LaCàN - Laboratori de Càlcul Numèric
http://hdl.handle.net/2117/2072
2017-02-27T16:36:58ZCollective cell durotaxis emerges from long-range intercellular force transmission
http://hdl.handle.net/2117/100437
Collective cell durotaxis emerges from long-range intercellular force transmission
Sunyer, Raimon; Conte, Vito; Escribano, Jorge; Elosegui Artola, Alberto; Labernadie, Anna; Valon, Leo; Navajas Navarro, Daniel; Garcia Aznar, José Manuel; Muñoz Romero, José; Trepat, Xavier
The ability of cells to follow gradients of extracellular matrix stiffness—durotaxis—has been implicated in development, fibrosis, and cancer. Here, we found multicellular clusters that exhibited durotaxis even if isolated constituent cells did not. This emergent mode of directed collective cell migration applied to a variety of epithelial cell types, required the action of myosin motors, and originated from supracellular transmission of contractile physical forces. To explain the observed phenomenology, we developed a generalized clutch model in which local stick-slip dynamics of cell-matrix adhesions was integrated to the tissue level through cell-cell junctions. Collective durotaxis is far more efficient than single-cell durotaxis; it thus emerges as a robust mechanism to direct cell migration during development, wound healing, and collective cancer cell invasion.
2017-02-01T10:48:46ZSunyer, RaimonConte, VitoEscribano, JorgeElosegui Artola, AlbertoLabernadie, AnnaValon, LeoNavajas Navarro, DanielGarcia Aznar, José ManuelMuñoz Romero, JoséTrepat, XavierThe ability of cells to follow gradients of extracellular matrix stiffness—durotaxis—has been implicated in development, fibrosis, and cancer. Here, we found multicellular clusters that exhibited durotaxis even if isolated constituent cells did not. This emergent mode of directed collective cell migration applied to a variety of epithelial cell types, required the action of myosin motors, and originated from supracellular transmission of contractile physical forces. To explain the observed phenomenology, we developed a generalized clutch model in which local stick-slip dynamics of cell-matrix adhesions was integrated to the tissue level through cell-cell junctions. Collective durotaxis is far more efficient than single-cell durotaxis; it thus emerges as a robust mechanism to direct cell migration during development, wound healing, and collective cancer cell invasion.Modeling the kinematics of multi-axial composite laminates as a stacking of 2D TIF plies
http://hdl.handle.net/2117/100431
Modeling the kinematics of multi-axial composite laminates as a stacking of 2D TIF plies
Ibañez, Ruben; Abisset-Chavanne, Emmanuelle; Chinesta, Francisco; Huerta, Antonio
Thermoplastic composites are widely considered in structural parts. In this paper attention is paid to sheet forming of continuous fiber laminates. In the case of unidirectional prepregs, the ply constitutive equation is modeled as a transversally isotropic fluid, that must satisfy both the fiber inextensibility as well as the fluid incompressibility. When the stacking sequence involves plies with different orientations the kinematics of each ply during the laminate deformation varies significantly through the composite thickness. In our former works we considered two different approaches when simulating the squeeze flow induced by the laminate compression, the first based on a penalty formulation and the second one based on the use of Lagrange multipliers. In the present work we propose an alternative approach that consists in modeling each ply involved in the laminate as a transversally isotropic fluid – TIF - that becomes 2D as soon as incompressibility constraint and plane stress assumption are taken into account. Thus, composites laminates can be analyzed as a stacking of 2D TIF models that could eventually interact by using adequate friction laws at the inter-ply interfaces.
2017-02-01T10:10:33ZIbañez, RubenAbisset-Chavanne, EmmanuelleChinesta, FranciscoHuerta, AntonioThermoplastic composites are widely considered in structural parts. In this paper attention is paid to sheet forming of continuous fiber laminates. In the case of unidirectional prepregs, the ply constitutive equation is modeled as a transversally isotropic fluid, that must satisfy both the fiber inextensibility as well as the fluid incompressibility. When the stacking sequence involves plies with different orientations the kinematics of each ply during the laminate deformation varies significantly through the composite thickness. In our former works we considered two different approaches when simulating the squeeze flow induced by the laminate compression, the first based on a penalty formulation and the second one based on the use of Lagrange multipliers. In the present work we propose an alternative approach that consists in modeling each ply involved in the laminate as a transversally isotropic fluid – TIF - that becomes 2D as soon as incompressibility constraint and plane stress assumption are taken into account. Thus, composites laminates can be analyzed as a stacking of 2D TIF models that could eventually interact by using adequate friction laws at the inter-ply interfaces.Fourth order phase-field model for local max-ent approximants applied to crack propagation
http://hdl.handle.net/2117/100372
Fourth order phase-field model for local max-ent approximants applied to crack propagation
Amiri, Fatemeh; Millán, Daniel; Arroyo Balaguer, Marino; Silani, Mohammad; Rabczuk, Timon
We apply a fourth order phase-field model for fracture based on local maximum entropy (LME) approximants. The higher order continuity of the meshfree LME approximants allows to directly solve the fourth order phase-field equations without splitting the fourth order differential equation into two second order differential equations. We will first show that the crack surface can be captured more accurately in the fourth order model. Furthermore, less nodes are needed for the fourth order model to resolve the crack path. Finally, we demonstrate the performance of the proposed meshfree fourth order phase-field formulation for 5 representative numerical examples. Computational results will be compared to analytical solutions within linear elastic fracture mechanics and experimental data for three-dimensional crack propagation.
2017-01-31T11:50:05ZAmiri, FatemehMillán, DanielArroyo Balaguer, MarinoSilani, MohammadRabczuk, TimonWe apply a fourth order phase-field model for fracture based on local maximum entropy (LME) approximants. The higher order continuity of the meshfree LME approximants allows to directly solve the fourth order phase-field equations without splitting the fourth order differential equation into two second order differential equations. We will first show that the crack surface can be captured more accurately in the fourth order model. Furthermore, less nodes are needed for the fourth order model to resolve the crack path. Finally, we demonstrate the performance of the proposed meshfree fourth order phase-field formulation for 5 representative numerical examples. Computational results will be compared to analytical solutions within linear elastic fracture mechanics and experimental data for three-dimensional crack propagation.A 3D CFD numerical study of the bubble generation process into a bubble Tjunction generator and its comparison with experimental data: Part II
http://hdl.handle.net/2117/100325
A 3D CFD numerical study of the bubble generation process into a bubble Tjunction generator and its comparison with experimental data: Part II
Arias Calderón, Santiago; Villardi de Montlaur, Adeline de
This work is a continuation of the 3D numerical study of the bubble generation process into a T-junction bubble generator (1 mm of internal diameter) obtained with the commercial Computational Fluid Dynamics
solver ANSYS Fluent v15.0.7 and presented in Part I. A complementary comparison with experimental data reproducing the same conditions is provided here.
The second part of this study focuses on the analysis of the geometry of the continuous and disperse phases in the bubble and slug flow regimes in air-water mixtures. The bubble size dispersion is very low in the considered flow patterns both in experiments and simulations. The concept of unit cell is used to identify three characteristic lengths of the two-phase flow, namely, the unit cell length, the liquid slug length and the
bubble length. The relationship between these lengths and the bubble generation frequency, the gas mean velocity, the gas and liquid superficial velocities and volume average void fraction is analyzed. Numerical
simulations provide values in accordance with the experimental ones, but always quantitatively smaller.
2017-01-30T16:03:36ZArias Calderón, SantiagoVillardi de Montlaur, Adeline deThis work is a continuation of the 3D numerical study of the bubble generation process into a T-junction bubble generator (1 mm of internal diameter) obtained with the commercial Computational Fluid Dynamics
solver ANSYS Fluent v15.0.7 and presented in Part I. A complementary comparison with experimental data reproducing the same conditions is provided here.
The second part of this study focuses on the analysis of the geometry of the continuous and disperse phases in the bubble and slug flow regimes in air-water mixtures. The bubble size dispersion is very low in the considered flow patterns both in experiments and simulations. The concept of unit cell is used to identify three characteristic lengths of the two-phase flow, namely, the unit cell length, the liquid slug length and the
bubble length. The relationship between these lengths and the bubble generation frequency, the gas mean velocity, the gas and liquid superficial velocities and volume average void fraction is analyzed. Numerical
simulations provide values in accordance with the experimental ones, but always quantitatively smaller.A 3D CFD numerical study of the bubble generation process into a bubble Tjunction generator and its comparison with experimental data: Part I
http://hdl.handle.net/2117/100319
A 3D CFD numerical study of the bubble generation process into a bubble Tjunction generator and its comparison with experimental data: Part I
Arias Calderón, Santiago; Villardi de Montlaur, Adeline de
This work presents a 3D numerical study of the bubble generation process into a bubble generator obtained with the commercial Computational Fluid Dynamics solver ANSYS Fluent v15.0.7, and its comparison with experimental data reproducing the same conditions. The bubble generator is formed by two perpendicular capillaries in which liquid and gas are injected at perpendicular directions into a 1 mm internal diameter capillary T-junction with a total length of 10 mm. The fluids used in experiments and CFD simulations are air and water, both of them considered incompressible and isothermal, at a room temperature of 25º. A total of
23 different cases are studied for different injection conditions, and results between numerical simulations and experiments are compared.
In this first part of the analysis, we focus on the flow pattern regimes and the dynamics of the bubble generation process. In addition to the new numerical simulations presented here, a new model has been used to predict the bubble generation frequency and tested with both
experimental and numerical data. Results on bubble generation frequency are also presented by means of the non-dimensional Strouhal number. Same types of patterns, bubble and slug flow regimes, are obtained in simulations and experiments. In order to perform an exhaustive validation and comparison of numerical simulations with experimental data, several parameters have been selected: bubble velocity, volumetric void fraction, bubble generation frequency, Strouhal number and bubble equivalent diameter. Numerical simulations agree qualitatively, but not always quantitatively, with experimental results.
2017-01-30T15:42:57ZArias Calderón, SantiagoVillardi de Montlaur, Adeline deThis work presents a 3D numerical study of the bubble generation process into a bubble generator obtained with the commercial Computational Fluid Dynamics solver ANSYS Fluent v15.0.7, and its comparison with experimental data reproducing the same conditions. The bubble generator is formed by two perpendicular capillaries in which liquid and gas are injected at perpendicular directions into a 1 mm internal diameter capillary T-junction with a total length of 10 mm. The fluids used in experiments and CFD simulations are air and water, both of them considered incompressible and isothermal, at a room temperature of 25º. A total of
23 different cases are studied for different injection conditions, and results between numerical simulations and experiments are compared.
In this first part of the analysis, we focus on the flow pattern regimes and the dynamics of the bubble generation process. In addition to the new numerical simulations presented here, a new model has been used to predict the bubble generation frequency and tested with both
experimental and numerical data. Results on bubble generation frequency are also presented by means of the non-dimensional Strouhal number. Same types of patterns, bubble and slug flow regimes, are obtained in simulations and experiments. In order to perform an exhaustive validation and comparison of numerical simulations with experimental data, several parameters have been selected: bubble velocity, volumetric void fraction, bubble generation frequency, Strouhal number and bubble equivalent diameter. Numerical simulations agree qualitatively, but not always quantitatively, with experimental results.Computational modeling of acute myocardial infarction
http://hdl.handle.net/2117/100078
Computational modeling of acute myocardial infarction
Sáez Viñas, Pablo; Kuhl, E.
Myocardial infarction, commonly known as heart attack, is caused by reduced blood supply and damages the heart muscle because of a lack of oxygen. Myocardial infarction initiates a cascade of biochemical and mechanical events. In the early stages, cardiomyocytes death, wall thinning, collagen degradation, and ventricular dilation are the immediate consequences of myocardial infarction. In the later stages, collagenous scar formation in the infarcted zone and hypertrophy of the non-infarcted zone are auto-regulatory mechanisms to partly correct for these events. Here we propose a computational model for the short-term adaptation after myocardial infarction using the continuum theory of multiplicative growth. Our model captures the effects of cell death initiating wall thinning, and collagen degradation initiating ventricular dilation. Our simulations agree well with clinical observations in early myocardial infarction. They represent a first step toward simulating the progression of myocardial infarction with the ultimate goal to predict the propensity toward heart failure as a function of infarct intensity, location, and size.
This is an Accepted Manuscript of an article published by Taylor & Francis Group in Computer Methods in Biomechanics and Biomedical Engineering on October, 2016, available online at: http://www.tandfonline.com/10.1080/10255842.2015.1105965
2017-01-25T18:46:40ZSáez Viñas, PabloKuhl, E.Myocardial infarction, commonly known as heart attack, is caused by reduced blood supply and damages the heart muscle because of a lack of oxygen. Myocardial infarction initiates a cascade of biochemical and mechanical events. In the early stages, cardiomyocytes death, wall thinning, collagen degradation, and ventricular dilation are the immediate consequences of myocardial infarction. In the later stages, collagenous scar formation in the infarcted zone and hypertrophy of the non-infarcted zone are auto-regulatory mechanisms to partly correct for these events. Here we propose a computational model for the short-term adaptation after myocardial infarction using the continuum theory of multiplicative growth. Our model captures the effects of cell death initiating wall thinning, and collagen degradation initiating ventricular dilation. Our simulations agree well with clinical observations in early myocardial infarction. They represent a first step toward simulating the progression of myocardial infarction with the ultimate goal to predict the propensity toward heart failure as a function of infarct intensity, location, and size.Elliptic harbor wave model with perfectly matched layer and exterior bathymetry effects
http://hdl.handle.net/2117/99974
Elliptic harbor wave model with perfectly matched layer and exterior bathymetry effects
Modesto Galende, David; Fernandez Mendez, Sonia; Huerta, Antonio
Standard strategies for dealing with the Sommerfeld condition in elliptic mild-slope models require strong assumptions on the wave field in the region exterior to the computational domain. More precisely, constant bathymetry along (and beyond) the open boundary, and parabolic approximations–based boundary conditions are usually imposed. Generally, these restrictions require large computational domains, implying higher costs for the numerical solver. An alternative method for coastal/harbor applications is proposed here. This approach is based on a perfectly matched layer (PML) that incorporates the effects of the exterior bathymetry. The model only requires constant exterior depth in the alongshore direction, a common approach used for idealizing the exterior bathymetry in elliptic models. In opposition to standard open boundary conditions for mild-slope models, the features of the proposed PML approach include (1) completely noncollinear coastlines, (2) better representation of the real unbounded domain using two different lateral sections to define the exterior bathymetry, and (3) the generation of reliable solutions for any incoming wave direction in a small computational domain. Numerical results of synthetic tests demonstrate that solutions are not significantly perturbed when open boundaries are placed close to the area of interest. In more complex problems, this provides important performance improvements in computational time, as shown for a real application of harbor agitation.
2017-01-24T18:45:56ZModesto Galende, DavidFernandez Mendez, SoniaHuerta, AntonioStandard strategies for dealing with the Sommerfeld condition in elliptic mild-slope models require strong assumptions on the wave field in the region exterior to the computational domain. More precisely, constant bathymetry along (and beyond) the open boundary, and parabolic approximations–based boundary conditions are usually imposed. Generally, these restrictions require large computational domains, implying higher costs for the numerical solver. An alternative method for coastal/harbor applications is proposed here. This approach is based on a perfectly matched layer (PML) that incorporates the effects of the exterior bathymetry. The model only requires constant exterior depth in the alongshore direction, a common approach used for idealizing the exterior bathymetry in elliptic models. In opposition to standard open boundary conditions for mild-slope models, the features of the proposed PML approach include (1) completely noncollinear coastlines, (2) better representation of the real unbounded domain using two different lateral sections to define the exterior bathymetry, and (3) the generation of reliable solutions for any incoming wave direction in a small computational domain. Numerical results of synthetic tests demonstrate that solutions are not significantly perturbed when open boundaries are placed close to the area of interest. In more complex problems, this provides important performance improvements in computational time, as shown for a real application of harbor agitation.A new equilibrated residual method improving accuracy and efficiency of flux-free error estimates
http://hdl.handle.net/2117/99967
A new equilibrated residual method improving accuracy and efficiency of flux-free error estimates
Parés Mariné, Núria; Díez, Pedro
This paper presents a new methodology to compute guaranteed upper bounds for the energy norm of the error in the context of linear finite element approximations of the reaction–diffusion equation. The new approach revisits the ideas in Parés et al. (2009) [6, 4], with the goal of substantially reducing the computational cost of the flux-free method while retaining the good quality of the bounds. The new methodology provides also a technique to compute equilibrated boundary tractions improving the quality of standard equilibration strategies. The zeroth-order equilibration conditions are imposed using an alternative less restrictive form of the first-order equilibration conditions, along with a new efficient minimization criterion. This new equilibration strategy provides much more accurate upper bounds for the energy and requires only doubling the dimension of the local linear systems of equations to be solved.
2017-01-24T17:24:44ZParés Mariné, NúriaDíez, PedroThis paper presents a new methodology to compute guaranteed upper bounds for the energy norm of the error in the context of linear finite element approximations of the reaction–diffusion equation. The new approach revisits the ideas in Parés et al. (2009) [6, 4], with the goal of substantially reducing the computational cost of the flux-free method while retaining the good quality of the bounds. The new methodology provides also a technique to compute equilibrated boundary tractions improving the quality of standard equilibration strategies. The zeroth-order equilibration conditions are imposed using an alternative less restrictive form of the first-order equilibration conditions, along with a new efficient minimization criterion. This new equilibration strategy provides much more accurate upper bounds for the energy and requires only doubling the dimension of the local linear systems of equations to be solved.A distortion measure to validate and generate curved high-order meshes on CAD surfaces with independence of parameterization
http://hdl.handle.net/2117/99966
A distortion measure to validate and generate curved high-order meshes on CAD surfaces with independence of parameterization
Gargallo Peiró, Abel; Roca Navarro, Xevi; Peraire Guitart, Jaume; Sarrate Ramos, Josep
A framework to validate and generate curved nodal high-order meshes on Computer-Aided Design (CAD) surfaces is presented. The proposed framework is of major interest to generate meshes suitable for thin-shell and 3D finite element analysis with unstructured high-order methods. First, we define a distortion (quality) measure for high-order meshes on parameterized surfaces that we prove to be independent of the surface parameterization. Second, we derive a smoothing and untangling procedure based on the minimization of a regularization of the proposed distortion measure. The minimization is performed in terms of the parametric coordinates of the nodes to enforce that the nodes slide on the surfaces. Moreover, the proposed algorithm repairs invalid curved meshes (untangling), deals with arbitrary polynomial degrees (high-order), and handles with low-quality CAD parameterizations (independence of parameterization). Third, we use the optimization procedure to generate curved nodal high-order surface meshes by means of an a posteriori approach. Given a linear mesh, we increase the polynomial degree of the elements, curve them to match the geometry, and optimize the location of the nodes to ensure mesh validity. Finally, we present several examples to demonstrate the features of the optimization procedure, and to illustrate the surface mesh generation process.
This is the accepted version of the following article: [Gargallo-Peiró, A., Roca, X., Peraire, J., and Sarrate, J. (2016) A distortion measure to validate and generate curved high-order meshes on CAD surfaces with independence of parameterization. Int. J. Numer. Meth. Engng, 106: 1100–1130. doi: 10.1002/nme.5162], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nme.5162/abstract
2017-01-24T17:02:08ZGargallo Peiró, AbelRoca Navarro, XeviPeraire Guitart, JaumeSarrate Ramos, JosepA framework to validate and generate curved nodal high-order meshes on Computer-Aided Design (CAD) surfaces is presented. The proposed framework is of major interest to generate meshes suitable for thin-shell and 3D finite element analysis with unstructured high-order methods. First, we define a distortion (quality) measure for high-order meshes on parameterized surfaces that we prove to be independent of the surface parameterization. Second, we derive a smoothing and untangling procedure based on the minimization of a regularization of the proposed distortion measure. The minimization is performed in terms of the parametric coordinates of the nodes to enforce that the nodes slide on the surfaces. Moreover, the proposed algorithm repairs invalid curved meshes (untangling), deals with arbitrary polynomial degrees (high-order), and handles with low-quality CAD parameterizations (independence of parameterization). Third, we use the optimization procedure to generate curved nodal high-order surface meshes by means of an a posteriori approach. Given a linear mesh, we increase the polynomial degree of the elements, curve them to match the geometry, and optimize the location of the nodes to ensure mesh validity. Finally, we present several examples to demonstrate the features of the optimization procedure, and to illustrate the surface mesh generation process.A Lagrangian–Eulerian finite element algorithm for advection–diffusion–reaction problems with phase change
http://hdl.handle.net/2117/99876
A Lagrangian–Eulerian finite element algorithm for advection–diffusion–reaction problems with phase change
Oliveira, Beñat; Afonso, Juan Carlos; Zlotnik, Sergio
This paper presents a particle-based Lagrangian–Eulerian algorithm for the solution of the unsteady advection–diffusion–reaction heat transfer equation with phase change. The algorithm combines a Lagrangian formulation for the advection + reaction problem with the Eulerian-based heat source method for the diffusion + phase change problem. The coupling between the Lagrangian and Eulerian subproblems is achieved with a phase change detector scheme based on a local latent heat balance and a consistent/conservative interpolation technique between Lagrangian particles and the Eulerian grid. This technique makes use of an auxiliary (finer) Eulerian grid that provides a simple and efficient method of tracking internal heterogeneities (e.g. phase boundaries), allows the use of higher order integration quadratures, and facilitates the implementation of multiscale techniques. The performance of the proposed algorithm is compared against one- and two-dimensional benchmark problems, i.e. pure rigid-body advection, isothermal and non-isothermal phase change, two-phase advective heat transfer and chemical reactions coupled with diffusion and advection. The numerical results confirm that the proposed solution method is accurate, oscillation-free and useful for and applicable to a wide range of fully coupled problems in science and engineering.
2017-01-23T15:28:21ZOliveira, BeñatAfonso, Juan CarlosZlotnik, SergioThis paper presents a particle-based Lagrangian–Eulerian algorithm for the solution of the unsteady advection–diffusion–reaction heat transfer equation with phase change. The algorithm combines a Lagrangian formulation for the advection + reaction problem with the Eulerian-based heat source method for the diffusion + phase change problem. The coupling between the Lagrangian and Eulerian subproblems is achieved with a phase change detector scheme based on a local latent heat balance and a consistent/conservative interpolation technique between Lagrangian particles and the Eulerian grid. This technique makes use of an auxiliary (finer) Eulerian grid that provides a simple and efficient method of tracking internal heterogeneities (e.g. phase boundaries), allows the use of higher order integration quadratures, and facilitates the implementation of multiscale techniques. The performance of the proposed algorithm is compared against one- and two-dimensional benchmark problems, i.e. pure rigid-body advection, isothermal and non-isothermal phase change, two-phase advective heat transfer and chemical reactions coupled with diffusion and advection. The numerical results confirm that the proposed solution method is accurate, oscillation-free and useful for and applicable to a wide range of fully coupled problems in science and engineering.