Dissertations / Theses on the topic 'Tunnel problem'

Squeezing or time-dependent creep deformation of rock has been encountered frequently in tunnels. It is particularly common in tunnels excavated in very soft rock or heavily fractured rock under significant in-situ stresses. In Taiwan, due to the inferior geological setting and the young sedimentary rock formations, squeezing in tunnels was found to be a very common problem from the recent case histories of some large span road tunnels. This research reviewed the existing rock creep models, and an adequate creep model for representing the creep behaviour of soft rock or a weak rock mass in general was selected based on testing data of some soft rock cores. A numerical code was developed and validated by using tunnel physical model test. Actual tunnel case histories were also used to develop the creep analysis method for practical engineering purpose.

The aerodynamic behavior of wind tunnels with porous, flexible walls formed from tensioned Kevlar has been characterized and new measurement techniques in such wind tunnels explored. The objective is to bring the aerodynamic capabilities of so-called Kevlar-wall test sections in-line with those of traditional solid-wall test sections. The primary facility used for this purpose is the 1.85-m by 1.85-m Stability Wind Tunnel at Virginia Tech, and supporting data is provided by the 2-m by 2-m Low Speed Wind Tunnel at the Japanese Aerospace Exploration Agency, both of which employ Kevlar-wall test sections that can be replaced by solid-wall test sections. The behavior of Kevlar fabric, both aerodynamically and mechanically, is first investigated to provide a foundation for calculations involving wall interference correction and determination of the boundary conditions at the Kevlar wall. Building upon previous advancements in wall interference corrections for Kevlar-wall test sections, panel method codes are then employed to simulate the wind tunnel flow in the presence of porous, flexible Kevlar walls. An existing two-dimensional panel method is refined by examining the dependency of correction performance on key test section modeling assumptions, and a novel three-dimensional method is presented. Validation of the interference corrections, and thus validation of the Kevlar-wall aerodynamic performance, is accomplished by comparing aerodynamic coefficients between back-to-back tests of models carried out in the solid- and Kevlar-wall test sections. Analysis of the test results identified the existence of three new mechanisms by which Kevlar walls cause wall-interference. Additionally, novel measurements of the boundary conditions are made during the Kevlar-wall tests to characterize the flow at the boundary. Specifically, digital image correlation is used to measure the global deformation of the Kevlar walls under wind loading. Such data, when used in conjunction with knowledge of the pre-tension in the Kevlar wall and the material properties of the Kevlar, yields the pressure loading experienced by the wall. The pressure loading problem constitutes an inverse problem, and significant effort is made towards overcoming the ill-posedness of the problem to yield accurate wall pressure distributions, as well as lift measurements from the walls. Taken as a whole, this document offers a comprehensive view of the aerodynamic performance of Kevlar-wall test sections.
Ph. D.

Orientador: Clovis Perin Filho
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Científica
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Resumo: Túneis de congelamento são equipamentos utilizados pela industria alimentícia para o condicionamento térmico de produto tais como iogurte, sorvete, leite, carne e derivados. Assim, geralmente estão no fim do processo de produção de produtos altamente perecíveis. Quando um túnel representa m gargalo do processo, ele causa transtornos à produção que podem até interrompê-la. Este trabalho visa a abordagem do problema de operação eficiente e túneis de congelamento quanto ao aspecto de carregamento. Primeiramente abordamos o problema estático e suas relaxações e restrições. No problema estático determinístico, o instante de chegada das bandejas de produtos e o tempo de exposição necessário para seu condicionamento são conhecidos de antemão. Deve-se, então, programar por completo o carregamento do refrigerador definindo, para cada bandeja, em que nível do túnel deve ser colocada ou se deve ser rejeitada. Resultados teóricos são obtidos, particularmente para o caso (relaxado) do refrigerador de gavetas. Várias possibilidades de abordagem do problema estático são discutidas. Em seguida abordamos o problema dinâmico, onde não se dispõe do conhecimento prévio dos parâmetros de cada bandeja. Estes só ficam definidos a partir da chegada de cada bandeja, quando então a decisão quanto ao carregamento ou rejeição da bandeja deve ser tomada. Para o problema dinâmico são apresentadas várias políticas, que são testadas num caso real e em cenários hipotéticos nele baseados. Para avaliação de desempenho das políticas usamos limites' inferiores calculados com base no desenvolvimento teórico do problema estático. Os resultados são muito satisfatórios para uma classe de políticas a que chamamos de encadeamento.
Abstract: Freezing tunnels are food industry facilities for conditioning of meat, ice-cream, milk, yogurt, etc. They are very unwished botlenecks because they are positioned at the end of the production process of highly perishable items (low in-process inventory). The freezing tunnel loading problem is that of maximizing its production in terms of the amount of frozen trays of products. The purpose of this study is to model this problem and develop methods for solving its static and dynamic versions. In the static problem, the arrival time and the conditioning time of each tray are known in advance for the entire loading period. One should then completely schedule the loading of the tunnel. Each tray must be assigned to a position in the tunnel or be rejected. . We discuss several approaches and show some theoretical results for relaxed problems. In the dynamic problem, the arrival and the demand of trays are not known in advance. In this case, the decisions must take place at the arrival times. Several policies are developed. Some real case based scenarios are used for testing the policies. The study shows the potential gains with the application of some policies, mainly those ofthe class we named 'chain policies'.
Mestrado
Mestre em Matemática Aplicada

The regional economic impact of the Channel Tunnel has engendered much public and private sector interest. Previous studies examining the regional implications of the Tunnel have argued that related development pressures will be largely confined to South East England, further widening the "North-South" divide. Economic Potential Analysis was earlier employed by Clark el. al. (1969) and Keeble et. al. (1982a) to model the geographical impact of the Tunnel on the relative accessibility of the UK regions. The conclusions drawn from these studies support the proposition that the South East would gain at the expense of the more peripheral regions. However, the important implications of a rail-only Tunnel have yet to be modelled. The results of the present study show that opportunities created by the Tunnel could be spread more evenly than had previously been predicted. However, following a review of the legislative and policy environment of the Tunnel and related infrastructure, it is argued that as a result of British Government inaction the more peripheral UK regions are likely to be unable to maximise any potential benefits created. Nonetheless, the overall regional economic impact of the Tunnel will depend ultimately on the reactions of the business community (Pieda 1989a&b). The findings of a questionnaire survey carried out for this thesis reveal a considerable degree of similarity in perceptions and anticipated usage of the Tunnel for companies in the South East and South West, including the "Far South West". If this similarity is apparent after the Tunnel opens, the regional economic structure of the UK might only be marginally affected.

There is a huge potential of underground constructions in the Himalayan region for hydropower, transport systems and conservation of environment. However, the tectonic activities have resulted with a fragile regional geology. Moreover, the high mountainous topography causes high overburden pressure in the underground structures causing squeezing and other stability problems. Thus the huge tunnelling potential can only be materialised by applying professional and scientific approaches.

This thesis focuses on the stress induced problems with special reference to squeezing. Main objectives of this study were to review and check validity of the available tunnel stability assessment methods, to carry out relevant laboratory tests and interpret the results, and to use a numerical modelling code. In the present study, two projects have been used as case studies, both located in Nepal Himalayan region. These are Khimti1 hydropower project - a completed project; and Melamchi water supply project - yet to be constructed. Both projects include tunnels through series of weak rock mass strata with high overburden stress.

One of the factors that may cause stability problems in a tunnel is the stress level acting around the opening. A tunnel fails when the stress exceeds the strength of rock mass. If the stress level does not exceed the rock mass strength, but is sufficient up to a critical level to cause creep, it may lead to rock failure after some time. In a tunnel stability assessment, the determination of the critical stress level is important. Creep tests were carried out on the Melamchi gneiss and the critical stress level has been determined.

The resulted creep test curves were calibrated to obtain rheological parameters. Tunnel deformations including time-effect, were calculated for a given stress level. Based on the creep test results at various uniaxial stress levels, an equation is obtained for the relation between the strain rate and stress level. Back analyses have been carried out using the available empirical, semi-analytical and analytical methods and FLAC3D code; the results have been found to be in close agreement with the tunnel convergence measurements in the Khimti tunnel. So these methods were used in the Melamchi tunnel design.

In the 66 squeezing tunnel cases from around the world and the Khimti case study, it was observed that the rock mass strength (corresponding to rock type) has a significant influence on squeezing phenomena. Thus the available squeezing prediction criteria based on the rock mass classification alone, need to be updated by including rock mass strength as well. Similarly, ‘valley side effect of topography’ has been found to influence the tunnel deformation in the Khimti project. It has opened an area for a further study to correlate the valley side effect of topography to the stress increase in the tunnel.

The aim of this project work is the design and realization of an instantaneous concentration measurement system to be used with binary gas mixtures. The design is focused on the simplicity of the set up and on its compactness, and it is specifically intended to be used in wind tunnel applications. The outcome of the design process for the specified system is an aspirating hot-wire probe based on a polypropylene 3D printed body and a simple single wire sensor. Specifically, a 3D printing machine based on the Material Jetting (MJ) technology was used for the probe manufacturing. One of the most important design features is the possibility to get access to the wire through the removal of a single probe component, which is a nearly effortless operation. This feature allows to repair the broken wire sensor without the need of substitute the whole probe. From these design specifications it could be understood that due also to its dimensions, the probe must be handled with care, and it cannot operate inside hot flows or uncontrolled flow temperature and pressure conditions. It was not possible to test the probe behaviour in presence of flows with composition variations due to the lack of the necessary instrumentation to perform this kind of experiments. Nonetheless, the design effectiveness could be confirmed by verifying that the hot-wire signal remained constant when the probe was exposed to a variable speed constant composition flow. This proved the probe insensitivity to external flow speed, and it opened the possibility to further testing sessions involving gases.

Ce travail de thèse est consacré à l’étude d’auto-assemblages de molécules organiques π-conjuguées par microscopie à effet tunnel (STM)sous ultra-vide sur une surface de silicium dopée bore. Le manuscrit est constitué de cinq chapitres : dans le premier chapitre, nous présentons un état de l’art des assemblages organiques sur les surfaces métalliques et sur les semi-conducteurs. Le chapitre deux décrit le dispositif expérimental utilisé au cours de cette thèse. Il présente également le substrat de Si(111)-B et fournit les concepts théoriques associés à la microscopie à effet tunnel. Le troisième chapitre décrit en détail les réseaux supramoléculaires obtenus à partir d’une molécule aromatique halogénée de symétrieC2. L’adsorption de 4,4"-dibromo-p-terphényle conduit à la formation de deux types de structures compactes (l’une en bande et l’autre en chevron) stables à température ambiante et commensurables avec la surface. Nous montrons que ces architectures sont pilotées conjointement par la liaison hydrogène, la liaison halogène et du π -stacking. Le quatrième chapitre étudie l’influence du nombre de cycles aromatiques sur la géométrie et la périodicité d’auto-assemblages obtenus sur Si (111) -B. Pour cela, nous avons synthétisé deux molécules organiques composées d’une partie centrale aromatique et de deux chaînes latérales (O-(CH2)9-CH3). La partie centrale est constituée respectivement de trois ou cinq cycles phényles terminées par des groupements cyano. Nous nous sommes également intéressés à l’influence des groupements terminaux sur l’organisation du réseau. Nous montrons que l’effet des groupements cyano sur les interactions "molécule/molécule" et sur les interactions "molécule/surface" est négligeable. A partir des travaux obtenus dans le chapitre 4, nous concluons notre manuscrit en présentant des réseaux supramoléculaires de molécules dipolaires. Ces réseaux forment des lignes de dipôles. Nous montrons que sur de petites échelles les molécules favorisent un alignement de leurs moments dipolaires
This work is dedicated to the investigation under ultra high vacuum of _-conjugated molecule on a silicon surface by means of scanningtunneling microscopy (STM). The manuscript consists of five chapters.In the first chapter, we present a state-of-the-art of organic assembly on metal and semiconductor.Chapter two describes the experimental setup using during thesis. It also shows Si(111)-B substrate and gives theoretical conceptsassociated with the scanning tunneling microscopy.The third chapter describes in detail the supramolecular network obtained from an aromatic halogenated molecule with C2 symmetry. Theadsorption of 4,4"-dibromo-p-terphenyl leads to the formation of two kinds of compacts structures (a stripe structure and a herringbonestructure). The formed networks are stable at room temperature and commensurable with the surface. These architectures are promotedby hydrogen bond, halogen bond and _-stacking.Chapter four studies influence of benzene ring number on the geometry and the periodicity of self-assemblies on Si(111)-B. To do that,we have synthesis two organics molecules composed of an aromatic central part and two laterals chains (O-(CH2)9-CH3). The centralpart is composed of respectively three or five phenyl ring ended by cyano groups. We are also interested to the terminal groups effecton the network organisation. We show that the cyano groups effect on the "molecule/molecule" interaction and the "molecule/surface"interaction are negligible. Basis of the work conducted on the chapter four, we conclude our manuscript by presenting supramolecularsnetworks of dipolar molecule. These networks form dipole lines. We show that on small scale the molecules promote an alignment of theirdipolar moments

The high complexity of vehicle front-end design, arising from considerations of aerodynamics, safety and styling, causes the airflow velocity profile at the radiator face to be highly distorted, leading to potentially reduced airflow volume for heat dissipation. A flow visualisation study showed that the bumper bar significantly influenced the cooling airflow, leading to three-dimensional vortices in its wake and generating an area of relatively low velocity across at least one third of the radiator core. Since repeatability and accuracy of on-road testing are prejudiced by weather conditions, wind-tunnel testing is often preferred to solve cooling airflow problems. However, there are constraints that limit the accuracy of reproducing on-road cooling performance from wind-tunnel simulations. These constraints included inability to simulate atmospheric conditions, limited tunnel test section sizes (blockage effects) and lack of ground effect simulations. The work presented in this thesis involved use of on-road and wind-tunnel tests to investigate the effects of most common constraints present in wind tunnels on accuracy of the simulations of engine cooling performance and radiator airflow profiles. To aid this investigation, an experimental technique for quantifying radiator airflow velocity distribution and an analytical model for predicting the heat dissipation rate of a radiator were developed. A four-hole dynamic pressure probe (TFI Cobra probe) was also used to document flow fields in proximity to a section of radiator core in a wind tunnel in order to investigate the effect of airflow maldistribution on radiator heat-transfer performance. In order to cope with the inability to simulate ambient temperature, the technique of Specific Dissipation (SD) was used, which had previously been shown to overcome this problem.

L'augmentation des performances des circuits intégrés s'est effectué durant les trentes dernières années par la miniaturisation du composant clé à savoir le transistor MOSFET. Cette augmentation de la densité d'intégration se heurte aujourd'hui à plusieurs verrous, notamment celui de la puissance consommée qui devient colossale. Il devient alors nécessaire de travailler sur de nouveaux composants, les transistors à effet tunnel, où les porteurs sont injectés par effet tunnel bande à bande permettant de limiter considérablement la puissance consommée en statique. Les nanofils semiconducteurs sont de bons candidats pour être intégrés comme canaux de ces nouveaux composants de part la possibilité de moduler leur gap et leur conductivité au cours de la croissance. Dans ce contexte, cette thèse traite de la croissance d'hétérostructures axiales Si/Si1-xGex élaborés par croissance VLS par RP-CVD. Tout d'abord, nous identifions les conditions de croissance pour réaliser des interface Si/Si1-xGex et Si1-xGex/Si abruptes. Les deux heterointerfaces sont toujours asymétrique quelle que soit la concentration en Ge ou le diamètre des nanofils ou des conditions de croissance. Deuxièmement, nous étudions les problématiques impliquées par l'ajout d'atomes dopants. Nous discutons de l'influence des paramètres de croissance (le rapport flux de gaz (Si / Ge), et la pression partielle de dopants) sur la morphologie des nanofils et la concentration de porteurs. Grâce à cette étude, nous avons été capable de faire croitre des hétérojonctions P-I-N. Troisièmement, nous présentons une technique basée sur la microscopie à sonde locale pour caractériser les hétérojonctions
After more than 30 years of successful scaling of MOSFET for increasing the performance and packing density, several limitations to further performance enhancements are now arising, power dissipation is one of the most important one. As scaling continues, there is a need to develop alternative devices with subthreshold slope below 60 mV/decade. In particular, tunnel field effect transistors, where the carriers are injected by quantum band to band tunneling mechanism can be promising candidate for low-power design. But, such devices require the implementation of peculiar architectures like axial heterostructured nanowires with abrupt interface. Using Au catalyzed vapor-liquid-solid synthesis of nanowires, reservoir effect restrains the formation of sharp junctions. In this context, this thesis addresses the growth of axial Si and Si1-xGex heterostructured nanowire with controlled interfacial abruptness and controlled doping using Au catalyzed VLS growth by RP-CVD. Firstly, we identify the growth conditions to realize sharp Si/Si1-xGex and Si1-xGex/Si interfacial abruptness. The two heterointerfaces are always asymmetric irrespective of the Ge concentration or nanowire diameter or growth conditions. Secondly, we study the problematics involved by the addition of dopant atoms and focus on the different approaches to realize taper free NWs. We discuss the influence of growth parameters (gas fluxes (Si or Ge), dopant ratio and pressure) on NW morphology and carrier concentration. With our growth process, we could successfully grow p-I, n-I, p-n, p-i-n type junctions in NWs. Thirdly, we present scanning probe microscopy to be a potential tool to delineate doped and hetero junctions in these as-grown nanowires. Finally, we will integrate the p-i-n junction in the NW in omega gate configuration

This thesis investigates the use of hot-film thermal anemometers to align a plate on a wind tunnel at Hill Air Force Base that is used to calibrate Angle of Attack Transmitters on F-16s. A reoccuring problem with this wind tunnel is that no two instruments can verify an angle reading of the the mounting plate for the Angle of Attack Transmitters to the air stream in the wind tunnel. Multiple thermal anemometer calibration methods, such as Jorgensen’s equation and a look-up table are implemented to attemp to achieve consistent measurements between multiple probes. The results show that it is neccessary to have conditions match between calibration and measurement when attempting to achieve high accuracy with angle measurements.

The optimal control theory has a sophisticated framework with powerful tools to solve practical problems in various fields of knowledge. However, this theory requires precise definition of the problems under consideration. In this respect, the correct weighting of the relative importance of the effects represented by aggregate elements to performance indexes is critical. The decision theory can help to overcome this mishap. In particular, the technique Analytic Hierarchy Process (AHP) is adequate for the task of consistently weigh the components of proposed performance indexes and has other advantages such as keeping a detailed record of the criteria, values, comparisons and judgments that guided decision making.

The present thesis work was developed in collaboration with the Ducati Corse Aerodynamic Department. It is focused on the measurement system employed on the MotoGP Wind Tunnel model in order to evaluate the cooling performances at the radiators. As first, an analysis of the current methodology is conducted. Based on the arrangement of hybrid-Kiel probes behind the radiators, it was observed that an improvement in the calibration procedure is required in order to account for inter-probe and support frame interference. Furthermore, a correlation process with the CFD simulation was carried out. A good agreement in trend with CFD results was displayed, despite a low accuracy. The need for higher spatial resolution was stated. In order to update the CFD implementation of the actual water radiator, the latter has been characterized in terms of pressure drop on a dedicate radiator test bench, provided by Dallara Automobili. A suitable convergent frame has been designed for the purpose. Finally, a new methodology for cooling performance evaluation was developed and calibrated. The method exploits a set of static and Kiel probes in a dummy radiator core. An honeycomb structure and a perforated plate are implemented to reproduce the real radiator behaviour. Experiments have been performed with half-radiator equipped with the new set up and the other half instrumented with Pitot tubes, showing good agreement between the two probe-types. A set of plates have been characterized. It allowed also to highlight the relevance of the solid part distribution - and related holes' diameter - on the pressure drop and the effect on the measured pressures from the probes.

Sufficient heat dissipation is crucial to the effective operation of friction based braking systems. Such cooling is generally provided by ensuring a sufficient supply of cooling air to the heated components, hence the aerodynamics in the region of the brake components is extremely important. The objective of the research was to develop an understanding of how aerodynamics could be used to improve the cooling of automotive disc brakes. Two separate sets of wind tunnel experiments were developed. Tests were performed on a vented disc (rotor) to measure the internal flow through the vents on a rotating vented disc under various conditions, including an isolated disc in still air, the disc in still air with the wheel on, the disc in moving air with the wheel on, and an on-road simulation using a ¼ car. On vehicle tests were also performed in a wind tunnel using a purpose built brake test rig. These tests measured the thermal performance of different brake discs under various operating parameters; including constant load braking, and cooling from high temperature under various speeds, wheels and disc types. It was found that airflow through vented rotors was significantly reduced during simulated on-road driving, compared to when measured in isolation, but not particularly affected by the vehicles speed. In the situations tested, vented discs offered a 40+% improvement in cooling over an equivalent sized solid rotors. However the research indicates that the greatest benefit of vented rotors over solid will be in vehicles where air entering the wheel cavity is limited, such as low drag vehicles. It was also found that the most significant improvements in brake thermal performance could be achieved by maximising the airflow into the region of the brake components; including increasing the open area of the wheel, and increasing the vehicle velocity. Other improvements can be achieved by using a wheel material with good conductive capability, and increasing the mass of the disc. Evidence of vortex shedding was also discovered in the airflow at the exit of an internal vented rotor, any reduction in this flow disturbance should lead to increased airflow with associated improvements in thermal performance.

Nowadays, thanks to the increase of computers capability to solve huge and complex problems, and also thanks to the endless effort of the geotechnical community to define better and more sophisticated constitutive models, the challenge to predict and simulate soil behavior has been eased. However, due to the increase in that sophistication, the number of parameters that define the problem has also increased. Moreover, frequently, some of those parameters do not have a real geotechnical meaning as they just come from mathematical expressions, which makes them difficult to identify. As a consequence, more effort has to be placed on parameters identification in order to fully define the problem. This thesis aims to provide a methodology to facilitate the identification of parameters of soil constitutive models by backanalysis. The best parameters are defines as those that minimize an objective function based on the differences between measurements and computed values. Different optimization techniques have been used in this study, from the most traditional ones, such as the gradient based methods, to the newest ones, such as adaptive genetic algorithms and hybrid methods. From this study, several recommendations have been put forward in order to take the most advantage of each type of optimization technique. Along with that, an extensive analysis has been carried out to determine the influence on soil parameters identification of what to measure, where to measure and when to measure in the context of tunneling. The Finite Element code Plaxis has been used as a tool for the direct analysis. A FORTRAN code has been developed to automate the entire backanalysis procedure. The Hardening Soil Model (HSM) has been adopted to simulate the soil behavior. Several soil parameters of the HSM implemented in Plaxis, such as E_50^ref, E_ur^ref, c and f, have been identified for different geotechnical scenarios. First, a synthetic tunnel case study has been used to analyze all the different approaches that have been proposed in this thesis. Then, two complex real cases of a tunnel construction (Barcelona Metro Line 9) and a large excavation (Girona High-Speed Railway Station) have been presented to illustrate the potential of the methodology. Special focus on the influence of construction procedures and instruments error structure has been placed for the tunnel backanalysis, whereas in the station backanalysis, more effort has been devoted to the potential of the concept of adaptive design by backanalysis. Moreover, another real case, involving a less conventional geotechnical problem, such as Mars surface exploratory rovers, has been also presented to test the backanalysis methodology and the reliability of the Wong & Reece wheel-terrain model; widely adopted by the terramechanics community, but nonetheless, still not fully accepted when analyzing lightweight rovers as the ones that have been used in recent Mars exploratory missions.
Actualmente, gracias al aumento de la capacidad de los ordenadores para resolver problemas grandes y complejos, y gracias también al gran esfuerzo de la comunidad geotécnica de definir mejores y más sofisticados modelos constitutivos, se ha abordado el reto de predecir y simular el comportamiento del terreno. Sin embargo, debido al aumento de esa sofisticación, también ha aumentado el número de parámetros que definen el problema. Además, frecuentemente, muchos de esos parámetros no tienen un sentido geotécnico real dado que vienen directamente de expresiones puramente matemáticas, lo cual dificulta su identificación. Como consecuencia, es necesario un mayor esfuerzo en la identificación de los parámetros para poder definir apropiadamente el problema. Esta tesis pretende proporcionar una metodología que facilite la identificación mediante el análisis inverso de los parámetros de modelos constitutivos del terreno. Los mejores parámetros se definen como aquellos que minimizan una función objetivo basada en la diferencia entre medidas y valores calculados. Diferentes técnicas de optimización han sido utilizadas en este estudio, desde las más tradicionales, como los métodos basados en el gradiente, hasta las más modernas, como los algoritmos genéticos adaptativos y los métodos híbridos. De este estudio, se han extraído varias recomendaciones para sacar el mayor provecho de cada una de las técnicas de optimización. Además, se ha llevado a cabo un análisis extensivo para determinar la influencia sobre qué medir, dónde medir y cuándo medir en el contexto de la excavación de un túnel. El código de Elementos Finitos Plaxis ha sido utilizado como herramienta de cálculo del problema directo. El desarrollo de un código FORTRAN ha sido necesario para automatizar todo el procedimiento de Análisis Inverso. El modelo constitutivo de Hardening Soil ha sido adoptado para simular el comportamiento del terreno. Varios parámetros del modelo constitutivo de Hardening implementado en Plaxis, como E_50^ref, E_ur^ref, c y f, han sido identificados para diferentes escenarios geotécnicos. Primero, se ha utilizado un caso sintético de un túnel donde se han analizado todas las distintas técnicas que han sido propuestas en esta tesis. Después, dos casos reales complejos de una construcción de un túnel (Línea 9 del Metro de Barcelona) y una gran excavación (Estación de Girona del Tren de Alta Velocidad) se han presentado para ilustrar el potencial de la metodología. Un enfoque especial en la influencia del procedimiento constructivo y la estructura del error de las medidas se le ha dado al análisis inverso del túnel, mientras que en el análisis inverso de la estación el esfuerzo se ha centrado más en el concepto del diseño adaptativo mediante el análisis inverso. Además, otro caso real, algo menos convencional en términos geotécnicos, como es la exploración de la superficie de Marte mediante robots, ha sido presentado para examinar la metodología y la fiabilidad del modelo de interacción suelo-rueda de Wong y Reece; extensamente adoptado por la comunidad que trabajo en Terramecánica, pero aún no totalmente aceptada para robots ligeros como los que se han utilizado recientemente en las misiones de exploración de Marte.

Abstract Physical activity provides important physical health benefits for young people. However, the information on physical activity in association with various social, educational and mental health factors among adolescents is scarce. This study aimed to evaluate how physical activity is related to adolescents’ emotional and behavioural problems, self-rated health, educational attainment and parental socio-economic position, and how these factors interrelate with each other. The study population consisted of the Northern Finland Birth Cohort 1986 (N = 9432). Data on physical activity, emotional and behavioural problems, self-rated health, educational attainment and parental socio-economic position at age 15–16 years was collected by postal inquiries in 2001–2002. Logistic regression models were used to study the associations between these factors. High parental socio-economic position was associated with being physically active among adolescents. Physical inactivity was related to emotional, social, thought and attention problems, and rule-breaking behaviour. Physical inactivity, emotional, behavioural and social problems, and low parental socio-economic position were related to poor self-rated health. In addition, higher levels of physical activity, fewer behavioural problems, and higher parental socio-economic position were associated with high self-perceived academic performance and future plans for higher education. Physical inactivity during adolescence is associated with several emotional and behavioural problems, and poor self-rated health, whereas being physically active is related to higher educational attainment. Developmentally appropriate and enjoyable physical activity could have an important role in enhancing adolescents’ health, well-being, and educational attainment
Tiivistelmä Liikunta edistää lasten ja nuorten fyysistä terveyttä. Liikunnan yhteyksistä sosiaalisiin tekijöihin, nuorten koulumenestykseen ja mielenterveyteen on kuitenkin vähän tietoa. Tämän tutkimuksen tavoitteena oli selvittää liikunnan yhteyksiä nuorten tunne-elämän ja käyttäytymisen häiriöihin, koettuun terveyteen ja koulumenestykseen. Lisäksi selvitettiin liikunnan, terveyteen ja koulutukseen liittyvien tekijöiden, sekä perheen sosioekonomisen aseman keskinäisiä suhteita. Tutkimusaineistona oli Pohjois-Suomen syntymäkohortti 1986 (N = 9432). Liikunta-aktiivisuus, perheen sosioekonominen asema, tunne-elämän ja käyttäytymisen häiriöiden esiintyvyys, koettu terveys ja koulumenestys selvitettiin postikyselyllä 15–16-vuotiaana vuosina 2001–2002. Muuttujien välisiä yhteyksiä testattiin logistisella regressioanalyysilla. Vanhempien korkea sosioekonominen asema oli yhteydessä nuorten liikunnalliseen aktiivisuuteen. Vähäinen liikunnan harrastaminen liittyi tunne-elämän häiriöihin, sosiaalisiin ongelmiin, ajatus- ja tarkkaavuushäiriöihin sekä sosiaaliseen käytöshäiriöön. Vähäinen liikunta, tunne-elämän ja käyttäytymisen häiriöt sekä vanhempien alhainen sosioekonominen asema liittyivät huonoon koettuun terveyteen. Lisäksi liikunnallinen aktiivisuus, vähäiset käyttäytymisen häiriöt sekä vanhempien korkea sosioekonominen asema olivat toisistaan riippumatta yhteydessä nuorten hyvään koulumenestykseen ja opintosuunnitelmiin. Tämän tutkimuksen tulokset osoittavat, että vähäinen liikunta on yhteydessä nuorten tunne-elämän ja käyttäytymisen häiriöihin sekä huonoon koettuun terveyteen, kun taas liikunnallinen aktiivisuus liittyy hyvään koulumenestykseen. On mahdollista, että monipuolisen, ikä- ja kehitystasolle sopivan liikunnan avulla voidaan edistää nuorten terveyttä ja hyvinvointia sekä koulutuksellisia edellytyksiä

This thesis investigates the turbulent flow in the wake of the wing-body junction of the NASA Common Research Model to further reveal its complex vortical structure and to contribute to the reference database used for Computational Fluid Dynamics validation activities. Compressible flows near two wall-boundary layers occurs not only at the wing-body junction but at every control surface of an airplane, therefore increased knowledge about this complex flow structure could potentially improve the estimates of drag performance and control surface efficiency, primarily for minimizing the environmental impact of commercial flight. The airplane model is modified by adding an inboard flap to investigate the influence from the deflection on the vorticity and velocity field. Future flap designs and settings are discussed from a performance improvement point of view, with the investigated flow influence in mind. The experimental measurements for this thesis were collected using a Cobra Probe, a dynamic multi-hole pressure probe, for Reynolds numbers close to one million based on the wing root chord. A pre-programmed three-dimensional grid was used to cover the most interesting parts of the junction flow. The facility used for the tests is a 120 cm by 80 cm indraft, subsonic wind tunnel at NASA Ames Research Center’s Fluid Mechanics Lab, which provides an on-set flow speed of around Mach 0.15, corresponding to approximately 48 m/s.
Den här avhandlingen undersöker det turbulenta flödet runt övergången mellan flygplanskropp och vinge på en NASA Common Research Model för att vidare utforska den komplexa, tredimensionella strukturen av flödet och bidra till NASA’s officiella databas för jämförelser med simulerade flöden. Kompressibla flöden nära tvåväggsgränsskikt uppkommer inte bara vid övergången mellan flygplanskropp och vinge utan även vid varje kontrollyta på ett flygplan. Ökad kunskap om flödets beteende vid sådana områden kan därför bidra till en bättre uppskattning av prestanda och effektivitet av kontrollytorna och flygplanet i sin helhet, vilket kan bidra till minskad miljöpåverkan från kommersiell flygtrafik. Flygplansmodellen är modifierad genom montering av en vingklaff på den inre delen av vingen, detta för att undersöka hur olika vinklar på klaffarnas nedböjning påverkar flödets struktur och hastighetsfält. Framtida klaffdesigner och inställningar för ökad prestanda diskuteras även utifrån denna påverkan. Mätningarna i vindtunneln gjordes med en Cobra Probe, ett dynamisk tryckmätningsinstrument, speciellt designad för turbulenta och instabila flöden. Reynoldsnumren som generades av den subsoniska, indrags-vindtunneln var ungefär en miljon baserad på vingrotens längd, vilket motsvarar knappt en tiondel av normala flygförhållanden för samma flygplansmodell.

Pour cette thèse, des systèmes donneur-accepteur (DA) modèles pour le photovoltaïque organique ont été étudiés par microscopie à force atomique en mode non contact (nc-AFM) et microscopie à sonde de Kelvin (KPFM). Ces systèmes DA présentent une structure et des propriétés électroniques mieux contrôlées que dans la plupart des hétérojonctions DA en volume.Afin, d'étudier les propriétés optoélectroniques d'architectures DA présentant une séparation de phase à l'échelle de la dizaine de nanomètres, il est indispensable d'optimiser la résolution des modes nc-AFM/KPFM. Dans ce travail, l'influence du régime d'interaction pointe-surface sur les mesures a été étudiée dans le cas d'auto-assemblages de P3DDT sur substrat HOPG. Nous avons ainsi démontré que l'imagerie dans le régime d'interaction à courte portée améliore non seulement la résolution latérale, mais permet également de réaliser des mesures de hauteur plus réalistes.Ensuite, un système DA à base de FG1:[70]PCBM a été étudié. Pour ce mélange DA, la nanostructure et l'échelle de la séparation de phase peuvent être ajustées grâce aux propriétés cristal liquide du composé donneur FG1. Les potentiels mesurés dans le noir sont consistants avec la morphologie attendue en surface et en volume. La relation entre le photo-potentiel de surface (SPV) et le régime d'interaction pointe-surface a pu être précisément analysée. Une résolution optimale est obtenue dans les images de SPV en travaillant près du seuil de dissipation.Enfin, une nouvelle génération de diades comprenant des groupements donneur et accepteur a été étudiée. La nature de l'auto-assemblage sur HOPG a été établie sur la base d'études comparatives de microscopie à effet tunnel et de nc-AFM, avec le support de simulations en mécanique et dynamique moléculaire. Les mesures de photo-potentiel de surface ont ensuite permis de démontrer qu'il était possible d'étudier les mécanismes de photo-génération des porteurs jusqu'à l'échelle de la mono-couche moléculaire
During this thesis, model donor-acceptor (DA) systems for organic photovoltaics have been studied by non-contact atomic force microscopy (nc-AFM) and Kelvin probe force microscopy (KPFM). To enhance the understanding of the optoelectronic processes on the nanoscale, DA systems with better defined structural and electronic properties than the one of most bulk heterojunction blends (BHJ), have been studied.With DA phase-separations of below 10nm in organic photovoltaic systems, the highest possible resolution has to be achieved by KPFM to investigate optoelectronic processes. It has been shown that nc-AFM/KPFM measurements in the regime of short range (SR) forces can increase imaging resolution. In preparation of such investigations, the influence of the interaction regime on the topographic measurement via KPFM has been studied for a self-assembly of P3DDT on HOPG. It is demonstrated that imaging in the SR-regime not only increases the lateral resolution, but also assures a correct topographic height values.In a next step, DA blends of FG1:[70]PCMB have been studied by KPFM. For these BHJs, the structure and the scale of the DA phase-separation can be tuned via the liquid crystal behavior of the donor FG1. The in dark potential contrasts are consistent with surface and bulk morphology. The relationship between the surface photovoltage (SPV) and the tip-sample interaction regime has been analyzed. An optimal resolution for SPV imaging is obtained when measuring next to the onset of dissipation.Finally, a new generation of DA dyad with donor and acceptor moieties has been studied. Its self-assembly on HOPG has been determined via a comparative study by scanning tunneling microscopy and nc-AFM plus molecular mechanics and dynamics simulations. By KPFM the charge carrier generation and collection has been analyzed down to the level of a single molecular layer. A clear relationship between the dyads' molecular assembly and their photovoltaic properties can be established

The path to future aero-engines with more efficient engine architectures requires advanced thermal management technologies to handle the demand of refrigeration and lubrication. Oil systems, holding a double function as lubricant and coolant circuits, require supplemental cooling sources to the conventional fuel based cooling systems as the current oil thermal capacity becomes saturated with future engine developments. The present research focuses on air/oil coolers, which geometrical characteristics and location are designed to minimize aerodynamic effects while maximizing the thermal exchange. The heat exchangers composed of parallel fins are integrated at the inner wall of the secondary duct of a turbofan. The analysis of the interaction between the three-dimensional high velocity bypass flow and the heat exchangers is essential to evaluate and optimize the aero-thermodynamic performances, and to provide data for engine modeling. The objectives of this research are the development of engine testing methods alternative to flight testing, and the characterization of the aerothermal behavior of different finned heat exchanger configurations. A new blow-down wind tunnel test facility was specifically designed to replicate the engine bypass flow in the region of the splitter. The annular sector type test section consists on a complex 3D geometry, as a result of three dimensional numerical flow simulations. The flow evolves over the splitter duplicated at real scale, guided by helicoidally shaped lateral walls. The development of measurement techniques for the present application involved the design of instrumentation, testing procedures and data reduction methods. Detailed studies were focused on multi-hole and fine wire thermocouple probes. Two types of test campaigns were performed dedicated to: flow measurements along the test section for different test configurations, i.e. in the absence of heat exchangers and in the presence of different heat exchanger geometries, and heat transfer measurements on the heat exchanger. As a result contours of flow velocity, angular distributions, total and static pressures, temperatures and turbulence intensities, at different bypass duct axial positions, as well as wall pressures along the test section, were obtained. The analysis of the flow development along the test section allowed the understanding of the different flow behaviors for each test configuration. Comparison of flow variables at each measurement plane permitted quantifying and contrasting the different flow disturbances. Detailed analyses of the flow downstream of the heat exchangers were assessed to characterize the flow in the fins¿ wake region. The aerodynamic performance of each heat exchanger configuration was evaluated in terms of non dimensional pressure losses. Fins convective heat transfer characteristics were derived from the infrared fin surface temperature measurements through a new methodology based on inverse heat transfer methods coupled with conductive heat flux models. The experimental characterization permitted to evaluate the cooling capacity of the investigated type of heat exchangers for the design operational conditions. Finally, the thermal efficiency of the heat exchanger at different points of the flight envelope during a typical commercial mission was estimated by extrapolating the convective properties of the flow to flight conditions.
Villafañe Roca, L. (2013). Experimental Aerothermal Performance of Turbofan Bypass Flow Heat Exchangers [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/34774
TESIS

碩士
國立臺北科技大學
冷凍空調工程系所
93
The follow-up construction of Taipei Metro system at underground station will establish a Platform Screen Door (PSD) system at platform. The platform screen door system can assure the safety of passengers within the platform and reduce the demands of environmental control as well as decrease the operational costs. However, owing to the influence of piston effect, the pressure can only be released through draught relief shaft. This is a challenge towards the PSD pressure resistance. The metro frequent round trips in the underground tunnels result in the effects of heat sink and the nearly saturation of soil heat retention ability, which make the temperature within tunnels to increase gradually. Thus, this thesis used the CFD (Computational Fluid Dynamics) method to analyze the effects of various designing parameters on PSD pressure for the G19 station of Songshan line. In addition, the effect of different air temperature within the tunnel on the problem of heat sink was addressed in this study. This thesis adopted the CFD software FLUENT6.1 to analyze the pressure variation resulting from the moving metro on the PSD. The dynamic mesh was employed to investigate the metro motion. The influence of metro speed, draught relief bypass shaft height, draught relief bypass shaft area, and two-way train to enter the station etc. on PSD pressure is considered in this study. The numerical results indicate that faster metro results in the larger pressure on the PSD. The higher the draught relief bypass shaft is, the worse the pressure-relieving ability is. The increase of draught relief bypass shaft area does not have significant change on pressure variation. The two-way metro entering the station at the same time is not good for the pressure depression because of the air drawing each other. In this study, the CFD software-AIRPAK2.1 is employed to simulate the heat sink effect of the tunnel. According to the numerical results, it is known that when the higher the designing air temperature is, the faster the hot saturation of soil occurs. For example, when the air temperature within the tunnel is maintained below 46℃, the soil can absorb about 200W for per meter long of tunnel, which can be regarded as the designing reference of heat rejection.

碩士
國立中央大學
土木工程學系在職專班
105
Abstract The use of shield tunnel has been in practice for a long time and has matured since its introduction into Taiwan. A shield tunnel is contracted for construction after the geological survey and drawing of the design. The construction contractor must analyze the data based on the geological survey information and supplementary geological reports, excavation path, ground water elevation, covering depth, radius of curvature, the outer diameter of tunnel boring machine and other factors and conditions and discuss with the manufacturer to determine the tunnel boring machine suitable for the geological conditions of this project. The selection and design of the shield machine and the planning and simulation works before the construction can lead to the success of the shield tunnel project or when one of the key factors and process are ignored due to cost consideration may lead to the delay or stop of the work which result in disasters, remedies are sought with tremendous costs incurred to find solutions. Using the actual construction cases, this paper explores and analyzes the issues to be noted and the construction difficulties encountered due to ignorance of the precaution measures as well as the solutions to the issues on the construction site based on the difficulties encountered and the process of the excavation by the tunnel boring machines which may encounter obstacles and have delays in their advances. It is hoped that the insights gained will serve as reference for study and analysis by those who are interested in the design and construction of shield tunnels.

碩士
銘傳大學
公共事務學系兩岸關係與安全管理碩士在職專班
100
A road tunnel is a special space which is designed in response to the topography. Due to the characteristics of being confined and undergrounded, road tunnel is different in road traffic management and in every kind of relief work compared to an ordinary road. Because of the special environmental characteristics of road tunnels, when the fire breaks out due to various accidents in the road tunnel, the high temperature of the fire at the scene will be over 1,000 ° C, causing damage to part of the tunnel structure and equipment, and hampering the initial relief implementation, which will more likely develop into major disasters. Recent years, there have been many traffic accidents in long tunnels in Europe, causing serious damages and heavy casualties. Hsueh Shan Tunnel is up to 12.9 km, and it’s security standard of disaster prevention must be higher than ordinary roads, and the tunnel should also have the ability of the contingency and disaster planning. Thus, when disaster strikes, there will be the best response strategy. Using case study methods, literature methods, comparative methods and depth interviews to conduct data collection and analysis, this thesis applies the security problem and management mechanism of Hsueh Shan Tunnel as a research. This thesis mainly explores disaster crisis management policies, security issues and management mechanisms on long highway tunnels. Finally, according to the study findings combined with the tunnel safety and management mechanisms and practical experiences, I propose the following four points in conclusion and hope to provide the relevant decision-making and practice units for reference to the strategy of the emergency response system in the future. 1.Shorten rescue time and mass evacuation. 2.Tunnel safety issues must be to strengthen. 3.Increase traffic safe distance inside the tunnel. 4.Increase the number of fluorescent signs for escape in tunnels.

This diploma thesis deals with roboethics and its associated moral and social dilemmas. The theoretical part of this thesis defines roboethics and presents the diverse opinions and approaches, deals with the position of robots in society and also subsequently examines the various problematic areas of the use of robots. The conclusion of the theoretical part of the thesis then focuses on autonomous vehicles, to which the quantitative and qualitative research parts of the thesis are devoted. The research part of this diploma thesis aims to find out the opinions on this issue of the Czech general public and Czech experts as well as to find out whether their opinions are aligned, how their opinions differ and lastly, which issues are the most important for the future development of this field.

Despite years of research in high speed boundary layer flow, there is still a need for insightful experiments to realize key features of the flow like boundary layer response to different conditions and related transition mechanisms. Volumes of data on the these problems point to the fact that there is still much to be understood about the nature of boundary layer instability causing transition and growth of boundary layer in different conditions. Boundary layer stability experiments have been found to be more useful, in which the boundary layer is perturbed and its behavior observed to infer useful conclusions. Also, apart from the stability part, the effect of various changes in boundary layer due to the perturbation makes interesting observation to gain more insight into the understood and the not so understood facets of the same. In view of the above, the effect of a steady axisymmetric thermal bump is investigated on a hypersonic boundary layer over a 60º sharp cone cylinder model. The thermal bump, placed near tip of the cone, perturbs the boundary layer, the behavior of which is observed by recording the wall heat flux on the cone and cylinder surface using platinum thin film sensors. The state of the boundary layer is qualitatively assessed by the wall heat flux comparisons between laminar and turbulent values. The same thermal bump also acts as a heat addition source to boundary layer in which case this recorded data provides a look into the effect of the heat addition to the wall heat flux. To gain a larger view of heat addition causing changes to the flow, effects of change in enthalpy are also considered. Experiments are performed in the IISc HST2 shock tunnel facility at 2MJkg−1 stag-nation enthalpy and Mach number of 8,with and without the thermal bump to form comparisons. Some experiments are also performed in the IISc HST3 free piston driven shock tunnel facility at 6MJkg−1, to investigate the effect of change in stagnation enthalpy on the wall heat flux. To support the experimental results theoretical comparisons and computational studies have also been carried out. The results of experiments show that the laminar boundary layer over the whole model remains laminar even when perturbed by the thermal bump. The wall heat flux measurements show change on the cone part where there seems to be fluctuation in the temperature gradients caused by the thermal bump, which decrease at first and then show an increase towards the base of the cone. The cylinder part remains the same with and without the thermal bump, indicating heavy damping effects by the expansion fan at cone cylinder junction. A local peak in wall heat flux is observed at the junction which is reduced by 64% by the action of the thermal bump. The possible reason for this is attributed to the increased temperature gradients at the wall due to delayed dissipation of heat that is accumulated in the boundary layer as a result of the thermal bump action. The comparison of data for enthalpies of 2MJkg−1 and 6MJkg−1 show that there are negligible real gas effects in the higher enthalpy case and they do not affect the wall heat flux much. Also it is found that the thermal bump fails to dump heat into the flow directly though it creates heat addition virtually by mere discontinuity in the surface temperature and causes temperature gradients fluctuation in the boundary layer. Considering the thermal bump action and the change in stagnation enthalpy of the flow, there seems to be no change in both cases that can be attributed to a common observation resulting from the factor of change in heat inside the boundary layer.

Excavation activities like open cutting and tunneling work may cause ground movements. Many of these activities are performed in urban areas where many structures and facilities already exist. These activities are close enough to affect adjacent structures. It is therefore important to understand how the ground movements due to excavations influence nearby structures. The goal of the proposed research is to investigate and develop analytical methods for addressing uncertainty during observation-based, adaptive design of deep excavation and tunneling projects. Computational procedures based on a Bayesian probabilistic framework are developed for comparative analysis between observed and predicted soil and structure response during construction phases. This analysis couples the adaptive design capabilities of the observational method with updated reliability indices, to be used in risk-based design decisions. A probabilistic framework is developed to predict three-dimensional deformation profiles due to supported excavations using a semi-empirical approach. The key advantage of this approach for practicing engineers is that an already common semi-empirical chart can be used together with a few additional simple calculations to better evaluate three-dimensional displacement profiles. A reliability analysis framework is also developed to assess the fragility of excavation-induced infrastructure system damage for multiple serviceability limit states. Finally, a reliability analysis of a shallow circular tunnel driven by a pressurized shield in a frictional and cohesive soil is developed to consider the inherent uncertainty in the input parameters and the proposed model. The ultimate limit state for the face stability is considered in the analysis. The probability of failure that exceeding a specified applied pressure at the tunnel face is estimated. Sensitivity and importance measures are computed to identify the key parameters and random variables in the model.

The Blanka tunnel has two boring sections: Brusnice tunnel and Královská obora tunnel. Both tunnels were boring in difficult geologycal conditions, but the geology conditions of these tunnels are not same. Also they had not the same hazards during boring. There was used a spectrum of different technical works with hazard reduction purpose and safety process of boring. There were three serious accidents, wnich everyone made a creater on the surface, but they have not the same causes. This text has a task to describe a geological survey before and during the boring of both tunnels. How other reasons affected the process of boring? How the tunnels were bored? What events preceded the everyone of three major failure? This text does not deal with economical things of boring and effects of specific personal influence on the process of boring. Key words Tunnel, excavation, Blanka, Brusnice, Letná, Stromovka park, Vltava river, underground water, geology, ordovik, New Austrian Tunnelling method, pilot tunnel, calotte, bench, bottom, arche, bolt, lining, grouting, collapse of ceiling, failure, tube, shale, quarzite, soil, loess, ballast, clay

Thesis (Ph. D.)--University of Wisconsin--Madison, 1985.
Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 231-236).

This thesis presents the implementation of the upper bound limit analysis in combination with finite elements and linear optimization for solving different stability problems in geomechanics under plane strain conditions. Although the nonlinear optimization techniques are becoming quite popular, the linear optimization has been adopted due to its simplicity in implementation and ease in attaining the convergence while performing the analysis. The objectives of the present research work are (i) to reduce the computational effort while using an upper bound finite element limit analysis with linear programming in dealing with geotechnical stability problems, and (ii) to obtain solutions for a few important geotechnical stability problems associated with reinforced earth, unsupported tunnels and a group of anchors. It is also intended to examine the developments of the failure patterns in all the cases. For carrying out the analysis for different stability problems, three noded triangular elements have been used throughout the thesis. The nodal velocities are treated as basic unknown variables and the velocity discontinuities are employed along the interfaces of all the elements. The soil mass is assumed to obey the Mohr-Coulomb’s failure criterion and an associated flow rule. The Mohr-Coulomb yield surface is linearized by means of an exterior regular polygon circumscribing the actual yield circle so that the finite element formulation leads to a linear programming problem. A simple technique has been proposed for reducing the computational effort while solving any geotechnical stability problem by using the upper bound finite element limit analysis and linear optimization. In the proposed method, the problem domain has been discretized into a number of different regions in which a particular order (number of sides) of the polygon has been specified to linearize the Mohr-Coulomb yield criterion. A greater order of the polygon needs to be chosen only in that part of the domain wherein the rate of the plastic strains becomes higher. The computational effort required to solve the problem with this implementation reduces considerably. By using the proposed method, the bearing capacity has been computed for smooth as well as rough strip footings and the results obtained are found to be quite satisfactory. The ultimate bearing capacity of a rigid strip footing placed over granular, cohesive-frictional and purely cohesive soils, reinforced with single and a group of two horizontal layers of reinforcements has been determined. The necessary formulation has been introduced to incorporate the inclusion of reinforcement in the analysis. The efficiency factors, and , to be multiplied with Nc and Nγ for finding the bearing capacity of reinforced foundations, have been established. The results have been obtained (i) for different values of soil friction angles in case of granular and cohesive-frictional soils, and (ii) for different rates at which the cohesion increases with depth for purely cohesive soil under undrained condition. The optimum positions of the reinforcements' layers corresponding to which and becomes maximum, have been established. The effect of the length of the reinforcements on the results has also been analyzed. As compared to cohesive soil, the granular soils, especially with greater values of frictional angle, cause much more predominant increase in the bearing capacity. The stability of a long open vertical trench laid in a fully cohesive and cohesive-frictional soil has been determined with an inclusion of single and a group of two layers of horizontal reinforcements. For different positions of the reinforcement layers, the efficiency factor (ηs), has been determined for several combinations of H/B, m and where H and B refer to height and width of the trench, respectively, and m accounts for the rate at which the cohesion increases linearly with depth for a fully cohesive soil with = 0. The effect of height to width of the long vertical trench on the stability number has been examined for both unreinforced and reinforced soils. The optimal positions of the reinforcements layers, corresponding to which becomes maximum, have been established. The required length of reinforcements to achieve maximum efficiency factor corresponding to optimum depth of reinforcement has also been determined. The magnitude of the maximum efficiency factor increases continuously with an increase in both m and . The effect of pseudo-static horizontal earthquake body forces on the stability of a long unsupported circular tunnel (opening) formed in a cohesive frictional soil has been determined. The stability numbers have been obtained for various values of H/D (H = tunnel cover, D = diameter of the tunnel), internal friction angle of soil, and the horizontal earthquake acceleration coefficient The computations revealed that the values of the stability numbers (i) decreases quite significantly with an increase in , and (ii) become continuously higher for greater values of H/D and . The failure patterns have also been drawn for different combinations of H/D, and . The geometry of the failure zone around the periphery of the tunnel becomes always asymmetrical with an inclusion of horizontal seismic body forces. The interference effect on the stability of two closely spaced parallel (twin) long unsupported circular tunnels formed in fully cohesive and cohesive-frictional soils has been evaluated. The variation of the stability number with S/D has been established for different combinations of H/D, m and ; where D refers to the diameter of each tunnel, S is the clear spacing between the tunnels, and is the internal friction angle of soil and m accounts for the rate at which the cohesion increases linearly with depth for a soil with = 0. On account of the interference of two tunnels, the stability number reduces continuously with a decrease in the spacing between the tunnels. The minimum spacing between the two tunnels required to eliminate the interference effect increases with (i) an increase in H/D and (ii) a decrease in the values of both m and . The failure patterns have also been generated for a few cases with different values of S/D. The size of the failure zone is found to become smaller for greater values of m and . The horizontal pullout capacity of a group of two vertical strip anchors embedded, along the same vertical plane in sand, at shallow depths has been determined. At collapse, it is assumed that the anchor plates are subjected to the same uniform horizontal velocity without any bending or tilt. The pullout resistance increases invariably with increases in the values of embedment ratio, friction angle of the sand mass and anchor-soil interface friction angle. The effect of spacing (S) between the anchors on their group collapse load is examined in detail. For a given embedment ratio, the total group failure load becomes maximum corresponding to a certain optimal spacing (Sopt). The values of Sopt increases with an increase in the value of , but the changes in the value of H/B and do not have any significant effect on Sopt. The vertical uplift capacity of a group of two horizontal strip plate anchors with the common vertical axis buried in purely cohesive as well as in cohesive frictional soil has been computed. The variation of the uplift factors Fc, Fq and F , due to the contributions of soil cohesion, surcharge pressure and unit weight, respectively, has been evaluated for different combinations of S/B and H/B. As compared to a single isolated anchor, the group of two anchors generates significantly greater magnitude of Fc. On the other hand, the factors Fq and F , for a group of two anchors are found to become almost equal to that of a single isolated anchor as long as the levels of the lower plate in the group and the single isolated anchor are kept the same. For the group of two horizontal strip plate anchors in purely cohesive soil, an increase of cohesion of soil mass with depth and the effect of self weight of the soil have been incorporated. The uplift factor Fcy both due to cohesion and unit weight of the soil has also been computed for the anchors embedded in clay under undrained condition. For given embedment ratios, the factor Fcy increases linearly with an increase in the normalized unit weight of soil mass upto a certain value before attaining a certain maximum magnitude. The computational results obtained for different research problems would be useful for design.

碩士
淡江大學
電機工程學系碩士班
94
Owing to the development of high technology, power device and power electronic device are widely used in the industry, which deteriorates the problem of harmonic and results in wrong operation of equipments and devices. The most common way to reduce harmonic distortion is to install the harmonic filters. Filters are divided into both active and passive types. Active filter does not meet the requirement of low cost consideration due to the high cost and complex construction and maintenance. Passive filter, however, because of its simple construction, convenient maintenance and cheaper cost, is widely adopted. This thesis utilizes the PSO algorithm to design the passive filter for the harmonic problems. According to the harmonic standard of Taiwan Power Company, system variation, manufacturing tolerance and temperature tolerance of capacitor and manufacturing tolerance of inductance are used to curb harmonic limit condition and to prevent series resonance, which cause the burning down of filters. This context also considers the cost and lifetime of filters as the object function. This study takes a low voltage distribution system as an example, using Matlab/Simulink software simulation to mount 5th, 7th and 11th of filters and get the results. In addition, this thesis compares the ant algorithm and immune algorithm and use optimal techniques to make the results perfect and practical, which prove the effective functions come up with by this context.

碩士
大葉大學
機械工程研究所
88
This thesis is divided into two parts: Part Ⅰ-“The important problems of conducting fluid dynamics experiments with soap film tunnels”and Part Ⅱ“The development of Digital Partical Image Velocimetry”. The main goal for the first part of the thesis is to investigate two key problems of conducting fluid dynamics experiments with soap film tunnels. These two problems are: (1) How important is the air friction to the soap film flow? (2) What does the interference pattern in the soap film represent? The first problem was answered by two sets of experiments conducted in a horizontal soap film tunnel. The tunnel was placed in a vacuum chamber. The first set of experiments is to observe the shedding frequencies of flows over a circular cylinder, via a laser Doppler anemometer. The second set of experiments is to measure the drag coefficients experienced by a normal flat plate, via a laser Doppler anemometer and the momentum defect method. Both set of experiments were conducted with and without vacuum. The objective is to find the influence of different ambient pressure (air friction) on the soap film flow. The vacuum chamber for the horizontal soap film tunnel has been established. The second subject was to interpret the physical meaning of those color fringes with a theoretical investigation and numerical simulation. It was showed that they resembled streamlines of 2-D flows in steadily flowing soap films. Photographs of flow over a circular cylinder and step were compared with theoretical investigation and numerical simulation. Good agreement is found. The physical meaning of those color fringes is streamlines in steady flow. The main goal for the second part of the thesis is to develop the software of Digital Partical Image Velocimetry. With tests of the numerical simulation and the benchmark test flow, the software of Digital Partical Image Velocimetry yields good results.

Thesis (Ph. D.)--Florida State University, 2006.
Advisors: Kevin Speer, Martin Wegkamp, Florida State University, College of Arts and Sciences, Dept. of Statistics. Title and description from dissertation home page (viewed Sept. 20, 2006). Document formatted into pages; contains x, 48 pages. Includes bibliographical references.

The introductions of large digital computers in the field of engineering have rendered possible the solution of a wide variety of problems without the need to violate the equilibrium and compatibility. The major requirement for such analysis is a good constitutive model that represents the stress strain behaviour of the materials in an accurate way. Nowadays for most of the geotechnical engineering applications the elastoplastic models like Mohr Coulomb model are widely used. All the existing constitutive models which represent the plastic behaviour of soil are developed from the fundamentals of classical theory of plasticity. The classical theory of plasticity is always associated with the concept of yield surface and potential surface to represent the plastic behaviour. The definition of yield surface depends on the location of the yield point. But in practical sense it is very difficult to find out the exact yield point for a material. The expression for yield and potential surfaces are simply mathematical expressions formulated for computational efficiency. Experimentally it is very difficult to find out the yield surface in the case of three dimensional stress spaces. The classical theory of plasticity is developed based on the mechanical process. It is believed that a theory which violates the thermodynamic principle is not able to represent the material behaviour accurately. the initial stage and combined to give the final state of stress. It was proved that the equation proposed by Wu and Wang (1983) can be used to represent the triaxial behaviour of sand very well. The dilation and densification behaviour can be predicted very well with the endochronic constitutive equations. The principal aim of this work is to implement the endochronic constitutive equation in the FLAC3D model library like any other constitutive model and validate it with the triaxial test data. After implementation and validation, the application of the particular constitutive model is extended to some practical geotechnical engineering problems like the stresses and displacements around an underground opening such as tunnels, surface settlement due to shallow tunneling, stress distribution below the footing, settlement analysis of footing on various foundation beds such as sand, clay and sand overlying clay bed, lateral displacement of the secant pile wall due to excavation and the force developed in the horizontal support etc. All the three problems validate the model with the analytical, experimental and field data respectively. The equation proposed by Wu and Wang (1983) is used for the present study. In order to validate the equation proposed by Wu and Wang (1983), MatLab programming is used. The hydrostatic, deviatoric and volumetric behaviour is obtained separately using the concerned equations. The equation is coded in the MatLab and analysis is done for a triaxial element test. Both drained and undrained analyses were done in order to study the behaviour. The pore pressure developed is captured separately with the equation proposed by Geoffrey et al (1975). The results obtained from the analysis of the MatLab were compared with that of the experimental results. The analysis shows that the equation captures the least plastic behaviour well for the triaxial element test. The dilation and densification behaviour obtained using the respective equation shows that it matches well with the experimental results. A parametric study is also conducted in MatLab to see how the parameters affect the stress strain and volumetric behaviour of the sand. The parametric study conducted with the MatLab shows that most of the parameters involved in the equation affect the plastic part of the stress strain curve rather than the initial elastic part. User defined constitutive model was written in visual C++ and compiled as DLL (Dynamic Link Library) files that will be loaded whenever it is needed in FLAC3D. In visual C++, header and source files were written by incorporating the constitutive equation proposed by Wu and Wang (1983), defining the variables and other functions etc, and a dynamic link library is created, which is then integrated into the 3D finite difference code FLAC3D using the CPPUDM module to simulate the stress strain behaviour of the materials. CPPUDM module is an additional option in FLAC3D to implement the user defined constitutive models. The visual C++ code was written in the form of incremental stress strain relationship. The model acts like any other constitutive model in the FLAC3D model library and can be loaded whenever it is required. For the validation of the model in FLAC3D, the data for the MatLab simulation were used. Both drained and undrained tests were simulated with the model. The results obtained from the analysis shows that by suitably selecting the parameters the model can simulate the stress strain behaviour of sand very well. The volumetric and deviatoric behaviour were observed and is matching well with the experimental data. In the case of the undrained test the pore pressure generation is well captured by the equation proposed by Geoffrey et al (1975). In urban areas the construction of shallow tunnels results in excessive settlements of the ground surface and thereby causes damage to the existing above ground structures. In order to minimize the settlements and to reduce the impact due to that, a prior analysis of the displacements and stresses around the opening is very important. Nowadays numerical analysis is widely used for the analysis of such structures. The most important requirement of such analysis is a constitutive model that can represent the unloading behaviour around the tunnel opening of sand very well. Here the endochronic constitutive model implemented in the FLAC3D model library is used to evaluate the stresses and displacements around the tunnel. In the analysis the tunnel is simulated as a cylindrical hole in an infinite medium with the in situ stress. The stresses at the springing line was observed and compared with the analytical solution. The results show that the results are matching well with the analytical results. The comparison of the results with that obtained using the Mohr Coulomb model is also done to see how the model differs from a widely used plastic model. By slightly adjusting the parameters the results obtained from both the models are in well agreement. The strain softening effect which is predominant around an underground opening due to the loosening of soil mass is well captured by the endochronic model compared to the Mohr Coulomb model. The settlement analysis shows that the model is almost in close agreement with the closed form solution proposed by Oteo & Sagaseta (1982) and the results obtained with the Mohr Coulomb model. The settlement trough formed for various shapes is wider and deeper than the Mohr Coulomb model. The vertical stress distribution around the opening of the tunnel is studied with varying the shape of the openings using the proposed constitutive model. The results obtained were compared with that of the Mohr Coulomb model. The slightly higher values in the case of endochronic model are basically due to its plastic nature. The displacement and stresses in the axial direction (along the excavation) is observed with the model. In the case of shallow tunnel the surface get influenced by the loosening of the soil mass which necessitates the use of the support system. The study shows that the model can be used for the simulation of underground opening like tunnel and will capture the behaviour well. Footings are structures used to support the buildings constructed above the ground. The settlement analysis of footings is very important when we consider the stability of the structures supported by it. The vertical stress distribution below the footing is studied using the endochronic constitutive model and compared with the analytical solution proposed by Boussinesq (1885). In the elastic range the model shows matching results with the Boussinesq’s solution. The settlement analysis of footing on various foundation beds such as sand, clay and sand overlying the clay bed were studied using the endochronic constitutive model implemented in the FLAC3D model library. The experimental data conducted in our lab (Sireesh (2006)) was used for the study. The results show that with the chosen parameters the results obtained with the endochronic model are in good agreement with the experimental data. The Mohr Coulomb model over predicts the results. This shows higher modulus value for the Mohr Coulomb model. By conducting the parametric study it was seen that by reducing the value of modulus for the Mohr Coulomb model, the results are in good agreement with the experimental value. The displacement and stress contours obtained for the two models were compared. By analyzing the displacement contours it is seen that the Mohr Coulomb model shows uniform settlement. In the case of endochronic model uniform settlement is observed for about 5% settlement that is in the elastic range. After a certain strain level the displacement contours are tilted more towards one side showing the rotational failure. Here the endochronic model captures the anisotropic behaviour associated with the materials like sand at higher strain level. This result is a concrete evidence that the model can capture the realistic behaviour very well compared to any other model. Even though the model developed is for sand its application can be extended to clay also. The size and shape of the footing is varied to study its effect on the pressure settlement curve. The analysis is done with square shape of 150mm side and circular shape of 150mm diameter. As there is not much variation in the area of influence, the shape has little influence on the pressure settlement curve. As the size of the footing increases the settlement increases for a given pressure. A parametric study is conducted by varying the modulus value used. The study shows that as the modulus value increases, the settlement reduces for a given bearing pressure. The endochronic model analysed with the lower modulus value shows that the model predicts the perfectly plastic behaviour, here the settlement increases for low value of bearing pressure. The application of endochronic model for the simulation of complex geotechnical engineering problems like footings is highly explored in the study. Nowadays most of the infrastructure facilities are concentrated towards the underground space. The excavation and construction of such structures in the urban areas results in damage to the existing above ground structures if the construction is done in close proximity to the structures. In the present study a staged excavation of an underground construction for the Bangalore metro project is simulated with the endochronic constitutive model. In the Bangalore metro project the excavation for the underground station is done at the cricket stadium site. At the site there are two major buildings such as the six storied Hindustan Aeronautical Limited building and 100 years old BSNL masonry building. To minimize the impact on these structures were a major concern during the construction of the work. A robust support system consists of secant pile walls, soldier piles and horizontal struts are installed at the site. The OSV method known as the Onsite Visualization and monitoring is conducted to minimize the damage to the existing structures and the accidents at the construction site. Sensors are connected to LEDs which show change in color when the displacements and forces cross the triggered value. The field instrumentation is done with inclinometers, tilt meters and strain gauges connected to the sensors to observe the lateral deformation of the secant pile wall, tilt of the HAL building and the forces developed in the horizontal struts. The monitoring of field data is done for a period of five months from July to November. From the analysis of the field observed data it is clear that the support system provided were strong enough to resist the forces due to unloading. The lateral deformation of the secant pile wall and the forces developed in the strut were numerically analysed using the endochronic constitutive model and the results were compared with the field monitored data. The results show that the model captures the behaviour very close to the field data for a slightly higher modulus than that reported in the geotechnical report (BMRC report). This may be due to the fact that the value of modulus calculated experimentally might have some error. The analysis with the Mohr Coulomb model shows that the model over predicts the results very close to the surface of the excavation. This indicates that the influence of load is more on that particular depth for the Mohr Coulomb model. But the stiffness of the lateral support system is uniform throughout the depth; the endochronic model predicts the result more accurately than the Mohr Coulomb model. The strut forces developed in the horizontal support system is observed using the two models. The strut forces in the field is affected by so many factors such as the temperature variation, stages of excavation and other live loads acting on the site, so an exact comparison with the field data is quite difficult. The analysis shows that even though it is difficult to simulate the exact three dimensional nature of the problem in the present study the endochronic constitutive model captures the behaviour very well. The results obtained shows that the endochronic constitutive model implemented in the FLAC3D model library provides a very promising solution like any other constitutive model. As the theory is based on the irreversible law of thermodynamics and the formulation of the constitutive equation are based on the internal energy concept it can represent the material behaviour in accordance with the laws of continuum mechanics. The anisotropic behaviour of soil at higher strain level is well represented through the footing problem. The endochronic constitutive model is a very simple one to simulate the stress strain behaviour of the materials without the concept of yield surface; the parameters used in the equation can be obtained directly from a single triaxial stress strain plot. This study highlights the importance of a model without the concept of yield surface to capture the stress strain behaviour of any materials. Since the model is of completely plastic nature it has its own uniqueness in capturing the material behaviour due to loading and unloading.

Deep ‘Analog Artificial Neural Networks’ (AANNs) perform complex classification problems with high accuracy. However, they rely on humongous amount of power to perform the calculations, veiling the accuracy benefits. The biological brain on the other hand is significantly more powerful than such networks and consumes orders of magnitude less power, indicating some conceptual mismatch. Given that the biological neurons are locally connected, communicate using energy efficient trains of spikes, and the behavior is non-deterministic, incorporating these effects in Artificial Neural Networks (ANNs) may drive us few steps towards a more realistic neural networks.

Emerging devices can offer a plethora of benefits including power efficiency, faster operation, low area in a vast array of applications. For example, memristors and Magnetic Tunnel Junctions (MTJs) are suitable for high density, non-volatile Random Access Memories when compared with CMOS implementations. In this work, we analyze the possibility of harnessing the characteristics of such emerging devices, to achieve neuro-inspired solutions to intricate problems.

We propose how the inherent stochasticity of nano-scale resistive devices can be utilized to realize the functionality of spiking neurons and synapses that can be incorporated in deep stochastic Spiking Neural Networks (SNN) for image classification problems. While ANNs mainly dwell in the aforementioned classification problem solving domain, they can be adapted for a variety of other applications. One such neuro-inspired solution is the Cellular Neural Network (CNN) based Boolean satisfiability solver. Boolean satisfiability (k-SAT) is an NP-complete (k≥3) problem that constitute one of the hardest classes of constraint satisfaction problems. We provide a proof of concept hardware based analog k-SAT solver that is built using MTJs. The inherent physics of MTJs, enhanced by device level modifications, is harnessed here to emulate the intricate dynamics of an analog, CNN based, satisfiability (SAT) solver.

Furthermore, in the effort of reaching human level performance in terms of accuracy, increasing the complexity and size of ANNs is crucial. Efficient algorithms for evaluating neural network performance is of significant importance to improve the scalability of networks, in addition to designing hardware accelerators. We propose a scalable approach for evaluating Liquid State Machines: a bio-inspired computing model where the inputs are sparsely connected to a randomly interlinked reservoir (or liquid). It has been shown that biological neurons are more likely to be connected to other neurons in the close proximity, and tend to be disconnected as the neurons are spatially far apart. Inspired by this, we propose a group of locally connected neuron reservoirs, or an ensemble of liquids approach, for LSMs. We analyze how the segmentation of a single large liquid to create an ensemble of multiple smaller liquids affects the latency and accuracy of an LSM. In our analysis, we quantify the ability of the proposed ensemble approach to provide an improved representation of the input using the Separation Property (SP) and Approximation Property (AP). Our results illustrate that the ensemble approach enhances class discrimination (quantified as the ratio between the SP and AP), leading to improved accuracy in speech and image recognition tasks, when compared to a single large liquid. Furthermore, we obtain performance benefits in terms of improved inference time and reduced memory requirements, due to lower number of connections and the freedom to parallelize the liquid evaluation process.

This work develops a discontinuous Galerkin finite element discretization of non- linear hyperbolic conservation equations with efficient and robust high order stabilization built on an entropy-based artificial viscosity approximation. The solutions of equations are represented by elementwise polynomials of an arbitrary degree p > 0 which are continuous within each element but discontinuous on the boundaries. The discretization of equations in time is done by means of high order explicit Runge-Kutta methods identified with respective Butcher tableaux. To stabilize a numerical solution in the vicinity of shock waves and simultaneously preserve the smooth parts from smearing, we add some reasonable amount of artificial viscosity in accordance with the physical principle of entropy production in the interior of shock waves. The viscosity coefficient is proportional to the local size of the residual of an entropy equation and is bounded from above by the first-order artificial viscosity defined by a local wave speed. Since the residual of an entropy equation is supposed to be vanishingly small in smooth regions (of the order of the Local Truncation Error) and arbitrarily large in shocks, the entropy viscosity is almost zero everywhere except the shocks, where it reaches the first-order upper bound. One- and two-dimensional benchmark test cases are presented for nonlinear hyperbolic scalar conservation laws and the system of compressible Euler equations. These tests demonstrate the satisfactory stability properties of the method and optimal convergence rates as well. All numerical solutions to the test problems agree well with the reference solutions found in the literature. We conclude that the new method developed in the present work is a valuable alternative to currently existing techniques of viscous stabilization.

Tese de doutoramento em Engenharia Mecânica, no ramo de Aerodinâmica Industrial e Engenharia do Vento, apresentada ao Departamento de Engenharia Mecânica da Faculdade de Ciências e Tecnologia da Universidade de Coimbra
The transport of soil particles by wind is of enormous relevance in a wide range of events from those related to agriculture (e.g., seed transport) to the formation and modification of the landscape. A classic example is sand dunes, which can be formed, moved, or entirely eroded due to aeolian processes. Still, aeolian transport of particles may cause serious damage in transportation, communications and severe environmental problems, such as the degradation of air quality due to dispersion of pollutants from stockpiles. The wind exposure will lead to the particles movement through several mechanisms, such as, suspension, creeping, saltation, and saltation bombardment. Consequently, the free surface will change over time due to entrainment and deposition phenomena. The main objective of this study is assessing the airflow characteristics over and around granular material complex three-dimensional piles when subjected to the wind erosion and its influence in the behavior of the free surface, as well as, in the sand emission rate. A literature review was made over the main subjects of interest to the present work, from the basics, such as granular material and aeolian transport mechanisms, to the key magnitudes involved in the wind erosion phenomena. Studies performed to calculate the dust emission from stockpiles are presented and reviewed along with the widely applied methodology from United States Environmental Protection Agency (USEPA). This methodology estimates the emission of particles from stockpiles only during specific erosion events, such as bursts, when in reality emissions occur in many other occasions. The present work offers the possibility of conducting the determination of emissions from stockpiles along time; this approach makes viable to follow the time-dependent evolution of the free surface enhancing in this way the accuracy of the predictions. Therefore, studies that are related to free surface progress are also reviewed. The present work has a significant experimental component, and the thesis describes in considerable detail the experimental apparatus and procedures, including wind tunnel, granular material, tested pile configurations and performed tests – in particular, erosion and shear stress (with Irwin probes) measurements. In addition, the use of Computational Fluid Dynamics (CFD) plays an important role in the present study; therefore, for completeness, key concepts related to CFD are included in this thesis along with a brief survey of studies that employ CFD methodology to evaluate aeolian erosion. The present CFD studies were conducted by using an open source CFD code – OpenFOAM (OF). The motivation for the selection of OF, as the CFD tool, is related to its wide acceptance in the scientific community; moreover, its application to the prediction and study of wind erosion is an original contribution to this field of research. Full description of the numerical model and its implementation are given along with the methodology used in the model validation. Two different pile configurations were studied - a two-dimensional triangular pile and a three-dimensional oblong pile. The increasing geometrical complexity of the piles allowed gaining gradual experience with the procedures and methodologies involved. The experimental and numerical studies for these cases and their results are analyzed and discussed. In what concerns the oblong piles, the numerical results are correlated with the registered free surface deformation of the piles and compared against other study available in the literature, in which oil film visualization tests were conducted and a different CFD tool was used. Considering that the model validation is partly performed against experimental results, particular attention was given to their accuracy. For the triangular piles, the comparison is primarily against the wall shear stress results obtained using the Irwin probes, which were built and calibrated for this work. The study of these probes was extensive and it led to an innovative and significant contribution to this field of research, which justifies an integrated, but autonomous Part B of this thesis. Due to the versatility of experimental apparatus built to assist the calibration of the Irwin probes, a more in-depth study was also carried out on the flow through rectangular ducts with a constant and variable cross-section. Finally, the main findings resulting from the present work are summed up and some recommendations for future work are given.
O transporte de partículas do solo pelo vento é de enorme relevância numa ampla gama de eventos, desde os relacionados com a agricultura (por exemplo, o transporte de sementes) até a formação e modificação da paisagem. Um exemplo clássico são as dunas de areia, que se podem formar, mover ou erodir totalmente devido a processos eólicos. Por outro lado, o transporte de partículas pode provocar sérios danos no sector dos transportes, comunicações e graves problemas ambientais, como a degradação da qualidade do ar devido à dispersão de poluentes provenientes de pilhas de armazenamento. A exposição ao vento pode levar ao movimento das partículas através de vários mecanismos, tais como, suspensão, arrastamento, saltação e bombardeamento das partículas em saltação. Consequentemente, a superfície livre irá mudar ao longo do tempo devido aos fenómenos de arrastamento e deposição. O objetivo principal deste estudo é investigar as características do fluxo de ar sobre e ao redor de pilhas tridimensionais (3D) complexas de material granular quando sujeitas à erosão do vento e avaliar a sua influência no comportamento da superfície livre, bem como na taxa de emissão. Uma revisão bibliográfica foi feita sobre os principais temas de interesse para o presente trabalho, desde o básico, como material granular e mecanismos de transporte eólicos, até às grandezas chave envolvidas nos fenómenos de erosão do vento. Estudos realizados para calcular a emissão de poeira de pilhas de armazenamento são apresentados e revistos juntamente com a metodologia, amplamente aplicada, da Agência de Proteção Ambiental dos Estados Unidos (United States Environmental Protection Agency - USEPA). Esta metodologia estima as emissões de partículas a partir de pilhas de armazenamento apenas durante eventos de erosão específicos, tais como rajadas, quando as emissões na realidade ocorrem em muitas outras ocasiões. O presente trabalho oferece a possibilidade de realizar a determinação de emissões de pilhas de armazenamento ao longo do tempo; esta abordagem torna viável seguir a evolução dependente do tempo da superfície livre, aumentando assim a precisão das previsões. Portanto, estudos relacionados com a evolução da superfície livre são também revistos. O presente trabalho tem uma componente experimental significativa, e a tese descreve em considerável detalhe a montagem experimental e os procedimentos, incluindo o túnel de vento, material granular, as configurações de pilhas testadas e os testes executadas – em particular, testes de erosão e de medição da tensão de atrito (com sondas Irwin). Adicionalmente, o uso da Dinâmica de Fluidos Computacional (em inglês: Computational Fluid Dynamics — CFD) desempenha um papel importante no presente estudo, assim sendo, para completar, conceitos chave relacionados a CFD estão incluídos nesta tese, juntamente com uma breve pesquisa de estudos que empregam a metodologia CFD para avaliar a erosão eólica. Os presentes estudos CFD foram realizados usando um software CFD de código aberto - OpenFOAM (OF). A motivação para a seleção do OF, como ferramenta CFD, está relacionada com a sua ampla aceitação na comunidade científica; e além disso, a sua aplicação na previsão e estudo da erosão eólica é uma contribuição original para este campo de pesquisa. A descrição completa do modelo numérico e da sua implementação são dadas juntamente com a metodologia utilizada na validação do modelo. Foram estudadas duas configurações de pilha diferentes - uma pilha triangular bidimensional (2D) e uma pilha tridimensional (3D) oblonga. A crescente complexidade geométrica das pilhas permitiu ganhar experiência de forma gradual com os procedimentos e metodologias envolvidos no estudo. Os estudos experimentais e numéricos para estes casos, bem como os seus resultados, são analisados e discutidos No que diz respeito às pilhas oblongas, os resultados numéricos são correlacionados com a deformação de superfície livre das pilhas e comparados com outro estudo disponível na literatura, no qual foram realizados testes de visualização de filmes de óleo e utilizada uma ferramenta CFD diferente. Considerando que a validação do modelo é parcialmente realizada através da comparação dados experimentais; especial atenção foi dada à sua precisão. Para as pilhas triangulares, a comparação é feita, principalmente, com resultados da tensão de atrito da parede medidos através das sondas Irwin, as quais foram construídas e calibradas para este trabalho. O estudo efetuado com estas sondas foi extenso e contribuiu de forma inovadora e significativa para esta área de pesquisa, o que justifica uma Parte B integrada, mas autónoma desta tese. Devido à versatilidade da montagem experimental construída para auxiliar a calibração das sondas Irwin, um estudo mais aprofundado foi também realizado sobre escoamentos em condutas retangulares com seção transversal constante e variável. Finalmente, as principais conclusões que resultam do presente trabalho são resumidas e sugerem-se algumas recomendações para o trabalho futuro.