A utilização de concreto projetado como suporte de túneis é uma prática amplamente difundida no mundo inteiro. Este tipo material possui a característica de começar a agir estruturalmente desde pequenas idades. Apesar disso, os correntes processos de dimensionamento de suportes negligenciam o desenvolvimento de suas propriedades com o tempo, em acoplamento aos efeitos tridimensionais da região onde se localiza a frente de escavação. O presente trabalho tem a finalidade de relatar os procedimentos utilizados na análise da influência de alguns parâmetros da interação maciço - suporte, sobre os esforços solicitantes e os deslocamentos radiais finais do suporte de um túnel, tanto para o caso de concreto projetado, com suas propriedades dependentes do tempo, quanto para materiais com propriedades constantes. São elaboradas soluções adimensionais para o problema da quantificação de esforços solicitantes no suporte e de deslocamentos radiais na interface entre maciço e suporte. Além disso, é proposta uma forma de se determinar, através destas soluções adimensionais, coeficientes de alívio de tensões que auxiliam em simulações bidimensionais de escavações subterrâneas. / The utilization of shotcrete as tunnel support is a widely diffused practice in the whole world. This kind of material has the feature of beginning to act structurally since early ages. Nevertheless, the current processes of support design neglect the development of its properties after some time in connection to the 3D effects of the region where the face of the tunnel is located. The present work relates the procedures adopted in analyzing the influence of some ground-support interaction parameters on the support internal forces and interface radial displacements of a tunnel, not only when shotcrete is used, with its time-dependent properties, but for materials with constant properties as well. Dimensionless solutions are developed for the support thrust and radial displacement quantification problem. Moreover, through this dimensionless solution, a way of quantifying stress relief factors, which are intermediate steps in 2D simulations of underground excavations, is proposed.

This thesis describes research on Efficient Discrete Modelling of Axisymmetric Radiating Structures . Investigating the possibilities of surmounting the inherent limitation in the Cartesian rectangular Transmission Line Modelling (TLM) method due to staircase approximation by efficiently implementing the 3D cylindrical TLM mesh led to the development of a numerical model for simulating axisymmetric radiating structures such as cylindrical and conical monopole antennas. Following a brief introduction to the TLM method, potential applications of the method are presented. Cubic and cylindrical TLM models have been implemented in MATLAB and the code has been validated against microwave cavity benchmark problems. The results are compared to analytical results and the results obtained from the use of commercial cubic model (CST) in order to highlight the benefit of using a cylindrical model over its cubic counterpart. A cylindrical TLM mesh has not previously been used in the modelling of axisymmetric 3D radiating structures. In this thesis, it has been applied to the modelling of both cylindrical monopole and the conical monopole. The technique can also be applied to any radiating structure with axisymmetric cylindrical shape. The application of the method also led to the development of a novel conical antenna with periodic slot loading. Prototype antennas have been fabricated and measured to validate the simulated results for the antennas.

Ces travaux concernent l'étude expérimentale e analytique de la turbulence en phase de développement dans les fluides hétérogènes à densité et à viscosité variable. Ils font appel à des outils de diagnostics expérimentaux (anémométrie à fil chaud, technique de diffusion Rayleigh, Vélocimétrie Doppler Laser), et au formalisme des équations de Navier-Stockes à viscosité variable. L'innovation porte sur l'indépendance de la mesure de la vitesse. Après sa validation, la plate-forme expérimentale est exploitée pour l'étude comparative d'un jet de propane émergeant dans un milieu air-néon, à viscosité et densité variable, avec un jet d'air classique, à même quantité de mouvement injectée initialement. Ce travail se poursuit ensuite par un approfondissement des propriétés dans le champ proche, complétés par une approche analytique à partir des réécritures des équations de Navier-Stokes à viscosité variable. / This work is devoted to the study of the undeveloped turbulence in heterogeneus gaseus mixtures, using experimental tools (Hot-wire Anemometry, Rayleigh Light Scattering, Laser Doppler Velocimetry) and analytical methods (variable-viscosity Navier Stokes equations). A new technique combining HWA and RLS is first adapted to reliabily measure the fluctuating velocity and concentration fields in variable-viscosity flows (herein, a propane-air mixture). A variable-viscosity round jet (propane emerging into an air-neon mixture) is characterized and compared with a turbulent air jet discharging into still air, at the same initial jet momentum. An analytical work is further performed with a particular focus on the jet axis, based on the Navier-Stokes equations including variable viscosity to support the experiments. It is shown that the kinetic energy dissipation rate is enhanced by several additional terms, particularly involving 'viscosity-velocity' correlations.

This thesis is concerned with several problems in general relativity and low energy string theory that are pertinent to the time evolution of the gravitational field. We present a formulation of the Einstein field equations in terms of variational techniques borrowed from geometric analysis. These equations yield the evolution equations for the Cauchy problems of both general relativity and low energy string theory. We then proceed to investigate the evolutionary linear stability of Schwarzschild-like solutions in higher dimensional relativity called black strings. These objects are determined to be linearly unstable. This motivates a further stability analysis of the charged p-brane solutions of low energy string theory. We show that one can eliminate linear instabilities in p-branes for sufficiently large values of charge. We also consider the characteristic problem of general relativistic magnetohydrodynamics (GRMHD). We compute the eigenvalues and eigenvectors of GRMHD and establish degeneracy conditions. Finally, we consider the initial value problem for axisymmetric GRMHD. We formulate the general Einstein and MHD equations under the assumption of a stationary axisymmetric spacetime without assuming the circularity condition.

This thesis develops a two dimensional, axisymmetric finite element package for solving continuum problems including rubbleization subsidence and nonlinear fracture mechanics. This package includes both a user friendly preprocessor, PRESCRUBS.BYU, and a versatile analysis code SCRUBS.BYU. PRESCRUBS.BYU systematically creates the data file necessary to run SCRUBS.BYU. SCRUBS.BYU provides many options of nonlinear static analysis using either linear or quadratic isoparametric finite elements. Sample problems are presented that demonstrate the capabilities of this package.

Detonation-based propulsion systems are known for their high efficiency and energy release when compared to deflagrative systems, making them an ideal candidate in hypersonic propulsion applications. One such engine is the Oblique Detonation Wave (ODW) engine, which has a similar architecture to traditional scramjets but shortens the combustor and isolator to an anchored ODW after fuel injection. Previous research has focused on using a two-dimensional wedge to induce an ODW while limiting total losses through the combustor. In this configuration, a two-dimensional wedge-based architecture entails a rectangular duct, limiting potential inlet design and increasing overall skin friction. However, an inward-turning axisymmetric ODW wedge architecture, where a two-dimensional wedge is revolved around a central axis, has yet to be examined in detail. The work at present aims to investigate the fundamental physics required to predict the Oblique Shock Wave (OSW) for an inward-turning axisymmetric flow, which is critical for designing a circular ODW engine combustor. Multiple steady simulations of inviscid and ideal air at Mach 4, 6, and 8 were performed over a 1-inch wedge with wedge angles of 16°, 18°, and 20°. The radius of the inlet boundary was also varied between 1, 3, and 5 inches to examine the effect of increasing the blockage ratio. The results showed that the shock angle for an inward-turning axisymmetric flow was up to 8% steeper than the analytical, two-dimensional wedge solution. Additionally, it was found that the OSW diverged further from the two-dimensional solution when the blockage ratio was increased. These findings provide insight into the flow physics that must be considered when designing inward-turning axisymmetric ODW engines.

No description available.

<p>This thesis investigates the effect of different passive suppression techniques of different configurations on the flow-excited acoustic resonance of an internal axisymmetric cavity. This type of acoustic resonance is observed in many practical applications such as valves installed in steam pipe lines, and gas transport system. An experimental setup of a cavity-duct system has been altered to facilitate the study of the suppression and/or delay of resonance over the range of Mach number of 0.07-0.4. Three different cavity depths have been studied d=12.5 mm, 25 mm, and 50 mm deep. For each depth, the cavity length is changed from L=25 mm to 50 mm. The investigation matrix includes the study of two rounding radii, two chamfer geometries and three different types of spoilers, all located at the leading edge of the cavity. A reference case of no suppression seat installed for each of the examined cavity geometries is tested. Rounding off cavity edges for both radii has increased the acoustic pressure level, yet delayed the onset of resonance. Chamfering the upstream edge of the cavity delayed the onset of resonance as a result of increasing the cavity characteristic length which delays the coupling of the shear layer perturbations and the acoustic field. The delay and the suppression of resonance achieved by the chamfer depend on the size of the cavity. All spoiler configurations have proven effectiveness in delaying and suppressing resonance for all cavities. The choice of spoiler configuration would depend on cavity size and robustness/strength of acoustic resonance.</p> / Master of Science (MSc)

This work primarily centers on measuring the physical properties of molten salts. It's dedicated to outlining the methodology, enhancing measurement methods, and scrutinizing data to uncover insights regarding the interaction between molten salt and solid structures in the context of designing and generating electrical energy in molten salt reactors. The initial phase of this research involved collaborating with Brigham Young University's molecular dynamics simulation group to create an Archimedean density measurement device. This endeavor was primarily geared towards generating empirical data for the purpose of enhancing molecular dynamics simulation data. The tasks encompassed designing and validating the experimental setup, with a particular focus on measuring the densities of a novel salt composition--FMgNaK, a prospective nuclear fuel salt fuel/coolant. In the next chapter, we delve into the development, validation, and significant improvement of the rotational Couette viscosity measurement method at high temperatures. Originally designed for room temperature conditions, the methodology failed to account for the substantial temperature difference between the calibration fluids and the molten salts. Consequently, we introduce a theory aimed at correcting errors stemming from the thermal expansion of the solid container material during the transition from calibration to high temperature fluid measurement. As part of this comprehensive discussion, we also present the correction applied during the validation testing of the viscosity setup, with a specific focus on a nitrate salt known as solar salt. The final experiment development centered on the creation and validation of the Axisymmetric Drop-Shape Analysis (ADSA) method for use with molten salt. However, working with a specific nitrate salt, known as solar salt, posed challenges due to its propensity to wet all common high temperature substrates. This high degree of wetting posed hindrances to several physical properties measurements. Therefore, the primary objective of this work was to identify a non-wetting substrate to enhance the accuracy of ADSA and other measurement methods. Within this context, we present the results of surface tension and contact angle measurements, which were derived from the ADSA method, and the development of a non-wetting substrate for use with solar salt. In the final stage of this research, the ADSA method was applied to FLiBe, a critical fluoride salt in molten salt nuclear reactor design, and tellurium-bearing FLiBe to examine its interaction with boron nitride, a key solid porous material used in reactor vessel structures. Surface tension and contact angle measurements were conducted on various substrates, revealing the influence of oxygen on boron nitride wetting. Additionally, the study confirmed that tellurium, despite its chemical similarity to oxygen, did not significantly affect surface tension or contact angle, ruling out a substantial impact on boron nitride infiltration. The chapter also presents comprehensive data on the surface tension and densities of FLiBe, FLiNaK, and the chloride salt NaCl-KCl.

Dark matter is now accepted as an integral part of our universe, and galaxy dynamics have long provided the most convincing observational evidence for dark matter. Spiral galaxies have traditionally been used for these studies because of their more simple kinematics, however elliptical galaxies need to be understood as well. In this dissertation I present deep long-slit spectroscopy from the University of Texas’ Hobby-Eberly Telescope for a sample of elliptical galaxies. For a subsample of galaxies I fit axisymmetric orbit-superposition models with a range of dark halo density profiles. I find that all three galaxies modeled require a significant dark halo to explain their motions. However, the shape of the dark halo is not the expected NFW profile, but rather a profile with a flat central slope. I also discuss the galaxy masses, anisotropies, and stellar mass-to-light ratios. / text