VII International Conference on Computational Methods for Coupled Problems in Science and Engineering (COUPLED 2017) Rhodes Island, Greece, 12-14 June, 2017
http://hdl.handle.net/2117/189880
2023-01-28T12:48:23ZSimulation of macrosegregation benchmark on a non-uniform computational node arrangement with a meshless method
http://hdl.handle.net/2117/190975
Simulation of macrosegregation benchmark on a non-uniform computational node arrangement with a meshless method
Hatic, Vanja; Sarler, Bozidar
An application of a meshless numerical method on a macrosegregation benchmark case is developed in the present paper. The test case is solidification in 2D rectangular cavity, filled with liquid metal and chilled from both sides. This is a highly non-linear problem due to a strong coupling of the macroscopic transport equations with the microsegregation model. The main result is the macrosegregation pattern of the solidified metal Al4.5wt%Cu alloy is used for evaluation of the problem. The model uses diffuse approximate meshless method with the second-order polynomial basis for spatial integration and explicit time-stepping. Simulations are performed on uniform and non-uniform computational node arrangements and compared to each other. The results on uniform and non-uniform node arrangements show a very good matching with the finite volume method results and results based on radial basis function collocation method. This shows that diffuse approximate method based on non-uniform node arrangements can be used for solving macrosegregation problems.
2020-06-17T15:24:46ZHatic, VanjaSarler, BozidarAn application of a meshless numerical method on a macrosegregation benchmark case is developed in the present paper. The test case is solidification in 2D rectangular cavity, filled with liquid metal and chilled from both sides. This is a highly non-linear problem due to a strong coupling of the macroscopic transport equations with the microsegregation model. The main result is the macrosegregation pattern of the solidified metal Al4.5wt%Cu alloy is used for evaluation of the problem. The model uses diffuse approximate meshless method with the second-order polynomial basis for spatial integration and explicit time-stepping. Simulations are performed on uniform and non-uniform computational node arrangements and compared to each other. The results on uniform and non-uniform node arrangements show a very good matching with the finite volume method results and results based on radial basis function collocation method. This shows that diffuse approximate method based on non-uniform node arrangements can be used for solving macrosegregation problems.The influence of thermal barriers in anisotropic media applied to PCB using MEC
http://hdl.handle.net/2117/190974
The influence of thermal barriers in anisotropic media applied to PCB using MEC
Anunciaçao Jr., N.C.; Oliveira, T.S.L.; Anflor, C.T.M.
Many electronical components were developed during the last years and many efforts were devoted to the miniaturization of their components due to the global tendency. The matrix in which the components are mounted are made of composite materials which presented anisotropic behaviour. The main goal of this work relies on determining the influence of the thermal barriers position inside of a PCB. The plate has 168 thermal barriers inside the domain where each one has a 360° of freedom of rotation. A Dirichlet boundary condition was imposed to all corners of the plate to analysis. The heat flux was observed at the A, B, and C corners, as the internal barriers were rotated. A quadratic boundary element was used and The multipoint Genetic Algorithm was employed in order to maximize the objective function at the corner A and minimizing at the corners B and C. Despite the elevated number of variables classified this problem such as non-convex, the final results showed good convergence.
2020-06-17T15:21:11ZAnunciaçao Jr., N.C.Oliveira, T.S.L.Anflor, C.T.M.Many electronical components were developed during the last years and many efforts were devoted to the miniaturization of their components due to the global tendency. The matrix in which the components are mounted are made of composite materials which presented anisotropic behaviour. The main goal of this work relies on determining the influence of the thermal barriers position inside of a PCB. The plate has 168 thermal barriers inside the domain where each one has a 360° of freedom of rotation. A Dirichlet boundary condition was imposed to all corners of the plate to analysis. The heat flux was observed at the A, B, and C corners, as the internal barriers were rotated. A quadratic boundary element was used and The multipoint Genetic Algorithm was employed in order to maximize the objective function at the corner A and minimizing at the corners B and C. Despite the elevated number of variables classified this problem such as non-convex, the final results showed good convergence.Numerical stability of a fixed point iterative method to determine patterns of turbulent flow in a rectangular cavity with different aspect ratios
http://hdl.handle.net/2117/190973
Numerical stability of a fixed point iterative method to determine patterns of turbulent flow in a rectangular cavity with different aspect ratios
Bermúdez, B.; Rangel-Huerta, A.; Alanís, D.; Guerrero S., W. Fermín
2D isothermal viscous incompressible flows are presented from the Navier-
Stokes equations in the Stream function-vorticity formulation and in the velocity-vorticity
formulation. The simulation is made using a numerical method based on a fixed point it- erative
process to solve the nonlinear elliptic system that results after time discretization. The
iterative process leads us to the solution of uncoupled, well-conditioned, symmetric linear
elliptic problems from which efficient solvers exist regardless of the space discretiza- tion. The
experiments take place on the lid driven cavity problem for Reynolds numbers up to Re = 10000 and
different aspect ratios A (A=ratio of the height to the width) A = 1 and A /= 1 such aAs = 1/2, till A = 3. It appears that with velocity
and vorticity variables is more difficult to solve this kind of flows, at least with a numerical
procedure similar to the one applied in stream function and vorticity variables to solve an
analogous nonlinear elliptic system. To obtain such flows is not an easy task, especially with the
velocity-vorticity formulation. We report here results for moderate Reynolds numbers (Re 10000),
although with them enough effectiveness is achieved to be able to vary the aspect ratio of the
cavity A, which causes the flow to be more unstable. Con- tribution in this work is to consider
rectangular cavities of drag, which can impact on isothermal turbulent flow patterns. Another
contribution is to include a wide region of the Reynolds number as well as different aspect ratios
where we tested stability of the
numerical scheme.
2020-06-17T15:17:21ZBermúdez, B.Rangel-Huerta, A.Alanís, D.Guerrero S., W. Fermín2D isothermal viscous incompressible flows are presented from the Navier-
Stokes equations in the Stream function-vorticity formulation and in the velocity-vorticity
formulation. The simulation is made using a numerical method based on a fixed point it- erative
process to solve the nonlinear elliptic system that results after time discretization. The
iterative process leads us to the solution of uncoupled, well-conditioned, symmetric linear
elliptic problems from which efficient solvers exist regardless of the space discretiza- tion. The
experiments take place on the lid driven cavity problem for Reynolds numbers up to Re = 10000 and
different aspect ratios A (A=ratio of the height to the width) A = 1 and A /= 1 such aAs = 1/2, till A = 3. It appears that with velocity
and vorticity variables is more difficult to solve this kind of flows, at least with a numerical
procedure similar to the one applied in stream function and vorticity variables to solve an
analogous nonlinear elliptic system. To obtain such flows is not an easy task, especially with the
velocity-vorticity formulation. We report here results for moderate Reynolds numbers (Re 10000),
although with them enough effectiveness is achieved to be able to vary the aspect ratio of the
cavity A, which causes the flow to be more unstable. Con- tribution in this work is to consider
rectangular cavities of drag, which can impact on isothermal turbulent flow patterns. Another
contribution is to include a wide region of the Reynolds number as well as different aspect ratios
where we tested stability of the
numerical scheme.Numerical stability of explicit and implicit co-simulation methods
http://hdl.handle.net/2117/190971
Numerical stability of explicit and implicit co-simulation methods
Li, P.; Meyer, T.; Lu, D.; Schweizer, B.
Within a co-simulation approach, the subsystems are integrated by specific solvers;
data exchange is accomplished only at certain user-defined macro-time points. Due to the
approximation of the coupling variables by polynomials and as a result of the data exchange
between the subsystems, errors are introduced, which may entail severe stability problems.
Hence, the development of stabilized coupling techniques is of special interest. To analyze the
stability of co-simulation approaches, we consider two coupled Dahlquist’s equations so that
the conventional linear stability analysis can be applied. Consequently, the stability of the cosimulation
method can be determined by calculating the spectral radius of the governing system
of recurrence equations. The numerical stability of classical explicit and implicit co-simulation
techniques is investigated here. Also, modified coupling approaches are discussed, which show
an improved stability behavior.
2020-06-17T15:11:24ZLi, P.Meyer, T.Lu, D.Schweizer, B.Within a co-simulation approach, the subsystems are integrated by specific solvers;
data exchange is accomplished only at certain user-defined macro-time points. Due to the
approximation of the coupling variables by polynomials and as a result of the data exchange
between the subsystems, errors are introduced, which may entail severe stability problems.
Hence, the development of stabilized coupling techniques is of special interest. To analyze the
stability of co-simulation approaches, we consider two coupled Dahlquist’s equations so that
the conventional linear stability analysis can be applied. Consequently, the stability of the cosimulation
method can be determined by calculating the spectral radius of the governing system
of recurrence equations. The numerical stability of classical explicit and implicit co-simulation
techniques is investigated here. Also, modified coupling approaches are discussed, which show
an improved stability behavior.Numerical simulations of micro jets produced with a double flow focusing nozzle
http://hdl.handle.net/2117/190968
Numerical simulations of micro jets produced with a double flow focusing nozzle
Belsak, Grega; Bajt, Sasa; Beyerlein, Kenneth R.; Sarler, Bozidar
Stable and reliable micro jets are important for many applications. Double flow focused micro jets are a novelty with an important advantage of significantly reduced sample consumption. Numerical simulations of double flow focused micro jets are a highly complex task. They represents a great computational challenge due to the multiphase nature of the problem, strong coupling between the gas and the two liquids and the sub-micron size cells needed. Simulations were performed with the open source computational fluid dynamics toolbox called OpenFOAM. Two multiphase solvers were used, one of which was modified in order to properly describe the interface between the focusing liquid and the gas. In this study two different incompressible physical models were considered and compared. A model with no mixing of the two fluids (multiphaseInterFoam solver) and a model where the diffusion of the two fluids is permitted (modified interMixingFoam solver). The results of simulations for the two different physical models using the same inlet parameters are presented. Additionally, a parametric analysis for the mixing case was performed to study the effects of different parameters on the jet formation. Particularly how the different diffusion values couple with the jet length, diameter and its stability. Results show a match in jet diameter and jet length for both models when the same set of parameters is used.
2020-06-17T14:37:03ZBelsak, GregaBajt, SasaBeyerlein, Kenneth R.Sarler, BozidarStable and reliable micro jets are important for many applications. Double flow focused micro jets are a novelty with an important advantage of significantly reduced sample consumption. Numerical simulations of double flow focused micro jets are a highly complex task. They represents a great computational challenge due to the multiphase nature of the problem, strong coupling between the gas and the two liquids and the sub-micron size cells needed. Simulations were performed with the open source computational fluid dynamics toolbox called OpenFOAM. Two multiphase solvers were used, one of which was modified in order to properly describe the interface between the focusing liquid and the gas. In this study two different incompressible physical models were considered and compared. A model with no mixing of the two fluids (multiphaseInterFoam solver) and a model where the diffusion of the two fluids is permitted (modified interMixingFoam solver). The results of simulations for the two different physical models using the same inlet parameters are presented. Additionally, a parametric analysis for the mixing case was performed to study the effects of different parameters on the jet formation. Particularly how the different diffusion values couple with the jet length, diameter and its stability. Results show a match in jet diameter and jet length for both models when the same set of parameters is used.Numerical simulation of shock-tube piston problems with adaptive, anisotropic meshes
http://hdl.handle.net/2117/190884
Numerical simulation of shock-tube piston problems with adaptive, anisotropic meshes
Re, Barbara; Dobrzynski, Cécile; Guardone, Alberto
Abstract. Numerical simulations of the flow generated inside a shock-tube by the motion
of a magnetically- driven piston are carried out using a novel finite volume adaptive
scheme for dynamic meshes. Local modifications of the grid topology, including the
addition or deletion of grid nodes are interpreted as a series of fictitious,
continuous deformations of the mesh, thus allowing mesh adaptation to be described
within the Arbitrary Lagrangian Eulerian (ALE) framework. The local deformations of the
mesh elements are taken into account in a conservative fashion by adding additional fictitious
fluxes to the ALE formulation of the governing equations for inviscid compressible flows. The
solution on the new grid is recovered without any explicit interpolation. Therefore, the method
automatically guarantees the solution to be conservative by construction. This peculiar
capability is here exploited in preliminary Fluid-Structure Interaction (FSI) computations of
compressible shocked flows with rigid, moving bodies. Anisotropic mesh adaptation is used to
improve the computational efficiency. The solution compares fairly
well with the analytical one-dimensional model.
2020-06-16T12:39:47ZRe, BarbaraDobrzynski, CécileGuardone, AlbertoAbstract. Numerical simulations of the flow generated inside a shock-tube by the motion
of a magnetically- driven piston are carried out using a novel finite volume adaptive
scheme for dynamic meshes. Local modifications of the grid topology, including the
addition or deletion of grid nodes are interpreted as a series of fictitious,
continuous deformations of the mesh, thus allowing mesh adaptation to be described
within the Arbitrary Lagrangian Eulerian (ALE) framework. The local deformations of the
mesh elements are taken into account in a conservative fashion by adding additional fictitious
fluxes to the ALE formulation of the governing equations for inviscid compressible flows. The
solution on the new grid is recovered without any explicit interpolation. Therefore, the method
automatically guarantees the solution to be conservative by construction. This peculiar
capability is here exploited in preliminary Fluid-Structure Interaction (FSI) computations of
compressible shocked flows with rigid, moving bodies. Anisotropic mesh adaptation is used to
improve the computational efficiency. The solution compares fairly
well with the analytical one-dimensional model.Mixed variational formulations for multi-field problems
http://hdl.handle.net/2117/190883
Mixed variational formulations for multi-field problems
Dittmann, M.; Hesch, C.
General thermoelastic material models have been investigated over the past decades,
see e.g. Reese and Govindjee [1], Holzapfel and Simo [2] and Miehe [3] among many oth- ers. In
this paper we present a novel computational framework for large strain thermo- elasticity. The
ideas of a new formulation for polyconvex large strain elasticity originally introduced by Ball [4]
and recently resumed by Bonet et al. [5] are extended to non-linear coupled thermoelasticity, see
also Dittmann [6]. In particular, the deformation gradient (line map), its co-factor (area map)
and its determinant (volume map) along with the absolute temperature are formulated as independent
variables to obtain a polyconvex free energy function. Moreover, we introduce work conjugate
stresses to the extended kine- matic set to define a complementary energy principle of
Hellinger-Reissner type, where the introduced conjugate stresses along with the deformed geometry
and the absolute tem- perature constitute the set of primal variables, see also Hesch condensed.Eventually,quasi-staticaswellastransientnumericalexamplesareinvesti-gatedtodemonstratethecapabilityoftheproposedframework. et al. [7]
for the application of a mixed Hu-Washizu type variational principle in the context of coupled
phase-field fracture problems. The finite element discretization relies on a quadratic
approximation of the deformed geometry and the absolute temperature, whereas discontinuous
linear interpolations are used for the conjugate stresses such that the stress unknowns can be
2020-06-16T12:35:14ZDittmann, M.Hesch, C.General thermoelastic material models have been investigated over the past decades,
see e.g. Reese and Govindjee [1], Holzapfel and Simo [2] and Miehe [3] among many oth- ers. In
this paper we present a novel computational framework for large strain thermo- elasticity. The
ideas of a new formulation for polyconvex large strain elasticity originally introduced by Ball [4]
and recently resumed by Bonet et al. [5] are extended to non-linear coupled thermoelasticity, see
also Dittmann [6]. In particular, the deformation gradient (line map), its co-factor (area map)
and its determinant (volume map) along with the absolute temperature are formulated as independent
variables to obtain a polyconvex free energy function. Moreover, we introduce work conjugate
stresses to the extended kine- matic set to define a complementary energy principle of
Hellinger-Reissner type, where the introduced conjugate stresses along with the deformed geometry
and the absolute tem- perature constitute the set of primal variables, see also Hesch condensed.Eventually,quasi-staticaswellastransientnumericalexamplesareinvesti-gatedtodemonstratethecapabilityoftheproposedframework. et al. [7]
for the application of a mixed Hu-Washizu type variational principle in the context of coupled
phase-field fracture problems. The finite element discretization relies on a quadratic
approximation of the deformed geometry and the absolute temperature, whereas discontinuous
linear interpolations are used for the conjugate stresses such that the stress unknowns can beComparative analysis of a transient heat flow and thermal stresses by analytical and numerical methods
http://hdl.handle.net/2117/190882
Comparative analysis of a transient heat flow and thermal stresses by analytical and numerical methods
Almeida, G.; Coelho, N.; Alkmim, N.
The study of heat flow problems is of extreme importance in engineering, there is a need to know the temperatures imposed and generated, when appropriate, in the structural parts to be able to evaluate the stresses that can arise due to the thermal variations. These stresses arise due to imposed constraints, ie bodies can not move freely and consequently undesirable cracks may arise when the stresses are greater than the resistive capacity of the stressed parts. The analysis of these problems can be done in both analytical or numerical way, with the use of calculation methods, such as the Finite Difference Method (FDM) and the Finite Element Method (FEM), with aid of computational programs such as MATLAB, PYTHON and ANSYS, as used in this work. The results presented here show simple cases of transient thermal variation and thermomechanical coupling by two methods of analysis, aiming at the validation of the numerical methods and softwares used. The solutions were satisfactory, the temperatures and stresses were coincident for different methods, making possible to start studying more complex problems with confidence in the implemented code.
2020-06-16T12:31:34ZAlmeida, G.Coelho, N.Alkmim, N.The study of heat flow problems is of extreme importance in engineering, there is a need to know the temperatures imposed and generated, when appropriate, in the structural parts to be able to evaluate the stresses that can arise due to the thermal variations. These stresses arise due to imposed constraints, ie bodies can not move freely and consequently undesirable cracks may arise when the stresses are greater than the resistive capacity of the stressed parts. The analysis of these problems can be done in both analytical or numerical way, with the use of calculation methods, such as the Finite Difference Method (FDM) and the Finite Element Method (FEM), with aid of computational programs such as MATLAB, PYTHON and ANSYS, as used in this work. The results presented here show simple cases of transient thermal variation and thermomechanical coupling by two methods of analysis, aiming at the validation of the numerical methods and softwares used. The solutions were satisfactory, the temperatures and stresses were coincident for different methods, making possible to start studying more complex problems with confidence in the implemented code.A coupled discrete-element model of fluid-saturated rock and the results of studying of the impact of a fluid on the shear strength of a rock under combined compression and shear
http://hdl.handle.net/2117/190879
A coupled discrete-element model of fluid-saturated rock and the results of studying of the impact of a fluid on the shear strength of a rock under combined compression and shear
Dimaki, Andrey V.; Shilko, Evgeny V.; Psakhie, Sergey G.
Within a discrete-element model of a porous permeable elastic-plastic rock, filled with a fluid, we have studied the shear strength of a fractured interface zone (a shear band) between blocks of a geological medium subject to compression and shear. Under these conditions, a fluid pore pressure is controlled by interplay of dilation of the elastic-plastic shear band and fluid transport between the blocks and the interface. We have found that the shear strength is a unique function of a combination of parameters, which includes viscosity of a fluid, permeability of the medium, shear rate and a characteristic size of the system. Based on the simulation results we have constructed the generalized binomial dependence of the shear strength of samples on the obtained combination of parameters.
2020-06-16T12:28:29ZDimaki, Andrey V.Shilko, Evgeny V.Psakhie, Sergey G.Within a discrete-element model of a porous permeable elastic-plastic rock, filled with a fluid, we have studied the shear strength of a fractured interface zone (a shear band) between blocks of a geological medium subject to compression and shear. Under these conditions, a fluid pore pressure is controlled by interplay of dilation of the elastic-plastic shear band and fluid transport between the blocks and the interface. We have found that the shear strength is a unique function of a combination of parameters, which includes viscosity of a fluid, permeability of the medium, shear rate and a characteristic size of the system. Based on the simulation results we have constructed the generalized binomial dependence of the shear strength of samples on the obtained combination of parameters.Stress concentration in ultra-thin coating with undulated surface profile
http://hdl.handle.net/2117/190878
Stress concentration in ultra-thin coating with undulated surface profile
Kostyrko, Sergey A.; Altenbach, Holm; Grekov, Mikhail A.
The uniaxial loading of an isotropic film-substrate system with a sinusoidal
surface profile and planar interface is considered under plain strain conditions. We for-
mulate the corresponding boundary value problem involving two-dimensional constitutive equations
for bulk materials and one-dimensional equations for membrane-type surface and interface with the
extra elastic constants as well as the residual surface stresses. The mixed boundary conditions
consist of the generalized Young–Laplace equations and rela- tions describing the continuous of
displacements across the surface and interphase regions. Using the linear perturbation technique
combined with the Goursat–Kolosov complex po- tentials and the superposition principle, the
original boundary value problem is reduced
to the analytical solution of the integral equations system.
2020-06-16T12:25:04ZKostyrko, Sergey A.Altenbach, HolmGrekov, Mikhail A.The uniaxial loading of an isotropic film-substrate system with a sinusoidal
surface profile and planar interface is considered under plain strain conditions. We for-
mulate the corresponding boundary value problem involving two-dimensional constitutive equations
for bulk materials and one-dimensional equations for membrane-type surface and interface with the
extra elastic constants as well as the residual surface stresses. The mixed boundary conditions
consist of the generalized Young–Laplace equations and rela- tions describing the continuous of
displacements across the surface and interphase regions. Using the linear perturbation technique
combined with the Goursat–Kolosov complex po- tentials and the superposition principle, the
original boundary value problem is reduced
to the analytical solution of the integral equations system.