Scholarly Works - Engineering


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  • ItemPublished versionOpen Access
    THE ‘P’ WORD – Plastic in the UK: practical and pervasive … but problematic
    (2020-10-12) Drewniok, Michal; Cullen, J; Cabrera Serrenho, André; Drewniok, Michal [0000-0003-1491-3401]; Cullen, Jonathan [0000-0003-4347-5025]; Cabrera Serrenho, Andre [0000-0002-0962-0674]
    Plastics are ubiquitous in modern society, owing to their usefulness, durability and how cheap and easy they are to produce. This makes plastics both a blessing and a curse. We manufacture a myriad of plastic materials, used in countless consumer products, which are highly valued by society. Everything from milk bottles to window frames, from sunglasses to face masks, contains plastic. Plastics are pervasive due to their practicality and profitability. And yet, plastics have a problem. The making, use and disposal of plastics creates challenging pollution issues. Significant CO2e (carbon dioxide equivalent) emissions are released across the life-cycle of plastic products and poor disposal means plastic makes its way into our waterways and oceans, creating serious environmental impacts. Fixing this problem is not simple. Even finding good data, on the production, use, disposal and recycling of plastics is challenging. This report tackles this data problem by mapping plastic flows through UK society, collating data from disparate sources on the production, use, disposal and recovery of plastics. With the resulting map of UK plastic flows, we can understand the latest trends in plastics use and identify opportunities for reducing the impacts of plastics in the future. We found that the way we have been disposing of plastics plays a critical role in two serious environmental impacts: greenhouse gas emissions and plastic ocean pollution. These problems arise because plastics are not circular in the UK. Less than 3% of plastics consumed are made of UK recycled plastics, and the vast majority of waste ends up being incinerated, landfilled or exported. Without any action this problem will get worse, as we will generate more plastic waste in coming decades from all the products made of plastic that we have been accumulating. Recycling more plastics in the UK could reduce incineration emissions, avoid mismanagement of exported waste and replace the need for the production of new plastics. However, current UK recycling capacity is only 12% of waste collected, and this is hampering the benefits recycling could provide. There are several other actions we should take, such as reducing excessive use of plastic packaging, and reducing the range of polymers used in various products to improve recycling yields. These should be combined with improved practices in the petrochemical industry, and enhanced reuse and recycling of plastics to achieve a meaningful reduction in greenhouse gas emissions.
  • ItemOpen Access
    Understanding risk in pharmaceutical supply chains
    (2020-05-21) Geyman, Catherine; Settanni, Ettore; Srai, jagjit; Settanni, Ettore [0000-0001-5174-9423]; Srai, Jag [0000-0003-2277-2127]
    The ReMediES (Reconfiguring Medicines End-to-end Supply) project - involving 22 industrial partners comprising global pharmaceutical companies, major contract manufacturing organisations, equipment manufacturers, and logistics specialists – examined future pharmaceutical supply chains supported by novel technology. These technology interventions spanned the end-to-end pharmaceutical supply chain: R&D, Primary Manufacturing, Secondary Manufacturing, and Distribution to patients. The ReMediES project delivered outputs that are captured in Badman and Srai (2018) – see academic references at the end of this document. This briefing sets out the key outputs emerging from the strand of activity linked specifically to the management of pharmaceutical supply risk.
  • ItemPublished versionOpen Access
    Folding of bistable composite tape-springs
    (University of Cambridge, Department of Engineering, 2019-01-31) Wang, Bing; Seffen, Keith; Guest, Simon; Wang, Bing [0000-0002-1480-3301]; Seffen, Keith [0000-0002-7725-0361]; Guest, Simon [0000-0002-0152-6579]
    Bistable composite tape-spring technologies have great potential in application to aircraft landing gears, in order to reduce weight, complexity and maintenance compared to the conventional lock-link assemblies. To investigate their implementation, the first area of interest is the ‘‘ploy’’ region, which corresponds to the transitional state between the folded and the extended configurations. We devise a simple ‘‘free’’ bending system with minimal constraints to study the folding nature of tape-spring structures in general. A finite element (FE) model is also established and calibrated using experimental data; a theoretical model is developed to provide further insights. The typical folding process consists of linear bending, torsional buckling, localisation and then folding; the shape of the central fold is developable; the ploy region is dominated by axial strains and transverse curvature changes. Here, we achieve a good agreement between experiments, simulation and theoretical analysis.
  • ItemOpen Access
    Sequential Monte Carlo Optimisation for Air Traffic Management
    (2015-06-08) Eele, AJ; Maciejowski, JM; Maciejowski, Jan [0000-0001-8281-8364]
    This report shows that significant reduction in fuel use could be achieved by the adoption of `free flight' type of trajectories in the Terminal Manoeuvring Area (TMA) of an airport, under the control of an algorithm which optimises the trajectories of all the aircraft within the TMA simultaneously while maintaining safe separation. We propose the real-time use of Monte Carlo optimisation in the framework of Model Predictive Control (MPC) as the trajectory planning algorithm. Implementation on a Graphical Processor Unit (GPU) allows the exploitation of the parallelism inherent in Monte Carlo methods, which results in solution speeds high enough to allow real-time use. We demonstrate the solution of very complicated scenarios with both arrival and departure aircraft, in three dimensions, in the presence of a stochastic wind model and non-convex safe-separation constraints. We evaluate our algorithm on flight data obtained in the London Gatwick Airport TMA, and show that fuel saving of about 30% can be obtained. We also demonstrate the flexibility of our approach by adding noise-reduction objectives to the problem and observing the resulting modifications to arrival and departure trajectories.
  • ItemPublished versionOpen Access
    Forging Identity: metal shaping people
    (2018) Allwood, Julian; Green, Julius; Tomic, Oggi
  • ItemOpen Access
    Towards end-to-end multi-domain dialogue modelling
    (2018-10-01) Budzianowski, PF; Casanueva, Inigo; Tseng, B-H; Gasic, M; Budzianowski, Pawel [0000-0003-0013-7931]; Gasic, Milica [0000-0003-0318-9147]
  • ItemAccepted versionOpen Access
    Role of boundary conditions in determining cell alignment in response to stretch
    (National Academy of Sciences, 2018-01-30) Deshpande, VS
    he ability of cells to orient in response to mechanical stimuli is essential to embryonic development, cell migration, mechanotrans- duction, and other critical physiologic functions in a range of organs. Endothelial cells, fibroblasts, mesenchymal stem cells, and osteo- blasts all orient perpendicular to an applied cyclic stretch when plated on stretchable elastic substrates, suggesting a common underlying mechanism. However, many of these same cells orient parallel to stretch in vivo and in 3D culture, and a compelling explanation for the different orientation responses in 2D and 3D has remained elusive. Here, we used an experimental system to conduct a series of experiments designed specifically to test the hypothesis that differences in strains transverse to the primary loading direc- tion give rise to the different alignment patterns observed in 2D and 3D cyclic stretch experiments (“strain avoidance”). We found that, in static or low-frequency stretch conditions, cell alignment in fibroblast-populated collagen gels correlated with the presence or absence of a restraining boundary condition rather than with compaction strains. Cyclic stretch could induce perpendicular align- ment in 3D culture but only at frequencies an order of magnitude greater than reported to induce perpendicular alignment in 2D. We modified a published model of stress fiber dynamics and were able to reproduce our experimental findings across all conditions tested as well as published data from 2D cyclic stretch experiments. These experimental and model results suggest an explanation for the ap- parently contradictory alignment responses of cells subjected to cyclic stretch on 2D membranes and in 3D gels.
  • ItemAccepted versionOpen Access
    Prototyping and load testing of thin-shell concrete floors
    (2018-07) Hawkins, WJ; Orr, John; Ibell, Tim; Shepherd, Paul; Benford, Ian; Mueller, C; Adriaenssens, S; Hawkins, William [0000-0003-4918-7665]; Orr, John [0000-0003-2687-6353]; Ibell, Timothy [0000-0002-5266-4832]
    Buildings are being constructed at ever faster rates, fuelled by population growth and urbanisation. The total worldwide floor area of buildings is expected to almost double over the next 40 years, the equivalent of constructing Paris every five days. The majority of the mass and embodied energy (60% to 70%) in a typical multi-storey building structure exists within the floors, making these a primary target for sustainable structural design. In a typical reinforced concrete slab, much of the concrete is assumed to be cracked and therefore not structurally utilised, but nevertheless adds significant weight. This project proposes a radical re-design of concrete floors, using precast textile-reinforced concrete shells with an in-situ foamed concrete fill. By harnessing membrane action, self-weight savings of 62% have been demonstrated for typical spans (compared to traditional flat slabs). This paper discusses the design, optimisation, construction, measurement, analysis and structural testing of two prototype shells, one with and one without foamed concrete fill. The construction accuracy was quantified using digital scanner measurements which were then used as a geometry input for the analysis model. Each shell was loaded both uniformly and asymmetrically to beyond the design loading before failure. The foamed concrete was found to provide only a small increase in strength and stiffness. A design methodology for full-scale, practical application is currently under development.
  • ItemAccepted versionOpen Access
    (Begell House, 2018-04-04) Cant, RS; Bilger, C; Cant, Stewart [0000-0003-1851-6665]
    High-fidelity numerical simulations of spray formation were conducted with the aim of improving fundamental understanding of airblast liquid-film atomization. The gas/liquid interaction in the near-nozzle region is investigated for a multitude of operating conditions in order to extrapolate phenomenological and breakup predictions. To reach this goal, the robust conservative level-set (RCLS) method was used. For a fixed prefilmer geometry, we performed a parametric study on the impact of various liquid and gas velocities on the topological evolution of the liquid interface. The behavior and development of the liquid film is found to be influenced mainly by the relative inertia of the gas and the liquid, the liquid surface tension, and interfacial shear stresses. Preliminary regime maps predicting the prefilming liquid-sheet atomization behavior are constructed based on our numerical results. Three distinct types of “regime” are reported: accumulation, ligament-merging, and three-dimensional wave mode. In addition, these results also show the influence of vortex action and rim-driven dynamics on the breakup mechanism at the atomizer edge. An increase in liquid injection speed leads to the generation of smaller droplets; whereas, an increase in air velocity does not point to one simple conclusion.
  • ItemPublished versionOpen Access
    Neural Machine Translation Decoding with Terminology Constraints
    (Association for Computational Linguistics) Hasler, eva; de Gspert, Adrià; Iglesias, Gonzalo; Byrne, WJ
    Despite the impressive quality improvements yielded by neural machine translation (NMT) systems, controlling their translation output to adhere to user-provided terminology con- straints remains an open problem. We describe our approach to constrained neural decod- ing based on finite-state machines and multi- stack decoding which supports target-side con- straints as well as constraints with correspond- ing aligned input text spans. We demonstrate the performance of our framework on multiple translation tasks and motivate the need for constrained decoding with attentions as a means of reducing misplacement and duplication when translating user constraints.
  • ItemAccepted versionOpen Access
    Static and Dynamic Effects of the Incomplete Ionization in Superjunction Devices
    (Institute of Electrical and Electronics Engineers (IEEE), 2018) Donato, N; Udrea, F; Donato, N [0000-0002-9892-0897]; Udrea, F [0000-0002-7288-3370]
    The incomplete ionization of impurity atoms affects the free carrier concentration of several wide bandgap semiconductor materials even at room temperature, thus modifying the electrical properties of power devices. In this paper, the influence of the partial ionization of the dopants on the static and dynamic behavior of wide bandgap semiconductor based SuperJunction devices has been numerically investigated through extensive 2D finite element simulations. Whereas this physical effect has only a minor impact on the static device’ characteristics, if a reverse bias pulse with a rise time comparable or smaller than the ionization time constant is applied to the structure, a “dynamic ionization” phenomenon can take place. The onset of this time dependent ionization is the cause of charge unbalance effects in the device structure, due to temporal dependence of the activated number of dopants. Electro-thermal simulations, which have been carried out for a 4H-SiC SuperJunction diode, show a non-uniform temperature distribution during the transients which leads, in turn, to the self-heating of the device. Through an accurate redesign of the cross-sectional view of the device, the drawbacks of the incomplete ionization have been mitigated and the device’ performance enhanced.
  • ItemPublished versionOpen Access
    Large Eddy Simulation of a Bluff Body Stabilised Premixed Flame Using Flamelets
    (Springer Nature, 2018) Massey, James C; Langella, Ivan; Swaminathan, N; Massey, James Charles [0000-0003-4585-9866]; Langella, Ivan [0000-0002-2884-9749]; Swaminathan, Swami [0000-0003-3338-0698]
    Large Eddy Simulations of an unconfined turbulent lean premixed flame, which is stabilised behind a bluff body, are conducted using unstrained flamelets as the sub-grid scale combustion closure. The statistics from the simulations are compared with the corresponding data obtained from the experiment and it is demonstrated that the experimental observations are well captured. The relative positioning of the shear layers and the flame brush are analysed to understand the radial variations of the turbulent kinetic energy at various streamwise locations. These results are also compared to confined bluff body stabilised flames, to shed light on the relative role of incoming and shear driven turbulence on the behaviour of the flame brush and the turbulent kinetic energy variation across it.
  • ItemAccepted versionOpen Access
    Liquefaction experiment and analysis projects (LEAP): Summary of observations from the planning phase
    (Elsevier, 2018) Manzari, MT; Ghoraiby, ME; Kutter, BL; Zeghal, M; Abdoun, T; Arduino, P; Armstrong, RJ; Beaty, M; Carey, T; Chen, Y; Ghofrani, A; Gutierrez, D; Goswami, N; Haigh, SK; Hung, WY; Iai, S; Kokkali, P; Lee, CJ; Madabhushi, SPG; Mejia, L; Sharp, M; Tobita, T; Ueda, K; Zhou, Y; Ziotopoulou, K; Haigh, Stuart [0000-0003-3782-0099]; Madabhushi, Gopal [0000-0003-4031-8761]
    The LEAP international collaboratory is introduced and its key objectives and main accomplishments during the planning phase of the US-LEAP (LEAP-2015) are presented. The main theme of LEAP-2015 was lateral spreading of sloping liquefiable soils. A summary of the results of the laboratory element tests performed on the selected soil (Ottawa F-65) is presented. The numerical simulations submitted by several predictors at different stages of the project are compared with the measured responses of sloping deposit specimens tested in a rigid box at six different centrifuge facilities around the world. The comparisons are presented for three rounds of simulations labeled here as types A, B, and C simulations. The type A simulations involved the response of the soil specimen to a prescribed base excitation with a maximum amplitude of 0.15. g (Motion #2). Comparisons of the numerical simulations with the experimental results show that a sub-set of type A simulations were in reasonably good agreement with the responses measured in the reference centrifuge experiment. The predictors subsequently assessed the performance of their type A simulations by comparing them to the measured responses, made the necessary adjustments in their models, and conducted a type B simulation of the response of the same soil specimen subjected to an amplified base excitation with a maximum amplitude of 0.25. g (Motion #4). In these type B simulations, the achieved base motions were used and the simulations showed an improved correlation with the experimental results. The predictors also conducted a type C simulation of the original test (Motion #2) using the base motions achieved on the six centrifuge facilities. The results showed very good agreement with the experimental results.
  • ItemPublished versionOpen Access
    Magnetization of YBCO film with ac travelling magnetic waves of relatively short wavelengths
    (AIP, 2017-02-13) Wang, W; Coombs, T; Coombs, Timothy [0000-0003-0308-1347]
    © 2017 Author(s). The magnetizations of the YBCO film with ac travelling magnetic waves of relatively short wavelengths were studied. The results have verified that the reported “intermediate value” of the superconducting current density [Wang et al., Appl. Phys. Lett. 104(3), 032602 (2014)] was caused by the existence of multiple transition regions in the sample: the magnetic poles induce ±JC in the pole regions, which produces two transition regions within each wavelength λ ( +JC→−JC→+JC, and vice versa, while the symbol → indicates the transition region). The current densities in the transition region are with intermediate values, which are smaller than the critical value. In case of relatively short wavelength, there are multiple transition regions, which occupy a large fraction of the YBCO sample with intermediate current values. Moreover, the wavelike current distributions might help explain the flux transportation and dc output voltage in HTS flux pump.
  • ItemPublished versionOpen Access
    Response heterogeneity: Challenges for personalised medicine and big data approaches in psychiatry and chronic pain
    (F1000 Research Ltd, 2018-01-15) Norbury, AE; Seymour, Ben; Norbury, Agnes [0000-0002-4377-3164]; Seymour, Benjamin [0000-0003-1724-5832]
    Response rates to available treatments for psychological and chronic pain disorders are poor, and there is a considerable burden of suffering and disability for patients, who often cycle through several rounds of ineffective treatment. As individuals presenting to the clinic with symptoms of these disorders are likely to be heterogeneous, there is considerable interest in the possibility that different constellations of signs could be used to identify subgroups of patients that might preferentially benefit from particular kinds of treatment. To this end, there has been a recent focus on the application of machine learning methods to attempt to identify sets of predictor variables (demographic, genetic, etc.) that could be used to target individuals towards treatments that are more likely to work for them in the first instance. Importantly, the training of such models generally relies on datasets where groups of individual predictor variables are labelled with a binary outcome category − usually ‘responder’ or ‘non-responder’ (to a particular treatment). However, as previously highlighted in other areas of medicine, there is a basic statistical problem in classifying individuals as ‘responding’ to a particular treatment on the basis of data from conventional randomized controlled trials. Specifically, insufficient information on the partition of variance components in individual symptom changes mean that it is inappropriate to consider data from the active treatment arm alone in this way. This may be particularly problematic in the case of psychiatric and chronic pain symptom data, where both within-subject variability and measurement error are likely to be high. Here, we outline some possible solutions to this problem in terms of dataset design and machine learning methodology, and conclude that it is important to carefully consider the kind of inferences that particular training data are able to afford, especially in arenas where the potential clinical benefit is so large.
  • ItemPublished versionOpen Access
    Comparison of permutationally invariant polynomials, neural networks, and Gaussian approximation potentials in representing water interactions through many-body expansions.
    (AIP, 2018-06-28) Nguyen, Thuong T; Székely, Eszter; Imbalzano, Giulio; Behler, Jörg; Csányi, Gábor; Ceriotti, Michele; Götz, Andreas W; Paesani, Francesco
    The accurate representation of multidimensional potential energy surfaces is a necessary requirement for realistic computer simulations of molecular systems. The continued increase in computer power accompanied by advances in correlated electronic structure methods nowadays enables routine calculations of accurate interaction energies for small systems, which can then be used as references for the development of analytical potential energy functions (PEFs) rigorously derived from many-body (MB) expansions. Building on the accuracy of the MB-pol many-body PEF, we investigate here the performance of permutationally invariant polynomials (PIPs), neural networks, and Gaussian approximation potentials (GAPs) in representing water two-body and three-body interaction energies, denoting the resulting potentials PIP-MB-pol, Behler-Parrinello neural network-MB-pol, and GAP-MB-pol, respectively. Our analysis shows that all three analytical representations exhibit similar levels of accuracy in reproducing both two-body and three-body reference data as well as interaction energies of small water clusters obtained from calculations carried out at the coupled cluster level of theory, the current gold standard for chemical accuracy. These results demonstrate the synergy between interatomic potentials formulated in terms of a many-body expansion, such as MB-pol, that are physically sound and transferable, and machine-learning techniques that provide a flexible framework to approximate the short-range interaction energy terms.
  • ItemAccepted versionOpen Access
    Phase-field study of electrochemical reactions at exterior and interior interfaces in Li-ion battery electrode particles
    (Elsevier, 2016-12-01) Zhao, Y; Xu, BX; Stein, P; Gross, D; Zhao, Ying [0000-0002-6439-1843]
    To study the electrochemical reaction on surfaces, phase interfaces, and crack surfaces in lithium ion battery electrode particles, a phase-field model is developed which describes fracture in large strains and anisotropic Cahn–Hilliard-Reaction. Thereby the concentration-dependency of the elastic properties and the anisotropy of diffusivity are also considered. The implementation in 3D is carried out by the isogeometric finite element method in order to treat the higher order terms in a straightforward manner. The electrochemical reaction is modeled through a modified Butler–Volmer equation to account for the influence of the phase change on the reaction on exterior surfaces. The reaction on the crack surfaces is considered through a volume source term weighted by a term related to the fracture order parameter. Based on the model, three characteristic examples are considered to reveal the electrochemical reactions on particle surfaces, phase interfaces, and crack surfaces, as well as their influence on the particle material behavior. The results show that both the anisotropy and the ratio between the timescales of reaction and diffusion can have a significant influence on the phase segregation behavior. In turn, the distribution of the lithium concentration strongly influences the reaction on the surface, especially when the phase interfaces appear on exterior surfaces or crack surfaces. The reaction rate increases considerably at phase interfaces due to the large lithium concentration gradient. Moreover, the simulations demonstrate that the segregation of a Li-rich and a Li-poor phase during delithiation can drive the cracks to propagate. The results indicate that the model can capture the electrochemical reaction on the freshly cracked surfaces.
  • ItemAccepted versionOpen Access
    Effect of Fan on Inlet Distortion: Mixed-fidelity Approach
    (American Institute of Aeronautics and Astronautics, 2018-06-01) Ma, Y; Cui, Jiahuan; Vadlamani, Nagabhushana; Tucker, Paul; Ma, Yunfei [0000-0003-0363-7376]; Vadlamani, Rao [0000-0002-8468-5216]; Tucker, Paul [0000-0002-0874-3269]
    Inlet distortion is typically encountered during off-design conditions on civil aircraft and in S-ducts in military aircraft. It is known to cause severe deterioration to the performance of a gas-turbine engine. As intakes become shorter, there is an increased interaction between the inlet distortion and the downstream fan. Previous studies in the literature use Reynolds-averaged Navier–Stokes or unsteady Reynolds-averaged Navier–Stokes to model this unsteady interaction, due to the substantial computational cost associated with high-fidelity methods such as large-eddy simulation/direct numerical simulation. On the other hand, it is well known that turbulence models have limitations in terms of predicting distorted flows. In this paper, a mixed-fidelity approach is proposed and employed to study the intake–fan interaction at an affordable computational cost. The results demonstrate that there are two mechanisms via which the fan affects the separated flow. First, the suction effect of the fan (effective up to almost half of the chord length upstream of the fan) alleviates the undesired distortion by “directly” changing the streamline curvature, intensifying the turbulence transport and closing the recirculation bubble much earlier. Second, the enhanced turbulence in the vicinity of the fan feeds back into the initial growth of the shear layer by means of the recirculating flow. This “indirect” feedback is found to increase turbulence production during the initial stages of formation of the shear layer. Both the direct and indirect effects of the fan significantly suppress the inlet distortion.
  • ItemAccepted versionOpen Access
    Pre-chamber ignition mechanism: Experiments and simulations on turbulent jet flame structure
    (Elsevier BV, 2018) Allison, PM; de Oliveira, M; Giusti, A; Mastorakos, E; Mastorakos, Epaminondas [0000-0001-8245-5188]
    This work investigates the effects of premixed combustion kinematics in pre-chamber volumes on the development of emitted hot jets from the igniter. The effects of fuel type, orifice diameter, and ignition location are evaluated experimentally, with high-speed OH* and CH* chemiluminescence imaging, and computationally with Large-Eddy Simulations (LES). The imaging experiments allowed for simultaneous viewing of combustion processes within a quartz chamber and of the developing jet flow. Results from these experiments provided insight on the temporal evolution of the jet relative to the growth of an ignited kernel within the chamber, as well as information on the emission or lack of emission of radical species from the chamber. Computational results provided data on the temporal behavior of the pressure within the chamber and profiles of the high velocity flow through the orifice. These results, combined, have shown that dependent on the strain rate and effective orifice size, local quenching of radical species at the orifice occurs which fundamentally change whether hot products, reactive layers, or both are present in the turbulent jet emission. The dynamic structure and composition of the turbulent jet controls its relevance as an effective ignition source.
  • ItemAccepted versionOpen Access
    Numerical Simulation and Analysis of a Saturated-Core-Type Superconducting Fault Current Limiter
    (Institute of Electrical and Electronics Engineers (IEEE), 2017) Jia, Y; Ainslie, MD; Hu, D; Yuan, J; Ainslie, Mark [0000-0003-0466-3680]