JOURNALS

Documents published in Scipedia

• Simulation of structural response to violent-free surface flows

  R. Löhner, C. Yang, E. Oñate

  (2008). Numerical Modeling of Coupled Phenomena in Science and Engineering, M.C. Suárez Arriaga, J. Bundschuh, F.J. Dominguez-Mota (Eds.)

  
  

  Abstract

  High sea states, waves breaking near shores andmoving ships, the interaction of extremewaveswith floating structures, green water on deck and sloshing (e.g. in liquid natural gas (LNG) tankers) are but a few examples of flows with violent free surface motion. The bodies exposed to these flows experience large, time-varying forces that can lead to fatigue and/or failure. It is therefore imperative to have a predictive capability in order to guarantee operability and optimize the lifespan under these conditions.

  Abstract
  High sea states, waves breaking near shores andmoving ships, the interaction of extremewaveswith floating structures, green water on deck and sloshing (e.g. in liquid natural [...]

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• A variational formulation for the multilayer perceptron

  R. Lopez, E. Oñate

  (2006). S. Kollias et al (Eds.), ICANN 2006, Part I, LNCS 4131, pp. 19-168, Germany.

  
  

  Abstract

  In this work we present a theory of the multilayer perceptron from the perspective of functional analysis and variational calculus. Within this formulation, the learning problem for the multilayer perceptron lies in terms of finding a function which is an extremal for some functional. As we will see, a variational formulation for the multilayer perceptron provides a direct method for the solution of general variational problems, in any dimension and up to any degree of accuracy. In order to validate this technique we use a multilayer perceptron to solve some classical problems in the calculus of variations.

  Abstract
  In this work we present a theory of the multilayer perceptron from the perspective of functional analysis and variational calculus. Within this formulation, the learning problem [...]

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• Analysis of the structure of gothic cathedrals. Application to Barcelona cathedral

  P. Roca, L. Pellegrini, E. Oñate, A. Hanganu

  (1998). Structural Analysis of Historical Constructions II, P. Roca, J.L. González, E. Oñate and P. B. Lourenço(Eds.), CIMNE, Barcelona, Spain

  
  

  Abstract

  The study of ancient structures composed of stone arches and vaults requires the use of specific techniques of analysis endowed with powerful procedures for the modelling of geometry, the simulation of the mechanical response of the various materials (including ashlar blocks and masonry, backings and fills) and the simulation of the structure or may have affected it through history. More specifically, those techniques must be able to reproduce the actual conditions of thrust equilibrium between the large number of curved, linear or two-dimensional members involved. The validity of several modelling techniques with a very different level of sophistication is studied through their use in the study of a particular Gothic construction: Barcelona Cathedral. The various techniques used were developed at the school of civil engineering of the technical university of Catalonia and have already been used in the analysis of a set historical constructions, including the Basilica of San Marco (Oñate et al., 1997) and the Crypt of the Colònia Güell (Roca, 1997). The present study of Barcelona Cathedral, now under development, is thus not only aimed at gaining a better understanding of various aspects of the resistance of Gothic constructions (and the southern and Catalan Gothic, in particular) but also at appraising the possibilities and limitations of various analytical techniques.

  Abstract
  The study of ancient structures composed of stone arches and vaults requires the use of specific techniques of analysis endowed with powerful procedures for the modelling [...]

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• Structural analysis and durability assesment of historical constructions using a finite element damage model

  E. Oñate, A. Hanganu, A. Barbat, S. Oller, R. Vitaliani, A. Saetta, R. Scotta

  (1997). Structural Analysis of Historical Constructions I, P. Roca, J.L. González, A.R. Marí and E. Oñate (Eds.), CIMNE, Barcelona, Spain

  
  

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• Prediction of elastic springback deffects in sheet stamping processes using finite element methods

  E. Oñate, J. Rojek

  (1997). Advanced Methods in Materials Processing Defects, Elsevier

  
  

  Abstract

  Undesiderable spring-back induced deformations are one of the cause for rejection of many stamped sheet parts. The paper presents the alternatives for predicting spring-back defects in the context of the most popular finite element (FE) formulations based on rigid-plastic and elasto-plastic material models, quasistatic (implicit) and explicit dynamic algorithms. Examples showing the possibilities and efficiency of the different FE procedures are also given.

  Abstract
  Undesiderable spring-back induced deformations are one of the cause for rejection of many stamped sheet parts. The paper presents the alternatives for predicting spring-back [...]

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• Numerical modelling of sheet metal forming problems

  E. Oñate, C. Agelet de Saracibar

  (1991). Numerical Modelling of Material Deformations Processes, C. Sturgess et al (Eds.), Springer Verlag, London

  
  

  Abstract

  Stamping of sheet-metal parts by means of punches and dies is a standard manufacturing process. However, despite its broad application in industry, the design of forming processes is still largely based on experimental techniques, such as the use of circular grid systems (Keeler 1968) or forming limit diagrams (Hecker 1973, Keeler 1974).

  Abstract
  Stamping of sheet-metal parts by means of punches and dies is a standard manufacturing process. However, despite its broad application in industry, the design of forming processes [...]

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• Finite Streifenmethode für Mindlinsche Platten und axialsymmetrische Schalen

  E. Oñate, B. Suárez, E. Hinton

  (1990). Finite Elemente Programme für Platten und Schalen, Springer-Verlag, Berlin, Germany

  
  

  Abstract

  Viele Konstruktionen besitzen konstante geometrische Eigenschaften entlang einer bestimmten Richtung. Derartige prismatische Strukturen sind bei Platten weit verbreitet, bei denen der Querschnitt der Platte in Längsrichtung oft konstant bleibt. Bei axialsymmetrischen Schalen bleibt der Querschnitt der Schale in Umfangsrichtung ebenfalls konstant (siehe Bild 2.1). Falls die Materialeigenschaften der Struktur ebenfalls in der gleichen Richtung konstant sind, kann die Berechnung durch eine Kombination der Methode der finiten Elemente und Fourierreihenentwicklung vereinfacht werden, um das transversale und longitudinale Verhalten zu erfassen.

  Abstract
  Viele Konstruktionen besitzen konstante geometrische Eigenschaften entlang einer bestimmten Richtung. Derartige prismatische Strukturen sind bei Platten weit verbreitet, bei [...]

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• Adaptive Mesh Refinement Techniques for Structural Problems

  E. Oñate, J. Castro

  (1990). The Finite Element Method in the 1990's, E. Oñate et al (Eds.), CIMNE/Springer Verlag

  
  

  Abstract

  In this paper some adaptive mesh refinement (AMR) strategies for finite element analysis of structural problems are discussed. Two mesh optimality criteria based on the equal distribution of: (a) the global error, and (b) the specific error over the elements are studied. It is shown that the correct evaluation of the rate of convergence of the different error norms involved in the AMR procedures is essential to avoid oscillations in the refinement process. The behaviour of the different AMR strategies proposed is compared in the analysis of some structural problems.

  Abstract
  In this paper some adaptive mesh refinement (AMR) strategies for finite element analysis of structural problems are discussed. Two mesh optimality criteria based on the equal [...]

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• Finite element analysis of sheet metal forming problems using a viscous voided shell formulation

  E. Oñate, C. Agelet de Saracibar

  (1988). Modelling of Metal Forming Processes, J.L. Chenot y E. Oñate (Eds.), Kluwer Academic Publisher, pp. 163-178

  
  

  Abstract

  A formal analogy between the equations of pure plastic and viscoplastic flow theory for void containing metals and those of standard non linear elasticity is presented. It is shown how by direct simplifications of the general equations, the standard incompressible flow expressions for non voided metals are obtained. The general formulation is particularized for the analysis of sheet metal forming problems and details of the viscous voided shell and membrane formulations for dealing with the axisymmetric case are given. Finally, some examples of applications of pure and hemispherical stretching and deep drawing of a circular sheet axe presented.

  Abstract
  A formal analogy between the equations of pure plastic and viscoplastic flow theory for void containing metals and those of standard non linear elasticity is presented. It [...]

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• Stabilization techniques for finite element analysis of convection-diffusion problems

  E. Oñate, M. Manzan

  (2000). Convection Heat Transfer, B. Sundén and G. Comini (Eds.), WIT Press, Southampton, United Kingdom

  
  

  Abstract

  The accurate solution of convection type problems on practical grids has been ever a challenging issue, and invariably some sort of stabilization is needed in order to get a physical solution. This has pushed researchers to develop various stabilization algorithms used in every day practice by numerical analysts. In this chapter some methods are presented along with a new finite increment calculus approach to obtain the different algorithms using higher order conservation equations.

  Abstract
  The accurate solution of convection type problems on practical grids has been ever a challenging issue, and invariably some sort of stabilization is needed in order to get [...]

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