The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform

Robert Bridson - One of the best experts on this subject based on the ideXlab platform.

  • Resolving Fluid Boundary layers with particle strength exchange and weak adaptivity
    ACM Transactions on Graphics, 2016
    Co-Authors: Xinxin Zhang, Robert Bridson
    Abstract:

    Most Fluid scenarios in graphics have a high Reynolds number, where viscosity is dominated by inertial effects, thus most solvers drop viscosity altogether: numerical damping from coarse grids is generally stronger than physical viscosity while resembling it in character. However, viscosity remains crucial near solid boundaries, in the Boundary layer, to a large extent determining the look of the flow as a function of Reynolds number. Typical graphics simulations do not resolve Boundary layer dynamics, so their look is determined mostly by numerical errors with the given grid size and time step, rather than physical parameters. We introduce two complementary techniques to capture Boundary layer dynamics, bringing more physical control and predictability. We extend the FLIP particle-grid method with viscous particle strength exchange[Rivoalen and Huberson 2001] to better transfer momentum at solid boundaries, dubbed VFLIP. We also introduce Weakly Higher Resolution Regional Projection (WHIRP), a cheap and simple way to increase grid resolution where important by overlaying high resolution grids on the global coarse grid.

Billy D. Todd - One of the best experts on this subject based on the ideXlab platform.

  • Propagation speed of a chemical wave front: effect of confinement
    Molecular Simulation, 2009
    Co-Authors: Jesper Schmidt Hansen, Billy D. Todd
    Abstract:

    In this paper we perform molecular dynamics simulations of a propagating chemical wave front in both confining and unconfining geometries. It is found that the wave front propagation speed is reduced in the case where the Fluid is confined and the channel width is sufficiently small, namely, in the order of 40 molecular diameters. For channel widths larger than 40 molecular diameters the effect from the wall on the front speed is negligible. In the wall–Fluid Boundary region the self-diffusion is a tensorial property; however, in the channel interior the diffusion is a simple scalar coefficient and equals that of the bulk phase. This fact is used to derive an anisotropic reaction diffusion equation. Via numerical analysis of the reaction diffusion equation it is found that a sufficient condition for the observed speed reduction is that the diffusion element parallel to the wall decreases as the distance to the wall decreases, i.e. in the wall–Fluid Boundary region. Furthermore, it is found that the front ...

  • Propagation speed of a chemical wave front: effect of confinement
    Molecular Simulation, 2009
    Co-Authors: Jesper Schmidt Hansen, Billy D. Todd
    Abstract:

    In this paper we perform molecular dynamics simulations of a propagating chemical wave front in both confining and unconfining geometries. It is found that the wave front propagation speed is reduced in the case where the Fluid is confined and the channel width is sufficiently small, namely, in the order of 40 molecular diameters. For channel widths larger than 40 molecular diameters the effect from the wall on the front speed is negligible. In the wall-Fluid Boundary region the self-diffusion is a tensorial property; however, in the channel interior the diffusion is a simple scalar coefficient and equals that of the bulk phase. This fact is used to derive an anisotropic reaction diffusion equation. Via numerical analysis of the reaction diffusion equation it is found that a sufficient condition for the observed speed reduction is that the diffusion element parallel to the wall decreases as the distance to the wall decreases, i.e. in the wall-Fluid Boundary region. Furthermore, it is found that the front speed is independent of the Fluid layering in this region and the normal diffusion element as long as it is non-zero and positive

  • Local linear viscoelasticity of confined Fluids.
    The Journal of chemical physics, 2007
    Co-Authors: Jesper Schmidt Hansen, Peter J. Daivis, Billy D. Todd
    Abstract:

    In this paper the authors propose a novel method to study the local linear viscoelasticity of Fluids confined between two walls. The method is based on the linear constitutive equation and provides details about the real and imaginary parts of the local complex viscosity. They apply the method to a simple atomic Fluid undergoing zero mean oscillatory flow using nonequilibrium molecular dynamics simulations. The method shows that the viscoelastic properties of the Fluid exhibit dramatic spatial changes near the wall-Fluid Boundary due to the high density in this region. It is also shown that the real part of the viscosity converges to the frequency dependent local shear viscosity sufficiently far away from the wall. This also provides valuable information about the transport properties in the Fluid, in general. The viscosity is compared with predictions from the local average density model. The two methods disagree in that the local average density model predicts larger viscosity variations near the wall-Fluid Boundary than what is observed through the method presented here.

Celine Grandmont - One of the best experts on this subject based on the ideXlab platform.

  • Existence of Weak Solutions for the Unsteady Interaction of a Viscous Fluid with an Elastic Plate
    SIAM Journal on Mathematical Analysis SIAM Journal of Mathematical Analysis, 2008
    Co-Authors: Celine Grandmont
    Abstract:

    We consider a three--dimensional viscous incompressible Fluid governed by the Navier--Stokes equations, interacting with an elastic plate located on one part of the Fluid Boundary. We do not neglect the deformation of the Fluid domain which consequently depends on the displacement of the structure. The purpose of this work is to study the solutions of this unsteady Fluid--structure interaction problem, as the coefficient modeling the viscoelasticity (resp. the rotatory inertia) of the plate tends to zero. As a consequence, we obtain the existence of at least one weak solution for the limit problem (Navier--Stokes equation coupled with a plate in flexion) as long as the structure does not touch the bottom of the Fluid cavity.

  • existence of weak solutions for the unsteady interaction of a viscous Fluid with an elastic plate
    Journal of Mathematical Fluid Mechanics, 2005
    Co-Authors: Antonin Chambolle, Benoit Desjardins, Maria J Esteban, Celine Grandmont
    Abstract:

    The purpose of this work is to study the existence of solutions for an unsteady Fluid-structure interaction problem. We consider a three-dimensional viscous incompressible Fluid governed by the Navier–Stokes equations, interacting with a flexible elastic plate located on one part of the Fluid Boundary. The Fluid domain evolves according to the structure’s displacement, itself resulting from the Fluid force. We prove the existence of at least one weak solution as long as the structure does not touch the fixed part of the Fluid Boundary. The same result holds also for a two-dimensional Fluid interacting with a one-dimensional membrane.

David Tskhakaya - One of the best experts on this subject based on the ideXlab platform.

  • The magnetized plasma–wall transition (PWT) and its relation to Fluid Boundary conditions
    Computer Physics Communications, 2007
    Co-Authors: Siegbert Kuhn, David Tskhakaya
    Abstract:

    Abstract The magnetized plasma–wall transition (PWT) region typically exhibits three characteristic subregions: the “Debye sheath”, the “magnetic presheath”, and the “collisional presheath”. The Fluid Boundary conditions for transport codes (simulating, e.g., the scrape-off layer (SOL) of a tokamak) are usually applied at the “magnetic presheath entrance”, where in the simplest model the ion velocity parallel to the magnetic field equals the local sound velocity . After reviewing the basic time-independent and collisionless models of the magnetized PWT, various extensions will be discussed which are due to E × B , ∇B and diamagnetic drifts, nonuniformity of the electric field parallel to the wall, and turbulence effects. In practically all cases considered, quantitative results can be obtained only by massive application of numerical methods of solution.

Hirokazu Takagi - One of the best experts on this subject based on the ideXlab platform.

  • Computational thermo-Fluid analysis of a disk brake
    Computational Mechanics, 2016
    Co-Authors: Kenji Takizawa, Shinichiro Tabata, Takashi Kuraishi, Tayfun E. Tezduyar, Hirokazu Takagi
    Abstract:

    We present computational thermo-Fluid analysis of a disk brake, including thermo-Fluid analysis of the flow around the brake and heat conduction analysis of the disk. The computational challenges include proper representation of the small-scale thermo-Fluid behavior, high-resolution representation of the thermo-Fluid Boundary layers near the spinning solid surfaces, and bringing the heat transfer coefficient (HTC) calculated in the thermo-Fluid analysis of the flow to the heat conduction analysis of the spinning disk. The disk brake model used in the analysis closely represents the actual configuration, and this adds to the computational challenges. The components of the method we have developed for computational analysis of the class of problems with these types of challenges include the Space---Time Variational Multiscale method for coupled incompressible flow and thermal transport, ST Slip Interface method for high-resolution representation of the thermo-Fluid Boundary layers near spinning solid surfaces, and a set of projection methods for different parts of the disk to bring the HTC calculated in the thermo-Fluid analysis. With the HTC coming from the thermo-Fluid analysis of the flow around the brake, we do the heat conduction analysis of the disk, from the start of the breaking until the disk spinning stops, demonstrating how the method developed works in computational analysis of this complex and challenging problem.