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• Formulación de elementos finitos estabilizada para problemas de transporte convectivo y flujo incompresible mediante técnicas de cálculo finitesimal

  E. Oñate

  (1999). Research Report, Nº PI169

  
  

  Abstract

  El trabajo muestra que los términos de estabilización para la solución por el MEF de problemas de transporte convectivo y de flujo incompresible, pueden obtenerse de manera natural utilizando aproximaciones de mayor orden en las ecuaciones de balance en un dominio finito. Este procedimiento de cálculo finitesimal permite reinterpretar muchos algoritmos de elementos finitos estabilizados utilizando en la práctica y proporciona también una expresión para calcular los parámetros de estabilización.

  Abstract
  El trabajo muestra que los términos de estabilización para la solución por el MEF de problemas de transporte convectivo y de flujo incompresible, pueden [...]

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• Macroscopic modelling of concrete aging regarding hydration and temperature effects

  M. Cervera, R. Faria, J. Oliver, T. Prato

  (1999). Research Report, Nº PI170

  
  

  Abstract

  A macroscopic model to account for the hydration and aging phenomena that occur during the early ages of concrete is proposed in this work. Assuming the percolation of water through the hydrates already formed as the dominant mechanism of cement hydration, a normalized variable called hydration degree is adopted in the model, which has an evolution law that can be easily calibrated through an adiabatic calorimetric test. This methodology allows an accurate prediction of the evolution of the hydration degree and the hydration heat production. The evolution of the compressive strength is related to the aging degree, a novel concept which accounts for the effect of the hydration degree and the influence of the curing temperature on the final mechanical properties of concrete, a feature not attended with classic maturity concepts. A wide set of experimental tests validates the proposed model for ordinary and high performance concretes. Fly ash admixture concretes with a large spectrum of cement substitutions can be also modelled with the proposed approach.

  Abstract
  A macroscopic model to account for the hydration and aging phenomena that occur during the early ages of concrete is proposed in this work. Assuming the percolation of water [...]

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• Enrichment and coupling of the finite element and meshless methods

  A. Huerta, S. Fernández-Méndez

  (1999). Research Report, Nº PI171

  
  

  Abstract

  A mixed hierarchical approximation based on finite elements and meshless methods is presented. Two cases are considered. The first one couples regions where finite elements or meshless methods are used to interpolate: continuity and consistency is preserved. The second one enriches a finite element mesh with processes. In both cases the same formulation is used, convergence is studied and examples are shown.

  Abstract
  A mixed hierarchical approximation based on finite elements and meshless methods is presented. Two cases are considered. The first one couples regions where finite elements [...]

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• Efficient unstructured quadrilateral meshes preserving the prescribed element size

  J. Sarrate, A. Huerta

  (1999). Research Report, Nº PI172

  
  

  Abstract

  This work devoted to the description of an algorithm for automatic quadrilateral mesh generation. The technique is based on a recursive decomposition of the domain into quadrilateral over complex geometries (there is not need for a previous step where triangles are generated). A background mesh with the desired element sizes allows to obtain the preferred sizes anywhere in the domain. The final mesh can be viewed as the optimal one given the objective function defined. The recursive algorithm induces an efficient data structure which optimizes the computer cost. Several examples are presents to show the efficiency of this algorithm

  Abstract
  This work devoted to the description of an algorithm for automatic quadrilateral mesh generation. The technique is based on a recursive decomposition of the domain into quadrilateral [...]

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• An improved algorithm to smooth graded quadrilateral meshes preserving the prescribed element size

  J. Sarrate, A. Huerta

  (1999). Research Report, Nº PI173

  
  

  Abstract

  In the generation of quadrilateral unstructured meshes, special attention is focused to the shape of the elements. This is because it is well known that the distortion of the elements and the accuracy of the analysis are closely related. However, in adaptive schemes it is also essential that the new generated mesh meets the prescribed element sizes in order to obtain a solution with the desired precision. In 1982 Giuliani developed a robust rezoning algorithm based on geometrical criteria. It gives proven results is a smooth element size distribution, but elements do not verify the prescribed element size when sharp distributions appear. This paper presents a modification of the Giuliani method that generates non-distorted elements while preserving the element size. Similar to the original method, this modification can be extended to three-dimensional cases

  Abstract
  In the generation of quadrilateral unstructured meshes, special attention is focused to the shape of the elements. This is because it is well known that the distortion of [...]

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• Probabilistic analysis of an a posteriori error estimator for Finite Elements

  P. Díez, J. Egozcue

  (1999). Research Report, Nº PI175

  
  

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• EMANT: Programa de análisis de problemas electrotécnicos mediante el método de los elementos finitos

  J. Mora, J. Canet, E. Oñate, C. Sacco, L. Martínez

  (1999). Research Report, Nº PI177

  
  

  Abstract

  La sencillez conceptual de la electrostática esconde todo un abanico de aplicaciones industriales que precisa de herramientas de cálculo numérico para su optimización. En particular, el diseño de aisladores para sistemas de alta tensión o de las cámaras de tratamiento de alimentos implica una cuidadosa elección de la geometría del sistema y materiales empleados. A la ayuda que supone el conocimiento de la distribución de los campos eléctricos asociados a cada prototipo desde el punto de vista de prestaciones del equipo (homogeneidad de campo, minimización de puntos triples), se añade la interesante posibilidad de contribuir a la comprensión del fenómeno físico (cómo se alteran los alimentos al aplicar un campo eléctrico intenso). Se recoge en las siguientes líneas la formulación desarrollada para escribir un código de resolución de problemas electrostáticos mediante el método de los elementos finitos, no tanto como nuevo problema sino como transición desde otras disciplinas como son la mecánica o transferencia de calor.

  Abstract
  La sencillez conceptual de la electrostática esconde todo un abanico de aplicaciones industriales que precisa de herramientas de cálculo numérico para [...]

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• An anisotropic elastoplastic constitutive model for large deformation analysis of fibre reinforced composites

  E. Car, S. Oller, E. Oñate

  (1999). Research Report, Nº PI178

  
  

  Abstract

  In this work a generalized anisotropic elastoplastic constitutive model in large deformation is presented. It is used for the analysis of fiber-reinforced composite materials in the frame of the finite element method. Mixing theory is applied to simulate the behavior of the composite material.  The elastic anisotropic behavior  is simulated with classical elasticity theory, while that of a non-proportional anisotropic solid is simulated by means of the proposed generalized anisotropic elastoplastic model. The  approach assumes the existence of a real anisotropic space and of a fictitious isotropic space where a mapped fictitious problem is solved. Both spaces are related by means of a linear transformation using a fourth order  tensor incorporating complete information on the real anisotropic material. Details of the numerical implementations of the model into a non-linear, large deformations finite element solution scheme are provided. Examples of application showing the performance of the model for the analysis of fiber-reinforced composite materials are given.

  Abstract
  In this work a generalized anisotropic elastoplastic constitutive model in large deformation is presented. It is used for the analysis of fiber-reinforced composite [...]

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• Numerical aerodynamic analysis of large buildings using a finite element model with application to a telescope building

  R. Codina, C. Morton, E. Oñate, O. Soto

  (1999). Research Report, Nº PI181

  
  

  Abstract

  Presents a numerical strategy for the aerodynamic analysis of large buildings, with an application to the simulation of the air flow within a telescope building. The finite element formulation is presented first, and then the methodology followed to obtain significant data from the calculations is described. The quality of the ventilation of the building is defined by the average residence times, and the feasibility of this ventilation by the actions created on the instruments and the general flow pattern.

  Abstract
  Presents a numerical strategy for the aerodynamic analysis of large buildings, with an application to the simulation of the air flow within a telescope building. The finite [...]

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• A finite element method for fluid-structure interaction with surface waves using a finite calculus formulation

  E. Oñate, J. García-Espinosa

  (2000). Research Report, Nº PI180

  
  

  Abstract

  A stabilized semi-implicit step finite element method for solving coupled fluid-structure interaction problems involving free surface waves is presented. The stabilized governing equations for the viscous fluid and the free surface are derived at a differential level via finite increment calculus procedure. A mesh updating technique based on solving a fictitious elastic problem on the moving mesh is described. Examples of the efficiency of the stabilized semi-implicit algorithm for the analysis of fluid-structure interaction problems in totally or partially submerged bodies is presented.  

  Abstract
  A stabilized semi-implicit step finite element method for solving coupled fluid-structure interaction problems involving free surface waves is presented. The stabilized governing [...]

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