Navegando por Autor "Awruch, Armando Miguel"

Agora exibindo 1 - 15 de 15

Item
An objective cracking criterion for the analysis of concrete dams
(1996) Araújo, José Milton de; Awruch, Armando Miguel
Cracking analysis by the finite element method may be accomplished using a continuum damage theory, but results are strongly affected by the adopted finite element mesh. A reduced tensile strength has been proposed in order to obtain objective results; however this approach may still be dependent on the adopted finite element mesh. An alternative model for concrete cracking, which is independent of the finite element mesh and especially suitable for the analysis of concrete dams, is proposed in this work.
Item
Cracking safety evaluation on gravity concrete dams during the construction phase
(1998) Araújo, José Milton de; Awruch, Armando Miguel
The cracking phenomenon in concrete gravity dams during the construction phase is analysed in this work. Stresses due to the self-weight of the dam, thermal gradients, creep and drying shrinkage are computed, taking into account the different stages of the construction process. A twodimensional constitutive model considering time dependent and temperature dependent mechanical properties is adopted for the concrete. Safety against cracking is obtained using a criterion independent of the finite element mesh.
Item
Finite element analysis of laminar and turbulent flows using LES and subgrid-scale models
(2006) Popiolek, Tales Luiz; Awruch, Armando Miguel; Teixeira, Paulo Roberto de Freitas
Numerical simulations of laminar and turbulent flows in a lid driven cavity and over a backward-facing step are presented in this work. The main objectives of this research are to know more about the structure of turbulent flows, to identify their three-dimensional characteristic and to study physical effects due to heat transfer. The filtered Navier–Stokes equations are used to simulate large scales, however they are supplemented by subgrid-scale (SGS) models to simulate the energy transfer from large scales toward subgridscales, where this energy will be dissipated by molecular viscosity. Two SGS models are applied: the classical Smagorinsky s model and the Dynamic model for large eddy simulation (LES). Both models are implemented in a three-dimensional finite element code using linear tetrahedral elements. Qualitative and quantitative aspects of two and three-dimensional flows in a lid-driven cavity and over a backward-facing step, using LES, are analyzed comparing numerical and experimental results obtained by other authors.
Item
Geometrically nonlinear static and dynamic analysis of composite laminates shells with a triangular finite element
(2008) Isoldi, Liércio André; Awruch, Armando Miguel; Teixeira, Paulo Roberto de Freitas; Morsch, Inácio Benvegnu
Geometrically nonlinear static and dynamic behaviour of laminate composite shells are analyzed in this work using the Finite Element Method (FEM). Triangular elements with three nodes and six degrees of freedom per node (three displacement and three rotation components) are used. For static analysis the nonlinear equilibrium equations are solved using the Generalized Displacement Control Method (GDCM) while the dynamic solution is performed using the classical Newmark Method with an Updated Lagrangean Formulation (ULF). The system of equations is solved using the Gradient Cojugate Method (GCM) and in nonlinear cases with finite rotations and displacements an iterativeincremental scheme is employed. Numerical examples are presented and compared with results obtained by other authors with different kind of elements and different schemes.
Item
Invertigação Numérica sobre um Corpo Axissimétrico em Escoamentos Supersônicos.
(2009) Bono, Gustavo; Popiolek, Tales Luiz; Awruch, Armando Miguel
As interações de origem viscosa e não viscosa podem induzir grandes alterações nos níveis de aquecimento e nas cargas de pressão na superfície dos veículos que voam no regime supersônico e hipersônico. Com o objetivo de entender os principais fenômenos deste tipo de interações emprega-se a Dinâmica dos Fluidos Computacional. Neste trabalho, emprega-se o Método dos Elementos Finitos para investigar a interação onda de choque/onda de choque (CC) sobre uma geometria definida por um conjunto cilindro hemisférico-cone-cilindro. O escoamento compressível é modelado empregando as equações de Euler para diferentes ângulos de ataque (10º e 20o) e números de Mach (M = 2.95 e 4.04)com elementos hexáedricos e tetraédricos. As principais características do escoamento são a complexa topologia do escoamento sobre a superfície com várias separações e suas interações, e a interação choque-choque para grandes ângulos de ataque. Finalmente, os resultados numéricos são comparados com dados experimentais.
Item
Linear static and dynamic analysis of thin laminated composite structures with a triangular finite element
(2010) Isoldi, Liércio André; Awruch, Armando Miguel; Morsch, Inácio Benvegnu; Teixeira, Paulo Roberto de Freitas
Linear static and dynamic behavior of thin laminate composite structures are analyzed in this study using the Finite Element Method (FEM). Triangular elements with three nodes and six degrees of freedom per node (three displacement and three rotation components) are used. For static analysis the equilibrium equations are solved using Pre-conditioned Gradient Conjugate Method (GCM) while the dynamic solution is performed using the classical Newmark Method. Analytical evaluation of consistent element mass matrix and determination of membrane and membrane-bending coupling element stiffness matrix in the explicit form are showed. Numerical examples are presented and compared with results obtained by other authors with different types of elements and different schemes, proving the validity and effectiveness of the developed model.
Item
Numerical simulation of fluid-structure interaction using the finite element method
(2005) Teixeira, Paulo Roberto de Freitas; Awruch, Armando Miguel
An algorithm to simulate 3D fluid–structure interaction problems using the finite element technique is presented in this work. A two-step Taylor–Galerkin scheme and linear tetrahedra elements are employed to analyze the fluid flow, which may be high or slightly compressible. An arbitrary Lagrangean–Eulerian (ALE) formulation is adopted, which must be compatible with the motion of the fluid–structure interface. A fractional method with velocity correction is used for incompressible fluids. The structure is analyzed using triangular elements with three nodes and six degrees of freedom in each node (three displacement components and three rotation components). Geometrically non-linear effects are included. The Newmark method is employed to integrate in time the dynamic equilibrium equations using an updated Lagrangean description. The algebraic system of equations is solved using the conjugated gradient method and an incremental-iterative scheme is used to solve the non-linear system resulting from finite displacements and rotations. The code is optimized to take advantages of vector processors. Some cases studies have been considered for validation of the computational algorithm. A two-dimensional supersonic flow over a clamped flat plate is analyzed in order to study the aeroelastic behavior of this plate. Vibrations due to wind action of an inflated membrane as well as vortex inducing vibrations in a panel immersed in a slightly compressible fluid are also studied.
Item
Numerical simulation of three dimensional incompressible flows using the finite element method
(2000) Teixeira, Paulo Roberto de Freitas; Awruch, Armando Miguel
A numerical algorithm to simulate 3-D incompressible flows of viscous fluids employing the finite element method is presented in this work. Space and time discretization of the complete set of differential equations were carried out using a semi-implicit two-step Taylor-Galerkin scheme and linear tetrahedral element. The code was written in FORTRAN language and was optimised in order to take advantages of vetorial processors existing in modern supercomputers. Examples including isothermal and non isothermal flows are presented to show the possibilities of the proposed algorithm as an important auxialiary tool for engineering design.
Item
On stochastic finite elements for structural analysis
(1994) Araújo, José Milton de; Awruch, Armando Miguel
This paper considers the stochastic finite element analysis of structures resulting from random spatial variability of material properties, when they are subjected to loads of deterministic nature. Direct Monte Carlo simulation, Monte Carlo with Neumann expansion of the stiffness matrix and Taylor series expansion combined with the classical finite element approach are applied and compared with respect to accuracy and computational efficiency. Dynamic and non-linear problems are also included.
Item
Probabilistic finite element analysis of concrete gravity dams
(1998) Araújo, José Milton de; Awruch, Armando Miguel
A methodology for the probabilistic analysis of concrete gravity dams is presented, Concrete properties and seismic excitation are considered as random variables. The seismic excitation is considered as a non-stationary stochastic process which is artificially generated. Concrete properties have random variations over the spatial domain. Structural response is obtained employing the finite element method to solve the equations of motion of the coupled system dam-reservoir-foundation. Structural safety is evaluated with respect to the main failure modes (cracking, concrete crushing and sliding at the dam-foundation interface) using the Monte Carlo method.
Item
Reliability analysis of laminated composite structures using finite elements and neural networks
(2010) Lopes, Paulo André Menezes; Gomes, Herbert Martins; Awruch, Armando Miguel
Saving of computer processing time on the reliability analysis of laminated composite structures using artificial neural networks is the main objective of this work. This subject is particularly important when the reliability index is a constraint in the optimization of structural performance, because the task of looking for an optimum structural design demands also a very high processing time. Reliability methods, such as Standard Monte Carlo (SMC), Monte Carlo with Importance Sampling (MC–IS), First Order Reliability Method (FORM) and FORM with Multiple Check Points (FORM–MCPs) are used to compare the solution and the processing time when the Finite Element Method (FEM) is employed and when the finite element analysis (FEA) is substituted by trained artificial neural networks (ANNs). Two ANN are used here: the Multilayer Perceptron Network (MPN) and the Radial Basis Network (RBN). Several examples are presented, including a shell with geometrically non-linear behavior, which shows the advantages using this methodology.
Item
Reliability based optimization of laminated composite structures using genetic algorithms and artificial neural networks
(2011) Gomes, Herbert Martins; Awruch, Armando Miguel; Lopes, Paulo André Menezes
The design of anisotropic laminated composite structures is very susceptible to changes in loading, angle of fiber orientation and ply thickness. Thus, optimization of such structures, using a reliability index as a constraint, is an important problem to be dealt. This paper addresses the problem of structural optimization of laminated composite materials with reliability constraint using a genetic algorithm and two types of neural networks. The reliability analysis is performed using one of the following methods: FORM, modified FORM (FORM with multiple checkpoints), the Standard or Direct Monte Carlo and Monte Carlo with Importance Sampling. The optimization process is performed using a genetic algorithm. To overcome high computational cost it is used Multilayer Perceptron or Radial Basis Artificial Neural Networks. It is shown, presenting two examples, that this methodology can be used without loss of accuracy and large computational time savings, even when dealing with non-linear behavior.
Item
Three dimensional flow simulations with the finite element technique over a multi-stage rocket
(2004) Scalabrin, Leonardo Costa; Azevedo, João Luiz Filgueiras de; Teixeira, Paulo Roberto de Freitas; Awruch, Armando Miguel
Aerodynamic flow simulations over the first Brazilian satellite launch vehicle, VLS, during its first-stage flight are presented. The three dimensional compressible flow is modeled by the Euler equations and a Taylor-Galerkin finite element method with artificial dissipation is used to obtain the numerical solution. Transonic and supersonic results for zero angle-of-attack are presented and compared to available experimental results. The influence of mesh refinement and artificial dissipation coeffcient on the transonic flow results are discussed. The results obtained for the supersonic simulations present good agreement with experimental data. The transonic simulation results capture the correct trends but they also indicate that this flight condition requires more refined meshes.
Item
Three dimensional simulation of high compressible flows using a subcycling algorithm for time integration
(1999) Teixeira, Paulo Roberto de Freitas; Awruch, Armando Miguel
An algorithm to simulate 3-D high compressible flows using the finite element method and a multi-time-step integration technique with subcycles is presented in this work. An explicit two-step Taylor-Galerkin scheme is adopted to integrate in time continuum equations. When explicit schemes are used, the time steps must satisfy some stability conditions. If the smallest critical time-step is adopted uniformely for the whole domain, the integration scheme may consume a large amount of CPU time. Multi-time-step integration techniques are very suitable in these cases because elements and nodes are separated into several groups and a different time-step is assigned to each group. In this way, each group of elements is integrated with a time interval wich is much closer to the critical time steps of the elements in the group. This results in great computational savings, mainly when elements size and properties are very different, leading to significative differences of the local critical time steps values. Multi-time-steps integration techniques are also very useful in transient problems, taking into account that at the end of each subcycle, values of the unknowns at the same time level are obtained. The multi-time-step algorithm is applied to analyze the supersonic flow (Mach=8,5) past a sphere immersed in a non viscous flow, and results and computational performance are compared with those obtained when a uniformly time-step is used over the whole domain.
Item
Three-dimensional simulation of high compressible flows using a multi-time-step integration technique with subcycles
(2001) Teixeira, Paulo Roberto de Freitas; Awruch, Armando Miguel
An algorithm to simulate three-dimensional high compressible flows using the finite element method and a multi-time-step integration technique with subcycles is presented in this work. An explicit two-step Taylor–Galerkin scheme is adopted to integrate in time the continuum equations. When explicit schemes are used, the time-steps must satisfy the CFL stability conditions. If the smallest critical time-step is adopted uniformly for the whole domain, the integration scheme may consume a large amount of CPU time. Multi-time-step integration techniques are very suitable in these cases because elements and nodes are separated into several groups and a different time-step is assigned to each group. In this way, each group of elements is integrated with a time interval which is much closer to the critical time-steps of the elements in the group. This results in great computational savings, mainly when element sizes and properties are very different, leading to significant differences in the local critical time-step values. Multi-time-steps integration techniques are also very useful in transient problems, taking into account that at the end of each subcycle, values of the unknowns at the same time level are obtained. The multi-time-step algorithm is applied to analyze the supersonic flow (Mach=8.5) past a sphere immersed in a non-viscous flow, and the results and computational performance are compared with those obtained when a uniform time-step is used over the whole domain.