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  • Computational fluid dynamics modelling of unconfined gas mixing of wastewater sludge in a full scale anaerobic digester

    Dapelo, Davide; Bridgeman, John (2015-09)
    In this paper, an Euler-Lagrange model for computational fluid dynamics was used to model a full-scale gas-mixed anaerobic digester. The flow profiles, local values of non-Newtonian viscosity and average shear rate were analysed. Recommendations to enhance the effectiveness of mixing were given. In particular, the gas mixing input power can be reduced without appreciable detrimental effects on the mixing effectiveness.
  • Analytical solution of suspended sediment concentration profile: relevance of dispersive flow term in vegetated channels

    Huai, W.; Yang, L.; Guo, Yakun (2020-07)
    Simulation of the suspended sediment concentration (SSC) has great significance in predicting the sediment transport rate, vegetation growth and the river ecosystem in the vegetated open channel flows. The present study focuses on investigating the vertical SSC profile in the vegetated open channel flows. To this end, a model of the dispersive flux is proposed in which the dispersive coefficient is expressed as partitioned linear profile above or below the half height of vegetation. The double-averaging method, i.e. time-spatial average, is applied to improve the prediction accuracy of the vertical SSC profile in the vegetated open channel flows. The analytical solution of SSC in both the submerged and the emergent vegetated open channel flows is obtained by solving the vertical double-averaging sediment advection-diffusion equation. The morphological coefficient, a key factor of the dispersive coefficient, is obtained by fitting the existing experimental data. The analytically predicted SSC agrees well with the experimental measurements, indicating that the proposed model can be used to accurately predict the SSC in the vegetated open channel flows. Results show that the dispersive term can be ignored in the region without vegetation, while the dispersive term has significant effect on the vertical SSC profile within the region of vegetation. The present study demonstrates that the dispersive coefficient is closely related to the vegetation density, the vegetation structure and the stem Reynolds number, but has little relation to the flow depth. With a few exceptions, the absolute value of the dispersive coefficient decreases with the increase of the vegetation density and increases with the increase of the stem Reynolds number in the submerged vegetated open channel flows.
  • Flexural performance of concrete beams reinforced with steel–FRP composite bars

    Ge, W.; Wang, Y.; Ashour, Ashraf F.; Lu, W.; Cao, D. (2020-05-16)
    Flexural performance of concrete beams reinforced with steel–FRP composite bar (SFCB) was investigated in this paper. Eight concrete beams reinforced with different bar types, namely one specimen reinforced with steel bars, one with fiber-reinforced polymer (FRP) bars and four with SFCBs, while the last two with hybrid FRP/steel bars, were tested to failure. Test results showed that SFCB/hybrid reinforced specimens exhibited improved stiffness, reduced crack width and larger bending capacity compared with FRP-reinforced specimen. According to compatibility of strains, materials’ constitutive relationships and equilibrium of forces, two balanced situations, three different failure modes and balanced reinforcement ratios as well as analytical technique for predicting the whole loading process are developed. Simplified formulas for effective moment of inertia and crack width are also proposed. The predicted results are closely correlated with the test results, confirming the validity of the proposed formulas for practical use.
  • Flexural Performance of Steel Reinforced ECC-Concrete Composite Beams Subjected to Freeze–Thaw Cycles

    Ge, W.; Ashour, Ashraf F.; Lu, W.; Cao, D. (2020-02-17)
    Experimental and theoretical investigations on the flexural performance of steel reinforced ECC-concrete composite beams subjected to freeze–thaw cycles are presented in this paper. Four groups of reinforced composite beams with different ECC height replacement ratios subject to 0, 50, 100 and 150 cycles of freeze–thaw were physically tested to failure. Experimental results show that the bending capacity decreases with the increase of freeze–thaw cycles regardless of ECC height replacement ratios. However, the ultimate moment, stiffness and durability of ECC specimens and ECC-concrete composite specimens are greater than those of traditional concrete specimens, owing to the excellent tensile performance of ECC materials. With the increase of ECC height, the crack width and average crack spacing gradually decrease. According to materials’ constitutive models, compatibility and equilibrium conditions, three failure modes with two boundary failure conditions are proposed. Simplified formulas for the moment capacity are also developed. The results predicted by the simplified formulas show good agreement with the experimental moment capacity and failure modes. A parametric analysis is conducted to study the influence of strength and height of ECC, amount of reinforcement, concrete strength and cycles of freeze–thaw on moment capacity and curvature ductility of ECC-concrete composite beams.
  • Interactive Fusion and Tracking For Multi‐Modal Spatial Data Visualization

    Elshehaly, Mai; Gračanin, D.; Gad, M.; Elmongui, H.G.; Matković, K. (2015-06)
    Scientific data acquired through sensors which monitor natural phenomena, as well as simulation data that imitate time‐identified events, have fueled the need for interactive techniques to successfully analyze and understand trends and patterns across space and time. We present a novel interactive visualization technique that fuses ground truth measurements with simulation results in real‐time to support the continuous tracking and analysis of spatiotemporal patterns. We start by constructing a reference model which densely represents the expected temporal behavior, and then use GPU parallelism to advect measurements on the model and track their location at any given point in time. Our results show that users can interactively fill the spatio‐temporal gaps in real world observations, and generate animations that accurately describe physical phenomena.
  • Characterisation of dissolved organic matter to optimise powdered activated carbon and clarification removal efficiency

    Shutova, Y.; Rao, N.R.H.; Zamyadi, A.; Baker, A.; Bridgeman, John; Lau, B.; Henderson, R.K. (2020)
    The character of dissolved organic matter (DOM) present in drinking water treatment systems greatly impacts its treatability by coagulation–flocculation. Powdered activated carbon dosing has been suggested to enhance DOM removal when combined with coagulation–flocculation. However, optimising powdered activated carbon (PAC) dosing requires further research. In this study, fluorescence spectroscopy combined with parallel factor analysis (PARAFAC) and liquid chromatography with organic carbon detection (LC–OCD) has been used to characterise DOM removal in three ways: (a) coagulation–flocculation–sedimentation without PAC dosing, (b) PAC dosing prior to- and (c) PAC dosing during coagulation–flocculation–sedimentation treatment. It was shown that only coagulation–flocculation–sedimentation preferentially removed biopolymer and humic substance chromatographic fractions and fluorescent DOM, whereas dosing PAC preferentially removed building blocks and low molecular weight neutral chromatographic fractions. The DOM treatability that was achieved when PAC was dosed both prior to- and during coagulation–flocculation–sedimentation was comparable, but higher than what was achieved without any PAC dosing. Introduction of PAC to the coagulation–flocculation–sedimentation process significantly improved DOM removal, with fluorescent components removed by 97%. This study also highlights that a combination of fluorescence spectroscopy and LC–OCD is essential to track the removal of both, fluorescent and non-fluorescent DOM fractions and understand their impacts on DOM treatability when using different treatment processes. Overall, lower residual DOM concentrations were obtained in the treated water when PAC adsorption and the coagulation–flocculation–sedimentation processes were combined when compared to treating the water with only one of the processes, despite differences in source water character of DOM.
  • Euler-Lagrange Computational Fluid Dynamics simulation of a full-scale unconfined anaerobic digester for wastewater sludge treatment

    Dapelo, Davide; Bridgeman, John (2018-03)
    For the first time, an Euler-Lagrange model for Computational Fluid Dynamics (CFD) is used to model a full-scale gas-mixed anaerobic digester. The design and operation parameters of a digester from a wastewater treatment works are modelled, and mixing is assessed through a novel, multi-facetted approach consisting of the simultaneous analysis of (i) velocity, shear rate and viscosity flow patterns, (ii) domain characterization following the average shear rate value, and (iii) concentration of a non-diffusive scalar tracer. The influence of sludge’s non-Newtonian behaviour on flow patterns and its consequential impact on mixing quality were discussed for the first time. Recommendations to enhance mixing effectiveness are given: (i) a lower gas mixing input power can be used in the digester modelled within this work without a significant change in mixing quality, and (ii) biogas injection should be periodically switched between different nozzle series placed at different distances from the centre.
  • A combined experimental and numerical approach to the assessment of floc settling velocity using fractal geometry

    Moruzzi, R.B.; Bridgeman, John; Silva, P.A.G. (2020-03)
    Sedimentation processes are fundamental to solids/liquid separation in water and wastewater treatment, and therefore a robust understanding of the settlement characteristics of mass fractal aggregates (flocs) formed in the flocculation stage is fundamental to optimized settlement tank design and operation. However, the use of settling as a technique to determine aggregates’ traits is limited by current understanding of permeability. In this paper, we combine experimental and numerical approaches to assess settling velocities of fractal aggregates. Using a non-intrusive in situ digital image-based method, three- and two-dimensional fractal dimensions were calculated for kaolin-based flocs. By considering shape and fractal dimension, the porosity, density and settling velocities of the flocs were calculated individually, and settling velocities compared with those of spheres of the same density using Stokes’ law. Shape analysis shows that the settling velocities for fractal aggregates may be greater or less than those for perfect spheres. For example, fractal aggregates with floc fractal dimension, Df ¼ 2.61, floc size, df > 320 μm and dp ¼ 7.5 μm settle with lower velocities than those predicted by Stokes’ law; whilst, for Df ¼ 2.33, all aggregates of df > 70 μm and dp ¼ 7.5 μm settled below the velocity calculated by Stokes’ law for spheres. Conversely, fractal settling velocities were higher than spheres for all the range of sizes, when Df of 2.83 was simulated. The ratio of fractal aggregate to sphere settling velocity (the former being obtained from fractal porosity and density considerations), varied from 0.16 to 4.11 for aggregates in the range of 10 and 1,000 μm, primary particle size of 7.5 μm and a three-dimensional fractal dimension between 2.33 and 2.83. However, the ratio decreases to the range of 0.04–2.92 when primary particle size changes to 1.0 μm for the same fractal dimensions. Using the floc analysis technique developed here, the results demonstrate the difference in settlement behaviour between the approach developed here and the traditional Stokes’ law approach using solid spheres. The technique and results demonstrate the improvements in understanding, and hence value to be derived, from an analysis based on fractal, rather than Euclidean, geometry when considering flocculation and subsequent clarification performance
  • Self-supervised monocular image depth learning and confidence estimation

    Chen, L.; Tang, W.; Wan, Tao Ruan; John, N.W. (2020-03-14)
    We present a novel self-supervised framework for monocular image depth learning and confidence estimation. Our framework reduces the amount of ground truth annotation data required for training Convolutional Neural Networks (CNNs), which is often a challenging problem for the fast deployment of CNNs in many computer vision tasks. Our DepthNet adopts a novel fully differential patch-based cost function through the Zero-Mean Normalized Cross Correlation (ZNCC) to take multi-scale patches as matching and learning strategies. This approach greatly increases the accuracy and robustness of the depth learning. Whilst the proposed patch-based cost function naturally provides a 0-to-1 confidence, it is then used to self-supervise the training of a parallel network for confidence map learning and estimation by exploiting the fact that ZNCC is a normalized measure of similarity which can be approximated as the confidence of the depth estimation. Therefore, the proposed corresponding confidence map learning and estimation operate in a self-supervised manner and is a parallel network to the DepthNet. Evaluation on the KITTI depth prediction evaluation dataset and Make3D dataset show that our method outperforms the state-of-the-art results.
  • Influence of type of granulators on formation of seeded granules

    Kitching, V.R.; Rahmanian, Nejat; Jamaluddin, N.H.; Kelly, Adrian L.; CCIP grant (Collaboration, Capacity and IP Develop-ment) fund from the University of Bradford. (2020-08)
    It has been shown that seeded granules of calcium carbonate can be produced in commercial batch high shear granulators such as the Cyclomix high-shear impact mixer. Seeded granules are attractive to the pharmaceutical industry due to their high uniformity and good mechanical properties which can assist efficient tablet manufacture. In the current study, attempts to produce seeded granules of Durcal 65 and PEG 4000 binder using hot melt granulation are reported, in response to the recent shift towards continuous pharmaceutical manufacturing. Various screw configurations and rotation speeds were investigated in a series of experiments to determine the relationship between process conditions and granule properties. Particle size analysis, strength measurement and structural characterisation were used to quantify granule properties. It was found that using a series of kneading elements arranged at a 60° staggering angle located near to the feed section of the extruder screw generated strong, spherical granules. From structural characterisation approximately 5–15% of extruded granules were found to be seeded. Twin screw melt granulation is therefore considered to be a promising technique for continuous production of seeded granules, although a more detailed investigation is required to optimise yield and quality.
  • The rise of crypto-ransomware in a changing cybercrime landscape: Taxonomising countermeasures

    Connolly, Lena Y.; Wall, D.S. (Elsevier, 2019-11)
    Year in and year out the increasing adaptivity of offenders has maintained ransomware's position as a major cybersecurity threat. The cybersecurity industry has responded with a similar degree of adaptiveness, but has focussed more upon technical (science) than ‘non-technical’ (social science) factors. This article explores empirically how organisations and investigators have reacted to the shift in the ransomware landscape from scareware and locker attacks to the almost exclusive use of crypto-ransomware. We outline how, for various reasons, victims and investigators struggle to respond effectively to this form of threat. By drawing upon in-depth interviews with victims and law enforcement officers involved in twenty-six crypto-ransomware attacks between 2014 and 2018 and using an inductive content analysis method, we develop a data-driven taxonomy of crypto-ransomware countermeasures. The findings of the research indicate that responses to crypto-ransomware are made more complex by the nuanced relationship between the technical (malware which encrypts) and the human (social engineering which still instigates most infections) aspects of an attack. As a consequence, there is no simple technological ‘silver bullet’ that will wipe out the crypto-ransomware threat. Rather, a multi-layered approach is needed which consists of socio-technical measures, zealous front-line managers and active support from senior management.
  • Information Security Behavior: A Cross-Cultural Comparison of Irish and US Employees

    Connolly, Lena Y.; Lang, M.; Wall, D.S. (Taylor & Francis, 2019-08-09)
    This study explores how aspects of perceived national culture affect the information security attitudes and behavior of employees. Data was collected using 19 semi-structured interviews in Ireland and the United States of America (US). The main findings are that US employees in the observed organizations are more inclined to adopt formalized information security policies and procedures than Irish employees, and are also more likely to have higher levels of compliance and lower levels of non-compliance.
  • Pier Scour Prediction in Non-Uniform Gravel Beds

    Pandey, M.; Olivetto, G.; Pu, Jaan H.; Sharma, P.K.; Ojha, C.S.P. (MDPI, 2020-06-13)
    Pier scour has been extensively studied in laboratory experiments. However, scour depth relationships based on data at the laboratory scale often yield unacceptable results when extended to field conditions. In this study, non-uniform gravel bed laboratory and field datasets with gravel of median size ranging from 2.7 to 14.25 mm were considered to predict the maximum equilibrium scour depth at cylindrical piers. Specifically, a total of 217 datasets were collected: 132 from literature sources and 85 in this study using new experiments at the laboratory scale, which constitute a novel contribution provided by this paper. From the analysis of data, it was observed that Melville and Coleman’s equation performs well in the case of laboratory datasets, while it tends to overestimate field measurements. Guo’s and Kim et al.’s relationships showed good agreements only for laboratory datasets with finer non-uniform sediments: deviations in predicting the maximum scour depth with non-uniform gravel beds were found to be significantly greater than those for non-uniform sand and fine gravel beds. Consequently, new K-factors for the Melville and Coleman’s equation were proposed in this study for non-uniform gravel-bed streams using a curve-fitting method. The results revealed good agreements between observations and predictions, where this might be an attractive advancement in overcoming scale effects. Moreover, a sensitivity analysis was performed to identify the most sensitive K-factors.
  • Nano/micro-structures and mechanical properties of ultra-high performance concrete incorporating graphene with different lateral sizes

    Dong, S.; Wang, Y.; Ashour, Ashraf F.; Han, B.; Ou, J. (Elsevier, 2020-10)
    The performance of cement-based materials can be controlled and tailored by adjusting the characteristics of reinforced nano inclusions. Therefore, the lateral size effect of graphene on the nano/micro-structures of ultra-high performance concrete (UHPC) was explored, and then the mechanical properties were investigated to analyze the structure–property correlation of composites in this paper. The test results show that due to nucleation site effect and the formation of core–shell elements, incorporating graphene with lateral size of > 50 µm improves the polymerization degree and mean molecule chain length of C-S-H gel by 242.6% and 56.3%, respectively. Meanwhile, the porosity and average pore volume of composites is reduced by 41.4% and 43.4%. Furthermore, graphene can effectively inhibit the initiation and propagation of cracks by crack-bridging, crack-deflection, pinning and being pulled-out effect, and the wrinkling characteristic is conductive to the enhancement of pinning effect. These improvements on nano- and micro- structures result in that the compressive strength, compressive toughness and three-point bending modulus of UHPC are increased by 43.5%, 95.7% and 39.1%, respectively, when graphene with lateral size of > 50 µm and dosage of 0.5% is added. Compared to graphene with lateral size of > 50 µm, graphene with average lateral size of 10 µm has less folds and larger effective size, then reducing the distance between core–shell elements. Hence, the addition of graphene with average lateral size of 10 µm leads to 21.1% reduction for Ca(OH)2 crystal orientation index, as well as 30.0% increase for three-point bending strength. It can be, therefore, concluded that the lateral size of graphene obviously influences the nano/micro-structures of UHPC, thus leading to the significantly different reinforcing effects of graphene on mechanical behaviors of UHPC.
  • Analytical and experimental investigations of dam-break flows in triangular channels with wet-bed conditions

    Wang, B.; Liu, X.; Zhang, J.; Guo, Yakun; Chen, Y.; Peng, Y.; Liu, W.; Yang, S.; Zhang, F. (2020-05-19)
    Based on the method of characteristics, an analytical solution for the one-dimensional shallow-water equations is developed to simulate the instantaneous dam-break flows propagating down a triangular wet bed channel in this study. The internal relationships between the hydraulic properties associated with the dam-break flow are investigated through the comparisons with the well-known analytical solutions for rectangular channels. Meanwhile, laboratory experiments are conducted in a prismatic, horizontal and smooth flume with a triangular cross-section. The non-intrusive digital image processing is applied for obtaining water surface profiles and stage hydrographs. Results show that the dam-break flow propagation depends on the dimensionless parameter defined as the ratio of initial tailwater depth over reservoir head. has significant effect on the dam-break wave in the downstream flooded area. For , the water surface profiles in the reservoir for different at a given time remains similar. For ≥ 0.5, extra negative waves occur in the reservoir, leading to the water surface undulations. Undular bores are generated at the dam site and propagate downstream. Time evolution of dam-break flows under three different reservoir heads is similar for the same . The inception of water surface profile change is earlier when the reservoir head is larger. The analytical model shows satisfactory agreement with the experimental results though some errors exist between the analytical solution and measurements due to the formation of extra negative waves, jet and undular bores. The similarities and discrepancies between the hydraulics in the triangular and rectangular channels are identified analytically in terms of the profiles of water depth, velocity, discharge, bore height and wave-front celerity with . The presented solution could be applied to predict the effect of wet bed condition on the dam-break wave in triangular channels, while laboratory measurement data could be used for validating analytical and numerical models.
  • Numerical simulation of the hydraulic performances and flow pattern of swallow-tailed flip bucket

    Zhang, L.; Zhang, J.; Guo, Yakun; Peng, Y. (2020-05-14)
    In this study, the evolution process of the swallow-tailed flip bucket water nappe entering into the plunge pool is simulated by using the standard 𝑘-𝜀 turbulence model and the volume of fluid method. The effects of the upstream opening width ratio and downstream bucket angle on the flow pattern, the unit discharge distribution and the impact pressure distribution are studied. Based on the numerical results, the inner and outer jet trajectories are proposed by using the data. Results show that the longitudinal stretching length decreases with the increase of the upstream opening width ratio, and increases with the increase of the downstream bucket angle. The water nappe enters the plunge pool in a long strip shape. Thus, the unit discharge distribution of water nappe entry is consistent with the pressure distribution at the plunge pool bottom. The upstream opening width ratio and downstream bucket angle should be chosen as their intermediate values in order to have a uniform discharge distribution and to reduce the pressure peak at the plunge pool floor, which is effectively to avoid instability and destruction of plunge pool floor.
  • Investigation of open channel flow with unsubmerged rigid vegetation by the lattice Boltzmann method

    Jing, H.; Cai, Y.; Wang, W.; Guo, Yakun; Li, C.; Bai, Y. (2020)
    Aquatic vegetation can significantly affect flow structure, sediment transport, bed scour and water quality in rivers, lakes, reservoirs and open channels. In this study, the lattice Boltzmann method is applied for performing the two dimensional numerical simulation of the flow structure in a flume with rigid vegetation. A multi-relaxation time model is applied to improve the stability of the numerical scheme for flow with high Reynolds number. The vegetation induced drag force is added in lattice Boltzmann equation model with the algorithm of multi-relaxation time in order to improve the simulation accuracy,. Numerical simulations are performed for a wide range of flow and vegetation conditions and are validated by comparing with the laboratory experiments. Analysis of the simulated and experimentally measured flow field shows that the numerical simulation can satisfactorily reproduce the laboratory experiments, indicating that the proposed lattice Boltzmann model has high accuracy for simulating flow-vegetation interaction in open channel.
  • Uncertainty relations in terms of the Gini index for finite quantum systems

    Vourdas, Apostolos (2020-04)
    Lorenz values and the Gini index are popular quantities in Mathematical Economics, and are used here in the context of quantum systems with finite-dimensional Hilbert space. They quantify the uncertainty in the probability distribution related to an orthonormal basis. It is shown that Lorenz values are superadditive functions and the Gini indices are subadditive functions. The supremum over all density matrices of the sum of the two Gini indices with respect to position and momentum states is used to define an uncertainty coefficient which quantifies the uncertainty in the quantum system. It is shown that the uncertainty coefficient is positive, and an upper bound for it is given. Various examples demonstrate these ideas.
  • Steam consumption minimization using genetic algorithm optimization method: an industrial case study

    Alabdulkarem, A.; Rahmanian, Nejat (2020)
    Condensate stabilization is a process where hydrocarbon condensate recovered from natural gas reservoirs is processed to meet the required storage, transportation, and export specifications. The process involves stabilizing of hydrocarbon liquid by separation of light hydrocarbon such as methane from the heavier hydrocarbon constituents such as propane. An industrial scale back-up condensate stabilization unit was simulated using Aspen HYSYS software and validated with the plant data. The separation process consumes significant amount of energy in form of steam. The objectives of the paper are to find the minimum steam consumption of the process and conduct sensitivity and exergy analyses on the process. The minimum steam consumption was found using genetic algorithm optimization method for both winter and summer conditions. The optimization was carried out using MATLAB software coupled with Aspen HYSYS software. The optimization involves six design variables and four constraints, such that realistic results are achieved. The results of the optimization show that savings in steam consumption is 34% as compared to the baseline process while maintaining the desired specifications. The effect of natural gas feed temperature has been investigated. The results show that steam consumption is reduced by 46% when the natural gas feed temperature changes from 17.7 to 32.7°C. Exergy analysis shows that exergy destruction of the optimized process is 37% less than the baseline process.

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