Documents published in 2020 : Scipedia

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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Formulation of enriched macro elements using trigonometric shear deformation theory for free vibration analysis of symmetric laminated composite plate assemblies
R. Rango, L. Nallim, S. Oller

Composite Structures (2015). Vol. 119, pp. 38-49

Abstract
The formulation of an enriched macro element suitable to analyze the free vibration response of composite plate assemblies is presented in this article. Based on the Trigonometric Shear Deformation Theory (TSDT) and the use of Gram–Schmidt orthogonal polynomials as enrichment functions a finite macro element is developed. In the TSDT framework, shear stresses are vanished at the top and bottom surfaces of the plates and shear correction factors are no longer required. The Principle of Virtual Work is applied to derive the governing equations of motion. A special connectivity matrix is obtained; so that hierarchically enriched global stiffness matrix and mass matrix of general laminated plate structures are derived, allowing to study generally coplanar plate assemblies by combining two or more macro elements. This procedure gives a matrix-eigenvalue problem that can be solved with optimum efficiency. Results of free vibration analysis for symmetric laminated plates of different thickness ratios, geometrical planform shapes and boundary conditions are presented. The accuracy of the formulation is ensured by comparing some numerical examples with those available in the literature.
Abstract
The formulation of an enriched macro element suitable to analyze the free vibration response of composite plate assemblies is presented in this article. Based on the Trigonometric [...]
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A finite points method approach for strain localization using the gradient plasticity formulation
L. Pérez, A. Campos, S. Lascano, S. Oller, A. Rodríguez-Ferran

mathematical problems in engineering (2014). Vol. 2014, p. 782079-1-782079-12

Abstract
The softening elastoplastic models present an unsuitable behavior after reaching the yield strength: unbounded strain localization. Because of the material instability, which is reflected in the loss of ellipticity of the governing partial differential equations, the solution depends on the discretization. The present work proposes to solve this dependency using the meshless Finite Points Method. This meshfree spatial discretization technique allows enriching the governing equations using gradient’s plasticity and introducing an internal length scale parameter at the material model in order to objectify the solution.
Abstract
The softening elastoplastic models present an unsuitable behavior after reaching the yield strength: unbounded strain localization. Because of the material instability, which [...]
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Comparative experimental analysis of the effect caused by artificial and real induced damage in composite laminates
M. Perez, L. Gil, M. Sánchez, S. Oller

Composite Structures (2014). (preprint) Vol. 112, pp. 169-178

Abstract
This paper presents the results of an extensive experimental campaign aimed to examine the effect upon the vibration response and on the residual load-bearing capacity caused by both: isolated artificially induced interlaminar damage and low-velocity impact induced damage in composite laminates. The experimental programme included modal testing, drop-weight impact testing, ultrasonic inspection, transverse quasi-static loading testing and compression testing conducted on a set of 72 carbon fibre-reinforced composite laminated coupons. Both types of damage caused measurable changes in laminate performance, however marked divergent trends were observed. The results allowed for conclusions to be drawn regarding the adequacy of the artificial damage approach and highlighted the importance and role of other forms of degradation upon damage tolerance of laminated composites containing damage.
Abstract
This paper presents the results of an extensive experimental campaign aimed to examine the effect upon the vibration response and on the residual load-bearing capacity caused [...]
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Impact damage identification in composite laminates using vibration testing
M. Perez, L. Gil, S. Oller

Composite Structures (2014). Vol. 108, pp. 267-276

Abstract
Due to the problems arising from impact damage in composite laminates, there is a need to develop fast, accurate, cost-effective and non-destructive testing methods to identify this type of damage at an early stage and thus enhance the service life of composite structures. This paper presents the results of an extensive experimental campaign conducted to investigate the feasibility of using vibration-based methods to identify damages sustained by composite laminates due to low-velocity impacts. The experimental programme included an evaluation of impact damage resistance and tolerance according to ASTM test methods, characterisation of induced damage by ultrasonic testing and quantification of the effects on the vibration response. The damage identification involved the detection, localisation, quantification and estimation of the remaining bearing capacity. Four damage indicators based on modal parameters were assessed by comparing pristine and damaged states. The results allowed for conclusions to be drawn regarding the capability and suitability of each damage indicator, including its ability to detect impact-induced damage, its precision in determining the location of damage, its sensitivity regarding damage extent and pertinent correlations with residual bearing capacity.
Abstract
Due to the problems arising from impact damage in composite laminates, there is a need to develop fast, accurate, cost-effective and non-destructive testing methods to identify [...]
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An Integrated Procedure for the Structural Design of a Composite Rotor-Hydrofoil of a Water Current Turbine (WCT)
S. Oller, L. Nallim

Applied Composite Materials (2013). Vol. 20 (6), pp. 1273-1288

Abstract
This paper shows an integrated structural design optimization of a composite rotor-hydrofoil of a water current turbine by means the finite elements method (FEM), using a Serial/Parallel mixing theory (Rastellini et al. Comput. Struct. 86:879–896, 2008, Martinez et al., 2007, Martinez and Oller Arch. Comput. Methods. 16(4):357–397, 2009, Martinez et al. Compos. Part B Eng. 42(2011):134–144, 2010) coupled with a fluid-dynamic formulation and multi-objective optimization algorithm (Gen and Cheng 1997, Lee et al. Compos. Struct. 99:181–192, 2013, Lee et al. Compos. Struct. 94(3):1087–1096, 2012). The composite hydrofoil of the turbine rotor has been design using a reinforced laminate composites, taking into account the optimization of the carbon fiber orientation to obtain the maximum strength and lower rotational-inertia. Also, these results have been compared with a steel hydrofoil remarking the different performance on both structures. The mechanical and geometrical parameters involved in the design of this fiber-reinforced composite material are the fiber orientation, number of layers, stacking sequence and laminate thickness. Water pressure in the rotor of the turbine is obtained from a coupled fluid-dynamic simulation (CFD), whose detail can be found in the reference Oller et al. (2012). The main purpose of this paper is to achieve a very low inertia rotor minimizing the start-stop effect, because it is applied in axial water flow turbine currently in design by the authors, in which is important to take the maximum advantage of the kinetic energy. The FEM simulation codes are engineered by CIMNE (International Center for Numerical Method in Engineering, Barcelona, Spain), COMPack for the solids problem application, KRATOS for fluid dynamic application and RMOP for the structural optimization. To validate the procedure here presented, many turbine rotors made of composite materials are analyzed and three of them are compared with the steel one.
Abstract
This paper shows an integrated structural design optimization of a composite rotor-hydrofoil of a water current turbine by means the finite elements method (FEM), using a [...]
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Impact damage prediction in carbon fiber-reinforced laminated composite using the matrix-reinforced mixing theory
M. Perez, X. Martinez, S. Oller, L. Gil, F. Rastellini, F. Flores

Composite Structures (2013). Vol. 104, pp. 239-248

Abstract
The impact damage tolerance of fiber-reinforced laminated composite materials is a source of concern, mainly due to internal induced damage which causes large reductions on the strength and stability of the structure. This paper presents a procedure based on a finite element formulation that can be used to perform numerical predictions of the impact induced internal damage in composite laminates. The procedure is based on simulating the composite performance using a micro-mechanical approach named matrix-reinforced mixing theory, a simplified version of the serial/parallel mixing theory that does not require neither the iterative procedure nor the calculation of the tangent stiffness tensor. The numerical formulation uses continuum mechanics to simulate the phenomenon of initiation and propagation of interlaminar damage with no need to formulate interface elements, resulting in a computationally less demanding formulation. To demonstrate the capability of numerical procedure when applied to a low-velocity impact problem, numerical results are compared with the experimental ones obtained in a test campaign performed on 44 laminates specimens subjected to an out-of-plane and concentrated impact event, according to ASTM test method. Results are in good agreement with experimental data in terms of delamination onset and the internal spatial distribution of induced damage.
Abstract
The impact damage tolerance of fiber-reinforced laminated composite materials is a source of concern, mainly due to internal induced damage which causes large reductions [...]
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Analytical and numerical analysis of human dental occlusal contact
F. Bastos, E. Casas, S. Oller

Computer Methods in Biomechanics and Biomedical Engineering (2013). Vol. 16 (5), pp. 495-503

Abstract
The knowledge of contact forces in teeth surfaces during mastication or para-functional movements can help to understand processes related to friction and wear of human dental enamel. The development of a numerical model for analysis of the occlusal contact between two antagonistic teeth is proposed, which includes three basic steps: the characterisation of the surface roughness, its homogenisation using an assumed distribution function and the numerical determination of the resulting forces. Finite element strain results for the main different asperities are statistically combined, deriving the predicted macroscopic behaviour of the interface. Axisymmetric and 3D numerical models with an elasto-plastic constitutive law are used to simulate micro-indentations and micro-contacts, respectively. The contact is allowed to occur locally in planes not necessarily parallel to the surface's mean plane, a problem for which there is no analytical solution. The three identified parameters, homogenised surface hardness (3.68 GPa), surface yield stress (3.08 GPa) and static friction coefficient (0.23), agree with the experimental values reported in the literature.
Abstract
The knowledge of contact forces in teeth surfaces during mastication or para-functional movements can help to understand processes related to friction and wear of human dental [...]
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An inverse approach for the mechanical characterisation of vascular tissues via a generalised rule of mixtures
F. Bellomo, S. Oller, L. Nallim

Computer Methods in Biomechanics and Biomedical Engineering (2012). Vol. 15 (12), pp. 1257-1262

Abstract
Mechanical factors such as stresses and strains play a major role in the growth and remodelling of soft biological tissues. The main constituents of tissue undergo different processes reacting to mechanical stimulus. Thereby, the characterisation of growth and remodelling requires an accurate estimation of the stresses and strains of their main components. Many soft tissues can be considered as composite materials and can be analysed using an appropriate rule of mixtures. Particularly, arterial tissue can be modelled as an isotropic soft matrix reinforced with preferentially oriented collagen fibres. An inverse approach to obtain the mechanical characterisation of each main component is proposed in this work. The procedure is based on a rule of mixtures raised in a finite deformation framework and generalised to include kinematics and compatibility equations for serial–parallel behaviour. This methodology allows obtaining the stress–strain relationship of the components fitting experimental data.
Abstract
Mechanical factors such as stresses and strains play a major role in the growth and remodelling of soft biological tissues. The main constituents of tissue undergo different [...]
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Study and prediction of the mechanical performance of a nanotube-reinforced composite
F. Otero, X. Martinez, S. Oller, O. Salomón

Composite Structures (2012). Vol. 94 (9), pp. 2920-2930

Abstract
Carbon nanotubes (CNTs) have been regarded as ideal reinforcements for high-performance composites. A key factor for the reinforcement efficiency is the interface bonding between the CNTs and the matrix. This paper presents a new constitutive model to predict the mechanical performance of composites made with CNTs. The model takes into account explicitly the performance of the interface between the matrix and the CNTs. The formulation developed is based in the mixing theory. It divides the composite in matrix and in a new material result of coupling the CNTs with the interface. The relation defined between interface and CNTs assumes that the load is transferred to the nanotubes along their ends and that in the central part the CNTs can develop their full strength. The composite non-linear behavior results from the non-linearities of its constituents. In case of interface damage, it also becomes non-linear the law defined to couple the interface with the CNTs. After describing the formulation, it is validated studying the elastic response of several composites made with different types of CNTs reinforcements. The non-linear behavior provided by the formulation is also studied. In both cases the numerical results are compared with experimental data showing good agreement.
Abstract
Carbon nanotubes (CNTs) have been regarded as ideal reinforcements for high-performance composites. A key factor for the reinforcement efficiency is the interface bonding [...]
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A constitutive model for tissue adaptation: Necrosis and stress driven growth
F. Bellomo, F. Armero, L. Nallim, S. Oller

Mechanics Research Communications (2012). Vol. 42 (SI), pp. 51-59

Abstract
This paper presents a general constitutive model for tissue stress driven growth and necrotic remodeling. The general theoretical framework is given by a kinematics formulation in large strain. The model allows the analysis of tissue behaviour considering the coupling of biological and mechanical fields, through the implementation of an internal variable that represents the bioavailability, together with the growth induced by mechanical stimuli. To take into account the tissue necrosis phenomenon a reinterpretation of the classical theory of mixtures is proposed. The proposed formulation is based on the consideration of two components, normal tissue and necrotic tissue, each one with its own volumetric participation, which is treated in an evolutive way, allowing simulating the phenomena of ischemia. This article also presents a brief description of the numerical implementation of the model as well as the obtained results, which shows the process of necrosis of part of the tissue, its influence on the surrounding healthy tissue, and the interaction between the nutrients availability and the stress driven growth and necrotic remodeling process.
Abstract
This paper presents a general constitutive model for tissue stress driven growth and necrotic remodeling. The general theoretical framework is given by a kinematics formulation [...]
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Dynamical analysis of long fiber-reinforced laminated plates with elastically restrained edges
F. Bellomo, R. Quinteros, S. Oller, L. Nallim

Advances in Acoustic and Vibration (2012). Vol. 2012, pp. 1-16

Abstract
This paper presents a variational formulation for the free vibration analysis of unsymmetrically laminated composite plates with elastically restrained edges. The study includes a micromechanics approach that allows starting the study considering each layer as constituted by long unidirectional fibers in a continuous matrix. The Mori-Tanaka method is used to predict the mechanical properties of each lamina as a function of the elastic properties of the components and of the fiber volume fraction. The resulting mechanical properties for each lamina are included in a general Ritz formulation developed to analyze the free vibration response of thick laminated anisotropic plates resting on elastic supports. Comprehensive numerical examples are computed to validate the present method, and the effects of the different mechanical and geometrical parameters on the dynamical behavior of different laminated plates are shown. New results for general unsymmetrical laminates with elastically restrained edges are also presented. The analytical approximate solution obtained in this paper can also be useful as a basis to deal with optimization problems under, for instance, frequency constraints.
Abstract
This paper presents a variational formulation for the free vibration analysis of unsymmetrically laminated composite plates with elastically restrained edges. The study includes [...]
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Nonlinear homogenization techniques to solve masonry structures problems
R. Quinteros, S. Oller, L. Nallim

Composite Structures (2012). Vol 94 (2), pp. 724-730

Abstract
The behaviour of masonry material subjected to different in-plane loading combination is studied in this work. The masonry is considered as a periodic composite material composed by a regular distribution of brick and mortar and it is analyzed using a homogenization technique. The mechanical properties of the masonry, as an orthotropic homogeneous material, depend on the geometrical and mechanical properties of the components based on the study of the equilibrium and compatibility of a basic cell. The masonry is a frictional material and its behaviour depends on the loading direction, for these reasons, a unilateral damage model is chosen for the analysis. This model describes the behaviour of brittle materials subjected to tension–compression cyclic loads based on the introduction of two damage variables and it assumes that the damage is due to the beginning and growth of cracks only in the mortar joints. It is considered that the bricks have a linear elastic constitutive relationship. Numerical applications are performed with a nonlinear finite element code in order to test the proposed procedure by comparing the results with those available in the literature and also with experimental data.
Abstract
The behaviour of masonry material subjected to different in-plane loading combination is studied in this work. The masonry is considered as a periodic composite material composed [...]
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Dimensionado sísmico de edificios porticados de hormigón armado mediante factores de amplificación con base en energía
J. Vielma-Perez, H. Barbat, S. Oller

Hormigón y Acero (2012). Vol. 63 (263), pp. 83-96

Abstract
El proyecto sismorresistente de estructuras actual se realiza mediante una serie de prescripciones normativas que persiguen garantizar su adecuado comportamiento. Los procedimientos actuales de análisis se realizan utilizando el comportamiento elástico, aplicando los factores de reducción de respuesta para obtener fuerzas sísmicas equivalentes, representativas del comportamiento inelástico que pueden alcanzar las estructuras al ser sometidas a la acción de sismos fuertes. A partir de los resultados del análisis elástico se obtienen los desplazamientos inelásticos, amplificados mediante factores que son función de los factores de reducción; sin embargo, se ha observado una amplia variación en los valores de los factores de amplificación prescritos en las normas a nivel mundial, por lo que se justifica profundizar en el estudio de dichos factores. En este trabajo se presenta un procedimiento de dimensionado sísmico con base en la respuesta no lineal. El procedimiento es aplicado a un conjunto de edificios regulares de hormigón armado de diferentes alturas, proyectados para niveles altos de amenaza sísmica y es evaluado aplicando análisis dinámico no lineal para tres Estados Límite, correlacionado con tres umbrales de daño que se definen a través de las derivas de planta. Los resultados demuestran que el procedimiento es adecuado para realizar el dimensionado sísmico de edificios, proporcionando al proyectista criterios de evaluación más cónsonos con las características de los edificios y de la amenaza sísmica.
Abstract
El proyecto sismorresistente de estructuras actual se realiza mediante una serie de prescripciones normativas que persiguen garantizar su adecuado comportamiento. Los procedimientos [...]
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Comportamiento de la interfaz concreto-epoxi-FRP utilizando la teoría de mezclas serie/paralelo
M. Molina, J. Cruz, S. Oller, H. Barbat, L. Gil

Ingeniería e investigación (2011). Vol. 31 (3), pp. 26-39

Abstract
Diversos estudios experimentales han mostrado que uno de los factores que afectan el comportamiento de estructuras de concreto externamente reforzadas con Fiberglass Reinforced Plastic (FRP, por sus siglas en inglés) es la adherencia entre el concreto y el FRP. En complemento a la experimentación, en este artículo se propone el uso de la teoría de mezclas serie/paralelo en la simulación numérica como una herramienta para estudiar el comportamiento de la interfaz concreto-epoxi-FRP. Además, se presenta un ejemplo en el que se analizan los resultados de la simulación de un ensayo de adherencia por flexión y se contrastan con los obtenidos experimentalmente.
Abstract
Diversos estudios experimentales han mostrado que uno de los factores que afectan el comportamiento de estructuras de concreto externamente reforzadas con Fiberglass [...]
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Non-destructive testing evaluation of low velocity impact damage in carbon fiber-reinforced laminated composites
M. Pérez, L. Gil, S. Oller

Ultrasound (2011). Vol. 66 (2), pp. 21-27

Abstract
Fiber-reinforced laminated composite materials are widely used in aircraft, modern vehicles and light-weight structures. With their high elastic modulus, high strength, and capability of being tailored for a several applications, these materials offer definite advantages compared to more traditional structural materials. However, their behavior under impact is of concern since those events may occur during manufacturing, normal operation or maintenance. The situation is critical for impacts that induce significant internal damage undetectable by visual inspection, which causes large reductions on the strength and stability of the structure. New standardized tests to assess the impact tolerance (ASTM D7136 and D7137) lose some of its appeal by its destructive nature as well as costs involved. Non-destructive techniques such as ultrasonic phased array or experimental modal analysis can be complementary in the evaluation of damage and structural integrity. The results of both destructive and non-destructive experiments carried out on forty-eight composite specimens are presented. A good correlation between incident impact energy and delaminated area as well as variation of eigenfrequencies is noticed. This study does not only provide a better understanding of the impact phenomenon but can also help in design and implementation of new test procedures for structural assessment.
Abstract
Fiber-reinforced laminated composite materials are widely used in aircraft, modern vehicles and light-weight structures. With their high elastic modulus, high strength, and [...]
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A general constitutive model for vascular tissue considering stress driven growth and biological availability
F. Bellomo, S. Oller, F. Armero, L. Nallim

Computer modeling in engineering and sciencies (2011). Vol. 80 (1), pp. 1-22

Abstract
Some of the key factors that regulate growth and remodeling of tissues are fundamentally mechanical. However, it is important to take into account the role of biological availability to generate new tissue together with the stresses and strains in the processes of natural or pathological growth. In this sense, the model presented in this work is oriented to describe growth of vascular tissue under "stress driven growth" considering biological availability of the organism. The general theoretical framework is given by a kinematic formulation in large strain combined with the thermodynamic basis of open systems. The formulation uses a multiplicative decomposition of deformation gradient, splitting it in a growth part and visco-elastic part. The strains due to growth are incompatible and are controlled by unbalanced stresses related to a homeostatic state. Growth implies a volume change with an increase of mass maintaining constant the density. One of the most interesting features of the proposed model is the generation of new tissue taking into account the contribution of mass to the system controlled through the biological availability. Because soft biological tissues in general have a hierarchical structure with several components (usually a soft matrix reinforced with collagen fibers), the developed growth model is suitable for the growth characterization of each component. This allows considering a different behavior for each of them in the context of a generalized theory of mixtures.
Abstract
Some of the key factors that regulate growth and remodeling of tissues are fundamentally mechanical. However, it is important to take into account the role of biological availability [...]
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Numerical Simulation of Matrix Reinforced Composite Materials Subjected to Compression Loads
X. Martinez, S. Oller

Archives of Comp. Meths. Engng. (2009). Vol. 16 (4), pp. 357-397

Abstract
This paper reviews the most common formulations to obtain the compression strength of long fiber composites due to fiber buckling. This failure mode was first studied by Rosen (Fibre Composite Materials, pp. 37–45, 1965) who defined two different fiber buckling modes, extensional and transverse. Further studies improved the first model proposed by Rosen by defining with more accuracy the mechanics of the problem. Although each formulation use a different approach to solve the problem, all of them agree in the dependence of fiber buckling on three main parameters: matrix shear strength, fiber initial misalignments and volumetric participation of the fibers in the composite. Once having described the different approaches used, and the parameters on which they depend, this paper describes a new formulation capable of obtaining the compression strength of composites taking into account the fiber buckling phenomenon. This formulation uses the serial/parallel mixing theory developed by Rastellini et al. (Comput. Struct. 86(9):879–896, 2008) to simulate the composite, and takes advantage of knowing the mechanical performance of the composite constituents to simulate the fiber buckling phenomenon. This is done with an homogenization procedure. It consists in introducing the interaction between fibers and matrix into their respective constitutive equations. The interaction between fiber and matrix takes into account fiber initial misalignments, its volumetric participation and the mechanical properties of both constituents. The new formulation proposed is implemented in a finite element code, taking into account that fibers can have different misalignment levels, and that the composite behaves differently if it is under tensile or compression forces. The mechanical performance of the formulation proposed is studied with several finite element simulations of compressed composites. Finally, the correctness of the formulation is proved by comparing the numerical results with the experimental tests provided by Barbero and Tomblin (Int. J. Solids Struct. 33(29):4379–4393, 1996), Tomblin et al. (Int. J. Solids Struct. 34(13):1667–1679, 1997).
Abstract
This paper reviews the most common formulations to obtain the compression strength of long fiber composites due to fiber buckling. This failure mode was first studied by Rosen [...]
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Determinación de umbrales de daño sísmico en edificios porticados de hormigón armado proyectados conforme al EC-2 y EC-8
J. Pérez, H. Barbat, S. Oller

Hormigón y Acero (2009). Vol. 60 (251), pp. 77-87

Abstract
El Proyecto por Prestaciones de edificios contempla una serie de Estados Límite que el proyectista debe aplicar a los edificios emplazados en zonas sísmicas. Sin embargo, actualmente existe la dificultad de poder incorporar estos Estados Límite en el proyecto convencional de estructuras. En este trabajo se estudia la determinación objetiva de los umbrales de daño correspondientes a unos Estados Límite específicos, aplicando criterios con base en desplomes relativos de niveles, calculados a partir de la respuesta no lineal de los edificios porticados de hormigón armado, proyectados según las disposiciones normativas del EC-2 y EC-8. Los resultados muestran que los valores de los umbrales de daño son prácticamente independientes de la altura del edificio y que se pueden incorporar al proceso de proyecto de forma racional, correlacionándolos además con los índices de daño sísmico, para facilitar la evaluación rápida de la respuesta sísmica de los edificios de hormigón armado.
Abstract
El Proyecto por Prestaciones de edificios contempla una serie de Estados Límite que el proyectista debe aplicar a los edificios emplazados en zonas sísmicas. [...]
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Estudio de estructuras de hormigón reforzadas con FRP mediante la teoría de mezclas serie/paralelo
S. Oller, M. Molina, H. Barbat, X. Martinez

Revista Internacional de Ingeniería de Estructuras (2009). Vol. 13-14 (1), pp. 29-54

Abstract
La simulación numérica del comportamiento de los materiales compuestos es un campo en desarrollo cuya aplicación a estructuras ha experimentado avances importantes que han conducido a mejores en el refuerzo de las mismas. En relación con este tema, el artículo parte de la teoría de mezclas serie/paralelo que permite deducir el comportamiento de los compuestos a partir de las ecuaciones constitutivas de los materiales componentes. Con el fin de destacar las ventajas que tiene esta herramienta en el análisis y el diseño de estructuras reparadas o rehabilitadas con polímeros reforzados con fibras largas (FRP), en el artículo se realizan análisis numéricos mediante modelos de elementos finitos de un conjunto de pórticos con distintas configuraciones de refuerzo. Los resultados obtenidos muestran que el uso esta teoría en los análisis de las estructuras reforzadas con FRP contribuyente a mejorar el diseño y el comportamiento de las estructuras.
Abstract
La simulación numérica del comportamiento de los materiales compuestos es un campo en desarrollo cuya aplicación a estructuras ha experimentado avances [...]
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Estudio de la interfaz hormigón-epoxi-frp de un ensayo de doble cortante por medio de la teoría de mezclas serie/paralelo
M. Herrera, J. Cruz, S. Oller, H. Barbat, L. Gil

Revista Internacional de Ingeniería de Estructuras (2009). Vol. 13-14 (1), pp. 99.116

Abstract
El uso de los compuestos para la rehabilitación y la reparación de estructuras de hormigón y de acero se ha ido imcrementando en las ultimas décadas. Frente a la necesidad de entender de una forma más apropiada el comportamiento de las estructuras reforzadas, la simulación numérica de los materiales compuestos ha surgido como una herramienta; sin embargo, es un campo que aún está en desarrollo. En este trabajo se desarrolla la teoría de mezclas serie/paralelo como una alternativa eficiente para el análisis de estructuras reforzados con fibras largas (FRP) y se estudia con detalle el comportamiento de la interfaz hormigón-adhesivo-FRP. Utilizando el programa de elementos finitos no lineal PLCDYN, se hace una simulación tridimensional de un ensayo de doble cortante y se compara con los resultados obtenidos en el laboratorio. Se han podido evidenciar las ventajas de esta teoría como herramienta para el análisis numérico de los materiales compuestos.
Abstract
El uso de los compuestos para la rehabilitación y la reparación de estructuras de hormigón y de acero se ha ido imcrementando en las ultimas décadas. [...]
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Discrete-continuum hybrid modelling of flowing and static regimes
I. Iaconeta, E. Oñate, A. LARESE

Monograph CIMNE (2019). M188

Abstract
Bulk handling, transport and processing of granular materials and powders are fundamental operations in a wide range of industrial processes and geophysical phenomena. Particulate materials, which can be found in nature, are usually characterized by a grain size which can range across several scales: from nanometre to the order of metre. Depending on the volume fraction and on the shear strain conditions, granular materials can have different behaviours and often can be expressed as a new state of matter with properties of solids, liquids and gases. For the above reasons, both the experimental and the numerical analysis of granular media is still a difficult task and the prediction of their dynamic behaviour still represents, nowadays, an important challenge. The main goal of the current monograph is the development of a numerical strategy with the objective of studying the macroscopic behaviour of dry granular flows in quasi-static and dense flow regime. The problem is defined in a continuum mechanics framework and the balance laws, which govern the behaviour of a solid body, are solved by using a Lagrangian formalism. The Material Point Method (MPM), a particle-based method, is chosen due to its features which make it very suitable for the solution of large deformation problems involving complex history-dependent constitutive laws. An irreducible formulation using a Mohr-Coulomb constitutive law, which takes into account geometric non-linearities, is implemented within the MPM framework. The numerical strategy is verified and validated against several benchmark tests and experimental results, available in the literature. Further, a mixed formulation is implemented for the solution of granular flows that undergo undrained conditions. Finally, the developed MPM strategy is used and tested against the experimental study performed for the characterization of the flowability of several types of sucrose. The capabilities and limitations of this numerical strategy are observed and discussed and the bases for future research are outlined.
Abstract
Bulk handling, transport and processing of granular materials and powders are fundamental operations in a wide range of industrial processes and geophysical phenomena. Particulate [...]
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Comportamiento sísmico de edificios de hormigón armado de ductilidad limitada
J. Vielma-Perez, H. Barbat, S. Oller

Acero y Hormigón (2008). Vol. 59 (248), pp. 87-101

Abstract
En el proyecto sismorresistente de edificios es necesario conocer previamente el valor de la ductilidad que éstos podrán llegar a alcanzar al ser sometidos a movimientos sísmicos fuertes. Los valores de ductilidad de referencia están incluidos en las normas de proyecto sismorresistente. Su estimación también puede hacerse bajo criterio de expertos o de la observación de la respuesta que los edificios han tenido ante determinados terremotos. Sin embargo, en el pasado, el problema se ha enfocado generalmente en la respuesta de edificios dúctiles, como son los edificios porticados con vigas de canto, sin que existan muchas referencias que permitan conocer la respuesta de los edificios de ductilidad limitada, entre los que se encuentran los edificios con forjados reticulares, que es la tipología más usual en España. En este trabajo se estudia la respuesta no lineal de edificios de ductilidad limitada, proyectados conforme a los requisitos de la instrucción española (EHE) y la norma sismorresistente NCSE-02, y se obtienen los valores de ductilidad a partir de dicha respuesta, lo que permiten verificar los valores de los factores de reducción aplicados en la determinación de las fuerzas sísmicas y los valores de reserva de resistencia. La evaluación de los edificios se complementa mediante la determinación de las curvas de fragilidad y de las matrices de probabilidad de daño, que permiten conocer la probabilidad de excedencia de Estados Límite previamente establecidos.
Abstract
En el proyecto sismorresistente de edificios es necesario conocer previamente el valor de la ductilidad que éstos podrán llegar a alcanzar al ser sometidos a [...]
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An analytical–numerical approach to simulate the dynamic behaviour of arbitrarily laminated composite plates
L. Nallim, S. Oller

Composite Structures (2008). Vol. 85 (4), pp. 311-325

Abstract
A general analytical–numerical approach developed for the dynamical analysis of unsymmetrically laminated plates of general quadrilateral planforms is presented in this work. An arbitrary quadrilateral thin flat laminate is mapped onto a square basic one, so that a unique macro-element is constructed for the whole plate. The Ritz method is applied to evaluate the governing equation in which the coupling effects of bending and stretching are contained. All possible transverse boundary conditions combining with the different in-plane constraints are considered in the analysis. The resulting algorithm possesses great flexibility, it is easy to program and it needs minimal input information. For these reasons, the proposed methodology results convenient for large scale structural design and analysis where repeated calculations are often required.
Abstract
A general analytical–numerical approach developed for the dynamical analysis of unsymmetrically laminated plates of general quadrilateral planforms is presented in this [...]
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Reserva de resistencia de edificios porticados de concreto armado diseñados conforme al ACI-318/IBC-2006
J. Vielma-Perez, H. Barbat, S. Oller

Ingeniería (2008). Vol. 18 (1-2), pp. 121-131

Abstract
La adecuada capacidad demostrada por los edificios sometidos a la acción de terremotos fuertes ha sido atribuida a la reserva de resistencia de la estructura. Sin embargo, la gran cantidad de factores que contribuyen en la reserva de resistencia, son un obstáculo para que esta haya sido incorporada de forma explícita y transparente en las normas de proyecto sismorresistente. En este artículo se aborda el tema de la reserva de resistencia, para lo que se estudia un conjunto de edificios regulares porticados de concreto armado que han sido proyectados conforme a las prescripciones del ACI318, con las cargas sísmicas prescritas en el IBC-2006. Los resultados muestran que la reserva de resistencia es independiente de la redundancia de los edificios y que los valores recomendados en el IBC-2006 subestiman la capacidad de los edificios con períodos intermedios y largos.
Abstract
La adecuada capacidad demostrada por los edificios sometidos a la acción de terremotos fuertes ha sido atribuida a la reserva de resistencia de la estructura. Sin embargo, [...]
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Confinamiento y ductilidad de los edificios de hormigón armado
J. Vielma-Perez, H. Barbat, S. Oller

Zuncho (2008). Vol. 15, pp. 22-29
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Seismic behaviour of limited ductility buildings
H. Barbat, J. Vielma-Perez, S. Oller

Civil Engineering (2008). Vol. 1 (10), pp. 3-12

Abstract
The most important aspects of the seismic design and behaviour of reinforced concrete buildings with limited ductility, like the buildings with waffled slabs or flat beams, are examined in this work. The structures with these typologies are the most used in Spain for new buildings and many seismic codes do not recommend their use in seismic areas. The expected seismic performance of these structures is studied herein by means of incremental non linear structural analysis (pushover analysis) which provides capacity curves. Their behaviour is compared with that of buildings with moment resisting frames designed according to the Spanish EHE and NCSE-02 codes and also to the ACI-318 (2005) and IBC-2003. The most important results of the study show that only the moment-resisting framed buildings exhibit sufficient ductility and overstrength to guarantee a stable seismic behaviour. The behaviour of limited ductility buildings is strongly influenced by the structural type; even if they are reinforced with ductile steel or if their confinement if improved, they exhibit slightly higher ductility
Abstract
The most important aspects of the seismic design and behaviour of reinforced concrete buildings with limited ductility, like the buildings with waffled slabs or flat beams, [...]
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Un índice de daño sísmico objetivo para la evaluación de los edificios de hormigón armado
J. Vielma-Perez, H. Barbat, S. Oller

Acero y Hormigón (2008). Vol. 59 (248), pp. 53-64

Abstract
En las normas que regulan el proyecto sismorresistente de edificios porticados se considera que los elementos estructurales (pilares y vigas) tienen un comportamiento no lineal durante la acción de un terremoto similar al de proyecto. Esto implica que dichos elementos se dañan y para el proyectista es de mucho interés poder estimar el daño global esperado en la estructura y relacionarlo tanto con la ductilidad de proyecto como con la demanda de ductilidad. Contrariamente a lo que ocurre con los edificios dúctiles, en el caso de los edificios proyectados para bajas ductilidades los índices de daño calculados a partir de un análisis por el método de elementos finitos, tienen valores que no reflejan adecuadamente el deterioro. Por esta razón, en este artículo se realiza una propuesta de un índice objetivo de daño formulado en función de la ductilidad y del valor de la rigidez elástica y la correspondiente al colapso del edificio y que es independiente de la tipología estructural utilizada. El procedimiento se ilustra mediante la aplicación del índice de daño propuesto a tres edificios dos de los cuales han sido proyectados para bajas ductilidades (edificio con forjados reticulares y edificio porticado con vigas planas) y el tercero, un edificio porticado con vigas de canto, proyectado para alta ductilidad. A los tres edificios se les ha determinado la respuesta estática no lineal mediante un procedimiento con control de fuerzas, así como el punto de capacidad por demanda. Los resultados obtenidos demuestran que el índice de daño objetivo propuesto proporciona unos valores que caracterizan adecuadamente el daño sufrido por los tres edificios.
Abstract
En las normas que regulan el proyecto sismorresistente de edificios porticados se considera que los elementos estructurales (pilares y vigas) tienen un comportamiento no lineal [...]
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Advanced composite material simulation
S. Oller, X. Martínez, H. Barbat, F. Rastellini

Ciência e tecnologia dos materiais (2008). Vol. 20 (1-2), pp. 2-14

Abstract
A computational methodology is presented for modeling the non-linear mechanical behavior of composite structures made of FRP (Fiber-Reinforced Polymers) laminates. The model is based on the appropriate combination of the constitutive models of compounding materials, considered to behave as isolated continua, together with additional “closure equations” that characterize the micro-mechanics of the composite from a morphological point of view. To this end, any appropriate constitutive model may be selected for each phase. Each component is modeled separately and the global response is obtained by assembling all contributions taking into account the interactions between components in a general phenomenological way. To model the behavior of a single uni-directional (UD) composite laminated, a Serial-Parallel continuum approach has been developed assuming that components behave as parallel materials in the fibers alignment direction and as serial materials in orthogonal directions. Taking into account the internal morphology of the composite material, it is devised a strategy for decoupling and coupling component phases. This methodology [Rastellini 2006], named "compounding of behavior", allows to take into consideration local non linear phenomenon in the compounding materials, like damage, plasticity, etc. in a coupled manner. It is based on the proper management of homogenous constitutive models, already available for each component. In this way, it is used all developments achieved in constitutive modeling for plain materials, what makes possible the transference of this technology to composites. A laminated theory complemented with the proposed UD model is employed to describe the mechanical behavior of multi-directional laminates. A specific solution strategy for the general non linear case is proposed. It provides quick local and global convergences, what makes the model suitable for large scale structures. The model brings answers on the non-linear behavior of composites, where classical micro-mechanics formulas are restricted to their linear elastic part. The methodology is validated through several numerical analyses and contrasted against experimental data and benchmark tests.
Abstract
A computational methodology is presented for modeling the non-linear mechanical behavior of composite structures made of FRP (Fiber-Reinforced Polymers) laminates. The model [...]
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Comparación de los factores de reducción de respuesta de la norma NCSE-02 y del Eurocódigo 8
J. Vielma-Perez, S. Oller, H. Barbat

Acero y Hormigón (2007). Vol. 246, pp. 79-95

Abstract
En los procedimientos de análisis y diseño sismorresistentes de estructuras se hace necesario introducir simplificaciones o aproximaciones que permitan estudiar la equivalencia entre el análisis elástico a partir del cual se efectúan los cálculos y el comportamiento elásto-plástico, que es el comportamiento real de las estructuras cuando son sometidas a la acción de terremotos fuertes. Una de estas simplificaciones, consiste en proyectar las estructuras de manera que dispongan de una resistencia lateral inferior a la que resulta de un dimensionado al límite elástico, lo que se consigue aplicando cargas laterales calculadas a partir de los espectros de diseño, que son espectros elásticos, afectados por factores de reducción de respuesta, conocidos como factores R. En este artículo se realiza una revisión exhaustiva del estado del arte de los factores de reducción de respuesta, partiendo de su definición, pasando por su implementación en las normas de diseño sismorresistente, hasta llegar a las nuevas propuestas de racionalización de su aplicación. Para poder alcanzar una mejor comprensión del tema, se realiza una comparación entre la aplicación de los factores de reducción de respuesta propuestos en la norma sismorresistente española NCSE-02 y en el Eurocódigo 8.
Abstract
En los procedimientos de análisis y diseño sismorresistentes de estructuras se hace necesario introducir simplificaciones o aproximaciones que permitan estudiar [...]
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Aspectes del disseny conceptual dels edificis de formigó armat
H. Barbat, J. Vielma-Perez, S. Oller

La Punxa (2007). Vol. 43, pp. 26-33
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A-posteriori error estimation for the finite point method with applications to compressible flow (preprint)
E. Ortega, R. Flores, E. Oñate, S. Idelsohn

A-posteriori error estimation for the finite point method with applications to compressible flow (2017). Computational Mechanics, 60 – 2, pp. 219 – 233

Abstract
An a-posteriori error estimate with application to inviscid compressible flow problems is presented. The estimate is a surrogate measure of the discretization error, obtained from an approximation to the truncation terms of the governing equations. This approximation is calculated from the discrete nodal differential residuals using a reconstructed solution field on a modified stencil of points. Both the error estimation methodology and the flow solution scheme are implemented using the Finite Point Method, a meshless technique enabling higher-order approximations and reconstruction procedures on general unstructured discretizations. The performance of the proposed error indicator is studied and applications to adaptive grid refinement are presented.
Abstract
An a-posteriori error estimate with application to inviscid compressible flow problems is presented. The estimate is a surrogate measure of the discretization error, obtained [...]
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Frequency and damping identification in flutter flight testing using singular value decomposition and QR factorization
J. Barros, R. Flores

Frequency and damping identification in flutter flight testing using singular value decomposition and QR factorization (2015). Proceedings of the institution of mechanical engineers - Part G. Journal of aerospace engineering. 229 – 2, pp. 323 – 332

Abstract
A new method, based on singular value decomposition and QR factorization, has been developed and applied to the analysis of F-18 flutter flight test data. The method is capable of identifying the frequency and damping of the critical aircraft modes, those responsible for the flutter phenomenon. The procedure relies on the capability of singular value decomposition for the analysis, modeling, and prediction of data series with periodic features and also on its power to identify matrix rank. The analysis of simulated and real flutter flight test data demonstrates the effectiveness, robustness, noise-immunity, and the capability for automation of the method proposed under specific conditions.
Abstract
A new method, based on singular value decomposition and QR factorization, has been developed and applied to the analysis of F-18 flutter flight test data. The method is capable [...]
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Aeroelastic analysis of parachute deceleration systems with empirical aerodynamics
E. Ortega, R. Flores

Aeroelastic analysis of parachute deceleration systems with empirical aerodynamics (2019). Proceedings of the institution of mechanical engineers - Part G. Journal of aerospace engineering. ISSN 0889-9746

Abstract
A technique for the aeroelastic solution of parachute decelerators is presented in this work. The methodology uses empirical aerodynamics, based on a filling-time inflation model and Ludtke’s area law, coupled to two explicit structural solution approaches. A mass-spring-damper technique allows solving the deployment of the system (when the grid is highly distorted) efficiently, and a finite element model is used for the accurate calculation of the structural loads and stresses during parachute opening and steady flight. The coupling strategy is staggered and the models share the same mesh. The methodology is intended for practical calculations of deceleration systems, and provides useful performance and structural data minimizing model complexity and computational cost. The suitability of the proposed technique is assessed by comparisons with reference test drop data.
Abstract
A technique for the aeroelastic solution of parachute decelerators is presented in this work. The methodology uses empirical aerodynamics, based on a filling-time inflation [...]
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On the solution of Lambert’s problem by regularization
D. Torre, R. Flores, E. Fantino, R. Flores

On the solution of Lambert’s problem by regularization (2018). Acta astronautica. 153, pp. 26 - 38

Abstract
Lambert’s problem is the two-point boundary-value problem resulting from a two-body orbital transfer between two position vectors in a given time. It lies at the very heart of several fundamental astrodynamics and space engineering problems and, as such, it has attracted the interest of scientists over centuries. In this work, we revisit the solution of Lambert’s problem based on Levi-Civita regularization developed by Carles Simó in 1973. We offer an exhaustive derivation of the theory, including proofs of all the results and the formulae employed, and we extend the algorithm to deal with multi-revolution transfers. Then, after investigating a range of initial guess search techniques and testing different numerical methods to approximate the solution, we propose a procedure in which the initial guess is assigned very efficiently by querying a pre-defined interpolating table. Then, in order to achieve both speed and robustness, we combine Newton-Raphson with safety checks to avoid out of boundary deviations to approximate the solution. We validate the method through several tests and applications, and we assess its convergence and performance. The algorithm presents no singularities, converges in all realistic scenarios and its computational cost is comparable with state of the art algorithms.
Abstract
Lambert’s problem is the two-point boundary-value problem resulting from a two-body orbital transfer between two position vectors in a given time. It lies at the very [...]
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Geosynchronous inclined orbits for high-latitude communications
E. Fantino, R. Flores, M. Carlo, A. Salvo, E. Cabot, R. Flores

Geosynchronous inclined orbits for high-latitude communications (2017). Acta astronautica. 140, pp. 570 – 582. ISSN 0094-5765

Abstract
We present and discuss a solution to the growing demand for satellite telecommunication coverage in the high-latitude geographical regions (beyond 55◦N), where the signal from geostationary satellites is limited or unavailable. We focus on the dynamical issues associated to the design, the coverage, the maintenance and the disposal of a set of orbits selected for the purpose. Specifically, we identify a group of highly inclined, moderately eccentric geosynchronous orbits derived from the Tundra orbit (geosynchronous, eccentric and critically inclined). Continuous coverage can be guaranteed by a constellation of three satellites in equally spaced planes and suitably phased. By means of a highprecision model of the terrestrial gravity field and the relevant environmental perturbations, we study the evolution of these orbits. The effects of the different perturbations on the ground track (which is more important for coverage than the orbital elements themselves) are isolated and analyzed. The physical model and the numerical setup are optimized with respect to computing time and accuracy. We show that, in order to maintain the ground track unchanged, the key parameters are the orbital period and the argument of perigee. Furthermore, corrections to the right ascension of the ascending node are needed in order to preserve the relative orientation of the orbital planes. A station-keeping strategy that minimizes propellant consumption is then devised, and comparisons are made between the cost of a solution based on impulsive maneuvers and one with continuous thrust. Finally, the issue of end-of-life disposal is discussed.
Abstract
We present and discuss a solution to the growing demand for satellite telecommunication coverage in the high-latitude geographical regions (beyond 55◦N), where the signal [...]
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Numerical simulation of the seismic behavior of building structures equipped with friction energy dissipators
S. Cruz, F. López-Almansa, S. Oller

Computers and Structures (2007). Vol. 85 (1-2), pp. 30-42

Abstract
This paper presents a new algorithm to simulate the seismic response of N-story building frames incorporating friction energy dissipators; a device per floor is considered. The frames with the dissipators are described by 2D lumped masses models with two degrees of freedom per floor, namely the horizontal displacements of the main structure and of the dissipators. The proposed algorithm consists of a modification of the linear acceleration method; the main innovation consists of checking at each calculation instant the sliding or sticking condition at each floor, hence, the number of “active” degrees of freedom changes continuously, ranging in between N (there is sticking condition at every dissipator) and 2N (there is sliding condition at every dissipator). Some results given by this algorithm are compared to experimental results from ad-hoc testing and to numerical results obtained with the ADINA software package. In both cases, agreement is satisfactory while the proposed method is more computationally efficient.
Abstract
This paper presents a new algorithm to simulate the seismic response of N-story building frames incorporating friction energy dissipators; a device per [...]
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Respuesta no lineal de edificios de concreto armado diseñados para baja ductilidad
J. Vielma-Perez, H. Barbat, S. Oller

Hormigón y Acero (2007). Vol. 45 (2), pp. 12-34

Abstract
En el diseño sismorresistente de edificios es necesario conocer previamente el valor de la ductilidad que éstos podrán llegar a alcanzar al ser sometidos a movimientos sísmicos fuertes. Los valores de ductilidad de referencia están incluidos en las normas de diseño sismorresistente. Su estimación también puede hacerse bajo criterio de expertos o de la observación de la respuesta que los edificios han tenido ante determinados terremotos. Sin embargo, generalmente el problema estudiado se ha centrado en la respuesta de edificios con respuesta dúctil, como son los edificios aporticados resistentes a momentos, sin que existan muchos datos que avalen la respuesta de los edificios de ductilidad limitada, entre los que se encuentran los edificios aporticados con vigas planas y los edificios con forjados reticulares. En este trabajo se estudia la respuesta no lineal de edificios de ductilidad limitada, proyectados conforme a los requisitos de la instrucción española (EHE) y la norma NCSE-02, y se obtienen los valores de ductilidad a partir de dicha respuesta, lo que permiten verificar los valores de los factores de reducción aplicados en la determinación de las fuerzas sísmicas y los valores de sobrerresistencia. De manera adicional, se estudia la respuesta de los edificios proyectados con aceros con diferentes características de ductilidad y tensión de plastificación. Finalmente, se comparan las respuestas de los edificios de ductilidad limitada con la respuesta de un edificio aporticado, verificándose el cumplimiento de las hipótesis consideradas para el proceso de análisis elástico de las mismas. Los resultados se comparan con los obtenidos de la respuesta no lineal de edificios con pórticos resistentes a momentos, diseñados según las normas españolas y la norma americana ACI-318.
Abstract
En el diseño sismorresistente de edificios es necesario conocer previamente el valor de la ductilidad que éstos podrán llegar a alcanzar al ser sometidos [...]
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Procedimiento de evaluación de edificios de concreto armado mediante un índice de daño sísmico objetivo
J. Vielma-Perez, H. Barbat, S. Oller

Revista Sul-Americana de Engenharia Estructural (2007). Vol. 4 (3), pp. 7-32

Abstract
En este trabajo se hace una revisión de los índices que permiten evaluar el daño sísmico de edificios, encontrando la necesidad de formular un índice objetivo que refleje adecuadamente el daño en los edificios de concreto armado, independientemente de la tipología estructural. Se expone un procedimiento de análisis no lineal de estructuras de concreto armado, aplicando control de fuerzas en el que se aplica como criterio de convergencia un índice de daño basado en elementos finitos. El procedimiento es validado mediante la comparación de resultados de dos pórticos de concreto armado, uno de los cuales es ensayado bajo la acción de cargas pseudo estáticas y el otro mediante la aplicación de cargas dinámicas. Los resultados muestran una buena aproximación de los resultados obtenidos mediante simulación numérica. Finalmente, el procedimiento se aplica en el cálculo de la curva de capacidad de tres edificios proyectados para diferentes niveles de ductilidad, evaluando el desempeño de los tres edificios mediante la aplicación del índice de daño sísmico objetivo.
Abstract
En este trabajo se hace una revisión de los índices que permiten evaluar el daño sísmico de edificios, encontrando la necesidad de formular un [...]
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Numerical tool to study RC structures under seismic loads using fiber reinforced polymers
X. Martinez, S. Oller, A. Barbat

Intersections = Intersectii (2007). Vol. 4 (2), pp. 50-64

Abstract
Strengthening or retrofitting existing structures in order to increase their ductility and improve their seismic response has traditionally been accomplished using conventional materials and construction techniques. Composite materials of a polymeric matrix reinforced with long fibers (FRP) have emerged as an alternative to these methods. To view the performance of these reinforcements when seismic loads are applied this work studies the structural response of a frame joint when a horizontal load is applied to it. Under a seismic load, joints are one of the weakest parts of these structures. The response of a plain concrete frame joint is compared with the response obtained when it is reinforced using FRP. Different configurations of FRP reinforcements are considered to compare their behavior. The structural response of all structures considered is obtained with a numerical simulation. This is done using the finite element method. Composites are treated using the mixing theory, which obtains the composite behavior by means of the composition of each component material properties. Each component is simulated with its own constitutive equation. The anisotropy usually found in composite components is treated using a mapped space theory. The debounding effects found in composite materials are treated using the formulation developed by E. Car and S. Oller [Car, 2000]. The results obtained validate the use of FRP reinforcements to improve frames seismic response. The structure load capacity is increased in a 20% when lateral reinforcements are applied to the joint. This can avoid the structure to collapse in a seismic case. They result also show a good performance of the numerical tool developed.
Abstract
Strengthening or retrofitting existing structures in order to increase their ductility and improve their seismic response has traditionally been accomplished using conventional [...]
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Factores de reducción de respuesta: estado del arte y estudio comparativo entre códigos
J. Vielma-Perez, A. Barbat, S. Oller

Revista Internacional de Ingeniería de Estructuras (2006). Vol. 11 (1), pp. 77-106

Abstract
En los procedimientos de análisis y diseño sismorresistentes de estructuras se hace necesario introducir simplificadores o aproximaciones que permitan estudiar la equivalencia entre el análisis elástico a partir del cual se efectúan los cálculos, con el comportamiento elástico plástico, que es el comportamiento real de las estructuras cuando son sometidas a la acción de terremotos fuertes. Una de estas simplificaciones consiste en proyectar las estructuras de manera que estas dispongan de una resistencia lateral inferior a la resistencia elástica, lo cual se consigue mediante la aplicación de cargas laterales calculadas a partir de espectros de diseño inelásticos, que no son más que los conocidos como factores R. En este artículo se realiza una revisión exhaustiva del estado del arte de los factores de reducción de respuesta, que comprende desde su propuesta original, pasando por su implementación en los códigos de diseño sismorresistente, hasta llegar a las nuevas propuestas de racionalización de su aplicación. Para poder alcanzar una mejor comprensión sobre el tema, es necesario realizar una comparativa entre aplicación de los factores de reducción de respuesta en los diferentes códigos de diseño sismorresistente a nivel mundial.
Abstract
En los procedimientos de análisis y diseño sismorresistentes de estructuras se hace necesario introducir simplificadores o aproximaciones que permitan estudiar [...]
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