Research Reports of the International Centre for Numerical Methods in Engineering (CIMNE) : Scipedia

Analysis of time dependent problems using exponential basis functions
B. Movahedian, B. Boroomand

(2011). PI364

Abstract
In this research we present a method based on using Exponential Basis Functions (EBFs) to solve a class of time dependent engineering problems. The solution is first approximated by a summation of EBFs satisfying the differential equation and then completed by satisfying the time dependent boundary conditions as well as the initial conditions through a collocation method. This can be performed by considering two approaches. In the first one the solution is split into three parts, i.e. a homogeneous solution obtained by homogeneous boundary conditions, a homogeneous solution obtained by non-homogeneous solution and finally a particular solution induced by source terms. In the second approach the solution is split into two parts, i.e. a homogeneous solution and a particular solution induced by source terms. The two approaches are then employed to construct a time marching algorithm for the solution of problems over a long period of time. We shall present the details of the application of the two approaches introduced to some mathematical and engineering problems. The details of the time marching algorithm proposed are explained. Several problems are solved to show the capabilities of the approaches used. Some benchmark problems are also devised and solved for further studies. It is shown that the one of the introduced approaches is capable of solving a class of problems with moving boundaries.
Abstract
In this research we present a method based on using Exponential Basis Functions (EBFs) to solve a class of time dependent engineering problems. The solution is first approximated [...]
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Exponential basis functions in solution of incompressible fluid problems with moving free surfaces
S. Zandi, B. Boroomand, S. Soghrati

(2011). PI363

Abstract
In this report, a new simple meshless method is presented for the solution of incompressible inviscid fluid flow problems with moving boundaries. A Lagrangian formulation established on pressure, as a potential equation, is employed. In this method, the approximate solution is expressed by a linear combination of exponential basis functions (EBFs), with complex-valued exponents, satisfying the governing equation. Constant coefficients of the solution series are evaluated through point collocation on the domain boundaries via a complex discrete transformation technique. The numerical solution is performed in a time marching approach using an implicit algorithm. In each time step, the governing equation is solved at the beginning and the end of the step, with the aid of an intermediate geometry. The use of EBFs helps to find boundary velocities with high accuracy leading to a precise geometry updating. The developed Lagrangian meshless algorithm is applied to variety of linear and nonlinear benchmark problems. Non-linear sloshing fluids in rigid rectangular two-dimensional basins are particularly addressed.
Abstract
In this report, a new simple meshless method is presented for the solution of incompressible inviscid fluid flow problems with moving boundaries. A Lagrangian formulation [...]
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Paralelización del código Stampack v7.10
W. Castelló, F. Flores

(2011). PI362

Abstract
El objetivo principal del presente informe es mostrar las mejoras en la performance del código Stampack, cuando se lo emplea en conjunto con OpenMP en máquinas del tipo multi-núcleo (ej.: Intel Core2 Duo, Intel Core2 Quad, etc) o multi-thread (ej.: Intel Core i3, i5, i7, etc). Esta última tecnología en los procesadores (multi-thread) permite aumentar de manera importante la potencia de cálculo, dado que además de contar con más de un procesador, permite aumentar los hilos (threads) de tareas simultaneas de cada núcleo. Por ejemplo un procesador Intel Core i3, puede tener dos procesadores y realizar dos tareas simultaneas por cada procesador, lo cual es equivalente a tener una máquina con cuatro procesadores. En el caso del procesador Intel Core i7 empleado en este trabajo cuenta con cuatro núcleos y la posibilidad de realizar dos tareas simultaneas por núcleo, lo cual equivale a tener ocho procesadores. La paralelización del software Stampack se ha realizado siguiendo la idea básica de modificar o intervenir mínimamente los archivos fuente originales de la versión serial. Bajo estas condiciones, se ha realizado un análisis de tiempos para detectar zonas del código que representen un importante porcentaje del tiempo total de cálculo. Para finalizar se debe destacar que el software paralelizado debe funcionar también de manera correcta cuando es ejecutado en ordenadores con un solo procesador, de manera que la versión paralela debe ser compatible en su totalidad con la versión serial original del código Stampack.
Abstract
El objetivo principal del presente informe es mostrar las mejoras en la performance del código Stampack, cuando se lo emplea en conjunto con OpenMP en máquinas [...]
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Simplificación de mallas de triángulos
M. Pasenau, C. Andújar

(2011). PI361

Abstract
El objetivo principal del proyecto de fin de carrera es el análisis, diseño, implementación y prueba de un algoritmo que permita simplificar rápidamente una malla de triángulos muy densa, tratando de minimizar tanto el error geométrico como el error de atributos definidos en la superficie, para que el usuario pueda interaccionar con ella en plataformas modestas.
Abstract
El objetivo principal del proyecto de fin de carrera es el análisis, diseño, implementación y prueba de un algoritmo que permita simplificar rápidamente [...]
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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). 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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El ciclo de las ideas en la I+D+I
E. Oñate

(2011). PI354

Abstract
Cuando se habla de la investigación, el desarrollo tecnológico y la innovación (I+D+I en siglas, que yo escribo todas en mayúsculas [1]) es frecuente confundir fines, medios y responsabilidades. La última moda parece que es exigir que los grupos que investigan en Universidades y Centros de I+D, sean "rentables". Es decir, se pretende que su investigación se financie con créditos públicos, que los resultados de la misma se implementen en el mercado rápidamente y que los beneficios de su comercialización sirvan para devolver los créditos y para refinanciar esos grupos. También parece que se echa de menos que las empresas investiguen más, es decir, que inviertan recursos en descubrir nuevos conocimientos. El límite caricaturesco de esas aspiraciones sería pretender que las empresas produjeran premios Nobel y que un grupo universitario estuviera entre los 10 primeros puestos en el ranking de la actividad económica de un país. Ciertamente, esto no es imposible, pero es altamente improbable. Lo contrario desgraciadamente es más frecuente. Es decir, que los investigadores universitarios en su afán por la supervivencia económica de sus grupos, descuiden sus tareas investigadoras y que las empresas, confundiendo lo que es un Departamento Técnico o de Proyectos, con un Departamento de Innovación, se consideren autosuficientes y menosprecien u obvien el contacto con el mundo de la I+D real.
Abstract
Cuando se habla de la investigación, el desarrollo tecnológico y la innovación (I+D+I en siglas, que yo escribo todas en mayúsculas [1]) es frecuente [...]
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On the use of exponential basis functions in the analysis of shear deformable laminated plates
M. Shahbazi, B. Boroomand, S. Soghrati

(2011). PI353

Abstract
In this report, we introduce a meshfree approach for static analysis of isotropic/orthotropic crossply laminated plates with symmetric/non-symmetric layers. Classical, first and third order shear deformation plate theories are employed to perform the analyses. In this method, the solution is first split into homogenous and particular parts and then the homogenous part is approximated by the summation of an appropriately selected set of exponential basis functions (EBFs) with unknown coefficients. In the homogenous solution the EBFs are restricted to satisfy the governing differential equation. The particular solution is derived using a similar approach and another series of EBFs. The imposition of the boundary conditions and determination of the unknown coefficients are performed by a collocation method through a discrete transformation technique. The solution method allows us to obtain semi-analytical solution of plate problems with various shapes and boundary conditions. The solutions of several benchmark plate problems with various geometries are presented to validate the results.
Abstract
In this report, we introduce a meshfree approach for static analysis of isotropic/orthotropic crossply laminated plates with symmetric/non-symmetric layers. Classical, first [...]
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Analysis of fluid-soil-structure interaction problems with the particle finite element method (PFEM)
E. Oñate, M. Celigueta, S. Idelsohn, F. Salazar, A. Larese, R. Rossi, B. Suárez, R. Morán

(2012). PI374

Abstract
We present some developments in the Particle Finite Element Method (PFEM) for analysis of coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). The PFEM uses an updated Lagrangian description to model the motion of material points in both the fluid and the solid domains (the later including soil/rocks 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 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 river beds, the stability of breakwaters and constructions under sea waves, the falling of landslides on houses and into a reservoir and the failure of rockfill dams in overspill situations.
Abstract
We present some developments in the Particle Finite Element Method (PFEM) for analysis of coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). [...]
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Methodologies for tracking of load extremes and error estimation using probabilistic techniques
R. Flores, E. Ortega, R. López

(2012). PI375

Abstract
This work, conducted at CIMNE under ALEF project task 1.2.3, presents an investigation about the potential capabilities of neural networks to assist simulation campaigns. The discrete gust response of an aircraft has been chosen as a typical problem in which the determination of the critical loads requires exploring a large parameter space. A very simple model has been used to compute the aerodynamic loads. This allows creating a large database while at the same time retaining some of the fundamental properties of the problem. Using this comprehensive dataset the effects of network structure, training method and sampling strategy on the level of approximation over the complete domain have been investigated. The capabilities of the neural network to predict the peak load as well as the critical values of the design parameters have also been assessed. The applicability of neural networks to the combination of multi-fidelity results is also explored.
Abstract
This work, conducted at CIMNE under ALEF project task 1.2.3, presents an investigation about the potential capabilities of neural networks to assist simulation campaigns. [...]
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A four-noded quadrilateral element for composite laminated plates/shell using the refined zigzag theory
A. Eijo, E. Oñate, S. Oller

(2012). PI378

Abstract
A new bilinear 4-noded quadrilateral element (called QLRZ) for the analysis of composite laminated and sandwich plates/shells based on the refined zigzag theory (RZT) proposed by Tessler et al. [1] is presented. The element has seven kinematic variables per node. Shear locking is avoided by introducing an assumed linear shear strain field. The performance of the element is studied in several examples where the reference solution is the 3D finite element analysis using 20-noded hexahedral elements. Finally, the capability for capturing delamination effects is analyzed.
Abstract
A new bilinear 4-noded quadrilateral element (called QLRZ) for the analysis of composite laminated and sandwich plates/shells based on the refined zigzag theory (RZT) proposed [...]
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Puente Tensairity para pasarela peatonal en el PMT-UPC de Castelldefels (737-PRO-CA-5385)
C. Estruch, B. Suárez, J. Marcipar

(2012). PI380

Abstract
Actualmente el espacio formado por el “Parc Mediterrani de la Tecnologia” y el Campus Universitario de la Universitat Politècnica de Catalunya (PMT-UPC) de Castelldefels está en expansión. Es por ello que se está pensando en la construcción de dos pasarelas peatonales para cruzar la laguna de laminación de la “Olla del Rei”, conectando de esta forma el PMT-UPC con el paseo del Pitort. Dado que el PMT-UPC pretende ser un referente ambiental y tecnológico, se plantea como alternativa óptima la construcción de una pasarela peatonal ligera diseñada mediante una novedosa tecnología neumática conocida y patentada con el nombre de Tensairity®. Las estructuras ligeras son un reto para el ingeniero estructural y un importante avance hacia una arquitectura sostenible. Tensairity® es un concepto que hace referencia a estructuras neumáticas ligeras basadas en una sutil interacción entre cables, elementos de compresión, membranas y aire a baja presión. En Tensairity®, compresión y tracción están físicamente separados por una membrana de tejido hinchada a baja presión, el fin de la cual es, por un lado pretensar el elemento de tracción, y por el otro estabilizar el elemento de compresión frente al pandeo. Esto permite llevar al material hasta su límite plástico, tanto para tracción como para compresión, dando como resultado vigas que pueden ser varios órdenes de magnitud más ligeras que las vigas metálicas convencionales, manteniendo siempre su misma capacidad de carga. Aplicaciones ideales para esta tecnología son cerchas, estructuras con grandes luces, estructuras temporales, pasarelas peatonales o incluso estructuras de despliegue rápido para casos de emergencia, entre otras. La pasarela peatonal objeto de este proyecto está compuesta por dos partes bien diferenciadas, una pasarela Tensairity® que cruza la laguna de laminación y dos estructuras de madera a modo de embarcaderos, una a cada lado de la pasarela y donde ésta se apoya hasta alcanzar los caminos que bordean el trazado de la laguna. La pasarela Tensairity® está formada por dos vigas Tensairity® compuestas cada una de ellas por un tubo hinchable de PVC en cuya parte superior se apoya una viga de madera a modo de elemento de compresión y en su parte inferior una cinta de carga a modo de elemento de tracción. Sobre estas dos vigas se sustenta la superestructura de la pasarela formada por vigas transversales de madera sobre las que se apoya el tablero y las barandillas, también de madera. Las estructuras de apoyo se construyen igualmente en madera, con una tipología estructural similar al de la pasarela y mediante el uso de pilotes que recuerda en cierta manera los embarcaderos presentes en los ríos, de forma que la estructura completa esté integrada en el entorno.
Abstract
Actualmente el espacio formado por el “Parc Mediterrani de la Tecnologia” y el Campus Universitario de la Universitat Politècnica de Catalunya (PMT-UPC) [...]
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Continuum modelling using the discrete element method. theory and implementation in an object-oriented software platform
M. Santasusana, E. Oñate

(2012). PI381

Abstract
The Discrete Element Method is a relatively new technique that has nowadays and intense research in the field of numerical methods. In its first conception, the method was designed for simulations of dynamic system of particles where each element is considered to be an independent and non-deformable entity that interacts with other particles by the laws of the contact mechanics and moves following the second Newton’s law. This first approach for the DEM has obtained excellent results for granular media simulations or another discontinuouslike case. The existing challenge nowadays for the DEM is to be able to simulate the behaviour on a continuous media discretized by a mesh of particles ruled by the equations of the DEM. Although there exist more adequate methods to solve the continuous problem as they are the different variants of the Finite Element Method, the DEM is expected to have a better behaviour when the failure of the media occurs; in terms of tracking the evolution of the fracture locally between the elements of the discretization and also the post-fractural behaviour of the material. Nowadays, there are several DEM codes that try to solve this problem although there is no one which can assure an accurate solution applicable universally to any case. The objective of the present work is to develop calculation software for the Discrete Element Method included in the platform for numerical methods KRATOS, which is developed in CIMNE. One of the goals of the so-called DEM-Application is to be able to reproduce a wide set of engineering problems; not only the discrete ones such as the excavation or agroalimentary applications but also to reproduce the continuous media, simulating compression test for concrete or asphalt samples for instance. In addition it is desired that the application permits the coupling with another methods, particularly the Finite Element Method. In order to do this, the present work includes the study of all the advances and ideas that, globally in the numerical method field and particularly in CIMNE, have been discussed to give other approaches and to keep improving and developing the to the Discrete Element Method.
Abstract
The Discrete Element Method is a relatively new technique that has nowadays and intense research in the field of numerical methods. In its first conception, the method was [...]
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Proper generalized decomposition for parameterized Helmholtz problems in heterogeneous and unbounded domains: Application to harbor agitation
D. Modesto, S. Zlotnik, A. Huerta

(2013). PI401

Abstract
Solving the Helmholtz equation for a large number of input data in an heterogeneous media and unbounded domain still represents a challenge. This is due to the particular nature of the Helmholtz operator and the sensibility of the solution to small variations of the data. Here a reduced order model is used to determine the scattered solution everywhere in the domain for any incoming wave direction and frequency. Moreover, this is applied to a real engineering problem: water agitation inside real harbors for low to mid-high frequencies. The Proper Generalized Decomposition (PGD) model reduction approach is used to obtain a separable representation of the solution at any point and for any incoming wave direction and frequency. Here, its applicability to such a problem is discussed and demonstrated. More precisely, the separability of the operator is addressed taking into account both the non-constant coe
Abstract
Solving the Helmholtz equation for a large number of input data in an heterogeneous media and unbounded domain still represents a challenge. This is due to the particular [...]
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Desarrollo y aplicación de un modelo de elementos finitos para cálculo de vigas con materiales compuestos laminados basado en la teoría de Timoshenko
A. Llanos, E. Oñate, F. Zárate

(2013). PI398

Abstract
Actualmente existen programas de MAT-fem para calcular vigas de material homogéneo, según la teoría de Euler-Bernoulli o de Timoshenko. El objetivo de la presente tesina es conseguir un nuevo programa capaz de calcular vigas de materiales compuestos con la teoría de Timoshenko. En el capítulo 1, se introducen los materiales compuestos describiendo las ventajas y aplicaciones que tienen hoy en día en el ámbito de la Ingeniería Cívil. En el capítulo 2 y 3 se expone la teoría de las vigas planas laminadas y, en particular, de las vigas compuestas de Timoshenko. El capítulo 4 explica cómo se ha llevado a cabo la implementación numérica y da paso al capítulo 5, en el que se exponen varios ejemplos. Por último, en el capítulo 6, se exponen las conclusiones que se extraen del trabajo realizado y de los resultados obtenidos. Finalmente se presentan los anejos. Primero, en el anejo 1, se muestra un ejemplo real de refuerzo de viga mediante materiales compuestos. En el segundo anejo se presentan más ejemplos de los expuestos en el quinto capítulo y, por último, se termina la tesina con el anejo 3, que presenta los distintos archivos de programación utilizados para el cálculo de vigas compuestas de Timoshenko.
Abstract
Actualmente existen programas de MAT-fem para calcular vigas de material homogéneo, según la teoría de Euler-Bernoulli o de Timoshenko. El objetivo de [...]
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Numerically stable formulas for a material point based explicit exponential integrator
P. Nadukandi

(2014). PI408

Abstract
We present numerically stable formulas for the analytical solution in the closed form of the so-called X-IVAS scheme in 3D. The X-IVAS scheme is a material point based explicit exponential integrator. An intermediate step in the X-IVAS scheme is the solution of tangent curves for piecewise linear vector fields defined on simplicial meshes. This is what we refer to as particle tracing of streamlines and independent formulas for the same can be easily distilled from the ones presented for the X-IVAS scheme. The formulas involve functions of matrices which are defined using the corresponding Newton interpolating polynomial. The evaluation of these formulas is stable, i.e. a certain number of significant digits in the computed values are guaranteed to be exact. Using the double-precision floating-point arithmetic specified by the IEEE 754 standard, we obtain at least 10 significant decimal digits in the worst case scenarios. These scenarios involve fourth-order divided differences of the exponential function. Additionally, an optimal series approximation of divided differences is presented which is an essential part of the exposition.
Abstract
We present numerically stable formulas for the analytical solution in the closed form of the so-called X-IVAS scheme in 3D. The X-IVAS scheme is a material point based [...]
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PARACHUTES: A computer program for calculating ram-air parachutes. Theory document
E. Ortega, R. Flores

(2016). PI415

Abstract
PARACHUTES is a computer program developed at the International Center for Numerical Methods in Engineering (CIMNE) for the simulation of ram-air (gliding) parachute systems. The solution methodology in PARACHUTES is based on two unsteady calculation modules which work in a coupled manner. The aerodynamics of the gliding parachute is solved by a low-order panel method and a finite-element technique is used for the structure. The latter allows modelling the suspension lines, textile fabric and suspended payloads of a typical parachute system by means of cable, membrane and solid linear elements. For specified flight conditions, the simulation program solves the fluid-structural problem governing the behavior of arbitrary parachute-payload configurations and also allows analyzing user-defined maneuvers. This document describes the theoretical formulation and the numerical procedures adopted in PARACHUTES.
Abstract
PARACHUTES is a computer program developed at the International Center for Numerical Methods in Engineering (CIMNE) for the simulation of ram-air (gliding) parachute systems. The [...]
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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). 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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On using linear elements in incompressible plane strain problems. A simple edge based approach for triangles
B. Boroomand, B. Khalilian

(2004). PI248

Abstract
In this paper a simple iterative method is presented for finite element solution of incompressible plane strain problems using linear elements. Instead of using a mixed formulation approach, we use an equivalent displacement/velocity approach in an iterative manner. Control volumes are taken for regions where are to exhibit incompressible behavior. For triangular elements the control volume is chosen as the area built on the parts of each pair of elements at the sides of an edge. In this case, elements are let to exchange volume. It is shown that the proposed edge based approach removes the deficiency of the linear triangular elements i.e. locking effect.Similar edge based approach is applied to the linear quadrilateral elements. However, if the control volume is chosen as the element volume the formulation gives similar results as the discontinuous mixed formulation using one pressure point without exhibiting instability behavior. The formulation is based on decomposition of the displacement/velocity field into deviatoric and volumetric parts. The volumetric part is iteratively eliminated without confronting locking or instability phenomenon. The iterative procedure is very cheap and simple to be implemented in any FEM code. Several examples are given to demonstrate the performance of the procedure.
Abstract
In this paper a simple iterative method is presented for finite element solution of incompressible plane strain problems using linear elements. Instead of using a mixed formulation [...]
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On application of two superconvergent recovery procedures to plate problems
B. Boroomand, M. Ghaffarian, O. Zienkiewicz

(2004). PI247

Abstract
In this paper a study is performed on application of two recovery methods, i.e. Superconvergent Patch Recovery (SPR) and the Recovery by Equilibrium of Patches (REP), to plate problems. The two recovery methods have been recognized to give similar results in adaptive solutions of two dimensional stress problems. While the former applies a least square fit over a set of values at the so called superconvergent points, the latter does not need any knowledge of such points and thus has a wider application especially in non-linear problems. The formulation of REP is extended to Reissner-Mindlin plate problems. The convergence rates of the recovered fields of the gradients obtained from application of the two methods are compared using series of regular triangular and rectangular meshes for thick and thin plate solution cases. Assumed strain formulation based elements, i.e. the elements formulated by Mixed Interpolation of Tensorial Components, as well as conventional from of elements based on selective integration schemes are employed for the study. In order to investigate the possibility of any improvement in the results by adding equilibrium constraints to SPR, as some authors suggest for simple two-dimensional problems, some weighted forms of such conditions are designed and added to the formulation. Comprehensive study has been given first by varying the weight terms to obtain the best enhanced results and then using the optimal values to investigate the effects of the constraints on the rate of convergence. It is observed that despite of the cost of this approach, due to the coupling of the gradient terms, no significant improvement is achieved.
Abstract
In this paper a study is performed on application of two recovery methods, i.e. Superconvergent Patch Recovery (SPR) and the Recovery by Equilibrium of Patches (REP), to plate [...]
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On application of the finite point method to heat and elasticity problems
B. Boroomand, A. Tabatabaie, E. Oñate

(2004). PI249

Abstract
A stabilized version of the Finite Point Method (FPM) is presented. A source of instability due to the evaluation of the base function using a least square procedure is discussed. A suitable mapping is proposed and employed to eliminate the ill-conditioning effect due to directional arrangement of the points. A step by step algorithm is given for finding the local rotated axes and the dimensions of the cloud using local average spacing and inertia moments of the points distribution. It is shown that the conventional version of FPM may lead to wrong results when the proposed mapping algorithm is not used.It is shown that another source for instability and non-monotonic convergence rate in collocation methods lies in the treatment of Neumann boundary conditions. Unlike the conventional FPM, in this work the Neumann boundary conditions and the equilibrium equations appear simultaneously in a weight equation similar to that of weighted residual methods. The stabilization procedure may be considered as an interpretation of the Finite Calculus (FIC) method. The main difference between the two stabilization procedures lies in choosing the characteristic length in FIC and the weight of the boundary residual in the proposed method. The new approach also provides a unique definition for the sign of the stabilization terms. The reason for using stabilization terms only at the boundaries is discussed and the two methods are compared. Several numerical examples are presented to demonstrate the performance and convergence of the proposed methods.
Abstract
A stabilized version of the Finite Point Method (FPM) is presented. A source of instability due to the evaluation of the base function using a least square procedure is discussed. [...]
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On application of robustness test for error estimators to patches near kinked boundaries in three dimensional problems: Part I: Formulation
B. Boroomand, F. Mossaiby

(2004). PI250

Abstract
In this part of the paper we shall use the formulation given in the first part to assess the quality of recovery based error estimators using two recovery methods, i.e. Superconvergent Patch Recovery (SPR) and Recovery by Equilibrium in Patches (REP). The recovery methods have been shown to be asymptotically robust and superconvergent when applied to two dimensional problems. In this study we shall examine the behavior of the recovery methods on several three dimensional mesh patterns for patches located either inside or at boundaries. This is performed by first finding an asymptotic finite element solution, irrespective of boundary conditions at far ends of the domain, and then applying the recovery methods. The test procedure near kinked boundaries is explained in a step by step manner. The results are given in a series of tables and figures for various cases of three dimensional mesh patterns. It has been experienced that the full superconvergent property is generally lost due to presence of boundary layer solution and the definition of the recoveries near boundaries though the results of the robustness test is still within an acceptable range.
Abstract
In this part of the paper we shall use the formulation given in the first part to assess the quality of recovery based error estimators using two recovery methods, i.e. Superconvergent [...]
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Avances en la formulación de membranas
J. Valdés

(2004). PI266

Abstract
Avances en el análisis mediante elementos finitos de membranas curvas con ''wrinkling'' sujetas a grandes desplazamientos son presentados. Este reporte trata el estudio de membranas por el método de los elementos finitos mediante un análisis con no linealidad geométrica para materiales hiperelásticos. Una formulación sencilla en términos del tensor gradiente de deformación es usada para elementos finitos triangulares lineales. También se hace el análisis de membranas presforzadas, como se encuentran generalmente en la vida cotidiana.
Abstract
Avances en el análisis mediante elementos finitos de membranas curvas con ''wrinkling'' sujetas a grandes desplazamientos son presentados. Este [...]
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Innovative numerical tools for the simulation of parachutes
E. Ortega, R. Flores, E. Oñate, C. Sacco, E. González

(2010). PI341

Abstract
The design and evaluation of parachute-payload systems is an important field of applications in which numerical analysis tools can make very important contributions. This work describes new numerical developments carried out at CIMNE in this field, which involve a coupled fluid-structural solver intended for the unsteady simulation of ram-air type parachutes and a set of complementary tools aimed at studying trajectory and control systems effects. For an efficient solution of the aerodynamic problem, an unsteady panel method has been chosen exploiting the fact that large areas of separated flow are not expected under nominal flight conditions of ram-air parachutes. Besides, a dynamic explicit solver based on a finite element technique is chosen for the structure. This approach yields a robust solution even when highly non-linear effects due to large displacements and material asymmetric behaviours are present. The numerical results show considerable accuracy and robustness. An added benefit of the proposed aerodynamic and structural techniques is that they can be easily vectored and thus suitable for use in parallel architectures. The main features of the developed computational tools are described in this work and several numerical examples are provided to illustrate the good performance and potential of the proposed techniques. Further improvements of the methodology being carried out and future lines of investigation are also presented.
Abstract
The design and evaluation of parachute-payload systems is an important field of applications in which numerical analysis tools can make very important contributions. This [...]
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Análisis de flujos en lámina libre y su interacción con sólidos y estructuras por el método de partículas y elementos finitos (PFEM)
E. Oñate, B. Suárez, F. Salazar, R. Morán, M. Celigueta, S. Latorre

(2011). PI365

Abstract
Se describen los conceptos básicos del método de partículas y elementos finitos (PFEM) para análisis de flujos de fluidos en lámina libre y su interacción con objetos sólidos y estructuras flotantes o sumergidas. Se presentan diversas aplicaciones del PFEM en los ámbitos de la ingeniería de puertos e hidráulica y al estudio de la caída de una avalancha sobre un embalse.
Abstract
Se describen los conceptos básicos del método de partículas y elementos finitos (PFEM) para análisis de flujos de fluidos en lámina libre [...]
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An adaptive finite point method for aeroelastic analysis
E. Ortega, E. Oñate, S. Idelsohn

(2011). PI368

Abstract
An adaptive Finite Point Method (FPM) for solving aeroelastic compressible flow problems is presented. The numerical methodology is based on a meshless upwind-biased discretization of the Euler equations, written in arbitrary Lagrangian-Eulerian (ALE) form, and integrated in time by means of a dual-time steeping technique. This procedure allows achieving accurate solutions circumventing stability constraints of time marching schemes but profiting from its explicit features. In order to exploit the meshless potential of the method, the domain deformation approach implemented is based on the spring network analogy and ''h''-adaptivity is also employed in the computations. Several numerical examples involving typical aeroelastic problems illustrate the performance of the proposed technique. Moreover, evidence about the computational cost and parallel performance of the method is given.
Abstract
An adaptive Finite Point Method (FPM) for solving aeroelastic compressible flow problems is presented. The numerical methodology is based on a meshless upwind-biased discretization [...]
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The particle finite element method. An overview
E. Oñate, S. Idelsohn, F. Pin, R. Aubry

(2004). PI243

Abstract
We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use of a Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are thus viewed as particles which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations, expressed in an integral from, are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility condition in the fluid is introduced via the finite calculus (FIC) method. A fractional step scheme for the transient coupled fluid-structure solution is described. Examples of application of the PFEM method to solve a number of fluid-structure interaction problems involving large motions of the free surface and splashing of waves are presented.
Abstract
We present a general formulation for analysis of fluid-structure interaction problems using the particle finite element method (PFEM). The key feature of the PFEM is the use [...]
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Sistemas de ayuda a la decisión en ingeniería civil. posibilidades y perspectivas
E. Oñate, J. Marcipar, J. Piazzese

Research Reports of the International Centre for Numerical Methods in Engineering (CIMNE) (2019). 30

Abstract
La eclosión de las Tecnologías de la Información y las Comunicaciones (TIC), y en particular de Internet, ha facilitado el desarrollo de sistemas que, apoyados por bases de datos y potentes programas de simulación, transforman la información que existe en relación con un problema concreto, en conocimiento que permite tomar decisiones para su solución. Los denominados Sistemas de Ayuda a la Decisión (SAD) son ya una realidad en múltiples áreas de la ingeniería. En este trabajo se analizan las posibilidades y perspectivas de los SAD en ingeniería civil y se presentan tres ejemplos concretos de su aplicación a la prevención del riesgo de inundaciones y a la gestión de las emergencias correspondientes, al diseño de instalaciones en proyectos urbanísticos y a la gestión energética en municipios.
Abstract
La eclosión de las Tecnologías de la Información y las Comunicaciones (TIC), y en particular de Internet, ha facilitado el desarrollo de sistemas que, [...]
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Improving an input of material model in the D-DEMPack package programme in the Kratos application for granular non-cohesive materials
H. Koszur

(2015). PI412

Abstract
The main objective of this document is to present an idea of calibration tests used to improve an input material model in the DEM simulations in the D-DEMPack package programme in the Kratos application, which is developed in CIMNE. Presented method lets increase the precision and validity of discrete element modeling work. The calibration tests presented in this protocol may be used for granular non-cohesive materials ( for loose, dry granular material). They concern only the sphere shape of particles. The tests were conducted on couple different sizes of particles, in this work are presented results for average diameter of grains equal to 5cm (normal distribution with standard deviation equal to 0,05). The results of research may provide a basis for proper computing project data for preparing material model for loose, dry granular material. Tested by the author methods have been developed based on an article [1].
Abstract
The main objective of this document is to present an idea of calibration tests used to improve an input material model in the DEM simulations in the D-DEMPack package programme [...]
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Advances in the formulation of the rotation-free basic shell triangle
E. Oñate, F. Flores

(2003). PI241

Abstract
A family of rotation-free three node triangular shell elements is presented. The simplest element of the family is based on an assumed constant curvature field expressed in terms of the nodal deflections of a patch of four elements and a constant membrane field computed from the standard linear interpolation of the displacements within each triangle. An enhanced version of the element is obtained by using a quadratic interpolation of the geometry in terms of the six patch nodes. This allows to compute an assumed linear membrane strain field which improves the in-plane behaviour of the original element. A simple and economic version of the element using a single integration point is presented. The efficiency of the different rotation-free shell triangles is demonstrated in many examples of application including linear and non linear analysis of shells under static and dynamic loads, the inflation and de-inflation of membranes and a sheet stamping problem.
Abstract
A family of rotation-free three node triangular shell elements is presented. The simplest element of the family is based on an assumed constant curvature field expressed in [...]
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Updated Lagrangian mixed finite element formulation for quasi and fully incompressible fluids
E. Oñate, J. Carbonell

(2013). PI393

Abstract
We present a mixed velocity-pressure finite element formulation for solving the updated Lagrangian equations for quasi and fully incompressible fluids. Details of the governing equations for the conservation of momentum and mass are given in both differential and variational form. The finite element interpolation uses an equal order approximation for the velocity and pressure unknowns. The procedure for obtaining stabilized FEM solutions is outlined. The solution in time of the discretized governing conservation equations using an incremental iterative segregated scheme is described. The linearization of these equations and the derivation of the corresponding tangent stiffness matrices is detailed. Other iterative schemes for the direct computation of the nodal velocities and pressures at the updated configuration are presented. The advantages and disadvantages of choosing the current or the updated configuration as the reference configuration in the Lagrangian formulation are discussed.
Abstract
We present a mixed velocity-pressure finite element formulation for solving the updated Lagrangian equations for quasi and fully incompressible fluids. Details of the governing [...]
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Stabilized solution of the multidimensional advection-diffusion-absorption equation using linear finite elements
E. Oñate, J. Miquel, F. Zárate

(2004). PI269

Abstract
A stabilized finite element method (FEM) for the multidimensional steady state advection-diffusion-absorption equation is presented. The stabilized formulation is based on the modified governing differential equations derived via the Finite Calculus (FIC) method. For 1D problems the stabilization terms act as a nonlinear additional diffusion governed by a single stabilization parameter. It is shown that for multidimensional problems an orthotropic stabilizing diffusion must be added along the principal directions of curvature of the solution. A simple iterative algorithm yielding a stable and accurate solution for all the range of physical parameters and boundary conditions is described. Numerical results for 1D and 2D problems with sharp gradients are presented showing the effectiveness and accuracy of the new stabilized formulation.
Abstract
A stabilized finite element method (FEM) for the multidimensional steady state advection-diffusion-absorption equation is presented. The stabilized formulation is based on [...]
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Lagrangian analysis of multiscale particulate flows with the particle finite element method
E. Oñate, M. Celigueta, S. Latorre, G. Casas, R. Rossi, J. Rojek

Comp. Part. Mech (2014). (prepint) Vol. 1 pp. 85-102; doi: 10.1007/s40571-014-0012-9

Abstract
We present a Lagrangian numerical technique for the analysis of flows incorporating physical particles of different sizes. The numerical approach is based on the Particle Finite Element Method (PFEM) which blends concepts from particle-based techniques and the FEM. The basis of the Lagrangian formulation for particulate flows and the procedure for modelling the motion of small and large particles that are submerged in the fluid are described in detail. The numerical technique for analysis of this type of multiscale particulate flows using a stabilized mixed velocity-pressure formulation and the PFEM is also presented. Examples of application of the PFEM to several particulate flows problems are given.
Abstract
We present a Lagrangian numerical technique for the analysis of flows incorporating physical particles of different sizes. The numerical approach is based on the Particle [...]
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Modelització del deflectòmetre d’impacte amb el mètode dels elements finits i les partícules
M. Font, E. Oñate, J. Carbonell

(2011). PI366

Abstract
El deflectòmetre d’impacte segurament és l’aparell més utilitzat per realitzar assaigs no destructius dels ferms. Els enginyers utilitzen el deflectòmetre d’impacte per estimar els mòduls elàstics de les diferents capes que conformen el ferm assumint una aproximació quasi estàtica del fenomen. Amb la utilització del Mètode dels Elements Finits i les Partícules (PFEM), per una banda es pot simular l’impacte que provoca el deflectòmetre d’impacte sobre el ferm, i de l’altra validar el PFEM com a model axisimètric de resposta dinàmica d’un ferm. La validació consisteix a comparar la concavitat de deflexions mesurada pel deflectòmetre d’impacte amb la concavitat de deflexions calculada amb el PFEM utilitzant els mòduls elàstics que proporciona el càlcul invers. Els capítols 2 i 3 inclouen el marc teòric en el qual es desenvolupa el treball. El capítol 2 inclou una introducció als ferms, presenta el concepte de deflexió, fa un repàs dels equips d’avaluació no destructiva i presenta un resum dels diferents mètodes existents per al càlcul de paviments flexibles. El capítol 3 és una introducció al Mètode dels Elements Finits i les Partícules. El capítol 4 presenta els desenvolupaments dels objectius plantejats. Per últim, es presenten unes consideracions finals, que inclouen les conclusions, possibles millores del programa d’ordinador emprat i propostes de futures línies d’investigació. Els annexes inclouen els resultats de tots els casos calculats amb les taules i les gràfiques corresponents.
Abstract
El deflectòmetre d’impacte segurament és l’aparell més utilitzat per realitzar assaigs no destructius dels ferms. Els enginyers utilitzen [...]
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Open tools for electromagnetic simulation programs
J. Mora, R. Otín, P. Dadvand, E. Escolano, M. Pasenau, E. Oñate

(2005). PI273

Abstract
Computational electromagnetism requires a wide range of numerical methods depending on the application, the topology of the geometry, the frequency and the quality of the solution. Different efforts have been done to develop a universal software package able to deal with any problem, by integrating existing specific modules in the same interface. Nevertheless, modern computational approaches suggest to use a common basic environment, as high level computing lenguage, to be adapted to the requirements done by the end-user. Following this philosophy, this paper proposes three useful computer tools, combining the most usual requirements, to be customised for any electromagnetic problem.
Abstract
Computational electromagnetism requires a wide range of numerical methods depending on the application, the topology of the geometry, the frequency and the quality of the [...]
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A particle finite element method for analysis of industrial forming processes
E. Oñate, A. Franci, J. Carbonell

(2014). PI406

Abstract
We present a generalized Lagrangian formulation for analysis of industrial forming processes involving thermally coupled interactions between deformable continua. The governing equations for the deformable bodies are written in a unified manner that holds both for fluids and solids. The success of the formulation lays on a residual-based expression of the mass conservation equation obtained using the Finite Calculus (FIC) method that provides the necessary stability for quasi/fully incompressible situations. The governing equations are discretized with the FEM via a mixed formulation using simplicial elements with equal linear interpolation for the velocities, the pressure and the temperature. The merits of the formulation are demonstrated in the solution of 2D and 3D thermally-coupled forming processes using the Particle Finite Element Method (PFEM).
Abstract
We present a generalized Lagrangian formulation for analysis of industrial forming processes involving thermally coupled interactions between deformable continua. The governing [...]
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Analysis of fluid-soil-structure interaction problems with the Particle Finite Element Method (PFEM)
E. Oñate, M. Celigueta, S. Idelsohn, F. Salazar, A. Larese, R. Rossi, B. Suárez, R. Morán

(2012). PI374

Abstract
We present some developments in the Particle Finite Element Method (PFEM) for analysis of coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). The PFEM uses an updated Lagrangian description to model the motion of material points in both the fluid and the solid domains (the later including soil/rocks 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 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 river beds, the stability of breakwaters and constructions under sea waves, the falling of landslides on houses and into a reservoir and the failure of rockfill dams in overspill situations.
Abstract
We present some developments in the Particle Finite Element Method (PFEM) for analysis of coupled problems in mechanics involving fluid-soil-structure interaction (FSSI). [...]
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Modelo evolutivo del impacto de técnicas VaR en los mercados financieros
B. Llacay, G. Peffer

(2004). PI260

Abstract
Recently, some authors have warned of the increasingly widespread use of risk management techniques by financial institutions, arguing that this can cause the market to become more unstable. To analyse these claims, we present a model based on evolutionary game theory of a financial market, where part of the investors use the VaR technique to manage their risk. We study the evolution of this market through simulation, and we confirm that the use of risk management models can induce instability regimes in the market, characterised by sudden changes in the asset price and sharp increases in the volatility.
Abstract
Recently, some authors have warned of the increasingly widespread use of risk management techniques by financial institutions, arguing that this can cause the market to become [...]
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Development of a 6-DoF simulator for analysis and evaluation of autonomous parafoil systems
E. González, C. Sacco, E. Ortega, R. Flores

(2011). PI356

Abstract
The role parachutes have in many civil, humanitarian and military applications call for new and improved computational tools aimed at tackling the current lack of software applications in the field. The present project, which is part of a research line being developed at CIMNE for these purposes, involves the development of numerical tools for the analysis and evaluation of autonomous parafoil systems. These tools, which are based on a 6-DOF dynamic parachute model and a GNC system implemented by means of PID algorithms, facilitate the user to test designs, develop and evaluate control strategies and analyze real-life drop scenarios. As an example of potential use, lateral and altitude control strategies were successfully developed and tested. Future implementations will include Monte Carlo simulations for statistical analysis of landing precision, parameter identification for flight-tests data reduction and an advanced GUI. The dynamic simulator presented in this work, together with the aerodynamic and structural tools developed by CIMNE, allow simulating the complete parachute-payload system, letting the designer to analyse design variations before building prototypes, the control system engineer to test different control strategies and the flight test engineer to predict the real performance of the system even before flying it once. In brief, involving simulation in the whole development process increases chances of success, shortening development time and costs.
Abstract
The role parachutes have in many civil, humanitarian and military applications call for new and improved computational tools aimed at tackling the current lack of software [...]
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Explicit dynamic analysis of thin membrane structures
R. Flores, E. Ortega, E. Oñate

(2011). PI351

Abstract
An explicit dynamic structural solver developed at CIMNE for the analysis of parachutes is presented. The canopy fabric has a negligible out-of-plane stiffness, therefore its numerical study presents important challenges. Both the large changes in geometry and the statically indeterminate character of the system are problematic from the numerical point of view. This report covers the reasons behind the particular choice of solution scheme as well as a detailed description of the underlying algorithm. Both the theoretical foundations of the method and details of implementation aiming at improving computational efficiency are given. Benchmark cases to assess the accuracy of the solution as well as examples of practical application showing the performance of the code are finally presented.
Abstract
An explicit dynamic structural solver developed at CIMNE for the analysis of parachutes is presented. The canopy fabric has a negligible out-of-plane stiffness, therefore [...]
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A Particle Finite Element Method (PFEM) for coupled thermal analysis of quasi and fully incompressible flows and fluid-structure interaction
E. Oñate, A. Franci, J. Carbonell

(2014). PI403

Abstract
We present a Lagrangian formulation for coupled thermal analysis of quasi and fully incompressible flows and fluid-structure interaction (FSI) problems that has excellent mass preservation features. The success of the formulation lays on a residual-based stabilized expression of the mass balance equation obtained using the Finite Calculus (FIC) method. The governing equations are discretized with the FEM using simplicial elements with equal linear interpolation for the velocities, the pressure and the temperature. The merits of the formulation in terms of reduced mass loss and overall accuracy are verified in the solution of 2D and 3D adiabatic and thermally-coupled quasi-incompressible free-surface flow problems using the Particle Finite Element Method (PFEM). Examples include the sloshing of water in a tank and the falling of a water sphere and a cylinder into a tank containing water.
Abstract
We present a Lagrangian formulation for coupled thermal analysis of quasi and fully incompressible flows and fluid-structure interaction (FSI) problems that has excellent [...]
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El papel de los modelos numéricos en la investigación y el diseño de aliviaderos de presas
F. Salazar, J. Mauro, J. Irazábal, A. Larese, R. R. Rossi, E. Oñate, R. Morán, M. Toledo

(2013). PI396

Abstract
El Centro Internacional de Métodos Numéricos en Ingeniería (CIMNE) es un centro de investigación dependiente del Gobierno de Cataluña y de la Universidad Politécnica de Cataluña creado en 1987. Su principal actividad es el desarrollo y aplicación de métodos numéricos innovadores para resolver problemas prácticos en diversos campos de la ingeniería, y se desarrolla fundamentalmente en el marco de proyectos de investigación nacionales e internacionales. En los últimos años el centro ha participado en diversos proyectos relacionados con la seguridad de presas, fundamentalmente hidráulica, pero también estructural, en cooperación con diversas empresas y organismos públicos de investigación como el CEDEX y la UPM. La presente comunicación describe brevemente los objetivos principales de los mencionados proyectos, haciendo hincapié en cómo la modelación numérica ha contribuido a alcanzarlos.
Abstract
El Centro Internacional de Métodos Numéricos en Ingeniería (CIMNE) es un centro de investigación dependiente del Gobierno de Cataluña y [...]
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El valor del cálculo en los sistemas de ayuda a la toma de decisiones en ingeniería
E. Oñate

Revista de Obras Públicas (2004). Vol. 151 (3449), pp. 41-48;

Abstract
El artículo revindica el valor de los métodos de cálculo que se enseñan en las Escuelas de Ingeniería, como herramientas indispensables en los nuevos sistemas de ayuda a la toma de decisiones (SAD). Los SAD integran base de datos, métodos de cálculo y módulos de inteligencia artificial, y su utilización se extiende cada día más para ayuda al diseño y gestión de infraestructuras y servicios de ingeniería. En el texto se describen varios desarrollos y aplicaciones recientes de SAD en ingeniería civil. El artículo acaba con una reflexión sobre los límites de los SAD. The paper stresses the value of the computational methods taught in engineering faculties as indispensable tools within the new decision support systems (DSS). The DSS integrate data bases, computational methods and artificial intelligence modules. They are increasingly used for supporting the design and management of civil constructions and services in engineering. The paper describes recent developments and applications of DSS in civil engineering. The text ends up with a discussion on the limits of the DSS.
Abstract
El artículo revindica el valor de los métodos de cálculo que se enseñan en las Escuelas de Ingeniería, como herramientas indispensables [...]
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Unified updated Lagrangian formulation for the analysis of quasi and fully incompressible fluids and solids and their interaction via a partitioned scheme and the PFEM
A. Franci, E. Oñate, J. Carbonell

(2014). PI407

Abstract
In this work, a unified updated Lagrangian formulation for solving fluid-structure interaction (FSI) problems is derived. The mixed velocity-pressure formulation for hypoelastic solids and quasi and fully incompressible Newtonian fluids is obtained as an extension of the velocity formulation derived for a general continuum. The space discretization for the fluid domain is performed via the Particle Finite Element Method (PFEM), where for the solid domain a standard FEM is used. Linear interpolation is used for both the velocity and the pressure fields. The global FSI problem is solved using a Gauss-Seidel iterative scheme. The required stabilization for dealing with incompressible situations is given by an enhanced formulation of the Finite Calculus (FIC) technique [Oñate et al.]. The efficiency of the proposed strategy is tested by solving benchmark FSI problems.
Abstract
In this work, a unified updated Lagrangian formulation for solving fluid-structure interaction (FSI) problems is derived. The mixed velocity-pressure formulation for hypoelastic [...]
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Metodología para la obtención de información geográfica, geofísica y geo-ambiental desde imágenes satelitales.
J. Piazzese, E. Oñate

(2004). PI244
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Advances on Finite Element Methods and Particle-based Methods for Metal Forming Processes
E. Oñate

(2011). PI360

Abstract
The paper presents an overview of the advances in recent years on the finite element method (FEM) and on particle-based methods for the simulation of industrial metal forming processes. More specifically, we present the evolution of the FEM in the field from the early plastic/viscoplastic flow approaches to the new stabilized FEM for analysis of multiphysics bulk forming processes. Also the paper describes the state of the art in the new rotation-free shell elements for simulation of sheet stamping processes. Finally, we present the so-called Particle Finite Element Method (PFEM), as a component of a family of new computational techniques integrating particle-based methods and mesh-based procedures. The PFEM is particularly suited for large deformation problems in solids and fluids involving nonlinear mechanical and geometrical effects, fluid-structure interactions and frictional contact situations. Applications of the FEM and the PFEM to several metal and material forming processes are presented.
Abstract
The paper presents an overview of the advances in recent years on the finite element method (FEM) and on particle-based methods for the simulation of industrial metal forming [...]
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The Cycle of Ideas in research, development and technology transfer
E. Oñate

(2011). PI358

Abstract
When people talks about research, development and technology transfer (RTD in short) and commercial industrial activities, it is quite usual to mix up objectives, resources and responsibilities. There is a growing opinion, spread by some public administrators and the media, that research groups at universities and RTD centers must be "profitable". In few words, many persons would wish that research is funded with competitive funds or even loans (either public or private) and that the outcomes of the research get into the market rapidly, so that the profits from marketing the corresponding products will allow research groups to be financially self-sustaining.
Abstract
When people talks about research, development and technology transfer (RTD in short) and commercial industrial activities, it is quite usual to mix up objectives, resources [...]
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Possibilities of the particle finite element method in computational mechanics
E. Oñate, S. Idelsohn, M. Celigueta, R. Rossi, S. Latorre

(2010). PI345

Abstract
We present some developments in the formulation of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in fluid and solid mechanics accounting for fluid-structure interaction and coupled thermal effects. The PFEM uses an updated Lagrangian description to model the motion of nodes (particles) in both the fluid and the structure domains. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of water drops. A mesh connects the nodes defining the discretized domain where the governing equations are solved as in the standard FEM. The necessary stabilization for dealing with the incompressibility of the fluid is introduced via the finite calculus (FIC) method. An incremental iterative scheme for the solution of the non linear transient coupled fluid-structure problem is described. Extensions of the PFEM to allow for frictional contact conditions at fluid-solid and solid-solid interfaces via mesh generation are described. A simple algorithm to treat erosion in the fluid bed is presented. Examples of application of the PFEM to solve a number of coupled problems such as the effect of large wave on structures, the large motions of floating and submerged bodies, bed erosion situations and melting and dripping of polymers under the effect of fire are given.
Abstract
We present some developments in the formulation of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in fluid and solid mechanics accounting [...]
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Interface GiD-SAP2000-VRML. Aplicación práctica a la modelización virtual de edificios del patrimonio histórico
F. Muñoz, J. Maristany, J. López-Rey

(2010). PI344

Abstract
The numerical modeling of historic buildings is an essential tool for understanding the structural behavior, even more whit the aim is to assume an analysis for conservation and / or rehabilitation. At present time, most building’s numerical simulation software is divided into three parts: the preprocessor, which prepares all the necessary information (geometry, boundary conditions, loads, etc.), the Analysis, where all calculations take place (FEM) and the postprocessing where decisions are taking based on the analysis of the results obtained in the previous steps (Muñoz, Maristany 1999). At that last point is, where the user of the computer programs usually find limitations in the graphical interpretation of the results. Some numerical results with endless list of numbers are not the best way to address the problem and its graphical output is not yet fully developed. That is, graphic interface is still very basic, let alone a real-time dynamic visualization in 3D. It`s important to have both powerful hardware and software tools to visualize the obtained results. Currently, there are emerging many structural analysis programs that have highly advanced postprocessing, but they still display limitations in space, they operate only on 2 or 3 dimensions with space constraints. For this reason, this paper seeks to integrate different current computer programs with 3D graphical representation. Thus, the visualization of numerical results (tension, stress and strain values) can be much more interesting. This is to enable users to virtually navigate in real time, through any 3D structure and better understand their behavior. In short, this research aims to develop an interface between the computer programs of structural calculations and representation software with virtual 3D graphics (vrml- virtual reality modeling language), with practical application to historic buildings. As a closure for the paper we develop a practical example based on Mexico City’s Cathedral tabernacle.
Abstract
The numerical modeling of historic buildings is an essential tool for understanding the structural behavior, even more whit the aim is to assume an analysis for conservation [...]
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Validation of the particle finite element method (PFEM) for simulation of rock slides in lakes and reservoirs
J. Irazábal, F. Salazar, E. Oñate

(2012). PI390

Abstract
The analysis of landslides in reservoirs is particularly interesting because the oscillation of the water surface elevation (especially rapid drawdowns) can foster their occurrence. The existence of the reservoir for a long enough time makes the material of the slopes turn saturated, thus its pore pressure raises and, as a consequence, its effective stress is reduced. This unstabilizing effect is partially compensated by the raise of total stress due to hydrostatic pressure generated by the water in the reservoir. A rapid drawdown eliminates the stabilization in a lapse which is frequently not enough for the pore pressure to be dissipated (this depends on the permeability of the material as well as on the velocity of the water level drop, but is quite frequent). In this situation, the probability of occurrence of a landslide is greater. In this report some validation cases are described, where the impact of sliding blocks against a mass of water is simulated, as well as the generation and propagation of the subsequent impulse wave. They are based on the experiments performed by Sælevik et al. [21].
Abstract
The analysis of landslides in reservoirs is particularly interesting because the oscillation of the water surface elevation (especially rapid drawdowns) can foster their occurrence. [...]
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On the arc length method: combining ideas and implementations aspects
N. Lafontaine, X. Wang, K. Huang, M. Yuan, E. Oñate

(2013). PI399

Abstract
In this work we introduced and implemented the AL method in NOLM program. Basically the actual implementation in NOLM is based in the work proposed by Lam and Morley (1992) and was coded with take into account the sign for no tracking back the solution. An ecient method was included for avoid complex roots and if the problem persist, two method is available to get the convergence. In case of no convergence is reached, we introduce a user factor, for reducing the arc-length, that should be taken betweens (0:5 - 0:75) per cent of the actual arc length. A linear truss-element, together to the isotropic smeared crack model was introduced for testing and benchmarking the AL method . During the work, we found several diculties to converge in the standard constitutive law implemented in NOLM when a softening parameter was introduced. It is caused by the no mechanical dissipation in the model. However, for a perfect plastic an hardening they get the corresponding results. All meshing process and post-processing was made with Gid[4], proving that it is possible to connect the developed owner software and this Pre-and post processing program.
Abstract
In this work we introduced and implemented the AL method in NOLM program. Basically the actual implementation in NOLM is based in the work proposed by Lam and Morley (1992) [...]
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Advances in the simulation of multi-fluid flows with the Particle Finite Element Method. Application to bubble dynamics.
M. Mier-Torrecilla, S. Idelsohn, E. Oñate

(2010). PI342

Abstract
In this work we extend the Particle Finite Element Method (PFEM) to multi-fluid flow problems with the aim of exploiting the fact that Lagrangian methods are specially well suited for tracking interfaces. We develop a numerical scheme able to deal with large jumps in the physical properties, included surface tension, and able to accurately represent all types of discontinuities in the flow variables. The scheme is based on decoupling the velocity and pressure variables through a pressure segregation method which takes into account the interface conditions. The interface is defined to be aligned with the moving mesh, so that it remains sharp along time, and pressure degrees of freedom are duplicated at the interface nodes to represent the discontinuity of this variable due to surface tension and variable viscosity. Furthermore, the mesh is refined in the vicinity of the interface to improve the accuracy and the efficiency of the computations. We apply the resulting scheme to the benchmark problem of a two-dimensional bubble rising in a liquid column presented in [[#cite-1|[1]]], and propose two breakup and coalescence problems to assess the ability of a multi-fluid code to model topology changes.
Abstract
In this work we extend the Particle Finite Element Method (PFEM) to multi-fluid flow problems with the aim of exploiting the fact that Lagrangian methods are specially well [...]
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Advances in the DEM and coupled DEM and FEM techniques in non linear solid mechanics
E. Oñate, F. Zarate, M. Celigueta, J. Gonzalez, J. Miquel, J. Carbonell, F. Garcia, S. Latorre, M. Santasusana

(2017). PI416

Abstract
In this chapter we present recent advances in the Discrete Element Method (DEM) and in the coupling of the DEM with the Finite Element Method (FEM) for solving a variety of problems in non linear solid mechanics involving damage, plasticity and multifracture situations.
Abstract
In this chapter we present recent advances in the Discrete Element Method (DEM) and in the coupling of the DEM with the Finite Element Method (FEM) for solving a variety of [...]
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El reto de la transferencia de los resultados de la investigación a la industria
E. Oñate

(2012). PI386

Abstract
En este trabajo se analizan algunas de las razones que dificultan y favorecen la transferencia de los resultados de la investigación que se desarrolla en entornos científicos al sector industrial. En concreto se analiza el proceso de la innovación y sus factores de impulso e inhibición. También se describe el ciclo que siguen las ideas, desde que se originan en un entorno científico hasta que se transforman en productos de éxito comercial. Finalmente, se presentan algunas recomendaciones para favorecer el proceso de transferencia de los resultados de la investigación a la industria y se propone la creación de un nuevo modelo de centro de I+D+I.
Abstract
En este trabajo se analizan algunas de las razones que dificultan y favorecen la transferencia de los resultados de la investigación que se desarrolla en entornos científicos [...]
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Analysis of the melting, burning and flame spread of polymers with the Particle Finite Element Method
E. Oñate, J. Marti, P. Ryzhakov, R. Rossi, S. Idelsohn

(2013). PI395

Abstract
A computational procedure for analysis of the melting, burning and flame spread of polymers under fire conditions is presented. The method, termed Particle Finite Element Method (PFEM), combines concepts from particle-based techniques with those of the standard finite element method (FEM). The key feature of the PFEM is the use of an updated Lagrangian description to model the motion of nodes (particles) in the thermoplastic material. Nodes are viewed as material points which can freely move and even separate from the main analysis domain representing, for instance, the effect of melting and dripping of polymer particles. A mesh connects the nodes defining the discretized domain where the governing equations are solved using the FEM. An incremental iterative scheme for the solution of the nonlinear transient coupled thermal-flow problem, including radiation, loss of mass by gasification and combustion is used. Examples of the possibilities of the PFEM for the modelling and simulation of the melting, burning and flame spread of polymers under different fire conditions are described.
Abstract
A computational procedure for analysis of the melting, burning and flame spread of polymers under fire conditions is presented. The method, termed Particle Finite Element [...]
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El papel de los modelos numéricos en la investigación y el diseño de aliviaderos de presas
F. Salazar, J. Mauro, J. Irazábal, A. Larese, R. Rossi, E. Oñate

(2013). PI396
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A stabilized Finite Element Method for analysis of fluid-structure interaction problems involving free surface waves
E. Oñate, J. García-Espinosa

Comput. Methods Appl. Mech. Engrg., (2017). Vol. 326, pp. 422-445; doi: 10.1016/j.cma.2017.08.014

Abstract
A stabilized semi-implicit fractional step finite element method for solving coupled fluid-structure interaction problems involving free surface waves is presented. The stabilized equations are derived at a differential level via a finite element calculus procedure. A new mesh updating technique based on solving a fictitious elastic problem on the moving mesh is described. One example of the efficiency of the stabilized semi-implicit algorithm for the coupled solution of fluid-structure interaction problems is presented.
Abstract
A stabilized semi-implicit fractional step finite element method for solving coupled fluid-structure interaction problems involving free surface waves is presented. The stabilized [...]
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Modeling and simulation of the effect of blast loading on structures using and adaptive blending of discrete and finite element methods
E. Oñate, C. Labra, F. Zárate, J. Rojek

(2012). PI373

Abstract
We present a new computational model for predicting the effect of blast loading on structures. The model is based in the adaptive coupling of the finite element method (FEM) and the discrete element method (DEM) for the accurate reproduction of multifracturing and failure of structures under blast loading. In the paper we briefly describe the basis of the coupled DEM/FEM technology and demonstrate its efficiency in its application to the study of the effect of blast loading on a masonry wall, a masonry tunnel and a double curvature dam.
Abstract
We present a new computational model for predicting the effect of blast loading on structures. The model is based in the adaptive coupling of the finite element method (FEM) [...]
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