EM - Escola de Minas

URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6

Notícias

A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.

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2001 - 200972010 - 201982020 - 20226

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Autor: search.filters.author.Araújo, Francisco Célio de

Resultados da Pesquisa

Agora exibindo 1 - 10 de 21
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    Time-domain analysis of framed structures based on “exact” structural-property matrices for nonprismatic Timoshenko’s elements.
    (2022) Pillon, Fenando R.; Ribeiro, Iara Souza; Araújo, Francisco Célio de; Degenhardt, Richard
    This paper applies a unified process to calculate ”exact” (consistent) finite-element (FE) matrices for framed structures having nonprismatic elements and including shear- deformation and rotational-inertia effects. In this process, the exact expressions for the element stiffness and nodal-load coefficients result from applying the principle of virtual forces (PVF) at the element level. Rigidity values, determined at a certain number of cross sections in the frame element, are employed to describe how the corresponding rigidities vary along its length. For that, interpolation polynomials of different orders are consid- ered. Exact Timoshenko’s shape functions, built under the most general cases of rigidity variation, are used for evaluating the mass matrix coefficients. In the applications, com- plex 2D frames with nonprismatic elements are considered to simulate bridge structures under seismic excitation and a generic harmonic load. Comparisons with highly accurate response time-histories obtained by employing ANSYS (3D) solid-FE models are effected to verify the robustness of the proposed formulation.
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    Nonlinear analysis of semirigid steel frames having nonprismatic shear-deformable members.
    (2022) Araújo, Francisco Célio de; Ribeiro, Iara Souza; Machado, Roberta Maria
    Starting from the principle of virtual forces (PVF), one devises a flexibility-type method to obtain, based on the Timoshenko beam theory (TBT), exact expressions for the structural properties of nonprismatic frame elements. One adopts polynomials of different orders to interpolate the sectional rigidity values over the elements and employs exact Timoshenko’s shape functions for evaluating deformation-dependent structural properties, such as geometric stiffness. In this respect, we present a mathematically formal process to obtain the changes in the preexisting element forces needed to calculate geometric stiffnesses. The procedure adopted in this paper easily allows one to include higher-order nonlinear terms in the analysis. Robustness of the proposed formulation is observed by conducting geometrically nonlinear analyses of 2D semirigid steel frames possessing nonprismatic members. General nonlinear curves describing the semirigid connections may be easily incorporated into the analysis.
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    Photogrammetric process to monitor stress fields inside structural systems.
    (2021) Honório, Leonardo de Mello; Pinto, Milena Faria; Hillesheim, Maicon José; Araújo, Francisco Célio de; Santos, Alexandre Bessa dos; Soares Júnior, Delfim
    This research employs displacement fields photogrammetrically captured on the surface of a solid or structure to estimate real-time stress distributions it undergoes during a given loading period. The displacement fields are determined based on a series of images taken from the solid surface while it experiences deformation. Image displacements are used to estimate the deformations in the plane of the beam surface, and Poisson’s Method is subsequently applied to reconstruct these surfaces, at a given time, by extracting triangular meshes from the corresponding points clouds. With the aid of the measured displacement fields, the Boundary Element Method (BEM) is considered to evaluate stress values throughout the solid. Herein, the unknown boundary forces must be additionally calculated. As the photogrammetrically reconstructed deformed surfaces may be defined by several million points, the boundary displacement values of boundary-element models having a convenient number of nodes are determined based on an optimized displacement surface that best fits the real measured data. The results showed the effectiveness and potential application of the proposed methodology in several tasks to determine real-time stress distributions in structures.
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    Nonuniform torsion analysis in tapered composite bars by including higher-order warping modes.
    (2022) Araújo, Francisco Célio de; Hillesheim, Maicon José; Renostro, Gabriel Viecelli; Telles, José Cláudio de Faria
    This paper presents a generalized formulation to describe nonuniform torsion in composite bars with variable cross section including higher-order warping modes. In that, the boundary-element subregion-by-subregion (BE SBS) technique is applied to determine the warping modes for cross sections constituted of any number of different materials. The distribution of the nonuniform warping along the axis is taken into account by multiplying the warping modes by derivatives of the associated twist angle functions. A new process based on the weighted residual method is proposed to solve the resulting global equilibrium equations. One also makes generic comments on the solution of the local coupled boundary-value problems (BVPs), which encompasses preconditioned Krylov solvers (embedded in the BE SBS technique), discontinuous boundary elements, and efficient (low-order) quadratures for singular and nearly-singular integrals. Efficiency and robustness of the technique are verified by comparing the present results with highly accurate 3D responses.
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    Simulação do processo de soldagem elétrica por centelhamento de um aço para trilhos ferroviários. Parte 2 : análise dilatométrica e numérica.
    (2020) Porcaro, Rodrigo Rangel; Araújo, Francisco Célio de; Godefroid, Leonardo Barbosa; Faria, Geraldo Lúcio de; Silva, Luiz Leite da
    Trilhos longos soldados por centelhamento elétrico (Flash Butt Welding - FBW) apresentam características desejáveis do ponto de vista do comportamento dinâmico da via, no entanto, as soldas são regiões de descontinuidade estrutural e mecânica onde se originam tensões residuais, e que estão associadas a falhas prematuras por fadiga. Ensaios de dilatometria foram empregados para simular os efeitos do tamanho de grão austenítico sobre a evolução microestrutural pós-soldagem. Simulações numéricas termomecânicas, não-lineares, no domínio do tempo, pelo Método dos Elementos Finitos (MEF), foram empregadas para avaliar os efeitos de modificações de parâmetros do processo de soldagem sobre as tensões residuais. Os resultados apresentados permitem compreender os mecanismos das alterações morfológicas da perlita na Zona Termicamente Afetada (ZTA) em termos de transformações de fases e podem ser utilizados para sistematicamente orientar mudanças nos parâmetros do processo ou controlar a taxa de resfriamento de modo a obter melhores condições metalúrgicas/mecânicas. Ademais, os resultados dos modelos numéricos mostram como a adoção de ZTA estreita influencia nas taxas de resfriamento e no desenvolvimento de tensões residuais em regiões críticas do componente.
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    A novel strategy to construct exact structural-property matrices for nonprismatic Timoshenko’s frame elements.
    (2020) Araújo, Francisco Célio de; Ribeiro, Iara Souza
    Assuming Timoshenko’s beam hypothesis, this paper proposes a unified strategy to derive exact finiteelement (FE) matrices for framed structures having elements with variable rigidity. Its basic idea is to apply the principle of virtual forces (PVF), at the element level, to obtain a flexibility-based set of equations from which structural-property and nodal-load coefficients can be directly evaluated. The variable physical-geometric characteristics along the frame elements are approximated by polynomials of different orders. For evaluating structural-property coefficients that depend on the deformation of the structure, as e.g. the geometric stiffness coefficients, one employs Timoshenko’s consistent shape functions. A novel process for building them under the most general cases of rigidity variation is presented in this paper. In this study, we particularly apply the technique to effect second-order analyses of 2D frames with nonprismatic elements.
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    An explicit direct FEM–BEM coupling procedure for nonlinear dynamics.
    (2019) Soares Júnior, Delfim; Araújo, Francisco Célio de
    In this work, an explicit direct FEM–BEM coupling procedure is proposed for nonlinear dynamics. In this procedure, each subdomain of the model is analysed separately taking into account proper interface conditions, allowing optimized solver procedures to be applied within each subdomain. In addition, the solution procedure is carried out directly (i.e., without any iterative process), since an explicit time-marching technique is employed within the FEM subdomains. In this context, a locally stabilized central difference approach is utilized, ensuring stability for the FEM analyses, as well as enhanced accuracy. Thus, a very efficient and versatile coupled solution takes place, allowing the direct and independent solution of the subdomains of the model, without regarding critical time-steps limitations within the explicit subdomains. A multi-level time-step algorithm is also considered here, enabling different time-steps to be applied to each subdomain of the model, further improving the flexibility of the coupled analyses. At the end of the paper, numerical applications are presented, illustrating the effectiveness and versatility of the proposed methodology.
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    Revisiting the BE SBS algorithm and applying it to solve torsion problems in composite bars : robustness and efficiency study.
    (2019) Araújo, Francisco Célio de; Hillesheim, Maicon José; Soares Júnior, Delfim
    The construction of truly competitive boundary-element (BE) codes, capable of analyzing real-life engineering problems, unavoidably requires the devising of coupling strategies to make the modeling of complex heterogeneous domains user-friendly. Thereby, high-performance algorithms for solving the highly sparse resulting system of equations are essential. Moreover, as discontinuous boundary elements are necessary to alleviate the modeling process of coupled domains, efficient (low-order) quadratures for integrating singular and nearly-singular fundamental kernels over the boundary elements must be implemented. This paper newly discusses the construction of the boundary-element subregion-by-subregion (BE SBS) technique based on a BEM formulation for torsion problems in general composite bars. One also presents details of the formulation of the Krylov solvers BiCG and BiCGSTAB-(l), embedded in the coupling algorithm. In addition, the BE SBS matrix structure itself is used to form an efficient sparse incomplete LU factorization (SILU) preconditioner to accelerate the iterative solution process. Torsion problems in bars with complex composite patterns (e.g. with many different materials) are analyzed to attest the efficiency and robustness of the whole boundary-element technique.
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    Simulação do processo de soldagem elétrica por centelhamento de um aço para trilhos ferroviários. Parte 1 : análise de tensões residuais via elementos finitos.
    (2019) Porcaro, Rodrigo Rangel; Araújo, Francisco Célio de; Godefroid, Leonardo Barbosa; Faria, Geraldo Lúcio de; Silva, Luiz Leite da
    Trilhos longos, soldados pelo processo Flash Butt Welding (FBW), são a realidade das ferrovias brasileiras de média e alta carga por eixo. Embora apresentem características desejáveis do ponto de vista do comportamento dinâmico da via, as soldas são regiões de descontinuidade estrutural e mecânica onde se originam tensões residuais, e que estão associadas a falhas prematuras por fadiga. Simulações numéricas termomecânicas, fisicamente não-lineares, no domínio do tempo, pelo Método dos Elementos Finitos (MEF), foram empregadas para avaliar o desenvolvimento de tensões residuais originadas durante o processo de soldagem. Uma nova abordagem para a inclusão do aporte de calor envolvido no processo é proposta. Os resultados numéricos são comparados a medidas experimentais de tensões residuais superficiais e aspectos macrográficos das juntas, incluindo largura da Zona Termicamente Afetada (ZTA) e dados de taxas de resfriamento. Os resultados mostram boa correlação entre as análises numéricas e medidas experimentais de tensões residuais. Aspectos fundamentais relacionados ao desenvolvimento de tensões residuais são esclarecidos a partir da correlação entre análises numérica e experimental. Ademais, verifica-se que os modelos computacionais podem ser utilizados na previsão de pontos críticos para nucleação de trincas por fadiga e/ou avaliar efeitos de variáveis de processo sobre o campo de tensões residuais.
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    Geometric nonlinear analysis of plane frames with generically nonuniform shear-deformable members.
    (2017) Araújo, Francisco Célio de; Ribeiro, Iara Souza; Silva, Kátia Inácio da
    This paper employs the Direct Stiffness Method (DSM) to carry out geometric nonlinear analysis of plane frames with nonuniform physical-geometric characteristics. At the element level, a flexibility system of equations based on the principle of virtual forces (PVF) is established to calculate the tangent stiffness matrix and the equivalent nodal loads. The formulation allows for the easy modeling of shear-deformable frame elements with generic rigidity variation along their axes. In addition, Green's theorem is considered to express all the necessary section properties in terms of boundary integrals. This considerably simplifies the modeling of complex cross sections of arbitrary shapes. A “boundary-element” mesh is then used to model the geometric description of the cross sections. At the structure level, to determine the nonlinear equilibrium trajectories for the frame, we apply a co-rotational updated Lagrangian formulation along with an incremental-iterative full Newton-Raphson process. Large displacements and internal member forces are accurately reconstituted. Frameworks having elements with geometrically complex cross-sections varying along their axes are analyzed to validate the strategy proposed.