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• A nodal-based implementation of a stabilized Finite Element Method for Incompressible Flow Problems

  R. Codina

  (1999). Research Report, Nº PI156

  
  

  Abstract

  The objective of this paper is twofold. First, a stabilized finite element method for the incompressible Navier-Stokes is presented, and several numerical experiments are conducted to check its performance. This method is able to deal with all the instabilities that the standard Galerkin method presents, namely, the pressure instability, the instability arising in convection dominated situations and also the less popular instabilities found when the Navier-Stokes equations have a dominant Coriolis force, or there is a dominant absorption term arising from the small permeability of the medium where the flow takes place. The second objective is to describe a nodal-based implementation of the finite element formulation introduced. This implementation is based on an a priori calculation of the integrals appearing in the formulation and then the construction of the matrix approximations, this matrix and this vector can be constructed directly for each nodal point, without the need to loop over element and thus making the calculations much faster. In order to be able to do this, all the variables have to be defined at the nodes of the finite element mesh, not on the elements. This is also so for the stabilization parameters of the formulation. However, doing this given rise to questions regarding the consistency and the conservation properties of the final scheme that are addressed in this paper.

  Abstract
  The objective of this paper is twofold. First, a stabilized finite element method for the incompressible Navier-Stokes is presented, and several numerical experiments are [...]

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• Simulation of Construction of RCC Dams. I: Temperature and Aging

  M. Cervera, J. Oliver, T. Prato

  (1999). Research Report, Nº PI157

  
  

  Abstract

  In this work a numerical procedure for the simulation of the construction process of Roller Compacted Concrete (RCC) dams is described. The basis of the work is a coupled thermos-chemo-mechanical model for the behaviour of concrete at early ages that allows to simulate the observed phenomena of hydration, aging, creep and damage. In this first part only the thermochemical aspects of the simulation of the construction process are presented. The proposed procedure can accurately predict the evolution in time of the hydration degree and the hydration heat production. This allows to obtain the temperature field inside the dam at any time during the construction and the following years. The evolution of the compressive and tensile strengths and elastic moduli can also be predicted in terms of the evolutions of the hydration degree and the temperature conditions.  Results from 2d and simplified vertical 1D models are compared and several parametric studies are carried out. The simulation and discussion of the mechanical aspects of the construction process are relegated to a companion paper that follows.

  Abstract
  In this work a numerical procedure for the simulation of the construction process of Roller Compacted Concrete (RCC) dams is described. The basis of the work is a coupled [...]

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• BLAY3D: 3D boundary layer code. User's guide.

  M. Storti

  (1999). Research Report, Nº PI158

  
  

  Abstract

  This is the user’s guide for the BLAY3D code (version 2.2 of December 28, 1998). BLAY3D is a fluid mechanics code for solving the incompressible Boundary Layer Equations (BLE), based on a spectral approximation in the transversal direction and a mesh-less approximation on the surface of the body. It contains a basic description of what are the BLE, the governing equations involved, how they are solved, which is the data and how is it entered in order to be processed by BLAY3D, what kind of result BLAY3D generates, and finally several examples are shown.

  Abstract
  This is the user’s guide for the BLAY3D code (version 2.2 of December 28, 1998). BLAY3D is a fluid mechanics code for solving the incompressible Boundary Layer Equations [...]

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• Transferencia de calor por conducción. Verificación del programa ED-Poiss

  S. Robles, F. Zárate

  (1999). Research Report, Nº PI161

  
  

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• Stabilization of incompressibility and convection through orthogonal sub-scale in finite element methods

  R. Codina

  (1999). Research Report, Nº PI162

  
  

  Abstract

  Two apparently different forms of dealing with the numerical instability due to the incompressibility constraint of the stokes problem are analyzed in this paper. The first of them is the stabilization thought the pressure gradient projection, which consists of adding a certain least-squares form of the difference between the pressure gradient and its L² projection onto the discrete velocity space in the variational equations of the problem. The second is a sub-grid scale method, whose stabilization effect is very similar to that of the Galerkin/least-squares method for the Stokes problem. It is shown here that the first method can also be recast in the framework of sub-grid scale method with a particular choice for the space of sub-scales. This leads to a new stabilization procedure, whose applicability to stabilize convection is also studied in this paper.  

  Abstract
  Two apparently different forms of dealing with the numerical instability due to the incompressibility constraint of the stokes problem are analyzed in this paper. The first [...]

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• On the constitutive modeling of coupled thermomechanical phase-change problems

  C. Agelet de Saracibar, M. Cervera, M. Chiumenti

  (1999). Research Report, Nº PI163

  
  

  Abstract

  This paper deals with a thermodynamically consistent numerical formulation for coupled thermoplastic problems including phase-change phenomena and frictional contact. The final goal is to get an accurate, efficient and robust numerical model, able for the numerical simulation of industrial solidification processes. Some of the current issues addressed in the paper are the following. A fractional step method arising from an operator split of the governing differential equations has been used to solve the nonlinear coupled system of equations, leading to a staggered product formula solution algorithm. Nonlinear stability issues are discussed and isentropic and isothermal operator splits are formulated. Within the isentropic split, a strong operator split design constraint is introduced, by requiring that the elastic and plastic entropy, as well as the phase-change induced elastic entropy due to the latent heat, remain fixed in the mechanical problem. The formulation of the model has been consistently derived within a thermodynamic framework. All the material properties have been considered to be temperature dependent. The constitutive behavior has been defined by a thermoviscous/elastoplastic free energy function, including a thermal multiphase change contribution. Plastic response has been modeled by a J2 temperature dependent model, including plastic hardening and thermal softening. The constitutive model proposed accounts for a continuous transition between the initial liquid state, the intermediate mushy state and the final solid state taking place in a solidification process. In particular, a pure viscous deviatoric model has been used at the initial fluid-like state. A thermomecanical contact model, including a frictional hardening and temperature dependent coupled potential, is derived within a fully consistent thermodinamical theory. The numerical model has been implemented into the computational finite element code COMET developed by the authors. Numerical simulations of solidification processes show the good performance of the computational model developed.

  Abstract
  This paper deals with a thermodynamically consistent numerical formulation for coupled thermoplastic problems including phase-change phenomena and frictional contact. The [...]

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• Advances in the stabilized finite point method for structural mechanics

  E. Oñate, F. Perazzo, J. Canet

  (1999). Research Report, Nº PI164

  
  

  Abstract

  The basis of the finite point method for the fully meshless solution of structure mechanics problems is described. A new stabilization technique based on a finite increment calculus procedure is used. The efficiency and accuracy of the stabilized finite point method in the meshless analysis of simple structural problems is shown in two examples of applications.

  Abstract
  The basis of the finite point method for the fully meshless solution of structure mechanics problems is described. A new stabilization technique based on a finite increment [...]

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• A methodology for analysis of fluid structure interaction accouting for free surface waves

  E. Oñate, J. García-Espinosa

  (1999). Research Report, Nº PI166

  
  

  Abstract

  A stabilized semi-implicit frictional step finite element method for solving coupled fluid-structure interaction problems involving free surface waves is presented. The stabilized equations are derived at a differential level via a finite element calculus procedure. A new mesh updating technique based on solving a fictitious elastic problem on the moving mesh is described. One example of the efficiency of the stabilized semi-implicit algorithm for the coupled solution of fluid-structure interaction problems is presented.

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

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• A finite point method for incompressible flow problems

  E. Oñate, C. Sacco, S. Idelsohn

  (1999). Research Report, Nº PI167

  
  

  Abstract

  A stabilized finite point method (FPM) for meshless analysis of incompressible fluid flow problems is presented. The stabilization approach is based in the finite increment calculus (FIC) procedure developed by Oñate. An enhanced fractional step procedure allowing the semi-implicit numerical solution of incompressible fluids using the FPM is described. Examples of application of the stabilized FPM to the solution of two incompressible flow problems are presented.  

  Abstract
  A stabilized finite point method (FPM) for meshless analysis of incompressible fluid flow problems is presented. The stabilization approach is based in the finite increment [...]

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• New rotation free shell triangle for crash-worthiness analysis in parallel PC networks

  E. Oñate, F. Zárate, X. Plana, L. Neamtu

  (1999). Research Report, Nº PI168

  
  

  Abstract

  A new three node shell triangular element with translational degree of freedom as the only modal variables is presented. The element formulation is based on combining a standard linear finite element interpolation with a cell centered finite volume scheme. Details of the implementation of the element in an explicit dynamic code operating in parallel on networks of PC’s are presented. The efficiency and applicability of the new rotation free shell triangle is shown in the solution of some contact/impact and crash-worthiness problem.  

  Abstract
  A new three node shell triangular element with translational degree of freedom as the only modal variables is presented. The element formulation is based on combining a standard [...]

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