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• Enhanced semi-explicit particle finite element method via a modified Strang splitting operator for incompressible flows

  J. Marti, E. Oñate

  Computational Particle Mechanics (2023). Published Online

  
  

  Abstract

  This work presents an enhanced version of the semi-explicit particle finite element method for incompressible flow problems. This goal is achieved by improving the methodology that results from applying the Strang splitting operator by adding an acceleration term. The advective step is evaluated on the mesh considering the new term leading to a more efficient algorithm. Two test cases are solved for validating the methodology and estimating its accuracy. The numerical results demonstrate that the proposed scheme improves the accuracy and the computational efficiency of the semi-explicit PFEM scheme.

  Abstract
  This work presents an enhanced version of the semi-explicit particle finite element method for incompressible flow problems. This goal is achieved by improving the methodology [...]

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• A prototype of a micro-scale model for the distribution of NO2 in urban areas

  I. Pouplana, S. Latorre, M. Maso, C. Alonso, E. Pérez, X. Guinart, I. Hernández, X. Baulies, E. Oñate

  Atmospheric Pollution Research (2023). Vol. 14 (2), 101668

  
  

  Abstract

  We present a new 2.5D model for predicting the concentration of nitrogen dioxide (NO2) at street level in an urban area. This work develops the first prototype of a tool that should provide fast quantitative answers to help decision-making on the suitability of implementing traffic restrictions during air pollution episodes. The model first solves the wind flow over the city streets ignoring vorticity and turbulence. The obtained velocity field is used to transport the pollutant via a semi-Lagrangian model, combining the particle finite element method of second generation (PFEM2) with the finite element method. A variable absorption term is used to account for the part of the contaminant entering and leaving the calculation plane. The NO2 emissions are estimated from the historical traffic data. The model has been tested during four air pollution episodes in the city of Barcelona (Spain), two in summer and two in winter. A comparison against experimental measurements has been performed at seven different locations throughout the city with promising results.

  Abstract
  We present a new 2.5D model for predicting the concentration of nitrogen dioxide (NO2) at street level in an urban area. This work develops the first prototype of a tool that [...]

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• Assessment of simplified momentum equations for free surface flows through rigid porous media

  W. Düsterhöft-Wriggers, A. LARESE, E. Oñate, R. Thomas

  Experimental and Computational Multiphase Flow (2023). Vol. 5, pp. 159–177

  
  

  Abstract

  In many applications, free surface flow through rigid porous media has to be modeled. Examples refer to coastal engineering applications as well as geotechnical or biomedical applications. Albeit the frequent applications, slight inconsistencies in the formulation of the governing equations can be found in the literature. The main goal of this paper is to identify these differences and provide a quantitative assessment of different approaches. Following a review of the different formulations, simulation results obtained from three alternative formulations are compared with experimental and numerical data. Results obtained by 2D and 3D test cases indicate that the predictive differences returned by the different formulations remain small for most applications, in particular for small porous Reynolds number ReP < 5000. Thus it seems justified to select a simplified formulation that supports an efficient algorithm and coding structure in a computational fluid dynamics environment. An estimated accuracy depending on the porous Reynolds number or the mean grain diameter is given for the simplified formulation.  

  Abstract
  In many applications, free surface flow through rigid porous media has to be modeled. Examples refer to coastal engineering applications as well as geotechnical or biomedical [...]

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• Development and coupling of numerical techniques for modeling micromechanical discrete and continuous media using real particle morphologies

  R. Valera, J. Irazábal González, M. Junior, M. Muniz, M. Castro, R. Martínez, J. Pena, L. Moreno, C. Recarey, E. Oñate

  Computational Particle Mechanics (2023). Vol.10 (1), pp. 121-141

  
  

  Abstract

  The main objective of this research is to formulate and couple technologies for modeling discrete and continuous media using real particle morphologies. To that end, two coupled formulations based on virtual modeling technologies of single real particles with another one called real particle packing technique are presented. The first formulation employs Fourier descriptors’ theory to virtually achieve the morphology and construct a repository of real particle geometries. The second formulation is a particle packing method, supported by advancing front techniques combined with dynamic methods. This method presents a stochastic formulation and allows the packing of particle systems following continuous, discrete and empirical statistical distributions. The coupling of both techniques is a very efficient tool to achieve discrete or continuous media geometries to solve engineering problems. Three different examples are developed to illustrate the usefulness of the formulations. The first one is a discrete angle-of-repose problem involving clusters of spheres (real particle morphologies are described with groups of spheres); in the second example the same angle-of-repose problem is resolved with real particles. In the third case, which involves continuous medium mechanics, a small-scale road engineering problem is modeled, specifically, the testing of an asphalt concrete.

  Abstract
  The main objective of this research is to formulate and couple technologies for modeling discrete and continuous media using real particle morphologies. To that end, two coupled [...]

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• An enhanced semi-explicit particle finite element method for incompressible flows

  J. Marti, E. Oñate

  Computational Mechanics (2022). Vol. 70, pp. 607–620

  
  

  Abstract

  In this paper an enhanced version of the semi-explicit Particle Finite Element Method for incompressible flow problems is presented. This goal is achieved by improving the solution of the advective sub-problem that results of applying the Strang operator splitting to the Navier–Stokes equations. An acceleration term is taken into account in the solution of the advective step and the Stokes problem. The solution of the advetive step is perfomed using a SPH kernel. Two test cases are solved for validating the methodology and estimating its accuracy. The numerical results demonstrate that the proposed scheme improves the accuracy of the semi-explicit PFEM scheme.

  Abstract
  In this paper an enhanced version of the semi-explicit Particle Finite Element Method for incompressible flow problems is presented. This goal is achieved by improving the [...]

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• A multiscale approach for the study of particle-laden flows using a continuous model

  S. Idelsohn, J. Gimenez, R. Lohner, E. Oñate

  Computer Methods in Applied Mechanics and Engineering (2022). Volume 401, Part A, 115174

  
  

  Abstract

  The methodology previously proposed by the authors to solve particle-laden turbulent flows through a multiscale approach is extended by introducing a continuous function for the dispersed phase concentration. The proposed continuous model is especially useful for studying the motion of particle streams in which gravitational and inertial effects cause the particles to deviate from a simple trajectory following the surrounding flow, as would be the case for the limit of very small, massless particles. The results show an excellent comparison between the solutions obtained using the continuous model and simulations evaluating the forces on each particle individually. Distinct advantages of the continuous approach are a much lower computational overhead, a better load balance and ease of parallelization. The multiscale methodology proposed may be used in the area of modeling and simulation of airborne infectious diseases.

  Abstract
  The methodology previously proposed by the authors to solve particle-laden turbulent flows through a multiscale approach is extended by introducing a continuous function for [...]

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• A deterministic pathogen transmission model based on high-fidelity physics

  R. Lohner, H. Antil, J. Gimenez, S. Idelsohn, E. Oñate

  Computer Methods in Applied Mechanics and Engineering (2022). Volume 401, Part A, 114929

  
  

  Abstract

  A deterministic pathogen transmission model based on high-fidelity physics has been developed. The model combines computational fluid dynamics and computational crowd dynamics in order to be able to provide accurate tracing of viral matter that is exhaled, transmitted and inhaled via aerosols. The examples shown indicate that even with modest computing resources, the propagation and transmission of viral matter can be simulated for relatively large areas with thousands of square meters, hundreds of pedestrians and several minutes of physical time. The results obtained and insights gained from these simulations can be used to inform global pandemic propagation models, increasing substantially their accuracy.

  Abstract
  A deterministic pathogen transmission model based on high-fidelity physics has been developed. The model combines computational fluid dynamics and computational [...]

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• Combination of 3D solid finite elements with rotation-free beam elements for non-linear analysis of fiber reinforced polymer rebars

  F. Zarate, T. Villette, X. Martinez, F. Rastellini Canela, D. Cendón, C. Andrade, E. Oñate

  Rev. int. métodos numér. cálc. diseño ing. (2023). Vol. 39, (2), 12

  
  

  Abstract

  We present a combination of three dimensional (3D) solid elements and rotation-free beam elements for non-linear analysis of fiber-reinforced polymer (FRP) of rebars. The matrix material is modelled by 3D solid elements while the fibers are modelled with rotation-free beam elements. The absence of rotation variables in the beam elements allows the straightforward coupling of 3D solid and beam elements using a formulation with displacement nodal degrees of freedom only. Both solid and beam elements are formulated in an updated Lagrangian description. The behavior of the matrix and the fiber material are modelled with an elastic-damage model. The efficiency and accuracy of the combined 3D-beam element formulation are verified in examples of application to the analysis of FRP rebars up to fracture in axial, bending and shear tests for which experimental results are available.

  Abstract
  We present a combination of three dimensional (3D) solid elements and rotation-free beam elements for non-linear analysis of fiber-reinforced polymer (FRP) of rebars. The [...]

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• A Lagrangian–Eulerian procedure for the coupled solution of the Navier–Stokes and shallow water equations for landslide-generated waves

  M. Maso, A. Franci, I. de-Pouplana, A. Cornejo Velázquez, E. Oñate

  Advanced Modeling and Simulation in Engineering Sciences (2022). Vol. 9(1), Article 15, 2022

  
  

  Abstract

  This work presents a partitioned method for landslide-generated wave events. The proposed strategy combines a Lagrangian Navier Stokes multi-fluid solver with an Eulerian method based on the Boussinesq shallow water equations. The Lagrangian solver uses the Particle Finite Element Method to model the landslide runout, its impact against the water body and the consequent wave generation. The results of this fully-resolved analysis are stored at selected interfaces and then used as input for the shallow water solver to model the far-field wave propagation. This one-way coupling scheme reduces drastically the computational cost of the analyses while maintaining high accuracy in reproducing the key phenomena of the cascading natural hazard. Several numerical examples are presented to show the accuracy and robustness of the proposed coupling strategy and its applicability to large-scale landslide-generated wave events. The validation of the partitioned method is performed versus available results of other numerical methods, analytical solutions and experimental measures.

  Abstract
  This work presents a partitioned method for landslide-generated wave events. The proposed strategy combines a Lagrangian Navier Stokes multi-fluid solver with an Eulerian [...]

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• A unified non-linear energy dissipation-based plastic-damage model for cyclic loading

  A. Cornejo Velázquez, S. Jiménez, L. Barbu, S. Oller, E. Oñate

  Computer Methods in Applied Mechanics and Engineering (2022). Vol. 400,115543

  
  

  Abstract

  A new energy-dissipation-based rate-independent constitutive law within the framework of elastoplasticity coupled with damage is proposed. With this methodology, the inelastic strains and the stiffness degradation exhibited by quasi-brittle materials under monotonic or cyclic loading conditions are taken into account. The proposed constitutive model is able to capture micro-cracks closure-reopening effects due to load reversal. A wide variety of hardening/softening laws on the stress–strain relationship are described and considered for the novel normalized plastic-damage energy dissipation internal variable. This normalized internal variable allows the model to be independent on the sign of the load and dissipate different fracture energies (tensile, compressive and potentially shear) in a natural way. Several numerical examples are presented in order to ensure the efficiency and validity of the proposed model for simulating the non-linear behaviour of quasi-brittle materials under monotonic and cyclic loading. Some numerical aspects of the implemented algorithm and the return mapping procedure are also described in detail and discussed.

  Abstract
  A new energy-dissipation-based rate-independent constitutive law within the framework of elastoplasticity coupled with damage is proposed. With this methodology, the inelastic [...]

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