COLLECTIONS

Documents published in Scipedia

• Computational fluid dynamics indicators to improve cardiovascular pathologies diagnosis

  E. Soudah, E. Oñate, M. Cervera

  Monograph CIMNE (2016). M167

  
  

  Abstract

  In recent years, the study of computational hemodynamics within anatomically complex vascular regions has generated great interest among clinicians. The progress in computational fluid dynamics, image processing and high-performance computing have allowed us to identify the candidate vascular regions for the appearance of cardiovascular diseases and to predict how this disease may evolve. In this monograph we attempt to introduce into medicine the computational predictive paradigm that has been used in engineering for many years. Several groups have tried to create predictive models for cardiovascular pathologies, but they have not yet begun to use them in clinical practice. Our final aim is to go further and obtain predictive variables to be used in the clinical field. We try to predict the evolution of aortic abdominal aneurysm, aortic coarctation and coronary artery disease in a personalized way for each patient. We propose diagnostic indicators that can improve the diagnosis and predict the evolution of the disease more efficiently than the methods used until now. In particular, a new methodology for computing diagnostic indicators based on computational hemodynamics and medical imaging is proposed. We have worked with data of anonymous patients to create real predictive technology that will allow us to continue advancing in personalized medicine and generate a more sustainable health systems. The objective of this monograph is therefore to develop predictive models for cardiovascular pathologies by merging medical imaging and computational techniques at a clinical level. It is expected in the near future that larger databases of patient-specific computational models will be available to doctors. These data can be used with predictive models to improve diagnosis and to define personalized therapies and treatments.

  Abstract
  In recent years, the study of computational hemodynamics within anatomically complex vascular regions has generated great interest among clinicians. The progress in computational [...]

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• Direct computation of instability points with inequality constraints using the Finite Element Method

  H. Tschöpe, E. Oñate, P. Wriggers

  Monograph CIMNE (2001). M61

  
  

  Abstract

  The objective of this monograph is to apply the computation methods for critical points to more complex mechanical problems involving inequality constraints. Prior to this extension to a new class of problems appropriate methods among the existing ones for the critical point detection are chosen. Therefore the CDM and the extended system as the most primising techniques will be compared and evaluated. A one step prediction of the critical load based on the extended system will be developed that enables a better evaluation. The possibilities of a combination of both methods will be examined. A conceivable combination is to use the prediction of a CDM computation as starting value for the extended system and enhance the convergence of the latter. In a second step critical point detection methods are extended to problems that involve inequality constraints. In this context constitutive damage models and contact problems are studied.

  Abstract
  The objective of this monograph is to apply the computation methods for critical points to more complex mechanical problems involving inequality constraints. Prior to this [...]

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• Tratamiento numérico de materiales compuestos mediante la teoría de homogeneización

  F. Zalamea, J. Miquel, S. Oller

  Monograph CIMNE (2002). M64

  
  

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• Desarrollo del método de puntos finitos en mecánica de fluidos

  C. Sacco

  Monograph CIMNE (2002). M66

  
  

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• Development of new computational methods for fluid-structure interaction analysis of multi-fractured media

  I. Pouplana, E. Oñate

  Monograph CIMNE (2018). M177

  
  

  Abstract

  The objective of this monograph is the derivation and implementation of a robust Finite Element formulation for the solution of solid-pore fluid coupled problems in multi-fractured porous media. A coupled displacement-pore pressure FEM formulation for solving solid-pore fluid interaction problems is first introduced. The interaction between both components is governed by two equations: the balance of momentum for the mixture solid-fluid and the mass balance for the pore fluid. Under nearly undrained-incompressible conditions, such formulation suffers from instability problems because of the violation of Babuska-Brezzi conditions. In order to work with elements of equal order interpolation for the displacement and pore pressure, the formulation is stabilized by means of the Finite Increment Calculus method (FIC). The FIC-stabilized formulation is tested against stable elements with a higher order interpolation for the displacement field in 2D and 3D examples. Continuum damage mechanics is the basis of the crack growth strategy for the proposed fracture propagation technique. The strain softening models used for quasi-brittle materials favour spurious strain localization and ill-posedness of the boundary value problem if the damage variable only depends on the strain state at the point under consideration. An integral-type non-local damage model associated to a characteristic length parameter is presented as a method to control the size of the fracture process zone and fully regularize the problem. Two examples are solved assessing the robustness of the model in front of changes in the spatial discretization. Quasi-zero-thickness interface elements are formulated to represent discontinuities in the porous domain. A bilinear cohesive fracture model is used to describe its mechanical behaviour, and a formulation derived from the cubic law models the fluid flow through the crack. Finally, a new methodology for the simulation of fracture propagation processes in saturated porous media is presented. The non-local damage model is used in conjunction with the interface elements to predict the degradation pattern of the domain and insert new fractures followed by remeshing. Fluid-driven fracture propagation examples in 2D and 3D are presented to illustrate the accuracy of the proposed technique.  

  Abstract
  The objective of this monograph is the derivation and implementation of a robust Finite Element formulation for the solution of solid-pore fluid coupled problems in multi-fractured [...]

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• Design of an inflatable, modular and portable footbridge

  A. Rodríguez, E. Oñate, J. Marcipar

  Monograph CIMNE (2017). M175

  
  

  Abstract

  Optimization of the use of resources and adaptability of the structures to their environment are new concerns in architecture and structural engineering. At the same time, ephemeral structures are gaining relevance in the market for their uses in maintenance and repair, organization of events, rescue and emergencies and temporary works. Inflatable structures satisfy two of the points aforementioned: they require small amounts of materials and are adequate for ephemeral structures, due to their low deflated volume and lightness. They are also adaptable in the sense that their overpressure determines their load carrying capacity. However, they are inadequate for environments where high external loads may be present. Tensairity appears as a solution to this problem, increasing the carrying capacity of inflatable structures without renouncing to their advantages. This technology adds two extra structural elements to inflatable beams, with greater strengths, in order to redistribute stresses along it. The inflatable element serves then to couple the two stiff elements and to avoid buckling. This work presents and explores design possibilities of Tensairity beams with special focus on their computational modelling. Then, research is carried out regarding modular Tensairity beams, thought as a solution for deployable footbridges. A prototype was built and tested in serviceability conditions to prove the fitness of the proposal to a commercial level.

  Abstract
  Optimization of the use of resources and adaptability of the structures to their environment are new concerns in architecture and structural engineering. At the same time, [...]

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• Numerical analysis of railway ballast behaviour using the Discrete Element Method

  J. Irazábal González, E. Oñate, F. Salazar

  Monograph CIMNE (2017). M174

  
  

  Abstract

  The development of high-speed train lines has increased significantly during the last twenty-five years, leading to more demanding loads in railway infrastructures. Most of these infrastructures were constructed using railway ballast, which is a layer of granular material placed under the sleepers whose roles are: resisting to vertical and horizontal loads and facing climate action. Moreover, the Discrete Element Method was found to be an effective numerical method for the calculation of engineering problems involving granular materials. For these reasons, the main objective of the work is the development of a numerical modelling tool based on the Discrete Element Method which allows the users to understand better the mechanical behaviour of railway ballast. The first task was the review of the specifications that ballast material must meet. Then, the features of the available Discrete Elements code, called ''DEMPack'', were analysed. After those revisions, it was found that the code needed some improvement in order to reproduce correctly and efficiently the behaviour of railway ballast. The main deficiencies identified in the numerical code were related to the contact between discrete element particles and planar boundaries and to the geometrical representation of such a irregular material as ballast. Contact interactions between rigid boundaries and Discrete Elements are treated using a new methodology called the Double Hierarchy method. This new algorithm is based on characterising contacts between rigid parts (meshed with a Finite Element-like discretisation) and spherical Discrete Elements. The procedure is described in the course of the work. Moreover, the method validation and the assessment of its limitations are also displayed. The representation of irregular particles using the Discrete Element Method is a very challenging issue, leading to different geometrical approaches. In this work, a deep revision of those approaches was performed. Finally, the most appropriate methods were chosen: spheres with rolling friction and clusters of spheres. The main advantage of the use of spheres is their low computational cost, while clusters of spheres stand out for their geometrical versatility. Some improvements were developed for describing the movement of each kind of particles, specifically, the imposition of the rolling friction and the integration of the rotation of clusters of spheres. In the course of this work the way to fill volumes with particles (spheres or clusters) was also analysed. The aim is to control properly the initial granulometry and compactness of the samples used in the calculations. After checking the correctness of the numerical code with simplified benchmarks, some laboratory tests for evaluating railway ballast behaviour were computed. The aim was to calibrate the ballast material properties and validate the code for the representation of railway ballast. Once the material properties were calibrated, some examples of a real train passing through a railway ballast track were reproduced numerically. This calculations allowed to prove the possibilities of the implemented tool. This publication is a revised version of the text of the PhD Thesis “Numerical analysis of railway ballast behaviour using the Discrete Element Method” of Joaquín Irazábal, presented at the Technical University of Catalonia on October 6th 2017

  Abstract
  The development of high-speed train lines has increased significantly during the last twenty-five years, leading to more demanding loads in railway infrastructures. Most of [...]

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• A Geometrical domain decomposition method in computational fluid dynamics

  G. Houzeaux, R. Codina

  Monograph CIMNE (2002). M70

  
  

  Abstract

  We present a detailed description of the implementation of the DD methods in the numerical framework of finite elements. We present interpolation techniques for Dirichlet and Neumann data as well as conservation algorithms.

  Abstract
  We present a detailed description of the implementation of the DD methods in the numerical framework of finite elements. We present interpolation techniques for Dirichlet [...]

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• Contributions to the continuum modeling of strong discontinuities in two-dimensional solids

  E. Samaniego, J. Oliver, A. Huespe

  Monograph CIMNE (2003). M72

  
  

  Abstract

  The objectives of this monograph are oriented to getting and efficient and robust computational tool that allows the simulation of complex problems in which strain localization aappears. All this relying on a mathematical model consistent from the classical continuum mechanics point of view.

  Abstract
  The objectives of this monograph are oriented to getting and efficient and robust computational tool that allows the simulation of complex problems in which strain localization [...]

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• A three dimensional setting for strong discontinuities modelling in failure mechanics

  E. Chaves, X. oliver

  Monograph CIMNE (2003). M73

  
  

  Abstract

  This work deals with the simulation of strain localization phenomena through the Strong Discontinuity Approach (SDA) for three dimensional (3D) problems. The main assumptions of this work are the isothermal quasi-static regime, small deformations and rotations, and a material describes as homogeneous and isotropic.

  Abstract
  This work deals with the simulation of strain localization phenomena through the Strong Discontinuity Approach (SDA) for three dimensional (3D) problems. The main assumptions [...]

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