Documents published in 2020 : Scipedia

Generation of segmental chips in metal cutting modeled with the PFEM
J. Prieto, J. Puigbó, J. Cante, J. Oliver, P. Jonsén

Computational Mechanics (2018). Vol. 61 (6), pp. 639-655

Abstract
The Particle Finite Element Method, a lagrangian finite element method based on a continuous Delaunay re-triangulation of the domain, is used to study machining of Ti6Al4V. In this work the method is revised and applied to study the influence of the cutting speed on the cutting force and the chip formation process. A parametric methodology for the detection and treatment of the rigid tool contact is presented. The adaptive insertion and removal of particles are developed and employed in order to sidestep the difficulties associated with mesh distortion, shear localization as well as for resolving the fine-scale features of the solution. The performance of PFEM is studied with a set of different two-dimensional orthogonal cutting tests. It is shown that, despite its Lagrangian nature, the proposed combined finite element-particle method is well suited for large deformation metal cutting problems with continuous chip and serrated chip formation.
Abstract
The Particle Finite Element Method, a lagrangian finite element method based on a continuous Delaunay re-triangulation of the domain, is used to study machining [...]
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FEMPAR: an object-oriented parallel finite element framework
S. Badia, A. Martín, J. Principe

Archives of Comp. Meths. Engng. (2018). Vol. 25 (2), pp. 195-271

Abstract
FEMPAR is an open source object oriented Fortran200X scientific software library for the high-performance scalable simulation of complex multiphysics problems governed by partial differential equations at large scales, by exploiting state-of-the-art supercomputing resources. It is a highly modularized, flexible, and extensible library, that provides a set of modules that can be combined to carry out the different steps of the simulation pipeline. FEMPAR includes a rich set of algorithms for the discretization step, namely (arbitrary-order) grad, div, and curl-conforming finite element methods, discontinuous Galerkin methods, B-splines, and unfitted finite element techniques on cut cells, combined with h-adaptivity. The linear solver module relies on state-of-the-art bulk-asynchronous implementations of multilevel domain decomposition solvers for the different discretization alternatives and block-preconditioning techniques for multiphysics problems. FEMPAR is a framework that provides users with out-of-the-box state-of-the-art discretization techniques and highly scalable solvers for the simulation of complex applications, hiding the dramatic complexity of the underlying algorithms. But it is also a framework for researchers that want to experience with new algorithms and solvers, by providing a highly extensible framework. In this work, the first one in a series of articles about FEMPAR, we provide a detailed introduction to the software abstractions used in the discretization module and the related geometrical module. We also provide some ingredients about the assembly of linear systems arising from finite element discretizations, but the software design of complex scalable multilevel solvers is postponed to a subsequent work.
Abstract
FEMPAR is an open source object oriented Fortran200X scientific software library for the high-performance scalable simulation of complex multiphysics problems governed by [...]
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Driving mechanisms and streamwise homogeneity in molecular dynamics simulations of nanochannel flows
J. Principe, V. Bitrián

Physical review fluids (2018). (Preprint) Vol. 3 (1), pp. 1-16

Abstract
In molecular dynamics simulations, nanochannel flows are usually driven by a constant force, that aims to represent a pressure difference between inlet and outlet, and periodic boundary conditions are applied in the streamwise direction resulting in an homogeneous flow. The homogeneity hypothesis can be eliminated adding reservoirs at the inlet and outlet of the channel which permits us to predict streamwise variation of flow properties. It also opens the door to drive the flow by applying a pressure gradient instead of a constant force. We analyze the impact of these modeling modifications in the prediction of the flow properties, and we show when they make a difference with respect to the standard approach. It turns out that both assumptions are irrelevant when low pressure differences are considered, but important differences are observed at high pressure differences. They include the density and velocity variation along the channel (the mass flow rate is constant) but, more importantly, the temperature increase and slip length decrease. Because viscous heating is important at high shear rates, these modeling issues are also linked to the use of thermostating procedures. Specifically, selecting the region where the thermostat is applied has a critical influence on the results. Whereas in the traditional homogeneous model the choices are limited to the fluid and/or the wall, in the inhomogeneous cases the reservoirs are also available, which permits us to leave the region of interest, the channel, unperturbed.
Abstract
In molecular dynamics simulations, nanochannel flows are usually driven by a constant force, that aims to represent a pressure difference between inlet and outlet, and periodic [...]
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Multilevel balancing domain decomposition at extreme scales
S. Badia, A. Martín, J. Principe

SIAM J. Numer. Anal. (2016). (preprint) Vol. 38 (1), pp. C22-C52

Abstract
In this paper we present a fully distributed, communicator-aware, recursive, and interlevel-overlapped message-passing implementation of the multilevel balancing domain decomposition by constraints (MLBDDC) preconditioner. The implementation highly relies on subcommunicators in order to achieve the desired effect of coarse-grain overlapping of computation and communication, and communication and communication among levels in the hierarchy (namely, interlevel overlapping). Essentially, the main communicator is split into as many nonoverlapping subsets of message-passing interface (MPI) tasks (i.e., MPI subcommunicators) as levels in the hierarchy. Provided that specialized resources (cores and memory) are devoted to each level, a careful rescheduling and mapping of all the computations and communications in the algorithm lets a high degree of overlapping be exploited among levels. All subroutines and associated data structures are expressed recursively, and therefore MLBDDC preconditioners with an arbitrary number of levels can be built while re-using significant and recurrent parts of the codes. This approach leads to excellent weak scalability results as soon as level-1 tasks can fully overlap coarser-levels duties. We provide a model to indicate how to choose the number of levels and coarsening ratios between consecutive levels and determine qualitatively the scalability limits for a given choice. We have carried out a comprehensive weak scalability analysis of the proposed implementation for the three-dimensional Laplacian and linear elasticity problems on structured and unstructured meshes. Excellent weak scalability results have been obtained up to 458,752 IBM BG/Q cores and 1.8 million MPI being, being the first time that exact domain decomposition preconditioners (only based on sparse direct solvers) reach these scales. (An erratum is attached.)
Abstract
In this paper we present a fully distributed, communicator-aware, recursive, and interlevel-overlapped message-passing implementation of the multilevel balancing domain decomposition [...]
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Mixed finite element methods with convection stabilization for the large eddy simulation of incompressible turbulent flows
O. Colomés, S. Badia, J. Principe

Comput. Methods Appl. Mech. Engrg., (2016). Vol. 304 (1), pp. 294-318

Abstract
The variational multiscale method thought as an implicit large eddy simulation model for turbulent flows has been shown to be an alternative to the widely used physical-based models. This method is traditionally combined with equal-order velocity–pressure pairs, since it provides pressure stabilization. In this work, we consider a different approach, based on inf–sup stable elements and convection-only stabilization. In order to do so, we consider a symmetric projection stabilization of the convective term using an orthogonal subscale decomposition. The accuracy and efficiency of this method compared with residual-based algebraic subgrid scales and orthogonal subscales methods for equal-order interpolation is assessed in this paper. Moreover, when inf–sup stable elements are used, the grad–div stabilization term has been shown to be essential to guarantee accurate solutions. Hence, a study of the influence of such term in the large eddy simulation of turbulent incompressible flows is also performed. Furthermore, a recursive block preconditioning strategy has been considered for the resolution of the problem with an implicit treatment of the projection terms. Two different benchmark tests have been solved: the Taylor–Green Vortex flow with Re=1600, and the Turbulent Channel Flow at Reτ=395 and Reτ=590.
Abstract
The variational multiscale method thought as an implicit large eddy simulation model for turbulent flows has been shown to be an alternative to the widely used physical-based [...]
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On the scalability of inexact balancing domain decomposition by constraints with overlapped coarse/fine corrections
S. Badia, A. Martín, J. Principe

Parallel Computing (2015). (Preprint) Vol. 50, pp. 1-24

Abstract
In this work, we analyze the scalability of inexact two-level balancing domain decomposition by constraints (BDDC) preconditioners for Krylov subspace iterative solvers, when using a highly scalable asynchronous parallel implementation where fine and coarse correction computations are overlapped in time. This way, the coarse-grid problem can be fully overlapped by fine-grid computations (which are embarrassingly parallel) in a wide range of cases. Further, we consider inexact solvers to reduce the computational cost/complexity and memory consumption of coarse and local problems and boost the scalability of the solver. Out of our numerical experimentation, we conclude that the BDDC preconditioner is quite insensitive to inexact solvers. In particular, one cycle of algebraic multigrid (AMG) is enough to attain algorithmic scalability. Further, the clear reduction of computing time and memory requirements of inexact solvers compared to sparse direct ones makes possible to scale far beyond state-of-the-art BDDC implementations. Excellent weak scalability results have been obtained with the proposed inexact/overlapped implementation of the two-level BDDC preconditioner, up to 93,312 cores and 20 billion unknowns on JUQUEEN. Further, we have also applied the proposed setting to unstructured meshes and partitions for the pressure Poisson solver in the backward-facing step benchmark domain.
Abstract
In this work, we analyze the scalability of inexact two-level balancing domain decomposition by constraints (BDDC) preconditioners for Krylov subspace iterative solvers, when [...]
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A highly scalable parallel implementation of balancing domain decomposition by constraints
S. Badia, A. Martín, J. Principe

SIAM J. Numer. Anal. (2014). (preprint) Vol. 36 (2), pp, C190-C218

Abstract
In this work we propose a novel parallelization approach of two-level balancing domain decomposition by constraints preconditioning based on overlapping of fine-grid and coarse-grid duties in time. The global set of MPI tasks is split into those that have fine-grid duties and those that have coarse-grid duties, and the different computations and communications in the algorithm are then re-scheduled and mapped in such a way that the maximum degree of overlapping is achieved while preserving data dependencies among them. In many ranges of interest, the extra cost associated to the coarse-grid problem can be fully masked by fine-grid related computations (which are embarrassingly parallel). Apart from discussing code implementation details, the paper also presents a comprehensive set of numerical experiments, that includes weak scalability analyses, with structured and unstructured meshes, and exact and inexact solvers for the 3D Poisson and linear elasticity problems on a pair of state-of-the-art multicore-based distributed-memory machines. This experimental study reveals remarkable weak scalability in the solution of problems with thousands of millions of unknowns on several tens of thousands of computational cores.
Abstract
In this work we propose a novel parallelization approach of two-level balancing domain decomposition by constraints preconditioning based on overlapping of fine-grid and coarse-grid [...]
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Implementation and Scalability Analysis of Balancing Domain Decomposition Methods
S. Badia, A. Martín, J. Principe

Archives of Comp. Meths. Engng. (2013). Vol. 20 (3), pp. 239-262

Abstract
In this paper we present a detailed description of a high-performance distributed-memory implementation of balancing domain decomposition preconditioning techniques. This coverage provides a pool of implementation hints and considerations that can be very useful for scientists that are willing to tackle large-scale distributed-memory machines using these methods. On the other hand, the paper includes a comprehensive performance and scalability study of the resulting codes when they are applied for the solution of the Poisson problem on a large-scale multicore-based distributed-memory machine with up to 4096 cores. Well-known theoretical results guarantee the optimality (algorithmic scalability) of these preconditioning techniques for weak scaling scenarios, as they are able to keep the condition number of the preconditioned operator bounded by a constant with fixed load per core and increasing number of cores. The experimental study presented in the paper complements this mathematical analysis and answers how far can these methods go in the number of cores and the scale of the problem to still be within reasonable ranges of efficiency on current distributed-memory machines. Besides, for those scenarios where poor scalability is expected, the study precisely identifies, quantifies and justifies which are the main sources of inefficiency.
Abstract
In this paper we present a detailed description of a high-performance distributed-memory implementation of balancing domain decomposition preconditioning techniques. This [...]
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Enhanced balancing Neumann-Neumann preconditioning in computational fluid and solid mechanics
S. Badia, A. Martín, J. Principe

Int. J. Numer. Meth. Engng. (2013). (preprint) Vol. 96 (4), pp. 203-230

Abstract
In this work, we propose an enhanced implementation of balancing Neumann-Neumann (BNN) preconditioning together with a detailed numerical comparison against the balancing domain decomposition by constraints (BDDC) preconditioner. As model problems, we consider the Poisson and linear elasticity problems. On one hand, we propose a novel way to deal with singular matrices and pseudo-inverses appearing in local solvers. It is based on a kernel identication strategy that allows us to eciently compute the action of the pseudo-inverse via local indenite solvers. We further show how, identifying a minimum set of degrees of freedom to be xed, an equivalent denite system can be solved instead, even in the elastic case. On the other hand, we propose a simple modication of the preconditioned conjugate gradient (PCG) algorithm that reduces the number of Dirichlet solvers to only one per iteration, leading to similar computational cost as additive methods. After these improvements of the BNN PCG algorithm, we compare its performance against that of the BDDC preconditioners on a pair of large-scale distributed-memory platforms. The enhanced BNN method is a competitive preconditioner for three-dimensional Poisson and elasticity problems, and outperforms the BDDC method in many cases.
Abstract
In this work, we propose an enhanced implementation of balancing Neumann-Neumann (BNN) preconditioning together with a detailed numerical comparison against the balancing [...]
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A finite element dynamical nonlinear subscale approximation for the low Mach number flow equations
M. Ávila, J. Principe, R. Codina

Journal of Computational Physics (2011). Vol. 230 (22), pp. 7988-8009

Abstract
In this work we propose a variational multiscale finite element approximation of thermally coupled low speed flows. The physical model is described by the low Mach number equations, which are obtained as a limit of the compressible Navier–Stokes equations in the small Mach number regime. In contrast to the commonly used Boussinesq approximation, this model permits to take volumetric deformation into account. Although the former is more general than the latter, both systems have similar mathematical structure and their numerical approximation can suffer from the same type of instabilities. We propose a stabilized finite element approximation based on the variational multiscale method, in which a decomposition of the approximating space into a coarse scale resolvable part and a fine scale subgrid part is performed. Modeling the subscale and taking its effect on the coarse scale problem into account results in a stable formulation. The quality of the final approximation (accuracy, efficiency) depends on the particular model. The distinctive features of our approach are to consider the subscales as transient and to keep the scale splitting in all the nonlinear terms. The first ingredient permits to obtain an improved time discretization scheme (higher accuracy, better stability, no restrictions on the time step size). The second ingredient permits to prove global conservation properties. It also allows us to approach the problem of dealing with thermal turbulence from a strictly numerical point of view. Numerical tests show that nonlinear and dynamic subscales give more accurate solutions than classical stabilized methods.
Abstract
In this work we propose a variational multiscale finite element approximation of thermally coupled low speed flows. The physical model is described by the low Mach number [...]
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A variational subgrid scale model for transient incompressible flows
G. Houzeaux, J. Principe

Int. J. Computational Fluid Dynamics (2008). Vol. 22 (3), pp. 135-152

Abstract
We introduce in this paper a variational subgrid scale model for the solution of the incompressible Navier-Stokes equations. With respect to classical multiscale-based stabilisation techniques, we retain the subgrid scale effects in the convective term and integrate the subgrid scale equation in time. The method is applied to the Navier-Stokes equations in an accelerating frame of reference and with Dirichlet (essential), Neumann (natural) and mixed boundary conditions. The concrete objective of the paper is to test a numerical algorithm for solving the non-linear subgrid scale equation and the introduction of the subgrid scale into the grid scale equation. The performance of the technique is demonstrated through the solution of two numerical examples: one to test the tracking of the subgrid scale in the convection term and the other to investigate the effects of considering the subgrid scale transient.
Abstract
We introduce in this paper a variational subgrid scale model for the solution of the incompressible Navier-Stokes equations. With respect to classical multiscale-based stabilisation [...]
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On the modelling of liquid steel processes
M. Goldschmit, S. Ferro, J. Principe, A. Coppola‐Owen

Latin American Applied Research (2002). Vol. 32 (3), pp. 263-273

Abstract
An iterative (k-L)-predictor / (epsilon)- corrector algorithm that models turbulent flow was developed in previous publications. In this paper, the 3D finite element turbulent model was used to analyze the liquid steel movement produced by gravity force, inert gas stirring or electromagnetic force stirring.
Abstract
An iterative (k-L)-predictor / (epsilon)- corrector algorithm that models turbulent flow was developed in previous publications. In this paper, the 3D finite element turbulent [...]
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A new approach to the analysis of vessel residence time distribution curves
S. Ferro, J. Principe, M. Goldschmit

Metallurgical and Materials Transactions B (2001). Vol. 32 (6), pp. 1185-1193

Abstract
Mathematical models for the evaluation of residence time distribution (RTD) curves on a large variety of vessels are presented. These models have been constructed by combination of different tanks or volumes. In order to obtain a good representation of RTD curves, a new volume (called convection diffusion volume) is introduced. The convection-diffusion volume allows the approximation of different experimental or numerical RTD curves with very simple models. An algorithm has been developed to calculate the parameters of the models for any given set of RTD curve experimental points. Validation of the models is carried out by comparison with experimental RTD curves taken from the literature and with a numerical RTD curve obtained by three-dimensional simulation of the flow inside a tundish.
Abstract
Mathematical models for the evaluation of residence time distribution (RTD) curves on a large variety of vessels are presented. These models have been constructed by [...]
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Applications of a (k–ϵ) model for the analysis of continuous casting processes
M. Goldschmit, J. Principe, M. Koslowski

Int. J. Numer. Meth. Engng. (1999). Vol. 46 (9), pp. 1505-1519

Abstract
The finite element solution of the turbulent Navier–Stokes equations developed via (k–ϵ) turbulence models was addressed in previous publications [1–4], where a (k–L)‐predictor/(ϵ)‐corrector iterative algorithm was developed. It was shown that the developed algorithm is robust and converges for the analyses of different flows without requiring the implementation of ad hoc numerical procedures. The turbulent convection–diffusion transport equations are solved by using the velocity distributions determined from the solution of the turbulent Navier–Stokes equations. The dispersion of a die in a turbulent flow can therefore be modelled and the obtained dispersion patterns are validated via flow visualizations in water models. In the present paper, the developed analysis capability is applied to the analysis of continuous casting processes.
Abstract
The finite element solution of the turbulent Navier–Stokes equations developed via (k–ϵ) turbulence models was addressed in previous publications [1–4], [...]
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A Generalized Finite Difference-Volume Hybrid Method Applied to Shallow-Water Equations
G. Tinoco Guerrero, F. Domínguez Mota, J. Tinoco-Ruiz, J. Martínez, N. Tinoco-Guerrero, M. Leppäranta, I. Mammarella

Revista Mexicana de Métodos Numéricos (2020). Vol. 4, 2

Abstract
Due to the importance of the shallow-water equations in models of real-life phenomena, in recent years the study and model of problems that involve them have been the object of interest of many people. By reason of this, it is imperative to have efficient numerical methods to obtain an approximation of the solutions of the shallow-water equations. Several authors have worked in approximations using the well-known finite volume and finite element methods, nevertheless, even when these methods compute good approximations to real-life behavior, the computational cost is usually high, which could be a limitation to the application of these methods. This paper presents an explicit Generalized Finite Difference-Volume Hybrid approximation to the solution of the shallow-water equations, solved on irregular regions meshed with logically rectangular grids; the numerical results show the accuracy obtained with a low-cost implementation. The proposed scheme is a hybridization of a generalized finite difference scheme with the finite volume method.
Abstract
Due to the importance of the shallow-water equations in models of real-life phenomena, in recent years the study and model of problems that involve them have been the object [...]
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Coupled effective stress analysis of insertion problems in geotechnics with the Particle Finite Element Method
L. Monforte, M. Arroyo, J. Puigbó, A. Gens

Computers and Geotechnics (2018). Vol. 101, pp. 114-129

Abstract
This paper describes a computational framework for the numerical analysis of quasi-static soil-structure insertion problems in water saturated media. The Particle Finite Element Method is used to solve the linear momentum and mass balance equations at large strains. Solid-fluid interaction is described by a simplified Biot formulation using pore pressure and skeleton displacements as basic field variables. The robustness and accuracy of the proposal is numerically demonstrated presenting results from two benchmark examples. The first one addresses the consolidation of a circular footing on a poroelastic soil. The second one is a parametric analysis of the cone penetration test (CPTu) in a material described by a Cam-clay hyperelastic model, in which the influence of permeability and contact roughness on test results is assessed.
Abstract
This paper describes a computational framework for the numerical analysis of quasi-static soil-structure insertion problems in water saturated media. The Particle Finite [...]
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Hydraulic conductivity from piezocone on-the-fly: a numerical evaluation
L. Monforte, M. Arroyo, A. Gens, J. Puigbó

Géotechnique Letters (2018). Vol. 8 (4), pp. 268-277

Abstract
Permeability is important in many geotechnical applications. The current (cone penetration test that gathers piezometer data (CPTu)) practice to obtain permeability values relies on dissipation tests, which are frequently slow and only linked to permeability through compressibility measures. On-the-fly methods offer an alternative approach in which permeability is directly linked to CPTu penetration measurements. Several on-the-fly methods have been proposed and their applicability and relative advantages are not fully clear. Numerical effective stress simulation of CPTu testing is used here to explore in a simplified but realistic setting the relative merits of different on-the-fly methods. It is found that for partly drained materials, the original simpler relation between cone metrics and normalised permeability works reasonably well. A continuous generalisation of Elsworth and Lee method to the full permeability range is proposed, noting the connection to the backbone normalised pore-pressure curve that describes the partly drained transition of cone penetration. The importance of an undrained limit beyond which the method produces large errors is emphasised.
Abstract
Permeability is important in many geotechnical applications. The current (cone penetration test that gathers piezometer data (CPTu)) practice to obtain permeability values [...]
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Numerical Methods for the Modelling of Chip Formation
J. Prieto, J. Puigbó, P. Jonsén

Archives of Comp. Meths. Engng. (2018). Epub ahead of print

Abstract
The modeling of metal cutting has proved to be particularly complex due to the diversity of physical phenomena involved, including thermo-mechanical coupling, contact/friction and material failure. During the last few decades, there has been significant progress in the development of numerical methods for modeling machining operations. Furthermore, the most relevant techniques have been implemented in the relevant commercial codes creating tools for the engineers working in the design of processes and cutting devices. This paper presents a review on the numerical modeling methods and techniques used for the simulation of machining processes. The main purpose is to identify the strengths and weaknesses of each method and strategy developed up-to-now. Moreover the review covers the classical Finite Element Method covering mesh-less methods, particle-based methods and different possibilities of Eulerian and Lagrangian approaches.
Abstract
The modeling of metal cutting has proved to be particularly complex due to the diversity of physical phenomena involved, including thermo-mechanical coupling, contact/friction [...]
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Low‐order stabilized finite element for the full Biot formulation in soil mechanics at finite strain
L. Monforte, P. Navas, J. Puigbó, M. Arroyo, A. Gens

International Journal for Numerical and Analytical Methods in Geomechanics (2019). Vol. 43 (7), pp. 1488-1515

Abstract
This article presents a novel finite element formulation for the Biot equation using low‐order elements. Additionally, an extra degree of freedom is introduced to treat the volumetric locking steaming from the effective response of the medium; its balance equation is also stabilized. The accuracy of the proposed formulation is demonstrated by means of numerical analyses.
Abstract
This article presents a novel finite element formulation for the Biot equation using low‐order elements. Additionally, an extra degree of freedom is introduced to treat [...]
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Reply to the Discussion on “Coupled effective stress analysis of insertion problems in geotechnics with the Particle Finite Element method”
L. Monforte, M. Arroyo, J. Puigbó, A. Gens

Computers and Geotechnics (2019). Vol. 109, pp. 209-292

Abstract
The discussers ask why a hyperelastic model was employed. There are several reasons why using an hyper-elastic model is preferable. Probably the most important one is that closed cycles do not produce nor dissipate energy [17, 8]; instead, using a hypoelastic model, closed cycles may produce or dissipate energy, which is inconsistent with the definition of an elastic deformation path. As stressed by Borja et al.[3], the use of an hypoelastic law with constant Poisson’s ratio in the context of the Modified Cam Clay may produce that closed-loop stress paths may result in a non-conservative elastic behavior; therefore, at the end of the loading path the elastic deformation might not be fully recovered. Also, hyper-elastic laws underpin the formulation of large-strain elastoplasticity [17]. By using this theory, the constitutive model is inherently frame-indiferent [17] and algorithmic objective [9].
Abstract
The discussers ask why a hyperelastic model was employed. There are several reasons why using an hyper-elastic model is preferable. Probably the most important one is that [...]
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A stable mesh-independent approach for numerical modelling of structured soils at large strains
L. Monforte, M. Ciantia, J. Puigbó, M. Arroyo, A. Gens

Computers and Geotechnics (2019). Vol. 116, pp. 103215-1/103215-14

Abstract
We describe the large strain implementation of an elasto-plastic model for structured soils into G-PFEM, a code developed for geotechnical simulations using the Particle Finite Element Method. The constitutive model is appropriate for naturally structured clays, cement-improved soils and soft rocks. Structure may result in brittle behavior even in contractive paths; as a result, localized failure modes are expected in most applications. To avoid the pathological mesh-dependence that may accompany strain localization, a nonlocal reformulation of the model is employed. The resulting constitutive model is incorporated into a numerical code by means of a local explicit stress integration technique. To ensure computability this is hosted within a more general Implicit-Explicit integration scheme (IMPLEX). The good performance of these techniques is illustrated by means of element tests and boundary value problems.
Abstract
We describe the large strain implementation of an elasto-plastic model for structured soils into G-PFEM, a code developed for geotechnical simulations using the Particle Finite [...]
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An implicit surface tension model for the analysis of droplet dynamics
A. Jarauta, P. Ryzhakov, J. Pons Prats, M. Secanell

Journal of Computational Physics (2018). Vol. 374, pp. 1196-1218

Abstract
A Lagrangian incompressible fluid flow model is extended by including an implicit surface tension term in order to analyze droplet dynamics. The Lagrangian framework is adopted to model the fluid and track its boundary, and the implicit surface tension term is used to introduce the appropriate forces at the domain boundary. The introduction of the tangent matrix corresponding to the surface tension force term ensures enhanced stability of the derived model. Static, dynamic and sessile droplet examples are simulated to validate the model and evaluate its performance. Numerical results are capable of reproducing the pressure distribution in droplets, and the advancing and receding contact angles evolution for droplets in varying substrates and inclined planes. The model is stable even at time steps up to 20 times larger than previously reported in literature and achieves first and second order convergence in time and space, respectively. The present implicit surface tension implementation is applicable to any model where the interface is represented by a moving boundary mesh.
Abstract
A Lagrangian incompressible fluid flow model is extended by including an implicit surface tension term in order to analyze droplet dynamics. The Lagrangian framework is adopted [...]
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Computational evaluation of cochlear implant surgery outcomes accounting for uncertainty and parameter variability
N. Mangado, J. Pons Prats, M. Coma, P. Mistrik, G. Piella, M. Ceresa, M. Ballester

Frontiers in Physiology (2018). Vol. 9, pp. 1-14

Abstract
Cochlear implantation (CI) is a complex surgical procedure that restores hearing in patients with severe deafness. The successful outcome of the implanted device relies on a group of factors, some of them unpredictable or difficult to control. Uncertainties on the electrode array position and the electrical properties of the bone make it difficult to accurately compute the current propagation delivered by the implant and the resulting neural activation. In this context, we use uncertainty quantification methods to explore how these uncertainties propagate through all the stages of CI computational simulations. To this end, we employ an automatic framework, encompassing from the finite element generation of CI models to the assessment of the neural response induced by the implant stimulation. To estimate the confidence intervals of the simulated neural response, we propose two approaches. First, we encode the variability of the cochlear morphology among the population through a statistical shape model. This allows us to generate a population of virtual patients using Monte Carlo sampling and to assign to each of them a set of parameter values according to a statistical distribution. The framework is implemented and parallelized in a High Throughput Computing environment that enables to maximize the available computing resources. Secondly, we perform a patient-specific study to evaluate the computed neural response to seek the optimal post-implantation stimulus levels. Considering a single cochlear morphology, the uncertainty in tissue electrical resistivity and surgical insertion parameters is propagated using the Probabilistic Collocation method, which reduces the number of samples to evaluate. Results show that bone resistivity has the highest influence on CI outcomes. In conjunction with the variability of the cochlear length, worst outcomes are obtained for small cochleae with high resistivity values. However, the effect of the surgical insertion length on the CI outcomes could not be clearly observed, since its impact may be concealed by the other considered parameters. Whereas the Monte Carlo approach implies a high computational cost, Probabilistic Collocation presents a suitable trade-off between precision and computational time. Results suggest that the proposed framework has a great potential to help in both surgical planning decisions and in the audiological setting process.
Abstract
Cochlear implantation (CI) is a complex surgical procedure that restores hearing in patients with severe deafness. The successful outcome of the implanted device relies on [...]
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Analysis of uncertainty and variability in finite element computational models for biomedical engineering: characterization and propagation
N. Mangado, G. Piella, J. Noailly, J. Pons Prats, M. Ballester

Frontiers in Bioengineering and Biotechnology (2016). Vol. 4, pp. 1-17

Abstract
Computational modeling has become a powerful tool in biomedical engineering thanks to its potential to simulate coupled systems. However, real parameters are usually not accurately known, and variability is inherent in living organisms. To cope with this, probabilistic tools, statistical analysis and stochastic approaches have been used. This article aims to review the analysis of uncertainty and variability in the context of finite element modeling in biomedical engineering. Characterization techniques and propagation methods are presented, as well as examples of their applications in biomedical finite element simulations. Uncertainty propagation methods, both non-intrusive and intrusive, are described. Finally, pros and cons of the different approaches and their use in the scientific community are presented. This leads us to identify future directions for research and methodological development of uncertainty modeling in biomedical engineering.
Abstract
Computational modeling has become a powerful tool in biomedical engineering thanks to its potential to simulate coupled systems. However, real parameters are usually not accurately [...]
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Ram-air parachute simulation with panel methods and staggered coupling
E. Ortega, R. Flores, J. Pons Prats

Journal of Aircraft (2016). (preprint) Vol. 54 (2), pp. 807-814
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Numerical study of droplet dynamics in a polymer electrolyte fuel cell gas channel using an embedded Eulerian-Lagrangian approach
A. Jarauta, P. Ryzhakov, M. Secanell, J. Pons Prats, P. Waghmare

Journal of Power Sources (2016). Vol. 323, pp. 201-212

Abstract
An embedded Eulerian-Lagrangian formulation for the simulation of droplet dynamics within a polymer electrolyte fuel cell (PEFC) channel is presented. Air is modeled using an Eulerian formulation, whereas water is described with a Lagrangian framework. Using this framework, the gas-liquid interface can be accurately identified. The surface tension force is computed using the curvature defined by the boundary of the Lagrangian mesh. The method naturally accounts for material property changes across the interface and accurately represents the pressure discontinuity. A sessile drop in a horizontal surface, a sessile drop in an inclined plane and droplets in a PEFC channel are solved for as numerical examples and compared to experimental data. Numerical results are in excellent agreement with experimental data. Numerical results are also compared to results obtained with the semi-analytical model previously developed by the authors in order to discuss the limitations of the semi-analytical approach.
Abstract
An embedded Eulerian-Lagrangian formulation for the simulation of droplet dynamics within a polymer electrolyte fuel cell (PEFC) channel is presented. Air is modeled using [...]
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On the application of the PFEM to droplet dynamics modeling in fuel cells
P. Ryzhakov, A. Jarauta, M. Secanell, J. Pons Prats

Comp. Part. Mech (2017). Vol. 4, pp. 285-295

Abstract
The Particle Finite Element Method (PFEM) is used to develop a model to study two-phase flow in fuel cell gas channels. First, the PFEM is used to develop the model of free and sessile droplets. The droplet model is then coupled to an Eulerian, fixed-grid, model for the airflow. The resulting coupled PFEM-Eulerian algorithm is used to study droplet oscillations in an air flow and droplet growth in a low-temperature fuel cell gas channel. Numerical results show good agreement with predicted frequencies of oscillation, contact angle, and deformation of injected droplets in gas channels. The PFEM-based approach provides a novel strategy to study droplet dynamics in fuel cells.
Abstract
The Particle Finite Element Method (PFEM) is used to develop a model to study two-phase flow in fuel cell gas channels. First, the PFEM is used to develop the model of free [...]
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A second-order semi-Lagrangian particle FEM (SL-PFEM) method for the incompressible Navier-Stokes equations
B. Servan Camas, J. García-Espinosa, J. Colom Cobb

Julio García-Espinosa's Presentations at Congresses and Seminars (2020). 1

Abstract
The Semi-Lagrangian Particle Finite Element Method (SL-PFEM) is a numerical method tailored for solving the fluid dynamics equations. Despite of its excellent numerical properties, such as a minimum numerical erosion in the convective transport and that it exhibits great stability, it has not yet received much attention in the scientific literature. In this presentation, a second order SL-PFEM scheme for solving the incompressible Navier-Stokes equations is presented. This scheme is based on the second order velocity Verlet algorithm, which uses an explicit integration for the particle’s trajectory and an implicit integration for the velocity. The algorithm is completed with a predictor-multicorrector scheme for the integration of the velocity correction using the Finite Element Method. A second order projector based on least squares is used to transfer the intrinsic variables information from the particles onto the background mesh, while a second order interpolation scheme is used to transfer the pressure gradient and viscous accelerations from the mesh to the particles.
Abstract
The Semi-Lagrangian Particle Finite Element Method (SL-PFEM) is a numerical method tailored for solving the fluid dynamics equations. Despite of its excellent numerical properties, [...]
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Industrial Application of Genetic Algorithms to Cost Reduction of a Wind Turbine Equipped with a Tuned Mass Damper
J. Pons Prats, M. Coma, J. Betran, X. Roca, G. Bugeda

(2018). Andrés-Pérez E., González L., Periaux J., Gauger N., Quagliarella D., Giannakoglou K. (eds) Evolutionary and Deterministic Methods for Design Optimization and Control With Applications to Industrial and Societal Problems. Computational Methods in Applied Sciences, vol 49. Springer, Cham

Abstract
Design optimization has already become an important tool in industry. The benefits are clear, but several drawbacks are still present, being the main one the computational cost. The numerical simulation involved in the solution of each evaluation is usually costly, but time and computational resources are limited. Time is key in industry. The present communication focuses on the methodology applied to optimize the installation and design of a Tuned Mass Damper. It is a structural device installed within the tower of a wind turbine aimed to stabilize the oscillations and reduce the tensions and the fatigue loads. The paper describes the decision process to define the optimization problem, as well as the issues and solutions applied to deal with a huge computational cost.
Abstract
Design optimization has already become an important tool in industry. The benefits are clear, but several drawbacks are still present, being the main one the computational [...]
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Monte Carlo-Based and Sampling-Based Methods and Their Range of Applicability
R. Schmidt, M. Voigt, M. Pisaroni, F. Nobile, P. Leyland, J. Prats, G. Bugeda

(2018). Hirsch C., Wunsch D., Szumbarski J., Łaniewski-Wołłk Ł., Pons-Prats J. (eds) Uncertainty Management for Robust Industrial Design in Aeronautics. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol 140. Springer, Cham

Abstract
The present section will focus on the applicability issues of Monte Carlo-based methods, as well as those methods based on sampling techniques. Special focus will be put on the Multi-Level Monte Carlo method and the two implementations developed during the UMRIDA project, namely the Continuous MLMC and MLMC. All named methods have been described in the above sections of this book.
Abstract
The present section will focus on the applicability issues of Monte Carlo-based methods, as well as those methods based on sampling techniques. Special focus will be put on [...]
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Summary of UMRIDA Best Practices
J. Pons Prats, G. Bugeda

(2018). Hirsch C., Wunsch D., Szumbarski J., Łaniewski-Wołłk Ł., Pons-Prats J. (eds) Uncertainty Management for Robust Industrial Design in Aeronautics. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol 140. Springer, Cham

Abstract
Uncertainty quantification (UQ) is becoming a strategic step in the design phase. Robust Design Optimization (RDO) is the following step. The Technological Readiness Level (TRL) of intrusive and non-intrusive methodologies is increasing rapidly, although several limitations remain. Nowadays, UQ is a major trend in research, because there is a lot of room for improvement.
Abstract
Uncertainty quantification (UQ) is becoming a strategic step in the design phase. Robust Design Optimization (RDO) is the following step. The Technological Readiness Level [...]
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General Introduction to Monte Carlo and Multi-level Monte Carlo Methods
R. Schmidt, M. Voigt, M. Pisaroni, F. Nobile, P. Leyland, J. Pons Prats, G. Bugeda

(2019). Hirsch C., Wunsch D., Szumbarski J., Łaniewski-Wołłk Ł., Pons-Prats J. (eds) Uncertainty Management for Robust Industrial Design in Aeronautics. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol 140. Springer, Cham

Abstract
In this chapter, we present a general introduction to Monte Carlo (MC)-based methods, sampling methodologies, stratification methods, and variance reduction techniques. In the first part, we will discuss the theoretical basis and the convergence proprieties of MC methods. The next part is devoted to pseudorandom and quasi-random number generation, the generation of random variables and the application of stratification. It is followed by techniques for correlation and discrepancy control. The third part presents the concept of Latin Hypercube Sampling (LHS). The last part introduces the concept of Multi-Level Monte Carlo (MLMC).
Abstract
In this chapter, we present a general introduction to Monte Carlo (MC)-based methods, sampling methodologies, stratification methods, and variance reduction techniques. In [...]
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Multi-level Monte Carlo Method
J. Pons Prats, G. Bugeda

(2019). Hirsch C., Wunsch D., Szumbarski J., Łaniewski-Wołłk Ł., Pons-Prats J. (eds) Uncertainty Management for Robust Industrial Design in Aeronautics. Notes on Numerical Fluid Mechanics and Multidisciplinary Design, vol 140. Springer, Cham

Abstract
Uncertainty quantification has gained interest during the recent years. Two clear examples are NODESIM-CFD and, the just finished, UMRIDA projects.
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Industrial application of genetic algorithms to cost reduction of a wind turbine equipped with a tuned mass damper
J. Pons Prats, M. Coma, J. Betran, X. Roca, G. Bugeda

(2018). Andrés-Pérez E., González L., Periaux J., Gauger N., Quagliarella D., Giannakoglou K. (eds) Evolutionary and Deterministic Methods for Design Optimization and Control With Applications to Industrial and Societal Problems. Computational Methods in Applied Sciences, vol 49. Springer, Cham

Abstract
Design optimization has already become an important tool in industry. The benefits are clear, but several drawbacks are still present, being the main one the computational cost. The numerical simulation involved in the solution of each evaluation is usually costly, but time and computational resources are limited. Time is key in industry. The present communication focuses on the methodology applied to optimize the installation and design of a Tuned Mass Damper. It is a structural device installed within the tower of a wind turbine aimed to stabilize the oscillations and reduce the tensions and the fatigue loads. The paper describes the decision process to define the optimization problem, as well as the issues and solutions applied to deal with a huge computational cost.
Abstract
Design optimization has already become an important tool in industry. The benefits are clear, but several drawbacks are still present, being the main one the computational [...]
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Description of the Test Cases
G. Bugeda, J. Periaux, N. Qin, J. Pons Prats

(2020). Qin N., Periaux J., Bugeda G. (eds) Advances in Effective Flow Separation Control for Aircraft Drag Reduction. Computational Methods in Applied Sciences, vol 52. Springer, Cham

Abstract
The high-level objective of MARS project was to understand the formation and behaviour of turbulent structures which affects the Reynolds stress and skin friction. The aim was, once understood, to apply flow control techniques in order to control these structures and reduce the overall drag derived from the Reynolds stress and mainly from the skin friction. Active flow control devices were the main interest; DBD plasma, Synthetic jets, Micro Blowing and Suction, Moving Surfaces were included on the list. To test all these devices, two test cases were defined, and a database and file repository were established in the project webserver. The present chapter is aimed to describe the test cases, including the set-up of the flow control devices, as well as to describe the file repository were all the data was stored.
Abstract
The high-level objective of MARS project was to understand the formation and behaviour of turbulent structures which affects the Reynolds stress and skin friction. The aim [...]
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Optimization of the Experimental Set-up for a Turbulent Separated Shear Flow Control by Plasma Actuator Using Genetic Algorithms
N. Benard, J. Pons Prats, J. Periaux, J. Bonnet, G. Bugeda

(2020). Qin N., Periaux J., Bugeda G. (eds) Advances in Effective Flow Separation Control for Aircraft Drag Reduction. Computational Methods in Applied Sciences, vol 52. Springer, Cham

Abstract
Since 1947, when Schubauer and Skramstad established the basis of the technology with its revolutionary work about steady state tools and mechanisms for the flow management, the progress of the flow control technology and the development of devices have progressed constantly. Anyway, the applicability of such devices is limited, and only few of them have arrived to the assembly workshop. The problem is that the range of actuation is still limited. Despite their operability limitations, flow control devices are of great interest for the aeronautical industry. The number of projects investigating this technology demonstrates the relevance of in the Fluid Dynamic field. The scientific interest focus not only on the industrial applications and the improvement of the technology, but also on the deep understanding of the physical phenomena associated to the flow separation, turbulence formation associated to the final drag reduction aim. A clear example of what has been mentioned is the EC MARS research project (MARS project, FP7 project number 266326, [2]). Its objectives are aimed to a better understanding of the Reynolds Stress and turbulent flow related to both drag reduction and flow control. The research was carried out through the analysis of several flow control devices and the optimization of the parameters for some of them was an important element of the research. When solving a traditional fluid dynamics optimisation problem numerical flow analysis are used instead of experimental ones due to their lower cost and shorter needed time for evaluation of candidate solutions. Nevertheless, in the particular case of the selected flow control plasma devices the experimental measurement of the performance of each candidate configuration has been much quicker than a numerical analysis. For this reason, the corresponding optimisation problem has been solved by coupling an evolutionary optimization algorithm with an experimental device. This paper discusses the design quality and efficiency gained by this innovative coupling.
Abstract
Since 1947, when Schubauer and Skramstad established the basis of the technology with its revolutionary work about steady state tools and mechanisms for the flow management, [...]
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Lessons learned associated with constructability application in a massive housing project
Z. Giménez, M. Briceño

Gaceta Técnica (2020). Vol. 20 (1), 8

Abstract
The architecture, engineering and construction industry has great activity and importance, it moves other areas to satisfy the infrastructure needs of most economic and social activities, such as housing, roads, education, industry and health, among others However, it is one of the industries with the lowest productivity and which seems not to have taken advantage, as do other production sectors in general, of the opportunities offered by some management philosophies to solve complications and difficulties. This article analyzes the most relevant lessons learned from the implementation, both in the previous phases and in the link or relations between them, and in the corporate area of the company, when applying the constructablity in the planning stages, design and acquisitions, guiding the objectives of multidisciplinary teams towards the integration of a housing project built in Barquisimeto, Venezuela. The methodology was used in the integral process of the project, prior to the preliminary project, which led to the continuation of benefits in costs, times and quality of the final product in a pilot project.
Abstract
The architecture, engineering and construction industry has great activity and importance, it moves other areas to satisfy the infrastructure needs of most economic and social [...]
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Drag reduction via turbulent boundary layer flow control
A. Abbas, G. Bugeda, E. Ferrer, S. Fu, J. Periaux, J. Pons Prats, E. Valero, Y. Zheng

Science China-Technological Sciences (2017). Vol. 60 (9), pp. 1281-1290 (Preprint)

Abstract
Turbulent boundary layer control (TBLC) for skin-friction drag reduction is a relatively new technology made possible through the advances in computational-simulation capabilities, which have improved the understanding of the flow structures of turbulence. Advances in micro-electronic technology have enabled the fabrication of active device systems able to manipulating these structures. The combination of simulation, understanding and micro-actuation technologies offers new opportunities to significantly decrease drag, and by doing so, to increase fuel efficiency of future aircraft. The literature review that follows shows that the application of active control turbulent skin-friction drag reduction is considered of prime importance by industry, even though it is still at a low technology readiness level (TRL). This review presents the state of the art of different technologies oriented to the active and passive control for turbulent skin-friction drag reduction and contributes to the improvement of these technologies.
Abstract
Turbulent boundary layer control (TBLC) for skin-friction drag reduction is a relatively new technology made possible through the advances in computational-simulation capabilities, [...]
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Turbulent separated shear flow control by surface plasma actuator: experimental optimization by genetic algorithm approach
N. Benard, J. Pons Prats, J. Periaux, G. Bugeda, P. Braud, J. Bonnet, E. Moreau

Experiments in Fluids (2016). (preprint) Vol. 57 (2), pp. 1-17

Abstract
The potential benefits of active flow control are no more debated. Among many others applications, flow control provides an effective mean for manipulating turbulent separated flows. Here, a nonthermal surface plasma discharge (dielectric barrier discharge) is installed at the step corner of a backward-facing step (U 0 = 15 m/s, Re h = 30,000, Re θ = 1650). Wall pressure sensors are used to estimate the reattaching location downstream of the step (objective function #1) and also to measure the wall pressure fluctuation coefficients (objective function #2). An autonomous multi-variable optimization by genetic algorithm is implemented in an experiment for optimizing simultaneously the voltage amplitude, the burst frequency and the duty cycle of the high-voltage signal producing the surface plasma discharge. The single-objective optimization problems concern alternatively the minimization of the objective function #1 and the maximization of the objective function #2. The present paper demonstrates that when coupled with the plasma actuator and the wall pressure sensors, the genetic algorithm can find the optimum forcing conditions in only a few generations. At the end of the iterative search process, the minimum reattaching position is achieved by forcing the flow at the shear layer mode where a large spreading rate is obtained by increasing the periodicity of the vortex street and by enhancing the vortex pairing process. The objective function #2 is maximized for an actuation at half the shear layer mode. In this specific forcing mode, time-resolved PIV shows that the vortex pairing is reduced and that the strong fluctuations of the wall pressure coefficients result from the periodic passages of flow structures whose size corresponds to the height of the step model.
Abstract
The potential benefits of active flow control are no more debated. Among many others applications, flow control provides an effective mean for manipulating turbulent separated [...]
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Review: Course in structural engineering. Regional center for technological developments for construction, seismology and seismic engineering CeDeReTec
J. Vielma-Perez

Gaceta Técnica (2020). Vol. 21(1), 2

Abstract
This is the review of the Structural Engineering Update course carried out at the Regional Center for Technological Developments for Seismology and Seismic Engineering Construction (CeDeReTec, Mendoza, Argentina) at the end of the year 2019. The presentations are shown and also reports on the activities carried out within the framework of the Project “Destructive Potential Generated by the Earthquake of Ecuador of April 16, 2016” are reported.
Abstract
This is the review of the Structural Engineering Update course carried out at the Regional Center for Technological Developments for Seismology and Seismic Engineering Construction [...]
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Docencia e investigación: ¿un falso dilema?
E. Montilla, G. Amblàs, G. Bugeda, S. Roca

Aula abierta (2013). Vol. 41 (2), pp. 13-22

Abstract
La Universidad Politécnica de Cataluña (UPC) dispone de un modelo de evaluación docente plenamente consolidado, que está adaptado a los requerimientos que emanan de la implantación del Espacio Europeo de Educación Superior. Dicho modelo de evaluación ha sido homologado por la Agència per a la Qualitat del Sistema Universitari de Catalunya (AQU Catalunya), la agencia de evaluación catalana y se basa en las directrices europeas más exigentes. Este modelo se ha empleado para evaluar la docencia del profesorado en seis convocatorias, por lo que se dispone de una información exhaustiva, tanto a nivel agregado como separado por colectivos y ámbitos de conocimiento. Por otro lado, también se dispone de información sobre la actividad investigadora del profesorado, medida mediante el número de sexenios obtenidos. En este artículo se presentan estos datos y se estudia si existe una correlación positiva entre la calidad de la docencia impartida y el reconocimiento de las tareas investigadoras de los profesores, medida a través del número de sexenios obtenidos. Nuestros resultados indican que tal correlación existe, aunque es más débil de lo que cabría esperar.
Abstract
La Universidad Politécnica de Cataluña (UPC) dispone de un modelo de evaluación docente plenamente consolidado, que está adaptado a los requerimientos [...]
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Sensitivity analysis of the hydrological and hydraulic parameters of the SWMM model and its application in urban drainage systems
K. Rivero, A. Aguilar, J. Ortiz

Gaceta Técnica (2020). Vol. 21(1), 1

Abstract
Simulation models are widely used for the design and management of urban drainage systems, such as the SWMM Stormwater Management Model. However, the quality of its results is directly related to the quality of the data provided, since an incorrect estimate of these may lead to a different behavior than expected in the real case. There is uncertainty in many hydrological and hydraulic input parameters of the model, since most of them are estimated and there are no measured data to calibrate it. In this work a sensitivity analysis is carried out to various parameters to detect the most influential in the simulation of urban drainage systems. It consisted of locally varying each of the parameters and assessing their influence on the variation of the flows and maximum levels at a point in the Copacoa Urbanization, Palavecino municipality of the Lara State, Venezuela. From the results obtained, it is concluded that for simulations of urban watersheds where impervious areas predominate, the least sensitive method for the generation of the rain hietrogram is that of alternate blocks, while the one with the greatest variability is the triangular hietrogram. Regarding the basin component, the most sensitive parameters are the percentage of impermeable area, the slope of the basin and the Manning coefficient assigned to the impermeable area. In relation to the duct, the Manning coefficient parameter also presented an appreciable sensitivity, but of a lesser magnitude compared to those obtained for the basin component.
Abstract
Simulation models are widely used for the design and management of urban drainage systems, such as the SWMM Stormwater Management Model. However, the quality of its results [...]
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Un caso práctico de meta-evaluación docente: el manual de evaluación de la Universidad Politécnica de Cataluña
E. Montilla, R. Vega, G. Amblàs, E. Martínez, L. Campeny, G. Bugeda, S. Roca

Aula Abierta (2012). Vol. 40 (2), pp. 11-24

Abstract
La Universidad Politécnica de Cataluña ha sido pionera en la introducción de un modelo de evaluación docente plenamente adaptado a las exigencias del Espacio Europeo de Enseñanza Superior. Además, su sistema de evaluación de la actividad docente del profesorado ha sido homologa- do por la AQU y ANECA. Dicho modelo de evaluación docente se basa en las más recientes directrices europeas y tiene como fundamento diversos indicadores indirectos. Este modelo se ha empleado para evaluar la docencia del profesorado en cinco convocatorias. Durante este periodo de tiempo se ha acumulado una información valiosísima que permite obtener datos agregados no sólo de la calidad de los docentes sino, también, de diversas características inherentes al proceso de evaluación, así como de la bondad de los indicadores empleados. En este artículo se presentan es- tos datos y se muestra un conjunto de datos agregados que permiten estimar la bondad y fiabilidad del proceso de evaluación, así como su aceptación por el profesorado evaluado.
Abstract
La Universidad Politécnica de Cataluña ha sido pionera en la introducción de un modelo de evaluación docente plenamente adaptado a las exigencias [...]
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Correlation between the dynamic cone penetrometer and the California support relationship in the field for the sub-rasant floor of the Portoviejo-Manta road
H. Merino, J. Morejón, L. Garzón, D. Cuasapaz

Gaceta Técnica (2020). Vol. 21(1), 7

Abstract
The Portoviejo – Manta road is a main land communication artery in the province of Manabí in Ecuador, a fundamental axis in the country's economic, social and tourism development. The decentralized autonomous government of the province of Manabí based on studies proposes an extension of the four existing lanes to six; for this, a comprehensive analysis involving a traffic, geological and geotechnical study is important. Given that this province at superficial levels presents a uniform clay formation, the present investigation evaluates the conditions of the track support terrain, proposing two dynamic cone penetrometer methods and the California support ratio, examining at the same time if the correlation between them exists. Standardized field and laboratory work was carried out over a length of 35 kilometers with paired tests every 500,00 m. The data obtained from the field and laboratory were processed and analyzed using statistical linear regression methods, validated through hypothesis testing and significance of the p-value. At first, a direct correlation was obtained between both methods and an equation with a correlation value of 0,80, with a significance of 7,246x10-5. A second multiple regression equation was carried out in which correlation values were obtained between the methods, plus the physical parameters of the soil of 0,82 and its corresponding p-value of 0,0091, thus validating the reliability of the results.
Abstract
The Portoviejo – Manta road is a main land communication artery in the province of Manabí in Ecuador, a fundamental axis in the country's economic, social [...]
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Editorial: Greater visibility of Gaceta Técnica journal
L. Casadei

Gaceta Técnica (2020). Vol. 21(1), 3

Abstract
Editorial: Greater visibility of Gaceta Técnica journal
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Calculation and design of a railway bridge section of metallic structure in El Vigía, Mérida state
G. Josue, C. Valero, F. Jesús, S. Carrasquero

Gaceta Técnica (2020). Vol. 21(1), 6

Abstract
This paper refers to the design and calculation of a 30,00 m section of metal beam, for a proposed railway bridge in the city of El Vigía, capital of the Alberto Adriani Municipality of Mérida State, Venezuela. The location of the bridge corresponds approximately to a route proposed by the State Railway Institute, Maracaibo Lake Route, in the National Railway Plan. The calculation hypothesis was made using simply supported beams, however the CSI Bridge 2017 calculation tool was used. The design of the beam section was carried out using the AASHTO LRFD 2014 standard, the analysis considerations loads and combinations were based on AREMA 2004. The freight train was the AREMA COOPER E-80, which is the most common idealized locomotive in the analysis. Other designed elements were the concrete slab, elastomeric supports, diaphragms or separators and stiffeners. The design of a 30,00 m section of metal beam of section I of 1.70 m high was obtained with sheets of 5.00 cm thick at the core and 10,00 cm for each wing, with a width 80,00 cm, all in A36 steel. The slab placed was 30,00 cm thick and 250 kg/cm2 concrete.
Abstract
This paper refers to the design and calculation of a 30,00 m section of metal beam, for a proposed railway bridge in the city of El Vigía, capital of the Alberto Adriani [...]
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Study of qualitative seismic vulnerability in armed concrete educational institutions in the Falcón State
A. Giménez, M. Olavarrieta, A. Acero, J. Chong, K. Ramones, L. Reinoza

Gaceta Técnica (2020). Vol. 21(1), 4

Abstract
The methodology for calculating the Prioritization Index for the Management of Seismic Risk in existing Buildings, came out as a result of the poor performance of structures that during the Cariaco 1997 earthquake, and the 1967 Caracas earthquake where the buildings collapsed, despite their apparent good state of conservation. In the case of four structures analyzed in this research, the Agustín Ocando Prosper School, the Agua Salobre Basic Bolivarian School, the Agustín Ocando Prosperous High School, and the Las Delicias Initial Education Center, these reinforced concrete buildings are located in the coastal zone of the Falcón State, in Venezuela, under the influence of the aggressive marine environment, and in the presence of the San Sebastian tectonic fault. The evaluation was carried out by applying the qualitative method of the Priority Index for Seismic Risk Management, verifying that the structures of the Agustín Ocando Prosperous School have a medium to high average vulnerability, however it is recommended to conduct detailed studies in modules 1 and 2 that have a very high frequency rating. For the Agua Salobre Bolivarian Basic School, the vulnerability index, corresponding to module 1, is medium high and the other group its classification is medium low; in Liceo Próspero Agustín Ocando modules 1 and 3 have a medium-high risk index and modules 1 and 3 are high. The Center of Initial Education Las Delicias, has the average risk index medium to low.
Abstract
The methodology for calculating the Prioritization Index for the Management of Seismic Risk in existing Buildings, came out as a result of the poor performance of structures [...]
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Review: The construction camera introduce BIM in barquisimeto
R. Arias

Gaceta Técnica (2020). Vol. 21(1), 5

Abstract
In November 2019, the Lara State Construction Camera promoted two activities related to the introduction of Building Information Modeling BIM methodology. The first one, the workshop “BIM Three letters that will transform the construction industry”. The second one with the conference "BIM the methodology that changes the professional DNA of engineers, architects and builders" with very good acceptance by professionals related to the construction area of the State. These activities aim to sow interest in the academia, engineers, architects, urban planners and builders, in adapting to the advances that are being presented in the sector, in the search to be much more competitive and to be on par with the professionals of others countries.
Abstract
In November 2019, the Lara State Construction Camera promoted two activities related to the introduction of Building Information Modeling BIM methodology. The first one, the [...]
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Double-shock control bump design optimization using hybridized evolutionary algorithms
D. Lee, L. Gonzalez, J. Periaux, G. Bugeda

Proceedings of the Institution of Mechanical Engineers. Part G, journal of aerospace engineering (2011). Vol. 225 (10), pp. 1175-1192

Abstract
This study investigates the application of two advanced optimization methods for solving active flow control (AFC) device shape design problem and compares their optimization efficiency in terms of computational cost and design quality. The first optimization method uses hierarchical asynchronous parallel multi-objective evolutionary algorithm and the second uses hybridized evolutionary algorithm with Nash-Game strategies (Hybrid-Game). Both optimization methods are based on a canonical evolution strategy and incorporate the concepts of parallel computing and asynchronous evaluation. One type of AFC device named shock control bump (SCB) is considered and applied to a natural laminar flow (NLF) aerofoil. The concept of SCB is used to decelerate supersonic flow on suction/pressure side of transonic aerofoil that leads to a delay of shock occurrence. Such active flow technique reduces total drag at transonic speeds which is of special interest to commercial aircraft. Numerical results show that the Hybrid-Game helps an EA to accelerate optimization process. From the practical point of view, applying a SCB on the suction and pressure sides significantly reduces transonic total drag and improves lift-to-drag (L/D) value when compared to the baseline design.
Abstract
This study investigates the application of two advanced optimization methods for solving active flow control (AFC) device shape design problem and compares their optimization [...]
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Estrategias e indicadores para la evaluación de la docencia en el marco del EEES
E. Garcia-Berro, F. Dapia, G. Amblas, G. Bugeda, S. Roca

Revista de investigación en educación (2009). Vol. 6, pp. 142-152

Abstract
En este artículo se describen las estrategias que ha emprendido la Universidad Politécnica de Cataluña (UPC) para implantar las nuevas titulaciones de Ingeniería adaptadas al Espacio Europeo de Enseñanza Superior (EEES). Estas estrategias pueden ser de utilidad para otras universidades. Partiendo de un análisis detallado del contexto general de la Universidad española y de la UPC en particular, se muestra el sistema de planificación estratégica de nuestra institución. Asimismo se describe en detalle el sistema de indicadores estadísticos que se usa para medir el rendimiento de centros y departamentos en el referido marco de planificación estratégica. Por último, también se detallan las acciones que se han emprendido para evaluar la actividad docente del profesorado.
Abstract
En este artículo se describen las estrategias que ha emprendido la Universidad Politécnica de Cataluña (UPC) para implantar las nuevas titulaciones de [...]
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A new adaptive remeshing scheme based on the sensitivity analysis of the SPR point wise error estimation
G. Bugeda

Comput. Methods Appl. Mech. Engrg., (2006). Vol. 195 (4-6), pp. 462-478

Abstract
This paper presents a formulation for the obtainment of the sensitivity analysis of a point wise error estimator with respect to the nodal coordinates using the adjoint state method. The proposed point wise error estimator is based on the SPR method. The numerical accuracy of the presented sensitivity analysis has been tested by perturbing a mesh. The capability of the presented sensitivity analysis for the detection of pollution error has also been tested. A new adaptive remeshing strategy based on the sensitivity analysis of the point wise error estimation has been developed and tested. This strategy produces very cheap meshes for the accurate evaluation of stresses at specific points.
Abstract
This paper presents a formulation for the obtainment of the sensitivity analysis of a point wise error estimator with respect to the nodal coordinates using the adjoint state [...]
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A comparison between new adaptive remeshing strategies based on point wise stress error estimation and energy norm error estimation
G. Bugeda

Commun. Numer. Meth. Engng (2002). Vol. 18 (7), 469-482

Abstract
Traditionally, the most commonly used mesh adaptive strategies for linear elastic problems are based on the use of an energy norm for the measurement of the error, and a mesh refinement strategy based on the equal distribution of the error between all the elements. However, little attention has been paid to the study of alternative error norms and alternative refinement strategies. This paper studies the feasibility of using alternative mesh refinement strategies based on — the use of the classical error energy norm and an optimality criterion based on the equal distribution of the density of error, — the use of alternative error norms based on measurements of the point wise error contained in the main magnitudes that control the equilibrium problem and/or the material constitutive equations such as the stresses (e.g. the Von Mises stress). The feasibility of using all the described strategies is demonstrated through the solution of a benchmark example. This example is also used for comparison between the described refinement criteria.
Abstract
Traditionally, the most commonly used mesh adaptive strategies for linear elastic problems are based on the use of an energy norm for the measurement of the error, and a mesh [...]
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A C++ object-oriented programming strategy for the implementation of the finite element sensitivity analysis for a non-linear structural material model
L. Gil, G. Bugeda

Advances in Engineering Software (2001). Vol. 32 (12), pp. 927-935

Abstract
The Finite Element Method (FEM) has become the most popular numerical method for solving a wide variety of complex engineering problems. However, from the programming point of view, when a FEM program has a lot of computational capabilities it is very difficult to maintain and enlarge the program codes. Recently the object-oriented programming paradigm has become a powerful method for overcoming such difficulties. This paper contains the description of an open environment for the FEM, written in C++, with explanations about how the sensitivity analysis and the non-linear material behaviour (damage models) have been taken into accoun
Abstract
The Finite Element Method (FEM) has become the most popular numerical method for solving a wide variety of complex engineering problems. However, from the programming [...]
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Shape sensitivity analysis for structural problems with non‐linear material behaviour
G. Bugeda, L. Gil

Int. J. Numer. Meth. Engng. (1999). Vol. 46 (9), pp. 1385-1404

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 non‐linear constitutive material model. Depending on the type of non‐linear behaviour two different approaches are proposed. First, a new direct (non‐incremental) formulation is proposed for material models characterized by the fact that the stresses at any time t can be expressed in terms of the strains at the same time t and, in some cases, the strains at a specific past time tu (tu<t). This is the case of elasticity (linear as well as non‐linear), perfect plasticity and damage models. Second, a more classical incremental approach is proposed for general plasticity cases. A special strategy is also proposed for material models with strain softening. The quality and reliability of the proposed approaches are assessed through their application in different examples.
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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A general methodology for structural shape optimization problems using automatic adaptive remeshing
G. Bugeda, J. Oliver

Int. J. Numer. Meth. Engng. (1993). Vol. 36 (18), pp. 3161-3185

Abstract
The proposed methodology is based on the use of the adaptive mesh refinement (AMR ) techniques in the context of 2D shape optimization problems analysed by the finite element method. A suitable and very general technique for the parametrization of the optimization problem, using B‐splines to define the boundary, is first presented. Then mesh generation, using the advancing frontal method, the error estimator and the mesh refinement criterion are studied in the context of shape optimization problems In particular, the analytical sensitivity analysis of the different items ruling the problem (B‐splines. finite element mesh, structural behaviour and error estimator) is studied in detail. The sensitivities of the finite element mesh and error estimator permit their projection from one design to the next one leading to an a priori knowledge of the finite element error distribution on the new design without the necessity of any additional structural analysis. With this information the mesh refinement criterion permits one to build up a finite element mesh on the new design with a specified and controlled level of error. The robustness and reliability of the proposed methodology is checked by means of several examples.
Abstract
The proposed methodology is based on the use of the adaptive mesh refinement (AMR ) techniques in the context of 2D shape optimization problems analysed by the finite element [...]
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Multiscale Computational Homogenization: Review and Proposal of a New Enhanced-First-Order Method
F. Otero, S. Oller, X. Martinez

(2017). Notas de Modelación y Métodos Numéricos VII. Mathematical Models for Material Sciences and their Industrial Application. Editores: J. Montalvo-Urquizo, M.A. Moreles, S. Botello. Centro de Investigación en Matemáticas (CIMAT) - CIMNE. pp. 71-112. ISBN 978-84-95999-88-7.

Abstract
The continuous increase of computational capacity has encouraged the extensive use of multiscale techniques to simulate the material behaviour on several fields of knowledge. In solid mechanics, the multiscale approaches which consider the macro-scale deformation gradient to obtain the homogenized material behaviour from the micro-scale are called first-order computational homogenization. Following this idea, the second-order FE2 methods incorporate high-order gradients to improve the simulation accuracy. However, to capture the full advantages of these high-order framework the classical boundary value problem (BVP) at the macro-scale must be upgraded to high-order level, which complicates their numerical solution. With the purpose of obtaining the best of both methods i.e. first-order and second-order, in this work an enhanced-first-order computational homogenization is presented. The proposed approach preserves a classical BVP at the macro-scale level but taking into account the high-order gradient of the macro-scale in the micro-scale solution. The developed numerical examples show how the proposed method obtains the expected stress distribution at the micro-scale for states of structural bending loads. Nevertheless, the macro-scale results achieved are the same than the ones obtained with a first-order framework because both approaches share the same macro-scale BVP.
Abstract
The continuous increase of computational capacity has encouraged the extensive use of multiscale techniques to simulate the material behaviour on several fields of knowledge. [...]
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Análisis no-lineal de materiales compuestos mediante la teoría de mezclas serie-paralelo
X. Martinez, S. Oller, F. Rastellini

(2014). Omnia Publisher. Capítulo 10 - p. 237-260. Aplicaciones avanzadas de los materiales compuestos en la obra civil y la edificación, ISBN: 978-84-941872-9-2

Abstract
Este libro presenta una panorámica del estado actual de los materiales compuestos y sus aplicaciones más relevantes en la obra civil y la edificación
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Análisis numérico de la reparación y refuerzo de estructuras con FRP
S. Oller, M. Molina, J. Vielma-Perez, X. Martinez

(2014). Omnia Publisher. Capítulo 11 - p. 261-291. Aplicaciones avanzadas de los materiales compuestos en la obra civil y la edificación, ISBN: 978-84-941872-9-2

Abstract
En este capítulo se presenta un procedimiento para evaluar la magnitud del daño local y el daño global en estructuras sometidas a acciones estáticas y dinámicas, con especial énfasis en el problema sísmico. Además de la formulación para la evaluación del daño, se introduce el concepto de refuerzo y reparación estructural mediante laminados compuestos de matriz epóxica con refuerzo de fibras de carbono. Para esta finalidad, se menciona la utilización de la teoría de mezclas para componer un material compuesto a partir de sus componentes básicas. También se evalúa el daño en estas estructuras reforzadas y/o reparadas y se comenta la influencia de estas mejoras en la valoración del daño global de la estructura
Abstract
En este capítulo se presenta un procedimiento para evaluar la magnitud del daño local y el daño global en estructuras sometidas a acciones estáticas [...]
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Study of Delamination in Composites by Using the Serial/Parallel Mixing Theory and a Damage Formulation
X. Martinez, S. Oller, E. Barbero

(2008). Mechanical response of composites. Ed. Pedro Camanho et al. pp. 119 - 140. Springer. ISBN 978-1-4020-8583-3

Abstract
This work presents a new procedure to deal with the delamination problem found in laminated composites, based in a continuum mechanics formulation. The procedure proposed obtains the composite constitutive performance with the Serial/Parallel mixing theory, developed by F. Rastellini. This theory characterizes composite materials by coupling the constitutive behaviour of the composite components, imposing an iso–strain relation among the components in the fibre (or parallel) direction and an iso–stress relation in the remaining directions (serial directions). The proposed procedure also uses a damage formulation to characterize the constitutive behaviour of matrix component in order to obtain the stress–strain performance of this material. With these two formulations, the delamination phenomenon is characterized naturally by the numerical simulation, being unnecessary the definition of special elements or computationally expensive techniques like the definition of contact elements or mesh separation. Matrix failure, as a result of the stress state found in it, leads to a reduction of the stiffness and strength capacity of the composite in its serial direction. This reduction provides a composite performance equivalent to what is found in a delaminated material. To prove the ability of the formulation proposed to solve delamination problems, the End Notch Failure test is numerically simulated and the results obtained are compared with experimental ones. The agreement found in the results with both simulations, numerical and experimental, validate the proposed methodology to solve the delamination problem.
Abstract
This work presents a new procedure to deal with the delamination problem found in laminated composites, based in a continuum mechanics formulation. The procedure proposed [...]
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Nuevo Modelo Discreto Multiescala (DM) para análisis no-lineales de materiales compuestos
S. Zaghi, X. Martinez, R. Rossi

Materiales Compuestos (2018). Vol. 2 (4), pp. 70-79

Abstract
En los últimos años el estudio del comportamiento de los materiales a nivel microscópico ha aumentado significativamente en términos de diseño de materiales de altas prestaciones. A pesar de los recientes avances de ordenadores de elevado rendimiento, la aplicación de métodos numéricos multiescala para simular grandes estructuras aún requiere costes computacionales prohibitivos. Éste trabajo presenta un procedimiento capaz de predecir la respuesta mecánica no-lineal de los materiales compuestos con el fin de reducir el coste computacional necesario para el análisis numérico de estructuras complejas. La solución de la estructura macroscópica a través del método multiescala de primer orden (FE2) se sustituirá por un modelo discreto obtenido de un análisis del comportamiento de un Volumen Representativo Elemental (RVE) del material. A través de las definiciones de un parámetro de daño equivalente (deq), función del esfuerzo global en la microescala, se realizarán una serie de ensayos virtuales en control de deformación, almacenando el estado de tensión-deformación alcanzado por ciertos niveles de deq en una base de datos. Analizando la evolución de la fractura en los materiales compuestos se puede observar como el régimen no-lineal se alcanza solo en algunos elementos de la estructura. Es por ello que se plantea un procedimiento, el Discrete Multiscale Threshold Surface (DMTS), en el que el análisis del RVE sirve para obtener la superficie en la que empieza el daño (deq >0). Esta ley permite saber si para un determinado estado tenso-deformacional el material ha dañado, sin necesidad de resolver el micro-modelo. Una vez iniciado el daño, se propone de generar de forma adaptiva un RVE con el que obtener el comportamiento dañado del material. Luego, el método FE2 se utilizará solo en los puntos de integración que hayan dañado. Este trabajo demuestra que el método FE2 puede ser remplazado por un Modelo Discreto Multiescala, representativo del material compuesto, obteniendo mejoras computacionales significativas.
Abstract
En los últimos años el estudio del comportamiento de los materiales a nivel microscópico ha aumentado significativamente en términos de diseño [...]
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Numerical analysis of interlaminar stresses in open-hole laminates under compression
A. Solis, S. Sanchez-Saez, X. Martinez, E. Barbero-Pozuelo

Composite Structures (2019). Vol. 217, pp. 89-99

Abstract
In this paper, the interlaminar stresses in open-hole laminates subjected to compressive loads are analysed using a numerical model. This model implements the Serial/Parallel Mixing Theory (S/PMT) and a Continuum Damage Mechanics (CDM) approach. The S/PMT estimates the global stiffness in the laminate from fibre and matrix properties. The CDM approach models the damage initiation due to fibre microbuckling. The global response estimated by the model was verified with experimental data from the literature. The model predicts that the damage initiates in the laminate middle-plane where the thickest block of plies oriented in the load direction is located, and progressively propagates to the nearest block of layers with the same orientation. Two laminate stacking sequences were analysed. The interlaminar stresses around the hole presented symmetry with respect to the load direction and the perpendicular axis, being located the maximum and minimum values in different angular positions for each stress component and laminate.
Abstract
In this paper, the interlaminar stresses in open-hole laminates subjected to compressive loads are analysed using a numerical model. This model implements the Serial/Parallel [...]
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Adaptive and off-line techniques for non-linear multiscale analysis
S. Zaghi, X. Martinez, R. Rossi, M. Petracca

Composite Structures (2018). (preprint) Vol. 206, pp. 215-233

Abstract
This paper presents two procedures, based on the numerical multiscale theory, developed to predict the mechanical non-linear response of composite materials under monotonically increasing loads. Such procedures are designed with the objective of reducing the computational cost required in these types of analysis. Starting from virtual tests of the microscale, the solution of the macroscale structure via Classical First-Order Multiscale Method will be replaced by an interpolation of a discrete number of homogenized surfaces previously calculated. These surfaces describe the stress evolution of the microscale at fixed levels of an equivalent damage parameter (). The information required for these surfaces to conduct the analysis is stored in a Data Base using a json format. Of the two methods developed, the first one uses the pre-computed homogenized surface just to obtain the material non-linear threshold, and generates a Representative Volume Element (RVE) once the material point goes into the nonlinear range; the second method is completely off-line and is capable of describing the material linear and non-linear behavior just by using the discrete homogenized surfaces stored in the Data Base. After describing the two procedures developed, this manuscript provides two examples to validate the capabilities of the proposed methods
Abstract
This paper presents two procedures, based on the numerical multiscale theory, developed to predict the mechanical non-linear response of composite materials under monotonically [...]
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and T is the automorfism. Si, U = (I, R) y S
A. Lechuga

Antonio Lechuga's personal collection (2020). 1
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Identification of Fracture Toughness for Discrete Damage Mechanics Analysis of Glass-Epoxy Laminates
E. Barbero, F. Cosso, X. Martinez

Applied Composite Materials (2014). Vol. 21, pp. 633-650

Abstract
A methodology for determination of the intralaminar fracture toughness is presented, based on fitting discrete damage mechanics (DDM) model predictions to available experimental data. DDM is constitutive model that, when incorporated into commercial finite element software via user material subroutines, is able to predict intralaminar transverse and shear damage initiation and evolution in terms of the fracture toughness of the composite. The applicability of the DDM model is studied by comparison to available experimental data for Glass-Epoxy laminates. Sensitivity of the DDM model to h- and p-refinement is studied. Also, the effect of in-situ correction of strength is highlighted.
Abstract
A methodology for determination of the intralaminar fracture toughness is presented, based on fitting discrete damage mechanics (DDM) model predictions to available experimental [...]
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Reliability design methodology for confined high pressure inflatable structures
E. Barbero, E. Sosa, X. Martinez, J. Gutierrez

Engineering Structures (2013). Vol. 51, pp. 1-9

Abstract
A design methodology for high pressure, inflatable structures is proposed. The inflatable structure may be partially confined inside large diameter conduits and tunnels. The design addresses the main structural requirements of the system, namely, fabric strength, geometric stability, and axial stability. The proposed design methodology is based on the concept of limit states. Load and resistance factors are identified for all the stochastic variables participating in the structural design equations. A formal methodology is used to estimate the load and resistance factors from known distributions of data for each of the stochastic variables. The concepts of basis values, coverage, and confidence are used along with the analytical treatment necessary to estimate the load and resistance factors. The analysis is applied to the cases of Normal, Log-normal, and Weibull distributions of data. Material characterization and data analysis are presented for fabric strength and friction coefficient between the inflatable and the confining conduit material. The system reliability is also evaluated.
Abstract
A design methodology for high pressure, inflatable structures is proposed. The inflatable structure may be partially confined inside large diameter conduits and tunnels. The [...]
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A discrete constitutive model for transverse and shear damage of symmetric laminates with arbitrary stacking sequence
E. Barbero, G. Sgambitterra, A. Adumitroaie, X. Martinez

Composite Structures (2011). Vol. 93 (2), pp. 1021-1030

Abstract
A damage constitutive model in conjunction with a 2-D finite element discretization is presented for predicting onset and evolution of matrix cracking and subsequent stiffness reduction of symmetric composite laminates with arbitrary stacking sequence subjected to membrane loads. The formulation uses laminae crack densities as the only state variables, with crack growth driven by both mechanical stress and residual stress due to thermal expansion. The formulation is based on fracture mechanics in terms of basic materials properties, lamina moduli, and critical strain energy release rates GIC and GIIC, only. No additional adjustable parameters are needed to predict the damage evolution. Spurious strain localization and mesh size dependence are intrinsically absent in this formulation. Thus, there is no need to define a characteristic length. Comparison of model results to experimental data is presented for various laminate stacking sequences. Prediction of crack initiation, evolution, and stiffness degradation compare very well to experimental data.
Abstract
A damage constitutive model in conjunction with a 2-D finite element discretization is presented for predicting onset and evolution of matrix cracking and [...]
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Analysis of the mock-up of a reactor containment building: comparison with experimental results
S. Jiménez, A. Cornejo Velázquez, L. Barbu, S. Oller, A. Barbat

Nuclear Engineering and Design (2020). Vol. 359, pp. 110454:1-110454:13

Abstract
The results of a predictive analysis of the mock-up of a reactor containment building, based on computer numerical simulation, are presented in this paper and compared with the results obtained in the context of the VeRCoRs project during the 2015–2018 experimental campaign. The analysis is based on the Serial-Parallel Rule of Mixtures theory applied on a three-dimensional finite element model of the building. All the singular parts of the structure (two buttresses, the main penetrations, the gusset, etc.) and the complete prestressing tendons system are included in the structural model. The non-linear constitutive models used to describe the behaviour of the concrete, reinforcing steel and the tendons are formulated. A description of the Serial-Parallel Rule of Mixtures algorithm is also given. The structural response computed for the successive pressure tests applied on the mock-up are compared with the monitored structural behaviour. Finally, results for a simulation considering the aging of the tendon system during 40 years are shown and discussed.
Abstract
The results of a predictive analysis of the mock-up of a reactor containment building, based on computer numerical simulation, are presented in this paper and compared with [...]
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High-cycle fatigue constitutive model and a load-advance strategy for the analysis of unidirectional fiber reinforced composites subjected to longitudinal loads
L. Barbu, S. Oller, X. Martinez, A. Barbat

Composite Structures (2019). Vol. 220, pp. 622-641

Abstract
A fatigue constitutive model valid for the composite constituent will be presented in this paper. The composite behaviour will be obtained by means of the serial/parallel mixing theory that is also used as a constitutive equation manager. The constitutive formulation is coupled with a load advancing strategy in order to reduce the computational cost of the numerical simulations. Validation of the constitutive formulation is done on pultruded glass fiber reinforced polymer profiles. Special emphasis is made on the comparison between the experimental and the numerical failure mode.
Abstract
A fatigue constitutive model valid for the composite constituent will be presented in this paper. The composite behaviour will be obtained by means of the serial/parallel [...]
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Methodology for the analysis of post-tensioned structures using a constitutive serial-parallel rule of mixtures: large scale non-linear analysis
L. Barbu, A. Cornejo Velázquez, X. Martinez, S. Oller, A. Barbat

Composite Structures (2019). Vol. 216, pp. 315-330

Abstract
The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finite-element (FE) model to simulate the constitutive behaviour of reinforced concrete structures strengthened with post-tensioned or pre-stressed tendons well beyond the elastic domain. The post-tensioned concrete is modelled as a composite material whose behaviour is described with the serial-parallel rule of mixtures (S-P RoM) (Rastellini et al., 2008; Martinez et al., 2008; Martinez et al., 2014 [3]) and the nonlinear behaviour of each component is accounted for by means of plasticity and damage models. 3D FE models were used, where the nonlinear material behaviour and geometrical analysis based on incremental-iterative load methods were adopted. Several examples are shown where the capabilities of the method on large scale structures are exhibited taking into account the self-weight, the post-tension load and different pressure loads. A new metric for computing the crack opening displacement inside a finite element is proposed.
Abstract
The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finite-element (FE) model to simulate the constitutive behaviour of reinforced [...]
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A FE 2 multi-scale implementation for modeling composite materials on distributed architectures
G. Giuntoli, J. Aguilar, M. Vázquez, S. Oller, G. Houzeaux

Coupled Systems Mechanics (2019). Vol. 8, pp. 99-109

Abstract
This work investigates the accuracy and performance of a FE2 multi-scale implementation used to predict the behavior of composite materials. The equations are formulated assuming the small deformations solid mechanics approach in non-linear material models with hardening plasticity. The uniform strain boundary conditions are applied for the macro-to-micro transitions. A parallel algorithm was implemented in order to solve large engineering problems. The scheme proposed takes advantage of the domain decomposition method at the macro-scale and the coupling between each subdomain with a micro-scale model. The precision of the method is validated with a composite material problem and scalability tests are performed for showing the efficiency.
Abstract
This work investigates the accuracy and performance of a FE2 multi-scale implementation used to predict the behavior of composite materials. The equations are formulated assuming [...]
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Damage assessment using modeling of large-scale confined masonry building
C. Escudero, S. Oller, X. Martinez, A. Barbat

Journal of Engineering Mechanics (2018). Vol. 144 (12), pp. 04018107-1/04018107-17

Abstract
The seismic behavior of a representative medium-rise building of Mexico City is evaluated using the capacity spectrum method. This method is widely used in the seismic assessment of buildings because it allows obtaining fragility curves which permit evaluating the ability of a building to resist earthquakes. A real full-height multistory model is proposed to test the capabilities of the algorithm exhibited. The model is outlined through structural drawings sized and structured in accordance with building code regulations for masonry structures in Mexico City. Computational requirements for the analysis of large structures are indicated in addition to improvements to a nonlinear computing code for better performance in terms of memory management and execution times. Finally, a comparison of obtained results and building code regulations is carried out, highlighting differences in the obtained results. The need to handle meshes with a high number of finite elements (FEs) led to development of a new layered finite element that can reproduce the nonlinear behavior of its constituent materials when there are out-of-plane stresses without having to introduce additional degrees of freedom. The proposed FE is compared with the standard FE, presenting different kinematics, and excellent results are obtained. This work emerges from the need to combine and improve existing technologies in the field of finite-element analysis. One such technology is the numerical simulation of the behavior of composite materials. Therefore, it was also necessary to develop a computing program capable of reading both finite-element meshes and patterns of fibers to calculate the information of the composite materials, such as volumetric participation and fiber’s orientation.
Abstract
The seismic behavior of a representative medium-rise building of Mexico City is evaluated using the capacity spectrum method. This method is widely used in the seismic assessment [...]
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On the analysis of non-homogeneous laminates using the refined zigzag theory
F. Flores, S. Oller, L. Nallim

Composite Structures (2018). Vol. 204, pp. 791-802

Abstract
This work shows possibilities and limitations of the refined zigzag theory (RZT) that has been used in different structural (beam, plate and shell) finite elements. The refined zigzag theory can deal with composite laminates, adding only one nodal degree of freedom per spatial dimension of the laminate, obtaining very good accuracy. It assumes that the in-plane displacements have a piece-wise linear shape across the thickness depending on the shear stiffness of each composite layer. This paper presents the main aspects of a beam/shell of revolution element used for the numerical simulations. The details of the refined zigzag theory are given also in order to discuss some limitations that occur when dealing with the non-linear phenomenon of delamination. Two examples are presented and discussed, including different inhomogeneities that show the limitations of the RZT for the treatment of partially delaminated beams
Abstract
This work shows possibilities and limitations of the refined zigzag theory (RZT) that has been used in different structural (beam, plate and shell) finite elements. The refined [...]
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Methodology for the analysis of post-tensioned structures using a constitutive serial-parallel rule of mixtures
A. Cornejo Velázquez, L. Barbu, C. Escudero, X. Martinez, S. Oller, A. Barbat

Computers and Structures (2018). Vol. 200, pp. 480-497

Abstract
The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finite-element (FE) model to simulate the constitutive behaviour of reinforced concrete structures strengthened with post-tensioned tendons taking into account the reduction of the pre-stressing stress due to the steel relaxation. The post-tensioned concrete is modelled as a composite material whose behaviour is described with the serial-parallel rule of mixtures (S/P RoM) (Rastellini et al, 2008; Martinez et al., 2008, 2014) whereas the stress relaxation of the steel is simulated using a viscoelastic model called Generalized Maxwell. A 3D FE model was used, where the nonlinear material behaviour and geometrical analysis based on incremental–iterative load methods were adopted. Validation by comparison with the analytic solution will be done for the case of a concrete beam with a linear steel tendon and for a parabolic pre-tensioned steel tendon embedded. Some viscoelastic cases are presented in order to perceive the behaviour of the Generalized Maxwell model. Several examples are shown where the capabilities of the method on large scale structures are exhibited.
Abstract
The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finite-element (FE) model to simulate the constitutive behaviour of reinforced [...]
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Outlook on ecologically improved composites for aviation interior and secondary structures
J. Bachmann, X. Yi, H. Gong, X. Martinez, G. Bugeda, S. Oller, K. Tserpes, E. Ramon, C. Paris, Z. Fang, Y. Li, Y. Liu, X. Liu, G. Xian, J. Tong, J. Wei, X. Zhang, J. Zhu

CEAS Aeronautical Journal (2018). Vol. 9, pp. 533-543

Abstract
Today, mainly man-made materials such as carbon and glass fibres are used to produce composite parts in aviation. Renewable materials such as natural fibres or bio-sourced resin systems have not found their way into aviation, yet. The project ECO-COMPASS aims to evaluate the potential applications of ecologically improved composite materials in the aviation sector in an international collaboration of Chinese and European partners. Natural fibres such as flax and ramie will be used for different types of reinforcements and sandwich cores. Furthermore, the bio-based epoxy resins to substitute bisphenol-A based epoxy resins in secondary structures are under investigation. Adapted material protection technologies to reduce environmental influence and to improve fire resistance are needed to fulfil the demanding safety requirements in aviation. Modelling and simulation of chosen eco-composites aims for an optimized use of materials while a life cycle assessment aims to prove the ecological advantages compared to synthetic state-of-the-art materials. In this paper, the status of selected ecologically improved materials will be presented with an outlook for potential application in interior and secondary structures.
Abstract
Today, mainly man-made materials such as carbon and glass fibres are used to produce composite parts in aviation. Renewable materials such as natural fibres or bio-sourced [...]
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Numerical study on the relevance of columns hidden failure modes in the seismic capacity of non-ductile RC Frames
B. Alfarah, F. López-Almansa, S. Oller

Journal of eathquake engineering (2018). (preprint) p. 1-18

Abstract
In simplified seismic structural analyses, not all the deterioration modes are adequately considered. This work discusses the relation among the hidden failure modes of columns of non-ductile reinforced concrete building frames and their global collapse mechanism. With this aim, a numerically efficient model is developed and implemented in OpenSEES. Two benchmark problems are analyzed with this model: the well-known Van Nuys Hotel and a prototype building designed for gravity loads only; in this last case, the results are compared with experiments on a one-third scale model. The obtained results confirm that simplified models grossly overestimate the building capacity.
Abstract
In simplified seismic structural analyses, not all the deterioration modes are adequately considered. This work discusses the relation among the hidden failure modes of columns [...]
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Multiscale computational homogenization: review and proposal of a new enhanced-first-order method
F. Otero, S. Oller, X. Martinez

Archives of Comp. Meths. Engng. (2018). Vol. 25 (2), pp. 479-505

Abstract
The continuous increase of computational capacity has encouraged the extensive use of multiscale techniques to simulate the material behaviour on several fields of knowledge. In solid mechanics, the multiscale approaches which consider the macro-scale deformation gradient to obtain the homogenized material behaviour from the micro-scale are called first-order computational homogenization. Following this idea, the second-order FE2 methods incorporate high-order gradients to improve the simulation accuracy. However, to capture the full advantages of these high-order framework the classical boundary value problem (BVP) at the macro-scale must be upgraded to high-order level, which complicates their numerical solution. With the purpose of obtaining the best of both methods i.e. first-order and second-order, in this work an enhanced-first-order computational homogenization is presented. The proposed approach preserves a classical BVP at the macro-scale level but taking into account the high-order gradient of the macro-scale in the micro-scale solution. The developed numerical examples show how the proposed method obtains the expected stress distribution at the micro-scale for states of structural bending loads. Nevertheless, the macro-scale results achieved are the same than the ones obtained with a first-order framework because both approaches share the same macro-scale BVP. This is a copy of the author 's final draft version of an article published in the Archives of computational methods in engineering.
Abstract
The continuous increase of computational capacity has encouraged the extensive use of multiscale techniques to simulate the material behaviour on several fields of knowledge. [...]
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On the feasibility of the computational modelling of the endoluminal vacuum-assisted closure of an oesophageal anastomotic leakage
E. Comellas, F. Bellomo, I. Rosales, L. Castilo, R. Sánchez, P. Turon, S. Oller

Royal Society Open Science (2018). Vol. 5 (3), pp. 1-23

Abstract
Endoluminal vacuum-assisted closure (E-VAC) is a promising therapy to treat anastomotic leakages of the oesophagus and bowel which are associated with high morbidity and mortality rates. An open-pore polyurethane foam is introduced into the leakage cavity and connected to a device that applies a suction pressure to accelerate the closure of the defect. Computational analysis of this healing process can advance our understanding of the biomechanical mechanisms at play. To this aim, we use a dual-stage finite-element analysis in which (i) the structural problem addresses the cavity reduction caused by the suction and (ii) a new constitutive formulation models tissue healing via permanent deformations coupled to a stiffness increase. The numerical implementation in an in-house code is described and a qualitative example illustrates the basic characteristics of the model. The computational model successfully reproduces the generic closure of an anastomotic leakage cavity, supporting the hypothesis that suction pressure promotes healing by means of the aforementioned mechanisms. However, the current framework needs to be enriched with empirical data to help advance device designs and treatment guidelines. Nonetheless, this conceptual study confirms that computational analysis can reproduce E-VAC of anastomotic leakages and establishes the bases for better understanding the mechanobiology of anastomotic defect healing.
Abstract
Endoluminal vacuum-assisted closure (E-VAC) is a promising therapy to treat anastomotic leakages of the oesophagus and bowel which are associated with high morbidity and mortality [...]
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RC structures cyclic behavior simulation with a model integrating plasticity, damage, and bond-slip
B. Alfarah, J. Murcia-Delso, F. Almansa, S. Oller

Earthquake engineering and structural dynamics (2018). (preprint) Vol. 47 (2), pp. 460-478

Abstract
The behavior of reinforced concrete structures under severe demands, as strong ground motions, is highly complex; this is mainly due to the complexity of concrete behavior and to the strong interaction between concrete and steel, with several coupled failure modes. On the other hand, given the increasing awareness and concern on the worldwide seismic risk, new developments have arisen in earthquake engineering; nonetheless, some developments are mainly based on simple analytical tools that are widely used, given their moderate computational cost. This research aims to provide a solid basis for validation and calibration of such developments by using computationally efficient continuum mechanics-based tools. Within this context, this paper presents a model for 3D simulation of cyclic behavior of RC structures. The model integrates a bond-slip model developed by one of the authors and the damage variable evolution methodology for concrete damage plastic model developed by some authors. In the integrated model, a new technique is derived for efficient 3D analysis of bond-slip of 2 or more crossing reinforcing bars in beam-column joints, slabs, footings, pile caps, and other similar members. The analysis is performed by implementing the bond-slip model in a user element subroutine of Abaqus and the damage variable evolution methodology in the original concrete damage plastic model in the package. Two laboratory experiments consisting of a column and a frame subjected to cyclic displacements up to failure are simulated with the proposed formulation.
Abstract
The behavior of reinforced concrete structures under severe demands, as strong ground motions, is highly complex; this is mainly due to the complexity of concrete behavior [...]
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Formulation of solid-shell finite elements with large displacements considering different transverse shear strains approximations
F. Flores, L. Nallim, S. Oller

Finite elements in analysis and design (2017). (Preprint) Vol. 130, pp. 39-52

Abstract
This work presents a general formulation and implementation in solid-shell elements of the refined zigzag theory and the trigonometric shear deformation theory in an unified way. The model thus conceived is aimed for use in the analysis, design and verification of structures made of composite materials, in which shear strains have a significant prevalence. The refined zigzag theory can deal with composite laminates economically, adding only two nodal degrees of freedom, with very good accuracy. It assumes that the in-plane displacements have a piece-wise linear shape across the thickness depending on the shear stiffness of each composite layer. The trigonometric theory assumes a cosine variation of the transverse shear strain. A modification of this theory is presented in this paper allowing its implementation with C0 approximation functions. Two existing elements are considered, an eight-node tri-linear hexahedron and a six-node triangular prism. Both elements use a modified right Cauchy-Green deformation tensor View the MathML source where five of its six components are linearly interpolated from values computed at the top and bottom surfaces of the element. The sixth component is computed at the element center and it is enhanced with an additional degree of freedom. This basic kinematic is improved with a hierarchical field of in-plane displacements expressed in convective coordinates. The objective of this approach is to have a simple and efficient finite element formulation to analyze composite laminates under large displacements and rotations but small elastic strains. The assumed natural strain technique is used to prevent transverse shear locking. An analytic through-the-thickness integration and one point integration on the shell plane is used requiring hourglass stabilization for the hexahedral element. Several examples are considered on the one hand to compare with analytical static solutions of plates, and on the other hand to observe natural frequencies, buckling loads and the non-linear large displacement behavior in double curved shells. The results obtained are in a very good agreement with the targets used.
Abstract
This work presents a general formulation and implementation in solid-shell elements of the refined zigzag theory and the trigonometric shear deformation theory in an unified [...]
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Designing experiments using digital fabrication in structural dynamics
R. Chacon, S. Oller

Journal of professional issues in engineering education and practice (2017). (Preprint) Vol. 143 (3), pp. 1-9

Abstract
In engineering, traditional approaches aimed at teaching concepts of dynamics to engineering students include the study of a dense yet sequential theoretical development of proofs and exercises. Structural dynamics are seldom taught experimentally in laboratories since these facilities should be provided with expensive equipment such as wave generators, data-acquisition systems, and heavily wired deployments with sensors. In this paper, the design of an experimental experience in the classroom based upon digital fabrication and modeling tools related to structural dynamics is presented. In particular, all experimental deployments are conceived with low-cost, open-source equipment. The hardware includes Arduino-based open-source electronics whereas the software is based upon object-oriented open-source codes for the development of physical simulations. The set of experiments and the physical simulations are reproducible and scalable in classroom-based environments.
Abstract
In engineering, traditional approaches aimed at teaching concepts of dynamics to engineering students include the study of a dense yet sequential theoretical development of [...]
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Multiscale thermo-mechanical analysis of multi-layered coatings in solar thermal applications
F. Montero-Chacón, S. Zaghi, R. Rossi, E. García-Pérez, I. Heras-Pérez, X. Martinez, S. Oller, M. Doblaré

Finite Elements in Analysis and Design (2017). (Preprint) Vol. 127, pp. 31-43

Abstract
Solar selective coatings can be multi-layered materials that optimize the solar absorption while reducing thermal radiation losses, granting the material long-term stability. These layers are deposited on structural materials (e.g., stainless steel, Inconel) in order to enhance the optical and thermal properties of the heat transfer system. However, interesting questions regarding their mechanical stability arise when operating at high temperatures. In this work, a full thermo-mechanical multiscale methodology is presented, covering the nano-, micro-, and macroscopic scales. In such methodology, fundamental material properties are determined by means of molecular dynamics simulations that are consequently implemented at the microstructural level by means of finite element analyses. On the other hand, the macroscale problem is solved while taking into account the effect of the microstructure via thermo-mechanical homogenization on a representative volume element (RVE). The methodology presented herein has been successfully implemented in a reference problem in concentrating solar power plants, namely the characterization of a carbon-based nanocomposite and the obtained results are in agreement with the expected theoretical values, demonstrating that it is now possible to apply successfully the concepts behind Integrated Computational Materials Engineering to design new coatings for complex realistic thermo-mechanical applications.
Abstract
Solar selective coatings can be multi-layered materials that optimize the solar absorption while reducing thermal radiation losses, granting the material long-term [...]
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MATERIALS AND METHODS
A. ducks, T. village, F. centre, A. randomly, S. Ghosh

Sumon Ghosh's personal collection (2020). 3

Abstract
This study was carried out to assess the status of household ducks and factors affects the producti vity of ducks in Companiganj upazila under Noakhali district of Bangladesh. For this study the information was collected by direct interview using a questionnaire from 30 households. The study showed that duck rearing was mostly lead by the women (80%) and their level of education varied from primary (43%) to higher secondary (7%). The average farm size was found to be six and they were mostly local ducks (90%). Marshy land s were common (67%) to the surroundings of the duck habitats. Most of the farmers depended on natural feed sources (60%) while some provided supplementary feed (40%) for their ducks. As a supplementary feed, 27% of the farmers used rice polish and17% used a mixture of rice polish and boil rice. Duck started their first laying at 6 months of age and the mean egg production per duck per year was 114 ±16 no. The diseases were more common during winter (63%) than other seasons of the year. It was found that good egg production (> mean production) was associated with the regular use of anthelmintics, supplementary feed, presence of marshy land and regular treatment. Zending was found to be good egg producer in marshy area than other three native breeds of ducks.
Abstract
This study was carried out to assess the status of household ducks and factors affects the producti vity of ducks in Companiganj upazila under Noakhali district of Bangladesh. [...]
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The Pattern of Highly Pathogenic Avian Influenza H5N1 Outbreaks in South Asia
S. Hossain, P. Ghosh, S. Ghosh, M. Hossain, C. Beard, M. and

(2019). The Pattern of Highly Pathogenic Avian Influenza H5N1 Outbreaks in South Asia

Abstract
ighly pathogenic avian influenza (HPAI) H5N1 has caused severe illnesses in poultry and in humans. More than 15,000 outbreaks in domestic birds from 2005 to 2018 and 861 human cases from 2003 to 2019 were reported across the world to OIE (Office International des Epizooties) and WHO (World Health Organization), respectively. We reviewed and summarized the spatial and temporal distribution of HPAI outbreaks in South Asia. During January 2006 to June 2019, a total of 1063 H5N1 outbreaks in birds and 12 human cases for H5N1 infection were reported to OIE and WHO, respectively. H5N1 outbreaks were detected more in the winter season than the summer season and PubMed to collect data from published articles using the following
Abstract
ighly pathogenic avian influenza (HPAI) H5N1 has caused severe illnesses in poultry and in humans. More than 15,000 outbreaks in domestic birds from 2005 to 2018 and 861 human [...]
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New draft 1
S. Ghosh

The Pattern of Highly Pathogenic Avian Influenza H5N1 Outbreaks in South Asia (2019). Chowdhury S, Hossain ME, Ghosh PK, Ghosh S, Hossain MB, Beard C, Rahman M, Rahman MZ. The Pattern of Highly Pathogenic Avian Influenza H5N1 Outbreaks in South Asia. Tropical Medicine and Infectious Disease. 2019 Dec;4(4):138.
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A new method of satellite radar altimeter waveform retracking based on waveform derivative
Z. Li, X. Liu, J. Guo, J. Yuan, Y. Niu, B. Ji

Rev. int. métodos numér. cálc. diseño ing. (2020). Vol. 36, (4), 50

Abstract
Waveform retracking for precise sea surface height (SSH) is an important method to improve the quality of satellite altimeter data. Combining the physical explanation of the function fitting and the high adaptability of empirical statistical methods, we effort to provide a comprehensive method for processing the waveforms over the open ocean and coastal area. The new retracking method that uses the maximum slope of leading edge to determine midpoint is proposed, the midpoint is determined by zero of second derivative of theoretical model. The unknown parameters are estimated based on the function fitting. Then combined with the advantage of empirical method, the leading edge midpoint is redetermined by interpolating the estimated midpoint on the measured waveform. The new method is validated by comparison with crossover discrepancies, geoid heights and tide gauges. The RMS of crossover discrepancy obtained by new method is 0.107 m, which is smaller than 0.192 m, 0.124 m, 0.121 m, 0.114 m, 0.112 m obtained by Ice-1,Threshold 50%, 5-β, MLE3 and MLE4 retrackers. The STD and improvement percent of the differences between SSHs obtained by new method and geoid heights are also better than the results of single kind of retracker. Comparison with tide gauge records, the STDs difference of height anomaly obtained by new method are 0.183 m and 0.269 m at different regions, which are smaller than 0.239 m, 0.220 m, 0.195 m and 0.303 m, 0.278 m, 0.272 m obtained by Ice-1, MLE4 and Threshold 50% retrackers, respectively. Therefore, the new method can recover more reliable SSH in the open ocean and coastal area.
Abstract
Waveform retracking for precise sea surface height (SSH) is an important method to improve the quality of satellite altimeter data. Combining the physical explanation of the [...]
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Multiscale computational first order homogenization of thick shells for the analysis of out-of-plane loaded masonry walls
M. Petracca, L. Pelà, S. Oller, G. Camata, E. Spacone

Comput. Methods Appl. Mech. Engrg., (2017). Vol. 315, pp. 273-301

Abstract
This work presents a multiscale method based on computational homogenization for the analysis of general heterogeneous thick shell structures, with special focus on periodic brick-masonry walls. The proposed method is designed for the analysis of shells whose micro-structure is heterogeneous in the in-plane directions, but initially homogeneous in the shell-thickness direction, a structural topology that can be found in single-leaf brick masonry walls. Under this assumption, this work proposes an efficient homogenization scheme where both the macro-scale and the micro-scale are described by the same shell theory. The proposed method is then applied to the analysis of out-of-plane loaded brick-masonry walls, and compared to experimental and micro-modeling results.
Abstract
This work presents a multiscale method based on computational homogenization for the analysis of general heterogeneous thick shell structures, with special focus on periodic [...]
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New methodology for calculating damage variables evolution in Plastic Damage Model for RC structures
B. Alfarah, F. Almansa, S. Oller

Engineering Structures (2016). (preprint) Vol. 132 (1 February), pp. 70-86

Abstract
This article presents the formulation of an enriched macro finite element based on the trigonometric shear deformation theory for the static analysis of symmetrically laminated composite plates. Shear correction factor is not required because this theory accounts for tangential stress-free boundary conditions on the plate boundary surfaces. The macro element is obtained using the principle of virtual work and Gram-Schmidt orthogonal polynomials as enrichment functions. The implementation of the obtained algorithm is simple and efficient, and allows studying general quadrilateral plates with a single macro element. Several examples are presented to show the capability and applicability of the developed formulation.
Abstract
This article presents the formulation of an enriched macro finite element based on the trigonometric shear deformation theory for the static analysis of symmetrically laminated [...]
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An enriched macro finite element for the static analysis of thick general quadrilateral laminated composite plates
R. Rango, L. Nallim, S. Oller

Mechanics of Advanced Materials and Structures (2016). Vol. 23 (10), pp. 1197-1206

Abstract
This article presents the formulation of an enriched macro finite element based on the trigonometric shear deformation theory for the static analysis of symmetrically laminated composite plates. Shear correction factor is not required because this theory accounts for tangential stress-free boundary conditions on the plate boundary surfaces. The macro element is obtained using the principle of virtual work and Gram-Schmidt orthogonal polynomials as enrichment functions. The implementation of the obtained algorithm is simple and efficient, and allows studying general quadrilateral plates with a single macro element. Several examples are presented to show the capability and applicability of the developed formulation.
Abstract
This article presents the formulation of an enriched macro finite element based on the trigonometric shear deformation theory for the static analysis of symmetrically laminated [...]
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Fluid dynamic design of an axial rotor for hydrokinetic riverbed turbine-improvement introduced by a high lift foil profile
S. Oller, L. Nallim

Environmental progress & sustainable energy (2016). (Preprint) Vol. 35 (4), pp. 1198-1206

Abstract
The main objective of this article is to achieve a very high lift rotor to take the maximum advantage of the kinetic energy of a slow velocity water flow, which belongs to a lowland river type. Low speed flux and lack of depth are the main obstacles in hydrokinetic operation. The use of a high lift aerodynamic profile and the gain of the rotor number of blades serve to accomplish the task. This work presents the fluid dynamic design for an axial hydrokinetic turbine rotor, studied in a three-dimensional (3D) numerical simulation by means of Computational Fluid Dynamics (CFD). The use of CFD techniques avoids some physical model assays. For the hydrokinetic turbine rotor design, first a one-dimensional (1D) theoretical design was carried out, starting with the selection of a suitable airfoil profile to create the hydrofoil blade. Then, the 3D rotor geometry was defined and studied carefully by means of CFD, to check its hydrodynamic behavior, that is, lift and drag, streamline velocities and pressure fields. The CFD results were obtained using an open CFD code (Kratos) This is the peer reviewed version of the following article: [Oller, S. A., Nallim, L. G. and Oller, S. (2016), Fluid dynamic design of an axial rotor for hydrokinetic riverbed turbine-improvement introduced by a high lift foil profile
Abstract
The main objective of this article is to achieve a very high lift rotor to take the maximum advantage of the kinetic energy of a slow velocity water flow, which belongs to [...]
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The usability of the Selig S1223 profile airfoil as a high lift hydrofoil for hydrokinetic application
S. Oller, L. Nallim

Journal of Applied Fluid Mechanics (2016). (preprint) Vol. 9 (2), pp. 537-542

Abstract
This work presents a numerical analysis of the ability of the high lift airfoil profile Selig S1223 for working as hydrofoil under water conditions. The geometry of the hydrofoil blade is designed through a suitable airfoil profile and then studied carefully by means of Computational Fluid Dynamics (CFD) in order to check its hydrodynamic behavior, i.e., including lift and drag analysis, and determinations of streamlines velocities and pressures fields. Finally conclusions on the use of this profile in a possible application for hydrokinetic turbine blades are detailed.
Abstract
This work presents a numerical analysis of the ability of the high lift airfoil profile Selig S1223 for working as hydrofoil under water conditions. The geometry of the hydrofoil [...]
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A homeostatic-driven turnover remodelling constitutive model for healing in soft tissues
E. Comellas, T. Gasser, F. Bellomo, S. Oller

Journal of the Royal Society Interface (2016). (preprint) Vol. 13 (116), pp. 1-14

Abstract
All rights reserved. Remodelling of soft biological tissue is characterized by interacting biochemical and biomechanical events, which change the tissue's microstructure, and, consequently, its macroscopic mechanical properties. Remodelling is a well-defined stage of the healing process, and aims at recovering or repairing the injured extracellular matrix. Like other physiological processes, remodelling is thought to be driven by homeostasis, i.e. it tends to re-establish the properties of the uninjured tissue. However, homeostasis may never be reached, such that remodelling may also appear as a continuous pathological transformation of diseased tissues during aneurysm expansion, for example. A simple constitutive model for soft biological tissues that regards remodelling as homeostatic-driven turnover is developed. Specifically, the recoverable effective tissue damage, whose rate is the sum of a mechanical damage rate and a healing rate, serves as a scalar internal thermodynamic variable. In order to integrate the biochemical and biomechanical aspects of remodelling, the healing rate is, on the one hand, driven by mechanical stimuli, but, on the other hand, subjected to simple metabolic constraints. The proposed model is formulated in accordance with continuum damage mechanics within an open-system thermodynamics framework. The numerical implementation in an in-house finite-element code is described, particularized for Ogden hyperelasticity. Numerical examples illustrate the basic constitutive characteristics of the model and demonstrate its potential in representing aspects of remodelling of soft tissues. Simulation results are verified for their plausibility, but also validated against reported experimental data. Remodelling of soft biological tissue is characterized by interacting biochemical and biomechanical events, which change the tissue's microstructure, and, consequently, its macroscopic mechanical properties. Remodelling is a well-defined stage of the healing process, and aims at recovering or repairing the injured extracellular matrix. Like other physiological processes, remodelling is thought to be driven by homeostasis, i.e. it tends to re-establish the properties of the uninjured tissue. However, homeostasis may never be reached, such that remodelling may also appear as a continuous pathological transformation of diseased tissues during aneurysm expansion, for example. A simple constitutive model for soft biological tissues that regards remodelling as homeostatic-driven turnover is developed. Specifically, the recoverable effective tissue damage, whose rate is the sum of a mechanical damage rate and a healing rate, serves as a scalar internal thermodynamic variable. In order to integrate the biochemical and biomechanical aspects of remodelling, the healing rate is, on the one hand, driven by mechanical stimuli, but, on the other hand, subjected to simple metabolic constraints. The proposed model is formulated in accordance with continuum damage mechanics within an open-system thermodynamics framework. The numerical implementation in an in-house finite-element code is described, particularized for Ogden hyperelasticity. Numerical examples illustrate the basic constitutive characteristics of the model and demonstrate its potential in representing aspects of remodelling of soft tissues. Simulation results are verified for their plausibility, but also validated against reported experimental data.
Abstract
All rights reserved. Remodelling of soft biological tissue is characterized by interacting biochemical and biomechanical events, which change the tissue's microstructure, [...]
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A generalized finite-strain damage model for quasi-incompressible hyperelasticity using hybrid formulation
E. Comellas, F. Bellomo, S. Oller

Int. J. Numer. Meth. Engng. (2016). (preprint) Vol. 105 (10), pp. 781-800

Abstract
A new generalized damage model for quasi‐incompressible hyperelasticity in a total Lagrangian finite‐strain framework is presented. A Kachanov‐like reduction factor (1 − D) is applied on the deviatoric part of the hyperelastic constitutive model. Linear and exponential softening are defined as damage evolution laws, both describable in terms of only two material parameters. The model is formulated following continuum damage mechanics theory such that it can be particularized for any hyperelastic model based on the volumetric–isochoric split of the Helmholtz free energy. However, in the present work, it has been implemented in an in‐house finite element code for neo‐Hooke and Ogden hyperelasticity. The details of the hybrid formulation used are also described. A couple of three‐dimensional examples are presented to illustrate the main characteristics of the damage model. The results obtained reproduce a wide range of softening behaviors, highlighting the versatility of the formulation proposed. The damage formulation has been developed to be used in conjunction with mixing theory in order to model the behavior of fibered biological tissues. As an example, the markedly different behaviors of the fundamental components of the rectus sheath were reproduced using the damage model, obtaining excellent correlation with the experimental results from literature.
Abstract
A new generalized damage model for quasi‐incompressible hyperelasticity in a total Lagrangian finite‐strain framework is presented. A Kachanov‐like reduction factor [...]
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Numerical validation of the incremental launching method of a steel bridge through a small-scale experimental study
R. Chacon, N. Uribe, S. Oller

Experimental Techniques (2016). (preprint) Vol. 40 (1), pp. 333-346

Abstract
The final publication is available at Springer via http://dx.doi.org/10.1007/s40799-016-0037-5 This article presents an experimental and a numerical study of an incremental launching process of a steel bridge. The former is deployed in a scale-reduced laboratory,whereas the latter is performed using the finite elementmethod. The numerical simulation is based upon realistic transient boundary conditions and accurately reproduces the elastic response of the steel bridge during launching. This numerical approach is validated experimentally with the scale-reduced test performed at the laboratory. The properly validated numerical model is subsequently systematically employed as a simulation tool of the process. The proposed simulation protocol might be useful for design and monitoring purposes of steel bridges to be launched. Results concerning strains, stresses, and displacements might be inferred from the model and thus compared to field measurements obtained in situ. The conditions presented at the end of the article are potentially useful for researchers and practice engineers alike.
Abstract
The final publication is available at Springer via http://dx.doi.org/10.1007/s40799-016-0037-5 This article presents an experimental and a numerical study of an incremental [...]
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Micro-mechanical approach for the vibration analysis of CFRP laminates under impact-induced damage
M. Perez, S. Oller, C. Felippa, L. Gil

Composites Part B: Enginnering (2015). (preprint) Vol. 83, pp. 306-316

Abstract
This paper deals with modelling the effect of low-velocity impact damage upon the vibration response of CFRP laminates through a micro-mechanical description of the induced internal damage. The serial-parallel (SP) continuum approach is used to estimate the map of induced internal damage by considering the micro-structural interaction between the composite constituents and modifying their constitutive performance through a continuum damage formulation. An eigenvalue analysis is then done to determine the modal response of impacted laminates. The validity of the modelling approach to successfully reproduce the vibration response of impacted coupons is assessed through a comparison with an experimental test series conducted on a set of 48 CFRP laminated coupons. The results confirm the ability of the described approach in comparison to competing ones used to reproduce the experimentally observed behaviour.
Abstract
This paper deals with modelling the effect of low-velocity impact damage upon the vibration response of CFRP laminates through a micro-mechanical description of the induced [...]
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Regularization of first order computational homogenization for multiscale analysis of masonry structures
M. Petracca, L. Pelà, S. Oller, G. Camata, E. Spacone

Computational Mechanics (2015). (preprint) Vol. 57 (2), pp. 257-276

Abstract
The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-015-1230-6 This paper investigates the possibility of using classical first order computational homogenization together with a simple regularization procedure based on the fracture energy of the micro-scale-constituents. A generalized geometrical characteristic length takes into account the size of the macro-scale element as well as the size of the RVE (and its constituents). The proposed regularization ensures objectivity of the dissipated energy at the macro-scale, with respect to the size of the FE in both scales and with respect to the size of the RVE. The proposed method is first validated against benchmark examples, and finally applied to the numerical simulation of experimental tests on in-plane loaded shear walls made of periodic masonry.
Abstract
The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-015-1230-6 This paper investigates the possibility of using classical first order computational [...]
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An efficient multi-scale method for non-linear analysis of composite structures
F. Otero, X. Martinez, S. Oller, R. Salomon, R. Omar

Composite Structures (2015). (preprint) Vol. 131, pp. 707-719

Abstract
The use of multi-scale procedures is encouraged by the continuous increase of computational capacity, but it is still a challenge performing a non-linear analysis of real composite structures without the aid of large computers. This work proposes a strategy to conduct non-linear multi-scale analysis in an efficient way. The proposed method considers that in a large structure, in general, material non-linear processes only take place in a localized region (or in a reduced number of finite elements, if a FE method is used). The strategy determines the elements that require a non-linear analysis defining of a non-linear activation function that accounts for the failure of the most critical point in the microstructure. The procedure conserves the dissipated energy through the scales, being mesh independent as the mesh objectivity concept is extended to the microstructure. The validity of the strategy proposed is proved with the analysis of academic examples showing not only the mesh independency but also the reduction of computational cost. Finally, an industrial composite component is solved using a standard computer, showing that the proposed strategy is capable of reducing the computational cost from 32 days and 14 hours (required by a classical multi-scale method) to less than 12 hours.
Abstract
The use of multi-scale procedures is encouraged by the continuous increase of computational capacity, but it is still a challenge performing a non-linear analysis of real [...]
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High cycle fatigue simulation: A new stepwise load-advancing strategy
L. Barbu, S. Oller, X. Martinez, A. Barbat

Engineering Structures (2015). (preprint) Vol. 97, pp. 118-129

Abstract
A stepwise load-advancing strategy for cyclic loading will be presented in this paper that yields convergence in reasonable computational time for highly nonlinear behaviour occurring past the S–N curve. The algorithm is also effective when dealing with combinations of cyclical loads. The strategy is coupled to a continuum damage model for mechanical fatigue analysis. A brief overview of the constitutive model is also presented although it is not the main focus of this work. The capabilities of the proposed procedure are shown in two numerical examples. The model is validated by comparison to experimental results.
Abstract
A stepwise load-advancing strategy for cyclic loading will be presented in this paper that yields convergence in reasonable computational time for highly nonlinear behaviour [...]
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Numerical homogenization for composite materials analysis: comparison with other micro mechanical formulations
F. Otero, S. Oller, X. Martinez, R. Salomon

Composite Structures (2015). (preprint) Vol. 122, pp. 405-416

Abstract
This work presents a two-scale homogenization procedure to analyze three dimension composite structures by FEM. The theory implemented is compared with other micro-structural formulations: micro models and serial parallel mixing theory, in terms of result accuracy and computational cost. The comparison shows that for linear analysis, the homogenization is an excellent alternative to the other formulations. Its computational cost is substantially lower than the one required by the micro-model and it is able to capture several micro-structural phenomena that it is not automatically recorded by the serial parallel methodology. It will also be shown that the extension of the proposed theory to the non-linear range stills represents a challenge. The major limitation is its computational cost because it requires to solve the sub scale at each gauss point and load step. However, the comparison shows that this cost is in terms of CPU time but not in terms of memory. Based on the results obtained, it can be concluded that the homogenization is an excellent alternative for simulation of materials with complex micro structures. The method is also very promising for non linear simulations, when coupled with a threshold criteria to decide whether it is necessary to analyze the RVE or not.
Abstract
This work presents a two-scale homogenization procedure to analyze three dimension composite structures by FEM. The theory implemented is compared with other micro-structural [...]
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Optimization method for the determination of material parameters in damaged composite structures
E. Comellas, S. P, S. Oller, S. Botello

Composite Structures (2015). (preprint) Vol. 122, pp. 417-424

Abstract
An optimization method to identify the material parameters of composite structures using an inverse method is proposed. This methodology compares experimental results with their numerical reproduction using the finite element method in order to obtain an estimation of the error between the results. This error estimation is then used by an evolutionary optimizer to determine, in an iterative process, the value of the material parameters which result in the best numerical fit. The novelty of the method is in the coupling between the simple genetic algorithm and the mixing theory used to numerically reproduce the composite behavior. The methodology proposed has been validated through a simple example which illustrates the exploitability of the method in relation to the modeling of damaged composite structures.
Abstract
An optimization method to identify the material parameters of composite structures using an inverse method is proposed. This methodology compares experimental results with [...]
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BeOpen Leaflet
BeOpen project (2020). 1
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