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• A coupled thermomechanical model for the solidification of cast metals

  D. Celentano, S. Oller, E. Oñate

  Int. J. Solids and Structures (1996). Vol. 33 (5), pp. 647-673

  
  

  Abstract

  A coupled thermomechanical model to simulate solidification problems in casting is presented. The model is formulated from a phenomenological point of view using a general isotropic thermoelasto-plasticity theory. Generalized phase-change effects accounting for the different thermomechanical behaviour of the solidifying material during its evolution from liquid to solid have been considered. For this purpose, a phase-change function, plastic evolution equations and a temperature-dependent constitutive law have been defined. Full thermomechanical effects as well as variable thermal and mechanical boundary conditions are also taken into account. Particular details concerning the numerical implementation of the model are given, where special emphasis is devoted to the resulting highly non-linear fully coupled finite element equations. The behaviour of this formulation is studied first in a simple quenching problem. Finally, a cylindrical casting test problem including phase-change phenomena, temperature-dependent constitutive properties and contact effects is analysed. Numerical results are compared with laboratory measurements.

  Abstract
  A coupled thermomechanical model to simulate solidification problems in casting is presented. The model is formulated from a phenomenological point of view using a general [...]

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• A plastic damage constitutive model for composite materials

  S. Oller, E. Oñate, J. Canet, S. Botello

  Int. J. Solids and Structures (1996). Vol. 33 (17), pp. 2501-2518

  
  

  Abstract

  In this paper a generalized elasto-plastic damage model for the analysis of multiphase frictional composite materials is presented. Details of the derivation of the secant and tangent constitutive equations are given. Mixing theory is used to insert the basic constitutive expressions for each substance on the multiphase composite solid. Details of the numerical implementation of the model into a general non-linear finite element solution scheme are presented. Some examples of linear and non-linear behaviour of composites are given.

  Abstract
  In this paper a generalized elasto-plastic damage model for the analysis of multiphase frictional composite materials is presented. Details of the derivation of the secant [...]

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• A hygro-thermo-mechanical constitutive model for multiphase composite materials

  S. Oller, E. Oñate

  Int. J. Solids and Structures (1996). Vol. 33 (20-22), pp. 3179-3186

  
  

  Abstract

  The paper describes a hygro-thermo-mechanical constitutive model appropriate for numerical simulation of multiphase composite material behaviour. The theory is based on the mixture of the basic substances of the composite and allows to evaluate the inter-dependent behaviour between the different compounding constitutive models. The initial anisotropy of each compounding can be taken into account by means of a mapped isotropic plastic formulation. This is a generalization of classic isotropic plasticity theory applied to orthotropic or anisotropic materials. The basic assumption is the existence of a stress and strain real anisotropic spaces and the respective fictitious isotropic spaces where a mapped fictitious problem is solved. Those spaces are related by means of two fourth order transformation tensor. The combination of mixing theory and the mapped isotropic plastic approach provides a powerful constitutive framework for the numerical treatment of bulk-fiber composite materials.

  Abstract
  The paper describes a hygro-thermo-mechanical constitutive model appropriate for numerical simulation of multiphase composite material behaviour. The theory is based [...]

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• A plastic-damage model for concrete

  J. Lubliner, J. Oliver, S. Oller, E. Oñate

  Int. J. Solids and Structures (1989). Vol. 25 (3), pp. 299-326

  
  

  Abstract

  In this paper a constitutive model based on an internal variable-formulation of plasticity theory for the non-linear analysis of concrete is presented. The model uses a new yield criterion which matches experimental data quite well and it accounts for both elastic and plastic stiffness degradations effects. Onset and amount of cracking can be studied by a simple postprocessing of the finite-element plasticity solution. The accuracy of the model is checked with some examples of application.

  Abstract
  In this paper a constitutive model based on an internal variable-formulation of plasticity theory for the non-linear analysis of concrete is presented. The model uses a new [...]

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• Flow of solids during forming and extrusion: Some aspects of numerical solutions

  O. Zienkiewicz, P. Jain, E. Oñate

  Int. J. Solids and Structures (1978). Vol. 14 (1), pp. 15-38

  
  

  Abstract

  In the extrusion and forming of solids the plastic (or viscoplastic) deformations are so large that the elastic strain is negligible. The problem thus becomes one of incompressible viscous, non-Newtonian flow with prescribed boundary velocities. Various formulations of such problems (analogous to those of incompressible solid mechanics) are possible, and the paper investigates two basic processes. Details of application to some examples of steady state flow in extrusion, drawing and rolling are given and transient free surface solutions are demonstrated for stretch forming and deep drawing. The formulation is shown to be capable of dealing with boundary friction and strain hardening. The coupling with thermal effects is demonstrated in the last section of the paper, and in addition, some practical problems of elastic spring-back which occur on the removal of load are discussed.

  Abstract
  In the extrusion and forming of solids the plastic (or viscoplastic) deformations are so large that the elastic strain is negligible. The problem thus becomes one of incompressible [...]

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• Real-time micro-modelling of city evacuations

  R. Löhner, E. Haug, C. Zinggerling, E. Oñate

  Comp. Part. Mech (2018). Vol. 5 (1), pp. 71-86

  
  

  Abstract

  A methodology to integrate geographical information system (GIS) data with large-scale pedestrian simulations has been developed. Advances in automatic data acquisition and archiving from GIS databases, automatic input for pedestrian simulations, as well as scalable pedestrian simulation tools have made it possible to simulate pedestrians at the individual level for complete cities in real time. An example that simulates the evacuation of the city of Barcelona demonstrates that this is now possible. This is the first step towards a fully integrated crowd prediction and management tool that takes into account not only data gathered in real time from cameras, cell phones or other sensors, but also merges these with advanced simulation tools to predict the future state of the crowd.

  Abstract
  A methodology to integrate geographical information system (GIS) data with large-scale pedestrian simulations has been developed. Advances in automatic data acquisition and [...]

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• Virtual modeling of polycrystalline structures of materials using particle packing algorithms and Laguerre cells

  C. Recarey Morfa, M. Farias, I. Pérez, E. Oñate

  Comp. Part. Mech (2018). Vol. 5 (2), pp. 213-226

  
  

  Abstract

  The influence of the microstructural heterogeneities is an important topic in the study of materials. In the context of computational mechanics, it is therefore necessary to generate virtual materials that are statistically equivalent to the microstructure under study, and to connect that geometrical description to the different numerical methods. Herein, the authors present a procedure to model continuous solid polycrystalline materials, such as rocks and metals, preserving their representative statistical grain size distribution. The first phase of the procedure consists of segmenting an image of the material into adjacent polyhedral grains representing the individual crystals. This segmentation allows estimating the grain size distribution, which is used as the input for an advancing front sphere packing algorithm. Finally, Laguerre diagrams are calculated from the obtained sphere packings. The centers of the spheres give the centers of the Laguerre cells, and their radii determine the cells’ weights. The cell sizes in the obtained Laguerre diagrams have a distribution similar to that of the grains obtained from the image segmentation. That is why those diagrams are a convenient model of the original crystalline structure. The above-outlined procedure has been used to model real polycrystalline metallic materials. The main difference with previously existing methods lies in the use of a better particle packing algorithm.

  Abstract
  The influence of the microstructural heterogeneities is an important topic in the study of materials. In the context of computational mechanics, it is therefore necessary [...]

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• Systemic characterization and evaluation of particle packings as initial sets for discrete element simulations

  C. Recarey Morfa, L. Cortés, M. Farias, I. Pérez, R. Valera, E. Oñate

  Comp. Part. Mech (2018). Vol. 5 (3), pp. 319-334

  
  

  Abstract

  A methodology that comprises several characterization properties for particle packings is proposed in this paper. The methodology takes into account factors such as dimension and shape of particles, space occupation, homogeneity, connectivity and isotropy, among others. This classification and integration of several properties allows to carry out a characterization process to systemically evaluate the particle packings in order to guarantee the quality of the initial meshes in discrete element simulations, in both the micro- and the macroscales. Several new properties were created, and improvements in existing ones are presented. Properties from other disciplines were adapted to be used in the evaluation of particle systems. The methodology allows to easily characterize media at the level of the microscale (continuous geometries—steels, rocks microstructures, etc., and discrete geometries) and the macroscale. A global, systemic and integral system for characterizing and evaluating particle sets, based on fuzzy logic, is presented. Such system allows researchers to have a unique evaluation criterion based on the aim of their research. Examples of applications are shown.

  Abstract
  A methodology that comprises several characterization properties for particle packings is proposed in this paper. The methodology takes into account factors such as dimension [...]

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• Air demand estimation in bottom outlets with the particle finite element method. Susqueda Dam case study.

  F. Salazar, J. San-Mauro, M. Celigueta, E. Oñate

  Comp. Part. Mech (2017). Vol. 4 (3), pp. 345-356

  
  

  Abstract

  Dam bottom outlets play a vital role in dam operation and safety, as they allow controlling the water surface elevation below the spillway level. For partial openings, water flows under the gate lip at high velocity and drags the air downstream of the gate, which may cause damages due to cavitation and vibration. The convenience of installing air vents in dam bottom outlets is well known by practitioners. The design of this element depends basically on the maximum air flow through the air vent, which in turn is a function of the specific geometry and the boundary conditions. The intrinsic features of this phenomenon makes it hard to analyse either on site or in full scaled experimental facilities. As a consequence, empirical formulas are frequently employed, which offer a conservative estimate of the maximum air flow. In this work, the particle finite element method was used to model the air–water interaction in Susqueda Dam bottom outlet, with different gate openings. Specific enhancements of the formulation were developed to consider air–water interaction. The results were analysed as compared to the conventional design criteria and to information gathered on site during the gate operation tests. This analysis suggests that numerical modelling with the PFEM can be helpful for the design of this kind of hydraulic works.

  Abstract
  Dam bottom outlets play a vital role in dam operation and safety, as they allow controlling the water surface elevation below the spillway level. For partial openings, water [...]

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• General advancing front packing algorithm for the discrete element method

  C. Recarey Morfa, I. Pérez, M. Farías, E. Oñate, R. Valera, H. Casañas

  Comp. Part. Mech (2018). Vol. 5, pp 13–33

  
  

  Abstract

  A generic formulation of a new method for packing particles is presented. It is based on a constructive advancing front method, and uses Monte Carlo techniques for the generation of particle dimensions. The method can be used to obtain virtual dense packings of particles with several geometrical shapes. It employs continuous, discrete, and empirical statistical distributions in order to generate the dimensions of particles. The packing algorithm is very flexible and allows alternatives for: 1—the direction of the advancing front (inwards or outwards), 2—the selection of the local advancing front, 3—the method for placing a mobile particle in contact with others, and 4—the overlap checks. The algorithm also allows obtaining highly porous media when it is slightly modified. The use of the algorithm to generate real particle packings from grain size distribution curves, in order to carry out engineering applications, is illustrated. Finally, basic applications of the algorithm, which prove its effectiveness in the generation of a large number of particles, are carried out.

  Abstract
  A generic formulation of a new method for packing particles is presented. It is based on a constructive advancing front method, and uses Monte Carlo techniques for the generation [...]

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