Showing papers on "Surface roughness published in 1981"
TL;DR: In this article, a quadrant analysis was used to investigate the events contributing to the Reynolds shear stress in zero pressure-gradient turbulent boundary layers over regularly arrayed rough surfaces of several different densities, and over a smooth surface.
Abstract: Quadrant analysis has been used to investigate the events contributing to the Reynolds shear stress in zero-pressure-gradient turbulent boundary layers over regularly arrayed rough surfaces of several different densities, and over a smooth surface. By partitioning the stress into ejections, sweeps, and inward and outward interactions, it is shown that sweeps account for most of the stress close to rough surfaces, and that the relative magnitude of the sweep component increases both with surface roughness and with proximity to the surface. The sweep-dominated region delineates a ‘roughness sublayer’ with a depth of up to several roughness element heights, in which the turbulence characteristics depend explicitly on the roughness. In the remainder of the inner (or constant-stress) layer, and in the outer layer, the flow obeys familiar similarity laws with respect to surface roughness.The difference ΔS0 between the fractional contributions of sweeps and ejections to the stress is shown to be well related everywhere to the third moments of the streamwise and normal velocity fluctuations. Experimental proportionalities are established between the third moments and δS0, and are shown to agree with predictions made from cumulant-discard theory.The time scale for the passage of large coherent structures past a fixed point, T, is assumed proportional to the mean time between occurrences in a specified quadrant of an instantaneous stress u'w’ at least H times the local mean stress u'w’, where H is a threshold level. For both the ejection and sweep quadrants and for any choice of H, it is found that T scales with the friction velocity u* and the boundary-layer thickness δ, such that Tu*/δ is invariant with change of surface roughness.
523 citations
TL;DR: In this article, an algorithm for estimating moisture content of a bare soil from the observed brightness temperature at 1.4 GHz is discussed and applied to a limited data base, based on a radiative transfer model calculation, with some modifications to take into account the effect of surface roughness.
Abstract: An algorithm for estimating moisture content of a bare soil from the observed brightness temperature at 1.4 GHz is discussed and applied to a limited data base. The method is based on a radiative transfer model calculation, which has been successfully used in the past to account for many observational results, with some modifications to take into account the effect of surface roughness. Besides the measured brightness temperatures, the three additional inputs required by the method are the effective soil thermodynamic temperature, the precise relation between moisture content and the smooth field brightness temperatures and a pair of parameters related to surface roughness. The procedures of estimating surface roughness parameters and of obtaining moisture content from observed brightness temperature are discussed. The algorithm is applied to observations from truck mounted and airborne radiometers. The estimated moisture contents compare favorably with the observations in the top 2 cm layer.
455 citations
TL;DR: Second harmonic generation at a silver-air interface was enhanced due to surface roughness by a factor of 10{sup 4} as mentioned in this paper, which is believed to be responsible for the effect An unusually broad luminescence background extending far beyond the antiStokes side of the second harmonic was also observed
Abstract: Second harmonic generation at a silver-air interface was enhanced due to surface roughness by a factor of 10{sup 4} The local field enhancement is believed to be responsible for the effect An unusually broad luminescence background extending far beyond the antiStokes side of the second harmonic was also observed
440 citations
TL;DR: In this article, the influence of surface roughness on the vortex shedding frequency in the wake of a single cylinder has been investigated in an atmospherical and a high-pressure wind tunnel.
Abstract: The influence of surface roughness on the vortex-shedding frequency in the wake of a single cylinder has been investigated. The experiments were carried out in an atmospherical and a high-pressure wind tunnel. The tests were started with a smooth cylinder. Then the wake flow of cylinders with relative roughnesses of ks/d = 75 × 10−5, 300 × 10−5, 900 × 10−5, and 3000 × 10−5 was investigated.For all roughness parameters tested the Strouhal number exhibited an increase in the critical flow regime. With growing roughness parameter the step in the curve became smaller. At transcritical flow conditions the Strouhal number was measured to be in the range of Sr = 0·25 ± 0·018 for all surface roughness tested. No regular vortex shedding could be observed in the critical flow range for the smooth cylinder with l/d = 3·38. When prolonging the test body to l/d = 6·75 the wake fluctuations became periodic.
365 citations
TL;DR: In this article, a simple analytical method is presented for calculation of deposition to both smooth and rough surfaces, and the main analysis is given for sublayer scale roughness, and approximations are given which indicate simple scaling laws for the process.
295 citations
TL;DR: A surface profiling instrument is described which produces digitized surface profiles and other statistical data and roughnesses measured with the instrument are compared with values obtained using other techniques.
Abstract: A surface profiling instrument is described which produces digitized surface profiles and other statistical data. Sharp styli are available that can give height resolution of the order of 1-2 A and lateral resolution of a few tenths of a micrometer on smooth surfaces. The stylus loading can be adjusted so that no permanent marks are left on the surface. Representative surface profiles and autocovariance functions are shown for various materials, and roughnesses measured with the instrument are compared with values obtained using other techniques.
256 citations
TL;DR: In this article, the authors show that the shear stresses are only important in an inner region close to the hill surface, so that, as suggested by Jackson and Hunt (1975), the perturbation to the mean flow outside this region is essentially inviscid.
Abstract: Wind tunnel measurements have been made of the streamwise mean and turbulent velocities over a rough, bell-shaped, two-dimensional hill, with height h and maximum slope 0.26, placed in a neutrally stable boundary layer of thickness 10 h and roughness length zo = 0.02 h. Close agreement is found between the mean velocity and predictions obtained from Taylor's (1977) computational model and Jackson and Hunt's (1975) analytical linearized model, for locations at or upwind of the hill top but not in the wake. Examination of the models shows that the shear stresses are only important in an inner region close to the hill surface, so that, as suggested by Jackson and Hunt (1975), the perturbation to the mean flow outside this region is essentially inviscid. the theory shows that over very rough surfaces, such as wooded or urban terrain, the height of this inner region can be of the same order as the height of the roughness elements (so that in our experiments no measurements could be made in this region).
In a second experiment flow over a smooth hill on a rough surface was studied. the additional increase of wind speed over the hill top can be estimated by assuming a linear superposition of the velocity changes produced by the changes in elevation and in surface roughness (in this case rough to smooth). In the lee of a hill, however, the change in roughness significantly alters the flow with flow separation being suppressed and here a linear superposition is not appropriate.
Finally we consider why observed changes in turbulence structure close to the surface differ from those well above the surface. Calculations of these changes based on the simple theoretical arguments of equilibrium shear layers and rapidly distorted turbulent flows agree well with turbulence measurements in wind tunnels and in the field.
220 citations
TL;DR: The synthesis of TiN by physical vapour deposition at temperatures below 500°C allows high speed steel to be coated after the final machining operation as mentioned in this paper, which can be used for watch cases and wrist bracelets where its abrasion resistance is far better than that of the standard 20 μm gold plaque.
204 citations
01 Apr 1981-Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology
TL;DR: In this paper, the needs of three classes of user, the machinist, the researcher and the quality control engineer, are discussed, and three kinds of descriptor, namely statistical height, extreme-value height and texture are identified, and examples of each are defined are critically compared, with appliations.
Abstract: Proliferation of redundant parameters for characterizing surface roughness is explained as a historical consequence of the predominant influence of instrument manufacturers over users. Problems of roughness characterization are introduced: high and low-pass filtering, transitional topographies, sampling error. The needs of three classes of user, the machinist, the researcher and the quality control engineer, are discussed. Three kinds of descriptor, namely statistical height, extreme-value height and texture are identified, and examples of each are defined are critically compared, with appliations. It is suggested that a classification comprising average roughness, skewness, high-spot count and extrema density might suffice for many engineering purposes
192 citations
01 Apr 1981-Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology
TL;DR: In this article, the state-of-the-art in a number of optical techniques including specular reflectance, total integrated scatter, diffuseness, angular scattering distributions, speckle, ellipsometry, and interferometry are reviewed.
Abstract: Optical techniques have great potential for non-destructive and on-line measurements of surface roughness during manufacturing. This paper reviews the state-of-the-art in a number of optical techniques including specular reflectance, total integrated scatter, diffuseness, angular scattering distributions, speckle, ellipsometry, and interferometry. The distinction is drawn between the more quantitative but slower profiling techniques and less quantitative, parametric techniques, which are faster and hence more useful for high-speed monitoring of surfaces. Overall, no currently available technique combines accuracy and speed and is therefore suitable as an on-line metrological tool for roughness measurement of engineering surfaces. Speckle techniques hold perhaps the greatest potential as accurate, high-speed metrological tools
184 citations
TL;DR: In this article, a ring torsion apparatus was used to evaluate friction between dry sand and a steel surface over wide ranges of surface roughness and sand density, and the deformation of sand near the steel surface was observed by X-radiography.
Abstract: A ring torsion apparatus was used to evaluate friction between-dry sand and a steel surface over wide ranges of surface roughness and sand density. The deformation of sand near the steel surface was observed by X-radiography. The apparatus is suitable for evaluating skin friction under well-defined test conditions. The test results show that frictional resistance is primarily governed by the roughness of the steel surface, irrespective of the density of the sand.
TL;DR: The possibility of using pulsed current in electrochemical machining at low electrolyte flow rate has been investigated in this article, where theoretical aspects of predicting electrolyte heating and limiting rate of mass transport are discussed in terms of simplified models.
TL;DR: In this paper, surface enhanced Raman scattering has been observed for silver-halide vibrations at 246 (AgCl), 166 (Ag-Br) and 117 cm−1 (Aa-I) at potentials cathodic to −0.6 V.
TL;DR: In this paper, the peak drained friction angle π(prime) is found to be closely related to that of rock joints, and the value of (prime) depends on the porosity following compaction, and on the degree of particle roundedness and surface smoothness.
Abstract: A practical method for estimating the shear strength of rockfill is developed. The peak drained friction angle π(prime) is found to be closely related to that of rock joints. In both cases the values of π(prime) are dependent on sample size, stress level, surface roughness, and on the uniaxial compression strength of the rock. Friction angles are therefore higher for smaller samples, and very high where stresses are low, as at the toe or near the face of a rockfill dam. Test data reviewed shows that the value of π(prime) for rockfill can be quantified by a equivalent roughness (R), and an equivalent particle strength (S). The value of (R) depends on the porosity following compaction, and on the degree of particle roundedness and surface smoothness. A practical method is proposed for physically measuring the full-scale shear strength of in-place compacted rockfill.
TL;DR: In this paper, the surface damage on silicon substrates caused by RSE has been investigated and four categories of defects are classified: precipitates surrounded by elastic strain field, surface roughness pattern, polycrystalline and amorphous silicon, and no defects.
Abstract: Surface damage on silicon substrates caused by RSE has been investigated. Defects are classified into four categories in order of destruction, namely, precipitates surrounded by elastic strain field, surface roughness pattern, polycrystalline and amorphous silicon, and no defects, based on the results of TEM and RHEED observation. In particular, precipitates which reach a depth more than 500 A were found to cause OSF. The surface damage consists of contamination (C, F, O) layer, C and defect mixed layer, and defect layer in order from the top. The degree of these defects and contaminations expand with increasing power density and etching duration. RSE conditions, where no defects are formed, were determined, e.g., within 1 minute at 0.4 W cm-2.
TL;DR: In this paper, an experimental investigation of the RR—-MR and MR-*RR transitions over concave and convex, smooth and rough wedges revealed that the wedge angle at which transition takes place (for a given Mach number) decreases and for a mesh 40 sand paper type surface roughness, the transition angle becomes independent of the incident shock wave Mach number.
Abstract: Conclusions An experimental investigation of the RR—-MR and MR-*RR transitions over concave and convex, smooth and rough wedges revealed that 1) as the surface roughness increases, the wedge angle at which transition takes place (for a given Mach number) decreases and 2) for a mesh 40 sand paper type surface roughness, it seems that the transition angle becomes independent of the incident shock wave Mach number, i.e., a) MR—>RR transition occurs at 6W =^54 deg and b) RR-MR transition takes place at Ow-21 deg. These results should be of great importance to those dealing with reflections of blast waves, since this type of problem involves nonstationary flows and high degrees of surface (ground) roughness.
TL;DR: In this paper, it was shown that surface roughness is not a prerequisite for the observation of SERS at the solid-liquid interface (i.e., an electrochemical cell) and that neither electrochemical anodization nor roughness (viz., quasi-spherical particles ⩾ 250 A in diameter) are necessary for SERS observation.
TL;DR: In this paper, the intensity variations of the inelastic background (I), of disorder induced Raman scattering from phonons (II) and of the SERS signal from adsorbed pyridine have been observed.
TL;DR: In this article, the possibility of determining transport parameters for the electrical conductivity from its dependence on the film thickness (size effect) is discussed, and the experimental curves have to be fitted for very small film thickness to permit a separation of these parameters.
TL;DR: In this article, a study was made of the near-threshold fatigue crack propagation behavior of a wrought nickel-base superalloy, Rene 95, with reference to the effect of crack size on the threshold stress intensity ΔK0 no detectable crack growth.
TL;DR: In this paper, the equations of motion for two-dimensional mean wind flow over single changes of surface roughness are solved numerically, using a scheme which has been adapted from computations of wind flow flow over hills.
TL;DR: In this paper, the effect of surface roughness on metal surface adhesion and microhardness was investigated in ultra-high vacuum conditions, and the authors found that a significant adhesion force is detected after the applied load has exceeded a critical value.
01 Jan 1981
TL;DR: In this article, the authors qualitatively describe the principles and presents some applications of the rapidly developing technique of automatic spectroscopic ellipsometry, as applied to the analysis of the properties of surfaces and interfaces of materials in bulk or thin film form.
Abstract: This paper qualitatively describes the principles and presents some applications of the rapidly developing technique of automatic spectroscopic ellipsometry, as applied to the analysis of the properties of surfaces and interfaces of materials in bulk or thin film form. Examples include composition and density measurements of polycrystalline and amorphous Si films, the determination of the best‐quality surfaces of bulk materials, oxidation of Si, optical profiling of microscopic surface roughness, determination of interface widths in semiconductor–oxide systems and CVD heterostructures, and nucleation of a‐Si films.
TL;DR: In this article, the influence of surface roughness on transitions between subcritical, critical supercritical and postcritical regimes around isolated circular cylinders in cross-flow was investigated in an open-jet wind tunnel, which was modified to obtain satisfactorily bidimensional conditions, with Reynolds numbers ranging from 2.6 × 10 4 to ∼2.8 × 10 5.
TL;DR: In this article, the depth resolution in compositional profiles of layers on rough substrates, analysed by ion sputtering with Auger electron spectroscopy or other surface analytical techniques, is evaluated in detail to define the precise effect of the substrate.
TL;DR: In this paper, the interaction of light with clusters and random distributions of metal hemispheroids on a perfect conducting flat surface is studied and significant SERS enhancements are found to arise from multiple plasmon contributions to the surface electromagnetic fields.
TL;DR: In this article, a one-dimensional microscopic quantum mechanical model is used to inquire whether it is possible to enhance the desorption rate by employing a laser to induce vibrational excitation of the chemisorptive bond.
TL;DR: In this article, the surface roughness effects and non-uniform donor distributions of nonlinear Mott-Schottky plots are discussed in relation to surface treatments and the occurrence of nonuniform donors distributions.
Abstract: Mechanical polishing and etching in acids or molten of electrodes frequently lead to nonlinear Mott‐Schottky plots. These surface treatments are discussed in relation to surface roughness effects and the occurrence of nonuniform donor distributions. Modified Mott‐Schottky equations are presented and discussed. They account quantitatively for surface roughness and nonuniform donor distributions, which can be induced not only by etching, but also by anodical aging, surface doping, reoxidation effects, and cathodical loading with hydrogen.
TL;DR: In this paper, the mean products of velocity fluctuations up to fourth order have been measured in a wind tunnel at the trailing edge of a flat plate, one side of which was covered with floor-sanding paper to produce a fully rough surface.
Abstract: Mean products of velocity fluctuations up to fourth order have been measured in a wind tunnel at the trailing edge of a flat plate, one side of which was covered with floor-sanding paper to produce a fully rough surface. This set-up permits easy comparison of structural parameters in smooth-wall and rough-wall boundary layers. The Reynolds-stress profiles and second-order parameters are closely the same on the rough and smooth surfaces; in particular the decrease in Reynolds shear stress near the rough surface, encountered by several other laboratory workers, was not found in the present results. The triple products are spectacularly altered for a distance of up to 10 roughness heights from the rough surface, and imply a large net rate of transport of turbulent energy and shear stress towards the surface. Comparison with other published data shows that the behaviour of this modified region depends on roughness geometry as well as on the roughness height itself; for example, the mean cube of the normal-component fluctuation remains positive (energy transport away from the surface) over sand or gravel roughness but goes negative, like the other energy-transport terms, over crop canopies.