JOURNALS

Documents published in Scipedia

• Experimental and numerical fracture tests in concrete. Towards the Virtual Laboratory

  F. Zarate, A. Gomez, E. Oñate

  Rev. int. métodos numér. cálc. diseño ing. (2019). Vol. 35, (1), 14

  
  

  Abstract

  This paper describes a computation methodology to evaluate the ultimate strength and fracture of concrete samples and structures and its application to four typical tests of experimental laboratories of strength of materials. The tests results are compared and analysed from the experimental and numerical points of view in order to highlight the need for experimental trials to use the information derived from numerical results and, in turn, to validate that numerical models follow the behaviour and physics that occur in laboratory tests This comparison allows to explain the different mechanisms that occur throughout the experiments.

  Abstract
  This paper describes a computation methodology to evaluate the ultimate strength and fracture of concrete samples and structures and its application to four typical tests [...]

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• A generalized streamline finite element approach for the analysis of incompressible flow problems including moving surfaces

  M. Cruchaga, E. Oñate

  Comput. Methods Appl. Mech. Engrg., (1999). Vol. 173, pp. 241-255

  
  

  Abstract

  In the present work a generalized streamline finite element formulation able to deal with incompressible flow problems is presented. In the finite element framework, this technique allows the use of equal order interpolation for the unknowns of the problem: velocity and pressure. In this context, stable and convergent solutions can be obtained without requiring tuning parameters defined outside this model. The tracking of moving surfaces is also included in the numerical model. This formulation has been checked in 21) and 3D tests.

  Abstract
  In the present work a generalized streamline finite element formulation able to deal with incompressible flow problems is presented. In the finite element framework, this [...]

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• Shape variable definition with C0 , C1 and C2 continuity functions

  G. Chiandussi, G. Bugeda, E. Oñate

  Comput. Methods Appl. Mech. Engrg., (2000). Vol. 188, pp. 727-742

  
  

  Abstract

  The present paper proposes a new technique for the definition of the shape design variables in 2D and 3D optimisation problems. It can be applied to the discrete model of the analysed structure or to the original geometry without any previous knowledge of the analytical expression of the CAD defining surfaces. The proposed technique allows the surface continuity to be preserved during the geometry modification process to be defined a priori. This capability allows for the definition of shape variables suitable for every kind of discipline involved in the optimisation process (structural analysis, fluid-dynamic analysis, crash analysis, aerodynamic analysis, etc.).

  Abstract
  The present paper proposes a new technique for the definition of the shape design variables in 2D and 3D optimisation problems. It can be applied to the discrete model of [...]

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• Lagrangian formulations to solve free surface incompressible inviscid fluid flows

  S. Idelsohn, M. Storti, E. Oñate

  Comput. Methods Appl. Mech. Engrg., (2001). Vol. 191 (6–7), pp. 583-593

  
  

  Abstract

  A particle method is presented for the solution of the incompressible inviscid fluid flow equation using a Lagrangian formulation. The interpolated function are those used in "meshless" approximations and the time integration is introduced in a semi-implicit way by a fractional step method. In this manner, both classical stabilization terms used in incompressible Euler equations are unnecessary: numerical diffusion for convective terms are unnecessary due to the Lagrangian formulation, and stabilization of pressure due to the incompressibility constraint for equal order interpolations is eliminated using the fractional step method.

  Abstract
  A particle method is presented for the solution of the incompressible inviscid fluid flow equation using a Lagrangian formulation. The interpolated function are those used [...]

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• On the simulation of flows with violent free surface motion

  R. Lohner, C. Yang, E. Oñate

  Comput. Methods Appl. Mech. Engrg., (2006). Vol. 195, pp. 5597–5620

  
  

  Abstract

  A volume of fluid (VOF) technique has been developed and coupled with an incompressible Euler/Navier–Stokes solver operating on adaptive, unstructured grids to simulate the interactions of extreme waves and three-dimensional structures. The present implementation follows the classic VOF implementation for the liquid–gas system, considering only the liquid phase. Extrapolation algorithms to obtain velocities and pressure in the gas region near the free surface have been implemented. The VOF technique is validated against the classic dam-break problem, as well as series of 2D sloshing experiments and results from smoothed particle hydrodynamics (SPH) calculations. These and a series of other examples demonstrate that the present CFD method is capable of simulating violent free surface flows with strong nonlinear behavior.

  Abstract
  A volume of fluid (VOF) technique has been developed and coupled with an incompressible Euler/Navier–Stokes solver operating on adaptive, unstructured grids to simulate [...]

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• To mesh or not to mesh. That is the question. . .

  S. Idelsohn, E. Oñate

  Comput. Methods Appl. Mech. Engrg., (2006). Vol. 195, pp. 4681–4696

  
  

  Abstract

  In the last decade a family of methods called meshless methods has been developed both for structural and fluid mechanics problems. After these ideas, a possible classification for numerical formulations may be to separate the methods that make use of a standard finite element mesh (such as those made of tetrahedra or hexahedra), from those that do not need a standard mesh, namely the meshless methods. For solving a partial different equation by a numerical method, a possible alternative may be either to use a mesh method or a meshless method. This paper discusses this issue to show that this choice is not, in the large majorities of the cases, the right question.

  Abstract
  In the last decade a family of methods called meshless methods has been developed both for structural and fluid mechanics problems. After these ideas, a possible classification [...]

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• A critical displacement approach for predicting structural instability

  E. Oñate, W. Matias

  Comput. Methods Appl. Mech. Engrg., (1996). Vol. 134 (1-2), pp. 135-161

  
  

  Abstract

  A new technique for predicting structural instability points using the finite element method is presented. The approach is based on the estimation of the critical displacement pattern by writing an approximation of the tangent stiffness singularity condition at the instability point. The critical load is subsequently computed by using a secant load-displacement relationship. Details of this procedure are given together with explicit forms of the secant stiffness matrix for finite element analysis of solids and trusses. The accuracy and effectiveness of the method are clearly shown in a number of examples of two- and three-dimensional bar structures.  

  Abstract
  A new technique for predicting structural instability points using the finite element method is presented. The approach is based on the estimation of the critical displacement [...]

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• A stabilized finite point method for analysis of fluid mechanics problems

  E. Oñate, S. Idelsohn, O. Zienkiewicz, R. Taylor, C. Sacco

  Comput. Methods Appl. Mech. Engrg., (1996). Vol. 195, pp. 6750-6777

  
  

  Abstract

  flow type problems is presented. The method is based on the use of a weighted least square interpolation procedure together with point collocation for evaluating the approximation integrals. Some examples of application to convective trasport and compressible flow problems are presented.

  Abstract
  flow type problems is presented. The method is based on the use of a weighted least square interpolation procedure together with point collocation for evaluating the approximation [...]

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• Derivation of stabilized equations for numerical solution of advective-diffusive transport and fluid flow problems

  E. Oñate

  Comput. Methods Appl. Mech. Engrg., (1998). Vol. 151 (1-2), pp. 233-265

  
  

  Abstract

  The concept of the so called “artificial or balancing diffusion” used to stabilize the numerical solution of advective–diffusive transport and fluid flow problems is revised in this paper. It is shown that the standard forms of the balancing diffusion terms, usually chosen in a heuristic manner, can be naturally found by introducing higher order approximations in the derivation of the governing differential equations via standard conservation (or equilibrium) principles. This allows us to reinterprete many stabilization algorithms and concepts used in every day practice by numerical analysts and also provides an expression for computing the stabilization parameter.

  Abstract
  The concept of the so called “artificial or balancing diffusion” used to stabilize the numerical solution of advective–diffusive transport and fluid flow [...]

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• An anisotropic elastoplastic constitutive model for large deformation analysis of fibre reinforced composites

  E. Car, S. Oller, E. Oñate

  Comput. Methods Appl. Mech. Engrg., (2000). Vol. 185, pp. 245-277

  
  

  Abstract

  In this work a generalized anisotropic elastoplastic constitutive model in large deformation is presented. It is used for the analysis of fiber-reinforced composite materials in the frame of the finite element method. Mixing theory is applied to simulate the behavior of the composite material.  The elastic anisotropic behavior  is simulated with classical elasticity theory, while that of a non-proportional anisotropic solid is simulated by means of the proposed generalized anisotropic elastoplastic model. The  approach assumes the existence of a real anisotropic space and of a fictitious isotropic space where a mapped fictitious problem is solved. Both spaces are related by means of a linear transformation using a fourth order  tensor incorporating complete information on the real anisotropic material. Details of the numerical implementations of the model into a non-linear, large deformations finite element solution scheme are provided. Examples of application showing the performance of the model for the analysis of fiber-reinforced composite materials are given.

  Abstract
  In this work a generalized anisotropic elastoplastic constitutive model in large deformation is presented. It is used for the analysis of fiber-reinforced composite materials [...]

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