Journal articles on the topic 'Macro rough'
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Fang, Hongwei, Xu Han, Guojian He, and Subhasish Dey. "Influence of permeable beds on hydraulically macro-rough flow." Journal of Fluid Mechanics 847 (May 25, 2018): 552–90. http://dx.doi.org/10.1017/jfm.2018.314.
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In this study, macro-rough flows over beds with different permeability values are simulated using the large-eddy simulation, and the results are analysed by applying the double-averaging (DA) methodology. Spheres of different sizes and arrangements were used to form the beds, which are deemed to be permeable granular beds. The influence of bed permeability on the turbulence dynamics and structure is investigated. It was observed that the scales of the spanwise vortical structures over more permeable beds are larger than those over less permeable beds. This is attributed to large-scale spanwise-alternate strips of varying Reynolds shear stress (RSS), emerging from the surface of macro-rough elements for the permeable beds. The DA stress balance suggests that the time-averaged spanwise vortical structure leads to a damping in DA RSS and an unusual peak of the form-induced stress in the main flow. In the streamwise direction, both large turbulent structures that originate from the Kelvin–Helmholtz-type instability and small turbulent structures that are associated with the turbulent transport across the gaps of the roughness elements are more prevalent over highly permeable beds. Near the bed, the relative magnitude of turbulent events shows a transition from a ejections-dominating to sweeps-dominating zone with vertical distance. Further, several hydrodynamic characteristics normalized by inner scales (kinematic viscosity to shear velocity ratio) show a greater dependency on permeability Reynolds number than those normalized by sediment size. The study provides an insight into the mechanism of mass transfer near the fluid–particle interface, which is vital to benthic and aquatic ecology.
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Huang, Shiping, and Anil Misra. "Micro–Macro-Shear-Displacement Behavior of Contacting Rough Solids." Tribology Letters 51, no. 3 (July 2, 2013): 431–36. http://dx.doi.org/10.1007/s11249-013-0178-y.
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Erpicum, S��bastien, Tobias Meile, Benjamin J. Dewals, Michel Pirotton, and Anton J. Schleiss. "2D numerical flow modeling in a macro-rough channel." International Journal for Numerical Methods in Fluids 61, no. 11 (December 20, 2009): 1227–46. http://dx.doi.org/10.1002/fld.2002.
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McLauchlin, Theodore. "Desertion, Terrain, and Control of the Home Front in Civil Wars." Journal of Conflict Resolution 58, no. 8 (September 3, 2014): 1419–44. http://dx.doi.org/10.1177/0022002714547901.
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This article examines desertion in civil wars, focusing on the role of combatants’ hometowns in facilitating desertion. Analyzing data from the Spanish Civil War, the article demonstrates that combatants who come from hill country are considerably more likely to desert than combatants whose hometowns are on flat ground. This is because evasion is easier in rough terrain. The finding implies that the cohesion of armed groups depends on control, not just positive incentives, and that control of territory in civil wars goes beyond rebel–government contestation, and consists also of control behind the lines. The article bridges micro and macro approaches to civil wars by indicating the multiple uses to which individuals can put structural conditions like rough terrain. This helps to clarify the macro-level link between rough terrain and civil war. It also shows that micro-level research can profitably examine structural variables alongside individual characteristics and endogenous conflict dynamics.
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Ghilardi, Tamara, Mário J. Franca, and Anton J. Schleiss. "Period and amplitude of bedload pulses in a macro-rough channel." Geomorphology 221 (September 2014): 95–103. http://dx.doi.org/10.1016/j.geomorph.2014.06.006.
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Sun, Qingchao, Xiaokai Mu, Bo Yuan, Jiawen Xu, and Wei Sun. "Characteristics extraction and numerical analysis of the rough surface macro-morphology." Engineering Computations 36, no. 3 (April 8, 2019): 765–80. http://dx.doi.org/10.1108/ec-08-2018-0347.
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PurposeThis paper aims to distinguish the relationship between the morphology characteristics of different scales and the contact performance of the mating surfaces. Also, an integrated method of the spectrum analysis and the wavelet transform is used to separate the morphology characteristics of the actual machined parts.Design/methodology/approachFirst, a three-dimensional (3D) surface profilometer is used to obtain the surface morphology data of the actual machined parts. Second, the morphology characteristics of different scales are realized by the wavelet analysis and the power spectral density. Third, the reverse modeling engineering is used to construct the 3D contact models for the macroscopic characteristics. Finally, the finite element method is used to analyze the contact stiffness and the contact area of the 3D contact model.FindingsThe contact area and the nominal contact pressure Pn have a nonlinear relationship in the whole compression process for the 3D contact model. The percentage of the total contact area of the macro-scale mating surface is about 70 per cent when the contact pressure Pn is in the range of 0-100 MPa, and the elastic contact area accounts for the vast majority. Meanwhile, when the contact pressure Pn is less than 10MPa, the influence factor (the relative error of contact stiffness) is larger than 50 per cent, so the surface macro-scale morphology has a weakening effect on the normal contact stiffness of the mating surfaces.Originality/valueThis paper provides an effective method for the multi-scale separation of the surface morphology and then lays a certain theoretical foundation for improving the surface quality of parts and the morphology design.
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Francisco, Arthur, and Noël Brunetière. "Full and Hybrid Multiscale Lubrication Modeling." Lubricants 10, no. 12 (November 23, 2022): 329. http://dx.doi.org/10.3390/lubricants10120329.
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The numerical solution for the lubrication of parallel rough surfaces cannot be obtained using the well-known flow factors of Patir and Cheng. Nor can it be determined using homogenization techniques. Is there an alternative, besides a purely long-term deterministic way of solving the problem? The present paper aims at proposing a multiscale approach in order to reduce the computing time, specific to deterministic resolutions, while maintaining good accuracy. The configuration is a parallel rough surface slider, with imposed hydrodynamic operating conditions. The domain consists of independent macro-elements, on which the Reynolds equation is solved. Then, the macro-element boundaries are adjusted to ensure global mass conservation. In its hybrid version, the algorithm replaces some well-chosen macro-elements by simple linear finite elements. The results clearly show the potential of our method. Because the lubrication of each macro-element can be processed independently, the multicore architecture of the processor is exploited. Even if the performance depends on the ratio roughness/height, the computing time is half than for the classical deterministic method, with a few percent errors. The work concludes with some recommendations on the configurations for which the multiscale method is best suited, such as surfaces with short correlation lengths.
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Bobji, M. S., and S. K. Biswas. "Deconvolution of hardness from data obtained from nanoindentation of rough surfaces." Journal of Materials Research 14, no. 6 (June 1999): 2259–68. http://dx.doi.org/10.1557/jmr.1999.0302.
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Variation of hardness with penetration in nanoindentation of a rough surface is a compound effect of variation in asperity geometry with penetration, designated geometric effect, and genuine property gradients with depth as may exist in a near-surface zone. We simulate indentation of a rough surface numerically to elucidate the geometric effects and validate it by some model “macro” experiments. Finally, we formulate a general framework to deconvolute genuine property variation by normalizing the measured hardness with the geometric effect.
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MIGNOT, EMMANUEL, E. BARTHELEMY, and D. HURTHER. "Double-averaging analysis and local flow characterization of near-bed turbulence in gravel-bed channel flows." Journal of Fluid Mechanics 618 (January 10, 2009): 279–303. http://dx.doi.org/10.1017/s0022112008004643.
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This investigation focuses on the characteristics of near-bed turbulence in fully rough gravel-bed open-channel flows. The analysis combines results obtained with the double-averaging methodology and local flow characterization, using velocity measurements provided by a high-resolution three-axis Acoustic Doppler Velocity Profiler (ADVP). As a result of the flow heterogeneity induced by the bed topography, the flow is not locally uniform in the near-bed region, and a double-averaging methodology is applied over a length scale much greater than the gravel size. In smooth- and rough-bed flow conditions, without macro-roughness bed elements, maximum turbulent kinetic energy (TKE) production occurs very close to z = 0, while in our case with fully rough flows with macro-roughness elements, maximum turbulence activity is found to occur at gravel crest levels zc (zc/h = 0.1). Turbulent diffusion also reaches a maximum at this elevation. The characteristics of the spatially averaged TKE budget are in good agreement with those obtained in flows over canopies. The hydrodynamic double-averaged properties have strong similarities with mixing layers and reattached mixing layers in flows over backward facing steps. Local time-averaged velocity profiles can be split into three typical classes, namely log, S-shaped and accelerated. It appears that the S-shaped class profiles, located in the wakes of the macro-roughness elements, exhibit an inflectional profile typical of mixing layers. They are of major importance in the double-averaged TKE budget, as they provide a local high contribution to the double-averaged TKE flux, TKE production and dissipation compared to the log class profiles. Consequently, double-averaged TKE production is roughly 75% greater than the dissipation rate at the point of maximal TKE production. Moreover the macro-roughness bed elements imply mixing-layer-type hydrodynamics that play a dominant role in the overall structure of mean near-bed turbulence of gravel-bed channel flows.
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Zha, Fusheng, Chen Chen, Wei Guo, Penglong Zheng, and Junyi Shi. "A free gait controller designed for a heavy load hexapod robot." Advances in Mechanical Engineering 11, no. 3 (March 2019): 168781401983836. http://dx.doi.org/10.1177/1687814019838369.
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As macroscopic rough terrains are time varying and full of local topographic mutations, stable locomotions of legged robots moving through such terrains in a fixed gait form can be hardly obtained. This problem becomes more severe as the size and weight of the robot increase. An ideal pre-planned gait changing method can also be hardly designed due to the same limitations. Aiming to solve the problem, a new kind of free gait controller applied to a large-scale hexapod robot with heavy load is developed. The controller consists of two parts, a free gait planner and a gait regulator. Based on the observed macro terrain changes, the free gait planner adopts the macro terrain recognition method and the status searching method for selecting the best leg support status automatically. The gait regulator is adopted for the correction of the selected status to cope with local topographic mutations. Detailed simulation experiments are presented to demonstrate that, with the designed controller, the adopted hexapod robot can change moving gaits automatically in terms of the terrain conditions and obtain stable locomotions through rough terrains.
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Beaudoin, Anthony, and Mohamad Farhat. "Impact of the fracture contact area on macro-dispersion in single rough fractures." Comptes Rendus. Mécanique 349, no. 2 (April 27, 2021): 203–24. http://dx.doi.org/10.5802/crmeca.82.
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Dubois, G., J. Cesbron, H. P. Yin, and F. Anfosso-Lédée. "Macro-scale approach for rough frictionless multi-indentation on a viscoelastic half-space." Wear 272, no. 1 (October 2011): 69–78. http://dx.doi.org/10.1016/j.wear.2011.07.011.
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Kosoy, Boris. "Micro channels in macro thermal management solutions." Thermal Science 10, no. 1 (2006): 81–98. http://dx.doi.org/10.2298/tsci0601081k.
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Modern progress in electronics is associated with increase in computing ability and processing speed, as well as decrease in size. Future applications of electronic devices in aviation, aero space and high performance consumer products? industry demand on very stringent specifications concerning miniaturization, component density, power density and reliability. Excess heat produces stresses on internal components inside the electronic device, thus creating reliability problems. Thus, a problem of heat generation and its efficient removal arises and it has led to the development of advanced thermal control systems. Present research analyses a thermodynamic feasibility of micro capillary heat pumped net works in thermal management of electronic systems, considers basic technological constrains and de sign availability, and identifies perspective directions for the further studies. Computer Fluid Dynamics studies have been per formed on the laminar convective heat transfer and pressure drop of working fluid in silicon micro channels. Surface roughness is simulated via regular constructal, and stochastic models. Three-dimensional numerical solution shows significant effects of surface roughness in terms of the rough element geometry such as height, size, spacing and the channel height on the velocity and pressure fields.
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Ai, Xiaolan, and Linqing Zheng. "A General Model for Microelastohydrodynamic Lubrication and Its Full Numerical Solution." Journal of Tribology 111, no. 4 (October 1, 1989): 569–76. http://dx.doi.org/10.1115/1.3261979.
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A general transient model for microelastohydrodynamic lubrication with Eyring fluid was established in this paper to describe the basic processes involved in thin film lubrication with rough surfaces, namely the process of a single asperity when it passes through the macro-EHL contact with or without sliding, and the process for a pair of asperities when they collide under macro-EHL pressure ambient. The solution of this model was performed by a relaxation iteration method that had been found to be simple and effective. Results showed some physical features that were previously unknown, and provided information to unlock the mysteries of several important failure mechanisms in lubricated concentrated contacts.
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Yan, Xiaoyu, Wei Wang, Xiaojun Liu, Jimin Xu, Lihong Zhu, and Bingxun Yang. "Using FEM to study the frictional instability induced by third-body particles confined in frictional interface." Industrial Lubrication and Tribology 72, no. 10 (June 1, 2020): 1239–44. http://dx.doi.org/10.1108/ilt-12-2019-0544.
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Purpose A finite element method (FEM) model of the frictional behavior of two rough surfaces with a group of third-body particles confined by the surface asperities is established. By monitoring the stress distribution, friction force and the displacement of the surfaces, how the frictional instability is induced by these particles is studied. This modeling job aims to explore the relation between the meso-scale behavior and the macro-scale frictional behavior of these particles. Design/methodology/approach By using FEM, a 2D model of two frictional rough surfaces with a group of elastic or elasto-plastic particles confined by surface asperities is established. The Mises stress, macro friction force and displacements of elements are monitored during compressing and shearing steps. Findings The macro friction coefficient is more stable under higher pressure and smaller under higher shearing speed. The dilatancy of the interface is caused by the elevation effect of the particles sheared on the peak of the lower surface, particles collision and third body supporting. The combined effect of particles motion and surface–surface contact will induce high-frequency displacements of surface units in restricted direction. Originality/value Previous studies about third-body tribology are mainly concentrated on the frictional behavior with large number of particles distributed homogeneously across the interface, but this paper focuses on the behavior of third-body particles confined by surface asperities. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2019-0544/
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Ghilardi, T., M. J. Franca, and A. J. Schleiss. "Bulk velocity measurements by video analysis of dye tracer in a macro-rough channel." Measurement Science and Technology 25, no. 3 (February 5, 2014): 035003. http://dx.doi.org/10.1088/0957-0233/25/3/035003.
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Foko Foko, Flavien, Lukas Rüth, Oliver Koch, and Bernd Sauer. "Study of the Plastic Behavior of Rough Bearing Surfaces Using a Half-Space Contact Model and the Fatigue Life Estimation According to the Fatemi–Socie Model." Lubricants 11, no. 3 (March 13, 2023): 133. http://dx.doi.org/10.3390/lubricants11030133.
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A multiscale approach for the fatigue life estimation of rolling bearings is presented in this paper and applied to inner rings of cylindrical roller bearings of the type NU208. The forces acting in the rolling contact are determined from system-oriented modeling at the macro level. The microscale contact simulations are carried out in a half-space contact model. The stresses on the inner ring are determined and used in the local fatigue approach, according to Fatemi–Socie, for fatigue life estimation. Four surface variants were investigated, one ideally smooth surface and three real (rough) surfaces. The three rough surface variants used different finishing processes: fine ground, hard turned, and rough ground were produced. A load case with a maximum pressure of 2.4 GPa in the roller-inner ring contact was investigated. In addition to the fatigue life estimation, the plasticity behavior (surface topography, resulting contact pressure, and residual stress) of the three manufactured surfaces stood in the focus of the work. As the comparison between experimental and simulated results confirms, good predictions can be made with the simulation model.
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Kuwata, Y., K. Suga, and Y. Kawaguchi. "An extension of the second moment closure model for turbulent flows over macro rough walls." International Journal of Heat and Fluid Flow 77 (June 2019): 186–201. http://dx.doi.org/10.1016/j.ijheatfluidflow.2019.04.003.
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Camargo, Chico Q., Jonathan Bright, and Scott A. Hale. "Diagnosing the performance of human mobility models at small spatial scales using volunteered geographical information." Royal Society Open Science 6, no. 11 (November 2019): 191034. http://dx.doi.org/10.1098/rsos.191034.
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Accurate modelling of local population movement patterns is a core, contemporary concern for urban policymakers, affecting both the short-term deployment of public transport resources and the longer-term planning of transport infrastructure. Yet, while macro-level population movement models (such as the gravity and radiation models) are well developed, micro-level alternatives are in much shorter supply, with most macro-models known to perform poorly at smaller geographical scales. In this paper, we take a first step to remedy this deficit, by leveraging two novel datasets to analyse where and why macro-level models of human mobility break down. We show how freely available data from OpenStreetMap concerning land use composition of different areas around the county of Oxfordshire in the UK can be used to diagnose mobility models and understand the types of trips they over- and underestimate when compared with empirical volumes derived from aggregated, anonymous smartphone location data. We argue for new modelling strategies that move beyond rough heuristics such as distance and population towards a detailed, granular understanding of the opportunities presented in different regions.
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Altunbas, Adlen, Behzad Soltanbeigi, and Ozer Cinicioglu. "DEM analysis of passive failure state behind a rigid retaining wall: effect of boundary conditions." E3S Web of Conferences 92 (2019): 14012. http://dx.doi.org/10.1051/e3sconf/20199214012.
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Discrete Element Modelling (DEM) is a virtual testing method that enables multiscale studies on granular materials. DEM provides a well-controlled testing environment, which enables precise systematic evaluation of the factors influencing the bulk response. The current study focuses on the behaviour of cohesionless backfills while a passive state of stress is simulated (i.e. rigid retaining wall translates toward backfill). Though particle-scale properties (e.g. size, shape and cohesion) play an important role on the macro response, the main objective in this study is to highlight the extent by which boundary conditions are important. Thus, identical dense packings are subject to the following boundary conditions: smooth/rough retaining wall and smooth/rough/periodic sidewalls (necessary for maintaining plain-strain conditions). Based on the DEM results, the failure surface geometries, wall pressure distribution and dilative response of the specimens are evaluated. It is seen that a curvilinear slip surface, similar to that observed in experiments, is only obtained once a rough retaining wall and periodic sidewalls are available. The overall observations suggest that the mobilisation of the passive state of stress, for a cohesionless granular assembly, is highly sensitive to the considered various boundary conditions.
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Mann, J. B., T. N. Farris, and S. Chandrasekar. "Effects of Friction on Contact of Transverse Ground Surfaces." Journal of Tribology 116, no. 3 (July 1, 1994): 430–37. http://dx.doi.org/10.1115/1.2928858.
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The two-dimensional plane-strain sliding contact of a smooth rigid roller on a transverse ground rough surface is analyzed. The rough surface is idealized as an elastic half-space with periodic roughness modeled as cylindrical ridges oriented transverse to the sliding direction. The contact problem is solved using a numerical iterative method in which each asperity contact is treated as a micro-Hertz contact, and the exact treatment of asperity interaction is included. The subsurface stress field is calculated using Westergaard stress functions. The subsequent analysis compares the rough surface stress fields with the corresponding smooth Hertz contact to evaluate the influence of surface roughness and friction on the subsurface stress distributions. The results show that the real area of contact is less than the corresponding smooth surface Hertz contact area, and the magnitude of the actual localized maximum contact pressure is always greater than the corresponding smooth surface contact pressure. The asperity level subsurface effective stresses are greater in magnitude than the maximum subsurface stress due to the macro-Hertz contact for low coefficients of friction, and for high coefficients of friction the maximum effective stresses occur on the bulk material surface.
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Bahrami, M., J. R. Culham, M. M. Yananovich, and G. E. Schneider. "Review of Thermal Joint Resistance Models for Nonconforming Rough Surfaces." Applied Mechanics Reviews 59, no. 1 (January 1, 2006): 1–12. http://dx.doi.org/10.1115/1.2110231.
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The thermal contact resistance (TCR) in a vacuum is studied. The TCR problem is divided into three different parts: geometrical, mechanical, and thermal. Each problem includes a macro- and microscale subproblem; existing theories and models for each part are reviewed. Empirical correlations for microhardness, and the equivalent (sum) rough surface approximation, are discussed. Suggested correlations for estimating the mean absolute surface slope are summarized and compared with experimental data. The most common assumptions of existing thermal analyses are summarized. As basic elements of thermal analyses, spreading resistance of a circular heat source on a half-space and flux tube are reviewed; also existing flux tube correlations are compared. More than 400 TCR data points collected by different researchers during the last 40years are grouped into two limiting cases: conforming rough and elastoconstriction. Existing TCR models are reviewed and compared with the experimental data at these two limits. It is shown that the existing theoretical models do not cover both of the above-mentioned limiting cases. This review article cites 58 references.
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Yang, Sanqiang, Xiaoyu Zhou, Lusheng Qin, Na Liu, and Yongli Cai. "Experimental Study on Macro-Mesoscopic Components and Indexes of Buton Gilsonite-Modified Asphalt." Advances in Materials Science and Engineering 2019 (December 10, 2019): 1–9. http://dx.doi.org/10.1155/2019/9170756.
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Gilsonite-modified asphalt is one of the hotspots of high-performance modified asphalt research. In this paper, the macroscopic composition and index of gilsonite-modified asphalt are analyzed; gilsonite, matrix asphalt, and modified asphalt with different gilsonite contents were analyzed by high- and low-temperature performance tests, antiaging performance test, four-component test, infrared spectral test, and SEM electroscope scanning test. The results showed that the content of aromatic fraction, colloid, and asphaltene in Buton gilsonite was 3.1%, 95.6%, and 32.9% higher than that of matrix asphalt, respectively. The gilsonite-modified asphalt had better high-temperature performance and antiaging performance. The optimum amount of gilsonite in gilsonite-modified asphalt should be 9%∼15%. The pore structure of gilsonite is more distributed, the surface is rough, which can produce greater cohesion with matrix asphalt, and the compatibility is better.
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ISHIGAMI, Genya, Kenji TSUCHIYA, Hirotaka SUZUKI, Kota KATSUSHIMA, and Shingo OZAKI. "High-fidelity Simulator of Construction Robot using Macro-Microscopic Interaction Mechanics of Machines in Rough Terrain." Proceedings of JSME annual Conference on Robotics and Mechatronics (Robomec) 2019 (2019): 2P1—D08. http://dx.doi.org/10.1299/jsmermd.2019.2p1-d08.
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Zhang, Li, Dong Hui Wen, Shi Ming Ji, Qiao Ling Yuan, and Zhen Hao Xu. "A Survey of the Machining Characteristics and Mechanical Polishing Technology of CVD Diamond Films." Advanced Materials Research 69-70 (May 2009): 192–97. http://dx.doi.org/10.4028/www.scientific.net/amr.69-70.192.
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The rough surfaces and non-uniform thicknesses of chemically vapor-deposited (CVD) diamond films and substrates affect their industrial application. In recent years, many polishing and planarization methods have been reported, but each method has its relative merits. This paper reviews the necessity for processing of the CVD diamond films first. Then the processing mechanism of micro-cracking and the characteristics of mechanical polishing of diamond films are discussed. The remove form of the material and surface characteristics are compared by three mechanical polishing method, including free abrasive polishing, fixation abrasive polishing and membrane on the membrane polishing method. No matter what form of mechanical polishing process is adopted, because of its inherent characteristics and the principles of processing, mechanical polishing CVD diamond films can only be as polish processing to remove large residual. The macro-surface roughness of processing is about the 2μm. The micro-rough surface roughness is for the 40nm or so. The material removal rate is 10nm/h.
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Fulton, Diane, Richard Fulton, and Thomas Garsombke. "The 3/2 Country Market Evaluation Model: Inclusive Emerging Market Paradigm." Journal of International Business Research and Marketing 6, no. 5 (July 2021): 11–16. http://dx.doi.org/10.18775/jibrm.1849-8558.2015.65.3002.
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The authors present a new country market selection model using a three filter/two phase approach to scanning: 1) a macro filter using mega aggregate country statistics (external environments) in the rough cut phase with “broad fit” company compatibilities (values, vision, goals, capabilities, management feel) and critical success factors (make or break issues); 2) anEM filter to consider and evaluate emerging country markets of potential, also in the rough cut phase, matching the EM factors “broad fit” with the critical success factors of the organization and 3) a micro filter using key success factors for the company and product, market structural factors, and industry/competition factors which produce a “narrow fit” in the diamond cut phase with the organization’s objectives, strategies and resources. The emerging markets will be given full consideration in this model and factors selected will be chosen with the “fit” of the specific company, product, strategies, internal and external environments pertinent to the unique blend of variables in the industry/organization.
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Bahrami, M., J. R. Culham, and M. M. Yovanovich. "Modeling Thermal Contact Resistance: A Scale Analysis Approach." Journal of Heat Transfer 126, no. 6 (December 1, 2004): 896–905. http://dx.doi.org/10.1115/1.1795238.
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A compact analytical model is developed for predicting thermal contact resistance (TCR) of nonconforming rough contacts of bare solids in a vacuum. Instead of using probability relationships to model the size and number of microcontacts of Gaussian surfaces, a novel approach is taken by employing the “scale analysis method.” It is demonstrated that the geometry of heat sources on a half-space for microcontacts is justifiable for an applicable range of contact pressure. It is shown that the surface curvature and contact pressure distribution have no effect on the effective microthermal resistance. The present model allows TCR to be predicted over the entire range of nonconforming rough contacts from conforming rough to smooth Hertzian contacts. A new nondimensional parameter, i.e., ratio of the macro- over microthermal resistances, is introduced as a criterion to identify three regions of TCR. The present model is compared to collected TCR data for SS304 and showed excellent agreement. Additionally, more than 880 experimental data points, collected by many researchers, are summarized and compared to the present model, and relatively good agreement is observed. The data cover a wide range of materials, mechanical and thermophysical properties, micro- and macrocontact geometries, and similar and dissimilar metal contacts.
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Zhang, Jian, Xianli Zhao, Canmian Liu, and Wei Wang. "Reliability Evolution of Elevators Based on the Rough Set and the Improved TOPSIS Method." Mathematical Problems in Engineering 2018 (July 18, 2018): 1–8. http://dx.doi.org/10.1155/2018/4784965.
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Focusing on reliability evaluation of elevator equipment operation, this paper builds a model for reliability evaluation of elevator equipment. First, we analyze the factors influencing the reliability of elevators and extract the initial evaluation indicators from four macro-perspectives: people, management, equipment, and environment, to build the index system for reliability evaluation of elevator equipment. And, we reduce the indicator set to remove the unnecessary indicators by using the rough set and weight the reduced indicators according to expert opinions. Finally, on this basis, we combine the grey number theory with the TOPSIS method to build an improved TOPSIS evaluation model, to evaluate the reliability of elevators and determine the optimal ordering.
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Jiang, Xiaofei, D. Y. Hua, H. S. Cheng, Xiaolan Ai, and Si C. Lee. "A Mixed Elastohydrodynamic Lubrication Model With Asperity Contact." Journal of Tribology 121, no. 3 (July 1, 1999): 481–91. http://dx.doi.org/10.1115/1.2834093.
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Most machine elements, such as gears and bearings, are operated in the mixed lubrication region. To evaluate lubrication performance for these tribological components, a contact model in mixed elastohydrodynamic lubrication is presented. This model deals with the EHL problem in the very thin film region where the film is not thick enough to separate the asperity contact of rough surface. The macro contact area is then divided into the lubricated area and the micro asperity contact areas by the contacted rough surfaces. In the case when asperity to asperity contact is present, Reynolds equation is only valid in the lubricated areas. Asperity contact pressure is determined by the interaction of two mating surfaces. The applied load is carried out by the lubricant film and the contacted asperities. FFT techniques are utilized to calculate the surface displacement (forward problem) by convolution and the asperity contact pressure (inverse problem) by deconvolution for non-periodic surfaces. With the successful implementation of FFT and multigrid methods, the lubricated contact problem can be solved within hours on a PC for the grids as large as one million nodes. This capability enables us to simulate random rough surfaces in a dense mesh. The load ratio, contact area ratio and average gap are introduced to characterize the performance of mixed lubrication with asperity contacts. Discussions are given regarding the asperity orientation as well as the effect of rolling-sliding condition. Numerical results of real rough topography are illustrated with effects of velocity parameter on load ratio, contact ratio, and average gap.
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Szmukler-Moncler, Serge, Cornelio Blus, David Morales Schwarz, and Germano Orrù. "Characterization of a Macro- and Micro-Textured Titanium Grade 5 Alloy Surface Obtained by Etching Only without Sandblasting." Materials 13, no. 22 (November 11, 2020): 5074. http://dx.doi.org/10.3390/ma13225074.
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Our purpose was to physically characterize the surface, and the subsurface, of a macro- and micro-textured titanium grade 5 dental implant surface obtained by etching only, without sandblasting. The topography, surface roughness, as well as the surface structure and subsurface distribution of elements, were determined by scanning electronic microscopy (SEM), non-contact profilometry, X-ray diffraction (XRD), and a concentration profile performed by Auger electron spectroscopy (AES). The hydrogen concentration in the implants was measured; the ability to generate nanostructures when stored in deionized water was also investigated. Under SEM, the surface resembled a sandblasted and etched titanium surface with its typical macro- and micro-texture; roughness was moderate with average roughness (Sa) 1.29 µm. No titanium hydride was found at the implant surface and no enrichment of any alloying element was identified at the surface and subsurface. Hydrogen concentration was 79 ppm, within the normative tolerance (<130 ppm). After storage in water for 6 months, densely packed finger-like nanostructures were observed. The clinical advantage of this textured titanium alloy surface is that it displays the typical macro- and micro-features of a moderately rough sandblasted and etched (SLA) titanium surface without leaving behind any foreign sandblasting material.
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Lee, John D., and Jennifer Morgan. "Identifying Clumsy Automation at the Macro Level: Development of a Tool to Estimate Ship Staffing Requirements." Proceedings of the Human Factors and Ergonomics Society Annual Meeting 38, no. 14 (October 1994): 878–82. http://dx.doi.org/10.1177/154193129403801418.
Full textAbstract:
Automation promises increased operating efficiency and suggests the opportunity to reduce the number of people required to operate commercial ships safely; however, clumsy automation may degrade safety and performance, rather than enhance it. This paper distinguishes between clumsy automation at the macro level and clumsy automation at the micro level and discusses macro level issues. Specifically, macro level clumsy automation refers to the failure to consider the broad implications of automation induced crew reductions. Clumsy automation may reduce workload and facilitate crew reductions during routine sailing, but these crew reductions may leave the vessel more vulnerable to unacceptable workload peaks during unusual and emergency situations (fires, unscheduled maintenance, rough seas, reduced visibility). In these situations, tasks not accommodated by the automation may overwhelm a crew that has been reduced by the introduction of automation. Currently, no systematic procedure exists to estimate the changes that automation implies for staffing levels and skill requirements. Avoiding the effects of clumsy automation depends on identifying techniques to broaden the study of automation to include the effects on the entire crew during all phases of ship operation. This paper describes a computer-based tool to help identify potential overload situations that would be difficult to anticipate through intuitive assessments of how automation and other factors affect crew requirements.
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Zhu, Yue, and Ho Yin Kan. "Aviation and Airspace Management under Rough Set Theory." Mathematical Problems in Engineering 2022 (September 10, 2022): 1–12. http://dx.doi.org/10.1155/2022/6736884.
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With the development of aviation industry, a series of problems have appeared in aviation and airspace, among which the most prominent problem is the congestion of aviation and airspace. Airspace congestion has become a major problem in the development of civil aviation in China. Especially in the central and eastern regions of China, airspace congestion is becoming more and more serious. To better solve the problem of airspace congestion, rough set theory and the Fuzzy C-means (FCM) model are first analyzed. By analyzing the temporal and spatial characteristics of traffic congestion in the control sector, a multisector traffic congestion identification model is established based on radar track data. Four multisector congestion characteristics including equivalent traffic volume, proximity, saturation, and traffic density are established. FCM and rough set theory are used to classify and identify sector congestion. Finally, the model based on FCM-rough set theory is compared with other methods based on the data of the regional control sector in northwest China. The experimental results show that the congestion recognition rate of the model is 92.6%, 93.5%, and 94.2%, and the congestion misjudgment rate is 1.5%, 1.2%, and 1.3%, respectively. Hence, the multisector congestion recognition model has a high recognition rate and a low misjudgment rate, and the overall discrimination result is relatively stable. By comparing the proposed method with other methods, it is concluded that the recognition accuracy of the model based on FCM theory is superior to other methods. In summary, the congestion situation of the sector is affected by a variety of macro- and micro-characteristics of the sector, and the congestion identification model is feasible and efficient. Multisector traffic congestion identification has certain application value for airspace planning, air traffic control-assisted decision making, and air traffic flow management. This work can optimize the aviation and airspace management system and provide relevant suggestions for the study of aviation and airspace congestion.
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Chern, Shin Yuh, Jeng Haur Horng, Cheng Han Tsai, and Hung Jung Tsai. "The Micro-Temperatures of the Peaks and Valleys of Sliding Rough Surfaces." Applied Mechanics and Materials 883 (July 2018): 53–62. http://dx.doi.org/10.4028/www.scientific.net/amm.883.53.
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The surface micro-temperature of sliding, rough bodies is an important factor affecting contact properties, such as chemical reactions of automatic injectors for medicine and chemical processes and surface failure of micro-and macro-devices. In this work, the Finite Element Method is used to analyze the micro-temperature of the peaks and valleys of multiplying asperity sliding contact surfaces. The affecting parameters include pressure, roughness, sliding speed, Peclet number, and thermal conductivity of rough surfaces. Analysis results showed that the effects of the studied parameters are different to those of peak and valley temperatures. While pressure increased, the increasing rate of the temperature rise parameter of valleys was larger than those of peaks. The temperature rise of peaks increased as roughness increased. On the contrary, the temperature rise of valleys decreased as roughness increased. Sliding speed and thermal conductivity played the most important roles in affecting the maximum micro-temperature rise. The temperature rise difference between peaks and valleys was almost proportional to thermal conductivity, and was inversely proportional to sliding speed for all cases. This transient thermal analysis enables precision control of interface micro-temperature for micro-moving devices.
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Song, Jin Long, Xin Liu, Yao Lu, Li Bo Wu, and Wen Ji Xu. "Fabrication of Superhydrophobic Surfaces on Aluminum Substrates via Electrochemical Etching and Re-Deposition." Applied Mechanics and Materials 197 (September 2012): 351–55. http://dx.doi.org/10.4028/www.scientific.net/amm.197.351.
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Superhydrophobic surfaces on metal substrates are often prepared via roughing the surfaces and lowering their surface energy. The superhydrophobic aluminum surface with a water contact angle of 162.5° and rolling angle less than 6° was fabricated via electrochemical etching and re-deposition using the alkalic Na3PO4 electrolyte and then fluorination treating. The surface morphology and chemical composition were characterized by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results show that the surface consists of the micrometer-scale lumps and protrusions, and many nanometer-scale mastoids are filled in these protrusions. These hierarchical micro/nanometer-scale binary structures, which are similar to the micro-structures of lotus leaf surfaces, play an important role in achieving superhydrophobicity. The main components of the binary geometric structures are Al2O3, AlPO4, and H2O. The effects of the processing time and processing voltage on the macro-morphology were also investigated. The macro-rough structures appeared on the edge of the aluminum surface firstly, and then spread gradually to the entire surface.
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Zhang, Qingdong, Shuo Li, Rui Li, and Boyang Zhang. "Multiscale Comparison Study of Void Closure Law and Mechanism in the Bimetal Roll-Bonding Process." Metals 9, no. 3 (March 18, 2019): 343. http://dx.doi.org/10.3390/met9030343.
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The void closure mechanism during the roll-bonding process was investigated using a multiscale approach, which includes contact deformation at the macro-scale and atomic bonding at the micro-scale. The closure process of the voids was observed using roll-bonding tests of 304 stainless steel/Q235 carbon steel. A finite element model was built to simulate the macroscopic deformation process of 304/Q235 material, and a molecular dynamics model established to simulate the deformation process of the microscopic rough peaks. The closure law and mechanism of interface voids at the macro- and micro-scales were studied. The results show that the closure rate of interface voids decreases with the decrease in the average contact stress during the contact deformation process. In the atomic bonding process, the void closure rate is slow in the elastic deformation process. The ordered atoms near the interface become disordered as plastic deformation occurs, which increases the void closure rate and hinders dislocation propagation through the interface, resulting in significant strengthening effects via plastic deformation. Ultimately, a perfect lattice is reconstructed with void healing. In addition, the interface morphology after roll-bonding at the macro scale was determined by the morphology of the 304 steel with larger yield strength ratio, while the interface morphology at the micro-scale was mainly determined by the morphology of the Q235 steel with a higher yield strength.
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Tjahjana, D. D. D. P., and Y. Waloyo. "Failure Analysis of Super Hard End Mill HSS-Co." Open Engineering 9, no. 1 (July 26, 2019): 202–10. http://dx.doi.org/10.1515/eng-2019-0025.
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AbstractThe failure of tools will make a large impact to the productivity, so it must be investigated to avoid the next failure. In this case, the super hard end mill HSS-Co list 4SE code 6210 was broken when it was used for side milling processing of mild steel AISI A36 with rotation speed, cutting speed and cutting depth of 540 rpm, 0.10 m/min (4 ipm) and 16 mm respectively. Standard procedure of failure analysis was performed including macro-micro investigation using Scanning Electron Microscopy (SEM) with energy-dispersive spectrometry (EDS) attachment, micro hardness test, and Finite Element Methods (FEM) simulation. The results of failure analysis showed that fracture occurred due to stress concentration and micro defects of the super hard end mill. Two parts of fracture surface, rough and fine surface were found. Based on SEM-EDS investigation, it was known that the content of tungsten (W) and cobalt (Co) elements on the rough and fine surface was inhomogeneous. Excessive Co and W elements appeared on the fine surface while they disappeared on the rough surface. Excessive Co will diffuse with tungsten and carbon and lead to the separation of tungsten and carbon elements, so it greatly destroyed the alloys and lead to form the non-stoichiometry carbide points. Hence, the defective manufacturing processes which made the elements distribute inhomogeneous is concluded as the reason of the super hard end mill failure.
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Pozdnуakova, Tatyana A., and Roman A. Bubenchikov. "The study of morphological and anatomical features of the herb astragalus glycyphyllus L." Aspirantskiy Vestnik Povolzhiya 22, no. 1 (July 3, 2022): 50–54. http://dx.doi.org/10.55531/2072-2354.2022.22.1.50-54.
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Aim to establish the morphological, anatomical and microdiagnostic features of the stem, leaf blade, calyx and corolla of Astragalus glycyphyllus in accordance with the regulatory documentation.
Material and methods. The object of the study was the herb Astragalus glycyphyllus harvested in the Kursk region in 2021 during the period of mass flowering of the plant. The State Pharmacopoeia XIV standard was used for macro- and microscopic analysis.
Results. The raw material of the licorice-leaved astragalus consists of non-woody leafy stems 20-25 cm long with flowers, whole and crushed leaves of a grayish-green color, parts of the stem and individual flowers of a greenish-yellow color. The microscopic analysis presented the stem of Astragalus glycyphyllus having a round-ribbed shape, covered on the outside with epidermis with straight-walled cells, with longitudinally wrinkled cuticle. Leaf cells have slightly sinuous walls with anomocytic stomata. The rachis in cross section has a triangular shape with small lateral outgrowths and anomocytic stomata. The epidermis of the rachis is pubescent with simple bicellular hairs with rough surface. Cells of the epidermis of the calyx from the prosenchymal form (in the tube of the calyx) to the parenchyma (in the pharynx, on the teeth of the calyx), anomocytic stomata. At the base of the corolla there are epidermal cells of a prosenchymal form, straight-walled with straight or beveled ends, in the limb of the corolla - epidermal cells of a prosenchymal form, straight-walled with a longitudinal wrinkled cuticle. The epidermis of the stem, leaves, rachis and calyx is pubescent with simple two-celled hairs on a short basal cell with a long terminal cell, with rough surface.
Conclusion. The macro- and microdiagnostic features of the herb Astragalus glycyphyllus were described to distinguish the raw material "Astragalus glycyphyllus herb".
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Aboutalebi, Seyed Hamed, Zahra Gholamvand, and Mansoor Keyanpour-Rad. "ELECTROSPINNING OF CONTINUOUS CARBON NAONOFIBER-FILLED COMPOSITE FIBERS." International Journal of Modern Physics: Conference Series 05 (January 2012): 545–50. http://dx.doi.org/10.1142/s2010194512002450.
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In order to translate the superior properties of carbon nanofibers (CNFs) to macro-scale structures, an electrospinning route capable of placing CNFs into a continuous nano-scale composite fibril is introduced. In this work, composite fibers were produced by electrospinning solution of polyacrylonitrile ( PAN ) with carbon nanofibers dispersed in dimethylformamide ( DMF ), which is an effective solvent for carbon nanofibers. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) demonstrated rough and globular surfaces on the CNF containing fibers. Raman spectra confirmed the presence of CNFs in the polymer fibers prepared employing the electrospinning method. Raman observation served as the direct evidence of successful filling of PAN fibers with CNFs and complemented the results obtained by SEM and AFM studies.
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Mu, Taopin, Xianyong Zhang, and Zhiwen Mo. "Double-Granule Conditional-Entropies Based on Three-Level Granular Structures." Entropy 21, no. 7 (July 3, 2019): 657. http://dx.doi.org/10.3390/e21070657.
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Rough set theory is an important approach for data mining, and it refers to Shannon’s information measures for uncertainty measurements. The existing local conditional-entropies have both the second-order feature and application limitation. By improvements of hierarchical granulation, this paper establishes double-granule conditional-entropies based on three-level granular structures (i.e., micro-bottom, meso-middle, macro-top ), and then investigates the relevant properties. In terms of the decision table and its decision classification, double-granule conditional-entropies are proposed at micro-bottom by the dual condition-granule system. By virtue of successive granular summation integrations, they hierarchically evolve to meso-middle and macro-top, to respectively have part and complete condition-granulations. Then, the new measures acquire their number distribution, calculation algorithm, three bounds, and granulation non-monotonicity at three corresponding levels. Finally, the hierarchical constructions and achieved properties are effectively verified by decision table examples and data set experiments. Double-granule conditional-entropies carry the second-order characteristic and hierarchical granulation to deepen both the classical entropy system and local conditional-entropies, and thus they become novel uncertainty measures for information processing and knowledge reasoning.
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Gu, Chunxing, Xianghui Meng, Di Zhang, and Youbai Xie. "A transient analysis of the textured journal bearing considering micro and macro cavitation during an engine cycle." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 231, no. 10 (February 6, 2017): 1289–306. http://dx.doi.org/10.1177/1350650117692721.
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This paper presents a transient analysis of the textured journal bearing system. A mass-conserving model is developed to consider the combined effects of the inter-asperity cavitation and the macroscopic cavitation between two rough textured surfaces. In this model, the inter-asperity cavitation induced by the roughness is considered by the statistical approach (the classic flow factor methodology), while the deterministic approach is used to deal with the macroscopic cavitation induced by textures and macroscopic geometry. Moreover, the system of discretized equations for this model is unconstrained by reformulating the cavitation conditions, which is in favor of improving the computational efficiency. Furthermore, based on the fully dynamic analysis, the present study examines the effect of different textures (dimple and groove) under the engine operating conditions. It is found that the position of journal center is changed according to the engine speed and then influences the potential reduction effects produced by texturing.
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BARAKAT, NASSER A. M., M. S. A. SOLIMAN, and FATMA A. ZAHRAN. "Macro- and micro-morphometrical seed characters in seven species of Egyptian Datura and Nicotiana (Solanaceae)." Phytotaxa 413, no. 2 (July 31, 2019): 149–58. http://dx.doi.org/10.11646/phytotaxa.413.2.4.
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This work describes and compares the external macro- and micro-morphometrical features of the seed of seven species of Datura and Nicotiana belonging to two tribes of the Solanaceae. Fourteen unique characters were measured and described, the results of which reveal marked differences, both among and within genera. The species of Datura exhibited higher values than those of Nicotiana in all morphometrically measured parameters, such as seed weight, size, perimeter, and surface area, with no or little variation in roundness and eccentricity. For qualitative features, the notched outline, rough texture, pitted ornamentation, circular hilum shape, and stellate coat pattern characterized all examined species of Nicotiana. The yellow colour of the seeds can be used to distinguish the seeds of Nicotiana glauca from the brown seeds of other Nicotiana species examined in this study. The circular shape of the hilum distinguishes the seeds of Datura innoxia from those of Datura metel, which have oral-shaped hilum. Considerable differences in seed coat morphology were found both among and within species. However, the size and shape of the seed can be useful and stable characters, and the position of the hilum had some taxonomic significance.
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Badika, Menes, Bassel El Merabi, Sophie Capdevielle, Frederic Dufour, Dominique Saletti, and Matthieu Briffaut. "Influence of Concrete–Rock Bonds and Roughness on the Shear Behavior of Concrete–Rock Interfaces under Low Normal Loading, Experimental and Numerical Analysis." Applied Sciences 12, no. 11 (June 1, 2022): 5643. http://dx.doi.org/10.3390/app12115643.
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Direct shear tests were performed to study the influence of concrete–rock bonds and roughness on the shear behavior of concrete–rock interfaces. The results of these tests show that the shear behavior of concrete–hardrock interfaces depends on the micro-roughness driving the formation of strong concrete–rock bonds and on the macro-roughness accounting for the influence of the surfaces interlocking. Based on this outcome and recent literature, a cohesive frictional model is used to simulate direct shear tests of bonded concrete–granite interfaces with the explicit representation of naturally rough interfaces. The results of these simulations show that the model has good prediction capability compared to the experimental results, opening up the pathway to numerically based robust statistical analysis.
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Wei, De Qiang, Xin Dong, and Shan Qiu Li. "Failure Analysis of Stress Corrosion Crack of 1Cr18Ni9 Stainless Steel Cylinder Body." Advanced Materials Research 591-593 (November 2012): 1094–97. http://dx.doi.org/10.4028/www.scientific.net/amr.591-593.1094.
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As a kind of corrosion resistant material, stainless steel is widely used in petroleum, chemical, pharmaceutical. Stress corrosion cracking is a main reason that why the stainless steel became disabled. Therefore, it is very necessary to research and study the stress corrosion cracking of stainless steel .The failure analysis to the sample is conducted aiming at the stress corrosion of the stainless steel piston cylinder in a factory. The analysis includes macro analysis, metallographic observation, scanning electron microscopy analysis and XRD analysis. The results of the study show that it is nonmetallic inclusion on the grain boundary, the chloridion in the industrial circulating water and the rough columnar austenitic grains in the organization of the samples that lead to the stress corrosion cracking of the piston cylinder.
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Grün, Jeremias, Simon Feldmeth, and Frank Bauer. "The sealing mechanism of radial lip seals: A numerical study of the tangential distortion of the sealing edge." Tribology and Materials 1, no. 1 (2022): 1–10. http://dx.doi.org/10.46793/tribomat.2022.001.
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The sealing behaviour of elastomeric radial lip seals is essentially affected by the sealing mechanism in the contact area between the sealing edge and the shaft surface. The relative motion between radial lip seal and shaft deforms the sealing edge tangentially in the circumferential direction. This mechanical deformation is considered essential for the sealing mechanism. In this study, a numerical approach is employed to simulate this deformation. A three-dimensional multiscale model serves this purpose. The radial lip seal geometry is described on the macro-scale. On the micro-scale, an artificial rough surface with a stochastic roughness distribution is applied to an ideal sealing edge surface. A new meshing algorithm is used to discretise different sealing edge surfaces and automatically generates structured hexahedral meshes of the sealing edges. Mesh transitions connect the resulting finely meshed sealing edge to the coarsely meshed global macro-scale mesh of the radial lip seal. The paper introduces the modelling method used to simulate the deformation of radial lip seals. Results are presented and discussed with reference to the sealing behaviour. This contributes to a better understanding of the sealing mechanism of radial lip seals. Keywords: radial lip seal, finite element analysis, surface roughness, elastic deformation, elastomers.
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Belousov, M. V., A. Yu Chernyshov, I. V. Ignatev, I. E. Kozin, A. V. Kavokin, H. M. Gibbs, and G. Khitrova. "Statistical Model Explaining the Fine Structure and Interface Reference of Localized Excitons in Type-II GaAs/AlAs Superlattices." Journal of Nonlinear Optical Physics & Materials 07, no. 01 (March 1998): 13–35. http://dx.doi.org/10.1142/s021886359800003x.
Full textAbstract:
Raman scattering experiments have allowed the determination of the spatial distribution of the thicknesses of GaAs and AlAs layers in a gradient GaAs/AlAs superlattice. A statistical model is developed which is consistent with all the data and ways to improve interface quality are suggested. The fine structures of XΓ and ΓΓ excitons observed in photoluminescence and differential reflection are found to be governed by the fractional parts of the average thickness of the layer (in monolayers). We conclude that each structure has two scales of fluctuations which form the relief of the AlAs surface. The largest fluctuations repeat the relief of the GaAs surface. The second scale has the size of a typical XΓ exciton Bohr radius. The smaller fluctuations disappear when the thickness of the AlAs layer is equal to an integer number of monolayers, which provide interfaces of the quality. The correlation of macro-rough fluctuations on the surface of AlAs and GaAs causes an asymmetry in the densities of states of type II excitons located at either AlAs-on-GaAs or GaAs-on-AlAs interfaces. Hence the lowest PL line is formed by excitons localized across the AlAs-on-GaAs interface. On the other hand, in structures with micro-rough but uncorrelated AlAs surfaces, the lowest energy state is expected to be occupied by excitons localized across the GaAs-on-AlAs interface.
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Kwak, Myeong Ja, Jongkyu Lee, Sanghee Park, Yea Ji Lim, Handong Kim, Su Gyeong Jeong, Joung-a. Son, et al. "Understanding Particulate Matter Retention and Wash-Off during Rainfall in Relation to Leaf Traits of Urban Forest Tree Species." Horticulturae 9, no. 2 (January 27, 2023): 165. http://dx.doi.org/10.3390/horticulturae9020165.
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Dynamic particulate matter (PM) behavior on leaves depends on rainfall events, leaf structural and physical properties, and individual tree crowns in urban forests. To address this dependency, we compared the observed relationships between PM wash-off ability and leaf traits on inner and outer crown-positioned leaves during rainfall events. Data showed significant differences in the PM wash-off ability between inner and outer crown-positioned leaves relative to rainfall events due to leaf macro- and micro-structure and geometric properties among tree species. Our results showed that PM wash-off effects on leaf surfaces were negatively associated with trichome density and size of leaf micro-scale during rainfall events. Specifically, Quercus acutissima with dense trichomes and micro-level surface roughness with narrow grooves on leaf surfaces showed lower total PM wash-off in both inner (−38%) and outer (105%) crowns during rainfall. Thus, their rough leaves in the inner crown might newly capture and/or retain more PM than smooth leaves even under rainfall conditions. More importantly, Euonymus japonicus, with a thin film-like wax coverage without trichome, led to higher total PM wash-off in both inner (368%) and outer (629%) crowns during rainfall. Furthermore, we studied the changes in PM wash-off during rainfall events by comparing particle size fractions, revealing a very significant association with macro-scale, micro-scale, and geometric features.
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Somov, Pavel A., Eugene S. Statnik, Yuliya Kan, Vladimir S. Pisarev, Svyatoslav I. Eleonsky, Dmitry Yu Ozherelkov, and Alexey I. Salimon. "FIB-DIC Residual Stress Evaluation in Shot Peened VT6 Alloy Validated by X-ray Diffraction and Laser Speckle Interferometry." Nanomaterials 12, no. 7 (April 6, 2022): 1235. http://dx.doi.org/10.3390/nano12071235.
Full textAbstract:
Ga-ion micro-ring-core FIB-DIC evaluation of residual stresses in shot peened VT6 (Ti-6Al-4V) alloy was carried out and cross-validated against other non-destructive and semi-destructive residual stresses evaluation techniques, namely, the conventional sin2ψ X-ray diffraction and mechanical hole drilling. The Korsunsky FIB-DIC method of Ga-ion beam micro-ring-core milling within FIB-SEM with Digital Image Correlation (DIC) deformation analysis delivered spatial resolution down to a few micrometers, while the mechanical drilling of circular holes of ~2 mm diameter with laser speckle interferometry monitoring of strains gave a rough spatial resolution of a few millimeters. Good agreement was also found with the X-ray diffraction estimates of residual stress variation profiles as a function of depth. These results demonstrate that FIB-DIC provides rich information down to the micron scale, it also allows reliable estimation of macro-scale residual stresses.
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Baglin, K. P. "Some Aspects of the Micro-Elastohydrodynamic Lubrication of Rough Cylinders Finished with a Circumferential Lay." Proceedings of the Institution of Mechanical Engineers, Part C: Mechanical Engineering Science 204, no. 3 (May 1990): 145–58. http://dx.doi.org/10.1243/pime_proc_1990_204_091_02.
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Earlier work has shown that sinusoidal asperities with a circumferential lay give rise to transverse pressure ripples within the nominally smooth elastohydrodynamic pressure distribution. The ripples can become sufficiently large to cause elastic deformation of the generating asperities. This paper assumes that the deformed shape can be described using the Westergaard ‘dry contact’ analysis with the load (that, fraction of the total load contained within the pressure ripple) being unknown a priori. Solution of the Reynolds equation leads to the production of non-dimensional plots which give the extent of asperity deformation and the micro-elastohydrodynamic lubrication film thickness underneath the asperities as functions of the operating variables. It is shown that sensible lubricant films can exist between rough surfaces even as the nominal ratio of undeformed roughness/macro film thickness approaches 10. Different non-dimensional plots exist for different ‘sharpness’ asperities, defined as the ratio of amplitude/wavelength. For low values of the ratio, appropriate to roller bearings for example, Westergaard-type flat formation is appropriate over the total range of operating conditions considered. With sharper asperities, such as occur with W-N gears, the Westergaard flat is appropriate for relatively small deformations but, with increasing deformation, side lobes must form within the predicted ‘flat’. It is argued that this analysis will remain appropriate while the system is capable of producing high pressure in the valleys of the sinusoid but will become inappropriate as asperity deformation approaches the value it would have when bearing the total load.
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Cao, Hui, Yu Tian, and Yonggang Meng. "A FRACTURE-INDUCED ADHESIVE WEAR CRITERION AND ITS APPLICATION TO THE SIMULATION OF WEAR PROCESS OF THE POINT CONTACTS UNDER MIXED LUBRICATION CONDITION." Facta Universitatis, Series: Mechanical Engineering 19, no. 1 (April 1, 2021): 023. http://dx.doi.org/10.22190/fume210108021c.
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Adhesive wear is one of the four major wear mechanisms and very common in almost all macro-, micro- or nanotribosystems. In an adhesive wear process, tiny material fragments are pulled off from one sliding surface and adhered onto the counterpart. Later these fragments form loose particles or transfer between the contact surfaces. Because of the topographical and physicochemical property non-uniformity of engineering surfaces, adhesive wear happens heterogeneously on the loaded sliding surfaces, and it is also discontinuous during sliding or rolling motion owing to the damage accumulation and fracture occurred inside the subsurface layers. Taking account of these characteristics, a novel fracture-induced adhesive wear criterion has been proposed in this study in order to predict local wear of material in sliding. Moreover, the proposed wear criterion is applied to predicting wear particle formation and morphology evolution of mixed lubricated rough surfaces during reciprocating sliding, and the simulation results are compared with the ball-on-disk experimental measurements.
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Arola, D., and M. Ramulu. "A Study of Kerf Characteristics in Abrasive Waterjet Machining of Graphite/Epoxy Composite." Journal of Engineering Materials and Technology 118, no. 2 (April 1, 1996): 256–65. http://dx.doi.org/10.1115/1.2804897.
Full textAbstract:
Kerf geometry, kerf wall features, and cutting front characteristics of an Abrasive Waterjet (AWJ) machined Graphite/Epoxy (Gr/Ep) laminate were studied. A macroscopic analyses suggests that geometrical features associated with AWJ machining of Gr/Ep laminates are influenced by three macro regions along the cutting depth. The presence of these regions, including initial damage at jet entry, smooth cutting, and rough cutting near the jet exit, depends on the operating conditions. Design of experiments and analysis of variance were used to determine the effect of cutting parameters on kerf characteristics and to develop empirical models for kerf profile and features of the three distinct macroscopic regions. Cutting front analysis revealed that the mechanisms of material removal in AWJ machining of Gr/Ep do not change over the jet penetration depth. In general, high quality uniform cuts may be obtained by minimizing initial damage at the jet entry and by extending the smooth cutting region beyond the laminate thickness through the appropriate choice of cutting parameters.