A system was designed to measure the effect of gap size on semi-span low Reynolds number wind tunnel experiments. The lift forces on NACA 1412, NACA 2412 and NACA 4412 half wings were measured using a strain gauge balance at chord Reynolds numbers of 100,000 and 200,000 and three different gap sizes including sealed gap. Pressure distributions on both airfoil top and bottom surfaces in the chord-wise direction near the gap were recorded for these airfoils. Also recorded was the span wise pressure distribution on both the airfoil surfaces at the quarter chord section. The results revealed that the presence of the gap, however small, affects the measurements. These effects were mainly observed in drop of lift and change in zero lift angle of attack and change in stall angle for the airfoil. The size of the gap is not linearly related to these changes, which also depend on the camber of the airfoil. These changes occur due to the flow through the gap from the lower surface to the upper surface of the model. The wing/end plate gap effect reduces along the span but is not fully restricted to the base of the model and the model behaves more like a full three-dimensional wing than a semi-span model. This study was made possible with the support of Department of Aerospace and Ocean Engineering, Virginia Polytechnic Institute and State University under the supervision of Dr. James Marchman / Master of Science

The purpose of this thesis was to understand the implications of ultrasound in the assessment of flexor tendon shear to establish its role in carpal tunnel syndrome. An in vitro and in vivo approach was used to examine ultrasound “shear” between the tendon and adjacent tenosynovium. Ultrasound shear is defined by the relative displacement between the tendon and tenosynovium, and has been considered a surrogate measure of tendon shear. However, the mechanical implications of relative displacement are not well understood. In Chapters 2 and 3, an in vitro approach was used to compare ultrasound to direct measurements of tendon displacement and tendon shear. Chapter 2 demonstrated the validity of colour Doppler ultrasonography in the evaluation of tendon displacement. Chapter 3 assessed the relationship between ultrasound shear and mechanical tendon shear using frictional work. We dispelled the notion that ultrasound shear represents tendon shear by showing it only captures the viscoelastic stretch of the tenosynovium in tendon shear; missing surface friction from neighbouring anatomical structures in the carpal tunnel. However, measuring viscoelastic resistance in tendon motion is important for the development of pathological fibrosis and thickening of the tenosynovium, a characteristic finding in carpal tunnel syndrome. In Chapter 4 we further established the clinical utility of ultrasound in vivo by showing ultrasound shear discriminated carpal tunnel syndrome symptomatic individuals from the healthy population. Ultrasound measures progressed with symptoms suggesting an etiological progression of fibrosis and thickening with carpal tunnel syndrome. This thesis concluded that ultrasound only partially represents tendon shear with the viscoelastic component, but underscored the clinical implications. Ultrasound provides a non-invasive assessment of viscoelastic resistance that will be highly valuable for our understanding of the role of wrist and hand motion in the etiology of injury with potential applications in the diagnosis of carpal tunnel syndrome. / Thesis / Master of Science in Kinesiology

Thesis / Master of Engineering (MEngr)

No description available.

The acoustic treatment and calibration of a new anechoic system for the Virginia Tech Stability Wind Tunnel has been performed. This novel design utilizes Kevlar cloth to provide a stable flow boundary, which eliminates the need for a free jet and jet catcher. To test this concept a series of measurements were performed both to validate the reduction in overall test section noise levels and to ascertain the effect of these modifications on the test section aerodynamics. An extensive program of experiments has been conducted to examine the performance of this new hardware under a range of conditions. These include baseline experiments that reveal the aerodynamic and aeroacoustic performance of the tunnel in its original configuration, treatment of the tunnel circuit with validation of in-flow noise reduction, wind tunnel tests to examine the effect of the test section acoustic treatment, and measurements of the aerodynamic and aeroacoustic characteristics of a NACA 0012 airfoil model over a range of angles of attack and Reynolds numbers. These measurements show that acoustically treating the walls of the circuit both upstream and downstream of the test section, as well as the fan, result in an overall reduction of 5 dB depending on frequency, of the in-flow noise level. These measurements also show that the complete system provides a reduction of between 15 to 20dB depending on frequency, in the in-flow background noise level. Measurements taken both within the test section and in the adjacent chambers also show that large Kevlar windows can be used to quietly and stably contain the flow, eliminating the need for an open-jet and jet catcher system, as well as overall noise levels competitive with many other facilities. Measurements on several airfoils at various angles of attack and Reynolds number show that the interference correction for the fully anechoic configuration is approximately -22% for model with a chord length equal to half the test section height. Aerodynamic measurements with the NACA 0012 airfoil show its lift, drag and boundary layer characteristics at high Reynolds numbers are consistent with theoretical expectations. Measurements of the window deflection as well as examination of flow transpiration through the Kevlar windows were accomplished, both with and without the NACA 0012 model. These measurements, along with the interference correction data, confirm that the Kevlar windows are a stable flow boundary. / Master of Science

Demand for new underground transportation systems and utility networks has increased the use of tunneling in soft ground. Many of these tunnels have to be constructed in difficult soil conditions, with strict constraints on ground movement control. Technological advances, such as the pressurized shield or the New Austrian Tunneling Method (NATM), have, to some extent, overcome these difficulties. But the complex interaction between tunneling procedure, ground response, and liner support is still not fully understood. In this dissertation, the three aspects of tunneling, face stability, liner design, and ground surface settlement are analyzed for conditions that might be experienced on current projects. The study is intended to clarify some of the phenomena associated with the use of advanced tunneling techniques in soft grounds, and help improve the current design practice. The NATM generally uses "hand-mining" equipment for excavation, and shotcrete as temporary support of the tunnel wall. The amount and timing of support is optimized by continuously adapting the construction procedure to the conditions found at the tunnel face. In the present study, the applications of the finite element method to tunneling are reviewed, and it is used to model NATM tunneling projects. Using parametric studies, a simplified design method is proposed which allows an estimate of the liner forces and settlements associated with NATM tunneling to be obtained. Pressurized shields are used in soils with little to zero stand-up time to support the tunnel face during excavation. In this work, the face stability of shield tunnels in cohesionless soils is examined using limit analysis principles. Upper bound estimates of the critical face pressure are found in good agreement with results from centrifuge model tests. Empirical correlations for settlement estimates are re-examined, in view of case history data for shield driven tunnels. The ground movements observed on the F3 and F4 contracts of the Washington Metro are analyzed. Earth pressure balance shields were used on these projects. It is shown that difliculties were common in mixed face conditions, unless adequate techniques were used to prevent ground collapse to occur. / Ph. D.

Ως θέμα της πραγματεύεται την Εργαστηριακή διερεύνηση των φυσικών και μηχανικών ιδιοτήτων των μαλακών βράχων και των αμμωδών εδαφών με εξέταση χαρακτηριστικών παραδειγμάτων αργιλομαργαϊκής σύστασης πετρωμάτων καθώς και τις τεχνικογεωλογικές συνθήκες κατά τη διάνοιξη της οδικής σήραγγας του Πλατάνου. Πραγματοποιήθηκε δειγματοληψία από το μέτωπο εκσκαφής της σήραγγας του Πλατάνου και χρησιμοποιήσαμε 3 δείγματα για τις εργαστηριακές δοκιμές. / -

Comportement différé, anisotrope à la descenderie de Saint-Martin-la-Porte / Time-dependent, anisotropic behavior of Saint-Martin-la-Porte gallery

Cette thèse a pour objectif la caractérisation de la vitesse de ventilation critique dans un tunnel ventilé longitudinalement lorsque survient un incendie. La vitesse critique est définie comme la vitesse de ventilation minimale pour laquelle l’ensemble des fumées nocives est repoussé à l’aval de l’incendie. Les méthodes utilisées sont théoriques, expérimentales et numériques. Dans une première approche, l’incendie est modélisé par un rejet de fluide plus léger que l’air ambiant. Dans les expériences, il s’agit soit de l’air chaud, soit d’un mélange d’air et d’hélium ce qui permet d’étudier les effets dits non-Boussinesq, c’est à dire induits par une large différence de densité entre le rejet flottant et l’air ambiant. Une modélisation théorique simple est également donnée afin d’expliquer les variations de la vitesse de ventilation critique en fonction des conditions à la source du rejet (flux de flottabilité et géométrie). Un bon accord est observé entre les résultats expérimentaux et le modèle théorique aussi bien pour les rejets dits forces (jets) que pour les rejets dits flottants (panaches). Des simulations numériques ont été également menées afin de fournir une comparaison quantitative des vitesses critiques obtenues dans le cas d’un incendie modélisé par un panache et le cas d’un feu. L’apparition d’une vitesse dite ’super-critique’ observée dans la littérature dans le cas de feux a été étudiée. L’effet sur la vitesse critique d’un feu de puissance faible peut très largement être modélisé par l’effet d’un rejet de fluide léger au sol. En revanche, un feu de forte puissance nécessite une modélisation des flammes et donc de puissance thermique produite en volume dans une partie non négligeable du tunnel. La présence de flammes représente donc une source distribuée de flux de flottabilité au-dessus et en aval du lieu d’injection des gaz de combustion. En conséquence, dans cette situation, le foyer ne peut être modélisé par une simple condition aux limites au sol du tunnel. L’effet sur la vitesse critique d’une éventuelle inclinaison ou pente du tunnel a été également étudié. Une inclinaison du tunnel dans le sens de la ventilation induit une diminution de la vitesse critique par rapport à un tunnel horizontal alors que pour une inclinaison en sens contraire la vitesse critique est augmentée. Cependant, cet effet dépend des conditions à la source du rejet. Pour les rejets flottants, l’effet de la pente du tunnel est important tandis que la vitesse critique devient de moins en moins dépendante de la pente au fur et à mesure que le rejet devient force. Le modèle théorique développé pour un rejet dans un tunnel horizontal a été adapté au cas avec pente et un bon accord a de nouveau été établi entre les résultats expérimentaux et le modèle théorique. Enfin, pour un feu, les simulations numériques ont montré que la pente influence très peu la vitesse critique. Dans une dernière partie, l’effet de la présence de véhicules dans le tunnel a été investigue aussi bien expérimentalement qu’avec l’outil numérique. Les véhicules sont modélisés par des blocs parallélépipédiques de différentes tailles places en amont de la source de flottabilité ou le feu. Il a été montré que seul le bloc proche de la source modifiait la valeur de la vitesse de ventilation critique alors que les blocs plus éloignés avaient une influence négligeable. De même, la vitesse critique obtenue en présence de blocs se rapproche très rapidement de celle obtenue pour un tunnel sans véhicule lorsque la distance entre la source et le bloc le plus proche augmente. Le paramètre qui influence le plus la vitesse critique est la position relative du bloc et de la source. Lorsque le bloc protège directement la source en étant placé à son côté aussi bien longitudinalement que latéralement, l’air frais de la ventilation n’impacte pas directement le rejet et la vitesse critique est augmentée par rapport à la situation sans bloc. [...] / This thesis investigates experimentally, theoretically and numerically the critical ventilation velocity in longitudinal ventilated tunnels in case of a fire. The critical velocity is defined as the minimum ventilation velocity that confines the front of the backlayer of harmful buoyant gases downwind of the source of emission. The fire is first modeled by a release of light gas in ambient air. In the experiments, the light fluid is an air/helium mixture. A simple mathematical model, based on the classical plume study, is formulated to interpret the variations of the critical velocity as a function of the source conditions (momentum and buoyancy fluxes and geometry). A good agreement is observed between the experimental results and the theoretical predictions for both the momentum-driven and buoyancy-driven releases. In addition, the non-Boussinesq effects, i.e. related to large differences between the densities of the buoyant plume and the ambient fluid, could be suitably modeled. Subsequently, the difference between a buoyant plume and a fire is studied, by combining experiments and numerical simulations. The reason for the appearance of the so-called ‘super-critical’ velocity, a ventilation velocity that becomes independent of the heat release rate when it becomes large, is discussed. It is shown that small fires can be reliably modeled as buoyant densimetric plumes released at ground level. The dynamics induced by larger fires require instead the modeling of large flames and hence a volumetric source of heat and buoyancy within the tunnel. In the simulation of fires, when the heat release rate is increased, the volume of combustion also increases, but the critical velocity remains nearly constant, which validates the appearance of the ‘super-critical’ velocity. The effect of tunnel inclination on the critical velocity is then studied. The influence of slope (defined as negative when the entrance of fresh air is at a lower elevation than the source) on the movement of smoke is mainly related to the role of the component of buoyancy along the tunnel axis. A positive slope helps the formation of the backlayer, while a negative slope helps reaching the critical condition. However, this effect depends on the source condition. Our experiments and numerical simulations on densimetric plumes suggest that the dynamical condition at the source affects the critical velocity of a buoyant plume: when the buoyant plume is momentum-driven, the influence of slope is small; when the buoyant plume is buoyancy-driven, the influence of slope is large. This behavior can be well described by a theoretical model based on the previous model of the critical velocity in a horizontal tunnel. These results have been extended to the case of fires by conducting numerical simulations and there is again a good agreement between the observed results and the theoretical model. In particular, the ratio of the critical velocities obtained for an inclined and an horizontal tunnel is independent of the power of the fire. Finally, the effect of vehicular blockage on the critical velocity is studied experimentally and numerically. The vehicles are modeled by blocks of different sizes placed upstream of the buoyancy or fire source. It is shown that only the block close to the source affects the critical velocity, whereas the effect of other blocks of the same size located further upstream is negligible. As the fire-blockage distance becomes larger, the critical velocity changes and becomes close to the value in an empty tunnel. The relative position between the blocks and the fire source has large influence on the critical velocity. When the blocks are placed at the center laterally, the ventilation flow cannot reach the fire plume directly, a larger critical velocity is needed compared with that in a corresponding empty tunnel. [...]

Une Jonction Tunnel Magnétique (JTM) est composée de deux couches minces métalliques ferromagnétiques (cobalt, fer, nickel) séparées par une barrière isolante ultramince (alumine) dans sa forme la plus simple. Cette structure a évolué depuis la première Magnéto Résistance Tunnel (MRT) à température ambiante en 1995. Actuellement, les jonctions tunnel magnétiques sont utilisées par la nouvelle génération de mémoires vives magnétiques (MRAM) et par les têtes de lecture des disques durs.<br /> Cette étude présente l'élaboration de jonctions Co/Al2O3/Co/Ni80Fe20 par pulvérisation ionique. On veut ainsi démontrer la potentialité de cette technique de dépôt, qui est peu utilisée dans ce domaine. La mesure de la Magnéto Résistance Tunnel a été effectuée selon deux méthodes. La première méthode a nécessité le développement d'un procédé de structuration réalisé en salle blanche, afin d'élaborer les contacts électriques nécessaires à la mesure. La deuxième méthode repose sur la technique appelée CIPT (Current In Plane Tunneling). Cette deuxième technique présente l'avantage de ne nécessiter aucune structure particulière. Les résultats obtenus ont conduit à des simulations de pulvérisation ionique, effectuées à l'aide du logiciel SRIM 2003. Elles permettront à terme d'optimiser les conditions d'élaboration des films minces.