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Documents published in Scipedia

• On the computational efficiency and implementation of block-iterative algorithms for nonlinear coupled Problems

  M. Cervera, R. Codina, M. Galindo

  Engineering Computations (1996). Vol. 13 (6), pp. 4-30

  
  

  Abstract

  Outlines a general methodology for the solution of the system of algebraic equations arising from the discretization of the field equations governing coupled problems. Considers that this discrete problem is obtained from the finite element discretization in space and the finite difference discretization in time. Aims to preserve software modularity, to be able to use existing single field codes to solve more complex problems, and to exploit computer resources optimally, emulating parallel processing. To this end, deals with two well-known coupled problems of computational mechanics – the fluid-structure interaction problem and thermally-driven flows of incompressible fluids. Demonstrates the possibility of coupling the block-iterative loop with the nonlinearity of the problems through numerical experiments which suggest that even a mild nonlinearity drives the convergence rate of the complete iterative scheme, at least for the two problems considered here. Discusses the implementation of this alternative to the direct coupled solution, stating advantages and disadvantages. Explains also the need for online synchronized communication between the different codes used as is the description of the master code which will control the overall algorithm.

  Abstract
  Outlines a general methodology for the solution of the system of algebraic equations arising from the discretization of the field equations governing coupled problems. Considers [...]

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• Seismic evaluation of concrete dams via continuum damage models

  M. Cervera, R. Faria, J. Oliver

  Earthquake Engineering Structural Dynamics (1995). Vol. 24 (9), pp. 1125-1245

  
  

  Abstract

  In this paper a general methodology for the analysis of large concrete dams subjected to seismic excitation is outlined. It is valid both for gravity dams (2D representation) and arch dams (3D representation). The method allows for non‐linear material behaviour of the dam, ‘transparent fictitious boundaries’ for dealing properly with in‐coming and out‐going seismic waves, and an efficient procedure to deal with dam‐soil‐fluid interaction. The mechanical behaviour of concrete is modelled using an isotropic damage model which allows for tension and compression damage, and exhibits stiffness recovery upon load reversals. Emphasis is placed in the treatment of fluid‐structure interaction, regarding both formulation and efficiency aspects. A gravity dam and an arch dam are analysed subjected to artificially generated earthquakes of different intensities, and the results are used to study the degree of (un)safety of the dams.

  Abstract
  In this paper a general methodology for the analysis of large concrete dams subjected to seismic excitation is outlined. It is valid both for gravity dams (2D representation) [...]

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• Análisis de terremotos históricos por sus efectos. El terremoto de Andalucía

  J. Arango

  Monograph Series in Earthquake Engineering, editor A. H. Barbat (1994). MIS07, ISBN: 84-87867-44-8

  
  

  Abstract

  El trabajo se organiza en dos partes: en la primera se analiza el potencial de licuefacción del suelo en aquellos lugares con referencias históricas fiables. En la segunda se evalúa la resistencia sísmica de un edificio de la época.

  Abstract
  El trabajo se organiza en dos partes: en la primera se analiza el potencial de licuefacción del suelo en aquellos lugares con referencias históricas fiables. [...]

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• Numerical Analysis of Dams with Extensive Cracking due to Concrete Hydration: Simulation of a Real Case

  M. Cervera, M. Galindo, J. Oliver

  Dam Engng. (1992). Vol. 3 (1), pp. 1-22.

  
  

  Abstract

  The paper presents the computational model developed to study an existing large gravity dam suffering from observed "pathological behavior" resulting concrete hydration. The combined effect of water intrusion and chemical and numerical studies. The present study was undertaken to simulate numerically the observed phenomenon and to predict future developments. Concrete is modelled using an isotropic continuum damage model including visco-elastic effects. The triggering of the volumetric expansion resulting from water intrusion is linked to the onset of damage at each a point, assuming that water enters dam mostly through the damaged areas. Transversal construction joints are modelled using smeared joints. Temperature and porewater pressure effects are included using assumed distributions based on available field data. Results are presented which match reasonably well with the available filed measurements.

  Abstract
  The paper presents the computational model developed to study an existing large gravity dam suffering from observed "pathological behavior" resulting concrete hydration. [...]

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• Nonlinear analysis of reinforced concrete plate and shell structures using 20-noded isoparametric brick elements

  M. Cervera, E. Hinton, O. Hassan

  Computers and Structures (1987). Vol. 25 (6), pp. 845-869

  
  

  Abstract

  This paper describes an efficient and accurate, 3-D finite element model which may be adopted in the nonlinear analysis of reinforced concerete plate and shell structures. Benchmark tests are undertaken to check the computational model.

  Abstract
  This paper describes an efficient and accurate, 3-D finite element model which may be adopted in the nonlinear analysis of reinforced concerete plate and shell structures. [...]

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• Preconditioned conjugate gradient method for the non‐linear finite element analysis with particular reference to 3D reinforced concrete structures

  M. Cervera, Y. Liu, E. Hinton

  Engineering Computations (1986). Vol. 3 (3), pp.235-242

  
  

  Abstract

  A hierarchically preconditioned conjugate gradient (PCG) method for finite element analysis is presented. Its use is demonstrated for the difficult problem of the non‐linear analysis of 3D reinforced concrete structures. Examples highlight the dramatic savings in computer storage and more modest savings in solution times obtained using PCG especially for large problems.

  Abstract
  A hierarchically preconditioned conjugate gradient (PCG) method for finite element analysis is presented. Its use is demonstrated for the difficult problem of the non‐linear [...]

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• Mixed stabilized finite element methods in nonlinear solid mechanics. Part III: Compressible and incompressible plasticity

  M. Cervera, M. Chiumenti, L. Benedetti, R. Codina

  Comput. Methods Appl. Mech. Engrg., (2015). (preprint) Vol. 285, pp. 752-775

  
  

  Abstract

  This paper presents the application of a stabilized mixed strain/displacement finite element formulation for the solution of nonlinear solid mechanics problems involving compressible and incompressible plasticity. The variational multiscale stabilization introduced allows the use of equal order interpolations in a consistent way. Such formulation presents two advantages when compared to the standard, displacement based, irreducible formulation: (a) it provides enhanced rate of convergence for the strain (and stress) field and (b) it is able to deal with incompressible situations. The first advantage also applies to the comparison with the mixed pressure/displacement formulation. The paper investigates the effect of the improved strain and stress fields in problems involving strain softening and localization leading to failure, using low order finite elements with continuous strain and displacement fields (P1P1 triangles or tetrahedra and Q1Q1quadrilaterals, hexahedra, and triangular prisms) in conjunction with an associative frictional Drucker–Prager plastic model. The performance of the strain/displacement formulation under compressible and nearly incompressible deformation patterns is assessed and compared to a previously proposed pressure/displacement formulation. Benchmark numerical examples show the capacity of the mixed formulation to predict correctly failure mechanisms with localized patterns of strain, virtually free from any dependence of the mesh directional bias. No auxiliary crack tracking technique is necessary.

  Abstract
  This paper presents the application of a stabilized mixed strain/displacement finite element formulation for the solution of nonlinear solid mechanics problems involving compressible [...]

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• A mixed three-field FE formulation for stress accurate analysis including the incompressible limit

  M. Chiumenti, M. Cervera, R. Codina

  Comput. Methods Appl. Mech. Engrg., (2015). (preprint) Vol. 238, pp. 1095-1116

  
  

  Abstract

  In previous works, the authors have presented the stabilized mixed displacement/pressure formulation to deal with the incompressibility constraint. More recently, the authors have derived stable mixed stress/displacement formulations using linear/linear interpolations to enhance stress accuracy in both linear and non-linear problems. In both cases, the Variational Multi Scale (VMS) stabilization technique and, in particular, the Orthogonal Subgrid Scale (OSS) method allows the use of linear/linear interpolations for triangular and tetrahedral elements bypassing the strictness of the inf–sup condition on the choice of the interpolation spaces. These stabilization procedures lead to discrete problems which are fully stable, free of volumetric locking or stress oscillations. This work exploits the concept of mixed finite element methods to formulate stable displacement/stress/pressure finite elements aimed for the solution of nonlinear problems for both solid and fluid finite element (FE) analyses. The final goal is to design a finite element technology able to tackle simultaneously problems which may involve isochoric behavior (preserve the original volume) of the strain field together with high degree of accuracy of the stress field. These two features are crucial in nonlinear solid and fluid mechanics, as used in most numerical simulations of industrial manufacturing processes. Numerical benchmarks show that the results obtained compare very favorably with those obtained with the corresponding mixed displacement/pressure formulation.

  Abstract
  In previous works, the authors have presented the stabilized mixed displacement/pressure formulation to deal with the incompressibility constraint. More recently, [...]

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• Numerical modeling of friction stir welding processes

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

  Comput. Methods Appl. Mech. Engrg., (2013). (preprint) Vol. 254, pp. 353-369

  
  

  Abstract

  This work describes the formulation adopted for the numerical simulation of the friction stir welding (FSW) process. FSW is a solid-state joining process (the metal is not melted during the process) devised for applications where the original metallurgical characteristics must be retained. This process is primarily used on aluminum alloys, and most often on large pieces which cannot be easily heat treated to recover temper characteristics. Heat is either induced by the friction between the tool shoulder and the work pieces or generated by the mechanical mixing (stirring and forging) process without reaching the melting point (solid-state process). To simulate this kind of welding process, a fully coupled thermo-mechanical solution is adopted. A sliding mesh, rotating together with the pin (ALE formulation), is used to avoid the extremely large distortions of the mesh around the tool in the so called stirring zone while the rest of the mesh of the sheet is fixed (Eulerian formulation). The orthogonal subgrid scale (OSS) technique is used to stabilize the mixed velocity–pressure formulation adopted to solve the Stokes problem. This stabilized formulation can deal with the incompressible behavior of the material allowing for equal linear interpolation for both the velocity and the pressure fields. The material behavior is characterized either by Norton–Hoff or Sheppard–Wright rigid thermo-visco-plastic constitutive models. Both the frictional heating due to the contact interaction between the surface of the tool and the sheet, and the heat induced by the visco-plastic dissipation of the stirring material have been taken into account. Heat convection and heat radiation models are used to dissipate the heat through the boundaries. Both the streamline-upwind/Petrov–Galerkin (SUPG) formulation and the OSS stabilization technique have been implemented to stabilize the convective term in the balance of energy equation. The numerical simulations presented are intended to show the accuracy of the proposed methodology and its capability to study real FSW processes where a non-circular pin is often used.

  Abstract
  This work describes the formulation adopted for the numerical simulation of the friction stir welding (FSW) process. FSW is a solid-state joining process (the metal is not [...]

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• Benchmarking on bifurcation and localization in J2 plasticity for plane stress and plane strain conditions

  M. Cervera, M. Chiumenti, D. Di Capua

  Comput. Methods Appl. Mech. Engrg., (2012). Vol. 241-244, pp. 206-224

  
  

  Abstract

  This paper studies the phenomenon of strain bifurcation and localization in J2plasticity under plane stress and plane strain conditions. Necessary conditions for the outcome of bifurcation, localization, stress boundedness and decohesion are analytically established. It is shown that the explicit consideration of these conditions allows for the determination of localization angles in certain situations of interest that can be used to conduct benchmark tests on finite element formulations. The relative merits of irreducible, (stabilized) mixed and (displacement and/or strain) enhanced formulations are discussed. Numerical examples show that the mixed displacement/pressure formulation is to be preferred to the standard irreducible schemes in order to predict correct failure mechanisms with localized patterns of plastic deformation. Mixed elements are shown to be practically free from mesh directional bias dependence.

  Abstract
  This paper studies the phenomenon of strain bifurcation and localization in J2plasticity under plane stress and plane strain conditions. Necessary conditions for the outcome [...]

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