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Dissertations / Theses on the topic 'Experiments and modelling'

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Published: 4 June 2021
Last updated: 8 February 2022

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1

Poland, G. A. "Neutron scattering experiments analysis and modelling." Thesis, University of Portsmouth, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328178.

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2

Bao, Sarina. "Filtration of Aluminium-Experiments, Wetting,and Modelling." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-15147.

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The present work deals with the inclusion removal mechanism in aluminium filtration and the use of alternative filter materials. Four routes are investigated. First, an overview of previous research on filtration knowledge is summarized. The filtration mechanism comprises two parts: transport of inclusions to the filter wall and attachment of inclusions on the wall. We have mainly investigated collision by interception and the wetting (surface tension) of inclusion-Al and Al-filter in this work. Second, the wetting behaviour of inclusion-Al and Al-filter is measured in the laboratory. In filtration it is important that particles to be removed contact, or come close to the filter walls. Therefore the metal carrying the inclusions must come into close contact,i.e. wet the filter material. A systematic and comprehensive investigation of the wetting behaviour in the molten aluminium-filter system is presented. In aluminium filtration,alumina is the most common filter material, even though alumina is not wetted by aluminium. Therefore we have investigated the use of alternative filter materials withimproved wetting. In the laboratory, SiC and graphite demonstrate good wetting bymolten aluminium. Problems with these materials exist, as SiC is easily oxidized to SiO2 and both react with aluminium to give Al4C3. However, SiO2 and SiC react slowly with aluminium, but this does not seem to influence the wetting. The wettability of the inclusion-Al may play a key role in aluminium filtration. Particlesto be removed should ideally have poor wetting with aluminium and filter should hasgood wetting with aluminium. A challenge is that SiC and Al4C3 inclusions show betterwetting with aluminium than alumina. Third, plant scale filtration experiments were carried out with Al2O3 and SiC industrial filters. Metal composition was not changed by the industrial filters. Improved wetting of aluminium on filter materials is an advantage in getting molten metal to infiltrate filtersand thus to improve the filtration efficiency. A SiC filter gives better filtration efficiency. Filtration efficiency increases with particle size. SiC reacts with aluminium so slowly that no carbide inclusions were produced in the industrial SiC filter with approximately 60% of SiC. SiC filters have better wetting than Al2O3 filters with aluminium. Thus SiC could be a good alternative filter material. Fourth, a theoretical model is developed regarding the interceptional and gravitational collision considering the filter as a collection of branches (cylinders). A filtration efficiency equation is derived based on particle diameter, branch diameter, porosity,filter thickness, filter specific surface area, and Reynolds number. The filtration efficiency decreases with the flow rate until it reaches a minimum, and then increases. Gravitational collision must be taken into account at the lower flowrates. The greater the velocity the less time particles have to settle. Thus gravitationalcollision efficiency decays with increasing flow rate. The interceptional collision efficiency increases with the velocity since then more liquid and particles come into contact with the collector. The interceptional collision efficiency that dominates at high velocities is the main topic of the model
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3

Modén, Carl S. "Transverse anisotropy in softwoods : Modelling and experiments." Licentiate thesis, KTH, Aeronautical and Vehicle Engineering, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3988.

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Transverse anisotropy is an important phenomenon of practical and scientific interest. Although the presence of ray tissue explains the high radial modulus in many hardwoods, experimental data in the literature shows that this is not the case for pine. It is possible that anisotropy in softwoods may be explained by the cellular structure and associated deformation mechanisms.

An experimental approach was developed by which local radial modulus in spruce was determined at sub-annual ring scale. Digital speckle photography (DSP) was used, and the density distribution was carefully characterized using x-ray densitometry and the SilviScan apparatus. A unique set of data was generated for radial modulus versus a wide range of densities. This was possible since earlywood density shows large density variations in spruce. Qualitative comparison was made between data and predictions from stretching and bending honeycomb models. The hypothesis for presence of cell wall stretching was supported by data.

A model for wood was therefore developed where both cell wall bending and stretching are included. The purpose was a model for predictions of softwood moduli over a wide range of densities. The relative importance of the deformation mechanisms was investigated in a parametric study. A two-phase model was developed and radial and tangential moduli were predicted. Comparison with experimental data showed good agreement considering the nature of the model (density is the only input parameter). Agreement is much better than for a regular honeycomb model. According to the model, cell wall bending dominates at both low and high densities during tangential loading. In radial loading, cell wall stretching dominates at higher densities.

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4

Modén, Carl. "Transverse anisotropy in softwoods : modelling and experiments /." Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3988.

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5

Li, Yuan. "Modelling and evaluation of paired-comparison experiments." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578648.

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Paired-comparison is a popular method for deriving scale values; scale values are numbers that represent observers' psychophysical responses to sets of physical stimuli. The method requires that each observer is presented with pairs of stimuli and is asked which of the pair is greater in terms of the psychophysical property being investigated (for example, which of the pair is lighter). However, it is time consuming (especially when the number of stimuli n is large) since there are n(n-l )/2 possible paired comparisons and all of these must be considered. It is possible to carry out a so-called incomplete paired-comparison experiment where only a proportion p (0 < p < 1) of the pairs are considered. This thesis primarily addresses questions about the design of incomplete paired-comparison experiments. For instance, what is the smallest value of p and how few observers are required that still allows reliable estimates of the scale values? Monte-Carlo computational simulations were carried out with an ideal observer model assigned with bias. Data were analyzed based on Morrissey's least-squares solution. This evaluation indicated that satisfactory results can be obtained with as few as 30% (in the case where each observer compared the same pairs) or ...... 10% (in the case where each observer compared different pairs) of paired comparisons. However, the actual proportion of paired comparisons depends upon k (the number of observers) and n (the number of stimuli). A table was produced that indicated the value of p required (for various values of n and k) required to give a certain level of performance (this was somewhat arbitrarily defined as r2 = 0.95; where r is the expected Pearson product- moment correlation coefficient between the estimated scale values and their true values). A psychophysical experiment was conducted employing both the paired-comparison method and the categorical judgement method to estimate scale values. Results from the paired-comparison experiment were consistent with those predicted from the Monte-Carlo computational simulations. The paired-comparison experiment was analysed for various values of p and its performance compared with results from the categorical judgement method where n = 10. For the paired-comparison method where p = 1 (where all of the pairs are considered) the estimated scale values were more accurate than those from the categorical judgement experiment; however, as p reduces, the accuracy of the scale values from the paired-comparison method also reduced. The point where the two techniques gave broadly similar performance was at p = 0.2 (where each observer compared different sets of pairs) or p = 0.4 (where all observers compared the same set of pairs),
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6

Diambra, Andrea. "Fibre reinforced sands : experiments and constitutive modelling." Thesis, University of Bristol, 2010. http://hdl.handle.net/1983/5135b1d5-8cd2-43fb-b204-3736d4beb6c3.

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The techniqueo f reinforcing soils with discrete flexible fibres is slowly gaining acceptancea nd support between practising engineers. However, little is known about the main factors governing the behaviour of this material and the main characteristics of its behaviour. This means that the applicability and potential of this soil improvement method have not been resolved. The present research aims to provide a considerable contribution in understanding the mechanisms governing the behaviour of this reinforced material and to develop a modelling tool which allows the-prediction of its mechanical behaviour. A procedure for the determination of the distribution of the orientation of fibre in reinforced specimens has been developed herein. It was found that the most common procedure for preparing reinforced specimens, moist tamping, leads to preferred sub-horizontal orientation of fibres. In view of these preliminary results an extensive campaign of compression and extension conventional triaxial tests for both drained and undrained condition has been perfon-ned.F ibres were found to be effective in increasingt he strengtho f the material but their effectiveness was found to be dependent on the orientation with respect to tensile strains. Fibres were also found to be effective in preventing the liquefaction of loose sand specimens: addition of fibres results in a densification of the sand matrix not only for the volume that they occupy but also for preventing the sand matrix from using some of the voids during the deformation process. A new constitutive modelling framework has been developed on the basis of the rule of mixtures of composite materials. This approach allows the adoption of separate constitutive laws for each constituent and to combine their effects in characterising the behaviour of the composite material. In this manner it is possible to select the complexity of the constitutive model of each constituent and to simulate peculiar aspect of its behaviour. Application of the model demonstrated how accurately the mechanical behaviour of fibre reinforced sand can be simulated with particular regard to the anisotropy of strength and the prevention of liquefaction
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7

Guevara, Rukoz Adriana. "Decoding perceptual vowel epenthesis : experiments & modelling." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEE069.

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Pourquoi des personnes ayant grandi dans des milieux linguistiques différents ne perçoivent-elles un même signal acoustique de la même manière ? Par exemple, il arrive que des auditeurs rapportent avoir entendu des voyelles non présentes dans l'acoustique de mots non-natifs, lorsque ceux-ci ne se conforment pas aux structures sonores permises dans leur langue (épenthèse vocalique perceptive). L'identité de la voyelle épenthétique varie en fonction des langues, mais aussi parmi les langues elles-mêmes. À quel point ce processus est-il dirigé par des informations directement accessibles dans le signal acoustique ? Quelle est la part de contribution de la phonologie native ? Comment sont combinés ces deux éléments lors du calcul du percept ? Deux familles principales de théories ont été proposées : les théories à deux étapes, et les théories à une étape. Les premières proposent une analyse initiale des catégories phonétiques, suivie de réparations faites par une grammaire abstraite. De leur côté, les théories à une étape proposent que tous les facteurs acoustiques, phonétiques, et phonologiques sont intégrés simultanément de manière probabiliste. Dans cette thèse, nous combinons expériences et de modélisation, afin d'évaluer si l'épenthèse est un processus à une ou deux étapes. En particulier, nous examinons ceci en mesurant le rôle des détails acoustiques dans les modulations de l'identité de la voyelle épenthétique. Dans un premier temps, des résultats d'expériences nous montrent que ces modulations sont influencées aussi bien par les détails acoustiques que par des processus phonologiques. Cependant, la plupart de la variation de l'identité de la voyelle épenthétique est expliquée par l'acoustique. De plus, nous présentons un modèle de perception à une étape qui utilise des exemplaires ; celui-ci est capable de reproduire les effets de la coarticulation qui ont été relevés dans les données expérimentales. Ces résultats constituent de l'évidence en faveur des modèles de perception étrangère à une étape. Dans un deuxième temps, nous présentons une implémentation du modèle à une étape proposé par Wilson et al. (2013), en utilisant des modèles HMM-GMM, issus du milieu de la reconnaissance automatique de la parole (RAP). Ces modèles se composent d'un modèle acoustique et d'un modèle de langage, qui déterminent la correspondence acoustique et phonotactique entre la parole et des transcriptions possibles, respectivement. Il nous est alors possible de les ajuster indépendamment afin d'évaluer leur influence relative dans l'épenthèse vocalique perceptuelle. Nous proposons une nouvelle manière d'utiliser ces modèles pour simuler des paradigmes de choix forcés utilisés pour étudier l'épenthèse vocalique chez des participants humains, en utilisant des modèles de langage contraints lors du processus de décodage de la parole. D’abord, nous utilisons cette nouvelle méthode afin de tester si des systèmes de RAP avec des modèles de langage à phonotactique à textit{n}-grammes donnent des résultats plus proches des résultats humains qu'un système de RAP avec un modèle de langage nul. De manière étonnante, les résultats montrent que le système à modèle de langage nul prédit le mieux la performance des participants. Puis, nous évaluons si certains effets traditionnellement attribués à des processus phonologiques peuvent être expliqués par l'acoustique. Bien que les résultats soient prometteurs, nos modèles ne sont capables de reproduire qu'une sous-partie des effets observés chez l'humain. Avant de pouvoir attribuer l'origine de ces effets à des processus phonologiques, il est nécessaire de tester des systèmes de RAP avec des modèles acoustiques plus performants. Nous énumérons des futures pistes de recherche d'utilisation de modèles améliorés, et nous soulignons les avantages de l'utilisation conjointe d'expériences comportementales et modélisations computationnelles afin d'élucider les mécanismes de la perception de la parole étrangère
Why do people of different linguistic background sometimes perceive the same acoustic signal differently? For instance, when hearing nonnative speech that does not conform to sound structures allowed in their native language, listeners may report hearing vowels that are not acoustically present. This phenomenon, known as perceptual vowel epenthesis, has been attested in various languages such as Japanese, Brazilian Portuguese, Korean, and English. The quality of the epenthesized vowel varies between languages, but also within languages, given certain phonemic environments. How much of this process is guided by information directly accessible in the acoustic signal? What is the contribution of the native phonology? How are these two elements combined when computing the native percept? Two main families of theories have been proposed as explanations: two-step and one-step theories. The former advocate an initial parsing of the phonetic categories, followed by repairs by an abstract grammar (e.g., epenthesis), while one-step proposals posit that all acoustic, phonetic, and phonological factors are integrated simultaneously in a probabilistic manner, in order to find the optimal percept. In this dissertation, we use a combination of experimental and modelling approaches in order to evaluate whether perceptual vowel epenthesis is a two-step or one-step process. In particular, we investigate this by assessing the role of acoustic details in modulations of epenthetic vowel quality. In a first part, results from two behavioural experiments show that these modulations are influenced by acoustic cues as well as phonology; however, the former explain most of the variation in epenthetic vowel responses. Additionally, we present a one-step exemplar-based model of perception that is able to reproduce coarticulation effects observed in human data. These results constitute evidence for one-step models of nonnative speech perception. In a second part, we present an implementation of the one-step proposal in Wilson et al. (2013) using HMM-GMM (hidden Markov models with Gaussian mixture models) from the field of automatic speech recognition. These models present two separate components, determining the acoustic and phonotactic matches between speech and possible transcriptions. We can thus tweak them independently in order to evaluate the relative influence of acoustic/phonetic and phonological factors in perceptual vowel epenthesis. We propose a novel way to simulate with these models the forced choice paradigm used to probe vowel epenthesis in human participants, using constrained language models during the speech decoding process. In a first set of studies, we use this method to test whether various ASR systems with textit{n}-gram phonotactics as their language model better approximate human results than an ASR system with a null (i.e., no phonotactics) language model. Surprisingly, we find that this null model was the best predictor of human performance.In a second set of studies, we evaluate whether effects traditionally attributed to phonology may be predictable solely from acoustic match. We find that, while promising, our models are only able to partially reproduce some effects observed in results from human experiments. Before attributing the source of these effects to phonology, it is necessary to test ASR systems with more performant acoustic models. We discuss future avenues for using enhanced models, and highlight the advantages of using a hybrid approach with behavioural experiments and computational modelling in order to elucidate the mechanisms underlying nonnative speech perception
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8

Ritter, Stefan. "Experiments in tunnel-soil-structure interaction." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273891.

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Urbanisation will require significant expansion of underground infrastructure, which results in unavoidable ground displacements that affect the built environment. Predicting the interaction between a tunnel, the soil and existing structures remains an engineering challenge due to the highly non-linear behaviour of both the soil and the building. This thesis investigates the interaction between a surface structure and tunnelling-induced ground displacements. Specifically, novel three-dimensionally printed building models with brittle material behaviour, similar to masonry, were developed and tested in a geotechnical centrifuge. This enabled replication of building models with representative global stiffness values and realistic building features including strip footings, intermediate walls, a rough soil-structure interface, building layouts and façade openings. By varying building characteristics, the impact of structural features on both the soil and building response to tunnelling in dense sand was investigated. Results illustrate that the presence of surface structures considerably altered the tunnelling-induced soil response. The building-to-tunnel position notably influences the magnitude of soil displacements and causes localised phenomena such as embedment of building corners. An increase of the façade opening area and building length reduces the alteration of the theoretical greenfield settlements, in particular the trough width. Moreover, the impact of varying the building layout is discussed in detail. For several building-tunnel scenarios, building distortions are quantified and the crucial role of building features is demonstrated. Structures spanning the greenfield inflection point experienced more deformation than identical structures positioned in either sagging or hogging, and partitioning a structure either side of the greenfield inflection point is shown to lead to unconservative damage assessments. Results also quantify the significant extent to which structural distortions increase as façade openings and building length increases. Observed building damage and cracking patterns confirm the reported trends. The experimental results are used to evaluate the performance of available methods to assess the behaviour of buildings to tunnelling. Predictions ignoring soil-structure interaction are usually overly conservative, while approaches based on the relative stiffness of a structure and the soil result in inconsistent predictions, though some methods performed better than others. Practical improvements to consider structural details when assessing this tunnel-soil-structure system are finally proposed.
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9

Poussart, Pascale Francine. "Late Ordovician glaciation, modelling experiments of a paradox." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ37415.pdf.

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10

Cantu-Perez, A. "Modelling and experiments of microchannels incorporating microengineered structures." Thesis, University College London (University of London), 2011. http://discovery.ucl.ac.uk/1310147/.

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Microreaction technology was conceived, thanks to the advances on microfabrication by the semiconductor industry. The first applications of microchannels used for performing reactions date back to the early nineties. Since then, many conferences dedicated to this topic are held worldwide such as the International Microreaction Technology Conference (IMRET) or the International Conference on Microchannels and Minichannels. The small dimensions of the microchannels lead to very high heat and mass transfer rates, reactions are therefore performed very efficiently on these devices. However, the small dimensions of the channels lead to high pressure drops. In addition, microchannels are very susceptible to clogging. This thesis studies the effect of different microchannel configurations in terms of mixing, mass transfer, residence time distribution and reaction. The objective is to design microreactors which incorporate different structures which make them efficient in terms of heat/mass transfer, but do not have the issue of high pressure drop and channel blockage.
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11

Mulvihill, Daniel Martin. "Studies of frictional interface behaviour : experiments and modelling." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:54e18b10-1167-40f1-9dc9-0ca529a56f34.

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Predictive models of structures containing frictional joints presently suffer from poor descriptions of interface behaviour at the joints. This thesis aims to address this shortfall by furthering the physical understanding of parameters affecting interface behaviour such as friction and contact stiffness. Aspects of friction and contact stiffness relevant to the characterisation of fretting joints are investigated by a combined modelling and experimental approach. Friction and wear behaviour in gross-slip fretting are investigated by in-line and rotational fretting tests. New 3D topography parameters are found to be useful in the analysis of surfaces during fretting. Wear-scar shape is found to be dependent on material. A phenomenon whereby friction increases during the gross-slip phase of individual cycles is found to be due to wear-scar interaction primarily through the interference of local features distributed over the contact area. These features are similar in size to the applied fretting stroke. A simple model to explain the behaviour is put forward which shows that wear-scar shape determines the form of the friction variation. A finite-element (FE) model of the interaction of an elastic-plastic asperity junction is used to predict sliding friction coefficients. The modelling differs from previous work by: permitting greater asperity overlaps, enforcing an interface shear strength, and allowing material failure. The results are also used to predict friction coefficients for a stochastic rough surface. The magnitudes of the predicted friction coefficients are generally representative of experimental measurements. Results suggest that friction arises from both plasticity and tangential interface adhesion. Contact stiffness is studied for both fretting and non-fretting. A technique to isolate the true interface stiffness from results derived from load-deflection data is developed by comparing experimental and FE results. In the fretting wear case, comparison of tangential contact stiffness results in the literature with FE results reveals an interface whose compliance dominates the response to the extent that stiffness is proportional to contact area. In fretting tests such as this, wear debris is thought to be a factor contributing to high interface compliance. Non-fretting experiments performed here show that, at higher pressures, interface domination is reduced as the contact approaches the smooth case. Experiments are performed where contact stiffness is measured simultaneously by both ultrasound and digital image correlation. The effect of normal and tangential loading upon the contact stiffness (normal and tangential) is investigated. Experimental evidence showing that ultrasound measures an ‘unloading’ stiffness while DIC measures a ‘loading’ stiffness is obtained for the case of tangential loading where the ‘DIC stiffness’ decreases with increasing tangential load whereas the ‘ultrasound stiffness’ remains approximately constant. On average, ultrasound gives magnitudes 3.5 and 2.5 times stiffer than the DIC results for the normal and tangential stiffness cases, respectively. The difference in magnitudes can largely be physically explained, and is relatively small considering the significant differences between the techniques. Therefore, both methods can claim to give valid measurements of contact stiffness – though each has its own limitations which are outlined herein.
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12

Bryers, Carl. "Quantitative modelling of ionospheric modification experiments at EISCAT." Thesis, Lancaster University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675678.

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13

De, Matos Paulo Fernando Pinto. "Plasticity induced fatigue crack closure: Modelling and Experiments." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491427.

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The understanding of fatigue crack closure has been proved to be a challenging and controversial topic among the fatigue community over the last three decades. Since the pioneering work of Elber, different forms of crack closure have been identified (e.g. roughness and oxide induced), however, plasticity-induced crack closure has been shown to be particularly relevant in engineering applications. The effect of the specimen (or component) thickness has been shown to have a significant effect on closure behaviour and this seems to be related to the relative size of the plastic zone. The state of stress at the crack front can be predominantly plane stress, or plane strain depending on the thickness and loading conditions. Real cracks are inherently three-dimensional; plane stress-like behaviour is found close to the region where the crack front intersects the free surface, whereas most of the crack front will experience something close to plane strain. The aim of this thesis is to investigate plasticity induced fatigue crack closure from both modelling and experimental points of view. On the modelling side combined analytical and numerical techniques and finite element analyses have been used to investigate 2D plane stress, 2D plane strain and 3D crack closure problems. The influence of different effects such as different material models, surface effects, crack front curvature and residual stresses have been investigated. The experimental part of this thesis gives particular attention to the investigation of thickness effects on the closure behaviour (both close to and remote from the surface) and on fatigue crack propagation. Fatigue crack propagation is measured optically and crack closure is assessed using traditional compliance techniques (clip gauge and back face strain gauge) and Digital Image Correlation methods. This last technique was proven to be a good alternative to gauges usually used to assess surface closure. Finally, experimental results are compared with modelling predictions in order to identify strengths and limitations of these techniques. This thesis supports that crack closure effects should be taken into account for fatigue life predictions of structures under variable amplitude loading.
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Chaulagain, Uddhab Prasad. "Radiative shocks : experiments, modelling and links to astrophysics." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066734.

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Les chocs radiatifs sont des chocs très violents qui sont caractérisés par des températures très élevées. Dans ce type de structure, une grande partie de l’énergie est convertie en rayonnement. Ces chocs sont présents dans de nombreux plasmas astrophysiques, notamment dans le cadre des jets et de l’accrétion stellaires, des restes de supernova etc. Ils peuvent être désormais générés sur terre en utilisant des lasers de grande puissance ce qui permet leur étude à l’interface entre l’astrophysique et la physique des plasmas.Cette thèse présente et discute les résultats d’une expérience réalisées sur l’installation Prague Asterix Laser System. Le choc est généré en focalisant le laser Infrarouge sur une cible de quelques millimètres de long, remplie de xénon à basse pression. Le choc ainsi généré se propage dans le gaz à une vitesse élevée, permettant d’atteindre le régime des chocs dom- inés par le flux radiatif. Nous avons utilisé différents diagnostics pour caractériser le choc, notamment une radiographie éclair, à l’aide d’un laser (Zinc) à 21.2 nm, capable de pénétrer les parties denses du plasma. Un autre important diagnostique consiste à analyser l’émission propre du plasma à l’aide d’une diode rapide.Les résultats expérimentaux montrent pour la première fois, et sans ambiguïté, une structure de choc complète, comprenant le post-choc et le précurseur. Nous avons aussi réalisé différentes mesures de la vitesse des chocs. Les résultats ont été comparés à ceux de simulations numériques, montrant un bon accord avec ces dernières
Radiative shocks are strong shocks which are characterized by a plasma at high temperatures emitting an important fraction of its energy as radiation. Radiative shocks are found in many astrophysical systems, including stellar accretion shocks, supernovae remnants, jet driven shocks, etc. Recently, radiative shocks have also been produced experimentally using high energy lasers. Thus opening the way to laboratory astrophysics studies of these universal phenomena.In this thesis we discuss the results of an experiment performed on the Prague Asterix Laser System facility. Shocks are generated by focusing the PALS Infrared laser beam on millimetre-scale targets filled with xenon gas at low pressure. The shock that is generated then propagates in the gas with a sufficiently high velocity such that the shock is in a radiative flux dominated regime. We used different diagnostics to characterize these shocks. The two main ones include a radiography of the whole shock structure using sub-nanosecond Zn X-ray laser at 21.2 nm, which is able to penetrate the dense post-shock layer, and a space-and-time resolved plasma self-emission using high speed diodes.The experimental results show, for the first time, an unambiguous shock structure which includes both the post-shock and the precursor, and we also obtained multiple shock velocity measurements from the different diagnostics. The experimental results are compared to simulations, and show good agreement with the numerical results
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15

Urso, Laura. "Modelling and experiments on NTM stabilisation at ASDEX Upgrade." Diss., lmu, 2009. http://nbn-resolving.de/urn:nbn:de:bvb:19-106262.

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16

Boogaard, Antonius Henricus van den. "Thermally enhanced forming of aluminium sheet modelling and experiments /." Enschede : University of Twente [Host], 2002. http://doc.utwente.nl/40378.

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17

Geldenhuys, Tiaan Andries. "Temporal gap detection in electric hearing : modelling and experiments." Pretoria :[s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-12182006-140911/.

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18

Kastner, Catharine Anne. "Combining experiments with modelling as applied to particle processes." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.707917.

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19

Akhtar, Naveed. "Single-chamber solid oxide fuel cells : modelling and experiments." Thesis, University of Birmingham, 2010. http://etheses.bham.ac.uk//id/eprint/626/.

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The objective of this work is to compare the performance of different geometries (i.e. planar, coplanar and micro tubular) under single-chamber (mixed-reactant) solid oxide fuel cell (SC-SOFC) conditions. In this respect, these designs have been computer analyzed and it is found that the micro-tubular design eliminates the possibility of cross diffusion/convection from the counter electrode, which is an inherent disadvantage in planar and co-planar designs. This is the first experimental report describing that the micro-tubular design offers the highest fuel utilization, cell efficiency and an acceptable level of performance (under single-chamber conditions) as compared to other designs. With the help of developed numerical model (also the first one, on mixed-reactant, micro-tubular design), it is demonstrated that there is a possibility of further improvement in performance, e.g. cell positioning, micro-tube diameter and cathode morphology (its micro-structure and material) are important factors to consider. Other parameters such as, flow rate, temperature and mixing ratio are also very effective in improving the cell performance but these parameters should be carefully controlled in order to avoid their counter-effects, like, lower fuel utilization, material degradation, anode coking and oxidation-reduction. There are some other parameters such as, electrode porosity, permeability and cathode radiative emissivity, which have minimal effect in performance enhancement and it is suggested before investing time on these parameters, a net energy and cost analysis would be very helpful. There are still some issues with choosing appropriate materials for building an SC-SOFC with both an acceptable lifetime and production of electrical energy. While it has been observed that most of the problems related to material degradation are thermally driven, it would be very helpful to lower the operating temperature by using intermediate temperature SOFC materials. Further to this, long term degradation studies and performance cycling will benefit in order to determine their suitability under mixed-reactant environment.
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20

Vlastnik, Vikki J. "Thermolysis of multiply-methylated acenes : experiments and mechanicstic modelling." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38845.

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21

Geldenhuys, Tiaan Andries. "Temporal gap detection in electric hearing : modelling and experiments." Diss., University of Pretoria, 2008. http://hdl.handle.net/2263/31555.

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To advance the understanding of electric hearing, from both a theoretical and practical perspective, the present study employs an engineering approach to examine whether a fundamental stochastic link exists between neural stimulation and perception. Through the use of custom-developed psychophysics software, temporal gap-detection experiments were carried out and compared with simulation results of a theoretical model. The results are informative, and the suggested modeling principles may be a step forward to a clearer understanding of how the hearing system perceives temporal stimuli. To enable the implementation of psycho-electric experiments involving cochlear implants, a software framework was developed for Matlab version 6.5, called the Psychoacoustics Toolbox, which can present stimuli either acoustically or (for interfacing with cochlear implants) using Cochlear Ltd. hardware. This toolbox facilitates easy setup of experiments based on extensible markup language (XML) templates, and allows for both adaptivestaircase procedures and presentation of a fixed set of stimuli to a participant. Multi-track interleaving of stimuli is also supported, as put forward by Jesteadt (1980), to allow for capturing of subjective responses (such as loudness perception). As part of this research, experiments were performed with three subjects, with a total of four cochlear implants. For the temporal gap-detection experiments, the rate of electrical stimulation varied over a range from 100 to 2700 pulses per second; both periodic stimulus sequences and stimuli reflecting a dead-time-modified Poisson process were used. Also, three spatially distinct stimulation sites were used with each implant to allow comparison among basal, central and apical cochlear responses. A biologically plausible psychophysical model (in contrast with a phenomenological one) was developed for predicting temporal gap-detection thresholds in electric hearing. The model was applied to both periodic and Poisson stimuli, but can easily be used with other kinds of stimuli. For comparison with experimental results, model predictions were made over the same range of stimulus rates. As a starting point, the model takes the neural stimuli, runs them through a neural filter, and then draws statistical interspike-interval (ISI) distribution data from the generated spikes. From the ISI statistics, psychometric curves can be calculated using the principles of Green and Swets (1966), from which predictions can be made for threshold measurements based on the percentage-correct mark for the specific experimental setup. With a model in place, simulations were executed to compare the model results with experimental measurements. In addition to the simulations, mathematical equations for the periodic types of stimuli were derived, given that numerical calculations could be made with higher computational e ciency for this kind of stimulus. These equations allowed for an investigation into the implications of varying the values of different neuron-model parameters. Clear similarities were found between the shapes of gap-threshold curves for experimental and modeled data, and qualitative links have been identified between model parameters and features recognized in threshold curves. For periodic stimuli, quantitative predictions of gap thresholds are close to experimental ones, although measured values cover a larger range. The results of experimental measurements using Poisson stimuli are generally somewhat larger than model predictions, although the shapes of the curves show resemblance. A possible explanation is that participants may find decision tasks involving Poisson stimuli, as opposed to periodic stimuli, confusing. Overall, model predictions and experimental results show close correspondence, suggesting Department of Electrical, Electronic and Computer Engineering. University of Pretoria. ii that the principles underlying the model are fundamentally correct. Copyright 2007, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Geldenhuys, TA 2007, Temporal gap detection in electric hearing : modelling and experiments, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-02232012-131459 / > E1091/gm
Dissertation (MEng)--University of Pretoria, 2012.
Electrical, Electronic and Computer Engineering
Unrestricted
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22

García-Cuevas, González Luis Miguel. "Experiments and Modelling of Automotive Turbochargers under Unsteady Conditions." Doctoral thesis, Universitat Politècnica de València, 2015. http://hdl.handle.net/10251/48458.

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The current global scenario, in which an ever increasing population with an ever growing transportation needs is coupled with a reduction in the fossil fuel production and increasing human-made pollution derived problems, leads automotive engine manufacturers to constant struggles for fuel consumption and emission reductions while keeping engine performance. One-dimensional simulation codes have become a key tool towards these objectives, but require continued accuracy refinements. Phenomena that were previously thought of a limited importance and could be extremely easily modelled now require the development of new methods to be accounted for. Among these phenomena are the turbocharger mechanical losses and the turbine behaviour under highly pulsating boundary conditions. This work is focused on the improvement of current one-dimensional models, for both mechanical losses prediction and high frequency pulsating flow turbine performance. After reviewing the state-of-the-art in experimental measurement and fast simulation of automotive turbochargers, this work presents first a experimental study of several turbochargers working under both steady-state and unsteady operating conditions, focusing on the general performance of the turbine and the losses in the power transmission between it and the compressor, even including internal pressure measurements in one of the tested units. All the measurements are corrected due to heat transfer, getting the purely adiabatic behaviour. Furthermore, a CFD simulation campaign of a radial turbine has been performed, thus obtaining a detailed description of its internal behaviour under highly pulsating flow. In the light of both the experimental and CFD-simulated results, a quasi-steady mechanical losses and a quasi-bidimensional turbine model have been developed. Both models have been validated using all the experimental and simulated data, proving a prediction accuracy improvements from the results of previous methods. The mechanical losses model offers a clear advantage over the usual practice of using a constant mechanical efficiency value for correcting the manufacturer’s turbocharger map, whereas the turbine model has demonstrated potential for turbine map extrapolation and has improved the instantaneous results over classic onedimensional turbine volute models for frequencies higher than 1000 Hz. Both models have been developed trying to keep a reduced computational cost, ensuring to exploit the specific characteristics of the processors where they are going to be run.
García-Cuevas González, LM. (2014). Experiments and Modelling of Automotive Turbochargers under Unsteady Conditions [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48458
TESIS
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Sitter, Randy Rudolf. "The design of quantal response experiments and the modelling of quantal response experiments over time." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26074.

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The problem of designing a quantal response experiment when estimation of the median effective dose (ED50) is of main interest is examined. The asymptotic variances of the maximum likelihood estimators of the ED50 for various 3 and 5 point designs, using the logit model, are compared to the minimum possible which is achieved with an inadvisable 1 point design (Cher-noff[5]). Alternate criteria for choosing a design that attempt to incorporate goodness-of-fit of the model are then examined. The modelling of quantal response experiments observed over time is also considered. A growth-curve approach to this problem was suggested by Carter and Hubert[3], and applied to a data set. The feasibility of this approach is discussed, and a simpler, more direct approach is proposed. The two models are applied to the presented data set, and the resulting fits are compared. The model proposed here appears to fit the data better. Inference about the ED50 using the two models is also compared.
Science, Faculty of
Statistics, Department of
Graduate
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24

Nikopour, Deilami Hasan. "Mechanics of fibre reinforced composite plates: Experiments and computational modelling." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114500.

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Fibre-reinforced composite plates consist of bonded layers of either unidirectionally or multi-directionally reinforced sub-elements, which are arranged in a way to achieve optimum deformability and failure characteristics. This thesis examines the effective elasticity properties of a unidirectionally reinforced carbon fibre-polyester composite. A computational simulation of an experimentally determined fibre arrangement is used to derive the effective elasticity properties of the transversely isotropic composite. The computational estimates for the elastic constants are compared with several theoretical estimates for the effective elasticity properties that are based on regular arrangement of the reinforcing fibres, their volume fraction and the elasticity properties of the constituents. This study also examines the flexural behavior of a locally loaded rectangular Carbon Fibre-Reinforced Polymer (CFRP) composite plate under different edge support conditions. The assembly of the laminae is used to construct a computational model of the plate. The layered composite CFRP plate used in the experimental investigation consisted of 11 layers of a polyester matrix reinforced with carbon fibres. The bulk fibre volume fraction in the plate was approximately 66%. The experimental results for the deflected shape of the plate were used to establish the validity of a computational approach that accounts for large deflections of the plate within the small strain range. This thesis also examines the role of a crack on the overall flexural behaviour of a circular layered composite CFRP plate with fixed boundary and different through crack configurations, which is subjected to uniform air pressure loading. In particular, the effect of crack length and orientation on the overall pressure-deflection behaviour of the plate is investigated. The assembly of the cracked laminae is also used to construct a non-linear model of the cracked plate.
Les plaques composites à renforts fibreux constituent en des ensembles de couches assemblées selon leur épaisseur de manière uni- ou multidirectionnelle afin d'obtenir des propriétiés de déformabilité ou de résistance optimales. Cette thèse se propose d'étudier les propriétiés élastiques effectives d'un composite à matrice de polyester renforcé par des fibres de carbone unidirectionnelle. Une simulation numérique est utilisée pour determiner les propriétiés élastiques equivalents dans l'hypothèse d'un comportement isotrope transverse au moyen d'un arrangement des fibres obtenu expérimentalement. Les estimation de ces constates élastiques obtenue par voie numérique sont comparées avec plusieurs estimations théoriques basées sur l'hypothèse d'un arrangement régulier des fibres et sur les fractions volumiques des constituants et leurs propriétés. Le travail est également étendu à l'identification des modules de glissement en plan et hors-plan d'une bande rectangulaire composite en polymère renforcée par des fibres de carbone. Les modules de glissement sont obtenus à partir de la rigidité torsionnelle déterminée expérimentalement et de technique de réduction de données basées sur le modèle de torsion de plaques rectangulaires orthotropes de Lekhnitskii. Cette etude examine également le comportement flexionnel d'une telle plaque rectangulaire chargée ponctuellement pour différentes conditions aux limites appliquées. L'assemblage du laminé est utilisé pour construire un modèle numérique de la plaque. La plaque laminée de composite utilisée dans les investigations expérimentales consiste en un ensemble de 11 couches à matrice polyester renforcée par des fibres de carbone. La fraction volumique de fibre dans la plaque est approximativement de 66%. Les résultats expérimentaux obtenus pour la déformée de la plaque ont été utilisée en vue de valider l'approche numérique qui prend en compte les grandes déflections sous l'hypothèse de petites déformations. Le travail investigue aussi l'effet d'une fissure sur le comportement global d'une plaque composite circulaire pour des conditions aux limites fixées et pour différentes configurations de fissures à travers la plaque, et soumise à une pression d'air uniforme. En particulier, l'influence de la longueur de fissure et de son orientation sur la réponse globale pression-déplacement est étudiée. L'assemblage de couches fissurées est également utilisé afin de construire un modèle non linéaire matériel de la plaque fissurée.
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25

Ciardi, Andrea. "Modelling of hypersonic jets in wire array Z-pinch experiments." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404428.

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26

Yuan, Kang. "Oxidation and Corrosion of New MCrAlX Coatings : Modelling and Experiments." Doctoral thesis, Linköpings universitet, Konstruktionsmaterial, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-111119.

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MCrAlY coatings (“M” for Ni and/or Co) are widely used for the protection of superalloy components operated at high temperatures such as in the hot sections of gas turbines. The exposure to high temperature can cause coating degradation due to oxidation or hot corrosion at the coating surface. Microstructures in the coating and the coating life are affected also by the diffusion of alloying elements through the coating-superalloy interface. This PhD project, by applying thermodynamic modelling and experimental tests, investigates the oxidation and hot corrosion behavior of new MCrAlX coatings, in which X, referring to minor elements, is used to highlight the functions of such elements. In order to understand and predict the coating degradation progress during thermal exposure, an oxidation-diffusion model has been established for MCrAlX coating-superalloy systems, which integrates the oxidation of aluminum at coating surface, diffusion of alloying elements, and the diffusion-blocking effect in the materials. The predicted chemical composition profile and microstructure agreed well with experimental results in a CoNiCrAlYSiTa-Inconel 792 system. The model was further applied in several coating-superalloy systems to study the influence of coating composition, superalloy composition and temperature on the evolution of microstructure in the coating and the coating life. The results have demonstrated the potential of the model in designing new durable MCrAlX coatings. In addition to the applications in coating-superalloy systems, the model was also adapted for studying the microstructural development in a superalloy in which internal oxidation and nitridation occurred in an oxidation process. The oxidation behavior of some HVOF MCrAlX coatings was studied by thermal exposure at different temperatures (900, 1000, 1100 °C). Different spinels formed above the alumina scale, depending on the oxidation temperature. The minor alloying elements, Ru and Ir, had no direct influence on the oxidation behavior but may affect the phase stability in the coating. MCrAlX coatings were also tested in 48-hour cycles at 900 °C in different hot corrosion environments containing sulphates and/or SO2. The results showed that the coating performance was dependent on coating quality, concentration of Al and Cr in the coating, and the hot corrosion condition. It was also found that the addition of SO2 in the environment may not necessarily be bad for hot corrosion resistance of some MCrAlY coatings.
ELFORSK, AGORA MATERIA, Strategic Faculty Grant AFM
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27

Carlsson, Per. "Entrained flow black liquor gasification : detailed experiments and mathematical modelling." Licentiate thesis, Luleå : Luleå university of technology, 2009. http://pure.ltu.se/ws/fbspretrieve/3076792.

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28

Caretta, Gianluca. "Coupled modelling and experiments in structural response to blast loading." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616225.

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29

Appelgren, Patrik. "Experiments with and modelling of explosively driven mangetic flux compression generators." Licentiate thesis, KTH, Rymd- och plasmafysik, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9638.

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This thesis presents work performed on explosively driven magnetic flux compression generators. This kind of devices converts the chemically stored energy in a high explosive into electromagnetic energy in the form of a powerful current pulse. The high energy density of the high explosives makes flux compression generators attractive as compact power sources. In order to study these devices a generator was designed at FOI in the mid-90ies. Two generators remained unused and became available for this licentiate work. The thesis reports experiments with, and simulations of, the operation of the two remaining generators. The aim was to fully understand the performance of the generator design and be able to accurately simulate its behaviour. The generators were improved and fitted with various types of diagnostics to monitor the generator operation. Two experiments were performed of which the first generator was operated well below its current capability limits while the second was stressed far above its limits. Since the generator generates a rapidly increasing current, a current measurement is the most important diagnostic revealing the current amplification of the generator and its overall performance. Further it is important to measure the timing of various events in the generator. With a common time reference it is possible to combine data from different probes and extract interesting information which cannot be directly obtained with a single measurement. Two types of numerical simulations have been performed: Hydrodynamic simulations of the high explosive interaction with the armature were used to verify the measured armature dynamics. A zero-dimensional code was used to perform circuit simulations of the generator. The model takes into account the inductance reduction due to the compression of the generator as well as the change in conductivity due to heating of the conductors in the generators.
QC 20101103
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30

Apperlgren, Patrik. "Experiments with and modelling of explosively driven mangetic flux compression generators." Licentiate thesis, KTH, Electric Power Systems, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9638.

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This thesis presents work performed on explosively driven magnetic flux compression generators. This kind of devices converts the chemically stored energy in a high explosive into electromagnetic energy in the form of a powerful current pulse. The high energy density of the high explosives makes flux compression generators attractive as compact power sources. In order to study these devices a generator was designed at FOI in the mid-90ies. Two generators remained unused and became available for this licentiate work.

The thesis reports experiments with, and simulations of, the operation of the two remaining generators. The aim was to fully understand the performance of the generator design and be able to accurately simulate its behaviour. The generators were improved and fitted with various types of diagnostics to monitor the generator operation.

Two experiments were performed of which the first generator was operated well below its current capability limits while the second was stressed far above its limits. Since the generator generates a rapidly increasing current, a current measurement is the most important diagnostic revealing the current amplification of the generator and its overall performance. Further it is important to measure the timing of various events in the generator. With a common time reference it is possible to combine data from different probes and extract interesting information which cannot be directly obtained with a single measurement.

 

 

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31

Sjølstad, Knut. "Deformation and Softening behaviour of commercial AlMn-alloys : Experiments and Modelling." Doctoral thesis, Norwegian University of Science and Technology, Department of Materials Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-143.

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A comprehensive study of the softening behaviour of two different non-heat treatable AlMn-alloys has been carried out. These alloys were a laboratory processed and an industrially processed AA3103-alloy. The primary objective of the laboratory processed alloy has been directed towards the relationship between the amount of manganese in supersaturated solid solution and the material behaviour during deformation and annealing. The focus for the industrially processed alloy was a detailed material characterisation during hot and cold rolling as well as to follow the softening behaviour of the alloy.

The cold rolled microstructures were characterised with respect to subgrain size, misorientation across the subgrain boundaries, particle break-up and global texture. As far as it concerns the cold deformed microstructure it was found that the different homogenisation treatments, resulting in different amount of Mn in supersaturation, had little effect on the deformed microstructure.

Detailed experimental work on the softening behaviour after cold deformation and the interaction between recrystallisation and precipitation, i.e. concurrent precipitation, has been carried out. Hardness and yield stress measurements, which defines the strength of the material, revealed that the softening behaviour was significantly slowed down in case of concurrent precipitation. It was further found that the precipitation reaction in this case occurred on the subgrain boundaries. Thus the precipitates considerably retarded the recrystallisation reaction as compared to the case when no precipitation occurred.

TTT-diagrams have been constructed on the basis of hardness and conductivity measurements. From these diagrams a characteristic temperature, Tc , for the different material conditions are identified. It was found that as the annealing was carried above this temperature the microstructure consisted of a fine grained equiaxed microstructure. Below Tc the grains become elongated in the rolling direction and the average grain size became much coarser.

With respect to recrystallisation texture, a very strong P-texture and in addition some ND-rotated cube texture was found in case of concurrent precipitation. This viistrong P-texture was investigated in detail, and it can be concluded that particle stimulated nucleation of recrystallisation (PSN) plays a significant role in the nucleation of these components. It was found that these texture components had a growth advantage in the early stage of annealing and that they are most probably a result of microgrowth selection, which often are related to a nucleation effect. When precipitation did not interact with recovery and recrystallisation the recrystallisation texture was either random or consisted of a weak cube texture.

The softening behaviour of the different materials has been modelled by a physically based softening model, which involves both the recovery and recrystallisation reactions. Both for the AlMn-alloys and for an additional commercially pure Al-alloy, relatively good model predictions were obtained for the softening behaviour when recrystallisation occurred prior to precipitation. However, when the softening reactions were retarded by heavy precipitation of dispersoids the model, in its original form, was not capable to predict the softening behaviour. In this case an additional retarding drag, which reduces the total number of viable recrystallisation nuclei, was added. With the addition of this drag relatively good model predictions were also obtained in case of concurrent precipitation. However, the model was not capable to predict the softening behaviour of the industrially processed AlMn-alloy particularly well.

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Marshall, Joshua Alexander. "Towards autonomous excavation of fragmented rock, experiments, modelling, identification and control." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ63336.pdf.

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33

Liu, Yaqing. "Transient Response of Grounding Systems Caused by Lightning: Modelling and Experiments." Doctoral thesis, Uppsala : Acta Universitatis Upsaliensis : Univ.-bibl. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4556.

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34

Xu, Bin. "Coal liquefaction in a flowing-solvent reactor : experiments and kinetic modelling." Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281764.

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35

Shivhare, Mahesh Ratanlal. "Design of experiments and modelling of the direct methanol fuel cell." Thesis, University of Newcastle Upon Tyne, 2008. http://hdl.handle.net/10443/749.

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Environmentally friendly polymer electrolyte membrane fuel cells (PEMFCs) have the potential to revolutionise mobile power sources. One of the more promising PEMFC candidates is the direct methanol fuel cell (DMFC). Significant commercial interest has been expressed in the DMFC as a consequence of it becoming a possible replacement technology for batteries and internal combustion engines. The DMFC is a simple system that utilises liquid fuel and which requires minimal ancil lary equipment, and hence are more suited to the logistics of portable and vehicular applications than hydrogen fuel cells. However, significant technological challenges remain that must be addressed prior to the DMFC becoming more commercially exploitable. These challenges include improving the poor anode kinetics of methanol oxidation and reducing methanol crossover. To aid the understanding of the various factors limiting the widespread application of the DMFC, the statistical method of design of experiments was applied. A fractional factorial design was implemented to understand the main effects and interactions of a number of operating parameters on the overall performance of the DMFC, in which the effect of the crossover of methanol through the membrane was considered. The statistical models developed facilitated the detection of key two-factor interactions of temperature with methanol concentration, type of oxidant and cathode back pressure, which suggested that an improvement in DMFC performance was achievable by reducing the effect of methanol crossover. Based on the outcomes of the parametric study, response surface methodology was applied to optimise catalyst layer formulation. The response surface method highlighted the significance of high catalyst loading and the non-linear behaviour of the Nafion@ content. Furthermore, the advantage of adding PTFE in the anode catalyst formulation, to make the anode morphology favourable for carbon dioxide gas evolution, was demonstrated. Steady state semi empirical models for the anode based on methanol oxidation kinetics and cathode considering the effect of methanol crossover through the membrane were also developed. The kinetic models for the anode illustrated the significance of water and surface intermediates in the methanol oxidation reaction on a dual site Pt-Ru catalyst and highlighted the subtle balance between the methanol adsorption-dehydrogenation step and the subsequent oxidative removal step. The cathode model developed provided insight into the effect of methanol crossover on the cathode open circuit potential and helped in reliable estimation of the cathode polarisation curve. Finally a combination of these two models was used in the prediction of the cell polarisation characteristic as a function of cell potential, temperature and amount of methanol crossed over through the membrane
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Miljkovic, Katarina. "Investigation of the dust around Europa by impact experiments and modelling." Thesis, Open University, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.520699.

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37

Nielsen, Christian. "An Analysis of Pre-Flashover Fire Experiments with Field Modelling Comparisons." University of Canterbury. Civil Engineering, 2000. http://hdl.handle.net/10092/8284.

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Firstly, this report investigates the behaviour of pre-flashover fires conducted in a two-compartment structure. Secondly, it looks at preliminary field modelling results of the pre-flashover fires using the SMARTFIRE program. A two-compartment structure was built so that pre-flashover fire experiments could be conducted. Each room in the compartment measured 2.4 m wide, 3.6 m long, and 2.4 m high. A doorway, with dimensions 2.0 m high and 0.8 m wide separated the rooms. All fires were placed in one room (the fire room) where seven fire experiments were conducted consisting of four differently sized fires. Six of the fires, 55 kW, 110 kW, and 160 kW in size were located in the centre of the fire room. The seventh fire was located in the corner of the fire room and was 110 kW in size. Thermocouple trees were located along the centre-line of the compartment so that vertical temperature profiles could be measured; floor and ceiling thermocouples accompanied the thermocouple trees. In addition, gas sampling points measuring O₂ and CO₂ concentrations were positioned evenly throughout the compartment. Temperature profiles in the fire room revealed constant cool lower layer and hot upper layer temperatures with a sharp temperature gradient between the two layers. Temperatures in the upper layer for the centrally located fires reached 130°C for the 55 kW fire, 200°C for the 110 kW fire, and 250°C for the 160 kW fire. Temperature profiles in the upper layer for the comer fire were not constant with height but showed a temperature gradient, where the temperature reached 335°C near the ceiling. Temperature profiles in the room next to fire room (the adjacent room) showed constant temperature profiles that were close to the ambient temperature in the lower layer. The upper layer temperature profiles displayed temperature gradients that continued up to the ceiling. Temperatures in the upper layer for the centrally located fires in the adjacent room reached 110°C for the 55 kW fire, 160°C for the 110 kW fire, 200°C for the 160 kW fire, and 225°C for the comer fire. Preliminary simulations of the four different fire experiments were conducted using the SMARTFIRE field modelling program. Each fire size simulated twice - one with and one without the six-flux radiation sub-model. A qualitative analysis revealed temperatures in the lower layer of the fire room were under predicted. Temperature gradients were predicted for the upper layer temperature profiles for the centrally located fires, rather than the constant upper layer temperature profiles that were seen experimentally. Overall, simulations predicted closer temperature profiles to the experimental results when the six-flux radiation sub-model was incorporated.
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Appelgren, Patrik. "Experiments with and modelling of explosively driven magnetic flux compression generators /." Stockholm : School of Electrical Engineering, Physical Electrotechnology, Kungliga Tekniska högskolan (KTH), 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9638.

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39

Fallas, Chinchilla Juan Carlos. "Modelling of high pressure instruments and experiments using finite element methods." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31250.

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The study of matter at extreme conditions has been of great importance for modern society. A correct understanding of materials and environments subject to high pressures and temperatures enabled the development of car and jet engines, manufacture of goods, energy production and space travels among other human milestones. Discoveries in magnetism, geology, chemistry, and crystallography have been reported in literature as well, illustrating relevant contributions of this research area. Science at extreme conditions constantly requires to innovate instruments and characterisation methods. Sophisticated proficiencies are needed to explore and reproduce conditions of interest for this field. Since the 1990s, high pressure instruments for neutron scattering have boosted the study of compressed matter. The design and subsequent improvement of the Paris-Edinburgh (PE) press and toroidal anvils successfully impacted this area, currently being the most extensively used instrument for high pressure neutron scattering, commonly used for pressures of the order of 10 GPa. Recent incorporation of toroidal anvils made of Zirconia Toughened Alumina (ZTA) has opened new experimental possibilities. Neutron transparency and mechanical resistance are key properties of this ceramic material. At this point it is essential to understand ZTA anvils design and working conditions in order to increase experimental capabilities and access new frontiers in compressed matter. Computer-based modelling technique Finite Element Analysis (FEA) has been a recent ally for instrumentation design and optimisation. Phenomena such as mechanical stress, deformations, and thermal distributions can be modelled in an object, gathering information regarding its mechanical stability, behaviour and failure. Although this method is popular in industrial and engineering design and applications, it has not been widely employed in high pressure research due to scarce information in material properties under extreme conditions, as well as in innovative ceramics and metallic alloys introduced in these types of scientific devices.
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Cancho, Daniel Barba. "Segregation-assisted creep in nickel-based superalloys : experiments, theory and modelling." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:33e157e8-0e68-49b1-9225-12f8a2039dee.

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Mid-temperature creep deformation in the range of 600 to 850°C is assuming greater importance in Ni-based superalloys. This is because the design operating temperature of the combustion cycle is increasing as the new generations turbofan engines become more efficient. The temperature at the rim of turbine disks and the root of turbine blades can be in this critical range of temperatures for significant portions of the mission cycle, leading to a complex time-dependent mode of plasticity called "microtwinning"'. Unfortunately this kind of coupled displacive-diffusive deformation mechanism is not yet well understood, and even the range of temperatures and stresses where microtwinning occurs is not clearly defined. This work explores the fundamentals of this phenomenon, from the kinetics of microtwinning to its influence on the mechanical behaviour of the material. To achieve this objective, coupled computational-experimental studies have been carried out. First, the contribution of microtwinning mechanism to the creep deformation of a single crystal superalloy is studied. The accumulated creep strain computed from quantitative stereology of the tested samples supports the role of this mechanism in conferring plastic deformation. Second, the chemical composition of the microtwins is analysed by means of atomic-resolution characterisation techniques (APT and TEM). Segregation of Î3'-stabilisers to the growing faults is found to be crucial for the understanding of the creep mechanisms in this range of temperatures. Third, a model for diffusion-controlled growth of microtwins is proposed and used to recover the experimental creep strain rates. This then provides the basis for a thermodynamically consistent constitutive model developed on the basis of crystal plasticity theory. The constitutive model is subsequently implemented into a finite element code to study the activation of the different plastic mechanisms within single crystal and polycrystalline aggregates depending on the crystal orientation. With the support of this model, a relation between the rotations of the crystal and the creep life of the different crystal orientations is established. The numerical and experimental results ultimately reveal the critical role of the microtwinning on the asymmetric behaviour of the alloy and thus, its influence on the mechanical performance.
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41

Taylor, Christopher Martin. "Direct laser sintering of stainless steel : thermal experiments and numerical modelling." Thesis, University of Leeds, 2004. http://etheses.whiterose.ac.uk/378/.

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SLS is a commercial solid freeform fabrication process. Layers of powder material are bonded by a laser beam to rapidly manufacture three dimensional freeform models. In this work, the direct SLS of room temperature single-phase steel powder beds is researched. Two approaches are adopted: - Experimental analysis of heat transfer in the process; - Numerical modelling of the process. Experimental work involves the use of analytical equations to calculate the thermal conductivity and laser energy absorptance of the SLS powder bed. Experiments take place in a range of representative situations. Two temperature measurement systems are used, requiring some custom-designed elements. Conductivity values in the range 0.07 to 0.25 W/(m. K) are found, dependent on atmospheric gas and powder particle size. Absorptance varies from 0.08 to 0.21, dependent on atmosphere and material type. Measurements are made to learn more about temperature variation in the bed with position and time. It is found that processed material melts and solidifies in under 4 seconds in studied cases. Numerical modelling involves developing and testing an existing Fortran model of the SLS process. A method is devised to visualise modelled parts in 3D. Preprocessing is simplified, and more status information is communicated during execution. The effect on modelled parts of changes made to the program are tested. The stability of part depth is improved. The nature of parts is categorised against input parameters. The area, relative density and morphology of manufactured and modelled single layer parts are compared. Manufactured scans are found to have a variable cross-sectional shape, whereas the cross-sectional shape of modelled scans does not change. Modelled parts are found to be significantly smaller than manufactured parts. Reasons for these two differences are suggested.
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42

Armin, Milad. "Interfering of two tandem cylinders undergoing VIV : mathematical modelling and experiments." Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27460.

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Behaviour of two cylinders in tandem subjected to a stream of steady uniform flow is investigated. This research includes experimental and mathematical simulation so that a better understanding of the interaction between two bodies undergoing vortex induced vibration (VIV) can be achieved while one is submerged in the wake of the other. Amplitude and frequency of oscillation are observed for both cylinders when they are placed at different distances from each other. Positioning cylinders at various spacings can help to shed some light on the interaction mechanism of the upstream wake and trailing cylinder. An experimental investigation was carried out in sub-critical Reynolds number and low mass-damping to simulate the conditions in which offshore structures are deployed. Initially, two identical cylinders are placed in-line with the stream at various spacings. The response of leading cylinder is observed to be similar to that of an isolated cylinder experiencing VIV at all spacings. On the other hand, trailing cylinder response is observed to increase with flow velocity at small and medium spacings. Moreover,as the spacing grows large downstream response becomes more similar to that of the leading cylinder. Motion trajectory of trailing cylinder is significantly influenced by the leading body, and does not follow the typical figure of eight observed for an isolated cylinder at all velocities. Frequency power spectrum of obtained time histories reveals that two sources of excitation exist for trailing cylinder. Corresponding motion to each excitation source is determined using Fast Fourier Transform. The second set of experiment was conducted using similar cylinders with different natural frequencies to observe how it influences the interaction between two cylinders. It was observed that behaviour of trailing cylinder alters in comparison with initial set up. However, two sources of excitation are still detected in this set-up. Mathematical simulation is pursued by modelling the oscillating cylinders with a simple mass-spring-damper system. Furthermore, the force exerted to cylinders by wake is simulated by wake oscillators which can capture the self-exciting and self-limiting nature of VIV phenomenon. Two equations are coupled together by assuming that wake force is proportional to cylinder acceleration. Then, the system of equations is solved analytically,and results are compared to those obtained by a SimuLink model of the system. SimuLink model is solved by numerical RungeKutta method. It was observed that model is successful in simulating leading cylinder vibration amplitude,while it, initially, fails drastically to predict the oscillation amplitude of trailing cylinder due to buffeting vortices. Two terms were added to accommodate the effect of upstream wake on the trailing cylinder, to modify the force in the equation of motion which is respectively proportional to acceleration and velocity of the cylinder. Moreover, acceleration term is determined by fitting a linear function of the variable to the difference between upstream and downstream wake force obtaining from the experimental investigation results. Additionally, the damping term is determined by optimization of variance between simulation and experiment results. Such an observation can confirm that upstream turbulent wake has a significant influence on added mass coeffcient of the trailing cylinder which both are observed to be dependent on upstream Strouhal number. Overall, the agreement between mathematical model and experimental results is evaluated for both cylinders. Model error for trailing cylinder is calculated between 20% to 30% in cross-flow direction. This error is lower than that of the leading cylinder which is a well established method in literature for simulating VIV of an isolated cylinder.
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43

Obregón, Mateo. "Hemispheric effects in binocular visual word recognition : experiments and cognitive modelling." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/9732.

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Functionally, a vertically split fovea should confer an advantage to the processor. Visual stumuli arriving to each eye would be vertically split and the two parts sent to different hemispheres, obeying the crossed nature of the visual pathways. I test the prediction of a functional advantage for the separate lateralisation of text processing from the two eyes. I explore this hypothesis by means of psycholinguistic experimentation and cognitive modelling. I employed a haploscope to show foveated text to the two eyes separately, controlling for location and presentation duration, and guaranteeing that each eye could not see the other eye's stimuli. I carried out a series of experiments, based on this novel paradigm, to explore the effects of a vertically split fovea on correctness of word perception. The experiments showed: (i) words presented exclusively to the contralateral hemifoveas are more correctly reported than words presented exclusively to the ipsilateral hemifoveas; (ii) the same full word shown to both eyes and available for fusion led to better perception; (iii) word endings with fewer type-count neighbours were more accurately reported, as were beginnings with larger type-count neighbours; (iv) uncrossed-eye stumuli were better perceived than crossed-eye stimuli; (v) principled roles in a model of isolated word recognition for lexical and sublexical neighbourhood statistics, syllabicity, hemispheric fine- and coarse-coding differences, sex of the reader, handedness, left and right eye, and visual pathways. Finally, I propose a connectionist model of visual word recognition that incorporates these findings and is a basis for further exploration.
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44

Tang, Alan Shung-tse. "Large amplitude forced roll motion in two dimensions : experiments and theory." Thesis, University of Southampton, 1991. https://eprints.soton.ac.uk/426607/.

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45

John, Paul. "Modelling Recreation Demand Using Choice Experiments : Using Swedish Snowmobilers Demand for Groomed trails." Thesis, Högskolan Dalarna, Nationalekonomi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:du-4642.

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This paper is concerned with the use of the choice experiment method for modeling the demand for snowmobiling . The Choice Experiment includes five attributes, standard, composition, length, price day card and experience along trail. The paper estimates the snowmobile owners’ preferences and the most preferred attributes, including their will-ingness to pay for a daytrip on groomed snowmobile trail. The data consists of the an-swers from 479 registered snowmobile owners, who answered two hypothetical choice questions each. Estimating using the multinominal logit model, it is found that snow-mobilers on average are willing to pay 22.5 SEK for one day of snowmobiling on a trail with quality described as skidded every 14th day. Furthermore, it is found that the WTP increases with the quality of trail grooming. The result of this paper can be used as a yardstick for snowmobile clubs wanting to develop their trail net worth, organizations and companies developing snowmobiling as a recreational activities and marketers in-terested in marketing snowmobiling as recreational activities.
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46

Friedman, Noémi. "Investigation of highly flexible, deployable structures : review, modelling, control, experiments and application." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2011. http://tel.archives-ouvertes.fr/tel-00675481.

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In this thesis, an extensive review on different transformable systems used in architecture and civil engineering is given. After the review, structures undergoing large displacements and instability phenomenon were highlighted. The main goal of the dissertation was to investigate the general behavior of a specific, immature self-deploying system, the antiprismatic structure proposed by Hegedus. The emphasis was mainly taken to the analysis of the packing behavior. First, a simplified planar model was identified sharing similar, highly nonlinear packing behavior. For both the 2D and the 3D structures numerical simulation of the packing was performed with different type of controls and the results were confirmed by analytical investigations. The research clarifies the mechanical behavior of the chosen system, provides tools to simulate the packing of the structure, options for control, and gives very simple approximations for main mechanical characteristics of the antiprismatic system in order to facilitate preliminary design and verification of the numerical results. The significance of snap-back behavior, occurring at the force-displacement diagram during packing was analyzed. Within the framework of the thesis a novel type of system, slightly deviating from the original one was also investigated. For the specific systems, small physical models were built and presented in this work, which led to the proposal of a novel type of expandable tube. An attempt was given to provide ideas for application of antiprismatic structures by combining the investigated system and different learnt existing systems from the architectural review.
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47

Verhoyen, Olivier. "Crystallization of polyethylene terephthalate in injection moulding : experiments, modelling and numerical simulation." Université catholique de Louvain, 1997. http://edoc.bib.ucl.ac.be:81/ETD-db/collection/available/BelnUcetd-03032009-173159/.

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48

Cooke, Andrew J. "Modelling of clogging in laboratory column experiments conducted with synthetic landfill leachate." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28554.pdf.

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49

Jackson, Andrea Valerie. "Hydrogen peroxide and organic hydroperoxides in the troposphere : experiments, measurements and modelling." Thesis, Lancaster University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337585.

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50

Abdul, Majid Azlan. "Coal blend combustion in a novel suspension-firing reactor : experiments and modelling." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.406468.

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