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Combined Effect of Surface Roughness and Slip Velocity on Jenkins Model Based Magnetic Squeeze Film in Curved Rough Circular Plates  [PDF]
Jimit R. Patel,Gunamani Deheri
International Journal of Computational Mathematics , 2014, DOI: 10.1155/2014/367618
Abstract: This paper aims to discuss the effect of slip velocity and surface roughness on the performance of Jenkins model based magnetic squeeze film in curved rough circular plates. The upper plate’s curvature parameter is governed by an exponential expression while a hyperbolic form describes the curvature of lower plates. The stochastic model of Christensen and Tonder has been adopted to study the effect of transverse surface roughness of the bearing surfaces. Beavers and Joseph’s slip model has been employed here. The associated Reynolds type equation is solved to obtain the pressure distribution culminating in the calculation of load carrying capacity. The computed results show that the Jenkins model modifies the performance of the bearing system as compared to Neuringer-Rosensweig model, but this model provides little support to the negatively skewed roughness for overcoming the adverse effect of standard deviation and slip velocity even if curvature parameters are suitably chosen. This study establishes that for any type of improvement in the performance characteristics the slip parameter is required to be reduced even if variance (?ve) occurs and suitable magnetic strength is in force. 1. Introduction Nowadays, magnetohydrodynamic flow of a fluid in squeeze film lubrication is of interest, because it prevents the unexpected variation of lubricant viscosity with temperature under various operating conditions. The effects of magnetic fluid in squeeze film lubrication have been encouraging because magnetic fluid has important applications in the industry with obvious relevance to technology-based world. Owing to the development of modern technology, the increasing use of magnetic fluids as lubricants has been highlighted. Magnetic fluids can be controlled and located at some preferred places in the presence of an external magnetic field. Because of these prominent phenomena, ferrofluids are widely used in different fields of sciences and technology, for instance, dampers, seals, sensors, loudspeakers, steppers and coating systems, ink-jet printing, and filtering. Neuringer and Rosensweig [1] proposed a simple flow model to describe the steady flow of magnetic fluids in the presence of slowly changing external magnetic fields. Numerous papers are available in the literature for the study of different types of bearing using Neuringer and Rosensweig flow model, for example, Tipei [2] in short bearing, Agrawal [3] and Shah and Bhat [4] in slider bearing, journal bearing by Nada and Osman [5] and Patel el al. [6], and circular plates by Shah and Bhat [7] and
Modeling the combined effect of surface roughness and shear rate on slip flow of simple fluids  [PDF]
Anoosheh Niavarani,Nikolai V. Priezjev
Physics , 2009, DOI: 10.1103/PhysRevE.81.011606
Abstract: Molecular dynamics (MD) and continuum simulations are carried out to investigate the influence of shear rate and surface roughness on slip flow of a Newtonian fluid. For weak wall-fluid interaction energy, the nonlinear shear-rate dependence of the intrinsic slip length in the flow over an atomically flat surface is computed by MD simulations. We describe laminar flow away from a curved boundary by means of the effective slip length defined with respect to the mean height of the surface roughness. Both the magnitude of the effective slip length and the slope of its rate-dependence are significantly reduced in the presence of periodic surface roughness. We then numerically solve the Navier-Stokes equation for the flow over the rough surface using the rate-dependent intrinsic slip length as a local boundary condition. Continuum simulations reproduce the behavior of the effective slip length obtained from MD simulations at low shear rates. The slight discrepancy between MD and continuum results at high shear rates is explained by examination of the local velocity profiles and the pressure distribution along the wavy surface. We found that in the region where the curved boundary faces the mainstream flow, the local slip is suppressed due to the increase in pressure. The results of the comparative analysis can potentially lead to the development of an efficient algorithm for modeling rate-dependent slip flows over rough surfaces.
QUARRY STABILITY ANALYSIS FOR COMPLEX SLIP SURFACES USING THE MATHSLOPE METHOD  [PDF]
Petar Hr?enjak
Rudarsko-Geolo?ko-Naftni Zbornik , 2004,
Abstract: Due to the specific characteristics of rock mass compared to other geological materials, the calculation of rock slope stability is very complex. One of the basic characteristics of rock masses is discontinuity, which, to the most degree, is formed by the geological structure and its elements. Because of discontinuities the slip surfaces of complex shapes are formed in rock slopes, mostly of straight and curved segments.The calculation of the stability factor of rock slopes for complex shapes of slip surfaces has been made possible by the development of the MathSlope method. The complex shape of slip surface has been achieved by introduction of planes of discontinuities in the slip surface. Thus, the setting up and searching procedure of critical slip surfaces of complex shapes is very different in the MathSlope method than in other ones.The example of back analysis for the quarry Vukov Dol shows the successfulness in determining the critical slip surface, as well as the calculation factor of stability for the complex shape of slip surface. Apart from calculating the factor of stability for the complex slip surface, the solution for the position of discontinuity on the slope is obtained, which matches with the real position on the quarry.
Chaotic mixing in a planar, curved channel using periodic slip  [PDF]
P. Garg,J. R. Picardo,S. Pushpavanam
Physics , 2014, DOI: 10.1063/1.4915902
Abstract: We propose a novel strategy for designing chaotic micromixers using curved channels confined between two flat planes. The location of the separatrix between the Dean vortices, induced by centrifugal force, is dependent on the location of the maxima of axial velocity. An asymmetry in the axial velocity profile can change the location of the separatrix. This is achieved physically by introducing slip alternatingly at the top and bottom walls. This leads to streamline crossing and Lagrangian chaos. An approximate analytical solution of the velocity field is obtained using perturbation theory. This is used to find the Lagrangian trajectories of fluid particles. Poincare sections taken at periodic locations in the axial direction are used to study the extent of chaos. The extent of mixing, for low slip and low Reynolds numbers, is shown to be greater when Dean vortices in adjacent half cells are counter-rotating. Wide channels are observed to have much better mixing than tall channels; an important observation not made for separatrix flows till now. Eulerian indicators are used to gauge the extent of mixing with varying slip length and it is shown that an optimum slip length exists which maximizes the mixing in a particular geometry.
Effects of Velocity-Slip and Viscosity Variation in Squeeze Film Lubrication of Two Circular Plates
R.R. Rao,K. Gouthami,J.V. Kumar
Tribology in Industry , 2013,
Abstract: A generalized form of Reynolds equation for two symmetrical surfaces is taken by considering velocity-slip at the bearing surfaces. This equation is applied to study the effects of velocity-slip and viscosity variation for the lubrication of squeeze films between two circular plates. Expressions for the load capacity and squeezing time obtained are also studied theoretically for various parameters. The load capacity and squeezing time decreases due to slip. They increase due to the presence of high viscous layer near the surface and decrease due to low viscous layer.
Effective velocity boundary condition at a mixed slip surface  [PDF]
M. Sbragaglia,A. Prosperetti
Physics , 2006, DOI: 10.1017/S0022112007005149
Abstract: This paper studies the nature of the effective velocity boundary conditions for liquid flow over a plane boundary on which small free-slip islands are randomly distributed. It is found that, to lowest order in the area fraction $\beta$ covered by free-slip regions with characteristic size $a$, a macroscopic Navier-type slip condition emerges with a slip length of the order of $a\beta$. The study is motivated by recent experiments which suggest that gas nano-bubbles may form on solid walls and may be responsible for the appearance of a partial slip boundary conditions for liquid flow. The results are also relevant for ultra-hydrophobic surfaces exploiting the so-called ``lotus effect''.
Effective slip boundary conditions for arbitrary periodic surfaces: The surface mobility tensor  [PDF]
Ken Kamrin,Martin Z. Bazant,Howard A. Stone
Physics , 2009, DOI: 10.1017/S0022112010001801
Abstract: In a variety of applications, most notably microfluidic design, slip-based boundary conditions have been sought to characterize fluid flow over patterned surfaces. We focus on laminar shear flows over surfaces with periodic height fluctuations and/or fluctuating Navier scalar slip properties. We derive a general formula for the "effective slip", which describes equivalent fluid motion at the mean surface as depicted by the linear velocity profile that arises far from it. We show that the slip and the applied stress are related linearly through a tensorial mobility matrix, and the method of domain perturbation is then used to derive an approximate formula for the mobility law directly in terms of surface properties. The specific accuracy of the approximation is detailed, and the mobility relation is then utilized to address several questions, such as the determination of optimal surface shapes and the effect of random surface fluctuations on fluid slip.
Curved Flats and Isothermic Surfaces  [PDF]
F. Burstall,U. Hertrich-Jeromin,F. Pedit,U. Pinkall
Mathematics , 1994,
Abstract: We show how pairs of isothermic surfaces are given by curved flats in a pseudo Riemannian symmetric space and vice versa. Calapso's fourth order partial differential equation is derived and, using a solution of this equation, a M\"obius invariant frame for an isothermic surface is built.
Anisotropic Diffusion on Curved Surfaces  [PDF]
Emma Naden,Thomas M?rz,Colin B. Macdonald
Mathematics , 2014,
Abstract: We demonstrate a method for filtering images defined on curved surfaces embedded in 3D. Applications are noise removal and the creation of artistic effects. Our approach relies on in-surface diffusion: we formulate Weickert's edge/coherence enhancing diffusion models in a surface-intrinsic way. These diffusion processes are anisotropic and the equations depend non-linearly on the data. The surface-intrinsic equations are dealt with the closest point method, a technique for solving partial differential equations (PDEs) on general surfaces. The resulting algorithm has a very simple structure: we merely alternate a time step of a 3D analog of the in-surface PDE in a narrow 3D band containing the surface with a reconstruction of the surface function. Surfaces are represented by a closest point function. This representation is flexible and the method can treat very general surfaces. Experimental results include image filtering on smooth surfaces, open surfaces, and general triangulated surfaces.
Spaces of nonnegatively curved surfaces  [PDF]
Taras Banakh,Igor Belegradek
Mathematics , 2015,
Abstract: We determine the homeomorphism type of the space of smooth complete nonnegatively curved metrics on surfaces of positive Euler characteristic equipped with the topology of $C^\gamma$ uniform convergence on compact sets, when $\gamma$ is infinite or is not an integer. If $\gamma=\infty$, the space of metrics is homeomorphic to the separable Hilbert space. If $\gamma$ is finite and not an integer, the space of metrics is homeomorphic to the countable power of the linear span of the Hilbert cube. We also prove similar results for some other spaces of metrics including the space of complete smooth Riemannian metrics on an arbitrary manifold.
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