In this study, efforts ensued to increase our knowledge of fluidization and gasification behavior of Geldart A particles using CFD. An extensive Eulerian-Eulerian numerical study was executed and simulations were compared and validated with experiments conducted at Utah State University. In order to improve numerical predictions using an Eulerian-Eulerian model, drag models were assessed to determine if they were suitable for fine particles classified as Geldart A. The results proved that if static regions of mass in fluidized beds are neglected, most drag models work well with Geldart A particles. The most reliable drag model for both single and binary mixtures was proved to be the Gidaspow-blend model. In order to capture the overshoot of pressure in homogeneous fluidization regions, a new modeling technique was proposed that modified the definition of the critical velocity in the Ergun correlation. The new modeling technique showed promising results for predicting fluidization behavior of fine particles. The fluidization behavior of three different mixtures of coal and poplar wood were studied. Although results indicated good mixing characteristics for all mixtures, there was a tendency for better mixing with higher percentages of poplar wood. In this study, efforts continued to model co-gasification of coal and biomass. Comparing the coal gasification of large (Geldart B) and fine (Geldart A) particles showed that using finer particles had a pronounced effect on gas yields where CO mass fraction increased, although H2 and CH4 mass fraction slightly decreased. The gas yields of coal gasification with fine particles were also compared using three different gasification agents. Modeling the co-gasification of coal-switchgrass of both fine particles of Geldart A and larger particles of Geldart B showed that there is not a synergetic effect in terms of gas yields of H2 and CH4. The gas yields of CO, however, showed a significant increase during co-gasification. The effects of gasification temperature on gas yields were also investigated. / Ph. D.

Newtonian theory was applied, in this analysis, to the elliptic cone segment at angles of attack and sideslip. Closed form expressions for the aerodynamic coefficients and static stability derivatives were obtained. Expressions for the full and half conic bodies were given and approximate expressions were given for the half cone case. The circular cone results were obtained as a special case of the general results. Comparisons of the theoretical calculations with experimental results at hypersonic speeds were made of the aerodynamic coefficients and static derivatives for several conic segments. Generally, good agreement was observed for specified ranges of fineness ratios and angles of attack. / Master of Science

This thesis describes the development and implementation of new computational techniques to predict installation losses for mixed compression inlets and a study of advanced technology nozzles. The new computational techniques have been created to predict drag and total pressure recovery for both axisymmetric and 2-D mixed compression inlet configurations. These inlets are designed for use in aircraft with sustained supersonic cruise capabilities such as the HSCT. The drag and pressure recovery prediction methods have been added to ACSYNT, an aircraft conceptual design program. Also included in this thesis is a survey of the performance of advanced technology nozzles. Axisymmetric and nonaxisymmetric geometries are considered, as are non thrust-vectoring nozzles. Only the internal losses of these nozzles are considered, and these losses are characterized by the thrust coefficient. The results of this survey have also been added to ACSYNT to extend the thrust prediction capabilities of the code. / Master of Science

This study focuses on measuring and normalizing the roughness noise of multiple roughness types across numerous layouts and flow speeds. Using the Virginia Tech Anechoic Wall Jet Facility, far field noise was recording for the flow of a turbulent wall jet boundary layer over cubes, hemispheres, and gravel, with element heights in the range of 14.3 - 55.2% of the boundary layer thickness. The sound radiated from the various layouts showed that the elements acted as independent sources when separated by three element diameters center-to-center or more. When the elements were placed shoulder to shoulder, interaction between the elements and shielding of the higher velocity flow lowered the noise per element produced. The far field roughness noise was then normalized using the theory of Glegg et al. (2007), which assumes a dipole efficiency factor. Comparisons were made between the theoretical drag spectrum model proposed by Glegg et al. (1987) and a modified version of this model made using the empirical data gathered. Overall, the theory of Glegg et al. (2007) succeeds greatly in collapsing the data into its non-dimensional drag spectra, but the original model spectrum did not fit well. The modified spectrum showed much greater fit with the data at all layouts and speeds. The collapse of the data using the theory of Glegg et al. (2007) confirms that roughness noise is dipole in nature. / Master of Science

This investigation sought first to determine the feasibility of generating a surrogate model of the interference drag between nacelles and wing-fuselage systems suitable for the inclusion in a multidisciplinary design optimization (MDO) framework. The target aircraft was a single-aisle, transonic aircraft with a freestream Mach number of 0.8 at 35,000 feet and a design lift coefficient of 0.5. Using an MDO framework is necessary for placing the nacelle because of the competing objectives of the disciplines involved in aircraft design including structures, acoustics, and aerodynamics. A secondary goal was to determine what tools are necessary for accurately capturing interference drag effects on the system. This research used both Euler computational fluid dynamics (CFD) with a coupled viscous drag estimation tool and Reynolds Averaged Navier-Stokes (RANS) CFD to estimate the system drag. The initial trade space exploration that varied the nacelle location across a baseline airframe configuration was completed with the Euler solver, and it showed that appreciable overlap between the wing and nacelle led to large increases in interference drag. A follow-on study was conducted with RANS CFD where the wing shape was tailored for each unique nacelle position. In comparing the results of the Euler and the RANS CFD, it was determined that RANS is required to accurately capture the flow features. Euler solvers can create artifacts due to the lack of viscous effects within the model. Wing tailoring is necessary because of the sensitivity of transonic flows to geometric changes and the addition of neighboring components, such as a nacelle. The research showed that for above and aft wing locations, a nacelle can overlap the trailing edge without incurring a drag penalty. Nacelles placed in the conventional location, forward and beneath the wing, displayed low interference drag effects, as the nacelle had a small and local impact on the wing's aerodynamics. Given the high cost of computing a RANS solution with wing tailoring, and the large design space for nacelle locations, building a surrogate model for interference drag was found to be prohibitive at this time. As the cost of computing and mesh generation decreases, collecting the data for building a surrogate model may become tractable. / Doctor of Philosophy / Engine placement on an aircraft is dependent on multiple disciplines. Engine placement affects the noise of the aircraft because the wing can shield or reflect the engine noise. Engine placement impacts the structural loads of an aircraft, with some positions requiring more reinforcement that adds to the cost and weight of the aircraft. Aerodynamically, the engine placement impacts the vehicle's drag. Taken together, the only means of trading the different disciplines' needs is through a multidisciplinary design optimization (MDO) framework. The challenge of MDO frameworks is that they require numerous solutions to effectively explore the trade space. Thus, MDO frameworks employ fast, low-order tools to compute hundreds or thousands of different combinations of features. A common approach to make running MDO analysis feasible is to develop surrogate models of the key considerations. Current aerodynamic drag build-ups for aircraft do not consider the interference drag associated with engine placement. The first goal of this research was to determine the feasibility of generating a surrogate model for inclusion in an MDO framework. In order to collect the data required for the surrogate, appropriate tools to capture the interference drag are required. Building a surrogate requires a large number of samples, thus the aerodynamic solver must be fast, robust, and accurate. An Euler (inviscid) computational fluid dynamics (CFD) was used do explore the engine placement design space to test the feasibility of building the surrogate model. The target aircraft was a single-aisle, transonic aircraft with a freestream Mach number of 0.8, flying at an altitude of 35,000 feet and a design lift coefficient of 0.5. The initial vehicle used a baseline wing, and the engine placement was varied across the wing span and fuselage. The results showed that the conventional location, where the engine is forward and beneath the wing, had the a modestly beneficial interference drag, though positions near the trailing edge and above the wing also showed neutral interference drag. In general, if the engine overlapped the wing, the interference drag increased dramatically. A follow-on study used Reynolds Averaged Navier-Stokes (RANS) CFD to investigate seven engine placements above and aft of the wing. Each of these positions had the wing tailored such that the wing performance would be typical of a good transonic wing. The results showed that with wing tailoring, a moderate amount of overlap between the wing and nacelle results in reduced or neutral interference drag. This is in contrast with the baseline wing results that showed moderate overlap led to large increases in interference drag. The results from this research suggest that building a surrogate model of interference drag for transonic aircraft is not feasible given today's computational resources. In order to accurately model the interference drag, one must use a RANS CFD solver and tailor the wing. These requirements increase the cost of evaluating an engine position such that collecting enough for a surrogate model is prohibitively expensive. As computational speeds increase, and the ability to automate CFD mesh generation becomes less time intensive, the feasibility may increase. Using an Euler solver is insufficient because of the lack of viscous effects in the flow. The lack of a boundary layer leads to artifacts appearing in the flow when the nacelle and wing are in close proximity.

Syftet med föreliggande studie är att bidra med kunskap om hur matematiklärare i årskurs 4–6 uppfattar och tänker om dialogiska drag. Dialogiska drag innebär att läraren skapar tillfällen där eleverna tillåts diskutera innehållet i matematiken. Studien bygger på semistrukturerade intervjuer som erhåller insikter i lärarnas perspektiv rörande deras tankar och uppfattningar kring dialogisk undervisning. Resultatet analyseras med hjälp av ett teoretiskt ramverk bestående av fyra grundläggande mål som bör uppfyllas för att genomföra givande dialogisk undervisning. Det kartlägger vilka mål lärarna strävar mot och i vilken utsträckning, samt vilka dialogiska drag de tillämpar för att uppnå dessa mål. Resultatet belyser att vissa mål uppnås i större utsträckning än andra, samt de fördelar, utmaningar och förutsättningar som identifieras med dialogbaserad undervisning.

Yes / Aquatic vegetation can significantly affect flow structure, sediment transport, bed scour and water quality in rivers, lakes, reservoirs and open channels. In this study, the lattice Boltzmann method is applied for performing the two dimensional numerical simulation of the flow structure in a flume with rigid vegetation. A multi-relaxation time model is applied to improve the stability of the numerical scheme for flow with high Reynolds number. The vegetation induced drag force is added in lattice Boltzmann equation model with the algorithm of multi-relaxation time in order to improve the simulation accuracy,. Numerical simulations are performed for a wide range of flow and vegetation conditions and are validated by comparing with the laboratory experiments. Analysis of the simulated and experimentally measured flow field shows that the numerical simulation can satisfactorily reproduce the laboratory experiments, indicating that the proposed lattice Boltzmann model has high accuracy for simulating flow-vegetation interaction in open channel. / National Natural Science Foundation of China (grant number: 11861003 and 11761005)

Under de senaste åren har den mobila tekniken i stort sett helt gått över till smartphones. Smartphones är i princip mer datorer än telefoner, som vi alltid bär med oss och som innehåller allt mer känslig information. Detta medför att kraven på säkerheten kring enheten ökar. Detta arbete undersöker om det är möjligt att finna en ny metod att låta användaren autentisera sig på, som är säkrare än de som är vedertagna idag, men samtidigt har liknande nivå av användbarhet. Vår idé, som vi arbetar med under namnet Colour a Symbol, baseras på att kombinera symboler och färger i par. För att utveckla idén skapade vi en funktionell prototyp, som sedan utvärderadesmed hjälp av en mindre testgrupp. Empirin visar på att Colour a Symbol har en god användbarhet, om än något för lång inloggningstid. Idéer för att förbättra inloggningstiden presenteras. Teoretiskt sett så är Colour a Symbol säkrare än exempelvis pinkod, men testgruppen var inte tillräckligt stor för att kunna bedöma den praktiska lösenordsrymden. Utformning av symboltema påverkar även förmodligen i hög grad den praktiska lösenordsrymden. Vår slutsats är att idén har en klar potential, men att det behövs ytterligare studier för att finslipa den. / During the past years mobile technology has moved almost entirely to smartphones. Smartphones are in essence more computers than phones, which we always carry with us and that contain ever more sensitive information. This requires that the level of security around the device increases. This study strives to find a new method of authenticating users, that is more secure than those that are established today, but at the same time has a similar level of usability. Our idea, which we work with under the name Colour a Symbol, is based upon making combinations of symbols and colours in pairs. In order to develop the idea we created a functional prototype, that was evaluated by a smaller test group. The empirical data implies that Colour a Symbol has good usability, if only a little too long login time. Ideas as to shorten the login time are suggested. Theoretically, Colour a Symbol is more secure than for an example pincode, but the test group was not large enough to estimate the practical password space. Design of the symbol theme probably also affects the practical password space to a high degree. Our conclusion is that the idea has clear potential, but that further studies are needed to fine-tune it.

No description available.

The flow of polymer solutions in the high Elasticity number, El, regime in complex geometries may lead to strong viscoelastic behaviour and eventually become unstable as the Weissenberg number, Wi, is increased beyond a critical level. So far, the success of numerical simulations in predicting the highly non-linear behaviour of polymer solutions in complex flows has been limited. In this thesis, selected constitutive models are evaluated under the high El flow regime in the cross-slot and contraction benchmark flows using a numerical technique based on the finite volume method. The numerical technique is implemented within the OpenFOAM framework and thoroughly validated in the benchmark flow. A modification to the FENE dumbbell model based on the non-affine deformation of polymer solutions is proposed, which enabled the prediction of some non-linear material functions and also enhanced numerical stability, allowing a higher Wi to be attained. Asymmetric flow instability in the cross-slot flow has been studied. Time-dependent stability diagrams were constructed based on Wi and the strain, ε, both of which govern the stretching of a polymer chain. In the contraction flow, elastic instability is simulated for the first time in this geometry. Substantial time-dependent asymmetric flow patterns were predicted as seen in experiments. The effect of the contraction ratio is investigated through a stability diagram. Three-dimensional finite element simulations were also carried out to study the effect of the aspect ratio in the contraction flow of a Phan-Thien-Tanner fluid. The simulations suggest that a lip vortex mechanism is a signature for the onset of strong viscoelastic behaviour.