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ROLE OF IMPURITIES ON DEFORMATION OF HCP CRYSTAL: A MULTISCALE APPROACHJanuary 2014 (has links)
abstract: Commercially pure (CP) and extra low interstitial (ELI) grade Ti-alloys present excellent corrosion resistance, lightweight, and formability making them attractive materials for expanded use in transportation and medical applications. However, the strength and toughness of CP titanium are affected by relatively small variations in their impurity/solute content (IC), e.g., O, Al, and V. This increase in strength is due to the fact that the solute either increases the critical stress required for the prismatic slip systems ({10-10}<1-210>) or activates another slip system ((0001)<11-20>, {10-11}<11-20>). In particular, solute additions such as O can effectively strengthen the alloy but with an attendant loss in ductility by changing the behavior from wavy (cross slip) to planar nature. In order to understand the underlying behavior of strengthening by solutes, it is important to understand the atomic scale mechanism. This dissertation aims to address this knowledge gap through a synergistic combination of density functional theory (DFT) and molecular dynamics. Further, due to the long-range strain fields of the dislocations and the periodicity of the DFT simulation cells, it is difficult to apply ab initio simulations to study the dislocation core structure. To alleviate this issue we developed a multiscale quantum mechanics/molecular mechanics approach (QM/MM) to study the dislocation core. We use the developed QM/MM method to study the pipe diffusion along a prismatic edge dislocation core. Complementary to the atomistic simulations, the Semi-discrete Variational Peierls-Nabarro model (SVPN) was also used to analyze the dislocation core structure and mobility. The chemical interaction between the solute/impurity and the dislocation core is captured by the so-called generalized stacking fault energy (GSFE) surface which was determined from DFT-VASP calculations. By taking the chemical interaction into consideration the SVPN model can predict the dislocation core structure and mobility in the presence and absence of the solute/impurity and thus reveal the effect of impurity/solute on the softening/hardening behavior in alpha-Ti. Finally, to study the interaction of the dislocation core with other planar defects such as grain boundaries (GB), we develop an automated method to theoretically generate GBs in HCP type materials. / Dissertation/Thesis / Doctoral Dissertation Mechanical Engineering 2014
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Computer-aided design of a glass window polymer coextrusion dieLakshminarayan, Balasubramanyam January 1984 (has links)
No description available.
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Примена триболошких истраживања на примарним деловима вентила у гасним системима природног гаса / Primena triboloških istraživanja na primarnim delovima ventila u gasnim sistemima prirodnog gasa / The application of tribological research on primary parts of valves in gas systemsAleksić Željko 01 July 2016 (has links)
<p>У раду је извршено триболошко истраживање у области граничног<br />подмазивања које се јавља на примарним деловима вентила у<br />системима природног гаса. Истраживања су извршена етапно, у<br />реалним и, лабораторијским условима, користећи савремене методе<br />триболошких експерименталних истраживања. Извршена је замена<br />могућим оптималним материјалима трибо парова у односу на реалне<br />ефектуиране материјале вентила. Креирана су нова мазива за област<br />граничног подмазивања у односу на инострана и извршено је<br />упоређивање по више критеријума. Статистичка, металографска,<br />хемијска и физичка испитивања трибо парова су извршена и<br />упоређивана.</p> / <p>U radu je izvršeno tribološko istraživanje u oblasti graničnog<br />podmazivanja koje se javlja na primarnim delovima ventila u<br />sistemima prirodnog gasa. Istraživanja su izvršena etapno, u<br />realnim i, laboratorijskim uslovima, koristeći savremene metode<br />triboloških eksperimentalnih istraživanja. Izvršena je zamena<br />mogućim optimalnim materijalima tribo parova u odnosu na realne<br />efektuirane materijale ventila. Kreirana su nova maziva za oblast<br />graničnog podmazivanja u odnosu na inostrana i izvršeno je<br />upoređivanje po više kriterijuma. Statistička, metalografska,<br />hemijska i fizička ispitivanja tribo parova su izvršena i<br />upoređivana.</p> / <p>In this paper an experimental tribological research was carried out at the field<br />of boundary lubrication wich appear on primary parts of valves in systems of<br />natural gas. Research was carried out in stages, at the real conditions and in<br />the laboratory, using modern methods of experimental research of wear.<br />Replacement of materials was made with possible optimized tribo pairs in<br />relation to the real effectuated materials of valve. The new lubricants were<br />created for boundary lubrication regime with respect to foreign and<br />comparison was made through more criteria. Statistical, metallographic,<br />chemical and physical test were performed with tribo pairs and compared.</p>
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[en] AN EXPEDITE IMPLEMENTATION OF THE HYBRID BOUNDARY ELEMENT METHOD FOR POTENTIAL AND ELASTICITY PROBLEMS / [pt] UMA IMPLEMENTAÇÃO EXPEDITA DO MÉTODO HÍBRIDO DOS ELEMENTOS DE CONTORNO PARA PROBLEMAS DE POTENCIAL E ELASTICIDADECARLOS ANDRES AGUILAR MARON 14 January 2015 (has links)
[pt] O desenvolvimento consistente do método convencional dos elementos de contorno (CBEM), com a adição de conceitos da versão simplificada do método híbrido dos elementos de contorno (HBEM), proveniente do potencial variacional de Hellinger-Reissner, conduz-se a um processo computacionalmente mais econômico, sem a necessidade de ter sua precisão numérica reduzida para problemas de grande escala, podendo ser bidimensional ou tridimensional, de potencial ou elasticidade. Conseguiu-se mostrar que as matrizes de potencial duplo e simples do CBEM, H e G, respectivamente, cuja avaliação numérica requer a manipulação de integrais singulares e impróprias, podem ser obtidas de maneira expedita, eliminando-se quase toda a integração numérica, com exceção de algumas integrais regulares.
Uma importante característica da formulação proposta, que advém da base variacional do HBEM, é a facilidade da obtenção de resultados em pontos internos, de maneira direta e sem a utilização de qualquer integral de contorno, já que a solução fundamental é a própria solução do problema.
O presente trabalho pertence a um projeto cujo resultado final deve ser um código computacional para problemas de grande escala (milhões de graus de liberdade). Nesta fase, alguns exemplos numéricos foram testados para avaliar a aplicabilidade do método expedito, o seu esforço computacional e a convergência do resultado para as variáveis envolvidas no método. Para isso, foram implementados algoritmos para problemas bidimensionais de potencial e elasticidade - usando elementos lineares, quadráticos e cúbicos - e tridimensionais - usando elementos triangulares e quadrilaterais, lineares e quadráticos nos dois casos. Os códigos computacionais foram implementados focando na solução de problemas de grande escala. Espera-se que numa etapa final o projeto possa ser bem mais eficaz, com a incorporação de procedimentos do método fast multipole. / [en] The consistent development of the conventional boundary elements method (CBEM) by adding the concepts of the hybrid boundary element simplified method (HBEM) , from the Hellinger-Reissner variational potential leads to a computationally less intensive procedure, although not necessarily less accurate for large scale, two-dimensional or three-dimensional problems of potential and elasticity. It was shown that both single-layer and double-layer potential matrices, G and H, respectively, are obtained in an expeditious way that vanish almost any numerical integration, except for a few regular integrals, even G and H evaluation requires the handling of singular and improper integrals. The proposed formulation comes from the HBEM variational base and its evaluation at internal points is straightforward without the application of any boundary integral, since the fundamental solution is the analytical one. This work belongs to a project that aims a computer code for large-scale problems (millions of degrees of freedom). At this stage, some numerical examples were analyzed to evaluate the applicability of the method expeditious its computational effort and convergence of the results for the variables involved in the method. It was developed by the algorithms implementation for potential and elasticity problems. In the case of two-dimensional were employed linear, quadratic and cubic elements and to the three-dimensional case were employed triangular, quadrilateral, linear and quadratic elements in both cases. The computational codes were always implemented focused on solving largescale problems. It is expected that in a final stage of the project with the incorporation procedure of the method fast multipole, it can be more efficiently.
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[en] THE SIMPLIFIED HYBRID BOUNDARY ELEMENT METHOD APPLIED TO TIME DEPENDENT PROBLEMS / [pt] O MÉTODO HÍBRIDO SIMPLIFICADO DOS ELEMENTOS DE CONTORNO APLICADO A PROBLEMAS DEPENDENTES DO TEMPORICARDO ALEXANDRE PASSOS CHAVES 22 March 2004 (has links)
[pt] O Método Híbrido dos Elementos de Contorno foi introduzido
em 1987. Desde então, o método foi aplicado com sucesso a
diferentes tipos de problemas de elasticidade e potencial,
inclusive problemas dependentes do tempo. Esta Tese
apresenta uma tentativa para consolidar a formulação
simplificada do Método Híbrido dos Elementos de Contorno
para a análise geral da resposta dinâmica de sistemas
elásticos. Baseado em um método de superposição modal, um
conjunto acoplado de equações diferenciais de movimento de
alta ordem é transformado em um conjunto desacoplado de
equações diferenciais de segunda ordem que podem ser
integradas normalmente por meio de procedimentos
conhecidos. Este método também é uma extensão de uma
formulação introduzida por J. S. Przemieniecki, para a
análise de vibração livre de barras e elementos de viga
baseada em uma série de freqüências. O método trata
estruturas restringidas, com condições iniciais não
homogêneas dadas como valores nodais e também através de
campos prescritos no domínio, assim como forças genéricas
de massa (além de forças inerciais). Esta tese também tem
por objetivo estabelecer a consolidação conceitual da
aplicação da versão simplificada do Método Híbrido dos
Elementos de Contorno a materiais com gradação funcional.
São obtidas várias classes de soluções fundamentais para
problemas de potencial dependentes e independentes do
tempo, para a análise no domínio da freqüência combinada
com uma técnica avançada (mencionada acima) de superposição
modal baseada em séries de freqüências. Com isso, consegue-
se a utilização de integrais somente no contorno mesmo para
materiais heterogêneos. Apresenta-se um grande número de
resultados numéricos de problemas bidimensionais, para
validação dos desenvolvimentos teóricos realizados. / [en] The hybrid boundary element method was introduced in 1987.
Since then, the method has been successfully applied to
different problems of elasticity and potential, including
time-dependent problems. This thesis presents an attempt to
consolidate a formulation for the general analysis of the
dynamic response of elastic systems. Based on a mode-
superposition technique, a set of coupled, higher-order
differential equations of motion is transformed into a set
of uncoupled second order differential equations, which may
be integrated by means of standard procedures. The first
motivation for these theoretical developments is the hybrid
boundary element method, a generalization of T. H. H.
Pian`s previous achievements for finite elements, which,
requiring only boundary integrals, yields a stiffness
matrix for arbitrary domain shapes and any number of
degrees of freedom. The method is also an extension of a
formulation introduced by J. S. Przemieniecki, for the free
vibration analysis of bar and beam elements based on a
power series of frequencies. It handles constrained and
unconstrained structures, non-homogeneous initial
conditions given as nodal values as well as prescribed
domain fields and general domain forces (other than
inertial forces). This thesis also focuses on establishing
the conceptual framework for applying the simplified
version of the hybrid boundary element method to
functionally graded materials. Several classes of
fundamental solutions for steady-state and time-dependent
problems of potential are derived for a frequency-domain
analysis combined with an advanced mode superposition
technique based on a power series of frequencies. Thus, the
boundary-only feature of the method is preserved even with
such spatially varying material property.Several numerical
examples are given in terms of an efficient patch test for
irregular bounded, unbounded and multiply connected regions
submitted to high gradients.
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Transition Zone In Constant Pressure Boundary Layer With Converging StreamlinesVasudevan, K P 01 1900 (has links)
The laminar-turbulent transition in viscous fluid flows is one of the most intriguing problems in fluid dynamics today. In view of the enormous applications it has in a variety of fields such as aircraft design, turbomachinery, etc., scientists have now realized the importance of tackling this problem effectively. Three-dimensional flows are usually associated with pressure gradient, streamline curvature, streamline convergence / divergence etc., all acting simultaneously. Towards a better understanding of the transition process and modeling the transition zone, it is important to study the effect of each of these parameters on the transitional flow. The present work aims at studying experimentally the effect of lateral streamline convergence alone on the laminar-turbulent transition zone under constant stream-wise pressure.
The experimental setup consists of a low turbulence wind tunnel with its test section modified to cause lateral streamline convergence under constant pressure. This is achieved by converging the side-walls and appropriately diverging the roof, thus maintaining a constant stream-wise pressure. The half angle of convergence is chosen as 100 , which is approximately the same as the half of the turbulent spot envelope in constant pressure two-dimensional flows.
Experiments are carried out to analyze the development of the laminar and transitional boundary layers, intermittency distribution in the transition zone and the overall characteristics of an artificially induced turbulent spot.
The laminar velocity profiles are found to be of the Blasius type for two-dimensional constant pressure flows. However, the converging streamlines are found to contribute to an increased thickness of the boundary layer as compared to the corresponding two-dimensional flow.
The intermittency distribution in the transition zone is found to follow the universal intermittency distribution for two-dimensional constant pressure flow. A simple linear-combination model for two-dimensional flows is found to perform very well in predicting the measured velocity profiles in the transition zone.
An artificially introduced turbulent spot is found to propagate along a conical envelope with an apex cone angle of 220 which is very nearly the value for a corresponding constant pressure two-dimensional flow. The spot shapes and celerities are also comparable to those in two-dimensional flow.
In summary, the present study brings out many similarities between a constant pressure laterally converging flow and a constant pressure two-dimensional flow.
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Aplicação do acoplamento entre o método dos elementos de contorno e o método dos elementos finitos para a análise bidimensional da interação solo-estrutura / Application of the coupling between the boundary element method and the finite element method for analysis of the bidimensional soil-structure interactionVieira, Camila de Sousa 03 April 2009 (has links)
This study aims the development of a computational tool used to analyze two dimensional problems of soil-structure interaction, where soil is modeled by Boundary Element Method (BEM) and structures are treated by the Finite Element Method (FEM). Fundamental solutions of Kelvin 2D and Melan to BEM are implemented, where boundary elements with linear approximation are used. Structures modeled with FEM are discretized with two-dimensional frame finite elements. Coupling among media is done using the sub-region technique, where conditions of compatibility of displacements and equilibrium of tractions are applied to the interfaces between various sub-regions. Both soil and structures are considered as composed of homogeneous, isotropic, elastic and linear materials. However, sub-region technique allows the soil to be considered as stratified. Application for various acting loads, on structure or on soil, are considered slow, therefore the proposed analyses are statics. Examples are presented using the developed computational code. / Fundação de Amparo a Pesquisa do Estado de Alagoas / O presente trabalho tem como objetivo o desenvolvimento de uma ferramenta computacional para analisar problemas bidimensionais de interação solo-estrutura, onde o solo é modelado pelo Método dos Elementos de Contorno (MEC) e as estruturas são tratadas pelo Método dos Elementos Finitos (MEF). São implementadas as soluções fundamentais de Kelvin 2D e Melan para o MEC, onde elementos de contorno com aproximação linear são utilizados. As estruturas modeladas pelo MEF são discretizadas por elementos finitos de pórtico bidimensional. O acoplamento entre os meios é feito pela utilização da técnica de sub-regiões, onde condições de compatibilidade de deslocamentos e condições de equilíbrio de forças são aplicadas às interfaces entre as diversas sub-regiões. Tanto o solo quanto as estruturas são considerados como compostos por materiais homogêneos, isotrópicos, elásticos e lineares. Porém, a técnica de sub-regiões permite que o solo seja considerado como estratificado. A aplicação dos diversos carregamentos atuantes, na estrutura ou no solo, é considerada lenta, assim, as análises propostas são estáticas. São apresentados exemplos de aplicação do código computacional desenvolvido.
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Estudo comparativo de controladores de estrutura variável por modos deslizantes aplicados a veículos subaquáticos autônomos / Comparative study of variavle structures controllers by sliding modes applied to autonomous underwater vehiclesCildoz, Mariana Uzeda 29 August 2014 (has links)
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Previous issue date: 2014-08-29 / This work presents a comparative study between four different sliding mode variable structure
control strategies (SMVSC) applied to autonomous underwater vehicles (AUV) positioning in
6 DOF, under the influence of wind, waves and marine currents. The addressed strategies are
the conventional CEV-MD control based on Lyapunov stability, the CEV-MD control based on
the equivalent control, the CEV-MD control based on the input-output stability and the CEVMD
adaptive control. The accomplished comparisons seek a satisfactory tradeoff between the
tracking performance and the closed-loop system stability in light of eliminating the chattering
phenomenon. In that sense, the analysis and synthesis of the respective SMVSC control laws is
carried out fromthe Lyapunov Stability Theory and the Barbalat s Lemma. As well as numerical
simulations are implemented to obtaining the respective performances of each SMVSC control
strategy presented. / Este trabalho apresenta um estudo comparativo entre quatro diferentes estratégias de controle
de estrutura variável por modos deslizantes (CEV-MD) aplicadas ao posicionamento de veículos
subaquáticos autônomos (VSA) em 6 GDL, sob a influência de ventos, ondas e correntes
marinhas. As estratégias abordadas são o controle CEV-MD convencional baseado na estabilidade
de Lyapunov, o controle CEV-MD baseado no controle equivalente, o controle CEV-MD
baseado na estabilidade entrada-saída e o controle CEV-MD adaptativo. As comparações realizadas
visam a eliminação do do fenômeno do chattering buscando um compromisso satisfatório
entre o desempenho de rastreamento e a estabilidade do sistema em laço fechado. Nesse sentido,
a análise e síntese das respectivas leis de controle CEV-MD é realizada a partir da Teoria
de Estabilidade de Lyapunov e do Lema de Barbalat. Assim como simulações numéricas são
implementadas para a obtenção dos respectivos desempenhos de cada estratégia de controle
CEV-MD apresentada.
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