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Roland G. Winkler - One of the best experts on this subject based on the ideXlab platform.

  • Hydrodynamic correlations of viscoelastic fluids by multiparticle Collision Dynamics simulations.
    The Journal of Chemical Physics, 2019
    Co-Authors: David Toneian, Gerhard Gompper, Gerhard Kahl, Roland G. Winkler
    Abstract:

    The emergent fluctuating hydroDynamics of a viscoelastic fluid modeled by the multiparticle Collision Dynamics (MPC) approach is studied. The fluid is composed of flexible, Gaussian phantom polymers that interact by local momentum-conserving stochastic MPCs. For comparison, the analytical solution of the linearized Navier-Stokes equation is calculated, where viscoelasticity is taken into account by a time-dependent shear relaxation modulus. The fluid properties are characterized by the transverse velocity autocorrelation function in Fourier space as well as in real space. Various polymer lengths are considered—from dumbbells to (near-)continuous polymers. Viscoelasticity affects the fluid properties and leads to strong correlations, which overall decay exponentially in Fourier space. In real space, the center-of-mass velocity autocorrelation function of individual polymers exhibits a long-time tail, independent of the polymer length, which decays as t−3/2, similar to a Newtonian fluid, in the asymptotic limit t → ∞. Moreover, for long polymers, an additional power-law decay appears at time scales shorter than the longest polymer relaxation time with the same time dependence, but negative correlations, and the polymer length dependence L−1/2. Good agreement is found between the analytical and simulation results.The emergent fluctuating hydroDynamics of a viscoelastic fluid modeled by the multiparticle Collision Dynamics (MPC) approach is studied. The fluid is composed of flexible, Gaussian phantom polymers that interact by local momentum-conserving stochastic MPCs. For comparison, the analytical solution of the linearized Navier-Stokes equation is calculated, where viscoelasticity is taken into account by a time-dependent shear relaxation modulus. The fluid properties are characterized by the transverse velocity autocorrelation function in Fourier space as well as in real space. Various polymer lengths are considered—from dumbbells to (near-)continuous polymers. Viscoelasticity affects the fluid properties and leads to strong correlations, which overall decay exponentially in Fourier space. In real space, the center-of-mass velocity autocorrelation function of individual polymers exhibits a long-time tail, independent of the polymer length, which decays as t−3/2, similar to a Newtonian fluid, in the asymptotic l...

  • Hydrodynamic correlations in shear flow: Multiparticle-Collision-Dynamics simulation study.
    Physical Review E, 2015
    Co-Authors: Anoop Varghese, Roland G. Winkler, Chien-cheng Huang, Gerhard Gompper
    Abstract:

    The nonequilibrium hydrodynamic correlations of a multiparticle-Collision-Dynamics (MPC) fluid in shear flow are studied by analytical calculations and simulations. The Navier-Stokes equations for a MPC fluid are linearized about the shear flow and the hydrodynamic modes are evaluated as an expansion in the wave vector. The shear-rate dependence and anisotropy of the transverse and longitudinal velocity correlations are analyzed. We demonstrate that hydrodynamic correlations in shear flow are anisotropic, specifically, the two transverse modes are no longer identical. In addition, our simulations reveal the directional dependence of the frequency and attenuation of the longitudinal velocity correlation function. Furthermore, the velocity autocorrelation functions of a tagged fluid particle in shear flow are determined. The simulation results for various hydrodynamic correlations agree very well with the theoretical predictions.

  • Bulk viscosity of multiparticle Collision Dynamics fluids.
    Physical Review E, 2015
    Co-Authors: Mario Theers, Roland G. Winkler
    Abstract:

    We determine the viscosity parameters of the multiparticle Collision Dynamics (MPC) approach, a particle-based mesoscale hydrodynamic simulation method for fluids. We perform analytical calculations and verify our results by simulations. The stochastic rotation Dynamics and the Andersen thermostat variant of MPC are considered, both with and without angular momentum conservation. As an important result, we find a nonzero bulk viscosity for every MPC version. The explicit calculation shows that the bulk viscosity is determined solely by the Collisional interactions of MPC.

  • multiparticle Collision Dynamics gpu accelerated particle based mesoscale hydrodynamic simulations
    Computer Physics Communications, 2014
    Co-Authors: Elmar Westphal, Chien-cheng Huang, Gerhard Gompper, Sunil P Singh, Roland G. Winkler
    Abstract:

    Abstract The Compute Unified Device Architecture (CUDA) programming language on a graphics processing unit (GPU) is exploited to develop a GPU-based simulation program for the multiparticle Collision Dynamics (MPC) approach, a particle-based mesoscale hydrodynamic simulation technique. The coarse-grained description of the fluid Dynamics in terms of ballistic motion and local stochastic interactions of particles renders MPC inherently highly parallel. We achieve a 1–2 orders of magnitude performance gain over a comparable CPU-core version of the algorithm, depending on the implementation (single threaded or OpenMP). Various aspects of the implementation are discussed in the context of an optimized performance.

  • Hydrodynamic correlations in multiparticle Collision Dynamics fluids.
    Physical Review E, 2012
    Co-Authors: Chien-cheng Huang, Gerhard Gompper, Roland G. Winkler
    Abstract:

    The emergent fluctuating hydroDynamics of the multiparticle Collision Dynamics (MPC) approach, a particle-based mesoscale simulation technique for fluid Dynamics, is analyzed theoretically and numerically. We focus on the stochastic rotation Dynamics implementation of the MPC method. The fluid is characterized by its longitudinal and transverse velocity correlation functions in Fourier space and velocity autocorrelation functions in real space. Particular attention is paid to the role of sound, which leads to piecewise negative correlation functions. Moreover, finite system-size effects are addressed with an emphasis on the role of sound. Analytical expressions are provided for the transverse and longitudinal velocity correlations, which are derived from the linearized Landau-Lifshitz Navier-Stokes equation adopted for an isothermal MPC fluid. The comparison of the analytical results with simulations shows excellent agreement above a minimal length scale. The simulations indicate a breakdown in hydroDynamics on length scales smaller than this minimal length. This demonstrates that we have an excellent analytical description and understanding of the MPC method and its limitations in terms of time and length scales.

Gerhard Gompper - One of the best experts on this subject based on the ideXlab platform.

  • Hydrodynamic correlations of viscoelastic fluids by multiparticle Collision Dynamics simulations.
    The Journal of Chemical Physics, 2019
    Co-Authors: David Toneian, Gerhard Gompper, Gerhard Kahl, Roland G. Winkler
    Abstract:

    The emergent fluctuating hydroDynamics of a viscoelastic fluid modeled by the multiparticle Collision Dynamics (MPC) approach is studied. The fluid is composed of flexible, Gaussian phantom polymers that interact by local momentum-conserving stochastic MPCs. For comparison, the analytical solution of the linearized Navier-Stokes equation is calculated, where viscoelasticity is taken into account by a time-dependent shear relaxation modulus. The fluid properties are characterized by the transverse velocity autocorrelation function in Fourier space as well as in real space. Various polymer lengths are considered—from dumbbells to (near-)continuous polymers. Viscoelasticity affects the fluid properties and leads to strong correlations, which overall decay exponentially in Fourier space. In real space, the center-of-mass velocity autocorrelation function of individual polymers exhibits a long-time tail, independent of the polymer length, which decays as t−3/2, similar to a Newtonian fluid, in the asymptotic limit t → ∞. Moreover, for long polymers, an additional power-law decay appears at time scales shorter than the longest polymer relaxation time with the same time dependence, but negative correlations, and the polymer length dependence L−1/2. Good agreement is found between the analytical and simulation results.The emergent fluctuating hydroDynamics of a viscoelastic fluid modeled by the multiparticle Collision Dynamics (MPC) approach is studied. The fluid is composed of flexible, Gaussian phantom polymers that interact by local momentum-conserving stochastic MPCs. For comparison, the analytical solution of the linearized Navier-Stokes equation is calculated, where viscoelasticity is taken into account by a time-dependent shear relaxation modulus. The fluid properties are characterized by the transverse velocity autocorrelation function in Fourier space as well as in real space. Various polymer lengths are considered—from dumbbells to (near-)continuous polymers. Viscoelasticity affects the fluid properties and leads to strong correlations, which overall decay exponentially in Fourier space. In real space, the center-of-mass velocity autocorrelation function of individual polymers exhibits a long-time tail, independent of the polymer length, which decays as t−3/2, similar to a Newtonian fluid, in the asymptotic l...

  • Hydrodynamic correlations in shear flow: Multiparticle-Collision-Dynamics simulation study.
    Physical Review E, 2015
    Co-Authors: Anoop Varghese, Roland G. Winkler, Chien-cheng Huang, Gerhard Gompper
    Abstract:

    The nonequilibrium hydrodynamic correlations of a multiparticle-Collision-Dynamics (MPC) fluid in shear flow are studied by analytical calculations and simulations. The Navier-Stokes equations for a MPC fluid are linearized about the shear flow and the hydrodynamic modes are evaluated as an expansion in the wave vector. The shear-rate dependence and anisotropy of the transverse and longitudinal velocity correlations are analyzed. We demonstrate that hydrodynamic correlations in shear flow are anisotropic, specifically, the two transverse modes are no longer identical. In addition, our simulations reveal the directional dependence of the frequency and attenuation of the longitudinal velocity correlation function. Furthermore, the velocity autocorrelation functions of a tagged fluid particle in shear flow are determined. The simulation results for various hydrodynamic correlations agree very well with the theoretical predictions.

  • multiparticle Collision Dynamics gpu accelerated particle based mesoscale hydrodynamic simulations
    Computer Physics Communications, 2014
    Co-Authors: Elmar Westphal, Chien-cheng Huang, Gerhard Gompper, Sunil P Singh, Roland G. Winkler
    Abstract:

    Abstract The Compute Unified Device Architecture (CUDA) programming language on a graphics processing unit (GPU) is exploited to develop a GPU-based simulation program for the multiparticle Collision Dynamics (MPC) approach, a particle-based mesoscale hydrodynamic simulation technique. The coarse-grained description of the fluid Dynamics in terms of ballistic motion and local stochastic interactions of particles renders MPC inherently highly parallel. We achieve a 1–2 orders of magnitude performance gain over a comparable CPU-core version of the algorithm, depending on the implementation (single threaded or OpenMP). Various aspects of the implementation are discussed in the context of an optimized performance.

  • Hydrodynamic correlations in multiparticle Collision Dynamics fluids.
    Physical Review E, 2012
    Co-Authors: Chien-cheng Huang, Gerhard Gompper, Roland G. Winkler
    Abstract:

    The emergent fluctuating hydroDynamics of the multiparticle Collision Dynamics (MPC) approach, a particle-based mesoscale simulation technique for fluid Dynamics, is analyzed theoretically and numerically. We focus on the stochastic rotation Dynamics implementation of the MPC method. The fluid is characterized by its longitudinal and transverse velocity correlation functions in Fourier space and velocity autocorrelation functions in real space. Particular attention is paid to the role of sound, which leads to piecewise negative correlation functions. Moreover, finite system-size effects are addressed with an emphasis on the role of sound. Analytical expressions are provided for the transverse and longitudinal velocity correlations, which are derived from the linearized Landau-Lifshitz Navier-Stokes equation adopted for an isothermal MPC fluid. The comparison of the analytical results with simulations shows excellent agreement above a minimal length scale. The simulations indicate a breakdown in hydroDynamics on length scales smaller than this minimal length. This demonstrates that we have an excellent analytical description and understanding of the MPC method and its limitations in terms of time and length scales.

  • Multi-particle Collision Dynamics simulations of sedimenting colloidal dispersions in confinement
    Faraday Discuss., 2010
    Co-Authors: Adam Wysocki, Roland G. Winkler, Gerhard Gompper, C. Patrick Royall, Hajime Tanaka, Alfons Van Blaaderen, Hartmut Löwen
    Abstract:

    The sedimentation of an initially inhomogeneous distribution of hard-sphere colloids confined in a slit is simulated using the multi-particle Collision Dynamics scheme which takes into account hydrodynamic interactions mediated by the solvent. This system is an example for soft matter driven out of equilibrium where various length and time scales are involved. The initial laterally homogeneous density profiles exhibit a hydrodynamic Rayleigh–Taylor-like instability. Solvent backflow effects lead to an intricate non-linear behaviour which is analyzed via the solvent flow field and the colloidal velocity correlation function. Our simulation data are in good agreement with real-space microscopy experiments.

K. Okuno - One of the best experts on this subject based on the ideXlab platform.

  • Collision Dynamics of MCI-molecule systems studied by multi-coincidence technique
    Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005
    Co-Authors: T. Kaneyasu, Toshiyuki Azuma, K. Okuno
    Abstract:

    Abstract Collision Dynamics and reaction processes in charge transfer Collisions of Kr 8+  + N 2 below 200 eV/u have been studied. We used a multi-coincidence technique which enables us to obtain kinematic information for both the fragment ions and the scattered projectile. The Collision phenomena observed in the time-of-flight spectra of target ions are well clarified in consideration of the kinematics in colliding particles. We found an anisotropy in charge-unbalanced fragmentation channels at lower Collision energy. The anisotropic behavior becomes significant not only with decreasing the Collision energy but also with increasing the charge imbalance of the fragment ion-pair. The Collision Dynamics in the Kr 8+  + N 2 system is characterized by the transverse recoil momentum and the anisotropic fragmentation.

  • Collision Dynamics of the kr8 n2 system studied by a multi coincidence technique
    Journal of Physics B, 2005
    Co-Authors: T. Kaneyasu, Toshiyuki Azuma, K. Okuno
    Abstract:

    We have developed a multi-coincidence technique to study MCI–molecule Collisions. Using this technique, complicated reaction processes and Collision Dynamics in Kr 8+ +N 2 Collisions have been successfully revealed in the energy region below 200 eV/u. The reaction processes in the single-, double-, tripleand quadruple-charge changing Collisions are resolved and three low-energy Collision phenomena, ‘peak-shifting’ of molecular ions, ‘peak-splitting’ and ‘anisotropic fragmentation’ of fragment ion pairs, are found in the time-of-flight spectra of target ions. By careful analysis of kinematics of all the products, it is concluded that the charge transfer in the Kr 8+ +N 2 Collisions is dominated by multi-electron capture processes followed by electron emission and the Collision Dynamics is characterized by the transverse momentum transfer from the ion to the molecule and the appearance of the ‘anisotropic fragmentation’.

T. Kaneyasu - One of the best experts on this subject based on the ideXlab platform.

  • Collision Dynamics of MCI-molecule systems studied by multi-coincidence technique
    Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2005
    Co-Authors: T. Kaneyasu, Toshiyuki Azuma, K. Okuno
    Abstract:

    Abstract Collision Dynamics and reaction processes in charge transfer Collisions of Kr 8+  + N 2 below 200 eV/u have been studied. We used a multi-coincidence technique which enables us to obtain kinematic information for both the fragment ions and the scattered projectile. The Collision phenomena observed in the time-of-flight spectra of target ions are well clarified in consideration of the kinematics in colliding particles. We found an anisotropy in charge-unbalanced fragmentation channels at lower Collision energy. The anisotropic behavior becomes significant not only with decreasing the Collision energy but also with increasing the charge imbalance of the fragment ion-pair. The Collision Dynamics in the Kr 8+  + N 2 system is characterized by the transverse recoil momentum and the anisotropic fragmentation.

  • Collision Dynamics of the Kr8+ + N2 system studied by a multi-coincidence technique
    Journal of Physics B: Atomic Molecular and Optical Physics, 2005
    Co-Authors: T. Kaneyasu, Toshiyuki Azuma, Kazuhiko Okuno
    Abstract:

    We have developed a multi-coincidence technique to study MCI–molecule Collisions. Using this technique, complicated reaction processes and Collision Dynamics in Kr 8+ +N 2 Collisions have been successfully revealed in the energy region below 200 eV/u. The reaction processes in the single-, double-, tripleand quadruple-charge changing Collisions are resolved and three low-energy Collision phenomena, ‘peak-shifting’ of molecular ions, ‘peak-splitting’ and ‘anisotropic fragmentation’ of fragment ion pairs, are found in the time-of-flight spectra of target ions. By careful analysis of kinematics of all the products, it is concluded that the charge transfer in the Kr 8+ +N 2 Collisions is dominated by multi-electron capture processes followed by electron emission and the Collision Dynamics is characterized by the transverse momentum transfer from the ion to the molecule and the appearance of the ‘anisotropic fragmentation’.

  • Collision Dynamics of the kr8 n2 system studied by a multi coincidence technique
    Journal of Physics B, 2005
    Co-Authors: T. Kaneyasu, Toshiyuki Azuma, K. Okuno
    Abstract:

    We have developed a multi-coincidence technique to study MCI–molecule Collisions. Using this technique, complicated reaction processes and Collision Dynamics in Kr 8+ +N 2 Collisions have been successfully revealed in the energy region below 200 eV/u. The reaction processes in the single-, double-, tripleand quadruple-charge changing Collisions are resolved and three low-energy Collision phenomena, ‘peak-shifting’ of molecular ions, ‘peak-splitting’ and ‘anisotropic fragmentation’ of fragment ion pairs, are found in the time-of-flight spectra of target ions. By careful analysis of kinematics of all the products, it is concluded that the charge transfer in the Kr 8+ +N 2 Collisions is dominated by multi-electron capture processes followed by electron emission and the Collision Dynamics is characterized by the transverse momentum transfer from the ion to the molecule and the appearance of the ‘anisotropic fragmentation’.

Chien-cheng Huang - One of the best experts on this subject based on the ideXlab platform.

  • Hydrodynamic correlations in shear flow: Multiparticle-Collision-Dynamics simulation study.
    Physical Review E, 2015
    Co-Authors: Anoop Varghese, Roland G. Winkler, Chien-cheng Huang, Gerhard Gompper
    Abstract:

    The nonequilibrium hydrodynamic correlations of a multiparticle-Collision-Dynamics (MPC) fluid in shear flow are studied by analytical calculations and simulations. The Navier-Stokes equations for a MPC fluid are linearized about the shear flow and the hydrodynamic modes are evaluated as an expansion in the wave vector. The shear-rate dependence and anisotropy of the transverse and longitudinal velocity correlations are analyzed. We demonstrate that hydrodynamic correlations in shear flow are anisotropic, specifically, the two transverse modes are no longer identical. In addition, our simulations reveal the directional dependence of the frequency and attenuation of the longitudinal velocity correlation function. Furthermore, the velocity autocorrelation functions of a tagged fluid particle in shear flow are determined. The simulation results for various hydrodynamic correlations agree very well with the theoretical predictions.

  • multiparticle Collision Dynamics gpu accelerated particle based mesoscale hydrodynamic simulations
    Computer Physics Communications, 2014
    Co-Authors: Elmar Westphal, Chien-cheng Huang, Gerhard Gompper, Sunil P Singh, Roland G. Winkler
    Abstract:

    Abstract The Compute Unified Device Architecture (CUDA) programming language on a graphics processing unit (GPU) is exploited to develop a GPU-based simulation program for the multiparticle Collision Dynamics (MPC) approach, a particle-based mesoscale hydrodynamic simulation technique. The coarse-grained description of the fluid Dynamics in terms of ballistic motion and local stochastic interactions of particles renders MPC inherently highly parallel. We achieve a 1–2 orders of magnitude performance gain over a comparable CPU-core version of the algorithm, depending on the implementation (single threaded or OpenMP). Various aspects of the implementation are discussed in the context of an optimized performance.

  • Hydrodynamic correlations in multiparticle Collision Dynamics fluids.
    Physical Review E, 2012
    Co-Authors: Chien-cheng Huang, Gerhard Gompper, Roland G. Winkler
    Abstract:

    The emergent fluctuating hydroDynamics of the multiparticle Collision Dynamics (MPC) approach, a particle-based mesoscale simulation technique for fluid Dynamics, is analyzed theoretically and numerically. We focus on the stochastic rotation Dynamics implementation of the MPC method. The fluid is characterized by its longitudinal and transverse velocity correlation functions in Fourier space and velocity autocorrelation functions in real space. Particular attention is paid to the role of sound, which leads to piecewise negative correlation functions. Moreover, finite system-size effects are addressed with an emphasis on the role of sound. Analytical expressions are provided for the transverse and longitudinal velocity correlations, which are derived from the linearized Landau-Lifshitz Navier-Stokes equation adopted for an isothermal MPC fluid. The comparison of the analytical results with simulations shows excellent agreement above a minimal length scale. The simulations indicate a breakdown in hydroDynamics on length scales smaller than this minimal length. This demonstrates that we have an excellent analytical description and understanding of the MPC method and its limitations in terms of time and length scales.

  • cell level canonical sampling by velocity scaling for multiparticle Collision Dynamics simulations
    Journal of Computational Physics, 2010
    Co-Authors: Chien-cheng Huang, Godehard Sutmann, Gerhard Gompper, Apratim Chatterji, Roland G. Winkler
    Abstract:

    A local Maxwellian thermostat for the multiparticle Collision Dynamics algorithm is proposed. The algorithm is based on a scaling of the relative velocities of the fluid particles within a Collision cell. The scaling factor is determined from the distribution of the kinetic energy within such a cell. Thereby the algorithm ensures that the distribution of the relative velocities is given by the Maxwell-Boltzmann distribution. The algorithm is particularly useful for non-equilibrium systems, where temperature has to be controlled locally. We perform various non-equilibrium simulations for fluids in shear and pressure-driven flow, which confirm the validity of the proposed simulation scheme. In addition, we determine the dynamic structure factors for fluids with and without thermostat, which exhibit significant differences due to suppression of the diffusive part of the energy transport of the isothermal system.

  • Stress tensors of multiparticle Collision Dynamics fluids.
    Journal of Chemical Physics, 2009
    Co-Authors: Roland G. Winkler, Chien-cheng Huang
    Abstract:

    Stress tensors are derived for the multiparticle Collision Dynamics algorithm, a particle-based mesoscale simulation method for fluctuating fluids, resembling those of atomistic or molecular systems. Systems with periodic boundary conditions as well as fluids confined in a slit are considered. For every case, two equivalent expressions for the tensor are provided, the internal stress tensor, which involves all degrees of freedom of a system, and the external stress, which only includes the interactions with the confining surfaces. In addition, stress tensors for a system with embedded particles are determined. Based on the derived stress tensors, analytical expressions are calculated for the shear viscosity. Simulations illustrate the difference in fluctuations between the various derived expressions and yield very good agreement between the numerical results and the analytically derived expression for the viscosity.