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• A simple triangular element for thick and thin plate and shell analysis

  E. Oñate, F. Zárate, F. Flores

  (1993). Research Report, Nº PI33

  
  

  Abstract

  A new plate triangle based on Reissner–Mindlin plate theory is proposed. The element has a standard linear deflection field and an incompatible linear rotation field expressed in terms of the mid‐side rotations. Locking is avoided by introducing an assumed linear shear strain field based on the tangential shear strains at the mid‐sides. The element is free of spurious modes, satisfies the patch test and behaves correctly for thick and thin plate and shell situations. The element degenerates in an explicit manner to a simple discrete Kirchhoff form.

  Abstract
  A new plate triangle based on Reissner–Mindlin plate theory is proposed. The element has a standard linear deflection field and an incompatible linear rotation field [...]

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• Utilisation de maillages adaptatifs dans un processus d'optimisation de formes en aérodynamique

  G. Bugeda, D. Joannas, E. Oñate

  (1993). Research Report, Nº PI34

  
  

  Abstract

  L’objet de ce rapport est de presenter l’approche choise par le CIMNE afin d’optimiser des forms, dans le cadre des équations du potentiel incompressible portant. Plus précisément, nous nous intéresserons ici à étudier l’influence de la partie “maillage adaptatif” sur la convergence globale d’un problème d’optimisation de formes. Les formes à optimiser sont des profils d’ailes d’avions (dimension 2). L’approche retenue utilice paramétrisation des formes considérées par des B-splines. Chaque domaine de calcul est alors discrétisé à l’aide d’un algorithme de maillage classique appelé méthode frontale avancée. Afin de definir à l’avance la taille des éléments de la d’erreur pour la solution des équations du potentiel incompressible (c’est l’influence de la précision requise pour cet estimateur, sur la convergence globale du processus, que nous étudierons). Enfin, on écrit le problème de reconstruction sous la forme d’un problème de minimisation, résolu par une méthode de quasi-Newton où le gradient de la fonctionnelle à minimiser est calculé exactement.  

  Abstract
  L’objet de ce rapport est de presenter l’approche choise par le CIMNE afin d’optimiser des forms, dans le cadre des équations du potentiel incompressible [...]

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• A new class of constitutive models for soils

  A. Crescenzo, A. Fusco

  (1993). Research Report, Nº PI35

  
  

  Abstract

  This work presents the theoretical framework of a new class of constitutive models, which allows to respect five simple physical hypotheses on the mechanical behavior of soils. The most significant of them is that the (effective) stress and the specific volume are the state variables of soils. The well-known Cam-Clay model may be seen as a particular case of the presented class of models. However, in its generality, this class of models allows to describe the progressive accumulation of plastic deformation under cyclic loading.

  Abstract
  This work presents the theoretical framework of a new class of constitutive models, which allows to respect five simple physical hypotheses on the mechanical behavior of soils. [...]

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• A generalized theory of plasticity

  A. Crescenzo, A. Fusco

  (1993). Research Report, Nº PI36

  
  

  Abstract

  The classical incremental theory of plasticity is not able to predict plastic strain accumulation during cycling loading. This because plastic deformation may occur only during loading conditions and when the stress point lies on the yield surface F. on the other hand, F remains fixed in the stress space durinf unloading conditions, so thar successice loading does not produce any plastic deformation until the stress point does not reach again F. this work presents a feneralizarion of the classical theory, which allows to describe plastic strain accumulation during cyclic loading. This obtained postulatinf that F follows always the stress point. Moreover, it is assumed the existence of a surface F, which bounds always F and of an elastic surface F, which bounds the stress states at which only elastic strain mat occur. In the limit case F=F the presented generalized theory recovers the classical one.   

  Abstract
  The classical incremental theory of plasticity is not able to predict plastic strain accumulation during cycling loading. This because plastic deformation may occur only during [...]

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• Evaluación de diferentes elementos finitos basados en la teoría de láminas de Simó

  F. Flores, E. Oñate

  (1993). Research Report, Nº PI38

  
  

  Abstract

  En este trabajo se presenta la evaluación de varios elementos basados en la teoría de láminas desarrollada por Simó y colaboradores [1-5]. Se ha implementado una versión simplificada del elemento de cuatro nodos y varios elementos triangulares. Los estudios se refieren principalmente al comportamiento no lineal geométrico dentro de una formulación lagrangeana total. Se presentan también algunos ejemplos con comportamiento no lineal material.  

  Abstract
  En este trabajo se presenta la evaluación de varios elementos basados en la teoría de láminas desarrollada por Simó y colaboradores [1-5]. Se ha [...]

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• Análisis dinámico de estructura de láminas y vigas

  F. Flores, E. Oñate

  (1993). Research Report, Nº PI39

  
  

  Abstract

  En este trabajo se realiza inicialmente un resumen teórico de las teorías de láminas y vigas desarrolladas por Simo y colaboradores [2-6,12-15]. Luego se presentan un elemento cuadrilátero y 4 elementos triangulares adecuados para el análisis no lineal geométrico y material en régimen dinámico. Se presentan también un elemento de viga y se propone un criterio de fluencia en esfuerzos generalizados. Se muestran algunos ejemplos del comportamiento de los elementos y la teoría subyacente, incluyendo problemas de contacto entre cuerpos deformables. Finalmente se presentan una metodología para la compatibilización de desplazamientos entre elementos de láminas, vigas y sólidos que permita el análisis de estructuras compuestas sin necesidad de elementos transición entre diferentes elementos y maneje rigidizadores excéntricos.   

  Abstract
  En este trabajo se realiza inicialmente un resumen teórico de las teorías de láminas y vigas desarrolladas por Simo y colaboradores [2-6,12-15]. Luego [...]

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• Finite element analysis of hot rolling processes

  O. Soto, E. Oñate, R. Codina

  (1993). Research Report, Nº PI40

  
  

  Abstract

  The numerical simulation of hot rolling forming processes is very important for the metallurgic industry. This is an efficient and economic tool to simulate the rolling process and to predict the evolution of some parameters like the velocity field, temperatures, strains, stresses and rolling forces. In this way, computer simulations are becoming a necessary tool in the design and optimization of hot rolling processes [2,3,4,5,21,25,26,27]. In this publication an incompressible flow based formulation to simulate hot rolling processes is presented. First, some theorical aspects about the process are shown as well as numerical solution using the finite element method. Finally, some numerical examples are presented.  

  Abstract
  The numerical simulation of hot rolling forming processes is very important for the metallurgic industry. This is an efficient and economic tool to simulate the rolling process [...]

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• The small-gap equation in rotary lip seals

  J. Heinrich, C. Vionnet

  (1993). Research Report, Nº PI42

  
  

  Abstract

  The study of a thin, incompressible Newtonian fluid layer trapped between two almost parallel, sliding surfaces has been actively pursued in the last decades. This subject includes lubrication applications such as slider bearing or the sealing of non-pressurized fluids with rubber rotary shaft seals. In the present work we analyze the flow of lubricant fluid through the micro-gap of rotary lip seals. This study is carried out assuming that a “small-gap” parameter δ attains an extreme value in the Navier-Stokes equations. In particular, the effect of surface roughness, excentricity and centrifugal forces is analyzed using the technique. The precise meaning of small gap is achieved by the particular limit δ=0 which, within the bounds of the hypotheses, predicts transport of lubricant through the sealed area by centrifugal instabilities. Numerical results obtained with the finite element method are presented.  

  Abstract
  The study of a thin, incompressible Newtonian fluid layer trapped between two almost parallel, sliding surfaces has been actively pursued in the last decades. This subject [...]

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• On the Computational efficiency and implementation of block-iterative algorithms for nonlienar coupled problems

  M. Cervera, R. Codina, J. Galindo

  (1993). Research Report, Nº PI43

  
  

  Abstract

  In this paper we outline a general methodology for the solution of the system of algebraic equations arising from the discretization of the field equations governing coupled problems. In our examples, we shall consider that this discrete problem is obtained from the finite element discretization in space and the finite difference discretization in time. Our motivation is to preserve software modularity, to be able to use existing single field codes to solve more complex problems, and to exploit computer resources optimally, emulating parallel processing. To this end we deal with two well-known coupled problems of computational mechanics – the fluid-structure interaction problem and thermally driven flows of incompressible fluids. The possibility of coupling the block-iterative loop with the nonlinearity of the problems is demonstrated through numerical experiments, which suggest that even a mild nonlinearity drives the convergence rate of the complete iterative scheme, at least for the two problems considered here. The paper discusses the implementation of this alternative to the direct coupled solution, stating advantages and disadvantages. The need for on-line synchronized communication between the different codes used is also explained, together with the description of the master code who will control overall algorithm.    

  Abstract
  In this paper we outline a general methodology for the solution of the system of algebraic equations arising from the discretization of the field equations governing coupled [...]

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• Search for general fluid mechanics algortihm

  O. Zienkiewicz, R. Codina

  (1993). Research Report, Nº PI44

  
  

  Abstract

  The paper outlines the formulation of a novel algorithm which can be used for the solution of both compressible and incompressible Navier-Stokes or Euler equations. Full incompressibility can be dealt with if the algorithm is used in tis semi-explicit form and its structure permits arbitrary interpolation functions to be used avoiding the Babuska-Brezzi restriction. In a fully explicit version it introduces a rational form balancing dissipation avoiding the use of arbitrary parameters and forms for this.

  Abstract
  The paper outlines the formulation of a novel algorithm which can be used for the solution of both compressible and incompressible Navier-Stokes or Euler equations. Full incompressibility [...]

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