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• A general methodology for structural shape optimization problems using automatic adaptive remeshing

  G. Bugeda, J. Oliver

  (1992). Research Report, Nº PI19

  
  

  Abstract

  The proposed methodology lies on the use of the adaptive mesh remeshing (AMR) technique in the context of 2D shape optimization problems analyzed by the Finite Element Method. A suitable and very general technique for the parametrization of the optimization problem, that uses B-splines to define the boundary, is first presented. Then, mesh generation, using the advancing frontal method, the error estimator and the remeshing criteria are studied in the context of shape optimization problems. Particularly, the analytical sensitivity analysis of the different items ruling the problem (B-splines, Finite Element Mesh, structural behaviour, and error estimator) is studied in detail. The sensitivities of the Finite Element Mesh and error estimator permit their projection from one design to the next one leading to an “a priori knowledge” of the finite element error distribution on the new design without the necessity of any additional structural analysis. With this information the remeshing criteria permits to build up a finite element mesh on the new design with aa specified and controlled level of error. The robustness and reliability of the proposed methodology is checked through several examples.

  Abstract
  The proposed methodology lies on the use of the adaptive mesh remeshing (AMR) technique in the context of 2D shape optimization problems analyzed by the Finite Element Method. [...]

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• Equivalent FE and BE forms of a substructure oriented boundary solutions approach

  J. Jirousek

  (1992). Research Report, Nº PI20

  
  

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• A perspective of recent developments in the finite element simulation of metal forming processes

  E. Oñate

  (1992). Research Report, Nº PI21

  
  

  Abstract

  This paper presents an overview of different computational procedures for finite element analysis of metal forming problems. Both the displacement and flow approaches are discussed together with other aspects like the treatment of temperature coupling, the techniques for geometry updating, the treatment of contact and friction, the use of quasi-static versus explicit dynamic methods and other topics of interest. Examples of applications of some of the methods proposed to extrusion, rolling, mould filling and sheet metal forming problems are presented.

  Abstract
  This paper presents an overview of different computational procedures for finite element analysis of metal forming problems. Both the displacement and flow approaches are [...]

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• Una panorámica de las posibilidades del MEF para análisis de procesos de conformado de metales.

  E. Oñate

  (1992). Research Report, Nº PI23

  
  

  Abstract

  Se presenta en este trabajo una breve panorámica de diferentes procedimientos para análisis de procesos de conformado de metales por el método de elementos finitos (MEF). Se describen las formulaciones de flujo y de sólido junto a diversos temas como el acoplamiento térmico, las técnicas para actualización de geometría, el tratamiento de contacto y rozamiento, el uso de métodos cuasi-estáticos frente a dinámicos explícitos y otros temas de interés. Asimismo, se presentan ejemplos de aplicación de algunos de los métodos propuestos a problemas de extrusión, laminado, llenado de moldes y embutición de chapa.  

  Abstract
  Se presenta en este trabajo una breve panorámica de diferentes procedimientos para análisis de procesos de conformado de metales por el método de elementos [...]

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• An anisotropic elastoplastic model based on an isotropic formulation

  S. Oller, S. Botello, J. Canet, E. Oñate

  (1993). Research Report, Nº PI41

  
  

  Abstract

  This paper shows a generalization of the classic isotropic plasticity theory to be applied to orthotropic or anisotropic materials. This approach assumes the existence of a real anisotropic space, and other fictitious isotropic space where a mapped fictitious problem is solved. Both spaces are related by means of a linear transformation using a fourth order transformation tensor that contains all the information concerning the real anisotropic material. The paper describes the basis of the spaces transformation proposed and the expressions of the resulting secant and tangent constitutive equations. Also details of the numerical integration of the constitutive equation are provided. Examples of application showing the good performance of the model for analysis of orthotropic materials and fibre‐reinforced composites are given.

  Abstract
  This paper shows a generalization of the classic isotropic plasticity theory to be applied to orthotropic or anisotropic materials. This approach assumes the existence of [...]

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• Caltep programa para el cálculo transitorio de la ecacuación de Poisson

  F. Zarate, E. Oñate

  (1993). Research Report, Nº PI27

  
  

  Abstract

  Esta publicación explica la utilización de un programa de elementos finitos que permita resolver la ecuación de Poisson transitoria, que rige una gran cantidad de problemas físicos como son la transición del calor a través de diversos medios, el flujo de un líquido a través de un medio permeable, problemas de magnetismo, etc. En la publicación describe las etapas que intervienen en un programa de elementos finitos para cálculo de la ecuación de Poisson transitoria incidiendo principalmente en la metodología general de la programación de las diferentes subrutinas, así como en su aplicación a varios problemas. En la última parte de esta publicación se presentan diversos ejemplos de aplicación del programa, así como un listado completo del mismo, una descripción de sus variables más significativas y las instrucciones para la entrada de datos.   

  Abstract
  Esta publicación explica la utilización de un programa de elementos finitos que permita resolver la ecuación de Poisson transitoria, que rige una gran [...]

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• A temperature‐based formulation for finite element analysis of generalized phase‐change problems

  D. Celentano, E. Oñate, S. Oller

  (1993). Research Report, Nº PI28

  
  

  Abstract

  A finite element formulation for solving multidimensional phase-change problems is presented. The formulation considers the temperature as the unique state variable, it is conservative in the weak form sense and it preserves the moving interface condition. In this work, a consistent Jacobian matrix that ensures numerical convergence and stability is derived. Also, a comparative analysis with other different phase-change finite element techniques is performed. Finally, two numerical examples are analyzed in order to show the performance of the proposed methodology.

  Abstract
  A finite element formulation for solving multidimensional phase-change problems is presented. The formulation considers the temperature as the unique state variable, it is [...]

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• Aerodynamic shape optimization using automatic adaptive remeshing

  G. Bugeda, E. Oñate, D. Joannas

  (1993). Research Report, Nº PI29

  
  

  Abstract

  This work presents a new methodology base on the use adaptive mesh refinement (AMR) techniques in the context of shape optimization problems analyzed by the Finite Element Method. A suitable and very general technique for the parametrization of the optimization problem using B-splines to define the boundary is first presented. Then, mesh generation using the advancing front method, the estimation of error and the mesh refinement criterion are studied in the context of shape optimization problems. In particular, the sensitivities of the different ingredients ruling the problem (B-splines, finite element mesh, flow behavior, and error estimator) are studied in detail. The sensitivities of the finite element mesh and the error estimator allow their projection from one design to the next, thus leading to an “a priori knowledge” of the error distribution on the new design without the need of any additional analysis. This information allows to build up a finite element mesh for the new design with a specified and controlled level error. The robustness and reliability of the proposed methodology is checked out with some 2D application examples.   

  Abstract
  This work presents a new methodology base on the use adaptive mesh refinement (AMR) techniques in the context of shape optimization problems analyzed by the Finite Element [...]

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• A methodology for adaptive mesh refinement in optimum shape design problems

  G. Bugeda, E. Oñate

  (1993). Research Report, Nº PI31

  
  

  Abstract

  This work presents a methodology based on the use of adaptive mesh refinement (AMR) techniques in the context of shape optimization problems analyzed by the Finite Element Method (FEM). A suitable and very general technique for the parametrization of the optimization problem using B-splines to define the boundary is first presented. Then, mesh generation using the advancing front method, the error estimation and the mesh refinement criteria are dealt with in the context of a shape optimization problems. In particular, the sensitivities of the different ingredients ruling the problem (B-splines, finite element mesh, design behaviour, and error estimator) are studied in detail. The sensitivities of the finite element mesh coordinates and the error estimator allow their projection from one design to the next, giving an “a priori knowledge” of the error distribution on the new design. This allows to build up a finite element mesh for the new design with a specified and controlled level of error. The robustness and reliability of the proposed methodology is checked out with some 2D examples.

  Abstract
  This work presents a methodology based on the use of adaptive mesh refinement (AMR) techniques in the context of shape optimization problems analyzed by the Finite Element [...]

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• A general procedure ofr deriving thin plate bending elements with one degree of freedom per node

  E. Oñate, M. Cervera

  (1993). Research Report, Nº PI32

  
  

  Abstract

  A general methodology for deriving thin plate bending elements with a single degree of freedom per node is presented. The formulation is based on the combination of a standard C₀ finite element interpolation for the deflection field with an independent approximation of the curvatures which are expressed in terms of the deflection gradient along the sides using a finite volume-like approach. The formulation is particularized for the simplest element of the family, i.e. the three node triangle with three degrees of freedom. The potential of the new element is shown through different examples of application.

  Abstract
  A general methodology for deriving thin plate bending elements with a single degree of freedom per node is presented. The formulation is based on the combination of a standard [...]

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