Showing papers on "Slip ratio published in 2010"
TL;DR: In this paper, slow slip events in subduction zones were modeled with 2-dimensional elasticity, rate-state friction, and a dilatancy law where porosity evolves toward steady state ss over distance dc and ss = 0 + ln(v/v0); v is slip speed.
Abstract: [1] The mechanics of slow slip events (SSE) in subduction zones remain unresolved. We suggest that SSE nucleate in areas of unstable friction under drained conditions, but as slip accelerates dilatancy reduces pore pressure p quenching instability. Competition between dilatant strengthening and thermal pressurization may control whether slip is slow or fast. We model SSE with 2-D elasticity, rate-state friction, and a dilatancy law where porosity evolves toward steady state ss over distance dc and ss = 0 + ln(v/v0); v is slip speed. We consider two diffusion models. Membrane diffusion (MD) is approximated by −(p − p∞)/tf where p and p∞ are shear zone and remote pore pressure and tf is a characteristic diffusion time. Homogeneous diffusion (HD) accurately models fault-normal flow with diffusivity chyd. For MD, linearized analysis defines a boundary ℰ = 1 − a/b between slow and fast slip, where ℰ ≡ f0e/βb(σ − p∞), f0, a, and b are friction parameters and β is compressibility. When ℰ 1 − a/b slip speeds remain quasi-static. For HD, Ep ≡ eh/(β (σ − p∞)) defines dilatancy efficiency, where h is shear zone thickness and v∞ is plate velocity. SSE are favored by large eh and low effective stress. The ratio Ep to thermal pressurization efficiency scales with 1/(σ − p∞), so high p∞ favors SSE, consistent with seismic observations. For Ep ∼ 10−3 transient slip rates, repeat times, average slip, and stress drops are comparable to field observations. Model updip propagation speeds are comparable to those observed along-strike. Many simulations exhibit slow phases driven by steady downdip slip and faster phases that relax the accumulated stress. Model SSE accommodate only a fraction of plate motion; the remaining deficit must be accommodated during coseismic or postseismic slip.
309 citations
TL;DR: In this paper, the authors proposed a second order slip flow model to predict viscous flow over a shrinking sheet, and the closed solution is an exact solution of the full governing Navier-Stokes equations.
260 citations
TL;DR: In this article, high-velocity friction tests were conducted on solid and hollow cylinders of Carrara marble, dolomite marble, silicate-bearing calcite marble and calcite gouge to investigate the strength of carbonate faults during seismic slip.
Abstract: [1] High-velocity friction tests were conducted on solid and hollow cylinders of Carrara (calcite) marble, dolomite marble, silicate-bearing calcite marble, and calcite gouge to investigate the strength of carbonate faults during seismic slip. The experiments, performed at normal stresses of 0.6–14.7 MPa, slip rates of 0.03–1.60 m/s, and room temperature in a rotary-shear friction testing machine, yielded an extraordinarily low steady state friction coefficient (<0.1) at slip rates of ∼1.1–1.2 m/s. The slip-weakening distance of 4–28 m became shorter at higher normal stress or frictional work rate. Strong velocity weakening was observed not only in steady state but also in nonsteady state friction, while the slip rate was changing; thus slip deceleration was accompanied by fault strength recovery. Large, rapid temperature rises in narrow shear localization zones (less than a few micrometers) induced carbonate decomposition, such as the breakdown of calcite into aggregates of CaO nanograins and CO2 in Carrara marble. Scanning electron microscope observation revealed that the shear localization zone in the highly porous decomposition product was a layer of scattered small grains (mostly <1 μm in diameter). These microstructures and the measured high permeability (∼10−14 m2) of the decomposed marble indicate that the dominant weakening mechanism in our experiments was possibly powder lubrication. Powder rheology at high slip rates is not yet well understood, but the frictional behavior of nanograins appears to be strongly velocity dependent. If decarbonation occurs during seismic slip in natural carbonate faults, powder lubrication may make the faults slippery even under fluid-drained conditions.
197 citations
TL;DR: In this paper, the authors studied the effect of micropolar fluid material parameters on the distribution of velocity, micro-rotation velocity and temperature fields for varying physical parameters such as the ratio of Grashof number to Reynolds number, viscosity ratio, width ratio, conductivity ratio and micropolastic fluid material parameter.
156 citations
TL;DR: In this paper, the boundary layer flow over a flat plat with slip flow and constant heat flux surface condition is studied, where the momentum and energy equations are coupled due to the presence of the temperature gradient along the plate surface.
149 citations
TL;DR: The paper develops a self-tuning PID control scheme with an application to ABS via combinations of fuzzy and genetic algorithms (GAs) to minimize the stopping distance, while keeping the slip ratio of the tires within desired range.
125 citations
TL;DR: In this article, the effects of interface curvature on the effective slip length are quantified for different shear-free fractions and groove-rib spatial periods normalized using the channel height.
Abstract: This article considers Couette and Poiseuille flows past superhydrophobic surfaces containing alternating micro-grooves and ribs aligned longitudinally to the flow. The effects of interface curvature on the effective slip length are quantified for different shear-free fractions and groove–rib spatial periods normalized using the channel height. The numerical results obtained demonstrate the importance of considering interface curvature effects in ascertaining the effective slip length. The effective slip length and performance of longitudinal grooves are compared with those corresponding to transverse grooves, for which analytical results are available for small shear-free fractions and normalized groove–rib periodic spacing. For the same shear-free fraction and interface protrusion angle, the effective slip length corresponding to the Poiseuille flow is found to be strongly affected by the normalized groove–rib spacing, in contrast to the Couette flow. For the Poiseuille flow, when the interface deforms by large protrusion angles into the liquid phase, the effective slip length approaches zero or becomes negative for large values of shear-free fraction and normalized groove–rib spacing due to significant flow blockage effects.
114 citations
TL;DR: In this paper, a gas-liquid two-phase flow in a microfluidic T-junction with nearly square microchannels of 113μm hydraulic diameter was investigated experimentally and numerically.
113 citations
TL;DR: In this article, the shape, size, velocity and acceleration of bubbles were measured using shadowgraphy, and liquid velocity measurement obtained using PIV/LIF with fluorescent tracer particles.
95 citations
TL;DR: In this article, the entrained flow and heat transfer of a non-Newtonian third grade fluid due to a linearly stretching surface with partial slip is considered, and a second order numerical scheme has been adopted to solve the obtained differential equations even without augmenting any extra boundary conditions.
81 citations
TL;DR: Wang et al. as discussed by the authors investigated wheel slip-sinkage problem, which is important for the design, control and simulation of lunar rovers, and experiments were carried out with a wheel-soil interaction test system to measure the sinkage of three types of wheels in dimension with wheel lugs of different heights and numbers under a series of slip ratios (0−0.6).
Abstract: In order to investigate wheel slip-sinkage problem, which is important for the design, control and simulation of lunar rovers, experiments were carried out with a wheel-soil interaction test system to measure the sinkage of three types of wheels in dimension with wheel lugs of different heights and numbers under a series of slip ratios (0−0.6). The curves of wheel sinkage versus slip ratio were obtained and it was found that the sinkage with slip ratio of 0.6 is 3−7 times of the static sinkage. Based on the experimental results, the slip-sinkage principle of lunar's rover lugged wheels (including the sinkage caused by longitudinal flow and side flow of soil, and soil digging of wheel lugs) was analyzed, and corresponding calculation equations were derived. All the factors that can cause slip sinkage were considered to improve the conventional wheel-soil interaction model, and a formula of changing the sinkage exponent with the slip ratio was established. Mathematical model for calculating the sinkage of wheel according to vertical load and slip ratio was developed. Calculation results show that this model can predict the slip-sinkage of wheel with high precision, making up the deficiency of Wong-Reece model that mainly reflects longitudinal slip-sinkage.
TL;DR: In this article, slip and heat transfer effects on peristaltic flow in an asymmetric channel have been examined and closed form solutions of momentum and energy equations are obtained for long wavelength and low Reynolds number approximations.
TL;DR: In this paper, the entrained flow and heat transfer of an electrically conducting non-Newtonian fluid due to a stretching surface subject to partial slip is considered, where the partial slip was controlled by a dimensionless slip factor, which varies between zero (total adhesion) and infinity (full slip).
TL;DR: In this paper, a model is proposed to predict the friction factor and Reynolds product f Re for developing slip flow and continuum flow in most noncircular microchannels, which has an approximate accuracy of 10% for most common duct shapes.
Abstract: Microscale fluid dynamics has received intensive interest due to the emergence of microelectro-mechanical systems (MEMS) technology. When the mean free path of the gas is comparable to the channel’s characteristic dimension, the continuum assumption is no longer valid and a velocity slip may occur at the duct walls. Noncircular cross sections are common channel shapes that can be produced by microfabrication. The noncircular microchannels have extensive practical applications in MEMS. The paper deals with issues of hydrodynamic flow development. Slip flow in the entrance of circular and parallel plate microchannels is first considered by solving a linearized momentum equation. It is found that slip flow is less sensitive to analytical linearized approximations than continuum flow and the linearization method is an accurate approximation for slip flow. Also, it is found that the entrance friction factor Reynolds product is of finite value and dependent on the Kn and tangential momentum accommodation coefficient but independent of the cross-sectional geometry. Slip flow and continuum flow in the hydrodynamic entrance of noncircular microchannels has been examined and a model is proposed to predict the friction factor and Reynolds product f Re for developing slip flow and continuum flow in most noncircular microchannels. It is shown that the complete problem may be easily analyzed by combining the asymptotic results for short and long ducts. Through the selection of a characteristic length scale, the square root of cross-sectional area, the effect of duct shape has been minimized. The proposed model has an approximate accuracy of 10% for most common duct shapes. ! DOI: 10.1115/1.4000692"
TL;DR: The results suggest that the amount of slip produced as a function of stiffness follows a common pattern that can be modeled through a fifth-order polynomial function.
Abstract: The paper investigates the effects of surface stiffness on the slip process aiming to obtain a better insight of the momentum transfer at nanoscale. The surface stiffness is modeled through the stiffness, κ, of spring potentials, which are employed to construct the thermal walls. It is shown that variations of stiffness, κ, influence the slip mechanism either toward slip or stick conditions. Increasing the values of κ alters the oscillation frequency and the mean displacement of the wall particles toward higher and lower values, respectively. Our results suggest that the amount of slip produced as a function of stiffness follows a common pattern that can be modeled through a fifth-order polynomial function.
TL;DR: This work describes 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, and finds that in the region where the curved boundary faces the mainstream flow, the local slip is suppressed due to the increase in pressure.
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.
TL;DR: A sliding-mode control is designed based on the slip ratio, yaw rate, and lateral acceleration of the vehicle to reduce the motor torque at each wheel to improve vehicle performance.
Abstract: A control algorithm is proposed for an independent motor-drive vehicle. A sliding-mode control is designed based on the slip ratio, yaw rate, and lateral acceleration of the vehicle to reduce the motor torque at each wheel. The performance of the control algorithm is evaluated by MATLAB/Simulink-CarSim cosimulation and experiments. A test car with two independent drive motors at the rear wheels is developed. From the simulation and vehicle test, it is found that the control algorithm improves vehicle performance.
TL;DR: In this article, viscous flow with a second-order slip condition over a permeable stretching surface is solved analytically, and the closed form solution reported is an exact solution of the full governing Navier-Stokes equations.
Abstract: In this paper, viscous flow with a second-order slip condition over a permeable stretching surface is solved analytically. The current work differs from the previous studies in the application of a new second-order slip velocity model. The closed form solution reported is an exact solution of the full governing Navier-Stokes equations. The effects of slip and mass transfer parameters are discussed.
TL;DR: In this article, the physical reason of the inclusion of the shear work in the heat balance equation is physically explained from the point of view of both conservation law of energy and the kinetic theory of gases.
TL;DR: In this paper, the effect of the partial slip, magnetic interaction parameter and second-grade fluid parameter on the velocity and temperature fields was investigated and it was found that the slip increases the momentum and thermal boundary layer thickness.
Abstract: The flow and heat transfer of an electrically conducting non-Newtonian second grade fluid due to a radially stretching surface with partial slip is considered. The partial slip is controlled by a dimensionless slip factor, which varies between zero (total adhesion) and infinity (full slip). Suitable similarity transformations are used to reduce the resulting highly nonlinear partial differential equations into ordinary differential equations. The issue of paucity of boundary conditions is addressed and an effective numerical scheme is adopted to solve the obtained differential equations even without augmenting any extra boundary conditions. The important findings in this communication are the combined effects of the partial slip, magnetic interaction parameter and the second grade fluid parameter on the velocity and temperature fields. It is interesting to find that the slip increases the momentum and thermal boundary layer thickness. As the slip increases in magnitude, permitting more fluid to slip past the sheet, the skin friction coefficient decreases in magnitude and approaches zero for higher values of the slip parameter, i.e., the fluid behaves as though it were inviscid. The presence of a magnetic field has also substantial effects on velocity and temperature fields.
TL;DR: In this paper, the steady two-dimensional magnetohydrodynamic stagnation flow towards a nonlinear stretching surface is studied, where the no-slip condition on the solid boundary is replaced with a partial slip condition.
Abstract: The steady two-dimensional magnetohydrodynamic stagnation flow towards a nonlinear stretching surface is studied. The no-slip condition on the solid boundary is replaced with a partial slip condition. A scaling group transformation is used to get the invariants. Using the invariants, a third-order ordinary differential equation corresponding to the momentum is obtained. An analytical solution is obtained in a series form using a homotopy analysis method. Reliability and efficiency of series solutions are shown by the good agreement with numerical results presented in the literature. The effects of the slip parameter, the magnetic field parameter, the velocity ratio parameter, the suction velocity parameter, and the power law exponent on the flow are investigated. The results show that the velocity and shear stress profiles are greatly influenced by these parameters.
TL;DR: In this paper, the authors compare the slip lengths predicted by a liquid-gas coupled model and that by an idealized zero-gas-shear model, where the velocities are analytically expressed in terms of eigenfunction series expansions.
Abstract: Comparisons between slip lengths predicted by a liquid-gas coupled model and that by an idealized zero-gas-shear model are presented in this paper. The problem under consideration is pressure-driven flow of a liquid through a plane channel bounded by two superhydrophobic walls which are patterned with longitudinal or transverse gas-filled grooves. Effective slip arises from lubrication on the liquid-gas interface and intrinsic slippage on the solid phase of the wall. In the mathematical models, the velocities are analytically expressed in terms of eigenfunction series expansions, where the unknown coefficients are determined by the matching of velocities and shear stresses on the liquid-gas interface. Results are generated to show the effects due to small but finite gas viscosity on the effective slip lengths as functions of the channel height, the depth of grooves, the gas area fraction of the wall, and intrinsic slippage of the solid phase. Conditions under which even a gas/liquid viscosity ratio as small as 0.01 may have appreciable effects on the slip lengths are discussed.
TL;DR: In this article, the phase distribution of a gas-liquid flow through a 1mm T junction has been studied and it was found that pressure has no influence in the phase split when it was increased from 0.13 to 0.18 MPa.
TL;DR: In this article, the slip lengths for four different aqueous monovalent electrolyte solutions through naturally hydrophilic and hydrophobically coated fused-silica channels with a depth of 33 μm were estimated using a local method based on a new particle velocimetry technique.
Abstract: Various studies have suggested that the no-slip condition may not hold for Newtonian liquids flowing over (for the most part) non-wetting surfaces. This paper describes an experimental study of steady Poiseuille flow at various Reynolds numbers up to 0.12 of four different aqueous monovalent electrolyte solutions through naturally hydrophilic and hydrophobically coated fused-silica channels with a depth of 33 μm. The slip lengths for these flows were estimated using a local method based on a new particle velocimetry technique that determines velocities at three different wall-normal distances within the first 400 nm next to the wall. These results are corrected using direct measurements of the near-wall particle distribution, which is highly non-uniform as expected due to repulsive electric double-layer interactions between the 100 nm tracer particles and the wall. In all cases, the slip lengths were not more than 23 nm and for all but one case, zero within their uncertainties. As illustrated here, the standard assumption of uniformly distributed tracers can significantly increase slip length estimates obtained using local methods and near-wall velocity data.
TL;DR: By comparing the velocity profiles of Poiseuille flows predicted from the Navier-Stokes equations with the corrected slip boundary condition with that from molecular-dynamics simulations, it is found that the flow behaviors in the models can be effectively captured.
Abstract: A corrected second-order slip boundary condition is proposed to solve the Navier-Stokes equations for fluid flows confined in parallel-plate nanochannels. Compared with the classical second-order slip boundary condition proposed by Beskok and Karniadakis, the corrected slip boundary condition is not only dependent on the Knudsen number and the tangential momentum accommodation coefficient, but also dependent on the relative position of the slip surface in the Knudsen layer. For the fluid flows in slip-flow regime with the Knudsen number less than 0.3, Couette cell is investigated using molecular-dynamics simulations to verify Newtonian flow behaviors by examining the constitutive relationship between shear stress and strain rate. By comparing the velocity profiles of Poiseuille flows predicted from the Navier-Stokes equations with the corrected slip boundary condition with that from molecular-dynamics simulations, it is found that the flow behaviors in our models can be effectively captured.
TL;DR: It is demonstrated numerically that the friction coefficient at the liquid-solid interface (the ratio of viscosity and slip length) undergoes a transition from a constant value to the power-law decay as a function of the slip velocity.
Abstract: The molecular mechanism of slip at the interface between polymer melts and weakly attractive smooth surfaces is investigated using molecular dynamics simulations. In agreement with our previous studies on slip flow of shear-thinning fluids, it is shown that the slip length passes through a local minimum at low shear rates and then increases rapidly at higher shear rates. We found that at sufficiently high shear rates, the slip flow over atomically flat crystalline surfaces is anisotropic. It is demonstrated numerically that the friction coefficient at the liquid-solid interface (the ratio of viscosity and slip length) undergoes a transition from a constant value to the power-law decay as a function of the slip velocity. The characteristic velocity of the transition correlates well with the diffusion velocity of fluid monomers in the first fluid layer near the solid wall at equilibrium. We also show that in the linear regime, the friction coefficient is well described by a function of a single variable, which is a product of the magnitude of surface-induced peak in the structure factor and the contact density of the adjacent fluid layer. The universal relationship between the friction coefficient and induced fluid structure holds for a number of material parameters of the interface: fluid density, chain length, wall-fluid interaction energy, wall density, lattice type and orientation, thermal or solid walls.
21 Mar 2010
TL;DR: This paper carries out simulations and experiments of the estimation method and the control method in turning motion with an electric vehicle, and verifies practical effectiveness of the proposed algorithm.
Abstract: In slip ratio control systems, it is necessary to detect vehicle velocity in order to detect the slip ratio. However, it is very difficult to measure the vehicle velocity directly. Then, we have proposed an estimation method and control method of slip ratio without detecting both the vehicle velocity and the acceleration. In this paper, we carry out simulations and experiments of the estimation method and the control method in turning motion with an electric vehicle. The vehicle motion is stable with the slip ratio control. We verify practical effectiveness of the proposed algorithm.
TL;DR: In this article, a new piezoelectric tire sensor is proposed for physically meaningful measurements of tire deformation. But this sensor can only estimate the lateral deformation of the tire.
Abstract: This paper introduces a simple approach for the analysis of tire deformation and proposes a new piezoelectric tire sensor for physically meaningful measurements of tire deformations. Tire deformation measurements in the contact patch can be used for the estimation of slip angle, tire forces, slip ratio and tire–road friction coefficient. The specific case of a wireless tire deformation sensor for the estimation of slip angle is taken up in this paper. A sensor in which lateral sidewall deformation can be decoupled from radial deformation is designed. The slope of the lateral deflection curve in the contact patch is used to calculate slip angle. A specially constructed tire test rig is used to experimentally evaluate the performance of the developed sensor. Results show that the developed sensor can accurately estimate slip angles up to values of 5°.
TL;DR: In this paper, the authors investigated the effect of slip on convective boundary layer flow and heat transfer over a stretching vertical surface in the presence of slip and found that fluid velocity decreases due to the increasing velocity slip parameter resulting in an increase in the temperature field.
Abstract: Unsteady mixed convective boundary layer flow and heat transfer over a stretching vertical surface in the presence of slip are investigated. It is noted that fluid velocity decreases due to the increasing velocity slip parameter resulting in an increase in the temperature field. The rate of heat transfer decreases with the velocity slip parameter while it increases with unsteadiness parameter. The same feature is also noticed for thermal slip parameter.
TL;DR: For an oscillating boundary of period and amplitude e, it is known that the asymptotic behavior when e tends to zero of a viscous fluid satisfying slip boundary conditions is the same as if we assume no-slip (adherence) boundary conditions as discussed by the authors.
Abstract: For an oscillating boundary of period and amplitude e, it is known that the asymptotic behavior when e tends to zero of a three-dimensional viscous fluid satisfying slip boundary conditions is the same as if we assume no-slip (adherence) boundary conditions. Here we consider the case where the period is still e but the amplitude is δe with δe/e converging to zero. We show that if tends to infinity, the equivalence between the slip and no-slip conditions still holds. If the limit of belongs to (0, +∞) (critical size), then we still have the slip boundary conditions in the limit but with a bigger friction coefficient. In the case where tends to zero the boundary behaves as a plane boundary. Besides the limit equation, we also obtain an approximation (corrector result) of the pressure and the velocity in the strong topology of L2 and H1 respectively.