Articles de revista
http://hdl.handle.net/2117/516
20170122T14:38:47Z

Multiscale computational homogenization: review and proposal of a new enhancedfirstorder method
http://hdl.handle.net/2117/98591
Multiscale computational homogenization: review and proposal of a new enhancedfirstorder method
Otero Gruer, Fermín Enrique; Oller Martínez, Sergio Horacio; Martínez García, Javier
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 macroscale deformation gradient to obtain the homogenized material behaviour from the microscale are called firstorder computational homogenization. Following this idea, the secondorder FE2 methods incorporate highorder gradients to improve the simulation accuracy. However, to capture the full advantages of these highorder framework the classical boundary value problem (BVP) at the macroscale must be upgraded to highorder level, which complicates their numerical solution. With the purpose of obtaining the best of both methods i.e. firstorder and secondorder, in this work an enhancedfirstorder computational homogenization is presented. The proposed approach preserves a classical BVP at the macroscale level but taking into account the highorder gradient of the macroscale in the microscale solution. The developed numerical examples show how the proposed method obtains the expected stress distribution at the microscale for states of structural bending loads. Nevertheless, the macroscale results achieved are the same than the ones obtained with a firstorder framework because both approaches share the same macroscale BVP.
This is a copy of the author 's final draft version of an article published in the Archives of computational methods in engineering. The final publication is available at Springer via http://dx.doi.org/10.1007/s1183101692050
20161219T15:01:40Z
Otero Gruer, Fermín Enrique
Oller Martínez, Sergio Horacio
Martínez García, Javier
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 macroscale deformation gradient to obtain the homogenized material behaviour from the microscale are called firstorder computational homogenization. Following this idea, the secondorder FE2 methods incorporate highorder gradients to improve the simulation accuracy. However, to capture the full advantages of these highorder framework the classical boundary value problem (BVP) at the macroscale must be upgraded to highorder level, which complicates their numerical solution. With the purpose of obtaining the best of both methods i.e. firstorder and secondorder, in this work an enhancedfirstorder computational homogenization is presented. The proposed approach preserves a classical BVP at the macroscale level but taking into account the highorder gradient of the macroscale in the microscale solution. The developed numerical examples show how the proposed method obtains the expected stress distribution at the microscale for states of structural bending loads. Nevertheless, the macroscale results achieved are the same than the ones obtained with a firstorder framework because both approaches share the same macroscale BVP.

The curious arithmetic of optical vortices
http://hdl.handle.net/2117/98471
The curious arithmetic of optical vortices
Molina Terriza, Gabriel; Recolons Martos, Jaume; Torner Sabata, Lluís
The superposition of noncoaxial light beams containing screw wavefront dislocations is shown to create light patterns with a richer vortex content than that given by the arithmetic of the topological charges of the individual beams. We report the experimental observation of this phenomenon.
© 2000 Optical Society of America
20161216T14:25:57Z
Molina Terriza, Gabriel
Recolons Martos, Jaume
Torner Sabata, Lluís
The superposition of noncoaxial light beams containing screw wavefront dislocations is shown to create light patterns with a richer vortex content than that given by the arithmetic of the topological charges of the individual beams. We report the experimental observation of this phenomenon.
© 2000 Optical Society of America

Guided to leaky mode transition in uniaxial optical slab waveguides
http://hdl.handle.net/2117/97541
Guided to leaky mode transition in uniaxial optical slab waveguides
Torner Sabata, Lluís; Recolons Martos, Jaume; Pérez Torres, Juan
The guidedtoleaky hybrid mode transition in slab optical waveguides made on uniaxial crystals such as LiNbO/sub 3/, or LiTaO/sub 3/, is analyzed. Two different guidedtoleaky transitions have been identified, namely the ordinary cutoff and the extraordinary cutoff, which occur when considering negative and positive birefringent materials, respectively. Analytical but transcendental expressions have been obtained, yielding the critical optical axis orientation, relative to the waveguide axis, above which the totally guided hybrid modes become leaky. The results indicate that the value of the critical orientation strongly depends on the waveguide parameters. The possibility of tuning this critical orientation to a desired value through the waveguide parameters is discussed.
20161130T15:37:45Z
Torner Sabata, Lluís
Recolons Martos, Jaume
Pérez Torres, Juan
The guidedtoleaky hybrid mode transition in slab optical waveguides made on uniaxial crystals such as LiNbO/sub 3/, or LiTaO/sub 3/, is analyzed. Two different guidedtoleaky transitions have been identified, namely the ordinary cutoff and the extraordinary cutoff, which occur when considering negative and positive birefringent materials, respectively. Analytical but transcendental expressions have been obtained, yielding the critical optical axis orientation, relative to the waveguide axis, above which the totally guided hybrid modes become leaky. The results indicate that the value of the critical orientation strongly depends on the waveguide parameters. The possibility of tuning this critical orientation to a desired value through the waveguide parameters is discussed.

Lagrangian finite element model for the 3D simulation of glass forming processes
http://hdl.handle.net/2117/90788
Lagrangian finite element model for the 3D simulation of glass forming processes
Ryzhakov, Pavel; García Espinosa, Julio; Oñate Ibáñez de Navarra, Eugenio
We propose here a numerical model for a threedimensional simulation of glass forming processes. Using the basic philosophy of the Particle Finite Element method (PFEM), we introduce several new features adapting the strategy to suit the problem of interest. A modified fractional step method for the solution of the flow equations is applied. This approach, on the one hand, inherits the computational efficiency of the original fractional step approach, and on the other hand shows better mass conservation features. These features are particularly attractive taking into account the importance of the correct prediction of the glass product’s wall thickness. A smart mesh update strategy and a simple mechanical contact scheme are introduced. In order to account for temperaturedependent viscosity, the heat equation is coupled to the mechanical model. Viscosity is obtained from the temperature field via an empirical law. The model is validated and an example modeling the processes in the final blow mold of the bottle manufacturing process is proposed.
20161014T13:42:47Z
Ryzhakov, Pavel
García Espinosa, Julio
Oñate Ibáñez de Navarra, Eugenio
We propose here a numerical model for a threedimensional simulation of glass forming processes. Using the basic philosophy of the Particle Finite Element method (PFEM), we introduce several new features adapting the strategy to suit the problem of interest. A modified fractional step method for the solution of the flow equations is applied. This approach, on the one hand, inherits the computational efficiency of the original fractional step approach, and on the other hand shows better mass conservation features. These features are particularly attractive taking into account the importance of the correct prediction of the glass product’s wall thickness. A smart mesh update strategy and a simple mechanical contact scheme are introduced. In order to account for temperaturedependent viscosity, the heat equation is coupled to the mechanical model. Viscosity is obtained from the temperature field via an empirical law. The model is validated and an example modeling the processes in the final blow mold of the bottle manufacturing process is proposed.

A laminated structural finite element for the behavior of large nonlinear reinforced concrete structures
http://hdl.handle.net/2117/89389
A laminated structural finite element for the behavior of large nonlinear reinforced concrete structures
Escudero Torres, Cuauhtemoc; Oller Martínez, Sergio Horacio; Martínez García, Javier; Barbat Barbat, Horia Alejandro
In order to correctly predict the kinematics of complex structures, analysis using threedimensional finite elements (3DFEs) seems to be the best alternative. However, simulation of large multilayered structures with many plies can be unaffordable with 3DFEs because of the excessive computational cost, especially for nonlinear materials. In addition, the discretization of very thin layers can lead to highly distorted FEs carrying numerical issues, therefore, reduced models arise as an affordable solution.
This paper describes a new finite element formulation to perform numerical simulations of laminated reinforced concrete structures. The intention of this work is that the proposed scheme can be applied in the analysis of reallife structures where a high amount of computational resources are needed to fulfill the meshing requirements, hence the resulting formulation has to be a compromise between simplicity and efficiency.
So that, the condensation of a dimension (thickness), mandatory to model threedimensional structures with twodimensional finite elements (2DFEs), leads to refer all layers contained within such FEs to a plane, which is typically named middle plane or geometrical plane, since its sole function is to serve as a geometrical reference. This work is based on the assumption that the geometrical plane has to be distinguished from a mechanical plane, which is where the resultant stiffness of all layers is contained. It is also assumed in this work that the mechanical plane changes its position due to nonlinear response of the component materials.
20160829T10:23:57Z
Escudero Torres, Cuauhtemoc
Oller Martínez, Sergio Horacio
Martínez García, Javier
Barbat Barbat, Horia Alejandro
In order to correctly predict the kinematics of complex structures, analysis using threedimensional finite elements (3DFEs) seems to be the best alternative. However, simulation of large multilayered structures with many plies can be unaffordable with 3DFEs because of the excessive computational cost, especially for nonlinear materials. In addition, the discretization of very thin layers can lead to highly distorted FEs carrying numerical issues, therefore, reduced models arise as an affordable solution.
This paper describes a new finite element formulation to perform numerical simulations of laminated reinforced concrete structures. The intention of this work is that the proposed scheme can be applied in the analysis of reallife structures where a high amount of computational resources are needed to fulfill the meshing requirements, hence the resulting formulation has to be a compromise between simplicity and efficiency.
So that, the condensation of a dimension (thickness), mandatory to model threedimensional structures with twodimensional finite elements (2DFEs), leads to refer all layers contained within such FEs to a plane, which is typically named middle plane or geometrical plane, since its sole function is to serve as a geometrical reference. This work is based on the assumption that the geometrical plane has to be distinguished from a mechanical plane, which is where the resultant stiffness of all layers is contained. It is also assumed in this work that the mechanical plane changes its position due to nonlinear response of the component materials.

Impact of logistics and shipping in the sustainable development of societies
http://hdl.handle.net/2117/86595
Impact of logistics and shipping in the sustainable development of societies
Martínez Marín, Jesús Ezequiel
Definitely, although not very obvious, shipping affects the daily lives of the majority of the
world population. The socioeconomic implications of logistics undoubtedly affect the social
development of cities. With the implementation of sustainability in the supply chain, and not
only think of a commercial profit but in an overall benefit in mind the impact it is having on the
ecosystem. Solutions, research and discussion topics to open an academic contribution is
interesting, that would open up discussions.
20160504T15:24:37Z
Martínez Marín, Jesús Ezequiel
Definitely, although not very obvious, shipping affects the daily lives of the majority of the
world population. The socioeconomic implications of logistics undoubtedly affect the social
development of cities. With the implementation of sustainability in the supply chain, and not
only think of a commercial profit but in an overall benefit in mind the impact it is having on the
ecosystem. Solutions, research and discussion topics to open an academic contribution is
interesting, that would open up discussions.

Validation on large scale tests of a new hardening–softening law for the Barcelona plastic damage model
http://hdl.handle.net/2117/86285
Validation on large scale tests of a new hardening–softening law for the Barcelona plastic damage model
Barbu, Lucia Gratiela; Martínez García, Javier; Oller Martínez, Sergio Horacio; Barbat Barbat, Horia Alejandro
20160427T16:27:14Z
Barbu, Lucia Gratiela
Martínez García, Javier
Oller Martínez, Sergio Horacio
Barbat Barbat, Horia Alejandro

An efficient multiscale method for nonlinear analysis of composite structures
http://hdl.handle.net/2117/85989
An efficient multiscale method for nonlinear analysis of composite structures
Otero Gruer, Fermín Enrique; Martínez García, Javier; Oller Martínez, Sergio Horacio; Salomon Rotlisbeger, Ramon Omar
The use of multiscale procedures is encouraged by the continuous increase of computational capacity, but it is still a challenge performing a nonlinear analysis of real composite structures without the aid of large computers. This work proposes a strategy to conduct nonlinear multiscale analysis in an efficient way. The proposed method considers that in a large structure, in general, material nonlinear 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 nonlinear analysis defining of a nonlinear 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 multiscale method) to less than 12 hours.
20160420T13:54:56Z
Otero Gruer, Fermín Enrique
Martínez García, Javier
Oller Martínez, Sergio Horacio
Salomon Rotlisbeger, Ramon Omar
The use of multiscale procedures is encouraged by the continuous increase of computational capacity, but it is still a challenge performing a nonlinear analysis of real composite structures without the aid of large computers. This work proposes a strategy to conduct nonlinear multiscale analysis in an efficient way. The proposed method considers that in a large structure, in general, material nonlinear 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 nonlinear analysis defining of a nonlinear 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 multiscale method) to less than 12 hours.

A FEM fluidstructure interaction algorithm for analysis of the seal dynamics of a SurfaceEffect Ship
http://hdl.handle.net/2117/84942
A FEM fluidstructure interaction algorithm for analysis of the seal dynamics of a SurfaceEffect Ship
García Espinosa, Julio; Capua, Daniel di; Serván Camas, Borja; Ubach Fuentes, PereAndreu; Oñate Ibáñez de Navarra, Eugenio
This paper shows the recent work of the authors in the development of a timedomain FEM model for evaluation of the seal dynamics of a surface effect ship. The fluid solver developed for this purpose, uses a potential flow approach along with a streamline integration of the free surface. The paper focuses on the free surfacestructure algorithm that has been developed to allow the simulation of the complex and highly dynamic behaviour of the seals in the interface between the air cushion, and the water.; The developed fluidstructure interaction solver is based, on one side, on an implicit iteration algorithm, communicating pressure forces and displacements of the seals at memory level and, on the other side, on an innovative wetting and drying scheme able to predict the water action on the seals. The stability of the iterative scheme is improved by means of relaxation, and the convergence is accelerated using Aitken's method.; Several validations against experimental results have been carried out to demonstrate the developed algorithm. (C) 2015 Elsevier B.V. All rights reserved.
20160331T11:20:03Z
García Espinosa, Julio
Capua, Daniel di
Serván Camas, Borja
Ubach Fuentes, PereAndreu
Oñate Ibáñez de Navarra, Eugenio
This paper shows the recent work of the authors in the development of a timedomain FEM model for evaluation of the seal dynamics of a surface effect ship. The fluid solver developed for this purpose, uses a potential flow approach along with a streamline integration of the free surface. The paper focuses on the free surfacestructure algorithm that has been developed to allow the simulation of the complex and highly dynamic behaviour of the seals in the interface between the air cushion, and the water.; The developed fluidstructure interaction solver is based, on one side, on an implicit iteration algorithm, communicating pressure forces and displacements of the seals at memory level and, on the other side, on an innovative wetting and drying scheme able to predict the water action on the seals. The stability of the iterative scheme is improved by means of relaxation, and the convergence is accelerated using Aitken's method.; Several validations against experimental results have been carried out to demonstrate the developed algorithm. (C) 2015 Elsevier B.V. All rights reserved.

Development of a decision support system for optimization of the performance of sailing yachts
http://hdl.handle.net/2117/84909
Development of a decision support system for optimization of the performance of sailing yachts
García Espinosa, Julio; Ortigosa Barragán, Inma; Fernandez, A
In this paper, the conception and design of a new monitoring system for a racing yachts rig is presented. The sensors developed are able to process the measured strain data, by applying artificial neural networks (ANN) algorithms, and then evaluate the load acting on an element and identify the direction of the action of that force. This way, it is possible to identify the actual operating conditions of the yacht rig. The required data for ANN training is generated from the results obtained from different finite element method (FEM) computational models of the device. Furthermore, during the design phase of the system, different experimental campaigns were carried out. The experimental tests were designed to serve as proof of concept, as well as to validate the different procedures used in the system development and application.; The developed monitoring system is wireless, lowintrusive and easily adaptable to any yacht configuration. This work also presents the integration of the monitoring system into a coupled fluidstructure computation model for the sails and rig of a boat. The resulting system is an efficient tool for evaluating performance and decision support in the adjustment of a sailboat rig. (C) 2014 CIMNE (Universitat Politecnica de Catalunya). Published by Elsevier Espana, S.L.U. All rights reserved.
20160330T16:45:12Z
García Espinosa, Julio
Ortigosa Barragán, Inma
Fernandez, A
In this paper, the conception and design of a new monitoring system for a racing yachts rig is presented. The sensors developed are able to process the measured strain data, by applying artificial neural networks (ANN) algorithms, and then evaluate the load acting on an element and identify the direction of the action of that force. This way, it is possible to identify the actual operating conditions of the yacht rig. The required data for ANN training is generated from the results obtained from different finite element method (FEM) computational models of the device. Furthermore, during the design phase of the system, different experimental campaigns were carried out. The experimental tests were designed to serve as proof of concept, as well as to validate the different procedures used in the system development and application.; The developed monitoring system is wireless, lowintrusive and easily adaptable to any yacht configuration. This work also presents the integration of the monitoring system into a coupled fluidstructure computation model for the sails and rig of a boat. The resulting system is an efficient tool for evaluating performance and decision support in the adjustment of a sailboat rig. (C) 2014 CIMNE (Universitat Politecnica de Catalunya). Published by Elsevier Espana, S.L.U. All rights reserved.