1,720,956 research outputs found
Avaliação numérica avançada de elementos de madeira e treliças metálicas sob temperaturas elevadas.
No full textPrograma de Pós-Graduação em Engenharia Civil. Departamento de Engenharia Civil, Escola de Minas, Universidade Federal de Ouro Preto.A presente pesquisa teve como objetivo principal avaliar numericamente o desempenho de estruturas de madeira em situação de incêndio e treliças metálicas sob altas temperaturas. A capacidade resistente dos elementos estruturais de madeira é comprometida quando este material é exposto à condição de elevadas temperaturas, uma vez que suas propriedades físico-mecânicas se deterioram em função do aumento da temperatura, da mesma forma que para barras de treliça de aço. Os aspectos do problema de transmissão de calor e do comportamento da madeira sob altas temperaturas e os fundamentos da análise de estruturas baseada no Método dos Elementos Finitos (MEF) são abordados. Neste contexto, empregou-se a formulação baseada no MEF referenciado no sistema corrotacional para acompanhar os grandes deslocamentos e rotações do sistema estrutural. Já o comportamento inelástico do material foi simulado por meio do acoplamento entre o Método da Rótula Plástica Refinado (MRPR) e o Método da Compatibilidade de Deformações (MCD). Dessa forma, os módulos computacionais, CS- ASA/FA (Computational System for Advanced Structural Analysis/Fire Analysis) e CS- ASA/FSA (Computational System for Advanced Structural Analysis/Fire Structural Analysis) foram expandidos e adaptados para a análise avançada não linear de estruturas de madeira sob temperaturas elevadas. Adicionalmente, foram implementadas diversas formulações não lineares de treliças, modelos constitutivos e carregamento térmico, para viabilizar tais análises a partir do CS-ASA, permitindo análises avançadas de elementos treliçados sob altas temperaturas. As metodologias desenvolvidas e aplicadas foram verificadas pelo sucesso das análises de elementos estruturais de madeira em situação de incêndio utilizando os resultados experimentais e numéricos disponíveis na literatura.The main objective of this research was to numerically evaluate the performance of timber structures under fire conditions and metal trusses under high temperatures. The load- bearing capacity of timber structural elements is compromised when exposed to high temperatures, as their physical and mechanical properties deteriorate due to the increase in temperature, similar to those of steel truss bars. The study addresses aspects of heat transmission and timber behavior under high temperatures, as well as the fundamentals of structural analysis based on the Finite Element Method (FEM). In this context, a FEM- based formulation referenced to the co-rotational system was used to monitor the large displacements and rotations of the structural system. The inelastic behavior of the material was simulated by coupling the Refined Plastic Hinged Method (RPHM) with the Strain Compatibility Method (SCM). Thus, the computational modules CS-ASA/FA (Computational System for Advanced Structural Analysis/Fire Analysis) and CS- ASA/FSA (Computational System for Advanced Structural Analysis/Fire Structural Analysis) were expanded and adapted for advanced nonlinear analysis of timber structures under elevated temperatures. Additionally, several nonlinear truss formulations, constitutive models, and thermal loading were implemented to enable such analyses using CS-ASA, enabling advanced analyses of truss elements under high temperatures. The developed and applied methodologies were verified by the successful analysis of timber structural elements under fire conditions using experimental and numerical results available in the literature
Numerical strategies for optimizing the nonlinear solution of structural problems.
No full textPrograma de Pós-Graduação em Engenharia Civil. Departamento de Engenharia Civil, Escola de Minas, Universidade Federal de Ouro Preto.É crescente a busca por ferramentas computacionais capazes de realizar simulações
numéricas de sistemas estruturais com comportamento não linear. Para problemas estáticos
não lineares, em particular, é fundamental a implementação e uso de estratégias numéricas
com o objetivo de obter de forma completa as trajetórias de equilíbrio da estrutura, superando
possíveis pontos críticos (pontos limite e de bifurcação). No contexto dos métodos de
discretização (Método dos Elementos Finitos, Método das Diferenças Finitas, Método dos
Elementos de Contorno, etc), em que estratégias incrementais e iterativas são geralmente
adotadas, os solvers não lineares devem ser eficientes nas duas fases do processo de solução
(predita e corretiva), para cada passo do carregamento aplicado. São implementadas neste
trabalho duas estratégias para tornar o procedimento de solução não linear mais robusto e
eficiente: o ciclo iterativo de Potra-Pták e a técnica de otimização da busca linear. A primeira
estratégia consiste em uma modificação do processo iterativo de Newton-Raphson, na qual
são realizadas duas avaliações da função gradiente, representada pelas forças desequilibradas
do sistema estrutural. Por sua vez, a busca linear é a técnica que visa escalonar o vetor de
deslocamentos corretivos na fase iterativa, procurando garantir e acelerar a convergência do
processo. Essas estratégias numéricas são detalhadas, implementadas (na ferramenta
computacional CS-ASA, Computational System for Advanced Structural Analysis) e usadas
em análises de estruturas com forte não linearidade. Através dos resultados numéricos
obtidos, percebe-se que as estratégias empregadas são alternativas válidas e eficientes para
a análise não linear geométrica de vigas, colunas, pórticos e arcos, proporcionando, em geral,
a redução no número de incrementos de carga, iteração e tempo de processamento para obter
o caminho de equilíbrio de forma completa.The search for computational tools capable of numerical simulations of the structural
systems nonlinear behavior has been growing. For nonlinear static problems, in particular,
it is essential to implement and use numerical strategies to plot the complete structure
equilibrium path, overcoming possible critical points (limit and bifurcation points). In the
context of discretization methods (Finite Element Method, Finite Difference Method,
Boundary Element Method, etc.), where iterative incremental strategies are generally
adopted, nonlinear solvers must be efficient in both phases of the solution process (predictor
and corrector) for each loading step. Two strategies are implemented in this work to make
the nonlinear solver more robust and efficient: the Potra-Pták iterative cycle and the line
search optimization technique. The first strategy consists of a modification of the iterative
process proposed by Newton-Raphson, in which two evaluations of the gradient function
(unbalanced forces) are performed. In turn, the linear search is the optimization technique
that aims to scale the vector of corrective displacements in the iterative phase, seeking to
ensure and accelerate the convergence of the process. These numerical strategies are
described, implemented (in the CS-ASA, Computational System for Advanced Structural
Analysis) and used in analysis of structures with strong nonlinearity. Through the numerical
results obtained, it can be concluded that the strategies employed are valid and efficient
alternatives for the geometrically nonlinear analysis of steel beams, columns, frames and
arches, generally reducing the number of load step increments, iteration and time processing
to obtain the structure equilibrium path completely
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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