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Adaptive finite element simulation of incompressible flows by hybrid continuous-discontinuous Galerkin formulations

Tue, 16 Apr 2013 12:27:53 GMT

Title: Adaptive finite element simulation of incompressible flows by hybrid continuous-discontinuous Galerkin formulations Authors: Badia Rodríguez, Santiago I.; Baiges Aznar, Joan Abstract: In this work we design hybrid continuous-discontinuous finite element spaces that permit discontinuities on non-matching element interfaces of non-conforming meshes. Then, we develop an equal-order stabilized finite element formulation for incompressible flows over these hybrid spaces, which combines the element interior stabilization of SUPGtype continuous Galerkin formulations and the jump stabilization of discontinuous Galerkin formulations. Optimal stability and convergence results are obtained. For the adaptive setting, we use an standard error estimator and marking strategy. Numerical experiments show the optimal accuracy of the hybrid algorithm both for uniformly and adaptively refined non-conforming meshes. The outcome of this work is a finite element formulation that can naturally be used on nonconforming meshes, as discontinuous Galerkin formulations, while keeping the much lower CPU cost of continuous Galerkin formulations.

Un caso práctico de meta-evaluación docente: el manual de evaluación de la Universidad Politécnica de Cataluña

Mon, 15 Apr 2013 15:46:10 GMT

Title: Un caso práctico de meta-evaluación docente: el manual de evaluación de la Universidad Politécnica de Cataluña Authors: García-Berro Montilla, Enrique; de la Vega, Ricardo; Gemma, Amblàs; Martínez, Erica; Laura, Campeny; Bugeda Castelltort, Gabriel; Roca, Santiago Abstract: La Universidad Politécnica de Cataluña ha sido pionera en la introducción de un modelo de eva- luación docente plenamente adaptado a las exigencias del Espacio Europeo de Enseñanza Supe- rior. Además, su sistema de evaluación de la actividad docente del profesorado ha sido homologa- do por la AQU y ANECA. Dicho modelo de evaluación docente se basa en las más recientes di- rectrices europeas y tiene como fundamento diversos indicadores indirectos. Este modelo se ha em- pleado para evaluar la docencia del profesorado en cinco convocatorias. Durante este periodo de tiempo se ha acumulado una información valiosísima que permite obtener datos agregados no só- lo de la calidad de los docentes sino, también, de diversas características inherentes al proceso de evaluación, así como de la bondad de los indicadores empleados. En este artículo se presentan es- tos datos y se muestra un conjunto de datos agregados que permiten estimar la bondad y fiabilidad del proceso de evaluación, así como su aceptación por el profesorado evaluado.

An orthotropic damage model for the analysis of masonry structures

Tue, 05 Mar 2013 17:20:17 GMT

Title: An orthotropic damage model for the analysis of masonry structures Authors: Pelà, Luca; Cervera Ruiz, Miguel; Roca Fabregat, Pedro Abstract: This paper presents a numerical model for nonlinear analysis of masonry structural elements based on Continuum Damage Mechanics. The material is described at the macro-level, i.e. it is modeled as a homogeneous orthotropic continuum. The orthotropic behavior is simulated by means of an original methodology, resulting from the concept of mapped tensors from the anisotropic field to an auxiliary workspace. The application of this idea to strain-based Continuum Damage Models is innovative and leads to several computational benefits. The suitability of the model for representing the behavior of different types of brickwork masonry is shown via the simulation of experimental tests.

Comportamiento sismico de los edificios de Lorca

Fri, 08 Feb 2013 13:59:10 GMT

Title: Comportamiento sismico de los edificios de Lorca Authors: Carreño Tibaduiza, Martha Liliana; Lantada Zarzosa, Maria de Las Nieves; Irizarry, Janira; Valcarcel, Jairo Andrés; Barbat Barbat, Horia Alejandro; Goula Suriñach, Xavier Abstract: Después de ocurrido el terremoto de Lorca, el 11 de mayo de 2011, el Institut Geològic de Catalunya (IGC), la Universidad Politécnica de Cataluña (UPC) y la Asociación Española de Ingeniería Sísmica (AEIS) organizaron, junto con las asociaciones de ingeniería sísmica francesa (AFPS) y portuguesa (SPES), una visita técnica con el objeto de realizar observaciones que permitieran calibrar, verificar y validar los métodos utilizados en las evaluaciones de riesgo sísmico en zonas urbanas. Este artículo resume los aspectos más destacados en cuanto a la observación de la vulnerabilidad de edificios de vivienda, así como de edificios de especial importancia como son hospitales y escuelas. After the earthquake of Lorca, May 11, 2011, the Geological Institute of Catalonia (IGC), the Technical University of Catalonia (UPC) and the Spanish Association for Earthquake Engineering (AEIS) organized a technical visit in order to compile information that allow to calibrate, to verify and to validate the methods used in seismic risk assessments in urban areas. This article summarizes the highlights regarding the vulnerability of residential buildings and buildings of special importance such as hospitals and schools.

Unconditionally stable operator splitting algorithms for the incompressible magnetohydrodynamics (MHD) system discretized by a stabilized finite element formulation based on projections

Fri, 11 Jan 2013 19:35:58 GMT

Title: Unconditionally stable operator splitting algorithms for the incompressible magnetohydrodynamics (MHD) system discretized by a stabilized finite element formulation based on projections Authors: Badia Rodríguez, Santiago I.; Planas Badenas, Ramon; Gutierrez Santacreu, Juan Vicente Abstract: In this article we propose different splitting procedures for the transient incompressible MHD system that are unconditionally stable. We consider two levels of splitting, on one side we perform the segregation of the fluid pressure and magnetic pseudo-pressure from the vectorial fields computation. At the second level, the fluid velocity and induction fields are also decoupled. This way, we transform a fully coupled indefinite multi-physics system into a set of smaller definite ones, clearly reducing the CPU cost.With regard to the finite element approximation, we stick to an unconditionally convergent stabilized finite element formulation, since it introduces convection stabilization, allows to circumvent inf-sup conditions (clearly simplifying implementation issues) and is able to capture nonsmooth solutions of the magnetic sub-problem. However, residual-based finite element formulations are not suitable for segregation, since they lose the skew-symmetry of the off-diagonal blocks. Therefore, in this work we have proposed a novel term-by-term stabilization of the MHD system based on projections that is still unconditionally convergent.

Estudio numérico-experimental de la interfaz hormigón-epoxi-FRP para una estructura reforzada sometida a doble corte

Thu, 10 Jan 2013 15:11:45 GMT

Title: Estudio numérico-experimental de la interfaz hormigón-epoxi-FRP para una estructura reforzada sometida a doble corte Authors: Molina, Maritzabel; Cruz Solís, Juan José; Oller Martínez, Sergio Horacio; Barbat Barbat, Horia Alejandro; Gil Espert, Lluís

An inverse approach for the mechanical characterisation of vascular tissues via a generalised rule of mixtures

Fri, 28 Dec 2012 09:16:24 GMT

Title: An inverse approach for the mechanical characterisation of vascular tissues via a generalised rule of mixtures Authors: Bellomo, Facundo; Oller Martínez, Sergio Horacio; Nallim, Liz Abstract: Mechanical factors such as stresses and strains play a major role in the growth and remodelling of soft biological tissues. The main constituents of tissue undergo different processes reacting to mechanical stimulus. Thereby, the characterisation of growth and remodelling requires an accurate estimation of the stresses and strains of their main components. Many soft tissues can be considered as composite materials and can be analysed using an appropriate rule of mixtures. Particularly, arterial tissue can be modelled as an isotropic soft matrix reinforced with preferentially oriented collagen fibres. An inverse approach to obtain the mechanical characterisation of each main component is proposed in this work. The procedure is based on a rule of mixtures raised in a finite deformation framework and generalised to include kinematics and compatibility equations for serial–parallel behaviour. This methodology allows obtaining the stress–strain relationship of the components fitting experimental data.

On an unconditionally convergent stabilized finite element approximation of resistive magnetohydrodynamics

Fri, 28 Dec 2012 07:41:49 GMT

Title: On an unconditionally convergent stabilized finite element approximation of resistive magnetohydrodynamics Authors: Badia Rodríguez, Santiago I.; Codina, Ramon; Planas Badenas, Ramon Abstract: In this work, we propose a new stabilized finite element formulation for the approximation of the resistive magnetohydrodynamics equations. The novelty of this formulation is the fact that it always converges to the physical solution, even for singular ones. A detailed set of numerical experiments have been performed in order to validate our approach.

Finite point method to solve shallow water equations

Thu, 13 Dec 2012 16:54:30 GMT

Title: Finite point method to solve shallow water equations Authors: Ortega, Enrique; Oñate Ibáñez de Navarra, Eugenio; Idelsohn Barg, Sergio Rodolfo; Buachart, Chinapat Abstract: An adaptive Finite Point Method (FPM) for solving shallow water problems is presented. The numerical methodology we propose, which is based on weighted-least squares approximations on clouds of points, adopts an upwind-biased discretization for dealing with the convective terms in the governing equations. The viscous and source terms are discretized in a pointwise manner and the semi-discrete equations are integrated explicitly in time by means of a multi-stage scheme. Moreover, with the aim of exploiting meshless capabilities, an adaptive h-refinement technique is coupled to the described flow solver. The success of this approach in solving typical shallow water flows is illustrated by means of several numerical examples and special emphasis is placed on the adaptive technique performance. This has been assessed by carrying out a numerical simulation of the 26th December 2004 Indian Ocean tsunami with highly encouraging results. Overall, the adaptive FPM is presented as an accurate enough, cost-effective tool for solving practical shallow water problems.

Viscoelasticity and damage model for creep behaviour of historical masonry structures

Tue, 04 Dec 2012 14:28:33 GMT

Title: Viscoelasticity and damage model for creep behaviour of historical masonry structures Authors: Roca Fabregat, Pedro; Cervera Ruiz, Miguel; Pelà, Luca; Clemente, Roberto; Chiumenti, Michèle Abstract: This paper presents a continuum model for the simulation of the viscous effects and the long-term damage ac-cumulation in masonry structures. The rheological model is based on a generalized Maxwell chain representation with a constitutive law utilizing a limited number of internal variables. Thanks to its computational efficiency, this approach is suitable for the analysis of large and complex structures. In the paper, the viscous and damage models are presented and their coupling is discussed. The FE simulation of the construction process of the representative bay of Mallorca Cathedral is presented, together with the analysis of the long-term effects. The parameters of the model are tentatively calibrated on the basis of the time-dependent viscous deformations detected during the cathedral monitoring.

On stabilized finite element methods based on the Scott-Zhang projector: circumventing the inf-sup condition for the Stokes problem

Wed, 14 Nov 2012 17:36:27 GMT

Title: On stabilized finite element methods based on the Scott-Zhang projector: circumventing the inf-sup condition for the Stokes problem Authors: Badia Rodríguez, Santiago I. Abstract: In this work we propose a stabilized nite element method that permits us to circumvent discrete inf-sup conditions, e.g. allowing equal order interpolation. The type of method we propose belongs to the family of symmetric stabilization techniques, which are based on the introduction of additional terms that penalize the di erence between some quantities, i.e. the pressure gradient in the Stokes problem, and their nite element projections. The key feature of the formulation we propose is the de nition of the projection to be used, a non-standard Scott-Zhang projector that is well-de ned for L1() functions. The resulting method has some appealing features: the projector is local and nested meshes or enriched spaces are not required.

Continuum FE models for the analysis of Mallorca Cathedral

Mon, 08 Oct 2012 12:30:49 GMT

Title: Continuum FE models for the analysis of Mallorca Cathedral Authors: Roca Fabregat, Pedro; Cervera Ruiz, Miguel; Pelà, Luca; Clemente, Roberto; Chiumenti, Michèle Abstract: From the theoretical point of view, systems composed by masonry arches or vaults would require, during construction, the simultaneous activation of all structural elements in order to reach the optimum balance of thrusts. This is not obviously the case of complex ancient masonry constructions, whose long and gradual building process may have contributed to their deformed condition and even to damage. In this paper, the possible influence of the construction process as well as that of later long-term deformation on the final condition of the building is investigated in the case of a complex and large historical structure, namely Mallorca Cathedral. A FE code has been specifically developed for the present study. The code is able to account for construction processes through sequential-evolutionary analyses, with the description of masonry mechanical damage and long-term deformation. The representative bay of the cathedral is analyzed taking into account different construction phases, as emerged from historical research. The response of such substructure to transverse earthquake equivalent forces is then investigated. In this case, the damage model is improved with a local crack-tracking algorithm. This numerical strategy models the tensile damage as distinct cracks, leading to a better prediction of realistic collapsing mechanisms.

Numerical simulations of negatively buoyant jets in an immiscible fluid using the Particle Finite Elemept Method

Wed, 11 Jul 2012 12:08:55 GMT

Title: Numerical simulations of negatively buoyant jets in an immiscible fluid using the Particle Finite Elemept Method Authors: Mier Torrecilla, Mónica de; Geyer Traver, Adelina; Phillips, Jeremy C.; Idelsohn Barg, Sergio Rodolfo; Oñate Ibáñez de Navarra, Eugenio Abstract: Negatively buoyant jets consist in a dense fluid injected vertically upward into a lighter ambient fluid. The numerical simulation of this kind of buoyancy-driven flows is challenging as it involves multiple fluids with different physical properties. In the case of immiscible fluids, it requires, in addition, to track the motion of the interface between fluids and accurately represent the discontinuities of the flow variables. In this paper, we investigate numerically the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid using the Particle Finite Element Method and compare the two-dimensional numerical results with experiments on the injection of a jet of dyed water through a nozzle in the base of a cylindrical tank containing rapeseed oil. In both simulations and experiments, the fountain inlet flow velocity and nozzle diameter have been varied to Cover a wide range of Froude Fr and Reynolds Re numbers (0.1 < Fr < 30, 8 < Re < 1350), reproducing both weak and strong laminar fountains. The flow behaviors observed for the different numerical simulations fit in the regime map based on the Re and Fr values of the experiments, and the maximum fountain height is in good agreement with the experimental observations, suggesting that particle finite element method is a useful tool for the study of immiscible two-fluid systems.

Constitutive and geometric nonlinear models for the seismic analysis of RC structures with energy dissipators

Fri, 11 May 2012 18:28:54 GMT

Title: Constitutive and geometric nonlinear models for the seismic analysis of RC structures with energy dissipators Authors: Mata, P.; Barbat Barbat, Horia Alejandro; Oller Martínez, Sergio Horacio; Boroschek Krauskopf, Rubén Luis Abstract: Nowadays, the use of energy dissipating devices to improve the seismic response of RC structures constitutes a mature branch of the innovative procedures in earthquake engineering. However, even though the benefits derived from this technique are well known and widely accepted, the numerical methods for the simulation of the nonlinear seismic response of RC structures with passive control devices is a field in which new developments are continuously preformed both in computational mechanics and earthquake engineering. In this work, a state of the art of the advanced models for the numerical simulation of the nonlinear dynamic response of RC structures with passive energy dissipating devices subjected to seismic loading is made. The most commonly used passive energy dissipating devices are described, together with their dissipative mechanisms as well as with the numerical procedures used in modeling RC structures provided with such devices. The most important approaches for the formulation of beam models for RC structures are reviewed, with emphasis on the theory and numerics of formulations that consider both geometric and constitutive sources on nonlinearity. In the same manner, a more complete treatment is given to the constitutive nonlinearity in the context of fiber-like approaches including the corresponding cross sectional analysis. Special attention is paid to the use of damage indices able of estimating the remaining load carrying capacity of structures after a seismic action. Finally, nonlinear constitutive and geometric formulations for RC beam elements are examined, together with energy dissipating devices formulated as simpler beams with adequate constitutive laws. Numerical examples allow to illustrate the capacities of the presented formulations.

A nodal-based finite element approximation of the Maxwell problem suitable for singular solutions

Wed, 18 Apr 2012 17:33:06 GMT

Title: A nodal-based finite element approximation of the Maxwell problem suitable for singular solutions Authors: Badia Rodríguez, Santiago I.; Codina, Ramon Abstract: A new mixed finite element approximation of Maxwell’s problem is proposed, its main features being that it is based on a novel augmented formulation of the continuous problem and the introduction of a mesh dependent stabilizing term, which yields a very weak control on the divergence of the unknown. The method is shown to be stable and convergent in the natural H(curl; ) norm for this unknown. In particular, convergence also applies to singular solutions, for which classical nodal based interpolations are known to suffer from spurious convergence upon mesh refinement.