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• Stability analysis of mixed finite element formulations with special mention of equal‐order interpolations

  S. Idelsohn, M. Storti, N. Nigro

  Int. J. Numer. Meth. Fluids (1995). Vol. 20 (8-9), pp. 1003-1022

  
  

  Abstract

  We present a method to assess the stability of pairs of interpolation spaces for mixed formulations. The method is based on a straightforward calculation of the eigenvalues of the discrete matrices through Fourier decomposition in plane waves and is intended to give, via straightforward numerical computations, a sharper determination of stability than the well‐known ‘patch test’ of Zienkiewicz et al. Special attention is devoted to the study of stability and accuracy of equal‐order interpolations

  Abstract
  We present a method to assess the stability of pairs of interpolation spaces for mixed formulations. The method is based on a straightforward calculation of the eigenvalues [...]

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• Fractures prediction in concrete structures combining the finite and discrete element methods

  F. Zarate, E. Oñate

  Hormigón y Acero (2018). (prepint) 69, Supl 1, pp. 53-69

  
  

  Abstract

  This paper presents the basic concepts and application of the strategy that combines finite element methods (FEM) and discrete elements (DEM)for the study of the propagation of fractures in concrete structures. The calculation of the structure, modeled as a continuum, begins with the FEMand the DEM is used to start and grow the cracks that may appear in the structure. This methodology has been proposed by the authors in two andthree dimensions. Recently, the use of one-dimensional steel elements embedded in the continuum has been added to model the reinforcement inconcrete structures. The work presents different examples of application to the study of the breakage of parts and structures of concrete in massand armed, as well as the multiple breakage of a historic structure of masonry due to an earthquake.

  Abstract
  This paper presents the basic concepts and application of the strategy that combines finite element methods (FEM) and discrete elements (DEM)for the study of the propagation [...]

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• Two‐phase flow modelling in gas‐stirred liquid vessels with SUPG‐stabilized equal‐order interpolations

  N. Nigro, M. Storti, S. Idelsohn

  Int. J. Numer. Meth. Fluids (1994). Vol. 19 (1), pp. 1-22

  
  

  Abstract

  The modelling of liquid flow in gas‐stirred vessels is described. A simple two‐phase model accounts for the buoyancy effect of bubbles. Friction between liquid and gas is modelled with the hypothesis of independent bubbles. The resulting PDE system is discretized with an original version of the SUPG‐FEM technique which stabilizes both the convection term and equal‐order interpolations for velocity and pressure, which are known to be unstable for incompressible flows. The resulting steady state discrete system is solved via pseudotemporal explicit iteration with a local time step and a preconditioning to homogenize the temporal scales for liquid and gas.

  Abstract
  The modelling of liquid flow in gas‐stirred vessels is described. A simple two‐phase model accounts for the buoyancy effect of bubbles. Friction between liquid and gas [...]

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• Adaptive refinement criterion for elliptic problems discretized by FEM

  M. Storti, N. Nigro, S. Idelsohn

  Commun. Numer. Meth. Engng (1993). Vol. 9 (9), pp. 729-743

  
  

  Abstract

  In a recent paper we presented a data structure to be used with multigrid techniques on non‐homogeneously refined FEM meshes. This paper focuses on the adaptive refinement techniques used there. The error estimate is obtained from standard Taylor series. For each element we compute its efficiency in terms of the size, the norm of the second derivatives of the unknown and the parameter p, where Lp is the chosen norm. The way the norm influences the optimal mesh is studied. The number of elements to be refined at each step is such to produce a fast convergence to the optimal mesh, followed by successive homogeneous refinements. We hope that the analysis of these two subjects could be of value for people working with other (perhaps very dissimilar) adaptive refinement techniques (error estimate and data structure, for instance).

  Abstract
  In a recent paper we presented a data structure to be used with multigrid techniques on non‐homogeneously refined FEM meshes. This paper focuses on the adaptive refinement [...]

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• A fast and accurate method to solve the incompressible Navier‐Stokes equations

  S. Idelsohn, N. Nigro, J. Gimenez, R. Rossi, J. Marti

  Engineering Computations (2013). Vol. 30 (2), pp. 197-222

  
  

  Abstract

  Purpose   – The purpose of this paper is to highlight the possibilities of a novel Lagrangian formulation in dealing with the solution of the incompressible Navier‐Stokes equations with very large time steps.   Design/methodology/approach   – The design of the paper is based on introducing the origin of this novel numerical method, originally inspired on the Particle Finite Element Method (PFEM), summarizing the previously published theory in its moving mesh version. Afterwards its extension to fixed mesh version is introduced, showing some details about the implementation.   Findings   – The authors have found that even though this method was originally designed to deal with heterogeneous or free‐surface flows, it can be competitive with Eulerian alternatives, even in their range of optimal application in terms of accuracy, with an interesting robustness allowing to use large time steps in a stable way.   Originality/value   – With this objective in mind, the authors have chosen a number of benchmark examples and have proved that the proposed algorithm provides results which compare favourably, both in terms of solution time and accuracy achieved, with alternative approaches, implemented in in‐house and commercial codes.

  Abstract
  Purpose   – The purpose of this paper is to highlight the possibilities of a novel Lagrangian formulation in dealing with the solution [...]

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• Using pseudo-concentrations in the analysis of transient forming processes

  H. Antúnez, S. Idelsohn

  Engineering Computations (1992). Vol. 9 (5), pp. 547-559

  
  

  Abstract

  The pseudo‐concentration method is applied to the analysis of transient processes. A simple, easy‐to‐handle model is obtained by keeping an Eulerian description: it does not require remeshing after a certain amount of plastic deformation. The range of applicability of the method is extended to non‐confined (even with several free surfaces) processes. It is shown the need of distinct handling of free surfaces according to their orientation to the direction of the flow. A seamless tube rolling process, a cylinder upsetting and a backward extrusion are modelled. Experimental data and results obtained by other methods are used to compare and discuss the performance of the model.

  Abstract
  The pseudo‐concentration method is applied to the analysis of transient processes. A simple, easy‐to‐handle model is obtained by keeping an Eulerian description: it [...]

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• Fracture analysis of a surface-coated ceramic by speckle photography and finite elements

  E. Barbero, G. Kaufmann, S. Idelsohn

  Optics & Laser Technology (1990). Vol. 22 (1), pp. 17-22

  
  

  Abstract

  The fracture behaviour of a four-point bend surface-coated ceramic specimen with a through-the-thickness crack was experimentally investigated. Speckle photography was used to measure opening displacements over the specimen surface and across the crack line. For a glazed and unglazed specimen, stress-intensity factors were experimentally determined by means of a method that uses data not restricted to the singularity-dominated zone. Stress-intensity factors were numerically calculated using a three-dimensional finite element analysis and their variations along the crack front were also evaluated. Experimental results agree reasonably well with the numerical results. Results show the influence of the glaze on the fracture behaviour of the composite material.

  Abstract
  The fracture behaviour of a four-point bend surface-coated ceramic specimen with a through-the-thickness crack was experimentally investigated. Speckle photography was used [...]

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• Evaluation of finite-element calculations in a part-circular crack by coherent optics techniques

  G. Kaufmann, A. Lopergolo, S. Idelsohn, E. Barbero

  Experimental Mechanics (1987). Vol. 27 (2), pp. 154-157

  
  

  Abstract

  Two techniques, speckle photography and holographic interferometry, were used to test three-dimensional finite-element calculations in an internally pressurized cylinder with an external part-circular crack. Opening displacements along the crack line were measured by speckle photography. Radial displacements were obtained from holographic fringe patterns. Good agreement between experimental and numerical data is obtained. Stress-intensity factor variations along the crack front are calculated from numerical results.

  Abstract
  Two techniques, speckle photography and holographic interferometry, were used to test three-dimensional finite-element calculations in an internally pressurized cylinder with [...]

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• Inelastic seismic analysis of a building structure designed by argentine codes

  V. Sonzogni, A. Cardona, S. Idelsohn

  Earthquake Engineering Structural Dynamics (1984). Vol. 12 (6), pp. 721-736

  
  

  Abstract

  A reinforced concrete frame‐wall structure of a building designed in accordance to standard practice in Argentina was analysed by the procedures prescribed by current Argentine Codes. In addition, the inelastic step‐by‐step response of the structure to design spectrum‐compatible accelerograms was studied by means of a special element for inelastic dynamic analysis of reinforced concrete frames. Results obtained by the different methods of analysis are presented

  Abstract
  A reinforced concrete frame‐wall structure of a building designed in accordance to standard practice in Argentina was analysed by the procedures prescribed by current Argentine [...]

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• A comparative computational study of blood flow through prosthetic heart valves using the finite element method

  S. Idelsohn, L. Costa, R. Ponso

  Journal of Biomechanics (1985). Vol. 18 (2), pp. 97-115

  
  

  Abstract

  The steady flow of blood through three common types of prosthetic heart valves was simulated numerically using the finite element method. The velocity, pressure and stress fields were obtained for the disk-type, tilting-disk and ball-type prosthetic heart valves in aortic position, for increasing Reynolds numbers up to 900, 1500 and 2000 respectively. Computer graphics of calculated velocities are presented, showing in detail the accelerated flow, recirculation and stagnation areas developed in the prosthesis. Maximum wall shear stresses were found at 0.5, 1.4, and 1.2 diameters from the sewing ring downstream for the disk, tilting-disk and ball valves being the values of 55, 18 and 33 dyn cm−2 respectively. In the vicinity of the occluder, maximum shear stresses of 38, 30 and 47 dyn cm−2 respectively were computed. The flow characteristics and performance for each valve are compared, the results are presented in terms of energy loss and maximum shear stress. The velocity and stress fields are compared with in vitro evaluations found in the literature

  Abstract
  The steady flow of blood through three common types of prosthetic heart valves was simulated numerically using the finite element method. The velocity, pressure and stress [...]

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