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• Estado del arte sobre aplicación de métodos numéricos y la simulación de escenarios de riesgo y al cálculo de la seguridad estructural

  A. Barbat, L. Pujades, O. Cardona

  (2007). Research Report, Nº PI300

  
  

  Abstract

  En este informe se estudian los métodos numéricos orientados hacia el cálculo de la seguridad de las estructuras, a la evaluación de su vulnerabilidad y riesgo, así como al desarrollo de escenarios de riesgo. Partiendo de una amplia revisión bibliográfica, se realiza una descripción del marco conceptual del riesgo, insistiéndose en las formulaciones que se han dado a los conceptos de amenaza, vulnerabilidad, fragilidad y daño involucrados en la definición del riesgo. A pesar de que los conceptos analizados son válidos para cualquier tipo de elemento en riesgo, para responder al principal objetivo de este estudio se pone énfasis en las estructuras de edificación y en las zonas urbanas. Dicho objetivo es el de estudiar los métodos de última generación orientados a la evaluación del daño esperado tanto en edificios individuales (lo que implica examinar su seguridad y vulnerabilidad) como en zonas urbanas (para las que se describirán procedimientos de simulación de escenarios de riesgo.) Después de incluir los principios relacionados con la evaluación de diferentes amenazas naturales (terremotos, tsunamis, erupciones volcánicas, huracanes, inundaciones, deslizamientos, avalanchas, etc.) para las que se introduce el concepto de escenario de amenaza, el presente estudio se centra más en la amenaza sísmica, al tener esta una mayor influencia en la seguridad de las estructuras que se hallan en zonas urbanas. Se describe, primeramente, del método del índice de vulnerabilidad, desarrollado en el ámbito del riesgo sísmico, que permite caracterizar la vulnerabilidad de las estructuras. Unas funciones de vulnerabilidad semiempíricas permite estimar el daño estructural para diferentes intensidades de la acción y para diferentes índices de vulnerabilidad estructural. En el segundo lugar, se examina el método del espectro de capacidad que se fundamenta en modelos de análisis no lineal de las estructuras y de curvas de fragilidad estructural. La acción se define mediante el espectro de demanda. El método proporciona las probabilidades de ocurrencia para diferentes estados mencionados, utilizándose como ejemplo la ciudad de Barcelona para la se han desarrollado escenario de riesgo para la amenaza sísmica.

  Abstract
  En este informe se estudian los métodos numéricos orientados hacia el cálculo de la seguridad de las estructuras, a la evaluación de su vulnerabilidad [...]

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• Bounds of functional outputs for parabolic problems. Part II: Bounds of the exact solution

  N. Parés, P. Díez, A. Huerta

  (2007). Research Report, Nº PI299

  
  

  Abstract

  The paper introduces a methodology to compute upper and lower bounds for linear-functional outputs of the exact solutions of parabolic problems. In this second part, the bounds account for the error both in space and time. The assumption stating that the error introduced by the time marching scheme is negligible, used in the first part, is removed here. The bounds are computed starting from an approximation of the exact solution, associated with a spatial mesh and a time grid. Nevertheless, the bounds are guaranteed with respect to the exact solution, with no reference to any mesh or time discretization.

  Abstract
  The paper introduces a methodology to compute upper and lower bounds for linear-functional outputs of the exact solutions of parabolic problems. In this second part, the bounds [...]

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• Robust design methods in aerospace engineering

  M. Kouhi, E. Oñate, G. Bugeda

  (2008). Research Report, Nº PI328

  
  

  Abstract

  This document is an introduction to some important methodologies that have been developed in robust design in aerospace engineering. After describing the concept of robustness and uncertainty, multipoint, minimax, expected value, second order second moment and Taguchi methods are mentioned. At the end of this report, Game Theory, as one of the approach for multi objective optimization problems has been introduced.

  Abstract
  This document is an introduction to some important methodologies that have been developed in robust design in aerospace engineering. After describing the concept of robustness [...]

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• Implementation of a general algorithm for incompressible and compressible flows within the multi-physics code Kratos and preparation of fluid-structure coupling

  R. Rossi, E. Oñate, A. Maymó

  (2008). Research Report, Nº PI327

  
  

  Abstract

  This diploma thesis deals with the implementation of a fluid solver for incompressible and compressible flows within the multi-physics framework Kratos. The presentation of this environment based on the finite element method (FEM) and an introduction to multidisciplinary problems in general are the starting point of this work and help understanding the following steps more easily. Originating from the basic conservation equations for mass, momentum and energy, the Euler equations for inviscid flow are derived. In this context some approximations are presented that avoid the solution of the energy equation and allow the use of a general approach for the simulation of incompressible, slightly compressible and barotropic flow. The implementation of the incompressible case is outlined step-by-step: Having discretized the continuous problem, a fractional step scheme is presented in order to uncouple pressure and velocity components by a split of the momentum equation. Emphasis is placed on the nodal implementation using an edge-based data structure. Moreover, the orthogonal subscale stabilization - necessary because of the finite element discretization - is explained very briefly. Subsequently, the solver is extended to compressible regime mentioning the respective modifications. For validation purposes numerical examples of incompressible and compressible flows in two and three dimensions round of this first part. In a second step, the implemented flow solver is prepared for the fluid-structure coupling. After presenting solving procedures for multi-disciplinary problems, the arbitrary Lagrangian Eulerian (ALE) formulation is introduced and the conservation equations are modified accordingly. Some preliminary tests are performed, particularly with regard to mesh motion and adjustment of the boundary conditions. Finally, expectations for the envisaged fluid-structure coupling are brought forward.

  Abstract
  This diploma thesis deals with the implementation of a fluid solver for incompressible and compressible flows within the multi-physics framework Kratos. The presentation of [...]

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• PUMI: An explicit ED unstructural finite element solver for the Euler equations

  R. Flores, E. Ortega

  (2008). Research Report, Nº PI326

  
  

  Abstract

  The PUMI flow solver has been developed at CIMNE in to address the need for fast solutions of the flow field around complex geometries. Nowadays calculations involving a number of cells on the order of ten million are performed routinely. PUMI was created to deal with this kind of large-scale problem using modest hardware, therefore special emphasis was placed on the computational efficiency of the code. Design guidelines where minimum memory requirement, very fast single-threaded performance as well as satisfactory parallel scaling up to a moderate number of threads (as found on current desktop hardware using a small number of multi-core CPUs. In order to speedup the mesh generation activities an unstructured finite element formulation was selected. This papers describes the theoretical basis of the algorithms as well as detail of the implementation that increase the robustness and efficiency of the code.

  Abstract
  The PUMI flow solver has been developed at CIMNE in to address the need for fast solutions of the flow field around complex geometries. Nowadays calculations involving a number [...]

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• A cooling system for a hybrid PV/thermal linear concentrator

  D. Chemisana, J. Cipriano, M. Ibáñez, B. Mesih, A. Mellor

  (2008). Research Report, Nº PI325

  
  

  Abstract

  This paper presents the thermal evaluation of an evacuated PVT collector designed to operate under concentrated radiation (15 suns). Finite volume 3D numerical computations have been carried out in order to study the thermal characteristics of different rectangular cross section aluminium pipes and to test the performance of the PVT collector with several laminar flow rates. Experiments with the same laminar flows show the same behavior than in the numerical results.

  Abstract
  This paper presents the thermal evaluation of an evacuated PVT collector designed to operate under concentrated radiation (15 suns). Finite volume 3D numerical computations [...]

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• A finite point method for adaptive three-dimensional compressible flow calculation

  E. Ortega, E. Oñate, S. Idelsohn

  (2008). Research Report, Nº PI323

  
  

  Abstract

  The Finite Point Method (FPM) is a meshless technique which is based on both, a Weighted Least-Squares numerical approximation on local clouds of points and a collocation technique which allows obtaining the discrete system of equations. The research work we present is part of a major investigation into the capabilities of the FPM to deal with threedimensional applications concerning real compressible fluid flow problems. In the first part of this work, the upwind biased scheme employed for solving the flow equations is described. Secondly, with the aim of exploiting meshless capabilities, an h-adaptive methodology for two and three-dimensional compressible flow calculations is developed. This adaptive technique applies a solution-based indicator in order to identify local clouds where new points should be inserted in or existing points could be safely removed from the computational domain. The flow solver and the adaptive procedure have been evaluated and the results are highly encouraging. Several numerical examples are provided throughout the article in order to illustrate their performance.

  Abstract
  The Finite Point Method (FPM) is a meshless technique which is based on both, a Weighted Least-Squares numerical approximation on local clouds of points and a collocation [...]

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• Lift maximization with uncertainties for high lift devices optimization

  Z. Tang, J. Periaux, G. Bugeda, E. Oñate

  (2008). Research Report, Nº PI322

  
  

  Abstract

  In this paper, the aerodynamic shape optimization problems with uncertain operating conditions has been addressed. After a review of robust control theory and the possible approaches to take into account uncertainties, the use of Taguchi robust design methods in order to overcome single point design problems in Aerodynamics is proposed. Under the Taguchi concept, a design with uncertainties is converted into an optimization problem with two objectives which are the mean performance and its variance, so that the solutions are as less sensitive to the uncertainty of the input parameters as possible. Furthermore, the Multi-Criterion Evolutionary Algorithms (MCEAs) are used to capture a set of compromised solutions (Pareto front) between these two objectives. The flow field is analyzed by Navier-Stokes computation using an unstructured mesh. The proposed approach drives to the solution of a multi-objective optimization problem that is solved using a modification of a Nondominated Sorting Genetic Algorithm (NSGA). In order to reduce the number of expensive evaluations of the fitness function a Response Surface Modeling (RSM) is employed to estimate the fitness value using the polynomial approximation model. During the solution of the optimization problem a Semi-torsional Spring Analogy is used for the adaption of the computational mesh to all the obtained geometrical configurations. The proposed approach is applied to the robust optimization of the 2D high lift devices of a business aircraft by maximizing the mean and minimizing the variance of the lift coefficients with uncertain free-stream angle of attack at landing and takeoff flight conditions, respectively.

  Abstract
  In this paper, the aerodynamic shape optimization problems with uncertain operating conditions has been addressed. After a review of robust control theory and the possible [...]

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• Validación experimental del Particle Finite Element Method (PFEM)

  E. Oñate, A. LARESE, S. Idelsohn, M. Celigueta, R. Rossi

  (2008). Research Report, Nº PI318

  
  

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• Desarrollo de un soporte metálico intravascular

  M. Bordone, E. Oñate, E. Soudah, M. Chiumenti

  (2008). Research Report, Nº PI317

  
  

  Abstract

  Las enfermedades cardiovasculares son la primera causa de muerte de la población Europea. Se estima que la mortalidad por enfermedades cardiovasculares es la mitad de la mortalidad total en toda Europa y provoca 4,35 millones de fallecidos cada año en los 52 estados miembros de la Región Europea. Según la Organización Mundial de la Sanidad (OMS) más de 1,9 millones de muertos en la Unión Europea, además de ser la principal causa de deshabilitad y reducción de calidad de vida. Estos tipos de enfermedades afectan sobre todo a la mayor parte de la población, y, sabiendo que el porcentaje de ancianos en la nuestra sociedad sigue subiendo, se puede fácilmente entender que las cardio-patologías puedan constituir siempre un riesgo elevado para la salud de los países occidentales. La cirugía moderna busca cada día soluciones menos invasivas, como por ejemplo a través de cirugía llamada mini-invasiva. La cirugía mini-invasiva es la técnica quirúrgica que consiente acceder a cavidades internas sin operar incisiones (cirugía en abierto). En esta definición, es trivial intuir que entran sobre todo las técnicas endoscópicas que han permitido realizar muchas operaciones de diferente grado de peligrosidad produciendo numerosos beneficios y reduciendo los índices de riesgo. En la cirugía cardiovascular no es raro encontrar problemáticas de tener que insertar aparatos como stent, válvulas cardiacas, sondas y muchas cosas más a través pequeños orificios (como vasos sanguíneos, por ejemplo, la femoral, la aorta la carótida o la subclavia). Estos aparatos van a ser posicionados o conducidos a través de guías (catéteres) que los conducen hasta el sitio destinado. El hecho de utilizar catéteres que tienen que penetrar por estas vías obliga a que estos aparatos respecten dimensiones muy pequeñas. Es interesante entonces estudiar como estas estructuras deben de soportar esfuerzos de compresión y de expansión cuando vienen insertadas en el catéter y luego se sueltan. El ejemplo en el cual enfocaremos nuestro estudio va a ser un soporte metálico intravascular para cualquier aparato necesite ser anclado en el interior de una vena o arteria.

  Abstract
  Las enfermedades cardiovasculares son la primera causa de muerte de la población Europea. Se estima que la mortalidad por enfermedades cardiovasculares es la mitad [...]

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