http://hdl.handle.net/2117/6145 2013-05-18T23:39:11Z 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/2117/17588 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/2117/17433 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/2117/16972 Title: A note on upper bound formulations in limit analysis Authors: Muñoz Romero, José; Huerta, Antonio; Bonet, Javier; Peraire, Jaume Abstract: In this paper we study some recent formulations for the computation of upper bounds in limit analysis. We show that a previous formulation presented by the authors does not guarantee the strictness of the upper bound, nor does it provide a velocity field that satisfies the normality rule everywhere. We show that these deficiencies are related to the quadrature employed for the evaluation of the dissipation power. We derive a formulation that furnishes a strict upper bound of the load factor, which in fact coincides with a formulation reported in the literature. From the analysis of these formulations we propose a post-process which consists in computing exactly the dissipation power for the optimum upper bound velocity field. This post-process may further reduce the strict upper bound of the load factor in particular situations. Finally, we also determine the quadratures that must be used in the elemental and edge gap contributions so that they are always positive and their addition equals the global bound gap. 2012-11-20T11:29:50Z http://hdl.handle.net/2117/16723 Title: Boundary conditions for gradient-enhanced models with smoothed displacements Authors: Tamayo Mas, Elena; Rodríguez Ferran, Antonio Abstract: Los modelos de gradiente basados en desplazamientos suavizados son una alternativa a los modelos estándares para simular numéricamente el proceso de fallo de materiales. En esta formulación alternativa coexisten los campos de desplazamientos mecánicos u con los desplazamientos suavizados ˜u, que se obtienen de solucionar una ecuación de difusión-reacción. Análogamente a los modelos de regularización estándares, prescribir condiciones de contorno en esta formulación 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 homogéneas (reminiscencia de los modelos de gradiente estándares) permiten obtener resultados numéricos realistas; mediante las condiciones de contorno de Neumann no homogéneas, en cambio, los resultados son físicamente admisibles. Sin embargo, estas condiciones no aseguran conservación 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 regularización: (a) reproducibilidad de orden 1 (u = ˜u si u es un campo lineal), (b) desplazamientos suavizados a lo largo del contorno y (c) conservación de volumen. En este trabajo se han llevado a cabo varios ensayos numéricos bidimensionales con el fin de ilustrar la influencia de las distintas condiciones de contorno. 2012-10-15T15:28:04Z http://hdl.handle.net/2117/16600 Title: NURBS-Enhanced Finite Element Method (NEFEM) Authors: Sevilla Cárdenas, Rubén; Fernandez Mendez, Sonia; Huerta, Antonio Abstract: The development of NURBS-Enhanced Finite Element Method (NEFEM) is revisited. This technique allows a seamless integration of the CAD boundary representation of the domain and the finite element method (FEM). The importance of the geometrical model in finite element simulations is addressed and the benefits and potential of NEFEM are discussed and compared with respect to other curved finite element techniques. 2012-10-02T13:40:10Z http://hdl.handle.net/2117/16167 Title: Assembling sparse matrices in MATLAB Authors: Zlotnik, Sergio; Díez, Pedro Abstract: The assembly of sparse matrices is a key operation in finite element methods. In this study we analyze several factors that may have an influence on the efficiency of the assembly procedure. Different insertion strategies are compared using two metrics: a Cost function (the number of memory movements) and actual computing time. An improved algorithm implemented in MATLAB is proposed. It reduces both memory operations and computing time for all tested cases. The efficiency of the assembly process is found to be highly dependent on node and element numbering. The effect of the classic reverse Cuthill–McKee algorithm is, in most cases, positive and reduces computation costs. Finally, the case where a sparse matrix has to be re-assembled at each time step is studied. The efficiency of the assembly is improved if the matrix pattern is entirely or partially inherited from previous steps. 2012-07-03T13:55:06Z http://hdl.handle.net/2117/16106 Title: Subduction dynamics and the origin of Andean orogeny and the Bolivian orocline Authors: Capitanio, F.A.; Faccenna, C.; Zlotnik, Sergio; Stegman, D.R. Abstract: The building of the Andes results from the subduction of the oceanic Nazca plate underneath the South American continent1. However, how and why the Andes and their curvature, the Bolivian orocline, formed in the Cenozoic era (65.5 million years (Myr) ago to present), despite subduction continuing since the Mesozoic era(251.0–65.5 Myr ago), is still unknown. Three-dimensional numerical subduction models demonstrate that variations in slab thickness, arising from the Nazca plate’s age at the trench, produce a cordilleran morphology consistent with that observed. The age-dependent sinking of the slab in the mantle drives traction towards the trench at the base of the upper plate, causing it to thicken. Thus, subducting older Nazca plate below the Central Andes can explain the locally thickened crust and higher elevations. Here we demonstrate that resultant thickening of the South American plate modifies both shear force gradients and migration rates along the trench to produce a concave margin that matches the Bolivian orocline. Additionally, the varying forcing along the margin allows stress belts to form in the upper-plate interior, explaining the widening of the Central Andes and the different tectonic styles found on their margins, the Eastern and Western Cordilleras. The rise of the Central Andes and orocline formation are directly related to the local increase of Nazca plate age and an age distribution along the margin similar to that found today; the onset of these conditions only occurred in the Eocene epoch. This may explain the enigmatic delay of the Andean orogeny, that is, the formation of the modern Andes. 2012-06-20T11:44:39Z