Articles de revista
http://hdl.handle.net/2117/6145
20171017T13:28:53Z

Coexistence of wrinkles and blisters in supported graphene
http://hdl.handle.net/2117/108583
Coexistence of wrinkles and blisters in supported graphene
Zang, Kuan; Arroyo Balaguer, Marino
Blisters induced by gas trapped in the interstitial space between supported graphene and the substrate are commonly observed. These blisters are often quasispherical with a circular rim, but polygonal blisters are also common and coexist with wrinkles emanating from their vertices. Here, we show that these different blister morphologies can be understood mechanically in terms of free energy minimization of the supported graphene sheet for a given mass of trapped gas and for a given lateral strain. Using a nonlinear continuum model for supported graphene closely reproducing experimental images of blisters, we build a morphological diagram as a function of strain and trapped mass. We show that the transition from quasispherical to polygonal of blisters as compressive strain is increased is a process of stretching energy relaxation and focusing, as many other crumpling events in thin sheets. Furthermore, to characterize this transition, we theoretically examine the onset of nucleation of short wrinkles in the periphery of a quasispherical blister. Our results are experimentally testable and provide a framework to control complex outofplane motifs in supported graphene combining blisters and wrinkles for strain engineering of graphene.
20171010T10:43:11Z
Zang, Kuan
Arroyo Balaguer, Marino
Blisters induced by gas trapped in the interstitial space between supported graphene and the substrate are commonly observed. These blisters are often quasispherical with a circular rim, but polygonal blisters are also common and coexist with wrinkles emanating from their vertices. Here, we show that these different blister morphologies can be understood mechanically in terms of free energy minimization of the supported graphene sheet for a given mass of trapped gas and for a given lateral strain. Using a nonlinear continuum model for supported graphene closely reproducing experimental images of blisters, we build a morphological diagram as a function of strain and trapped mass. We show that the transition from quasispherical to polygonal of blisters as compressive strain is increased is a process of stretching energy relaxation and focusing, as many other crumpling events in thin sheets. Furthermore, to characterize this transition, we theoretically examine the onset of nucleation of short wrinkles in the periphery of a quasispherical blister. Our results are experimentally testable and provide a framework to control complex outofplane motifs in supported graphene combining blisters and wrinkles for strain engineering of graphene.

Numerical modeling of erosion using an improvement of the extended finite element method
http://hdl.handle.net/2117/108059
Numerical modeling of erosion using an improvement of the extended finite element method
Cottereau, Régis; Díez, Pedro
We present in this paper a numerical model of the erosion of a soil that accounts for both the flow in the open fluid and the flow of fluid through the porous soil. The interface between the open fluid and the soil is represented using a levelset function, and the erosion is controlled by the shear stress vector. The evaluation of the approximate value of this gradient is particularly focused on, and an improved method, called XFE+ method, is presented. Numerical results in 2D and 3D illustrate the accuracy and the potentiality of this method.
This is an Accepted Manuscript of an article published by Taylor & Francis Group in "European journal of environmental and civil engineering" on 2011, available online at: http://www.tandfonline.com/doi/abs/10.1080/19648189.2011.9714848
20170927T09:09:01Z
Cottereau, Régis
Díez, Pedro
We present in this paper a numerical model of the erosion of a soil that accounts for both the flow in the open fluid and the flow of fluid through the porous soil. The interface between the open fluid and the soil is represented using a levelset function, and the erosion is controlled by the shear stress vector. The evaluation of the approximate value of this gradient is particularly focused on, and an improved method, called XFE+ method, is presented. Numerical results in 2D and 3D illustrate the accuracy and the potentiality of this method.

The main factors and rules of stress shadow of perpendicular cracks
http://hdl.handle.net/2117/108040
The main factors and rules of stress shadow of perpendicular cracks
Wang, Daobing; Zhou, Fujian; Ge, Hongkui; Zlotnik, Sergio; Yang, Xiangtong; Peng, Jinlong
Based on elasticity theory, we use numerical Galerkin finite element discretization method and implement Matlab finite element code to simulate “stress shadow” distributions of mutual orthogonal fractures. The principal stress and principal distributions have the symmetry characteristic on the intersection (coordinate origin). The relationships between stress shadow and flow pressure ratio, pore pressure, fluid pressure and horizontal stress contract are analyzed, respectively. By these techniques of variable displacement construction, changing the viscosity of the fracturing fluid, exploitation of oil and gas wells changing pump rate and fracturing fluid viscosity, reducing pore pressure and increasing the injection volume, taking the advantages of shadow effect, it is likely to produce a complex fracture network.
20170926T16:58:22Z
Wang, Daobing
Zhou, Fujian
Ge, Hongkui
Zlotnik, Sergio
Yang, Xiangtong
Peng, Jinlong
Based on elasticity theory, we use numerical Galerkin finite element discretization method and implement Matlab finite element code to simulate “stress shadow” distributions of mutual orthogonal fractures. The principal stress and principal distributions have the symmetry characteristic on the intersection (coordinate origin). The relationships between stress shadow and flow pressure ratio, pore pressure, fluid pressure and horizontal stress contract are analyzed, respectively. By these techniques of variable displacement construction, changing the viscosity of the fracturing fluid, exploitation of oil and gas wells changing pump rate and fracturing fluid viscosity, reducing pore pressure and increasing the injection volume, taking the advantages of shadow effect, it is likely to produce a complex fracture network.

Monitoring a PGD solver for parametric power flow problems with goaloriented error assessment
http://hdl.handle.net/2117/107471
Monitoring a PGD solver for parametric power flow problems with goaloriented error assessment
García Blanco, Raquel; Borzacchiello, Domenico; Chinesta, Francisco; Díez, Pedro
The parametric analysis of electric grids requires carrying out a large number of Power Flow computations. The different parameters describe loading conditions and grid properties. In this framework, the Proper Generalized Decomposition (PGD) provides a numerical solution explicitly accounting for the parametric dependence. Once the PGD solution is available, exploring the multidimensional parametric space is computationally inexpensive. The aim of this paper is to provide tools to monitor the error associated with this significant computational gain and to guarantee the quality of the PGD solution. In this case, the PGD algorithm consists in three nested loops that correspond to 1) iterating algebraic solver, 2) number of terms in the separable greedy expansion and 3) the alternated directions for each term. In the proposed approach, the three loops are controlled by stopping criteria based on residual goaloriented error estimates. This allows one for using only the computational resources necessary to achieve the accuracy prescribed by the end user. The paper discusses how to compute the goaloriented error estimates. This requires linearizing the error equation and the Quantity of Interest to derive an efficient error representation based on an adjoint problem. The efficiency of the proposed approach is demonstrated on benchmark problems.
This is the peer reviewed version of the following article: [GarcíaBlanco, R., Borzacchiello, D., Chinesta, F., and Diez, P. (2017) Monitoring a PGD solver for parametric power flow problems with goaloriented error assessment. Int. J. Numer. Meth. Engng, 111: 529–552. doi: 10.1002/nme.5470], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nme.5470/full. This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving.
20170906T17:48:16Z
García Blanco, Raquel
Borzacchiello, Domenico
Chinesta, Francisco
Díez, Pedro
The parametric analysis of electric grids requires carrying out a large number of Power Flow computations. The different parameters describe loading conditions and grid properties. In this framework, the Proper Generalized Decomposition (PGD) provides a numerical solution explicitly accounting for the parametric dependence. Once the PGD solution is available, exploring the multidimensional parametric space is computationally inexpensive. The aim of this paper is to provide tools to monitor the error associated with this significant computational gain and to guarantee the quality of the PGD solution. In this case, the PGD algorithm consists in three nested loops that correspond to 1) iterating algebraic solver, 2) number of terms in the separable greedy expansion and 3) the alternated directions for each term. In the proposed approach, the three loops are controlled by stopping criteria based on residual goaloriented error estimates. This allows one for using only the computational resources necessary to achieve the accuracy prescribed by the end user. The paper discusses how to compute the goaloriented error estimates. This requires linearizing the error equation and the Quantity of Interest to derive an efficient error representation based on an adjoint problem. The efficiency of the proposed approach is demonstrated on benchmark problems.

A semianalytical scheme for highly oscillatory integrals over tetrahedra
http://hdl.handle.net/2117/107470
A semianalytical scheme for highly oscillatory integrals over tetrahedra
Hospital Bravo, Raúl; Sarrate Ramos, Josep; Díez, Pedro
This paper details a semianalytical procedure to efficiently integrate the product of a smooth function and a complex exponential over tetrahedral elements. These highly oscillatory integrals appear at the core of different numerical techniques. Here, the Partition of Unity Method (PUM) enriched with plane waves is used as motivation. The high computational cost or the lack of accuracy in computing these integrals is a bottleneck for their application to engineering problems of industrial interest. In this integration rule, the nonoscillatory function is expanded into a set of Lagrange polynomials. In addition, Lagrange polynomials are expressed as a linear combination of the appropriate set of monomials, whose product with the complex exponentials is analytically integrated, leading to 16 specific cases that are developed in detail. Finally, we present several numerical examples to assess the accuracy and the computational efficiency of the proposed method, compared to standard GaussLegendre quadratures.
This is the peer reviewed version of the following article: [HospitalBravo, R., Sarrate, J., and Díez, P. (2017) A semianalytical scheme for highly oscillatory integrals over tetrahedra. Int. J. Numer. Meth. Engng, 111: 703–723. doi: 10.1002/nme.5474], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nme.5474/full. This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving.
20170906T17:36:23Z
Hospital Bravo, Raúl
Sarrate Ramos, Josep
Díez, Pedro
This paper details a semianalytical procedure to efficiently integrate the product of a smooth function and a complex exponential over tetrahedral elements. These highly oscillatory integrals appear at the core of different numerical techniques. Here, the Partition of Unity Method (PUM) enriched with plane waves is used as motivation. The high computational cost or the lack of accuracy in computing these integrals is a bottleneck for their application to engineering problems of industrial interest. In this integration rule, the nonoscillatory function is expanded into a set of Lagrange polynomials. In addition, Lagrange polynomials are expressed as a linear combination of the appropriate set of monomials, whose product with the complex exponentials is analytically integrated, leading to 16 specific cases that are developed in detail. Finally, we present several numerical examples to assess the accuracy and the computational efficiency of the proposed method, compared to standard GaussLegendre quadratures.

A subsystem identification method based on the path concept with coupling strength estimation
http://hdl.handle.net/2117/107082
A subsystem identification method based on the path concept with coupling strength estimation
Magrans Fontrodona, Francesc Xavier; PobletPuig, Jordi; Rodríguez Ferran, Antonio
For complex geometries, the definition of the subsystems is not a straightforward task. We present here a subsystem identification method based on the direct transfer matrix, which represents the firstorder paths. The key ingredient is a cluster analysis of the rows of the powers of the transfer matrix. These powers represent highorder paths in the system and are more affected than loworder paths by damping.
Once subsystems are identified, the proposed approach also provides a quantification of the degree of coupling between subsystems. This information is relevant to decide whether a subsystem may be analysed in a computer model or measured in the laboratory independently of the rest or subsystems or not. The two features (subsystem identification and quantification of the degree of coupling) are illustrated by means of numerical examples: plates coupled by means of springs and rooms connected by means of a cavity.
20170822T10:10:36Z
Magrans Fontrodona, Francesc Xavier
PobletPuig, Jordi
Rodríguez Ferran, Antonio
For complex geometries, the definition of the subsystems is not a straightforward task. We present here a subsystem identification method based on the direct transfer matrix, which represents the firstorder paths. The key ingredient is a cluster analysis of the rows of the powers of the transfer matrix. These powers represent highorder paths in the system and are more affected than loworder paths by damping.
Once subsystems are identified, the proposed approach also provides a quantification of the degree of coupling between subsystems. This information is relevant to decide whether a subsystem may be analysed in a computer model or measured in the laboratory independently of the rest or subsystems or not. The two features (subsystem identification and quantification of the degree of coupling) are illustrated by means of numerical examples: plates coupled by means of springs and rooms connected by means of a cavity.

Catalogue of vibration reduction index formulas for heavy junctions based on numerical simulations
http://hdl.handle.net/2117/106840
Catalogue of vibration reduction index formulas for heavy junctions based on numerical simulations
PobletPuig, Jordi; GuigouCarter, Catherine
The vibration reduction index (Kij) is a key parameter in the prediction of flanking transmissions according to the EN12354 standard. Formulas for the evaluation of Kij in L, T and X junctions that depend on the mass ratio are available in the Annex E. Junctions of straight elements with different thickness or thin elastic layers are also included. However, other junction types that are important for building industry are not considered: Hshaped junctions, L or T junctions not forming a right angle, asymmetrical Tjunctions , Xjunctions where only one of the parts is different (thickness or material) from the other two/three. In the current research, expressions for these noncovered junctions are provided. They are obtained by means of numerical simulations based on the spectral finite element method. Kij is predicted for a large population of junctions, considering usual thicknesses and heavy material combinations (no lightweight frame systems have been considered). Statistical analysis is carried out to obtain relatively simple formulae that could be used in acoustic design projects without the need for timeconsuming computations with finite element software.
© (2017) S. Hirzel Verlag/European Acoustics Association.
The definitive publisherauthenticated version is available online at http://www.ingentaconnect.com/contentone/dav/aaua/2017/00000103/00000004/art00011 and http//dx.doi.org/10.3813/AAA.919091.
Readers must contact the publisher for reprint or permission to use the material in any form.
20170725T14:29:02Z
PobletPuig, Jordi
GuigouCarter, Catherine
The vibration reduction index (Kij) is a key parameter in the prediction of flanking transmissions according to the EN12354 standard. Formulas for the evaluation of Kij in L, T and X junctions that depend on the mass ratio are available in the Annex E. Junctions of straight elements with different thickness or thin elastic layers are also included. However, other junction types that are important for building industry are not considered: Hshaped junctions, L or T junctions not forming a right angle, asymmetrical Tjunctions , Xjunctions where only one of the parts is different (thickness or material) from the other two/three. In the current research, expressions for these noncovered junctions are provided. They are obtained by means of numerical simulations based on the spectral finite element method. Kij is predicted for a large population of junctions, considering usual thicknesses and heavy material combinations (no lightweight frame systems have been considered). Statistical analysis is carried out to obtain relatively simple formulae that could be used in acoustic design projects without the need for timeconsuming computations with finite element software.

Coupled mantle dripping and lateral dragging controlling the lithosphere structure of the NWMoroccan margin and the Atlas Mountains: A numerical experiment
http://hdl.handle.net/2117/105402
Coupled mantle dripping and lateral dragging controlling the lithosphere structure of the NWMoroccan margin and the Atlas Mountains: A numerical experiment
Zlotnik, Sergio; JiménezMunt, Ivone; Fernández Gómez, Manel
Recent studies integrating gravity, geoid, surface heat flow, elevation and seismic data indicate a prominent lithospheric mantle thickening beneath the NWMoroccan margin (LAB >200 kmdepth) followed by thinning beneath the Atlas Domain (LAB about 80 kmdepth). Such unusual configuration has been explained by the combination of mantle underthrusting due to oblique AfricaEurasia convergence together with viscous dripping fed by asymmetric lateral mantle dragging, requiring a strong crustmantle decoupling. In the present work we examine the physical conditions under which the proposed asymmetric mantle drip and drag mechanism can reproduce this lithospheric configuration. We also analyse the influence of varying the kinematic boundary conditions as well as the mantle viscosity and the initial lithosphere geometry. Results indicate that the proposed dripdrag mechanism is dynamically feasible and only requires a lateral variation of the lithospheric strength. The further evolution of the gravitational instability can become either in convective removal of the lithospheric mantle, mantle delamination, or subduction initiation. The model reproduces the main trends of the presentday lithospheric geometry across the NWMoroccan margin and the Atlas Mountains, the characteristic time of the observed vertical movements, the amplitude and rates of uplift in the Atlas Mountains and offers an explanation to the Miocene to Pliocene volcanism. An abnormal constant tectonic subsidence rate in the margin is predicted. (C) 2013 Elsevier B.V. All rights reserved.
20170614T10:13:23Z
Zlotnik, Sergio
JiménezMunt, Ivone
Fernández Gómez, Manel
Recent studies integrating gravity, geoid, surface heat flow, elevation and seismic data indicate a prominent lithospheric mantle thickening beneath the NWMoroccan margin (LAB >200 kmdepth) followed by thinning beneath the Atlas Domain (LAB about 80 kmdepth). Such unusual configuration has been explained by the combination of mantle underthrusting due to oblique AfricaEurasia convergence together with viscous dripping fed by asymmetric lateral mantle dragging, requiring a strong crustmantle decoupling. In the present work we examine the physical conditions under which the proposed asymmetric mantle drip and drag mechanism can reproduce this lithospheric configuration. We also analyse the influence of varying the kinematic boundary conditions as well as the mantle viscosity and the initial lithosphere geometry. Results indicate that the proposed dripdrag mechanism is dynamically feasible and only requires a lateral variation of the lithospheric strength. The further evolution of the gravitational instability can become either in convective removal of the lithospheric mantle, mantle delamination, or subduction initiation. The model reproduces the main trends of the presentday lithospheric geometry across the NWMoroccan margin and the Atlas Mountains, the characteristic time of the observed vertical movements, the amplitude and rates of uplift in the Atlas Mountains and offers an explanation to the Miocene to Pliocene volcanism. An abnormal constant tectonic subsidence rate in the margin is predicted. (C) 2013 Elsevier B.V. All rights reserved.

Flight and passenger delay assignment optimization strategies
http://hdl.handle.net/2117/105306
Flight and passenger delay assignment optimization strategies
Villardi de Montlaur, Adeline de; Delgado Muñoz, Luis
This paper compares different optimization strategies for the minimization of flight and passenger delays at two levels: pretactical, with onground delay at origin, and tactical, with airborne delay close to the destination airport. The optimization model is based on the ground holding problem and uses various cost functions. The scenario considered takes place in a busy European airport and includes realistic values of traffic. A passenger assignment with connections at the hub is modeled. Statistical models are used for passenger and connecting passenger allocation, minimum time required for turnaround and tactical noise; whereas uncertainty is also introduced in the model for tactical noise. Performance of the various optimization processes is presented and compared to ration by schedule results.
20170609T15:10:25Z
Villardi de Montlaur, Adeline de
Delgado Muñoz, Luis
This paper compares different optimization strategies for the minimization of flight and passenger delays at two levels: pretactical, with onground delay at origin, and tactical, with airborne delay close to the destination airport. The optimization model is based on the ground holding problem and uses various cost functions. The scenario considered takes place in a busy European airport and includes realistic values of traffic. A passenger assignment with connections at the hub is modeled. Statistical models are used for passenger and connecting passenger allocation, minimum time required for turnaround and tactical noise; whereas uncertainty is also introduced in the model for tactical noise. Performance of the various optimization processes is presented and compared to ration by schedule results.

Use of wiris quizzes in an online calculus course
http://hdl.handle.net/2117/105260
Use of wiris quizzes in an online calculus course
Calm, Remei; Masià, Ramon; Olivé, Carme; Parés Mariné, Núria; Pozo Montero, Francesc; Ripoll, Jordi; Sancho Vinuesa, Teresa
Calculus courses often present a large number of difficulties to undergraduate students of scientific studies, especially in engineering degrees. These difficulties are sometimes related to teaching and assessment strategies. In this paper, a teaching innovation experience is presented within the framework of the Universitat Oberta de Catalunya. This teaching experience is focused on a continuous assessment through a systematic use of the socalled WIRIS quizzes. Academic outcomes are very positive from both quantitative and qualitative viewpoints.
20170609T06:29:14Z
Calm, Remei
Masià, Ramon
Olivé, Carme
Parés Mariné, Núria
Pozo Montero, Francesc
Ripoll, Jordi
Sancho Vinuesa, Teresa
Calculus courses often present a large number of difficulties to undergraduate students of scientific studies, especially in engineering degrees. These difficulties are sometimes related to teaching and assessment strategies. In this paper, a teaching innovation experience is presented within the framework of the Universitat Oberta de Catalunya. This teaching experience is focused on a continuous assessment through a systematic use of the socalled WIRIS quizzes. Academic outcomes are very positive from both quantitative and qualitative viewpoints.