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Xiangming Yu - One of the best experts on this subject based on the ideXlab platform.
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wake behind a three dimensional dry transom stern part 1 flow structure and large scale air entrainment
Journal of Fluid Mechanics, 2019Co-Authors: Kelli Hendrickson, Gabriel Weymouth, Xiangming YuAbstract:We present high-resolution implicit large eddy simulation (iLES) of the turbulent air-entraining flow in the wake of three-dimensional Rectangular dry transom sterns with varying speeds and half-beam-to-draft ratios $B/D$ . We employ two-phase (air/water), time-dependent simulations utilizing conservative volume-of-fluid (cVOF) and boundary data immersion (BDIM) methods to obtain the flow structure and large-scale air entrainment in the wake. We confirm that the convergent-corner-wave region that forms immediately aft of the stern wake is ballistic, thus predictable only by the speed and (Rectangular) Geometry of the ship. We show that the flow structure in the air–water mixed region contains a shear layer with a streamwise jet and secondary vortex structures due to the presence of the quasi-steady, three-dimensional breaking waves. We apply a Lagrangian cavity identification technique to quantify the air entrainment in the wake and show that the strongest entrainment is where wave breaking occurs. We identify an inverse dependence of the maximum average void fraction and total volume entrained with $B/D$ . We determine that the average surface entrainment rate initially peaks at a location that scales with draft Froude number and that the normalized average air cavity density spectrum has a consistent value providing there is active air entrainment. A small parametric study of the Rectangular Geometry and stern speed establishes and confirms the scaling of the interface characteristics with draft Froude number and Geometry. In Part 2 (Hendrikson & Yue, J. Fluid Mech. , vol. 875, 2019, pp. 884–913) we examine the incompressible highly variable density turbulence characteristics and turbulence closure modelling.
Kelli Hendrickson - One of the best experts on this subject based on the ideXlab platform.
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wake behind a three dimensional dry transom stern part 1 flow structure and large scale air entrainment
Journal of Fluid Mechanics, 2019Co-Authors: Kelli Hendrickson, Gabriel Weymouth, Xiangming YuAbstract:We present high-resolution implicit large eddy simulation (iLES) of the turbulent air-entraining flow in the wake of three-dimensional Rectangular dry transom sterns with varying speeds and half-beam-to-draft ratios $B/D$ . We employ two-phase (air/water), time-dependent simulations utilizing conservative volume-of-fluid (cVOF) and boundary data immersion (BDIM) methods to obtain the flow structure and large-scale air entrainment in the wake. We confirm that the convergent-corner-wave region that forms immediately aft of the stern wake is ballistic, thus predictable only by the speed and (Rectangular) Geometry of the ship. We show that the flow structure in the air–water mixed region contains a shear layer with a streamwise jet and secondary vortex structures due to the presence of the quasi-steady, three-dimensional breaking waves. We apply a Lagrangian cavity identification technique to quantify the air entrainment in the wake and show that the strongest entrainment is where wave breaking occurs. We identify an inverse dependence of the maximum average void fraction and total volume entrained with $B/D$ . We determine that the average surface entrainment rate initially peaks at a location that scales with draft Froude number and that the normalized average air cavity density spectrum has a consistent value providing there is active air entrainment. A small parametric study of the Rectangular Geometry and stern speed establishes and confirms the scaling of the interface characteristics with draft Froude number and Geometry. In Part 2 (Hendrikson & Yue, J. Fluid Mech. , vol. 875, 2019, pp. 884–913) we examine the incompressible highly variable density turbulence characteristics and turbulence closure modelling.
Gabriel Weymouth - One of the best experts on this subject based on the ideXlab platform.
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wake behind a three dimensional dry transom stern part 1 flow structure and large scale air entrainment
Journal of Fluid Mechanics, 2019Co-Authors: Kelli Hendrickson, Gabriel Weymouth, Xiangming YuAbstract:We present high-resolution implicit large eddy simulation (iLES) of the turbulent air-entraining flow in the wake of three-dimensional Rectangular dry transom sterns with varying speeds and half-beam-to-draft ratios $B/D$ . We employ two-phase (air/water), time-dependent simulations utilizing conservative volume-of-fluid (cVOF) and boundary data immersion (BDIM) methods to obtain the flow structure and large-scale air entrainment in the wake. We confirm that the convergent-corner-wave region that forms immediately aft of the stern wake is ballistic, thus predictable only by the speed and (Rectangular) Geometry of the ship. We show that the flow structure in the air–water mixed region contains a shear layer with a streamwise jet and secondary vortex structures due to the presence of the quasi-steady, three-dimensional breaking waves. We apply a Lagrangian cavity identification technique to quantify the air entrainment in the wake and show that the strongest entrainment is where wave breaking occurs. We identify an inverse dependence of the maximum average void fraction and total volume entrained with $B/D$ . We determine that the average surface entrainment rate initially peaks at a location that scales with draft Froude number and that the normalized average air cavity density spectrum has a consistent value providing there is active air entrainment. A small parametric study of the Rectangular Geometry and stern speed establishes and confirms the scaling of the interface characteristics with draft Froude number and Geometry. In Part 2 (Hendrikson & Yue, J. Fluid Mech. , vol. 875, 2019, pp. 884–913) we examine the incompressible highly variable density turbulence characteristics and turbulence closure modelling.
William D. Nix - One of the best experts on this subject based on the ideXlab platform.
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a microbeam bending method for studying stress strain relations for metal thin films on silicon substrates
Journal of The Mechanics and Physics of Solids, 2005Co-Authors: J.n. Florando, William D. NixAbstract:Abstract We have developed a microbeam bending technique for determining elastic–plastic, stress–strain relations for thin metal films on silicon substrates. The method is similar to previous microbeam bending techniques, except that triangular silicon microbeams are used in place of Rectangular beams. The triangular beam has the advantage that the entire film on the top surface of the beam is subjected to a uniform state of plane strain as the beam is deflected, unlike the standard Rectangular Geometry where the bending is concentrated at the support. To extract the average stress–strain relations for the film, we present a method of analysis that requires computation of the neutral plane for bending, which changes as the film deforms plastically. This method can be used to determine the elastic–plastic properties of thin metal films on silicon substrates up to strains of about 1%. Utilizing this technique, both yielding and strain hardening of Cu thin films on silicon substrates have been investigated. Copper films with dual crystallographic textures and different grain sizes, as well as others with strong 〈1 1 1〉 textures have been studied. Three strongly textured 〈1 1 1〉 films were studied to examine the effect of film thickness on the deformation properties of the film. These films show very high rates of work hardening, and an increase in the yield stress and work hardening rate with decreasing film thickness, consistent with current dislocation models.
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A Microbeam Bending Method for Studying Stress-Strain Relations for Metal Thin Films on Silicon Substrates
2004Co-Authors: J.n. Florando, William D. NixAbstract:We have developed a microbeam bending technique for determining elastic-plastic, stress-strain relations for thin metal films on silicon substrates. The method is similar to previous microbeam bending techniques, except that triangular silicon microbeams are used in place of Rectangular beams. The triangular beam has the advantage that the entire film on the top surface of the beam is subjected to a uniform state of plane strain as the beam is deflected, unlike the standard Rectangular Geometry where the bending is concentrated at the support. We present a method of analysis for determining two Ramberg-Osgood parameters for describing the stress-strain relation for the film. These parameters are obtained by fitting the elastic-plastic model to the measured load-displacement data, and utilizing the known elastic properties of both film and substrate. As a part of the analysis we compute the position of the neutral plane for bending, which changes as the film deforms plastically. This knowledge, in turn, allows average stress-strain relations to be determined accurately without forcing the film to closely follow the Ramberg-Osgood law. The method we have developed can be used to determine the elastic-plastic properties of thin metal films on silicon substrates up to strains of about 1%. Utilizingmore » this technique, both yielding and strain hardening of Cu thin films on silicon substrates have been investigated. Copper films with dual crystallographic textures and different grain sizes, as well as others with strong textures have been studied. Three strongly textured films were studied to examine the effect of film thickness on the deformation properties of the film. These films show very high rates of work hardening, and an increase in the yield stress and work hardening rate with decreasing film thickness, consistent with current dislocation models.« less
Luca Sanguinetti - One of the best experts on this subject based on the ideXlab platform.
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Rayleigh Fading Modeling and Channel Hardening for Reconfigurable Intelligent Surfaces
IEEE Wireless Communications Letters, 2020Co-Authors: Luca SanguinettiAbstract:A realistic performance assessment of any wireless technology requires the use of a channel model that reflects its main characteristics. The independent and identically distributed Rayleigh fading channel model has been (and still is) the basis of most theoretical research on multiple antenna technologies in scattering environments. This letter shows that such a model is not physically appearing when using a reconfigurable intelligent surface (RIS) with Rectangular Geometry and provides an alternative physically feasible Rayleigh fading model that can be used as a baseline when evaluating RIS-aided communications. The model is used to revisit the basic RIS properties, e.g., the rank of spatial correlation matrices and channel hardening.
