COLLECTIONS

Documents published in Scipedia

• A viscoplastic model including non-linear isotropic and kinematic hardening

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

  (1998). Research Report, Nº PI143

  
  

  Abstract

  In this work the formulation of a general elasto-viscoplastic constitutive model is consistently derived within a thermodynamic framework. The constitutive behavior has been by a elasto-plastic free energy function. Plastic response has been modeled considering a J2 viscoplastic constitutive model, including non-linear isotropic and kinematic hardening. Time integration and linearization of the constitutive model is also introduced. Finally, a number of numerical tests will show the mechanical response of a specimen submitted to a loading-unloading cycle.

  Abstract
  In this work the formulation of a general elasto-viscoplastic constitutive model is consistently derived within a thermodynamic framework. The constitutive behavior has been [...]

  • 9
  •  read

• Numerical differentiation for local and global tangent operators in computational plasticity

  G. Chiandussi, G. Bugeda, E. Oñate

  (1998). Research Report, Nº PI144

  
  

  Abstract

  A simple method to automatically update the finite element mesh of the analysis domain is proposed. The method considers the mesh as a fictitious elastic body subjected to prescribed displacements at selected boundary points. The mechanical properties of each mesh element are appropriately selected in order to minimize the deformation and the distortion of the mesh elements. Different selection strategies have been used and compared in their application to simple examples. The method avoids the use of remeshing in the solution of shape optimization problems and reduces the number of remeshing steps in the solution of coupled fluid–structure interaction problems.

  Abstract
  A simple method to automatically update the finite element mesh of the analysis domain is proposed. The method considers the mesh as a fictitious elastic body subjected to [...]

  • 10
  •  read

• Thermo-chemo-mechanical model for concrete. I: Hydration and aging

  M. Cervera, J. Oliver, T. Prato

  (1998). Research Report, Nº PI146

  
  

  Abstract

  In this work a coupled thermo-chemo-mechanical model for the behavior of concrete at early ages is proposed. The model allows simulation of the observed phenomena of hydration, aging, damage, and creep. It is formulated within an appropriate thermodynamic framework, from which the state equations are derived. In this first part, the formulation and assessment of the thermochemical aspects of the model are presented. It is based on the reactive porous media theory, and it can accurately predict the evolution in time of the hydration degree and the hydration heat production. The evolution of the compressive and tensile strengths and elastic moduli is related to the aging degree, a concept introduced to account for the effect of the curing temperature in the evolution of the mechanical properties. The short- and long-term mechanical behavior is modeled by means of a viscoelastic damage model that accounts for the aging effects. The formulation and assessment of the mechanical part of the model are relegated to a companion paper.

  Abstract
  In this work a coupled thermo-chemo-mechanical model for the behavior of concrete at early ages is proposed. The model allows simulation of the observed phenomena of hydration, [...]

  • 8
  •  read

• A simple method for automatic update of finite element meshes

  G. Chiandussi, G. Bugeda, E. Oñate

  (1998). Research Report, Nº PI147

  
  

  Abstract

  A simple method to automatically update the finite element mesh of the analysis domain is proposed. The method considers the mesh as a fictitious elastic body subjected to prescribed displacements at selected boundary points. The mechanical properties of each mesh element are appropriately selected in order to minimize the deformation and the distortion of the mesh elements. Different selection strategies have been used and compared in their application to simple examples. The method avoids the use of remeshing in the solution of shape optimization problems and reduces the number of remeshing steps in the solution of coupled fluid–structure interaction problems

  Abstract
  A simple method to automatically update the finite element mesh of the analysis domain is proposed. The method considers the mesh as a fictitious elastic body subjected to [...]

  • 7
  •  read

• A stabilized finite element method for generalized stationary incompressible flows

  R. Codina

  (1999). Research Report, Nº PI148

  
  

  Abstract

  In this paper we describe a finite element formulation for the numerical solution of the stationary Navier-Stokes equations including Coriolis forces and the permeability of the medium. The stabilized method is based on the algebraic version of the sub-grid scale approach. We first describe this technique for general systems of convection-diffusion-reaction equations and then we apply it to linearized flow equations. The important point is the design of the matrix of stabilization parameters that the method has. This design is based on the identification of the stability problems of the Galerkin method and a scaling of variables argument to determine which coefficients must be included in the stabilization matrix. This, together with the convergence analysis of the linearized problem, leads to a simple expression for the stabilization parameters in the general situation considered in the paper. The numerical analysis of the linearized problem also shows that the method has optimal convergence properties.    

  Abstract
  In this paper we describe a finite element formulation for the numerical solution of the stationary Navier-Stokes equations including Coriolis forces and the permeability [...]

  • 8
  •  read

• Rotation‐free triangular plate and shell elements

  E. Oñate, F. Zárate

  (1999). Research Report, Nº PI149

  
  

  Abstract

  The paper describes how the finite element method and the finite volume method can be successfully combined to derive two new families of thin plate and shell triangles with translational degrees of freedom as the only nodal variables. The simplest elements of the two families based on combining a linear interpolation of displacements with cell centred and cell vertex finite volume schemes are presented in detail. Examples of the good performance of the new rotation‐free plate and shell triangles are given.

  Abstract
  The paper describes how the finite element method and the finite volume method can be successfully combined to derive two new families of thin plate and shell triangles with [...]

  • 7
  •  read

• A stabilized finite element method for incompressible viscous flows using a finite increment calculus formulation

  E. Oñate

  (1999). Research Report, Nº PI150

  
  

  Abstract

  A stabilized finite element formulation for incompressible viscous flows is derived. The starting point are the modified Navier-Stokes equations incorporating naturally the necessary stabilization terms via a finite increment calculus (FIC) procedure. Application of the standard finite element Galerkin method to the modified differential equations leads to a stabilized discrete system of equations overcoming the numerical instabilities emanating from the advective terms and those due to the lack of compatibility between approximate velocity and pressure fields. The FIC method also provides a natural explanation for the stabilization terms appearing in all equations for both the Navier-Stokes and the simpler Stokes equations. Transient solution schemes with enhanced stabilization properties are also proposed. Finally a procedure for computing the stabilization parameters is presented.

  Abstract
  A stabilized finite element formulation for incompressible viscous flows is derived. The starting point are the modified Navier-Stokes equations incorporating naturally the [...]

  • 12
  •  read

• Numerical differentiation for Non-Trivial consistent tangent matrices: An application to the MRS-Lade model

  A. Pérez-Foguet, A. Rodríguez-Ferran, A. Huerta

  (1999). Research Report, Nº PI151

  
  

  Abstract

  In Reference the authors have shown that numerical differentiation is a competitive alternative to analytical derivatives for the computation of consistent tangent matrices. Relatively simple models were treated in that reference. The approach is extended here to a complex model: the MRS-Lade model. This plastic model has a cone-cap yield surface and exhibits strong coupling between the flow vector and the hardening moduli. Because of this, derivating these quantities with respect to stresses and internal variables –crucial step in obtaining consistent tangent matrices- is rather involved. Numerical differentiation is used here to approximate these derivatives. The approximated derivatives are then used 1) to compute consistent tangent matrices (global problem) and 2) to integrate the constitutive equation at each Gauss point (local problem) with the Newton-Raphson method. The choice of the stepsize (i.e. the perturbation in the approximation schemes), based on the concept of relative stepsize, poses no difficulties. In contrast to previous approaches the global problems. The computational efficiency (CPU time) and robustness of the proposed approach is illustrated by means of several numerical examples, where the major relevant topics are discussed in details.

  Abstract
  In Reference the authors have shown that numerical differentiation is a competitive alternative to analytical derivatives for the computation of consistent tangent matrices. [...]

  • 7
  •  read

• Thermo‐mechanical analysis of industrial solidification processes

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

  (1999). Research Report, Nº PI153

  
  

  Abstract

  The paper presents an up‐to‐date finite element numerical model for fully coupled thermo‐mechanical problems, focussing in the simulation of solidification processes of industrial metal parts. The proposed constitutive model is defined by a thermo‐visco‐elasto‐(visco)plastic free energy function which includes a contribution for thermal multiphase changes. Mechanical and thermal properties are assumed to be temperature‐dependent, and viscous‐like strains are introduced to account for the variation of the elastic moduli during the cooling process. The continuous transition between the initial fluid‐like and the final solid‐like behaviour of the part is modelled by considering separate viscous and elasto‐plastic responses as a function of the solid fraction. Thermo‐mechanical contact conditions between the mould and the part are specifically considered, assuming that the heat flux is a function of the normal pressure and the thermal and mechanical gaps. A fractional step method arising from an operator split of the governing equations is used to solve the non‐linear coupled system of equations, leading to a staggered product formula solution algorithm suitable for large‐scale computations. Representative simulations of industrial solidification processes are shown, and comparison of computed results using the proposed model with available experimental data is given.

  Abstract
  The paper presents an up‐to‐date finite element numerical model for fully coupled thermo‐mechanical problems, focussing in the simulation of solidification processes [...]

  • 5
  •  read

• New degrees of freedom in computational mechanics: mesh free finite point method, rotation free shell triangles and moving free meshes

  E. Oñate

  (1999). Research Report, Nº PI154

  
  

  Abstract

  The paper presents an overview of some recent developments in computational mechanics introducing new degrees of “freedom” allowing the solution of more challenging problems. First advances in the finite point method for fully mesh free solution in fluid and solid mechanics are described. Next, new rotation free shell triangles incorporating membrane and bending effects are presented. Finally, a simple method allowing free movement of meshes is described. Examples of application of all the “free” methods are given.  

  Abstract
  The paper presents an overview of some recent developments in computational mechanics introducing new degrees of “freedom” allowing the solution of more challenging [...]

  • 8
  •  read