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• Analysis of the melting, burning and flame spread of polymers with the particle finite element method

  E. Oñate, J. Marti, P. Ryzhakov, R. Rossi, S. Idelsohn

  Computer Assisted Methods in Engineering and Sciences (2013). Vol. 20 (3), pp. 165-184

  
  

  Abstract

  A computational procedure for analysis of the melting, burning and flame spread of polymers under fire conditions is presented. The method, termed particle finite element method (PFEM), combines concepts from particle-based techniques with those of the standard finite element method (FEM). The key feature of the PFEM is the use of an updated Lagrangian description to model the motion of nodes (particles) in the thermoplastic material. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of melting and dripping of polymer particles. A mesh connects the nodes defining the discretized domain where the governing equations are solved using the FEM. An incremental iterative scheme for the solution of the nonlinear transient coupled thermal-flow problem, including radiation, loss of mass by gasification and combustion is used. Examples of the possibilities of the PFEM for the modelling and simulation of the melting, burning and flame spread of polymers under different fire conditions are described.

  Abstract
  A computational procedure for analysis of the melting, burning and flame spread of polymers under fire conditions is presented. The method, termed particle finite element [...]

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• Analysis of the discharge capacity of radial-gated spillways using CFD and ANN – Oliana Dam case study

  F. Salazar, R. Morán Moya, R. Rossi, E. Oñate

  Journal of Hydraulic Research (2013). (preprint) Vol. 51 (3), pp. 244-252

  
  

  Abstract

  The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana Dam is considered as a case study and the discharge capacity is predicted both by the application of a level-set-based free-surface solver and by the use of traditional empirical formulations. The results of the analysis are then used for training an artificial neural network to allow real-time predictions of the discharge in any situation of energy head and gate opening within the operation range of the reservoir. The comparison of the results obtained with the different methods shows that numerical models such as the FEM can be useful as a predictive tool for the analysis of the hydraulic performance of radial-gated spillways.

  Abstract
  The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana [...]

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• Olgierd Cecil Zienkiewicz obituary

  M. Kleiber, E. Oñate

  Archives of Comp. Meths. Engng. (2009). Vol. 16, pp. 465

  
  

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• Control of the finite element discretization error during the convergence of structural shape optimization algorithms

  G. Bugeda, J. Ródenas, J. Albelda, E. Oñate

  Int. J. Simul. Multidisci. Des. Optim. (2009). Vol. 3 (3), pp. 363-369

  
  

  Abstract

  This work analyzes the influence of the discretization error contained in the Finite Element (FE) analyses of each design configuration proposed by structural shape optimization algorithms over the behaviour of the algorithm. If the FE analyses are not accurate enough, the final solution will neither be optimal nor satisfy the constraints. The need for the use of adaptive FE analysis techniques in shape optimum design will be shown. The paper also proposes the use of the algorithm described in [1] in order to reduce the computational cost associated to the adaptive FE analysis of each geometrical configuration when evolutive optimization algorithms are used.

  Abstract
  This work analyzes the influence of the discretization error contained in the Finite Element (FE) analyses of each design configuration proposed by structural shape optimization [...]

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• Advances in the particle finite element method for fluid-structure interaction problems

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

  Computational Mechanics (2006). Vol. 6, pp. 41-62

  
  

  Abstract

  We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use of a Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are thus viewed as particles 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, expressed in an integral from, 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. A fractional step scheme for the transient coupled fluid-structure solution is described. Examples of application of the PFEM to solve a number of fluid-structure interaction problems involving large motions of the free surface and splashing of waves are presented.

  Abstract
  We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use [...]

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• The rotation-free BST shell element for linearized buckling analysis of steel structures

  A. Agüero, F. Pallarés, E. Oñate

  Int. J. Computational Methods in Engineering Science and Mechanics (2006). Vol. 7 (3), pp. 209-215

  
  

  Abstract

  In this paper the ability of the basic shell triangular (BST) element to perform linearized buckling analysis is evaluated. The results have been compared with analytical solutions and other finite elements in the literature, such as ANDES3, ANDES4, QSEL, FFQC and BCIZ. This type of analysis is applied to the design of steel structures to obtain the collapse load of panels using the effective width of the plate. In this approach, which is currently recommended by most of the design standards, a semi-empirical/analytical method is used to take into account the nonlinear geometric and material behavior, geometric imperfections and residual stresses. To obtain the critical loads two methods have been mainly applied: the finite strip method and the finite element method, which is more appropriate to deal with any boundary condition and loading pattern. In practice, to obtain the local and distortional buckling, some assumptions related to the interaction between plates are made in order to obtain practical formulae that can be applied; these simplifications can lead to unsafe results, so the linearized buckling analysis must be carried out in a proper way, taking into account the interactions. It is concluded that the BST element presents an excellent behavior to predict the critical loads in compression and shear, and therefore this element must be utilized in future codes when this type of analysis turn out to be mandatory.

  Abstract
  In this paper the ability of the basic shell triangular (BST) element to perform linearized buckling analysis is evaluated. The results have been compared with analytical [...]

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• Simulación de problemas de desgaste, en la interacción herramienta de corte terreno, empleando el método de los elementos discretos

  C. Recarey Morfa, E. Oñate, J. Canet, J. Rojek, F. Zarate, S. Burrel

  Ingeniería Civil (2006). Vol. 141, pp. 19-34

  
  

  Abstract

  Se presenta un modelo numérico que emplea elementos discretos esféricos o también denominados elementos distintos. Este modelo se aplica en la simulación de problemas de desgaste. El movimiento de elementos esféricos se describe por medio de las ecuaciones de Newton-Euler. Se emplea en la formulación una integración explícita, la cual, brinda una buena eficiencia computacional. Los elementos esféricos interactúan recíprocamente entre sí a través de las fuerzas de contacto. El esquema de búsqueda de contacto es muy eficaz, y está basado en las estructuras de oct-tree. El modelo constitutivo de contacto presenta una singularidad muy especial, ya que puede simular las fuerzas de cohesión que permiten modelar la fractura y descohesión de los materiales. El estudio de desgastes se realiza a partir de una formulación termo­acoplada que se aplica a nivel experimental, o escala reducida, y además in-situ o escala real.

  Abstract
  Se presenta un modelo numérico que emplea elementos discretos esféricos o también denominados elementos distintos. Este modelo se aplica en la simulación [...]

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• Posibilidades de los métodos numéricos en el mundo industrial

  E. Oñate

  Col·lecció Aula de Ciència i Cultura (2002). Nº 13, pp. 9-33

  
  

  Abstract

  Se presentan en el artículo las ideas básicas de qué son los métodos numéricos, cuáles son los métodos numéricos más populares, cómo se aplican para resolver ecuaciones diferenciales de interés práctico en ingeniería y qué posibilidades y limitaciones tienen para ayudarnos a entender mejor el mundo que nos rodea. El contenido del artículo se completa con diversas aplicaciones prácticas del método de elementos finitos a diversos problemas de ingeniería.

  Abstract
  Se presentan en el artículo las ideas básicas de qué son los métodos numéricos, cuáles son los métodos numéricos más [...]

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• A large strain plasticity model for anisotropic materials - composite material application

  E. Car, S. Oller, E. Oñate

  International Journal of Plasticity (2001). Vol. 17 (11), pp. 1437-1463

  
  

  Abstract

  In this work a generalized anisotropic model in large strains based on the classical isotropic plasticity theory is presented. The anisotropic theory is based on the concept of mapped tensors from the anisotropic real space to the isotropic fictitious one. In classical orthotropy theories it is necessary to use a special constitutive law for each material. The proposed theory is a generalization of classical theories and allows the use of models and algorithms developed for isotropic materials. It is based on establishing a one-to-one relationship between the behavior of an anisotropic real material and that of an isotropic fictitious one. Therefore, the problem is solved in the isotropic fictious space and the results are transported to the real field. This theory is applied to simulate the behavior of each material in the composite. The whole behavior of the composite is modeled by incorporating the anisotropic model within a model based on a modified mixing theory.

  Abstract
  In this work a generalized anisotropic model in large strains based on the classical isotropic plasticity theory is presented. The anisotropic theory is based on the concept [...]

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• Optimización de embarcaciones de recreo mediante la utilización de un código CFD

  M. López-Rodríguez, J. García-Espinosa, E. Oñate

  Ingeniería Naval (2001). Vol. 784, pp. 122-130

  
  

  Abstract

  En la actualidad las más avanzadas técnicas para diseño naval ya no se restringen sólo a proyectos de alto coste; si no que también ahora son de aplicación en el campo de las embarcaciones de recreo y turísticas, dando con ello un valor añadido al proyecto final. La utilización de un código CFD para el mayor conocimiento del comportamiento hidrodinámico de las embarcaciones de recreo y turísticas es de una gran utilidad debido a las complejidades que en el diseño de estas se presentan. Estas herramientas nos van a proporcionar una serie de datos como sustentación lateral en las embarcaciones de vela o interacción entre cascos en catamaranes con deriva lateral, que de otra forma nunca pudieran conocerse. Los resultados hidrodinámicos obtenidos nos sirven para comparar las diferentes alternativas, y para además obtener unos valores que directamente son usados para la predicción de velocidad de la embarcación, que más tarde se verán refrendadas por las pruebas de mar. La utilización de técnicas CFD, basadas en el método de los elementos finitos, para la resolución de las ecuaciones de Reynolds (RANSE), incluyendo efectos de superficie libre, hace que todo esto sea posible. En este trabajo se presentan diversos resultados de aplicación del código CFD SHYNE a varias embarcaciones deportivas y de recreo. SHYNE está basado en la técnica del Cálculo Finitesimal para la integración de las ecuaciones de Reynolds.

  Abstract
  En la actualidad las más avanzadas técnicas para diseño naval ya no se restringen sólo a proyectos de alto coste; si no que también ahora [...]

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