M.Ing. (Mechanical Engineering) / Please refer to full text to view abstract

<div>The quiet-flow capabilities of the Boeing/AFOSR Mach-6 Quiet Tunnel have been well established in the last decade, but a full characterization of the nozzle flow is an ongoing project. Pitot probes outtted with Kulite pressure transducers were used to further the investigation of the tunnel's flowfield. Noise levels were calculated by integrating the power spectral densities of the measured pitot pressure fluctuations, and experiments were performed to investigate several aspects of the flow.</div><div><br></div><div><div>First, the temperature distribution along the nozzle was varied to determine if heating had an effect on the stability of the laminar nozzle-wall boundary layer. Runs made with initial stagnation pressures slightly above the maximum quiet pressure determined that additional nozzle-wall heating did not have an effect on the amount of runtime which experienced quiet flow. In addition, pitot-probe measurements were taken at various locations to better determine the axial dependence of the noise levels. Experiments were also performed using pitot probes of varying forward-facing diameters to determine the effects of probe geometry on the measured fluctuations. The results were found to differ signicantly from simulations and from a previous set of experimental data, but a likely cause of the discrepancies was not found. A pitot probe mounted on the base of a cone confirmed that the aft end of a model does experience quiet flow. Finally, characterization of the flowfield was attempted when the tunnel is run using helium. The measured pressures for these experiments have a signicant level of uncertainty because the sensor calibration changes as helium diffuses across the diaphragm. Nevertheless, the measurements suggest that there may be periods of uniform flow, although these periods remain unstable and unsteady.</div></div><div><br></div><div><br></div>

Les jonctions tunnel magnétiques épitaxiées sont des systèmes modèles permettant de confronter l’expérience à la théorie de l’effet tunnel polarisé en spin. Celles à barrière de MgO(001) font à ce titre l’objet de nombreuses études, dont certaines ont permis d’établir expérimentalement l’existence de phénomènes tunnel cohérents dépendant de la symétrie des états de Bloch. Les expériences réalisées au cours de cette thèse visent à identifier et contrôler plusieurs propriétés des interfaces, de la barrière et des électrodes qui s’expriment dans le transport tunnel. Nous étudions les conséquences d’un excès d’oxygène à l’interface Fe/MgO dans les jonctions Fe/MgO/Fe(001). La réalisation d’un empilement modèle Fe/p(1×1) O/MgO/Fe(001) nous permet de confirmer certains effets attendus, notamment la formation d’une barrière additionnelle à l’interface pour les états de symétrie ?1. Cependant, et contre toute attente, la magnétorésistance dépend peu de la présence d’oxygène. Elle est en revanche très sensible à la qualité cristallographique des interfaces. Nous démontrons ainsi les influences néfastes du désordre et du désaccord paramétrique entre la barrière de MgO et l’électrode sous-jacente. L’emploi d’alliages Fe V de composition variable permet de réduire le désaccord paramétrique et de diminuer la densité de dislocations, ce qui conduit à une forte augmentation de la magnétorésistance. Nous étudions enfin comment les structures électroniques des alliages Fe Co et Fe V se manifestent dans le transport tunnel. Des mesures de photoémission résolue en spin nous permettent de sonder directement les bandes ? et les états de résonnance interfaciale des surfaces (001) libres ou recouvertes de MgO. / Epitaxial magnetic tunnel junctions are model systems in order to test the spin polarized tunnel effect theory. MgO(001) based junctions are thus subject of many studies. Some of them experimentally established the existence of coherent tunnelling involving the symmetry of Bloch states. However quantitatively, characteristics of real junctions strongly deviate from predictions. The role of imperfections in the barrier and at the interfaces is suspected but the current knowledge of dominant mechanisms is still limited. This thesis experiments aim at identifying and controlling several properties of the interfaces, of the barrier and of the electrodes which influence tunnelling. We study the consequences of an excess of oxygen at the Fe/MgO interface in Fe/MgO/Fe(001) junctions. Preparing a model Fe/p(1×1) O/MgO/Fe(001) stacking allows us to confirm some expected effects, namely the appearance of an additionnal potential barrier at the interface for states with ?1 symmetry. However, and unexpectedly, the magnetoresistance little depends on the presence of oxygen. On the other hand, it is very sensitive to the crystallographic quality of interfaces. We show evidence for the detrimental influence of disorder and of the misfit between the MgO barrier and the supporting electrode. Using Fe V alloys with variable composition allows us to reduce the misfit and the dislocations density, which in turn induces a great enhancement of the magnetoresistance. We finally investigate how the electronic structures of Fe Co and Fe V alloys express themselves in tunnelling. In addition, we probe by spin resolved photoemission the ? bands and interfacial resonance states of free and MgO covered (001) surfaces.

The freight rail industry is essential to the US infrastructure and there is significant motivation to improve its efficiency. The aerodynamic drag associated with transport of commodities by rail is becoming increasingly important as the cost of diesel fuel increases. For intermodal railcars a significant amount of aerodynamic drag is a result of the large distance between containers that often occurs and the resulting pressure drag resulting from the separated flow that results due to their non-streamlined shape. This thesis reports on research that has been done to characterize the aerodynamic drag on intermodal train builds and allow their builds to be optimized for fuel efficiency. Data was obtained through wind tunnel testing of G-scale (1/29) models. Drag on these models was measured using a system of isolated load cell balances and the wind tunnel speed was varied from 20 to 100 mph. Several common intermodal scenarios were explored and the aerodynamic drag for each was characterized. These scenarios were the partial loading of containers on rail cars, the influence of the gap between containers, the use of a streamlined container near the front of the train, and the inclusion of semi-trailers on railcars. For each case multiple build configurations were tested and the drag results were compared to determine the optimal build for each scenario.

This thesis involves the experimental testing of a bluff body with a blunt base to evaluate the effectiveness of end-plate tabs in reducing drag. The bluff body is fitted with interchangeable end plates; one plate is flush with the rest of the exterior and the other plate has small tabs protruding perpendicularly into the flow. The body is tested in the Cal Poly 3ft x 4ft low speed wind tunnel. Testing is conducted in three phases. The first phase was the hot-wire measurement of streamwise velocity of the near wake behind the bluff body. An IFA300 thermal anemometry system with a hot-wire probe placed behind the model measures the wake velocity fluctuations. The power spectral density on the model without tabs shows large spikes at Strouhal numbers of 0.266, 0.300, and 0.287 at corresponding Re = 41,400, 82,800, 124,200 where vortex shedding occurs. The model with tabs shows no such peaks in power and therefore has attenuated vortex generation in the wake flow at that location. The second phase of testing was pressure testing the model through the use of pressure ports on the exterior of the bluff body. A Scanivalve pressure transducer measured multiple ports almost simultaneously through tubing that was connected to the model internally and routed through the model’s strut mount and outside of the wind tunnel. This pressure testing shows that the model with tabs is able to achieve up to 36% increase in Cp at Reh = 41,400 on the base region of the bluff body and no negative pressure spikes that occur as a result of vortex shedding. The last phase of testing is the measurement of total drag on the model through a sting balance mount. This testing shows that the drag on the model is reduced by 14% at Re = 41,400. However it also shows that as velocity increased, the drag reduction is reduced and ultimately negated at Re = 124,200 with no drag loss at all. The addition of tabs as a passive flow control device did eliminate vortex shedding and alter the base pressure of the bluff body. This particular model however showed no reduction in total drag on the model at high Reynolds numbers higher than 124,000. Further study is necessary to isolate the exact geometry and flow velocities that should be able to produce more favorable drag results for a bluff body with this type of passive flow control device.

Comportement différé, anisotrope à la descenderie de Saint-Martin-la-Porte

<p>Kostnaden att bygga färdigt tunneln genom Hallandsås överstiger vida nyttan av hela tunneln. En ekonom ställer sig då frågan varför tunneln byggs färdigt. Sedan tunnelbygget avstannat efter att olika problem dykt upp har kostnadssidan noga utretts. En sista(?) utredning pågår just nu. I höst kommer denna att bli färdig. Den kommer att visa om det går att bygga färdigt och ungefär till vilket pris. Nyttosidan däremot har inte några djupare utredningar tagit tag i. Denna är komplicerad. Det finns många svårfångade värden, som flera skulle behöva närmare analys. I en samhällsekonomisk kalkyl är nyttosidan lika viktig som kostnadssidan. I den första utredningen från 1990 om tunnelbygget utgjorde värdet av resenärernas tidsvinst mer än hälften av nyttosidan. En intressant fråga att ställa sig då är om värdet på tiden för resenärerna verkligen är detsamma då de färdas på åsen som då de åker i tunneln. Om restidsvärdet vore annorlunda skulle ju en stor del av nyttosidan förändras. I en SP (stated preferens) undersökning gjord på tåg vid färd över Hallandsås har jag funnit att betalningsviljan för att fortsätta åka tåg över åsen är större än betalningsviljan för att åka tunnel genom Hallandsås och spara 10 minuter. Det visar sig vidare att tunnelåkande i sig har en högre tidskostnad för tågresenärer. Att med endast denna empiri som underlag finna ett säkert tunnelvärde tillämpbart på alla tunnlar låter sig inte göras. Allt för mycket känslor kan finnas kring tunneln genom Hallandsås. Värdering av andra faktorer än just tunnelåkandet i sig kan inte uteslutas.</p>

Kostnaden att bygga färdigt tunneln genom Hallandsås överstiger vida nyttan av hela tunneln. En ekonom ställer sig då frågan varför tunneln byggs färdigt. Sedan tunnelbygget avstannat efter att olika problem dykt upp har kostnadssidan noga utretts. En sista(?) utredning pågår just nu. I höst kommer denna att bli färdig. Den kommer att visa om det går att bygga färdigt och ungefär till vilket pris. Nyttosidan däremot har inte några djupare utredningar tagit tag i. Denna är komplicerad. Det finns många svårfångade värden, som flera skulle behöva närmare analys. I en samhällsekonomisk kalkyl är nyttosidan lika viktig som kostnadssidan. I den första utredningen från 1990 om tunnelbygget utgjorde värdet av resenärernas tidsvinst mer än hälften av nyttosidan. En intressant fråga att ställa sig då är om värdet på tiden för resenärerna verkligen är detsamma då de färdas på åsen som då de åker i tunneln. Om restidsvärdet vore annorlunda skulle ju en stor del av nyttosidan förändras. I en SP (stated preferens) undersökning gjord på tåg vid färd över Hallandsås har jag funnit att betalningsviljan för att fortsätta åka tåg över åsen är större än betalningsviljan för att åka tunnel genom Hallandsås och spara 10 minuter. Det visar sig vidare att tunnelåkande i sig har en högre tidskostnad för tågresenärer. Att med endast denna empiri som underlag finna ett säkert tunnelvärde tillämpbart på alla tunnlar låter sig inte göras. Allt för mycket känslor kan finnas kring tunneln genom Hallandsås. Värdering av andra faktorer än just tunnelåkandet i sig kan inte uteslutas.

The goal of this study is to assess the potential of using bench-scale fire testing to screen materials for the Steiner tunnel fire test. It is hypothesized that the chemical and physical changes made to a material to improve its fire performance in small scale fire tests will have a predictable response in the Steiner tunnel. This hypothesis is based on the observation that fire test results can, in some cases, provide insight on a material's relative fire hazard, and the assumption that the relative hazard should be consistent across scale. The ASTM E84 Steiner tunnel test provides a relative ranking of material hazard in two categories. The horizontal Flame Spread Index (FSI) is used to rank the flame hazard of a material, and the Smoke Developed Index (SDI) is used to rank the smoke hazard of a material. Two fire tests are proposed to independently assess each hazard at the bench-scale. The ASTM E1354 cone calorimeter test measures a material's open-flaming heat release rate; it is proposed that the cone calorimeter test can be used to assess a material's relative flame hazard. The ISO 5659-2 smoke density chamber test measures a material's closed-environment smoke development; it is proposed that the smoke density chamber test can be used to assess a material's relative smoke hazard. The material selected for this study is fire-retarded sprayed polyurethane foam (FRSPF) insulation. Specific details of the foam chemistry, fire retardants, and the manufacturer are confidential. Generally, the foam can be described as medium-density (approximately 2 lbs/ft³), closed-celled, and semi-rigid. The fire retardant additives are comprised of differing ratios and concentrations of phosphorous- and halogen-containing compounds. A series of 30 Steiner tunnel tests is conducted on 20 different formulations. Repeated testing is conducted on several formulations in order to assess variability in the Steiner tunnel test results. Cone calorimeter and smoke density chamber tests are conducted on a subset of those formulations, in sets of 3-5 tests per formulation. Key performance indicators are identified from each fire test, relationships between those indicators are examined, and correlations are presented where strong relationships are apparent. Empirical prediction models are proposed for FSI and SDI based on the success rate of prediction, and minimization of error between experimental (measured) and modelled (predicted) results. It is concluded that for the materials tested in this study, there is sufficient evidence of consistency in relative performance to recommend bench-scale screening tests as a cost-effective alternative to repeated Steiner tunnel testing.

An experimental wind tunnel study on the dynamic response of a 300 m tall guyed telecommunication mast under various wind loads was undertaken at the Boundary Layer Wind Tunnel Laboratory (BLWTL) in the University of Western Ontario, London, Canada. Although the dynamic response of guyed masts subjected to turbulent wind loads has been routinely analyzed using a number of numerical models, typically in the frequency domain, limited experimental verification of the dynamic analysis results has been performed. Full-scale measurements, where available, have proven to be difficult to correlate with analytical models due to the tremendous uncertainty inherent in field measurements. As a result, the need for systematic validation of existing analytical models remains.<p>In this investigation, a representative 300 m tall guyed telecommunication mast has been designed and modeled to an appropriate scale. Based on Canadian Standard CSA S37-01, and an empirical study on 41 existing guyed masts, the 300 m tall guyed mast was designed using wind load conforming to representative Canadian climate data obtained from National Building Code of Canada (NBCC 1995). Appropriate properties for the dynamically scaled full aeroelastic model were derived from the 300 m tall prototype guyed mast, which was intended to represent a realistic guyed mast for broadcasting applications in Canada.<p>The wind tunnel test of the guyed mast model was carried out in both open country and over water exposures, simulating medium and low turbulence flow conditions, respectively. Dynamic response characteristics measured during the wind tunnel tests have been analysed and summarized, including dynamic displacements, bending moments, response spectra and peak factors, as well as natural frequencies, mode shapes and structural damping. Comparisons have been made with predictions obtained from an existing frequency domain analysis model. <p>The wind tunnel test results show that good agreement was generally achieved between the frequency domain analytical model and the wind tunnel model with respect to both the magnitude and distribution of the monitored responses. It was found that measured dynamic bending moments were distributed in a fairly uniform manner over the mast height, and that mean (static) bending moments exhibit large variations, along with near-zero response zones at points of contraflexure. It was also found that nonlinear damping effects, associated with vibrations of the highly slackened leeward guys on the upper levels of the mast, may be beneficial in reducing dynamic mast displacements. <p>The spectrum studies indicated that lowest modes were dominated by large guy movements at top guy level and small mast movements, the middle modes were characterized by coupled effects between the guyed cables and mast, meanwhile the highest modes involved significant mast movements with little guy vibration. It is evident that the top of the mast displacement are dominated by the first and second modes.