The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
Frederick B. Pierson - One of the best experts on this subject based on the ideXlab platform.
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suitability of terrestrial laser scanning for studying Surface Roughness Effects on concentrated flow erosion processes in rangelands
Catena, 2011Co-Authors: Jan U.h. Eitel, Lee A. Vierling, Jason C Williams, Osama Z Alhamdan, Frederick B. PiersonAbstract:Surface Roughness is thought to affect concentrated flow erosion – a major mechanism of soil loss on disturbed rangelands. However, quantifying Surface Roughness in the field at appropriately fine spatial scales is laborious and the scale at which to conduct meaningful Roughness measurements is difficult to discern. Rapid, objective, and repeatable field methods are therefore needed to accurately measure Surface Roughness across a range of spatial scales to advance our understanding and modeling of concentrated flow erosion processes. Surface Roughness can be derived from Surface topography mapped at the sub-cm level using a field-portable terrestrial laser scanner (TLS). To test the suitability of terrestrial laser scanning for studying Surface Roughness Effects on erosion processes in rangelands, we used concentrated flow simulation techniques at 8.5 m2 plots that were randomly placed at rangeland sites in southeastern Oregon and southwestern Idaho, USA. Local Surface Roughness (locRMSH) was calculated as the standard deviation of TLS mapped Surface heights within moving windows varying in size from 30 × 30 to 90 × 90 mm. The mean locRMSH of the eroded area and entire plot were negatively correlated (r2 > 0.71, RMSE 0.74, RMSE < 90.07 g min− 1, respectively) with concentrated flow erosion. The strength of the locRMSH–erosion relationship and regression model parameters were affected by the moving window size, emphasizing the scale dependence of the locRMSH–erosion relationship. Adjusting locRMSH for slope Effects decreased the strength of the locRMSH–erosion relationship from r2 < 0.83 to < 0.26. Our results indicate that TLS is a useful tool to enhance our current understanding of the effect of Surface Roughness on overland flow erosion processes and advance hydrologic and erosion model parameter development. Further research is needed to evaluate the locRMSH – concentrated flow erosion relationship over a wider range of soil properties, Surface conditions, and spatial extents.
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Suitability of terrestrial laser scanning for studying Surface Roughness Effects on concentrated flow erosion processes in rangelands
CATENA, 2011Co-Authors: Jan U.h. Eitel, C. Jason Williams, Lee A. Vierling, Osama Z. Al-hamdan, Frederick B. PiersonAbstract:Surface Roughness is thought to affect concentrated flow erosion – a major mechanism of soil loss on disturbed rangelands. However, quantifying Surface Roughness in the field at appropriately fine spatial scales is laborious and the scale at which to conduct meaningful Roughness measurements is difficult to discern. Rapid, objective, and repeatable field methods are therefore needed to accurately measure Surface Roughness across a range of spatial scales to advance our understanding and modeling of concentrated flow erosion processes. Surface Roughness can be derived from Surface topography mapped at the sub-cm level using a field-portable terrestrial laser scanner (TLS). To test the suitability of terrestrial laser scanning for studying Surface Roughness Effects on erosion processes in rangelands, we used concentrated flow simulation techniques at 8.5 m2 plots that were randomly placed at rangeland sites in southeastern Oregon and southwestern Idaho, USA. Local Surface Roughness (locRMSH) was calculated as the standard deviation of TLS mapped Surface heights within moving windows varying in size from 30 × 30 to 90 × 90 mm. The mean locRMSH of the eroded area and entire plot were negatively correlated (r2 > 0.71, RMSE 0.74, RMSE
James White - One of the best experts on this subject based on the ideXlab platform.
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Surface Roughness Effects in the Region Between High Wave Number and High Bearing Number Limited Lubricant Flows
Journal of Tribology, 2013Co-Authors: James WhiteAbstract:The ability to predict Surface Roughness Effects is now well established for gas bearings that satisfy the requirements for either high wave number–limited or high bearing number–limited conditions. However, depending on the parameters involved, a given bearing configuration may not satisfy either of these limited requirements for analysis of Roughness Effects. Well-established methods for the analysis of Surface Roughness Effects on gas lubrication are not yet available outside of these two limited regions. With that as motivation, this paper then reports an analytical investigation of rough Surface gas-bearing Effects for the region bounded on one side by high wave number–limited conditions and on the other by high bearing number–limited Effects. It emphasizes the gas-bearing region, where shear-driven flow rate and pressure-driven flow rate due to Surface Roughness are of the same order of magnitude. This paper makes use of the compressible continuum form of the Reynolds equation of lubrication together with multiple-scale analysis to formulate a governing lubrication equation appropriate for the analysis of striated Roughness Effects collectively subject to high bearing number (Λ→∞), high inverse Roughness length scale (β→∞), and unity order of magnitude-modified bearing number based on Roughness length scale (Λ2=Λ/β=O(1)). The resulting lubrication equation is applicable for both moving and stationary Roughness and can be applied in either averaged or un-averaged form. Several numerical examples and comparisons are presented. Among them are results that illustrate an increased sensitivity of bearing force to modified bearing number for Λ2=O(1). With Λ2 in this range, bearings with either moving or stationary Roughness exhibit increased force sensitivities, but the Effects act in opposite ways. That is, while an increase in modified bearing number causes a decrease in force for stationary Roughness, the same increase in modified bearing number causes an increase in force for moving Roughness.
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Comparison of Moving and Stationary Surface Roughness Effects on Bearing Performance, With Emphasis on High Knudsen Number Flow
Journal of Tribology, 2012Co-Authors: James WhiteAbstract:Low clearance gas bearing applications require an understanding of Surface Roughness Effects at increased levels of Knudsen number. Because very little information has been reported on the relative air-bearing influence of Roughness location, this paper is focused on a comparison of the Effects of moving and stationary striated Surface Roughness under high Knudsen number conditions. First, an appropriate lubrication equation will be derived based on multiple-scale analysis that extends the work of White (2010, “A Gas Lubrication Equation for High Knudsen Number Flows and Striated Rough Surfaces,” ASME J. Tribol., 132, p. 021701). The resulting Roughness averaged equation, applicable for both moving and stationary Roughness over a wide range of Knudsen numbers, allows an arbitrary striated Roughness orientation with regard to both (1) the direction of Surface translation and (2) the bearing coordinates. Next, the derived lubrication equation is used to analyze and compare the influences produced by a stepped transverse Roughness pattern located on the moving and the stationary bearing Surface of a wedge bearing geometry of variable inclination. Computed results are obtained for both incompressible and compressible lubricants, but with an emphasis on high Knudsen number flow. Significant differences in air-bearing performance are found to occur for moving versus stationary Roughness.
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Surface Roughness Effects on Air Bearing Performance Over a Wide Range of Knudsen and Wave Numbers
Journal of Tribology, 2010Co-Authors: James WhiteAbstract:Design of a near contact air bearing interface such as that created by a recording head slider and data storage disk requires consideration of a lubrication equation that is appropriate for high Knudsen number flows. The Poiseuille flow database reported by Fukui and Kaneko, 1990 ["A Database for Interpolation of Poiseuille Flow Rates for High Knudsen Number Lubrication Problems," ASME J. Tribol., 112, pp. 78―83] is appropriate over a wide range of Knudsen numbers and is used throughout the data storage industry for analysis of the low flying recording head slider air bearing. However, at such low clearances, the topography of the air bearing Surfaces also comes into question, making it important to consider both rarefaction and Surface Roughness Effects in the air bearing design. In order to simplify the air bearing analysis of rough Surfaces, averaging techniques for the lubrication equation have been developed for situations where the number of Roughness elements (or waves) is either much greater or much less than the gas bearing number. Between these two extremes there are currently no Roughness averaging methods available. Although some analytical and numerical studies have been reported for continuum and first-order slip conditions with simple geometries, little or no results have appeared that include both Surface Roughness and high Knudsen number flows outside the limited ranges where Surface averaging techniques are used. In order to better understand the influence of transverse Surface Roughness over a wide range of Knudsen numbers and the relationship of key parameters involved, this paper describes a primarily analytical air bearing study of a wide, rough Surface slider bearing using the Poiseuille flow database reported by Fukui and Kaneko. The work is focused outside the limited ranges where current Surface averaging methods for the lubrication equation are expected to be valid.
Jan U.h. Eitel - One of the best experts on this subject based on the ideXlab platform.
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suitability of terrestrial laser scanning for studying Surface Roughness Effects on concentrated flow erosion processes in rangelands
Catena, 2011Co-Authors: Jan U.h. Eitel, Lee A. Vierling, Jason C Williams, Osama Z Alhamdan, Frederick B. PiersonAbstract:Surface Roughness is thought to affect concentrated flow erosion – a major mechanism of soil loss on disturbed rangelands. However, quantifying Surface Roughness in the field at appropriately fine spatial scales is laborious and the scale at which to conduct meaningful Roughness measurements is difficult to discern. Rapid, objective, and repeatable field methods are therefore needed to accurately measure Surface Roughness across a range of spatial scales to advance our understanding and modeling of concentrated flow erosion processes. Surface Roughness can be derived from Surface topography mapped at the sub-cm level using a field-portable terrestrial laser scanner (TLS). To test the suitability of terrestrial laser scanning for studying Surface Roughness Effects on erosion processes in rangelands, we used concentrated flow simulation techniques at 8.5 m2 plots that were randomly placed at rangeland sites in southeastern Oregon and southwestern Idaho, USA. Local Surface Roughness (locRMSH) was calculated as the standard deviation of TLS mapped Surface heights within moving windows varying in size from 30 × 30 to 90 × 90 mm. The mean locRMSH of the eroded area and entire plot were negatively correlated (r2 > 0.71, RMSE 0.74, RMSE < 90.07 g min− 1, respectively) with concentrated flow erosion. The strength of the locRMSH–erosion relationship and regression model parameters were affected by the moving window size, emphasizing the scale dependence of the locRMSH–erosion relationship. Adjusting locRMSH for slope Effects decreased the strength of the locRMSH–erosion relationship from r2 < 0.83 to < 0.26. Our results indicate that TLS is a useful tool to enhance our current understanding of the effect of Surface Roughness on overland flow erosion processes and advance hydrologic and erosion model parameter development. Further research is needed to evaluate the locRMSH – concentrated flow erosion relationship over a wider range of soil properties, Surface conditions, and spatial extents.
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Suitability of terrestrial laser scanning for studying Surface Roughness Effects on concentrated flow erosion processes in rangelands
CATENA, 2011Co-Authors: Jan U.h. Eitel, C. Jason Williams, Lee A. Vierling, Osama Z. Al-hamdan, Frederick B. PiersonAbstract:Surface Roughness is thought to affect concentrated flow erosion – a major mechanism of soil loss on disturbed rangelands. However, quantifying Surface Roughness in the field at appropriately fine spatial scales is laborious and the scale at which to conduct meaningful Roughness measurements is difficult to discern. Rapid, objective, and repeatable field methods are therefore needed to accurately measure Surface Roughness across a range of spatial scales to advance our understanding and modeling of concentrated flow erosion processes. Surface Roughness can be derived from Surface topography mapped at the sub-cm level using a field-portable terrestrial laser scanner (TLS). To test the suitability of terrestrial laser scanning for studying Surface Roughness Effects on erosion processes in rangelands, we used concentrated flow simulation techniques at 8.5 m2 plots that were randomly placed at rangeland sites in southeastern Oregon and southwestern Idaho, USA. Local Surface Roughness (locRMSH) was calculated as the standard deviation of TLS mapped Surface heights within moving windows varying in size from 30 × 30 to 90 × 90 mm. The mean locRMSH of the eroded area and entire plot were negatively correlated (r2 > 0.71, RMSE 0.74, RMSE
Nicholas J. Hills - One of the best experts on this subject based on the ideXlab platform.
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Calculation of Surface Roughness Effects on air-riding seals
Journal of Engineering for Gas Turbines and Power, 2004Co-Authors: C. Guardino, John W. Chew, Nicholas J. HillsAbstract:The Effects of Surface Roughness on air-riding seals are investigated here using the Rayleigh-pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various 2D or 3D Roughness patterns on the stationary wall. A 'unit-based' approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of Surface Roughness on the net lift force. The Effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.
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Calculation of Surface Roughness Effects on Air-Riding Seals
Volume 3: Turbo Expo 2002 Parts A and B, 2002Co-Authors: C. Guardino, John W. Chew, Nicholas J. HillsAbstract:The Effects of Surface Roughness on air-riding seals are investigated here using the Rayleigh-pad as an example. Both incompressible and compressible flows are considered using both CFD analysis and analytical/numerical solutions of the Reynolds equation for various 2D or 3D Roughness patterns on the stationary wall. A ‘unit-based’ approach for incompressible flows has also been employed and is shown to be computationally much less expensive than the full-geometry solution. Results are presented showing the effect of Surface Roughness on the net lift force. The Effects of varying the Reynolds number are demonstrated, as well as comparative results for static stiffness.Copyright © 2002 by ASME
Hans-jörg Bauer - One of the best experts on this subject based on the ideXlab platform.
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Experimental Study of Surface Roughness Effects on a Turbine Airfoil in a Linear Cascade— Part I: External Heat Transfer
Journal of Turbomachinery, 2011Co-Authors: M. Lorenz, A. Schulz, Hans-jörg BauerAbstract:The present experimental study is part of a comprehensive heat transfer analysis on a highly loaded low pressure turbine blade and endwall with varying Surface Roughness. Whereas a former paper [1] focused on full span heat transfer of a smooth airfoil and Surface Roughness Effects on the endwall, in this work further measurements at the airfoil midspan with different deterministic Surface Roughness are considered. Part I investigates the external heat transfer enhancement due to rough Surfaces whereas part II focuses on Surface Roughness Effects on aerodynamic losses. A set of different arrays of deterministic Roughness is investigated in these experiments, varying the height and eccentricity of the Roughness elements, showing the combined influence of Roughness height and anisotropy of the rough Surfaces on laminar to turbulent transition and the turbulent boundary layer as well as boundary layer separation on the pressure and suction side. It is shown that — besides the known effect of Roughness height — eccentricity of Roughness plays a major role in the onset of transition and the turbulent heat transfer. The experiments are conducted at several free-stream turbulence levels (Tu1 = 1.4% to 10.1%) and different Reynolds numbers.Copyright © 2010 by ASME
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Experimental Study of Surface Roughness Effects on a Turbine Airfoil in a Linear Cascade: Part I—External Heat Transfer
Volume 4: Heat Transfer Parts A and B, 2010Co-Authors: M. Lorenz, A. Schulz, Hans-jörg BauerAbstract:The present experimental study is part of a comprehensive heat transfer analysis on a highly loaded low pressure turbine blade and endwall with varying Surface Roughness. Whereas a former paper [1] focused on full span heat transfer of a smooth airfoil and Surface Roughness Effects on the endwall, in this work further measurements at the airfoil midspan with different deterministic Surface Roughness are considered. Part I investigates the external heat transfer enhancement due to rough Surfaces whereas part II focuses on Surface Roughness Effects on aerodynamic losses. A set of different arrays of deterministic Roughness is investigated in these experiments, varying the height and eccentricity of the Roughness elements, showing the combined influence of Roughness height and anisotropy of the rough Surfaces on laminar to turbulent transition and the turbulent boundary layer as well as boundary layer separation on the pressure and suction side. It is shown that — besides the known effect of Roughness height — eccentricity of Roughness plays a major role in the onset of transition and the turbulent heat transfer. The experiments are conducted at several free-stream turbulence levels (Tu1 = 1.4% to 10.1%) and different Reynolds numbers.Copyright © 2010 by ASME
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experimental study of Surface Roughness Effects on a turbine airfoil in a linear cascade part ii aerodynamic losses
ASME Turbo Expo 2010: Power for Land Sea and Air, 2010Co-Authors: M. Lorenz, A. Schulz, Hans-jörg BauerAbstract:The present experimental study is part of a comprehensive analysis accounting for heat transfer and aerodynamic losses on a highly loaded low pressure turbine blade with varying Surface Roughness. Whereas part I focuses on heat transfer measurements at airfoil midspan with different deterministic Surface Roughnesses, part II investigates Surface Roughness Effects on aerodynamic losses of the same airfoil. A set of different arrays of deterministic Roughness (the same as used in part I) is investigated in these experiments. The height and eccentricity of the Roughness elements is varied, showing the combined influence of Roughness height and anisotropy on the losses produced in the boundary layers. It is shown that the boundary layer loss is dominated by the suction side. Therefore, the investigations focus on measurements of the suction side boundary layer thickness at midspan directly upstream of the trailing edge. The experiments are conducted at several free-stream turbulence levels (Tu1 = 1.4% to 10.1%) and different Reynolds numbers. The measurements reveal that suction side boundary layer thickness is increased by up to 190% if Surface Roughness shifts the transition onset upstream. However, in some cases, at low Reynolds numbers and free-stream turbulence, Surface Roughness suppresses boundary layer separation and decreases the trailing edge boundary layer thickness by up to 30%.© 2010 ASME