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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5 resultados
Resultados da Pesquisa
Item Closed-form solutions for the symmetric nonlinear free oscillations of pyramidal trusses.(2021) Santana, Murillo Vinícius Bento; Gonçalves, Paulo Batista; Silveira, Ricardo Azoubel da MotaThis work presents the development of analytical solutions regarding the symmetric free vibrations of pyramidal trusses, considering a general large strain measure. In this case, the undeformed and deformed configurations of the continuum are significantly different, requiring a clear distinction between them. Illustrative examples considering the quadratic (Green–Lagrange) and logarithmic (Hencky) strain measures are used to exemplify the influence of the strain measure on the results. Pyramidal trusses are well-known bistable structures and in the unloaded configurations may present different analytical solutions depending on the initial conditions: small amplitude vibrations around each stable equilibrium configuration or large cross-well vibrations. These families of solution are separated by two homoclinic orbits, constituting the boundaries of the two potential wells, which are related to the saddle point initial conditions. In addition, closed-form time solutions for the undamped vibrations are derived and the nonlinear frequency–amplitude relations, which are a measure of the degree and type of nonlinearity (hardening or softening), are obtained. Finally, a semi-analytical procedure for the damped vibrations is also constructed.Item Numerical fundamentals and interactive computer graphics system for the nonlinear analysis of planar frames.(2019) Santana, Murillo Vinícius Bento; Silveira, Ricardo Azoubel da MotaRecent scientific and computational advances have facilitated the analysis of slender structural systems subject to instability. With the employment of more sophisticated numerical tools and algorithms, it is possible to accurately determine the critical points (limit and bifurcation loads) as well as the post-critical behavior of the structural system. In the computational context, efficient data structures are needed to enable code and graphic interface expansion for the generation of models and visualization of the results obtained. Thus, an interactive object-orientated graphic computational system is presented herein. It has been developed using MATLAB/GUI, with pre-processing, analysis and post-processing capacities for planar structural frames. The nonlinear finite element developed and implemented for the structure modeling is formulated considering second order effects. Therefore, with the computational tool presented, the geometric nonlinear effects and stability of the structural system can be directly addressed, and the visualization of the numerical results are accessed through interactive controls that permit data inclusion and analysis verification. The engineer-designer can see the structural model discretization, the equilibrium path, its deformation configuration, the force and bending moment diagrams at the moment that he runs the program and in each load step. It is also possible to export the images, videos or tables of the obtained numerical results. The example presented demonstrates the capacity of the developed graphic computational system.Item Stability and load capacity of an elasto-plastic pyramidal truss.(2019) Santana, Murillo Vinícius Bento; Gonçalves, Paulo Batista; Silveira, Ricardo Azoubel da MotaThe present work investigates, using a corotational finite element formulation considering large displacements and rotations, geometric imperfections and an elasto-plastic material constitutive law, the nonlinear behavior of a pyramidal space truss under vertical and horizontal loads. Additionally novel analytical closed-form solutions for the nonlinear equilibrium paths, natural frequencies and critical parameters are derived for comparison purposes and investigation of the influence of geometric and material parameters on the truss stability. This geometry has an immediate practical interest since these structures are currently used in many present-day applications, either as main structural component or as a constitutive element. Four types of nonlinear instability phenomena are investigated theoretically and numerically: saddle-node (limit point) bifurcation, pitchfork bifurcation, individual Eulerian bars buckling and elasto-plastic buckling. Through a detailed parametric analysis the interaction between these buckling phenomena, using the FE tool, is investigated. In addition, the effect of elastic supports is considered. The influence of these phenomena on the load carrying capacity of the structure and its imperfection sensitivity is duly discussed in the present work. Finally, a detailed parametric analysis of a large roof composed of pyramidal truss units is conducted and the influence of the geometric parameters on its bistable behavior and load carrying capacity is investigated.Item Nonlinear oscillations and dynamic stability of an elastoplastic pyramidal truss.(2019) Santana, Murillo Vinícius Bento; Gonçalves, Paulo Batista; Silveira, Ricardo Azoubel da MotaPyramidal space trusses are currently used in many present-day engineering applications, either as main parts or as a constitutive element. The present work studies, using a corotational finite element formulation considering large displacements and rotations and an elastoplastic material behavior with isotropic strain hardening, the nonlinear dynamic behavior of a pyramidal space truss. A bilinear hysteretic model with kinematic hardening is used to represent the material nonlinearity. An appropriate strain measure in such processes is the logarithmic strain. However, the engineering strain and the quadratic strain measures have been usually used to perform the elastic stability analysis of such structures. Thus, in the present work results using both the quadratic and the logarithmic strain measures are compared. First, the static nonlinear behavior is investigated in order to understand the influence of nonlinearities and static preload on the potential energy landscape, which controls the dynamics of the truss. These structures exhibit a two-well potential function that leads to coexisting in-well and cross-well solution branches, resulting in several coexisting periodic, quasi-periodic and chaotic attractors. The influence of the constitutive law, strain measure, truss geometry and support flexibility on the static stability is then investigated. Based on these results, a detailed parametric analysis of the nonlinear truss response under vertical load is conducted using bifurcations diagrams of the Poincaré map to investigate the effect of the constitutive law, strain measure, truss geometry and load control parameters on the bifurcation scenario, coexisting attractors and dynamic buckling loads. The effect of the strain hardening parameter is particularly emphasized, allowing a more comprehensive picture of the dynamical behavior exhibited by the bistable system. Properties of the response are further illustrated by samples of time and phase plane responses and the related Poincaré section plots. In addition to known behaviors, a rich class of solutions and bifurcations, including jump phenomena, symmetry-breaking, period-doubling cascades, fold and chaos is detected.Item Desenvolvimento de sistema computacional via MATLAB/GUI (Graphical User Interface) para análise geometricamente não linear de estruturas.(2015) Santana, Murillo Vinícius Bento; Silveira, Ricardo Azoubel da MotaCom os avanços científicos e tecnológicos, o engenheiro estrutural passou a desenvolver e/ou ter acesso a programas computacionais que possibilitam análises numéricas mais avançadas. Isso vem proporcionando aumento da segurança e economia dos projetos. Para a concepção de estruturas mais esbeltas, a realização de análises não lineares geométricas, em que os efeitos de segunda ordem são explicitamente incluídos, torna-se cada vez mais comum. Nesse contexto, esta dissertação tem como objetivo avaliar o comportamento não linear geométrico estático de sistemas estruturais reticulados planos através do desenvolvimento e emprego de um sistema computacional gráfico interativo, denominado aqui AFA-OPSM (Advanced Frame Analysis - Ouro Preto School of Mines). Esse sistema utiliza os recursos de programação gráficos interativos (GUI) do software MATLAB, e apresenta, de forma acoplada, as etapas de pré-processamento, análise estrutural e pósprocessamento. Destaca-se ainda que ele é construído segundo o paradigma da programação orientada à objetos (POO), em que várias estratégias de solução não linear foram incorporadas. As formulações não lineares de elementos finitos são desenvolvidas considerando as teorias de treliças, de viga de Euler-Bernoulli e de Timoshenko, nos referenciais Lagrangiano total e co-rotacional. Os resultados numéricos obtidos, assim como os recursos gráficos interativos do AFA-OPSM, são avaliados através do estudo de problemas estruturais clássicos de estabilidade encontrados na literatura, alguns considerados fortemente não lineares.