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Garcia, Sagrado Ana Pilar. "Boundary layer and trailing edge noise sources." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612074.
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Obrist, Dominik. "On the stability of the swept leading-edge boundary layer /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/6767.
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Wang, Hongwei. "Boundary Layer Characteristics on a Tiltrotor Blade Model." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/33630.
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Boundary layer characteristics at the trailing edge of a tiltrotor blade model were measured using a flattened pitot probe and a single hot wire. The blade was mounted in Virginia Tech Stability Wind tunnel stationary on a turntable on the wind tunnelâ s upper wall with the tip pointing down. The measurement point was located at 1 mm behind the trailing edge to make it possible to measure the flow near the blade surface and measure the boundary layer on both sides of the trailing edge in a same run. Mean velocity profiles were measured for a variety of Reynolds numbers and angles of attack. Turbulence intensity and spectral measurements were performed using a single hot wire at the highest Reynolds number. Conclusion was reached that both of the flattened pitot probe and single hot wire are good for boundary layer thickness measurements. Displacement thickness, which is important in trailing edge noise prediction, was calculated from the profile data and fit using an algebra expression against the tip angle of attack. Once the relationship between tip angle of attack and local effective angle of attack is obtained by lifting line theory, the results can be used in the trailing edge noise prediction code.Master of Science
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Cziegler, István. "Turbulence and transport phenomena in edge and scrape-off-layer plasmas." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/77484.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 171-178).
This thesis reports recent experimental studies of edge turbulence structure using gas-puff-imaging at high time resolution in a radially broad zone at the low-field-side of Alcator C-Mod[1], and highlights the connections between its characteristics and particle transport. Within the framework of this thesis a new detector system has been designed and built for viewing the steep gradient outboard midplane region at minor radii 0.9 < r/rma, < 1.1, where turbulence is postulated to be driven [2, 3]. The design is optimized for the study of edge and scrape-off-layer turbulence, based on previous studies of these regions. Analysis of the data from this diagnostic in Ohmic L-modes from the electron diamagnetic drift propagating turbulence in the closed field line region of the plasma edge shows a strong scaling of the fluctuation power 5/n with the density normalized to the tokamak density limit ne/ng; in addition, a critical physical scale is found at ... ~ 0.1, where the critical wavenumber is normalized to ps, the ion Larmor radius at the sound speed, also known as the drift scale. The characteristic size scale shows very little variation with operating parameters. The analysis of the physical scale includes spectral analysis, yielding robust spectral indices beta= ~4.5 for larger wavenumbers and a sensitive spectral shape for lower wavenumbers, and the first spectral transfer measurement of turbulence on C-Mod, showing that the critical scale feeds power into the turbulence. A connection is found to the quasi-coherent mode (QCM), a modelike edge fluctuation characteristic of the Enhanced D-Alpha H-mode, which also appears at ... ~ 0.1 and has decreased inverse transfer but greatly enhanced forward transfer compared to the L-mode levels.
by István Cziegler.
Ph.D.
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Schuster, William. "Trailing edge noise produced by the scattering of boundary layer turbulence." Diss., The University of Arizona, 2002. http://hdl.handle.net/10150/280089.
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Noise generated at the trailing edges of airfoils can be an important contributor to the sound levels of aircraft and turbomachinery. Previous work on trailing edge noise has largely neglected the role of the mean boundary-layer profile in the sound generation process. In the present work, a trailing edge scattering problem is formulated using a piecewise-linear symmetric mean flow with a non-zero slip velocity at the centerline, providing a representation that is intermediate between the boundary layer and wake flows. The airfoil is modeled as a zero-thickness, semi-infinite flat plate, appropriate for noise generation by sharp trailing edges in the presence of a high Reynolds number flow. The mean boundary-layer profile adjacent to the airfoil surface supports naturally-occurring vortical disturbances that have a non-trivial pressure field and convect at speeds between the slip and free stream velocities. Using these pressure disturbances to represent the turbulent field that is incident on the trailing edge, a mixed boundary value problem is formulated and solved using the Wiener-Hopf technique. This scattering problem is solved for both low Mach number and O(1) Mach number flows. The results show that the presence of the mean flow profile can significantly increase the amplitude of the sound radiated to the far field. In the O(1) Mach number case, the directivity of the scattered field is also appreciably altered. The results of the scattering problem are used along with a simplified model of the wall pressure wavenumber-frequency spectrum to generate a prediction for the power spectrum of the scattered sound field.
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Satter, Md Mahbub. "Design and theoretical study of Wurtzite III-N deep ultraviolet edge emitting laser diodes." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53042.
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Designs for deep ultraviolet (DUV) edge emitting laser diodes (LDs) based on the wurtzite III-nitride (III-N) material system are presented. A combination of proprietary and commercial advanced semiconductor LD simulation software is used to study the operation of III-N based DUV LDs theoretically. Critical factors limiting device performance are identified based on an extensive literature survey. A comprehensive design parameter space is investigated thoroughly with the help of advanced scripting capabilities. Several design strategies are proposed to eliminate the critical problems completely or partially.
A DUV LD design is proposed based exclusively on AlInN active layers grown epitaxially on bulk AlN substrates because AlInN offers a promising alternative to AlGaN for the realization of LDs and LEDs operating in the DUV regime. The proposed AlInN-based design also features a tapered electron blocking layer (EBL) instead of a homogeneous one. Tapered EBLs redistribute the interfacial polarization charge volumetrically throughout the entire EBL thickness via compositional grading, and eliminate the parasitic inversion layer charge.
AlGaN based DUV LD designs are explored also because at present, it may be difficult to grow AlInN epitaxially with superior crystalline quality. Polarization charge matching is proposed to improve electron and hole wavefunction overlap within the active region. Although the strategy of polarization charge matching has already been proposed in the literature to enhance performance of visible wavelength LEDs and LDs, the proposed design presents the first demonstration that polarization charge matching is also feasible for DUV LDs operating at sub-300 nm wavelengths.
A lateral current injection (LCI) LD design is proposed featuring polarization-charge-matched barriers and regrown Ohmic contacts to avoid a group of issues related to the highly inefficient p-type doping of wide bandgap III-N materials in vertical injection designs. The proposed design partially decouples the problem of electrical injection from that of optical confinement. Although the idea of an LCI LD design has been proposed in the literature in the 90s to be used as longer wavelength active sources in optoelectronic integrated circuits using GaInAsP/InP and related material systems, the proposed design is the first theoretical demonstration that this concept can be applied to DUV LDs based on III-N material system.
To solve the problem of hole transport in vertical injection designs, a DUV LD design based exclusively on AlGaN material system is presented, featuring an inverse-tapered p-waveguide layer instead of an EBL. Several EBL designs are investigated, and compared with conventionally-tapered EBL design. Through judicious volumetric redistribution of fixed negative polarization charge, inverse tapering may be exploited to achieve nearly flat valence band profiles free from barriers to hole injection into the active region, in contrast to conventional designs. Numerical simulations demonstrate that the inverse tapered strategy is a viable solution for efficient hole injection in vertical injection DUV LDs operating at shorter wavelengths (< 290 nm).
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Ferdous, Wahid Khan. "An ID-based mutually authenticated edge-to-edge security architecture for bridged provider networks to secure layer-2 communications." Doctoral thesis, Universitat Pompeu Fabra, 2011. http://hdl.handle.net/10803/32050.
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IEEE standardized a Layer-2 security, named Media Access Control security (MACsec), for interoperability. It provides link-based security through hop-by-hop operation. The link-constrained security of MACsec eliminates the confidentiality of user data inside bridges. Hence, high-speed Ethernet-based Broadband networks are susceptible to attacks in large network deployment, where bridges need to be resided in street cabinets, road side poles or public places for easy user access. We propose an ID-based mutually authenticated edge-to-edge security architecture to address this remaining gap (i.e., secure bridging) in layer-2 service provider networks. The major challenge for this scenario is the combination of complete security, simplicity, better performance and scalability in a single solution. Our solution addresses all challenges and simplifies- key distribution by an extension of 802.1x-EAP authentication protocol, key agreement by an ID-based mutually authenticated two-pass key agreement protocol and secure data transmission by a modification of the replay protection mechanism of 802.1AE.IEEE va estandarditzar seguretat a nivell 2, anomenada Media Access Control, que s'enfoca a proporcionar interoperabilitat, seguretat a nivell d'enllaç, i operació salt-a-salt. La seguretat restringida de MACsec elimina la confidencialitat de les dades de l'usuari dins dels dispositius. Per tant, les xarxes d'alta velocitat basades en Ethernet són susceptibles als atacs en grans desplegaments, on els bridges han de ser guardats a distribuïdors a nivell de carrer o llocs públics d'accés fàcil. Per fer front al problema a les xarxes de proveïdors de capa 2 aquí proposem una arquitectura de seguretat extrem-a-extrem, autenticada mútuament i basada en identitat. El principal repte per a aquest escenari és la combinació d'una seguretat completa, simplicitat, millor rendiment i escalabilitat en una única solució. La nostra solució ataca tots els reptes i simplifica- (1) la distribució de claus mitjançant una ampliació del protocol d'autenticació 802.1x-EAP protocol, (2) l'acord de claus amb un protocol de doble passada autenticat mútuament i basat en identitat, i (3) la transmissió segura de dades mitjançant una modificació del mecanisme de 'protecció de resposta' de 802.1AE.
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Davu, Sandeep. "Connection Oriented Mobility Using Edge Point Interactivity." Kent State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=kent1206469405.
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Nichols, Dawn Elizabeth. "Boundary layer receptivity of a flat plate with a rounded leading edge." Thesis, University of East Anglia, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395146.
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Li, Yifan. "Edge partitioning of large graphs." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066346/document.
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Dans cette thèse nous étudions un problème fondamental, le partitionnement de graphe, dans le contexte de la croissance rapide des données, le volume des données continues à augmenter, allant des réseaux sociaux à l'internet des objets. En particulier, afin de vaincre les propriétés intraitables existant dans de nombreuses graphies, par exemple, la distribution des degrés en loi de puissance, nous appliquons un nouveau mode pour coupe de sommet, à la place de la méthode traditionnelle (coupe de bord), ainsi que pour assurer une charge de travail équilibrée et raisonnablement dans le traitement de graphe distribué. En outre, pour réduire le coût de communication inter-partitions, nous proposons une méthode de partition de bord basée sur les blocs, qui peut explorer efficacement les structures graphiques sous-jacentes au niveau local. , afin d'optimiser l'exécution de l'algorithme de graphe. Par cette méthode, le temps d'exécution et des communications généraux peuvent être considérablement réduits par rapport aux approches existantes. Les challenges qui se posent dans les grands graphiques comprennent également leur grande variété. Comme nous le savons, la plupart des applications graphiques au monde réel produisent des ensembles de données hétérogènes, dans lesquels les sommets et / ou les arêtes peuvent avoir des différents types ou des différentes étiquettes. De nombreuses algorithmes de fouille de graphes sont également proposés avec beaucoup d'intérêt pour les attributs d'étiquette. Pour cette raison, notre travail est étendu aux graphes de multicouches en prenant en compte la proximité des arêtes et la distribution des étiquettes lors du processus de partitionnement. En fin de cette thèse, Nous démontré à la ses performances exceptionnelles sur les ensembles de données du monde réelIn this thesis, we mainly focus on a fundamental problem, graph partitioning, in the context of unexpectedly fast growth of data sources, ranging from social networks to internet of things. Particularly, to conquer intractable properties existing in many graphs, e.g. power-law degree distribution, we apply the novel fashion vertex-cut, instead of the traditional edge-cut method, for achieving balanced workload in distributed graph processing. Besides, to reduce the inter-partition communication cost, we present a block-based edge partition method who can efficiently explore the locality underlying graphical structures, to enhance the execution of graph algorithm. With this method, the overhead of both communication and runtime can be decreased greatly, compared to existing approaches. The challenges arising in big graphs also include their high-variety. As we know, most of real life graph applications produce heterogenous datasets, in which the vertices and/or edges are allowed to have different types or labels. A big number of graph mining algorithms are also proposed with much concern for the label attributes. For this reason, our work is extended to multi-layer graphs with taking into account the edges closeness and labels distribution during partitioning process. Its outstanding performance over real-world datasets is demonstrated finally
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Heinrich, Roland Adolf Eberhard. "Flat-plate leading edge receptivity to various free-stream disturbance structures." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184860.
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The receptivity process by which two-dimensional, time-harmonic freestream disturbances generate instability waves in the incompressible Blasius boundary layer is investigated analytically. The importance of the leading edge region and the linear nature of the receptivity process are discussed, and Goldstein's (1983a, 1983b) theoretical framework for the leading edge receptivity problem is reviewed. His approach utilizes asymptotic matching of a region close to the leading edge, which is governed by the linearized unsteady boundary layer equation, with a region further downstream, which is described by an Orr-Sommerfeld type equation. The linearized unsteady boundary layer equation is solved numerically, using the slip velocity and pressure gradient obtained from the inviscid interaction of the freestream disturbance with the semi-infinite plate. A new method is developed to extract the receptivity coefficient from this numerical solution. The receptivity coefficient determines the amplitude of the instability wave--a quantity not available from classical stability theory. The freestream disturbances investigated are oblique plane acoustic waves, vortical gusts of various orientations convected downstream with freestream speed U(∞), and a Karman vortex street passing above the plate surface with speed U(p). In addition, the case of a semi-infinite plate in a channel of finite width subject to an upstream traveling acoustic wave on the upper plate surface is considered. For oblique acoustic waves, the dominant receptivity mechanism is related to scattering of the waves by the leading edge. In contrast, for vortical gusts the receptivity produced by leading edge scattering is very small. The boundary layer receptivity to a Karman vortex street is found to be a strong function of the speed ratio U(p)/U(∞). A pronounced influence of channel walls, which is related to the alternate cut-on of higher modes in the upstream and downstream channel halves, is found. A comparison of the present results with available experiments shows good qualitative and quantitative agreement.
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Cerminara, Adriano. "Boundary-layer receptivity and breakdown mechanisms for hypersonic flow over blunt leading-edge configurations." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/412641/.
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Direct numerical simulations have been performed to study receptivity and breakdown mechanisms for hypersonic flow over blunt leading-edge configurations with imposed freestream acoustic disturbances. Both two-dimensional (2D) and three-dimensional (3D) fast and slow acoustic wave models have been used. The former has been adopted for 2D simulations over a blunt-nose wedge probe designed to measure freestream noise levels in hypersonic wind tunnels; the latter has been used to perform 3D simulations for a span-periodic blunt wedge in unswept and swept configurations, and for a three-dimensional generic forebody model. In the 2D wedge simulations, an analysis of the post-shock wave structure shows that fast acoustic waves are efficiently transmitted across the shock as refracted waves, while slow acoustic waves generate convected waves. The wall response to the fast mode highlights a resonance-modulation behaviour in the nose region. An estimation of the freestream noise levels in the DLR high-enthalpy (HEG) and low-enthalpy (RWG) hypersonic wind tunnels has been performed, showing higher noise levels for the HEG wind tunnel at high Mach numbers. The 3D wedge simulations have been used to study the characteristics of the receptivity and breakdown mechanisms associated with different wave types (fast/slow), disturbance amplitudes, and sweep angles. The fast-mode induced transition has been observed to be a much more rapid and powerful process than the slow-wave related transition, because of the role played by the fast-mode resonance mechanism at the leading edge. Finally, the numerical simulations performed for a generic forebody geometry have enabled comparison with a recent transition experiment carried out in the Mach 6 Purdue hypersonic wind tunnel in noisy conditions. In this case, slow acoustic waves show the most similar transition patterns to the experimental case, and, in particular, are more efficient than fast waves in triggering nonlinear growth of streamwise streaks, related to crossflow inflectional instabilities located in the off-centerline leading-edge region.
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Khapko, Taras. "Edge states and transition to turbulence in boundary layers." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-186038.
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The focus of this thesis is the numerical study of subcritical transition to turbulence in boundary-layer flows. For the most part, boundary layers with uniform suction are considered. Constant homogeneous suction counteracts the spatial growth of the boundary layer, rendering the flow parallel. This enables research approaches which are not feasible in the context of spatially developing flows. In the first part, the laminar–turbulent separatrix of the asymptotic suction boundary layer (ASBL) is investigated numerically by means of an edge-tracking algorithm. The obtained edge states experience recurrent dynamics, going through calm and bursting phases. The self-sustaining mechanism bears many similarities with the classical regeneration cycle of near-wall turbulence. The recurrent simple structure active during calm phases is compared to the nucleation of turbulence events in bypass transition originating from delocalised initial conditions. The implications on the understanding of the bypass-transition process and the edge state's role are discussed. Based on this understanding, a model is constructed which predicts the position of the nucleation of turbulent spots during free-stream turbulence induced transition in spatially developing boundary-layer flow. This model is used together with a probabilistic cellular automaton (PCA), which captures the spatial spreading of the spots, correctly reproducing the main statistical characteristics of the transition process. The last part of the thesis is concerned with the spatio-temporal aspects of turbulent ASBL in extended numerical domains near the onset of sustained turbulence. The different behaviour observed in ASBL, i.e. absence of sustained laminar–turbulent patterns, which have been reported in other wall-bounded flows, is associated with different character of the large-scale flow. In addition, an accurate quantitative estimate for the lowest Reynolds number with sustained turbulence is obtainedQC 20160429
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Abdalla, Ibrahim E. "Numerical studies of separated boundary layer transition on a flat plate with a blunt leading edge." Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/14102.
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In this work the physics of transitional separated-reattched flow with and without free-stream turbulence on a blunt leading edge plate have been studied numerically employing the Large Eddy Simulation approach. One of the fundamental features of 'turbulent' separated-reattached flows is two basic modes of characteristic frequencies. The higher-frequency mode is associated with the usual large scale motions in the shear layer while the lower-frequency mode reflects overall separation bubble growth/decay dynamics or shear layer flapping as it is frequently called in the literature. It has been drawn from the current study that the low-frequency mode will not occur in low-Reynolds number transitional separated-reattached flows and the phenomena appears to be an integral feature of a fully turbulent separation. The numerical data have been comprehensively analysed to elucidate the entire transition process. Coherent structures have been visualised in the different stages of transition. In the case with no-free-stream turbulence, the 2D Kelvin - Holmholtz rolls are the dominant structures in the early stage of transition and the well known A-shaped vortices commonly associated with flat plate boundary layer transition are the common features in the late transition stages. Many experimental studies have indicated that the separated shear layer on a blunt plate is unstable owing to the Kelvin-Holmholtz instability. However, sufficient and detailed evidence has not been given in separated boundary layer transition studies to show that the instability mechanism at work is indeed the Kelvin-Holmholtz instability in this particular geometry. In the current study, it has been shown that the primary instability is indeed of the Kelvin-Holmholtz type. The results also strongly support the idea that 'helical-pairing' instability could be the secondary instability responsible for the breakdown to turbulence in the late stages of transition. The addition of free-stream turbulence result in the transition OCCllring earlier leading to a short mean reattachment bubble length. The coherent structures which are clearly observed in the no-free-stream turbulence case have been barely visible. The primary instability was found to be the same as in the no-free-stream turbulence case, i.e., Kelvin - Helmholtz instability.
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Smith, A. "Some effects of transpiration on the boundary layer at the leading edge of a swept wing." Thesis, Cranfield University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391579.
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Baudoin, Camille. "Numerical evaluations of mechanisms governing the heat transport in the edge plasma of tokamaks." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0053/document.
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La fusion nucléaire est une solution technologique prometteuse pour une nouvelle source d'énergie. Cependant, utiliser la par fusion nucléaire confinement magnétique comme source d'énergie constitue un challenge scientifique et technologique car cela requière à la fois un bon confinement du plasma de cœur et un contrôle des flux de chaleurs arrivant à la paroi. Ce travail est motivé par la problématique de la gestion des flux de chaleur dans les réacteurs de fusion. Cela est nécessaire pour éviter d'endommager les coûteux composants faisant face au plasma. La compréhension des mécanismes physiques régissant le transport de la chaleur dans le plasma de bord est une tâche critique pour le design des futures machines. Dans ce contexte, il est nécessaire de faire des prédictions fiables de l'étalement de la chaleur dans le but de dimensionner correctement ces futures machines. Cela appelle à un fondement théorique décrivant la manière dont l'énergie s'échappe du plasma. Des études théoriques et expérimentales ont tenté aboutir à cette fin, cependant les mécanismes en jeux ne sont toujours pas clairs. Pour atteindre ce but, la modélisation numérique est un complément nécessaire aux expériences. Ce travail de thèse est dédié à l'étude numérique des différents aspects du transport de la chaleur dans le plasma de bord un utilisant les approches fluides. Une attention particulière est porté à deux mécanismes suspectés de joué un grand rôle dans le transport de la chaleur : le transport intermittent due à la turbulence et le transport convectif à large échelle par les vitesses dérives. Le problème a été traité avec une approche graduelle en utilisant différent outils numériquesFusion devices are a promising solution for a new source of energy. However, using fusion reaction to produce power within a magnetic confinement is a scientific and technological challenge as it requires a high confinement in the core plasma at the same time as a good control of plasma exhaust on the material walls. This work is motivated by the key problematic of power handling in fusion power plants necessary to avoid damaging the expensive plasma facing components (PFC). The understanding of the physics underlying the heat transport, and more specifically is a critical task for the engineering design of future Tokamak devices. In this context, it is mandatory to make reliable predictions of the power spreading in order to correctly size the future Tokamaks. This calls for a theoretical ground describing the way energy escapes the core plasma through the separatrix and deposits on the PFCs. Some theoretical and experimental studies attempt to achieve such a task, however no definitive conclusion have been drawn yet. To achieve this goal, numerical modelling is a necessary complement to experimental results. This PhD work has been dedicated to the study of the different aspects of the heat transport in the edge plasma using a numerical fluid approach. Special focus was devoted to two types of mechanisms suspected to play an important role in the heat transport: intermittent turbulence; the large-scale convective transport
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Millican, Anthony J. "Bio-Inspired Trailing Edge Noise Control: Acoustic and Flow Measurements." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78376.
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Trailing edge noise control is an important problem associated mainly with wind turbines. As turbulence in the air flows over a wind turbine blade, it impacts the trailing edge and scatters, producing noise. Traditional methods of noise control involve modifying the physical trailing edge, or the scattering efficiency. Recently, inspired by the downy covering of owl feathers, researchers developed treatments that can be applied to the trailing edge to significantly reduce trailing edge noise. It was hypothesized that the noise reduction was due to manipulating the incoming turbulence, rather than the physical trailing edge itself, representing a new method of noise control. However, only acoustic measurements were reported, meaning the associated flow physics were still unknown. This thesis describes a comprehensive wall jet experiment to measure the flow effects near the bio-inspired treatments, termed “finlets” and “rails,” and relate those flow effects to the noise reduction. This was done using far-field microphones, a single hot-wire probe, and surface pressure fluctuation microphones. The far-field noise results showed that each treatment successfully reduced the noise, by up to 7 dB in some cases. The surface pressure measurements showed that the spanwise coherence was slightly reduced when the treatments were applied to the trailing edge. The velocity measurements clearly established the presence of a shear layer near the top of the treatments. As a whole, the dataset led to the shear-sheltering hypothesis: the bio-inspired treatments are effective based on reducing the spanwise pressure correlation and by sheltering the trailing edge from turbulent structures with the shear layer they create.Master of Science
This thesis describes a project aimed at developing a technology inspired by the silent flight of owls, with the end goal of using this technology to reduce the noise generated by wind turbines. Specifically, the phenomenon known as "trailing edge noise" is the primary source of wind turbine noise, and is the noise source of interest here. It occurs when air turbulence (which can be thought of as unsteady air fluctuations) crashes into the rear (trailing) edge of wind turbine blades, scattering and producing noise. Typically, methods of reducing this noise source involve changing the shape of the trailing edge; this may not always be practical for existing wind turbines. Recently, inspired by the downy covering of owl feathers, researchers developed treatments that can be applied directly to the trailing edge, significantly reducing trailing edge noise. This bio-inspired concept was verified with numerous acoustic measurements. Based on those measurements, researchers hypothesized that the noise reduction was achieved by manipulating the incoming turbulence before it scattered off the trailing edge, rather than by changing the existing wind turbine blade, representing a new method of trailing edge noise control. However, as only acoustic measurements (not flow measurements) were reported, the changes in turbulence could not be examined. With the above motivation in mind, this thesis describes a comprehensive wind tunnel experiment to measure the changes in the aerodynamics and turbulence near the bio-inspired treatments, and relate those changes to the reduction in trailing edge noise. This was done using a hot-wire probe to measure the aerodynamics, as well as microphones to measure the radiated noise and surface pressure fluctuations. As a whole, the experimental results led to the shear-sheltering hypothesis: the bio-inspired treatments are effective based on the creation of a shear layer (a thin region between areas with different air speeds) which shelters the trailing edge from some turbulence, as well as by de-correlating surface pressure fluctuations along the trailing edge.
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Gobel, Teresa M. "Aircraft observations of the atmospheric boundary layer in the vicinity of the marginal ice zone under conditions of flow parallel to the ice edge." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA241072.
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Thesis (M.S. in Meteorology and Oceanography)--Naval Postgraduate School, September 1990.Thesis Advisor(s): Shaw, W.J. Second Reader: Nuss, W.A. "September 1990." Description based on title screen as viewed on December 29, 2009. DTIC Identifier(s): Marine atmospheres, marginal ice zones, geostropic wind, atmospheric boundary layer, stratus clouds, cumulus clouds, stratocumulus clouds, wind velocity, temperature inversion, air ice interactions. Author(s) subject terms: Marginal ice zone. Includes bibliographical references (p. 45-46). Also available in print.
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Khapko, Taras. "Transition to turbulence in the asymptotic suction boundary layer." Licentiate thesis, KTH, Stabilitet, Transition, Kontroll, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-141344.
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The focus of this thesis is on the numerical study of subcritical transition to turbulence in the asymptotic suction boundary layer (ASBL). Applying constant homogeneous suction prevents the spatial growth of the boundary layer, granting access to the asymptotic dynamics. This enables research approaches which are not feasible in the spatially growing case. In a first part, the laminar–turbulent separatrix of the ASBL is investigated numerically by means of an edge-tracking algorithm. The consideration of spanwise-extended domains allows for the robust localisation of the attracting flow structures on this separatrix. The active part of the identified edge states consists of a pair of low- and high-speed streaks, which experience calm phases followed by high energy bursts. During these bursts the structure is destroyed and re-created with a shift in the spanwise direction. Depending on the streamwise extent of the domain, these shifts are either regular in direction and distance, and periodic in time, or irregular in space and erratic in time. In all cases, the same clear regeneration mechanism of streaks and vor- tices is identified, bearing strong similarities with the classical self-sustaining cycle in near-wall turbulence. Bifurcations from periodic to chaotic regimes are studied by varying the streamwise length of the (periodic) domain. The resulting bifurcation diagram contains a number of phenomena, e.g. multistability, intermittency and period doubling, usually investigated in the context of low-dimensional systems. The second part is concerned with spatio–temporal aspects of turbulent ASBL in large domains near the onset of sustained turbulence. Adiabatically decreasing the Reynolds number, starting from a fully turbulent state, we study low-Re turbulence and events leading to laminarisation. Furthermore, a robust quantitative estimate for the lowest Reynolds number at which turbulence is sustained is obtained at Re QC 20140213
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MOCERINO, LUCA. "Hardware-Aware Cross-Layer Optimizations of Deep Neural Networks for Embedded Systems." Doctoral thesis, Politecnico di Torino, 2022. http://hdl.handle.net/11583/2972558.
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Gracias, William Agnelo. "The numerical study of filament dynamics in tokamak scrape-off layer plasmas." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0731.
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La présence de structures filamentaires est souvent rapportée dans plusieurs machines de fusion nucléaire à confinement magnétique, spécialement sur lequel s'appelle Tokamak. Etant porteurs de grandes quantités des particules et chaleur, la présence des filaments dans le bord du tokamak (le scrape-off layer, SOL) pourraient poser des dangers aux superficies solides du tokamak. Pour mieux comprendre leur comportement, dans le cadre de cette thèse doctorale, les filaments sont étudiés par les expériences numériques en utilisant un modèle 3D fluide istherme, TOKAM3X en les considerant comme structures isolées et structures spontanées. Cette manière de les étudier permet de faire divers analyses paramétriques – par exemple la resistivité parallèle du plasma et la présence d'un cisaïllement magnétique, et au même temps les propriétés du filaments (comme sa longeur parallèle, et son intensité de densité). Ces études montrent un impact fort de la resistivité parallèle sur la velocité des filaments et en conséquence peut modifier leur temps de vie dans le bord de la machine. Les résultats des simulations sur le cisaïllement magnétique et la séparatrice indiquent qu'ils sont des ingrédients clés pour la destruction et génération des filaments. En plus, la comparaison entre les filaments initialisés (seeded) et les filaments formés spontanément montre qu'ils ne sont pas parreils dans leur comportement, bien que leurs characteristiques moyennées en temps sont bien conservéesFilamentary transport has been experimentally observed in a multitude of magnetically confined fusion devices, especially of the tokamak type. Filaments are carriers of large quantities of particles and heat and as such, their presence in the SOL has implications for the target surface design in future fusion reactors. To better understand their nature, this doctoral thesis studies filaments through computer simulations as isolated structures and spontaneously forming structures, using a 3D fluid model called the TOKAM3X. Parametric studies using the model for studying the effect of the plasma's parallel resistivity and magnetic shear, and also the filament's parallel extension and size/density amplitude are performed and analysed. The studies reveal the strong impact of the parallel resistivity on filament velocities and hence their lifetimes in the SOL. The doctoral work also looked at the impact of strong local magnetic shear and the separatrix on the motion and generation of filaments. The results from the simulations performed reveal that strong shear mechanisms may be key to the destruction and formation of filaments. Further, a comparison of spontaneously forming and seeded filaments shows that seeded filaments do not behave completely the same way as spontaneously forming ones. But their mean velocity characteristics are still retained to a good degree
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Carter, Casey Joseph. "Aerodynamic Performance of a Flow Controlled Compressor Stator Using an Imbedded Ejector Pump." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/31297.
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A high-turning compressor stator with a unique flow control design was developed and tested. Both boundary layer suction and trailing edge blowing developed from a single supplied motive pressure source are employed on the stator. Massflow removed through boundary layer suction is added to the motive massflow, and the resulting combined flow is used for trailing edge blowing to reduce the total pressure deficit generated by the stator wake. The effectiveness of the flow control design was investigated experimentally by measuring the reduction in the total pressure loss coefficient. The experiment was conducted in a linear transonic blowdown cascade wind tunnel. The inlet Mach number for all tests was 0.79, with a Reynolds number based on stator chordlength of 2,000,000. A range of inlet cascade angles was tested to identify the useful range of the flow control design. The effect of different supply massflows represented as a percentage of the passage throughflow was also documented. Significant reductions in the total pressure loss coefficient were accomplished with flow control at low cascade angles. A maximum reduction of 65% in the baseline (no flow control) loss coefficient was achieved by using a motive massflow of 1.6% of the passage throughflow, at cascade angle of 0°. The corresponding suction and blowing massflow ratio was approximately 1:3.6. Cascade angle results near 0° showed significant reductions in the loss coefficient, while increases in the cascade angle diminished the effects of flow control. Considerable suction side separation and the presence of a leading edge shock are noticeable as the cascade angle is increased, and contribute to the losses across the stator surface. Also identified was the estimated increase in wake turning due to flow control of up to 4.5°.Master of Science
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Maltoni, Pietro. "Progetto di un acceleratore hardware per layer di convoluzioni depthwise in applicazioni di Deep Neural Network." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24205/.
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Il progressivo sviluppo tecnologico e il costante monitoraggio, controllo e analisi della realtà circostante ha condotto allo sviluppo di dispositivi IoT sempre più performanti, per questo si è iniziato a parlare di Edge Computing. In questi dispositivi sono presenti le risorse per elaborare i dati dai sensori direttamente in locale. Questa tecnologia si adatta bene alle CNN, reti neurali per l'analisi e il riconoscimento di immagini. Le Separable Convolution rappresentano una nuova frontiera perchè permettono di diminuire in modo massiccio la quantità di operazioni da eseguire su tensori di dati dividendo la convoluzione in due parti: una Depthwise e una Pointwise. Tutto questo porta a risultati molto affidabili in termini di accuratezza e velocità ma è sempre centrale il problema legato al consumo di potenza in quanto i dispositivi si affidano solamente ad una batteria interna. Per questo è necessario avere un buon trade-off tra consumi e capacità computazionale. Per rispondere a questa sfida tecnologica lo stato dell'arte in questo ambito propone soluzioni diverse, composte da cluster con core ottimizzati e istruzioni dedicate o FPGA. In questa tesi proponiamo un acceleratore hardware sviluppato in PULP orientato al calcolo di layer di convoluzioni Depthwise. Grazie ad una logica HWC dei dati in memoria e al Window Buffer, una finestra che trasla sull'immagine per effettuare le convoluzioni canale per canale è stato possibile sviluppare una architettura del datapath orientata al riuso dei dati; questo porta l’acceleratore ad avere come risultato in uscita uno throughput massimo di 4 pixel per ciclo di clock. Con le performance di 6 GOP/s, un' efficienza energetica di 101 GOP/j e un consumo di potenza nell'ordine dei mW, dati ottenuti attraverso l'integrazione dell'IP all'interno del cluster di Darkside, nuovo chip di ricerca con tecnologia TSCM a 65 nm, l'acceleratore Depthwise si candida ad essere una soluzione ideale per questo tipo di applicazioni.
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Vandeputte, Thomas William. "Effects of Flow Control on the Aerodynamics of a Tandem Inlet Guide Vane." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/31011.
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An aerodynamic investigation was performed to assess the effectiveness of combined boundary layer suction and trailing edge blowing at reducing the blade profile losses and the wake momentum deficit of a cascade of tandem IGVâ s operating at realistic flow conditions. Two trailing edge blowing designs were tested: metal-angle blowing, which oriented the blowing jets very near to the blade exit angle, and deviation-angle blowing, which oriented the blowing jets at a significant deviation angle from the blade exit angle. Both blowing designs used the same boundary layer suction arrangement. A linear cascade of five IGVâ s was tested with a flap deflection angle of 40 degrees and an inlet Mach number of 0.3. The Reynolds number based on the overall IGV chord length for these experiments was greater than 500,000. The inlet and exit angles of the IGV at this flap setting were 0 degrees and 55 degrees, respectively. Tests performed with no flow control showed significant suction surface flow separation that generated large wakes with high losses and large momentum deficits. The application of boundary layer suction reduced the baseline pressure loss coefficient and wake momentum thickness by 22%. A suction mass flow of 0.4% of the passage flow was used to obtain these results. The addition of metal-angle blowing with the suction resulted in total reductions of 48% and 38% for the pressure loss coefficient and wake momentum thickness. A blowing mass flow of 3.1% of the passage flow was used in addition to 0.4% suction mass flow to obtain these results. The application of the deviation-angle blowing was detrimental to the aerodynamics of the IGV, as both the pressure loss coefficient and wake momentum thickness increased slightly over their suction-only values. This was attributed to a manufacturing defect which distorted the flow of the blowing jet. The results of the deviation-angle blowing experiments were not considered representative of the design intent and reinforced the importance of the hole design for creating a proper blowing jet. While low speed tests of this cascade showed results and trends very similar to those of previous research, the application of flow control proved to be less effective at higher speeds due to the generation of significantly larger wakes.Master of Science
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Schrader, Lars-Uve. "Receptivity of Boundary-Layer Flows over Flat and Curved Walls." Doctoral thesis, KTH, Stabilitet, Transition, Kontroll, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-25439.
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Direct numerical simulations of the receptivity and instability of boundary layers on flat and curved surfaces are herein reported. Various flow models are considered with the aim to capture aspects of flows over straight and swept wings such as wall curvature, pressure variations, leading-edge effects, streamline curvature and crossflow. The first model problem presented, the flow over a swept flat plate, features a crossflow inside the boundary layer. The layer is unstable to steady and traveling crossflow vortices which are nearly aligned with the free stream. Wall roughness and free-stream vortical modes efficiently excite these crossflow modes, and the associated receptivity mechanisms are linear in an environment of low-amplitude perturbations. Receptivity coefficients for roughness elements with various length scales and for free-stream vortical modes with different wavenumbers and frequencies are reported. Key to the receptivity to free-stream vorticity is the upstream excitation of streamwise streaks evolving into crossflow modes. This mechanism is also active in the presence of free-stream turbulence. The second flow model is that of a Görtler boundary layer. This flow type forms on surfaces with concave curvature, e.g. the lower side of a turbine blade. The dominant instability, driven by a vertically varying centrifugal force, appears as pairs of steady, streamwise counter-rotating vortical rolls and streamwise streaks. The Görtler boundary layer is in particular receptive to free-stream vortical modes with zero and low frequencies. The associated mechanism builds on the excitation of upstream disturbance streaks from which the Görtler modes emerge, similar to the mechanism in swept-plate flows. The receptivity to free-stream vorticity can both be linear and nonlinear. In the presence of free-stream turbulence, nonlinear receptivity is more likely to trigger steady Görtler vortices than linear receptivity unless the frequencies of the free-stream fluctuations are very low. The third set of simulations considers the boundary layer on a flat plate with an elliptic leading edge. This study aims to identify the effect of the leading edge on the boundary-layer receptivity to impinging free-stream vortical modes. Three types of modes with streamwise, vertical and spanwise vorticity are considered. The two former types trigger streamwise disturbance streaks while the latter type excites Tollmien-Schlichting wave packets in the shear layer. Simulations with two leading edges of different bluntness demonstrate that the leading-edge shape hardly influences the receptivity to streamwise vortices, whereas it significantly enhances the receptivity to vertical and spanwise vortices. It is shown that the receptivity mechanism to vertical free-stream vorticity involves vortex stretching and tilting - physical processes which are clearly enhanced by blunt leading edges. The last flow configuration studied models an infinite wing at 45 degrees sweep. This model is the least idealized with respect to applications in aerospace engineering. The set-up mimics the wind-tunnel experiments carried out by Saric and coworkers at the Arizona State University in the 1990s. The numerical method is verified by simulating the excitation of steady crossflow vortices through micron-sized roughness as realized in the experiments. Moreover, the receptivity to free-stream vortical disturbances is investigated and it is shown that the boundary layer is most receptive, if the free-stream modes are closely aligned with the most unstable crossflow modeQC 20101025
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Hussain, S. "A study of the interaction between a glancing shock wave and a turbulent boundary layer : the effects of leading edge bluntness and sweep." Thesis, Cranfield University, 1985. http://dspace.lib.cranfield.ac.uk/handle/1826/10712.
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The effects of leading edge bluntness and sweep angle on the three
dimensional glancing shock wave - boundary layer interaction have been
investigated. A large number of hemi-cylindrically blunted fins with
leading edge diameter ranging from 0 to l.Oin, with leading
edge sweep angles between 0° and 75° were tested. The incidence
angle was varied from 0° to 21°. The shock wave from each configuration
interacted with a fully developed turbulent boundary layer growing along
the tunnel side wall. The free stream Mach number in the 9in x 9in
continuous flow supersonic wind tunnel was 2.4 and the Reynolds number
based on boundary layer thickness was 5 x 10^. Experimental investigations
included oil smear tests, surface pressure surveys, schlieren pictures
of the inviscid shock envelopes and shock structure in the plane of
symmetry.
The study highlighted the significant effects of bluntness and sweep
on the scale and character of the interaction. While bluntness intensified
the interaction, sweep alleviated its intensity. The most dramatic effect
of sweep angle was observed when the leading edge was swept from 0° to 30°.
Sufficiently outboard of the plane of symmetry, the features of blunt
and sharp fins became similar. The boundary between the inner "bluntness
dominated" and the outer "viscous dominated" regions shifted inboard
at the higher incidence and sweep angles.
The characteristic surface oil flow patterns showed little change for
sweep angles up to A = 60°. Leading edge bluntness increased the scale of
the interaction almost linearly while leaving its character unchanged.
The multiplicity of the separation and attachment lines on the side wall
and the fin surface, suggested a system of vortices in the interaction
region. Flow field models have been proposed over the range of sweep
angles considered in the present study. The number and strength of the
vortices is seen to depend on the leading edge bluntness, sweep
and the incidence angle.
The important parameters governing the primary separation distance
and the peak pressure in the plane of symmetry have been identified.
Correlation formulae suggest a strong interdependence of the various
parameters concerned.
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Gleissner, Filip. "Koexistence mobilních komunikačních systémů GSM-EDGE a UMTS." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-233470.
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The dissertation thesis deals with the investigation of the coexistence of GSM–EDGE and UMTS systems with focus on the physical layer of the systems. The aim is to provide a set of recommendations for practical cooperation while the systems operate in both the separated and the common radio bands. A detailed description of signal processing of both the systems on the physical layer is presented. On the basis of this description, models of both systems were created and implemented in the MATLAB environment. The simulations are focused on the physical layer quality parameters, especially the bit error ratio evaluation for various ratios of useful signal power to noise power during the transmission over the radio channel. Simulation is also used to examine the quality of received useful signal while it is interfered by signals from the same and adjacent channels. The purpose is to determine the isolation between these adjacent channels, when the bit error ratio of the useful signal does not exceed a certain reference value. The simulation results are subsequently subjected to comparison with the results of the experimental measurements in laboratory conditions. Before the measurements are carried out, a study of possible interference types is performed. Consequently, the crucial parameters of the measuring equipment used are verified. From the results of simulations and measurements, the proposal of a minimum and recommended carrier separation between both the systems is presented in order to efficiently utilize the assigned frequency spectrum. Furthermore, for the cooperation in both the separated and the common radio bands, the necessary precautions are given for reaching the required isolation and thereby inter-system interference minimization.
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Schumann, Matthew Thomas. "The effect of ion-orbit-loss on the distribution of ion, energy and momentum from the edge plasma into the scrape-off layer in tokamaks." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53519.
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Some of the outflowing ions in the plasma edge have sufficient energy to access orbits which allow them to free-stream out of the confined plasma region and be lost to the wall or divertor. The effects of this ion-orbit-loss (IOL) on the poloidal distribution of ion, energy and momentum fluxes from the plasma edge into the tokamak scrape-off layer (SOL) are analyzed for a representative DIII-D H-mode discharge. IOL yields large fluxes of particle, energy and momentum, distributed poloidally over the SOL, but predominantly into the outboard SOL, significantly changing the fluxes due to transport processes for confined ions within the edge plasma. An intrinsic co-current rotation in the edge of the plasma is produced by the preferential loss of counter-current ions
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Gunasekaran, Sidaard. "Relationship Between the Free Shear Layer, the Wingtip Vortex and Aerodynamic Efficiency." University of Dayton / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1470231642.
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Palombo, Carlo Loris. "Development and validation of an improved wall-function boundary condition for computational aerodynamics." Thesis, KTH, Strömningsmekanik och Teknisk Akustik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293754.
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Computational Fluid Dynamics is a powerful and widely used tool for developing projectsthat concern flow motion, in very different fields. Industrial CFD solvers are continuouslydeveloped with the aim of improving accuracy and reducing the computational cost of thesimulations. Turbulent wall-flow cases are particular demanding as the presence of a solidsurfaceinterface generates steep gradients in the proximity of the wall. Resolving suchgradients can be crucial to obtain a consistent solution but also very expensive in terms ofgrid refinement, and hence computational time. Wall functions are widely used and offersignificant computational savings when it comes to near-wall flow resolution. Previous wallfunction implemented in the M-Edge solver suffered by poor performances in complex flowscharacterized by strong pressure-gradient phenomena, such as separation. A new formulationhas been developed and validated for k − omega and Spalart-Allmaras turbulence models. Testsimulations started from simple and near-ideal cases (2D zero pressure gradient flat plate)and advanced to always more complex flow cases and geometries (full 3D general fighter).Every case has been run coupling the wall-function boundary condition with three differentturbulence models: the Menter SST, the Menter BSL with an EARSM and the Spalart-Allmaras one-equation model. Overall results showed the upgraded performance of new wallfunction in flow resolution together with more agile grid requirements, faster and deeperconvergence of the residuals and a general reduction in computational time.Berör strömmande fluider inom mycket olika områden. Industriella CFD-lösare utvecklaskontinuerligt i syfte att förbättra noggrannheten och minska beräkningskostnaderna försimuleringarna. Turbulent strömning nära väggar är särskilt krävande eftersom närvaron avett fast ytgränssnitt genererar stora gradienter i närheten av väggen. Att lösa upp sådanagradienter kan vara avgörande för att få en konsistent lösning men också mycket beräkningskrävandepå grund av nödvändig nätförfining.Väggfunktioner används ofta och ger betydandereduktioner i beräkningstid när det gäller att lösa upp strömningen nära vägg. En tidigareväggfunktion implementerad i M-Edge-lösaren led av dåliga prestanda i komplexa flödenmed starka tryckgradienter, såsom separation. En ny formulering har utvecklats och valideratsför k − omega och Spalart-Allmaras turbulensmodeller. Den har testats för enkla generiska fall(2D-plan platta utan tryckgradient) och för mer avancerade och komplexa strömningsfall ochgeometrier (komplett 3D-stridsflygplan).Varje fall har körts med väggfunktionens randvillkorkopplat med tre olika turbulensmodeller: Menter SST, Menter BSL med EARSM och Spalart-Allmaras enekvationsmodell. De övergripande resultaten visar att nya väggfunktionen gerbetydande förbättringar i att beskriva strömningen tillsammans med reducerade krav pånätupplösning, snabbare och djupare konvergens av lösningen och en allmän minskning avberäkningstiden.
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Staša, Josef. "Texturní analýza snímků sítnice se zaměřením na směrovost vrstvy nervových vláken." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219648.
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Hlavním cílem této diplomové práce byla texturní analýzou fundus snímku se zaměřením na směrovost vrstvy nervových vláken. Úvodní část popisuje fyziologii lidského oka a glaukomové onemocnění. Jedná se tedy o literární rešerši. Hlavní část této práce je pak zaměřena na metody texturní analýzy za účelem zobrazení směrovosti nervových vláken. Metody byly realizovány a otestovány v programovém prostředí Matlab R2009b.
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Sinha, Priyanjana [Verfasser], Thomas Sunn [Akademischer Betreuer] Pedersen, Thomas Sunn [Gutachter] Pedersen, and Bruce [Gutachter] Lipschultz. "Edge and scrape-off layer physics modeling for Wendelstein 7-X in preparation of the operation phases OP1.2 and OP2 / Priyanjana Sinha ; Gutachter: Thomas Sunn Pedersen, Bruce Lipschultz ; Betreuer: Thomas Sunn Pedersen." Greifswald : Universität Greifswald, 2020. http://d-nb.info/1213447569/34.
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Sommer, Oliver. "Ein Beitrag zur Untersuchung des Verhaltens dünner Flüssigkeitsfilme nahe gekrümmten Substratoberflächen." Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-154946.
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In der vorliegenden Arbeit wurde das Verhalten dünner Flüssigkeitsfilme an gekrümmten Substratoberflächen durch experimentelle Beschichtungsversuche basierend auf der non-invasiven laserinduzierten Fluoreszenzmesstechnik und durch numerische Filmsimulationen mit Hilfe des Volume-of-Fluid Mehrphasenmodells untersucht. Besonderes Interesse galt dabei dem Finden optimaler Einflussgrößenkombinationen zur Reduzierung des Fettkanten-Effekts. In der hierfür durchgeführten Parameterstudie wurden sowohl Applikationsparameter wie der Kantenrundungsradius und die Applikationsschichtdicke als auch Stoffparameter der untersuchten Flüssigkeit wie die Viskosität und die Oberflächenspannung variiert. Neben qualitativen Beschreibungen der entstandenen Fettkantengestalten sind als Resultate auch Größen zur Quantifizierung der Fettkanten festgelegt worden und systematisch dargestellt. Es konnte nachgewiesen werden, dass ungünstige und geeignete Parameterkonfigurationen existieren, welche prägnante bzw. kaum auffällige Fettkanten erzeugen, insbesondere im Experiment. Über die dabei eingreifenden Mechanismen der zugrundeliegenden Strömungen wurden konkrete Hypothesen aufgestellt, auch um die resultierenden Proportionalitäten der Fettkantengrößen bezüglich der Einflussgrößen zu plausibilisieren. Weiterhin konnte eine Aussage über die Signifikanz der untersuchten Einflussgrößen getroffen werden. Abschließend wurde eine geeignete dimensionslose Kenngröße generiert, um den Fettkanten-Effekt parameterübergreifend beschreiben zu können, wodurch mittels der Ähnlichkeitstheorie auch eine gewisse Abschätzung des Fettkanten-Effekts ermöglicht wirdIn this study the behaviour of a thin liquid layer at a curved solid edge was examined by experimental coating investigations based on the laser-induced fluorescence technique and by numerical film simulations based on the Volume-of-Fluid multiphase flow model, respectively. The main motivation was to find optimal combinations of influencing quantities to reduce the fat-edge effect. Therefore a study of these quantities was performed, in which application parameters like edge radii of curvature and application layer thicknesses as well as determining liquid properties like viscosity and surface tension have been varied. Results are described qualitatively at corresponding fat-edge shapes and quantified by suitable fat-edge parameters, which had to be identified and selected. It could be shown that adverse and appropriate influencing parameter combinations exist, which generate conspicuous and less distinctive fat-edges, respectively - especially in laboratory experiments. The experimental findings and proportionalities regarding fat-edge shapes and dimensions are found to be physically plausible. Furthermore an order of significance of the influencing quantities established. Eventually, a dimensionless quantity was derived by dimensional analysis, which describes the fat-edge effect. Thus, the fat-edge effect has also been described by the application of similarity theory and the corresponding dimenionless number, respectively
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Thomas, Daniel. "Réalisation de transistors à un électron par encapsulation d’îlots nanométriques de platine dans une matrice diélectrique en utilisant un procédé ALD." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI131/document.
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L'introduction du transistor à un électron (SET) a secoué l'industrie des semi-conducteurs, avec des promesses d'efficacité inégalée. Cependant, le coût et la complexité associés à la réalisation d'un fonctionnement stable ont fortement entravé leur adoption. Après être tombé en dehors des grâces de l'industrie, la recherche universitaire a continué à pousser, démontrant des techniques novatrices pour la création de SET. Au cœur de ce problème de stabilité, il y a le besoin de construire de manière contrôlable des nanoislands de moins de 10 nm. Parmi les méthodes disponibles pour cette formation nanoisland, le dépôt de couche atomique (ALD) se distingue comme un processus hautement contrôlable industriellement. La deuxième barrière à l'entrée est la création d'électrodes nanogap, utilisées pour injecter du courant à travers ces nanoislands, pour lesquelles les chercheurs se sont largement appuyés sur des techniques de fabrication non évolutives comme la lithographie par faisceau d'électrons et le faisceau ionique focalisé. La technique d'évaporation de bord d'ombre surmonte les problèmes de complexité et d'échelle de la fabrication de nanogap, ouvrant de nouvelles possibilités. Dans ce travail, ALD sera démontré comme une superbe technique pour la culture de vastes réseaux 3D de nanoparticules de platine sous 2nm encapsulées dans Al2O3. ALD a fourni un moyen de faire croître ces matrices de nanoparticules en un seul processus, sous vide et à basse température. Grâce à l'évaporation du bord d'ombre, la lithographie UV a ensuite été utilisée pour former des électrodes nanogap avec des largeurs latérales élevées (100μm), avec des écarts démontrés au-dessous de 7 nm. La combinaison de ces techniques aboutit à un procédé de fabrication à haut rendement et à faible besoin pour la construction de SET complets. A partir des transistors résultants, de fines lamelles ont été préparées à l'aide de FIB et des modèles 3D ont été reconstruits par tomographie TEM pour analyse. La caractérisation électrique a été effectuée jusqu'à 77K, avec une modélisation révélant le transport de Poole-Frenkel en parallèle à un éventuel cotunneling. Des blocus de Coulomb stables, la signature des SET, ont été observés avec une périodicité régulière et étaient identifiables jusqu'à 170K. L'optimisation de ce processus pourrait produire des SETs de surface élevée capables de fonctionner de manière stable à température ambianteThe introduction of the single electron transistor (SET) shook the semiconductor industry, with promises of unrivaled efficiency. However, the cost and complexity associated with achieving stable operation have heavily hindered their adoption. Having fallen out of the graces of industry, academic research has continued to push, demonstrating novel techniques for SET creation. At the core of this stability issue is a need to controllably build nanoislands smaller than 10nm. Among the methods available for this nanoisland formation, atomic layer deposition (ALD) sets itself apart as an industrially scalable, highly controllable process. The second barrier to entry is the creation of nanogap electrodes, used to inject current through these nanoislands, for which researchers have leaned heavily on non-scalable fabrication techniques such as electron beam lithography and focused ion beam. The shadow edge evaporation technique overcomes the complexity and scaling issues of nanogap fabrication, opening new possibilities. In this work, ALD will be demonstrated as a superb technique for growing vast 3D arrays of sub 2nm platinum nanoparticles encapsulated in Al2O3. ALD provided a means of growing these nanoparticle matrices in a single process, under vacuum, and at low temperatures. Through shadow edge evaporation, UV lithography was then utilized to form nanogap electrodes with high lateral widths (100µm), with gaps demonstrated below 7nm. The combination of these techniques results in a high yield, low requirement fabrication process for building full SETs. From the resulting transistors, thin lamellas were prepared using FIB and 3D models were reconstructed via TEM tomography for analysis. Electrical characterization was performed down to 77K, with modeling revealing Poole-Frenkel transport alongside possible cotunneling. Stable Coulomb blockades, the signature of SETs, were observed with regular periodicity and were identifiable up to 170K. Optimization of this process could yield high surface area SETs capable of stable operation at room temperature
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Leaman, Nye Abigail. "Scattering of internal gravity waves." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/238679.
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Internal gravity waves play a fundamental role in the dynamics of stably stratified regions of the atmosphere and ocean. In addition to the radiation of momentum and energy remote from generation sites, internal waves drive vertical transport of heat and mass through the ocean by wave breaking and the mixing subsequently produced. Identifying regions where internal gravity waves contribute to ocean mixing and quantifying this mixing are therefore important for accurate climate and weather predictions. Field studies report significantly enhanced measurements of turbulence near 'rough' ocean topography compared with those recorded in the ocean interior or near more gradually varying topography (e.g. Toole et al. 1997, J. Geophys. Res. 102). Such observations suggest that interaction of waves with rough topography may act to skew wave energy spectra to high wavenumbers and hence promote wave breaking and fluid mixing. This thesis examines the high wavenumber scatter and spatial partitioning of wave energy at 'rough' topography containing features that are of similar scales to those characterising incident waves. The research presented here includes laboratory experiments using synthetic schlieren and PIV to visualise two-dimensional wavefields produced by small amplitude oscillations of cylinders within linear salt-water stratifications. Interactions of wavefields with planar slopes and smoothly varying sinusoidal topography are compared with those with square-wave, sawtooth and pseudo knife-edge profiles, which have discontinuous slopes. Far-field structures of scattered wavefields are compared with linear analytical models. Scatter to high wavenumbers is found to be controlled predominantly by the relative slopes and characterising length scales of the incident wavefield and topography, as well as the shape and aspect ratio of the topographic profile. Wave energy becomes highly focused and the spectra skewed to higher wavenumbers by 'critical' regions, where the topographic slope is comparable with the slope of the incident wave energy vector, and at sharp corners, where topographic slope is not defined. Contrary to linear geometric ray tracing predictions (Longuet-Higgins 1969, J. Fluid Mech. 37), a significant back-scattered field can be achieved in near-critical conditions as well as a forward scattered wavefield in supercritical conditions, where the slope of the boundary is steeper than that of the incident wave. Results suggest that interaction with rough benthic topography could efficiently convert wave energy to higher wavenumbers and promote fluid mixing in such ocean regions.
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Sugita, Satoru. "Etude par simulation numérique du transport radial dans le plasma de bord du tokamak." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10010/document.
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Il est maintenant accepté expérimentalement que les filaments de plasma alignés sur le champ magnétique, appelés “blobs”, jouent un rôle important dans le transport dans le plasma de bord. Dans cette thèse, les phénomènes fondamentaux du transport dans le plasma de bord sont étudiés en mettant l'accent sur le phénomène de filaments plasma. Dans un premier temps, les mécanismes de propagation de blobs uniques sont envisagés. Puis la génération de blobs par la turbulence de bord est étudiée, et le transport turbulent est discuté entant que phénomène collectif. Des particularités du transport turbulent, incluant les blobs auto-organisés, sont reliées à un transport de type Bohm (c'est à dire des perturbations avec des corrélations radiales longues, et un coefficient de transport effectif quisuit la dépendance Bohm). De plus, en prolongement de ce travail, un effort initial vers une transposition du transport non-local au plasmade bord est décriteRecently, it has been accepted that magnetic field aligned plasma filaments, referred to as "blobs" play important roles in the transport of Scrape-off Layer (SoL) plasmas. In this thesis, putting an emphasis on the plasma blob phenomenon, we study fundamental processes of SoL transport using numerical simulation. At first, weinvestigate the propagation mechanisms of single and isolated blobs.Next, we study the generation of blobs from edge turbulence, and discuss the SoL turbulent transport as a collective phenomenon. Features of turbulent transport, which includes the self-organized blobs in SoL, are identified as Bohm-like transport (i.e., the perturbation with long radial correlations and the effective transport coefficient that follows the dependence of Bohm-like transport). Additionally, as an advancement of study, we describe an initial effort to extend the view of non local transport to edge plasmas
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Schrader, Lars-Uve. "Receptivity of Boundary Layers under Pressure Gradient." Licentiate thesis, Stockholm : Mekanik, Kungliga Tekniska högskolan, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9379.
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Amin-Nejad, Siavash. "Automatic edge trimming of fabric embroideries by laser." Thesis, University of Liverpool, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399288.
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McLaren-Jones, Jennifer Sian Elizabeth. "Band edge lasing in chiral nematic liquid crystals." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288382.
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For the last 20 years, there has been considerable interest in chiral nematic liquid crystal band edge lasers. The birefringent molecules of chiral nematic liquid crystals form a periodic helical structure, which results in a photonic bandgap for circularly polarised light with the same sense of rotation as the helix. A large increase in effective gain is seen for a fluorescent gain medium within the liquid crystal at the band edges, resulting in lasing. Applications of liquid crystal lasers could include miniature medical diagnostic tools, large-area holographic laser displays, and environmental sensing. The wavelength of emission from dye-doped chiral nematic liquid crystals is highly flexible, with lasers demonstrated across the visible range and near infra-red. This thesis investigates two routes for improving the functionality of chiral nematic liquid crystal lasers, supported by mathematical modelling of expected lasing wavelengths based on reflection and transmission by anisotropic layers. Perovskite is tested as a replacement for fluorescent laser dyes as a gain medium,both in the form of quantum dots dispersed in liquid crystal, and as films placed in liquid crystal structures. It is shown that while the perovskite tested provides some emission, it is not compatible for lasing in these devices, and suggestions for building on these results are made. In-plane switching is tested and developed as a means to achieve tuning of the laser wavelength, demonstrating a continuous wavelength shift of 15 nm, from 600.71 nm to 585.03 nm, over a voltage range of 100 V. This is an improvement on previous tuning in related devices, and may be extended with optimisation of cell thickness,electrode geometry, and initial lasing wavelength. Accurate descriptions of the refractive index profile of the liquid crystal and perovskite are developed and included in mathematical modelling, in addition to descriptions of the wavelength-dependent gain of a laser dye and perovskite. Suggestions for developing this modelling are made, particularly by the inclusion of accurate modelling of the distortion caused by in-plane switching.
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Poette, Christopher. "La fragmentation du paysage : impact sur l'écoulement atmosphérique et la stabilité au vent des peuplements forestiers." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0387/document.
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A l’heure actuelle, seuls des facteurs locaux, stationnels, sont considérés pour le calcul des risques liés au vent alors que le vent qui aborde un peuplement forestier est affecté par les surfaces sur lesquelles il vient de passer ; les lisières en particulier jouent un rôle important sur l’écoulement atmosphérique, en contribuant à générer de la turbulence. Dans un paysage fragmenté, constitué d’une mosaïque de surfaces de différentes hauteurs et rugosités, la multiplicité des lisières est ainsi susceptible d’avoir des effets cumulatifs perceptibles à l’échelle régionale, qui pourraient contribuer de manière significative à la fragilité des massifs face à des tempêtes. Certains niveaux de fragmentation semblent susceptibles de conduire à un accroissement des risques en cas de vent violent. Bien que la région de lisière a été étudiée de manière approfondie dans le passé en raison de leur importance pour la détermination des vitesses de vent, des niveaux de turbulence et des échanges entre l’atmosphère et la canopée, il n’y a aucune étude de l’impact de lisières multiples ou de la fragmentation des forêts sur les caractéristiques de la couche limite à l’échelle du paysage. Quelques rares études laissent penser que la fragmentation du paysage pourrait moduler de manière significative la structure turbulente de la couche limite atmosphérique mais ces études concernent des réseaux de brisevents plutôt qu’un ensemble de parcelles forestières. On cherche par conséquent à caractériser les champs de vent et de turbulence pour ces différentes configurations. Pour ce faire, une expérimentation en soufflerie à été réalisée, visant à caractériser l’écoulement sur des maquettes de paysage présentant cinq degrés de fragmentation (L = ~ 5, ~ 10, ~15, ~20, ~30h, où L est la distance entre deux patchs de forêts régulièrement espacés et h est la hauteur de la canopée). Un cas homogène a également été simulé et sert ici de référence. Pour le modèle de canopée choisi, ces expérimentations montrent que l’énergie cinétique turbulente présente dans la basse atmosphère ne passe pas par un maximum pour une valeur de l’espacement intermédiaire comme il était supposé à l’origine. Le cas homogène est la configuration la plus rugueuse. Pour de grands espacements l’influence d’une parcelle ne se fait guère sentir sur la suivante et lorsqu’ils sont faibles l’écoulement ne "ressent" guère les clairières et présente des caractéristiques semblables au cas homogène. Nous avons également évalué un modèle atmosphérique de type "simulation des grandes échelles" à l’aide des données présentées précédemment. Le modèle est capable de reproduire les grandes caractéristiques de la turbulence telles que les vitesses de vent horizontales et verticales, l’énergie cinétique turbulente, les contraintes de Reynolds et les coefficients d’asymétrie horizontale et verticale en tous points du domaine. Cela nous a permis de confirmer la validité des calculs numériques et de simuler l’écoulement sur une plus large gamme de paysages fragmentés. Les résultats démontrent l’importance de l’indice foliaire pour le calcul de la rugosité effective sur une succession de patchs de forêtAt present only the characteristics of a forest stand and its immediate environment are taken into account in calculating forest wind risk. However, it is known that the wind is strongly affected by the surfaces over which it has previously flowed. Forest edges in particular play an important role in determining the characteristics of the atmospheric flow by generating increased turbulence, triggering the formation of coherent tree scale structures. In a fragmented landscape, consisting of surfaces of different heights and roughness, the multiplicity of edges may have cumulative effects at the regional scale leading to increased forest damage during storms. Flow changes in the atmospheric boundary-layer across surface roughness changes have received extensive study in the past because of their importance in determining velocities, turbulence levels and exchange between the atmosphere and biosphere or ground. There have also been a number of studies across single forest edges both in the field, wind-tunnels and computer models. However, there have been no studies of flow across multiple forest edges or the impact of forest fragmentation on the characteristics of the boundary-layer. The only studies on multiple surface changes have been wind-tunnel examination of the flow though and across multiple wind-breaks. In this thesis we show results from a series of wind tunnel experiments on a range of levels of forest fragmentation. Five gap spacings (L = ~ 5, ~ 10, ~15, ~20, ~30h, where L is the length of the gap and h is the canopy height) were investigated using 3D laser doppler velocimetry in order to assess the effects of fragmented landscapes on mean and turbulent wind characteristics. The fragmentation was two-dimensional with the transition between forest and gaps only being along the wind direction and the forest and gaps were continuous perpendicular to the wind direction. The wind speeds and turbulence characteristics are compared against measurements from a single forest edge in the wind tunnel, which acts as a reference. No enhancement of turbulence formation at a particular level of fragmentation was observed but there was a consistent pattern of wind speed and turbulence back from the first edge of each simulation with the horizontal velocity at tree top increasing and the turbulent kinetic energy decreasing as gap size increased. We also compare mean wind speeds (U and W) and turbulence characteristics (variance in u, v, and w; skewness in U, V, and W; Reynold’s stress, and TKE) at all points in the experimental measurement domain of the wind tunnel with Large Eddy Simulation (LES) results, which allows us to confirm the validity of the LES calculations and to conduct a wider range of experiments than was possible in the wind-tunnel. The results demonstrate the importance of the frontal area index or roughness density of elements (in this case trees) in determining the nature of the flow and the effective roughness of the overall surface. They also show that as the gaps between forest blocks increases the flow transitions (at a gap size between 10 to 15 tree heights) from flow comparable to that over a continuous forest to flow across a set of isolated forest blocks
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Pokric, Boris. "Laser based machine vision for three-dimensional surface analysis." Thesis, Leeds Beckett University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297358.
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Crompton, Matthew John. "The thin aerofoil leading edge separation bubble." Thesis, University of Bristol, 2001. http://hdl.handle.net/1983/25312c88-4d89-4149-bee9-d56cf80d9735.
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Reddy, Manoj Kumar M. "A new adaptive edge enhancement algorithm for color laser printers /." Online version of thesis, 2007. http://hdl.handle.net/1850/5535.
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Sampaio, Dora Isabel Martins. "Ageing 'on the edge' : later-life migration in the Azores." Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/72966/.
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This thesis looks at the diversity of living and ageing experiences in the Azores, exploring the complex intersections between migration, place and older people through a relational lens. It seeks to make a number of original contributions: mapping out the ageing–migration nexus within geographical research; bringing together, under a common theoretical framework, three different types of later-life migrants – labour, lifestyle and return migrants – seldom looked at in a comprehensive comparative manner; putting in dialogue the narratives of migrants and non-migrants; and tapping into a distinctive and, thus far, largely overlooked geographical setting – the Azores. This is a research dually ‘on the edge': for its geographical focus on a nine-island archipelago remotely located in the North Atlantic, and by examining a migrant population chronologically ‘at the extreme' of the age spectrum. The research is empirically grounded on in-depth life narrative interviews, complemented by other research techniques such as participant observation, a focus group, and photography. The thesis offers several key findings: above all, it exposes later-life migration as fundamentally diverse and shaped by migrants' aged, gendered, classed, and ethnicised subjectivities; ageing is seen as a fluid process and an ongoing social construct. Later-life (migration) should be viewed as not necessarily vulnerabilising, but potentially empowering and liberating; and later-life migration decision-making is found to be complex and multi-layered, showing that economic and lifestyle motives can no longer be analysed separately and that a holistic approach is crucial for a richer understanding of the migration process. Stemming from this, four themes emerge from older migrants' living and ageing experiences in the Azores: ‘home' and ambiguous belongings; cultures of ageing and ageing care; ageing in specific relation to place; and intimacy, loss and their negotiations. These show the importance of moving beyond simple binaries of older age as ‘progress' or ‘decline', and recognising later-life as an active negotiative process.
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Lismonde, Baudouin. "Champ de vitesse au bord d'attaque et dans le spot laminaire d'un écoulement sur une plaque plane." Grenoble 1, 1987. http://www.theses.fr/1987GRE10074.
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Calcul numerique des champs de vitesse, de pression et de temperature dans la zone pres du bord d'attaque ou il faut utiliser une approximation d'ordre 3 de la couche limite. Mesure des trois composantes de la vitesse de l'ecoulement perturbe par un microjet instantane traversant la couche limite laminaire
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Gazárek, Jiří. "Texturní analýza snímků sítnice se zaměřením na detekci nervových vláken." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-217559.
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The thesis is focused on detection of local disappearance of the neural layer on retina in fundus-camera images. The first chapter describes the human eye physiology, the glaucoma disease and the analyzed data. The second chapter compares four different approaches that should enable automatic detection of a possible damage to the retinal neural layer. These four approaches have been tested and evaluated; three of them showed an acceptable correlation with the medical expert conclusions – the directional spectral approach, the edge based approach and the difference local brightness. The last approch via local co-occurrence matrices has not turned out to be informative with the respect to the issue concerned. Then a program for the automatic detection of the nerve fibre layer loss areas has been designed, realized and evaluated. This task is solved in the last chapter. A relatively good agreement between the medical expert conclusions and the conclusions detected automatically by this program has been reached.
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Spáčil, Michal. "Analýza retinálních snímků se zaměřením na detekci vrstvy nervových vláken." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219196.
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Goal of this work is to theoretically develop and then program a system in Matlab environment to be used as a detection tool for layer of retinal neuron pathways . First part engages oneself upon the problem of analysis within spectral plane and results of using filters conceived upon statistical occurrences of certain frequencies in used samples. Second part than deals with use of gabor filters to detect neuron pathways and the statistical results gained by their use. Based on the results an analysis tool was programmed.
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Janda, Miloš. "Detekce hran pomocí neuronové sítě." Master's thesis, Vysoké učení technické v Brně. Fakulta informačních technologií, 2010. http://www.nusl.cz/ntk/nusl-237175.
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Aim of this thesis is description of neural network based edge detection methods that are substitute for classic methods of detection using edge operators. First chapters generally discussed the issues of image processing, edge detection and neural networks. The objective of the main part is to show process of generating synthetic images, extracting training datasets and discussing variants of suitable topologies of neural networks for purpose of edge detection. The last part of the thesis is dedicated to evaluating and measuring accuracy values of neural network.
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Serkan, Mert Kirkici Hulya. "Laser beam shaping optical system design methods and their application in edge-emitting semiconductor laser-based lidar systems." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2007%20Fall%20Dissertations/Serkan_Mert_22.pdf.
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Saxena, Vivek. "Turbulence distortion around leading edges and its effect on boundary layer." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360934.
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