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Computational fluid dynamics (CFD) modelling has made significant contributions to the analysis and treatment of obstructive sleep apnoea (OSA). While several investigations have considered the flow field within the airway and its effect on airway collapse, the effect of breathing on the pharynx region is still poorly understood. We address this gap via a combined experimental and numerical study of the flow field within the pharynx and its impacts upon airway collapse. Two 3D experimental models of the upper airway were constructed based upon computerised tomography scans of a specific patient diagnosed with severe OSA; (i) a transparent, rigid model for flow visualisation, and (ii) a semi-flexible model for understanding the effect of flow on pharynx collapse. Validated simulation results for this geometry indicate that during inhalation, negative pressure (with respect to atmospheric pressure) caused by vortices drives significant narrowing of the pharynx. This narrowing is strongly dependent upon whether inhalation occurs through the nostrils. Thus, the methodology presented here can be used to improve OSA treatment by improving the design methodology for personalised, mandibular advancement splints (MAS) that minimise OSA during sleep.

At present, most multiscale simulation approaches to model the temperature evolution of the molten pool, and the resulting microstructure evolution for selective laser melting, assume an equilibrium freezing range and steady state solidification conditions. This is despite the solidification conditions being observed to be highly unsteady and non-equilibrium. These two assumptions lead to inaccurate predictions of the temperature evolution of the molten pool and thus microstructure predictions. To demonstrate this, an approach to scale-bridging computational models of the laser additive manufacturing process is presented, in which the temperature history is passed from a macroscale molten pool simulation to a microscale phase-field simulation. This linkage is achieved by volume mapping of the temperature field from the grid of the molten pool simulation to the grid of the microstructure simulation. To describe the system evolution at the scale of the molten pool, a computational fluid dynamics (CFD) method that captures the laser–metal interaction, vapour production, gas recoil pressure, fluid flow, surface tension, Marangoni flow, and heat conduction, convection, and radiation is applied. To capture the chemical kinetics of the phase-transition, a non-equilibrium CALPHAD-integrated phase-field (PF) model is applied. The discrepancy between the predictions of the solid front isotherm is quantified as ⩾ 100 K for an Al-10Si alloy under the large observed cooling rate. This leads to a spatial discrepancy in the solidification front between the CFD model, which assumes equilibrium freezing behaviour, and the PF model, which does not, of approximately 10 µm over 50 µs in the present case. Under these conditions, present formulations of multiphase CFD cannot accurately predict the solidification behaviour because of the assumption of equilibrium at the solid–liquid interface. Strategies for reconciling this discrepancy for materials that exhibit rapid solidification under large thermal undercooling will need to be developed for multiscale simulation of additive manufacturing to advance.

Enhanced natural gas recovery (EGR) with supercritical (sc)CO2 sequestration offers the prospect of increased natural gas recovery. High-fidelity reservoir simulations offer a method to quantify the risk of contamination of produced gas by the injected scCO2. Simulations of scCO2 mixing with the reservoir gas have been reported; however the effects of connate water on EGR have not been effectively explored. We extend a prior EGR simulation tool (Patel, May and Johns, 2016; Ref. [1]) to incorporate connate water accounting for its effect on dispersivity and permeability; chemical equilibrium is modelled using a novel, computationally efficient Lagrange multiplier-based approach. The code is applied to a ‘quarter five-spot’ benchmark scenario. The inclusion of connate water generally resulted in a reduction in breakthrough time and a decrease in methane recovery. The connate water's largest effect was to change the scCO2 flow field, which sank towards the reservoir floor, flooded the lowermost accessible layers and entered the production well via a high throughput channel (‘coning’). The magnitude of these effects were, however, sensitive to well perforation depth, the influence of which was subsequently studied systematically. Well perforation depth was found to determine the duration of these sinking and coning events in a non-linear manner.

Australia is a major exporter of wheat to South East (SE) Asia. Much of this wheat is low protein, fails in standard bake tests and is not traded as bread wheat. Some SE Asian bakeries observed that these doughs spread too significantly to be usable on current bread manufacturing lines. However, high-spread doughs are suited to sheeting lines and can produce high quality products. For confirmation, a pilot-scale dough sheeting line was constructed consisting of four roll-stands and a folder/lapper. Rollers were fitted with sensors to measure roll forces and dough sheet thicknesses. The first roll stand was also used to test flours for dough rheology. The sensors captured flour effects on dough flow quality during sheeting (‘sheetability’). The offline dough rheology data correlated with ‘online’ dough sheetability. The Australian flour doughs flowed more steadily through the roll stands than conventional bread doughs and also produced high quality sandwich breads.

EGR (Enhanced natural gas recovery) with CO2 sequestration offers the prospect of significant environmental and economic benefits by increasing gas recovery while simultaneously sequestering the greenhouse gas. Field-scale deployment is currently limited as the risks of contamination of the produced gas by injected CO2 are poorly understood. Reservoir simulations offer a method to quantify the risk but only if sufficiently accurate. For the first time, finite element simulations are presented for several EGR scenarios that incorporate the most accurate models available for fluid mixture and rock properties. Specifically, the GERG-2008 EOS (equation of state) is utilised to describe the supercritical fluid mixture's density, as are reference correlations linked to the most accurate experimental data available for diffusivity and viscosity. Realistic values for rock dispersivity and tortuosity determined from high-accuracy core-flooding and NMR (nuclear magnetic resonance) experiments were also integrated. The relative impacts of these properties were investigated for a benchmark layered reservoir with a quarter 5-spot well pattern. Recovery efficiency at different CO2 injection rates was also investigated and was determined to be the dominant consideration: a 100-fold rate increase improved recovery from 53% to 69% while CO2 breakthrough time decreased by less than expected. Collectively, these results emphasise the importance of accurate reservoir simulations for EGR.

Dough extension tests are used in industry to rate flours for dough processability. The results impact flour selection for product use. Previously, it was shown that dough extension data correlated poorly with dough sheetability irrespective of whether doughs were tested fresh or rested. It was noted that sample shapes varied between specimens of flours. To understand how sample shape affects extensigraph tests, a finite element (FE) simulation-based approach was taken. Real extensigraph samples were drawn on a computer equipped with the commercial FE package ABAQUS and using the anisotropic Bergstrom Boyce model with Mullins damage (ABBM) constitutive model to describe the dough's rheology. Results show that the force-extension traces were affected by sample shape, and that thinning occurs more from the sides than the bulk for slumped samples. The FE predictions for sample shape effects on hook force were validated against real tests. Similar dependencies on sample shape are also predicted for the alveograph and Kieffer micro-extensigraph tests.

Extrusion of solid-liquid particulate pastes is a well-established process in industry for continuously forming products of defined cross-sectional shape. At low extrusion velocities, the solids and liquid phases can separate due to drainage of liquid through the interparticle pores, termed liquid phase migration (LPM). The effect of wall friction, die shape and extrusion speed on LPM in a cylindrically axisymmetric ram extruder is investigated using a two-dimensional finite element model of paste extrusion based on soil mechanics principles (modified Cam-Clay). This extends the smooth walled model reported by Patel et al. (2007) to incorporate a simplified Tresca wall friction condition. Three die entry angles (90°, 60° and 45°) and two extrusion speeds are considered. The extrusion pressure is predicted to increase with the Tresca friction factor and the extent of LPM is predicted to increase with decreasing ram speed (both as expected). The effects of wall friction on LPM are shown to be dictated by the die shape and ram displacement: there are few general rules relating extruder design and operating conditions to extent of LPM, so that finite element-based simulation is likely to be needed to predict the onset of LPM accurately., PowdermatriX Faraday Programme under EPSRC project GR/S/70340

Traditionally, chapattis are flatbreads made from atta (wholemeal Indian wheat flour). Non-atta chapattis have not been popular due to substandard product quality. To investigate what makes atta special for making chapattis, products were made using atta, Australian wholemeal wheat flour, gluten-free lupin flour, and a blend of lupin and wheat flours. Doughs were characterised by measuring strain-hardening and elastic recovery in compression and also bubble structures via 3-D X-ray micro-tomography. A method was developed to identify and separate bran, which appears as bubbles, in scans of doughs. Results highlighted the following: (1) elasticity of doughs is important for stabilising bubbles during rolling and baking, (2) atta doughs are low in strain-hardening but high in elasticity and retain bubbles the best after baking, and (3) lupins can be used to increase elasticity of Australian wheat flour doughs and to make gluten-free chapattis.

Current practices in testing flours call for measuring dough strength, not elasticity. Sheeting is a common method for processing developed doughs, the elasticity of which governs dough’s sheetability as dough springs back exiting rollers. To characterise dough sheetability, a study was conducted testing 18 different doughs made from six different flours. Each dough was sheeted using an instrumented sheeter and data for exit sheet thickness and roll forces were captured under a range of sheeting conditions. The true rheological properties of doughs were measured and used to calibrate the ABBM constitutive model for dough (1). Numerical simulations of sheeting operations were conducted; the R 2 coefficients between measured and predicted sheet thicknesses and roll forces (vertical and horizontal) were nearly all >0.9. Relaxation times were derived from dough model parameters and revealed that flour quality for dough elasticity should be assessed by examining moisture effects on dough relaxation time.

Chemical leaveners are used in doughs to generate carbon dioxide, as an alternative to yeast, in making a range of bakery products. In this study, the effects of fungal α-amylase and ascorbic acid on chemically leavened doughs were followed by measuring dough extensibility, true rheological properties, the amount of free liquid in doughs following ultracentrifugation and the quality of baked products. As with yeasted doughs, the bake qualities of chemically leavened doughs also improved in the presence of fungal α-amylases. The bake qualities were not affected when the equivalent amount of ascorbic acid was added. The differences in dough formulations were detected from measurements of true rheological properties, not from extensibilities of doughs. The amount of free liquid was larger and of lower viscosity in doughs containing α-amylases. The properties of the continuous liquid phase were found to be important in defining the rheological and baking qualities of doughs.

Solid–liquid pastes featuring high volume fractions of particulates are frequently used in ceramic forming operations. When pastes are used it is important that the particulate distribution remains uniform throughout the body. The stresses imposed during extrusion processing can, however, promote differential flow between the solid and liquid phases giving rise to product and processing problems. Reliable models for predicting phase distribution changes in these multi-phase systems are in their infancy. This paper reports progress towards developing simulation techniques and practical systems to verify the numerical approaches. Pastes containing glass spheres suspended in a highly viscous Newtonian fluid have been extruded at various speeds and solids loadings. Load and liquid content data are presented which form the basis for model verification. Soil mechanics approaches are used here to encapsulate the inherently multi-phase nature of these systems. The modified Cam–Clay model has been implemented in a finite element analysis simulation of ram extrusion using the ABAQUS platform. The simulation requires regular and extensive remeshing and monitoring of the conservation of mass. Predictions of extrusion pressures and deformation behaviour are compared with the experimental data for a series of square-ended and conical dies.

Particulate pastes undergoing extrusion can exhibit differential velocities between the solid and liquid phases, termed liquid phase migration (LPM). This is observed experimentally but understanding and predictive capacity for paste and extruder design is limited. Most models for LPM feature one-dimensional analyses. Here, a two-dimensional finite element model based on soil mechanics approaches (modified Cam-Clay) was developed where the liquid and the solids skeleton are treated separately. Adaptive remeshing routines were developed to overcome the significant mesh distortion arising from the large strains inherent in extrusion. Material data to evaluate the model's behaviour were taken from the literature. The predictive capacity of the model is evaluated for different ram velocities and die entry angles (smooth walls). Results are compared with experimental findings in the literature and good qualitative agreement is found. Key results are plots of pressure contributions and extrudate liquid fraction against ram displacement, and maps of permeability, liquid velocity and voids ratio. Pore liquid pressure always dominates extrusion pressure. The relationship between extrusion geometry, ram speed and LPM is complex. Overall, for a given geometry, higher ram speeds give less migration. Pastes flowing into conical entry dies give different voids ratio distributions and do not feature static zones. Copyright © 2007 John Wiley & Sons, Ltd.

The precise coordination of Directional Overcurrent Relays (DOCRs) is required to identify fault timely, effectively and isolate them from the network to avoid possible outages in a power system. The DOCRs coordination is an optimization problem including highly nonlinear constraints. In this paper, Cuckoo Search Algorithm (CSA) is implemented to solve coordination problem of DOCRs on two different case studies. The parameters of CSA are effectively tuned to obtain global best solution for the DOCRs coordination problem. The obtained results using the proposed method are compared with Genetic Algorithm (GA) and hybrid GA-Nonlinear programming (GA-NLP) methods. The result shows that the effective modification of CSA parameters can obtain feasible and superior solution for this complex problem.

A Green function method is presented which enables computation of laminar flow of an incompressible Newtonian fluid in circular and annular pipes, subject to an arbitrary forcing periodic pressure gradient, in terms of Bessel functions. The response to a step change in pressure gradient in an annular pipe is presented. The method allows direct calculation of wall shear stress and flow rates generated by pulsed flows, which are of interest in fouling mitigation and cleaning-in-place systems.

Polymer films may be formed by drying aqueous suspensions of colloidal polymer particles (latexes) on a substrate. Higher-performance films may be obtained by using nanocomposite particles in the latexes. In particular, polymer-clay nanocomposites show good potential in producing stiff, optically transparent, scratch-resistant coatings. The final film must be continuous (i.e., crack-free). This work predicts the minimum temperature, relative to the glass-transition temperature, at which a given suspension forms a crack-free nanocomposite film. The model extends a previous model for film formation with inclusion-free latexes (Routh, A. F.; Russel, W. B. Langmuir 1999, 15, 7762-7773). The inclusions are modeled as rigid cylinders, and the polymer is modeled as linearly viscoelastic. The major term arising in the extended model is the interfacial shear stress between the polymer and the inclusions. Film formation slows as the shear stress increases, and this effect is proportional to the magnitude of the stress, the inclusion volume fraction, and the inclusion aspect ratio.

Extensive movement of the liquid phase relative to the solids in solid–liquid pastes during extrusion forming is an undesirable process phenomenon. The impact of formulation and flow pattern on liquid phase migration (LPM) during extrusion of model pharmaceutical pastes (40–50 wt% microcrystalline cellulose/water) has been investigated by ram extrusion through square-entry and 45° conical-entry dies, and by lubricated squeeze flow (extensional flow). Threshold velocities for LPM were observed in both configurations. Squeeze flow testing showed that dilation during extension can cause LPM, while ram extrusion featured both dilation effects and drainage due to compaction. The threshold velocities observed in the two configurations agreed when presented as characteristic shear rates. The threshold velocity increased with paste solids content.

Petroleum based mineral insulating liquid has being used for a long long time as transformer oil. As there are limited reserves of precious petroleum, the search is on for an alternate suitable synthetic liquid. An effort has been made to evaluate LAB (linear alkyl benzene) as per relevant standard specification (IS: 335-1993) for a new transformer oil. It is observed that it also conforms to the requirements of equivalent international standards e.g., LEC 296, BS 148, ASTM D 3487. This is also compatible with different construction materials of transformer as well as mineral insulating oil in service. Significant improvement in pour point and ageing characteristics of indigenous paraffinic transformer oil is observed due to blending of LAB. The lower gassing tendency of LAB makes it a good substitute as a capacitor impregnant. There is a need to conduct long term ageing studies and field trials to ensure its reliability as a liquid dielectric.

Without a comprehensive training set, it is difficult to train neural networks (NN) to solve a complex learning task. Usually, the more complex the problem or task the NNs have to learn, the less likely it is that there is a realistic training set that could be used for (supervised) training. One way to overcome this limitation is to implement an evolutionary approach to train NNs. We report the results of a novel implementation of an evolutionary computational technique, based on a modified genetic algorithm (GA), to evolve feedforward NN topologies and weight distributions. The learning task was for two fairly simple but autonomous agents (controlled by NNs) to learn to co-operate in order to accomplish a task. Given the complexity of the task, an evolutionary approach to a search for an appropriate NN topology and weight distribution seems to be a promising and viable approach, as our results show. The implications of the results are further discussed. >

About a dozen field failures of very large (UHV) forced oil-cooled power transformers had been attributed to flow electrification of transformer oil. During the flow of hydrocarbon insulating oil through cellulosic insulation ducts in transformer, charge separation occurs at the interface of cellulose and oil. The negative ions accumulated on the cellulose may lead to dielectric breakdown in oil or at the interface. Considerable work is being done on this subject since last one decade. Now research activities are focused broadly on three fronts. First on standardization of measurement techniques, identification of affecting parameters and finally suppression up to safe limit. Most of the studies done so far have been on naphthanic based transformer oil. In this study an attempt has been made to evaluate paraffinic based transformer oil and study the effect of different parameters' e.g., type and quantity of paper, mounting position of paper, etc. on charge density. Although not much significance is given to electrical resistivity of oil in various international specifications, an interesting relationship is observed here with charge density. Mitigation of charge density by adding BTA (Benzotriazol) and LAB (Linear alkyl benzene) is found satisfactory without affecting oil characteristics.

Chapattis are a staple in the diet of people living in the sub-continent of India. They are widely made using atta flour in homes and in small scale industries. Atta is flour obtained by grinding wheat grown in the Indian sub-continent. Atta dough is made by mixing flour with only salt and water. It is rolled into circular disks and baked on open hot stoves. High quality chapattis puff during baking and remain soft and pliable over a considerable period of time. Attempts to make chapattis of the same quality have been made in countries outside of the Indian sub-continent using local flours. However, it has not been possible to produce products of a similar quality. The same issue of quality – sub-standard puffing and texture, has also hindered fortifying atta by adding nutrition-rich additives, like pulse flours. A project was carried out in our laboratory comparing quality of chapattis made with Indian atta with those made with local wholemeal flour (WW), mixes of local wholemeal flour (L+WW) and lupin flour and 100% lupin flour. Lupin is a legume, high in protein and fibre with no starch. Having no gluten, lupin dough lacks extensibility. All chapattis made from these four different flours, including those made with 100% lupin dough, puffed fully. Qualitatively, the quality of chapattis made with atta was equivalent to those made with the mix of lupin flour and WW flour. To understand these surprising results, doughs were characterized by measurement of true rheological properties and by image analyses of pore structures in doughs using a Skyscan CT scanner. Results showed that atta dough was more porous and retained more elasticity and porosity compared to other doughs. Dough extensibility was not a requirement for puffing of chapattis. These results provide new methods for characterizing atta dough quality and methods to guide addition of additives atta to improve nutritional profiles.

Defects present in 12 human permanent teeth were classified on the basis of their macroscopic appearance as hypoplasia (three teeth), diffuse opacities (three teeth), white demarcated opacities (one tooth but two defects), or yellow demarcated opacities (five teeth but six defects). The hardness values and SEM appearance of the defective enamel were determined after the teeth were sectioned through the lesion(s) and were distinctive for each type of defect. The thin enamel of the hypoplastic lesions was either opaque (with reduced hardness values) or translucent (with near-normal hardness values and sometimes a change in prism orientation external to an incremental line). The enamel of the diffuse and demarcated opacities was of normal thickness. The changes in the macroscopic and SEM appearance, and the reduced hardness values of the diffuse patchy opacities, were restricted to the outer 150 μm of the enamel. The demarcated opacities varied in position and depth, and in places had a clearly marked boundary with the adjacent normal enamel. Hardness values were related to color change, with yellow lesions being softer than white. Although prism direction was normal within demarcated opacities, prism outlines were less distinct. The findings suggest that temporary and permanent dysfunction of ameloblasts can occur in both secretory and maturation phases, influencing the final appearance of the lesion.