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• Evaluation of the performance of ballasted railway structures subjected to high-speed train loads by the Discrete Element Method

  . s:, J. Irazábal, F. Salazar, E. Oñate, J. Irazábal González

  J. Irazábal's Conference proceedings (2019). 1

  
  

  Abstract

  Conventional and high-speed train lines are being constructed all over the world with the objective of improving the mobility of both people and goods. Most of these infrastructures are built with railway ballast, a granular material whose main functions are resisting train loads and facing climate actions. The growth in popularity of railway infrastructures has led to an increasing interest in the development of numerical models to evaluate their performance and improve their maintenance. To this respect, the Discrete Element Method (DEM) is an approach that considers the discontinuous nature of granular materials, such as railway ballast. Moreover, it can also be used to compute the behaviour of continuum materials, such as rails and bearing plates, applying the so-called bonded DEM. The code used is developed within DEMPack, a specific software tool for modelling physical problems using the DEM. After evaluating the different geometrical alternatives for representing railway ballast and considering the high amount of material involved in the full-scale tests (more than 130,000 particles) the calculations were carried out using the most efficient option, spheres with rolling friction. This geometrical simplification is not suitable for small-scale tests, however, previous analysis showed that it is accurate enough for reproducing the macroscopic behaviour of the ballast layer. The numerical results correctly capture the effect of changing several parameters such as ballast compaction, inter-particle friction or grain size. It can be concluded that the DEM increases the possibilities for analysing innovative solutions aiming to improve ballasted tracks design, maintenance and performance, since real case-scenarios can be studied with enough accuracy and feasible time.

  Abstract
  Conventional and high-speed train lines are being constructed all over the world with the objective of improving the mobility of both people and goods. Most of these infrastructures [...]

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• Towards the Virtual Wind Tunnel for civil engineering applications

  R. Zorrilla, E. Oñate, R. Rossi

  Monograph CIMNE (2020). M189

  
  

  Abstract

  This monograph develops a numerical tool (the Virtual Wind Tunnel, VWT) for the reso-lution of problems involving fluid flow around structures. Due to the limitations that traditional methods may have in this context, the VWT is based on the use of fixed mesh technologies (CutFEM-type) combined with an implicit representation of the embedded bodies. One of the main contributions of the monograph is the use of such fixed mesh methods to solve lightweight thin-walled structures problems. Hence, two embedded formulations capable of representing the flow around bodies with and without internal volume are proposed. The first one results in a simpler implementation and lower computational effort but can only represent a slip behavior of the wall. The second one gets rid of such limitation by including a Nitsche imposition of the Navier-slip condition, thus allowing modelling any wall behavior as a wall law would do. The applicability range of the VWT includes the fluid–structure i nteraction problem (FSI). To that purpose an improvement for the boundary condition imposition of the FM-ALE algorithm mesh motion problem is also proposed. Moreover, the implementation, which has been conceived to be easily extended to any other coupled problem, is also treated. The validation of the technologies within the VWT includes multiple theoretical test cases as well as feasible industrial applications. Among these, the FSI analysis of a 4-point tent during a strong wind episode deserves to be highlighted as it showcases the achievement of the initial objective of the monograph.

  Abstract
  This monograph develops a numerical tool (the Virtual Wind Tunnel, VWT) for the reso-lution of problems involving fluid flow around structures. Due to the limitations that [...]

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• Detailed simulation of viral propagation in the built environment (preprint)

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

  Computational Mechanics (2020). 10.1007/s00466-020-01881-7

  
  

  Abstract

  A summary is given of the mechanical characteristics of virus contaminants and the transmission via droplets and aerosols. The ordinary and partial differential equations describing the physics of these processes with high fidelity are presented, as well as appropriate numerical schemes to solve them. Several examples taken from recent evaluations of the built environment are shown, as well as the optimal placement of sensors.

  Abstract
  A summary is given of the mechanical characteristics of virus contaminants and the transmission via droplets and aerosols. The ordinary and partial differential equations [...]

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• An embedded Finite Element framework for the resolution of strongly coupled Fluid–Structure Interaction problems. Application to volumetric and membrane-like structures

  R. Zorrilla, R. Rossi, R. Wüchner, E. Oñate

  Computer Methods in Applied Mechanics and Engineering (2020). Volume 368, pp. 113179

  
  

  Abstract

  This work presents a Fluid–Structure Interaction framework for the robust and efficient simulation of strongly coupled problems involving arbitrary large displacements and rotations. We focus on the application of the proposed tool to lightweight membrane-like structures. Nonetheless, all the techniques we present in this work can be applied to both volumetric and volumeless bodies. To achieve this, we rely on the use of embedded mesh methods in the fluid solver to conveniently handle the extremely large deflections and eventual topology changes of the structure. The coupling between the embedded fluid and mechanical solvers is based on an interface residual black-box strategy. We validate our proposal by solving reference benchmarking examples that consider both volumetric and volumeless geometries. Whenever it is possible, we also compare the embedded solution with the one obtained with our reference body fitted solver. Finally we present a real-life application of the presented embedded Fluid–Structure Interaction solver.

  Abstract
  This work presents a Fluid–Structure Interaction framework for the robust and efficient simulation of strongly coupled problems involving arbitrary large displacements [...]

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• Análisis numérico del proceso de filtración en presas de escollera

  C. Tapia, E. Oñate, A. LARESE

  (2009). Research Report, IT-591

  
  

  Abstract

  Las presas de materiales sueltos funcionan como presas de gravedad, el peso propio de los materiales que la componen aportan la resistencia necesaria para soportar el empuje horizontal y la flexión que producen las aguas en el trasdós. El inconveniente principal de éstas presas está en el sobrevertido. Si se produce una avenida y el agua vierte sobre la presa, ésta se comporta de manera inestable y puede colapsarse y desmoronarse. Se sabe que este fenómeno del sobrevertido es una de las principales razones por las que colapsan este tipo de presas, pero se trata de un fenómeno poco conocido y poco desarrollado. Por ello existe un interés cada vez mayor en el estudio del comportamiento de las presas de materiales sueltos cuando se lleva a cabo el llenado, y el sobrevertido de agua sobre el talud aguas abajo. Este estudio está limitado por la ausencia de un método de cálculo, por lo que es esencial llegar a constituir un método numérico que modelice el comportamiento físico de estos procesos en dichas presas.

  Abstract
  Las presas de materiales sueltos funcionan como presas de gravedad, el peso propio de los materiales que la componen aportan la resistencia necesaria para soportar el empuje [...]

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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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