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  • 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.
41

Modeling and experimental evaluation of the effective bulk modulus for a mixture of hydraulic oil and air

2013 September 1900 (has links)
The bulk modulus of pure hydraulic oil and its dependency on pressure and temperature has been studied extensively over the past years. A comprehensive review of some of the more common definitions of fluid bulk modulus is conducted and comments on some of the confusion over definitions and different methods of measuring the fluid bulk modulus are presented in this thesis. In practice, it is known that there is always some form of air present in hydraulic systems which substantially decreases the oil bulk modulus. The term effective bulk modulus is used to account for the effect of air and/or the compliance of transmission lines. A summary from the literature of the effective bulk modulus models for a mixture of hydraulic oil and air is presented. Based on the reviews, these models are divided into two groups: “compression only” models and “compression and dissolve” models. A comparison of various “compression only” models, where only the volumetric compression of air is considered, shows that the models do not match each other at the same operating conditions. The reason for this difference is explained and after applying some modifications to the models, a theoretical model of the “compression only” model is suggested. The “compression and dissolve” models, obtained from the literature review, include the effects of the volumetric compression of air and the volumetric reduction of air due to the dissolving of air into the oil. It is found that the existing “compression and dissolve” models have a discontinuity at some critical pressure and as a result do not match the experimental results very well. The reason for the discontinuity is discussed and a new “compression and dissolve” model is proposed by introducing some new parameters to the theoretical model. A new critical pressure (PC) definition is presented based on the saturation limit of oil. In the new definition, the air stops dissolving into the oil after this critical pressure is reached and any remaining air will be only compressed afterwards. An experimental procedure is successfully designed and fabricated to verify the new proposed models and to reproduce the operating conditions that underlie the model assumptions. The pressure range is 0 to 6.9 MPa and the temperature is kept constant at °C. Air is added to the oil in different forms and the amount of air varies from about 1 to 5%. Experiments are conducted in three different phases: baseline (without adding air to the oil), lumped air (air added as a pocket of air to the top of the oil column) and distributed air (air is distributed in the oil in the form of small air bubbles). The effect of different forms and amounts of air and various volume change rates are investigated experimentally and it is shown that the value of PC is strongly affected by the volume change rate, the form, and the amount of air. It is also shown that the new model can represent the experimental data with great accuracy. The new proposed “compression and dissolve” model can be considered as a general model of the effective bulk modulus of a mixture of oil and air where it is applicable to any form of a mixture of hydraulic oil and air. However, it is required to identify model parameters using experimental measurements. A method of identifying the model parameters is introduced and the modeling errors are evaluated. An attempt is also made to verify independently the value of some of the parameters. The new proposed model can be used in analyzing pressure variations and improving the accuracy of the simulations in low pressure hydraulic systems. The new method of modeling the air dissolving into the oil can be also used to improve the modeling of cavitation phenomena in hydraulic systems.
42

Local controllability of affine distributions

Aguilar, CESAR 12 January 2010 (has links)
In this thesis, we develop a feedback-invariant theory of local controllability for affine distributions. We begin by developing an unexplored notion in control theory that we call proper small-time local controllability (PSTLC). The notion of PSTLC is developed for an abstraction of the well-known notion of a control-affine system, which we call an affine system. Associated to every affine system is an affine distribution, an adaptation of the notion of a distribution. Roughly speaking, an affine distribution is PSTLC if the local behaviour of every affine system that locally approximates the affine distribution is locally controllable in the standard sense. We prove that, under a regularity condition, the PSTLC property can be characterized by studying control-affine systems. The main object that we use to study PSTLC is a cone of high-order tangent vectors, or variations, and these are defined using the vector fields of the affine system. To better understand these variations, we study how they depend on the jets of the vector fields by studying the Taylor expansion of a composition of flows. Some connections are made between labeled rooted trees and the coefficients appearing in the Taylor expansion of a composition of flows. Also, a relation between variations and the formal Campbell-Baker-Hausdorff formula is established. After deriving some algebraic properties of variations, we define a variational cone for an affine system and relate it to the local controllability problem. We then study the notion of neutralizable variations and give a method for constructing subspaces of variations. Finally, using the tools developed to study variations, we consider two important classes of systems: driftless and homogeneous systems. For both classes, we are able to characterize the PSTLC property. / Thesis (Ph.D, Mathematics & Statistics) -- Queen's University, 2010-01-11 20:11:45.466
43

Conformal Vector Fields With Respect To The Sasaki Metric Tensor Field

Simsir, Muazzez Fatma 01 January 2005 (has links) (PDF)
On the tangent bundle of a Riemannian manifold the most natural choice of metric tensor field is the Sasaki metric. This immediately brings up the question of infinitesimal symmetries associated with the inherent geometry of the tangent bundle arising from the Sasaki metric. The elucidation of the form and the classification of the Killing vector fields have already been effected by the Japanese school of Riemannian geometry in the sixties. In this thesis we shall take up the conformal vector fields of the Sasaki metric with the help of relatively advanced techniques.
44

Atividades práticas para o ensino do conceito de tangente no 9° ano

Cruzado, Fábio Leandro 02 September 2016 (has links)
Submitted by Izabel Franco (izabel-franco@ufscar.br) on 2016-10-26T19:04:54Z No. of bitstreams: 1 DissFLC.pdf: 1637955 bytes, checksum: b94dbdba30fb59739948038e7cc356cf (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-11-08T18:30:42Z (GMT) No. of bitstreams: 1 DissFLC.pdf: 1637955 bytes, checksum: b94dbdba30fb59739948038e7cc356cf (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-11-08T18:30:48Z (GMT) No. of bitstreams: 1 DissFLC.pdf: 1637955 bytes, checksum: b94dbdba30fb59739948038e7cc356cf (MD5) / Made available in DSpace on 2016-11-08T18:30:55Z (GMT). No. of bitstreams: 1 DissFLC.pdf: 1637955 bytes, checksum: b94dbdba30fb59739948038e7cc356cf (MD5) Previous issue date: 2016-09-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / We introduce some geometric experiments to the students, and particularly the handling of right-angled triangles, with the clear purpose of inserting, firming and emphasizing the importance, historical and practical, of the concept and meaning of the geometric tangent in an entire acute angle in triangle. Later, the students built a rudimentary theodolite that was used to measure vertical angles of tops inaccessible objects from the ground and consequently the estimate of their heights. The prospect objects were trees, poles, masts, antennas, spotlights, among other more familiar to the students of the ninth grade in elementary school. / Neste trabalho apresentamos aos alunos alguns experimentos geométricos e, sobretudo, a manipulação de triângulos retângulos, com o claro objetivo de inserir, fixar e ressaltar a importância, histórica e prática, do conceito e do significado geométrico da tangente de um ângulo agudo. Posteriormente, os alunos construíram um teodolito rudimentar que foi utilizado para medir ângulos verticais de topos de objetos inacessíveis em relação ao solo e consequentemente o cálculo de suas alturas. Os objetos explorados foram árvores, postes, mastros, antenas, refletores, entre outros mais familiares para os estudantes do nono ano do Ensino Fundamental.
45

Existência de conexões versus módulos projetivos

Silva, Rafael Barbosa da 03 May 2013 (has links)
Made available in DSpace on 2015-05-15T11:46:16Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 578974 bytes, checksum: e512f47deae8cd03667ae8e7c2143b34 (MD5) Previous issue date: 2013-05-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The notions of connection and covariant derivative has its origin in the field of Riemannian geometry , where there is no distinction between them. In fact, in this study we found that these notions are equivalent if we consider modules over K-algebras of finite type. We also show that the existence of connections implies the existence of covariant derivative. The main goal of this study is to determine which modules admit connections. We easily verified that the projective modules admit connections. In fact, they form an affine space. But we also display a module that is not projective and has connection. Later, inspired by Swan's theorem, we explore in a straightforward way modules formed by sections of the tangent bundle of some surfaces in 3-dimensional real space. Finally, we study the notion of connection introduced by Alain Connes in modules over K-algebras not necessarily commutative. And we find in that context that the modules that have connection are exactly the projectives modules. / As noções de conexão e derivada covariante tem sua origem na área de geometria riemanniana, onde não existe distinção entre elas. De fato, nós verificamos neste trabalho, que estas noções são equivalentes se considerarmos módulos sobre K-álgebras comutativas de tipo finito. Também mostramos que a existência de conexões implica na existência de derivada covariante. O objetivo central deste trabalho é determinar que módulos admitem conexão. Verificamos facilmente que os módulos projetivos admitem conexões. De fato, elas formam um espaço afim. Mas também exibimos um módulo não projetivo que possui conexão. Posteriormente, inspirados pelo teorema de Swan, exploramos de maneira direta os módulos formados pelas seções do fibrado tangente de algumas superfícies no espaço 3- dimensional real. Por fim, estudamos a noção de conexão introduzida por Alain Connes em módulos sobre K-álgebras não necessariamente comutativas. E verificamos nesse contexto que os módulo que admitem conexão são exatamente os módulos projetivos.
46

Singularidades das Superfícies Regradas em R3 / Singularities of Ruled Surface in R3

Rodrigo Martins 18 February 2004 (has links)
Estudaremos as singularidades genéricas de superfécies regradas em R3. O objetivo do trabalho é mostrar que as singularidades genéricas que ocorrem no conjunto das superfícies regradas são as mesmas que ocorrem no conjunto das aplicações diferenciáveis de R2 em R3, enquanto que as singularidades genéricas das superfícies desenvolvíveis, que formam um subconjunto das superfícies regradas, são mais degeneradas. / We study generic singularities of ruled surfaces in R3. In this work we show that generic singularities appearing in the set of ruled surfaces are the same that occur in the set of map germs from R2 to R3, while the generic singularities of developable surfaces are more degenerate.
47

Métodos de otimização de terceira ordem / Third order optimization methods

Ferreira, Daiane Gonçalves, 1988- 22 August 2018 (has links)
Orientadores: Margarida Pinheiro Mello, Maria Aparecida Diniz Ehrhardt / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação Científica / Made available in DSpace on 2018-08-22T15:49:27Z (GMT). No. of bitstreams: 1 Ferreira_DaianeGoncalves_M.pdf: 1441315 bytes, checksum: 1196d8b21c6254dbdd0e0d68266fa707 (MD5) Previous issue date: 2013 / Resumo: Métodos de Otimização de terceira ordem, embora de longa tradição, eram considerados, até passado recente, impraticáveis, devido à taxa com que o esforço computacional cresce em função da dimensão do problema. Avanços no desenvolvimento de estruturas de dados, rotinas que trabalham com estas estruturas e a exploração da esparsidade de grande parte dos problemas encontrados na prática já permitem implementações destes métodos que podem torná-los competitivos com métodos de segunda ordem. O objeto desta dissertação é a apresentação do método de Halley, um método de terceira ordem, sua implementação em MATLAB e a realização de testes computacionais, visando uma comparação empírica de sua eficiência frente ao método de Newton, o método de segunda ordem mais empregado na atualidade / Abstract: Higher order optimization methods, though of long-standing tradition, until recently have been deemed impractical, due to the rate of increase of the computational effort as a function of the size of the problem. Advances in the development of data structures, routines that work with these structures and the use of the sparsity of a vast range of practical problems have led to implementations of these methods that are competitive with second order methods. The object of this dissertation is the study of Halley's method, a thirdorder method, the development of a MATLAB implementation thereof and its testing, aiming at an empirical comparison of its efficiency against that of Newton's method, the second-order method most widely used today / Mestrado / Matematica Aplicada / Mestra em Matemática Aplicada
48

Otimização em Meteorologia: cálculo de perturbações condicionais não-lineares ótimas / Optimization in Meteorology: computation of conditional nonlinear optimal perturbations

Jessé Américo Gomes de Lima 11 May 2012 (has links)
Neste trabalho estudamos as aplicações do método do Gradiente Espectral Projetado (SPG) em Meteorologia nos campos de previsibilidade, estabilidade e sensibilidade. Inicialmente revisamos os Vetores Singulares Lineares (LSVs) e em seguida apresentamos a teoria das Perturbações Condicionais Não-Lineares Ótimas (CNOPs). Enquanto os métodos clássicos estão baseados no Modelo Tangente Linear, as CNOPs são uma formulação do mesmo problema baseado em Programação Não-Linear. As CNOPs são descritas na literatura como responsáveis por melhorias em relação aos métodos anteriores. Finalmente analisamos três exemplos de aplicação do método à problemas de previsibilidade, estabilidade e sensibilidade. / A revision about applications of Spectral Projected Gradient (SPG) in meteorology is done in the fields of predictability, stability and sensitivity. Initially we review about Linear Singular Vectos (LSVs) and we present the Conditional Nonlinear Optimal perturbations (CNOPs). While the classic methods are based on the Tangent Linear Model, CNOPs are another formulation of the problem based on Nonlinear Programming. CNOPs are described in bibliography as responsible by better results than older methods. Finally we analyze three applications in predictability, stability and sensibility.
49

Iterative methods for the solution of the electrical impedance tomography inverse problem.

Alruwaili, Eman January 2023 (has links)
No description available.
50

Comparison of Dielectric Loss Measuring Methods on Epoxy Samples under Harmonic Distorted Voltages

Linde, Thomas, Backhaus, Karsten 21 November 2024 (has links)
The increasing number of power electronic devices in medium voltage networks lead to a harmonic distortion of the voltage waveforms in electrical systems. Medium frequency components up to several kHz are superimposed on the fundamental grid voltage. The distorted voltage waveforms stresses the insulation systems due to the additional current and hence additional dielectric losses. The heat generated from dielectric losses is suspected to be an accelerator to insulation ageing below partial discharge inception. Therefore, the systematic assessment of the losses and their correct quantification is crucial to designing reliable insulation systems with a high lifetime. The investigation of losses under nonsinusoidal and distorted voltage waveforms is not trivial and has been subject to little research to date, compared to investigations at 50 or 60 Hz. In this paper, several approaches of quantifying dielectric losses under multifrequent voltage waveforms are presented and compared. The losses of cast resin specimens are quantified with a test setup using a reference measurement method. The loss computation algorithms range from previously utilised Extrapolation and Superposition approaches to a direct power measurement technique. The results presented in this contribution show that the different measurement procedures provide considerably different outcomes for which possible explanations are given. The presented data indicates that realistic field strength conditions should be ensured in order to quantify the losses under distorted voltage waveformes correctly.

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