Surface Roughness Geometry Research Articles

Effects of Surface Roughness and Bend Geometry on Mass Transfer in an S-Shaped Back to Back Bend at Reynolds Number of 200,000

Experiments were performed to investigate the local development of roughness and its effect on mass transfer in an S-shaped bend at Reynolds number of 200,000. The tests were performed over four consecutive time periods using a 203-mm-diameter test section with a dissolving gypsum lining to water in a closed flow loop at a Schmidt number of 1200. The surface roughness and the mass transfer over the test periods were measured using X-ray computed tomography (CT) scans of the surface. Two regions of high mass transfer are found: along the intrados of the first and second bends. The surface roughness in these two regions, characterized by the height-to-spacing ratio, grows more rapidly than in the upstream pipe. There is an increase in the mass transfer with time, which corresponds well with the local increase in the height-to-spacing ratio of the roughness. The two regions of high mass transfer enhancement in the bend can be attributed to both a roughness effect and a flow effect due to the bend geometry. The geometry effect was determined by normalizing the local mass transfer with that in a straight pipe with equivalent surface roughness. The mass transfer enhancement due to the geometry effect was found to be relatively constant for the two high mass transfer regions, with a value of approximately 1.5.

Contribution to pavement friction modelling: an introduction of the wetting effect

ABSTRACTThis paper presents a friction model describing the tyre rubber/road interaction that takes into account the viscoelasticity of the tyre rubber, the texture of the road surface and a water layer between the tyre/road interface by introducing explicitly a computation of the water layer effect in the calculation process of the hysteretic friction. The geometry of the wetted portion of the interface model is simplified by transforming it into an equivalent hydrodynamic bearing. Utilising the Reynolds equation, the bearing load capacity is calculated and the resulting forces are subtracted from the contact load when calculating the forces of the hysteretic friction. The mechanical behaviour of the rubber is represented in the model by Kelvin–Voigt model. The frictional forces due to hysteresis are calculated at any given operating conditions (load, slip speed, etc.) from the contact geometry of rough surfaces caused by the viscoelastic behaviour of rubber. To validate the model, a set of surfaces including real pavements and artificially textured slabs were selected covering a wide range of microtexture and macrotexture combinations and the computed and measured friction compared. To describe the contact geometry of rough surfaces using macrotexture and to measure actual friction, the Circular Track Meter and the Dynamic Friction Tester devices were used, respectively. The friction coefficients computed using the model were compared to the measured friction coefficients. The obtained results are presented in the paper and proved to provide high correlation between the measured and modelled friction. The model is capable to predict wet friction at low as well as high speeds on wet surfaces, thus proving to be capable to take adequately the wetting effect on the variation of friction with increasing speed. Recommendations are provided to improve the model and extend it to a tyre friction model.

Better Estimated IEM Input Parameters Using Random Fractal Geometry Applied on Multi-Frequency SAR Data

Microwave remote sensing can measure surface geometry. Via the processing of the Synthetic Aperture Radar (SAR) data, the earth surface geometric parameters can be provided for geoscientific studies, especially in geological mapping. For this purpose, it is necessary to model the surface roughness against microwave signal backscattering. Of the available models, the Integral Equation Model (IEM) for co-polarized data has been the most frequently used model. Therefore, by the processing of the SAR data using this model, the surface geometry can be studied. In the IEM, the surface roughness geometry is calculable via the height statistical parameter, the rms-height. However, this parameter is not capable enough to represent surface morphology, since it only measures the surface roughness in the vertical direction, while the roughness dispersion on the surface is not included. In this paper, using the random fractal geometry capability, via the implementation of the power-law roughness spectrum, the precision and correctness of the surface roughness estimation has been improved by up to 10%. Therefore, the random fractal geometry is implemented through the calculation of the input geometric parameters of the IEM using the power-law surface spectrum and the spectral slope. In this paper, the in situ roughness measurement data, as well as SAR images at frequencies of L, C, and X, have been used to implement and evaluate the proposed method. Surface roughness, according to the operational frequencies, exhibits a fractal or a diffractal behavior.

Improved tooth trajectory model for prediction of milled surface geometry

ABSTRACTThe prediction on surface roughness and surface geometry in peripheral milling operation is a crucial but tedious task. The current researches concerned are almost based on circular tooth trajectory assumption to simplify analysis and modeling, and some models derived from true tooth trajectory are not concise enough or have certain limitation when put into practice. A novel idea on account of the principle of curvature circle approximation to true tooth path curve in cutting contact point nearby is presented, and the relevant mathematical theory is established. Then by means of specific curvature circles, mathematical models and analysis methods of surface roughness are discussed systematically, which cover two situations—cutting with and without runout effect. The validity and superiority of the models are demonstrated by experimental studies and numerical simulations. Finally, based on the suggested models and analytical methods, the effects of runout, feed rate, and cutter geometry on surface roughness and geometry are studied in depth, and several significant mathematical formulas and quantitative conclusions are reached, which would contribute to the theory of milled surface studies.

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

Amorphous Molybdenum Sulfide Deposited Graphene Liquid Crystalline Fiber for Hydrogen Evolution Reaction Catalysis

Adhesion force mapping on wood by atomic force microscopy: influence of surface roughness and tip geometry.

This study attempts to address the interpretation of atomic force microscopy (AFM) adhesion force measurements conducted on the heterogeneous rough surface of wood and natural fibre materials. The influences of wood surface roughness, tip geometry and wear on the adhesion force distribution are examined by cyclic measurements conducted on wood surface under dry inert conditions. It was found that both the variation of tip and surface roughness of wood can widen the distribution of adhesion forces, which are essential for data interpretation. When a common Si AFM tip with nanometre size is used, the influence of tip wear can be significant. Therefore, control experiments should take the sequence of measurements into consideration, e.g. repeated experiments with used tip. In comparison, colloidal tips provide highly reproducible results. Similar average values but different distributions are shown for the adhesion measured on two major components of wood surface (cell wall and lumen). Evidence supports the hypothesis that the difference of the adhesion force distribution on these two locations was mainly induced by their surface roughness.

Gas-tight Thermally Joined Metal-thermoplastic Connections by Pulsed Laser Surface Pre-treatment

Thermal joining of laser-structured metals and thermoplastics has been proven to deliver a high joint strength. A novel idea is to apply this process onto metal-thermoplastic joints in order to produce gas-tight hybrid connections which can be used in several technical applications.The surface pre-treatment of aluminum by infrared pulsed laser radiation was focused in this study. Depending on different cumulative energies two main surface topologies, stochastic and deterministic groove structures, were manufactured. Consequently, heat conduction joining by infrared laser radiation was used to join the metal with polypropylene. The influence of laser structuring on surface roughness and groove geometry was analyzed by scanning electron and laser scanning microscopy. The wetting of the thermoplastic was investigated by optical microscopy. The gas-tightness was identified by a helium leak test and climate testing was performed to analyze the long-term durability. The results indicate that depending on the surface morphology of the metal, durable gas-tight connections can be created by thermal joining.

Influence of shape on the optical properties of hematite aerosol

AbstractMineral dust particles are the second highest emitted aerosol type by mass. Due to changes in particle size, composition, and shape that are caused by physical processes and reactive chemistry, optical properties vary during transport, contributing uncertainty in the calculation of radiative forcing. Hematite is the major absorbing species of mineral dust. In this study, we analyzed the extinction cross sections of nigrosin and hematite particles using cavity ring‐down aerosol extinction spectroscopy (CRD‐AES) and have measured particle shape and size distributions using transmission electron microscopy. Nigrosin was also used in this study as a spherical standard for absorbing particles. The size‐selected nigrosin particles have a narrow size distribution, with extinction cross sections that are described by Mie theory. In contrast, the size distribution of size‐selected hematite particles is more polydisperse. The extinction cross sections were modeled using Mie theory and the discrete dipole approximation (DDA). The DDA was used to model more complex shapes that account for the surface roughness and particle geometry. Of the four models used, Mie theory was the simplest to implement, but had significant error with a 26.1% difference from the CRD‐AES results. By increasing the complexity of the models using the DDA, we determined that spheroids had a 14.7% difference, roughened spheres a 12.8% difference, and roughened spheroids a 11.2% difference from the experimental results. Using additional parameters that account for particle shape is necessary to model the optical properties of hematite particles and leads to improved extinction cross sections for modeling aerosol optical properties.

SISCO: surface irrigation simulation, calibration and optimisation

A model is described which applies the full one-dimensional version of the Saint–Venant equations for open channel flow to simulate the process of surface irrigation. The resulting software for surface irrigation simulation, calibration and optimisation, abbreviated to SISCO, was developed for use in a standard PC environment. Unlike some other models currently in use, SISCO can accommodate temporal variations in inflow rates and spatial variability in soil infiltration, surface roughness, slope and furrow geometry. The main focus of the paper is in regard to the calibration functionality, whereby it is capable of estimating the soil infiltration characteristic and Manning roughness from various combinations of practically obtainable field measurements.

КОНТАКТНАЯ МЕХАНИКА ФРАКТАЛЬНЫХ ПОВЕРХНОСТЕЙ

Communication of a classical statistical method of an assessment of geometry of rough surfaces and fractal approach is shown. Procedures of modeling of fractal surfaces are described. Adequacy of models to real surfaces is checked on the spectral density and the offered criterion of adequacy. The communication between deformation of microroughness and loading giving a full picture of an elasto-plastic condition of a spot of contact at the set rapprochement is received.

Microfacet-based interference simulation for multilayer films

It has proved difficult to visualize the iridescent colors of objects coated with multilayer films in ray-based tracers. A physical-based full spectrum scattering model is proposed in this paper; this model applies the multi-beam interference equations to explain the multiple reflection and refraction of light inside the thin films in order to simulate the phase and amplitude variations of light related to iridescent colors. The Fresnel coefficients for the metallic and dielectric films are introduced respectively to photo-realistically render the wave properties of multilayer films. The solution is further extended to take into account the geometry of rough surfaces instead of a smooth averaging surface where the anisotropic and isotropic scattering characteristics are well explained. We demonstrate the validity of the proposed model by visualizing wave effects for diverse metallic or dielectric multilayer film structures and a Morpho butterfly.

Simulation of synthetic gecko arrays shearing on rough surfaces

To better understand the role of surface roughness and tip geometry in the adhesion of gecko synthetic adhesives, a model is developed that attempts to uncover the relationship between surface feature size and the adhesive terminal feature shape. This model is the first to predict the adhesive behaviour of a plurality of hairs acting in shear on simulated rough surfaces using analytically derived contact models. The models showed that the nanoscale geometry of the tip shape alters the macroscale adhesion of the array of fibres by nearly an order of magnitude, and that on sinusoidal surfaces with amplitudes much larger than the nanoscale features, spatula-shaped features can increase adhesive forces by 2.5 times on smooth surfaces and 10 times on rough surfaces. Interestingly, the summation of the fibres acting in concert shows behaviour much more complex that what could be predicted with the pull-off model of a single fibre. Both the Johnson-Kendall-Roberts and Kendall peel models can explain the experimentally observed frictional adhesion effect previously described in the literature. Similar to experimental results recently reported on the macroscale features of the gecko adhesive system, adhesion drops dramatically when surface roughness exceeds the size and spacing of the adhesive fibrillar features.

Modeling and Energy Efficiency of Abrasive Flow Machining on Tooling Industry Case Study

On account on nowadays trends in the field of finishing, hand polishing has to be replaced with superior process. An alternative is abrasive flow machining (AFM). In this paper, the influence of the process parameters and abrasive fluid flow on surface integrity, i.e. surface roughness and micro geometry, are investigated. The models correlating abrasive fluid flow and surface roughness are developed. To prove the efficiency, energy consumption analysis is performed comparing AFM and novel upgrade of it, i.e. AFM with movable rotatable mandrel. Results show that novel AFMmm is efficiently capable to remove WEDM (wire electric discharge machining) damaged surface, induce compressive residual stresses and produce polishing surface under dry conditions. Moreover, the novel upgrade of AFM process is besides finishing, capable also controlling the micro topography of the product.

The effects of surface roughness geometry of flow undergoing Poiseuille flow by molecular dynamics simulation

Numerical simulation of Poiseuille flow of liquid Argon in a rough nano-channel using the non-equilibrium molecular dynamics simulation is performed. Density and velocity profiles across the channel are investigated in which roughness is implemented only on the lower wall. The Lennard–Jones potential is used to model the interactions between all particles. The effects of surface roughness geometry, gap between roughness elements (or roughness periodicity), surface roughness height and surface attraction energy on the behavior of the flow undergoing Poiseuille flow are presented. Results show that surface shape and roughness height have a decisive role on the flow behaviors. In fact, by increasing the roughness ratio (height to base ratio), the slip velocity and the maximum velocity in the channel cross section are reduced, and the density fluctuations near the wall increases. Results also show that the maximum density near the wall for a rough surface is less than a smooth wall. Moreover, the simulation results show that the effect of triangle roughness surface on the flow behavior is more than the cylindrical ones.

Molecular dynamics simulation of Poiseuille flow in a rough nano channel with checker surface roughnesses geometry

Molecular dynamics simulation is applied to investigate the effects of checker surface roughness geometry on the flow of liquid argon through nanochannels that the roughness is implemented on the lower channel wall. The Lennard-Jones potential is used to model the interactions between particles and periodic boundary condition is applied in the flow direction. Density and velocity profiles across the channel are investigated for channel that the lower surface is decorated with the checker surface roughness elements. Result show that as the surface attraction energy or the roughness height increase the density layering in the near the wall is enhanced by higher values or secondary layering phenomena.

Experimental Investigations on Fusion Cutting Stainless Steel with Fiber and CO2 Laser Beams

First results of an experimental study on inert-gas fusion cutting stainless steel with different types of laser are presented. In particular, the cutting capabilities of a fiber and a CO2 laser beam with similar Rayleigh length have been compared as a function of material thickness with respect to achievable maximum cutting speed, cut edge surface roughness and cut kerf geometry. The most interesting finding achieved so far concerns the observation that the cut kerfs are nearly identical in size but differ qualitatively in shape for both laser teypes.

직사각형 형상의 표면조도 변화에 의한 난류변동분 해석

표면조도에 의해 발생하는 난류유동은 공학적, 물리적 분야에서 매우 중요하게 다루어지고 있다. 표면조도는 선박에서도 설계, 용접, 도장 등 각각의 단계에서 다양한 측면으로 고려되어야 할 중요한 요소이다. 본 연구는 표면조도 형상을 일반화하여 PIV기법을 적용하여 수조실험을 수행하였다. 표면조도 조건은 거칠기 형상의 간격에 대해 변화를 주었으며, 실험유속은 Re = <TEX>$1.1{\times}10^4$</TEX>, Re = <TEX>$2.0{\times}10^4$</TEX>, Re = <TEX>$2.9{\times}10^4$</TEX> 에서 시간평균에 대한 난류강도를 알아보았다. 거칠기 계수 증가에 따라 표면 거칠기 형상 근처에서 발생한 난류성분에 의해 난류강도는 강하게 나타났으며, 자유흐름 영역으로 갈수록 유동 방향의 변동이 전혀 없는 흐름이 나타났다. 실험유속 조건 변화에 대한 난류강도의 편차는 크게 영향을 받지 않았다. In physical engineering, the turbulent flow on the surface roughness is very important. With the welding, design and paint, the hull surface roughness at each stage in the various aspects are important factors to be considered. In this study, the hull surface roughness geometry that was generalized to the PIV was applied to the tank test. The roughness of the surface changed the distance of the interval. Experimental velocity is Re = <TEX>$1.1{\times}10^4$</TEX>, Re = <TEX>$2.0{\times}10^4$</TEX> and Re = <TEX>$2.9{\times}10^4$</TEX>. The turbulent intensity at the time-average were examined The roughness coefficient occurred with increasing turbulence intensities was stronger. The turbulence intensity away from the roughness in the shape was zero. The variation of turbulence intensity at the experimental flow conditions change was not affected.

Model of Anisotropic Electrical Resistivity in Rough Thin Films

In this work a new model of electrical resistivity is proposed in order to study the relationship between surface roughness geometry and thin films resistivity. The model is based on the numerical dynamic averaging of electron mean free path over whole simulated structure of rough film. For current-in-plane configuration the resistivity increases with decreasing film thickness faster than for current-perpendicular-to-plane one. Our simulations showed that big roughness depth and fine in-plane spatial period of roughness are crucial factors increasing the resistivity of ultrathin metallic layers.

나노 채널에서의 표면 거칠기와 경계 습윤의 효과

The nanofluidics is characterized by a large surface-to-volume ratio, so that the surface properties strongly affect the flow resistance. We present here the results showing that the effect of wetting properties and the surface roughness may considerably reduce the friction of fluid past the boundaries. For a simple fluid flowing over hydrophilic and hydrophobic surfaces, the influences of surface roughness are investigated by the nonequilibrium molecular dynamics (NEMD) simulations. The fluid slip at near a solid surface highly depends on the wall-fluid interaction. For hydrophobic surfaces, apparent fluid slips are observed on smooth and rough surfaces. The solid wall is modeled as a rough atomic sinusoidal wall. The effects on the boundary condition of the roughness characteristics are given by the period and amplitude of the sinusoidal wall. It was found that the slip velocity for wetting conditions at interface decreases with increasing effects of surface roughness. The results show the surface rougheness and wettability determines the slip or no-slip boundary conditions. The surface roughness geometry shows significant effects on the boundary conditions at the interface.

親水性キャリア粒子を用いた複合粒子研磨法に関する研究(機械要素,潤滑,設計,生産加工,生産システムなど)

The four-body polishing in which polymer particles are applied as a carrier of abrasives solved many problems of conventional polishing but some problems remained such as bubbling phenomenon and time-dependent deterioration of removal rate. In order to solve these problems, we advanced some experiments by employing some hydrophilic polymers and inorganic particles as the carrier particle. As a result, a hydrophilic polystyrene particle which was given a hydrophilic group on the surface accomplished better removal rate than untreated polystyrene particle. The bubbling problem was relieved completely by application of amorphous calcium phosphate particle. Though the removal rate decreased by employing some kind of porous inorganic particles, a distinguished surface roughness and edge geometry was obtained. Meanwhile, the removal rate was improved compared to the conventional polishing by using a molten-silica and an aggregated-silica particle. There are two maximum removal rates when the concentration of the silica particle was regulated. Furthermore, an exceptional removal rate was attained by optimizing the concentration of molten silica particles and changing the polishing conditions.