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Rossa A.L.,Engineering Simulation and Scientific Software | Coutinho A.L.G.A.,Federal University of Rio de Janeiro
Computers and Fluids | Year: 2013

A good representation of the displacement front and the interface between different density fluids are essential in gravity currents simulations. Adaptive meshes play a key issue to ensure the solution quality performing the automatic refinement locally in regions where it is necessary, leaving most of the domain coarsely discretized. In this work, a stabilized FEM is applied to modelling three-dimensional gravity currents phenomena. Parallel AMR/C, provided by the libMesh FEM open source library, is performed, and the results obtained by different adaptivity configurations are compared with those from fixed meshes. An a posteriori error estimator for the mesh AMR/C procedure based on scalar flux jumps between adjacent elements is adopted. Mesh adaptivity proves to be a very effective approach in reducing the total number of elements and at the same time to be able to successfully capture the main characteristics of the flow dynamics, as the development of Kelvin-Helmholtz billows and the formation of lobes and clefts. © 2013.

Kabche J.P.,Engineering Simulation and Scientific Software | Pacheco M.R.,Engineering Simulation and Scientific Software | Thesi I.,Engineering Simulation and Scientific Software | Largura L.C.,Petrobras
ASME International Mechanical Engineering Congress and Exposition, Proceedings | Year: 2010

Bolted connections are largely employed in various types of engineering structures to transfer loads from one member to another. In particular, the off-shore industry has made extensive use of these connections, predominantly at the sub-sea level. In spite of their advantages, bolted joints are critical regions and may become sources of structural weakness due to large stress concentrations. Under severe operating conditions, micro-cracks can develop in the bolt, creating regions of elevated stress which may significantly reduce the integrity of the connection and ultimately lead to failure. This paper presents the three-dimensional finite element analysis of a steel locked bolt assembly aimed to assess the effect of micro-cracks on the structural integrity of the assembly using the commercial finite element package ANSYS. Non-linear contact between the bolt and nut threads is considered, where frictional sliding between components is allowed. A bi-linear isotropic hardening model is used to account for non-linear material behavior. The assembly is loaded by applying a pre-load of fifty percent of the yield stress of the material, according to the AP1-6A Norm. Two geometric models are investigated: a healthy locked bolt assembly with no initial cracks; and a damaged model, where a circular crack is introduced at the root of the bolt threads. The effect of the crack size is studied by modeling the crack with three different radius sizes. The J-lntegral fracture mechanics methodology was used to study the stress concentrations in the damaged model. Copyright & 2009 by ASME.

Zareian F.,University of California at Irvine | Sampere C.,Forell Elsesser Engineers Inc. | Sandoval V.,Engineering Simulation and Scientific Software | McCormick D.L.,Simpson Gumpertz and Heger | And 2 more authors.
Earthquake Spectra | Year: 2012

This paper summarizes the EERI reconnaissance team findings on damage to the Chilean wine industry after the 27 February 2010 Offshore Maule Earthquake. Wine production is one of the major industries in Chile, with an annual production of approximately one million metric tons. It is estimated that the total loss to the wine industry is over 125 million liters, with infrastructure damage estimated as high as US$430. Most of the damage was concentrated in older wineries with collapse of adobe walls and timber roofs or ribbed brick vaults. Damage to steel fermentation tanks was widespread among all wineries visited with the severity of such damage depending on the type of tank anchorage. Local buckling of legs in legged tanks or excessive movement followed by the tank falling off the support pad led to toppling that ruptured piping or valves. Stacked barrels, stored bottles of wine, and production lines were also damaged. © 2012, Earthquake Engineering Research Institute.

Mologni J.F.,Engineering Simulation and Scientific Software | Alves M.A.R.,University of Campinas | Braumgratz F.,University of Campinas | Fonseca E.,University of Campinas | And 2 more authors.
Journal of Aerospace Technology and Management | Year: 2010

Preliminary studies on field emission (FE) arrays comprised of carbon nanotubes (CNT) as an electron source for electric propulsion system show remarkably promising results. Design parameters for a carbon nanotube (CNT) field-emission device operating on triode configuration were numerically simulated and optimized in order to enhance the e-beam focusing quality. An additional focus gate (FG) was integrated to the device to control the profile of the emitted e-beam. An axisymmetric finite element model was developed to calculate the electric field distribution on the vacuum region and a modified Fowler-Nordheim (FN) equation was used to evaluate the current density emission and the effective emitter area. Afterward, a FE simulation was employed in order to calculate the trajectory of the emitted electrons and define the electron-optical properties of the e-beam. The integration of the FG was fully investigated via computational intelligence techniques. The best performance device according to our simulations presents a collimated e-beam profile that suits well for field emission displays, magnetic field detection and electron microscopy. The automated computational design tool presented in this study strongly benefits the robust design of integrated electron-optical systems for vacuum field emission applications, including electrodynamic tethering and electric propulsion systems.

Rangel Pacheco M.,Engineering Simulation and Scientific Software | Paul Kabche J.,Engineering Simulation and Scientific Software | Thesi I.,Engineering Simulation and Scientific Software | Nunes Diesel F.,Engineering Simulation and Scientific Software
ASME International Mechanical Engineering Congress and Exposition, Proceedings | Year: 2010

Friction Stir Welding (FSW) is a solid-state welding process which generates heat through mechanical friction between a moving workpiece and a fixed component, in order to plastically combine materials. This process has been gaining considerable attention due to several key advantages, which include: good mechanical properties of the combined materials after welding, absence of toxic fumes and molten material spatter, low environmental impact, and low concentration of defects while allowing a large variation of parameters and materials. Although a reasonable number of experimental investigations on FSW are available in the literature, numerical modeling of this process has not been performed on a large scale. In that light, this paper presents a numerical investigation of the temperature distribution in plates welded by FSW, using finite element analysis. The finite element model developed includes friction between the workpiece and the fixed component, as well as the corresponding heat dissipation that results from plastic deformation of the material. The model was found appropriate for estimating important welding characteristics, such as the heat-affected zone (HAZ), and their sensitivity to various welding parameters. Copyright © 2009 by ASME.

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