Documents published in 2019 : Scipedia

Langrangian formulation for incompressible fluids using finite calculus and the finite element method
E. Oñate, S. Idelsohn, F. Pin

(2003). Kuznetsov Y., Neittanmaki P. and Pironneau O. (Eds.),CIMNE, Barcelona, Spain

Abstract
We present a general formulation for incompressible fluid flow analysis using the finite element method (FEM) and a lagrangian description. The necessary stabilization for dealing with the incompressibility condition is introduced via the so called finite calculus (FIC) method. Both a quasi-implicit algorithm and a fractional step scheme are described. Examples of application of the lagrangian flow description are presented.
Abstract
We present a general formulation for incompressible fluid flow analysis using the finite element method (FEM) and a lagrangian description. The necessary stabilization for [...]
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The CIMNE model for generating knowledge on computational engineering and its transfer to society
E. Oñate

Research Report (2017). PI417

Abstract
We present an overview of the model implemented by the International Centre for Numerical Methods in Engineering (CIMNE, www.cimne.com ) for the generation of scientific and technical knowledge on computational engineering, understood in the broad sense, the subsequent generation of product resulting from the research activities and the transfer of these products to society for their exploitation in the industrial sector. We present examples of application of the CIMNE model to a number of academic, scientific and industry activities of CIMNE.
Abstract
We present an overview of the model implemented by the International Centre for Numerical Methods in Engineering (CIMNE, www.cimne.com ) for the generation of scientific [...]
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Nothing
Victor Cardoso Nungaray's personal collection (2019). 1
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Estudio de estimación de parámetros constitutivos en el método de elementos discretos o de partículas
C. Recarey, E. Oñate, J. Miquel, F. Zárate, J. Rojek, S. Burrell

Monograph CIMNE (2005). M93

Abstract
Se presenta un modelo numérico que emplea elementos discretos esféricos o también denominados elementos distintos. Este modelo se aplica en la simulación de rocas, suelos, medios granulares y otros materiales. El movimiento de elementos esféricos se describe por medio de las ecuaciones de dinámica del cuerpo rígido. Se emplea en la formulación una integración explícita, la cual, brinda una buena eficiencia computacional.
Abstract
Se presenta un modelo numérico que emplea elementos discretos esféricos o también denominados elementos distintos. Este modelo se aplica en la simulación [...]
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Numerical simulation of multifluid flows with the particle finite element method
M. Mier, S. Idelsohn, E. Oñate

Monograph CIMNE (2010). M115

Abstract
In this monograph we have focused on understanding the basic physical principles of multi-fluid flows and the difficulties that arise in their numerical simulation. We have extended the Particle Finite Element Method to problems involving several different fluids with the aim of exploiting the fact that Lagrangian methods are specially well suited for tracking any kind of interfaces. We have developed a numerical scheme able to deal with large jumps in the physical properties (density and viscosity), include surface tension, and accurately represent all types of discontinuities in the flow variables at the interface. The scheme is based on decoupling the nodes position, velocity and pressure variables through the Picard linearization and a pressure segregation method which takes into account the interface conditions. The interface has been defined to be aligned with the moving mesh, so that it remains sharp along time. Furthermore, pressure degrees of freedom have been duplicated at the interface nodes to represent the discontinuity of this variable due to surface tension and variable viscosity, and the mesh has been refined in the vicinity of the interface to improve the accuracy of the computations.
Abstract
In this monograph we have focused on understanding the basic physical principles of multi-fluid flows and the difficulties that arise in their numerical simulation. We have [...]
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Computational model of the human urinary bladder
V. Monteiro, E. Oñate, S. Oller

Monograph CIMNE (2013). M148

Abstract
The proposal of an artificial bladder is still a challenge to overcome. Bladder cancer is among the most frequent cases of oncologic diseases in United States and Europe. It is considered a major medical problem once this disease has high rates of reoccurrence, often leading to the extirpation of this organ. The most refined solution to replace this organ is the ileal bladder, which consists of a neobladder made of the patient’s intestinal tissue. Unfortunately this solution presents not only functional mechanical problems, described on the literature as voiding and leaking problems, but also biological ones (i.e. bone loss, given the absorption by the intestine of substances that should be eliminated from the organism). Urged by the urological community of the Hospital Clinic de Barcelona and backgrounded by its experience in the numerical simulation of biomedical structures, the Center of Numerical Methods in Engineering (CIMNE) had the initiative to provide the research of the mechanics of the urinary bladder and the simulation of fluid structure interaction (FSI) to account for the filling and voiding of this organ with urine. The Finite Element Method (FEM) simulation of the real bladder and the comprehensive understanding of the mechanics of this organ and its interaction with urine will give the possibility to propose geometrical improvements and study suitable materials for an artificial solution to address the cases on which the bladder needs to be removed. To reach this goal, first we proceeded to the bibliographic review of mathematical models of the urinary apparatus and to a comprehensive study of the physiology and dynamics of the bladder. A review of the major urological structures, kidney, ureter and urethra, takes place. To consider boundary conditions other surrounding structures to the urinary system are also studied. In the second part of the thesis, we propose the numerical model to study the human urinary bladder. The behavior of the detrusor muscle during filling and voiding of the bladder with urine and its ability to promote the storage of urine under low pressure need to be accurately represented, requiring the implementation of a non-linear constitutive model. The mathematical model needs to be capable to simulate the mechanical variables that govern this organ and the properties of the urine. The nonlinear behavior of living tissues is implemented and validated with examples from the literature. The quasi-incompressibility property of urine and the navierstokes equations for the fluid are taken into account. The geometry of the bladder needs to be taken into account, and the implementation of a 3D computational model obtained from the computerized tomography of a cadaver male adult is considered. The data has been treated to consider boundary conditions. Two models have been conceived: one meshed with four nodes tetrahedral and another meshed with shell elements. FSI must work for the simulation of filling and voiding of the bladder. Due to the close densities of the materials the scheme used to solve fluid-structure needs to be carefully selected. The proposed numerical model and the filling and voiding analysis are finally validated with standardized urodynamic tests. The final part of the thesis, the simulation of a neobladder is presented, being the first step to simulate numerically artificial materials for bladder replacement.
Abstract
The proposal of an artificial bladder is still a challenge to overcome. Bladder cancer is among the most frequent cases of oncologic diseases in United States and Europe. [...]
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Development and applications of the finite point method to compressible aerodynamics problems
E. Ortega, E. Oñate, S. Idelsohn

Monograph CIMNE (2014). M143

Abstract
This work deals with the development and application of the Finite Point Method (FPM) to compressible aerodynamics problems. The research focuses mainly on investigating the capabilities of the meshless technique to address practical problems, one of the most outstanding issues in meshless methods. The FPM spatial approximation is studied firstly, with emphasis on aspects of the methodology that can be improved to increase its robustness and accuracy. Suitable ranges for setting the relevant approximation parameters and the performance likely to be attained in practice are determined. An automatic procedure to adjust the approximation parameters is also proposed to simplify the application of the method, reducing problem- and user-dependence without affecting the flexibility of the meshless technique. The discretization of the flow equations is carried out following wellestablished approaches, but drawing on the meshless character of the methodology. In order to meet the requirements of practical applications, the procedures are designed and implemented placing emphasis on robustness and efficiency (a simplification of the basic FPM technique is proposed to this end). The flow solver is based on an upwind spatial discretization of the convective fluxes (using the approximate Riemann solver of Roe) and an explicit time integration scheme. Two additional artificial diffusion schemes are also proposed to suit those cases of study in which computational cost is a major concern. The performance of the flow solver is evaluated in order to determine the potential of the meshless approach. The accuracy, computational cost and parallel scalability of the method are studied in comparison with a conventional FEM-based technique. Finally, practical applications and extensions of the flow solution scheme are presented. The examples provided are intended not only to show the capabilities of the FPM, but also to exploit meshless advantages. Automatic hadaptive procedures, moving domain and fluid-structure interaction problems, as well as a preliminary approach to solve high-Reynolds viscous flows, are a sample of the topics explored. All in all, the results obtained are satisfactorily accurate and competitive in terms of computational cost (if compared with a similar mesh-based implementation). This indicates that meshless advantages can be exploited with efficiency and constitutes a good starting point towards more challenging applications.
Abstract
This work deals with the development and application of the Finite Point Method (FPM) to compressible aerodynamics problems. The research focuses mainly on investigating [...]
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On the orthogonal subgrid scale pressure stabilization of small and finite deformation J2 Plasticity
C. Agelet de Saracibar, M. Chiumenti, M. Cervera, Q. Valverde

Monograph Series on Computational Modeling of Forming Processes (2004). Angelet de Saracibar (ed.), Monograph CMFP2, 76pp., CIMNE, ISBN: 84-95999-62-5

Abstract
The use of stabilization methods is becoming an increasingly well-accepted technique due to their success in dealing with numerous numerical pathologies that arise in a variety of applications in computational mechanics. In this monograph a multiscale finite element method technique to deal with pressure stabilization of nearly incompressibility problems in nonlinear solid mechanics at small and finite deformations J2 plasticity is presented. A mixed formulation involving pressure and displacement fields is used as starting point. Within the finite element discretization setting, continuous linear interpolation for both fields is considered. To overcome the Babuˇska-Brezzi stability condition, a multiscale stabilization method based on the Orthogonal Subgrid Scale (OSGS) technique is introduced. Suitable nonlinear expression of the stabilization parameters are proposed. The main advantage of the method is the possibility of using linear triangular or tetrahedral finite elements, which are easy to generate and, therefore, very convenient for practical industrial applications. Numerical results obtained using the OSGS stabilization technique are compared with results provided by the P1 standard Galerkin displacements linear triangular/tehrahedral element, P1/P1 standard mixed linear displacements/ linear pressure triangular/tetrahedral element and Q1/P0 mixed bilinear/ trilinear displacements/constant pressure quadrilateral/hexahedral element for 2D/3D nearly incompressible problems in the context of nonlinear small and finite deformation J2 plasticity models.
Abstract
The use of stabilization methods is becoming an increasingly well-accepted technique due to their success in dealing with numerous numerical pathologies that arise in [...]
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Strain Localization and Failure Mechanics for Elastoplastic Damage Solids
J. Wu, M. Cervera

Monograph CIMNE (2014). Barcelona: Centre Internacional de Mètodes Numèrics en Enginyeria (CIMNE), ISBN 978-84-943307-0-4

Abstract
This work investigates systematically strain localization and failure mechanics for elastoplastic damage solids. Two complementary methodologies, i.e., traction-based discontinuities localized in an elastic solid and strain localization of a stress-based inelastic softening solid, are addressed. In the former it is assumed a priori that the discontinuity (band) forms with a continuous stress field and along the known orientation. A traction-based failure criterion is introduced to characterize the discontinuity (band) and the orientation is determined from Mohr’s maximization postulate. If the (apparent) displacement jumps are retained as independent variables, the strong/regularized discontinuity approaches follow, requiring constitutive models for both the bulk and discontinuity (band). Elimination of the displacement jumps at the material point level results in the embedded/smeared discontinuity approaches in which an overall inelastic constitutive model fulfilling the static constraint suffices. The second methodology is then adopted to check whether the assumed strain localization can occur and identify its consequences on the resulting approaches. The kinematic constraint guaranteeing stress boundedness/continuity upon strain localization is established for general inelastic softening solids. Application to a unified elastoplastic damage model naturally yields all the ingredients of a localized model for the discontinuity (band), justifying the first methodology. Two dual but not necessarily equivalent approaches, i.e., the traction-based elastoplastic damage model and the stress-based projected discontinuity model, are identified. The former is equivalent to the embedded/smeared discontinuity approaches, whereas in the later the discontinuity orientation and associated failure criterion, not given a priori, are determined consistently from the kinematic constraint. The bi-directional connections and equivalence conditions between the traction- and stress-based approaches are classified. Closed-form 2D results under plane stress condition are also given, with the classical Rankine, Mohr-Coulomb, von Mises and Drucker-Prager criteria analyzed as the illustrative examples. A generic failure criterion of either elliptic, parabolic or hyperbolic type, is then considered in a unified manner, resulting in many failure criteria frequently employed in practice.
Abstract
This work investigates systematically strain localization and failure mechanics for elastoplastic damage solids. Two complementary methodologies, i.e., traction-based discontinuities [...]
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On the Computational Modeling and Numerical Simulation of FSW Processes
C. Agelet de Saracibar, M. Chiumenti, M. Cervera, N. Dialami, D. Santiago, G. Lombera

Monograph Series on Computational Modeling of Forming Processes (2012). Angelet de Saracibar (ed.), Monograph CMFP3, Barcelona: Centre Internacional de Mètodes Numèrics en Enginyeria (CIMNE), ISBN 84-939640-0-9

Abstract
This paper deals with the computational modeling and numerical simulation of the material flow around the probe tool in a Friction Stir Welding (FSW) process. Within the paradigmatic framework of the multiscale stabilization methods, suitable subgrid scale stabilized coupled thermomechanical formulations have been developed using an Eulerian description. Norton-Hoff and Sheppard-Wright thermo-rigid-viscoplastic constitutive material models have been considered. Constitutive equations for the subgrid scale models have been proposed and an approximation of the subgrid scale variables has been given. In particular Algebraic Subgrid Scale (ASGS) and Orthogonal Subgrid Scale (OSGS) methods for P1/P1/P1 linear elements have been considered. Furthermore, it has been shown that well known classical stabilized formulations, such as the Galerkin Least-Squares (GLS) or Streamline Upwind/Petrov-Galerkin (SUPG) methods, can be recovered as particular cases of the multiscale stabilization framework considered. Within the framework of a product formula algorithm, the resulting algebraic system of equations has been solved using a staggered procedure, in which a mechanical problem, defined by the plastic strain rate incompressibility equation and the quasi-static linear momentum balance equation, is solved at a constant temperature and a thermal problem, defined by the energy balance equation, is solved keeping constant the mechanical variables. The computational model has been implemented in the in-house developed FE software COMET. An assessment of the influence of the thermal deformation in the formulation has been carried out. Results obtained show that the influence of the thermal deformation is very small and can be neglected, getting a fully incompressible formulation. Finally, the computational model implemented in COMET has been validated through a number of examples, including a 3D numerical simulation of a FSW process. Numerical results obtained have been compared with experimental results available in the literature. A good agreement on the temperature distribution has been obtained and predicted peak temperatures compare well, both in value and position, with the experimental results available.
Abstract
This paper deals with the computational modeling and numerical simulation of the material flow around the probe tool in a Friction Stir Welding (FSW) process. Within the paradigmatic [...]
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Residual stress and distortion of rectangular and S-shaped Ti-6Al-4V parts by Directed Energy Deposition: Modelling and experimental calibration
X. Lu, X. Lin, M. Chiumenti, M. Cervera, Y. Hu, X. Ji, L. Ma, H. Yang, W. Huang

Additive Manufacturing (2019). (preprint) Vol. 26, pp. 166-179

Abstract
Residual stresses and distortion in Additive Manufactured (AM) parts are two key obstacles which seriously hinder the wide application of this technology. Nowadays, understanding the thermomechanical behavior induced by the AM process is still a complex task which must take into account the effects of both the process and the material parameters, the microstructure evolution as well as the pre-heating strategy. One of the challenges of this work is to increase the complexity of the geometries used to study the thermomechanical behavior induced by the AM process. The reference geometries are a rectangular and a S-shaped structures made of 44-layers each. The samples have been fabricated by Directed Energy Deposition (DED). In-situ thermal and distortion histories of the substrate are measured in order to calibrate the 3D coupled thermo-mechanical model. Once the numerical results showed a good agreement with the temperature measurements, the validated model has been used to predict the residual stresses and distortions. Different process parameters have been analyzed to study their sensitivity to the process assessment. Different preheating strategies have been also analyzed to check their effectiveness on the mitigation of both distortions and residual stresses. Finally, some simplifications of the actual scanning sequence are proposed to reduce the computational cost without loss of the accuracy of the simulation framework.
Abstract
Residual stresses and distortion in Additive Manufactured (AM) parts are two key obstacles which seriously hinder the wide application of this technology. Nowadays, understanding [...]
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In situ measurements and thermo-mechanical simulation of Ti–6Al–4V laser solid forming processes
X. Lu, X. Lin, M. Chiumenti, M. Cervera, Y. Hu, X. Ji, L. Ma, W. Huang

Int. J. Mechanical Sciences (2019). (preprint) Vol. 153-154, pp. 119-130

Abstract
Residual stresses and distortions are two technical obstacles for popularizing the additive manufacturing (AM) technology. The evolution of the stresses in AM components during the thermal cycles of the metal depositing process is not yet clear, and more accurate in situ measurements are necessary to calibrate and validate the numerical tools developed for its simulation. In this work a fully coupled thermo-mechanical analysis to simulate the laser solid forming (LSF) process is carried out. At the same time, an exhaustive experimental campaign is launched to measure the temperature evolution at different locations, as well as the distortions and both the stress and strain fields. The thermal and mechanical responses of single-wall coupons under different process parameters are recorded and compared with the numerical models. Good agreement between the numerical results and the experimental measurements is obtained. Sensitivity analysis demonstrates that the AM process is significantly affected by the laser power and the feeding rate, while poorly influenced by the scanning speed.
Abstract
Residual stresses and distortions are two technical obstacles for popularizing the additive manufacturing (AM) technology. The evolution of the stresses in AM components during [...]
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Out-of-plane seismic response and failure mechanism of masonry structures using finite elements with enhanced strain accuracy
G. Vlachakis, M. Cervera, G. Barbat, S. Salaustros

Engineering Failure Analysis (2019). (preprint) Vol. 97, pp. 534-555

Abstract
The out-of-plane response is a complex and at the same time key aspect of the seismic vulnerability of masonry structures. It depends on several factors, some of which are the material properties, the quality of the walls, the geometry of the structure, the connections between structural elements and the stiffness of the diaphragms. During the last years, a wide variety of numerical methods has been employed to assess the out-ofplane behaviour of unreinforced masonry structures. Finite element macro-modelling approaches are among the most famous as they allow modelling large structures at a reasonable computational cost. However, macro-modelling approaches may result in a non-realistic representation of localized cracks and a dependency of the numerical solution on the finite element mesh. Mixed strain/displacement finite elements have been recently proposed as a remedy to the above numerical pathologies. Due to the independent interpolation of strains and displacements these finite element formulations are characterized by an enhanced accuracy in strain localization and crack propagation problems, being at the same time practically mesh independent. For these reasons, mixed finite elements are employed in this work for the out-of-plane assessment of unreinforced masonry structures, being at the same time their first real-scale application. A full-scale experimental campaign of two masonry structures, a stone and a brick one, subjected to shaking-table tests is chosen as reference benchmark. Their structural response under seismic actions is numerically assessed through nonlinear static analysis. The proposed approach is validated through the comparison of the numerical results with the experimental ones, as well as with the results obtained using standard irreducible finite elements.
Abstract
The out-of-plane response is a complex and at the same time key aspect of the seismic vulnerability of masonry structures. It depends on several factors, some of which are [...]
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Effect of the tool tilt angle on the material flow and heat generation in Friction Stir Welding
N. Dialami, M. Cervera, M. Chiumenti

Metals (2019). Vol. 9 (1), pp. 28-45

Abstract
This work studies the effect of the tool tilt angle on the generated heat and the material flow in the work pieces joint by Friction Stir Welding (FSW). An apropos kinematic framework together with a two-stage speed-up strategy is adopted to simulate the FSW problem. The effect of tilt angle on the FSWelds is modeled through the contact condition by modifying an enhanced friction model. A rotated friction shear stress is proposed, the angle of rotation depending on the process parameters and the tilt angle. The proposed rotation angle is calibrated by the experimental data provided for a tilt angle 2.5◦ . The differences of generated heat and material flow for the cases of tool with tilt angle of 0◦ and 2.5◦ are discussed. It is concluded that due to the higher temperature, softer material and greater frictional force in the trailing side of the tool, the material flow in the rear side of the FSW tool with the title angle is considerably enhanced, which assists to prevent the generation of defect.
Abstract
This work studies the effect of the tool tilt angle on the generated heat and the material flow in the work pieces joint by Friction Stir Welding (FSW). An apropos kinematic [...]
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Tool development for fully coupled simulation of offshore wind turbine
J. Gutiérrez Romero, B. Servan Camas, A. García, J. Colom Cobb, J. García-Espinosa

VIII International Conference on Computational Methods in Marine Engineering (Marine 2019), Gothenburg (Sweden)

Abstract
Nowadays the marine renewable energies are getting an important role in the transformation of the energy model. And tools for predicting the performance of these new technologies are essential in their commercial development. An example of these are floating wind turbines (FWT), and this work presents the coupling and verification of a set of tools to carry out fully coupled simulation of FWTs. These tools are built on the seakeeping software SeaFEM [1, 2, 3, 4, 5] and on the aeroelastic simulator code FAST [6]. First, the basic features of each tools are explained. Second, a coupling strategy to assess the performance of FWTs is presented. Third, the results obtained coupling SeaFEM-FAST are used for an inter-code comparison against those obtained coupling Hydrodyn-FAST. Forth, an intensive analysis of a FWT based on the NREL 5 MW baseline is carried out taking into account the environmental conditions of the selected location. These coupled computations are carried out following the Design Load Cases proposed by IEC rules [7] to assess the Ultimate Limit State (ULS). Finally, some comparison and conclusions based on the obtained results are drawn.
Abstract
Nowadays the marine renewable energies are getting an important role in the transformation of the energy model. And tools for predicting the performance of these new technologies [...]
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The fast multipole boundary element method for anisotropic material problems
A. Dias, E. Albuquerque, L. Campos, P. Sollero, A. Júnior

Journal's Papers (2019). 63

Abstract
This paper presents a two-dimensional fast multipole boundary element method for large-scale analysis of anisotropic elastic problems. The expansions and fast multipole operations it uses are similar to those in formulations of fast multipole boundary element method already presented for potential and isotropic elastostatic problems. The anisotropic fundamental solutions used in here are based on the Lekhnitskii formalism. They are expanded in order to allow the development of fast multipole operations. To assess the accuracy of the expansions, the fundamental solutions and some terms of the boundary element influence matrices obtained by direct integration of kernels are compared to those obtained by the fast multipole expansion. Moreover, to validate the method, numerical solutions are compared to analytical solutions. The proposed formulation has quasi-linear complexity that is ideal for solving large scale problems. The main conclusion of this paper is that the proposed formulation is more effective than the conventional boundary element method. It is faster and uses less memory, allowing the analysis of larger problems in less time.
Abstract
This paper presents a two-dimensional fast multipole boundary element method for large-scale analysis of anisotropic elastic problems. The expansions and fast multipole operations [...]
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Finite Element Analysis of Membrane Structures
R. Taylor, E. Oñate, P. Ubach de Fuentes

Recent Advances in Textile Membranes and Inflatable Structures (2005). Springer Verlag, pp. 47 - 68

Abstract
This paper summarizes the development for a large displacement formulation of a membrance composed of three-node triangular elements. A formulation in terms of the deformation gradient is first constructed in terms of nodal variables. In particular, the use of the right Cauchy-Green deformation tensor is shown to lead to a particulary simple representation in terms of nodal quantities. This may then be used to construct general models for use in static and transient analyses.
Abstract
This paper summarizes the development for a large displacement formulation of a membrance composed of three-node triangular elements. A formulation in terms of the deformation [...]
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Posibilidades de los métodos numéricos en obras subterráneas
E. Oñate, B. Suarez, J. Canet

Avances en Mecánica de Medios Continuos. Simposium en honor al Profesor J. A. Garrido García (2007). E. Alarcón, A. Foces, F. París (Eds.), pp. 195-210

Abstract
Se presenta un resumen de las posibilidades de diversos métodos numéricos basados en la combinación de técnicas de elementos finitos y de partículas para la simulación de problemas típicos de obras subterráneas, tales como la excavación de túneles y la inundación de cavidades.
Abstract
Se presenta un resumen de las posibilidades de diversos métodos numéricos basados en la combinación de técnicas de elementos finitos y de [...]
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Thermo-mechanical analysis of laminated composites exposed to fire
D. Di Capua, J. García-Espinosa, R. Pacheco, O. Casals, T. Korhonen, T. Hakkarainen, A. Paajanen

VIII International Conference on Computational Methods in Marine Engineering (Marine 2019), Gothenburg (Sweden)

Abstract
This presentation introduces a numerical model for the thermo-mechanical analysis of laminated composite structures under the fire action. The coupling between the thermal and mechanical behaviour is considered in weak form (temperatures field modify mechanical properties but displacements field do not modify thermal properties). The thermal part of model is based on the approach presented in Henderson et al. (1985). This model takes into account the energy transfer processes of heat conduction, pyrolysis of the polymer matrix, and diffusion of decomposition gases. The mechanical behaviour of the composites is based on the serial/parallel mixing theory (Rastellini et al., 2008) which is modified to take into account the thermal degradation of the mechanical properties. Numerical results obtained with this model are compared with some experimental tests presented in the literature. Application of the developed model to the analysis of fire scenarios in composite ships is evaluated.
Abstract
This presentation introduces a numerical model for the thermo-mechanical analysis of laminated composite structures under the fire action. The coupling between the thermal [...]
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Advances in the simulation of ship navigation in ice
J. Colom Cobb, B. Servan Camas, J. García-Espinosa, E. Oñate

VIII International Conference on Computational Methods in Marine Engineering (Marine 2019), Gothenburg (Sweden)

Abstract
Navigation in the arctic regions is becoming more usual as new navigations routes are being opened due to the retreatment of the ice. This means that ships will be navigating in brash ice, which is the accumulation of floating ice made up of blocks no larger than two meters across, bringing up new concerns on the interaction of ice locks with the ship. In this work, we tackle these concerns and present the advances towards the development of a computational model for simulation of this navigation condition including the interaction among the ship and the ice blocks. The computational tool developed in this work is based on the coupling of a Semi-Lagrangian Particle Finite Element Method (SL-PFEM) with a multi rigid-body dynamics tool. The Particle Finite Element Method [1] is a versatile framework for the analysis of fluid-structure interaction problems. The PFEM combines Lagrangian particle-based techniques with the advantage of the integral formulation of the Finite Element Method (FEM). It has been shown [1][2] to successfully simulate a wide variety of complex engineering problems, e.g. free-surface/multi-fluid flows with violent interface motions, multi-fluid mixing and buoyancy-driven segregation problems etc. The latest development within the framework of the PFEM is the X-IVAS (eXplicit Integration along the Velocity and Acceleration Streamlines) scheme [2][3]. It is a semi-implicit scheme built over a Semi-Lagrangian (SL) formulation of the PFEM. In this work, the SL-PFEM model has been coupled with a multibody dynamics solver, able to handle the interactions between thousands of bodies, representing the different ice blocks. The interaction between the fluid flow and the ice blocks is taking into account by enriching the finite element space at the boundaries of the different blocks. This work is part of the research project NICESHIP sponsored by the U.S. Office of Naval Research under Grant N62909-16-1-2236.
Abstract
Navigation in the arctic regions is becoming more usual as new navigations routes are being opened due to the retreatment of the ice. This means that ships will be navigating [...]
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A second-order semi-Lagrangian particle FEM method for the incompressible NavierStokes equations
B. Serván-Camas, J. Colom-Cobb, J. García-Espinosa, P. Nadukhandi

VIII International Conference on Computational Methods in Marine Engineering (Marine 2019), Gothenburg (Sweden)

Abstract
In this work, a second-order semi-Lagrangian particle finite element method (SL-PFEM) is presented. The method is based on the second order velocity Verlet algorithm, using an explicit scheme to integrate the particles’ trajectories, and an implicit Crank-Nicholson scheme to integrate the particle’s velocities. The projection of the particle´s intrinsic variables onto the finite element (FE) mesh is based on a second-order global least-square. The elliptic part of the Navier-Stokes equations is discretized with the Crank-Nicholson scheme and solved using an iterative process. The method is verified against available analytical solutions, and applied to the classic flow around a cylinder problem.
Abstract
In this work, a second-order semi-Lagrangian particle finite element method (SL-PFEM) is presented. The method is based on the second order velocity Verlet algorithm, using [...]
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Stabilization via finite calculus in finite element computations
E. Oñate

Finite Element Methods: 1970's and Beyond (2004). Franca L.P., Tezduyar T.E. and Masud A. (Eds.),CIMNE, Barcelona, Spain

Abstract
The expression “finite calculus” refers to the derivation of the governing differential equations in mechanics by invoking balance of fluxes, forces, etc. in a space-time domain of finite size. The governing equations resulting from this approach are different from those of infinitesimal calculus theory and they incorporate new terms which depend on the dimensions of the balance domain. The new governing equations allow to derive naturally stabilized numerical schemes using any discretization procedure. The paper discusses the possibilities of the finite calculus method for the finite element solution of convection-diffusion problems with sharp gradients and incompressible fluid flow.
Abstract
The expression “finite calculus” refers to the derivation of the governing differential equations in mechanics by invoking balance of fluxes, forces, etc. in a [...]
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FE Analysis of membrane systems including wrinkling and coupling
R. Rossi, E. Oñate, V. Renato

(2005). Springer Verlag, pp. 89 - 108

Abstract
Current work summarizes the experience of the writer in the modeling of membrane systems. A first subsection describes an efficient membrane model, together with a reliable solution procedure. The following section addresses the simulation of the wrinkling phenomena providing details of a new solution procedure. The last one proposes an efficient technique to obtain the solution of the fluid structural interaction problem.
Abstract
Current work summarizes the experience of the writer in the modeling of membrane systems. A first subsection describes an efficient membrane model, together with a reliable [...]
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Enhanced Rotation-Free Basic Shell Triangle. Applications to Sheet Metal Forming
E. Oñate, F. Flores, L. Neamtu

Computational Plasticity (2007). E. Oñate and R. Owen (Eds.), pp. 239-265

Abstract
An enhanced rotation-free three node triangular shell element (termed EBST) is presented. The element formulation is based on a quadratic interpolation of the geometry in terms of the six nodes of a patch of four triangles associated to each triangular element. This allows to compute an assumed constant curvature field and an assumed linear membrane strain field which improves the in-plane behaviour of the element. A simple and economic version of the element using a single integration point is presented. The implementation of the element into an explicit dynamic scheme is described. The efficiency and accuracy of the EBST element and the explicit dynamic scheme are demonstrated in many examples of application including the analysis of a cylindrical panel under impulse loading and sheet metal stamping problems.
Abstract
An enhanced rotation-free three node triangular shell element (termed EBST) is presented. The element formulation is based on a quadratic interpolation of the geometry in [...]
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A unified symmetrical formulation for interactions between elastic solids and incompressible fluids
S. Idelsohn, E. Oñate, J. Marti

Variational Formulations in Mechanics: Theory and Applications (2007). E. Taroco, E.A. de Souza Neto and A.A. Novotny (Eds.), CIMNE, Barcelona, Spain

Abstract
We present a general Lagrangian formulation for treating elastic solids and quasi/fully incompressible fluids in a unified form. The formulation allows to treat solid and fluid subdomains in a unified manner in fluid-structure interaction (FSI) situations. The use for both fluid and solid of a Lagrangian formulation avoid convective terms allowing to approximate the problem via a Variational Formulation. In our work the FSI problem is solved via the Particle Finite Element Method (PFEM). The PFEM is an effective technique for modeling complex interactions between floating and submerged bodies and free surface flows, accounting for splashing of waves, large motions of the bodies and frictional contact conditions. Applications of the unified Lagrangian formulation to a number of FSI problems are given.
Abstract
We present a general Lagrangian formulation for treating elastic solids and quasi/fully incompressible fluids in a unified form. The formulation allows to treat solid and [...]
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Fluid-soil-structure interaction analysis with the particle finite element method
E. Oñate, M. Celigueta, S. Idelsohn, F. Salazar, B. Suarez

Bytes and Science (2012). G. Zavarise and D. Boso (Eds.), pp. 119 - 130, CIMNE, Barcelona Spain

Abstract
We present some developments and applications of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure interaction.
Abstract
We present some developments and applications of the Particle Finite Element Method (PFEM) for analysis of complex coupled problems in mechanics involving fluid-soil-structure [...]
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Experiences in the Design Analysis and Construction of Low Pressure Inflatable Structures
J. Marcipar, E. Oñate, J. Canet

Recent Advances in Textile Membranes and Inflatable Structures (2005). Springer Verlag, pp. 241 - 257
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Applications of a Rotation-Free Triangular Element for Finite Strain Analysis of Thin Shells and Membranes
F. Flores, E. Oñate

Recent Advances in Textile Membranes and Inflatable Structures (2005). Springer Verlag, pp. 69 - 88

Abstract
This paper shows applications of a recently developed shell element to the analysis of thin shell and membrane structures. The element is a three node triangle with only translational DOFs (rotation free) that uses the configuration of the three adjacent elements to evaluate the strains. This allows to compute (constant) bending strains and (linear) membrane strains. A total Lagrangian formulation is used. Strains are defined in terms of the principal stretches. This allows to consider rubber materials and other type of materials using the Hencky stress-strain pair. An explicit central difference scheme is used to integrate the momentum equations. Several examples, including inflation and deflation of membranes show the excellent convergence properties and robustness of the element for large strain analysis of thin shells and membranes.
Abstract
This paper shows applications of a recently developed shell element to the analysis of thin shell and membrane structures. The element is a three node triangle with only translational [...]
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Membrane Structures Formed by Low Pressure Inflatable tubes. New Analysis Methods and Recent Constructions
E. Oñate, F. Flores, J. Marcipar

(2008). E. Oñate and B. Kröplin (eds.), pp. 163-196

Abstract
This paper shows applications of a recently developed thin shell element adequate for the analysis of membrane and inflatable structures. The element is a three node triangle with only translational degrees of freedom that uses the configuration of the three adjacent elements to evaluate the strains in terms of the nodal displacements only. This allows to compute (constant) bending strains and (linear) membrane strains using a total Lagrangian formulation. Several examples, including inflation and deflation of membranes and some practical applications to the analysis, design and construction of membrane structures formed by low pressure inflatable tubes are presented.
Abstract
This paper shows applications of a recently developed thin shell element adequate for the analysis of membrane and inflatable structures. The element is a three node triangle [...]
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Prediction of joint line remnant defect in friction stir welding
N. Dialami, M. Cervera, M. Chiumenti, A. Segatori

Int. J. Mechanical Sciences (2019). Vol. 151, pp. 61-69

Abstract
This work studies computationally and experimentally the joint line remnant defects emerging in friction stir welding (FSW) due to oxide layer propagation into the weld. A finite element-based model is used for the computational simulation. To follow the evolution of the oxide layer originally placed between the butted surfaces, a material tracing technique is incorporated in the numerical model. This approach allows tracking the position of the tracers representing oxide layer particles knowing the nodal velocities. A robust and fast two-stage numerical strategy is adopted for the analysis of FSW process to solve the underlying thermo-mechanical problem. The first stage is a speed-up stage solved on a fixed mesh that allows to quickly obtain the steady state. Oxide layer evolution is traced in the second stage where the rotation of the tool is modelled. Experimentally, to produce a clearly dispersed oxide line in the weld, one of the workpieces is anodized while the other one is taken as extruded. The computationally obtained oxide layer patterns are compared to those obtained experimentally using macrograph analysis of the joint cross section. The effect of the pin features and the process parameters on the final result is studied. The results show that with appropriate modelling of the material tracers in FSW, significant agreement can be attained between the computed and measured post-FSW oxide layer evolved results.
Abstract
This work studies computationally and experimentally the joint line remnant defects emerging in friction stir welding (FSW) due to oxide layer propagation into the weld. A [...]
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Challenges, tools and applications of tracking algorithms in the numerical modelling of cracks in concrete and masonry structures
S. Salaustros, M. Cervera, L. Pelà

Archives of Comp. Meths. Engng. (2018). (preprint) Published online, pp. 1-45

Abstract
The importance of crack propagation in the structural behaviour of concrete and masonry structures has led to the development of a wide range of finite element methods for crack simulation. A common standpoint in many of them is the use of tracking algorithms, which identify and designate the location of cracks within the analysed structure. In this way, the crack modelling techniques, smeared or discrete, are applied only to a restricted part of the discretized domain. This paper presents a review of finite element approaches to cracking focusing on the development and use of tracking algorithms. These are presented in four categories according to the information necessary for the definition and storage of the crack-path. In addition to that, the most utilised criteria for the selection of the crack propagation direction are summarized. The various algorithmic issues involved in the development of a tracking algorithm are discussed through the presentation of a local tracking algorithm based on the smeared crack approach. Challenges such as the modelling of arbitrary and multiple cracks propagating towards more than one direction, as well as multi-directional and intersecting cracking, are detailed. The presented numerical model is applied to the analysis of small- and large-scale masonry and concrete structures under monotonic and cyclic loading.
Abstract
The importance of crack propagation in the structural behaviour of concrete and masonry structures has led to the development of a wide range of finite element methods for [...]
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Modeling of microstructure evolution of Ti6Al4V for Additive Manufacturing
E. Salsi, M. Chiumenti, M. Cervera

Metals (2018). Vol. 8 (8), pp. 633-657

Abstract
AM processes are characterized by complex thermal cycles that have a deep influence on the microstructural transformations of the deposited alloy. In this work, a general model for the prediction of microstructure evolution during solid state transformations of Ti6Al4V is presented. Several formulations have been developed and employed for modeling phase transformations in other manufacturing processes and, particularly, in casting. The proposed model is mainly based on the combination and modification of some of these existing formulations, leading to a new overall model specifically dedicated to AM. The accuracy and suitability of the integrated model is enhanced, introducing new dedicated features. In fact the model is designed to deal with fast cooling and re-heating cycles typical of AM processes because: (a) it is able to consider incomplete transformations and varying initial content of phases and (b) it can take into account simultaneous transformations.The model is implemented in COMET, an in-house Finite Element (FE)-based framework for the solution of thermo-mechanical engineering problems. The validation of the microstructural model is performed by comparing the simulation results with the data available in the literature. The sensitivity of the model to the variation of material parameters is also discussed.
Abstract
AM processes are characterized by complex thermal cycles that have a deep influence on the microstructural transformations of the deposited alloy. In this work, a general [...]
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Numerical analysis of the manufacturing processes of a mock-up of the ITER NHF First Wall Panel
J. González, M. Chiumenti, M. Cervera, C. Agelet de Saracibar, F. Samaniego, I. Cobo

Fusion Engineering and Design (2018). (preprint) Vol. 135, Part A, pp. 65-73

Abstract
The objective of ITER is to build a new Tokamak, with the goal of demonstrating the scientific and technical feasibility of fusion power. The First Wall Panels are the inner component of the reactor, built with different materials that must support high heat flux levels inside the vacuum vessel. The manufacturing processes of the First Wall are a complex procedure including bending, hipping and cutting procedures which, in general, lead to residual stresses and distortions of the fabricated component. In this work, the analysis of the thermo-mechanical response of a simplified prototype of the ITER NHF First Wall Panel is presented from the numerical point of view. The experimental procedure within each phase of the whole manufacturing process is described. Residual stresses and distortions have been measured and analyzed. The numerical simulation of the manufacturing process includes the description of the main hypothesis, the applied loads and the boundary conditions assumed at every stage of the process. Special attention is paid to the simulation of machining and cutting by means of an ad-hoc element deactivation strategy. The numerical results are compared with the experimental evidence to show the prediction capability and the limitations of the proposed numerical model.
Abstract
The objective of ITER is to build a new Tokamak, with the goal of demonstrating the scientific and technical feasibility of fusion power. The First Wall Panels are the inner [...]
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An empirical comparison of machine learning techniques for dam behaviour modelling
F. Salazar, M. Toledo, R. Morán Moya, E. Oñate

Structural Safety (2015). Vol 56, pp. 9-17

Abstract
Predictive models are essential in dam safety assessment. Both deterministic and statistical models applied in the day-to-day practice have demonstrated to be useful, although they show relevant limitations at the same time. On another note, powerful learning algorithms have been developed in the field of machine learning (ML), which have been applied to solve practical problems. The work aims at testing the prediction capability of some state-of-the-art algorithms to model dam behaviour, in terms of displacements and leakage. Models based on random forests (RF), boosted regression trees (BRT), neural networks (NN), support vector machines (SVM) and multivariate adaptive regression splines (MARS) are fitted to predict 14 target variables. Prediction accuracy is compared with the conventional statistical model, which shows poorer performance on average. BRT models stand out as the most accurate overall, followed by NN and RF. It was also verified that the model fit can be improved by removing the records of the first years of dam functioning from the training set.
Abstract
Predictive models are essential in dam safety assessment. Both deterministic and statistical models applied in the day-to-day practice have demonstrated to be useful, although [...]
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Structural shape sensitivity analysis for nonlinear material models with strain softening
G. Bugeda, L. Gil, E. Oñate

Structural Optimization (1999). Vol. 17 (2-3), pp. 162-171

Abstract
This paper describes some considerations around the analytical structural shape sensitivity analysis when the structural behaviour is computed using the finite element method with a nonlinear constitutive material model. Traditionally, the structural sensitivity analysis is computed using an incremental approach based on the incremental procedures for the solution of the structural equilibrium problem. In this work, a direct (nonincremental) formulation for computing these structural sensitivities, that is valid for some specific nonlinear material models, is proposed. The material models for which the presented approach is valid are characterized by the fact that the stresses at any timet can be expressed in terms of the strains at the timet and, in some cases, the strains at a specific past timet u (t u<t). This is the case of elasticity (linear as well as nonlinear), perfect plasticity and damage models. A special strategy is also proposed for material models with strain softening. For the cases where it is applicable, the sensitivity analysis proposed here allows us to compute the structural sensitivities around any structural equilibrium point after finishing the solution process and it is completely independent of the numerical scheme used to solve the structural equilibrium problem. This possibility is particularized for the case of a damage model considering a strain-softening behaviour. Finally, the quality and reliability of the proposed approach is assessed through its application to some example
Abstract
This paper describes some considerations around the analytical structural shape sensitivity analysis when the structural behaviour is computed using the finite element method [...]
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Wireless sensor networks for strain monitoring during steel bridges launching
R. Chacón, F. Guzmán, E. Mirabell, E. Real, E. Oñate

Structural Health Monitoring (2009). Vol. 8 (3), pp. 195-205

Abstract
n this paper, an experimental test performed on a hybrid steel plate girder was subjected to concentrated loads at the end of an unstiffened panel is presented. This load was intended to produce a typical reaction of the piers while launching steel girders in bridges. In this test, strain measurements were taken with conventional pre-wired gauges as well as with newly developed wirelessly connected strain-measuring system. Both measurements were carefully compared and the accuracy of the developed system was demonstrated. Results were also compared with numerical simulations deployed with FE models and on such a basis; the reliability of the developed wireless system was proven. Finally, suggestions of potential research trends in this area are provided
Abstract
n this paper, an experimental test performed on a hybrid steel plate girder was subjected to concentrated loads at the end of an unstiffened panel is presented. This load [...]
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Early detection of anomalies in dam performance: A methodology based on boosted regression trees
F. Salazar, M. Toledo, J. González, E. Oñate

Structural Control Health Monitoring (2017). Vol. 24 (11), Article Number: e2012

Abstract
The advances in information and communication technologies led to a general trend towards the availability of more detailed information on dam behaviour. This allows applying advanced data‐based algorithms in its analysis, which has been reflected in an increasing interest in the field. However, most of the related literature is limited to the evaluation of model prediction accuracy, whereas the ulterior objective of data analysis is dam safety assessment. In this work, a machine‐learning algorithm (boosted regression trees) is the core of a methodology for early detection of anomalies. It also includes a criterion to determine whether certain discrepancy between predictions and observations is normal, a procedure to compute a realistic estimate of the model accuracy, and an original approach to identify extraordinary load combinations. The performance of causal and noncausal models is assessed in terms of their ability to detect different types of anomalies, which were artificially introduced on reference time series generated with a numerical model of a 100‐m‐high arch dam. The final approach was implemented in an online application to visualise the results in an intuitive way to support decision making.
Abstract
The advances in information and communication technologies led to a general trend towards the availability of more detailed information on dam behaviour. This allows applying [...]
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Robust multidisciplinary unmanned aerial system design optimisation
D. Lee, J. Periaux, L. González, K. Srinivas, E. Oñate

Structural and Multidisciplinary Optimization (2012). Vol. 45 (3), pp. 433-450

Abstract
There are many applications in aeronautical/aerospace engineering where some values of the design parameters/states cannot be provided or determined accurately. These values can be related to the geometry (wingspan, length, angles) and or to operational flight conditions that vary due to the presence of uncertainty parameters (Mach, angle of attack, air density and temperature, etc.). These uncertainty design parameters cannot be ignored in engineering design and must be taken into the optimisation task to produce more realistic and reliable solutions. In this paper, a robust/uncertainty design method with statistical constraints is introduced to produce a set of reliable solutions which have high performance and low sensitivity. Robust design concept coupled with Multi-Objective Evolutionary Algorithms (MOEAs) is defined by applying two statistical sampling formulas; mean and variance/standard deviation associated with the optimisation fitness/objective functions. The methodology is based on a canonical evolution strategy and incorporates the concepts of hierarchical topology, parallel computing and asynchronous evaluation. It is implemented for two practical Unmanned Aerial System (UAS) design problems; the first case considers robust multi-objective (single-disciplinary: aerodynamics) design optimisation and the second considers a robust multidisciplinary (aero-structures) design optimisation. Numerical results show that the solutions obtained by the robust design method with statistical constraints have a more reliable performance and sensitivity in both aerodynamics and structures when compared to the baseline design. KeywordsRobust/uncertainty design–Multi-objective–Multidisciplinary–UAS–Evolutionary algorithms
Abstract
There are many applications in aeronautical/aerospace engineering where some values of the design parameters/states cannot be provided or determined accurately. These values [...]
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Discrete/finite element modelling of rock cutting with TBM disc cutter
C. Labra, J. Rojek, E. Oñate

Rock Mechanics and Rock Engineering (2017). Vol. 50 (3), pp. 621-638

Abstract
This paper presents advanced computer simulation of rock cutting process typical for excavation works in civil engineering. Theoretical formulation of the hybrid discrete/finite element model has been presented. The discrete and finite element methods have been used in different subdomains of a rock sample according to expected material behaviour, the part which is fractured and damaged during cutting is discretized with the discrete elements while the other part is treated as a continuous body and it is modelled using the finite element method. In this way, an optimum model is created, enabling a proper representation of the physical phenomena during cutting and efficient numerical computation. The model has been applied to simulation of the laboratory test of rock cutting with a single TBM (tunnel boring machine) disc cutter. The micromechanical parameters have been determined using the dimensionless relationships between micro- and macroscopic parameters. A number of numerical simulations of the LCM test in the unrelieved and relieved cutting modes have been performed. Numerical results have been compared with available data from in-situ measurements in a real TBM as well as with the theoretical predictions showing quite a good agreement. The numerical model has provided a new insight into the cutting mechanism enabling us to investigate the stress and pressure distribution at the tool–rock interaction. Sensitivity analysis of rock cutting performed for different parameters including disc geometry, cutting velocity, disc penetration and spacing has shown that the presented numerical model is a suitable tool for the design and optimization of rock cutting process.
Abstract
This paper presents advanced computer simulation of rock cutting process typical for excavation works in civil engineering. Theoretical formulation of the hybrid discrete/finite [...]
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Possibilities of the particle finite element method for fluid-structure interaction problems with free surface waves
E. Oñate, S. Idelsohn, F. Del Pin, R. Aubry

Revue Européenne des Éléments Finis (2004). Vol. 13, pp. 637-666

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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An Implicit Material Point Method Applied to Granular Flows
I. Iaconeta, A. Larese, R. Rossi, E. Oñate

Procedia Engineering (2017). Vol. 175, pp. 226-232

Abstract
The main objective of this work lies in the development of a variational implicit Material Point Method (MPM), implemented in the open source Kratos Multiphysics framework. The ability of the MPM technique to solve large displacement and large deformation problems is widely recognised and its use ranges over many problems in industrial and civil engineering. In the current work the continuum based implicit MPM is applied to engineering applications, where granular material flow is involved. For the resolution of the length and time scale of these particular problems, both continuum and discrete models are typically used. Even if discrete techniques predict more feasible results, nowadays, their use is limited to the investigation of element tests of particles, or to the simulation of reduced systems, not allowing to make important decisions in the analysis and design of granular processes. Some advantages of MPM over discrete methods are tested, such as, the ability to simulate granular flow at the large scale with acceptable computational cost and the capability to get information of stress and strain state in a more straightforward way. The focus of this paper is a comparative study between an irreducible and a mixed formulation, both implemented in the MPM code, to assess the improvement in accuracy and reliability of the numerical results when the latter formulation is adopted.
Abstract
The main objective of this work lies in the development of a variational implicit Material Point Method (MPM), implemented in the open source Kratos Multiphysics framework. [...]
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Modelling and simulation of the sea-landing of aerial vehicles using the Particle Finite Element Method
P. Ryzhakov, R. Rossi, A. Viña, E. Oñate

Ocean Engng. (2013). Vol. 66, pp. 92-100

Abstract
In this paper the Particle Finite Element Method (PFEM) is applied to the simulation of the sea-landing of an unmanned aerial vehicle (UAV). The problem of interest consists in modelling the impact of the vehicle against the water surface, analyzing the main kinematic and dynamic quantities (such as loads exerted upon the capsule at the moment of the impact). The PFEM, a methodology well-suited for free-surface flow simulation is used for modelling the water while a rigid body model is chosen for the vehicle. The vehicle under consideration is characterized by low weight. This leads to difficulties in modelling the fluid–structure interaction using standard Dirichlet–Neumann coupling. We apply a modified partitioned strategy introducing the interface Laplacian into the pressure Poisson's equation for obtaining a convergent FSI solution. The paper concludes with an industrial example of a vehicle sea-landing modelled using PFEM.
Abstract
In this paper the Particle Finite Element Method (PFEM) is applied to the simulation of the sea-landing of an unmanned aerial vehicle (UAV). The problem of interest consists [...]
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An extended class of multilayer perceptron
R. López, E. Oñate

Neurocomputing (2008). Vol. 71 (13-15), pp. 2538-2543

Abstract
In this work an extended class of multilayer perceptron is presented. This includes independent parameters, boundary conditions and lower and upper bounds. In some cases, such extensions contain a priori information of the problem. On some other situations they are necessary in order to define a correct representation for the solution. The use of this augmented class of neural network is illustrated through a case study in the optimal control theory. The numerical results are compared against the analytical solution.
Abstract
In this work an extended class of multilayer perceptron is presented. This includes independent parameters, boundary conditions and lower and upper bounds. In some cases, [...]
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A co-rotational 8-node assumed strain shell element for postbuckling analysis of laminated composite plates and shells
G. Lomboy, K. Kim, E. Oñate

Mechanics of Advanced Materials and Structures (2007). Vol. 14 (2), pp. 89-105

Abstract
A nonlinear resultant shell element is developed for the solution of problems of composite plates and shells undergoing nonlinear static and nonlinear dynamic behavior with progressive layer failure. The formulation of the tangent stiffness is defined on the mid-surface and is efficient for analyzing thick laminated plates and shells by incorporating bending moments and transverse shear resultant forces in the geometric stiffness. The composite element is free of both membrane and shear locking behavior by using the assumed natural strain method, such that the element also performs very well as thin laminate shells. An equilibrium approach is used to derive the improved transverse shear stiffness, instead of using a shear correction factor. The proposed formulation is computationally efficient and the test results show good agreement with references. The composite shell element is extended to determine ply failures in laminated composite structures undergoing nonlinear static or dynamic behavior. The failure analysis is done by first, computing for the inter-laminar stresses at each gauss point in an element. Having obtained the stresses in each layer, checking for failure is performed based on a chosen failure criterion. Four failure criteria are available to enable the user to adopt the appropriate criterion for the type of problem parameters present.
Abstract
A nonlinear resultant shell element is developed for the solution of problems of composite plates and shells undergoing nonlinear static and nonlinear dynamic behavior with [...]
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Analysis of segmentally constructed prestressed concrete bridges using hexahedral elements with realistic tendon profiles
P. Norachan, K. Kim, E. Oñate

Journal of Structural Engineering (2014). Vol. 140 (6), pp. 04014028/1-17

Abstract
The paper presents a systematically numerical procedure based on the finite-element method for three-dimensional analysis of segmentally constructed prestressed concrete bridges using hexahedral elements including realistic tendon profiles. The enhanced assumed strain (EAS) is used in the formulation of the hexahedral element in order to improve the element performances. Both the geometric nonlinearity and time-dependent effects due to creep, shrinkage, and aging of the concrete and relaxation of the prestress are taken into account, while variations of the structural configuration due to changes of the structural geometry and boundary conditions during the construction process are also incorporated. To include realistic tendon profiles, the idealized prestressing tendon is represented by a system of piecewise linear prestressing segments. Several numerical examples in a wide range of prestressed concrete structures are presented to demonstrate the validity and efficiency of the proposed procedure. Finally, application to the erection of a segmentally erected prestressed concrete bridge is discussed at the end of the paper.
Abstract
The paper presents a systematically numerical procedure based on the finite-element method for three-dimensional analysis of segmentally constructed prestressed concrete bridges [...]
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Modeling of ground excavation with the particle finite-element method
J. Carbonell, E. Oñate, B. Suarez

Journal of Engineering Mechanics (2010). Vol. 136 (4), pp. 455-463

Abstract
An excavation process is a nonlinear dynamic problem that includes geometrical, material, and contact nonlinearities. The simulation of ground excavation has to face contact interaction in a changing geometry composed by several solid domains. The particle finite-element method (PFEM) is based on a Lagrangian description for modeling the motion of a continuum medium. The PFEM is particularly suitable for modeling a fluid motion with free surfaces. The application of the PFEM in ground excavation includes the use of the remeshing process, α-shape concepts for detecting the domain boundary, contact mechanics laws, material constitutive models, and surface wear models. Everything is correctly matched to quantify the excavation and the corresponding damage caused to the ground. The erosion and wear parameters of the soil/rock material govern the evolution of the excavation process. The preliminary results presented in this paper show that the PFEM it is a very suitable tool for the simulation of ground excavation processes.
Abstract
An excavation process is a nonlinear dynamic problem that includes geometrical, material, and contact nonlinearities. The simulation of ground excavation has to face contact [...]
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Approximating the Basset force by optimizing the method of van Hinsberg et al.
G. Casas, A. Ferrer, E. Oñate

Journal of Computational Physics (2018). Vol. 352, pp. 142-171

Abstract
In this work we put the method proposed by van Hinsberg et al. to the test, highlighting its accuracy and efficiency in a sequence of benchmarks of increasing complexity. Furthermore, we explore the possibility of systematizing the way in which the method's free parameters are determined by generalizing the optimization problem that was considered originally. Finally, we provide a list of worked-out values, ready for implementation in large-scale particle-laden flow simulations.
Abstract
In this work we put the method proposed by van Hinsberg et al. to the test, highlighting its accuracy and efficiency in a sequence of benchmarks of increasing complexity. [...]
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Volumetric constraint models for anisotropic elastic solids
C. Felippa, E. Oñate

Journal of Applied Mechanics (2004). Vol. 71 (5), pp. 731-734

Abstract
We study three “incompressibility flavors” of linearly-elastic anisotropic solids that exhibit volumetric constraints: isochoric, hydroisochoric and rigidtropic. An isochoric material deforms without volume change under any stress system. An hydroisochoric material does so under hydrostatic stress. A rigidtropic material undergoes zero deformations under a certain stress pattern. Whereas the three models coalesce for isotropic materials, important differences appear for anisotropic behavior. We find that isochoric and hydroisochoric models under certain conditions may be hampered by unstable physical behavior. Rigidtropic models can represent semistable physical materials of arbitrary anisotropy while including isochoric and hydroisochoric behavior as special cases.
Abstract
We study three “incompressibility flavors” of linearly-elastic anisotropic solids that exhibit volumetric constraints: isochoric, hydroisochoric and rigidtropic. [...]
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Active transonic aerofoil design optimization using robust multiobjective evolutionary algorithms
D. Lee, J. Periaux, L. González, E. Oñate, N. Qin

Journal of Aircraft (2011). Vol. 48 (3) pp. 1084-1094

Abstract
The use of adaptive wing/aerofoil designs is being considered, as they are promising techniques in aeronautic/ aerospace since they can reduce aircraft emissions and improve aerodynamic performance of manned or unmanned aircraft. This paper investigates the robust design and optimization for one type of adaptive techniques: active flow control bump at transonic flow conditions on a natural laminar flow aerofoil. The concept of using shock control bump is to control supersonic flow on the suction/pressure side of natural laminar flow aerofoil that leads to delaying shock occurrence (weakening its strength) or boundary-layer separation. Such an active flow control technique reduces total drag at transonic speeds due to reduction of wave drag. The location of boundary-layer transition can influence the position and structure of the supersonic shock on the suction/pressure side of aerofoil. The boundarylayer transition position is considered as an uncertainty design parameter in aerodynamic design due to the many factors, such as surface contamination or surface erosion. This paper studies the shock-control-bump shape design optimization using robust evolutionary algorithms with uncertainty in boundary-layer transition locations. The optimization method is based on a canonical evolution strategy and incorporates the concepts of hierarchical topology, parallel computing, and asynchronous evaluation. Two test cases are conducted: the first test assumes the boundary-layer transition position is at 45% of chord from the leading edge, and the second test considers robust design optimization for the shock control bump at the variability of boundary-layer transition positions. The numerical result shows that the optimization method coupled to uncertainty design techniques produces Pareto optimal shock-control-bump shapes, which have low sensitivity and high aerodynamic performance while having significant total drag reduction.
Abstract
The use of adaptive wing/aerofoil designs is being considered, as they are promising techniques in aeronautic/ aerospace since they can reduce aircraft emissions and improve [...]
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Numerical Investigation of Wind-Tunnel Model Deformations Caused by the Twin-Sting Support System
F. Flores, E. Ortega, E. Oñate

Journal of Aircraft (2010). Vol. 47, pp. 708-714

Abstract
The present work is part of a broader investigation aimed at improving the understanding of the aerodynamics of the rear aircraft section. Complex flow phenomena (e.g., the thick fuselage boundary layer at the rear end) present a challenge to the accurate predictions of aerodynamic performance. Significant efficiency gains are expected from improved-fidelity computations and experimental techniques. As part of a joint effort between several research institutions and industrial partners, a series of wind-tunnel test campaigns focusing on accurate rear-end measurements was planned. To obtain accurate tail-force data, a nonstandard live-rear-end test model was adopted. This technique uses a mechanically separate rear-end section attached to the main body through internal balances, allowing direct measurement of the force acting on the tail. This mechanical setup precludes the use of a conventional tail-coneattached sting. Moreover, to minimize aerodynamic interference on the empennage caused by the support system, a wing-attached twinsting mounting was chosen
Abstract
The present work is part of a broader investigation aimed at improving the understanding of the aerodynamics of the rear aircraft section. Complex flow phenomena (e.g., [...]
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Robust design optimization in aeronautics using stochastic analysis and evolutionary algorithms
J. Pons-Prats, G. Bugeda, F. Zárate, E. Oñate

Journal of Aerospace Engineering (2011). Vol. 225, (10), pp. 1131-1151

Abstract
Uncertainties are a daily issue to deal with in aerospace engineering and applications. Robust optimization methods commonly use a random generation of the inputs and take advantage of multi-point criteria to look for robust solutions accounting with uncertainty definition. From the computational point of view, the application to coupled problems, like computational fluid dynamics (CFD) or fluid–structure interaction (FSI), can be extremely expensive. This study presents a coupling between stochastic analysis techniques and evolutionary optimization algorithms for the definition of a stochastic robust optimization procedure. At first, a stochastic procedure is proposed to be applied into optimization problems. The proposed method has been applied to both CFD and FSI problems for the reduction of drag and flutter, respectively.
Abstract
Uncertainties are a daily issue to deal with in aerospace engineering and applications. Robust optimization methods commonly use a random generation of the inputs and take [...]
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A monolithic FE formulation for the analysis of membranes in fluids
R. Rossi, P. Ryzhakov, E. Oñate

International Journal of Space Structures (2009). Vol. 24 (4), pp. 205-210

Abstract
We propose here an efficient approach for treating the interaction between membranes and fluids. Slight compressibility of the fluid is assumed. Classical total Lagrangian formulation including wrinkling is adopted for the membrane representation, whereas fluid is treated in an updated Lagrangian manner, developed in the current work. Assumption of slight compressibility of the fluid enables one to define the monolithic fluid-membrane system in a natural way. The displacements are the primary variables of both the fluid and the membrane domains. The formulation adopts the Particle Finite Element Method (PFEM) philosophy for free-surface identification and mesh regeneration. Three examples illustrate the functionality of the formulation in application to FSI problems involving motion of membranes in water
Abstract
We propose here an efficient approach for treating the interaction between membranes and fluids. Slight compressibility of the fluid is assumed. Classical total Lagrangian [...]
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Discrete element simulation of rock cutting
J. Rojek, E. Oñate, C. Labra, H. Kargl

Int. J. Rock Mechanics and Mining Sciences (2011). Vol. 48 (6), pp. 996-1010

Abstract
This paper presents numerical modelling of rock cutting processes. The model consists of a tool–rock system. The rock is modelled using the discrete element method, which is suitable to study problems of multiple material fracturing such as those involved in rock cutting. Both 2D and 3D models are considered in this work. The paper presents a brief overview of the theoretical formulation and calibration of the discrete element model by a methodology combining the dimensional analysis with simulation of the unconfined compressive strength (UCS) and indirect tension (Brazilian) tests. The rock cutting process with roadheader picks, which is typical for underground excavation, has been simulated. The results of the 2D and 3D analyses have been compared with one another, and numerical results have been compared with the available experimental data.
Abstract
This paper presents numerical modelling of rock cutting processes. The model consists of a tool–rock system. The rock is modelled using the discrete element method, [...]
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Numerical and Experimental Study of Overtopping and Failure of Rockfill Dams
A. Larese, R. Rossi, E. Oñate, M. Toledo, R. Morán Moya, H. Campos

International Journal of Geomechanics (2015). Vol. 15 (4), pp. 04014060-1 (published online)

Abstract
This paper aims to present and validate a numerical technique for the simulation of the overtopping and onset of failure in rockfill dams caused by mass sliding. This goal is achieved by coupling a fluid dynamic model for the simulation of the free surface and through-flow problems together with a numerical technique for the calculation of the rockfill response and deformation. Both the flow within the dam body and in its surroundings are taken into account. An extensive validation of the resulting computational method is performed by solving several failure problems on physical models of rockfill dams for which experimental results have been obtained by the authors.
Abstract
This paper aims to present and validate a numerical technique for the simulation of the overtopping and onset of failure in rockfill dams caused by mass sliding. This goal [...]
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A FIC‐based stabilized mixed finite element method with equal order interpolation for solid–pore fluid interaction problems
I. de-Pouplana, E. Oñate

Int. J. Numer. Anal. Meth. Geomech. (2017). Vol. 41 (1), pp. 110-134

Abstract
A new mixed displacement‐pressure element for solving solid–pore fluid interaction problems is presented. In the resulting coupled system of equations, the balance of momentum equation remains unaltered, while the mass balance equation for the pore fluid is stabilized with the inclusion of higher‐order terms multiplied by arbitrary dimensions in space, following the finite calculus (FIC) procedure. The stabilized FIC‐FEM formulation can be applied to any kind of interpolation for the displacements and the pressure, but in this work, we have used linear elements of equal order interpolation for both set of unknowns. Examples in 2D and 3D are presented to illustrate the accuracy of the stabilized formulation for solid–pore fluid interaction problems.
Abstract
A new mixed displacement‐pressure element for solving solid–pore fluid interaction problems is presented. In the resulting coupled system of equations, the balance [...]
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Numerical modelling of landslide‐generated waves with the particle finite element method (PFEM) and a non‐Newtonian flow model
F. Salazar, J. Irazábal González, A. Larese, E. Oñate

Int. J. Numer. Anal. Meth. Geomech. (2016). Vol. 40 (6), pp. 809-826

Abstract
Landslide‐generated impulse waves may have catastrophic consequences. The physical phenomenon is difficult to model because of the uncertainties in the kinematics of the mobilised material and to the intrinsic complexity of the fluid–soil interaction. The particle finite element method (PFEM) is a numerical scheme that has successfully been applied to fluid–structure interaction problems. It uses a Lagrangian description to model the motion of nodes (particles) in both the fluid and the solid domains (the latter including soil/rock and structures). A mesh connecting the particles (nodes) is re‐generated at every time step, where the governing equations are solved. Various constitutive laws are used for the sliding mass, including rigid solid and the Newtonian and non‐Newtonian fluids. Several examples of application are presented, corresponding both to experimental tests and to actual full‐scale case studies. The results show that the PFEM can be a useful tool for analysing the risks associated with landslide phenomena, providing a good estimate to the potential hazards even for full‐scale events.
Abstract
Landslide‐generated impulse waves may have catastrophic consequences. The physical phenomenon is difficult to model because of the uncertainties in the kinematics of the [...]
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Multiscale analysis using a coupled discrete/finite element model
J. Rojek, E. Oñate

Interaction and Multiscale Mechanics: An International Journal (IMMIJ) (2007). Vol. 1 (1), pp. 1-31

Abstract
The present paper presents multiscale modelling via coupling of the discrete and finite element methods. Theoretical formulation of the discrete element method using spherical or cylindrical particles has been briefly reviewed. Basic equations of the finite element method using the explicit time integration have been given. The micr-macro transition for the discrete element method has been discussed. Theoretical formulations for macroscopic stress and strain tensors have been given. Determination of macroscopic constitutive properties using dimensionless micro-macro relationships has been proposed. The formulation of the multiscale DEM/FEM model employing the DEM and FEM in different subdomains of the same body has been presented. The coupling allows the use of partially overlapping DEM and FEM subdomains. The overlap zone in the two coupling algorithms is introduced in order to provide a smooth transition from one discretization method to the other. Coupling between the DEM and FEM subdomains is provided by additional kinematic constraints imposed by means of either the Lagrange multipliers or penalty function method. The coupled DEM/FEM formulation has been implemented in the authors’ own numerical program. Good performance of the numerical algorithms has been demonstrated in a number of examples.
Abstract
The present paper presents multiscale modelling via coupling of the discrete and finite element methods. Theoretical formulation of the discrete element method using spherical [...]
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Modelación del ensayo brasileño empleando modelación discreta
C. Recarey Morfa, E. Oñate, J. Rojek, J. Canet, F. Zárate, G. Cadoce, C. Labra

Ingeniería Civil (2005). Vol. 139, pp. 112-124

Abstract
Se presenta un modelo de elementos discretos o distintos (MED) en la modelizacion del ensayo de traccion indirecta o ensayo brasileno (Brazilian Test). Se realiza una comparacion entre los resultados obtenidos por el MED, con la de otros autores [26,35] que emplean el MEF. Se obtienen buenos resultados en el proceso de simulacion del ensayo brasileno, y la comparacion con el MEF (método de los elementos finitos) es muy efectiva. Se evidencia la similitud fisica que existe entre los resultados obtenidos por el MED y ensayos experimentales, lo que posibilita demostrar la fiabilidad y veracidad de la formulacion realizada. (A). English abstract: This work deals whit the use of the Distinct Element Method (DEM) to simulate an indirect traction test, also known as "the Brazilian test" A comparison is realized between results obtained with the DEM, and those obtained by other authors [26, 35] using the Finite Element Method (FEM). The Brazilian test's simulation gives good results and the comparison is very effective. There is a similarity between the results obtained using the DEM and those obtained from real experiments, similarity which proves the reliability and the veracity of this formulation.
Abstract
Se presenta un modelo de elementos discretos o distintos (MED) en la modelizacion del ensayo de traccion indirecta o ensayo brasileno (Brazilian Test). Se realiza una comparacion [...]
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Triangular prismatic solid-shell element with generalised deformation description
V. Mataix Ferrándiz, F. Flores, R. Rossi, E. Oñate

European Journal of Computational Mechanics (2018). Vol. 27 (1), pp. 1-32

Abstract
The solid-shells are an attractive kind of element for the simulation of f orming processes, due to the fact that any kind of generic 3D constitutive law can be employed without any kind of additional modification, besides the thermomechanic problem is formulated without additional assumptions. Additionally, this type of element allows the three-dimensional description of the deformable body, thus contact on both sides of the element can be treated easily. The present work consists in the development of a triangular prism element as a solid-shell, for the analysis of thin/thick shell, undergoing large deformations. The element is formulated in total Lagrangian formulation, and employs the neighbour (adjacent) elements to perform a local patch to enrich the displacement field. In the original formulation by Flores, a modified right Cauchy-Green deformation tensor () is obtained; in the present work a modified deformation gradient () is obtained, which allows to generalise the methodology and allows to employ a wide range of constitutive laws. The element is based in three modifications: (a) a classical assumed strain approach for transverse shear strains (b) an assumed strain approach for the in-plane components using information from neighbour elements and (c) an averaging of the volumetric strain over the element. The objective is to use this type of elements for the simulation of shells avoiding transverse shear locking, improving the membrane behaviour of the in-plane triangle and to handle quasi-incompressible materials or materials with isochoric plastic flow. Some examples have been evaluated to show the good performance of the element and results.
Abstract
The solid-shells are an attractive kind of element for the simulation of f orming processes, due to the fact that any kind of generic 3D constitutive law can be employed without [...]
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Interpretation of dam deformation and leakage with boosted regression trees
F. Salazar, M. Toledo, E. Oñate, B. Suarez

Engineering Structures (2016). Vol. 119, pp. 230-251

Abstract
Predictive models are essential in dam safety assessment. They have been traditionally based on simple statistical tools such as the hydrostatic-season-time (HST) model. These tools are well known to have limitations in terms of accuracy and reliability. In the recent years, the examples of application of machine learning and related techniques are becoming more frequent as an alternative to HST. While they proved to feature higher flexibility and prediction accuracy, they are also more difficult to interpret. As a consequence, the vast majority of the research is limited to prediction accuracy estimation. In this work, one of the most popular machine learning techniques (boosted regression trees), was applied to model 8 radial displacements and 4 leakage flows at La Baells Dam. The possibilities of model interpretation were explored: the relative influence of each predictor was computed, and the partial dependence plots were obtained. Both results were analysed to draw conclusions on dam response to environmental variables, and its evolution over time. The results show that this technique can efficiently identify dam performance changes with higher flexibility and reliability than simple regression models.
Abstract
Predictive models are essential in dam safety assessment. They have been traditionally based on simple statistical tools such as the hydrostatic-season-time (HST) model. These [...]
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Finite element modelling of fracture propagation in saturated media using quasi-zero-thickness interface elements
I. de-Pouplana, E. Oñate

Computers and Geotechnics (2018). Vol. 96, pp. 103-117

Abstract
A new computational technique for the simulation of 2D and 3D fracture propagation processes in saturated porous media is presented. A non-local damage model is conveniently used in conjunction with interface elements to predict the degradation pattern of the domain and insert new fractures followed by remeshing. FIC-stabilized elements of equal order interpolation in the displacement and the pore pressure have been successfully used under complex conditions near the undrained-incompressible limit. A bilinear cohesive fracture model describes the mechanical behaviour of the joints. A formulation derived from the cubic law models the fluid flow through the crack. Examples in 2D and 3D, using 3-noded triangles and 4-noded tetrahedra respectively, are presented to illustrate the accuracy and robustness of the proposed methodology.
Abstract
A new computational technique for the simulation of 2D and 3D fracture propagation processes in saturated porous media is presented. A non-local damage model [...]
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Numerical modelling of granular materials with spherical discrete particles and the bounded rolling friction model. Application to railway ballast
J. Irazábal González, F. Salazar, E. Oñate

Computers and Geotechnics (2017). Vol. 85, pp. 220-229

Abstract
The Discrete Element Method (DEM) was found to be an effective numerical method for the calculation of engineering problems involving granular materials. However, the representation of irregular particles using the DEM is a very challenging issue, leading to different geometrical approaches. This document presents a new insight in the application of one of those simplifications known as rolling friction, which avoids excessive rotation when irregular shaped materials are simulated as spheric particles. This new approach, called the Bounded Rolling Friction model, was applied to reproduce a ballast resistance test.
Abstract
The Discrete Element Method (DEM) was found to be an effective numerical method for the calculation of engineering problems involving granular materials. [...]
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Computationally optimized formulation for the simulation of composite materials and delamination failures
X. Martinez, F. Rastellini, S. Oller, F. Flores, E. Oñate

Composites Part B: Enginnering (2011). Vol. 42 (2), pp. 134-144

Abstract
The numerical simulation of complex failure modes of composite materials, such as delamination, can be computationally very demanding, as it requires special elements and/or numerical strategies to characterize damage onset and propagation. This work presents several formulations developed to optimize the computational performance of an explicit finite element code designed specifically for the simulation of large scale composite structures. The composite mechanical performance is obtained with the matrix-reinforced mixing theory, a simplified version of the serial/parallel mixing theory that does not require an iterative procedure or the calculation of the tangent stiffness matrix. The number of elements required to perform the simulation is reduced by stacking several layers inside a single finite element. This work also proposes a modification of the isotropic damage law, capable of taking into account the residual strength provided by friction in type II fracture modes. The ability of these formulations to successfully predict the mechanical performance of composite materials is assessed with the ply drop-off test. In this test a laminate with a change of thickness in its mid-span is loaded until it breaks due to a delamination process. The formulation proposed obtains a very accurate prediction of the experimental response of the test, as it provides a very good characterization of the initial laminate stiffness, the delamination onset, and its propagation along the specimen.
Abstract
The numerical simulation of complex failure modes of composite materials, such as delamination, can be computationally very demanding, as it [...]
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A hierarchical finite element for composite laminated beams using a refined zigzag theory
L. Nallim, S. Oller, E. Oñate, F. Flores

Composite Structures (2017). Vol. 163, pp. 168-184

Abstract
In this work a kinematics for laminated beams enriched with a refined formulation ZigZag (RZT), originally presented by Tessler et al. in 2007, introduced in a hierarchical one dimensional type “p” finite element is presented. The finite element employs Lagrange polynomials for the approximation of the degrees of freedom of the ends (nodes) and orthogonal Gram-Schmidt polynomials to the internal degrees of freedoms. This finite element allows a very low discretization, is free of shear locking and behaves very well when the analysis of laminated composites with accurate determination of local stresses and strains at laminar level is necessary. This element has been validated in the analysis of laminated beams with various sequences of symmetric and asymmetric stacking, studying in each case its accuracy and stability.
Abstract
In this work a kinematics for laminated beams enriched with a refined formulation ZigZag (RZT), originally presented by Tessler et al. in 2007, introduced in a hierarchical [...]
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Two-noded zigzag beam element accounting for shear effects based on an extended Euler Bernoulli theory
D. Di Capua, E. Oñate

Composite Structures (2015). Vol. 132, pp 1192-1205

Abstract
We present a new 2-noded beam element based on the refined zigzag theory and the classical Euler–Bernoulli beam theory for the static analysis of composite laminate and sandwich beams. The proposed element is able to take into account distortion effects due to shear elastic strains and can predict delamination. The element has four degrees of freedom per node. A C1 cubic Hermite interpolation is used for the vertical deflection while a C0 linear interpolation is employed for the other kinematics variables. The stiffness matrix and the load vector are calculated in explicit form using exact integration. The element is free from shear locking as confirmed with numerical tests on a wide range of the slenderness ratios. Numerical results show the ability of the EEBZ2 element to reproduce accurately the vertical deflection along the beam length and complex zigzag distributions of the axial displacement and the stresses across the thickness. Delamination effects are modeled by incorporating of an additional zigzag function corresponding to the kinematics of a zero thickness layer where delamination occurs. An example showing the capability of the new EEBZ2 element for accurately reproducing delamination effects is presented.
Abstract
We present a new 2-noded beam element based on the refined zigzag theory and the classical Euler–Bernoulli beam theory for the static analysis of composite laminate [...]
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Delamination in laminated plates using the 4-noded quadrilateral qlrz plate element based on the refined zigzag theory
A. Eijo, E. Oñate, S. Oller

Composite Structures (2014). Vol. 108, pp. 456-471

Abstract
A numerical method based on the Refined Zigzag Theory (RZT) to model delamination in composite laminated plate/shell structures is presented. The originality of this method is the use of 4-noded quadrilateral plate finite elements whit only seven variables per node to discretize the plate/shell geometry. The ability to capture the relative displacement between consecutive layers in fracture mode II and III is the more important advantage of this element, denoted QLRZ. A continuum isotropic damage model is used to model the mechanical behavior of the plies. The material non-lineal problem is solved with the modified Newton–Raphson method. The RZT plate theory, the QLRZ finite element and the isotropic damage model are described in this work. Also, the implicit integration algorithm is presented. The performance of the numerical model is analyzed by studying the delamination in a rectangular plate for two different laminates, using the 3D analysis as the reference solution
Abstract
A numerical method based on the Refined Zigzag Theory (RZT) to model delamination in composite laminated plate/shell structures is presented. The originality of this method [...]
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A numerical model of delamination in composite laminated beams using the LRZ beam element based on the refined zigzag theory
A. Eijo, E. Oñate, S. Oller

Composite Structures (2013). Vol. 104, pp. 270-280

Abstract
A method based on the Refined Zigzag Theory (RZT) to model delamination in composite laminated beam structures is presented. The novelty of this method is the use of one-dimensional finite elements to discretize the geometry of the beam. The key property of this beam element, named LRZ, is the possibility to capture the relative displacement between consecutive layers which occurs during delamination. The fracture mode that the LRZ element is capable to predict is mode II. In order to capture the relative displacement using the LRZ element it is necessary to adapt the RZT theory as presented in this paper. The mechanical properties of the layers are modeled using a continuum isotropic damage model. The modified Newton–Raphson method is used for solving the non-linear problem. The RZT theory, the LRZ finite element and the isotropic damage model are described in the paper. Also, the implicit integrations algorithm is presented. The performance of the LRZ element is analyzed by studying the delamination in a beam for two different laminates, using the plane stress solution as a reference.
Abstract
A method based on the Refined Zigzag Theory (RZT) to model delamination in composite laminated beam structures is presented. The novelty of this method is the use of one-dimensional [...]
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Robust design optimisation of advance hybrid (fiber-metal) composite structures
D. Lee, C. Morillo, S. Oller, G. Bugeda, E. Oñate

Composite Structures (2013). Vol. 99, pp. 181-192

Abstract
Hybrid Composite Structures (HCSs) are consisting of alternating layers of Fiber-Reinforced Polymer and metal sheets. Mechanical properties and responses for off-design conditions of HCSs can be improved using an innovative methodology coupling Multi-Objective Genetic Algorithm and robust design method. The concept of robust design approach ensures that a structure will be tolerant to unexpected loading and operating conditions. In this paper, two applications are considered; the first is to maximise the stiffness of the HCS while minimising its total weight through a Multi-Objective Design Optimisation. The second application considers a Robust Multi-Objective Design Optimisation (RMDO) to minimise total weight of HCS and to minimise both, the normalised mean displacement and the standard deviations of displacement, considering critical load cases. For the optimisation process, a distributed/parallel Multi-Objective Genetic Algorithm in robust multi-objective optimisation platform is used and it is coupled to a Finite Element Analysis based composite structure analysis tool to find the optimal combination of laminates sequences for HCSs. Numerical results show the advantages in mechanical properties of HCS over the metal structures, and also the use of RMDO methodology to obtain higher characteristics of HCS in terms of mechanical properties and its stability at the variability of load cases.
Abstract
Hybrid Composite Structures (HCSs) are consisting of alternating layers of Fiber-Reinforced Polymer and metal sheets. Mechanical properties and responses for off-design [...]
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Multilayered composite structure design optimisation using distributed/parallel multi-objective evolutionary algorithms
D. Lee, C. Morillo, G. Bugeda, S. Oller, E. Oñate

Composite Structures (2012). Vol. 94 (3), pp. 1087-1096

Abstract
This paper presents a research work on stacking sequence design optimisation for multilayered composite plate using a parallel/distributed evolutionary algorithm. The stacking sequence of fibres has a dramatic influence on the strength of multilayered composite plates. Multiple layers of fibre-reinforced material systems offer versatility in engineering material design due to the fact that the stacking sequence of each orthotropic layer can offer full advantage of superior mechanical properties. Numerical results show that the optimal composite structures have lower weight, higher stiffness and also affordable cost when compared to the extreme and intermediate composite structures. In addition, the benefits of using a parallel optimisation system are also presented.
Abstract
This paper presents a research work on stacking sequence design optimisation for multilayered composite plate using a parallel/distributed evolutionary algorithm. [...]
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Finite element modeling of free surface flow in variable porosity media
A. Larese, R. Rossi, E. Oñate

Archives of Comp. Meths. Engng. (2015). Vol. 22 (4), pp. 637-653

Abstract
The aim of the present work is to present an overview of some numerical procedures for the simulation of free surface flows within a porous structure. A particular algorithm developed by the authors for solving this type of problems is presented. A modified form of the classical Navier–Stokes equations is proposed, with the principal aim of simulating in a unified way the seepage flow inside rockfill-like porous material and the free surface flow in the clear fluid region. The problem is solved using a semi-explicit stabilized fractional step algorithm where velocity is calculated using a 4th order Runge–Kutta scheme. The numerical formulation is developed in an Eulerian framework using a level set technique to track the evolution of the free surface. An edge-based data structure is employed to allow an easy OpenMP parallelization of the resulting finite element code. The numerical model is validated against laboratory experiments on small scale rockfill dams and is compared with other existing methods for solving similar problems.
Abstract
The aim of the present work is to present an overview of some numerical procedures for the simulation of free surface flows within a porous structure. A particular algorithm [...]
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Data-Based Models for the Prediction of Dam Behaviour: A Review and Some Methodological Considerations
F. Salazar, R. Morán Moya, M. Toledo, E. Oñate

Archives of Comp. Meths. Engng. (2017). Vol. 24 (1), pp. 1-21

Abstract
Predictive models are an important element in dam safety analysis. They provide an estimate of the dam response faced with a given load combination, which can be compared with the actual measurements to draw conclusions about dam safety. In addition to numerical finite element models, statistical models based on monitoring data have been used for decades for this purpose. In particular, the hydrostatic-season-time method is fully implemented in engineering practice, although some limitations have been pointed out. In other fields of science, powerful tools such as neural networks and support vector machines have been developed, which make use of observed data for interpreting complex systems . This paper contains a review of statistical and machine-learning data-based predictive models, which have been applied to dam safety analysis . Some aspects to take into account when developing analysis of this kind, such as the selection of the input variables, its division into training and validation sets, and the error analysis, are discussed. Most of the papers reviewed deal with one specific output variable of a given dam typology and the majority also lack enough validation data. As a consequence, although results are promising, there is a need for further validation and assessment of generalisation capability. Future research should also focus on the development of criteria for data pre-processing and model application.
Abstract
Predictive models are an important element in dam safety analysis. They provide an estimate of the dam response faced with a given load combination, which can be compared [...]
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An Object-oriented Environment for Developing Finite Element Codes for Multi-disciplinary Applications
P. Dadvand, R. Rossi, E. Oñate

Archives of Comp. Meths. Engng. (2010). Vol. 17 (3), pp 253-297

Abstract
The objective of this work is to describe the design and implementation of a framework for building multi-disciplinary finite element programs. The main goals are generality, reusability, extendibility, good performance and memory efficiency. Another objective is preparing the code structure for team development to ensure the easy collaboration of experts in different fields in the development of multi-disciplinary applications. Kratos, the framework described in this work, contains several tools for the easy implementation of finite element applications and also provides a common platform for the natural interaction of different applications. To achieve this, an innovative variable base interface is designed and implemented. This interface is used at different levels of abstraction and showed to be very clear and extendible. A very efficient and flexible data structure and an extensible IO are created to overcome difficulties in dealing with multi-disciplinary problems. Several other concepts in existing works are also collected and adapted to coupled problems. The use of an interpreter, of different data layouts and variable number of dofs per node are examples of such approach. In order to minimize the possible conflicts arising in the development, a kernel and application approach is used. The code is structured in layers to reflect the working space of developers with different fields of expertise. Details are given on the approach chosen to increase performance and efficiency. Examples of application of Kratos to different multidisciplinary problems are presented in order to demonstrate the applicability and efficiency of the new object oriented environment.
Abstract
The objective of this work is to describe the design and implementation of a framework for building multi-disciplinary finite element programs. The main goals are generality, [...]
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Nonlinear Formulations of a Four-Node Quasi-Conforming Shell Element
G. Lomboy, S. Suthasupradit, K. Kim, E. Oñate

Archives of Comp. Meths. Engng. (2009). Vol. 16 (2), pp. 189-250

Abstract
The quasi-conforming technique was introduced in the 1980’s to meet the challenge of inter-elements conforming problems and give a unified treatment of both conforming and nonconforming elements. While the linear formulation is well established, the nonlinear formulation based on the quasi-conforming technique that includes geometric and material nonlinearity is presented in this paper. The formulation is derived in the framework of an updated Lagrangian stress resultant, co-rotational approach. The geometric nonlinear formulation provides solutions to buckling and postbuckling behaviour while the material nonlinear formulation considers the spread of plasticity within the element while maintaining an explicit construction of element matrices. Aside from the elasto-plastic constitutive relation, formulations on laminate composites and reinforced concrete are also presented. The formulations of laminate composite and reinforced concrete material are present based on the layer concept, the material properties can vary throughout the thickness and across the surface of a shell element. The various failure criteria for laminate composite are included in the formulation which makes it possible to analyses the progressive failure of fibre and matrix. For the reinforced concrete material, the nonlinearities as a result of tensile cracking, tension stiffening between cracks, the nonlinear response of concrete in compression, and the yielding of the reinforcement are considered. The steel reinforcement is modeled as a bilinear material with strain hardening.
Abstract
The quasi-conforming technique was introduced in the 1980’s to meet the challenge of inter-elements conforming problems and give a unified treatment of both conforming [...]
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Geometry optimization of the diffuser for the supersonic wind tunnel using genetic algorithm and adaptive mesh refinement technique
M. Kouhi, M. Manshadi, E. Oñate

Aerospace Science and Technology (2014). Vol. 36, pp. 64-74, 2014

Abstract
Design of two-dimensional supersonic diffusers as a part of the wind tunnel is investigated in this paper. A methodology based on the mixture of try-and-error method and optimization algorithm is developed to handle the design problem. In the first design step, using try-and-error approach, the main parameters related to the geometry of diffuser such as length, angle and area ratio between the throat and the outlet are determined assuming a diffuser with linear walls. The design criterion in this step is the fact that the shock wave should be created near the diffuser throat in order to benefit from the maximum efficiency of diffuser. In the second design step, considering the optimization methodology, it is tried to improve the optimum design obtained in the first step by modifying the wall point locations and keeping the rest of the geometry fixed. Hence, an optimization problem is defined to find the best curve for the diffuser wall instead of the a linear one used the in the first step. The objective function of this problem is to minimize the output Mach number using Genetic Algorithm (GA). The fluid flow is evaluated using the Euler equations in the conservative form where the Streamline-Upwind/Petrov–Galerkin (SUPG) finite element scheme is used to discretize the flow equations. In order to capture the flow solution around the shock waves accurately, the adaptive mesh refinement technique is coupled to the flow solution. The demonstrated results show the efficiency of the proposed method for designing supersonic diffusers
Abstract
Design of two-dimensional supersonic diffusers as a part of the wind tunnel is investigated in this paper. A methodology based on the mixture of try-and-error method [...]
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Advances in discrete element modelling of underground excavations
C. Labra, J. Rojek, E. Oñate, F. Zárate

Acta Geotechnica (2009). Vol. 3 (4), pp. 317-322

Abstract
The paper presents advances in the discrete element modelling of underground excavation processes extending modelling possibilities as well as increasing computational efficiency. Efficient numerical models have been obtained using techniques of parallel computing and coupling the discrete element method with finite element method. The discrete element algorithm has been applied to simulation of different excavation processes, using different tools, TBMs and roadheaders. Numerical examples of tunnelling process are included in the paper, showing results in the form of rock failure, damage in the material, cutting forces and tool wear. Efficiency of the code for solving large scale geomechanical problems is also shown
Abstract
The paper presents advances in the discrete element modelling of underground excavation processes extending modelling possibilities as well as increasing computational efficiency. [...]
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Journal's Papers (2019). 62
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Casa's personal collection (2019). 1
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Regions, innovation systems, and the North-South divide in Italy
L. Leydesdorff, I. Cucco

El profesional de la información (2019). Vol. 28, (2), 88

Abstract
Innovation systems are not bound by administrative or political boundaries. Using information theory, we measure innovation-systemness as synergy among size-classes, postal addresses, and technological classes (NACE-codes) of firm-level data collected by Statistics Italy at different scales. Italy is organized in twenty regions, but there is also a traditional divide between the North and the South of the country. At which levels is how much innovation-systemness indicated? The greatest synergy is retrieved by considering the country in terms of Northern and Southern Italy as two sub-systems, with Tuscany included as part of Northern Italy. We suggest that separate innovation strategies could be developed for these two parts of the country. The current focus on regions for innovation policies may to some extent be an artifact of the statistics and EU policies. In terms of sectors, both medium- and high-tech manufacturing (MHTM) and knowledge-intensive services (KIS) are proportionally integrated in the various regions
Abstract
Innovation systems are not bound by administrative or political boundaries. Using information theory, we measure innovation-systemness as synergy among size-classes, postal [...]
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Las empresas de formación del futuro. El ejercicio de la calidad como estrategia de supervivencia
M. Fandos Igado, I. Aguaded

Educación XX1 (2009). ISSN 0211-819X

Abstract
El debate sobre la calidad en y de la educación es, además de muy interesante, muy complejo. Este trabajo aporta una reflexión sobre la misma sobre algunos ejes escasamente analizados, ya que nos adentra en una visión empresarial desde la perspectiva educativa. Las empresas de formación, como el caso concreto que analizamos, Master-D, parten, como premisa de actuación, de que la praxis concreta de la calidad es necesariamente una garantía de supervivencia, futuro y progreso.
Abstract
El debate sobre la calidad en y de la educación es, además de muy interesante, muy complejo. Este trabajo aporta una reflexión sobre la misma sobre algunos [...]
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Formación del profesorado y software social Teacher Training and Social Software
I. Aguaded, E. López Meneses

Estudios sobre educación (2010). ISSN 1578-7001

Abstract
En un mundo en el que se imponen las tecnologías de la información y la comunicación, la Universidad española tiene el reto de la adaptación al Espacio Europeo de Educación Superior con la demanda de importantes cambios estructurales y especialmente metodológicos en los procesos de enseñanza/aprendizaje. En este contexto, el software social aparece como una herramienta que, estratégicamente utilizada, puede generar consistentes innovaciones pedagógicas. En este trabajo se presenta un estudio del uso estratégico y constructivista de los blogs. Durante el curso 2008/09, alumnos de tres cursos y especialidades distintas de Magisterio de la Universidad de Extremadura compartieron prácticas y reflexionaron activamente sobre su propio proceso académico a través de los blogs. Se analizan específicamente sus concepciones sobre la introducción de las TIC y los blogs en el aula. Se detecta que cuando el alumnado tiene oportunidades para decidir algunos aspectos de su formación, ésta se hace más consciente y motivadora, y mejora sensiblemente, en este caso con el uso de tecnologías novedosas como los blogs, resultando, por ello, un importante y útil recurso pedagógico en la formación de los estudiantes.
Abstract
En un mundo en el que se imponen las tecnologías de la información y la comunicación, la Universidad española tiene el reto de la adaptación [...]
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Aprendizaje cooperativo on-line a través de foros en un contexto universitario: un análisis del discurso y de las redes
R. Tirado Morueta, Á. Hernando, I. Aguaded

Estudios sobre educación (2011). ISSN 1578-7001

Abstract
La investigación que presentamos en este artículo es el resultado de un proyecto de innovación docente, realizado a través del campus virtual de la Universidad de Huelva, en el que los sujetos fueron estudiantes de tercer curso de la Diplomatura de Educación Social que cursaban el practicum. Se presenta el análisis de los procesos de aprendizaje colaborativo en un contexto asincrónico de prácticas curriculares a través del análisis del discurso y de la densidad e intensidad de las redes sociales creadas. Esta interpretación permitirá concebir próximas experiencias e investigaciones que avancen en la concepción de indicadores de calidad para estos métodos de aprendizaje.
Abstract
La investigación que presentamos en este artículo es el resultado de un proyecto de innovación docente, realizado a través del campus virtual de [...]
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Campus virtuales en las universidades andaluzas: tipologías de uso educativo, competencias docentes y apoyo institucional
Á. Hernando, I. Aguaded

Teoría de la educación (2011). ISSN 1130-3473

Abstract
Este artículo, reflejo del Proyecto de Investigación de Excelencia «Plataformas de teleformación para la virtualización de asignaturas», muestra el estado general del uso de la enseñanza virtual en las universidades de Andalucía occidental, con el objetivo de identificar el uso educativo de las plataformas digitales actualmente en la educación superior. Mediante un cuestionario específico, se identifican variables de los recursos digitales utilizados, funcionalidades, competencias tecnológicas del profesorado y medidas institucionales. El análisis de correspondencias múltiples (ACM) permitió identificar cuatro tipos de usos educativos asociados: a) grupo mayoritario de docentes que utilizan este medio principalmente con carácter informativo y con baja competencia; b) grupo de docentes con elevada competencia que hacen un uso frecuente y extendido de las plataformas; c) grupo de profesores que utilizan ocasionalmente las plataformas en un contexto carente de medidas de impulso y sin capacitación tecnológica; y d) grupo minoritario de profesores que hacen un uso ampliado de las plataformas, con elevada competencia tecnológica y en un contexto estimulante para el uso de las TIC.
Abstract
Este artículo, reflejo del Proyecto de Investigación de Excelencia «Plataformas de teleformación para la virtualización de asignaturas», [...]
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The effect of centralization and cohesion on the social construction of knowledge in discussion forums
R. Tirado Morueta, Á. Hernando, I. Aguaded

Interactive learning environment (2012). ISSN 1445-1917

Abstract
Interactive relationships in online learning communities can influence the process and quality of knowledge building. The aim of this study is to empirically investigate the relationships between network structures and social knowledge building in an asynchronous writing environment through discussion forums in a learning management system. The quality of the knowledge construction process is evaluated through content analysis, and the network structures are analyzed using a social network analysis of the response relations among participants during online discussions. Structural equation modeling is used to analyze relations between network structures and knowledge construction. Working on data extracted from a 6-week distance-learning experiment, we analyzed how 10 groups developed collaborative learning social networks when participants worked together on case resolution. The results show a positive correlation between cohesion and centralization, and the positive influence of the cohesion index and the centralization index on social presence and cognitive presence in knowledge building. However, this must be understood within the context of social networks in which messages sent to all group members occupy the center. This underlines the need for reinforcing participations that are directed to the group as a whole, and the importance of the fact the network contains both central and intermediate members. By contrast, we propose that the combination of analysis techniques used is a good option for this type of study while recognizing that it is necessary to continue validating the instruments in terms of their own theoretical suppositions.
Abstract
Interactive relationships in online learning communities can influence the process and quality of knowledge building. The aim of this study is to empirically investigate the [...]
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Incidencia de los hábitos de ocio y consumo de drogas sobre las medidas de prevención de la drogadicción en universitarios
I. Gutiérrez, I. Aguaded

Educación XX1 (2013). ISSN 1139-613X

Abstract
A partir de variables relativas a la ocupación del tiempo de ocio y sus hábitos de consumo de drogas, este estudio se propone identificar diferentes subgrupos de estudiantes universitarios que permitan definir estrategias que eviten el inicio del consumo de drogas y su reducción ajustadas a sus preferencias e intereses. Utilizando como método de clasificación de conglomerados K medias se identifican seis conglomerados de estudiantes bien diferenciados entre sí e internamente estables en función de sus hábitos de consumo de drogas y ocupación del tiempo de ocio. A continuación se aplica el test de chi cuadrado de Pearson, encontrándose relaciones significativas entre la variable tipo de conglomerado y las estrategias preventivas preferidas. Finalmente, el análisis de regresión logística binaria permite identificar estrategias preventivas favorables y desfavorables según el conglomerado. En conclusión, se observan relaciones de dependencia entre los hábitos de consumo y ocupación del tiempo de ocio de cada subgrupo. La oferta cultural y deportiva se entiende como una medida atractiva para subgrupos de estudiantes que practican deporte y/o disfrutan con la actividad cultural, mientras que conglomerados más pasivos prefieren la oferta de asignaturas con propósitos preventivos. No obstante, todo ello ha de entenderse en el marco de una estrategia de prevención universal consciente de la pluralidad de la comunidad universitaria y atenta a sus demandas.
Abstract
A partir de variables relativas a la ocupación del tiempo de ocio y sus hábitos de consumo de drogas, este estudio se propone identificar diferentes subgrupos [...]
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El grado de competencia mediática en la ciudadanía andaluza
J. Sánchez Carrero, I. Aguaded

Estudios sobre el mensaje periodístico (2013). ISSN 1134-1629

Abstract
Conocer el grado de competencia mediática de la ciudadanía es hoy un reto crucial para entender la sociedad de la información en la que estamos inmersos y, por ende, una tarea imprescindible para establecer acciones formativas en alfabetización mediática. Este trabajo recoge los resultados globales de investigación obtenidos en una variada muestra de la ciudadanía andaluza y e inserto en un amplio estudio realizado a nivel estatal durante los últimos años con la implicación de las 17 Comunidades Autónomas y abanderado por el Consejo Audiovisual de Cataluña. El estudio define, en primer lugar, el polisémico término competencia mediática para luego segmentarlo en sus seis dimensiones clave: estética, lenguaje, ideología y valores, tecnología, producción y programación, y recepción y audiencia. La presente investigación concluye que la población que constituye la muestra carece de competencia mediática en dichas dimensiones, por lo se hace necesaria la integración de una asignatura educación mediática en el currículo escolar.
Abstract
Conocer el grado de competencia mediática de la ciudadanía es hoy un reto crucial para entender la sociedad de la información en la que estamos inmersos [...]
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Influencias de las creencias del profesorado sobre el uso de la tecnología en el aula
R. Tirado Morueta, I. Aguaded

Revista de educación (2014). ISSN 0034-592X

Abstract
Esta investigación, enmarcada en un proyecto I+D+i financiado por el Gobierno de España, tiene por objetivo comprobar cómo las creencias del profesorado sobre el significado y sentido de la tecnología en la educación actúan a modo de factores impulsores o, por el contrario, a modo de barreras para el uso de la tecnología en centros educativos. Metodológicamente, para mostrar estas influencias se elabora un cuestionario basado en las concepciones teóricas sobre la tecnología planteadas por Aviram y Richarson; tiene una consistencia interna (alfa de Crombach) de 0,869. Se realizan un análisis de regresión logística (RL) y un análisis de correspondencias múltiples (ACM) de los datos obtenidos a partir de una muestra de 324 profesores pertenecientes a los primeros centros TIC andaluces, en el marco de las medidas de impulso promovidas por el Gobierno de la Comunidad Autónoma de Andalucía desde 2002. El análisis factorial previo a la RL permite diferenciar cuatro factores (creencias) que se denominan ad hoc: sociorreformista, contrarios a la tecnología, críticos y humanistas. Asimismo, el ACM, permite diferenciar tres grupos de profesores: sociorreformistas, sociorreformistas moderados y profesores sin opinión sobre la tecnología. Los resultados de la RL muestran una influencia positiva de las creencias etiquetadas como sociorreformistas en la frecuencia de uso de las TIC, mientras que las creencias contrarias y críticas muestran una clara influencia negativa. Asimismo, el ACM permite comprobar que el grupo de profesores con creencias sociorreformistas es el que está más próximo, en el plano factorial, al uso regular de las TIC en el aula. Finalmente, se sugieren líneas de investigación que profundicen en el problema y permitan abordarlo integralmente.
Abstract
Esta investigación, enmarcada en un proyecto I+D+i financiado por el Gobierno de España, tiene por objetivo comprobar cómo las creencias del profesorado [...]
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La TV por IP en la Universidad: Un reto de divulgación científica televisiva para jóvenes chilenos
I. Aguaded

Estudios sobre el mensaje periodístico (2014). ISSN 1134-1629

Abstract
Diseñar nuevos modelos de televisión en el contexto de la sociedad digital se convierte en una necesidad desde el ámbito de la investigación y la academia. El presente trabajo analiza los intereses y necesidades de información expresados por jóvenes espectadores chilenos, con el objeto de diseñar una IPTV universitaria, modalidad de TV por Internet, que incorpora, mediante las múltiples interacciones que genera Internet los contenidos audiovisuales preferidos por dicho público meta, con énfasis en lo cultural y educativo. Los jóvenes chilenos están de acuerdo en que el nuevo medio prevalecerá sobre los demás y contribuirá a la adquisición de nuevos saberes, procedimientos y utilidades para ser utilizados en la vida cotidiana, así como al incremento de la cultura científica y su participación ciudadana activa
Abstract
Diseñar nuevos modelos de televisión en el contexto de la sociedad digital se convierte en una necesidad desde el ámbito de la investigación y [...]
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Experiencias de posgrado sobre computación en la red (cloud computing) con software social
I. Aguaded, E. López Meneses

Estudios sobre educación (2014). ISSN 1578-7001

Abstract
La investigación, desarrollada con estudiantes de un Máster Oficial en Comunicación y Educación en el curso 2011/12, se centró en indagar introspectivamente en el alumnado las ventajas y debilidades de la computación en nube (cloud computing), a través de metodologías activas con mapas conceptuales elaborados con el software Mindomo y, posteriormente, enviadas a un edublog. El trabajo pretendía fomentar su autonomía en el proceso de construcción del conocimiento, mediante estas aplicaciones 2.0, diseñando mapas interactivos sobre computación en nube. Entre los resultados obtenidos, después de la codificación e interpretación de la información, se constata que las aplicaciones Web 2.0 son estrategias metacognitivas activas que orientan la recreación del conocimiento colectivo, permitiendo la categorización de conceptos relevantes y facilitando el pensamiento creativo
Abstract
La investigación, desarrollada con estudiantes de un Máster Oficial en Comunicación y Educación en el curso 2011/12, se centró en indagar [...]
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Media competence in adult citizens in Andalusia, Spain
I. Aguaded, R. Tirado Morueta, Á. Hernando

Media competence in adult citizen in Andalusia, Spain (2014). 1369-118X

Abstract
Videogames, televisions, and computers in all their forms, and smartphones, are everywhere to the extent that the time spent in front of a screen by all sectors of society now takes up most of the leisure time of the citizens of all four corners of the world. Yet in the face of this barrage of media, citizens have developed few formative experiences for acquiring these audiovisual and media languages or for increasing their audiovisual and media skills. The main aim of this study is to assess media competence in the Spanish region of Andalusia with the use of an instrument specially designed for the purpose. The measurement criteria and indicators of this tool are shaped by media literacy paradigms and leading international reference models, in particular the model proposed by Hobbs. The instrument consists of indicators which, according to their features, are measured via subjective or objective questions and multiple choice (ordinal or nominal) options. Measurement is standardized by the interpretation of the responses to the items on a scale of 1– 4. The construct is validated by means of factorial analysis to confirm the presence of the five factors (criteria) that form the instrument. The sample consists of 667 adult citizens aged 18–55, resident in Andalusia. The results corroborate the influence of demographic factors on media literacy levels and help identify clusters of citizens that can facilitate the design of targeted literacy projects. The results show that media competence is a construct articulated by dimensions of a varied nature that correlate in many different ways to distinctive social groups within this study.
Abstract
Videogames, televisions, and computers in all their forms, and smartphones, are everywhere to the extent that the time spent in front of a screen by all sectors of society [...]
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Validación de la escala ehealth literacy (EHEALS) en población universitaria española
I. Aguaded

Revista española de salud pública (2015).

Abstract
Fundamento: Una de las escalas más empleadas para medir de forma rápida y sencilla la competencia en eSalud es la eHealth Literacy Scale (eHEALS), sin embargo, no existe su validación en castellano. Por ello, el objetivo de este estudio fue adaptar y validar al contexto español la escala eHEALS. Métodos: Se administró la traducción al español de la escala eHEALS, junto a otras escalas para medir algunos indicadores del bienestar psicológico (autoestima, vitalidad subjetiva y satisfacción con la vida). Se utilizó una muestra de 447 estudiantes universitarios de edades entre los 18 y los 45 años. Se realizó un análisis factorial exploratorio, un análisis factorial confirmatorio, análisis de invarianza, de fiabilidad, de estabilidad temporal y de correlaciones bivariadas. Resultados: El análisis factorial exploratorio mostró una estructura monofactorial que explicó el 52,55% de la varianza, con elevados pesos factoriales de sus ítems. Se obtuvo una fiabilidad de 0,87 y una correlación test-retest de 0,78. El análisis factorial confirmatorio mostró unos índices de ajustes adecuados: χ2 = 66,60; p=0,00; χ2/gl=4,44; índice de ajuste comparativo =0,97); índice de ajuste incremental =0,97; índice tucker-lewis =0,94; error de aproximación cuadrático medio=0,08; residuo cuadrático medio estandarizado=0,05. No hubo diferencias por sexo. En cuanto a la validez de criterio, se obtuvieron correlaciones estadísticamente significativas y positivas e entre 0,12 y 0,16 con tres indicadores del bienestar psicológico (autoestima, vitalidad subjetiva y satisfacción con la vida). Conclusiones: La versión española de la eHEALS testada ha mostrado ser una escala válida y fiable para medir la competencia en eSalud en el alumnado universitario.
Abstract
Fundamento: Una de las escalas más empleadas para medir de forma rápida y sencilla la competencia en eSalud es la eHealth Literacy Scale (eHEALS), sin embargo, [...]
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De la demonización a la polarización: un análisis desde el discurso digital del gobierno y la oposición venezolana
L. Romero-Rodríguez, I. Aguaded

Argos (2015). ISSN 0254-1637

Abstract
Se analizarán cuantitativa y cualitativamente los mensajes de los representantes más importantes del gobierno y la oposición venezolana a través de sus cuentas en la red Twitter, mediante el análisis de contenido de base interpretativa, en función de identificar y evaluar la propensión discursiva en este espacio digital a la demonización y en consecuencia, la ampliación de la polarización y el antagonismo existente en ese país. Entre los principales resultados se encuentra que se ha trasladado la tónica de enfrentamiento al escenario digital, se profundiza la demonización y la invisibilización de la «otredad» y se utilizan las redes sociales como medio de control social para desmovilizar las acciones democráticas de la disidencia.
Abstract
Se analizarán cuantitativa y cualitativamente los mensajes de los representantes más importantes del gobierno y la oposición venezolana a través [...]
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The capacity of elderly citizens to access digital media in Andalusia (Spain)
R. Tirado Morueta, Á. Hernando Gómez, I. Aguaded

Taylor & Francis (2016). ISSN 1369-118X

Abstract
In most of the European Union (EU) countries, including Spain, there has been an increase in the number of inhabitants aged 55 years or older. As of 2014, in the EU (27) more than 65% of the population uses the internet daily. However, among the elderly, the percentage is drastically lower. This type of occurrence is found in technologically advanced societies, and turns the older citizens into a forgotten collective. With the digital divide (defined as physical access to the internet) surmounted in these countries, a new divide is becoming apparent in terms of personal use and societal participation. In this article, through the use of multivariate analysis techniques, we identify a new divide in Andalusia, Spain, with respect to the frequency of access to new media and the use citizens make of them. We will discuss the influence of the elderly's immediate environment as a source of opportunity for the Information and Communication Technologies to improve our quality of life and as a medium for more active social participation.
Abstract
In most of the European Union (EU) countries, including Spain, there has been an increase in the number of inhabitants aged 55 years or older. As of 2014, in the EU (27) more [...]
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Consumo informativo y competencias digitales de estudiantes de periodismo de Colombia, Perú y Venezuela
I. Aguaded

Convergencia (2016). ISSN 1405-1435

Abstract
El objeto del presente artículo es profundizar en los hábitos de consumo infor-mativo que se perfilan en estudiantes del grado de comunicación en Colombia, Perú y Ve-nezuela, en particular sobre la tendencia a la infoxicación y sobresaturación informativa de su propio ecosistema comunicativo, así como indagar sobre las competencias comunicativas que han obtenido en su formación. La metodología se centró en un cuestionario autoad-ministrado digital de carácter cuantitativo, aplicado a 1.603 estudiantes de tercer año en universidades privadas de Medellín, Lima y Caracas. Entre las principales conclusiones se destaca un intensivo consumo de internet y redes sociales que supera las cinco horas diarias, con especial atención a que la mayor parte de los contenidos recibidos a través de sus redes son pseudoinformaciones y que la formación en competencias mediáticas para el consumo informativo se hace preminentemente de manera autodidacta.
Abstract
El objeto del presente artículo es profundizar en los hábitos de consumo infor-mativo que se perfilan en estudiantes del grado de comunicación en Colombia, [...]
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El impacto bibliométrico del movimiento MOOC en la comunidad científica española
I. Aguaded, E. Vázquez Cano, E. López Meneses

Educación XX1 (2016). ISSN 1139-613X

Abstract
España ha sido durante el año 2013 el país líder europeo en oferta de cursos MOOC y se encuentra en una posición puntera a nivel mundial en el número de cursos masivos ofertados en 2014. Esta prolífica actividad se está trasladando al mundo divulgativo y científico en forma de entradas en blogs, redes sociales y páginas web, así como en forma de artículos científicos y libros que intentan analizar el movimiento desde diferentes aproximaciones metodológicas. Hasta el momento, no se ha analizado la repercusión bibliométrica del impacto del movimiento MOOC en la comunidad científica española, por lo que el objetivo de esta investigación, es realizar un estudio bibliométrico de la repercusión científica en forma de artículo o libro de investigación en revistas y editoriales españolas durante el periodo comprendido entre enero de 2010 y junio de 2014. El estudio se afronta desde una metodología descriptiva y cuantitativa tomando como referencia indicadores bibliométricos de producción, en número de citas e indicadores de visibilidad y de impacto en diferentes bases de datos: Wos/Social Science Citation Index, Scopus, In-Recs, Google Scholar y la categorización de revistas científicas españolas (ANEP/FECYT). Los resultados muestran que el impacto de la producción científica española en formato libro y artículo en prestigiosas bases de datos internacionales (Wos-SSCI/Scopus) es muy bajo, aunque el impacto nacional según categorización ANEP/FECYT e In-Recs es moderadamente alto.
Abstract
España ha sido durante el año 2013 el país líder europeo en oferta de cursos MOOC y se encuentra en una posición puntera a nivel mundial [...]
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Toward a taxonomy of newspaper information quality: An experimental model and test applied to Venezuela dimensions found in information quality
L. Romero-Rodríguez, I. Aguaded

Journalism (2016). ISSN 1464-8849

Abstract
The quality of information from communication media is a topic that has been dealt with by various theorists through the analysis of the final products of information. This research work offers an analysis model of the quality of information of printed news media by the use of three indexes of categories and structured dimensions that will allow for the assessment and evaluation of the quality of information from the media, and the identification of the incidence of political-economic conditions of the journalistic environment’s macro-environment. For this, an experimental test of two Venezuelan media outlets was performed. Their use allowed us to conclude that political polarization and discourse of social confrontation, as well as economic factors such as inflation and pay scales had a proportionally direct effect on the quality of information products.
Abstract
The quality of information from communication media is a topic that has been dealt with by various theorists through the analysis of the final products of information. This [...]
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Empirical study of a sequence of access to Internet use in Ecuador
R. Tirado Morueta, D. Zambrano, I. Aguaded, I. Gutiérrez

Telematics and Informatics (2017). ISSN 0736-5853

Abstract
Ecuador is a country that represents the efforts that a few countries in the Latin American and the Caribbean region are making on infrastructures, regulations and policies that are favorable towards the use of the Internet. However, although the digital divide in its most basic form (physical access and use) is closing with respect to developed countries, a new, more complex digital divide is moving forward, and is related to the socio-economic advantages of the Internet. This study, which used a random sample stratified by provinces and which comprised 3754 respondents representing the secondary school students in Ecuador, had as objectives: (a) to verify the relationship and sequence among the different levels to access the Internet found on secondary school students; and (b) to verify to what degree the student’s family status influenced the different levels of Internet access. Through the empirical analysis of a structural model, the results showed a sequence between the relationships found among the different levels of Internet access, as well as the cumulative effect of the technical resources and levels of digital literacy on the academic use of the Internet. Likewise, it was observed that the influence of the student’s family status lost strength as the level of Internet access increased.
Abstract
Ecuador is a country that represents the efforts that a few countries in the Latin American and the Caribbean region are making on infrastructures, regulations and policies [...]
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Revistas Iberoamericanas de Educación en SciELO Citation Index y Emerging Source Citation Index
R. Repiso, E. Jiménez-Contreras, I. Aguaded

Revista española de documentación científica (2017). ISSN: 0210-0614

Abstract
El presente trabajo es un análisis de las revistas de Educación iberoamericanas en SciELO Citation Index y Emerging Source Citation Index, dos de los nuevos productos incorporados a Web of Science. Para ello se analizan las revistas de Educación iberoamericanas presentes en estos productos, por separado y conjuntamente. Se compara su cobertura con otras bases de datos externas referentes (Scopus, Redalyc, Google Scholar Metrics and, Social Sciences Citation Index) así como la presencia de las revistas estudiadas en otras bases de datos. Igualmente se analizan características de las revistas como la representatividad por países, la tipología editorial, periodicidad de las cabeceras, antigüedad y la producción medida en artículos. En definitiva, Web of Science demuestra cubrir mejor el área de Educación Iberoamericana que su rival Scopus.
Abstract
El presente trabajo es un análisis de las revistas de Educación iberoamericanas en SciELO Citation Index y Emerging Source Citation Index, dos de los nuevos [...]
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Comunicar: calidad, visibilización e impacto
M. Pérez-Rodríguez, R. García Ruiz, I. Aguaded

Revista Española de Pedagogía (2018).

Abstract
Las revistas científicas del ámbito de las ciencias sociales están experimentando un proceso de cambio para alcanzar los estándares de calidad exigidos por las agencias evaluadoras del conocimiento. Este trabajo plantea una revisión de los principales aspectos que pueden ser mejorados para que las revistas del área puedan lograr un mejor posicionamiento, visibilización e impacto. Considerando su destacada trayectoria, que la convierte en un referente en el ámbito de las ciencias sociales, se analiza el modelo de la revista Comunicar, teniendo en cuenta la relación entre artículos recibidos y publicados, la autoría, las metodologías y los criterios de calidad priorizados por la revista. Se concluye con una reflexión acerca de la existencia de una nueva cultura científica, los posibles parámetros de calidad de las revistas y sus indicadores, la importancia del autor de textos científicos y su formación, el establecimiento de temas de interés más allá de lo local o individual, la visibilización y transferencia y la incorporación de otros modos de medir el impacto de los trabajos, más en consonancia con los recursos de la sociedad digital.
Abstract
Las revistas científicas del ámbito de las ciencias sociales están experimentando un proceso de cambio para alcanzar los estándares de calidad [...]
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A two-step monolithic method for the efficient simulation of incompressible flows
P. Ryzhakov, J. Cotela, R. Rossi, E. Oñate

Int. J. Numer. Meth. Fluids (2014). Vol 74 (12), pp. 919-934

Abstract
We propose a simple technique for improving computationally the efficiency of monolithic velocity–pressure solvers for incompressible flow problems. The idea consists in solving the discrete nonlinear system of governing equations in two steps: introducing ‘artificial’ compressibility first and afterwards correcting the solution by solving the original incompressible system. The speed‐up is obtained because of a better conditioning of the modified discrete system solved at the prediction step. The formulation can be easily implemented into existing monolithic codes requiring minor modification only. The paper concludes with two examples validating the formulation and facilitating the estimation of the obtained speed‐up. For the tests chosen, an average speed‐up is approximately double, suggesting that the method is a feasible approach for incompressible flows' simulation.
Abstract
We propose a simple technique for improving computationally the efficiency of monolithic velocity–pressure solvers for incompressible flow problems. The idea consists [...]
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Multi-objective aerodynamic shape optimization using MOGA coupled to advanced adaptive mesh refinement
M. Kouhi, D. Lee, G. Bugeda, E. Oñate

Computers and Fluids (2013). Vol. 88, pp. 298-312

Abstract
This paper demonstrates the big influence of the control of the mesh quality in the final solution of aerodynamic shape optimization problems. It aims to study the trade-off between the mesh refinement during the optimization process and the improvement of the optimized solution. This subject is investigated in the transonic airfoil design optimization using an Adaptive Mesh Refinement (AMR) technique coupled to Multi-Objective Genetic Algorithm (MOGA) and an Euler aerodynamic analysis tool. The methodology is implemented to solve three practical design problems; the first test case considers a reconstruction design optimization that minimizes the pressure error between a predefined pressure curve and candidate pressure distribution. The second test considers the total drag minimization by designing airfoil shape operating at transonic speeds. For the final test case, a multi-objective design optimization is conducted to maximize both the lift to drag ratio (L/D) and lift coefficient (Cl). The solutions obtained with and without adaptive mesh refinement are compared in terms of solution improvement and computational cost. Numerical results clearly show that the use of adaptive mesh refinement can improve the solution accuracy while reducing significant computational cost in both single- and multi-objective design optimizations.
Abstract
This paper demonstrates the big influence of the control of the mesh quality in the final solution of aerodynamic shape optimization problems. It aims to study the trade-off [...]
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