• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 32
  • 24
  • 10
  • 5
  • 2
  • 1
  • 1
  • 1
  • Tagged with
  • 101
  • 30
  • 23
  • 21
  • 20
  • 20
  • 17
  • 16
  • 15
  • 13
  • 13
  • 12
  • 12
  • 12
  • 12
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Skjuvhållfasthetsbestämning i kohesionsjord : en del av ett utvecklingsprojekt för en ny vingförsöksutrustning

Lundin, Frida January 2018 (has links)
The report is part of the development project run by Ingenjörsfirman Geotech AB, where some of the field investigations were carried out in collaboration with Bohusgeo AB. The aim of the thesis is to do field investigations with the new Vane Geotech Nova (Nova-vane) equipment, and compare the results with known and proven methods. The vane test is an in situ method that determines the undrained shear strength, for example for clay soils. Eight tests have been performed with the Nova-vane and they have been compared with the Nilcon-vane, an electronic Nilcon-vane, a CPT-probing and Direct shear tests in the laboratory. Parameter determination has been done with CRS-tests and ordinary laboratory routine examination. According to earlier research, the time for failure, waiting time and rotational speed are parameters that have been tested in order to know how they affect the evaluated shear strength in clay soils. Previous investigations from 1950 to 1990 show that the parameters mentioned above have a major impact on the evaluated shear strength. When comparing already known evaluation methods for the undrained shear strength, it has been found that the Nova-vane generates shear strength measurements are far too low. The reason why the Nova-vane shows lower undrained shear strengths than other methods may be due to a number of factors. The analysis of the tests shows that the rotation speed has not been constant, as the rotation is becoming faster and faster, the time to failure varies between a few seconds to several minutes over the recommended time to failure. Another major factor is the deviating angle compared to the vertical plane, the vane has been driven down with. In the eight tests, the rotational speed has been a difficult parameter to control. The electric engine used, a modified Geotech EVT 2000 electric vane instrument, could only apply different energies and are normally used for 22 mm probe rods. Which specific applied force on the rods generating the correct rotational speed, depends entirely on the properties of the clay. When 36 mm probe rods are used together with the electric engine the rotational speed is even more difficult to control. According to the SGF recommended standard from 1993 states that the time to failure of a vane test should be between 2 and 4 minutes, from the time the vane is activated. It primarily depends on the speed of rotation, which means that the time for failure was also a difficult parameter to control. The angle with which the Nova-vane is driven increases with depth to about 30° at 30 meters. While the angle of CPT-probing increases only 5° at 30 meters. The driven angle could have significance to the shear strength, although it is difficult to conclude what kind. The Nova-vane is the only vane borer that can measure which angle it is driven down with. The increasing angle is assumed to depend on the geometry of the instrument and not on the properties of the clay. The conclusion is that the measurement with the Nova-vane gives lower values than the other methods. However, the range of values proves only small differences down to the depth of 20 meters. The system as a whole is working with an acceptable accuracy, although a stronger engine and a more precise control of the engine speed is needed. More tests have to be done to determine how the Nova-system can be designed and how the investigation should be performed to get equal values as other proven methods. / Rapporten är en del av ett utvecklingsprojekt som drivs av Ingenjörsfirman Geotech AB, där viss del av fältundersökningar utförts i samarbete med Bohusgeo AB. Examensarbetets roll har varit att utföra fältförsök med den nya vingförsöksutrustningen typ Vane Geotech Nova (Nova-vingsond) för att sedan sammanställa och jämföra resultaten med redan kända och väl beprövade metoder. Vingförsöksmetoden är en in situ metod som bestämmer den odränerade skjuvhållfastheten i kohesionsjord. Åtta försök med Nova-vingsond har utförts och jämförts med Nilcon-vingar och eldriven Nilcon-vinge samt CPT-sondering och direkta skjuvförsök i laboratorium. Även CRS-försök och rutinundersökning i laboratorium har gjorts, för parameterbestämning. Enligt undersökningar i tidigare forskning har: tiden till brott, väntetiden och rotationshastigheten varit parametrar som testats för att se hur de påverkar den utvärderade skjuvhållfastheten i lerjordar. Tidigare forskning utförd mellan 1950 och 1990, visar att nämnda parametrar har en stor inverkan på den utvärderade skjuvhållfastheten. Vid jämförelser mellan Nova-vingsonden och andra utförda försök inom provtagningslokalen ger Nova-vingsonden lägre odränerad skjuvhållfasthet, vilket kan bero på flertalet faktorer. Analysen av försöken påvisar att hastigheten inte har varit konstant utan att rotationen blir allt snabbare, tiden till brott varierar mellan några få sekunder till flera minuter över den rekommenderade tiden till brott. Samt att neddrivningsvinkeln är avvikande från det tänkta vertikalplanet. I de åtta försöken har rotationshastigheten varit en svårstyrd parameter. Den elektriska rotationsmotorn som har använts är en modifierad Geotech EVT 2000. Den elektriska är dimensionerad för sondstänger med en diameter på 22 mm och har en effektinställning. Vilken rotationshastighet som den specifika effekten genererar beror helt på lerans egenskaper, vilket gör att rotationshastighet är svår att ställa in på rotationsmotorn, speciellt med 36 mm sondstänger. Tiden till brott för vingförsöksmetoden ska enligt SGF standard från 1993 vara mellan 2 och 4 minuter från dess att vingen aktiverats. Den beror framför allt av rotationshastigheten, vilket medför att även tiden till brott var en svårstyrd parameter. Nova-vingsonden visar en växande neddrivningsvinkel mot djupet, vid 30 meter cirka 30°, i jämförelse med CTP-sonden som endast ökade med 5° på 30 meter.  Neddrivnings-vinkeln kan ha betydelse för den erhållna skjuvhållfastheten, dock är det en svår att bestämma hur. Nova-vingsonden är den enda vingförsöksmetod som har en lodenhet. CPT-sonden har också en lodenhet, den gav mindre utslag. Neddrivningsvinkeln bero förmodligen på instrumentets geometri och inte på lerans egenskaper. För att kunna styra rotationshastigheten och på så vis tiden till brott behövs en utvecklad utrustning. Främst krävs en starkare motor som rotationshastgeten går att ställa in på, övriga komponenter anses vara tillräckligt noggranna, dock behöver viss systemutveckling ske. Slutsatsen blir att de utförda mätningarna med Nova-vingsonden visar lägre resultat än övriga bestämningar. Då det är många parametrar som har inverkan på resultatet, behövs fler undersökningar göras för att fastställa hur Nova-systemet ska konstrueras och hur försök ska utföras för att erhålla likvärdiga resultat som övriga metoder.
12

Conformal Propellant Tanks and Vane Design

Robert Paul Beggs (11927936) 28 April 2022 (has links)
<p>Current small satellite propellant tank design is driven by three factors: volume op-timization, manufacturing capability, and propellant management. Conformal propellanttanks offer solutions to the design challenges of optimizing satellite volume and manufac-turing costs. Conformal propellant tank designs that meet these challenges have unknowneffects on propellant management. Compounding this uncertainty is the industry shift to-wards new green propellants with large contact angles. Improper propellant managementcan deliver gas to a thruster or leave propellant trapped away from the tank outlet whiledraining. Both scenarios reduce the lifespan of satellites.</p> <p>Stamping is one manufacturing process that can produce tanks that optimize volumeand are relatively easy to manufacture. The effects of the stamping process on tank shapeand propellant management is evaluated through testing four different tank geometries. Thestamping process sometimes leaves behind a seam where two sides of a tank are joinedtogether. A total of six tank and vane combinations are tested. One set of traditional tanksserve as a control. Three tanks tested share vane geometry and have different interiors toevaluate the effects of the stamping process on propellant management. The first tank hasa smooth interior, the second has a seam at the joints and the third tank has a seam andridges for increased stiffness. The last two tanks have an interior in the shape of an arc andhave different vanes. The experiment is flown on the ZeroG airplane to test the tank andvane designs in a weightless environment.</p> <p>The experiment consists of a payload rack, eleven experimental pods and one powerdistribution pod. Each experimental pod is designed to be modular and independent fromall other experimental pods. Each experimental pod hosts a camera, electrical box, secondcontainment and fluid system with four tanks.</p> <p>The results of this study show no discernible difference could be observed between tankswith or without a seam from the stamping process. When ridges are added to a tank thatare parallel to the contact line, liquid may not wick into the ridge if it is dry. If the ridgeis wet the liquid spreads out on the surface of the tank further. The differences betweenpropellant positioning for zero and nonzero contact angle fluids are discussed</p> <p><br></p>
13

Lactose Hydrolysis by Fungal and Yeast Lactase: Influence on Freezing Point and Dipping Characteristics of Ice Cream

Matak, Kristen E. 19 January 1999 (has links)
Two studies were conducted to examine the effects of lactose hydrolysis on freezing point and dipping characteristics of ice cream. The overall research objective was to determine changes in freezing point, texture and ease of dipping ice cream as a result of lactose hydrolysis. It was also the goal of this research to relate observations from the sensory dippability study with hardness and yield stress data to determine if the latter methods could be used as an alternative to human testing of dippability. In the first experiment, ice cream mixes were treated with lactase (EC 3.2.1.23) to cause 0 to 83% lactose hydrolysis. Lactose hydrolysis decreased the freezing point from -1.63oC in the control (0% hydrolysis) to -1.74oC in the 83% hydrolyzed sample (p < 0.05). Firmness decreased from 0.35 J in the control sample to 0.08 J in the 83% hydrolyzed sample. Lactose hydrolyzed samples melted at a faster rate than the control. There was a difference (p < 0.05) in ease of dipping between samples treated with lactase and the control. There were no perceived differences in sweetness and coldness. In the second study, ice cream mixes were treated with lactase (EC 3.2.1.23) from the microbial sources Kluyveromyces lactis and Aspergillus oryzae to cause 0 to 100% lactose hydrolysis. Compression measurements and yield stress as measured by the vane method were both affected by the temperature of the samples. R2 values for compression measurements as related to lactose hydrolysis were higher then those obtained for yield stress measurements. Human evaluation determined a difference (p < 0.05) between the control samples (0% hydrolyzed) and the treatment groups (80% and 100% hydrolyzed). This research demonstrated a relationship between lactose hydrolysis and ease of dipping ice cream. The results implied that the effect of lactose hydrolysis on the dipping characteristics could be evaluated successfully by three different methods: the vane method, compression measurements, and human evaluation. Changes in freezing point due to lactose hydrolysis were minimal, implying that monitoring freezing point is not enough to determine textural characteristics. / Master of Science
14

Effects of Realistic First-Stage Turbine Endwall Features

Cardwell, Nicholas Don 03 January 2006 (has links)
The modern gas turbine engine requires innovative cooling techniques to protect its internal components from the harsh operating environment typically seen downstream of the combustor. Much research has been performed on the design of these cooling techniques thus allowing for combustion temperatures higher than the melting point of the parts within the turbine. As turbine inlet temperatures and efficiencies continue to increase, it becomes vitally important to correctly and realistically model all of the turbine's external cooling features so as to provide the most accurate representation of the associated heat transfer to the metal surfaces. This study examines the effect of several realistic endwall features for a turbine vane endwall. The first study addresses the effects of a mid-passage gap, endwall misalignment, and roughness on endwall film-cooling. The second study focuses on the effect of varying the combustor-to-turbine gap width. Both studies were performed in a large-scale low speed wind tunnel with the same vane geometry. Geometric and flow parameters were varied and the variation in endwall cooling effectiveness was evaluated. Results from these studies show that realistic features, such as surface roughness, can reduce the effectiveness of endwall cooling designs while other realistic features, such as varying the combustor-to-turbine gap width, can significantly improve endwall cooling effectiveness. It was found that, for a given coolant mass flowrate, a narrow combustor-turbine gap width greatly increased the coverage area of the leaked coolant, even increasing adiabatic effectiveness upstream of the vane stagnation point. The turbine designer can also more efficiently utilize leaked coolant from the combustor-to-turbine gap by controlling endwall misalignment, thereby reducing the overall amount of film-cooling needed for the first stage. / Master of Science
15

Impact of duty cycle on wear progression in variable-displacement vane oil pumps

Doikin, Aleksandr, Habib Zadeh, Esmaeil, Campean, Felician, Proest, Martin, Brown, A., Sherratt, A. 02 November 2018 (has links)
Yes / Variable-displacement vane oil pumps are increasingly employed in automotive powertrains for their efficiency benefits through reduced losses. However, confirming long life reliability of a new commodity based on limited data available from product development tests and early field experience is a significant challenge, which is addressed by the work presented in this paper. The approach presented combines physical examination of pumps returned from tests, with analysis of damage factors for pump wear progression, and an analysis of functional parameters for the powertrain system focused on the cause effect linkages across the systems hierarchy. The metrology results from physical measurements of used parts provide useful insights for the wear progression and the expected service performance of the pump. The paper also expands towards a data driven approach based on ECU data analysis that could provide a pathway towards the development of online health monitoring and diagnostics of the oil pumps. / Research project: “Intelligent Personalised Powertrain Health Care”, funded by Jaguar Land Rover.
16

Aerodynamic Investigation of Upstream Misalignment over the Nozzle Guide Vane in a Transonic Cascade

Lee, Yeong Jin 06 June 2017 (has links)
The possibility of misalignments at interfaces would be increased due to individual parts' assembly and external factors during its operation. In actual engine representative conditions, the upstream misalignments have effects on turbines performance through the nozzle guide vane passages. The current experimental aerodynamic investigation over the nozzle guide vane passage was concentrated on the backward-facing step of upstream misalignments. The tests were performed using two types of vane endwall platforms in a 2D linear cascade: flat endwall and axisymmetric converging endwall. The test conditions were a Mach number of 0.85, Re_ex 1.5*10^6 based on exit condition and axial chord, and a high freestream turbulence intensity (16%), at the Virginia tech transonic cascade wind tunnel. The experimental results from the surface flow visualization and the five-hole probe measurements at the vane-passage exit were compared with the two cases with and without the backward-facing step for both types of endwall platforms. As a main source of secondary flow, a horseshoe vortex at stagnation region of the leading edge of the vane directly influences other secondary flows. The intensity of the vortex is associated with boundary layer thickness of inlet flow. In this regard, the upstream backward-facing step as a misalignment induces the separation and attachment of the inlet flow sequentially, and these cause the boundary layer of the inlet flow to reform and become thinner locally. The upstream-step positively affects loss reduction in aerodynamics due to the thinner inlet boundary layer, which attenuates a horseshoe vortex ahead of the vane cascade despite the development of the additional vortices. And converging endwall results in an increase of the effect of the upstream misalignment in aerodynamics, since the inlet boundary layer becomes thinner near the vane's leading edge due to local flow acceleration caused by steep contraction of the converging endwall. These results show good correlation with many previous studies presented herein. / Master of Science
17

Development of Design Guidelines for In-Stream Flow Control Structures

Radspinner, Robert Ryan 18 June 2009 (has links)
The use of in-stream flow control structures for channel stabilization has become increasingly popular due to its potential cost-effectiveness and ecological benefits. These structures help to protect the bank from erosion and lateral migration. However, a large number of these projects fail due to inadequate design guidelines. This study aims to create authoritative design guidelines which are based on hydraulic and physical criteria attributed to the channel reach. In this report, some of the most common types of in-stream structures have been reviewed and results from a practitioner experience survey have been analyzed. This research has allowed for the selection of the most promising structures which will be studied later in the project. / Master of Science
18

Heat Transfer Measurements Using Thin Film Gauges and Infrared Thermography on a Film Cooled Transonic Vane

Reagle, Colin James 16 June 2009 (has links)
This work presents a comparison of thin film gauge (TFG) and infrared (IR) thermography measurement techniques to simultaneously determine heat transfer coefficient and film cooling effectiveness. The first comparison was with an uncooled vane where heat transfer coefficient was measured at Mex=0.77 and Tu=16%. Relatively good agreement was found between the results of the two methods and the effect of recovery temperature and data reduction time was analyzed. Improvements were made to the experimental set up for the next comparison, a showerhead film cooled vane. This geometry was tested at BR=0, 2.0, Mex=0.76 and Tu=16%. The TFG and IR results did not compare well for heat transfer coefficient or film cooling effectiveness. The effects of measured and calculated recovery temperature were analyzed as well as the respective data reduction methods, though the analysis could not account for the effectiveness trend seen on the suction surface. Finally, a vane with showerhead and shaped film cooling holes were presented at BR=0, 1.7, 2.0, 2.8, Mex=0.85, and Tu=13% to assess a new film cooling geometry measured with the IR technique. Similarities on the suction surface trend between the different film cooled geometries tested with IR indicate a flaw in the experiment that will require further analysis, changes and testing to complete the comparison with TFG. / Master of Science
19

"An Experimental Investigation of Showerhead Film Cooling Performance in a Transonic Vane Cascade at Low Freestream Turbulence"

Bolchoz, Ruford Joseph 17 June 2008 (has links)
In the drive to increase cycle efficiency, gas turbine designers have increased turbine inlet temperatures well beyond the metallurgical limits of engine components. In order to prevent failure and meet life requirements, turbine components must be cooled well below these hot gas temperatures. Film cooling is a widely employed cooling technique whereby air is extracted from the compressor and ejected through holes on the surfaces of hot gas path components. The cool air forms a protective film around the surface of the part. Accurate numerical prediction of film cooling performance is extremely difficult so experiments are required to validate designs and CFD tools. In this study, a first stage turbine vane with five rows of showerhead cooling was instrumented with platinum thin-film gauges to experimentally characterize film cooling performance. The vane was tested in a transonic vane cascade in Virginia Tech's heated, blow-down wind tunnel. Two freestream exit Mach numbers of 0.76 and 1.0—corresponding to exit Reynolds numbers based on vane chord of 1.1x106 and 1.5x106, respectively—were tested at an inlet freestream turbulence intensity of two percent and an integral length scale normalized by vane pitch of 0.05. The showerhead cooling scheme was tested at blowing ratios of 0 (no cooling), 1.5, and 2.0 and a density ratio of 1.35. Midspan Nusselt number and film cooling effectiveness distributions over the surface of the vane are presented. Film cooling was found to augment heat transfer and reduce adiabatic wall temperature downstream of injection. In general, an increase in blowing ratio was shown to increase augmentation and film cooling effectiveness. Increasing Reynolds number was shown to increase heat transfer and reduce effectiveness. Finally, comparing low turbulence measurements (Tu = 2%) to measurements performed at high freestream turbulence (Tu = 16%) by Nasir et al. [13] showed that large-scale high freestream turbulence can reduce heat transfer coefficient downstream of injection. / Master of Science
20

Flow Field Computations of Combustor-Turbine Interactions in a Gas Turbine Engine

Stitzel, Sarah M. 05 April 2001 (has links)
The current demands for higher performance in gas turbine engines can be reached by raising combustion temperatures to increase thermal efficiency. Hot combustion temperatures create a harsh environment which leads to the consideration of the durability of the combustor and turbine sections. Improvements in durability can be achieved through understanding the interactions between the combustor and turbine. The flow field at a combustor exit shows non-uniformities in pressure, temperature, and velocity in the pitch and radial directions. This inlet profile to the turbine can have a considerable effect on the development of the secondary flows through the vane passage. This thesis presents a computational study of the flow field generated in a non-reacting gas turbine combustor and how that flow field convects through the downstream stator vane. Specifically, the effect that the combustor flow field had on the secondary flow pattern in the turbine was studied. Data from a modern gas turbine engine manufacturer was used to design a realistic, low speed, large scale combustor test section. This thesis presents the results of computational simulations done in parallel with experimental simulations of the combustor flow field. In comparisons of computational predictions with experimental data, reasonable agreement of the mean flow and general trends were found for the case without dilution jets. The computational predictions of the combustor flow with dilution jets indicated that the turbulence models under-predicted jet mixing. The combustor exit profiles showed non-uniformities both radially and circumferentially, which were strongly dependent on dilution and cooling slot injection. The development of the secondary flow field in the turbine was highly dependent on the incoming total pressure profile. For a case with a uniform inlet pressure in the near-wall region no leading edge vortex was formed. The endwall heat transfer was found to also depend strongly on the secondary flow field, and therefore on the incoming pressure profile from the combustor. / Master of Science

Page generated in 0.0897 seconds