http://hdl.handle.net/2117/2072 2013-05-22T18:50:45Z 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/2117/18648 Title: Unravelling the linkages between water, sanitation, hygiene and rural poverty: The WASH poverty index Authors: Giné Garriga, Ricard; Pérez Foguet, Agustí Abstract: Many studies have reported the effect of water supply, sanitation and hygiene (WASH) in improving health and ultimately alleviating poverty. Current coverage estimates show however that a large proportion of people in the world still do not have access to a simple pit latrine or a source of safe drinking water, and this situation worsens in rural areas. To help end these appalling figures, much effort has gone into the development of policy instruments which support decision-making, i.e. planning, targeting and prioritization. Indices and indicators are increasingly recognised as powerful tools for such purposes. This paper details the theoretical framework and development of a multidimensional, WASH-focused, thematic indicator: the WASH Poverty Index (WASH PI). It describes the methodology in index construction and disseminates achieved results in a variety of forms to promote the utility of the tool for the integrated analysis of WASH and poverty linkages. The article uses Kenya as initial case study to illustrate the application of the index. Overall, WASH PI helps identify priority areas and guide appropriate action and policy-making towards improved service delivery. 2013-04-05T12:30:32Z http://hdl.handle.net/2117/18442 Title: Formation of tip-vortices on triangular prismatic-shaped cliffs. Part 2: A computational fluid dynamics study Authors: Villardi de Montlaur, Adeline de; Cochard, S.; Fletcher, D.F. Abstract: The flow over triangular-shaped cliffs is studied through Computational Fluid Dynamics simulations, using the RANS approach closed with the SST turbulence model. The formation of tip-vortices on the sides of the cliff is studied, taking into account the influence of the cliff geometry and the incoming wind. CFD results are compared with experimental data on 2D planes located above the cliff. Good agreement between the two is obtained once small experimental deviations from the nominal cliff geometry are accounted for in the simulations. In addition, 3D results, such as visualization of the vortices, allow a better understanding of the complex flow over such geometry to be achieved. 2013-03-20T13:03:06Z http://hdl.handle.net/2117/18440 Title: Formation of tip-vortices on triangular prismatic-shaped cliffs. Part 1: A wind tunnel study Authors: Cochard, S.; Letchford, C.W.; Earl, T. A.; Villardi de Montlaur, Adeline de Abstract: Speed-up over topography has long been recognized as significant for structural design and wind energy applications. Here wind flow over cliffs that have a sawtooth plan are studied for speed-up effects under different wind directions. The study undertook PIV measurements to document the mean and turbulence changes in three dimensions for simulated atmospheric boundary layer flow in the University of Sydney BLWT. As the flow approaches the cliffs, it accelerates and moves up to pass the obstruction and generates two strong vortices on the top surface of the cliff. Small changes in wind direction not only lead to significantly different speed-up ratios, but also influence the location of the vortices and the level of turbulence. The complexity of the flow field is revealed in this unique three-dimensional study. 2013-03-20T12:50:01Z http://hdl.handle.net/2117/18175 Title: A truss element for modelling reversible softening in living tissues Authors: Muñoz Romero, José; Conte, Vito; Asadipour, Nina; Miodownik, M. Abstract: We resort to non-linear viscoelasticity to develop a truss element able to model reversible softening in lung epithelial tissues undergoing transient stretch. Such a Maxwell truss element is built by resorting to a three-noded element whose mid-node is kinematically constrained to remain on the line connecting the end-nodes. The whole mechanical system undergoes an additive decomposition of the strains along the truss direction where the total contribution of the mid-node is accounted for by using a null-space projection and static condensation techniques. Assembling of such line-elements in 3D networks allows us to model extended regions of living tissues as well as their anisotropies. 2013-03-11T13:35:34Z http://hdl.handle.net/2117/18030 Title: Shape dynamics, lipid hydrodynamics, and the complex viscoelasticty of bilayer membranes Authors: Rahimi Lenji, Mohammad; Arroyo Balaguer, Marino Abstract: Biological membranes are continuously brought out of equilibrium, as they shape organelles, package and transport cargo, or respond to external actions. Even the dynamics of plain lipid membranes in experimental model systems are very complex due to the tight interplay between the bilayer architecture, the shape dynamics, and the rearrangement of the lipid molecules.We formulate and numerically implement a continuum model of the shape dynamics and lipid hydrodynamics, which describes the bilayer by its midsurface and by a lipid density field for each monolayer. The viscoelastic response of bilayers is determined by the stretching and curvature elasticity, and by the inter-monolayer friction and the membrane interfacial shear viscosity. While the bilayer equilibria are well understood theoretically, dynamical calculations have relied on simplified continuum approaches of uncertain transferability, or on molecular simulations reaching very limited length and time scales. Our approach incorporates the main physics, is fully nonlinear, does not assume predefined shapes, and can access a wide range of time and length scales. We validate it with the well understood tether extension. We investigate the tubular lipid transport between cells, the dynamics of bud absorption by a planar membrane, and the fate of a localized lipid density asymmetry in vesicles. These axisymmetric examples bear biological relevance and highlight the diversity of dynamical regimes that bilayers can experience. 2013-03-01T10:50:28Z 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/2117/17588 Title: Finite element simulation of a local scale Air Quality Model over complex terrain Authors: Oliver Serra, Albert; Montero, Gustavo; Montenegro, Rafael; Rodríguez, Eduardo; Escobar, J.M.; Pérez Foguet, Agustí Abstract: In this paper we propose a finite element method approach for modelling the air quality in a local scale over complex terrain. The area of interest is up to tens of kilometres and it includes pollutant sources. The proposed methodology involves the generation of an adaptive tetrahedral mesh, the computation of an ambient wind field, the inclusion of the plume rise effect in the wind field, and the simulation of transport and reaction of pollutants. We apply our methodology to simulate a fictitious pollution episode in La Palma island (Canary Island, Spain). 2013-02-06T10:00:04Z 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/2117/17433 Title: Shape dynamics, lipid hydrodynamics and the complex viscoelasticty of bilayer membranes Authors: Rahimi Lenji, Mohammad; Arroyo Balaguer, Marino Abstract: Biological membranes are continuously brought out of equilibrium, as they shape organelles, package and transport cargo, or respond to external actions. Even the dynamics of plain lipid membranes in experimental model systems are very complex due to the tight interplay between the bilayer architecture, the shape dynamics, and the rearrangement of the lipid molecules. We formulate and numerically implement a continuum model of the shape dynamics and lipid hydrodynamics, which describes the bilayer by its midsurface and by a lipid density field for each monolayer. The viscoelastic response of bilayers is determined by the stretching and curvature elasticity, and by the inter-monolayer friction and the membrane interfacial shear viscosity. While the bilayer equilibria are well understood theoretically, dynamical calculations have relied on simplified continuum approaches of uncertain transferability, or on molecular simulations reaching very limited length and time scales. Our approach incorporates the main physics, is fully nonlinear, does not assume predefined shapes, and can access a wide range of time and length scales. We validate it with the well understood tether extension. We investigate the tubular lipid transport between cells, the dynamics of bud absorption by a planar membrane, and the fate of a localized lipid density asymmetry in vesicles. These axisymmetric examples bear biological relevance and highlight the diversity of dynamical regimes that bilayers can experience. 2013-01-18T21:37:39Z http://hdl.handle.net/2117/17144 Title: Modal-based prediction of sound transmission through slits and openings between rooms Authors: Poblet-Puig, Jordi; Rodríguez Ferran, Antonio Abstract: The transmission of sound through slits and openings between cuboid-shaped rooms is analysed. A deterministic model that describes the pressure fields inside the rooms in terms of eigenfunctions and uses the Dirichlet-to-Neumann technique in order to reproduce the slit effect is presented. An efficient formulation of the problem is obtained thanks to the splitting of the original domain into three domains: sending room, slit, receiving room. The geometry and boundary conditions of the problem can be modelled in detail like in an element-based numerical technique (such as the finite element method) but with smaller computational costs. The model is compared with numerical solutions, existent models and published experimental data. Afterwards it is used to analyse some aspects such as the influence of slit dimensions, opening position, room properties (dimensions and absorption) that cannot be taken into account with the available models. These usually suppose that the slit or opening connects two unbounded acoustic domains. 2012-12-18T15:42:34Z http://hdl.handle.net/2117/17050 Title: Condiciones de contorno en modelos de gradiente con desplazamientos suavizados Authors: Tamayo Mas, Elena; Rodríguez Ferran, Antonio Abstract: Los modelos de gradiente basados en desplazamientos suavizados son una alternativa a los modelos est´andares para simular num´ericamente el proceso de fallo de materiales. En esta formulaci´on alternativa coexisten los campos de desplazamientos mec´anicos u con los desplazamientos suavizados eu, que se obtienen de solucionar una ecuaci´on de difusi´on-reacci´on. An´alogamente a los modelos de regularizaci´on est´andares, prescribir condiciones de contorno en esta formulaci´on alternativa es un problema abierto. Sin embargo, imponer estas condiciones para el campo de desplazamientos (en lugar de la variable de estado interna) presenta ciertas facilidades. El objetivo de este trabajo es estudiar la influencia de dichas condiciones: ni las condiciones de Dirichlet (prescritas en un principio) ni las condiciones de Neumann homog´eneas (reminiscencia de los modelos de gradiente est´andares) permiten obtener resultados num´ericos realistas; mediante las condiciones de contorno de Neumann no homog´eneas, en cambio, los resultados son f´ısicamente admisibles. Sin embargo, estas condiciones no aseguran conservaci´on de volumen, que es una propiedad interesante en algunos modelos constitutivos. Por este motivo, se proponen unas nuevas condiciones de contorno (condiciones combinadas) que satisfacen las propiedades necesarias para la regu- larizaci´on: (a) reproducibilidad de orden 1 (u = eu si u es un campo lineal), (b) desplazamientos suavizados a lo largo del contorno y (c) conservaci´on de volumen. En este trabajo se han llevado a cabo varios ensayos num´ericos bidimensionales con el fin de ilustrar la influencia de las distintas condiciones de contorno. 2012-11-29T12:33:45Z http://hdl.handle.net/2117/17048 Title: Computable bounds of 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 elds for both the original problem and the adjoint problem associated with the quantity of interest. Here, the ux-free technique is considered to compute the admissible stress elds. 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 con dence are reduced. 2012-11-29T12:18:31Z 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