EE - Escola de Engenharia
URI permanente desta comunidadehttps://rihomolog.furg.br/handle/1/512
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- ItemOn stochastic finite elements for structural analysis(1994) Araújo, José Milton de; Awruch, Armando MiguelThis 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.
- ItemAn objective cracking criterion for the analysis of concrete dams(1996) Araújo, José Milton de; Awruch, Armando MiguelCracking 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.
- ItemProbabilistic finite element analysis of concrete gravity dams(1998) Araújo, José Milton de; Awruch, Armando MiguelA 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.
- ItemCracking safety evaluation on gravity concrete dams during the construction phase(1998) Araújo, José Milton de; Awruch, Armando MiguelThe 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.
- ItemThree dimensional simulation of high compressible flows using a subcycling algorithm for time integration(1999) Teixeira, Paulo Roberto de Freitas; Awruch, Armando MiguelAn 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.
- ItemNumerical simulation of fluid-structure interaction using the finite element method(2005) Teixeira, Paulo Roberto de Freitas; Awruch, Armando MiguelAn 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.
- ItemNumerical simulation of three dimensional incompressible flows using the finite element method(2000) Teixeira, Paulo Roberto de Freitas; Awruch, Armando MiguelA 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.
- ItemThree-dimensional simulation of high compressible flows using a multi-time-step integration technique with subcycles(2001) Teixeira, Paulo Roberto de Freitas; Awruch, Armando MiguelAn 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.
- ItemThree 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 MiguelAerodynamic 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.
- ItemFinite element analysis of laminar and turbulent flows using LES and subgrid-scale models(2006) Popiolek, Tales Luiz; Awruch, Armando Miguel; Teixeira, Paulo Roberto de FreitasNumerical 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.