http://hdl.handle.net/2117/6471 2013-05-24T05:14:44Z http://hdl.handle.net/2117/19298 Title: A phase-field fracture model of ferroelectric materials under electro-mechanical loading Authors: Abdollahi Hosnijeh, Amir; Arias Vicente, Irene Abstract: A phase-field model is proposed for the coupled simulation of microstructure and fracture evolution in ferroelectric materials. The model is based on energetic phase-field approaches for brittle fracture and ferroelectric domain formation and evolution. The variational nature of these approaches makes their coupling very natural. However the main challenge is to encode the electro-mechanical conditions of the sharp crack faces into the phase-field framework since the crack in this model is smeared and represented by an internal layer. We develope the model for different crack face boundary conditions. Simulations show the microstructure induced by the presence of the crack. Interactions between the microstructure and the crack are investigated under different electro-mechanical loadings. 2013-05-16T12:58:07Z http://hdl.handle.net/2117/17689 Title: Numerical tool for modeling steel fiber reinforced concrete Authors: Molins i Borrell, Climent; Pros Parés, Alba; Díez, Pedro Abstract: Steel Fiber Reinforced Concrete (SFRC) allows overcoming brittleness and weakness in tension, the main drawbacks of plain concrete. The goal of the present presentation is to present an ad-hoc numerical strategy to account for the contribution of the fibers in the simulation of the mechanical response of SFRC. In the model presented, the individual fibers immersed in the concrete bulk are accounted for in their actual location and orientation. The selected approach is based on the ideas introduced in the Immersed Boundary (IB) methods. These methods were developed to account for 1D (or 2D) solids immersed in 2D (or 3D) fluids. Here, the concrete bulk is playing the role of the fluid and the cloud of steel fibers is acting as the immerse boundary (that is a 1D structure in a 2D or 3D continuous). Thus, the philosophy of the IB methodology is used to couple the behavior of the two systems, the concrete bulk and the fiber cloud, precluding the need of matching finite element meshes. In the proposed approach, the meshes of the concrete bulk and fiber cloud are independent and the models are coupled imposing displacement compatibility and equilibrium of the two systems. The concrete bulk is modeled using any nonlinear model. The constitutive model for the fibers is designed to account for the complex interaction between fibers and concrete. The fiber models are based on previous investigations describing the concrete-fiber interaction and its dependence on the factors identified to be relevant: shape of the fiber (straight or hooked) and angle between the fiber and the crack plane. 3D examples with fibers distributed and oriented randomly are reproduced using the proposed approach. 2013-02-12T18:16:39Z http://hdl.handle.net/2117/17479 Title: A new procedure to smooth and untangle meshes on parameterized surfaces Authors: Gargallo Peiró, Abel; Roca Navarro, Xevi; Sarrate Ramos, Josep Abstract: We present a technique to extend any distortion (quality) measure for planar meshes to meshes on parameterized surfaces. The resulting distortion (quality) measure is expressed in terms of the parametric coordinates of the nodes. This extended distortion (quality) measure can be used to check the quality and validity of both triangle and quadrilateral surface meshes. We also apply it to simultaneously smooth and untangle surface meshes by minimizing the extended distortion measure. The minimization is performed in terms of the parametric coordinates of the nodes and therefore, the nodes always lie on the surface. Finally, we include several examples to illustrate the applicability of the proposed technique. Specifically, we extend several Jacobian-based measures, and we us them to smooth and untangle triangle and quadrilateral meshes on CAD surfaces. 2013-01-22T13:20:16Z http://hdl.handle.net/2117/17033 Title: A geometric bridge between regularised damage and energetically equivalent cracks Authors: Tamayo Mas, Elena; Rodríguez Ferran, Antonio Abstract: In order to achieve a better characterisation of a whole failure process, models which combine damage and fracture mechanics have recently been proposed. Here, a new combined methodology is presented: in order to describe damage inception and its diffuse propagation, a gradient-enhanced continuum model based on smoothed displacements is used, which is coupled to a discontinuous one to describe the final stages of the process. Special emphasis should be placed on the difficulties concerning the transition between continuous damage growth and fracture. On the one hand, and in order to conserve the energy dissipation through the change of models, an appropriate cohesive law must be defined. In this paper, the proposed technique to define this law is explained. On the other hand, the direction of the crack path should be determined. Here, a new strategy is proposed: the discontinuity is propagated following the direction dictated by the medial axis of the damaged domain. That is, a geometric tool, widely used in the computer graphics field, is used here to locate cracks. 2012-11-27T13:23:46Z http://hdl.handle.net/2117/17032 Title: Computable bounds of linear functional outputs in linear visco- elastodynamics Authors: Verdugo Rojano, Francesc; Díez, Pedro Abstract: This work presents a new technique yielding computable bounds of quantities of interest in the framework of linear visco-elastodynamics. A novel expression for the error representation is introduced, alternative to the previous ones using the Cauchy-Schwarz inequality. The proposed formulation utilizes symmetrized forms of the error equations to derive error bounds in terms of energy error measures. The practical implementation of the method is based on constructing admissible fields for both the original problem and the adjoint problem associated with the quantity of interest. Here, the flux-free technique is considered to compute the admissible stress fields. The proposed methodology yields estimates with better quality than the ones based on the Cauchy-Schwarz inequality. In the studied examples the bound gaps obtained are approximately halved, that is the estimated intervals of confidence are reduced. 2012-11-27T13:17:58Z http://hdl.handle.net/2117/17031 Title: Optimally convergent high-order X-FEM for problems with voids and inclusions Authors: Sala Lardies, Esther; Fernandez Mendez, Sonia; Huerta, Antonio Abstract: Solution of multiphase problems shows discontinuities across the material interfaces, which are usually weak. Using the eXtended Finite Element Method (X-FEM), these problems can be solved even for meshes that do not match the geometry. The basic idea is to enrich the interpolation space by means of a ridge function that is able to reproduce the discontinuity inside the elements. This approach yields excellent results for linear elements, but fails to be optimal if high-order interpolations are used. In this work, we propose a formulation that ensures optimal convergence rates for bimaterial problems. The key idea is to enrich the interpolation using a Heaviside function that allows the solution to represent polynomials on both sides of the interface and, provided the interface is accurately approximated, it yields optimal convergence rates. Although the interpolation is discontinuous, the desired continuity of the solution is imposed modifying the weak form. Moreover, in order to ensure optimal convergence, an accurate description of the interface (which also defines an integration rule for the elements cut by the interface) is needed. Here, we comment on different options that have been successfully used to integrate high-order X-FEM elements, and describe a general algorithm based on approximating the interface by piecewise polynomials of the same degree that the interpolation functions. 2012-11-27T13:02:14Z http://hdl.handle.net/2117/16963 Title: A multi-mesh adaptive scheme for air quality modeling with the finite element method Authors: Monforte, Lluis; Pérez Foguet, Agustí Abstract: A multi-mesh adaptive scheme for convection-diffusion-reaction problems is presented. The proposal is applied to air quality modeling, especifically to the simulation of a pollutant punctual emissions. The performance of the proposal is analyzed with different nonlinear reaction models, including the photochemical model CB05 implmented within the Comunity Multiscale Air Quality model, which involves sixty-two species and very different characteristic reaction times. The problem is solved with splitting of transport and reaction processes. This allows to discretize the species in distinct computational meshes, adapted to the distribution of the error indicator of each case. A common reference mesh is used for all species and during all problem evolution. A remeshing technique based on imposing the volume of new elements is used to define and update the computational meshes. An error indicator well suited for problems involving large variation of the unknowns is used. A single-mesh strategy, with remeshing adapted to the most demanding specie in each part of the domain, is used for comparison. The results of the examples presented show that the accuracy of single and multi-mesh strategies are similar. Instead, computational cost of multi-mesh is lower than single-mesh in most cases. Reduction increases with the number of species and the number of plumes. An example of a punctual emissor in a three-dimensional domain, with realistic values of CB05 components, is presented. 2012-11-20T09:39:30Z http://hdl.handle.net/2117/16867 Title: Simulation of damage on laminates Authors: Curiel Sosa, José Luis; Muñoz Romero, José; Pinho, S.T.; Li, Q.; Beg, O.A. Abstract: An experimental study on controlled faulty perturbed flexible structures is developed using an active mass damper actuator, where the flexible structure is subject to external perturbation and sensor faults. To attenuate the disturbance effects on the flexible structure, we present three robust controllers: one is based on dynamics LMI control technique design, other is an improvement of the first one but adding a chattering term, and the last one is the second one but with the chattering gain adjusted dynamically. According to experiments, where a flexible two level building with active mass damper (by Quanser), external perturbation, and sensor faults, evidence that the proposed LMI controller with chattering term where its gain is dynamically adjusted presents the best closed-loop system behavior. 2012-11-08T10:10:58Z http://hdl.handle.net/2117/16770 Title: An SEA-like model for double walls filled with absorbing materials Authors: Díaz Cereceda, Cristina; Poblet-Puig, Jordi; Rodríguez Ferran, Antonio Abstract: Modelling absorbing materials with statistical energy analysis (SEA) is an open issue. They are neither reverberant subsystems nor conservative couplings. The absorbing material layers located inside the cavities of double walls should be treated as non-conservative couplings between the wall leaves. However, the standard SEA formulation cannot take into account non-conservative couplings. In this work, an equivalent circuit analogy is used to deduce how to introduce these couplings in an SEA-like system. Besides, a technique for obtaining the SEA-like factors associated to a double wall filled with absorbing material is presented. These factors are computed from numerical simulations of the vibroacoustic leaf-absorbing material-leaf system and applied for solving larger problems with SEA. 2012-10-22T08:57:24Z http://hdl.handle.net/2117/16769 Title: A numerical technique for obtaining SEA coupling loss factors in double walls Authors: Díaz Cereceda, Cristina; Poblet-Puig, Jordi; Rodríguez Ferran, Antonio Abstract: Double walls usually consist of two leaves of material connected by steel studs. Aside from improving the structural performance, studs create a vibration transmission path which connects the two leaves. There is interest in reliable models of the acoustic performance of these structures, for the frequency range required in regulations. Statistical energy analysis allows reaching high frequencies with a low computational cost. However, the best SEA approach for modelling double walls is not clear in the literature. The cavity may be considered as a subsystem or treated as a connecting device between the two leaves. The effect of the cavity is also often neglected compared to the coupling provided by the studs. In this work, numerical techniques are used to evaluate these approaches and to define a combined deterministic–statistical approach that accounts for all the transmission phenomena. 2012-10-22T08:45:50Z http://hdl.handle.net/2117/16115 Title: Sound transmission through double walls: statistical and deterministic models Authors: Díaz Cereceda, Cristina; Poblet-Puig, Jordi; Rodríguez Ferran, Antonio Abstract: Double walls are increasingly used in construction. Due to this, there is interest in reliable models of their sound insulation for the frequency range reguired in regulations (50-5000Hz). These models can be either statistical or deterministic. In this work, the finite layer method (FLM) is presented as a numerical technique for solving the problem in a deterministic way. it is used for discretising the Helmholtz equation in the cavity and combines a finite element method (FEM) discretisation in the direction perpendicular to the wall with trigonometric functions in the two in plane directions. The FLM exploits the simple geometry of the double wall and accounts for all its boundary and interface conditions with a reasonable computational cost. The statistical energy analysis (SEA) is a more suitable framework of analysis for vibroacoustic problems in large domains such as buildings. However, the best SEA approach for modelling double walls is not clear in the literature. The cavity is considered as a subsystem or treated as a connecting device between the two leaves depending on the autor. The finite layer method is a used to evaluate the performance of these two approaches, concluding that both considerations have to be taken into account together to reproduce the real behaviour. Finally, the FLM is used to define a combined deterministic energy based approach to deal with this kind of problems. 2012-06-21T09:56:14Z http://hdl.handle.net/2117/15917 Title: Enforcing interface flux continuity in enhanced XFEM: stability analysis Authors: Díez, Pedro; Zlotnik, Sergio; Cottereau, Régis Abstract: XFEM is found to be an efficient approach for solving multiphase problems. 2012-05-24T10:56:17Z http://hdl.handle.net/2117/15916 Title: Are high-order and hybridizable discontinuous galerkin methods competitive Authors: Huerta, Antonio; Roca Navarro, Francisco Javier; Angeloski, Aleksander; Peraire Guitart, Jaume Abstract: The talk covered several issues motivated by a practical engineering wave propagation problem: real-time evaluation of wave agitation in harbors. The first part, presented the application of a reduced order model in the framework of a Helmholtz equation with non-constant coefficients in an unbounded domain. This problem requires large numbers of degrees of freedom (ndof) because relatively high frequencies with small (compared with the domain size) geometric features must be considered. 2012-05-24T10:52:06Z http://hdl.handle.net/2117/15891 Title: Hybridizable discontinuous Galerkin p-adaptivity for wave problems Authors: Giorgiani, Giorgio; Fernandez Mendez, Sonia; Huerta, Antonio Abstract: A p-adaptive Hybridizable Discontinuous Galerkin (HDG) method is presented for the solution of wave problems. The HDG method allows to drastically reduce the coupled degrees of freedom of the computation seeking for an approximation of the solution that is defined only on the edges of the mesh. The particular choice of the numerical fluxes driven by the hybridization technique allows to obtain an optimally converging solution not only for the primal unknown but also for its derivative. This characteristic allows to perform a post-process of the solution that provides a super-convergent solution. The discontinuous character of the solution provides an optimal framework for a p-adaptive technique. The post-processed solution of the HDG method is used to construct a cheap and reliable error estimator that drives an element by element modification of the approximation degree. The proposed p-adaptive HDG method is compared with high-order CG computation with static condensation of the interior nodes. A challenging problem is considered for the comparison: a non-homogeneous scattering problem in an open domain. 2012-05-18T08:36:49Z http://hdl.handle.net/2117/15806 Title: Efficiency and accuracy of high-order computations and reduced order modelling in coastal engineering wave propagation problems Authors: Modesto Galende, David; Giorgiani, Giorgio; Zlotnik, Sergio; Huerta, Antonio Abstract: Several numerical issues have to be considered when solving wave propagation problems, between which there are the artificial boundary conditions, the small geometrical features that can be influential or the variable coefficients. Apart from them, two issues are mainly addressed and discussed. Firstly, low order elements need very high wave resolution for capturing the solution in the area of interest, leading to extremely dense meshes. High-order finite elements are proposed to be an efficient and accurate solution for solving the problem. Secondly, the very large number of test cases. When designing harbour models, a huge number of incident waves, in term of wavelengths and directions, have to be studied. The excessive computational cost to carry out all the possible direct problems prevents the whole data evaluation, inducing the lost of important information. Reduced order models may be an alternative if they are computable, efficient and accurate. The applicability of Proper Generalized Decomposition (PGD) is exploited. Unlike previous PGD contributions, which deal with elliptic problems, the present work is focused on a more challenging scenario for the separable representation due to the loss of the elliptic behaviour. The proposed PGD involves a separable representation of the unknown reflected wave in space, wave number and angle of incidence. Such decomposition appears to be really interesting for practical purpose, where goal-oriented results are critical for a wide range of frequencies and incident waves. Moreover, when accuracy and efficiency are of concern, the number of terms in the reduced model are determined by means of an error estimation based on the dual formulation of the problem. 2012-05-09T13:59:06Z