No description available.

No description available.

The object of this study is to incorporate a nonlinear material law for wood in the finite element program ABAQUS to develop effective finite element models of glulam domes, and to investigate the buckling behavior of glulam domes using this finite element program. The material law is implemented with a FORTRAN subroutine. Results from thorough testing of the subroutine are presented. The dome is then modeled with I-DEAS and, analyzed with ABAQUS. The modeling procedure is briefly discussed, and the results from the stability analysis of the dome are presented. Finally, conclusions and further research scope based on this study are presented. / Master of Science

<div>The growing need to improve the power density of compact thermal systems necessitates developing new techniques to modulate the convective heat transfer efficiently. In the present research, acoustic streaming is evaluated as a potential technology to achieve this objective. Numerical simulations using the linearized and fully non-linear Navier-Stokes equations are employed to characterize the physics underlying this process. The linearized Navier-Stokes equations accurately replicate the low-frequency flow unsteadiness, which is used to find the optimal control parameters. Local and global stability analysis tools were developed to identify the modes with a global and positive heat transfer effect.</div><div><br></div><div>High-fidelity numerical simulations are performed to evaluate the effect of the excitation at selected frequencies, directed by the linear stability analysis, on the heat and momentum transport in the flow. Results indicate that, under favorable conditions, superimposing an acoustic wave, traveling along with the flow, can <i>resonate</i> within the domain and lead to a significant heat transfer enhancement with minimal skin friction losses. Two main flow configurations are considered; at the fixed Reynolds number Re_b=3000, in the supersonic case, 10.1% heat transfer enhancement is achieved by an 8.4% skin friction increase; however, in the subsonic case, 10% enhancement in heat transfer only caused a 5.3% increase to the skin friction. The deviation between these two quantities suggests a violation of the Reynolds analogy. This study is extended to include a larger Reynolds number, namely Re_b=6000 at M_b=0.75 and a similar response is observed. The effect of excitation amplitude and frequency on the resonance, limit-cycle oscillations, heat transfer, and skin friction are also investigated here.</div><div><br></div><div>Applying acoustic waves normal to the flow in the spanwise direction disrupts the near-wall turbulent structures that are primarily responsible for heat and momentum transport near the solid boundary. Direct numerical simulations were employed to investigate this technique in a supersonic channel flow at M_b=1.5 and Re_b=3000. The external excitation is applied through a periodic body force in the spanwise direction, mimicking loudspeakers placed on both walls that are operating with a 180^o phase shift. By keeping the product of forcing amplitude A_f and pulsation period (<i>T</i>) constant, spanwise velocity perturbations are generated with a similar amplitude at different frequencies. Under this condition, spanwise pulsations at <i>T</i>=20 and <i>T</i>=10 show up to 8% reduction in Nusselt number as well as the skin friction coefficient. Excitation at higher or lower frequencies fails to achieve such high level of modulations in heat and momentum transport processes near the walls.<br> <br>In configurations involving a spatially-developing boundary layer, a computational setup that includes laminar, transitional, and turbulent regions inside the domain is considered and the impact of acoustic excitation on this flow configuration has been characterized. Large-eddy simulations with dynamic Smagorinsky sub-grid scale modeling has been implemented, due to the excessive computational cost of DNS calculations at high-Reynolds numbers. The optimal excitation frequency that resembles the mode chosen for the fully-developed case has been identified via global stability analysis. Fully non-linear simulations of the spatially-developing boundary layer subjected to the excitation at this frequency reveal an interaction between the <i>pulsations</i> and the perturbations originated from the tripping which creates a re-laminarization zone traveling downstream. Such technique can locally enhance or reduce the heat transfer along the walls.<br></div>

Doctor of Philosophy / Department of Electrical and Computer Engineering / Shelli K. Starrett / Monitoring and control of modern power systems have become very complex tasks due to the interconnection of power grids. These large-scale power grids confront system operators with a huge set of system inputs and control parameters. This work develops and compares intelligent systems-based algorithms which may be considered by power system operators or planners to help manage, process, and evaluate large amounts of data due to varying conditions within the system. The methods can be used to provide assistance in making operational control and planning decisions for the system in a timely manner. The effectiveness of the proposed algorithms is tested and validated on four different power systems. First, Artificial Neural Network (ANN) models are developed and compared for two different voltage collapse indices and utilizing two different-sized sets of inputs. The ANNs monitor and evaluate the voltage profile of a system and generate intelligent conclusions regarding the status of the system from a voltage stability perspective. A feature reduction technique, based on the analysis of generated data, is used to decrease the number of inputs fed to the ANN, decreasing the number of physical quantities that need to be measured. The major contribution of this work is the development of four different algorithms to control the VAR resources in a system. Four different objectives were also considered in this part of the work, namely: minimization of the number of control changes needed, minimization of the system power losses, minimization of the system's voltage deviations, and consideration of the computational time required. Each of the algorithms is iterative in nature and is designed to take advantage of a method of decoupling the load flow Jacobian matrix to decrease the time needed per iteration. The methods use sensitivity information derived from the load flow Jacobian and augmented with equations relating the desired control and dependent variables. The heuristic-sensitivity based method is compared to two GA-based methods using two different objective functions. In addition, a FL algorithm is added to the heuristic-sensitivity algorithm and compared to a PS-based algorithm. The last part of this dissertation presents the use of one of the GA-based algorithms to identify the size of shunt capacitor necessary to enhance the voltage profile of a system. A method is presented for utilizing contingency cases with this algorithm to determine required capacitor size.

No description available.

The main purpose of this thesis is to define the stability of a system of linear difference equations of the form, ∇y(t) = Ay(t), and to analyze the stability theory for such a system using the eigenvalues of the corresponding matrix A in nabla discrete calculus and nabla fractional discrete calculus. Discrete exponential functions and the Putzer algorithms are studied to examine the stability theorem. This thesis consists of five chapters and is organized as follows. In the first chapter, the Gamma function and its properties are studied. Additionally, basic definitions, properties and some main theorem of discrete calculus are discussed by using particular example. In the second chapter, we focus on solving the linear difference equations by using the undetermined coefficient method and the variation of constants formula. Moreover, we establish the matrix exponential function which is the solution of the initial value problems (IVP) by the Putzer algorithm.

[pt] O trabalho propõe uma metodologia para elaboração de modelos geológicos e geomecânicos (3D) e realização de análises de estabilidade (2D)de taludes rochosos de minas a céu aberto, com base nos dados da mina de Morro da Mina, fornecidos pela empresa VALE, a qual esta pertence. A metodologia está dividida em duas etapas: modelagem e análises de estabilidade. Para a modelagem, foi utilizado o software Petrel 2004, que oferece ferramentas geoestatísticas, possibilitando a extrapolação das informações geotécnicas pontuais c`, fi, RQD, Q e RMR, obtidas por meio de testemunhos de sondagem, para o maciço inteiro. Utilizou-se a técnica de Krigagem Ordinária. O modelo gerado representou bem a distribuição destas propriedades no espaço. Na etapa de análise de estabilidade, foram utilizadas seções resultantes da modelagem geomecânica. Dois tipos de análises foram realizados: análises cinemáticas, com utilização do software Dips, da Rocscience, e análises por equilíbrio limite dos taludes globais e das bancadas, utilizando-se o software Slide 5.0, também da Rocscience. No primeiro tipo, realizado com dois conjuntos de mapeamentos diferentes, foi constatado que as bancadas devem receber bastante atenção nesta mina, e no segundo tipo, foi verificada a segurança quanto à ruptura circular das bancadas e taludes globais, porém recentemente ocorreu uma ruptura em um dos locais analisados. Os programas RocData 4.0 e RocProp, ambos da Rocscience, foram utilizados para estimar os parâmetros de resistência de Mohr-Coulomb, e os softwares AutoCAD 2004 e Microsoft Office Excel auxiliaram na preparação dos arquivos de entrada no Petrel 2004 e no Slide 5.0. / [en] This work presents a methodology to develop geological and geomechanic models (3D) and to carry out stability analyses (2D) of rock slopes of open pit mine, based on data of Morro da Mina mine, provided by the mining company VALE. The methodology is divided in two stages: modelling and stability analyses. For the modelling, the software Petrel 2004, which allows the use of geostatistical tools, was used, being possible the spatial distribution of geotechnical information, obtained from borehole cores, for the whole rock mass. The technique of Ordinary Kriging was used. The modeled properties were the following: c`, fi, RQD, Q e RMR. The generated model represented well the spatial distribution of these properties. The stability analyses were carried out using 2D sections and the necessary rock mass parameters were obtained from the geomechanical model. Two types of analyses were carried out: kinematic analyses, with use of the software Dips, from Rocscience, and limit equilibrium analyses of the global slopes and the benches, where the software Slide 5.0, also from Rocscience was used. The Kinematic analyses, carried out considering two sets of joint orientations, suggested that the benches have to receive enough attention in this mine, and the limit equilibrium analyses for circular failure of the benches and global slopes indicated high factors of safety. However, before this work initiating a failure already had happened in one of the sections analyzed. The programs RocData 4.0 and RocProp, both from Rocscience, were used to estimate the Mohr-Coulomb strength parameters, and the programs AutoCAD 2004 and Microsoft Office Excel helped at the development of the input files in the Petrel 2004 and Slide 5.0.

Ce manuscrit présente une étude couplée, numérique et théorique, portant sur les écoulements tournants transitionnels et turbulents. L'accent y est mis sur la formation de structures macroscopiques cohérentes au sein de l'écoulement, générées par des procédés rendus fortement tri-dimensionnels par la présence des couches limites sur les disques et le long des parois cylindriques extérieure (carter) et/ou intérieure (moyeu). La complexité de ces écoulements pose de véritables difficultés en recherche fondamentale mais les résultats de ces travaux ont aussi une importance non négligeable pour les machines industrielles tournantes, depuis les disque-durs jusqu'aux turbopompes spatiales, la conception de ces dernières étant la motivation première pour ces travaux de thèse. Ce travail peut être divisé en deux sous-parties. Dans un premier temps, les cavités industrielles sont modélisées par de simples cavités rotor/stator lisses pour y étudier la dynamique de l'écoulement. Comme les campagnes expérimentales sur les machines industrielles ont révélé de dangereux phénomènes instationnaires en leur sein, l'accent est mis sur l'obtention et l'étude des fluctuations de pression dans les écoulements modèles. Ensuite, les SGE de trois configurations de turbine industrielle réelle sont réalisées pour étudier les fluctuations de pression in situ et appliquer les diagnostiques éprouvés sur les géométries modèles. / This thesis provides a numerical and theoretical investigation of transitional and turbulent enclosed rotating flows, with a focus on the formation of macroscopic coherent flow structures. The underlying processes are strongly threedimensional due to the presence of boundary layers on the discs and on the walls of the outer (resp. inner) cylindrical shroud (resp. shaft). The complexity of these flows poses a great challenge in fundamental research however the present work is also of importance for industrial rotating machinery, from hard-drives to space engines turbopumps - the design issues of the latter being behind the motivation for this thesis. The present work consists of two major investigations. First, industrial cavities are modeled by smooth rotor/stator cavities and therein the dominant flow dynamics is investigated. For the experimental campaigns on industrial machinery revealed dangerous unsteady phenomena within the cavities, the emphasis is put on the reproduction and monitoring of unsteady pressure fluctuations within the smooth cavities. Then, the LES of three configurations of real industrial turbines are conducted to study in situ the pressure fluctuations and apply the diagnostics already vetted on academic problems.

An overview of unsteady incompressible jet flows is presented, with the primary interest being radially developing jets in cylindrical polar coordinates. The radial free jet emanates from some orifice, being axisymmetric about the transverse (z) axis and possessing reflectional symmetry across its z=0 centreline. The radial wall jet is also axisymmetric about the transverse axis, however in this case impermeability and no-slip conditions are imposed at the wall, which is situated at z=0. The numerical solution of a linear perturbation superposed on the free jet, whose temporal form is assumed to be driven by a periodic source pulsation, gives rise to a wave-like disturbance whose amplitude grows downstream as its local wavelength decreases. An asymptotic analysis of this linear perturbation, which applies to the wall jet as well with some minor changes, captures the exact nature of the exponential spatial growth, and also algebraic attenuation of the growth. The linear theory is only valid for a small amplitude pulsation (|ε| << 1, where ε is the perturbation amplitude). When a nonlinear pulsation (ε = O(1)) is applied to the radial free jet, any linear theory must be dropped. Solving the full nonlinear system of equations reveals singular behaviour at a critical downstream location, which corresponds to the presence of an infinitely steep downstream gradient. The replacement of molecular diffusivity with a larger-scale eddy viscosity does little to affect the qualitative growth of the linear perturbation. In order for an experimental study to reproduce any of the discussed boundary-layer results, we must consider the behaviour of jet-type flows at finite Reynolds number. This involves solving the full Navier-Stokes equations numerically, to determine the Reynolds number at which we should expect to qualitatively recover boundary-layer behaviour. The steady solution for the radial free jet and its linear pulsation are studied in this way, as is the linear pulsatile planar free jet. We may enhance the streamwise velocity of a radial jet by applying swirl around the z axis. Modulating this swirl is looked at as a possible mechanism to induce the previously discussed pulsation, which then motivates the introduction of a finite spinning disk problem. In this case the system may be completely confined within an enclosed cylinder, making a hypothetical experimental approach somewhat more approachable.