Articles de revista
http://hdl.handle.net/2117/6145
Mon, 24 Oct 2016 18:21:13 GMT2016-10-24T18:21:13ZOptimizing mesh distortion by hierarchical iteration relocation of the nodes on the CAD entities
http://hdl.handle.net/2117/90814
Optimizing mesh distortion by hierarchical iteration relocation of the nodes on the CAD entities
Ruiz Gironés, Eloi; Roca Navarro, Xevi; Sarrate Ramos, Josep
Mesh untangling and smoothing is an important part of the meshing process to obtain high-quality discretizations. The usual approach consists on moving the position of the interior nodes while considering fixed the position of the boundary ones. However, the boundary nodes may constrain the quality of the whole mesh, and high-quality elements may not be generated. Specifically, thin regions in the geometry or special configurations of the boundary edges may induce low-quality elements. To overcome this drawback, we present a smoothing and untangling procedure that moves the interior nodes as well as the boundary ones, via an optimization process. The objective function is defined as a regularized distortion of the elements, and takes the nodal Cartesian coordinates as input arguments. When dealing with surface and edge nodes, the objective function uses the nodal parametric coordinates in order to avoid projecting them to the boundary. The novelty of the approach is that we consider a single target objective function (mesh distortion) where all the nodes, except the vertex nodes, are free to move on the corresponding CAD entity. Although the objective function is defined globally, for implementation purposes we propose to perform a node-by-node process. To minimize the objective function, we consider a block iterated non-linear Gauss-Seidel method using a hierarchical approach. That is, we first smooth the edge nodes, then the face nodes, and finally the inner nodes. This process is iterated using a node-by-node Gauss-Seidel approach until convergence is achieved.
Tue, 18 Oct 2016 07:55:09 GMThttp://hdl.handle.net/2117/908142016-10-18T07:55:09ZRuiz Gironés, EloiRoca Navarro, XeviSarrate Ramos, JosepMesh untangling and smoothing is an important part of the meshing process to obtain high-quality discretizations. The usual approach consists on moving the position of the interior nodes while considering fixed the position of the boundary ones. However, the boundary nodes may constrain the quality of the whole mesh, and high-quality elements may not be generated. Specifically, thin regions in the geometry or special configurations of the boundary edges may induce low-quality elements. To overcome this drawback, we present a smoothing and untangling procedure that moves the interior nodes as well as the boundary ones, via an optimization process. The objective function is defined as a regularized distortion of the elements, and takes the nodal Cartesian coordinates as input arguments. When dealing with surface and edge nodes, the objective function uses the nodal parametric coordinates in order to avoid projecting them to the boundary. The novelty of the approach is that we consider a single target objective function (mesh distortion) where all the nodes, except the vertex nodes, are free to move on the corresponding CAD entity. Although the objective function is defined globally, for implementation purposes we propose to perform a node-by-node process. To minimize the objective function, we consider a block iterated non-linear Gauss-Seidel method using a hierarchical approach. That is, we first smooth the edge nodes, then the face nodes, and finally the inner nodes. This process is iterated using a node-by-node Gauss-Seidel approach until convergence is achieved.Adaptividade e estimativas de erro orientadas por metas aplicadas a um benchmark test de propagação de onda
http://hdl.handle.net/2117/90741
Adaptividade e estimativas de erro orientadas por metas aplicadas a um benchmark test de propagação de onda
Steffens, Lindaura; Díez, Pedro; Parés Mariné, Núria; Alves, Marcelo Krajnc
O objetivo deste artigo é estudar a eficiência e a robustez de técnicas adaptativas e estimativas de erro orientadas por metas para um benchmark test. As técnicas utilizadas aqui são baseadas em um simples pós-processo das aproximacções de elementos finitos. As estimativas de erro orientadas por metas são obtidas por analisar o problema direto e um problema auxiliar, o qual está relacionado com a quantidade de interesse específico. O procedimento proposto é válido para quantidades lineares e não-lineares. Além disso, são discutidas diferentes representacções para o erro e é analisada a influência do erro de dispersão. Os resultados numéricos mostram que as estimativas de erro fornecem boas aproximações ao erro real e que a técnica de refino adaptativo proposta conduz a uma redução mais rápida do erro.
Thu, 13 Oct 2016 12:42:25 GMThttp://hdl.handle.net/2117/907412016-10-13T12:42:25ZSteffens, LindauraDíez, PedroParés Mariné, NúriaAlves, Marcelo KrajncO objetivo deste artigo é estudar a eficiência e a robustez de técnicas adaptativas e estimativas de erro orientadas por metas para um benchmark test. As técnicas utilizadas aqui são baseadas em um simples pós-processo das aproximacções de elementos finitos. As estimativas de erro orientadas por metas são obtidas por analisar o problema direto e um problema auxiliar, o qual está relacionado com a quantidade de interesse específico. O procedimento proposto é válido para quantidades lineares e não-lineares. Além disso, são discutidas diferentes representacções para o erro e é analisada a influência do erro de dispersão. Os resultados numéricos mostram que as estimativas de erro fornecem boas aproximações ao erro real e que a técnica de refino adaptativo proposta conduz a uma redução mais rápida do erro.Un método de captura de choques basado en las funciones de forma para Galerkin discontinuo de alto orden
http://hdl.handle.net/2117/90730
Un método de captura de choques basado en las funciones de forma para Galerkin discontinuo de alto orden
Casoni Rero, Eva; Peraire Guitart, Jaume; Huerta, Antonio
En este artículo se presenta un método de alto orden de Galerkin discontinuo para problemas de flujo com- presible, en los cuales es muy frecuente la aparición de choques. La estabilización se introduce mediante una nueva base de funciones. Esta base tiene la flexibilidad de variar localmente (en cada elemento) entre un espacio de funciones polinómicas continuas o un espacio de funciones polinómicas a trozos. Así, el método propuesto proporciona un puente entre los métodos estándar de alto orden de Galerkin disconti- nuo y los clásicos métodos de volúmenes finitos, manteniendo la localidad y compacidad del esquema. La variación de las funciones de la base se define automáticamente en función de la regularidad de la solución y la estabilización se introduce mediante el operador salto, estándar en los métodos Galerkin disconti- nuo. A diferencia de los clásicos métodos de limitadores de pendiente, la estrategia que se presenta es muy local y robusta, y es aplicable a cualquier orden de aproximación. Además, el método propuesto no requiere refinamiento adaptativo de la malla ni restricción del esquema de integración temporal. Se consideran varias aplicaciones de las ecuaciones de Euler que demuestran la validez y efectividad del método, especialmente para altos órdenes de aproximación.
Thu, 13 Oct 2016 11:33:45 GMThttp://hdl.handle.net/2117/907302016-10-13T11:33:45ZCasoni Rero, EvaPeraire Guitart, JaumeHuerta, AntonioEn este artículo se presenta un método de alto orden de Galerkin discontinuo para problemas de flujo com- presible, en los cuales es muy frecuente la aparición de choques. La estabilización se introduce mediante una nueva base de funciones. Esta base tiene la flexibilidad de variar localmente (en cada elemento) entre un espacio de funciones polinómicas continuas o un espacio de funciones polinómicas a trozos. Así, el método propuesto proporciona un puente entre los métodos estándar de alto orden de Galerkin disconti- nuo y los clásicos métodos de volúmenes finitos, manteniendo la localidad y compacidad del esquema. La variación de las funciones de la base se define automáticamente en función de la regularidad de la solución y la estabilización se introduce mediante el operador salto, estándar en los métodos Galerkin disconti- nuo. A diferencia de los clásicos métodos de limitadores de pendiente, la estrategia que se presenta es muy local y robusta, y es aplicable a cualquier orden de aproximación. Además, el método propuesto no requiere refinamiento adaptativo de la malla ni restricción del esquema de integración temporal. Se consideran varias aplicaciones de las ecuaciones de Euler que demuestran la validez y efectividad del método, especialmente para altos órdenes de aproximación.Melt fracturing and healing: a mechanism for rhyolite magma degassing and origin of obsidian
http://hdl.handle.net/2117/90728
Melt fracturing and healing: a mechanism for rhyolite magma degassing and origin of obsidian
Cabrera, Agustín; Weinberg, Roberto F.; Wright, Heather M. N.; Zlotnik, Sergio; Cas, Ray A.F.
We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate that rhyolite melt degassed through the fault surface. Transects define a trough of low water content coincident with the fault trace, surrounded on either side by high-water-content plateaus. Plateaus indicate that obsidian on either side of the fault equilibrated at different pressure-temperature (P-T) conditions before being juxtaposed. The curves into the troughs indicate disequilibrium and water loss through diffusion. If we assume constant T, melt equilibrated at pressures differing by 0.74 MPa before juxtaposition, and the fault acted as a low-P permeable path for H2O that diffused from the glass within time scales of 10 and 30 min. Assuming constant P instead, melt on either side could have equilibrated at temperatures differing by as much as 100 °C, before being brought together. Water content on the fault trace is particularly sensitive to post-healing diffusion. Its preserved value indicates either higher temperature or lower pressure than the surroundings, indicative of shear heating and dynamic decompression. Our results reveal that water contents of obsidian on either side of the faults equilibrated under different P-T conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched. Degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity, and could be an efficient mechanism of producing low-water-content obsidian.
Thu, 13 Oct 2016 11:13:13 GMThttp://hdl.handle.net/2117/907282016-10-13T11:13:13ZCabrera, AgustínWeinberg, Roberto F.Wright, Heather M. N.Zlotnik, SergioCas, Ray A.F.We present water content transects across a healed fault in pyroclastic obsidian from Lami pumice cone, Lipari, Italy, using synchrotron Fourier transform infrared spectroscopy. Results indicate that rhyolite melt degassed through the fault surface. Transects define a trough of low water content coincident with the fault trace, surrounded on either side by high-water-content plateaus. Plateaus indicate that obsidian on either side of the fault equilibrated at different pressure-temperature (P-T) conditions before being juxtaposed. The curves into the troughs indicate disequilibrium and water loss through diffusion. If we assume constant T, melt equilibrated at pressures differing by 0.74 MPa before juxtaposition, and the fault acted as a low-P permeable path for H2O that diffused from the glass within time scales of 10 and 30 min. Assuming constant P instead, melt on either side could have equilibrated at temperatures differing by as much as 100 °C, before being brought together. Water content on the fault trace is particularly sensitive to post-healing diffusion. Its preserved value indicates either higher temperature or lower pressure than the surroundings, indicative of shear heating and dynamic decompression. Our results reveal that water contents of obsidian on either side of the faults equilibrated under different P-T conditions and were out of equilibrium with each other when they were juxtaposed due to faulting immediately before the system was quenched. Degassing due to faulting could be linked to cyclical seismic activity and general degassing during silicic volcanic activity, and could be an efficient mechanism of producing low-water-content obsidian.The solution of linear mechanical systems in terms of path superposition
http://hdl.handle.net/2117/89392
The solution of linear mechanical systems in terms of path superposition
Magrans Fontrodona, Francesc Xavier; Poblet-Puig, Jordi; Rodríguez Ferran, Antonio
We prove that the solution of any linear mechanical system can be expressed as a linear combination of signal transmission paths. This is done in the framework of the Global Transfer Direct Transfer (GTDT) formulation for vibroacoustic problems. Transmission paths are expressed as powers of the transfer matrix. The key idea of the proof is to generalise the Neumann series of the transfer matrix --which is convergent only if its spectral radius is smaller than one-- into a modified Neumann series that is convergent regardless of the eigenvalues of the transfer matrix. The modification consists in choosing the appropriate combination coefficients for the powers of the transfer matrix in the series. A recursive formula for the computation of these factors is derived. The theoretical results are illustrated by means of numerical examples. Finally, we show that the generalised Neumann series can be understood as an acceleration (i.e. convergence speedup) of the Jacobi iterative method.
Mon, 29 Aug 2016 10:40:45 GMThttp://hdl.handle.net/2117/893922016-08-29T10:40:45ZMagrans Fontrodona, Francesc XavierPoblet-Puig, JordiRodríguez Ferran, AntonioWe prove that the solution of any linear mechanical system can be expressed as a linear combination of signal transmission paths. This is done in the framework of the Global Transfer Direct Transfer (GTDT) formulation for vibroacoustic problems. Transmission paths are expressed as powers of the transfer matrix. The key idea of the proof is to generalise the Neumann series of the transfer matrix --which is convergent only if its spectral radius is smaller than one-- into a modified Neumann series that is convergent regardless of the eigenvalues of the transfer matrix. The modification consists in choosing the appropriate combination coefficients for the powers of the transfer matrix in the series. A recursive formula for the computation of these factors is derived. The theoretical results are illustrated by means of numerical examples. Finally, we show that the generalised Neumann series can be understood as an acceleration (i.e. convergence speedup) of the Jacobi iterative method.Regression curves for vibration transmission across junctions of heavyweight walls and floors based on finite element methods and wave theory
http://hdl.handle.net/2117/89391
Regression curves for vibration transmission across junctions of heavyweight walls and floors based on finite element methods and wave theory
Hopkins, Carl; Crispin, Charlotte; Poblet-Puig, Jordi; Guigou-Carter, Catherine
Sound insulation prediction models in European and International standards use the vibration reduction index to calculate flanking transmission across junctions of walls and floors. These standards contain empirical relationships between the ratio of mass per unit areas for the walls/floors that form the junction and a frequency-independent vibration reduction index. Calculations using wave theory show that there is a stronger relationship between the ratio of characteristic moment impedances and the transmission loss from which the vibration reduction index can subsequently be calculated. In addition, the assumption of frequency-independent vibration reduction indices has been shown to be incorrect due to in-plane wave generation at the junction. Therefore numerical experiments with FEM, SFEM and wave theory have been used to develop new regression curves between these variables for the low-, mid- and high-frequency ranges. The junctions considered were L-, T- and X-junctions formed from heavyweight walls and floors. These new relationships have been implemented in the prediction models and they tend to improve the agreement between the measured and predicted airborne and impact sound insulation.
Mon, 29 Aug 2016 10:34:56 GMThttp://hdl.handle.net/2117/893912016-08-29T10:34:56ZHopkins, CarlCrispin, CharlottePoblet-Puig, JordiGuigou-Carter, CatherineSound insulation prediction models in European and International standards use the vibration reduction index to calculate flanking transmission across junctions of walls and floors. These standards contain empirical relationships between the ratio of mass per unit areas for the walls/floors that form the junction and a frequency-independent vibration reduction index. Calculations using wave theory show that there is a stronger relationship between the ratio of characteristic moment impedances and the transmission loss from which the vibration reduction index can subsequently be calculated. In addition, the assumption of frequency-independent vibration reduction indices has been shown to be incorrect due to in-plane wave generation at the junction. Therefore numerical experiments with FEM, SFEM and wave theory have been used to develop new regression curves between these variables for the low-, mid- and high-frequency ranges. The junctions considered were L-, T- and X-junctions formed from heavyweight walls and floors. These new relationships have been implemented in the prediction models and they tend to improve the agreement between the measured and predicted airborne and impact sound insulation.A modal-spectral model for flanking transmissions
http://hdl.handle.net/2117/89390
A modal-spectral model for flanking transmissions
Poblet-Puig, Jordi
A model for the prediction of direct and indirect (flanking) sound transmissions is presented. It can be applied to geometries with extrusion symmetry. The structures are modelled with spectral finite elements. The acoustic domains are described by means of a modal expansion of the pressure field and must be cuboid-shaped. These reasonable simplifications in the geometry allow the use of more efficient numerical methods. Consequently the coupled vibroacoustic problem in structures such as junctions is efficiently solved.
The vibration reduction index of T-junctions with acoustic excitation and with point force excitation is compared. The differences due to the excitation type obey quite general trends that could be taken into account by prediction formulas. However, they are smaller than other uncertainties not considered in practice. The model is also used to check if the sound transmissions of a fully vibroacoustic problem involving several flanking paths can be reproduced by superposition of independent paths. There exist some differences caused by the interaction between paths, which are more important at low frequencies.
Mon, 29 Aug 2016 10:30:50 GMThttp://hdl.handle.net/2117/893902016-08-29T10:30:50ZPoblet-Puig, JordiA model for the prediction of direct and indirect (flanking) sound transmissions is presented. It can be applied to geometries with extrusion symmetry. The structures are modelled with spectral finite elements. The acoustic domains are described by means of a modal expansion of the pressure field and must be cuboid-shaped. These reasonable simplifications in the geometry allow the use of more efficient numerical methods. Consequently the coupled vibroacoustic problem in structures such as junctions is efficiently solved.
The vibration reduction index of T-junctions with acoustic excitation and with point force excitation is compared. The differences due to the excitation type obey quite general trends that could be taken into account by prediction formulas. However, they are smaller than other uncertainties not considered in practice. The model is also used to check if the sound transmissions of a fully vibroacoustic problem involving several flanking paths can be reproduced by superposition of independent paths. There exist some differences caused by the interaction between paths, which are more important at low frequencies.Master-slave approach for the modelling of joints with dependent degrees of freedom in flexible mechanisms
http://hdl.handle.net/2117/87479
Master-slave approach for the modelling of joints with dependent degrees of freedom in flexible mechanisms
Muñoz Romero, José; Jelenic, Gordan; Crisfield, M. A.
The analysis of multibody systems requires an exact description of the kinematics of the joints involved. In the present work the master–slave approach is employed and endowed with the possibility of including several more complex types of joints. We present the formulation for joints where some relation between the different released degrees of freedom exists such as the screw joint, the rack-and-pinion joint or the cam joint. These joints are implemented in conjunction with geometrically exact beams and an energy-momentum conserving time-stepping algorithm
Mon, 30 May 2016 08:41:00 GMThttp://hdl.handle.net/2117/874792016-05-30T08:41:00ZMuñoz Romero, JoséJelenic, GordanCrisfield, M. A.The analysis of multibody systems requires an exact description of the kinematics of the joints involved. In the present work the master–slave approach is employed and endowed with the possibility of including several more complex types of joints. We present the formulation for joints where some relation between the different released degrees of freedom exists such as the screw joint, the rack-and-pinion joint or the cam joint. These joints are implemented in conjunction with geometrically exact beams and an energy-momentum conserving time-stepping algorithmSpectral 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.
Tue, 17 May 2016 07:55:41 GMThttp://hdl.handle.net/2117/870832016-05-17T07:55:41ZCanas 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.Boundary element method based on preliminary discretization
http://hdl.handle.net/2117/87019
Boundary element method based on preliminary discretization
Poblet-Puig, Jordi; Valyaev, Valery; Shanin, Andrey
A new numerical method for solving wave diffraction problems is given. The method is based on the concept of boundary elements; i.e., the unknown values are the field values on the surface of the scatterer. An analog of a boundary element method rather than a numerical approximation of the initial (continuous) problem is constructed for an approximate statement of the problem on the discrete lattice. Although it reduces the accuracy of the method, it helps to simplify the implementation significantly since the Green functions of the problem are no longer singular. In order to ensure the solution to the diffraction problem is unique (i.e., to suppress fictitious resonances), a new method is constructed similarly to the CFIE approach developed for the classical boundary element method.
The final publication is available at Springer via http://dx.doi.org/10.1134/S2070048214020082
Thu, 12 May 2016 13:41:06 GMThttp://hdl.handle.net/2117/870192016-05-12T13:41:06ZPoblet-Puig, JordiValyaev, ValeryShanin, AndreyA new numerical method for solving wave diffraction problems is given. The method is based on the concept of boundary elements; i.e., the unknown values are the field values on the surface of the scatterer. An analog of a boundary element method rather than a numerical approximation of the initial (continuous) problem is constructed for an approximate statement of the problem on the discrete lattice. Although it reduces the accuracy of the method, it helps to simplify the implementation significantly since the Green functions of the problem are no longer singular. In order to ensure the solution to the diffraction problem is unique (i.e., to suppress fictitious resonances), a new method is constructed similarly to the CFIE approach developed for the classical boundary element method.