Articles de revista
http://hdl.handle.net/2117/6145
2015-12-01T09:46:27ZEsquema adaptativo para problemas tridimensionales de convección-difusión
http://hdl.handle.net/2117/26367
Esquema adaptativo para problemas tridimensionales de convección-difusión
Monforte, Lluis; Pérez Foguet, Agustí
We present an adaptive scheme for three-dimensional convection-diffusion problems discretized by the Finite Element Method. The adaptive scheme is based on a remeshing strategy that applies a maximum volume constraint to the elements of a reference mesh. The remeshing can increase or decrease drastically the size of the elements in a single step automatically. With this strategy, the mesh quality does not deteriorate; as a consequence, the number of iterations required to solve the system of linear equations using iterative algorithms is kept constant. Two examples of very different characteristics are presented in order to analyze the proposal for a wide range of situations. The first is a three-dimensional extension of the Smolarkiewicz problem and the second is a simplified version of a point source pollutant transport problem. The results show the flexibility of the proposal. An optimal remeshing frequency, from a computational cost and accuracy of the results point of view, can be defined for both kinds of problems.
2015-02-16T14:14:57ZMonforte, LluisPérez Foguet, AgustíWe present an adaptive scheme for three-dimensional convection-diffusion problems discretized by the Finite Element Method. The adaptive scheme is based on a remeshing strategy that applies a maximum volume constraint to the elements of a reference mesh. The remeshing can increase or decrease drastically the size of the elements in a single step automatically. With this strategy, the mesh quality does not deteriorate; as a consequence, the number of iterations required to solve the system of linear equations using iterative algorithms is kept constant. Two examples of very different characteristics are presented in order to analyze the proposal for a wide range of situations. The first is a three-dimensional extension of the Smolarkiewicz problem and the second is a simplified version of a point source pollutant transport problem. The results show the flexibility of the proposal. An optimal remeshing frequency, from a computational cost and accuracy of the results point of view, can be defined for both kinds of problems.Arbitrary Lagrangian–Eulerian (ALE) formulation for hyperelastoplasticity
http://hdl.handle.net/2117/26359
Arbitrary Lagrangian–Eulerian (ALE) formulation for hyperelastoplasticity
Rodríguez Ferran, Antonio; Pérez Foguet, Agustí; Huerta, Antonio
The arbitrary Lagrangian–Eulerian (ALE) description in non-linear solid mechanics is nowadays stan-
dard for hypoelastic–plastic models. An extension to hyperelastic–plastic models is presented here.
A fractional-step method—a common choice in ALE analysis—is employed for time-marching: every
time-step is split into a Lagrangian phase, which accounts for material e>ects, and a convection phase,
where the relative motion between the material and the ?nite element mesh is considered. In contrast to
previous ALE formulations of hyperelasticity or hyperelastoplasticity, the deformed con?guration at the
beginning of the time-step, not the initial undeformed con?guration, is chosen as the reference con?g-
uration. As a consequence, convecting variables are required in the description of the elastic response.
This is not thecasein previous formulations, whereonly theplastic responsecontains convection
terms. In exchange for the extra convective terms, however, the proposed ALE approach has a major
advantage: only the quality of the mesh in the spatial domain must be ensured by the ALE remeshing
strategy; in previous formulations, it is also necessary to keep the distortion of the mesh in the material
domain under control. Thus, the full potential of the ALE description as an adaptive technique can be
exploited here. These aspects are illustrated in detail by means of three numerical examples: a necking
test, a coining test and a powder compaction tes
2015-02-16T09:40:36ZRodríguez Ferran, AntonioPérez Foguet, AgustíHuerta, AntonioThe arbitrary Lagrangian–Eulerian (ALE) description in non-linear solid mechanics is nowadays stan-
dard for hypoelastic–plastic models. An extension to hyperelastic–plastic models is presented here.
A fractional-step method—a common choice in ALE analysis—is employed for time-marching: every
time-step is split into a Lagrangian phase, which accounts for material e>ects, and a convection phase,
where the relative motion between the material and the ?nite element mesh is considered. In contrast to
previous ALE formulations of hyperelasticity or hyperelastoplasticity, the deformed con?guration at the
beginning of the time-step, not the initial undeformed con?guration, is chosen as the reference con?g-
uration. As a consequence, convecting variables are required in the description of the elastic response.
This is not thecasein previous formulations, whereonly theplastic responsecontains convection
terms. In exchange for the extra convective terms, however, the proposed ALE approach has a major
advantage: only the quality of the mesh in the spatial domain must be ensured by the ALE remeshing
strategy; in previous formulations, it is also necessary to keep the distortion of the mesh in the material
domain under control. Thus, the full potential of the ALE description as an adaptive technique can be
exploited here. These aspects are illustrated in detail by means of three numerical examples: a necking
test, a coining test and a powder compaction tesNumerical differentiation for local and global tangent operators in computational plasticity
http://hdl.handle.net/2117/26356
Numerical differentiation for local and global tangent operators in computational plasticity
Pérez Foguet, Agustí; Rodríguez Ferran, Antonio; Huerta, Antonio
In this paper, numerical di¿erentiation is applied to integrate plastic constitutive laws and to compute the corresponding consistent
tangent operators. The derivatives of the constitutive equations are approximated by means of di¿erence schemes. These derivatives are
needed to achieve quadratic convergence in the integration at Gauss-point level and in the solution of the boundary value problem.
Numerical di¿erentiation is shown to be a simple, robust and competitive alternative to analytical derivatives. Quadratic convergence
is maintained, provided that adequate schemes and stepsizes are chosen. This point is illustrated by means of some numerical
examples.
2015-02-16T09:16:20ZPérez Foguet, AgustíRodríguez Ferran, AntonioHuerta, AntonioIn this paper, numerical di¿erentiation is applied to integrate plastic constitutive laws and to compute the corresponding consistent
tangent operators. The derivatives of the constitutive equations are approximated by means of di¿erence schemes. These derivatives are
needed to achieve quadratic convergence in the integration at Gauss-point level and in the solution of the boundary value problem.
Numerical di¿erentiation is shown to be a simple, robust and competitive alternative to analytical derivatives. Quadratic convergence
is maintained, provided that adequate schemes and stepsizes are chosen. This point is illustrated by means of some numerical
examples.Implementing pro-poor policies in a decentralized context: the case of the Rural Water Supply and Sanitation Program in Tanzania
http://hdl.handle.net/2117/26354
Implementing pro-poor policies in a decentralized context: the case of the Rural Water Supply and Sanitation Program in Tanzania
Jiménez Fernández de Palencia, Alejandro; Pérez Foguet, Agustí
This paper examines the challenge of achieving
a balance between the implementation of centrally
designed pro-poor policies and the decentralization of
responsibilities to local governments in many African
countries. It analyzes the implementation of the Rural
Water Supply and Sanitation Program in Tanzania. Key
mechanisms for planning and allocating resources are
analyzed at ministry, district, and village levels. Results
show that a mixture of policy incoherencies, technical
shortcomings and political influence determine that only a
small proportion of funds reaches the underserved areas.
We argue that a greater connection between the bottom-up
and top-down planning mechanisms, and a sharp increase
of downwards accountability are needed before decentral-
ized decision-making result in better resources allocation.
Meanwhile a bigger intervention from central government
is needed.
2015-02-16T09:06:23ZJiménez Fernández de Palencia, AlejandroPérez Foguet, AgustíThis paper examines the challenge of achieving
a balance between the implementation of centrally
designed pro-poor policies and the decentralization of
responsibilities to local governments in many African
countries. It analyzes the implementation of the Rural
Water Supply and Sanitation Program in Tanzania. Key
mechanisms for planning and allocating resources are
analyzed at ministry, district, and village levels. Results
show that a mixture of policy incoherencies, technical
shortcomings and political influence determine that only a
small proportion of funds reaches the underserved areas.
We argue that a greater connection between the bottom-up
and top-down planning mechanisms, and a sharp increase
of downwards accountability are needed before decentral-
ized decision-making result in better resources allocation.
Meanwhile a bigger intervention from central government
is needed.Dimensionless analysis of HSDM and application to simulation of breakthrough curves of highly adsorbent porous media
http://hdl.handle.net/2117/26352
Dimensionless analysis of HSDM and application to simulation of breakthrough curves of highly adsorbent porous media
Pérez Foguet, Agustí; Casoni Rero, Eva; Huerta, Antonio
The homogeneous surface diffusion model (HSDM) is widely used for adsorption modeling of aqueous solutions. The Biot number is usually used to characterize model behavior. However, some limitations of this characterization have been reported recently, and the Stanton number has been proposed as a complement to be considered. In this work, a detailed dimensionless analysis of HSDM is presented and limit behaviors of the model are characterized, confirming but extending previous results. An accurate and efficient numerical solver is used for these purposes. The intraparticle diffusion equation is reduced to a system of two ordinary differential equations, the transport-reaction equation is discretized by using a discontinuous Galerkin method, and the overall system evolution is integrated with a time-marching scheme. This approach facilitates the simulation of HSDM with a wide range of dimensionless numbers and with a correct treatment of shocks, which appear with nonlinear adsorption isotherms and with large Biot numbers and small surface diffusivity modulus. The approach is applied to simulate the breakthrough curves of granular ferric hydroxide. Published experimental data is adequately simulated.
2015-02-16T08:50:14ZPérez Foguet, AgustíCasoni Rero, EvaHuerta, AntonioThe homogeneous surface diffusion model (HSDM) is widely used for adsorption modeling of aqueous solutions. The Biot number is usually used to characterize model behavior. However, some limitations of this characterization have been reported recently, and the Stanton number has been proposed as a complement to be considered. In this work, a detailed dimensionless analysis of HSDM is presented and limit behaviors of the model are characterized, confirming but extending previous results. An accurate and efficient numerical solver is used for these purposes. The intraparticle diffusion equation is reduced to a system of two ordinary differential equations, the transport-reaction equation is discretized by using a discontinuous Galerkin method, and the overall system evolution is integrated with a time-marching scheme. This approach facilitates the simulation of HSDM with a wide range of dimensionless numbers and with a correct treatment of shocks, which appear with nonlinear adsorption isotherms and with large Biot numbers and small surface diffusivity modulus. The approach is applied to simulate the breakthrough curves of granular ferric hydroxide. Published experimental data is adequately simulated.Adaptive finite element simulation of stack pollutant emissions over complex terrains
http://hdl.handle.net/2117/26322
Adaptive finite element simulation of stack pollutant emissions over complex terrains
Oliver Serra, Albert; Montero Garcia, Gustavo; Montenegro Armas, Rafael; Rodriguez Barrera, Eduardo; Escobar Sánchez, José M.; Pérez Foguet, Agustí
A three-dimensional finite element model for the pollutant dispersion is presented. In these environmental processes over a complex terrain, a mesh generator capable of adapting itself to the topographic characteristics is essential. The first stage of the model consists on the construction of an adaptive tetrahedral mesh of a rectangular region bounded in its lower part by the terrain and in its upper part by a horizontal plane. Once the mesh is constructed, an adaptive local refinement of tetrahedra is used in order to capture the plume rise. Wind measurements are used to compute an interpolated wind field, that is modified by using a mass-consistent model and perturbing its vertical component to introduce the plume rise effect. Then, we use an Eulerian convection–diffusion–reaction model to simulate the pollutant dispersion. In this work, the transport of pollutants is considered and dry deposition is formulated as a boundary condition. The discretization of the stack geometry allows to define the emissions as boundary conditions. The proposed model uses an adaptive finite element space discretization, a Crank-Nicolson time scheme, and a splitting operator. This approach has been applied in La Palma island. Finally, numerical results and conclusions are presented.
2015-02-12T13:18:48ZOliver Serra, AlbertMontero Garcia, GustavoMontenegro Armas, RafaelRodriguez Barrera, EduardoEscobar Sánchez, José M.Pérez Foguet, AgustíA three-dimensional finite element model for the pollutant dispersion is presented. In these environmental processes over a complex terrain, a mesh generator capable of adapting itself to the topographic characteristics is essential. The first stage of the model consists on the construction of an adaptive tetrahedral mesh of a rectangular region bounded in its lower part by the terrain and in its upper part by a horizontal plane. Once the mesh is constructed, an adaptive local refinement of tetrahedra is used in order to capture the plume rise. Wind measurements are used to compute an interpolated wind field, that is modified by using a mass-consistent model and perturbing its vertical component to introduce the plume rise effect. Then, we use an Eulerian convection–diffusion–reaction model to simulate the pollutant dispersion. In this work, the transport of pollutants is considered and dry deposition is formulated as a boundary condition. The discretization of the stack geometry allows to define the emissions as boundary conditions. The proposed model uses an adaptive finite element space discretization, a Crank-Nicolson time scheme, and a splitting operator. This approach has been applied in La Palma island. Finally, numerical results and conclusions are presented.A multimesh adaptive scheme for air quality modeling with the finite element method
http://hdl.handle.net/2117/26313
A multimesh adaptive scheme for air quality modeling with the finite element method
Monforte, Lluis; Pérez Foguet, Agustí
A multimesh adaptive scheme for convection–diffusion–reaction problems for a large number of components
is presented. The problem is solved by splitting transport and reaction processes. This way, the evaluation
of the nonreactive part for each component and the reaction at each node constitute independent tasks. This
allows to discretize each component of the solution on a distinct computational mesh, adapted on the basis
of its error indicator. The standard single-mesh strategy is used for comparison. Simulations of a point emis-
sion in a 3D domain are presented. Low remeshing periods of the adaptive scheme are found to be optimal,
in terms of computational cost and accuracy, for the nonreactive problem. Examples with several reaction
terms, with an increase of the complexity, are then presented. Results show that the accuracy of single-mesh
and multimesh strategies are similar. Instead, the computational cost of the multimesh strategy is lower than
the single-mesh in the majority of the examples; this process is controlled by the stiff behavior of the reactive
term. The problem size of the multimesh scheme is much lower, and therefore, larger spatial discretizations
can be simulated for a given available memory. The efficiency of the multimesh strategy increases with
the number of species and the number of species that develop a plume. Finally, an example of a punctual
emission considering realistic values of the initial concentrations and using the Community Multiscale Air
Quality-CBO5 reaction model, which involves 62 components, is presented; the small-scale structure of the
different nitrogen components near the emitter is capture
2015-02-12T09:26:28ZMonforte, LluisPérez Foguet, AgustíA multimesh adaptive scheme for convection–diffusion–reaction problems for a large number of components
is presented. The problem is solved by splitting transport and reaction processes. This way, the evaluation
of the nonreactive part for each component and the reaction at each node constitute independent tasks. This
allows to discretize each component of the solution on a distinct computational mesh, adapted on the basis
of its error indicator. The standard single-mesh strategy is used for comparison. Simulations of a point emis-
sion in a 3D domain are presented. Low remeshing periods of the adaptive scheme are found to be optimal,
in terms of computational cost and accuracy, for the nonreactive problem. Examples with several reaction
terms, with an increase of the complexity, are then presented. Results show that the accuracy of single-mesh
and multimesh strategies are similar. Instead, the computational cost of the multimesh strategy is lower than
the single-mesh in the majority of the examples; this process is controlled by the stiff behavior of the reactive
term. The problem size of the multimesh scheme is much lower, and therefore, larger spatial discretizations
can be simulated for a given available memory. The efficiency of the multimesh strategy increases with
the number of species and the number of species that develop a plume. Finally, an example of a punctual
emission considering realistic values of the initial concentrations and using the Community Multiscale Air
Quality-CBO5 reaction model, which involves 62 components, is presented; the small-scale structure of the
different nitrogen components near the emitter is captureTrace metal content of sediments close to mine sites in the andean region
http://hdl.handle.net/2117/25790
Trace metal content of sediments close to mine sites in the andean region
Yacoub López, Cristina; Pérez Foguet, Agustí; Miralles Esteban, Núria
This study is a preliminary examination of heavy metal pollution in sediments close to two mine sites in the upper part of the Jequetepeque River Basin, Peru. Sediment concentrations of Al, As, Cd, Cu, Cr, Fe, Hg, Ni, Pb, Sb, Sn, and Zn were analyzed. A comparative study of the trace metal content of sediments shows that the highest concentrations are found at the closest points to the mine sites in both cases. The sediment quality analysis was performed using the threshold effect level of the Canadian guidelines (TEL). The sediment samples analyzed show that potential ecological risk is caused frequently at both sites by As, Cd, Cu, Hg, Pb, and Zn. The long-term influence of sediment metals in the environment is also assessed by sequential extraction scheme analysis (SES). The availability of metals in sediments is assessed, and it is considered a significant threat to the environment for As, Cd, and Sb close to one mine site and Cr and Hg close to the other mine site. Statistical analysis of sediment samples provides a characterization of both subbasins, showing low concentrations of a specific set of metals and identifies the main characteristics of the different pollution sources. A tentative relationship between pollution sources and possible ecological risk is established.
2015-01-16T12:01:59ZYacoub López, CristinaPérez Foguet, AgustíMiralles Esteban, NúriaThis study is a preliminary examination of heavy metal pollution in sediments close to two mine sites in the upper part of the Jequetepeque River Basin, Peru. Sediment concentrations of Al, As, Cd, Cu, Cr, Fe, Hg, Ni, Pb, Sb, Sn, and Zn were analyzed. A comparative study of the trace metal content of sediments shows that the highest concentrations are found at the closest points to the mine sites in both cases. The sediment quality analysis was performed using the threshold effect level of the Canadian guidelines (TEL). The sediment samples analyzed show that potential ecological risk is caused frequently at both sites by As, Cd, Cu, Hg, Pb, and Zn. The long-term influence of sediment metals in the environment is also assessed by sequential extraction scheme analysis (SES). The availability of metals in sediments is assessed, and it is considered a significant threat to the environment for As, Cd, and Sb close to one mine site and Cr and Hg close to the other mine site. Statistical analysis of sediment samples provides a characterization of both subbasins, showing low concentrations of a specific set of metals and identifies the main characteristics of the different pollution sources. A tentative relationship between pollution sources and possible ecological risk is established.Automatic subsystem identification in statistical energy analysis
http://hdl.handle.net/2117/24965
Automatic subsystem identification in statistical energy analysis
Díaz Cereceda, Cristina; Poblet-Puig, Jordi; Rodríguez Ferran, Antonio
An automatic methodology for identifying SEA (statistical energy analysis) subsystems within a vibroacoustic system is presented. It consists in dividing the system into cells and grouping them into subsystems via a hierarchical cluster analysis based on the problem eigenmodes. The subsystem distribution corresponds to the optimal grouping of the cells, which is defined in terms of the correlation distance between them. The main advantages of this methodology are its automatic performance and its applicability both to vibratory and vibroacoustic systems. Moreover, the method allows the definition of more than one subsystem in the same geometrical region when required. This is the case of eigenmodes with a very different mechanical response (e.g. out-of-plane or in-plane vibration in shells).
2014-12-09T18:47:12ZDíaz Cereceda, CristinaPoblet-Puig, JordiRodríguez Ferran, AntonioAn automatic methodology for identifying SEA (statistical energy analysis) subsystems within a vibroacoustic system is presented. It consists in dividing the system into cells and grouping them into subsystems via a hierarchical cluster analysis based on the problem eigenmodes. The subsystem distribution corresponds to the optimal grouping of the cells, which is defined in terms of the correlation distance between them. The main advantages of this methodology are its automatic performance and its applicability both to vibratory and vibroacoustic systems. Moreover, the method allows the definition of more than one subsystem in the same geometrical region when required. This is the case of eigenmodes with a very different mechanical response (e.g. out-of-plane or in-plane vibration in shells).Understanding and strain-engineering wrinkle networks in supported graphene through simulations
http://hdl.handle.net/2117/24943
Understanding and strain-engineering wrinkle networks in supported graphene through simulations
Zhang, Kuan; Arroyo Balaguer, Marino
Wrinkle networks are ubiquitous buckle-induced delaminations in supported graphene, which locally modify the electronic structure and degrade device performance. Although the strong property-deformation coupling of graphene can be potentially harnessed by strain engineering, it has not been possible to precisely control the geometry of wrinkle networks. Through numerical simulations based on an atomistically informed continuum theory, we understand how strain anisotropy, adhesion and friction govern spontaneous wrinkling. We then propose a strategy to control the location of wrinkles through patterns of weaker adhesion. This strategy is deceptively simple, and can in fact fail in several ways, particularly under biaxial compression. However, within bounds set by the physics of wrinkling, it is possible to robustly create by strain a variety of wrinkle network geometries and junction configurations. Graphene is nearly unstrained in the planar regions bounded by wrinkles, highly curved along wrinkles, and highly stretched and curved at junctions, which can either locally attenuate or amplify the applied strain depending on their configuration. These mechanically self-assembled networks are stable under the pressure produced by an enclosed fluid and form continuous channels, opening the door to nano-fluidic applications.
2014-12-05T13:38:53ZZhang, KuanArroyo Balaguer, MarinoWrinkle networks are ubiquitous buckle-induced delaminations in supported graphene, which locally modify the electronic structure and degrade device performance. Although the strong property-deformation coupling of graphene can be potentially harnessed by strain engineering, it has not been possible to precisely control the geometry of wrinkle networks. Through numerical simulations based on an atomistically informed continuum theory, we understand how strain anisotropy, adhesion and friction govern spontaneous wrinkling. We then propose a strategy to control the location of wrinkles through patterns of weaker adhesion. This strategy is deceptively simple, and can in fact fail in several ways, particularly under biaxial compression. However, within bounds set by the physics of wrinkling, it is possible to robustly create by strain a variety of wrinkle network geometries and junction configurations. Graphene is nearly unstrained in the planar regions bounded by wrinkles, highly curved along wrinkles, and highly stretched and curved at junctions, which can either locally attenuate or amplify the applied strain depending on their configuration. These mechanically self-assembled networks are stable under the pressure produced by an enclosed fluid and form continuous channels, opening the door to nano-fluidic applications.