loading requires evaluation of magnitude, spatial distribution and variability, including how each is affected by scaled distance.
An experimentally driven study, characterising near-field blast loading from spherical charges across five scaled distances of 0.17-1.03 m/kg1/3 is presented. The methodology utilises digital image correlation to determine full field spatial resolution of structural response and loading data. An approach to inferring specific impulse from the velocity uptake of the plate is demonstrated and assessed.
Loading data is presented as a series of specific impulse distributions, characterising the magnitude, shape profile and variability. The results of all tests fit to a bell-shaped trend of centrally normalised specific impulse, which forms the basis of a two-part rapid predictor of near-field loading. This model is validated against experimental results and compared with other fast-running models. Loading variability is rigorously assessed and shown to be greater at scaled distances less than 0.5~m/kg m/kg1/3. An investigation of early-time features in the loading reveals they do not directly influence the spread in loading magnitude. However, it is noted that greater temporal resolution within the data may reveal the effect that time of arrival has on the loading imparted across the plate.
This thesis characterises near-field loading magnitude at a spatial resolution that is not viable with direct measurement techniques across scaled distances of 0.17-1.03 m/kg1/3. Furthermore, it has provided tools with which a blast engineer can rapidly predict the loading a protective structure must withstand when exposed to close proximity explosive events
Exploring adolescent engagement in physical activity: Insights from junior parkrun and underserved communities
No full textBackground
Adolescent physical activity is critical for physical, mental, and social well-being, yet participation rates remain low, particularly in socioeconomically deprived areas. These disparities contribute to long-term health inequalities, making physical activity promotion a public health priority. This study investigated factors influencing adolescent participation in junior parkrun, a community-based initiative aimed at addressing such disparities. This research focuses on socioeconomically deprived areas to better understand barriers and facilitators to participation, providing insights for improving health equity.
Methods
A mixed-methods approach incorporated quantitative and qualitative data. Participation data from parkrun and junior parkrun events were analysed to identify trends and demographic characteristics. Semi-structured interviews and focus groups with adolescents, parents, and community stakeholders explored perceived barriers and facilitators to participation. Observations of junior parkrun events offered contextual understanding. Data analysis included descriptive statistics, thematic analysis, and integrated interpretation of findings to compare case study sites.
Results
Findings revealed significant socioeconomic disparities in participation patterns, with lower involvement among adolescents from more socioeconomically deprived areas. Key barriers included logistical challenges (such as transport and scheduling), digital exclusion, and local trust and cultural perceptions related to physical activity. Facilitators highlighted the role of community support, accessible venues, and inclusive programming. Comparisons between case studies identified localised influences, such as differences in event organisation and community engagement, impacting participation.
Conclusions
Despite persistent inequalities in participation, community-based initiatives like junior parkrun can help address adolescent health disparities. However, barriers must be tackled to maximise impact. Findings underscore the need for tailored strategies to remove obstacles and enhance facilitators in socioeconomically deprived areas. Results contribute to evidence supporting policies and interventions that promote equitable physical activity access, improving adolescent health outcomes and reducing disparities
Designing and Implementing Efficient and Secure Hardware Primitives for ML-KEM
No full textThe transition to post-quantum cryptography (PQC) has become a critical urgency in securing digital communications against the emerging threat of quantum computing. The Module-Lattice Key Encapsulation Mechanism (ML-KEM), formerly known as CRYSTALS-KYBER and recently standardised by National Institute of Standards and Technology (NIST) as the primary PQC algorithm for key encapsulation mechanism, offers strong theoretical security guarantees but poses significant implementation challenges in terms of efficient and secure implementation. This thesis presents the design, optimisation, and verification of efficient and secure hardware polynomial multipliers for ML-KEM, with a focus on performance, area efficiency, and resistance to side-channel and fault injection attacks. Towards this goal, the residue number system (RNS) and the redundant residue number system (RRNS) were considered as efficient and inherently secure methods of implementation.
Firstly, a high-speed number theoretic transform (NTT)-based polynomial multiplier for ML-KEM is presented. The proposed architecture uses RNS to accelerate the main operation in the NTT, i.e., integer modular multiplication. The design uses read only memory (ROM)-based architecture to implement the RNS design and is integrated with an efficient memory access to form a hardware accelerator on a Field Programmable Gate Array (FPGA), yielding a significant improvement over state-of-the-art results. Secondly, an RNS NTT-based polynomial multiplier for ML-KEM is presented. The RNS methodology is extended to the whole polynomial multiplication of ML-KEM for efficiency and side-channel protection. The results of the FPGA implementation and experimental side-channel leakage evaluation show an efficient implementation and effectiveness in protecting against side-channel leakage. Thirdly, a fault detection architecture for the polynomial multiplication of ML-KEM is proposed. The design utilises the RRNS and is applied to the polynomial multiplication of ML-KEM. The proposed method can detect single faults in RRNS residues with 100% error coverage and the FPGA implementation results show minimal area and time overhead
Hong Kong People and the Sino-British Joint Declaration, 1978-1984
Full text linkIn the early 1980s, British and Chinese officials engaged in confidential, bilateral negotiations over the future of Hong Kong. These talks produced the 1984 Sino-British Joint Declaration under which Britain agreed to hand Hong Kong to China in 1997, effectively marking the end of the British Empire. In the existing literature, the Sino-British negotiations have been examined the perspective of diplomacy and interactions between officials. The role of Hong Kong people in influencing the talks has gone almost entirely unnoticed.
This thesis examines how Hong Kong people attempted to influence British, Chinese and colonial officials during the Sino-British negotiations. It ranges across different segments of Hong Kong society including businesspeople, the Governor’s appointed advisors, representative bodies, pressure groups, student unions, residents’ associations and more. It identifies successful and unsuccessful attempts to shape the negotiations, examines why some Hong Kong people were effective while others were not, and traces the influence of Hong Kong people on the Joint Declaration.
This thesis contributes to the literature on Hong Kong’s handover by examining the underexplored yet pivotal role played by Hong Kong people. In so doing, it adds to research on the influence of the citizens of colonies on processes of decolonisation, international negotiation and diplomacy. In recent years, at least a million Hong Kong people have shown their dissent towards the implementation of the Joint Declaration through protests. An officially mandated version of Hong Kong’s history is writing over the colonial past and placing primary sources at threat of destruction. This thesis is therefore a timely re-examination of the Sino-British negotiations that puts Hong Kong people at the centre of the most pivotal event in their city’s history
Understanding the formation of the "Great Atlantic Sargassum Belt"
Full text linkThe aim of this thesis is to develop a Lagrangian particle tracking model to explore the
2011 formation of the ’Great Atlantic Sargassum Belt’ (GASB). A new population of free-
floating Sargassum was discovered approximately 20 degrees south of its existing source,
the North Atlantic Subtropical Gyre, also known as the Sargasso Sea. This new population
blooms within the Equatorial Atlantic and flows into coastal waters within the Caribbean
Sea, creating a multitude of environmental and socioeconomic issues.
Firstly, I produced a particle tracking model to simulate Sargassum transport across the
North Atlantic Ocean ±7 years around the anomalous initial bloom of the GASB. Simu-
lations demonstrated an increase in particle transport between the Sargasso Sea and the
Equatorial Atlantic in 2010/2011 when the residual transport from waves (Stokes drift)
was included in the advection field and that the transport path includes the not previously
considered Azores Current.
Next, I added a Sargassum biological model to the particle tracking outputs to explore
along-trajectory changes in biomass to those Sargassum particles that formed the GASB.
Enhanced growth rates were observed within the path of particle trajectories, indicative
of an upwelling event within that region. Results were able to further support that the
GASB was formed due to an anomalous transport event rather than an extreme bloom of
an existing population.
Lastly, I dived deeper into the GASB interannual variability by applying the Sargassum
biological model to a simple box model of the Equatorial Atlantic. Outputs of the box
model were able to determine that variability in GASB biomass was significantly linked
to phosphate availability
Computational Evaluation, characterization and screening of materials and molecules for sustainable applications
Full text linkComputational simulation is wildly used for materials evaluation, characterization and property prediction, playing a critical role in advancing material science. In this thesis, we focus on three sustainable applications: suppression of lignin repolymerization, CO2 adsorption, and photocatalytic CO2 conversion, approached from a computational aspect. Density Functional Theory (DFT) was used to evaluate and characterize an initial set of candidate molecules and materials. We developed and applied a systematic computational framework that integrates chemical model construction, target property evaluation, reaction pathway analysis, performance differentiation, and high-throughput screening. This multiscale approach enabled the identification of promising cation scavengers for biomass pretreatment, functional molecules and MOFs with enhanced CO₂ binding affinities, and photocatalysts with suitable band structures and reaction energetics for solar-driven CO₂ conversion.
Our results not only provide insight into the underlying structure-property relationships but also offer valuable guidance for experimental validation and future material design aimed at sustainable development and carbon mitigation
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