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• Pulse fracture simulation in shale rock reservoirs. DEM and FEM-DEM approaches

  J. Gonzalez, F. Zarate, E. Oñate

  Comp. Part. Mech (2018). (prepint) Vol. 5 (3), pp. 355-373

  
  

  Abstract

  In this paper we analyze the capabilities of two numerical techniques based on DEM and FEM-DEM approaches for the simulation of fracture in shale rock caused by a pulse of pressure. We have studied the evolution of fracture in several fracture scenarios related to the initial stress state in the soil or the pressure pulse peak. Fracture length and type of failure have been taken as reference for validating the models. The results obtained show a good approximation to FEM results from the literature.

  Abstract
  In this paper we analyze the capabilities of two numerical techniques based on DEM and FEM-DEM approaches for the simulation of fracture in shale rock caused by a pulse of [...]

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• Incompressible lagrangian fluid flow with thermal coupling

  R. Aubry, S. Idelsohn, E. Oñate

  Monograph CIMNE (2006). M95

  
  

  Abstract

  A method is presented for the solution of an incompressible viscous fluid flow with heat transfer and solidification using a fully Lagrangian description of the motion. The originality of this method consists in assembling various concepts and techniques which appear naturally due to the Lagrangian formulation. First of all, the Navier-Stokes equations of motion coupled with the Boussinesq approximation must be reformulated in the Lagrangian framework, whereas they have been mostly derived in an Eulerian context. Secondly, the Lagrangian formulation implies to follow the material particles during their motion, which means to convect the mesh in the case of the Finite Element Method (FEM), the spatial discretisation method chosen in this work. This provokes various difficulties for the mesh generation, mainly in three dimensions, whereas it eliminates the classical numerical difficulty to deal with the convective term, as much in the Navier-Stokes equations as in the energy equation. Even without the discretization of the convective term, an efficient iterative solver, which constitutes the only viable alternative for three dimensional problems, must be designed for the class of Generalized Stokes Problems (GSP), which could be able to behave well independently of the mesh Reynolds number, as it can vary greatly for coupled fluid-thermal analysis. Moreover, it offers a natural framework to treat free-surface problems like wave breaking and rough fluid-structure contact. On one hand, the convection of the mesh during one time step after the resolution of the non-linear system provides explicitly the locus of the domain to be considered. On the other hand, fluid-to-fluid and fluid-to-wall contact, as well as the update of the domain due to the remeshing, must be accurately and efficiently performed. Finally, the solidification of the fluid coupled with its motion through a variable viscosity is considered An efficient overall algorithm must be designed to bring the method effective, particularly in a three dimensional context, which is the ambition of this monograph. Various numerical examples are included to validate and highlight the potential of the method.

  Abstract
  A method is presented for the solution of an incompressible viscous fluid flow with heat transfer and solidification using a fully Lagrangian description of the motion. [...]

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• A three dimensional FEM-DEM technique for predicting the evolution of fracture in geomaterials and concrete

  F. Zarate, A. Cornejo Velázquez, E. Oñate

  Comp. Part. Mech (2018). (prepint) Vol. 5 (3) , pp. 411-420

  
  

  Abstract

  This paper extends to three dimensions (3D) the computational technique developed by the authors in 2D for predicting the onset and evolution of fracture in a finite element mesh in a simple manner based on combining the finite element method (FEM) and the discrete element method (DEM) approach Zarate2D. Once a crack is detected at an element edge, discrete elements are generated at the adjacent element vertexes and a simple DEM mechanism is considered in order to follow the evolution of the crack. The combination of the DEM with simple 4-noded linear tetrahedron elements correctly captures the onset of fracture and its evolution, as shown in several 3D examples of application.

  Abstract
  This paper extends to three dimensions (3D) the computational technique developed by the authors in 2D for predicting the onset and evolution of fracture in a finite element [...]

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• A coupled fluid FEM-DEM technique for predicting blasting operations in tunnels

  F. Zarate, J. Gonzalez, J. Miquel, R. Lohner, E. Oñate

  Underground Space (2018). Vol. 3 (4), pp. 310-316, (prepint)

  
  

  Abstract

  We present recent developments in the coupling of the finite element method (FEM) and the discrete element method (DEM) for analysis of rock blasting operations in tunnels. The coupled FEM-DEM technique has proven to be an efficient procedure for predicting the multi-fracture of rock induced by the loads generated in blasting situations. The coupled FEM-DEM procedure is applied in the tunnel construction, as well as to gas pressure blasting pyrotechnics situations to break rock for excavation of the tunnel front. In the latter case the effect of gas explosion is modelled by solving with the FEM the equations of gas dynamics in the analysis domain. The effect of the gas forces in the underlying rock mass is modelled via an embedded fluid-structure interaction method. The efficiency of the coupled FEM-DEM technique is demonstrated in several examples of fracture tests and rock blasting problems related to tunnel engineering. The examples presented show that the combination of the DEM with simple 3-noded linear triangular elements (for 2D problems) correctly captures the onset of fractures and their evolution accounting for the penetration of the gas in the failure domain [[#cite-1|[1,2]]].

  Abstract
  We present recent developments in the coupling of the finite element method (FEM) and the discrete element method (DEM) for analysis of rock blasting operations in tunnels. [...]

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• Decisin support system for risk assessment and management of floods

  E. Oñate, J. Piazzese, J. Dolz, M. Gómez, E. Bladé

  Monograph CIMNE (2005). M92

  
  

  Abstract

  The objective of the RAMFLOOD project is to develop and validate a new decision support system (DSS) for the risk assessment and management of emergency scenarios due to severe floods. The DSS combines environmental and geo-physical data from earth observation, with advanced computer simulation and graphical visualisation methods and artificial intelligence techniques, for generating knowledge contributing to the risk prevention of floods and the design of effective response actions maximising the safety of infrastructures and human life.

  Abstract
  The objective of the RAMFLOOD project is to develop and validate a new decision support system (DSS) for the risk assessment and management of emergency scenarios due to severe [...]

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• Un método de elementos finitos para análisis hidrodinámico de estructuras navales

  J. García-Espinosa, E. Oñate, H. Sierra

  Monograph CIMNE (2000). M59

  
  

  Abstract

  En este trabajo se presenta una metodología basada en el método de los elementos finitos para el análisis de problemas de flujo incompresible en fluidodinámica naval. Esta metodología se basa en la obtención de unas nuevas ecuaciones diferenciales, basadas en criterios discretos, alternativas a las tradicionales ecuaciones de Navier-Stokes. El punto más novedoso del presente trabajo es la aplicación del método de análisis de flujo incomprensible mencionado a problemas navales.

  Abstract
  En este trabajo se presenta una metodología basada en el método de los elementos finitos para el análisis de problemas de flujo incompresible en fluidodinámica [...]

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• Nuevos elementos finitos para el anaálisis dinámico elastoplástico no lineal de estructuras laminares

  P. Cendonya, E. Oñate, J. Miquel

  Monograph CIMNE (1997). M36

  
  

  Abstract

  Los objetivos de este trabajo se enmarcan en el análisis de estructuras laminares delgadas sometidas a un régimen dinámico de cargas, que dan origen a grandes cambios de forma sobre la estructura. Se consideran dos nuevas formulaciones de elementos finitos de lámica delgada, siendo una de ellas una nueva formulación que solo considera los desplazamientos de la superficie media del elemento como variables cinemáticas, independizándose de los grados rotacionales de libertad.

  Abstract
  Los objetivos de este trabajo se enmarcan en el análisis de estructuras laminares delgadas sometidas a un régimen dinámico de cargas, que dan origen a [...]

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• El método de desplazamiento crítico para la predicción de puntos límite y de bifurcación en estructuras

  W. Matias, E. Oñate

  Monograph CIMNE (1997). M35

  
  

  Abstract

  Se presenta la descripción Lagrangiana Generalizada para el análisis estático de sólidos con no linealidad geométrica. Se describen las relaciones incrementales básicas de la cinemática, de la estática y del modelo constitutivo. Se obtiene la forma incremental completa de las ecuaciones de equilibrio no lineales a través del principio de los trabajos visuales. La discretización de dichas ecuaciones por el método de los elementos finitos conduce a la obtención de una expresión paramétrica general y no simétrica de la matriz de rigidez secante incremental. Se obtienen formas simétricas de dicha matriz asignando determinados valores a los parámetros. A partir de la matriz de rigidez secante incremental se deduce, de forma directa, la clásica expresión de la matriz de rigidez tangente empleada en problemas no lineales. Se formula, de manera incremental, la matriz de rigidez secante a través de la descripción Lagrangiana Generalizada, de tal modo que se pueda obtener una relación entre incrementos finitos de fuerzas y desplazamientos. Se discuten las posibilidades de aplicación de la matriz secante en el análisis no lineal de estabilidad, de bifurcación y de carga límite en sistemas estructurales. Se presenta una nueva técnica de predicción de puntos críticos para el análisis de inestabilidad estructural. Este método se basa en la determinación de un campo de desplazamiento crítico  que aproxima el modo de bifurcación o el modo de deformación crítico del sistema estructural. Se determinan estos desplazamientos críticos imponiendo la condición de singularidad en una expresión aproximada de la matriz de rigidez tangente en el punto crítico. La carga crítica se obtiene a posteriori, de modo directo, utilizando la relación secante entre carga y desplazamiento. Se detalla este procedimiento y las formas explícitas de las matrices secante y tangente para elementos de barra y de sólido en dos y tres dimensiones. Se muestra la eficiencia y la buena aproximación de los resultados en la simulación numérica de varios ejemplos.

  Abstract
  Se presenta la descripción Lagrangiana Generalizada para el análisis estático de sólidos con no linealidad geométrica. Se describen las [...]

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• Combination of a non-local damage model for quasi-brittle materials with a mesh-adaptive finite element technique

  I. de-Pouplana, E. Oñate

  Finite Elements in Analysis and Design (2016). Vol. 112, pp. 26-39

  
  

  Abstract

  Progressive fracture in quasi-brittle materials is often treated via strain softening models in continuum damage mechanics. Such constitutive relations favour spurious strain localization and ill-posedness of boundary value problems. The introduction of non-local damage models together with a characteristic length parameter controlling the size of the fracture process zone is known to regularize the problem. In order to account for the non-locality of these models, it is crucial to work with fine spatial discretizations at the damage progress zone. In this paper we present a non-local damage model in combination with a mesh-adaptive finite element technique that can help automatize the analysis of progressive fracture problems in an efficient manner. Classical two-dimensional examples are given to illustrate the presented approach.

  Abstract
  Progressive fracture in quasi-brittle materials is often treated via strain softening models in continuum damage mechanics. Such constitutive relations favour spurious strain [...]

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• The challenge of mass conservation in the solution of free‐surface flows with the fractional‐step method: Problems and solutions

  S. Idelsohn, E. Oñate

  Int. J. Numer. Meth. Biomed. Engng (2010). Vol. 26 (10), pp. 1313-1330

  
  

  Abstract

  The purpose of this paper is to put in evidence that the fractional‐step method (FSM) used to solve the incompressible transient Euler and Navier–Stokes equations for free‐surface flows has a problem inherent to the method that may produce unacceptable variations of the domain volume. A simple modification of the free‐surface boundary term is introduced in order to reduce considerably the volume loss and preserve the computational advantages of the FSM.

  Abstract
  The purpose of this paper is to put in evidence that the fractional‐step method (FSM) used to solve the incompressible transient Euler and Navier–Stokes equations [...]

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