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• Adaptive control of uncertain coupled mechanical systems: application to base-isolated structures

  J. Rodellar, E. Ryan, A. Barbat

  (1994). Research Report, Nº PI45

  
  

  Abstract

  A problem of feedback stabilization is addressed for a class of uncertain nonlinear mechanical systems with n degrees of freedom and nc < n control inputs. Each system of the class has the structure of two coupled subsystems with nc and nr degrees of freedom, respectively, a prototype being an uncertain base isolated building structure with n degrees of freedom actively controlled via actuators applying forces to specific degrees of freedom of the base movement, nc < n in number. A nonlinear adaptive feedback strategy is described, which, under appropriate assumptions on the system uncertainties, guarantees a form of practical stability of the zero state. Numerical simulations are also presented to illustrate the application of the control strategy to a base isolated building.

  Abstract
  A problem of feedback stabilization is addressed for a class of uncertain nonlinear mechanical systems with n degrees of freedom and nc < n control inputs. Each system [...]

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• Hybrid control of buildings with nonlinear base isolation

  A. Barbat, J. Rodellar, .. Ryan, N. Molinares

  (1994). Research Report, Nº PI46

  
  

  Abstract

  A hybrid seismic control system for buildings structures is considered, which combines a class of passive nonlinear base isolator with an active control system. The active control forces are applied to the structural base with the objective of reducing its displacements. An adaptive control law is formulated to compute the control forces in order to assure a form of stable behaviour of the system under seismic excitation and in the presence of uncertainties in the characteristics of the building of the hybrid control system. The global behavoiur of the structure-base isolator system is such that the absolute base displacement is significantly reduced, the price paid being a slight increase of the response of the structure.  

  Abstract
  A hybrid seismic control system for buildings structures is considered, which combines a class of passive nonlinear base isolator with an active control system. The active [...]

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• SLAP: Programa para modelado numérico de procesos de esterolitografía utilizando el método de los elementos finitos.

  G. Lombera, G. Bugeda, M. Cervera, E. Oñate

  (1994). Research Report, Nº PI47

  
  

  Abstract

  Dentro de todos los procesos denominados “Rapid Prototyping”, se presenta en esta publicación el denominado estereolitografía. Estos procesos cuyo origen se remontan a fines de la década de los ochenta, poseen un gran interés por parte de las industrias, dado que posibilitan a la fabricación de piezas en tiempos muy inferiores a los obtenidos por los métodos tradicionales y una gran versatilidad en cuanto a materiales y formas utilizadas. Las máquinas actualmente existentes en el mercado generan de forma automática la pieza a partir de su representación geométrica en un ordenador. El modelado numérico del proceso se justifica por la necesidad de poder predecir la geometría final de la pieza con el objeto de realimentar el proceso variando los parámetros de control, con el fin de obtener la pieza deseada con la mayor precisión posible. En esta publicación se presenta un resumen de las posibilidades del programa “SLAP” desarrollado en el CIMNE (Centro Internacional de Métodos Numéricos en Ingeniería) para simular mediante el método de los Elementos Finitos procesos de fabricación de prototipos por estereolitografía. Asimismo, se presentan las instrucciones para la utilización práctica del programa y algunos ejemplos de aplicación.  

  Abstract
  Dentro de todos los procesos denominados “Rapid Prototyping”, se presenta en esta publicación el denominado estereolitografía. Estos procesos cuyo [...]

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• Derivation of the secant stiffness matrix for non linear finite element analysis of solids and trusses

  E. Oñate

  (1994). Research Report, Nº PI49

  
  

  Abstract

  In this paper the general non symmetric parametric form of the incremental secant stiffness matrix for nonlinear analysis of solids using the finite element method is derived. A convenient symmetric expression for a particular value of the parameters is obtained. The geometrically nonlinear formulation is based on a Generalized Lagrangian approach. Detailed expressions of all the relevant matrices involved in the analysis 3D solids are obtained. The possibilities of application of the secant stiffness matrix for nonlinear structural problems including stability, bifurcation and limit load analysis are also discussed. Examples of application are given for the nonlinear analysis of pin joined frames.  

  Abstract
  In this paper the general non symmetric parametric form of the incremental secant stiffness matrix for nonlinear analysis of solids using the finite element method is derived. [...]

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• 3D finite element computations for viscous aerodynamic flows around automobiles

  T. Fischer, J. Canet, O. Fruitos, E. Oñate

  (1994). Research Report, Nº PI50

  
  

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• Petrov-Galerkin methods for the transient advective-diffusive equation with sharp gradients

  S. Idelsohn, J. Heinrich, E. Oñate

  (1994). Research Report, Nº PI51

  
  

  Abstract

  A Petrov–Galerkin formulation based on two different perturbations to the weighting functions is presented. These perturbations stabilize the oscillations that are normally exhibited by the numerical solution of the transient advective–diffusive equation in the vicinity of sharp gradients produced by transient loads and boundary layers. The formulation may be written as a generalization of the Galerkin Least‐Square method.

  Abstract
  A Petrov–Galerkin formulation based on two different perturbations to the weighting functions is presented. These perturbations stabilize the oscillations that are normally [...]

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• Block iterative scheme of the seismic response of base isolated buildings

  A. Barbat, N. Molinares, R. Codina

  (1994). Research Report, Nº PI52

  
  

  Abstract

  Base insolation systems partially uncoupled a structure from the seismic ground motion by means of specially designed, replaceable, devices inserted between the structure and its foundation. These devices are capable of absorbing part of the energy induced by earthquake [1-4] and drastically reduce the seismic action transmitted to the structure. A numerical simulation of their effect on the seismic response of structures requires algorithms capable of analyzing structures with both elastomeric (hysteric) bearing and sliding (frictional) bearings [5,6]. Different numerical schemes for solving the equations of motion have been proposed. The most often used numerical procedures are monolithic step-by-step integration schemes, that is, schemes that lead to algebraic systems of equations involving both the degrees of freedom corresponding to the structure and the foundation. On the other hand, there is the possibility of coupling these two sets of unknowns interactively, rather than by solving the full algebraic system. These iterative methods, when combined with the proper linearization of the nonlinear terms, yield block iterative schemes as those considered in this paper. Their capability for solving other problems, such as the dam-fluid interaction or the motion of thermally driven flows, is described in reference [7]. In this paper, the application of schemes of this type in computing the seismic response of building structures with base isolation is considered, being this a problem of two systems coupled across their boundary conditions. The corresponding equations of motion are first written and details concerning the possibilities of numerical computation of the seismic response are given. Different manners of formulating block iterative schemes are described in a generic form and are then applied to the studied case. Their effectiveness in then explored on the basis of a complete numerical example.

  Abstract
  Base insolation systems partially uncoupled a structure from the seismic ground motion by means of specially designed, replaceable, devices inserted between the structure [...]

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• A review of some finite element families for thick and thin plate and shell analysis

  E. Oñate

  (1994). Research Report, Nº PI53

  
  

  Abstract

  This paper describes a number of triangular and quadrilateral plate and Shell elements derived via Reissner-Mindlin plate theory and mixed interpolation. It shown how by introducing the adequate constrains the original thick plate element evolve into DK forms adequate for this situations only. This evolution process allows to revisite some classical elements like the Morley triangle and also to derive simple plate and shell triangles and quadrilates with only translational degrees of freedom as nodal variables.

  Abstract
  This paper describes a number of triangular and quadrilateral plate and Shell elements derived via Reissner-Mindlin plate theory and mixed interpolation. It shown how by introducing [...]

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• Seismic evaluation of concrete dams via continuum damage models

  M. Cervera, J. Oliver, M. Galindo

  (1994). Research Report, Nº PI54

  
  

  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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• Random vibration of systems subjected to support motion

  A. Barbat

  (1994). Research Report, Nº PI55

  
  

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