Artykuły w czasopismach: „Rough boundary”

1

Denk, Robert, David Ploß, Sophia Rau i Jörg Seiler. "Boundary value problems with rough boundary data". Journal of Differential Equations 366 (wrzesień 2023): 85–131. http://dx.doi.org/10.1016/j.jde.2023.04.001.

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Raupach, M. R., R. A. Antonia i S. Rajagopalan. "Rough-Wall Turbulent Boundary Layers". Applied Mechanics Reviews 44, nr 1 (1.01.1991): 1–25. http://dx.doi.org/10.1115/1.3119492.

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This review considers theoretical and experimental knowledge of rough-wall turbulent boundary layers, drawing from both laboratory and atmospheric data. The former apply mainly to the region above the roughness sublayer (in which the roughness has a direct dynamical influence) whereas the latter resolve the structure of the roughness sublayer in some detail. Topics considered include the drag properties of rough surfaces as functions of the roughness geometry, the mean and turbulent velocity fields above the roughness sublayer, the properties of the flow close to and within the roughness canopy, and the nature of the organized motion in rough-wall boundary layers. Overall, there is strong support for the hypothesis of wall similarity: At sufficiently high Reynolds numbers, rough-wall and smooth-wall boundary layers have the same turbulence structure above the roughness (or viscous) sublayer, scaling with height, boundary-layer thickness, and friction velocity.

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3

Engel, Konrad, i Tran Dan Thu. "Boundary optimization for rough sets". Discrete Mathematics 341, nr 9 (wrzesień 2018): 2465–77. http://dx.doi.org/10.1016/j.disc.2018.05.023.

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Yu, Wei Wei, Xiao Qin Guan, Yi Hui Li i Hang Lin. "Boundary Effect to the Safety Factor of Slope in Geo-Material". Advanced Materials Research 382 (listopad 2011): 84–87. http://dx.doi.org/10.4028/www.scientific.net/amr.382.84.

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Boundary conditions have great impact on the stability of three dimensional geo-material, like slope, which is one of the oldest applications in geotechnical engineering. In order to analyze the impact of boundary condition to factor of safety of slope, the 3D stability analysis was then extended to the “rough-smooth” and “smooth-smooth” boundary. By studying slopes with the same geometric condition and shear strength parameters, the results show that the safety factors obtained from “rough-smooth” boundary are smaller than those got from “rough-smooth” boundary and bigger than those got from “smooth-smooth” boundary. The study also indicates that when the width to height ratio (W/H) of homogeneous symmetric slope satisfies certain condition, the “rough-rough” boundary equals to the “rough-smooth” boundary. The factor of safety and shape of slip surface got from these two kinds of boundary condition are of the same. Study results can give guidance for the real practice.

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5

Ligrani, Phillip M., i Robert J. Moffat. "Structure of transitionally rough and fully rough turbulent boundary layers". Journal of Fluid Mechanics 162, nr -1 (styczeń 1986): 69. http://dx.doi.org/10.1017/s0022112086001933.

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Ashrafian, Alireza, i Stein Tore Johansen. "Wall boundary conditions for rough walls". Progress in Computational Fluid Dynamics, An International Journal 7, nr 2/3/4 (2007): 230. http://dx.doi.org/10.1504/pcfd.2007.013015.

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Chen, Xinfu, Xiao-Ping Wang i Xianmin Xu. "Effective contact angle for rough boundary". Physica D: Nonlinear Phenomena 242, nr 1 (styczeń 2013): 54–64. http://dx.doi.org/10.1016/j.physd.2012.08.018.

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Acharya, M., J. Bornstein i M. P. Escudier. "Turbulent boundary layers on rough surfaces". Experiments in Fluids 4, nr 1 (1986): 33–47. http://dx.doi.org/10.1007/bf00316784.

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9

DeSanto, John A. "Impedance at a rough waveguide boundary". Wave Motion 7, nr 4 (lipiec 1985): 307–18. http://dx.doi.org/10.1016/0165-2125(85)90002-2.

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MCDANIEL, SUZANNE T. "RENORMALIZING ROUGH-SURFACE SCATTER". Journal of Computational Acoustics 10, nr 01 (marzec 2002): 53–68. http://dx.doi.org/10.1142/s0218396x02001541.

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Exact and approximate solutions to the rough-surface scattering problem are compared to examine the predictive capability of renormalized surface scattering theory. Numerical results are presented for scattering from one-dimensional rough periodic surfaces on which the Dirichlet (acoustic pressure-release) and Neumann (acoustically rigid) boundary conditions are imposed. For scattering from Dirichlet surfaces, the predictions of renormalized scattering theory are found to provide better agreement with exact solutions than perturbation theory. For this boundary condition, many convergent approximations exist, and the small-slope approximation is found to yield an improvement to renormalization. For the Neumann boundary condition, renormalization provides good agreement with exact solutions for scattering from slightly rough surfaces. The Kirchhoff approximation, the only other convergent approximation applicable to the Neumann problem, provides agreement with exact solutions for scattering from moderately rough surfaces for angles of scatter and incidence far from grazing.

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Katayama, Kiyofumi, Kazuo Tanaka i Masahiro Tanaka. "Numerical analysis of frequency characteristics of transmitted waves by random waveguide". AIP Advances 12, nr 10 (1.10.2022): 105305. http://dx.doi.org/10.1063/5.0099016.

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The frequency characteristics of the transmitted waves by the two-dimensional single-mode waveguide with a slightly rough boundary are investigated in detail. Two realizations of the waveguide with random rough boundaries are considered. Since the boundary element method based on the guided-mode extracted integral equation is employed, the boundary condition on the random rough boundary is accurately satisfied. It is found that the strong resonances with high Q-factor are created close to the cutoff frequency of the second-mode in the waveguide and they cause the small transmission (high reflection). It is shown that the Q-factors of these resonances increase with a decrease in the rms of the rough boundaries. It is shown that the rough boundary whose rms is about several thousand times smaller than the wavelength creates a strong enhanced electric field whose intensity is about several hundred times larger than that of the incident mode.

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Yang, Zhibin, Xiaoming Zhai, David P. Marshall i Guihua Wang. "An Idealized Model Study of Eddy Energetics in the Western Boundary “Graveyard”". Journal of Physical Oceanography 51, nr 4 (kwiecień 2021): 1265–82. http://dx.doi.org/10.1175/jpo-d-19-0301.1.

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AbstractRecent studies show that the western boundary acts as a “graveyard” for westward-propagating ocean eddies. However, how the eddy energy incident on the western boundary is dissipated remains unclear. Here we investigate the energetics of eddy–western boundary interaction using an idealized MIT ocean circulation model with a spatially variable grid resolution. Four types of model experiments are conducted: 1) single eddy cases, 2) a sea of random eddies, 3) with a smooth topography, and 4) with a rough topography. We find significant dissipation of incident eddy energy at the western boundary, regardless of whether the model topography at the western boundary is smooth or rough. However, in the presence of rough topography, not only the eddy energy dissipation rate is enhanced, but more importantly, the leading process for removing eddy energy in the model switches from bottom frictional drag as in the case of smooth topography to viscous dissipation in the ocean interior above the rough topography. Further analysis shows that the enhanced eddy energy dissipation in the experiment with rough topography is associated with greater anticyclonic, ageostrophic instability (AAI), possibly as a result of lee wave generation and nonpropagating form drag effect.

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13

Glovnea, R. P., A. V. Olver i H. A. Spikes. "Lubrication of Rough Surfaces by a Boundary Film-Forming Viscosity Modifier Additive". Journal of Tribology 127, nr 1 (1.01.2005): 223–29. http://dx.doi.org/10.1115/1.1828069.

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In previous work it was shown that some functionalized polymers used as viscosity index improvers are able to form thick boundary lubricating films. This behavior results from adsorption of the polymer on metal surfaces to form a layer of enhanced viscosity adjacent to the surface. In the current work the behavior of one such polymer in rough surface contact conditions is studied, using both model and real rough surfaces. It is found that the polymer is able to form a thick boundary film in rough surface contact, just as it does with smooth surfaces. It is also shown that the effect of this boundary film is to significantly reduce friction in rolling-sliding, rough surface, lubricated contact.

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14

VOLINO, R. J., M. P. SCHULTZ i K. A. FLACK. "Turbulence structure in rough- and smooth-wall boundary layers". Journal of Fluid Mechanics 592 (14.11.2007): 263–93. http://dx.doi.org/10.1017/s0022112007008518.

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Turbulence measurements for rough-wall boundary layers are presented and compared to those for a smooth wall. The rough-wall experiments were made on a woven mesh surface at Reynolds numbers approximately equal to those for the smooth wall. Fully rough conditions were achieved. The present work focuses on turbulence structure, as documented through spectra of the fluctuating velocity components, swirl strength, and two-point auto- and cross-correlations of the fluctuating velocity and swirl. The present results are in good agreement, both qualitatively and quantitatively, with the turbulence structure for smooth-wall boundary layers documented in the literature. The boundary layer is characterized by packets of hairpin vortices which induce low-speed regions with regular spanwise spacing. The same types of structure are observed for the rough- and smooth-wall flows. When the measured quantities are normalized using outer variables, some differences are observed, but quantitative similarity, in large part, holds. The present results support and help to explain the previously documented outer-region similarity in turbulence statistics between smooth- and rough-wall boundary layers.

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15

McIlroy, Hugh M., i Ralph S. Budwig. "The Boundary Layer Over Turbine Blade Models With Realistic Rough Surfaces". Journal of Turbomachinery 129, nr 2 (1.02.2005): 318–30. http://dx.doi.org/10.1115/1.2218572.

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Results are presented of extensive boundary layer measurements taken over a flat, smooth plate model of the front one-third of a turbine blade and over the model with an embedded strip of realistic rough surface. The turbine blade model also included elevated freestream turbulence and an accelerating freestream in order to simulate conditions on the suction side of a high-pressure turbine blade. The realistic rough surface was developed by scaling actual turbine blade surface data provided by U.S. Air Force Research Laboratory. The rough patch can be considered to be an idealized area of distributed spalls with realistic surface roughness. The results indicate that bypass transition occurred very early in the flow over the model and that the boundary layer remained unstable (transitional) throughout the entire length of the test plate. Results from the rough patch study indicate the boundary layer thickness and momentum thickness Reynolds numbers increased over the rough patch and the shape factor increased over the rough patch but then decreased downstream of the patch. It was also found that flow downstream of the patch experienced a gradual retransition to laminar-like behavior but in less time and distance than in the smooth plate case. Additionally, the rough patch caused a significant increase in streamwise turbulence intensity and normal turbulence intensity over the rough patch and downstream of the patch. In addition, the skin friction coefficient over the rough patch increased by nearly 2.5 times the smooth plate value. Finally, the rough patch caused the Reynolds shear stresses to increase in the region close the plate surface.

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16

Ullah, Shah Neyamat, Yu Xia Hu, David White i Samuel Stanier. "Lateral Boundary Effect in Centrifuge Tests for Spudcan Penetration in Uniform Clay". Applied Mechanics and Materials 553 (maj 2014): 458–63. http://dx.doi.org/10.4028/www.scientific.net/amm.553.458.

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The effect of the centrifuge strongbox boundary on the penetration resistance of a spudcan foundation in uniform clay has been studied using Large Deformation FE analysis. Both smooth and rough strongbox boundaries were considered with various strongbox sizes. The spudcan penetration resistance and soil flow mechanisms were analysed. It was observed that, when the strongbox size was reduced, the spudcan penetration resistance was decreased for a smooth boundary and increased for a rough boundary. The depth of cavity formed above the spudcan during its penetration, in most cases, was determined by the soil flow around mechanism without cavity wall failure. However, cavity wall failure could be initiated when a smooth strongbox boundary was very close to the spudcan. The strongbox boundary effect on the spudcan penetration resistance can be avoided when the distance of the strongbox boundary to the spudcan centre is larger than 1.5 times of spudcan diameter for a rough boundary; or 2 times of spudcan diameter for a smooth boundary.

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17

Goluskin, David, i Charles R. Doering. "Bounds for convection between rough boundaries". Journal of Fluid Mechanics 804 (9.09.2016): 370–86. http://dx.doi.org/10.1017/jfm.2016.528.

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We consider Rayleigh–Bénard convection in a layer of fluid between rough no-slip boundaries where the top and bottom boundary heights are functions of the horizontal coordinates with square-integrable gradients. We use the background method to derive an upper bound on the mean heat flux across the layer for all admissible boundary geometries. This flux, normalized by the temperature difference between the boundaries, can grow with the Rayleigh number ($Ra$) no faster than $O(Ra^{1/2})$ as $Ra\rightarrow \infty$. Our analysis yields a family of similar bounds, depending on how various estimates are tuned, but every version depends explicitly on the boundary geometry. In one version the coefficient of the $O(Ra^{1/2})$ leading term is $0.242+2.925\Vert \unicode[STIX]{x1D735}h\Vert ^{2}$, where $\Vert \unicode[STIX]{x1D735}h\Vert ^{2}$ is the mean squared magnitude of the boundary height gradients. Application to a particular geometry is illustrated for sinusoidal boundaries.

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18

Leighton, M., N. Morris, M. Gore, R. Rahmani, H. Rahnejat i PD King. "Boundary interactions of rough non-Gaussian surfaces". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 230, nr 11 (5.08.2016): 1359–70. http://dx.doi.org/10.1177/1350650116656967.

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Bandyopadhyay, Promode R., i Ralph D. Watson. "Structure of rough-wall turbulent boundary layers". Physics of Fluids 31, nr 7 (1988): 1877. http://dx.doi.org/10.1063/1.866686.

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CASTRO, IAN P. "Rough-wall boundary layers: mean flow universality". Journal of Fluid Mechanics 585 (7.08.2007): 469–85. http://dx.doi.org/10.1017/s0022112007006921.

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Mean flow profiles, skin friction, and integral parameters for boundary layers developing naturally over a wide variety of fully aerodynamically rough surfaces are presented and discussed. The momentum thickness Reynolds number Reθ extends to values in excess of 47000 and, unlike previous work, a very wide range of the ratio of roughness element height to boundary-layer depth is covered (0.03 < h/δ > 0.5). Comparisons are made with some classical formulations based on the assumption of a universal two-parameter form for the mean velocity profile, and also with other recent measurements. It is shown that appropriately re-written versions of the former can be used to collapse all the data, irrespective of the nature of the roughness, unless the surface is very rough, meaning that the typical roughness element height exceeds some 50% of the boundary-layer momentum thickness, corresponding to about $h/\delta\,{\widetilde{>}}\,0.2$.

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Hsu, Tai-Wen, i Shan-Hwei Ou. "Wave boundary layers in rough turbulent flow". Ocean Engineering 24, nr 1 (styczeń 1997): 25–43. http://dx.doi.org/10.1016/0029-8018(95)00074-7.

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Yamakita, Tomonori, Katsuki Goto, Jun Yoshida, Hidemiki Kawashima i Yoshiyuki Tsuji. "236 Turbulent Boundary Layer over Rough-wall". Proceedings of Conference of Tokai Branch 2013.62 (2013): 143–44. http://dx.doi.org/10.1299/jsmetokai.2013.62.143.

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Loureiro, J. B. R., i A. P. Silva Freire. "Transient thermal boundary layers over rough surfaces". International Journal of Heat and Mass Transfer 71 (kwiecień 2014): 217–27. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2013.11.076.

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Vanderwel, Christina, i Bharathram Ganapathisubramani. "Turbulent Boundary Layers Over Multiscale Rough Patches". Boundary-Layer Meteorology 172, nr 1 (16.04.2019): 1–16. http://dx.doi.org/10.1007/s10546-019-00430-x.

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Garcia, Matt, Eugene N. A. Hoffman, Elijah J. LaLonde, Christopher S. Combs, Mason Pohlman, Cary Smith, Mark T. Gragston i John D. Schmisseur. "Effects of Surface Roughness on Shock-Wave/Turbulent Boundary-Layer Interaction at Mach 4 over a Hollow Cylinder Flare Model". Fluids 7, nr 9 (23.08.2022): 286. http://dx.doi.org/10.3390/fluids7090286.

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Although it is understood that surface roughness can impact boundary layer physics in high-speed flows, there has been little research aimed at understanding the potential impact of surface roughness on high-speed shock-wave/boundary-layer interactions. Here, a hollow cylinder flare model was used to study the potential impact of distributed surface roughness on shock-wave/boundary-layer interaction unsteadiness. Two surface conditions were tested—a smooth steel finish with an average roughness of 0.85 μm and a rough surface (3K carbon fiber) with an average roughness value of 9.22 μm. The separation shock foot from the shock-wave/boundary-layer interaction on the hollow cylinder flare was tracked by analyzing schlieren images with a shock tracking algorithm. The rough surface increased boundary layer thickness by approximately a factor of 10 compared to the smooth case, significantly altering the interaction scaling. Despite normalizing results, based on this boundary layer scaling, the rough surface case still exhibited mean shock foot positions further upstream more than the smooth surface case. Power spectra of the unsteady shock foot location data demonstrated that the rough surface case exhibited unsteady motion with attenuated energy relative to the smooth-wall case.

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Hosni, M. H., H. W. Coleman i R. P. Taylor. "Measurement and Calculation of Fluid Dynamic Characteristics of Rough-Wall Turbulent Boundary-Layer Flows". Journal of Fluids Engineering 115, nr 3 (1.09.1993): 383–88. http://dx.doi.org/10.1115/1.2910150.

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Experimental measurements of profiles of mean velocity and distributions of boundary-layer thickness and skin friction coefficient from aerodynamically smooth, transitionally rough, and fully rough turbulent boundary-layer flows are presented for four surfaces—three rough and one smooth. The rough surfaces are composed of 1.27 mm diameter hemispheres spaced in staggered arrays 2, 4, and 10 base diameters apart, respectively, on otherwise smooth walls. The current incompressible turbulent boundary-layer rough-wall air flow data are compared with previously published results on another, similar rough surface. It is shown that fully rough mean velocity profiles collapse together when scaled as a function of momentum thickness, as was reported previously. However, this similarity cannot be used to distinguish roughness flow regimes, since a similar degree of collapse is observed in the transitionally rough data. Observation of the new data shows that scaling on the momentum thickness alone is not sufficient to produce similar velocity profiles for flows over surfaces of different roughness character. The skin friction coefficient data versus the ratio of the momentum thickness to roughness height collapse within the data uncertainty, irrespective of roughness flow regime, with the data for each rough surface collapsing to a different curve. Calculations made using the previously published discrete element prediction method are compared with data from the rough surfaces with well-defined roughness elements, and it is shown that the calculations are in good agreement with the data.

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Veran, Stéphanie, Yvan Aspa i Michel Quintard. "Effective boundary conditions for rough reactive walls in laminar boundary layers". International Journal of Heat and Mass Transfer 52, nr 15-16 (lipiec 2009): 3712–25. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2009.01.045.

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Myrhaug, D. "Note on Water Drag on Sea Ice for Different Surface Roughness". Journal of Offshore Mechanics and Arctic Engineering 113, nr 1 (1.02.1991): 67–69. http://dx.doi.org/10.1115/1.2919898.

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The approach in Myrhaug [1], where a simple analytical theory describing the motion in a turbulent planetary boundary layer near a rough seabed was presented, is extended to smooth and transitional smooth-to-rough turbulent flow. An inverted boundary layer similar to that at the seabed is applicable under the sea ice. The water drag coefficient at the ice surface and the direction of the surface shear stress are presented for rough, smooth and transitional turbulent flows.

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Schaal, M., P. Lamparter i S. Steeb. "Fractal Behaviour of Amorphous Ni32Pd52P16 Studied by SANS". Zeitschrift für Naturforschung A 44, nr 1 (1.01.1989): 4–6. http://dx.doi.org/10.1515/zna-1989-0102.

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Abstract Small angle neutron scattering (SANS) was done with meltspun amorphous Ni32Pd52P16 in the as-quenched state as well as after annealing at 533 K, 570 K. and 607 K, 20 h each. The double logarithmic plot of the structure factor versus the momentum transfer shows linear behaviour with noninteger Porod-slopes. The results are interpreted with the scattering from fractally rough inner surfaces.The as-quenched state contains fluctuations of the scattering length density associated with smooth boundary interfaces. Annealing yields rough boundary interfaces, the roughness being largest after the 570 K annealing. Annealing at the higher temperature of 607 K yields less rough boundary interfaces.

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Taylor, Robert Ian. "Rough Surface Contact Modelling—A Review". Lubricants 10, nr 5 (13.05.2022): 98. http://dx.doi.org/10.3390/lubricants10050098.

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It has been shown experimentally that boundary friction is proportional to load (commonly known as Amontons’ law) for more than 500 years, and the fact that it holds true over many scales (from microns to kilometres, and from nano-Newtons to Mega-Newtons) and for materials which deform both elastically and plastically has been the subject of much research, in order to more fully understand its wide applicability (and also to find any deviations from the law). Attempts to explain and understand Amontons’ law recognise that real surfaces are rough; as such, many researchers have studied the contact of rough surfaces under both elastic and plastic deformation conditions. As the focus on energy efficiency is ever increasing, machines are now being used with lower-viscosity lubricants, operating at higher loads and temperatures, such that the oil films separating the moving surfaces are becoming thinner, and there is a greater chance of mixed/boundary lubrication occurring. Because mixed/boundary lubrication occurs when the two moving rough surfaces come into contact, it is thought timely to review this topic and the current state of the theoretical and experimental understanding of rough-surface contact for the prediction of friction in the mixed/boundary lubrication regime.

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Tomoya, Murakami, Mochizuki Shinsuke i Kameda Takatsugu. "1054 TURBULENT STRUCTURE IN A BOUNDARY LAYERE DEVELOPED OVER THREE-DIMENSIONAL ROUGH WALLS". Proceedings of the International Conference on Jets, Wakes and Separated Flows (ICJWSF) 2013.4 (2013): _1054–1_—_1054–6_. http://dx.doi.org/10.1299/jsmeicjwsf.2013.4._1054-1_.

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Li, Hong, Guo Yin Wang, Guang Lei Gou i Wen Liu. "Boundary Variable Precision Dominance-Based Rough Set Approach in Multicriteria Sorting Problems". Advanced Materials Research 734-737 (sierpień 2013): 3102–6. http://dx.doi.org/10.4028/www.scientific.net/amr.734-737.3102.

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This paper provides a novel method of boundary variable precision dominance-based rough set approach (BVP-DRSA) to solve multicriteria sorting problem that differs from usual classification problems since it takes into account preference orders in the description of objects by condition and decision attributes. The major contribution of our BVP-DRSA method is that it combines variable precision and dominance-based rough set approach (DRSA). This approach is different from the dominance-based rough set approach (DRSA) because it takes boundary into account and can deal with boundary directly. Comparative experiments form datasets of UCI and empirical results shows that our BVP-DRSA is far more efficient than directly using already known classing algorithms and DRSA.

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Meyers, Timothy, Jonathan B. Forest i William J. Devenport. "The wall-pressure spectrum of high-Reynolds-number turbulent boundary-layer flows over rough surfaces". Journal of Fluid Mechanics 768 (9.03.2015): 261–93. http://dx.doi.org/10.1017/jfm.2014.743.

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Experiments have been performed on a series of high-Reynolds-number flat-plate turbulent boundary layers formed over rough and smooth walls. The boundary layers were fully rough, yet the elements remained a very small fraction $({<}1.4\,\%)$ of the boundary-layer thickness, ensuring conditions free of transitional effects. The wall-pressure spectrum and its scaling were studied in detail. One of the major findings is that the rough-wall turbulent pressure spectrum at vehicle relevant conditions is comprised of three scaling regions. These include a newly discovered high-frequency region where the pressure spectrum has a viscous scaling controlled by the friction velocity, adjusted to exclude the pressure drag on the roughness elements.

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Wahed Khalifa, Hamiden Abd El, Dragan Pamucar, Amina Hadj Kacem i W. A. Afifi. "A Novel Approach for Characterizing Solutions of Rough Optimization Problems Based on Boundary Region". Computational Intelligence and Neuroscience 2022 (24.03.2022): 1–12. http://dx.doi.org/10.1155/2022/8662289.

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Rough set theory, presented by Pawlak in 1981, is one of the most well-known methods for communicating ambiguity by estimating an item based on some knowledge rather than membership. The concept of a rough function and its convexity and differentiability in regard to its boundary region are discussed in this work. The boundary notion is also used to present a new form of rough programming issue and its solutions. Finally, numerical examples are provided to demonstrate the proposed method and emphasize its advantages over other approaches.

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INUIGUCHI, MASAHIRO. "ATTRIBUTE REDUCTION IN VARIABLE PRECISION ROUGH SET MODEL". International Journal of Uncertainty, Fuzziness and Knowledge-Based Systems 14, nr 04 (sierpień 2006): 461–79. http://dx.doi.org/10.1142/s0218488506004126.

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In this paper, attribute reduction in variable precision rough set model is discussed. Several kinds of reducts preserving some of lower approximations, upper approximations, boundary regions and the unpredictable region are discussed. Relations among those kinds of reducts are investigated. As a basis for reduct computation, Boolean function representations of the preservation of lower approximations, upper approximations, boundary regions and the unpredictable region are discussed. Throughout this paper, the great difference between the analysis using variable precision rough sets and the classical rough set analysis is emphasized.

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Šimurda, David, Jindřich Hála, Martin Luxa i Tomáš Radnic. "Optical and Hot-Film Measurements of the Boundary Layer Transition on a Naca Airfoil". E3S Web of Conferences 345 (2022): 01011. http://dx.doi.org/10.1051/e3sconf/202234501011.

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This study explores the possibilities of identifying position of a boundary layer transition using hot film measurements complemented by classical optical methods i.e. interferometry and schlieren method. The subject of the measurement is a NACA 0010-64 airfoil with varying leading edge surface quality corresponding to smooth surface and rough surface with Ra ~ 50 and Ra ~ 100. Measurements are performed at several subsonic regimes and a transonic regime. Despite several shortcomings of the experimental setup, the method proved to be useful in providing information on the boundary layer transition. Measurements show that in the case of smooth leading edge, the onset of the boundary layer transition shifts upstream with increasing inlet Mach number and the major portion of the boundary layer is transitional. This is in accordance with other published results on the boundary layer transition on this kind of airfoils [1]. In all cases with the rough leading edge, the complete transition takes place on the rough portion of the surface already.

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NOTT, PRABHU R. "Boundary conditions at a rigid wall for rough granular gases". Journal of Fluid Mechanics 678 (18.04.2011): 179–202. http://dx.doi.org/10.1017/jfm.2011.105.

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We derive boundary conditions at a rigid wall for a granular material comprising rough, inelastic particles. Our analysis is confined to the rapid flow, or granular gas, regime in which grains interact by impulsive collisions. We use the Chapman–Enskog expansion in the kinetic theory of dense gases, extended for inelastic and rough particles, to determine the relevant fluxes to the wall. As in previous studies, we assume that the particles are spheres, and that the wall is corrugated by hemispheres rigidly attached to it. Collisions between the particles and the wall hemispheres are characterized by coefficients of restitution and roughness. We derive boundary conditions for the two limiting cases of nearly smooth and nearly perfectly rough spheres, as a hydrodynamic description of granular gases comprising rough spheres is appropriate only in these limits. The results are illustrated by applying the equations of motion and boundary conditions to the problem of plane Couette flow.

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SCHULTZ, M. P., i K. A. FLACK. "The rough-wall turbulent boundary layer from the hydraulically smooth to the fully rough regime". Journal of Fluid Mechanics 580 (21.05.2007): 381–405. http://dx.doi.org/10.1017/s0022112007005502.

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Turbulence measurements for rough-wall boundary layers are presented and compared to those for a smooth wall. The rough-wall experiments were made on a three-dimensional rough surface geometrically similar to the honed pipe roughness used by Shockling, Allen & Smits (J. Fluid Mech. vol. 564, 2006, p. 267). The present work covers a wide Reynolds-number range (Reθ = 2180–27 100), spanning the hydraulically smooth to the fully rough flow regimes for a single surface, while maintaining a roughness height that is a small fraction of the boundary-layer thickness. In this investigation, the root-mean-square roughness height was at least three orders of magnitude smaller than the boundary-layer thickness, and the Kármán number (δ+), typifying the ratio of the largest to the smallest turbulent scales in the flow, was as high as 10100. The mean velocity profiles for the rough and smooth walls show remarkable similarity in the outer layer using velocity-defect scaling. The Reynolds stresses and higher-order turbulence statistics also show excellent agreement in the outer layer. The results lend strong support to the concept of outer layer similarity for rough walls in which there is a large separation between the roughness length scale and the largest turbulence scales in the flow.

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Hosni, M. H., H. W. Coleman i R. P. Taylor. "Heat Transfer Measurements and Calculations in Transitionally Rough Flow". Journal of Turbomachinery 113, nr 3 (1.07.1991): 404–11. http://dx.doi.org/10.1115/1.2927889.

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Experimental data on a rough surface for both transitionally rough and fully rough turbulent flow regimes are presented for Stanton number distribution, skin friction coefficient distribution, and turbulence intensity profiles. The rough surface is composed of 1.27-mm-dia hemispheres spaced in a staggered array four base diameters apart on an otherwise smooth wall. Special emphasis is placed on the characteristics of heat transfer in the transitionally rough flows. Stanton number data are reported for zero pressure gradient incompressible turbulent boundary layer air flow for nominal free-stream velocities of 6, 12, 28, 43, 58, and 67 m/s, which give x-Reynolds numbers up to 10,000,000. These data are compared with previously published rough surface data, and the classification of a boundary layer flow into transitionally rough and fully rough regimes is explored. Moreover, a new heat transfer model for use in the previously published discrete element prediction approach is presented. Computations using the discrete element model are presented and compared with data obtained from two different rough surfaces. The discrete element predictions for both surfaces are found to be in substantial agreement with the data.

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Hsu, John R. C. "ROUGH TURBULENT BOUNDARY LAYER IN SHORT-CRESTED WAVES". Coastal Engineering Proceedings 1, nr 20 (29.01.1986): 21. http://dx.doi.org/10.9753/icce.v20.21.

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Prior to the investigation of rough turbulent boundary layer in a short-crested wave, the oscillatory laminar boundary layer at the bed is considered. Supported by numerical results of water-particle motions close to the bottom, the general patterns of kinematics in the laminar boundary layer within this wave system are reported in order to promote the understanding of the complex phenomenon. To propose a suitable method for turbulent boundary layer within such a wave system, a two-layer model using time-independent viscosity coefficient is first studied. Potential application of this model to short-crested waves is considered. From numerical results it is found that the time-invariant viscosity model is useful but can not produce velocity profile with flow reversal. It is suggested that a time-varying viscosity model may be more appropriate.

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Mocenni, C., E. Sparacino i J. P. Zubelli. "Effective rough boundary parametrization for reaction-diffusion systems". Applicable Analysis and Discrete Mathematics 8, nr 1 (2014): 33–59. http://dx.doi.org/10.2298/aadm140126002m.

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We address the problem of parametrizing the boundary data for reaction- diffusion partial differential equations associated to distributed systems that possess rough boundaries. The boundaries are modeled as fast oscillating periodic structures and are endowed with Neumann or Dirichlet boundary conditions. Using techniques from homogenization theory and multiple-scale analysis we derive the effective equation and boundary conditions that are satisfied by the homogenized solution. We present numerical simulations that validate our theoretical results and compare it with the alternative approach based on solving the same equation with a smoothed version of the boundary. The numerical tests show the accuracy of the homogenized solution to the effective system vis a vis the numerical solution of the original differential equation. The homogenized solution is shown undergoing dynamical regime shifts, such as anticipation of pattern formation, obtained by varying the diffusion coefficient.

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Jensen, B. L., B. M. Sumer i J. Fredsøe. "Turbulent oscillatory boundary layers at high Reynolds numbers". Journal of Fluid Mechanics 206 (wrzesień 1989): 265–97. http://dx.doi.org/10.1017/s0022112089002302.

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This study deals with turbulent oscillatory boundary-layer flows over both smooth and rough beds. The free-stream flow is a purely oscillating flow with sinusoidal velocity variation. Mean and turbulence properties were measured mainly in two directions, namely in the streamwise direction and in the direction perpendicular to the bed. Some measurements were made also in the transverse direction. The measurements were carried out up to Re = 6 × 106 over a mirror-shine smooth bed and over rough beds with various values of the parameter a/ks covering the range from approximately 400 to 3700, a being the amplitude of the oscillatory free-stream flow and ks the Nikuradse's equivalent sand roughness. For smooth-bed boundary-layer flows, the effect of Re is discussed in greater detail. It is demonstrated that the boundary-layer properties change markedly with Re. For rough-bed boundary-layer flows, the effect of the parameter a/ks is examined, at large values (O(103)) in combination with large Re.

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Wu, Yang, Zhilu Liu, Yongmin Liang, Xiaowei Pei, Feng Zhou i Queji Xue. "Photoresponsive superhydrophobic coating for regulating boundary slippage". Soft Matter 10, nr 29 (2014): 5318–24. http://dx.doi.org/10.1039/c4sm00799a.

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Bergstrom, D. J., O. G. Akinlade i M. F. Tachie. "Skin Friction Correlation for Smooth and Rough Wall Turbulent Boundary Layers". Journal of Fluids Engineering 127, nr 6 (28.04.2005): 1146–53. http://dx.doi.org/10.1115/1.2073288.

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In this paper, we propose a novel skin friction correlation for a zero pressure gradient turbulent boundary layer over surfaces with different roughness characteristics. The experimental data sets were obtained on a hydraulically smooth and ten different rough surfaces created from sand paper, perforated sheet, and woven wire mesh. The physical size and geometry of the roughness elements and freestream velocity were chosen to encompass both transitionally rough and fully rough flow regimes. The flow Reynolds number based on momentum thickness ranged from 3730 to 13,550. We propose a correlation that relates the skin friction, Cf, to the ratio of the displacement and boundary layer thicknesses, δ*∕δ, which is valid for both smooth and rough wall flows. The results indicate that the ratio Cf1∕2∕(δ*∕δ) is approximately constant, irrespective of the Reynolds number and surface condition.

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Ali, Sk Zeeshan, i Subhasish Dey. "Origin of the scaling laws of developing turbulent boundary layers". Physics of Fluids 34, nr 7 (lipiec 2022): 071402. http://dx.doi.org/10.1063/5.0096255.

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In this Perspective article, we seek the origin of the scaling laws of developing turbulent boundary layers over a flat plate from the perspective of the phenomenological theory of turbulence. The scaling laws of the boundary-layer thickness and the boundary shear stress in rough and smooth boundary-layer flows are established. In a rough boundary-layer flow, the boundary-layer thickness (scaled with the boundary roughness) and the boundary shear stress (scaled with the dynamic pressure) obey the “2/(1− σ)” and “(1+ σ)/(1− σ)” scaling laws, respectively, with the streamwise distance (scaled with the boundary roughness). Here, σ is the spectral exponent. In a smooth boundary-layer flow, the boundary-layer thickness (scaled with the viscous length scale) and the boundary shear stress (scaled with the dynamic pressure) obey the “8/(5 − 3 σ)” and “3(1+ σ)/(5 − 3 σ)” scaling laws, respectively, with the Reynolds number characterized by the streamwise distance.

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Hosni, M. H., H. W. Coleman i Robert P. Taylor. "Rough-Wall Heat Transfer in Tbrbulent Boundary Layers". International Journal of Fluid Mechanics Research 25, nr 1-3 (1998): 212–19. http://dx.doi.org/10.1615/interjfluidmechres.v25.i1-3.180.

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Alexander, W. Nathan, William J. Devenport i Stewart A. L. Glegg. "Predictions of Sound from Rough Wall Boundary Layers". AIAA Journal 51, nr 2 (luty 2013): 465–75. http://dx.doi.org/10.2514/1.j051840.

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Wang, Lu. "Harmonic map heat flow with rough boundary data". Transactions of the American Mathematical Society 364, nr 10 (1.10.2012): 5265–83. http://dx.doi.org/10.1090/s0002-9947-2012-05473-0.

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Smalley, R. J., R. A. Antonia i L. Djenidi. "Self-preservation of rough-wall turbulent boundary layers". European Journal of Mechanics - B/Fluids 20, nr 5 (wrzesień 2001): 591–602. http://dx.doi.org/10.1016/s0997-7546(01)01152-9.

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CAL, RAÚL BAYOÁN, BRIAN BRZEK, T. GUNNAR JOHANSSON i LUCIANO CASTILLO. "The rough favourable pressure gradient turbulent boundary layer". Journal of Fluid Mechanics 641 (25.11.2009): 129–55. http://dx.doi.org/10.1017/s0022112009991352.

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Laser Doppler anemometry measurements of the mean velocity and Reynolds stresses are carried out for a rough-surface favourable pressure gradient turbulent boundary layer. The experimental data is compared with smooth favourable pressure gradient and rough zero-pressure gradient data. The velocity and Reynolds stress profiles are normalized using various scalings such as the friction velocity and free stream velocity. In the velocity profiles, the effects of roughness are removed when using the friction velocity. The effects of pressure gradient are not absorbed. When using the free stream velocity, the scaling is more effective absorbing the pressure gradient effects. However, the effects of roughness are almost removed, while the effects of pressure gradient are still observed on the outer flow, when the mean deficit velocity profiles are normalized by the U∞ δ∗/δ scaling. Furthermore, when scaled with U2∞, the 〈u2〉 component of the Reynolds stress augments due to the rough surface despite the imposed favourable pressure gradient; when using the friction velocity scaling u∗2, it is dampened. It becomes ‘flatter’ in the inner region mainly due to the rough surface, which destroys the coherent structures of the flow and promotes isotropy. Similarly, the pressure gradient imposed on the flow decreases the magnitude of the Reynolds stress profiles especially on the 〈v2〉 and -〈uv〉 components for the u∗2 or U∞2 scaling. These effects are reflected in the boundary layer parameter δ∗/δ, which increase due to roughness, but decrease due to the favourable pressure gradient. Additionally, the pressure parameter Λ found not to be in equilibrium, describes the development of the turbulent boundary layer, with no influence of the roughness linked to this parameter. These measurements are the first with an extensive number of downstream locations (11). This makes it possible to compute the required x-dependence for the production term and the wall shear stress from the full integrated boundary layer equation. The finding indicates that the skin friction coefficient depends on the favourable pressure gradient condition and surface roughness.

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