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• Possibilities of the particle finite element method for fluid-soil-structure interaction problems

  E. Oñate, M. Celigueta, S. Idelsohn, F. Salazar, B. Suarez

  (2011). Research Report, Nº PI357

  
  

  Abstract

  We present some developments in the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the solid domains (the later including soil/rock and structures). A mesh connects the particles (nodes) defining the discretized domain where the governing equations for each of the constituent materials are solved as in the standard FEM. The stabilization for dealing with an incompressibility continuum is introduced via the finite calculus (FIC) method. An incremental iterative scheme for the solution of the non linear transient coupled FSSI problem is described. The procedure to model frictional contact conditions and material erosion at fluid-solid and solid-solid interfaces is described. We present several examples of application of the PFEM to solve FSSI problems such as the motion of rocks by water streams, the erosion of a river bed adjacent to a bridge foundation, the stability of breakwaters and constructions sea waves and the study of landslides.

  Abstract
  We present some developments in the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction [...]

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• Advances in the Simulation of Ship Navigation in Brash Ice

  J. García-Espinosa, B. Servan Camas, J. Colom Cobb, E. Oñate

  13th World Congress in Computational Mechanics (WCCM 2018), New York (USA)

  
  

  Abstract

  Brash ice is the accumulation of floating ice made up of blocks no larger than two meters across. Navigation in brash ice is becoming more usual as new navigation routes are being opened in the Artic regions. This navigation brings new concerns regarding the interaction of ice blocks with the ship. This work presents recent advances towards the development of a computational model for simulation of this navigation condition including the interaction among the ship and the ice blocks. The computational tool developed in this work is based on the coupling of a Semi-Lagrangian Particle Finite Element Method (SL-PFEM) with a multi rigid-body dynamics tool. The Particle Finite Element Method (Idelsohn et al. 2004) is a versatile framework for the analysis of fluid-structure interaction problems. The PFEM combines Lagrangian particle-based techniques with the advantage of the integral formulation of the Finite Element Method (FEM). It has been shown (Idelsohn et al. 2014 and  Nadukandi et al. 2017) to successfully simulate a wide variety of complex engineering problems, e.g. free-surface/multi-fluid flows with violent interface motions, multi-fluid mixing and buoyancy-driven segregation problems etc. The latest development within the framework of the PFEM is the X-IVAS (eXplicit Integration along the Velocity and Acceleration Streamlines) scheme. It is a semi-implicit scheme built over a Semi-Lagrangian (SL) formulation of the PFEM. In this work, the SL-PFEM model has been coupled with a multibody dynamics solver, able to handle the interactions between thousands of bodies, representing the different ice blocks. The interaction between the fluid flow and the ice blocks is taking into account by enriching the finite element space at the boundaries of the different blocks. This work is part of the research project NICESHIP sponsored by the U.S. Office of Naval Research under Grant N62909-16-1-2236.

  Abstract
  Brash ice is the accumulation of floating ice made up of blocks no larger than two meters across. Navigation in brash ice is becoming more usual as new navigation routes are [...]

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• Reflexiones sobre el tránsito de la idea al producto en el entorno de la Escuela de Ingenieros de Caminos de Barcelona

  E. Oñate

  (2011). Research Report, Nº PI359

  
  

  Abstract

  Se presentan unas reflexiones sobre el ciclo que las ideas recorren desde que surgen en un entorno universitario hasta que se transforman en un producto industrial. Se concretan estas reflexiones en el contexto de la Escuela Técnica Superior de Ingenieros de Caminos, Canales y Puertos de la Universitat Politècnica de Catalunya y se presentan algunos ejemplos de éxitos en la implantación del denominado Círculo de las Ideas.

  Abstract
  Se presentan unas reflexiones sobre el ciclo que las ideas recorren desde que surgen en un entorno universitario hasta que se transforman en un producto industrial. Se concretan [...]

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• Lagrangian FE methods for coupled problems in fluid mechanics

  P. Ryzhakov, E. Oñate, R. Rossi, S. Idelsohn

  Monograph CIMNE (2010). M121

  
  

  Abstract

  Lagrangian finite element methods emerged in fluid dynamics when the deficiencies of the Eulerian methods in treating free surface flows (or generally domains undergoing large shape deformations) were faced. Their advantage relies upon natural tracking of boundaries and interfaces, a feature particularly important for interaction problems. Another attractive feature is the absence of the convective term in the fluid momentum equations written in the Lagrangian framework resulting in a symmetric discrete system matrix, an important feature in case iterative solvers are utilized. Unfortunately, the lack of the control over the mesh distortions is a major drawback of Lagrangian methods. In order to overcome this, a Lagrangian method must be equipped with an efficient re-meshing tool. This work aims at developing formulations and algorithms where maximum advantage of using Lagrangian finite element fluid formulations can be taken. In particular we concentrate our attention at fluid-structure interaction and thermally coupled applications, most of which originate from practical “real-life” problems. Two fundamental options are investigated - coupling two Lagrangian formulations (e.g. Lagrangian fluid and Lagrangian structure) and coupling the Lagrangian and Eulerian fluid formulations. In the first part of this work the basic concepts of the Lagrangian fluids, the so-called Particle Finite Element Method (PFEM) [1], [2] are presented. These include nodal variable storage, mesh re-construction using Delaunay triangulation/tetrahedralization and alpha shape-based method for identification of the computational domain boundaries. This shall serve as a general basis for all the further developments of this work. Next we show how an incompressible Lagrangian fluid can be used in a partitioned fluid-structure interaction context. We present an improved Dirichlet-Neumann strategy for coupling the incompressible Lagrangian fluid with a rigid body. This is finally applied to an industrial problem dealing with the sea-landing of a satellite capsule. In the following, an extension of the method is proposed to allow dealing with fluid-structure problems involving general flexible structures. The method developed takes advantage of the symmetry of the discrete system matrix and by introducing a slight fluid compressibility allows to treat the fluid-structure interaction problem efficiently in a monolithic way. Thus, maximum benefit from using a similar description for both the fluid (updated Lagrangian) and the solid (total Lagrangian) is taken. We show next that the developed monolithic approach is particularly useful for modeling the interaction with light-weight structures. The validation of the method is done by means of comparison with experimental results and with a number of different methods found in literature. The second part of this work aims at coupling Lagrangian and Eulerian fluid formulations. The application area is the modeling of polymers under fire conditions. This kind of problem consists of modeling the two subsystems (namely the polymer and the surrounding air) and their thermomechanical interaction. A compressible fluid formulation based on the Eulerian description is used for modeling the air, whereas a Lagrangian description is used for the polymer. For the surrounding air we develop a model based upon the compressible Navier-Stokes equations. Such choice is dictated by the presence of high temperature gradients in the problem of interest, which precludes the utilization of the Boussinesq approximation. The formulation is restricted to the sub-sonic flow regime, meeting the requirement of the problem of interest. The mechanical interaction of the subsystems is modeled by means of a one-way coupling, where the polymer velocities are imposed on the interface elements of the Eulerian mesh in a weak way. Thermal interaction is treated by means of the energy equation solved on the Eulerian mesh, containing thermal properties of both the subsystems, namely air and polymer. The developments of the second part of this work do not pretend to be by any means exhaustive; for instance, radiation and chemical reaction phenomena are not considered. Rather we make the first step in the direction of modeling the complicated thermo-mechanical problem and provide a general framework that in the future can be enriched with a more detailed and sophisticated models. However this would affect only the individual modules, preserving the overall architecture of the solution procedure unchanged. Each chapter concludes with the example section that includes both the validation tests and/or applications to the real-life problems. The final chapter highlights the achievements of the work and defines the future lines of research that naturally evolve from the results of this work.

  Abstract
  Lagrangian finite element methods emerged in fluid dynamics when the deficiencies of the Eulerian methods in treating free surface flows (or generally domains undergoing [...]

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• Advances in the Simulation of Ship Navigation in Ice

  J. García-Espinosa, B. Servan Camas, J. Colom Cobb, E. Oñate, S. Latorre, M. Celigueta

  37th International Conference on Ocean, Offshore & Arctic Engineering (OMAE 2018), Madrid (Spain)

  
  

  Abstract

  Brash ice is the accumulation of floating ice made up of blocks no larger than two meters across. Navigation in brash ice is becoming more usual as new navigation routes are being opened in the Artic regions. This navigation brings new concerns regarding the interaction of ice blocks with the ship. This work presents recent advances towards the development of a computational model for simulation of this navigation condition including the interaction among the ship and the ice blocks. The computational tool developed in this work is based on the coupling of a Semi-Lagrangian Particle Finite Element Method (SL-PFEM) with a multi rigid-body dynamics tool. The Particle Finite Element Method (Idelsohn et al. 2004) is a versatile framework for the analysis of fluid-structure interaction problems. The PFEM combines Lagrangian particle-based techniques with the advantage of the integral formulation of the Finite Element Method (FEM). It has been shown (Idelsohn et al. 2014 and  Nadukandi et al. 2017) to successfully simulate a wide variety of complex engineering problems, e.g. free-surface/multi-fluid flows with violent interface motions, multi-fluid mixing and buoyancy-driven segregation problems etc. The latest development within the framework of the PFEM is the X-IVAS (eXplicit Integration along the Velocity and Acceleration Streamlines) scheme. It is a semi-implicit scheme built over a Semi-Lagrangian (SL) formulation of the PFEM. In this work, the SL-PFEM model has been coupled with a multibody dynamics solver, able to handle the interactions between thousands of bodies, representing the different ice blocks. The interaction between the fluid flow and the ice blocks is taking into account by enriching the finite element space at the boundaries of the different blocks. This work is part of the research project NICESHIP sponsored by the U.S. Office of Naval Research under Grant N62909-16-1-2236.

  Abstract
  Brash ice is the accumulation of floating ice made up of blocks no larger than two meters across. Navigation in brash ice is becoming more usual as new navigation routes are [...]

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• Static and Seismic Analysis of the Janneh Arch-gravity Dam

  L. Gracia, I. de-Pouplana, F. Salazar, E. Oñate

  (2017). 14th International Benchmark Workshop on the Numerical Analysis of Dams. Stockholm, Sweden, 2017

  
  

  Abstract

  The static and seismic analysis of Janneh arch-gravity dam (157 m) is carried out by considering a combination of self-weight, hydrostatic, uplift and seismic loads. Linear and nonlinear analyses are performed for both static and seismic cases. Nonlinear behavior is studied by means of joint elements in the contact between the rock foundation and the dam following a bilinear cohesive law. The hydrodynamic effects derived to seismic loads are also considered. Hydrodynamic Westergaard’s approach is applied in the pseudo-static analysis, and the Westergaard’s generalized added mass is used for time-history case.

  Abstract
  The static and seismic analysis of Janneh arch-gravity dam (157 m) is carried out by considering a combination of self-weight, hydrostatic, uplift and seismic loads. Linear [...]

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• Modelo higro-termo-mecánico para estructuras hormigón armado expuestas al fuego

  D. Capua, A. Marí, E. Oñate

  Monograph CIMNE (2009). M113

  
  

  Abstract

  Cuando una estructura de hormigón armado queda expuesta a la acción del fuego se producen, tanto en el hormigón como en el acero, un conjunto de fenómenos físicoquímicos que pueden comprometer la estabilidad de la misma. Entre los procesos más importantes destaca el de eclosión (spalling). Se considera que las posibles causas del spalling pueden ser un elevado crecimiento de la presión en los poros (spalling hidráulico) o un exagerado aumento de las tensiones de compresión debidas a la dilatación térmica restringida. Para poder tener en cuenta en el análisis el spalling hidráulico es necesario considerar un modelo que tenga en cuenta la componente hídrica del hormigón. En esta monografía se presenta un modelo higro-termo-mecánico que permite representar el comportamiento general del hormigón armado expuesto a elevadas temperaturas y en particular simular el fenómeno de spalling. Se parte de proponer un marco termodinámico consistente a partir del cual se derivan las variables de estado que se utilizan posteriormente para el desarrollo de las ecuaciones de gobierno del problema. Asimismo se proponen modelos constitutivos para el comportamiento mecánico del hormigón y del acero. Una vez establecidos las ecuaciones de gobierno del problema se describen los aspectos numéricos para su resolución. Para la integración espacial del problema se utiliza el Método del los Elementos Finitos y para la integración temporal el Método de Diferencias Finitas. Se propone un esquema iterativo en bloque para el tratamiento del acoplamiento. Se ha desarrollado un programa de cálculo diseñado especialmente para materializar la metodología numérica propuesta en esta monografía. Para la validación del modelo propuesto se presentan ejemplos en los que se comparan los resultados obtenidos numéricamente con resultados experimentales. Finalmente, se presentan un conjunto de ejemplos que muestran la capacidad del modelo propuesto para captar el comportamiento general de una estructura de hormigón armado expuesta al fuego y en especial el fenómeno de spalling.  

  Abstract
  Cuando una estructura de hormigón armado queda expuesta a la acción del fuego se producen, tanto en el hormigón como en el acero, un conjunto de fenómenos [...]

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• Tratamiento numérico de los Materiales Compuestos

  E. Car, S. Oller, E. Oñate

  Monograph CIMNE (2000). M57

  
  

  Abstract

  La principal dificultad que se encuentra en el momento de diseñar estructuras con materiales compuestos es la falta de modelos constitutivos que permitan si- mular su comportamiento.  Las técnicas analíticas convencionales utilizadas para el estudio de materiales simples isótropos no resultan adecuadas para el análisis de materiales compuestos. Tampoco ha resultado satisfactoria la representación de un compuesto mediante un único material ortótropo con propiedades del conjunto. Puede observarse en distintas referencias los intentos que ha habido para modelar el comportamiento de materiales compuestos, utilizando la técnica de elementos fi- nitos para el análisis y diseño de estructuras, donde la correlación entre los análisis y los resultados experimentales no resulta satisfactoria (Ali, 1996) (Klintworth y Macmillian, 1992). El proceso de diseño de componentes en materiales compuestos se ha basado, principalmente, en métodos empíricos, observándose en la literatura la ausencia de análisis o simulaciones del comportamiento de materiales compuestos sometidos a niveles de esfuerzos que sobrepasan el límite elástico.  

  Abstract
  La principal dificultad que se encuentra en el momento de diseñar estructuras con materiales compuestos es la falta de modelos constitutivos que permitan si- mular [...]

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• Modelado de Multifractura Discreta en Materiales Quasi-Frágiles Monografía

  N. Lafontaine, E. Oñate, R. Rossi, C. Pu

  Monograph CIMNE (2016). M158

  
  

  Abstract

  In this work, a new modal reanalysis algorithm based on AMLS method is proposed for local, nontop ological,high rank modifications. Instead of using some perturbation technique[44, 85] or using the Kirsch Combined method[223, 226], the proposed reanalysis procedure uses AMLS method to perform the reanalysisexp lo itin g the concept of substructure. The modification affects a particular path on the hierarchical partitiontree, which traces back from the modified nodes to the root node. In our proposed modal reanalysis algorithmonly the modified substructures and affected substructures due to the propagation need to be recalculated. This algorithm can significantly improve the efficiency compared to the full recalculation. Some of the advantages are: 1. Larger substructure size increases moderately the accurate of the AMLS method. For medium substructure size, the efficiency of AMLS method can be improved using a sparse linear solver and sparse eigen solver. 2. If the modified substructures are recalculated using exact method, the reanalysis does not affect the precision of the final results by AMLS method. The eigen-values computed are accurate as the precision of AMLS method is. 3. The amplitude of modification is not limited to small modification change, as being required by approximate method. 4. It is only required to identify the corresponding modified and affected sub-structures for performing the recalculation and save the data of the non-modified sub-structures. In the worst case, the computational cost is no more than the fresh AMLS-solution. 5. It is more suitable for large-scale eigen value problem with local high-rank modifications.  

  Abstract
  In this work, a new modal reanalysis algorithm based on AMLS method is proposed for local, nontop ological,high rank modifications. Instead of using some perturbation technique[44, [...]

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• Numerical modelling of railway ballast behaviour using the Discrete Element Method (DEM) and spherical particles

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

  (2015). IV International Conference on Particle-Based Methods. Fundamentals and Applications (PARTICLES 2015)

  
  

  Abstract

  In the last two decades there has been a great development of high-speed train lines. This advance has led to more demanding loads in railway infrastructures and the appearance of a new problem called ballast flight that happens when some stones rise when the train passes. For these reasons, the development of an application that allows the numerical modelling of the ballast superstructure under different stresses can be very useful, as it will enable design optimization. The DEM is being considered an effective and powerful method for the calculation of engineering problems with granular and discontinuous materials. Railroad ballast layer consists of discrete aggregate particles, so that DEM is one of the most suitable ways to simulate the behavior of particulate ballast material. However, the computational cost of contact calculation between irregular particles is high and limits the calculation capability. From the point of view of micro-scale analysis, it is essential to represent the exact geometry of the particle. On the other hand, if the interest lies in the behavior of the granular material as a whole, the geometry is not a determining factor. Besides that, setting up a simulation of granular material taking care of the exact geometry of each particle will not be efficient. Current work presents the methodology followed to achieve accurate results in the calculation of railway ballast behaviour using DEM and spherical particles. The use of spherical particles reduces the computational cost and makes the simulation set up efficient. Validation results for the calculation of the lateral resistance force against a sleeper moving inside a ballast bed are presented. Regarding ballast flight problem, some high speed ballast collision calculations have also been performed.

  Abstract
  In the last two decades there has been a great development of high-speed train lines. This advance has led to more demanding loads in railway infrastructures and the appearance [...]

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