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• Aplicación del método PFEM a la simulación de procesos de transferencia propios de la industria pulvimetalúrgica

  C. González, J. Cante, J. Oliver

  Monograph CIMNE (2010). M117

  
  

  Abstract

  El objetivo primario del trabajo es desarrollar desde el enfoque de la ingeniería la metodología PFEM, la cual se fundamenta en una reinterpretación alternativa los métodos clásicos masivamente aceptados. Como objetivos adicionales de la monografía se tienen aplicar el PFEM a problemas complejos pertenecientes a la pulvimetalurgia, exhibir sus potencialidades en otros campos de la ingeniería y vislumbrar algunas líneas de investigación y desarrollo futuros.

  Abstract
  El objetivo primario del trabajo es desarrollar desde el enfoque de la ingeniería la metodología PFEM, la cual se fundamenta en una reinterpretación [...]

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• Flood. An open source neural networks C++ library

  R. López

  Monograph CIMNE (2010). M120

  
  

  Abstract

  The multilayer perceptron is an important model of neural network, and much of the literature in the eld is referred to that model. The multilayer perceptron has found a wide range of applications, which include function re- gression, pattern recognition, time series prediction, optimal control, optimal shape design or inverse problems. All these problems can be formulated as variational problems. That neural network can learn either from databases or from mathematical models. Flood is a comprehensive class library which implements the multilayer perceptron in the C++ programming language. It has been developed follow- ing the functional analysis and calculus of variations theories. In this regard, this software tool can be used for the whole range of applications mentioned above. Flood also provides a workaround for the solution of function opti- mization problems.

  Abstract
  The multilayer perceptron is an important model of neural network, and much of the literature in the eld is referred to that model. The multilayer perceptron has found a [...]

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• Numerical modelling of crack formation in powder compaction processes

  J. Hernández, J. Oliver, J. Cante

  Monograph CIMNE (2009). M114

  
  

  Abstract

  The primary objective of this work is precisely to fill this gap by developing a constitutive model that attempts to describe the mechanical behavior of the powder during both pressing and ejection phases, with special emphasis on the representation of the cracking phenomenon. The constitutive relationships are derived within the general framework of rate-independent, isotropic, finite strain elastoplasticity. The yield function is defined in stress space by three surfaces intersecting nonsmoothly, namely, an elliptical cap and two classical Von Mises and Drucker-Prager yield surfaces. The distinct irreversible processes occurring at the microscopic level are macroscopically described in terms of two internal variables: an internal hardening variable, associated with accumulated compressive (plastic) strains, and an internal softening variable, linked with accumulated (plastic) shear strains. The innovative part of our modeling approach is connected mainly with the characterization of the latter phenomenological aspect: strain softening. Incorporation of a softening law permits the representation of macroscopic cracks as high gradients of inelastic strains (strain localization). Motivated by both numerical and physical reasons, a parabolic plastic potential function is introduced to describe the plastic flow on the linear Drucker-Prager failure surface. A thermodynamically consistent calibration procedure is employed to relate material parameters involved in the softening law to fracture energy values obtained experimentally on Distaloy AE specimens.

  Abstract
  The primary objective of this work is precisely to fill this gap by developing a constitutive model that attempts to describe the mechanical behavior of the powder during [...]

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• Regularized maxwell equations and nodal finite elements for electromagnetic field computations in frequency domain

  R. Otín, E. Oñate

  Monograph CIMNE (2011). M123

  
  

  Abstract

  In this work we present an alternative approach to the usual finite element formulation based on edge elements and double-curl Maxwell equations. This alternative approach is based on nodal elements and regularized Maxwell equations. The advantages are that, without adding extra unknowns (such as Lagrange multipliers), it provides spurious-free solutions and well-conditioned matrices. Besides, its integral representation involves a less singular kernel (order 1 instead of 3), which makes this approach best suited to hybridization with integral numerical techniques. On the other hand, a new set of difficulties arises that were not present in the classical formulation. The main drawback is that a globally wrong solution is obtained when the electromagnetic field has a singularity in the problem domain. Also, boundary conditions and field discontinuities are more laborious to implement. This work explains how to overcome these difficulties and demonstrates that accurate solutions can be obtained with nodal elements and the regularized formulation. We also present ERMES, the C++ implementation of the finite element approach depicted above and the main deliverable of this work. We compute with ERMES the scattering parameters of microwave filters and the specific absorption rate induced in a body when exposed to electromagnetic fields. ERMES is also the computational tool used in two novel numerical models introduced in this work. The first one characterizes electromagnetic metal forming processes and the second one the transfer impedance of cable shields. The electromagnetic metal forming model calculates the driving Lorentz force and estimates the optimum frequency at which it is attained the maximum workpiece deformation. The main advantage of the approach is that it provides an explicit relation between the capacitance of the capacitor bank and the frequency of the discharge, which is a key parameter in the design of an electromagnetic forming system. The successful application of the regularized formulation in this model reveals its excellent behavior in the low-frequency (quasi-static) regime. The second numerical model introduced in this work computes the transfer impedance of cable shields. The model reproduces the high frequency behavior of the transfer impedance more accurately than the approaches found in the literature and, moreover, it is able to analyze a wider variety of geometries and materials.

  Abstract
  In this work we present an alternative approach to the usual finite element formulation based on edge elements and double-curl Maxwell equations. This alternative approach [...]

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• The Particle Finite Element Method. An effective numerical technique for fluid-soil-structure interaction problems

  E. Oñate, M. Celigueta, S. Idelsohn, F. Salazar, B. Suarez

  (2012). Issues on Mechanical and Civil Engineering. A Symposium to honour Prof. Enrique Alarcón. M. Doblaré, Ja. Domínguez, Jo. Domínguez, A. Fraile, F. García, S. Gómez, A. Martín, F. París (Eds.)

  
  

  Abstract

  We present some developments in the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the solid domains (the later including soil/rock and structures). A mesh connects the particles (nodes) defining the discretized domain where the governing equations for each of the constituent materials are solved as in the standard FEM. The stabilization for dealing with an incompressibility continuum is introduced via the finite calculus (FIC) method. An incremental iterative scheme for the solution of the non linear transient coupled FSSI problem is described. The procedure to model frictional contact conditions and material erosion at fluid-solid and solid-solid interfaces is described. We present several examples of application of the PFEM to solve FSSI problems such as the motion of rocks by water streams, the erosion of a river bed adjacent to a bridge foundation, the stability of breakwaters and constructions sea waves and the study of landslides.

  Abstract
  We present some developments in the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction [...]

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• Possibilities of the Particle Finite Element Method in computational mechanics

  E. Oñate, S. Idelsohn, M. Celigueta, R. Rossi, S. Latorre

  (2010). Computer Methods in Mechanics, M. Kuzma, K. Wilmanski (Eds.), Chapter 15, pp. 271-310., Springer-Verlag, Berlin, Heidelberg

  
  

  Abstract

  We present some developments in the formulation of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in fluid and solid mechanics accounting for fluid-structure interaction and coupled thermal effects. The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility of the fluid is introduced via the finite calculus (FIC) method. An incremental iterative scheme for the solution of the non linear transient coupled fluid-structure problem is described. Extensions of the PFEM to allow for frictional contact conditions at fluid-solid and solid-solid interfaces via mesh generation are described. A simple algorithm to treat erosion in the fluid bed is presented. Examples of application of the PFEM to solve a number of coupled problems such as the effect of large wave on structures, the large motions of floating and submerged bodies, bed erosion situations and melting and dripping of polymers under the effect of fire are given.

  Abstract
  We present some developments in the formulation of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in fluid and solid mechanics accounting [...]

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• Posibilidades de los métodos numéricos en obras subterráneas

  E. Oñate, B. Suarez, J. Canet

  (2007). Avances en Mecánica de Medios Continuos. Simposium en honor al Profesor J. A. Garrido García. E. Alarcon, A. Forces, F. París (Eds.), pp. 195-210

  
  

  Abstract

  Se presenta un resumen de las posibilidades de diversos métodos numéricos basados en la combinación de técnicas de elementos finitos y de partículas para la simulación de problemas típicos de obras subterráneas, tales como la excavación de túneles y la inundación de cavidades.

  Abstract
  Se presenta un resumen de las posibilidades de diversos métodos numéricos basados en la combinación de técnicas de elementos finitos y de partículas [...]

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• Finite elements versus finite volumes. Is there really a choice?

  O. Zienkiewicz, E. Oñate

  (1992). Non linear computational mechanics. State of the art. P. Wriggers,R. Wagner and E. Stein (eds.), Chapter IV, Beam, Plate and Shell Formulations, pp. 240-254, Springer Verlag

  
  

  Abstract

  The finite volume method appears to be a particular case of finite elements with a non Galerkin weighting. It is course less accurate for self adjoint problems but has some computationally useful features for first order equations involving only surface integrals. For certain problems this is a substational economy and leads to computationally useful approximations.

  Abstract
  The finite volume method appears to be a particular case of finite elements with a non Galerkin weighting. It is course less accurate for self adjoint problems but has some [...]

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• Numerical simulation of industrial sheet forming processes

  E. Oñate

  Monograph CIMNE (1993). M23

  
  

  Abstract
  This monograph presents different finite element based mathematical models and computational methods for numerical simulation of industrial sheet metal forming processes.

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• II International Workshop. Information Technologies and Computing Techniques for the Agro-Food Sector

  E. Balsa, J. Mora, J. Banga, E. Oñate

  Monograph CIMNE (2003). M86

  
  

  Abstract

  This  monographs of proceedings includes all extended abstracts, which will be presented during the AfoT. These presentations will cover a wide range of topics: - Modelling and simulation operations and process plants. - Food process optimisation, scheduling and control. - Food properties measurements and quality control. - Simulation of complex processes, for example those requiring computational fluid dynamics, CFD. - The use of new information technologies to develop decision support sytems.

  Abstract
  This  monographs of proceedings includes all extended abstracts, which will be presented during the AfoT. These presentations will cover a wide range of topics: - [...]

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