The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform

Sriram Shankaran - One of the best experts on this subject based on the ideXlab platform.

  • a higher order generalized ghost fluid method for the poor for the three dimensional two phase flow computation of underwater implosions
    Journal of Computational Physics, 2008
    Co-Authors: Charbel Farhat, Arthur Rallu, Sriram Shankaran
    Abstract:

    The ghost fluid method for the poor (GFMP) is an elegant, computationally efficient, and nearly conservative method for the solution of two-phase flow problems. It was developed in one dimension for the stiffened gas equation of state (EOS) and one-step time-discretization algorithms. It naturally extends to three dimensions but its extension to higher-order, multi-step time-discretization schemes is not straightforward. Furthermore, the original GFMP and many other ghost fluid methods fail to handle the large density and pressure jumps that are encountered in underwater implosions. Therefore, the GFMP is generalized in this work to an arbitrary EOS and multi-fluid problems with multiple EOSs. It is also extended to three dimensions and developed for higher-order, multi-step time-discretization algorithms. Furthermore, this method is equipped with an exact two-phase Riemann solver for computing the fluxes across the material interface without crossing it. This aspect of the computation is a departure from the standard approach for computing fluxes in ghost fluid methods. It addresses the stiff nature of the two-phase air/water problem and enables a better handling of the large discontinuity of the density at the air/water interface. As the original GFMP, the proposed method is contact preserving, computationally efficient, and nearly conservative. Its superior performance in the presence of large density and pressure jumps is demonstrated for shock-tube problems. Its practicality and accuracy are also highlighted with the three-dimensional simulation of the implosion of an air-filled and submerged Glass Sphere.

  • A higher-order generalized ghost fluid method for the poor for the three-dimensional two-phase flow computation of underwater implosions
    Journal of Computational Physics, 2008
    Co-Authors: Charbel Farhat, Arthur Rallu, Sriram Shankaran
    Abstract:

    The ghost fluid method for the poor (GFMP) is an elegant, computationally efficient, and nearly conservative method for the solution of two-phase flow problems. It was developed in one dimension for the stiffened gas equation of state (EOS) and one-step time-discretization algorithms. It naturally extends to three dimensions but its extension to higher-order, multi-step time-discretization schemes is not straightforward. Furthermore, the original GFMP and many other ghost fluid methods fail to handle the large density and pressure jumps that are encountered in underwater implosions. Therefore, the GFMP is generalized in this work to an arbitrary EOS and multi-fluid problems with multiple EOSs. It is also extended to three dimensions and developed for higher-order, multi-step time-discretization algorithms. Furthermore, this method is equipped with an exact two-phase Riemann solver for computing the fluxes across the material interface without crossing it. This aspect of the computation is a departure from the standard approach for computing fluxes in ghost fluid methods. It addresses the stiff nature of the two-phase air/water problem and enables a better handling of the large discontinuity of the density at the air/water interface. As the original GFMP, the proposed method is contact preserving, computationally efficient, and nearly conservative. Its superior performance in the presence of large density and pressure jumps is demonstrated for shock-tube problems. Its practicality and accuracy are also highlighted with the three-dimensional simulation of the implosion of an air-filled and submerged Glass Sphere. ?? 2008 Elsevier Inc. All rights reserved.

L S Fletcher - One of the best experts on this subject based on the ideXlab platform.

  • thermal performance of a wire mesh hollow Glass Sphere composite structure
    Journal of Thermophysics and Heat Transfer, 2011
    Co-Authors: E. E. Marotta, L S Fletcher
    Abstract:

    DOI: 10.2514/1.T3609 Anexperimentalinvestigationexploringtheuseofawire-screen-mesh/hollow-Glass-microSpherecombinationasa thermal insulation media was conducted with three primary variables. These included the number of wire-mesh layers, the size of microSphere filler material, and temperature range. The test facility used included vertically stacked samples that were thermally and mechanically controlled (e.g., via gas bellows that controlled its vertical movement). From the temperature profile in the upper and lower samples, the value of the effective thermal conductivity was determined with use of the Fourier law of heat conduction. The number of screen mesh layers investigated were two, four, six, and eight, with each separated by a metallic liner. The filler materials included air andS15,S35,andS60HShollow-GlassmicroSpherestestedattemperaturesof27,57,93,and127Cwithaninterface pressure of 138 kPa (20 psi). The experimental results indicated that the number of layers was the primary factor in determining the effective thermalconductivity value andthusthe structure’sinsulation effectiveness. Increasing the number of wire-mesh layers resulted in acorresponding increase in effective thermal conductivity, whereas changes in temperature had negligible effect. The effective thermal conductivity values for the proposed structure ranged from 0.22 to 0:65 W=m-K, the lowest was for the two-layer case with air as filler material. Wire-screen-mesh insulation with air in the interstices leads to improved insulation, but the use of hollow-Glass microSpheres does not improve the insulation capabilities.

  • Thermal Performance of a Wire-Mesh/Hollow-Glass-Sphere Composite Structure
    Journal of Thermophysics and Heat Transfer, 2011
    Co-Authors: D.k. Kim, E. E. Marotta, L S Fletcher
    Abstract:

    An experimental investigation exploring the use of a wire-screen-mesh/hollow-Glass-microSphere combination as a thermal insulation media was conducted with three primary variables. These included the number of wire-mesh layers, the size of microSphere filler material, and temperature range. The test facility used included vertically stacked samples that were thermally and mechanically controlled (e.g., via gas bellows that controlled its vertical movement). From the temperature profile in the upper and lower samples, the value of the effective thermal conductivity was determined with use of the Fourier law of heat conduction. The number of screen mesh layers investigated were two, four, six, and eight, with each separated by a metallic liner. The filler materials included air and S15, S35, and S60HS hollow-Glass microSpheres tested at temperatures of 27, 57, 93, and 127 C with an interface pressure of 138 kPa (20 psi). The experimental results indicated that the number of layers was the primary factor in determining the effective thermal conductivity value and thus the structure's insulation effectiveness. Increasing the number of wire-mesh layers resulted in a corresponding increase in effective thermal conductivity, whereas changes in temperature had negligible effect. The effective thermal conductivity values for the proposed structure ranged from 0.22 to 0.65 W/m-K, the lowest was for the two-layer case with air as filler material. Wire-screen-mesh insulation with air in the interstices leads to improved insulation, but the use of hollow-Glass microSpheres does not improve the insulation capabilities.

Oliver B Wright - One of the best experts on this subject based on the ideXlab platform.

  • interferometric imaging of surface acoustic waves on a Glass Sphere
    Journal of Applied Physics, 2010
    Co-Authors: Paul H Otsuka, Osamu Matsuda, Motonobu Tomoda, Oliver B Wright
    Abstract:

    We use an ultrafast optical pump and probe technique to investigate the propagation of subgigahertz surface acoustic waves on a 1 mm diameter Glass Sphere with an aluminum coating. A fiber-based pump setup generates the surface waves and a common-path interferometer images them in the time domain over the Sphere surface as they pass through the pole opposite the source of excitation. Fourier analysis allows the acoustic spectrum of the acoustic source to be extracted and waves traveling in opposite directions to be isolated.

Cesar A. Gonzalez - One of the best experts on this subject based on the ideXlab platform.

  • Experimental sensitivity study of inductive phase shift spectroscopy as non-invasive method for hypoperfusion vs bleeding volumetric detection in brain
    2008 30th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2008
    Co-Authors: Omar Flores, Boris Rubinsky, Cesar A. Gonzalez
    Abstract:

    Hypoperfusion and bleeding in brain are medical conditions that involve a decrease and an increase of the relative amount of blood in tissue respectively. Both pathologies result in brain edema. This study evaluates experimentally the sensitivity of an induction based non-invasive technique for detection of changes of fluid volume through phase shift measurements as a possible method to distinguish brain hypoperfusion and bleeding process by volumetric monitoring. An induction coil-spherical head model was build and tested. The model involves two different diameter coils coaxially centered on a two-compartment Glass Sphere head model centrally placed with respect to the coils. Fluid volumes of physiological saline in 1ml decrement and increments were used to simulate different hypoperfusion and bleeding levels respectively. Inductive phase shift measurements were measured in a whole bandwidth (1 kHz – 1 GHz) by an experimental inductive spectrometer. The results show significant phase shift increase as a function of frequency and fluid volume in both pathologies simulated. At certain frequencies the hypoperfusion and bleeding phase shifts increase run in opposite ways. The experiments suggest that the tested technique has the potential to distinguish the processes of hypoperfusion and bleeding in brain by non-invasive, continuous and volumetric monitoring.

  • Inductive Phase Shift Spectroscopy for Volumetric Brain Edema Detection: An Experimental Simulation
    2007 29th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2007
    Co-Authors: Cesar A. Gonzalez, Rafael Rojas, Cleva Villanueva, Boris Rubinsky
    Abstract:

    This study evaluates experimentally an induction based non-invasive technique for detection of changes of fluid volume through phase shift measurements as a possible method for volumetric brain edema monitoring. An induction coil - spherical head model was build and tested. The model involves two different diameter coils coaxially centered on a two- compartment Glass Sphere head model centrally placed with respect to the coils. Three different fluid volumes of physiological saline in 20 ml increments were used to simulate different edema levels. Phase shift of the impedance coils as a function of relative fluid volume was measured at five frequencies (40, 50, 100, 200 and 300 MHz) by a commercial vector network analyzer. The results show significant phase shift increase as a function of frequency and fluid volume. The experiments with the coil- spherical head system suggest that the tested technique has the potential to become a practical configuration for non-invasive volumetric brain edema monitoring.

Peter Gudmundson - One of the best experts on this subject based on the ideXlab platform.