This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the s... more This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the simulation of bubbly flows including rupture and breakup of bubbles. The FSLBM uses a volume of fluid approach to reduce the problem of a liquid-gas two-phase flow to a single-phase free surface simulation. In bubbly flows compression effects leading to an increase or decrease of pressure in the suspended bubbles cannot be neglected. Therefore, the free surface simulation is augmented by a bubble model that supplies the missing information by tracking the topological changes of the free surface in the flow. The new model presented here is capable of handling the effects of bubble breakup and coalesce without causing a significant computational overhead. Thus, the enhanced bubble model extends the applicability of the FSLBM to a new range of practically relevant problems, like bubble formation and development in chemical reactors or foaming processes.
We present a fast, cell-centered multigrid solver and apply it to image denoising and nonrigid di... more We present a fast, cell-centered multigrid solver and apply it to image denoising and nonrigid diffusion based image registration. In both applications real time performance is required in 3D and the multigrid method has to be compared to solvers based on Fast Fourier Transform. The optimization of the underlying variational approach results for image denoising directly in one time step of a parabolic linear heat equation, for image registration a non-linear 2nd order system of partial differential equations is obtained. This system is solved by a fixpoint iteration using a semi-implicit time discretization, where each time step again results in an elliptic linear heat equation. The multigrid implementation comes close to real time performance for medium size medical images in 3D for both applications and is compared to a solver based on Fast Fourier Transform using available libraries.
The International Journal of Advanced Manufacturing Technology, 2014
This paper investigates in hatching process strategies for additive manufacturing using an electr... more This paper investigates in hatching process strategies for additive manufacturing using an electron beam by numerical simulations. The underlying physical model and the corresponding three dimensional thermal free surface lattice Boltzmann method of the simulation software are briefly presented. The simulation software has already been validated on the basis of experiments up to 1.2 kW beam power by hatching a cuboid with a basic process strategy, whereby the results are classified into 'porous', 'good' and 'uneven', depending on their relative density and top surface smoothness. In this paper we study the limitations of this basic process strategy in terms of higher beam powers and scan velocities to exploit the future potential of high power electron beam guns up to 10 kW. Subsequently, we introduce modified process strategies, which circumvent these restrictions, to build the part as fast as possible under the restriction of a fully dense part with a smooth top surface. These process strategies are suitable to reduce the build time and costs, maximize the beam power usage and therefore use the potential of high power electron beam guns.
This paper extends 3D simulation results of layer hatching process strategies for additive manufa... more This paper extends 3D simulation results of layer hatching process strategies for additive manufacturing by electron beam melting (EBM) applications to exploit the future energy potential of electron guns with higher beam power. The physical model, discretized by a three dimensional thermal lattice Boltzmann method, is briefly presented. The numerical implementation is validated on the basis of an experimental process window up to 1.2 kW beam power of hatching a cuboid with a basic, state-of-the-art process strategy, whereby the numerical results are classified into three categories: 'porous', 'good' and 'swelling', depending on the part density and quality of the surface. In this paper we extend and improve the basic process strategy, to use higher beam powers. First, the numerical process window is extended, to determine the limits of this technique. Then we introduce different process strategies of the electron beam to build the part as fast as possible under the restriction of a dense part with a good dimensional accuracy. These process strategies can be used to improve the quality of the parts, reduce the build time and costs, maximize the beam power usage and, therefore, use the full potential of high power electron guns.
ABSTRACT This paper introduces a three dimensional (3D) thermal lattice Boltzmann method for the ... more ABSTRACT This paper introduces a three dimensional (3D) thermal lattice Boltzmann method for the simulation of electron beam melting processes. The multi-distribution approach incorporates a state-of-the-art volume of fluid free surface method to handle the complex interaction between gas, liquid, and solid phases. The paper provides a detailed explanation of the modeling of the electron beam gun properties, such as the absorption rate and the energy dissipation. Additionally, an algorithm for the construction of a realistic powder bed is discussed. Special emphasis is placed to a parallel, optimized implementation due to the high computational costs of 3D simulations. Finally, a thorough validation of the heat equation and the solid–liquid phase transition demonstrates the capability of the approach to considerably improve the electron beam melting process.
International Journal of High Performance Computing Applications, 2013
We consider multiphysics applications from algorithmic and architectural perspectives, where "alg... more We consider multiphysics applications from algorithmic and architectural perspectives, where "algorithmic" includes both mathematical analysis and computational complexity and "architectural" includes both software and hardware environments. Many diverse multiphysics applications can be reduced, en route to their computational simulation, to a common algebraic coupling paradigm. Mathematical analysis of multiphysics coupling in this form is not always practical for realistic applications, but model problems representative of applications discussed herein can provide insight. A variety of software frameworks for multiphysics applications have been constructed and refined within disciplinary communities and executed on leading-edge computer systems. We examine several of these, expose some commonalities among them, and attempt to extrapolate best practices to future systems. From our study, we summarize challenges and forecast opportunities.
This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the s... more This paper presents an enhancement to the free surface lattice Boltzmann method (FSLBM) for the simulation of bubbly flows including rupture and breakup of bubbles. The FSLBM uses a volume of fluid approach to reduce the problem of a liquid-gas two-phase flow to a single-phase free surface simulation. In bubbly flows compression effects leading to an increase or decrease of pressure in the suspended bubbles cannot be neglected. Therefore, the free surface simulation is augmented by a bubble model that supplies the missing information by tracking the topological changes of the free surface in the flow. The new model presented here is capable of handling the effects of bubble breakup and coalesce without causing a significant computational overhead. Thus, the enhanced bubble model extends the applicability of the FSLBM to a new range of practically relevant problems, like bubble formation and development in chemical reactors or foaming processes.
We present a fast, cell-centered multigrid solver and apply it to image denoising and nonrigid di... more We present a fast, cell-centered multigrid solver and apply it to image denoising and nonrigid diffusion based image registration. In both applications real time performance is required in 3D and the multigrid method has to be compared to solvers based on Fast Fourier Transform. The optimization of the underlying variational approach results for image denoising directly in one time step of a parabolic linear heat equation, for image registration a non-linear 2nd order system of partial differential equations is obtained. This system is solved by a fixpoint iteration using a semi-implicit time discretization, where each time step again results in an elliptic linear heat equation. The multigrid implementation comes close to real time performance for medium size medical images in 3D for both applications and is compared to a solver based on Fast Fourier Transform using available libraries.
The International Journal of Advanced Manufacturing Technology, 2014
This paper investigates in hatching process strategies for additive manufacturing using an electr... more This paper investigates in hatching process strategies for additive manufacturing using an electron beam by numerical simulations. The underlying physical model and the corresponding three dimensional thermal free surface lattice Boltzmann method of the simulation software are briefly presented. The simulation software has already been validated on the basis of experiments up to 1.2 kW beam power by hatching a cuboid with a basic process strategy, whereby the results are classified into 'porous', 'good' and 'uneven', depending on their relative density and top surface smoothness. In this paper we study the limitations of this basic process strategy in terms of higher beam powers and scan velocities to exploit the future potential of high power electron beam guns up to 10 kW. Subsequently, we introduce modified process strategies, which circumvent these restrictions, to build the part as fast as possible under the restriction of a fully dense part with a smooth top surface. These process strategies are suitable to reduce the build time and costs, maximize the beam power usage and therefore use the potential of high power electron beam guns.
This paper extends 3D simulation results of layer hatching process strategies for additive manufa... more This paper extends 3D simulation results of layer hatching process strategies for additive manufacturing by electron beam melting (EBM) applications to exploit the future energy potential of electron guns with higher beam power. The physical model, discretized by a three dimensional thermal lattice Boltzmann method, is briefly presented. The numerical implementation is validated on the basis of an experimental process window up to 1.2 kW beam power of hatching a cuboid with a basic, state-of-the-art process strategy, whereby the numerical results are classified into three categories: 'porous', 'good' and 'swelling', depending on the part density and quality of the surface. In this paper we extend and improve the basic process strategy, to use higher beam powers. First, the numerical process window is extended, to determine the limits of this technique. Then we introduce different process strategies of the electron beam to build the part as fast as possible under the restriction of a dense part with a good dimensional accuracy. These process strategies can be used to improve the quality of the parts, reduce the build time and costs, maximize the beam power usage and, therefore, use the full potential of high power electron guns.
ABSTRACT This paper introduces a three dimensional (3D) thermal lattice Boltzmann method for the ... more ABSTRACT This paper introduces a three dimensional (3D) thermal lattice Boltzmann method for the simulation of electron beam melting processes. The multi-distribution approach incorporates a state-of-the-art volume of fluid free surface method to handle the complex interaction between gas, liquid, and solid phases. The paper provides a detailed explanation of the modeling of the electron beam gun properties, such as the absorption rate and the energy dissipation. Additionally, an algorithm for the construction of a realistic powder bed is discussed. Special emphasis is placed to a parallel, optimized implementation due to the high computational costs of 3D simulations. Finally, a thorough validation of the heat equation and the solid–liquid phase transition demonstrates the capability of the approach to considerably improve the electron beam melting process.
International Journal of High Performance Computing Applications, 2013
We consider multiphysics applications from algorithmic and architectural perspectives, where "alg... more We consider multiphysics applications from algorithmic and architectural perspectives, where "algorithmic" includes both mathematical analysis and computational complexity and "architectural" includes both software and hardware environments. Many diverse multiphysics applications can be reduced, en route to their computational simulation, to a common algebraic coupling paradigm. Mathematical analysis of multiphysics coupling in this form is not always practical for realistic applications, but model problems representative of applications discussed herein can provide insight. A variety of software frameworks for multiphysics applications have been constructed and refined within disciplinary communities and executed on leading-edge computer systems. We examine several of these, expose some commonalities among them, and attempt to extrapolate best practices to future systems. From our study, we summarize challenges and forecast opportunities.
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Papers by Ulrich Rüde