Дисертації з теми "Computationat modelling"
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Gault, Richard. "Computational modelling of tinnitus." Thesis, Ulster University, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.730910.
Повний текст джерелаАнотація:
Tinnitus affects 10-15% of the population and causes a diminished quality of life for 1-3% of people. Without a clear understanding of the mechanisms that generate and sustain tinnitus, treatment plans can only attempt to manage the problem rather than address the underlying causes of tinnitus. As 85% of tinnitus sufferers have hearing loss, tinnitus was originally considered to be a problem of the ear. Moreover the remaining tinnitus sufferers are postulated to have hidden hearing loss. Subsequent research has found that tinnitus is a problem extending beyond the ear. Experimental findings have identified tinnitus related activity throughout the auditory system. It is unclear how this activity is created and how it leads to the perception of a phantom sound. This thesis aims to identify the factors involved in the development of tinnitus related activity and the manifestation of a phantom sound; computational models of the auditory system are developed to address this primary objective. In this thesis, a biologically inspired model of the auditory periphery is created, called the peripheral model, which emulates tinnitus related activity in the auditory brainstem and accurately models hidden hearing loss in line with empirical data. The peripheral model is extended to model correlates of tinnitus associated with the thalamocortical network. Finally a perceptual model of tinnitus is developed using a Linear Mixed Effects (LME) approach to show how tinnitus related activity leads to the perception of a phantom sound. The outcomes from the development of the peripheral model include an accurate model of cochlear synaptopathy to replicate hidden hearing loss as well as the finding that hidden hearing loss can instigate adaptive changes that result in tinnitus related activity. Extending the peripheral model to include the thalamocortical network led to the discovery that tinnitus requires changes to both the bottom-up and top-down signals in the auditory system. The result provides a significant step forward towards understanding the mechanisms underpinning tinnitus related activity. The peripheral model and the result from the investigation of the thalamocortical network provide the underpinning basis upon which to develop the perceptual model of tinnitus using a LME approach. The LME model provides a state of the art perceptual model of tinnitus that accurately models characteristics of tinnitus such as pitch and loudness. The results provide a significant advancement in the understanding of tinnitus generation and the evidence to motivate and direct further studies, which could lead to improved treatment methods for this condition.
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Engelhardt, Markus Jochen. "Computational modelling of shakedown." Thesis, University of Leicester, 1999. http://hdl.handle.net/2381/30173.
Повний текст джерелаАнотація:
The work presented is concerned with the implementation and exploitation of an iterative non-linear programming technique, based on the elastic compensation method, for solving limit load and shakedown problems. Such solutions are required in the design of structures or components subjected to complex combinations of static and cyclic loading, in structural integrity procedures and life cycle assessment. To achieve these aims, a brief review of the problem, the historical development of shakedown theory and recent developments of methods addressing these issues are given in the early chapters. This is followed by the implementation of the above method to generate limit load solutions for elastic-plastic materials subject to the von Mises yield condition. The method was found to be numerically stable and convergence could be guaranteed for upper bound limit load solutions if a number of sufficient convergence criteria are adhered to. These are stated during the provided convergence proofs. Upon studying the behaviour of the method, i.e. quality and sensitivity of solutions, computational effort as well as identifying error sources, this implementation is extended to solve limit load problems for arbitrary yield surfaces. This was found to be possible, but dependent on the nature of the yield surface and limits to the implementation in its present form were identified. The method was then implemented using a different formulation capable of solving limit and, more importantly, shakedown problems for elastic-plastic materials subject to the von Mises yield criterion. A number of benchmark problems were considered, an example of which is the classic Bree problem, which is concerned with shakedown of components subjected to a static mechanical load in combination with thermal transients. The method performed well and was then used to solve novel shakedown problems, such as shakedown states where creep must be considered. Acceptable creep behaviour for a given shakedown state could also be calculated using minor additions. The final issue considered was cyclic creep solutions. Rapid cycle creep solutions could be generated as a stress history can be considered, which is of a similar form to shakedown. Finally, conclusions were drawn and remaining issues discussed.
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Baird, Scott. "Computational modelling of fuel cells." Thesis, Loughborough University, 2001. https://dspace.lboro.ac.uk/2134/10917.
Повний текст джерелаАнотація:
Industrial applications of fuel cell technologies offer a major research opportunity. To realise the goal of practical commercial applications of this developing technology will involve the integration of the latest developments in electrical, fluid and chemical engineering systems. Although each field is well developed in its own right, the novel concept of combining these technologies within computational models offers the potential for new understanding and design procedures to be created. This multi-disciplinary approach would offer new insights into the fundamental physical phenomena, as well as creating tools that can be used for designing fuel cells and is the major focus of the research described in this thesis. Power storage fuel cells are the subject of this research. This particular fuel cell is a bipolar stack with two, single phase, liquid electrolytes. A review of the current techniques highlighted the need to address the study of the loss mechanisms present in the fuel cell. The prediction of short circuits created by the electrically conductive fluids required an electrical model. The power consumed driving the fluid system compelled a fluid dynamics model. These were combined within this work, to optimise the geometrical properties of this type of fuel cell based on general chemical kinetic and operating parameters. In order to satisfy the operating requirement of even distribution of reactants to the active areas, a finite-volume technique based on a computational fluid dynamics (CFD) code was developed. This enabled the prediction of the transport processes for fluid flow, electrical energy transfer and chemical species conversion throughout the fuel cell. The complexity of the multi-disciplinary CFD method required the use of parallel computers to reduce the lead times. The CFD approach is employed best studying small sections of the fuel cell system highlighting important phenomena. This research has already influenced design variations and has guided the direction of additional research, namely ways of electrically isolating the fluid without interrupting the flow. This work has successfully demonstrated that computational modelling can predict fuel cell electrochemical phenomena in a fraction of the time and cost of experimental procedures. This research is being used to benefit the design process and further the exploitation of fuel cell technologies. Finally, by extending the research into porous media and two phase flow these techniques could be applied to all types of fuel cell.
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Ioannou, Panagiotis. "Computational modelling of working memory." Thesis, University of Surrey, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.658622.
Повний текст джерелаАнотація:
Computational modelling empowers scientists to test hypotheses that they could not have done so otherwise, mainly because of the complexity of the system to be tested. In order to investigate particular postulates, computational neuroscientists build quantitative models of the central nervous system in great detail, and in different levels of organisation. In this thesis, by simulating morphologically reconstructed neurons and composing networks consisting of these neurons, we investigate and aim to bridge the gap between neuroscientific hypotheses and levels of organisation. All of our investigations fall under, but are not limited to, the working memory concept, a theoretical system designed to address the information processing in order to achieve cognition. To begin with, we investigate macroscopic neural oscillations as observed during working memory tasks. We show the criticality of inter-regional delay coupling effect on synchronisation phase-shift, and that near zero-lag synchronisation can be achieved via the M3 structural motif. After showing that spiking neurons can successfully model macroscopic phenomena, we focus on the microscopic level, where we simulate a number of interconnecting neurons and proceed to scrutinise their complex behaviour and the information processing capabilities they exhibit. Specifically, we explore the effect of spiking network parameters on polychronization and the sustainability of spikes based on short-term synaptic dynamics. We show that the models are extremely sensitive to neuronal parameters including type of connectivity, axonal delays, density and topology. In the end we investigate two contradicting theories of forgetting in short term memory: the temporal and the non-temporal approaches. We show that the sustained representation of memory cues highly depend on the size of their neuronal counterparts, and that both the temporal and the non temporal approaches can have a role to play in sustaining information, and that they do not necessarily contradict each other.
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Narbutas, Vilius. "Computational modelling of visual search." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8772/.
Повний текст джерелаАнотація:
Visual search traditionally has two main competing theories of parallel and serial search and this architectural issue has not been solved to this day. The latest developments in the field have suggested a possibility that response time distributions may aid in differentiating the two competing theories. For this purpose we have used the best available serial model Competitive Guided Search and two biologically-plausible parallel models inspired by the theory of biased competition. The parallel models adopted a winner-take-all mechanism from Selective Attention for Identification Model as base model that was extended to form a novel model for explaining response time distributions. These models are analytically intractable, therefore we adopted a more accurate kernel density estimator for representing unknown probability density function. Introduced robustness properties to the fitness method and developed a more efficient algorithm for finding the parameter solutions. Then these methods were applied for comparison of the respective models and concluded that winner-takes-all model poorly generalises to response time distributions. The results were followed by introducing a novel Asymmetrical Dynamic Neural Network model that managed to explain distributional changes better than Competitive Guided Search model.
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Sheppard, Terence. "Computational modelling of multiphase catalysis." Thesis, Queen's University Belfast, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676713.
Повний текст джерелаАнотація:
Simulating heterogeneous catalytic processes occurring at solid-liquid interfaces requires the use of quantum mechanical methods to allow for a description of bond breaking and bond forming. These methods must also allow a sufficiently sized statistical sampling of the liquid to be gathered. Current approaches based on density functional theory (DFT) are too expensive to satisfy these requirements so it is therefore desirable to develop alternative, faster methods. Self consistent tight binding (TB) methods, which are derived from a second-order expansion of the Kohn-Sham energy functional and use a parametrised Hamiltonian matrix, can be significantly faster than DFT making them ideal for the above task. In this thesis we describe the development of a TB model for organic molecules containing carbon, hydrogen and oxygen. This model has been fitted using a combination of intuition, analytical fitting and genetic optimisation. We have also developed a framework for the description of inter-molecular Van der Waals interactions using long-ranged empirical potentials. We have shown that this model is capable of describing the gas-phase structural and dynamic properties of a range of organic molecules, as well as the structure and dynamics of liquid-phase alcohols and solvated organic molecules. We have also shown how the the model can be used to describe chemical reactions in solution. The model forms part of a larger collection which also includes models for water and titania. All models within this collection share a single transferable oxygen species. When combined with a parametrisation of a metal such as platinum this collection could be used for the study of catalytic processes.
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Bauer, Paul. "Computational modelling of enzyme selectivity." Doctoral thesis, Uppsala universitet, Struktur- och molekylärbiologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-326108.
Повний текст джерелаАнотація:
Enantioselective reactions are one of the ways to produce pure chiral compounds. Understanding the basis of this selectivity makes it possible to guide enzyme design towards more efficient catalysts. One approach to study enzymes involved in chiral chemistry is through the use of computational models that are able to simulate the chemical reaction taking place. The potato epoxide hydrolase is one enzyme that is known to be both highly enantioselective, while still being robust upon mutation of residues to change substrate scope. The enzyme was used to investigate the epoxide hydrolysis mechanism for a number of different substrates, using the EVB approach to the reaction both in solution and in several enzyme variants. In addition to this, work has been performed on new ways of performing simulations of divalent transition metals, as well as development of new simulation software.
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Boyett, Robin Ernest. "Computational studies of hydrophobic porphyrins." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241621.
Повний текст джерела
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Kite, Matthew J. S. "Computational modelling of clay pipe extrusion." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources. Online version available for University members only until June 9, 2014, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=25966.
Повний текст джерела
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Sandström, Malin. "Computational Modelling of Early Olfactory Processing." Doctoral thesis, KTH, Beräkningsbiologi, CB, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-12090.
Повний текст джерелаАнотація:
Chemical sensing is believed to be the oldest sensory ability. The chemical senses, olfaction and gustation, developed to detect and analyze information in the form of air- or waterborne chemicals, to find food and mates, and to avoid danger. The organization of the olfactory system follows the same principles in almost all living animals, insects as well as mammals. Likely, the similarities are due to parallel evolution – the same type of organisation seems to have arisen more than once. Therefore, the olfactory system is often assumed to be close to optimally designed for its tasks.Paradoxically, the workings of the olfactory system are not yet well known,although several milestone discoveries have been made during the last decades. The most well-known is probably the disovery of the olfactory receptor gene family,announced in 1991 by Linda Buck and Richard Axel. For this and subsequent work, they were awarded a Nobel Prize Award in 2004. This achievement has been of immense value for both experimentalists and theorists, and forms the basis of the current understanding of olfaction. The olfactory system has long been a focus for scientific interest within several fields, both experimental and theoretical, and it has often been used asa model system. And ever since the field of computational neuroscience was founded, the functions of the olfactory system have been investigated through computational modelling. In this thesis, I present several approaches to biologically realistic computational models of parts of the olfactory system, with an emphasis on the earlier stages of the vertebrate olfactory system – olfactory receptor neurons (ORNs) and the olfactory bulb (OB). I have investigated the behaviour of the enzyme CaMKII, which is known to be critical for olfactory adaptation (suppression of constant odour stimuli) in the ORN, using a biochemical model. By constructing several OB models of different size, I have shown that the size of the OB network has an impact on its ability to process noisy information. Taking into account the reported variability of geometrical, electrical and receptor-dependent neuronal characteristics, I have been able to model the frequency response of a population of ORNs. I have used this model to find the key properties that govern most of the ORN population’s response, and investigated some of the possible implications of these key properties in subsequent studies of the ORN population and the OB – what we call the fuzzy concentration coding hypothesis.Detektion av kemiska ämnen anses allmänt vara den äldsta sensoriska förmågan. De kemiska sinnena, lukt och smak, utvecklades för att upptäcka och analysera kemisk information i form av luft- eller vattenburna ämnen, för att hitta mat och partners, och för att undvika fara. Luktsystemet är organiserat efter samma principer hos nästan alla djurarter, insekter såväl som däggdjur. Troligen beror likheterna på parallell evolution – samma organisation verkar ha uppstått mer än en gång. Därför antas det ofta att luktsystemet är nära optimalt anpassat för sina arbetsuppgifter.Paradoxalt nog är luktsystemets arbetsprinciper ännu inte väl kända, även om flera banbrytande framsteg gjorts de senaste decennierna. Det mest välkända är nog upptäckten av genfamiljen av luktreceptorer, som tillkännagavs 1991 av Linda Buck och Rikard Axel. För detta och efterföljande arbete belönades de med Nobelpriset år 2004. Upptäckten har varit mycket värdefull för både experimentalister och teoretiker, och är grunden för vår nuvarande förståelse av luktsystemet. Luktsystemet har länge varit ett fokus för vetenskapligt intresse inom flera fält, experimentella såväl som teoretiska, och har ofta använts som ett modellsystem. Och ända sedan fältet beräkningsneurobiologi grundades har luktsystemet undersökts genom datormodellering. I denna avhandling presenterar jag flera ansatser till biologiskt realistiskaberäkningsmodeller av luktsystemet, med tonvikt på de tidigare delarna av ryggradsdjurens luktsystem – luktreceptorceller och luktbulben. Jag har undersökt beteendet hos enzymet CaMKII, som anses vara kritiskt viktigt för adaptation (undertryckning av ständigt närvarande luktstimuli) i luktsystemet, i en biokemisk modell. Genom att konstruera flera olika stora modeller av luktbulben har jag visat att storleken på luktbulbens cellnätverk påverkar dess förmåga att behandla brusig information. Genom att ta hänsyn till nervcellernas rapporterade variationer i geometriska, elektriska och receptor-beroende karaktärsdrag har jag lyckats modellera svarsfrekvenserna från en population av luktreceptorceller. Jag har använt denna modell för att hitta de nyckelprinciper som styr huvuddelen av luktreceptorneuron-populationens svar, ochundersökt några av de tänkbara konsekvenserna av dessa nyckelprinciper i efterföljande studier av luktreceptorneuron-populationen och luktbulben – det vi kallar ”fuzzy concentration coding”-hypotesen.
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Mahrukh, Mahrukh. "Computational modelling of thermal spraying processes." Thesis, Cranfield University, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/10039.
Повний текст джерелаАнотація:
The main aim of this project is to model the effects of varied injection parameters on the gas dynamics and droplet dynamics of the HVSFS and SP- HVOFS processes for improving the droplet breakup and evaporation to enhance the nanoparticles heating and deposition efficiency. Thermal spraying processes are widely used to generate thermal-, corrosion-, and wear-resistant layers over the machine parts, to increase the durability of the equipment under severe environmental conditions. The liquid feedstock is used to achieve nanostructured coatings. It is used either in the form of a suspension or a solution precursor. The suspension is a mixture of solid nanoparticles suspended in a liquid medium consisting, for instance, of water, ethanol, or isopropanol. This dispersion mechanism in a liquid carrier provides adequate flowability to the nanoparticles, which cannot be handled by conventional gas- based feeding systems, whereas the solution precursor is mixed at the molecular level; hence, more uniform phase composition and properties are expected in the sprayed coatings as compared to the suspension and conventional powder spraying. Firstly, experiments are conducted to analyse the effects of different precursor concentrations, solvent types and injection nozzles on the size and morphology of synthesized nanoparticles. The results indicate that the particle size increased with increasing precursor concentration due to the variations in the physical properties of the mixture solution. The higher precursor concentrations had an adverse effect on the droplet atomization and evaporation process that led to bigger size particle formation. The use of aqueous solvent has some limits and with higher precursor concentration the surface tension increases that resulted in the reduction of droplets’ disintegration, and thus bigger size precursor droplets generate larger nanoparticles. A mixture of aqueous-organic solvents and pure organic precursors are preferred to improve the process efficiency of the nanoparticles size and morphology. Furthermore, the nanoparticles size can be controlled by using liquid feedstock atomization before injecting into the HVOF torch. A new effervescent injection nozzle is designed and compared to different types of existing injection nozzles, to see the variations in the droplet disintegration, and its effects on the performance of the HVOF torch processes. It is detected that the atomization would result in smaller size particles with homogeneous morphology. In a numerical study, different droplet injection types are analysed to see their effects on the gas and droplet dynamics inside the HVOF torch. The group-type injection (GTI) and effervescent-type atomization (ETI) are used effectively to overcome the heat losses and delays in the droplet evaporation. These approaches reduce the thermal and kinetic energy losses in the suspension-fed-HVOF torch, thereby improving the coating formation. The effects of using multicomponent water-ethanol mixture injection in the HVOF torch are also modelled, and its impact on the droplet breakup and evaporation are studied. The organic solvents have a low heat of vaporization and surface tension, and can effectively be used in the HVOF spraying process over the water-based solvents. Furthermore, nanoparticles are suspended in the liquid feedstock and injected into the HVOF torch. The effect of increasing nanoparticles’ concentration in the feedstock and its consequence on the gas dynamics, droplet breakup and evaporation are analysed. The augmentation in the nanoparticles loading in the suspension droplets can decrease the droplet breakup and evaporation rate because the required heat of vaporization increases significantly. Moreover, the size of injection droplet affects the droplet fragmentation process; bigger sized droplets observed a delay in their evaporation that resulted in coating porosity. The results suggest that smaller droplet sizes are preferred in coating applications involving a higher concentration of nanoparticles with high melting point. Further, the gas flow rates (GFRs) are regulated to control the droplet dispersion, atomization and evaporation inside the solution precursor fed-HVOF torch. The size of the droplet diameter is decreased by an increment in the GFR, as higher combustion rates increase the combustion flame enthalpy and kinetic energy. Moreover, the increase in the oxygen/fuel flow rates dilutes the injected precursor. It reduces ZrO2 concentration in the process and decreases the rate of particle collision; as a result, non-agglomerated nanoparticles can be obtained.
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Wilson, Dean Robert. "Computational modelling of turbulent magnetohydrodynamic flows." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/computational-modelling-of-turbulent-magnetohydrodynamic-flows(787a2a9d-f2f6-42e0-b218-a7b6e3041e04).html.
Повний текст джерелаАнотація:
The study of magnetohydrodynamics unifies the fields of fluid mechanics and electrodynamics to describe the interactions between magnetic fields and electrically conducting fluids. Flows described by magnetohydrodynamics form a significant aspect in a wide range of engineering applications, from the liquid metal blankets designed to surround and remove heat from nuclear fusion reactors, to the delivery and guidance of nanoparticles in magnetic targeted drug delivery. The ability to optimize these, and other, processes is increasingly reliant on the accuracy and stability of the numerical models used to predict such flows. This thesis addresses this by providing a detailed assessment on the performance of two electromagnetically extended Reynolds-averaged Navier-Stokes models through computations of a number of electromagnetically influenced simple channel and Rayleigh-Bènard convective flows. The models tested were the low-Re k-ε linear eddy-viscosity model of Launder and Sharma (1974), with electromagnetic modifications as proposed by Kenjereš and Hanjalić (2000), and the low-Re stress-transport model of Hanjalić and Jakirlić (1993), with electromagnetic modifications as proposed by Kenjereš and Hanjalić (2004). First, a one-dimensional fully-developed turbulent channel flow was considered over a range of Reynolds and Hartmann numbers with a magnetic field applied in both wall-normal and streamwise directions. Results showed that contributions from the electromagnetic modifications were modest and, whilst both models inherently captured some of the reduction in mean strain that a wall-normal field imposed, results from the stress-transport model were consistently superior for both magnetic field directions. Then, three-dimensional time-dependent Rayleigh-Bènard convection was considered for two different Prandtl numbers, two different magnetic field directions and over a range of Hartmann numbers. Results revealed that, at sufficiently high magnetic field strengths, a dramatic reorganization of the flow structure is predicted to occur. The vertical magnetic field led to a larger number of thinner, more cylindrical plumes whilst the horizontal magnetic field caused a striking realignment of the roll cells' axes with the magnetic field lines. This was in agreement with both existing numerical simulations and physical intuition. The superior performance of the modified stress-transport model in both flows was attributed to both its ability to provide better representation of stress generation and other processes, and its ability to accommodate the electromagnetic modifications in a more natural, and exact, fashion. The results demonstrate the capabilities of the stress-transport approach in modelling MHD flows that are relevant to industry and offer potential for those wishing to control flow structure or levels of turbulence without recourse to mechanical means.
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Bashar, Hasanain. "Meta-modelling of intensive computational models." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/13667/.
Повний текст джерелаАнотація:
Engineering process design for applications that use computationally intensive nonlinear dynamical systems can be expensive in time and resources. The presented work reviews the concept of a meta-model as a way to improve the efficiency of this process. The proposed meta-model will have a computational advantage in implementation over the computationally intensive model therefore reducing the time and resources required to design an engineering process. This work proposes to meta-model a computationally intensive nonlinear dynamical system using reduced-order linear parameter varying system modelling approach with local linear models in velocity based linearization form. The parameters of the linear time-varying meta-model are blended using Gaussian Processes regression models. The meta-model structure is transparent and relates directly to the dynamics of the computationally intensive model while the velocity-based local linear models faithfully reproduce the original system dynamics anywhere in the operating space of the system. The non-parametric blending of the meta-model local linear models by Gaussian Processes regression models is ideal to deal with data sparsity and will provide uncertainty information about the meta-model predictions. The proposed meta-model structure has been applied to second-order nonlinear dynamical systems, a small sized nonlinear transmission line model, medium sized fluid dynamics problem and the computationally intensive nonlinear transmission line model of order 5000.
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Keddie, Alastair John. "Computational modelling of corrosion protection systems." Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.439541.
Повний текст джерела
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Su, Fangzhong. "Computational modelling of word sense sentiment." Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.577555.
Повний текст джерелаАнотація:
In recent years, sentiment analysis which employs computational models to tackle opin- ion, attitude, emotion or judgement in text has become an important discipline in the area of natural language processing. It also has great potential in real world applications, ranging from personal decisions such as recognizing customer opinions in movie or hotel service reviews, to industry or government concerns such as analyzing user feedback on new products or tracking the public's reaction to national or international events. The main objective of this thesis is to investigate the interaction between word sense ambiguity and sentiment analysis. Towards this goal, it validates three key hypotheses: (1) sentiment can be assigned to word senses by humans, and sentiment assignment at the word sense level is also more reliable than at the word level; (2) word sense sentiment can be assigned by automatic algorithms with high accuracy and limited training data; and (3) word sense sentiment can improve word translation. This work begins with an investigation of the reliability of manual subjectivity and polarity label assignment on word senses. High agreement is gained from the human annotation study, indicating that subjectivity and polarity labelling on word senses is a well-defined task and should be suitable for automatic learning as well. Then various ma- chine learning approaches including heuristic unsupervised learning, supervised learning, and graph-based semi-supervised learning are proposed to automatically determine word sense sentiment. The experimental results show the effectiveness of all the three learn- ing models. In particular, for word sense subjectivity classification, the proposed semi- supervised graph-cut approach significantly outperforms the unsupervised heuristic-based approach, the supervised approach, as well as all prior competing approaches proposed by other researchers. We then automatically generate a complete subjectivity lexicon of more than 110,000 word senses by the semi-supervised graph-cut approach. Lastly, the poten- tial application of word sense sentiment information in cross-lingual lexical substitution is also explored. We posit a new assumption that good word substitutions will transfer a word's contextual sentiment from the source language into the target language. In prac- tice, to test this assumption, the word sense subjectivity information is incorporated as an additional feature in a system for English-Chinese lexical substitution. The usefulness of word sense sentiment information is then confirmed by experiments, as the incorpora- tion of subjectivity information yields significant improvement over a sentiment-unaware system.
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Przulj, Vlado. "Computational modelling of vortex shedding flows." Thesis, City University London, 1998. http://openaccess.city.ac.uk/7565/.
Повний текст джерелаАнотація:
This study describes the development and application of a two--<:limensional CFD method for vortex shedding flows past square and circular cylinders. The overall approach can be regarded as a compromise between the accuracy and computational costs, especially for high-Reynolds number flows. The latter are modelled by variants of the k - E eddy-viscosity model which is used in conjunction with wall functions. The governing equations, expressed through Cartesian vector and tensor components, are discretised using the finite volume method with a colocated storage arrangement for all variables. Body-fitted (non-orthogonal) structured or block-structured numerical grids can be used. Fully implicit, first-order accurate time discretisation is adopted, while the space discretisation is formally second-order accurate. In order to ensure a bounded solution, the high-resolution MINMOD and SMART schemes are implemented. The numerical method is validated against experimental data for various laminar flow situations: (i) single square and circular cylinders in a uniform flow, (ii) two circular cylinders in tandem submerged in a uniform flow and (iii) a circular cylinder in oscillatory flows. In the case of the uniform flow over single cylinders, the issues affecting the accuracy and reliability of two dimensional numerical solutions are addressed. It is shown that numerical uncertainties caused by a choice of the solution domain width (the blockage) very often cancel time and space discretisation errors. Further, advantages of high-resolution bounded schemes such as the MINMOD and SMART are confirmed. Variations of the mean drag coefficient and Strouhal number with Reynolds number are accurately predicted for the Reynolds number below 200, i.e. for two dimensional flow conditions. For these conditions, some physical features of vortex shedding are emphasized. For other flow configurations, parametric studies are conducted to investigate effects of additional factors on the integral vortex shedding parameters and flow regimes. In all cases, the present results compare well to the published experimental and numerical data. Various versions of the k - E model are considered for turbulent flow predictions. A new model, with an unsteady modification related to the production of the dissipation rate, is proposed. This model and the RNGmodel are validated against data for vortex shedding f{'om single square and circular cylinders. In the case of a square cylinder (Re = 20,000), both models yield satisfactory results for the integral parameters and most of the time-averaged and phase-averaged flow variables. These results stand comparison with those obtained by other models or LES methods. For a circular cylinder, the boundary layers are laminar before flow separation over a wide range of Reynolds numbers, up to 1 X 106 . On the other hand, the tested k - E models are based on the principal assumption that the flow is turbulent everywhere. Consequently, the flow separation is predicted wrongly which leads to unsccessful predictions of other vortex shedding results. Better results are obtained for the postcritical regime (Re > 106), where the boundary layers are turbulent before separation.
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Lucas, Timothy David. "Computational modelling of the golf stroke." Thesis, University of Glasgow, 1999. http://theses.gla.ac.uk/5001/.
Повний текст джерелаАнотація:
The golf stroke was computationally modelled using finite element analysis. Results for the impact between the club head and the ball compared well with previous research, both practical and theoretical. The results imply that for thick face club heads, such as irons, club head performance is independent of material stiffness but highly dependent on the friction of the interface and the clubhead geometry. The three ball flight predictors (speed, trajectory and spin rate) as a function of clubhead parameters are shown to be non-trivial. Acceptable models of impact could be achieved using rigid faces for thick face clubheads with the centre of mass and clubhead inertia accurately described. Results on ball construction effects imply that both the stiffness and mass distribution throughout the ball affect performance. The large deformations of the ball mean that classic rigid body mechanics cannot suffice in golf impact predictions. A model of the golf swing based on a double pendulum was constructed and shaft performance examined for various styles of golf swing. Shaft parameters thought to affect performance were quantitatively evaluated and results compared well with previous research. Increased club head speeds at impact were achieved with shafts of lighter weight or reduced bending stiffness for all styles of golf swing examined. The cause of bending forward of the shaft at impact was identified to occur from the large centrifugal forces acting on the head and the increased bending stiffness of the shaft also due to centrifugal force. On a detailed level shaft behaviour was affected by vibrations which appeared chaotic due to the changing stiffness of the system. This is expected to be less of an effect in an actual golf shot due to the damping provided by the human participant.
18
Delis, Anargiros. "Computational modelling of open channel flow." Thesis, University of the West of England, Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244309.
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19
Ashmore, D. R. "Computational modelling of bearing cage dynamics." Thesis, University of Nottingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289465.
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Lin, Dah-Chan. "Computational modelling of solid fuel combustion." Thesis, Cranfield University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305380.
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21
Forster, M. "Computational modelling of transonic circulation control." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3018248/.
Повний текст джерелаАнотація:
This Ph.D. thesis focusses upon computational fluid dynamics simulations of circulation control in transonic freestream speeds for applications to unmanned combat air vehicles. The work addresses Coanda shape designs and their effectiveness for transonic circulation control using supersonic jets, with comparisons against traditional control surfaces. Previous works have thus far only investigated transonic circulation control on elliptical sectioned wings with unrepresentatively thick trailing edges and improvements in performance made by considering elliptical Coanda devices or increasing radii of curvature. In this work, a supercritical aerofoil was first modified to accommodate a small Coanda surface with minimal effects on the base drag and a comparison made between the performance of using several Coanda designs and a hinged control surface. The use of a step was demonstrated to make a circulation control device with a simple converging nozzle as effective as ailerons and flaps up to moderate deflection angles and that the limitations are due to breakdowns in the mean flow in a similar fashion to traditional devices. In addition an optimisation study was performed using modern numerical methods on the contouring of the Coanda surface, which identified a shape that performed well for both transonic and subsonic freestream conditions. Circulation control was then applied to a three-dimensional unmanned combat air vehicle planform and assessed at transonic conditions for use in roll, pitch and yaw control. From the range of conditions investigated the findings suggest that, for a three-dimensional representative geometry, circulation control can match the performance of conventional controls for roll and pitch. The results also suggest that for benign transonic conditions, circulation control can also provide control similar effectiveness to split flaps for yaw control. The findings open up insights into transonic circulation control and hopefully will promote further research in both academia and industry, where a lack of CFD validation quality experimental data for a transonic test case with supersonic blowing prohibits the technology from advancing.
22
Hawker, N. A. "Computational Modelling of Intense Bubble Collapse." Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.679060.
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23
Jayapal, Prabha. "Computational modelling of the hydrogenase enzymes." Thesis, University of Manchester, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548684.
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24
Maheswaran, Satheesh. "Computational modelling of epithelial cell interactions." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1445678/.
Повний текст джерелаАнотація:
This thesis describes and evaluates approaches to computational models of Epithelial cell interactions. It begins with a review of existing approaches and in particular includes a rational reconstruction of a model of squamous epithelial cell interactions previously described by Stekel Stekel et al., 1995 . Suggestions for improving this model are made, including methods for analysing spatial clusters of cells using Delau- nay triangulation and heterogeneity of epithelial tissue using connective component labeling. Histological images of oral epithelium are used to develop a classification of base ment membrane shape in normal and dysplastic tissues. The method combines Fourier descriptors for shape representation, Principal Component Analysis for data reduction and the closest mean and support vector machine algorithms for pattern recognition. This approach is suggested as a general technique for evaluating the output of simulation models which involve curvilinear features in a shape-based clas sification of the tissues modelled. A new model of epithelial cell interactions is proposed by extending the Glazier- Graner framework for cell sorting Graner, 1993, Graner and Sawada, 1993 . The model includes biological processes such as cell division, differentiation, adhesion and death. In particular, the roles of differential adhesion and cell division during the-development of epithelium are discussed. The typical ordered structure of a healthy epithelium is shown to arise provided differential adhesion and cell division are modelled appropriately.
25
Channon, Yvonne Mary. "Computational modelling of heulandite-type zeolites." Thesis, Keele University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389603.
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26
Vengadasalam, Kirijen. "Computational modelling of coalescence filtration process." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/17323/.
Повний текст джерелаАнотація:
The low water-diesel interfacial tensions arising in biodiesels pose a problem for fuel filters designed to separate water contamination from diesel fuel. Such filters operate by passing the fuel through a fibrous non-woven material with the aim of capturing small water droplets on the fibres and holding them while further droplets coalesce with the captured droplets until the droplets are large enough to be carried away from the fibres and subsequently settle out of the fuel by gravity. The coalescence process is however less effective at lower interfacial tensions. The main purpose of this research is to explore the mechanisms at work in a coalescence filter by developing and applying computer simulations of the process, and to understand the effects of fibre properties such as wettability, size and separation on the filtration performance. Following a detailed review of the relevant literature, a macroscopic simulation of the flow within a filter housing is first presented, using finite element analysis via COMSOL Multiphysics to establish the main flow patterns through the filter system. The filter medium itself in this model is treated as a continuous porous medium. The flow at the pore/fibre scale is then analysed by means of a multiphase lattice Boltzmann method based on the multicomponent Shan-Chen model. The wettability of the fibres is incorporated through specification of a fluid density at the solid surfaces, allowing easy control of the local contact angle. The code developed is tested against previously published and validated finite volume/volume-of-fluid simulations of free droplet coalescence, with good agreement seen in the predicted dynamics. The interactions between individual water droplets and fibres is explored, in particular to establish critical conditions (flow speed, fibre contact angle, droplet/fibre size, droplet-fibre separation, fuel viscosity etc.) under which droplets carried by the flow can be captured by fibres, and the conditions under which droplets are released from fibres. The results confirm the difficulties in achieving rapid and effective coalescence when the interfacial tension is low, and reveal the sensitivity of the droplet-fibre dynamics to the contact angle on the fibres and the relative size of the droplets and fibres. In particular larger fibres are not effective for small droplets, so small fibres are essential in the filtration process. Also investigated are the dynamics of multiple droplets with arrays of fibres representing the filtration media. It is found that higher contact angles ( > 120°) lead to lower capture efficiency compared to lower contact angle, while contact angles less than 106° tend to produce a small variation in capture efficiency and capture most of the droplets at a filter porosity of 0.87. It is concluded that the inlet layer of the filter should have fibres with 78° contact angle and the exit layer fibres with contact angle 106°.
27
Rapson, Michael James. "An extensible computational cochlear modelling framework." Doctoral thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/5117.
Повний текст джерелаАнотація:
Includes abstract.Includes bibliographical references.
Cochlear models are used by many people for many purposes. Each purpose has different accuracy and complexity requirements, so no single model will be suitable for every purpose. A wide range of cochlear models has already been proposed, and the diversity in the field is only increasing. The proposed framework allows a large subset of models to be implemented and compared, facilitating modelling efforts. It uses the finite element method and state space techniques in an object orientated library, and is suitable for time domain cochlear models. In the face of the diversity noted, the physiology of the cochlea itself limits the scope of the possible models to consider. A general modelling framework is described in broad strokes, narrowing to provide full details of its implementation and use for a smaller set of models. Various published models were accurately replicated in the framework, and it was used to verify a silicon cochlea model. Studies into the mathematics behind fluid-structure interaction in the cochlea show that the set of models considered is characteristic of cochlear models in general, ensuring the desired extensibility of the modelling framework. These studies also have various implications for the cochlear modelling community at large.
28
Faddy, James M. "Computational modelling for shock tube flows /." [St. Lucia, Qld.], 2000. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16174.pdf.
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Steiglechner, Peter. "A Spatially Explicit Agent-Based Model of Human-Resource Interaction on Easter Island." Thesis, KTH, Numerisk analys, NA, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277730.
Повний текст джерелаАнотація:
The history of Easter Island, with its cultural and ecological mysteries, has attracted the interests of archaeologists, anthropologists, ecologists, and economists alike. Despite the great scientific efforts, uncertainties in the available archaeological and palynological data leave a number of critical issues unsolved and open to debate. The maximum size reached by the human population before the arrival of Europeans and the temporal dynamics of deforestation are some of the aspects still fraught with controversies. By providing a quantitative workbench for testing hypotheses and scenarios, mathematical models are a valuable complement to the observational-based approaches generally used to reconstruct the history of the island. Previous modelling studies, however, have shown a number of shortcomings in the case of Easter Island, especially when they take no account of the stochastic nature of population growth in a temporally and spatially varying environment. Here, I present a new stochastic, Agent-Based Model characterised by (1) realistic physical geography of the island and other environmental constraints (2) individual agent decision-making processes, (3) non-ergodicity of agent behaviour and environment, and (4) randomised agent-environment interactions. I use the model and the best available data to determine plausible spatial and temporal patterns of deforestation and other socioecological features of Easter Island prior to the European contact. I further identify some non-trivial connections between microscopic decisions or constraints (like local confinement of agents' actions or their adaptation strategy to environmental degradation) and macroscopic behaviour of the system that can not easily be neglected in a discussion about the history of Easter Island before European contact.Påsköns historia har, med dess kulturella och ekologiska mysterier, väckt intressen hos arkeologer, antropologer, ekologer och ekonomer. Trots de stora vetenskapliga ansträngningarna lämnar osäkerheten i de tillgängliga arkeologiska och palynologiska data ett antal kritiska frågor olösta och öppna för debatt. Den maximala storleken som den mänskliga befolkningen nådde före européernas ankomst, och avskogningens tidsmässiga dynamik, är några av de aspekter som fortfarande är fyllda med kontroverser. Genom att tillhandahålla en kvantitativ arbetsbänk för att testa hypoteser och scenarier är matematiska modeller ett värdefullt komplement till de observationsbaserade metoder som vanligtvis används för att rekonstruera öns historia. Tidigare modelleringsstudier har emellertid visat ett antal brister i fallet med Påskön, särskilt när de inte tar hänsyn till den stokastiska karaktären av befolkningsökningen i en tillfällig och rumsligt varierande miljö. Här presenters en ny stokastisk, agentbaserad modell som kännetecknas av (1) realistisk fysisk geografi av ön och andra miljömässiga begränsningar, (2) individuella beslutsprocesser av agenter, (3) icke-ergodicitet av agentens beteende och miljö och (4) randomiserade agent-miljöinteraktioner. Modellen används tillsammans med de bästa tillgängliga data för att bestämma rimliga rumsliga och temporära mönster av avskogning och andra socioekologiska egenskaper på Påskön före européers ankoms. Vidare identifieras några icke-triviala förbindelser mellan mikroskopiska beslut eller begränsningar (till exempel lokal inneslutning av agentens handlingar eller deras anpassningsstrategi till miljöförstöring) och makroskopiskt beteende hos systemet som inte lätt kan försummas i en diskussion om påsköns historia före europeisk kontakt.
30
Hand, Karen Jayne. "Computational studies of protein-ligand interactions." Thesis, University of York, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282271.
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31
Reams, Charles. "Modelling energy efficiency for computation." Thesis, University of Cambridge, 2012. https://www.repository.cam.ac.uk/handle/1810/244102.
Повний текст джерелаАнотація:
In the last decade, efficient use of energy has become a topic of global significance, touching almost every area of modern life, including computing. From mobile to desktop to server, energy efficiency concerns are now ubiquitous. However, approaches to the energy problem are often piecemeal and focus on only one area for improvement. I argue that the strands of the energy problem are inextricably entangled and cannot be solved in isolation. I offer a high-level view of the problem and, building from it, explore a selection of subproblems within the field. I approach these with various levels of formality, and demonstrate techniques to make improvements on all levels.
32
Greaves, Richard Brian. "Computational studies of protein structure and function." Thesis, University of York, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387165.
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33
Palit, Arnab. "Computational modelling of diastole for human ventricle." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/79182/.
Повний текст джерелаАнотація:
Diastolic heart failure (DHF) with normal systolic pump function has been typically observed in the majority of HF patients. DHF changes regular diastolic behaviour of left-ventricle (LV), and increases the ventricular wall stress. Therefore, normalisation of increased LV wall stress is the cornerstone of many existing and new therapeutic treatments. However, information regarding such regional stress-strain distribution for human LV is extremely limited in the literature. Thus, the study aimed at estimating the normal range and regional variation of diastolic stress-strain field in healthy human LVs, and exploring the infl uence of fibre structure, geometrical heterogeneity and material properties on passive infl ation of LV. It is envisaged that such information could be used as targets for future in-silico studies to design optimised HF treatments. FE modelling of passive diastolic mechanics was carried out using personalised ventricular geometry, that was constructed from magnetic resonance imaging (MRI), and structure-based orthotropic constitutive law. Laplace-Dirichlet-Region growing-Finite element (LDRF) algorithm was developed in order to assign the myocardium fibre map on ventricular geometry. The effect of right ventricle (RV) deformation, that has not been taken into account by the majority of researchers due to modelling simplification, was investigated for the first time by comparing the results predicted by bi-ventricle (BV) and single LV models, constructed from the aforementioned MRI data. In addition, personalised in-vivo measurement of fibre structure, that might be different in individual subjects and diseased conditions, is still an open question. Therefore, the sensitivity of LV diastolic mechanics to the details of the fibre structure was accomplished for the first time using eight different fibre orientations. In-vivo passive orthotropic myocardium properties for healthy human myocardium, indispensable for personalised LV wall stress estimation, was identified, and subsequently, the regional variations of LV wall stress-strain were investigated by incorporating geometrical heterogeneity, personalised myocardium properties and LV base movements in the FE models. RV deformation increased average fibre and sheet stress-strain in LV wall during diastole, and therefore, the effect should always be included in cardiac biomechanics study. Any pathological remodelling, that increased the amount of transmural fibre angle, led to an additional LV infl ation. The study indicates that a change in fibre orientation may contribute to the heart failure with preserved ejection fraction (HFpEF) development. Future therapeutic intervention should consider the effect of altered fibre orientation for better outcome. Due to the ill-posed nature of the inverse optimisation problem, the average myocardial stiffness was extracted by identifying the normal ranges of the parameters. A novel method was developed by combining FE modelling, response surface method (RSM) and genetic algorithm (GA) to identify the passive orthotropic myocardium properties for healthy human myocardium using routinely used clinical data. These myocardium properties can directly be utilised in future computational studies. Although the regional stress-strain distribution of the LV wall was highly heterogeneous amongst the individuals, it was observed that the inner wall of the LV experienced higher fibre stress compared to the outer wall. The LV wall near the base and the lateral region received greater stress-strain compared to the other regions. The incorporation of LV base movement (not addressed in the literature) improved the FE model predictions, and therefore, it is recommended to be considered in later studies. In addition, normal ranges of various stress-strain components in different regions of LV wall were reported for five healthy human ventricles considering RV deformation, LV base movement, and subject-specific myocardium properties. This information could be used as a reference map for future studies. The study revealed that the FE modelling can be employed to analyse the effect of geometry, fibre-structure and material properties on normal ventricular mechanics, and therefore, can provide a greater insight into the underlying mechanics of failing heart and plan for optimised surgical intervention. Hence, the research has impacts on computational cardiac biomechanics as well as clinical cardiac physiology fields.
34
Welch, S. "Computational modelling of diesel engine smoke emission." Thesis, Cranfield University, 1995. http://dspace.lib.cranfield.ac.uk/handle/1826/4611.
Повний текст джерелаАнотація:
This thesis is addressed to the problem of predicting the emission of exhaust smoke
from the diesel engine. A simulation program based on a zonal phenomenological
combustion model has been developed, permitting analysis of soot modelling
techniques. For the first time, a comparative study of the common soot model
expressions has been undertaken. Model sensitivities and behaviour have been
critically assessed in order to determine the key model parameters and to establish
a more solid predictive capability. Validation of both the combustion and soot
predictions was made by means of comparison with the extensive experimental
data-set of Kamimoto.
The combustion model results showed a very good match between -predicted and
experimental heat release curves. The only notable weakness derived from the
method chosen to represent the effect of air swirl on the jet. Otherwise, the
combustion predictions were deemed to be sufficiently accurate to serve as an
effective platform for soot model development and analysis.
The predictions of exhaust smoke for different operating conditions revealed the
importance of accurately describing the overall air-to-fuel ratio in the spray. The
effect of load variation was poorly represented due to neglect of the transfer of
combustion products between the model zones.
Soot rate predictions were generally quantitatively poor, thus requiring expression
calibration. The comparative study of soot expressions identified a ranking of
sensitivities of the formation expressions. Though oxidation is conceptually simpler,
more distinct qualitative differences were observed in the behaviour of the
expressions. The predictions of exhaust soot were found to be highly sensitive to
the 'matching' of the formation and oxidation expressions over the period of the
combustion process, and with poorly matched expressions, a very high sensitivity
to the soot model constants was shown. The best results were obtained by use of
simple quasi-chemical rate expressions.
35
Petrauskas, Karolis. "Computational Modelling of Biosensors of Complex Geometry." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110701_105911-89480.
Повний текст джерелаАнотація:
Biosensors are analytical devices mainly used to detect analytes and measure their concentrations. Mathematical modeling is widely used for optimizing and analyzing an operation of biosensors for reducing price of development of new biosensors. The object of this research is mathematical and computer models, describing an operation of biosensors, made of several parts with different properties. The dissertation covers models, formulated in one and two-dimensional spaces by partial differential equations with non-linear members, and solved numerically, using the method of finite differences. The numerical models are implemented by a computer program. An original mathematical model for a biosensor with a carbon nanotube electrode is presented in the dissertation. The conditions at which the one-dimensional mathematical model can be used instead of two-dimensional one for accurate prediction of the biosensor response are investigated. Elements, used to build models of biosensors with a complex structure, were systemized. The biosensor description language is proposed and the computer software, simulating an operation of biosensors in the one-dimensional space and a rectangular domain of the two-dimensional space, is developed. An adequateness of the model for the biosensor with the carbon nanotube electrode and the impact of structural and geometrical properties on a response of the biosensor were investigated, performing computer experiments using the developed software.Biojutikliai yra įrenginiai, skirti medžiagoms aptikti bei jų koncentracijoms matuoti. Siekiant sumažinti biojutiklių gamybos kaštus yra pasitelkiamas matematinis biojutikliuose vykstančių procesų modeliavimas. Disertacijoje nagrinėjami matematiniai ir kompiuteriniai biojutiklių modeliai, aprašantys biojutiklių, sudarytų iš kelių, skirtingas savybes turinčių dalių, veikimą. Nagrinėjami modeliai yra formuluojami vienmatėje bei dvimatėje erdvėse, aprašomi diferencialinėmis lygtimis dalinėmis išvestinėmis su netiesiniais nariais ir yra sprendžiami skaitiškai, naudojant baigtinių skirtumų metodą. Skaitiniai modeliai yra įgyvendinami kompiuterine programa. Disertacijoje pateikiamas originalus matematinis modelis biojutikliui su anglies nanovamzdelių elektrodu, nustatyti kriterijai, apibrėžiantys, kada biojutiklį su perforuota membrana galima modeliuoti vienmačiu modeliu. Darbe susisteminti elementai, naudojami biojutiklių modelių formulavimui, pagrindinį dėmesį skiriant biojutiklio struktūrinėms savybėms modeliuoti. Apibrėžta biojutiklių modelių aprašo kalba ir sukurta programinė įranga, leidžianti modeliuoti biojutiklių veikimą vienmačiais modeliais arba modeliais, formuluojamais stačiakampėje dvimatės erdvės srityje. Taikant sukurtą biojutiklių modeliavimo programinę įrangą, ištirtas biojutiklio su anglies nanovamzdelių elektrodu modelio adekvatumas ir struktūrinių bei geometrinių savybių įtaka biojutiklio elgsenai.
36
Line, Andrew James. "Computational modelling of helicopter high-frequency dynamics." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413420.
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37
Battersby, Paul. "Modelling supercritical fluid extraction using computational chemistry." Thesis, Northumbria University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245390.
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Macdonald, Alison. "The computational modelling of collecting lymphatic vessels." Thesis, University of Exeter, 2008. http://hdl.handle.net/10036/47054.
Повний текст джерелаАнотація:
This thesis details a 1-d model of a lymphatic vessel, developed from a model by Reddy. Some additions to the modelling techniques were found to be necessary to prevent numerical phenomena not found in experiment. Furthermore the details of the wall and valve were important to the mechanics of the system. This developed model presents flow characteristics which are not represented in the existing lumped parameter or 1-d models of the lymphatic system. Additional terms allow more realistic representation of some modes of flow such as those occurring during collapse. The model was validated using Poiseuille flow calculations and experimental work. Features found in experiment were reproduced in the model. Such as the shark tooth shape of the radius time graph. A study of the sensitivity of the model to experimental parameters was performed. Features that increased flow included: increased compliance of the vessel, a larger diameter, amplitude of contraction or frequency, or a faster contraction wave. A lumped parameter model, relating the radius directly to the pressure, was investigated but this did not reproduce flow features such as the shark tooth shaped radius with time relationship or the radius peak at the beginning of a contraction or passive relaxation of the vessel. In the 1-d model the time constant of this passive relaxation increased with the magnitude of contraction. This value may have physiological relevance.
39
Abdelgaied, Abdellatif Abdelfadeel Younes. "Computational wear modelling of knee joint replacements." Thesis, University of Leeds, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582519.
Повний текст джерелаАнотація:
Due to the fact that a growing number of young patients require joint replacements, the expected lifetime of the prostheses is considerably increasing, and patient activities are becoming more demanding. New materials and designs are being introduced. The technical challenge lies in developing new designs, with high-performance materials, and low wear to improve prosthesis life. The main issue is to pre-clinically investigate the new materials and designs. Many researchers have reported wear in total knee replacements investigated in simulators. A single simulator test can be very expensive and take a long time to run. Computational wear modelling is an alternative attractive solution to these limitations, particularly when combined with experimental studies to provide input as well as validation. However, historical computational wear models have adopted the classical Archard's wear law, which was developed for metallic materials, and have selected wear factors arbitrarily from literature. It is known that such an approach is not generally true for polymeric bearing materials and is difficult to implement due to the dependence of wear factors on contact pressure as well as cross-shear. Therefore, these studies are generally not independent and lack general predictability. The objective of the present study was to develop a new computational wear model for the knee implants, where the wear volume dependent on sliding distance and contact area, based on an independent experimentally determined non-dimensional wear coefficient. The effects of cross-shear and creep on wear predictions were also considered. Independent experimental pin-on-plate multi- directional wear tests were conducted to provide the required input parameters. The output results from the new computational model were compared with the data from the experimental knee simulation tests in Leeds and parametric studies for different designs, materials and different operating conditions were conducted. The results suggested that the computational wear modelling, based on the new wear law and the independent -experimentally calculated non-dimensional wear coefficient, were more reliable, and therefore provide a more robust virtual modelling platform. In addition, the results showed that potential methods for increasing the expected total knee replacement lifetime might be to introduce less conforming knee replacement and to use cross-linked polyethylene as a bearing material.
40
Sarhosis, Vasilis. "Computational modelling of low bond strength masonry." Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.550342.
Повний текст джерелаАнотація:
The development of a computational model for low bond strength brick masonry is described. Cracking and failure in such masonry occurs typically at the interface between the masonry units and the mortar joints. As a result software based on a 2- dimensional discrete element analysis (UDEC) was used. One feature of the research was the method used to identify the material parameters for the constitutive model. The conventional method of obtaining material parameters from the results of testing small samples of masonry was thought to be problematic. Instead, the material parameters were obtained from the results of tests carried out in the laboratory on single leaf wall panels, each containing a large opening. Each panel was subjected to a gradually increasing vertical in-plane static point load until it collapsed. The wall panel tests were also modelled using UDEC. An optimization procedure was then used to tune the parameters used initially in UDEC in order to better simulate the pre- and post-cracking behaviour and the behaviour close to collapse of the panels tested in the laboratory. Having obtained the material parameters for UDEC, the model was then validated by comparing the UDEC-predicted behaviour of wall panels different to those used to determine the material parameters, with those tested in the laboratory. Some of the panels used for the validation process were reinforced with bed joint reinforcement, others were unreinforced but were of deeper and longer span construction. Good correlation was obtained between the results from the computational model and those obtained from tests in the laboratory.
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Taddese, Bruck. "Computational modelling of G protein-coupled receptors." Thesis, University of Essex, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589439.
Повний текст джерелаАнотація:
G protein-coupled receptors (GPCRs) comprise the most "drugable" family of transmembrane proteins, GPCRs share a common structural template and a general mechanism of signal transduction, but vary greatly in sequence conservation, ligand recognition and function. The current set of class A GPCR crystal structures have facilitated the modelling of class A GPCRs. However, other classes of GPCRs have not been so easy to study. The main focus presented in this thesis is the utilisation of class A GPCR structural information to model medically important GPCRs other than class A GPCRs via molecular modelling. The lack of sequence conservation hampers modelling non-class A GPCRs using class A GPCR crystal structures. A plant GPCR, namely GCR1, has sequence homology to more than one GPCR family (class A, Band E GPCRs) and has been used to align the transmembrane region of class A and B GPCRs. Consequently, we have presented a computational protocol for the identification of putative plant GPCRs that may similarly be used to address the difficult issue of alignment between GPCR families but in this respect only GCR1 was found to be useful. GCR1 is still an orphan GPCR with no known cognate ligand. We first assessed whether GCR 1 was a valid GPCR via homology modelling and molecular dynamics. We found that GCR1 has more similarities to class A and class S GPCRs than was previously acknowledged and further support evidence that GCR1 is a GPCR. Consequently, using the class A - GCR1 - class B alignment, we have produced active and inactive homology models of the CGRP receptor, a prototypical class B GPCR. In conjunction with mutation data, these models were used to identify a number of distinct class B motifs and their class A equivalents for the first time. Finally, molecular dynamic simulations were used to further confirm the role of the class B motifs.
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Lee, Rabinder. "Aspects of affective action choice : computational modelling." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.542964.
Повний текст джерела
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Kardos, T. N. "Modelling Smoke Flow Using Computational Fluid Dynamics." University of Canterbury. Civil Engineering, 1996. http://hdl.handle.net/10092/8278.
Повний текст джерелаАнотація:
There have been a number of experimental investigations into the backdraft phenomena. A backdraft occurs in the event of a ventilation source being formed in a compartment, within which a fire has been burning for a sufficiently long enough time to form a deep layer of excess pyrolyzates. The source of fresh air will flow into the compartment in the form of a gravity current. It is the gravity current feature of backdrafts that this research project focuses on.
Application of Computational Fluid Dynamics (CFD) to fire problems is expanding, including the development of specific programs for fire engineering applications. The experimental programme that was used in this research project highlights the difficulties of analysing fluid flows by using CFD simulations. The Flow3D program was used to obtain a more detailed understanding of the behaviour of a gravity current, allowing a detailed study of fluid dynamics which cannot be investigated experimentally. The simulations used two different vent configurations, with the CFD model being validated on the experimental results of salt water tank models. The simulations preformed compared well to the experimental data that was used for scaled salt water tank experiments.
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Street, David Alan. "Computational modelling of the stirred reaction vessels." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305422.
Повний текст джерела
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Horton, Caroline Alison. "Computational modelling of cell signalling pathway dynamics." Thesis, University of Liverpool, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433816.
Повний текст джерела
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Marshall, David A. "Patient-specific computational modelling of embolic stroke." Thesis, University of Leicester, 2018. http://hdl.handle.net/2381/43056.
Повний текст джерелаАнотація:
Embolic stroke occurs when arterial debris or thrombus detaches from the insides of the diseased arteries and moves through the bloodstream to block arteries supplying the brain. Stroke is a major clinical problem but few researchers have attempted to model embolus transport. Existing methods available for modelling stroke have numerous strengths and limitations. This aim of this thesis is to investigate approaches to modelling the transport of emboli through the cerebral vasculature with a view to performing patient-specific simulations toward a better understanding of the pathophysiology of stroke. This thesis is divided into three sections. In section one I investigate flow models of the cerebral circulation, reviewing anatomy and computational blood flow modelling, before creating a 0D model of the circle of Willis, produce a flow phantom of the cerebral vasculature, segment and analyse patient MR angiograms, and apply the 0D model to patient anatomy. In section two I discuss and review computational modelling of embolus transport, adapt a fractal embolus trajectory model and an embolus sizing algorithm to patient-specific data using measurements from MR angiograms, then discuss the results of patient measurements and the embolus trajectory simulations. In section three I discuss applying a fluid dynamics method called smoothed-particle hydrodynamics (SPH) to modelling emboli in the blood, I review SPH models of blood flow, present feasibility studies for applying SPH to emboli, and finally create an in-house code for simulating emboli, which is applied to embolus migration in a tube.
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Skylaris, Chris-Kriton. "The computational modelling of heavy atom chemistry." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624478.
Повний текст джерела
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Sorathiya, Anilkumar. "Computational modelling approaches to HIV-1 dynamics." Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609918.
Повний текст джерела
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Xia, X. "Computational modelling study of yttria-stabilized zirconia." Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/20483/.
Повний текст джерелаАнотація:
Interatomic potential and quantum mechanical simulation techniques have been applied to both the bulk and surfaces of yttrium-stabilized cubic zirconia (YSZ) with special reference to its role in partial oxidation reaction at high temperature. The stabilities of pure ZrO2 phases and surfaces have been examined. The bulk structures of low pressure phases are reproduced with the observed order of stability: monoclinic > tetragonal > cubic zirconia. The relative stability of plane cubic ZrO2 surfaces is predicted to be (111)c > (110)c > (100)c > (310)c. In addition, the stability of topological surfaces is found to be reduced with the coordination number of Zr ions at the topological sites in the order: plane > step > kink > corner. The dispersion of defects in YSZ systems has been studied, considering both the dopant content and surface segregation. In the bulk, the yttrium dopants tend to form a pair with two yttrium atoms close to each other and preferentially occupying the 1st or 2nd nearest neighbour (NN) sites to the compensating oxygen vacancy. At the surface, yttrium segregates to the top layers (up to 4-5 Å) of the dominant (111) surface of YSZ. The composition of the outermost surface of YSZ is predicted to be independent of Y bulk concentration and reach a maximum Y/Zr ratio of 1:1. In relation to catalytic oxidation, the interaction between oxygen molecules and the (111) surfaces of pure c-ZrO2 and YSZ have been investigated using quantum-mechanical DFT-GGA methods. The adsorption states of oxygen and the pathways for dissociation have been indentified on the plane and stepped (111) surfaces. In general, the creation of oxygen vacancies by yttrium doping provides an active site for oxygen adsorption. In addition, the low-coordinated Zr cations on the YSZ surfaces can attract strongly reduced oxygen species and the most stable adsorption state of oxygen is adopted to achieve a higher bond saturation of the neighbouring Zr site.
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Zhang, Ning. "The computational modelling of electromagnetic acoustic imaging." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:2c4c9946-b90c-43a3-9039-1c7df2dcd976.
Повний текст джерелаАнотація:
The Electromagnetic Acoustic (EMA) technique is a novel multi-modal technique for medical imaging. It is sensitive, in principle, to contrast in mechanical properties and electrical properties and has potential in a number of applications such as breast tumour detection where there will be contrast between diseased and healthy tissue and high intensity focused ultrasound monitoring, where there will be contrast when tissue is ablated. A complete computational model for the EMA imaging is developed. The model considers the linear or nonlinear propagation of ultrasound in soft tissue, the dynamic response of the viscoelastic soft tissue to acoustic radiation force (ARF) stimulation and scattering of electromagnetic waves with and without the Doppler effect. The suitability of the EMA imaging for breast tumour detection is evaluated, modelling a tumour as a spherical inclusion in an infinite homogeneous background tissue with clinically relevant material properties. The results show that variations of the mechanical properties of underlying healthy breast tissue and tumour tissue in clinically feasible range should result in a change in the amplitude of the first Doppler component (FDC) of up to 50%, and varying the electrical contrast leads to a change in the ratio of the FDC and unshifted component (UC) of less than 1 dB. The relative difference between the first Doppler component and the unshifted component is greater than 68 dB and therefore the frequency demodulation may pose a significant challenge if EMA imaging is used for breast tumour detection. The feasibility of using the EMA imaging for real-time monitoring of High Intensity Focused Ultrasound (HIFU) therapy is also investigated. Simulations conducted with realistic liver tissue properties show that the induced Doppler effect in the scattered EM wave is not well correlated with the growth of thermal lesion, therefore it is unlikely to be a good indicator of the lesion size. EMA imaging may not be appropriate for monitoring HIFU therapy.