Showing papers on "Surface roughness published in 1976"
TL;DR: In this article, the threshold speeds of particles with different densities were determined as a function of particle diameter and in terms of threshold parameter vs. particle friction Reynolds number in wind-tunnel experiments performed to determine the threshold friction speed of particles.
207 citations
TL;DR: A FECO scanning interferometer is described, which has been used to determine statistics of polished surfaces having roughnesses under 100 A rms and was found to have smaller rms slopes than other surfaces of comparable roughness and scattered less than predicted by simple scalar scattering theory.
Abstract: A brief review of techniques for measuring surface roughness and optical figure
is given. One of the most promising of these techniques for measuring the
roughness of optical surfaces is interferometry employing fringes of equal
chromatic order (feco). A feco scanning interferometer is
described, which has been used to determine statistics of polished surfaces
having roughnesses under 100 A rms. The scanning interferometer resolves
square surface elements 2 μm on a side and
statistically characterizes the surface in terms of these elements. Height- and
slope-distribution functions, rms roughness, rms slope, and modified
autocovariance length distributions have been measured for selected optical
surfaces. Nearly all surfaces had Gaussian distributions of heights and slopes,
but none had Gaussian distributions of autocovariance lengths. Surfaces such as
electropolished copper, electroless nickel, and single-point diamond-machined
copper were found to have smaller rms slopes than other surfaces of comparable
roughness and scattered less than predicted by simple scalar scattering
theory.1,2 On the other hand, heavily scratched surfaces such
as polished potassium chloride had larger slopes and produced more scattering
than expected from simple theory.
207 citations
01 Nov 1976
197 citations
TL;DR: In this article, the scattering of nearly monoenergetic He and Ne atoms of thermal energies from the clean (001) face of LiF at low temperature was investigated using molecular beam techniques, and diffraction peaks were resolved over a wide range of incident and final angles.
163 citations
TL;DR: Theoretically, the bottom of the channel has been located at a distance of 35% of the diameter below the tops of the hemispheres as discussed by the authors, and the equivalent sand roughness of the bottom is equal to 2.5 times the diameter of the top.
Abstract: Characteristics of free surface flow over a bed consisting of hemispherical roughness elements have been studied experimentally. Theoretical bottom of the channel has been located at a distance of 35% of the diameter below the tops of hemispheres. Usual logarithmic laws are valid for velocity distribution and friction factor as long as flow depth is large relative to roughness height. Equivalent sand roughness of the bottom is equal to 2.5 times the diameter of hemispheres. At large values of relative roughness, on the other hand, lower velocities are observed than the logarithmic law predicts, and friction factor also increases by as much as 50%. Intensity of turbulence fluctuations decreases with the increase of relative roughness. Probability density function of velocity fluctuations near the rough bed tends away from the normal distribution.
135 citations
TL;DR: In this article, the solar absorptance αs and total hemispherical emittance et,H properties of two potential solar selective coating systems are reported, one is a semiconductor-pigmented paint which consists of a hightemperature silicone binder mixed with small particles of Ge, Si, or PbS.
Abstract: Solar absorptance αs and total hemispherical emittance et,H properties of two potential solar selective coating systems are reported. The first coating system studied is a semiconductor‐pigmented paint which consists of a high‐temperature silicone binder mixed with small particles of Ge, Si, or PbS. Although most of the paints have αs values above 0.90, all the paints suffer from high et,H values (∠0.70 to 0.90), which are shown to be due to the high emittance of the silicone binder itself. The second system studied is electroplated films of ’’black nickel’’ and a proprietary ’’black chrome.’’ Both αs and et,H values have been obtained as a function of the electroplating time and the substrate surface roughness. Increasing the plating time initially increases both αs and et,H; however, for long plating times, there is no improvement in αs, while et,H continues to increase. By increasing the surface roughness of nickel‐plated substrates, the solar absorptance can be increased while maintaining approximatel...
127 citations
TL;DR: Aircraft observations of the microwave emission from the wind-driven foam-covered Bering Sea substantiate earlier results and show that the combination of surface roughness and white water yields a significant microwave brightness temperature dependence on wind speed over a wide range of microwave wavelengths, with a decreasing dependence for wavelengths above 6 cm as mentioned in this paper.
Abstract: Aircraft observations of the microwave emission from the wind-driven foam-covered Bering Sea substantiate earlier results and show that the combination of surface roughness and white water yields a significant microwave brightness temperature dependence on wind speed over a wide range of microwave wavelengths, with a decreasing dependence for wavelengths above 6 cm. The spectral characteristic of brightness temperature as a function of wind speed is consistent with a foam model in which the bubbles give rise to a cusped surface between the foam and the sea. In the fetch-limited situation the contribution of the wave structure at the surface appears to increase as the foam coverage decreases. Although the data show that the thin streaks are the most important part of the white water signature, there is some evidence for the contribution of whitecaps.
118 citations
IBM1
117 citations
TL;DR: In this paper, a method is described where the rough surface is illuminated simultaneously by the two plane waves and the ensemble-averaged coherence function, that is, the correlation function, of the scattered field is measured by using a two-waves interferometer.
Abstract: In a previous article we have shown that the two speckle patterns produced from the same rough surface illuminated by two coherent plane waves under two different angles of incidence are correlated. The correlation depends on the surface roughness. In this paper a method is described where the rough surface is illuminated simultaneously by the two plane waves. The ensemble-averaged coherence function, that is, the correlation function, of the scattered field is measured by using a two-waves interferometer. This affords a real-time measurement of the surface roughness in the range of large roughness (σ > λ). The theoretical calculations have been performed for a normally distributed surface. The experimental results are in good agreement with theory. We describe the optical arrangement of an instrument based on this principle.
108 citations
TL;DR: In this paper, the authors derived the attenuation length of Rayleigh surface waves in the presence of surface roughness using a Green's function method and showed that the contribution of roughness-induced scattering into bulk transverse and longitudinal acoustic waves and into Rayleigh waves is proportional to the square of the rms amplitude of the roughness.
106 citations
TL;DR: In this paper, a theoretical analysis of thickness and grain size dependence of the limit strain in isotropic sheet metals under biaxial tension is presented, where sheet surfaces are assumed to consist of asperities which increase proportionally with the equivalent strain and the grain diameter of the material.
TL;DR: In this paper, the statistical properties of speckle intensity variations produced by coherent light in the far-field diffraction plane of an iluminated area of an object are studied experimentally as a function of the radius of an illuminating beam over the object and are found to have a relation to its surface roughness and correlation lenght.
TL;DR: In this article, the velocity distribution and the hydraulic roughness in flows over 20 permeable beds made up of different sizes and gradings of spherical particles were determined, and the results showed that the virtual zero of the velocity profile was depressed below the surface of the bed due to flow occurring in the permeable bed material.
Abstract: Tests were carried out to determine the velocity distribution and the hydraulic roughness in flows over 20 permeable beds made up of different sizes and gradings of spherical particles. Corresponding tests were carried out to determine the surface rugosity and the permeability of these beds. The investigation showed that the virtual zero of the velocity profile was depressed below the surface of the bed due to flow occurring in the permeable bed material. Despite this the hydraulic roughness of the permeable beds was higher than that for equivalent impermeable beds of the same surface rugosity. There was strong correlation between the hydraulic roughness of permeable beds and a simple parameter which included both a characteristic particle size of the bed material, and the permeability.
TL;DR: In this paper, the average contrast of image speckle patterns was used to measure surface roughness and correlation length of the objects from the experimental curve of the contrast variation versus the point spread of the imaging system.
Abstract: As a practical monitoring tool for measurements of surface roughness properties, a new instrument is actually constructed on the basis of using the average contrast of image speckle patterns. With this instrument an experimental investigation on the contrast variation of image speckle patterns is conducted systematically for various surface roughnesses of the objects under different conditions of an optical imaging system. It is found that the roughness and correlation length of the objects can be precisely determined from the experimental curve of the contrast variation versus the point spread of the imaging system. The present method using image speckle patterns is superior to the previous one which uses the contrast variation of speckle patterns in the diffraction field.
TL;DR: In this paper, the theory of speckle in partially coherent, monochromatic light is extended to cover the entire range of object roughness, and general relations are derived for the spatial correlation and the spatial Wiener spectrum.
Abstract: The theory of speckle in partially coherent, monochromatic light is extended to cover the entire range of object roughness. For “almost white-noise” objects it is shown how the speckle statistics are related to a Gaussian approximation of the object statistics. Within this approximation, general relations are derived for the spatial speckle correlation and the spatial Wiener spectrum. The theory is applied to calculate rms speckle contrast as function of object roughness, coherence of the illumination, and receiver plane defocusing.
TL;DR: In this paper, the effect of the cutting parameters on the surface roughness in a turning operation has been investigated using response surface methodology, and the mathematical prediction models for surface roughs have been obtained for a common mild steel.
TL;DR: In this paper, a formalism is presented for extracting diffusion coefficients from concentration profiles measured by analytical techniques such as Auger electron spectroscopy, secondary ion mass spectrometry, low energy and high energy ion scattering.
TL;DR: In this article, the authors present some examples of imaging radar oceanographic observations and discuss physical phenomena on the surface that may cause the radar image, including the tangent plane model, the Bragg-Rice model, and the Rayleigh scattering model.
Abstract: The paper presents some examples of imaging radar oceanographic observations and discusses physical phenomena on the surface that may cause the radar image. The different ocean scattering theories are briefly discussed, including the tangent plane model, the Bragg-Rice model, and the Rayleigh scattering model. All but one of the images presented were obtained with an L-band HH-polarized radar; they include deep-ocean swells, coastal swells, wave refractions, internal waves, ship wakes, abrupt transitions in open-ocean surface roughness, surface slicks, island wind shadowing, and currents. Analyses are shown to suggest that the primary source of the L-band imagery of ocean surface patterns is the variation of small-scale surface roughness and local tilt angle. It is also noted that surface irregularities behave as isotropic scatterers for a radar wavelength of 25 cm.
TL;DR: In this paper, exact solutions for the surface roughness dependence of the speakle contrast were obtained for a class of simple models, and a recent gaussian-field approximation to the speckle statistics was generalized, and shown to give results in good agreement with the exact results obtained.
TL;DR: In this article, the influence of surface roughness on the onset or breakdown voltage in air and SF 6 was investigated by applying the streamer theory of electrical discharges and considering the role of ionization characteristic, gas pressure, shape and size of electrode surface protrusions.
Abstract: This paper describes investigations on the influence of surface roughness on the onset or breakdown voltage in air and SF 6 . Applying the streamer theorie of electrical discharges the role of ionization characteristic, gas pressure, shape and size of electrode surface protrusions is discussed. The maximum allowable field gradients of electrode surfaces with hemispherical, spherical, and filamentary irregularities were computed in air and SF 6 . Pictures of a sparked electrode surface, showing slze and shape of surface roughness, were made using an electron scanning microscope. A comparison between computed breakdown field gradients of rough electrodes and experimental results obtained by employing different electrode configurations in a wide pressure range confirmed the theoretical considerations.
TL;DR: In this paper, the effect of surface roughness on elastohydrodynamic contact between two rollers is investigated. But the results of these two cases show that the effects are similar to those found in elasthydrodynamic contacts.
Abstract: The Christensen theory of stochastic models [7] for hydrodynamic lubrication of rough surfaces is extended to elastohydrodynamic lubrication between two rollers. The Grubin-type equation including asperity effects in the inlet region is derived. Solutions for the reduced pressure at the entrance as a function of the ratio of the average nominal film thickness to the r.m.s. surface roughness (in terms of standard deviation σ), have been obtained numerically. Results were obtained for purely transverse as well as purely longitudinal surface roughness for cases with or without slip. The reduced pressure is shown to decrease slightly by considering longitudinal surface roughness. The transverse surface roughness, on the other hand, has a slight beneficial effect on the average film thickess at the inlet. The same approach was used to study the effect of surface roughness on lubrication between rigid rollers and lubrication of an infinitely-wide slider bearing. Results of these two cases show that the effects of surface roughness are similar to those found in elastohydrodynamic contacts.
TL;DR: In this article, surface roughness measurements obtained by applying Beckmann's theory on the scattering of electromagnetic waves from rough surfaces to ground glass surfaces are presented and shown to agree closely for each surface.
Abstract: Results are presented of surface roughness measurements obtained by applying Beckmann's theory on the scattering of electromagnetic waves from rough surfaces to the scattering of laser light from ground glass surfaces. Measurements of the variance of surface height obtained in several scattering geometries and also from stylus measurements are presented and shown to agree closely for each surface. Also results are presented which show that the usual assumption of a Gaussian form for the autocorrelation function of surface height does not apply to the surfaces being studied here.
TL;DR: In this paper, the intensity distribution and average contrast of image speckle patterns for two different kinds of objects having an asymmetrical random surface and a Gaussian random surface combined with a periodic sinusoidal variation are investigated on a computer as a function of the surface roughness properties of objects and the point spread of an optical imaging system.
Abstract: As a further extension of the previous paper and by considering actual objects, the intensity distribution and average contrast of image speckle patterns for two different kinds of objects having an asymmetrical random surface and a Gaussian random surface combined with a periodic sinusoidal variation are investigated on a computer as a function of the surface roughness properties of objects and the point spread of an optical imaging system. The computer simulation study for objects with the asymmetrical random surface indicates that a variation of the average speckle contrast as a function of the above parameters takes almost the same behavior as for objects with a purely Gaussian random surface. The study for objects with the combined surface of Gaussian random and sinusoidal variations shows that the average speckle contrast strongly depends on the combination ratio of these two variations characterized by their standard deviation and correlation length. It becomes again clear that the maximum value of the image speckle contrast is dependent upon the rms surface roughness of objects but not upon their surface profile.
TL;DR: In this paper, the flow resistance in a plate roughened by equally spaced wires at right angles to the flow direction was investigated experimentally by measuring the turbulent boundary layer developing along it.
Abstract: The flow resistance in a plate roughened by equally spaced wires at right angles to the flow direction was investigated experimentally by measuring the turbulent boundary layer developing along it. Measurements of pressure distribution around a roughness element revealed that the pressure drag accounts for a large portion of the surface resistance and remaining skin frictional part is almost equal to that of a smooth plate. Measurements were also made for plates having three-dimensional roughness. These plates were roughened by short wires in a staggered manner. In this case, the boundary layer was found to have a three-dimensional structure due to accompanying secondary currents.
TL;DR: In this paper, the bright hollow cone of scattered light from a silver film due to surface plasmon excitation is discussed, and the power per solid angle scattered into the cone on the prism side of the metal film is an order of magnitude greater than that scattered on the air side.
TL;DR: The effect of surface roughness of leaves on the retention and spreading of oil drops is considered and the significance of the spreading of spray drops is discussed in relation to the application of pesticides.
Abstract: SUMMARY
The effect of surface roughness of leaves on the retention and spreading of oil drops is considered. Three types of roughness have been recognized. Leaf hairs and protruding or recessed veins underlying the cuticle constitute a macroscopic roughness. Microscopic roughness is determined by epidermal cell size and arrangement, which influence the geometry of the grooves between these cells. Ultra-microscopic roughness is determined by the size, shape and organization of the epicuticular wax system. The effect of environmental conditions on surface roughness is also considered and the significance of the spreading of spray drops is discussed in relation to the application of pesticides.