Articles de revista
http://hdl.handle.net/2117/428
2018-04-19T21:11:27ZAnalysis of the discharge capacity of radial gated-spillways using CFD and ANN: Oliana Dam case study
http://hdl.handle.net/2117/113669
Analysis of the discharge capacity of radial gated-spillways using CFD and ANN: Oliana Dam case study
Salazar González, Fernando; Morán Moya, Rafael; Rossi, Riccardo; Oñate Ibáñez de Navarra, Eugenio
The paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana Dam is considered as a case study and the discharge capacity is predicted both by the application of a level-set-based free-surface solver and by the use of traditional empirical formulations. The results of the analysis are then used for training an artificial neural network to allow real-time predictions of the discharge in any situation of energy head and gate opening within the operation range of the reservoir. The comparison of the results obtained with the different methods shows that numerical models such as the FEM can be useful as a predictive tool for the analysis of the hydraulic performance of radial-gated spillways.
2018-02-02T20:05:25ZSalazar González, FernandoMorán Moya, RafaelRossi, RiccardoOñate Ibáñez de Navarra, EugenioThe paper focuses on the analysis of radial-gated spillways, which is carried out by the solution of a numerical model based on the finite element method (FEM). The Oliana Dam is considered as a case study and the discharge capacity is predicted both by the application of a level-set-based free-surface solver and by the use of traditional empirical formulations. The results of the analysis are then used for training an artificial neural network to allow real-time predictions of the discharge in any situation of energy head and gate opening within the operation range of the reservoir. The comparison of the results obtained with the different methods shows that numerical models such as the FEM can be useful as a predictive tool for the analysis of the hydraulic performance of radial-gated spillways.A compressible Lagrangian framework for the simulation of the underwater implosion of large air bubbles
http://hdl.handle.net/2117/113668
A compressible Lagrangian framework for the simulation of the underwater implosion of large air bubbles
Kamran, Kamran; Rossi, Riccardo; Oñate Ibáñez de Navarra, Eugenio; Idelsohn Barg, Sergio Rodolfo
A fully Lagrangian compressible numerical framework for the simulation of underwater implosion of a large air bubble is presented. Both air and water are considered compressible and the equations for the Lagrangian shock hydrodynamics are stabilized via a variationally consistent multiscale method. A nodally perfect matched definition of the interface is used and then the kinetic variables, pressure and density, are duplicated at the interface level. An adaptive mesh generation procedure, which respects the interface connectivities, is applied to provide enough refinement at the interface level. This framework is verified by several benchmarks which evaluate the behavior of the numerical scheme for severe compression and expansion cases. This model is then used to simulate the underwater implosion of a large cylindrical bubble, with a size in the order of cm. We observe that the conditions within the bubble are nearly uniform until the converging pressure wave is strong enough to create very large pressures near the center of the bubble. These bubble dynamics occur on very small spatial (0.3 mm), and time (0.1 ms) scales. During the final stage of the collapse Rayleigh–Taylor instabilities appear at the interface and then disappear when the rebounce starts. At the end of the rebounce phase the bubble radius reaches 50% of its initial value and the bubble recover its circular shape. It is when the second collapse starts, with higher mode shape instabilities excited at the bubble interface, that leads to the rupture of the bubble. Several graphs are presented and the pressure pulse detected in the water is compared by experiment.
2018-02-02T20:02:18ZKamran, KamranRossi, RiccardoOñate Ibáñez de Navarra, EugenioIdelsohn Barg, Sergio RodolfoA fully Lagrangian compressible numerical framework for the simulation of underwater implosion of a large air bubble is presented. Both air and water are considered compressible and the equations for the Lagrangian shock hydrodynamics are stabilized via a variationally consistent multiscale method. A nodally perfect matched definition of the interface is used and then the kinetic variables, pressure and density, are duplicated at the interface level. An adaptive mesh generation procedure, which respects the interface connectivities, is applied to provide enough refinement at the interface level. This framework is verified by several benchmarks which evaluate the behavior of the numerical scheme for severe compression and expansion cases. This model is then used to simulate the underwater implosion of a large cylindrical bubble, with a size in the order of cm. We observe that the conditions within the bubble are nearly uniform until the converging pressure wave is strong enough to create very large pressures near the center of the bubble. These bubble dynamics occur on very small spatial (0.3 mm), and time (0.1 ms) scales. During the final stage of the collapse Rayleigh–Taylor instabilities appear at the interface and then disappear when the rebounce starts. At the end of the rebounce phase the bubble radius reaches 50% of its initial value and the bubble recover its circular shape. It is when the second collapse starts, with higher mode shape instabilities excited at the bubble interface, that leads to the rupture of the bubble. Several graphs are presented and the pressure pulse detected in the water is compared by experiment.A fast and accurate method to solve the incompressible Navier-Stokes equations
http://hdl.handle.net/2117/113667
A fast and accurate method to solve the incompressible Navier-Stokes equations
Idelsohn Barg, Sergio Rodolfo; Nigro, Norberto; Gimenez, Juan; Rossi, Riccardo; Martí, Julio Marcelo
Purpose: The purpose of this paper is to highlight the possibilities of a novel Lagrangian formulation in dealing with the solution of the incompressible Navier-Stokes equations with very large time steps.
Design/methodology/approach: The design of the paper is based on introducing the origin of this novel numerical method, originally inspired on the Particle Finite Element Method (PFEM), summarizing the previously published theory in its moving mesh version. Afterwards its extension to fixed mesh version is introduced, showing some details about the implementation.
Findings: The authors have found that even though this method was originally designed to deal with heterogeneous or free-surface flows, it can be competitive with Eulerian alternatives, even in their range of optimal application in terms of accuracy, with an interesting robustness allowing to use large time steps in a stable way.
Originality/value: With this objective in mind, the authors have chosen a number of benchmark examples and have proved that the proposed algorithm provides results which compare favourably, both in terms of solution time and accuracy achieved, with alternative approaches, implemented in in-house and commercial codes.
2018-02-02T19:57:55ZIdelsohn Barg, Sergio RodolfoNigro, NorbertoGimenez, JuanRossi, RiccardoMartí, Julio MarceloPurpose: The purpose of this paper is to highlight the possibilities of a novel Lagrangian formulation in dealing with the solution of the incompressible Navier-Stokes equations with very large time steps.
Design/methodology/approach: The design of the paper is based on introducing the origin of this novel numerical method, originally inspired on the Particle Finite Element Method (PFEM), summarizing the previously published theory in its moving mesh version. Afterwards its extension to fixed mesh version is introduced, showing some details about the implementation.
Findings: The authors have found that even though this method was originally designed to deal with heterogeneous or free-surface flows, it can be competitive with Eulerian alternatives, even in their range of optimal application in terms of accuracy, with an interesting robustness allowing to use large time steps in a stable way.
Originality/value: With this objective in mind, the authors have chosen a number of benchmark examples and have proved that the proposed algorithm provides results which compare favourably, both in terms of solution time and accuracy achieved, with alternative approaches, implemented in in-house and commercial codes.A contact algorithm for shell problems via Delaunay-based meshing of the contact domain
http://hdl.handle.net/2117/113666
A contact algorithm for shell problems via Delaunay-based meshing of the contact domain
Kamran, Kamran; Rossi, Riccardo; Oñate Ibáñez de Navarra, Eugenio
The simulation of the contact within shells, with all of its different facets, represents still an open challenge in Computational Mechanics. Despite the effort spent in the development of techniques for the simulation of general contact problems, an all-seasons algorithm applicable to complex shell contact problems is yet to be developed. This work focuses on the solution of the contact between thin shells by using a technique derived from the particle finite element method together with a rotation-free shell triangle. The key concept is to define a discretization of the contact domain (CD) by constructing a finite element mesh of four-noded tetrahedra that describes the potential contact volume. The problem is completed by using an assumed-strain approach to define an elastic contact strain over the CD.
2018-02-02T19:52:52ZKamran, KamranRossi, RiccardoOñate Ibáñez de Navarra, EugenioThe simulation of the contact within shells, with all of its different facets, represents still an open challenge in Computational Mechanics. Despite the effort spent in the development of techniques for the simulation of general contact problems, an all-seasons algorithm applicable to complex shell contact problems is yet to be developed. This work focuses on the solution of the contact between thin shells by using a technique derived from the particle finite element method together with a rotation-free shell triangle. The key concept is to define a discretization of the contact domain (CD) by constructing a finite element mesh of four-noded tetrahedra that describes the potential contact volume. The problem is completed by using an assumed-strain approach to define an elastic contact strain over the CD.Multi-scale analysis of the early damage mechanics of ferritized ductile iron
http://hdl.handle.net/2117/106765
Multi-scale analysis of the early damage mechanics of ferritized ductile iron
Fernandino, D.O.; Cisilino, A. P.; Toro, S.; P.J., Sánchez
A multi-scale analysis of the linear elastic and the early damage stages of ferritic ductile iron is introduced in this work. The methodology combines numerical and experimental analyses in the macro and micro scales. Experiments in the micro-scale are used for the characterization of the material micro constituents and the assessment of the micro-scale damage mechanisms; experiments in the macro-scale provide the data to calibrate and validate the models. The 2D multi-scale problem is modeled using the pre-critical regime of the Failure-Oriented Multi-Scale Variational Formulation, which is implemented via a FE2 approach. Finite element analysis in the micro-scale is customized to account for plastic deformation and matrix-nodule debonding. The multi-scale model is found effective for capturing the sequence and extent of the damage mechanisms in the micro-scale and to estimate, via inverse analyses, parameters of the matrix-nodule debonding law. Results allow to develop new insights for the better understanding of the ductile iron damage mechanics and to draw conclusions related to the modeling aspects of the multi-scale simulation.
2017-07-24T14:44:08ZFernandino, D.O.Cisilino, A. P.Toro, S.P.J., SánchezA multi-scale analysis of the linear elastic and the early damage stages of ferritic ductile iron is introduced in this work. The methodology combines numerical and experimental analyses in the macro and micro scales. Experiments in the micro-scale are used for the characterization of the material micro constituents and the assessment of the micro-scale damage mechanisms; experiments in the macro-scale provide the data to calibrate and validate the models. The 2D multi-scale problem is modeled using the pre-critical regime of the Failure-Oriented Multi-Scale Variational Formulation, which is implemented via a FE2 approach. Finite element analysis in the micro-scale is customized to account for plastic deformation and matrix-nodule debonding. The multi-scale model is found effective for capturing the sequence and extent of the damage mechanisms in the micro-scale and to estimate, via inverse analyses, parameters of the matrix-nodule debonding law. Results allow to develop new insights for the better understanding of the ductile iron damage mechanics and to draw conclusions related to the modeling aspects of the multi-scale simulation.Optimization-based design of a heat flux concentrator
http://hdl.handle.net/2117/100524
Optimization-based design of a heat flux concentrator
Peralta, Ignacio; Fachinotti, Víctor D.; Ciarbonetti, Ángel A.
To gain control over the diffusive heat flux in a given domain, one needs to engineer a thermal metamaterial with a specific distribution of the generally anisotropic thermal conductivity throughout the domain. Until now, the appropriate conductivity distribution was usually determined using transformation thermodynamics. By this way, only a few particular cases of heat flux control in simple domains having simple boundary conditions were studied. Thermal metamaterials based on optimization algorithm provides superior properties compared to those using the previous methods. As a more general approach, we propose to define the heat control problem as an optimization problem where we minimize the error in guiding the heat flux in a given way, taking as design variables the parameters that define the variable microstructure of the metamaterial. In the present study we numerically demonstrate the ability to manipulate heat flux by designing a device to concentrate the thermal energy to its center without disturbing the temperature profile outside it.
2017-02-02T18:52:05ZPeralta, IgnacioFachinotti, Víctor D.Ciarbonetti, Ángel A.To gain control over the diffusive heat flux in a given domain, one needs to engineer a thermal metamaterial with a specific distribution of the generally anisotropic thermal conductivity throughout the domain. Until now, the appropriate conductivity distribution was usually determined using transformation thermodynamics. By this way, only a few particular cases of heat flux control in simple domains having simple boundary conditions were studied. Thermal metamaterials based on optimization algorithm provides superior properties compared to those using the previous methods. As a more general approach, we propose to define the heat control problem as an optimization problem where we minimize the error in guiding the heat flux in a given way, taking as design variables the parameters that define the variable microstructure of the metamaterial. In the present study we numerically demonstrate the ability to manipulate heat flux by designing a device to concentrate the thermal energy to its center without disturbing the temperature profile outside it.Modelo multi-escala con fracturas cohesivas en ambas escalas
http://hdl.handle.net/2117/96833
Modelo multi-escala con fracturas cohesivas en ambas escalas
Labanda, Nicolás A.; Giusti, Sebastián M.; Luccioni, Bibiana M.
En este trabajo se presentan resultados preliminares sobre un modelo multi-escala semiconcurrente para materiales con ablandamiento. Se propone una formulación mixta para la simulación de discontinuidades en los desplazamientos a ser usada en ambas escalas. La tensión sobre la fisura es considerada como incógnita del sistema de ecuaciones junto al campo de desplazamientos, y el salto se obtiene mediante la relación constitutiva (Ley tensión-separación). Se reformulan los principios axiomáticos propuestos por P.J. Blanco y S.M. Giusti (P.J. Blanco y S.M. Giusti, Journal of Elasticity, (2013)) y el concepto de inyección propuesto por P.J. Sánchez et al (P.J. Sánchez et al, Comp. Methods Appl. Mech. Engrg, 200:1220-1236 (2011)) para lograr una respuesta objetiva. La tensión proyectada sobre la normal de la fisura de la macro escala se inyecta en la fisura localizada del RVE, logrando como variable dual el salto en el campo de desplazamiento para la escala superior. De esta forma, en la fase estable del material la inyección en la transición de escalas mantiene la estructura clásica (partiendo de una compatibilización de deformaciones), mientras que en la fase no estable el proceso de transición sigue un camino inverso (partiendo de una compatibilización de tensiones sobre la localización en la micro escala). De esta manera se logra una inyección híbrida mediante deformaciones en el primer caso y tensiones en el segundo caso. Finalmente, se presentan ejemplos de homogeneización de la respuesta en problemas de fractura transversal de compuestos reforzados con fibras longitudinales.
2016-11-18T13:19:47ZLabanda, Nicolás A.Giusti, Sebastián M.Luccioni, Bibiana M.En este trabajo se presentan resultados preliminares sobre un modelo multi-escala semiconcurrente para materiales con ablandamiento. Se propone una formulación mixta para la simulación de discontinuidades en los desplazamientos a ser usada en ambas escalas. La tensión sobre la fisura es considerada como incógnita del sistema de ecuaciones junto al campo de desplazamientos, y el salto se obtiene mediante la relación constitutiva (Ley tensión-separación). Se reformulan los principios axiomáticos propuestos por P.J. Blanco y S.M. Giusti (P.J. Blanco y S.M. Giusti, Journal of Elasticity, (2013)) y el concepto de inyección propuesto por P.J. Sánchez et al (P.J. Sánchez et al, Comp. Methods Appl. Mech. Engrg, 200:1220-1236 (2011)) para lograr una respuesta objetiva. La tensión proyectada sobre la normal de la fisura de la macro escala se inyecta en la fisura localizada del RVE, logrando como variable dual el salto en el campo de desplazamiento para la escala superior. De esta forma, en la fase estable del material la inyección en la transición de escalas mantiene la estructura clásica (partiendo de una compatibilización de deformaciones), mientras que en la fase no estable el proceso de transición sigue un camino inverso (partiendo de una compatibilización de tensiones sobre la localización en la micro escala). De esta manera se logra una inyección híbrida mediante deformaciones en el primer caso y tensiones en el segundo caso. Finalmente, se presentan ejemplos de homogeneización de la respuesta en problemas de fractura transversal de compuestos reforzados con fibras longitudinales.Meso-scale fracture simulation using an augmented Lagrangian approach
http://hdl.handle.net/2117/96829
Meso-scale fracture simulation using an augmented Lagrangian approach
Labanda, Nicolás A.; Giusti, Sebastián M.; Luccioni, Bibiana M.
A cohesive zone model implemented in an augmented Lagrangian functional is used for simulation of meso-scale fracture problems in this paper. The method originally developed by Lorentz is first presented in a rigorous variational framework. The equivalence between the stationary point of the one-field problem and the saddle point of the mixed formulation is proved by solving the double inequality of the mixed functional. An adaptation to simulate fracture phenomena in the meso-scale via mesh modification is also presented as an algorithm to insert zero-thickness interface elements based on Lagrange multipliers, boarding the non-trivial task of the field interpolation for different crack paths (plain and tortuous). A suitable tool to study the matrix fracture and debonding phenomena in composites with strongly different component stiffnesses that avoids ill-conditioning matrices associated with intrinsic cohesive zone models is obtained. The method stability is discussed using a simple patch test. Some numerical applications to fracture problems taking into account the mesostructure and, particularly, the study of transverse failure of longitudinal fiber reinforced epoxy and the fracture in concrete specimens are included in the paper. Comparing the numerical results with the experimental results obtained by other researchers, the paper introduces a discussion about the influence of coarse aggregate volume in meso-scale fracture mechanisms in concrete L-shaped specimens.
2016-11-18T13:01:40ZLabanda, Nicolás A.Giusti, Sebastián M.Luccioni, Bibiana M.A cohesive zone model implemented in an augmented Lagrangian functional is used for simulation of meso-scale fracture problems in this paper. The method originally developed by Lorentz is first presented in a rigorous variational framework. The equivalence between the stationary point of the one-field problem and the saddle point of the mixed formulation is proved by solving the double inequality of the mixed functional. An adaptation to simulate fracture phenomena in the meso-scale via mesh modification is also presented as an algorithm to insert zero-thickness interface elements based on Lagrange multipliers, boarding the non-trivial task of the field interpolation for different crack paths (plain and tortuous). A suitable tool to study the matrix fracture and debonding phenomena in composites with strongly different component stiffnesses that avoids ill-conditioning matrices associated with intrinsic cohesive zone models is obtained. The method stability is discussed using a simple patch test. Some numerical applications to fracture problems taking into account the mesostructure and, particularly, the study of transverse failure of longitudinal fiber reinforced epoxy and the fracture in concrete specimens are included in the paper. Comparing the numerical results with the experimental results obtained by other researchers, the paper introduces a discussion about the influence of coarse aggregate volume in meso-scale fracture mechanisms in concrete L-shaped specimens.Inverse finite element modeling of shells using the degenerate solid approach
http://hdl.handle.net/2117/89892
Inverse finite element modeling of shells using the degenerate solid approach
Fachinotti, Víctor D.; Albanesi, Alejandro E.; Martínez Valle, José M.
The Inverse Finite Element Method (IFEM) for degenerate solid shells is introduced. IFEM allows determining the undeformed shape of a body (in this case, a shell-like body) such that it attains a desired shape after large elastic deformations. The model is based on the degenerate solid approach, which enables the use of the standard constitutive laws of Solid Mechanics. First, IFEM is applied to three popular benchmarks for validation purposes. Then, the capabilities of IFEM for inverse design are demonstrated by means of its application to the design of a microvalve.
2016-09-13T17:54:45ZFachinotti, Víctor D.Albanesi, Alejandro E.Martínez Valle, José M.The Inverse Finite Element Method (IFEM) for degenerate solid shells is introduced. IFEM allows determining the undeformed shape of a body (in this case, a shell-like body) such that it attains a desired shape after large elastic deformations. The model is based on the degenerate solid approach, which enables the use of the standard constitutive laws of Solid Mechanics. First, IFEM is applied to three popular benchmarks for validation purposes. Then, the capabilities of IFEM for inverse design are demonstrated by means of its application to the design of a microvalve.Spectral analysis of the Beznar dam accelerogram. Comparison with results in the northeastern of Spain
http://hdl.handle.net/2117/87083
Spectral analysis of the Beznar dam accelerogram. Comparison with results in the northeastern of Spain
Canas Torres, José Antonio; Barbat Barbat, Horia Alejandro; Pujades Beneit, Lluís; Egozcue Rubí, Juan José; Sarrate Ramos, Josep
Numerical analysis applied to the Beznar dam accelerograms (longitudinal and transversal components) shows that the Fourier amplitude spectrum is a good approximation to the pseudo-velocity spectra. Thís fact makes possible to use displacement ar velocíty seismograrns to generate acceleration of the ground in places
where acceleration data are not available.
Maximae accelerations determined near and at the Beznar dam are compared wíth the predicted acceleration values far the regían compressed by the Pyrenees Mountains, the lberic System and the Catalonia Coastal Mountains usíng a established theoretical formula
far this region. Theoretical and observad values are consistent among them.
2016-05-17T07:55:41ZCanas Torres, José AntonioBarbat Barbat, Horia AlejandroPujades Beneit, LluísEgozcue Rubí, Juan JoséSarrate Ramos, JosepNumerical analysis applied to the Beznar dam accelerograms (longitudinal and transversal components) shows that the Fourier amplitude spectrum is a good approximation to the pseudo-velocity spectra. Thís fact makes possible to use displacement ar velocíty seismograrns to generate acceleration of the ground in places
where acceleration data are not available.
Maximae accelerations determined near and at the Beznar dam are compared wíth the predicted acceleration values far the regían compressed by the Pyrenees Mountains, the lberic System and the Catalonia Coastal Mountains usíng a established theoretical formula
far this region. Theoretical and observad values are consistent among them.