Showing papers on "Surface roughness published in 1968"
TL;DR: In this article, the authors describe experiments in the lower atmosphere in which the wind passes from one surface to another with different roughness, and observations were made of the variation of surface stress, and of the development of velocity profiles in the region of flow modification over the downwind surface.
Abstract: This paper describes experiments in the lower atmosphere in which the wind passes from one surface to another with different roughness. Observations were made of the variation of surface stress, and of the development of velocity profiles in the region of flow modification over the downwind surface. Measurements are compared with the theories of Taylor, Elliot, and Panofsky and Townsend, and with the growth of a boundary layer on a flat plate. A large proportion of the surface stress adjustment occurs rapidly after the transition in agreement with Taylor's assumption. Velocity changes agree fairly well with the Panofsky and Townsend theory in the smooth-rough direction, but not so well in the reverse. Growth of the modified region follows the 4/5 power law of boundary layer growth. It is concluded that the height/fetch criterion for a good micrometeorological site is about 1/200.
278 citations
TL;DR: In this article, the authors used wind profile surveys, drift current measurements and water surface observations for a wide range of wind velocities in a wind-wave tank, and found that the velocity distribution essentially follows the logarithmic law near the water surface and the velocitydefect law toward the outer edge of the boundary layer.
Abstract: The present study consists of wind profile surveys, drift current measurements and water surface observations for a wide range of wind velocities in a wind–wave tank. It is confirmed that the velocity distribution essentially follows the logarithmic law near the water surface and the velocity-defect law toward the outer edge of the boundary layer. The wind stresses and surface roughnesses calculated from these distributions are divided into two groups separated by the occurrence of the wave-breaking phenomenon. For low wind velocities the surface roughness is dictated by ripples, and the wind-stress coefficient varies with U0−½, where U0 is the free-stream wind velocity. The surface roughness is proportional to the average height of the basic gravity wave at higher wind velocities; the stress coefficient is then proportional to U0. In addition, it is found that Charnock's expression (k ∝ u*2/g) holds only at high wind velocities, and that the constant of proportionality determined from the present experiment correlates very well with field observations. A new technique, involving the use of various-sized surface floats to determine the drift current gradient and the surface drift current, has been developed. A good agreement is shown between the gradients obtained from the measured currents and those determined from the wind stresses. Finally, the wind-stress coefficient is shown to be larger than the friction coefficient for turbulent flow along a solid rough surface; the difference is shown to be the wave drag of the wind over the water surface.
152 citations
68 citations
01 Oct 1968
TL;DR: In this paper, the integral for the average scattered power from a rough surface obtained from physical optics is shown to be proportional to the joint probability density function for the surface slopes in the high-frequency limit.
Abstract: The integral for the average scattered power from a rough surface obtained from physical optics is shown to be proportional to the joint probability density function for the surface slopes in the high-frequency limit.
66 citations
58 citations
48 citations
01 Sep 1968
TL;DR: In this paper, the results of an experimental study of changes in surface roughness and contact conditions as running-in and wear take place are described, under conditions of mixed lubrication in both sliding and sliding with rolling.
Abstract: The paper will describe the results of an experimental study of changes in surface roughness and contact conditions as running-in and wear take place. Line contacts under conditions of mixed lubrication in both sliding and sliding with rolling have been studied.
31 citations
TL;DR: In this article, the effect of surface roughness on the normal spectral emittance and on the spectral angular dependence of thermal radiation was investigated for tungsten at 2800°K over a wavelength range of 0.3-6 μm.
Abstract: The effect of surface roughness on the normal spectral emittance and on the spectral angular dependence of thermal radiation was investigated for tungsten at 2800°K over a wavelength range of 0.3–6 μm. The normal emittance of rough surfaces is higher than of flat surfaces for all wavelengths, the largest increase occurring in the infrared. In the angular dependence of thermal radiation a minimum was found which depends on the surface geometry and on the wavelength. The values are interpreted in terms of emission from flat facets, which do not radiate according to Lambert's cosine law.
22 citations
TL;DR: The reflectance of silver decreases in the energy range of surface plasmons because of coupling between light and surface waves via surface roughness as mentioned in this paper, and the reflectance increases with the number of surface waves.
22 citations
TL;DR: In this paper, the authors analyze specular reflectance of optically smooth surfaces using the theory of surface radiation properties, and show that the reflectance depends on the surface geometry.
21 citations
TL;DR: In this paper, it was shown that the domain wall coercive force of Permalloy films is related to the film thickness by an inverse 4/3 power law provided the films were above 2000 A in thickness.
Abstract: The paper deals with the control of substrate topography to achieve the magnetic properties necessary for electroplated wire memory elements. A number of surface preparation techniques have been studied using control of the plating variables of deposited copper films. Scanning electron microscopy has made possible quantitative measurements of some of the surface topographies. It is shown that the domain wall coercive force of Permalloy films is related to the film thickness by an inverse 4/3 power law providing the films were above 2000 A in thickness. Measurements made of the coercive force for constant thickness Permalloy films as a function of surface roughness showed that it is related to the frequency and amplitude of nodular growths and that there is a maximum at a particular nodular frequency. Using the data obtained, a choice of substrate and film thickness can be made to match the requirements of a particular memory element.
TL;DR: In this paper, the results of measurement of electrostatic streaming currents in turbulent flow through round pipes have been correlated in terms of non-dimensional groups, and a nondimensional current group is found to vary with the same power of the Reynolds number as does the skin friction coefficient.
01 Aug 1968
TL;DR: In this article, a model study of canopy flow over high roughness elements was carried out using roughness consisting of pegs 9. cm high and 0.48 cm in diameter arranged in four patterns.
Abstract: : A model study of canopy flow over high roughness elements was carried out using roughness consisting of pegs 9. cm high and 0.48 cm in diameter arranged in four patterns. The mean velocity and the turbulence intensity were measured within and above the roughness elements. Empirical expressions derived from field measurements for mean velocity profiles, turbulent velocity, and turbulence intensity were used to examine the data obtained in this model study. The logarithmic profile was adapted to analyze the data of mean velocity above the canopy. In this analysis, the friction velocity and the roughness parameter were calculated from the mean velocity profiles and related to the density of roughness elements to show the effects of roughness density on the flow field. The growth of the internal boundary layer was estimated from the mean velocity profiles and the turbulence intensity. The results of estimation were compared with semi-imperical equations. Although the coefficient of anisotropy above the canopy in this model study is larger than in the field, the model study gave data about the turbulent flow field similar to the field data. Hence, this model was verified to be suitable for the study of diffusion. (Author)
TL;DR: In this article, the boundary layer velocity profiles of published wind tunnel results are reanalyzed in terms of the relation between the roughness length z0 and roughness Reynolds number, and it is concluded that there is insufficient experimental evidence for the assertion of fully developed roughness.
Abstract: It is widely stated in wind erosion studies that the boundary layer flow of surfaces of sand is aerodynamically rough at the inception of particle motion. At comparable roughness Reynolds numbers in water, however, the roughness state is considered as transitional. Clarification of the matter is important if the nature of fluid force acting on the surface particles is to be understood. In this study the boundary layer velocity profiles of published wind tunnel results are reanalyzed in terms of the relation between the roughness length z0 and the roughness Reynolds number. For aerodynamically rough flow, the ratio z0/k is expected to be constant as the Reynolds number (V*k/ν) varies. Most of the evidence indicates that the boundary flow is transitional rather than rough. Furthermore, the results do not follow the classical work of Nikuradse for uniform sand roughness. This may be due to the uncertainties in defining the reference datum (z = 0) and the effective roughness element length k. It is concluded that there is insufficient experimental evidence for the assertion of fully developed roughness.
TL;DR: The important systems parameters, including the depth and rapidity of fading, associated with a given communication link are evaluated and the extension to other links is indicated.
Abstract: On a communication link between two terminals using essentially isotropic antennas, where at least one of the terminals is in the general vicinity of an extended rough surface, scattering from that surface introduces multipath fading which must be taken into account in assessing the performance of the link. Fading, of course, occurs only if the terminal or the surface changes position with time. This paper discusses the characteristics of fading under the assumption that the surface is rigid but the terminal is moving relative to the rough surface. The important systems parameters, including the depth and rapidity of fading, associated with a given communication link are evaluated. The extension to other links is indicated.
TL;DR: In this article, the effect of surface roughness has been investigated experimentally and found to lead to spuriously high values of the diffusion coefficient, and the magnitude of the error has been estimated as a function of Dt and the degree of roughness.
Abstract: The effect of surface roughness has been investigated experimentally and found to lead to spuriously high values of the diffusion coefficient. The magnitude of the error has been estimated as a function of Dt and the degree of roughness. The results indicate that surface roughness may contribute the major source of error in the determination of very small diffusion coefficients. The presence of an uneven source surface may also account for the anomalous tracer penetration profiles which are observed in the vicinity of the surface and, corresponding to which, anomalous values of D have been frequently reported.
TL;DR: In this article, the space and time variation of a monochromatic acoustic plane wave reradiated by the moving, rough surface of the ocean is described using coherence theory.
Abstract: The space and time variation of a monochromatic acoustic plane wave reradiated by the moving, rough surface of the ocean is described using coherence theory. The complex degree of coherence of the pressure field is calculated approximately for the extreme cases of slightly rough and very rough surfaces. For both of these cases, the results are specialized to the situation of a wind‐generated sea described by the Neumann‐Pierson directional wave spectrum, and the dependencies of the coherence upon surface roughness and the angles of incidence and observation are shown. For the case of a slightly rough surface, the reradiation is principally a reflection, and the coherence in the direction of specular reflection is the same as that for a smooth surface. Away from this direction, there is scattering, and the coherence depends upon the surface roughness. For very rough surfaces, there is diffuse scattering in all directions with no reflection, and the coherence depends upon the surface roughness for all angles of observation.
01 Sep 1968
TL;DR: In this article, a technique analyzes the statistics of the Fourier components of the surface roughness of materials and uses conventional optical data processing procedures to compute the surface surface surface smoothing.
Abstract: A report is given of preliminary work on a process of studying surface roughness of materials. The technique analyzes the statistics of the Fourier components of the surface roughness and uses conventional optical data processing procedures.
01 Jan 1968
TL;DR: In this paper, a number of methods are given to decrease the influence of oxidation in rough turning in such a way that tool life could be improved considerably, and a finish turning with varying feed was made more suitable for the workshop.
Abstract: Since the paper “Some Special Aspects of Carbide Tool Wear”(1) was offered in Pittsburgh in 1963, we have made some progress in the field of oxidation in rough turning and on varying feed in finish turning.
In this paper a number of methods are given to decrease the influence of oxidation in rough turning in such a way that tool life could be improved considerably.
Finish turning with varying feed was made more suitable for the workshop. Surface roughness could be improved three or four times by this method.
TL;DR: Geometric optics approach to calculate surface roughness effects on microwave emissivity from Moon and Venus from the point of view of geometrical optics was proposed in this paper, with the objective of calculating the impact of roughness on the microwave signal.
Abstract: Geometric optics approach to calculating surface roughness effects on microwave emissivity from Moon and Venus
01 Apr 1968
TL;DR: Radar reflectivity measurement of lunar surface roughness for selecting possible landing sites was used for selecting landing sites for the first time in 2018 as discussed by the authors, with the objective of selecting suitable landing sites.
Abstract: Radar reflectivity measurement of lunar surface roughness for selecting possible landing sites
01 Jun 1968
TL;DR: In this paper, a two-dimensional time dependent numerical model of the atmospheric boundary layer is formulated and used to investigate various characteristics of air motion when a change occurs in roughness and/or temperature characteristics of the underlying surface.
Abstract: : A two-dimensional time dependent numerical model of the atmospheric boundary layer is formulated and used to investigate various characteristics of air motion when a change occurs in roughness and/or temperature characteristics of the underlying surface. The integrations have been carried out for steady-state situations also. The model incorporates the effects of penetrative convection, diabatic influence associated with small-scale eddy diffusion, and pressure effects induced by horizontal nonuniformity of terrain in temperature and roughness. The results show that warm surfaces do not necessarily increase the height of internal boundary layers in the vicinity of surface discontinuity. The effects of discontinuity are quite appreciable at large fetches downwind from the discontinuity. (Author)
TL;DR: Spectral reflectance in the 0.23 to 2.65μ region was measured on sintered oxides of Al2O3, CeO2, TiO2 and ZnO, and the data were interpreted in terms of changes in the distance between the particles, the water content and the surface roughness as discussed by the authors.
Abstract: Spectral reflectance in the 0.23 to 2.65μ region was measured on sintered oxides of Al2O3, CeO2, TiO2, Y2O3, and ZnO. The oxides were sintered at various temperatures up to 1550°C. Large changes in reflectance occurred as a result of different extents of sintering of the specimens. The data were interpreted in terms of changes in the distance between the particles, the water content, and the surface roughness. Loss of trace-water and decrease in surface roughness result in an increase in reflectance, whereas shrinkage of the specimen causes a decrease in reflectance.
TL;DR: In this paper, the effect of surface roughness on strength and durability of adhesive joints is explained on the basis of a molecular mechanism of interaction of the glue with the surface roughnesses.
Abstract: The effect of the thickness of the glue line on the bond strength of construction materials is examined and the dependence of the optimal thickness of the glue line on surface roughness and glue viscosity is shown. The effect of surface roughness on strength and durability of adhesive joints is explained on the basis of a molecular mechanism of interaction of the glue with the surface roughnesses and an approximate expression is derived for the depth of penetration of the glue into microcavities of the surface as a function of the geometric parameters of the microcavities, specific pressure, and surface tension of the interface with the air.