Slip Regime Research Articles

Influence of wall slip, thixotropy and lubrication regime on the instrumental sensory evaluation of topical formulations.

Drawing parallels from rheotribology can be used to develop a robust instrumental protocol for non-subjective characterization, product development and design of topical dosage forms with desired sensory attributes. However, instrumental characterization of cosmetic products can be influenced by the measurement protocol, thixotropy, flow anomalies like shear banding or wall slip and nature of the film formed on the skin surface. In this study, we evaluated the influence of above parameters on the instrumental sensory evaluation of 12 topical formulations of different galenic forms. Oscillatory strain sweep measurements (SAOS and LAOS) were performed to investigate the influence of frequency and wall slip on the material parameters. The textural attributes at different consumer touchpoints were evaluated by accounting time-dependent simulation of viscoelastic flow. Further, the influence of film thickness and sample drying on the tactile properties of the topical formulations were studied on a non-biological skin model using a sliding probe tribometer. The study shows that the flow properties of the semi-solid formulations depend on the timescale of the problem. A few formulations exhibited wall slip to varying degrees in the linear viscoelastic regime where the behaviour was found not to be characteristic of a particular topical dosage form. The material functions obtained from the Lissajous plots suggest that the non-linear flow behaviour of different galenic forms is least influenced by the boundary conditions imposed by the measurement geometry. The results were statistically analysed using principal component analysis where the attributes used for discriminating skin creams during pick up and rub out are found to be closely associated with non-linear rheology. The friction coefficient exhibited speed dependence where it formed different parametric group with rheological data depending on the lubrication regime. The study highlights that correlations are possible amongst rheological, tribological and instrumental textural analysis data, which can act an impetus for the development of models to predict attributes that drive perception at different consumer touchpoints. However, the choice of instrumental settings, anomalies associated with rheological measurements and friction dependence on a number of parameters can influence the model prediction.

Influence of Wear Profile Geometry on Critical Plane Fatigue Crack Initiation Criteria in Plane and Axisymmetric Elastic Fretting Contacts

The subsurface elastic stress fields in plane and axisymmetric contacts with friction under oscillating tangential loading are calculated via a very robust, high-precision method, which operates with appropriate superpositions of analytic solutions for the respective Hertzian contact problems. Based on the stress fields, two critical plane fatigue crack initiation criteria—the Smith-Watson-Topper (SWT) parameter and the Findley parameter—are evaluated for three types of contact profile geometries: (unworn) parabolic contact, the partial slip limiting wear profile of an initially parabolic contact, and truncated parabolic contact. Appropriate scaling laws are introduced to formulate a general solution in terms of non-dimensional variables. The crack initiation criteria are determined in the full subsurface loading plane. It is found that the truncated profile—which may originate from sliding wear—has practically the same local distribution of crack initiation criteria as the unworn profile, despite the (weak) stress singularity at the edge of the flat face. The partial slip limiting wear profile, on the other hand, exhibits a strong edge stress singularity at the boundary of the permanent stick zone, the crack initiation criteria are drastically increased (and theoretically infinite). Also, while for the unworn and truncated profiles high values of the crack initiation criteria are extremely localized around “hotspots” at the surface, for the partial slip limiting wear profile they reach much deeper into the subsurface material. This offers a new explanation for the dominance of fatigue failure in the partial slip regime of fretting. The differences between plane and axisymmetric cases are generally small. The SWT parameter is generally more localized than the Findley parameter.

Irreversibility analysis of micropolar nanofluid flow using Darcy–Forchheimer rule in an inclined microchannel with multiple slip effects

AbstractThe present work explores the consequence of the flow of micropolar fluid in an inclined microchannel when exposed to linear radiation in presence of a magnetic field. The microchannel is embedded with a porous medium and the Darcy–Forchheimer model is implemented. The walls of the microchannel facilitate the simultaneous suction and injection of the micropolar fluid. A multiple slip regime and temperature jump conditions were assumed at the boundaries. The equations are modeled and nondimensionalized using nondimensional entities and further solved with the aid of the Runge–Kutta–Fehlberg method. Entropy generated in the medium and ratio of irreversibilities is also computed. Results so obtained deliberate that enhancement in Darcy number has caused an increment in entropy generation rate whereas the opposite nature is attained for the Bejan number. Magnifying the radiation parameter has resulted in diminishing the profile of entropy generation rate and Bejan number.

The effect of phase difference and stiffness ratio on fretting fatigue behavior under variable normal load conditions

This paper investigated the effect of variable normal load on the fretting fatigue mechanism. A kinetics-based Q- P curve analysis method was proposed to assist testing system design and experiment result analysis. Based on this method, a biaxial fretting fatigue testing system was designed. Experimental and numerical investigation was carried out to discuss the effect of biaxial loading phase difference (the phase difference between bulk load and cyclic normal load) and stiffness ratio (the stiffness ratio between pad fixture and flat specimen) on the fretting fatigue mechanism. Based on the critical plane approach and proposed Q- P curves analysis method, it is found that the fretting status is partial slip regime under small stiffness ratio conditions. The stress/strain which is influenced by phase difference is the main factor of fretting fatigue damage in this condition. Furthermore, the mean stress of the normal load on the critical plane is compressive stress. It directly influences the fatigue damage under partial slip regime. With the increase of stiffness ratio and phase difference (from 0° to 90°), the fretting status changes from partial slip regime to gross slip regime, which means that the influence of wear increases. Wear inhibits the initiation of fatigue cracks, which has a positive influence on fretting fatigue life. As a result, the fretting failure mode gradually changes from fatigue to wear.

Heat transport performance of hydromagnetic hybrid nanofluid under the slip regime

Heat transport performance of hydromagnetic hybrid nanofluid under the slip regime

Helmholtz vibrations in bowed strings.

For almost 160 years, it has been known that Helmholtz oscillations, unique to vibrating strings in bowed instruments (violin, cello, etc.), have two distinct regimes: "slip" and "stick." During the slip regime, the force at the bow-string interaction is attributed to friction between the sliding bow hair and the vibrating string, with a friction coefficient that decreases with increasing relative velocity. Yet the hair-string interaction during the stick regime is less understood. We propose that the interaction force during the stick regime is proportional to the product of the longitudinal acoustic impedance of the bow hair to the relative bow-string velocity. We validate this hypothesis by solving the string's differential equation of motion, including an enhanced formulation to avoid parasitic high-frequency oscillations. This physical model enables us to analyze, in real time, the characteristics of the Helmholtz oscillations, including the string shape, excitation of harmonics, Schelleng ripples, and string energy, showing that the bowed string gains energy during the stick regime and loses energy during the slip regime.

Kinetic modeling of fractal aggregate mobility

Although the mobility or transport parameters, such as lift drag and pitching moments for regular-shaped particulates, are widely studied, the mobility of irregular fractal-like aggregates generated by the aggregation of monomers is not well understood. These particulates which are ubiquitous in nature, and industries have very different transport mechanisms as compared to their spherical counterpart. A high-fidelity direct simulation Monte Carlo (DSMC) study of two fractal aggregates of different shapes or dimensions is undertaken in the slip and transitional gas regime to understand the underlying mechanism of gas-particle momentum transfer that manifests as the orientation-averaged mobility parameters of the particulates. The study specifically focuses on the viscous contribution of these parameters and develops a non-linear correlation for drag and lift parameters p and q obtained from DSMC by normalizing the axial and lateral forces. The drag parameter p predicted a monotonic increase in fractal particulate drag with respect to a spherical monomer while the lift parameter q shows an initial increasing trend but a decreasing tendency toward the high Mach number or high compressibility regime. The approximate model that captures the compressibility and rarefaction effects of the fractal mobility is used to study the evolution of these particulates in a canonical Rankine vortex to illustrate the wide disparity in the trajectories of the fractal aggregate vs a spherical geometry approximation generally found in the literature.

State-specific boundary conditions for nonequilibrium gas flows in slip regime.

Boundary conditions for fluid-dynamic variables of strongly nonequilibrium multicomponent gas mixture flows in slip regime are derived systematically by two different approaches. The flow is described in the framework of the state-to-state model for coupled detailed vibrational and chemical kinetics. The specular-diffusive model is applied for particles interaction with the solid wall, and the surface is assumed to be partially catalytic with possible state-specific chemical reactions and vibrational energy transitions described by a simple model based on the analogy with recombination coefficients. The first theoretical approach uses the technique proposed by Grad whereas the second one is based on the kinetic boundary condition. It is shown that for the Maxwell scattering kernel the two approaches are equivalent; at the same time, the approach based on the kinetic boundary condition provides more rigorous mathematical description of the problem and can be easily generalized for other scattering kernels and gas-surface interaction models accounting for surface inner geometry. The resulting boundary conditions are expressed in terms of state-specific transport coefficients: thermal conductivity, multicomponent diffusion of vibrational states, thermal diffusion, shear and bulk viscosity, and relaxation pressure. The dependence of the boundary conditions on the normal mean stress is obtained for the first time. Under thermal equilibrium conditions, the derived expressions reduce to known relations obtained earlier in the one-temperature approach.

Hybrid nanoliquid flow through a microchannel with particle shape factor, slip and convective regime

PurposeThis study aims to portray the systematic study of hybrid nanofluid with particle shape effect on significant heat transfer enhancement. The steady flow of hybrid nanoliquid in a microchannel with the aid of porous medium has been considered. The dispersion of copper and Al2O3 in water is taken as hybrid mixture. The impact of thermal radiation, slip length and convective conditions on flow and thermal features are examined numerically.Design/methodology/approachThe modelled equations are made dimensionless by means of nondimensional entities. The solutions are computed numerically by the implementation of Runge–Kutta-based shooting technique. The results depict that the shape of hybrid mixtures plays a significant role in convective heat transfer. Relevant results on flow velocity, temperature, Nusselt number and friction factor for various physical constraints have been perused. The obtained outcomes are displayed graphically.FindingsThe acquired results depict that Nusselt number augments with Eckert number and solid volume fraction of hybrid nanoparticles, which has a vibrant role in enriching the heat transfer coefficient. Also, it is emphasized that the Nusselt number is larger for blade-shaped nanoparticle compared to other shapes.Originality/valueThe analysis of individual effect of thermal radiation, Joule heating, viscous dissipation and magnetic field on the flow of Cu and Al2O3 hybrid nanofluid through microchannel has vivacious role in augmenting heat transmission. Along with this, the impact of porous medium, shape factor, slip and convective peripheral conditions are also emphasized.

Torsion Wear Behavior of PEEK-on-UHMWPE as an All-Polymer Joint Combination in Total Knee Replacement

Polyether ether ketone (PEEK) has been considered as an alternative material to cobalt chrome in the femoral component of a total knee replacement. In this article, the experimental simulation of torsion wear for a PEEK and CoCr femoral head against an ultra-high-molecular-weight polyethylene (UHMWPE) tibial pad was carried out using a two-station knee simulator. The testing results showed that T-θ curves of torsion wear for PEEK-on-UHMWPE bearing couples showed three types of morphological characteristics, such as linear, elliptical, and parallelogram shapes. With an increase in torsion angular displacement, T-θ curves changed from the linear to the parallelogram type, and the relative motion state changed from the partial slip regime coordinated by the elastic deformation to the slip regime with plastic deformation. With an increase in normal load, the T-θ curve changed from the parallelogram to the elliptical type, and the relative motion state changed from the slip regime to the mixed slip regime. Under intermediate torsion wear conditions, the wear factors of UHMWPE were 11.25 ± 2.08 × 10−6 mm3/C and 14.65 ± 2.49 × 10−6 mm3/C against PEEK and CoCr. Under high torsion wear conditions, the wear factors were 20.51 ± 3.23 × 10−6 mm3/C and 23.26 ± 3.01 × 10−6 mm3/C, respectively. The wear surface of UHMWPE against PEEK showed slight adhesive wear and plastic deformation in the center, and abrasive wear with local fatigue spalling was found at the edges. The wear topographies presented characteristics similar to the CoCr bearing combination.

Couette flow in a rectangular channel in the whole range of the gas rarefaction

The mass flow rate of a Couette flow in a long rectangular channel is calculated for constant or linear wall velocities in the whole range of the gas rarefaction and in a wide range of the width-to-height ratio. Analytical solutions for arbitrary width-to-height ratios are given for the hydrodynamic regime, the slip regime, and the free molecular regime. Therefore, both the velocity field and the mass flow rate can be calculated. In the transitional regime, simulations via direct simulation Monte Carlo method are performed. The results are provided as reduced flow rates in tabulated data, which can be used for any constant or linear increasing wall velocity (e.g., bounding walls of working chambers in positive displacement vacuum pumps).

Effect of wear debris on fretting fatigue crack initiation

Both wear and fatigue occur in fretting condition, and they interact with one another during the whole process. Fretting fatigue is commonly analysed without considering the effect of wear in partial slip regime, although wear affects the lifetime of crack initiation. This paper investigates, for the first time, the effect of wear debris on fretting fatigue crack initiation. To investigate the effect of debris, first fretting wear characteristics in partial slip regime are analysed for loading conditions. Then, the effect of wear on fretting fatigue crack initiation is investigated using Ruiz parameters and critical plane methods without considering the debris effect. Through the results, we can see that loading conditions affect the wear profiles in different ways. Moreover, wear has a significant effect on the fatigue in partial slip regime without considering debris especially on the crack initiation location. Finally, considering wear debris in the analysis, its effect on critical plane parameters is investigated. It is found that by considering the wear debris effect, the fretting fatigue crack initiation location is shifted towards the trailing edge. The predictions of both crack initiation location and lifetime show a good agreement with the experimental data.

Interaction between a non-concentric rigid sphere immersed in a micropolar fluid and a spherical envelope with slip regime

A semi-analytical investigation of a quiescent micropolar fluid between a rigid sphere and a non-concentric spherical envelope with a slip regime is obtained. Two different cases have been considered one is the hydrodynamic drag strength and the translational wall correction factor (TWCF) exerted by the fluid on the inner sphere are proportional to the translational velocities and the second is the hydrodynamic torque and the rotational wall correction factor (RWCF) are applied to the inner sphere which is proportional to the angular velocities. The numerical solution is composed of the superposition of the fundamental solutions in the two spherical coordinate systems setups on the poles of the rigid sphere and the spherical envelope by using a collocation scheme. The boundary conditions, slip, and spin-slip are presented on the sphere’s surfaces. The results were achieved numerically with excellent convergence for the parameters, size ratio, separation distance, micropolarity parameter, slip, slip-spin parameters. Limiting cases are agreeable with the obtainable results in the literature.

Boundary conditions for fluid-dynamic parameters of a single-component gas flow with vibrational deactivation on a solid wall

Boundary conditions for fluid-dynamic parameters of a strongly non-equilibrium singlecomponent rarefied gas flow in the slip regime are obtained using kinetic-theory methods. The gas flow is described in the frame of the state-to-state approach assuming vibrational energy exchange as the slow relaxation process. The set of governing equations including conservation equations coupled with additional relaxation equations for vibrational state populations is presented. The gas-solid surface interaction is considered on the basis of the specular-diffusive model, and possible vibrational deactivation/excitation processes on the wall are taken into account. The obtained boundary conditions depend on the accommodation and deactivation coefficients along with the transport coefficients such as the multi-component vibrational energy diffusion and thermal diffusion coefficients; the thermal conductivity; the bulk and shear viscosity coefficients and the relaxation pressure. The dependence of boundary conditions on the normal mean stress has been obtained for the first time. In the particular case of the gas without internal degrees of freedom, the slip velocity and the temperature jump can be reduced to the well-known in the literature expressions. Implementation of the state-specific boundary conditions should not cause additional computational costs in numerical simulations of viscous flows in the state-to-state approach, since the slip/jump equations depend on the transport coefficients which have to be evaluated regardless of the boundary conditions used in the code.

Heat Transfer Characteristics of Mildly Rarefied Gaseous Flows in the Slip Regime

Heat Transfer Characteristics of Mildly Rarefied Gaseous Flows in the Slip Regime

Nanoscale Fluid-Structure Interaction Model for Multilayer Graphene Based-Resonators: Slip and Transition Flow Regimes

Nanoscale Fluid-Structure Interaction Model for Multilayer Graphene Based-Resonators: Slip and Transition Flow Regimes

Fretting Wear Behaviour of Zr Alloy Cladding Tube Under Partial Slip Regime with Different Duration in Simulated Primary Water of Pwr

Fretting Wear Behaviour of Zr Alloy Cladding Tube Under Partial Slip Regime with Different Duration in Simulated Primary Water of Pwr

Impact of injection rate ramp-up on nucleation and arrest of dynamic fault slip

Fluid injection into underground formations reactivates preexisting geological discontinuities such as faults or fractures. In this work, we investigate the impact of injection rate ramp-up present in many standard injection protocols on the nucleation and potential arrest of dynamic slip along a planar pressurized fault. We assume a linear increasing function of injection rate with time, up to a given time t_c after which a maximum value Q_m is achieved. Under the assumption of negligible shear-induced dilatancy and impermeable host medium, we solve numerically the coupled hydro-mechanical model and explore the different slip regimes identified via scaling analysis. We show that in the limit when fluid diffusion time scale t_w is much larger than the ramp-up time scale t_c, slip on an ultimately stable fault is essentially driven by pressurization at constant rate. Vice versa, in the limit when t_c/t_w gg 1, the pressurization rate, quantified by the dimensionless ratio dfrac{Q_m t_w}{t_c Q^*} with Q^* being a characteristic injection rate scale, does impact both nucleation time and arrest distance of dynamic slip. Indeed, for a given initial fault loading condition and frictional weakening property, lower pressurization rates delay the nucleation of a finite-sized dynamic event and increase the corresponding run-out distance approximately proportional to propto left( dfrac{Q_m t_w}{t_c Q^*}right) ^{-0.472}. On critically stressed faults, instead, the ramp-up of injection rate activates quasi-static slip which quickly turn into a run-away dynamic rupture. Its nucleation time decreases non-linearly with increasing value of dfrac{Q_m t_w}{t_c Q^*} and it may precede (or not) the one associated with fault pressurization at constant rate only.

Simulation applicability verification of various slip models in micro-nozzle

The micro-nozzle allows small spacecraft to realize the orbital maneuvering and precise station-keeping. Due to the rarefaction effect of the gas flow in micro-nozzles, the velocity-slip and temperature-jump exists near inner wall, and thus, affecting the operating characteristics of micro-nozzles. Various gas-solid theories and models have been developed to describe the velocity slip and temperature jump in computational fluid dynamics (CFD). In this study, numerical simulations of a micro-nozzle with five classical slip boundary models, which are based on the Maxwell scattering and Langmuir adsorption, are conducted to analyze the applicability of these models through comparing with the results obtained by direct simulated Monte Carlo (DSMC) method. The results show that the inlet pressure dramatically influences the flow regime of the micro-nozzle. The lower the inlet pressure, the higher the influence of the rarefaction effect. The results also indicate that the Langmuir slip model can accurately simulate the flow field in the transition regime. However, the modified Maxwell and Langmuir models proposed by Agrawal et al. (2008) and Le et al. (2012), respectively, are valid in the slip regime.

Grad's distribution functions-based gas kinetic scheme for simulation of flows beyond Navier–Stokes level

Conventional gas kinetic scheme (GKS) has been successfully utilized to obtain the accurate solution of Navier–Stokes (NS) equations. However, when it comes to flows beyond NS level, the conventional GKS is not reliable because its initial gas distribution function is approximated by the first-order Chapman–Enskog expansion, which merely recovers the NS equations. In order to make an extension for flows beyond NS level, we propose the Grad's distribution functions-based GKS in this paper. This scheme retains the advantage of conventional GKS and constructs the numerical fluxes through a time-dependent gas distribution function, which is derived from the integral solution of Boltzmann equation. In the present scheme, the initial gas distribution function in the local solution of Boltzmann equation is approximated by Grad's 13 and 26 distribution functions. Furthermore, the high-order moments in the initial Grad's distribution function are calculated by moment relationship directly, and thus, the solution of complicated partial differential equations for these high-order moments is avoided. Four benchmark numerical examples are tested to validate the performance of the present scheme, and the results demonstrate that the present scheme can not only recover NS solutions in the continuum region but also predict reasonable results for flows in the slip and transition regimes.