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Raymond Panneton - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic viscous permeability of an open-cell aluminum foam: Computations versus experiments
    Journal of Applied Physics, 2008
    Co-Authors: Camille Perrot, Fabien Chevillotte, Raymond Panneton
    Abstract:

    Is it possible to find a two-dimensional (2D) periodic unit cell representative of the dynamic viscous dissipation properties of a real porous media? This is a challenging question addressed in this paper through a review of tools and methods of experimental and computational micro(poro)mechanics. The combination of advanced experimental imaging and numerical homogenization techniques provides a unique opportunity to understand and assess the limits of two-dimensional Models of microstructures, as a potential basis for the engineering prediction of macroscopic properties of acoustical materials. This is illustrated for a real sample of open-cell aluminum foam. The conclusion, based on this analysis, is that the 2D periodic foam Model Geometry provides a reliable estimate of the dynamic permeability, except in the low frequency range. This is not surprising because in the 2D periodic foam Model Geometry, ligaments are always perpendicular to the flow direction, thus decreasing artificially the static permeability of the viscous flow.

  • Dynamic viscous permeability of an open-cell aluminum foam: Computations versus experiments
    Journal of Applied Physics, 2008
    Co-Authors: Camille Perrot, Fabien Chevillotte, Raymond Panneton
    Abstract:

    Is it possible to find a two-dimensional (2D) periodic unit cell representative of the dynamic viscous dissipation properties of a real porous media? This is a challenging question addressed in this paper through a review of tools and methods of experimental and computational micro(poro)mechanics. The combination of advanced experimental imaging and numerical homogenization techniques provides a unique opportunity to understand and assess the limits of two-dimensional Models of microstructures, as a potential basis for the engineering prediction of macroscopic properties of acoustical materials. This is illustrated for a real sample of open-cell aluminum foam. The conclusion, based on this analysis, is that the 2D periodic foam Model Geometry provides a reliable estimate of the dynamic permeability, except in the low frequency range. This is not surprising because in the 2D periodic foam Model Geometry, ligaments are always perpendicular to the flow direction, thus decreasing artificially the static perme...

Akiyoshi Hatayama - One of the best experts on this subject based on the ideXlab platform.

  • effects of the extraction voltage on the beam divergence for a h ion source
    Journal of Applied Physics, 2019
    Co-Authors: M Lindqvis, J Lettry, S Nishioka, K Hoshino, K Miyamoto, Akiyoshi Hatayama
    Abstract:

    Negative hydrogen (H −) ion sources have a wide range of applications. The general requirement for these H − ion sources is to produce intense H − ion beams with good beam optics. The purpose of this paper is to clarify the effects of the beam extraction voltage on the beam divergence angle by three-dimensional Particle-in-Cell (PIC) Modeling. Perveance matching has been studied for a wide range of the extraction voltage with the Model Geometry of a Linac4 H − ion source. The extracted H − beam divergence angle is evaluated for extraction voltages ranging from 7 to 14 kV by using the Keio-BFX PIC code. The results show divergence minima in the range of 9.2–11.5 kV for the case without surface H − production, which correspond to experimental results. The dependence of divergence on the extraction voltage is explained by the change of the shape of the meniscus. In particular, a flat meniscus corresponds to low beam divergence, and particles extracted through the center of the meniscus have a lower divergence than particles extracted near the Plasma Electrode.Negative hydrogen (H −) ion sources have a wide range of applications. The general requirement for these H − ion sources is to produce intense H − ion beams with good beam optics. The purpose of this paper is to clarify the effects of the beam extraction voltage on the beam divergence angle by three-dimensional Particle-in-Cell (PIC) Modeling. Perveance matching has been studied for a wide range of the extraction voltage with the Model Geometry of a Linac4 H − ion source. The extracted H − beam divergence angle is evaluated for extraction voltages ranging from 7 to 14 kV by using the Keio-BFX PIC code. The results show divergence minima in the range of 9.2–11.5 kV for the case without surface H − production, which correspond to experimental results. The dependence of divergence on the extraction voltage is explained by the change of the shape of the meniscus. In particular, a flat meniscus corresponds to low beam divergence, and particles extracted through the center of the meniscus...

  • Modeling of neutrals in the linac4 h ion source plasma hydrogen atom production density profile and hα intensity by collisional radiative Model
    Review of Scientific Instruments, 2014
    Co-Authors: T Yamamoto, J Lettry, Akiyoshi Hatayama, T Shibata, M Ohta, M Yasumoto, K Nishida, S Mattei, K Sawada, U Fantz
    Abstract:

    To control the H0 atom production profile in the H− ion sources is one of the important issues for the efficient and uniform surface H− production. The purpose of this study is to construct a collisional radiative (CR) Model to calculate the effective production rate of H0 atoms from H2 molecules in the Model Geometry of the radio-frequency (RF) H− ion source for Linac4 accelerator. In order to validate the CR Model by comparison with the experimental results from the optical emission spectroscopy, it is also necessary for the Model to calculate Balmer photon emission rate in the source. As a basic test of the Model, the time evolutions of H0 production and the Balmer Hα photon emission rate are calculated for given electron energy distribution functions in the Linac4 RF H− ion source. Reasonable test results are obtained and basis for the detailed comparisons with experimental results have been established.

Ulf Lindström - One of the best experts on this subject based on the ideXlab platform.

  • Supersymmetric Sigma Model Geometry
    Symmetry, 2012
    Co-Authors: Ulf Lindström
    Abstract:

    This is a review of how sigma Models formulated in Superspace have become important tools for understanding Geometry. Topics included are: The (hyper)kahler reduction; projective superspace; the generalized Legendre construction; generalized Kahler Geometry and constructions of hyperkahler metrics on Hermitian symmetric spaces.

  • Supersymmetric Sigma Model Geometry
    arXiv: High Energy Physics - Theory, 2012
    Co-Authors: Ulf Lindström
    Abstract:

    This is a review of how sigma Models formulated in Superspace have become important tools for understanding Geometry. Topics included are: The (hyper)k\"ahler reduction; projective superspace; the generalized Legendre construction; generalized K\"ahler Geometry and constructions of hyperk\"ahler metrics on Hermitean symmetric spaces.

Camille Perrot - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic viscous permeability of an open-cell aluminum foam: Computations versus experiments
    Journal of Applied Physics, 2008
    Co-Authors: Camille Perrot, Fabien Chevillotte, Raymond Panneton
    Abstract:

    Is it possible to find a two-dimensional (2D) periodic unit cell representative of the dynamic viscous dissipation properties of a real porous media? This is a challenging question addressed in this paper through a review of tools and methods of experimental and computational micro(poro)mechanics. The combination of advanced experimental imaging and numerical homogenization techniques provides a unique opportunity to understand and assess the limits of two-dimensional Models of microstructures, as a potential basis for the engineering prediction of macroscopic properties of acoustical materials. This is illustrated for a real sample of open-cell aluminum foam. The conclusion, based on this analysis, is that the 2D periodic foam Model Geometry provides a reliable estimate of the dynamic permeability, except in the low frequency range. This is not surprising because in the 2D periodic foam Model Geometry, ligaments are always perpendicular to the flow direction, thus decreasing artificially the static permeability of the viscous flow.

  • Dynamic viscous permeability of an open-cell aluminum foam: Computations versus experiments
    Journal of Applied Physics, 2008
    Co-Authors: Camille Perrot, Fabien Chevillotte, Raymond Panneton
    Abstract:

    Is it possible to find a two-dimensional (2D) periodic unit cell representative of the dynamic viscous dissipation properties of a real porous media? This is a challenging question addressed in this paper through a review of tools and methods of experimental and computational micro(poro)mechanics. The combination of advanced experimental imaging and numerical homogenization techniques provides a unique opportunity to understand and assess the limits of two-dimensional Models of microstructures, as a potential basis for the engineering prediction of macroscopic properties of acoustical materials. This is illustrated for a real sample of open-cell aluminum foam. The conclusion, based on this analysis, is that the 2D periodic foam Model Geometry provides a reliable estimate of the dynamic permeability, except in the low frequency range. This is not surprising because in the 2D periodic foam Model Geometry, ligaments are always perpendicular to the flow direction, thus decreasing artificially the static perme...

J. P. Du Plessis - One of the best experts on this subject based on the ideXlab platform.

  • Analytical determination of the effect of compression on the permeability of fibrous porous media
    Chemical Engineering Science, 2014
    Co-Authors: S. Woudberg, M. C. Heyningen, Laurence Le Coq, J. Legrand, J. P. Du Plessis
    Abstract:

    An existing geometric pure scale Model is geometrically adapted from an isotropic to an anisotropic structure in order to determine the effects of compression on permeability. In this analysis, streamvvise compression is accounted for by incorporating the compression porosity relationship into the analytical Model, while permeability is expressed in terms of the fiber diameter and the pore scale linear dimensions of the geometric Model. The linear dimensions are determined from several required input characteristics, namely, the measured hydraulic pore diameters, the porosity, and the compression ratios. The proposed Model is applied to determine the airflow through a compressed non woven glass fiber filter, with results that are corroborated with experimental permeability data. The Model is further validated against experimental permeability data for glass and nylon fibers as well as for airflow through a soft fibrous porous medium. Despite the simple Model Geometry, permeability predictions of the Correct order of magnitude are obtained, with the significant effects of compression On permeability observed in the experimental data verified by these analytic permeability predictions. (C) 2014 Elsevier Ltd. All rights reserved.