Dissertations / Theses on the topic 'Temperature modelling'
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MacLachlan, Craig S. "Numerical modelling of low temperature plasma." Thesis, University of Glasgow, 2009. http://theses.gla.ac.uk/911/.
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The intention of this thesis is to gain a better understanding of basic physical processes occurring in low temperature plasmas. This is achieved by applying both analytic and numerical models. Low temperature plasmas are found in both technological and astrophysical contexts. Three different situations are investigated: an instability in electronegative plasmas; electron avalanches during plasma initiation; and a phenomenon called the Critical Ionisation Velocity interaction. Industrial plasma discharges with electronegative gases are found to be unstable in certain conditions. Fluctuations in light emission, particle number densities and potential are observed. The instability has been reproduced in a variety of experiments. Reports from the experiments are discussed to characterise the key features of the instability. An, as yet un-considered, physical process that could explain the instability is introduced. The instability relies on the plasma's transparency to the electric field. This mechanism is investigated using simple zero-dimensional numerical and analytic models. The results from the models are compared to experimental results. The calculated frequencies are in good agreement with the experimental measurements. This shows that the instability mechanism described here is relevant. For the remaining two problems a three-dimensional particle model is constructed. This model calculates the trajectories of each individual particle. The potential field is solved self-consistently on a computational mesh. Poisson's equation is solved using a Multigrid technique. This iterative solution method uses many grids, of different resolutions, to smooth the error on all spatial scales. The mathematical foundation and details of the components of the Multigrid method are presented. Several test cases where analytic solutions of Poisson's equation exist are used to determine the accuracy of the solver. The implemented solver is found to be both efficient and accurate. Collisions are vitally important to the evolution of plasmas. The chemistry resulting from collisions is the reason why plasmas are so useful in technological applications. Electron collisions are included in the particle model using a Monte-Carlo technique. A basic method is given and several improvements are described. The most efficient combination of improvements is determined through a series of test cases. The error resulting from the collision selection process is characterised. Technological plasmas are formed from the electrical breakdown of a neutral gas. At atmospheric pressure the breakdown occurs as an electron avalanche. The particle model is used to simulate the nanosecond evolution of the avalanche from a single electron-ion pair. Special attention is paid to the inelastic collisions and the creation of metastables. The inelastic losses are used to estimate the photon emission from the electron avalanche. The Critical Ionisation Velocity phenomena is investigated using the particle model. When a neutral gas streams across a magnetised plasma the ionisation rate increases rapidly if the speed of the neutrals exceeds a critical value. Collisions between neutrals and positive ions create pockets of unbalanced negative charge. Electrons in these pockets are accelerated by their potential field and can reach energies capable of ionisation. The evolution of such an electron overdensity is simulated and their energy gain under different density and magnetic field conditions is calculated. The results from the simulation may explain the discrepancy between laboratory and space experiments.
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Huang, Taotao. "Quench modelling of high temperature superconductor." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/65717/.
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HTS magnets have been developed to generate high magnetic fields because its high critical field at low temperatures. For HTS magnets, the design of thermal stability and protection is based on understanding of its quench behaviour. However, there are few experimental and numerical results on the quench behaviour of HTS at low temperatures. This thesis work is mainly dedicated to investigate the quench behaviour of high temperature superconductor (HTS) at low temperatures by 1D and 2D numerical analysis. In addition, this work also investigates the critical current of HTS coils made from Bi/Ag2223 tape at 77K under self-field. The ANSYS implementation of a general quench model capable of handling nonlinear heat generation over a large temperature range of current sharing, e.g. for HTS at low temperatures, has been successfully validated for HTS at high temperatures and LTS with reference to predictions by the classical quench theory. The numerical model also revealed that the classical theory usually overestimates the minimum quench energy MQE as self-heating is neglected during the development of MPZ. The effective medium approximation for the coil thermal-electrical properties was also found to be sufficient for practical HTS coils. Simulation of 1D HTS conductors at low temperatures using the non-linear heat generation model revealed a different quench behaviour from that of LTS conductors. Firstly, while the minimum quench energy MQE is well defined, it is almost an order of magnitude smaller than the enthalpy of the minimum propagation zone. Hence the growth of MPZ is entirely due to self-heating while MQE is just a sufficient trigger. Secondly, for a practically defined MQE with 95% of the ”true” minimum, there is a large variation of the size of MPZ and the corresponding quench temperature. Thirdly, there appears a simple scaling between the average MPZ heat generation Gq and the temperature range (Tq − Tcs) of MPZ. 2D analysis of HTS coils showed the MQE is an order of magnitude larger than that from 1D analysis because of radial heat conduction. For practical coils, the geometry ii and boundary cooling have an important influence on their quench behaviour while the MPZs are larger and hotter. Two single pancake coils of 50mm inner diameter and 20 turns were manufactured and tested at 77K. The current carrying characteristics of HTS coils was evaluated by using the method based on the Ic-B of bifilar tape and agree well with measured results. One bifilar pancake coil was fabricated and tested at 77K. The measured critical current is 108A and about 20% larger than that of a single pancake coil.
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Al-Khateeb, Ashraf Kamal. "Modelling of low-temperature laser produced plasmas." Thesis, Queen's University Belfast, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322766.
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Almutairi, Fajhan Hilal Hamad. "Fibre optic distributed temperature sensors applications and temperature modelling in intelligent wells environments." Thesis, Heriot-Watt University, 2007. http://hdl.handle.net/10399/63.
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Holmgren, Anders. "Mean Value Modelling of the intake manifold temperature." Thesis, Linköping University, Department of Electrical Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-61.
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The emission legislations and the new On Board Diagnostics (OBD) legislations are becoming more strict and making the demands on control and fault detection higher. One way to
control and diagnose the engine is to use a control/diagnose strategy based on physical models and therefore better models are necessary. Also, to be competitive and meet the markets demand of higher power, longer durability and better fuel economy, the models needs to be improved continuously. In this thesis a mean value model of the intake system that predicts the charge air temperature has been developed. Three models of different complexity for the intercooler heat-exchanger have been investigated and validated with various results. The suggested intercooler heat-exchanger model is implemented in the mean value model of the intake system and the whole model is validated on three different data sets. The model predicts the intake manifold temperature with a maximum absolute error of 10.12 K.
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Nikolopoulos, Christos. "Mathematical modelling of modulated-temperature differential scanning calorimetry." Thesis, Heriot-Watt University, 1997. http://hdl.handle.net/10399/659.
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Jiang, Zhong. "Temperature modulated differential scanning calorimetry : modelling and applications." Thesis, University of Aberdeen, 2000. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU603190.
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The research described in this thesis focused on the TMDSC technique with respect to both theoretical problems and applications. Theoretically, modelling work has been performed to address the effects of heat transfer in the measuring cell on both dynamic and quasi-isothermal TMDSC experiments. The problems of heat transfer generally influence the measured complex heat capacity and phase angle values, but eventually affect the precise measurements of other frequency dependent quantities such as the in-phase and out-of-phase heat capacities. A procedure has been suggested to correct the measured phase angle obtained by dynamic TMDSC using the scaled complex heat capacity trace (Chapter 3). The modulation frequency dependence of the instrumental phase angle has been fully investigated using more realistic models in terms of various heat transfer interface qualities, sample properties and sensor properties. In these models, it is emphasised that the measured temperatures are the sensor temperatures rather than the sample temperatures, thus, the contributions of the sensor's properties to the heat transfer are, for the first time, separated from the overall effects (Chapter 4 and Chapter 5). The consequent effects of heat transfer on the sample's heat capacity measurements are investigated based on the models suggested (Chapter 6). All the modelling results are compared with the corresponding experimental data obtained by ADSC (Mettler-Toledo Ltd) and they are in good agreement. Ripples and fluctuations which appear on the experimental signals during the glass transition and cold crystallisation transition have been simulated using* a simple model in which the period of the modulation signals changes with the time during the transitions, and then, been shown to be artefacts of the Fourier transformation process used by TMDSC evaluations (Chapter 7). The applications of TMDSC to both research and commercial samples are reported in terms of differing either the experimental conditions or the thermal history of the sample. Separating of time dependent kinetic processes from the time independent dynamic processes has been applied on the studies of the glass transition (for polycarbonate and poly(ethylene terephthalate)), the cold crystallisation (for poly(ethylene terephthalate)), the melting transition (for poly(ethylene terephthalate) and lead/tin alloys), the clearing transition of a liquid crystal polymer, and the vitrification of an epoxy resin under quasi-isothermal conditions. The main conclusion drawn from these studies is that the in-phase heat capacity is greatly influenced by the frequency of the temperature modulations even when the underlying heating (or cooling) rate remains the same. This strongly implies that the sample undergoes different structural change under different modulation conditions for the melting transition and clearing transition, but not for the glass transition and cold crystallisation. However, the interpretations of the in-phase heat capacity and out-of- phase heat capacity still need to be clarified. The detection of the glass transition and clearing point for the liquid crystal polymers, and the determination of wax appearance temperature for crude oils, show the ability of TMDSC for combining the sensitivity of a measurement at high instantaneous heating or cooling rates with the resolution obtained by measuring at a low underlying heating or cooling rates. The work on the isothermal curing of the epoxy resins displays the ability of TMDSC on measuring the heat capacity of the sample and its variation under the quasi-isothermal conditions. The frequency dependent complex heat capacity during the glass transition provides a window to measure the apparent activation energy of the transition, which is different, in some extent, from the window used by conventional DSC. The results are correlated by a shift factor. Some shortcomings of TMDSC, however, have been noticed in both modelling and application work. Firstly, any experiments for the purpose of either understanding or the quantitative measurements of TMDSC output quantities should be performed under carefully selected conditions which can satisfy the linear response assumption. Secondly, some signals in particular those associated with kinetic processes may not be fully sampled by TMDSC due to the limit of the observing window of a modulation. Thirdly, when the sensitivity is improved on TMDSC by separating the kinetics processes and noises from the dynamic processes, the TMDSC evaluation procedure introduces mathematical artefacts into the output signals. As a consequence, it is preferable to include as many temperature modulations as possible within any transition being studied in order to obtain good quality experimental signals by eliminating or minimising these artefacts, which, however, is not an easy task for some very abrupt transitions such as melting of metals.
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Fernández, S. Alejandro D. "Modelling the temperature dependences of Silicon Carbide BJTs." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-202754.
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Silicon Carbide (SiC), owing to its large bandgap, has proved itself to be a very viable semiconductor material for the development of extreme temperature electronics. Moreover, its electrical properties like critical field (Ecrit) and saturation velocity (vsat) are superior as compared to the commercially abundant Silicon, thus making it a better alternative for RF and high power applications. The in-house SiC BJT process at KTH has matured a lot over the years and recently developed devices and circuits have shown to work at temperatures exceeding 500˚C. However, the functional reliability of more complex circuits requires the use of simulators and device models to describe the behavior of constituent devices. SPICE Gummel Poon (SGP) is one such model that describes the behavior of the BJT devices. It is simpler as compared to the other models because of its relatively small number of parameters. A simple semi-empirical DC compact model has been successfully developed for low voltage applications SiC BJTs. The model is based on a temperature dependent SiC-SGP model. Studies over the temperature dependences for the SGP parameters have been performed. The SGP parameters have been extracted and some have been optimized over a wide temperature range and they have been compared with the measured data. The accuracy of the developed compact model based on these parameters has been proven by comparing it with the measured data as well. A fairly accurate performance at the required working conditions and correlation with the measured results of the SiC compact model has been achieved.
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Roth, Lyndsey B. "Modelling landcover-induced increases in daytime summer temperatures near Mount Adams, Washington." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 59 p, 2009. http://proquest.umi.com/pqdweb?did=1885544291&sid=4&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Hayes, R. C. "Temperature dependance of silicon bipolar transistor D.C. parameters." Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381268.
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Grilli, Francesco. "Numerical modelling of high temperature superconducting tapes and cables /." [S.l.] : [s.n.], 2004. http://library.epfl.ch/theses/?display=detail&nr=2909.
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Gaspari, Valerio. "Low temperature characterization and modelling of Si:SiGe heterostructure devices." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409010.
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Abeykoon, Yapa Mudiyanselage Chamil Eranda Kumara. "Modelling and control of melt temperature in polymer extrusion." Thesis, Queen's University Belfast, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.554339.
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The extrusion process serves as one of the main methods for processing polymer materials and thermal homogeneity of the process output presents a major challenge for high quality extruded products. Despite considerable research, process monitoring and control still remains difficult and engineers have to deal with issues such as the selection of process settings and product quality control primarily by trial and error. In this study, it was recognised that melt temperature was the most appropriate parameter for real-time investigation of process melt quality and a new strategy for polymer extrusion process control incorporating an inferential thermal monitoring technique was examined. An experimental evaluation showed that existing point/bulk measurement techniques were poor at capturing in-process thermal fluctuations although they are common in practice and therefore a multi point thermocouple mesh technique was selected to use in the experiments. As the thermocouple mesh was not yet robust enough for industrial applications, an inferential thermal monitoring technique was explored to use in the prospective process controller. Initially, attempts were made to inferentially predict the process thermal stability via screw load torque and melt pressure dynamics and these were not successful. Therefore, the experimental data collected from the thermocouple mesh was used to develop a dynamic model to predict the temperature profile of the extruder output melt flow and this model was used to develop a soft sensor for real-time prediction of a melt temperature profile. The possible prediction errors of the soft sensor were corrected by a feedback model engaged with a physical infrared temperature sensor measurement. Simulation results showed that the soft sensor is capable of predicting melt temperatures at different radial locations of the melt flow with good accuracy and the feedback model prediction error was always less than ±2.25% of the full scale reading; hence this provided a promising approach for inferential process thermal monitoring. Ultimately, a model-based control approach incorporating the soft sensor and fuzzy logic was proposed to minimise melt temperature variance across the extruder output melt flow while achieving the desired average melt temperature by manipulating the major process variables (i.e. screw speed and all the barrel zone temperatures). Simulation results showed that the proposed controller was good in achieving its targets over the experimental results. Therefore, this offers a new method to operate extruders at high screw speeds whilst achieving both high energy and thermal efficiencies. The proposed control framework is industrially usable with the development of the required process models as it uses only readily measurable process parameters for its operation. Presently, the controller's operation is specific to a given machine and material and hence the development of generalised models should help to widen its scope. Although the single screw extruders were used for research, the proposed methodology should be applicable to other multi screw extruders as well where the development of the required models is possible.
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Bejarno, Mercedes Andrade. "Monthly average temperature modelling for Valle del Cauca (Colombia)." Thesis, University of Reading, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515761.
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Jonasson, Jan-Erik. "Modelling of temperature, moisture and stresses in young concrete." Doctoral thesis, Luleå tekniska universitet, Byggkonstruktion och -produktion, 1994. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25735.
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The present study consists of three areas, namely modelling of- (1) temperature, (2) moisture state, and (3) stresses in young concrete. The derivation of models, examination of material data, and development of computer programs have progressed differently in these areas. The first area, modelling of temperatures, is the most comprehensive and complete, since it has been researched more extensively than the other areas. On the other hand, the way of modelling stresses in this study is purely theoretical and has not been tested against empirical data, but gives some guidelines for future applications. Finally, the modelling of moisture state is somewhere in between the other two areas. The results can be applied to different fields of concreting, such as estimation of form stripping times, estimation of necessary measures to be taken in winter concreting, study of drying shrinkage cracking, and study of stresses due to varying temperatures in early age concretes. The aim of this report is not to discuss applications, but to give the background and material data used in the models for calculating the temperature, moisture state, and stresses in young concrete. It is shown that temperature can be modelled to within an accuracy of 1 to 2°C which is acceptable for most applications. However, it is essential to have good knowledge of both material data and environmental conditions. For the study of moisture states, a consistent model for the description of desorption and absorption isotherms has been developed. The treatment of both desorption and absorption isotherms in the same theoretical framework makes it possible to introduce scanning curves between these limit curves for subsequent drying and wetting. The effects of alkali have been modelled as an alkali equilibrium isotherm estimated from the known amounts of sodium and potassium oxides in the cement. The alkali influenced curve can be combined with any description of the isotherms with respect to the physically bound water. The need for considering the effects of alkali for higher humidities has been shown in moisture calculations.Godkänd; 1994; 20070426 (ysko)
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Irvine, Richard John. "Temperature and physical modelling studies of open windrow composting." Thesis, Abertay University, 2002. https://rke.abertay.ac.uk/en/studentTheses/bd4b95a9-3587-41ab-b3de-60628fe5f63b.
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There is a growing demand for sustainable forms of waste management due to both legislative pressures (e.g. the European Union Landfill Directive (99/31/EC)) and increasing public awareness of environmental issues. Composting of biodegradable waste materials to produce a stabilized beneficial multi-functional product (compost) is being widely promoted. Currently, the most popular method of composting is the open windrow method, whereby the mixed and shredded feedstocks are arranged in long rows termed windrows and turned on a regular basis. During the process the waste material is subject to aerobic exothermic microbial decomposition. Commercial composting operations suffer from the problem that much of the processing is performed using empirical approaches. Improved understanding of the composting process based on scientific methodology is required to allow composting to develop its potential as an economic, safe and reliable method of sustainable waste management. This study used a series of large scale windrow-based seasonal field trials employing urban green waste as a feedstock, to investigate in unprecedented detail the temperature trends and patterns of behaviour within such structures. In addition physical-chemical profiling was undertaken. It demonstrated that windrow temperature development is not uniform in either a spatial or temporal sense. Temperature variation is a key feature of composting. All regions of typical windrows exhibited thermophilic and mesophilic temperature zones throughout the composting process. There was little seasonal variation. Sustained high temperatures were most widespread in the core regions at a height of around lm. Thus, these areas should not be favoured during temperature assessment to avoid bias results. It was demonstrated that current methods of temperature assessment are inadequate. It is suggested that greater numbers of data points are collected at varying positions and instead of simply calculating overall mean temperature that individual trends are plotted. The use of temperature frequency distribution histograms and cumulative temperature plots is additionally advised. Increased windspeed (greater than approximately 15MPH) was demonstrated to be a major factor preventing the development and sustaining of thermophilic temperatures within windrows. It is recommended that commercial composters routinely assess windspeed and direction. Changes in organic matter content, bulk density and pH provided an indication of the composting process in the long term but lacked the sensitivity of temperature measurement. Surveying using electronic tacheometry allowed changes in windrow shape and volume to be assessed. The field trial data allowed a novel physical compost model to be developed, based upon open windrow composting of urban green waste. Existing models are based on in-vessel composting systems and are technically flawed in certain key aspects. The model successfully simulated the initial stages of windrow composting, which was proven by experimentation and comparison with field trial data. The use of low level internal feedstock heating was demonstrated to be a viable method of stimulating natural enhanced microbial activity. A non- insulated model windrow and the employment of an environmental simulation system allowed the natural relationship between windrow and external environment to be modelled. The importance of such a model to the compost scientist and waste manager is highlighted. The study showed that it is possible to successfully physically model the open windrow composting process.
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Liu, Weijie. "Advanced modelling for sheet metal forming under high temperature." Thesis, Troyes, 2017. http://www.theses.fr/2017TROY0019/document.
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L’objectif de cette thèse est de proposer deux approches complémentaires de modélisation et de simulation numériques des procédés de mise en forme de structures minces. La première est une approche inverse multi-pas, délibérément simplifiée, pour simuler et "optimiser" rapidement et à moindre coût des procédés d’emboutissage de tôles minces, tout en maintenant une bonne précision dans le calcul des contraintes. Un solveur statique implicite est développé en introduisant plusieurs configurations intermédiaires construites efficacement en utilisant une technique de programmation quadratique avec projection. La deuxième approche, de nature incrémentale, repose sur (i) une formulation d’équations de bilan et d’équations de comportement multi-physiques fortement couplés formulées dans le cadre des milieux micromorphes ; (ii) une discrétisation spatiale par EF et temporelle par DF avec un solveur global dynamique explicite et une intégration locale itérative implicite. Une attention particulière est accordée aux aspects thermiques avec l’introduction d’une microtempérature et ses premiers gradients conduisant à l’obtention de deux équations thermiques fortement couplées généralisant de nombreux modèles non locaux proposés dans la littérature. L'approche inverse multi-pas a été implémentée dans le code maison KMAS et l’approche incrémentale non locale a été implémentée dans ABAQUS/Explicit. Des études paramétriques sont menées et des validations sur des exemples simples et sur des procédés d’emboutissage sont réaliséesThe aim of this thesis is to propose two complementary approaches for modeling and numerical simulations of thin sheet metal forming processes. The first one is a deliberately simplified multi-step inverse approach to simulate and "optimize" rapidly and inexpensively thin-sheet stamping processes while maintaining good accuracy in the stress calculation. An implicit static solver is developed by introducing several efficiently constructed intermediate configurations using a quadratic programming technique with projection. The second approach, which is of an incremental nature, is based on (i) a formulation of equilibrium equations and strongly coupled multiphysical behavior equations formulated in the context of micromorphic continua; (ii) spatial discretization by FEM and time discretization by FD with an explicit dynamic global solver and implicit iterative local integration scheme. Particular attention is paid to the nonlocal thermal aspects with the introduction of a micro-temperature and its first gradients leading to two strongly coupled thermal equations generalizing several thermal nonlocal models proposed in the literature. The multi-step inverse approach was implemented in the KMAS in house code while the nonlocal incremental approach was implemented in ABAQUS/Explicit. Parametric studies are performed and validations are carried out on simple examples and on deep drawing processes
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Tewkesbury, Heather. "Mathematical modelling of heat transfer in chocolate moulding." Thesis, University of Birmingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340442.
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Martinsson, Joel. "Controlled Start Transmission Wet Clutch Temperature Modeling and Application." Thesis, Linköpings universitet, Fordonssystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-122166.
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Controlled Start Transmissions (CST) can be described as a mechanical transmission combined with a wet clutch for controlled torque output. CST:s are commonly used to start up heavy loads for example mining conveyors. Several CST:s can work together to share the load. The transferred torque is controlled by a hydraulic wet clutch which is a proven technology for high torque transfer and low wear. This thesis is a part of a project to increase the knowledge and improve the CST design and control performance. The heat generation in the wet clutch is the focus of this thesis. Literature review shows that most research is done in order to get high accuracy for smaller clutches and most of the high torque engagements have very short transients.Models for the CST clutch heat generation together with thermal behavior have been developed and investigated. This includes a temperature model together with a kinetic model of the gearbox and a clutch torque model. Validation of separate model components and sensitivity analysis of the parameters are made. The developed model is then analyzed by comparing measurements from a commission site and simulations to get an idea of how much heat is generated.
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Reszka, Pedro. "In-depth temperature profiles in pyrolyzing wood." Thesis, University of Edinburgh, 2008. http://hdl.handle.net/1842/2602.
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The move towards performance-based design of the fire resistance of structures requires more accurate design methods. An important variable in the fire performance of timber structures is the in-depth temperature distribution, as wood is weakened by an increase of temperature, caused by exposure to high heat fluxes. A proper prediction of temperature profiles in wood structural elements has become an essential part of timber structural design. Current design methods use empirically determined equations for the temperature distribution but these assume constant charring rates, do not account for changes in the heating conditions, and were obtained under poorly defined boundary conditions in fire resistance furnaces. As part of this research project, a series of experimental in-depth temperature measurements were done in wood samples exposed to various intensities of radiant heat fluxes, with clearly defined boundary conditions that allow a proper input for pyrolysis models. The imposed heat fluxes range from 10 kW/cm 2, which generates an almost inert behaviour, to 60 kW/cm 2, where spontaneous flaming is almost immediately observed. Mass loss measurements for all the imposed heat fluxes were also performed. The second part of this project dealt with the modelling of the pyrolysis process, with an emphasis placed on temperature prediction. The main objective was to identify the simplest model that can accurately predict temperature distributions in wood elements exposed to fires. For this, an analysis of the different terms which have been included by several models in the energy equation has been done, by quantifying its magnitude. Five models with different degrees of simplification have been developed. Comparison with the experimental data has shown that a simple and accurate model of temperature profiles must include the rise in the solid sensible heat, the heat transferred by conduction, the heat of moisture evaporation, the heat of pyrolysis reaction and the effect of char oxidation.
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Beaulieu, Marieke. "Cyanobacteria in North America: modelling across nutrient and temperature gradients." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=117103.
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The toxin-producing potential of some freshwater cyanobacterial species and their ability to form dense blooms makes the possibility of an increase in their biomass of concern to lake managers and the general public. Modelling of cyanobacterial biomass and dominance in inland water bodies has demonstrated that cyanobacterial biomass increases concomitantly with nutrients in freshwater systems. Though temperature and water-column stratification are increasingly cited as factors promoting cyanobacterial biomass, support for this has been mainly provided by laboratory studies and individual lake studies. Furthermore it is not well known if models developed across large spatial gradients perform adequately at regional scales where responses could be modulated by additional unconsidered regionally-distinct variables. This thesis evaluates the effects of temperature, nutrients and other predictors on cyanobacterial biomass in North American lakes, through general models and when accounting for water body type and region of origin. A novel analysis of an existing dataset comprising single sample dates of over 1000 lakes in the United States showed that temperature was a significant predictor of cyanobacterial biomass. The effect of temperature was shown to be independent of those of nutrients and increases in total phytoplankton biomass. This suggests that warming alone might result in an increase in cyanobacterial biomass in lakes. The effects of the different variables varied between the lake systems considered (deep or shallow; natural lake or reservoir) with the strongest relationships found in deep natural lakes. An unpublished dataset of 88 Canadian lakes was used to test the effects of nutrients and temperature across regions using seasonally averaged data. These robust models provide some support for differing responses among regions, suggesting caution when applying general models to specific regions. Additionally, cyanobacterial genera biomass distribution in lakes was found to be explained by multiple environmental variables. Generally, nitrogen was found to be a significantly better predictor of cyanobacterial biomass than total phosphorus suggesting that nitrogen-fixation by cyanobacteria is less prevalent that previously estimated. Together, this thesis advances our understanding of the variables driving cyanobacterial biomass in lakes and demonstrates that under continued nutrient enrichment and warming temperatures increases in cyanobacterial biomasses in North American lakes could be expected.Les proliférations de cyanobactéries sont des sujets de préoccupation à l'échelle globale en raison de leur capacité de former des écumes denses qui épuisent l'oxygène dissoute et qui peuvent produire des toxines, nuisant à l'utilisation des plans d'eau tant pour l'eau potable que les loisirs. La modélisation de la biomasse et de la dominance des cyanobactéries a préalablement démontré que leur abondance augmente de façon concomitante avec les nutriments dans les systèmes d'eau douce. Bien que la température et la stratification de la colonne d'eau soient de plus en plus citées comme facteurs favorisant la prolifération des cyanobactéries, ces associations sont surtout basées sur des études en laboratoire et de lacs individuels. En outre, il n'a pas été bien démontré que les modèles développés sur d'importants gradients spatiaux s'appliquent de façon adéquate à l'échelle régionale, où la biomasse pourrait aussi être modulée par des variables additionnels. Cette thèse évalue les effets de la température, des nutriments et d'autres prédicteurs sur la biomasse des cyanobactéries dans les lacs d'Amérique du Nord, à travers le développement de modèles général ainsi que des modèles tenant compte des spécificités régionales. Dans le premier chapitre, je présente une analyse exhaustive d'un ensemble de données de plus de 1000 lacs. Utilisant cet ensemble de données, où la plupart des lacs ont été échantillonnés une seule fois au cours de la saison de croissance, j'ai démontré que les concentrations de nutriments (azote et phosphore) et la température étaient des prédicteurs significatifs de la biomasse des cyanobactéries. L'effet de la température sur la biomasse des cyanobactéries est statistiquement indépendant de celui des nutriments. Ces résultats suggèrent que le réchauffement des eaux de surface pourrait entraîner une augmentation de la biomasse des cyanobactéries dans les lacs. Les effets des variables différaient entre les systèmes étudies (profonds, peu profond ; lac naturel, réservoir). Les meilleurs modèles ont été développés pour lacs naturels profonds. Dans le deuxième chapitre de cette thèse, j'ai examiné un ensemble de données inédites basées sur les moyennes saisonnières de 88 lacs provenant de trois régions du Canada (l'Alberta, la Colombie-Britannique et l'Ontario). J'ai développé des modèles prédictifs généraux et examiné comment les modèles pouvaient différer entre les régions en utilisant la modélisation linéaire générale et la modélisation à effets mixtes. Les prédicteurs environnementaux ressortant furent similaires à ceux du premier chapitre mais, tel qu'attendu, les modèles utilisant les moyennes saisonnières expliquèrent une plus grande proportion de la variance de la biomasse des cyanobactéries car elles sont plus représentatives. Ces modèles ont aussi relevé des différences claires entre l'Ontario et les autres provinces mais l'inclusion d'avantage de lacs de l'Ontario dans l'analyse serait nécessaire afin de résoudre pourquoi c'est le cas. Dans l'ensemble, cette thèse enrichit notre compréhension des variables influençant la prolifération des cyanobactéries dans les lacs. Elle démontre clairement que, par l'enrichissement continu en nutriments et le réchauffement des eaux de surface, une augmentation de la biomasse des cyanobactéries dans les lacs nord-américains serait attendue.
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Pilditch, Stephen Robert. "Modelling high temperature phosphoric acid doped polymer electrolyte fuel cells." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519580.
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Benny, S. "High temperature water gas shift catalysts : a computer modelling study." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20444/.
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The high-temperature (HT) Water Gas Shift (WGS) reaction has considerable technological relevance for lowering CO content during the conversion of natural gas or liquid hydrocarbons to hydrogen. Conventional HT-WGS catalysts based on oxides of iron and chromium are well established industrially. However, it is crucial to remove any impurities present such as Cr6+, S or N during the catalytic process. In particular, Cr6+ is regarded as a Class I carcinogen and its presence is restricted by EU legislation. Even though Cr6+ is reduced during the catalytic process, caution must still be taken to eliminate any further impurities. Hence, it is desirable to identify alternative promoters and develop a Cr-free HT-WGS catalyst. This thesis presents results obtained using atomistic simulation techniques to investigate the effect of Cr3+ and possible alternative dopants in three important iron oxide materials, Hematite (α-Fe2O3), Maghemite (γ-Fe2O3) and Magnetite (Fe3O4). The starting point is to develop an understanding of the structural properties and distribution of Cr3+ on the bulk and surface material of hematite. The critical stage of understanding the role of Cr3+ provides the basis from which criteria for novel dopants can be assessed. Al3+ and Mn3+ are proposed as the promising candidates on the basis of this study. The research has been extended to other complex iron oxides, such as maghemite and magnetite. In summary, the role of chromium in the HT-WGS reaction has been investigated to establish criteria for effective, alternative promoter dopants. This investigation has provided a detailed insight into the atomic level behaviour of Cr3+, Mn3+, Al3+ impurities in three major iron oxide phases. The alternative dopants predicted in this study have been the subject of parallel experimental studies conducted by Johnson Matthey. The results of this study are already benefiting the design of more efficient iron-oxide catalysts for the HT-WGS reaction.
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Thornblad, Johan. "Drivetrain Modelling and Clutch Temperature Estimation in Heavy Duty Trucks." Thesis, Linköpings universitet, Fordonssystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-108117.
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An existing drivetrain model with clutch temperature dynamics has been used to simulate the behaviour of a heavy duty truck. During the implementation of the model in MATLAB/Simulink modularity and simplicity was greatly emphasized. This was done in order to facilitate the use of the model in various applications as well as making it easy to understand. The main contributions of the thesis is however the adaptation of a clutch temperature and wear observer for use in an on-line application in the gearbox management system (GMS). The process of taking the observer from an off-line simulation environment to running on-line includes taking into consideration the configuration and limitations of the GMS as well as adapting the interface of the observer. Concretely this means dealing with the limitations of the available data types in the GMS, compensating for the effect of biased measurements as well as accounting for the different dynamics of the sensor-types used in the clutch.In a simulation environment the performance of the adapted observer has been studied and its ability to compensate for heat expansion and wear in the clutch shown.En existerande drivlinemodell med temperaturdynamik i kopplingen har använts för att simulera beteendet hos en lastbil. Vid implementation av modellen i MATLAB/Simulink betonades vikten av en enkel och modulär struktur. Detta gjordes för att underlätta användning av modellen i olika applikationer samt för att göra den lätt att förstå.De huvudsakliga bidragen i uppsatsen är anpassningen av en temperatur- och slitageobeservatör på kopplingen för användning i realtid av växellådans styrenhet. För att ta observatören från simulerings- till realtidsmiljö måste styrenhetens konfiguration och begränsningar beaktas samt gränssnittet hos observatören anpassas. Konkret betyder detta att hänsyn till begränsningarna hos de olika datatyper som används i kopplingens styrenhet tagits, att den negativa inverkan som brusiga mätsignaler kan få begränsats samt att skillnader i dynamik hos de olika sensortyper som används i kopplingen kompenserats för. Med simuleringar har prestandan hos den anpassade observatören studerats samt dess förmåga att kompensera för värmeutvidgning och slitage i kopplingen visats.
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Harris, Richard. "The modelling and simulation of temperature effects in hydraulic systems." Thesis, University of Bath, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.256905.
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Phibbs, Samuel Anthony. "Idealised and regional modelling study on cyclones' sensitivity to temperature." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/57118.
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Idealised tropical and extratropical cyclones, and a historic medicane are simulated using the Coupled-Ocean-Atmosphere-Wave-Sediment Transport Modeling System. This manuscript examines the sensitivity of: surface wind and waves to ocean temperature for tropical cyclones (TCs); precipitation to atmospheric temperature for extra-tropical cyclones; wind, waves and precipitation to simultaneous increases in atmospheric and oceanic temperature for the medicane. More intense and larger TCs, with higher waves, form when ocean temperature is increased. The maximum significant wave height increases more than the maximum wind speed for TCs up to hurricane-force wind. Above hurricane-force wind this relationship is reversed. This is explained by the wind drag coefficient dependence on wind speed. The relative increase in the footprint of high waves is considerably greater than the increase in the maximum wave height as ocean temperature is increased. This suggests a future warmer ocean will result in a large increase in the surface area of damaging waves generated by TCs. For the extratropical cyclones the footprint of extreme precipitation (total surface area where accumulated precipitation exceeds high thresholds) and the accumulation in different sized catchment areas is examined. The footprint of extreme precipitation grows considerably with temperature. When the catchment areas are ranked in order of total precipitation, super Clausius-Clapeyron behaviour of the 99th percentile is found for all the catchment sizes. This surprising result for larger catchment areas is due to spatially concentrated changes in the extreme precipitation. A more intense, significantly larger medicane generally developed when temperatures were increased. The greater area of high winds led to increases in both the maximum significant wave height and the footprint of high waves. The mean and extreme precipitation increased with temperature slightly and substantial faster than Clausius-Clapeyron scaling respectively, this was accompanied by a larger but less fragmented footprint of extreme precipitation.
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Fangohr, Hans. "Computational modelling of the vortex state in high-temperature superconductors." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/45928/.
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The vortex state in high temperature superconductors is investigated using computer simulations. Vortices are represented as particles and we employ Langevin dynamics to study the statics and dynamics of the system. We show that the long-range nature of the vortex-vortex interaction can result in numerical artefacts, and provide two techniques to overcome these problems: (i) using a ‘smooth’ cut-off which reduces the interaction force near the cut-off smoothly to zero, and (ii) an infinite lattice summation technique applicable for a K0-Bessel function interaction potential. Using these methods, we investigate a two-dimensional vortex system driven over a weak random potential. We observe the moving Bragg glass regime, and study the recently predicted critical transverse force. Our results agree with and extend other theoretical and numerical works, and provide important confirmation for the moving glass theory. We investigate the critical transverse force as a function of system size, temperature, driving force and disorder strength. We provide numerical estimates to assist experimentalists in verifying its existence. We study vortex matter in three-dimensional layered superconductors in the limit of zero Josephson coupling. The long-range nature of the electromagnetic interaction between pancake vortices in the c-direction allows us to employ a meanfield method: all attractive inter-layer interactions are described by a substrate potential, which pancakes experience in addition to the in-layer pancake repulsion. Using an averaged pancake-density, we iteratively re-compute the substrate potential. The self-consistent method converges, depending on temperature, either to a pancake lattice or a pancake liquid. We investigate different methods to perform these simulation efficiently, and compute the instability line for the transition from solid to liquid, the melting line and the entropy jump across the transition.
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McCreesh, Nicola Frances. "Modelling the effects of temperature changes on Schistosoma mansoni transmission." Thesis, Durham University, 2015. http://etheses.dur.ac.uk/10984/.
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Schistosomiasis is a chronic parasitic disease, estimated to affect 237 million people worldwide. It is caused by infection with Schistosoma helminths, which spend part of their lifecycles in aquatic snails. The mortality, development and fecundity rates of the parasites and their intermediate host snails are very sensitive to water temperature. The distribution and prevalence of schistosome parasites are therefore likely to be affected by climate change, however the potential effects of this have been largely neglected. Only two mathematical models of temperature and schistosome transmission in Africa have previously been developed, and neither explicitly simulated all temperature-dependent stages of the parasite and snail lifecycles. The aim of this thesis is to advance understanding of the potential effects of climate change on S. mansoni transmission, using an agent-based modelling approach. A mathematical model of water temperature, snail population dynamics and S. mansoni transmission was developed. The model was parameterised using data from Biomphalaria pfeifferi, the most widespread intermediate host species in Africa, and the dynamics of the model were explored. Infection risk was shown to be highest (above 90% of the maximum) at a constant temperature of 15-19°C. Simulating diurnal variation in temperature and/or higher cercaria and miracidium removal rates increased the optimum temperature for transmission to 16-26°C. The effect of simulating different species of intermediate host snail was also investigated. Simulating Bi. alexandrina and Bi. glabrata increased the temperature at which infection risk was highest to 19-21°C and 20-26°C respectively. The model was run using climate projections for eastern Africa. Comparisons of model output at baseline with empirical data showed that suitable temperatures are necessary but not sufficient for both schistosome transmission, and for high prevalences of schistosomiasis. All else being equal, infection risk may increase by up to 20% over most of the area over the next 20 and 50 years. Increases may be higher in Rwanda, Burundi, south-west Kenya and eastern Zambia, and schistosomiasis may become newly endemic in parts of these areas. The results for 20 years’ time are robust to changes in simulated snail habitats. There is greater uncertainty about the effects of different habitats on changes in risk in 50 years’ time.
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Barham, S. Y. "Time series analysis in the detection of breast cancer." Thesis, Bucks New University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384665.
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Vidal, Fábio Duarte. "Modelling ventilation phenomena in passive houses." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/17314.
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Mestrado em Engenharia CivilThe present dissertation aims to combine the use of Computational Fluid Dynamics (CFD) software, to support the design of ventilation systems in passive houses. Sustainable construction is an increasing concern in the current construction market, finding in these houses a valid alternative in order to enhance energy savings in this sector. A passive house is known for achieving high levels of thermal comfort without consuming too much energy. In addition to an extremely rigorous thermal insulation, the use of highly efficient ventilation systems is one of the main factors in achieving such levels of comfort. Therefore, this dissertation intends to study the circulation of air associated to the mechanical ventilation system of a passive house in Portugal and consequent analysis of its thermal comfort. To achieve such purpose, a CFD commercial program called FLOW-3D® will be used. It was necessary to perform a validation of the program by comparing air velocities obtained numerically by the program and experimentally through the registration of air velocities in the studied passive house with the use of digital anemometers. Lastly, after the validation described above, an analysis over the thermal comfort of the building was performed, based on temperature registrations obtained experimentally and velocity values obtained from the numerical simulations.
A presente dissertação visa aliar o uso de programas de simulação numérica de fluidos, mais concretamente a mecânica dos fluidos computacional (CFD), no apoio à conceção de sistemas de ventilação em casas passivas. A construção sustentável é cada vez mais uma preocupação no mercado atual da construção, encontrando nessas casas uma alternativa muito válida no que toca a poupanças de energia neste setor. Uma casa passiva é reconhecida por obter altos níveis de conforto térmico sem necessidade de grandes consumos de energia. Para além de um isolamento térmico rigoroso, o uso de sistemas de ventilação de elevada eficiência é um dos principais fatores para atingir tais níveis de conforto. Esta dissertação pretende, por isso, fazer um estudo da circulação de ar resultante de um sistema de ventilação mecânica numa casa passiva construída em Portugal e a consequente análise do conforto térmico que nela se obtém, tendo sido utilizado um programa comercial de CFD, o FLOW-3D®. Foi necessário realizar uma validação do programa através da comparação de valores de velocidade do ar obtidos numericamente pelo respetivo algoritmo de cálculo e experimentalmente através do registo de velocidades do ar na casa passiva objeto de estudo, tendo-se utilizado para o efeito anemómetros digitais. Por fim, após a validação descrita anteriormente, foi feita uma análise do conforto térmico do edifício em estudo com base em registos de temperatura obtidos experimentalmente e de velocidades do ar obtidos da simulação efetuada.
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Prakash, del Valle Carlos. "Thermal modelling of an FZG test gearbox." Thesis, KTH, Maskinkonstruktion (Inst.), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-157256.
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Gearboxes are always subject of study in order to increase their efficiency. Energy losses in gear contacts are transformed into heat which is distributed among the gearbox components increasing their temperature. A thermal model of the gearbox brings the opportunity of a deeper understanding of the heat dissipated related to the power losses in the gear contact. A MATLAB program based on ordinary differential equations was developed in order to make a thermal model of an FZG test gearbox. The model is based on a thermal network where each node represents a machine element. The thermal network is composed by thermal resistances due to deformation in the gear contact, conduction, convection and radiation. With thermal resistances, power losses and thermal inertia of each element, the temperature evolution was obtained by applying the First Principle of Thermodynamics. Due to the temperature evolution, heat transfer between different elements was estimated. Additionally, experimental results from an FZG test rig were implemented in the model and also used to verify its accuracy. Furthermore, additional features to the model such as a cooling system and spray lubrication were also studied. Results show a wide capability and handling of the program in terms of thermal analysis: heat flux direction and magnitude, visual tools such as thermal network of the test gearbox, as well as the analysis of different operating conditions. With these tools, an approach to the minimum amount of lubricant necessary and other ways to quench overheating could then be reached. Keywords: Thermal network, FZG gear test rig, heat flow, temperature, MATLAB, ODE.Växellådor är ständigt ett forskningsområde för att förbättra deras verkningsgrad. Energiförluster i kuggkontakter omvandlas till värme som sprids i växellådan som sedan värmer upp komponenterna. En termisk modell av växellådan gör det möjligt för djupare förståelse hur värmen sprids i förhållande till energiförlusterna i kuggkontakten. Ett MATLAB-program baserat på ordinära differential-ekvationer utvecklades för att göra en termisk modell av en växellåda i en kuggrigg från FZG. Modellen är baserad på ett termiskt nätverk där varje nod representerar en maskinkomponent. Det termiska nätverket består av resistanser som uppstår på grund av deformation i kuggkontakten, ledning, konvektion och strålning. Med termiska resistanser, energiförluster, termisk tröghet från komponenterna och genom att applicera termodynamikens första grundsats kunde temperatur-genereringen bestämmas. Från temperatur-genereringen kunde värme-ledningen mellan komponenter uppskattas. Testresultat från en FZG-kuggrigg användes för att verifiera modellens noggrannhet. Andra egenskaper till modellen, som ett annat kylsystem och spraysmörjning studerades för att undersöka möjligheteten att adderas till modellen. Resultat visar på en bred användning av modellen i avseende på termisk analys: värmeflödets storlek och riktning, ett visuellt redskap för växellådans temperatur och hur växellådans temperatur varierar under olika driftförhållanden. Med de här redskapen kan den minsta oljemängden som behövs för att smörja kuggkontakten undersökas och hur kylning av kugghjulen kan förbättras. Nyckelord: Termiskt nätverk, FZG kugghjuls-rigg, värmeflöde, temperatur, MATLAB, ODE
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Tidy, Tiago Emanuel Ramos. "Modelling of volumetric solar receivers with nanoparticle suspensions." Master's thesis, Universidade de Évora, 2015. http://hdl.handle.net/10174/16213.
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This work addresses the modelling of nanofluid-based volumetric receivers aiming the improvement of solar energy harvesting and conversion systems. A numerical heat transfer model (1-D) was developed to predict the energy gain in a non-flowing receiver, in which both receiver height and particles volume fraction were optimized. Various combinations of base fluids (water, mineral oils, ethylene glycol) and nanoparticles (graphite, carbon nanotubes) were considered by modelling their optical and thermodynamic properties. Specific characteristics and advantages of volumetric receivers were emphasized by comparing numerical results with those obtained for a surface-based receiver, and by experimental measurements. A two-dimensional numerical model was also developed to investigate the performance of a parallel plate volumetric receiver with a fully developed laminar flow under various operation conditions. It was found that a better performance was obtained when using solid particles of carbon nanotubes; RESUMO:
Modelação de recetores solares volúmicos com nanopartículas suspensas
Este trabalho aborda a modelação de recetores volúmicos com nanofluidos tendo como objetivo o melhoramento de sistemas de captação e conversão de energia solar. Foi desenvolvido um modelo numérico de transferência de calor unidimensional para prever a energia ganha num recetor estagnado, onde a altura e a fração volúmica de partículas foram otimizadas. Várias combinações de fluidos (água, óleos minerais, etileno glicol) e nanopartículas (grafite, nanotubos de carbono) foram consideradas através da modelação das suas propriedades óticas e radiativas. As características específicas e vantagens dos recetores volúmicos foram destacadas através da comparação dos resultados numéricos com os obtidos num recetor de superfície, e através de medidas experimentais. Foi também desenvolvido um modelo numérico bidimensional para investigar o desempenho de um receptor volúmico com escoamento laminar e plenamente desenvolvido entre placas paralelas, sob várias condições de operação. Verificou-se que o melhor desempenho foi obtido usando partículas sólidas de nanotubos de carbono.
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Ibbotson, Simon David. "A modelling study of interannual variability in the middle atmosphere." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325487.
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Lapthorn, Andrew Craig. "High Temperature Superconducting Partial Core Transformers." Thesis, University of Canterbury. Electrical and Computer Engineering, 2012. http://hdl.handle.net/10092/7130.
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The thesis begins by providing an introduction to transformer theory. An ideal transformer is examined first, followed by full core transformer theory. The partial core transformer is then introduced and compared to the full core design. An introduction to superconductors is then presented where a simplified theory of superconductivity is given. High temperature superconductors are then examined including their physical structure, superconducting properties and the design of the superconducting wire.
The early development of high temperature superconducting partial core transformers at the University of Canterbury is then examined. Early partial core development is discussed followed by some material testing at cryogenic temperatures. This work lead into the development of the first high temperature superconducting partial core transformer. This transformer failed during testing and an examination of the failure mechanisms is presented. The results of the failure investigation prompted an alternative winding insulation design which was implemented in a full core superconducting transformer.
The modelling used to design a high temperature superconducting partial core transformer is then presented. Based upon the reverse design method, the modelling is used to determine the components of the Steinmetz equivalent transformer circuit. The modelling includes a combination of circuit theory and finite element analysis. An ac loss model for high temperature superconductors is also presented.
A new 15 kVA, 230-230V high temperature superconducting partial core transformer was designed, built and tested. The windings are layer wound with first generation Bi2223 high temperature superconductor. The modelling was used to predict the performance of the transformer as well as the ac losses of the high temperature superconductor. A series of electrical tests were performed on the transformer including open circuit, short circuit, resistive load, overload, ac withstand voltage and fault ride through tests. The test results are compared with the model. The transformer was found to be 98.2% efficient at rated power with 2.86% voltage regulation.
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Zahariev, Konstantin. "Dynamics and modelling of the oceanic surface boundary layer." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0009/NQ37350.pdf.
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Mason, Ian George. "A study of power, kinetics, and modelling in the composting process." Thesis, University of Canterbury. Civil Engineering, 2007. http://hdl.handle.net/10092/1214.
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This thesis explores the roles of physical and mathematical modelling in the prediction of temperature profiles in the composting process. A literature-based evaluation of the performance of laboratory- and pilot scale composting reactors, showed that physical models used in composting research frequently do not properly simulate the full-scale composting environment, and may therefore produce results which are not applicable at full scale. In particular, self-heating, laboratory-scale, reactors typically involve significant convective/conductive/radiative losses, even with insulation present. This problem can be overcome by using controlled temperature difference or controlled heat flux laboratory reactors, which allow convective/conductive/radiative heat fluxes to be controlled to levels close to those occurring in full-scale systems. A new method of assessing the simulation performance of composting systems is presented. This utilises the areas bounded by the temperature-time profile and reference temperatures of 40 and 55 ℃ (A₄₀ and A₅₅), the times for which these temperatures are exceeded (t₄₀ and t₅₅), and times to peak temperature. An evaluation of published temperature profiles showed a marked difference in these parameters when comparing many laboratory- and full-scale reactors. The impact of aeration is illustrated, and laboratory- and pilot-scale reactors able to provide good temperature profile simulation, both qualitatively and quantitatively, are identified. Mathematical models of the composting process are reviewed and their ability to predict temperature profiles assessed. The most successful models in predicting temperature profiles have incorporated either empirical kinetic expressions, or utilised a first-order model, with empirical corrections for temperature and moisture. However, no temperature models have been able to predict maximum, average and peak temperatures to within 5, 2 and 2 ℃ respectively, or to predict the times to reach peak temperatures to within 8 h, although many models were able to successfully predict temperature profile shape characteristics. An evaluation of published constant-temperature and varying-temperature substrate degradation profiles revealed very limited evidence to support the application of single exponential, double exponential or non-logarithmic Gompertz functions in modelling substrate degradation kinetics, and this was identified as a potential weakness in the temperature prediction model. A new procedure for correcting substrate degradation profiles generated at varying temperature to a constant temperature of 40 ℃ was developed and applied in this analysis, and on experimental data generated in the present work. A new approach to the estimation of substrate degradation profiles in the composting process, based on a re-arrangement of the heat balance around a reactor, was developed, and implemented with both a simulated data set, and data from composting experiments conducted in a laboratory-scale constant temperature difference (CTD) reactor. A new simulated composting feedstock for use in these experiments was prepared from ostrich feed pellets, office paper, finished compost and woodchips. The new modelling approach successfully predicted the generic shape of experimental substrate degradation profiles obtained from CO2 measurements, but under the conditions and assumptions of the experiment, the profiles were quantitatively different. Both measured CO2-carbon (CO2-C) and predicted biodegradable volatile solids carbon (BVS-C) profiles were moderately to well fitted by single exponential functions with similar rate coefficients. When corrected to a constant temperature of 40 ℃, these profiles gave either multi-phase or double exponential profiles, depending upon the cardinal temperatures used in the temperature correction procedure. If it is assumed that the double exponential model generated is correct, this work provides strong evidence that a substrate degradation curve generated under appropriate laboratory conditions at 40 ℃ would, given the correct cardinal temperatures, generate a correct substrate degradation profile under varying temperature conditions, and that this in turn would enable an accurate and precise prediction of the temperature profile using a heat and mass balance approach. This finding opens the door for the development of a simple laboratory test for composting raw material characterisation, but underlines the need for accurate estimates of the physical cardinal temperatures. Experimental factors appear to be the likely cause of the dysfunction between previously reported substrate degradation patterns and existing substrate degradation models, and suggestions for further research are provided in order to more precisely and accurately quantify these factors.
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Purcell, Anne 1960. "Mathematical modelling of temperature evolution in the hot rolling of steel." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=30269.
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The CANMET-McGill Mathematical Model has been expanded and improved to provide a more comprehensive predictive tool for simulation of temperature evolution in the hot rolling of steel. The model uses a Windows(TM)-based, user-friendly, graphical interface and the explicit finite-difference method in two dimensions to simulate the rolling of flat product.Data input options were expanded to allow an initial temperature gradient in the steel to be rolled, the inclusion of a runout table in the calculations, specific chemical compositions and a choice of emissivity values.
A novel, chemistry-dependent thermal conductivity term was developed to account for the variation in heat conduction through the thickness of the steel and to ensure that the temperature of the entire cross-section is accurately predicted. In addition, the model now calculates a heat of transformation for phase changes from austenite to ferrite, pearlite and bainite.
An automated self-calibration module was included to facilitate the calibration of the model's predictions to empirically obtained temperature setpoints.
The model's temperature predictions were validated against both industrial and laboratory data with excellent results.
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Svensson, Magnus. "Modelling soil temperature and carbon storage changes for Swedish boreal forests." Licentiate thesis, KTH, Land and Water Resources Engineering, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1711.
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With the use of a process-orientated ecosystem model andmeasurements conducted at different Swedish coniferous forestsites, abiotic and biotic interactions between tree and soilwere identified and related to governing factors. Two differentmodelling approaches to describe soil temperatures at two sitesincluding hydrological transects were tested (I). The approachin which both canopy and soil were considered proved to be amore flexible tool to describe soil temperatures, especiallyduring snow-free winter periods. Five sites along a climatetransect covering Sweden were used to describe soil carbon poolchanges during an 80-year period simulation (II). The dynamicmodelling approach, with a feedback between abiotic and bioticsub-models, was successful in describing simplified patterns offorest stand dynamics and furthermore in differentiatingbetween climate and nitrogen availability factors. The largereffect of nitrogen availability compared to climate on soilcarbon pool changes was clearly shown.
Keywords:SPAC; soil surface energy balance; Norwayspruce; canopy; LAI; climate; nitrogen; CoupModel
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Purcell, Anne. "Mathematical modelling of temperature evolution in the hot rolling of steel." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0029/MQ64245.pdf.
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Bansil, M. S. "Computer modelling of Bourdon gauges used for pressure and temperature sensing." Thesis, City University London, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.354897.
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Ship, Kar Seng. "Modelling and performance simulation of a high temperature superconducting synchronous generator." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431954.
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Gao, R. "Bias temperature instability modelling and lifetime prediction on nano-scale MOSFETs." Thesis, Liverpool John Moores University, 2018. http://researchonline.ljmu.ac.uk/8989/.
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Bias Temperature Instability (BTI) is one of the most important reliability concerns for Metal Oxide Semiconductor Field Effect Transistors (MOSFET), the basic unit in integrated circuits. As the development MOSFET manufacturing technology, circuit designers need to consider device reliability during design optimization. An accurate BTI lifetime prediction methodology becomes a prerequisite. Typical BTI lifetime standard is ten years, accelerated BTI tests under high stress voltages are mandatory. BTI modelling is needed to project BTI lifetime from high voltages (accelerated condition) to operating voltage. The existing two mainstream BTI models: 1). The Reaction-Diffusion (R-D) framework and 2). The Two-Stage model cannot provide accurate lifetime prediction. Quite a few fitting parameters and unjustifiable empirical equations are needed in the R-D framework to predict the lifetime, questioning its predicting capability. The Two-stage model cannot project device lifetime from high voltages to operating voltage. Moreover, the scaling down of MOSFET feature size brings new challenges to nano-scale device lifetime prediction: 1). Nano-scale devices’ current is fluctuating due to the impact of a single charge is increasing as MOSFET scaling down, repetitive tests need to be done to achieve meaningful averaged results; 2). Nano-scale devices have significant Device-to-Device variability, making the lifetime a distribution instead of a single value. In this work a comprehensive As-grown Generation (A-G) framework based on the A-G model and defect centric theory is proposed and successfully predicts the Time Dependent Variability and lifetime on nano-scale devices. The predicting capability is validated by the good agreement between the test data and predicted values. It is speculated that the good predicting capability is due to the correct understanding of different types of defects. In the A-G framework, Time Dependent Variability is experimentally separated into Within-Device Fluctuation and the averaged degradation. Within-Device Fluctuation can be directly measured and the averaged degradation can be modelled using the A-G model. The averaged degradation in the A-G model contains: Generated Defects, As-grown Traps and Energy Alternating Defects. These defects have different kinetics against stress time thus need separate modelling. Various patterns such as Stress-Discharge-Recharge, multi-Discharging-based Multiple Pulses are designed to experimentally separate these defects based on their different charging/discharging properties. Fast-Voltage Step Stress technique is developed to reduce the testing time by 90% for the A-G framework parameter extraction, making the framework practical for potential use in industry.
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Fonseca, Rojas Mirla Josefina. "Phase behaviour modelling of water-hydrocarbon in high temperature petroleum reservoirs." Thesis, Heriot-Watt University, 2006. http://hdl.handle.net/10399/2152.
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Development of high pressure-high temperature (RPHT) reservoirs is increasingly being pursued world wide to exploit hydrocarbon from deep formation. Due to their extreme conditions (can be up to 2000e and 16000 psia), composition of RPHT fluids can be considerably different from that of conventional reservoirs, particularly the concentration of heavy hydrocarbons in the vapour phase can be quite high. Also, at high temperature the amount of water dissolved in the reservoir hydrocarbon phase could be significant and should be taken into account in detennining the phase and volumetric properties of the fluids. In this study, a model based on equations of state (BOS) was developed to predict phase behaviour of RPHT fluids in the presence of water. The conventional mixing rule was modified by adding a non-random element in the attractive term of EOS. This modification was required to describe the interaction between non-polar (hydrocarbon) and polar (water) compounds. The developed phase behaviour model with the added term to the conventional mixing rules was evaluated for predicting the phase behaviour of hydrocarbon mixtures in presence of water. The conventional (random) interaction parameters (kij) and the non-random interaction parameter of the asymmetric term (lpi) for water-hydrocarbons were determined by matching the solubility data of hydrocarbon-water binary systems in vapour-liquid equilibrium for light and in liquid-liquid equilibrium for intermediate and heavy hydrocarbons. A method based on the Krichevsky-Kasarnovsky equation was developed to correct the effect of pressure on fugacity of the solute in the liquid phase in liquid-liquid equilibrium. The determined binary interaction parameters (BIP) were generalised by correlating them with critical properties and the molecular weight of hydrocarbons. The reliability of the model was evaluated against measured data, not used in its development, over a wide range of pressure and temperature and compared with those of leading models reported in the literature. The model could reliably predict the presence of free water phase and the effect of pressure on the liquid water phase at high temperatures. It also reliably predicted the effect of water on saturation pressure of tested synthetic reservoir fluids. However, it failed to accurately reproduce the effect of addition of water on the volumetric behaviour of the liquid hydrocarbon phase.
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Gong, Yilun. "Modelling of diffusional phenomena in structural alloys for high temperature applications." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:ae400e27-5ebb-49e5-9af0-038b5440fa8c.
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This thesis is concerned with the physical metallurgy/corrosion of high temperature structural alloys, of the type used for some of the most demanding engineering applications yet devised by mankind. Both iron-based steels and nickel-based superalloys are used for such applications; the common thread in this thesis from the science perspective is the role played by defects such as vacancies which lead to degradation due to diffusional phenomena such as oxidation and creep. Modelling for typical diffusional behaviour is carried out at various length scales in this work. First, the vacancy formation free energy in fcc-nickel is calculated by using highly-accurate ab initio thermodynamics including relevant temperature effects such as phonon vibrations and magnetisms. Predictions show good agreement with experiments, with non-Arrhenius behaviour due to the anharmonicity suggested by calculations. Second, the oxidation kinetics is predicted for the Ni-Cr-O system by coupling CALPHAD thermodynamics and diffusional kinetics. A general (oxidation) diffusion model coupled with the homogenisation model is applied, allowing the treatment of metal, oxide and metal/oxide interface to be unified. Predicted oxidation kinetics considering oxide phases (halite, corundum and spinel) and metallic phases (fcc and bcc) show reasonable agreement with experiments. Proposed quantification of entropy-production potentially allows the long-debated question concerning the rate-controlling steps (phases) in high temperature corrosion process to be answered. Last, the failure (breakaway oxidation) mechanisms of a critical Fe9Cr1Mo nuclear component exposed to CO2 are studied by high-resolution characterisations. Based upon theories of carbon diffusion in ferrite and Boudouard surface reaction, the temperature-dependent lifetime - linked with carbon saturation in metal - is rationalised at accelerated conditions and is extrapolated to service conditions.
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Marklund, Magnus. "Modelling and simulation of pressurised black liquor gasification at high temperature." Licentiate thesis, Luleå tekniska universitet, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-17796.
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Black liquor (BL), a by-product of the chemical pulping process, is an important liquid fuel in the pulp and paper industry. It contains almost all of the inorganic cooking chemicals along with the lignin and other organic matter separated from the wood during pulping in the digester. To recover the organic combustion heat and cooking chemicals (sodium and sulphur) from the produced black liquor in kraft pulping, Tomlinson kraft recovery boilers are traditionally used. However, the kraft recovery boiler is not thermodynamically efficient and suffers from problems with explosion phenomena, fouling, and emissions. A potential technology for improving the recovery cycle is pressurised gasification of black liquor. However, uncertainties about the reliability and robustness of the technology are preventing a large-scale market introduction. One important step towards a greater trust in the process reliability is the development of simulation tools that can provide a better understanding of the process and improve performance through optimisation. This licentiate thesis is concerned with the modelling and simulation of an entrained flow gasifier for pressurised gasification of black liquor at high temperature. The thesis comprises three papers presenting the simulation results obtained from different models using CFD (Computational Fluid Dynamics). In paper A a simplified gasification model, considering just the gas phase, is used to make a qualitative study of the effect of burner spray angle on the gas flow in the gasifier. In paper B the simulation results from a more advanced model with gas/droplet interaction, are compared to the results presented in paper A. Finally, in paper C a complex model for pressurised gasification of black liquor droplets is presented and used to study the influence of uncertainties in model parameters.Godkänd; 2003; 20070122 (ysko)
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Atti, O. F. "Modelling outflow and low temperature induced crack propagation in pressurised pipelines." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1445271/.
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This thesis describes the development and refinement of a rigorous mathematical model for simulating outflow following the failure of pressurised single pipelines and pipeline networks containing multi-component hydrocarbon mixtures. The same model is then extended to simulate the progression of a defect in the pipeline into a running fracture. The outflow model is based on homogeneous equilibrium assumption with the conservation equations resolved using the Method of Characteristics (MOC). The model addresses some of the shortcomings associated with the incorrect posing of boundary conditions reported in earlier works. Both types of failures including pipeline puncture as well as full-bore rupture are modelled. Typical pressurised pipeline inventories include permanent gases and liquids, condensable gases, flashing liquids as well as two-phase liquid gas mixtures. Model validation is performed against the Isle of Grain field data as well as those logged during the Piper Alpha tragedy. In cases where real data are not available, a mass conservation index is determined to assess the accuracy of the numerical simulation. In most cases, good agreement between the simulated and field data along with reasonable mass conservation indices (close to unity) are observed. A significant aspect of the work involves the development of methodologies for reducing the computation run time. This has involved the use of various numerical grid discretisation schemes such as simple and nested grids as well as the development of a quadratic interpolation scheme. Investigations using different types of pipeline inventories show that the nested grid system is primarily effective in reducing the computation run time when used in conjunction with long pipelines (ca. > 0 km) containing gases. For other cases, the use of the simple grid system is recommended. The interpolation scheme involves the construction of a database encompassing a pre defined fluid pressure/enthalpy range. This method is found to be universally effective in reducing the computational run time by as much as 80 % for all types of inventories without a loss in accuracy. This computational run time saving is made in comparison to when actual flash calculations are made. The crack propagation model invokes fracture mechanics principles and accounts for the important processes taking place during depressurisation including the thermal, and pressure stresses in the pipe wall to simulate the progression of a simple defect into a running fracture. The application of the model to an isolated exposed pipeline, where the released inventory freely moves away from the discharge plane shows rapid localised cooling of the pipe wall to temperatures well below its ductile to brittle transition temperature. The resulting drop in the fracture toughness coupled with the pressure stresses at the defect plane suggests that catastrophic pipeline failure through a running fracture can arise. In the case of buried pipelines, such effects are found to be even more pronounced due to the additional thermal stresses in the pipe wall. The latter is brought about as a result of the cooling the pipe wall by the confined escaping gas. The above study for the first time quantitatively highlights the importance of taking into account the expansion induced cooling effects as a credible failure scenario when undertaking safety assessment of pressurised pipelines.
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Wilson, Simon J. "Thermal profiles in oxygen vacuum swing adsorption (VSA) : modelling, observations and optimisation." Monash University, Dept. of Chemical Engineering, 2001. http://arrow.monash.edu.au/hdl/1959.1/7766.
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Knox, Joanne Jennefer. "Aspects of modelling plain and reinforced concrete at elevated temperatures." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/7713.
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Extreme events such as the Mont Blanc Tunnel fire in 1999 (Bettelini et al. 2001) or the Windsor Tower fire in 2005 (Calavera et al. 2005) have shown how concrete failure at elevated temperatures can be hazardous to the safety of members of the public. Generally, there is an absence of understanding of the mechanical behaviour of both plain and reinforced concrete at elevated temperatures, which is essential for computational modelling. Since fire is an extreme event, a certain amount of damage within the structure would be seen to be permissible within its performance objectives. This necessitates analysis in the post-peak regime. As a material, concrete has a very low value of thermal conductivity. This means that large thermal gradients often occur within concrete, causing differential expansion of the material. This, coupled with the change in mechanical properties at elevated temperatures, further complicates analytical analysis procedures. This study investigates issues associated with computational modelling of plain and reinforced concrete at elevated temperatures and its residual behaviour (behaviour when tested after the material has been heated, for example in a fire, and then cooled). In order to achieve this, first the constitutive material properties of both plain and reinforced concrete at ambient and elevated temperatures were investigated. The study showed that mesh sensitivity and localisation of strain softening occurs in plain concrete under both tensile and compressive loading. Path dependency of the stress-strain behaviour of plain concrete was also demonstrated, when it was subjected to loading and heating. Tension stiffening was included in the reinforced concrete material model, to represent the interaction between concrete and reinforcing steel. Complex behaviours were seen for simple reinforced concrete benchmark tests, due to changing material properties at elevated temperatures and differential thermal expansion of steel and concrete. Non-linear load-displacement relationships were seen as a result of complex load-sharing between concrete and reinforcement. A hypothesis was proposed – that variation of temperatures during heating and cooling of a specimen will cause damage, and hence material degradation, in plain and reinforced concrete. On investigation, it was seen that damage due to differential thermal expansion plays a small part in the reduction of elastic load-displacement slope and peak strength seen in experimental data on residual tests, indicating that other factors identified in previous research also affect the residual behaviour of plain and reinforced concrete. Indeed, in reinforced concrete, when tension stiffening was included, it was found that damage due to differential thermal expansion and contraction had a negligible effect on the residual response in the pre-peak regime. The study also found that for a simply supported beam pure thermal expansion caused a localised response, while pure thermal gradient gave distributed yield. When both were present, in this study, distributed yield with no mesh sensitivity was seen. Realistic heating of a restrained reinforced concrete plane strain model caused compressive stresses accompanied by tensile longitudinal total strains and tensile longitudinal plastic strains throughout the depth of the slab, with the largest values occurring near to the model supports. Damage and recovery variables were found to have no effect on the response of the model. When a portal frame was exposed to heating, plastic strains were distributed throughout the beam, with column rotation limiting downward thermal bowing due to a uniformly distributed load or thermal gradient present. Application of displacement loading causing plastic damage changed the behaviour of the structure under heating – instead of symmetrical compressive plastic strains being induced, areas of varying tensile and compressive strain were caused within the beam. Throughout, simple, easily reproducible simulations were used so that single parameters could be altered and considered. This was important, so that the important parameters to computational modelling could be identified. These can be used to guide experimental series to ensure that they are investigated, in order to improve computational material models. Not all variations of parameters were investigated in this study, but it is clear where further repetition would be beneficial (e.g. in varying thermal expansion and thermal gradient ratios in heating regimes). This study looks to address experimentalists and people working in structural analysis, who would be interested in the parameters investigated, as well as practitioners who may want to use these results.
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Hess, Victor George. "Three-dimensional mathematical model of a high temperature polymer electrolyte membrane fuel cell." Doctoral thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/24481.
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Polymer electrolyte fuel cells are regarded as one of the most promising alternatives to the depleting and high pollutant fossil fuel energy sources. High temperature Polymer electrolyte fuel cells are especially suitable for stationary power applications. However, the length scale of a PEM fuel cells main components range from the micro over the meso to the macro level, and the time scales of various transport processes range from milliseconds up to a few hours. This combination of various spatial and temporal scales makes it extremely challenging to conduct in-situ measurements or other observations through experimental means. Thus, numerical simulation becomes a very important tool to help understand the underlying electrochemical dynamics and transient transport phenomena within PEM fuel cells. In this thesis research a comprehensive, three- dimensional mathematical model is developed which accounts for the convective and diffusive gas flow in the gas channel, multi-component diffusion in the porous backing layer, electrochemical reactions in the catalyst layers, as well as flow of charge and heat through the solid media. The governing equations which mathematically describe these transport processes, are discretized and solved using the finite-volume based software, Ansys FLUENT, with its in-built CFD-solvers. To handle the significant non-linearity stemming from these transport phenomena, a set of numerical under-relaxation schemes are developed using the programming language C++. Good convergence is achieved with these schemes, though the model is based on a serpentine single-channel flow approach. The model results are validated against experimental results and good agreement is achieved. The result shows that the activation overpotential is the greatest cause of voltage loss in a high temperature PEM fuel cell. The degree of oxygen depletion in the catalyst layer, under the ribs, is identified and quantified for a given set of input parameters. This factor is followed by membrane resistance to protonic migration. The model can thus be suitable applied as a tool to predict cell performance. The results also show that performance is influenced by not just one, but a combination of inter-related factors, thus temperature increases, and flow rate changes will only be effective if simultaneously, the concentration of inlet oxygen, and the mobility of proton-ions in the membrane is increased. Not only does the model results verify these phenomena, but provide a quantitative output for any given set of input parameters. It can therefore be suitably applied as an optimisation tool in high temperature PEM fuel cell design.
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Weaver, Andrew John. "Numerical and analytical modelling of oceanic/atmospheric processes." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/27560.
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Two problems in oceanic/atmospheric modelling are examined in this thesis. In the first problem the release of fresh water from a midlatitude estuary to the continental shelf is modelled numerically as a Rossby adjustment problem using a primitive equation model. As the initial salinity front is relaxed, a first baroclinic mode Kelvin wave propagates into the estuary, while along the continental shelf, the disturbance travels in the direction of coastally trapped waves but with a relatively slow propagation speed. When a submarine canyon extends offshore from the estuary, the joint effect of baroclinicity and bottom relief provides forcing for barotropic flow. The disturbance now propagates along the shelf at the first coastally trapped wave mode phase speed, and the shelf circulation is significantly more energetic and barotropic than in the case without the canyon. For both the experiments with and without a canyon an anticyclonic circulation is formed off the mouth of the estuary, generated by the surface outflow and deeper inflow over changing bottom topography. As the deeper inflow encounters shallower depth, the column of fluid is vertically compressed, thereby spinning up anticyclonically due to the conservation of potential vorticity. This feature is in qualitative agreement with the Tully eddy observed off Juan de Fuca Strait. A study of the reverse estuary (where the estuarine water is denser than the oceanic water) shows that this configuration has more potential energy available for conversion to kinetic energy than the normal estuary. Bass Strait may be considered as a possible reverse estuary source for the generation of coastally trapped waves. Model solutions are compared with field observations in the Bass Strait region and with the results of the Australian Coastal Experiment. The effects of a wider shelf and a wider estuary are examined by two more experiments. For the wider shelf, the resulting baroclinic flow is similar to that of the other runs, although the barotropic flow is weaker. The wide estuary model proves to be the most dynamic of all, with the intensified anticyclonic circulation now extending well into the estuary.
In the second problem the effect of the horizontal structure of midlatitude oceanic heating on the stationary atmospheric response is examined by means of a continuously stratified model and a simple two level model, both in the quasigeostrophic β-plane approximation.
Solutions are obtained for three non-periodic zonal heating structures (line source, segmented cosine, and segmented sine). Little difference is observed between the solutions for these two different models (continuously stratified and two level). There are two cases which emerge in obtaining analytic solutions. In case 1, for large meridional wavenumbers, there exists a large local response and a constant downstream response. In case 2, for small meridional wavenumbers, the far field response is now sinusoidal. A critical wavenumber separating these two cases is obtained. The effect of oceanic heating on the atmosphere over the Kuroshio region is examined in an attempt to explain the large correlations observed between winter Kuroshio oceanic heat flux anomalies, and the winter atmospheric surface pressure and 500 & 700 mb geopotential heights, both upstream and downstream of the heating region. In both models, the response is consistent with the observed
correlations. When western North Pacific heating and eastern North Pacific cooling are introduced into the models, a large low pressure response is observed over the central North Pacific. This feature is in excellent agreement with the observed correlations. A time dependent, periodic, two level model (with and without surface friction) is also introduced
in order to study the transient atmospheric response to oceanic heating. The height at which the thermodynamic equation is applied is found to be crucial in determining the response of this model. When the heating is entered into the model near to the surface, unstable modes are prevalent sooner than they would be when the heat forcing is applied at a higher level. As in the steady state models, two cases dependent on the meridional wavenumber ɭ emerge in the analysis. For small scale meridional heating structures (large ɭ), the response consists of an upper level high and a lower level low which propagate eastward with time. For large scale meridional heating structures (small ɭ) the response essentially consists of a wavenumber 3-4 perturbation superimposed on the solution for large ɭ.Science, Faculty of
Mathematics, Department of
Graduate