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Abdullah, Hishyar K. "Steady rivulets." Thesis, University of Essex, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328593.
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Ahmed, Kamel Abd El-Salam Attia. "Automobile cornering behaviour under steady and non-steady state conditions." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329475.
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Zaidi, Syed Khateeb. "Studies on steady state and post-steady state ultrafiltration of different solutes." Thesis, University of Ottawa (Canada), 2002. http://hdl.handle.net/10393/6271.
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Concentration polarization in ultrafiltration with fully retentive membrane under unstirred conditions has been studied using three different types of solutes: (a) solute which exerts osmotic pressure and also forms a gel (polyethylene glycol), (b) solute which exerts osmotic pressure but does not form a gel (dextran) and (c) solute which does not exert osmotic pressure but forms a gel (silica). An unequivocal determination of whether pressure independent flux regime is osmotically controlled or gel layer dominated, is still open for discussion in the membrane literature. The present work reports a method that could be used to address this issue. It is shown that analysis of post steady state transient filtration data leads to clear demarcation of osmotically limited and gel layer controlled filtration. A method for determining additional filtration resistance offered by the polarization layer to permeate flow in macromolecular ultrafiltration has been proposed and verified experimentally. It has also been shown that the polarization layer thickness is not sensitive to the feed pressure but varies as a function of the bulk solute concentration; higher the bulk concentration thicker is the polarization layer. A fundamental analysis of deposited gel layer has been presented based on constant pressure filtration theory for the solute, which only forms a gel layer (silica). This was used to calculate specific resistance of the solute particles. The concentration and pressure dependence of specific resistance was also reported while silica gel porosity was determined by the Kozeny-Carman equation.
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Söderberg, Sara. "Steamy, steady & sanctuary : The importance of crafting a shared sauna at Sunds Grustag." Thesis, Konstfack, Keramik & Glas, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:konstfack:diva-7717.
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Petit, Maxime. "Residency and trafficking of ILC2 in steady steate and th2 induced inflammatory conditions." Thesis, Université de Paris (2019-....), 2019. http://www.theses.fr/2019UNIP7095.
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Les ILC2s sont retrouvées au niveau des muqueuses comme les poumons et l’intestin, ainsi que dans divers ganglions et organes liés au métabolisme comme les tissus adipeux (ATs). Elles jouent un rôle important dans l’induction des réponses immunitaires de type Th2 comme équivalents innées dans lymphocytes Th2. Elles sont activées par des alarmines (IL-25 et IL-33) et des activateurs environnementaux (allergènes, métabolites et neuromédiateurs). Les ILC2s sécrètent des cytokines de type Th2 permettant de recruter et d’activer des cellules myéloïdes, d’augmenter la production de mucus et la contraction musculaire, ainsi que d’initier la réparation et le renouvellement des tissus. Cependant, une activation non contrôlée des ILC2s participe au développement de maladies chroniques. Les ILCs sont généralement considérées comme des cellules résidentes. Cependant, plusieurs études ont suggéré que la migration pourrait être un processus important pour la maturation des capacités effectrices. La circulation des ILCs reste peu documentée, et aucun mécanisme n’est pour l’instant capable d’expliquer le renouvellement des ILC2s pour agir dans de nombreux tissus suite à une stimulation. Nous avons montré que des quantités significatives d’ILC2s matures et immatures peuvent être collectées dans la lymphe du canal thoracique de souris canulées durant plusieurs heures. Les ILC2s circulantes forment 3 groupes distincts avec des expressions de molécules d’adhésion et récepteurs de migration spécifiques. Nos expériences de transferts cellulaires montrent que ces groupes spécifiques de molécules exprimées sont liés à des tropismes particuliers pour l’intestin, les poumons ou les ATs. Pour analyser le comportement des ILC2s dans un contexte de réponse de type Th2, nous avons injecter les cytokines IL-25 et IL-33 et étudié la lymphe de ces souris. La stimulation à l’IL-33 augmente le nombre de cellules ILC2s circulants dans la lymphe. Les différents groupes d’ILC2s montrent des réponses différentes à l’IL-33. Ainsi, les ILC2s migrants vers l’intestin sont majoritairement prolifératives tandis que le groupe migrant vers les poumons et les ATs secrètent de l’IL-5, de l’IL-13 et de l’Areg. Cela suggère que les ILC2s migrants de façon spécifique possèdent une empreinte fonctionnelle. Nous confirmons les fonctions des groupes d’ILC2s circulants en utilisant des modèles plus physiologiques mimant des réactions allergiques et des infections parasitaires (stimulation par la papaïne et le succinate). Les migrations vers l’intestin et les poumons jouent un rôle primordial dans l’induction de réponse de type Th2 par sécrétion d’IL-5 et d’IL-13, et à l’initiation de la réparation tissulaire par production d’Areg. De façon intéressante, les ILC2s migrants vers les poumons participent au renouvellement des populations résidentes participant principalement à la production d’Areg. Finalement, nous caractérisons un rôle important du trafic des ILC2s à différents temps suivant l’infection par Nippostrongulus brasiliensis, confirmant la fonction des ILC2s migrantesILC2s are found in mucosal tissues as lung and intestine, in lymph nodes, and in metabolic tissues such as the adipose tissues. They play important role in maintaining or inducing type-2 immune responses as innate equivalent of Th2 lymphocytes. They are activated by alarmins (IL-25 and IL-33) and by external activators (allergens, metabolites and neuromediators). ILC2s are secreting type-2 cytokines to facilitate the activation of other cells and to induce an important repair program. Their activation allows large type of events as diverse as myeloid cells recruitment and activation, mucus production, muscle contractility and tissue repair. They have key role in lung and adipose tissue development and maintain their homeostasis by early responding against parasitic pathogens. Abnormal activation of ILC2s is also participating to chronic diseases.ILCs are mostly considered as resident cells. However, different studies suggested that migration could be important for the maturation of their effector capacities and to correctly target the injured tissue. Circulation and trafficking of ILC subsets is still unclear. No mechanism is yet available to explain the turnover of ILC2s and how they can act in many tissues following stimuli.We found that large numbers of mature and immature ILC2s could be collected in the thoracic duct lymph of mice perfused over several hours, showing that ILC2s are in fact actively circulating through the hemo-lymphatic circuit. Furthermore, circulating mature ILC2s could be separated into three distinct subsets depending on their pattern of receptor and adhesion molecule expression. Cell transfer experiments proved that specific patterns are representative of specific tropism for gut, lung and adipose tissues.To analyse ILC2 behaviour in the context of a type-2 response, we injected IL-25 and IL-33 before lymph collection. IL-33 stimulation largely enhanced the number of circulating ILC2s in the lymph. These different ILC2 tissue targeted subsets responded differently to IL-33. Specifically, gut-trafficking ILC2s were mainly stimulated to proliferate whereas lung and adipose tissue subsets were stimulated to produce IL-13, IL-5 and Areg. This suggests that, in ILC2s, specific tissue targeting is associated with already imprinted functions while transiting through the hemo-lymphatic system. We confirmed these functions of circulating ILC2 subsets in more physiological context by mimicking allergy and helminth infection (stimulation by papain and succinate) where specific migration to lungs and intestine play important roles in mounting the type-2 response by IL-5/IL-13 secretion, and also initiating tissue repair by Areg production. Interestingly, we showed that lung migrating ILC2s participated to resident pool renewal that main function is Areg production. Finally, we characterized important trafficking of ILC2 at different stages of Nippostrongulus brasiliensis infection, confirming the functional relevance of ILC2 trafficking
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Bekiaris, Nikolaos Morari Manfred Morari Manfred. "Multiple steady states in distillation /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-09122007-075846.
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Stark, John. "Rearrangements, steady vortices and stability." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.518125.
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Jardine, Moira. "Steady models for magnetic reconnection." Thesis, University of St Andrews, 1989. http://hdl.handle.net/10023/13985.
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Magnetic reconnection is a fundamental physical process by which stored magnetic energy may be released. It is already known that different reconnection regimes result from changes in the nature of the plasma inflow towards the reconnection site. In this thesis, we examine both how the outflow region responds to changes both in the inflow and outflow boundary conditions and also how introducing compressibility affects the results. We find that if the inflow is converging, the outflow velocity is least, the width of the outflow region is greatest and the ratio of outflowing thermal to kinetic energy is greatest. Also, there is one free outflow parameter which would naturally be specified by the velocity of plasma leaving the reconnection site. We suggest that reverse currents seen in numerical simulations may result from the specification of an extra boundary condition. In addition, we find that the main effects of including compressibility are: to enhance convergence or divergence of the inflow; to increase the maximum reconnection rate where the inflow is converging; to increase the flow speed near the reconnection site where the inflow is diverging; to give faster, narrower outflow jets; to increase variations between regimes in the energy conversion and to increase the ratio of thermal to kinetic energy in the outflow jet.
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Easto, Jessica. "Steady, Girl, and Step Boldly." OpenSIUC, 2013. https://opensiuc.lib.siu.edu/theses/1214.
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AN ABSTRACT OF THE THESIS OF JESSICA EASTO, for the Master of Fine Arts degree in FICTION, presented on APRIL 17, 2013, at Southern Illinois University Carbondale. TITLE: STEADY, GIRL, AND STEP BOLDLY MAJOR PROFESSOR: Beth Lordan Steady, Girl, and Step Boldly is a pairing of two long stories.
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Baker, John Alex. "Quasi Steady Capillary Corner Flow." PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/139.
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It is possible to drain slender containers filled with wetting liquids via capillary flows along the interior corners of the container. Usually the well established equations governing such flows demand numerical techniques. In the case of container draining unique boundary conditions resulting from local section geometry allow for a quasi-steady assumption and in turn permit analytical solutions. The quasi-steady assumption may also be employed for certain problems in which the corner flows cause passive capillary migration of the fluid within the container. The analytic solutions are useful because of the ease in which geometric effects may be observed. Container draining and capillary migration by means of corner flows are studied in a variety of container geometries. It is shown that careful selection of cross sectional shape can be used to maximize drain rates and minimize capillary migration times. Three-dimensional effects for these flows are investigated in tapering containers. Some simple micro-scale experiments are reported that provide confidence in the assumptions and application of the important boundary conditions that enable the solutions.
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Hemmati, Sahar. "Steady-State Co-Kriging Models." Thesis, West Virginia University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10614907.
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In deterministic computer experiments, a computer code can often be run at different levels of complexity/fidelity and a hierarchy of levels of code can be obtained. The higher the fidelity and hence the computational cost, the more accurate output data can be obtained. Methods based on the co-kriging methodology Cressie (2015) for predicting the output of a high-fidelity computer code by combining data generated to varying levels of fidelity have become popular over the last two decades. For instance, Kennedy and O’Hagan (2000) first propose to build a metamodel for multi-level computer codes by using an auto-regressive model structure. Forrester et al. (2007) provide details on estimation of the model parameters and further investigate the use of co-kriging for multi-fidelity optimization based on the efficient global optimization algorithm Jones et al. (1998). Qian and Wu (2008) propose a Bayesian hierarchical modeling approach for combining low-accuracy and high-accuracy experiments. More recently, Gratiet and Cannamela (2015) propose sequential design strategies using fast cross-validation techniques for multi-fidelity computer codes.
This research intends to extend the co-kriging metamodeling methodology to study steady-state simulation experiments. First, the mathematical structure of co-kriging is extended to take into account heterogeneous simulation output variances. Next, efficient steady-state simulation experimental designs are investigated for co-kriging to achieve a high prediction accuracy for estimation of steady-state parameters. Specifically, designs consisting of replicated longer simulation runs at a few design points and replicated shorter simulation runs at a larger set of design points will be considered. Also, design with no replicated simulation runs at long simulation is studied, along with different methods for calculating the output variance in absence of replicated outputs.
Stochastic co-kriging (SCK) method is applied to an M/M/1, as well as an M/M/5 queueing system. In both examples, the prediction performance of the SCK model is promising. It is also shown that the SCK method provides better response surfaces compared to the SK method.
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Araki, Yoshikazu. "Stability of Steady States and Steady-State Limit of Elastoplastic Trusses under Quasi-Static Cyclic Loading." Kyoto University, 1997. http://hdl.handle.net/2433/77862.
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Asiri, Hassan M. "Steady motions of a satellite system." Thesis, University of Manchester, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489508.
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This thesis considers two systems: a dumb-bell satellite which is a system of two point masses connected by a massless rigid rod, and a gyrostat consisting of a dumbbell satellite with a gyroscope attached. Stability of relative equilibria of the dumbbell satellite in two dimensions is studied, where two types of relative equilibrium are obtained, which correspond to two orientations: radial and tangential. The only relative equilibrium which is found to be stable is the radial position, and this stability is only satisfied when the length of the dumb-bell satellite is smaller than the radius of the orbit. The reduced energy-momentum method is used through the augmented Hamiltonian.
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Larice, Giulianna S. "Classifying steady in emptying-filling boxes." Thesis, Imperial College London, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.529359.
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Lee, Jong-Suk Ruth. "On automated sequential steady-state simulation." Thesis, University of Canterbury. Computer Science, 2000. http://hdl.handle.net/10092/5612.
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The credibility of the final results from stochastic simulation has had limited discussion in the simulation literature so far. However, it is important that the final results from any simulations be credible. To achieve this, validation, which determines whether the conceptual simulation model is an accurate representation of the system under study, has to be done carefully. Additionally, a proper statistical analysis of simulation output data, including a confidence interval or other assessment of statistical errors, has to be conducted before any valid inferences or conclusions about the performance of simulated dynamic systems, such as for example telecommunication networks, are made.
There are many other issues, such as choice of a good pseudo-random number generator, elimination of initialisation bias in steady-state simulations, and consideration of auto correlations in collected observations, which have to be appropriately addressed for the final results to be credible. However, many of these issues are not trivial, particularly for simulation users who may not be experts in these areas.
As a consequence, a fully-automated simulation package, which can control all important aspects of stochastic simulation, is needed. This dissertation focuses on the following contributions to such a package for steady-state simulation: properties of confidence intervals (CIs) used in coverage analysis, heuristic rules for improving the coverage of the final CIs in practical applications, automated sequential analysis of mean values by the method of regenerative cycles, automatic detection of the initial transient period for steady-state quantile estimation, and sequential steady-state quantile estimation with the automated detection of the length of initial transient period.
One difficulty in obtaining precise estimates of a system using stochastic simulation can be the cost of the computing time needed to collect the large amount of output data required. Indeed there are situations, such as estimation of rare events, where, even assuming an appropriate statistical analysis procedure is available, the cost of collecting the number of observations needed by the analysis procedure can be prohibitively large. Fortunately, inexpensive computer network resources enable computationally intensive simulations by allowing us to run parallel and distributed simulations. Therefore, where possible, we extend the contributions to the distributed stochastic simulation scenario known as the Multiple Replications In Parallel (MRIP), in which multiple processors run their own independent replications of the simulated system but cooperate with central analysers that collect data to estimate the final results.
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Nguyen, Henry Q. "Steady state analysis of resonant converters." Honors in the Major Thesis, University of Central Florida, 1993. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/118.
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This item is only available in print in the UCF Libraries. If this is your Honors Thesis, you can help us make it available online for use by researchers around the world by following the instructions on the distribution consent form at http://library.ucf.edu/Systems/DigitalInitiatives/DigitalCollections/InternetDistributionConsentAgreementForm.pdf You may also contact the project coordinator, Kerri Bottorff, at kerri.bottorff@ucf.edu for more information.Bachelors
Engineering
Electrical Engineering
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Dall'Olmo, Riley Francesca. "Changing consumer attitudes in steady markets." Thesis, London Business School (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336390.
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Homem, Miguel Stone de Terra. "Steady state MHD : waves and instabilities." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408368.
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SANTOS, JORGESON OLIVEIRA RODRIGUES DOS. "STEADY-STATE VOLTAGE STABILITY ASSESSMENT METHOD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8942@1.
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COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIORAtualmente os sistemas elétricos altamente carregados estão enfrentando um crescente risco de estabilidade de tensão na medida que restrições ambientais e incertezas econômicas limitam o investimento em novas linhas de transmissão. Uma revisão dos problemas ocorridos em vários países indicam claramente que o problema de estabilidade de tensão é real e que o pior ainda está por vir [1]. Portanto existe a necessidade do desenvolvimento de ferramentas analíticas capazes de prever o colapso de tensão em redes complexas. Estas ferramentas devem ser capazes de quantificar com precisão as margens de estabilidade e os limites de transferência de potência, identificando os pontos fracos e as áreas susceptíveis á estabilidade de tensão. Um método para determinação das condições de estabilidade local de tensão é mostrado. A eficiência computacional desta ferramenta analítica é enfatizada em estudos de análise de cotingência. Estudos comparativos mostram a influência do modelo da carga estática, dos equivalentes de redes e da representação dos limites de geração ou absorção de potência reativa a partir da curva de capabilidade da máquina síncrona, no índice que avalia a estabilidade local de tensão. Um estudo sobre o determinante da matriz que serve como índice que avalia a estabilidade local de tensão. Neste trabalho são propostos novos estudos para dar continuidade aos avanços obtidos até o momento.
Nowadays, heavy loaded eletric power systems are facing voltage stability problems due to environmental restrictions and budget cuts. Power systems incidents involving voltage stability clearly show that it is real problem and worse conditions are expected [1]. Therefore, there is a need of developing analytical tools to detect voltage collapse in complex networks. These tools must show, with good accuracy, stability ranges and power transfer limits, identifying weak nodes and susceptible areas to voltage stability. It is show a method to determine local voltage stability conditions and its computational efficiency is emphasized through contingency analysis studies. Comparative studies show the influence of static load model, network equivalent and reactive power generation/absorption limits representation using the synchronous machine capability curve, over the index which evaluates local voltage stability. It is show a study about the determinant which plays as an index to evaluate local voltage stability. Suggestions are made for future research.
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Green, Henry Gregory. "Characteristics of steady and unsteady jets." Thesis, Imperial College London, 1987. http://hdl.handle.net/10044/1/38338.
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Melissa, Matthew (Matthew J. ). "Steady states in rapidly evolving populations." Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/115020.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Physics, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 63-68).
Populations are subject to mutations conferring beneficial effects, as well as mutations conferring deleterious effects. Even if deleterious mutations occur much more frequently than beneficial mutations, the contribution of deleterious mutations to the overall rate of change of the population-wide mean fitness may be limited, due to the efficient action of selection. However, in particularly rapidly evolving populations, the stochastic accumulation of deleterious mutations may negate a significant fraction of the fitness increments provided by beneficial mutations, or even result in an overall decrease in fitness over time. Here we obtain a constraint on beneficial and deleterious mutation rates and selection pressures in order for positive adaptation to counterbalance fitness decline via Muller's ratchet. The steady state that separates parameter regimes of positive adaptation and negative adaptation is characterized by appealing to the exponential dependence of fixation probabilities on fitness effect sizes. We consider a range of fitness-mediated epistatic interactions and the corresponding implications regarding the existence, location and stability of long-term evolutionary fixed points.
by Matthew Melissa.
S.M.
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Cartwright, Malcolm. "Modelling of non-ideal steady detonations." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/15940/.
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Steady state detonations of rate-stick explosives can be modelled via a streamline based approach. The Straight Streamline Approximation (SSA) is a method for predicting the shape of the shock front and sonic surface for an explosive rate-stick. The SSA model is implemented with different explosives models to verify its ability to accurately match high resolution Direct Numerical Simulations (DNS) beyond the simple polytropic EOS (equation of state) and power law reaction rate models. For explosive models using a reaction rate with an induction zone it shown that the SSA is unable to capture diameter effect curves when compared with DNS. The CREST model is implemented into the ZND and Wood-Kirkwood steady- state detonation models. Implementing the CREST model into the steady-state models required the development of a thermodynamic relation not published before. Rate- stick calculations are performed for the SSA model and compared with DNS for various explosive models. With a realistic equation of state there is a limit on the boundary that the SSA model can integrate to, beyond this the streamlines begin to converge and the model equations break down. This places a limit on the SSA’s modelling capabilities not previously reported. Equations for the post-shock streamline curvature with a reaction term are devel- oped. The streamline curvature is calculated for a polytropic EOS with and without reaction at the shock. It is shown that when reaction is a maximum at the shock the magnitude of the streamline curvature is reduced and, in some cases, changes the sign of the curvature. With no reaction at the shock the streamline curvature is signifi- cantly larger. Moreover DNS shows that the streamlines are more curved for reaction rates with induction zones when compared to simple power law reaction rates. The implications for the SSA’s validity are discussed.
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Pan, Wen Hsiung. "Steady State Analysis of Tropospheric Chemistry." PDXScholar, 1991. https://pdxscholar.library.pdx.edu/open_access_etds/1262.
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Hydroxyl radical HO plays a central role in controlling chemical processes in the troposphere. Current mechanisms are believed to accurately describe its formation, destruction and interaction with other atmospheric trace gases in clean air. Hydroperoxyl radical H0₂ is Iinked to HO in several chain processes and serves among other roles as a reservoir for HO. The relative concentration (H0₂/HO) in clean air is believed to be the order of 10². We here examine the conditions under which steady-state kinetics apply to HO₁ chemistry and derive simple relationships which can be used to predict HO and H0₂ concentration from measurable concentrations of the more stable trace gases. The equations assume a simple form for conditions where the ambient nitrogen oxide concentration is less than 1 ppb. These equations allow closed-form evaluation of the sensitivity of [HO] and [H0₂] to changes in the concentrations of the controlling species and allow assignment of uncertainty limits to the predictions of current tropospheric chemical models. Although most current efforts to test fast tropospheric photochemistry center upon measurements of ambient [HO], our equations indicate that tropospheric [H0₂] determinations may provide a more direct and accurate initial test of our knowledge of HO₁ chemistry in the unpolluted lower atmosphere. Overall the goal of this study is to benefit the experimenter by providing the information of insight and simple but reliable equations and to understand the conditions under which these measurements should be made and how best to interpret their results.
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Larsson, Roland. "Elastohydrodynamic lubrication under non-steady conditions." Doctoral thesis, Luleå tekniska universitet, Maskinelement, 1996. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18564.
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The six papers presented in this thesis consider the effects on elastohydrodynamic lubrication (ehl) of non-steady conditions. The vast majority of ehl investigations, both experiemental and theoretical, utilise steady state conditions, i.e. constant load, velocity, geometry and temperature. The lubricant is, however, in conditions that are far from those of steady state. Many components operate with varying load, velocity and geometry. Some examples are gears, rolling element bearings, cams and follower mechanisms and reciprocating seals. To predict the operation of these components it is necessary to consider the transient effects. The theory of elastohydrodynamic lubrication under non-steady conditions is presented in this thesis and applied to some practical cases. Papers A and B deal with the simulation of the lubrication in the contact between an impacting ball and a lubricated surface. These investigations give understanding of lubrication under impact loading and also fundamental understanding of the dynamics of an ehl contact. Paper C is an experimental investigation of the impacting ball problem. The deformation of the surfaces in the contact region is studied for different combinations of lubricant viscosities and impact velocities. Paper D and E deal with the breakdown mechanisms of a lubricant film. It is shown that lubricant film failure occurs at high sliding velocities if the load is non-stationary. This contradicts elastohydrodynamic theory since increasing sliding velocity implies increasing entrainment of lubricant and thus thicker lubricant film and less risk for failure. It is, however, shown in Paper E that starvation can be the reason why film failure occurs even if the conjunction is lubricated by a thick layer of lubricant. Paper F is a transient simulation of a meshing involute spur gear. Film thickness, pressure, friction and subsurface stresses are computed at different positions along the line of action. Two different sets of lubricant properties are used, the first oneGodkänd; 1996; 20070219 (rola)
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Jonoud, Sima. "Validation of steady-state upscaling techniques." Thesis, Imperial College London, 2006. http://hdl.handle.net/10044/1/7812.
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Small, Susan Anne. "Bone-conduction auditory steady-state responses." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31066.
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The purpose of this dissertation was to determine whether multiple auditory-state
responses (ASSRs) to bone-conduction stimuli can be used to investigate bone-conduction
hearing, an essential part of any audiometric assessment. Infant bone-conduction testing methods,
maturation of bone-conduction hearing, and ipsilateral/contralateral asymmetries in ASSRs were
also assessed. The results show that bone-conduction ASSRs can be used to estimate thresholds
in infants and adults with normal hearing. It was also found that choice of electroencephalogram
(EEG) conditioning and processing can avoid spurious ASSRs due to aliasing. Non-auditory
ASSRs (probably vestibular and indistinguishable from an auditory response) were also
identified for high-intensity air-conduction stimuli (problematic when diagnosing residual
hearing). Investigation of infant testing methods on bone-conduction threshold shows that: (i)
bone-oscillator coupling method (elastic-band vs. hand-held) has no effect on threshold, (ii) use
of different oscillator locations on the temporal bone does not affect threshold but a forehead
placement results in elevated thresholds, and (iii) infants do not appear to have an occlusion
effect (thus one can can assess with or without earphones). Young infants have much better low-frequency
bone-conduction hearing compared to adults, which increases with maturation beyond
24 months of age. Infant bone-conduction hearing is slightly poorer in the high frequencies,
improving significantly with age only at 2000 Hz. Within all infant groups, low-frequency
thresholds are better than high-frequency thresholds; for adults, 500-Hz thresholds are poorer
than high frequencies and there is no difference among thresholds above 500 Hz. Bone-conducted
signals are much more effective for infants across frequency, especially at low
frequencies. Normal levels for bone-conduction hearing in young and older infants are proposed.
Ipsilateral/contralateral asymmetries in air- and bone-conduction ASSRs are clearly present more often and are larger in infants compared to adults, and suggest that most infants have 10-30 dB of
interaural attenuation. These asymmetries have potential as a clinical tool for isolating the
cochlea that is contributing to the response in infants. The results of these studies indicate that
infants can now be screened for normal bone-conduction hearing with ASSRs; however, infants
with hearing loss must be tested before elevated bone-conduction ASSRs thresholds can be
interpreted.Medicine, Faculty of
Audiology and Speech Sciences, School of
Graduate
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Linden, Roger Dean. "Human auditory steady state evoked potentials." Thesis, University of Ottawa (Canada), 1985. http://hdl.handle.net/10393/4602.
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Olivares, Espinosa Hugo. "Steady-state model of neutron star crust." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21975.
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The advent of X-ray astronomy has turned the study of compact objects into one of the most active research fields in modern-day physics. Diverse luminosity phenomena have been remarked upon in neutron stars and it is believed that in many of them the neutron star crust plays a critical role. This work presents a steady-state model for the neutron star crust that describes, in particular, the profiles of temperature and flux along this region. It is divided as follows: First, a review of observational phenomena in neutron stars, where crust characteristics are thought to be crucial, are presented, alongside general aspects of the theoretical models applied. Second, the different elements that are needed to construct this model are considered. Third, the set of structure equations to be resolved and the calculations of the components of these equations are provided. Finally, the results are shown and discussed and the conclusion is presented.L'avènement de l'astronomie des rayons X a transformé l'étude des objets compacts en un des champs de recherche des plus actifs en physique moderne. Divers phénomènes de luminosité ont été observés dans les étoiles neutron et on estime que la croûte de l'étoile neutron joue un rôle important dans beaucoup de ces phénomènes. Cet ouvrage présente un modèle d'équilibre stable pour la croûte de l'étoile neutron qui décrit, en particulier, les profiles de température et flux dans cette région. L'ouvrage est divisé comme suit: Premièrement, une révision des phénomènes observés dans les étoiles neutron, où les caractéristiques de la croûte sont supposées être cruciaux, est présentée, avec les aspects généraux des modèles théoriques utilisés. Deuxièmement, les différents éléments nécessaires pour construire ce modèle sont examinés. Troisièmement, l'ensemble des équations de structure à résoudre et les calculs des composantes de ces équations sont présentés. Finalement, les résultats sont montrés et discutés et la conclusion est présentée.
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Shrestha, Purushottam. "Steady flow in steep open channel systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0026/MQ31403.pdf.
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Guo, Hongxin. "The 3-dimensional steady gradient Ricci soliton." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3303740.
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Thesis (Ph. D.)--University of California, San Diego, 2008.Title from first page of PDF file (viewed June 13, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 53-54).
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Bagshaw, M. J. "A study of steady state casting processes." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376872.
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Carroll, Lisa M. "Rapid steady state solidification of Al alloys." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298796.
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Mackman, Thomas James. "Surrogate model construction for steady aerodynamic loads." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633231.
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An efficient method for predicting steady aerodynamic loads with respect to varying geometric and flow parameters is to use a surrogate model to interpolate or approximate a finite set of Computational Fluid Dynamics (CFD) simulations. Further improvements to the strategy for constructing the surrogate have the potential to provide more accurate predicted values or to reduce the number of simulations required to achieve a model of sufficient quality. This work was originally motivated by the task of providing data for calculating structural loads for civil passenger aircraft, but is directly relevant for closely related applications such as providing aerodynamic data for flight mechanics analysis, and quantification of race-car aerodynamic performance. The objective at the outset was to develop aspects toward an improved surrogate modelling strategy for predicting aerodynamic data that enables a reduction in the overall simulation budget. To this end, the fundamental topics of adaptive sampling, model parameter tuning, and practical implementation for aerodynamic data have been investigated, with the goal of developing novel methods in each of these areas, and analysing their operation. Details of an adaptive sampling method based on a combination of curvature-adaptive and space-filling components are presented, including recovery of expected behaviour for analytic functions, formulation of the space-filling component, simultaneous addition of update points; and how best to optimise the criterion efficiently for multidimensional problems. An advanced strategy for choosing locally varying interpolation parameters is then presented, which works by optimising a single value to scale a prescribed local distribution of parameters, subject to constraints on the properties of the interpolation matrix. Following this, the use of various physics-based responses to drive the sampling algorithm and techniques for mitigating noise are investigated for application to aerodynamic data.
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Rowson, Quinton Anthony. "Steady-state vibration of DFT locomotive cabs." Thesis, University of Canterbury. Mechanical Engineering, 2001. http://hdl.handle.net/10092/6624.
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Back injuries and other illnesses for Tranz Rails Locomotive Engineers, is claimed to be
attributed to vibration of locomotive cabs. The purpose of this research was to conduct a
study in order to determine the complex motion of a DFT locomotive cab and to
objectively and quantifiably measure the vibration present in the locomotive.
This thesis examines the ability of a six Degrees Of Freedom rigid body mathematical
model of a DFT locomotive cab to determine the natural frequencies present. The goal
was to use this model to provide information on different mount alternatives, in order to
reduce vibration. The results of this model were inadequate for the selection of another
elastomeric mounting alternative. While experimental test of the locomotive cab showed
that the rigid body assumption was valid it was found that there are other continuous
vibrations and non-linear effects that are also very important in determining cab
vibration.
Auto-correlation results from acceleration measurements at the base of the mounts were
overlaid with the cross-correlation of the acceleration measurements of the cab side of the
mounts. These results showed that the current mounts have 100% transmissibility. In
some cases and directions the mount was shown to actually amplify the vibrational input
from the locomotive.
The amplitude of the steady-state vibration of the locomotive cab that was being
transmitted was so great that it rendered the dynamic characteristics of the cab
insignificant. From the experimental results, the elastomeric mounts were found to be
incapable of attenuating the vibration. In addition, the vibration levels due to locomotive
running are found to be well above comfort levels of various publications.
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馮達淸 and Tat-ching Fung. "Steady state solutions of nonlinear dynamic systems." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1989. http://hub.hku.hk/bib/B31231809.
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Aves, Mark Antony. "Multigrid multiblock computation of steady compressible flows." Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304393.
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Newberry, Anna Christina. "Driver perception of steady-state steering feel." Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.443038.
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Fung, Tat-ching. "Steady state solutions of nonlinear dynamic systems /." [Hong Kong] : University of Hong Kong, 1989. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12760055.
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Clinard, C., Owen D. Murnane, and J. Tampas. "Auditory Steady-State Response: Test-Retest Reliability." Digital Commons @ East Tennessee State University, 2006. https://dc.etsu.edu/etsu-works/1900.
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Zhou, Lu. "Numerical modelling of scour in steady flows." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEC015/document.
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Cette thèse porte sur le développement d’un modèle numérique de l’affouillement causée par des obstacles montes sur le lit, combinant les processus hydrodynamiques et morphologiques. Le modèle numérique est basé sur le solveur de champ d’écoulement polyphasique de l’outil CFD open-source OpenFOAMR qui est distribue par OpenCFD Ltd. Le module hydrodynamique du modèle résout les équations de Navier-Stokes avec moyennes de Reynolds (RANS) et les modèles des turbulences k-ε ou k-ω. Il existe deux interfaces dans le domaine de simulation: la surface libre entre l’eau et l’air, qui est suivi par la méthode de Volume de Fluide (VOF); et l’interface entre l’eau et le lit du sédiment, qui est représentée par un maillage de surface finie déformable construit à partir de la limite en bas du maillage de volume fini. En outre, un module morphologique qui a été développé dans le cadre du projet se compose de trois composantes: un modèle de transport de sédiments comprenant la charge suspendue et le charriage; l’équation d’Exner pour mesurer la déformation du lit; et un mécanisme de glissement du sable pour limiter la pente du lit à être plus petite que l’angle de repos du sédiment. Le changement morphologique est incorporé dans le modèle hydrodynamique par la déformation du maillage. Des conditions limites spéciales et des corrections nécessaires pour le calcul en parallèle sont également ajoutées au modèle. Chaque partie du modèle est validée séparément avec les tests préliminaires correspondants, y compris les fonctions de paroi rugueuse, les performances de la méthode VOF, le modèle de transport de charge suspendu et le mécanisme de glissement de sable. Le modèle numérique est ensuite appliqué pour étudier un affouillent bidimensionnelle cause par un jet immerge provenant d’une ouverture sous écluse. Comparaison des résultats de la simulation avec des données expérimentales prouve la capacité du modèle. Et les limites du modèle sont également discutées. Enfin, le modèle est appliqué à l’étude du champ d’écoulement tridimensionnel et de la formation d’affouillement autour d’un obstacle dans l’écoulement. Tout d’abord, la déformation du lit n’est pas activée. Le tourbillon en fer à cheval devant un obstacle et le champ d’écoulement turbulent autour d’un cylindre sur un lit lisse ou rugueux sont simulés. Deux types de simulation pour le module hydrodynamique sont effectués: une simulation qui utilise une surface fixe et rigide pour représenter l’interface air-eau, et une simulation incluant à la fois les domaines de l’eau et de l’air avec la surface libre suivie par la méthode VOF. Les influences de la surface libre sur le champ d’écoulement sont identifiées et discutées. La comparaison avec les données expérimentales confirme l’importance de la déformation de la surface libre sur le champ d’écoulement. Ensuite, le lit est autorisé à se déformer et le développement temporel de l’affouillement tridimensionnelle autour d’un cylindre sur le lit est simule. Le développement temporel d’affouillement et la profondeur maximale du trou calcule devant et derrière le cylindre conviennent assez bien avec les mesures expérimentales. Les influences de l’affouillement sur le champ d’écoulement sont aussi étudiées et la performance du modèle numérique développé est discutéeThis thesis describes the development of a numerical model for local scour caused by bed-mounted obstacles, combining the hydrodynamic and morphological processes. The basis of the numerical model is the multiphase flow field solver in the open-source CFD toolbox OpenFOAMR which is released by OpenCFD Ltd. The hydrodynamic module of the model solves the Reynolds Averaged Navier-Stokes (RANS) equations with either a k-ε or a k-ω model. There are two interfaces in the simulation domain: the free surface between water and air, which is tracked using the Volume of Fluid (VOF) method, and the interface between the water and the sediment, which is represented by a finite area mesh constructed from the bottom boundary of the finite volume mesh. A morphological module which has been developed as part of the project consists of three components: a sediment transport model which includes suspended load and bed load transport; the Exner equation to compute the bed deformation, and a sand-sliding mechanism to restrict the bed slope angle to be smaller than the angle of repose. The morphological changes are incorporated into the hydrodynamic field through deformation of the computational mesh. Additional boundary conditions and parallel computing corrections are also added into the model. Each individual part of the model has been validated separately with corresponding preliminary test cases including the rough wall functions, the performance of the VOF method, the suspended load transport model and the sand-sliding mechanism. The numerical model is then applied to study two-dimensional scour caused by a submerged jet issuing from an opening under sluice gate. Comparison of the simulation results with the experimental measurements proves the ability of the model for conducting two-dimensional simulations and the limitations of the model are also discussed. Finally, the model is applied to study the three-dimensional flow field and scour formation around an obstacle in flow. Initially, the bed deformation is not activated in the model. The horseshoe vortex formed in front of an obstacle in water and the turbulent flow field around a cylinder on smooth and rough beds are simulated. Two types of simulations for the hydrodynamic module are used: a rigid lid simulation with a slip boundary condition to represent the air-water interface, and a free surface simulation including both the water and air domains with the free surface tracked by the VOF method. The influences of the variation of the water depth on the flow field are identified and discussed. Comparison with the experimental data also confirms the importance of the water surface variation on the flow field. Next, the bed is allowed to deform in the model. The temporal development of three-dimensional scour around a cylinder on live-bed in a steady current is simulated. The development of the scour with time and the computed maximum scour depths in front of and behind the cylinder agree quite well with the experimental measurements. The influences of the scour process on the flow field are also studied and the performance of the numerical model is discussed
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Goldner, Daniel R. "Steady models of arctic shelf-basin exchange." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/53537.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1998.Includes bibliographical references (p. 159-166).
by Daniel Reed Goldner.
Ph.D.
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Wijetunge, Janaka Jayasekera. "Velocity measurements in oscillatory and steady flows." Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627385.
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Deshpande, Vikram S. "Steady-state deformation behaviour of bituminous mixes." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/272413.
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Medina, Medina Humberto Jesus. "Study of steady and pulsating impinging jets." Thesis, Queen's University Belfast, 2008. https://pure.qub.ac.uk/portal/en/theses/study-of-steady-and-pulsating-impinging-jets(8101f081-f0ca-4ef6-a895-369b489a1d17).html.
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An experimental investigation on the fluid mechanics of steady and pulsed impinging jets is presented in this thesis. An experimental facility was custom-builtin order to generate axisymmetric and incompressible impinging jets (pulsed and steady). In order to ensure that the velocity profiles at the exit were fully developed, the jet was discharged from a round nozzle of 50 diameters in length. The effects of the Reynolds number, the nozzle-to-plate spacing and the Strouhal number were investigated systematically. The range of the Reynolds numbers covered is 4000 to 10000 for the steady jets, and 4200 to 10240 for the pulsed jets. The nozzle-to-plate spacings considered are 2, 3 and 4 nozzle diameters,because at these distances heat transfer enhancement is present for pulsed jets. The Strouhal number ranges from 0 (steady case) to 0.5. It was found that the Reynolds number does not affect the flow field of impinging jets as significantly as the nozzle-to-plate spacing, in particular, for pulsed jets, which exhibit significant changes in the distribution of the Reynolds stresses near the impinging wall for small nozzle-to-plate spacings. In addition, it was also found that the axial convection term of the mean axial momentum balance near the impinging wall is significantly larger for a jet pulsed at St _ 0:5 than its steady counterpart when H=d = 4. This work also expands the present knowledge base of both steady and pulsed jets in three main areas; (1) it presents in-depth velocity measurements and turbulence statistics for pulsed and steady jets, (2) the transitional regime of impinging jets is examined, and finally, (3) it presents data for turbulence model validation of a real incompressible pulsed jet.
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Izagirre, Ane. "Interpolation approximations for steady-state performance measures." Thesis, Toulouse, INSA, 2015. http://www.theses.fr/2015ISAT0019/document.
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L'analyse de la performance à l'état stationnaire dans de nombreux systèmes de files d'attente est complexe et les résultats sous forme explicite ne sont disponibles que dans des cas particuliers. Nous avons donc développé des approximations pour des critères de performance importants à l'état stationnaire tels que la longueur de la file d'attente, le temps d'attente et le temps de traitement total. Nous analysons d'abord la performance dans des cas à faible et fort trafic. Nous montrons ensuite comment développer une approximation basée sur une interpolation qui est valable pour n'importe quelle condition de trafic. Un avantage de l'approche proposée est qu'elle n'est pas dépendante d’un modèle particulier et donc elle peut être appliquée à d'autres modèles de files d'attente complexes. Nous appliquons cette technique pour trois modèles largement utilisés dans l'évaluation des performances des réseaux stochastiques : le modèle du supermarché, la file d'attente Discriminatory-Processor-Sharing (DPS) et la file d'attente Relative Priority (RP). Le modèle du supermarché est une file d'attente à plusieurs serveurs où lorsqu’un client arrive, deux serveurs sont choisis au hasard dans un ensemble de serveurs. La politique Join-the-Shortest-Queue (JSQ) est ensuite utilisée parmi les deux serveurs sélectionnés. DPS et RP sont deux files d'attente à plusieurs classes et à serveur unique mettant en œuvre des priorités relatives entre les clients des différentes classes. La discipline DPS sert tous les clients simultanément, tandis que RP sert un seul client à la fois de manière non-préemptive. Nous montrons que dans certains cas, l'interpolation est exacte. Nous utilisons ensuite cette approximation pour déduire comment la performance dépend des paramètres des modèles, et nous effectuons des expériences numériques illustrant la précision de l'interpolation dans un grand nombre de cas de figureThe analysis of the steady-state performance in many queuing systems is complex and closed-form results are available only in particular cases. We therefore set out to develop approximations for important performance measures in steady-state such as the queue length vector, waiting time and sojourn time. We first analyse the performance in a light-traffic and heavy-traffic regime. We then show how to develop an interpolation-based approximation that is valid for any load in the system. An advantage of the approach taken is that it is not model dependent and hence could potentially be applied to other complex queuing models. We apply this technique to three widely used models in the performance evaluation of stochastic networks: The supermarket model, the Discriminatory-Processor-Sharing (DPS) queue and the Relative Priority (RP) queue. The supermarket model is a multi-server queue where upon arrival of a customer two servers are selected at random from the available pool of servers. The Join-the-Shortest-Queue policy is then used in isolation with these two servers. DPS and RP are both single-server multi-class queues that implement relative priorities among customers of the various classes. The DPS discipline serves all customers simultaneously while RP serves one customer at a time in a non-preemptive way. We show that in some instances the interpolation approximation is exact. We then use the approximation to draw structural insights onto the performance of the system, and we carry out numerical experiments that illustrate that the interpolation approximation is accurate over a wide range of parameters
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Lokharu, Evgeniy. "Small-amplitude steady water waves with vorticity." Doctoral thesis, Linköpings universitet, Matematik och tillämpad matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-134243.
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The problem of describing two-dimensional traveling water waves is considered. The water region is of finite depth and the interface between the region and the air is given by the graph of a function. We assume the flow to be incompressible and neglect the effects of surface tension. However we assume the flow to be rotational so that the vorticity distribution is a given function depending on the values of the stream function of the flow. The presence of vorticity increases the complexity of the problem and also leads to a wider class of solutions. First we study unidirectional waves with vorticity and verify the Benjamin-Lighthill conjecture for flows whose Bernoulli constant is close to the critical one. For this purpose it is shown that every wave, whose slope is bounded by a fixed constant, is either a Stokes or a solitary wave. It is proved that the whole set of these waves is uniquely parametrised (up to translation) by the flow force which varies between its values for the supercritical and subcritical shear flows of constant depth. We also study large-amplitude unidirectional waves for which we prove bounds for the free-surface profile and for Bernoulli’s constant. Second, we consider small-amplitude waves over flows with counter currents. Such flows admit layers, where the fluid flows in different directions. In this case we prove that the initial nonlinear free-boundary problem can be reduced to a finite-dimensional Hamiltonian system with a stable equilibrium point corresponding to a uniform stream. As an application of this result, we prove the existence of non-symmetric wave profiles. Furthermore, using a different method, we prove the existence of periodic waves with an arbitrary number of crests per period.
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Bedewi, Mohamed Amin Ahmed. "Non-steady state lubrication of counterformal contacts." Thesis, University of Leeds, 1985. http://etheses.whiterose.ac.uk/2605/.
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A theoretical study has been undertaken of the phenomenon of non-steady state lubrication of concentrated point and line contacts. This has been based upon a study of the effect of squeeze-film action in both hydrodynamically and elastohydrodynamically lubricated contacts. The work described in this thesis is in two main sections. The first is concerned with squeeze-film lubrication of lightly loaded point contacts where the surfaces are taken to be rigid. A complete analytical solution is developed considering both piezoviscous and isoviscous fluids. Formulae representing the relationships between the controlling parameters of hydrodynamic lubrication of point contacts with a pure squeeze action became available. In the second section general numerical solutions to the non-steady state hydrodynamic and elastohydrodynamic lubrication problems for line contacts are developed. The finite difference approximation method has been used to solve simultaneously the Reynolds, elasticity and load equations at successive time steps. To avoid convergence difficulties and reduce computing effort a tri-diagonal matrix algorithm has been incorporated. A wide range of line contact lubrication problems is considered. These include the hydrodynamic and elastohydrodynamic lubrication of cylinders with either pure squeeze-film action or under combined 'entraining' and 'squeeze-film' action. Graphical representations of pressure distributions and film shapes are presented in time sequence as the gap between the two cylinders changes. The variations of the dimensionless minimum film thickness, velocity of approach and peak pressure under various loading conditions are also included. The formation and development of the elastic indentation under constant load with squeeze-film action and with the combined effect of squeeze and entraining action has been ascertained. It has been established that the squeeze-film action plays an effective role in the enhancement of the smallest value of the minimum film thickness occurring under oscillating loading conditions. This effect is more pronounced in elastohydrodynamic than in hydrodynamic lubrication. This general analysis of time dependent lubrication problems for both hydrodynamic and elastohydrodynamic conditions permits specific studies to be undertaken of realistic machine components operating under non-steady state conditions.
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Blyth, Mark Gregory. "Steady flow in dividing and merging pipes." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/7633.
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Mateo, Villanueva Pedro Abdiel. "Toward the Validation of Depth-Averaged, Steady-State Simulations of Fluvial Flows Using Three-Dimensional, Steady-State, RANS Turbulence Models." DigitalCommons@USU, 2010. https://digitalcommons.usu.edu/etd/826.
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Calculations of fluvial flows are strongly influenced by geometry complexity and large overall uncertainty on every single measurable property, such as velocity and shear. Moreover, a considerable portion of the data obtained from computational simulations arose from two-dimensional, steady-state models. The present work states a different approach to perform computer-based simulations and analyze fluvial flows. For the first part, the suitability of OpenFOAM to be used as the main CFD solver to analyze fluvial flows is studied. Initially, two well documented channel configurations are computationally studied using OpenFOAM. Finally, these results are compared to the output obtained from one of the widely used quasi-3D CFD solvers used to perform studies about environmental hydraulics.
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Wilken, Nicolas John. "Experimental investigation of free-surface jet-impingement cooling by means of TiO2-water nanofluids." Diss., University of Pretoria, 2019. http://hdl.handle.net/2263/73456.
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The exponential advancements in the field of electronics and power generation have resulted in increased pressure on the thermal management of these systems where the desire for enhanced heat transfer is prevalent. A technique for enhancing heat transfer that has gained sufficient attention over the past two decades is to suspend nano-sized metallic particles in a base fluid in order to enhance its thermophysical properties. Fluids produced in such a manner are commonly termed nanofluids. Due to the promising heat transfer capabilities of nanofluids, many industrial applications are beginning to implement these fluids in their thermal practices. One of the potential applications where nanofluids may be used which has received a great deal of research attention is jet-impingement heat transfer. Concerning the existing publications on nanofluid jet impingement, most works within the steady state regime are limited to the cooling of Al2O3-water nanofluids, while transient studies do not account for cooling without the effects of boiling phenomena and for surfaces other than steel.
In this study, six particle volume fractions of TiO2-water ranging between 0.025 and 1% were prepared and characterised for appropriate cooling tests. The study was conducted within both the steady and transient state with the main objective of evaluating the thermal performance of the selected nanofluid and to determine the optimum particle concentration for jet-impingement cooling applications. Therefore, an experimental rig was designed and manufactured where a copper target surface of 42 mm was impinged upon by a 1.65 mm orifice nozzle at a non-dimensional nozzle-to-target height of 4. The results indicated that the use of nanofluids in impingement applications produced adverse effects, depending on the particle fraction considered.
With respect to the steady-state cooling tests, the copper surface was subjected to a constant heat flux of 145 watt and cooled by the different fluids at Reynolds numbers ranging between approximately 10 000 and 30 000. A maximum enhancement of 14.75% was observed in the measured Nusselt numbers, which occurred at a particle volume concentration of 0.05%. When increasing the volume fraction above 0.1%, unfavourable effects were observed for the heat transfer of the system in comparison with the base case tests of DI-water. Such trends were characterised by the trade-off between the enhancement in thermal conductivity and viscosity, both of which were increased with an increase in particle concentration. As for the effect of Reynolds number on the resulting thermal performance, a directly proportional relation was shown and could be described by the forced convection effect. The transient impingement tests showed that particle concentrations less than 0.1% produced an enhancement in cooling efficiency, while those of higher volume fractions showed negative effects. According to these tests the maximum enhancement was also obtained at a volume fraction of 0.05% and produced an average cooling efficiency enhancement of 16%.
The results of the investigation clearly showed that the use of TiO2-water nanofluids in jet-impingement cooling applications produced thermal enhancement depending on the selected particle concentration.Dissertation (MEng)--University of Pretoria, 2019.
NRF
Mechanical and Aeronautical Engineering
MEng
Unrestricted