JOURNALS

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• Modeling of ground excavation with the particle finite element method

  J. Puigbó, E. Oñate, B. Suárez

  Monograph CIMNE (2010). M116

  
  

  Abstract

  The present work introduces a new application of the Particle Finite Element Method (PFEM) for the modeling of excavation problems. Lagrangian descriptions of motion of the continuum medium are the natural way of describing motion in solid mechanics. Particle finite element methods are based in these solid mechanics settings that can treat large material deformations and rapidly changing boundaries. These capabilities are very suitable for modeling fluid motions and moving free surfaces. That is the reason that the most of the research and applications of PFEM can be found in the context of computational fluid dynamics (CFD) instead of solid mechanics. The satisfying results in modeling fluids have been the motivation to use this method in dynamic solid mechanics. The simulation of an excavation process is a non-linear dynamic problem. It contains geometrical, material and contact non-linearities. Modeling the contact process can be classiffied as the main difficulty. The simulation face the problems of: the detection of a changing geometry, the detection of contact between several solid domains, the estimation of correct interacting forces, the computation of the wear related to this contact forces and the removing of the material that has been excavated from the model. The PFEM have its fundamentals in the classical non linear finite element analysis. The formulation provides a foundation in the updated lagrangian formulation for solids. The dynamic problem is integrated using an implicit scheme. Remeshing strategies are employed in order to identify the boundary surfaces. A remeshing of the domain is introduced for the detection of rapidly changing boundaries. The Delaunay tessellation and the alpha-shape concept together, are used as a methodology to de_ne the boundary from a cloud of points. At the same time an interface mesh is created for contact recognition. A particular constitutive contact law has been developed for capturing contact normal and frictional forces using this mesh. By means of an Archard-type law, the excavation and damage caused in the ground is quantified. The erosion and wear parameters of the grounds under study determine the excavability. The behavior of the geomaterials is described using a Damage Model which model fracture in the continuum. The update and storage of the variables in particles have especial schemes for its correct treatment. The method and the meshing process is adapted for the simulation of an excavation problem. PFEM is presented as a very suitable tool for the treatment of excavation problem. The method gives solution for the analysis of all processes that derive from it. The method has a high versatility and a reasonable computational cost. The obtained results are really promising.

  Abstract
  The present work introduces a new application of the Particle Finite Element Method (PFEM) for the modeling of excavation problems. Lagrangian descriptions of motion of the [...]

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• Stabilized finite element methods for convection-diffusion-reaction, Helmholtz and Stokes problems

  P. Nadukandi, E. Oñate, J. García-Espinosa

  Monograph CIMNE (2012). M130

  
  

  Abstract

  We present three new stabilized finite element (FE) based Petrov–Galerkin methods for the convection–diffusion–reaction (CDR), the Helmholtz and the Stokes problems, respectively. The work embarks upon a priori analysis of some consistency recovery procedures for some stabilization methods belonging to the Petrov–Galerkin framework. It was found that the use of some standard practices (e. g.M-Matrices theory) for the design of essentially non-oscillatory numerical methods is not appropriate when consistency recovery methods are employed. Hence, with respect to convective stabilization, such recovery methods are not preferred. Next, we present the design of a high-resolution Petrov–Galerkin (HRPG) method for the CDR problem. The structure of the method in 1d is identical to the consistent approximate upwind (CAU) Petrov–Galerkin method [68] except for the definitions of the stabilization parameters. Such a structure may also be attained via the Finite Calculus (FIC) procedure [141] by an appropriate definition of the characteristic length. The prefix high-resolution is used here in the sense popularized by Harten, i. e.second order accuracy for smooth/regular regimes and good shock-capturing in non-regular regimes. The design procedure in 1d embarks on the problem of circumventing the Gibbs phenomenon observed in L2 projections. Next, we study the conditions on the stabilization parameters to circumvent the global oscillations due to the convective term. A conjuncture of the two results is made to deal with the problem at hand that is usually plagued by Gibbs, global and dispersive oscillations in the numerical solution. A multi dimensional extension of the HRPG method using multi-linear block finite elements is also presented. Next, we propose a higher-order compact scheme (involving two parameters) on structured meshes for the Helmholtz equation. Making the parameters equal, we recover the alpha-interpolation of the Galerkin finite element method (FEM) and the classical central finite difference method. In 1d this scheme is identical to the alphainterpolation method [140] and in 2d choosing the value 0.5 for both the parameters, we recover the generalized fourth-order compact Padé approximation [81, 168] (therein using the parameter gamma = 2). We follow [10] for the analysis of this scheme and its performance on square meshes is compared with that of the quasi-stabilized FEM [10]. Generic expressions for the parameters are given that guarantees a dispersion accuracy of sixth-order should the parameters be distinct and fourth-order should they be equal. In the later case, an expression for the parameter is given that minimizes the maximum relative phase error in 2d. A Petrov–Galerkin formulation that yields the aforesaid scheme on structured meshes is also presented. Convergence studies of the error in the L2 norm, the H1 semi-norm and the l1 Euclidean norm is done and the pollution effect is found to be small. Finally, we present a collection of stabilized FE methods derived via first-order and second-order FIC procedures for the Stokes problem. It is shown that several well known existing stabilized FE methods such as the penalty technique, the Galerkin Least Square (GLS) method [93], the Pressure Gradient Projection (PGP) method [35] and the orthogonal sub-scales (OSS) method [34] are recovered from the general iii residual-based FIC stabilized form. A new family of Pressure Laplacian Stabilization (PLS) FE methods with consistent nonlinear forms of the stabilization parameters are derived. The distinct feature of the family of PLS methods is that they are nonlinear and residual-based, i. e.the stabilization terms depend on the discrete residuals of the momentum and/or the incompressibility equations. The advantages and disadvantages of these stabilization techniques are discussed and several examples of application are presented.

  Abstract
  We present three new stabilized finite element (FE) based Petrov–Galerkin methods for the convection–diffusion–reaction (CDR), the Helmholtz and the Stokes [...]

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• Clasificadores basados en máquinas de soporte vertical para el diagnóstico y predicción de la enfermedad de Alzheimer

  G. Gavidia, E. Soudah, E. Oñate

  Monograph CIMNE (2012). M131

  
  

  Abstract

  En este trabajo, se estableció una metodología de soporte al diagnostico de AD, principalmente en sus etapas MCI ocasionado por AD y demencia ocasionada por AD. Para este fin fueron obtenidos casos clínicos de dos proyectos de investigación en demencia del tipo AD de reconocida trayectoria: las bases de datos Alzheimer's Disease Neuroimaging Initiative (ADNI) (www.loni.ucla.edu/ADNI) y la base de datos The Open Access Series of Imaging Studies (OASIS) (http://www.oasis-brains.org/). Asimismo, fueron establecidas dos tareas principales: la selección de variables predictoras de AD y la construcción de modelos de clasificacion basados en máquinas de soporte vectorial (SVM), entrenados a partir de las variables seleccionadas. Las variables predictoras seleccionadas estuvieron conformadas por biomarcadores morfométricos y características socio-demográficas y neuropsicológicas. Estas variables deberan ser útiles para la discriminación de casos clínicos en tres estados: (1) Estado normal (generalmente personas mayores sanas); (2) Estado MCI ocasionado por AD; y (3) Etapa de demencia ocasionada por AD. Por otro lado, los modelos SVM estarán enfocados a dos tareas principales: (1) Diagnóstico de AD mediante la discriminación entre sujetos sanos y sujetos con AD; y (2) Predicción de AD, orientada a la discriminación de sujetos MCI con riesgo de convertirse a AD y sujetos MCI sin riesgo de conversión. Asimismo, estos modelos deberán garantizar resultados aceptables, respecto a la sensibilidad y especificidad de las tareas de clasificación. Los resultados obtenidos en esta investigación son prometedores. Por un lado, el subconjunto de variables seleccionadas como relevantes para el diagnóstico de AD, tienen correlación con los resultados de investigaciones previas. Asimismo, en la etapa de testeo, los resultados demostraron que los modelos SVM son de gran utilidad para el soporte diagnóstico clínico de esta enfermedad, siendo capaces de discriminar sujetos con AD de sujetos sanos (diagnóstico) con una exactitud mayor al 99% y distinguir a los sujetos MCI con riesgo de conversión a AD de los sujetos MCI sin riego de conversión (predicción) con una exactitud superior al 94%.

  Abstract
  En este trabajo, se estableció una metodología de soporte al diagnostico de AD, principalmente en sus etapas MCI ocasionado por AD y demencia ocasionada por [...]

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• A coupled Eulerian-Pfem model for the simulation of overtropping in rockfill dams

  A. Larese, E. Oñate, R. Rossi

  Monograph CIMNE (2012). M133

  
  

  Abstract

  Rockfill dams are nowadays often preferred over concrete dams because of their economic advantages, their flexible and thank to the great advance achieved in geosciences and geomechanics. Unfortunately their behavior in case of overtopping is still an open issue. In fact very little is known on this phenomenon that in most cases leads to the complete finite failure o the structure with catastrophic consequences in term of loss of lives and economic damage. The principal aim of the present work is the development of a computational method to simulate the overtopping and the beginning of failure of the downstream shoulder of a rockfill dam. The whole phenomenon is treated in a continuous framework. The fluid free surface problem outside and inside the rockfill slop e is treated using a unique Eulerian fixed mesh formulation. A level set technique is employed to track the evolution of the free surface. The traditional Navier-Stokes equations are modified in order to automatically detect the presence of the porous media. The non-linear seepage is evaluated using a quadratic form of the resistance law for which the Ergun's coefficients have been chosen.  

  Abstract
  Rockfill dams are nowadays often preferred over concrete dams because of their economic advantages, their flexible and thank to the great advance achieved in geosciences and [...]

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• Coupled wave-structure analysis for naval and offshore applications

  J. García-Espinosa, B. Servan Camas, D. Di Capua, P. Ubach de Fuentes, E. Oñate

  V Computational Methods in Marine Engineering (Marine 2013) , Hamburg (Germany)

  
  

  Abstract

  Wave-structure interaction is a topic of great interest in naval and offshore engineering. This interest is growing in the last years due to the boost given by the development of the marine renewable energy field. In this context the development of an efficient time-domain coupled waves-structure solver is a main request from the industry. Up to date the numerical seakeeping simulation has been mostly carried out using the frequency domain. The reason might be that the computational cost of time domain simulations were too high and computational time was too large. Moreover assumptions like linear waves and the harmonic nature of water waves made the frequency domain to be the right choice. However nowadays computing capabilities make possible to carry out numerical simulations in the time domain in a reasonable time, with the advantage of making easier the introduction of non-linearities into the algorithm and therefore coupling with other phenomena. This presentation shows the work of the authors in developing a time-domain unstructured Finite Element Method (FEM) algorithm for analysis of coupled wave-structure interaction. For this purpose, a new diffraction-radiation solver using the FEM was developed. The solver has been implemented in GPU, using CUDA architecture. The speed-up obtained ranges from 5 to 10 times compare to the implementation in a standard CPU with a conjugate gradient and ILU preconditioner. The seakeeping analysis tool has been integrated within a coupled waves-structure analysis tool. The coupling algorithm is based on a partitioned iterative algorithm, using an interpolation library able to communicate pressure forces and displacements of the structure at memory level. Furthermore, an innovative wetting and drying scheme able to improve the evaluation of the water action on the structure. The accuracy of the new seakeeping formulation for analysis of waves and floating structures interaction has been verified in different validation cases and practical applications. 

  Abstract
  Wave-structure interaction is a topic of great interest in naval and offshore engineering. This interest is growing in the last years due to the boost given by the development [...]

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• Evaluating performance of the air cushion and seals of a Surface-Effect Ship (SES)

  J. García-Espinosa, B. Servan Camas, D. Di Capua, P. Ubach de Fuentes, E. Oñate

  Presentations Repository of the International Centre for Numerical Methods in Engineering (CIMNE) (2013).

  
  

  Abstract

  This presentation shows the recent work of the authors in the development of a time-domain FEM model for evaluation of the seal dynamics of a surface effect ship. The fluid solver developed for this purpose, uses a potential flow approach along with a stream-line integration of the free surface. The presentation focuses on the free surface-structure algorithm that has been developed to allow the simulation of the complex and highly dynamic behavior of the seals in the interface between the air cushion, and the water. The developed fluid-structure interaction solver is based, on one side, on an implicit iteration algorithm, communicating pressure forces and displacements of the seals at memory level and, on the other side, on an innovative wetting and drying scheme able to predict the water action on the seals. The stability of the iterative scheme is improved by means of relaxation, and the convergence is accelerated using Aitken’s method. Several validations against experimental results have been carried out to demonstrate the developed algorithm.

  Abstract
  This presentation shows the recent work of the authors in the development of a time-domain FEM model for evaluation of the seal dynamics of a surface effect ship. The fluid [...]

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• A computational model for the evaluation of the spray generation of a Wave Adaptive Modular Vessel

  J. García-Espinosa, E. Oñate, B. Servan Camas, P. Nadukandi, P. Becker

  Presentations Repository of the International Centre for Numerical Methods in Engineering (CIMNE) (2016).

  
  

  Abstract

  A Wave Adaptive Modular Vessel (WAM-V®) is a new class of ship that uses inflatable flexible hulls to conform to the surface of the water. It is similar in design to a catamaran, in that it has a twin hull design and no keel. However, the superstructure is not rigidly attached to the hulls; it uses shock absorbers and ball joints to articulate the vessel, which allows WAM-V to conform to the surface of the water while mitigating the stresses transmitted to the structure. Moreover, the inflatable hulls help to absorb the high frequency wave-loads. These features allow WAM-V to travel efficiently with low wave resistance in rough seas, by surfing on top of the waves rather than cut through them. The objective of the WAM-V is to be a lightweight watercraft capable of moving fast and efficiently on the surface of the sea. WAM-Vs are designed to allow for a variety of applications for either manned or unmanned operations and can be built in different lengths to match specific services. This presentation shows part of the work done in the project ‘Advanced Numerical Simulation and Performance Evaluation of WAM-V ® in Spray Generating Conditions’ developed by the International Center for Numerical Methods in Engineering (CIMNE) under Navy Grant N62909-12-1-7101 issued by the Office of Naval Research Global. The scope of that project included the performance analysis of the WAM-V in waves, taking into account the flexibility of the ship hulls, using fluid-structure interaction computational models. However, the focus of this paper is one of the primary concerns of that project; the development of a computational model for simulation of the WAM-V under spray generating conditions. In this regards, the final goal was to develop and demonstrate a computational engineering solver that could be used to design strategies to reduce the spray generation of the vessel.

  Abstract
  A Wave Adaptive Modular Vessel (WAM-V®) is a new class of ship that uses inflatable flexible hulls to conform to the surface of the water. It is similar in design to a [...]

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• Advances in the Development of the Discrete Element Method for Excavation Processes

  C. Labra, E. Oñate, J. Rojek

  Monograph CIMNE (2012). M132

  
  

  Abstract

  Modelling of granular materials, soils and rocks has been a challenging topic of investigation for decades. Classical continuum mechanics has been used to idealize soils and rocks, and numerical solution techniques such as finite element method (FEM) has been used to model these materials. Considering the idealization of the material, continuum mechanics allows the analysis of phenomena with discontinuous nature such as fracture in rock or soil via damage models. However, in more complex processes like rock milling or crushing, this kind of models are usually not suitable. Discrete models are more appropriate for problems with multiple discontinuities and particulate materials. The discrete element method (DEM) has been gaining popularity in analysis of granular materials, soils and rocks. Many aspects of this method still require more profound investigation. This work presents new developments of the discrete element method improving efficiency and accuracy of modelling of rock-like materials, especially in excavation processes. All the numerical algorithms has been implemented in an in-house software, which was then used to run numerical examples. The basic formulation of DEM with linear elastic-perfectly brittle contact model is presented. The main difference with other models found in the literature is the consideration of global stiffness and strength parameters that are constants in the whole model. The result of a simulations is strongly related with the configuration of the particle assembly used. Particle assemblies should be suficiently compact and ensure the isotropy to reproduce the physical properties of the modelled material. This work presents a novel technique for the generation of highly dense particle assemblies in arbitrary geometries, satisfying all the requirements for accurate discrete element simulations. One of the key issues in the use of the DEM is the estimation of the contact model parameters. A methodology is proposed for the estimation of the contact model parameters yielding required macroscopic properties of the material. The relationships between the contact model parameters and the mechanical properties of brittle materials, as well as the influence of the particles assembly configuration on the macroscopic properties, are analysed. A major dificulty in the application of the DEM to real engineering problems is the high computational cost in simulation involving a large number of particles. The most common way to solve this is the use of parallel computing techniques, where multiple processors are used. As an alternative, a coupling scheme between DEM and the finite element method (FEM) is proposed in the work. Within the hybrid DEM/FEM model, DEM is only used in the region of the domain where it provides an advantage over a continuum-based approach, as the FEM. The coupling is dynamically adapted, starting with the whole domain discretized with FEM. During the simulation, in the regions where a high stress level are found, a change of modelling method from continuum FEM to the discrete DEM is employed. Finally, all the developments are applied to the simulation of a real excavation process. An analysis of the rock cutting process with TBM disc cutters is performed, where DEM and the DEM/FEM coupling technique presents an important advantage over other simulation techniques.

  Abstract
  Modelling of granular materials, soils and rocks has been a challenging topic of investigation for decades. Classical continuum mechanics has been used to idealize soils and [...]

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• Desarrollo de una Herramienta de Procesamiento de Imágenes Médicas en MATLAB y su Integración en Medical GiD

  G. Gavidia, M. Cerrolaza, E. Oñate, E. Soudah, J. Pérez

  (2009). Technical Report, IT595

  
  

  Abstract

  El rápido avance de las tecnologías de adquisición de imágenes médicas ha hecho necesario el desarrollo de diversas aplicaciones en el área de la biomedicina. Por un lado, el trabajo que los médicos desarrollan en cuanto al análisis de las imágenes, es arduo y sujeto a errores, por lo que se hace necesaria la implementación de algoritmos de procesamiento que automaticen esta tarea y sirvan de soporte a los profesionales de la salud para realizar un diagnóstico fiable. Por otro lado, los biomédicos dedicados al modelado y simulación del cuerpo humano y el diseño de prótesis e implantes para tratamiento médico, requieren de modelos geométricos que consideren la complejidad característica de las estructuras anatómicas del cuerpo humano y les permita realizar un modelado discreto más preciso. Es por esto, que la comunidad de biomédicos, particularmente el área de analistas de imágenes médicas, hoy en día, dedican sus esfuerzos a extraer con ayuda del ordenador, información clínica, cualitativa y cuantitativa de las estructuras del cuerpo humano: tejidos blandos, duros, fluidos y sus patologías a partir del procesamiento de imágenes médicas de diversas modalidades: Tomografía Computarizada, Resonancia Magnética, Medicina Nuclear, entre otras.

  Abstract
  El rápido avance de las tecnologías de adquisición de imágenes médicas ha hecho necesario el desarrollo de diversas aplicaciones en el área [...]

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• CIMNE Verification of the validation analysis of Xfinas elements database

  E. Oñate, A. Larese

  (2009). Technical Report, IT570

  
  

  Abstract

  In order to validate the Xfinas code a very comprehensive series of test examples were solved by Prof Ki-Du Kim and his co-workers. A collection of the more representative benchmarks were chosen at CIMNE for testing the good behavior of every element implemented in the software. The aim of the validation work carried out at CIMNE has been to asses the accuracy of the Xfinas program. This was done studying the whole validation process carried out by Prof Ki-Du Kim’s team in detail. For this purpose we have chosen at CIMNE randomly the different benchmarks to be reproduced between those of the validation manual (VM from now on). In every example we checked the agreement of the results with the Xfinas validation data.

  Abstract
  In order to validate the Xfinas code a very comprehensive series of test examples were solved by Prof Ki-Du Kim and his co-workers. A collection of the more representative [...]

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