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• Combination of an adaptive remeshing technique with a coupled FEM-DEM approach for analysis of crack propagation problems (preprint)

  A. Cornejo, V. Mataix, F. Zarate, E. Oñate

  Computational Particle Mechanics (2020). Vol. 7, pp. 735–752, doi: 10.1007/s40571-019-00306-4

  
  

  Abstract

  This paper presents an enhanced coupled approach between the Finite Element Method (FEM) and the Discrete Element Method (DEM) in which an adaptative remeshing technique has been implemented. The remeshing technique is based on the computation of the Hessian of a selected nodal variable, i.e. the mesh is refined where the curvature of the variable field is greater. Once the Hessian is known, a metric tensor is defined node-wise that serves as input data for the remesher (MmgTools) that creates a new mesh. After remeshing, the mapping of the internal variables and the nodal values is performed and a regeneration of the discrete elements on the crack faces of the new mesh is carried out. Several examples of fracturing problems using the enhanced FEM-DEM formulation are presented. Accurate results in comparison with analytical and experimental solutions are obtained.

  Abstract
  This paper presents an enhanced coupled approach between the Finite Element Method (FEM) and the Discrete Element Method (DEM) in which an adaptative remeshing technique has [...]

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• Open tools for electromagnetic simulation programs

  J. Mora, R. Otín, P. Dadvand, E. Escolano, M. Pasenau, E. Oñate

  COMPEL: the international journal for computation and mathematics in electrical and electronic engineering (2006). Vol. 25 (3), pp. 551-564

  
  

  Abstract

  Purpose The aim of the paper is to propose three computer tools to create electromagnetic simulation programs: GiD, Kratos and EMANT. Design/methodology/approach The paper presents a review of numerical methods for solving electromagnetic problems and presentation of the main features of GiD, Kratos and EMANT. Findings The paper provides information about three computer tools to create electromagnetic simulation packages: GiD (geometrical modeling, data input, visualisation of results), Kratos (C++ library) and EMANT (finite element software for solving Maxwell equations). Research limitations/implications The proposed platforms are in development and future work should be done to validate the codes for expecific problems and to provide extensive manual and tutorial information. Practical implications The tools could be easily learnt by different user profiles: from end‐users interested in simulation programs to developers of simulation packages. Originality/value This paper offers an integrated vision of open and easily customisable tools for the demands of different users profiles.    

  Abstract
  Purpose The aim of the paper is to propose three computer tools to create electromagnetic simulation programs: GiD, Kratos and EMANT. Design/methodology/approach The [...]

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• FIC-FEM formulation for the multidimensional transient advection-diffusion-absorption equation (preprint)

  A. Puigferrat, I. de-Pouplana, E. Oñate

  Computer Methods in Applied Mechanics and Engineering (2020). Vol 365, pp. 112984, DOI: 10.1016/j.cma.2020.112984

  
  

  Abstract

  In this paper we present a stabilized FIC-FEM formulation for the multidimensional transient advection-diffusion-absorption equation. The starting point is the non-local form of the governing equations for the multidimensional transient advection-diffusion-absorption problems obtained via the Finite Increment Calculus (FIC) procedure. The FIC governing equations have a residual form that introduces a characteristic length vector that depends on streamline, absorption and shock capturing stabilization parameters, as well as on a characteristic element size that ensures a stabilized numerical solution using a standard Galerkin FEM. The value of the stabilization parameters is obtained as an extension of the steady-state form. The accuracy of the FIC-FEM formulation is verified in the solution of several transient advection-diffusion-absorption problems using regular meshes of 3-noded triangles and 4-noded quadrilaterals.

  Abstract
  In this paper we present a stabilized FIC-FEM formulation for the multidimensional transient advection-diffusion-absorption equation. The starting point is the non-local form [...]

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• Discrete-continuum hybrid modelling of flowing and static regimes

  I. Iaconeta, E. Oñate, A. LARESE

  Monograph CIMNE (2019). M188

  
  

  Abstract

  Bulk handling, transport and processing of granular materials and powders are fundamental operations in a wide range of industrial processes and geophysical phenomena. Particulate materials, which can be found in nature, are usually characterized by a grain size which can range across several scales: from nanometre to the order of metre. Depending on the volume fraction and on the shear strain conditions, granular materials can have different behaviours and often can be expressed as a new state of matter with properties of solids, liquids and gases. For the above reasons, both the experimental and the numerical analysis of granular media is still a difficult task and the prediction of their dynamic behaviour still represents, nowadays, an important challenge. The main goal of the current monograph is the development of a numerical strategy with the objective of studying the macroscopic behaviour of dry granular flows in quasi-static and dense flow regime. The problem is defined in a continuum mechanics framework and the balance laws, which govern the behaviour of a solid body, are solved by using a Lagrangian formalism. The Material Point Method (MPM), a particle-based method, is chosen due to its features which make it very suitable for the solution of large deformation problems involving complex history-dependent constitutive laws. An irreducible formulation using a Mohr-Coulomb constitutive law, which takes into account geometric non-linearities, is implemented within the MPM framework. The numerical strategy is verified and validated against several benchmark tests and experimental results, available in the literature. Further, a mixed formulation is implemented for the solution of granular flows that undergo undrained conditions. Finally, the developed MPM strategy is used and tested against the experimental study performed for the characterization of the flowability of several types of sucrose. The capabilities and limitations of this numerical strategy are observed and discussed and the bases for future research are outlined.

  Abstract
  Bulk handling, transport and processing of granular materials and powders are fundamental operations in a wide range of industrial processes and geophysical phenomena. Particulate [...]

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• A-posteriori error estimation for the finite point method with applications to compressible flow (preprint)

  E. Ortega, R. Flores, E. Oñate, S. Idelsohn

  A-posteriori error estimation for the finite point method with applications to compressible flow (2017). Computational Mechanics, 60 – 2, pp. 219 – 233

  
  

  Abstract

  An a-posteriori error estimate with application to inviscid compressible flow problems is presented. The estimate is a surrogate measure of the discretization error, obtained from an approximation to the truncation terms of the governing equations. This approximation is calculated from the discrete nodal differential residuals using a reconstructed solution field on a modified stencil of points. Both the error estimation methodology and the flow solution scheme are implemented using the Finite Point Method, a meshless technique enabling higher-order approximations and reconstruction procedures on general unstructured discretizations. The performance of the proposed error indicator is studied and applications to adaptive grid refinement are presented.

  Abstract
  An a-posteriori error estimate with application to inviscid compressible flow problems is presented. The estimate is a surrogate measure of the discretization error, obtained [...]

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• A Lagrangian nodal integration method for free-surface fluid flows

  A. Franci, M. Cremonesi, U. Perego, E. Oñate

  Comput. Methods Appl. Mech. Engrg., (2020). Vol. 361, 112816

  
  

  Abstract

  We present a Lagrangian nodal integration method for the simulation of Newtonian and non-Newtonian free-surface fluid flows. The proposed nodal Lagrangian method uses a finite element mesh to discretize the computational domain and to define the (linear) shape functions for the unknown nodal variables, as in the standard Particle Finite Element Method (PFEM). In this approach, however, the integrals are performed over nodal patches and not over elements, and strains/stresses are defined at nodes and not at Gauss points. This allows to limit the drawbacks associated with the remeshing and leads to a more accurate stress computation than in the classical elemental PFEM. Several numerical tests, in 2D and in 3D, are presented to validate the proposed nodal PFEM. In all cases, the method has shown a very good agreement with analytical solutions and with experimental and numerical results from the literature. A thorough comparison between nodal and elemental PFEMs is also presented, focusing on crucial issues, such as solution accuracy, convergence, mass conservation and sensitivity to mesh distortion.

  Abstract
  We present a Lagrangian nodal integration method for the simulation of Newtonian and non-Newtonian free-surface fluid flows. The proposed nodal Lagrangian method uses a finite [...]

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• Life prediction of structures. Numerical study and treatment of structural durability, a brief report

  S. Oller, E. Oñate

  Temes de Disseny (2002). Vol. 20, pp. 85-99

  
  

  Abstract

  This work is a brief report about the problem of life -or, durability study- of structural materials, undergoing mechanical, thermal and chemical actions. This document is approached from numerical techniques and, it highlights the potential of these types of tools un the study of structures undergoing very complex and coupled phenomena.

  Abstract
  This work is a brief report about the problem of life -or, durability study- of structural materials, undergoing mechanical, thermal and chemical actions. This document is [...]

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• Advances in the design and manufacturing of large scale inflatable hangars

  J. Marcipar, E. Oñate

  Videos of Plenary Lectures presented at FORM and FORCE - IASS Symposium 2019 and Structural Membranes 2019.

  
  

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• ODDLS: An overlapping domain decomposition level set method for simulation of free surface problems

  J. García-Espinosa, A. Valls, E. Oñate

  5-7 June 2007, Trondheim (Norway)

  
  

  Abstract

  This presentation introduces a new stabilized finite element method based on the finite calculus (Comput. Methods Appl. Mech. Eng. 1998; 151:233–267) and arbitrary Lagrangian–Eulerian techniques (Comput. Methods Appl. Mech. Eng. 1998; 155:235–249) for the solution to free surface problems. The main innovation of this method is the application of an overlapping domain decomposition concept in the statement of the problem. The aim is to increase the accuracy in the capture of the free surface as well as in the resolution of the governing equations in the interface between the two fluids. Free surface capturing is based on the solution to a level set equation. The Navier–Stokes equations are solved using an iterative monolithic predictor–corrector algorithm, where the correction step is based on imposing the divergence‐free condition in the velocity field by means of the solution to a scalar equation for the pressure. Examples of application of the ODDLS formulation (for overlapping domain decomposition level set) to the analysis of different free surface flow problems are presented.

  Abstract
  This presentation introduces a new stabilized finite element method based on the finite calculus (Comput. Methods Appl. Mech. Eng. 1998; 151:233–267) and arbitrary [...]

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• Advanced solid elements for sheet metal forming simulation

  V. Mataix Ferrándiz, R. Rossi, E. Oñate, F. flores

  (2016). Journal of Physics: Conferences Series, Cesar de Sa J. M. A., Neto E. S., Cardoso R. P. R., Adetoro O. B. (eds), Vol. 734 (3), pp. 032128

  
  

  Abstract

  The solid-shells are an attractive kind of element for the simulation of forming processes, due to the fact that any kind of generic 3D constitutive law can be employed without any additional hypothesis. The present work consists in the improvement of a triangular prism solid-shell originally developed by Flores. The solid-shell can be used in the analysis of thin/thick shell, undergoing large deformations. The element is formulated in total Lagrangian formulation, and employs the neighbour (adjacent) elements to perform a local patch to enrich the displacement field. In the original formulation a modified right Cauchy-Green deformation tensor (C) is obtained; in the present work a modified deformation gradient (F) is obtained, which allows to generalise the methodology and allows to employ the Pull-Back and Push-Forwards operations. The element is based in three modifications: (a) a classical assumed strain approach for transverse shear strains (b) an assumed strain approach for the in-plane components using information from neighbour elements and (c) an averaging of the volumetric strain over the element. The objective is to use this type of elements for the simulation of shells avoiding transverse shear locking, improving the membrane behaviour of the in-plane triangle and to handle quasi-incompressible materials or materials with isochoric plastic flow.

  Abstract
  The solid-shells are an attractive kind of element for the simulation of forming processes, due to the fact that any kind of generic 3D constitutive law can be employed without [...]

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