Slip Field Research Articles

Dual stratification effects on double-diffusive convective heat and mass transfer of a sheet-driven micropolar fluid flow

The intent of this study is to analyse the influence of nonlinear thermal radiation, thermophoresis, second order slip and magnetic field on the doubly stratified flow of a non-Newtonian micropolar fluid induced by a stretched sheet along with transport of thermal energy and mass species. The radiative heat flux term is modified using the non-linear Rosseland diffusion approximation. The partial differential equations governing the physics of the problem are recast into a set of coupled non-linear ordinary differential equations by using appropriate similarity transformations and later they are solved numerically using RKF-45 algorithm along with shooting technique. Results of the numerical solution are illustrated graphically for several sets of values of the governing parameters. Comparison of our results with the available results in literature for some special cases reveals close agreements. The results indicate that material parameter boosts the velocity and micro-rotation. The temperature ratio parameters that arise due to non-linear thermal radiation are seen to have opposite effect on temperature. It is seen that for strong thermal stratification reverse flow takes place accompanied by an undershoot in temperature. Excessive mass stratification and weaker molecular diffusivity resulted in a significant undershoot of species concentration.

Multiple slip effects on magnetic-Carreau fluid in a suspension of gyrotactic microorganisms over a slendering sheet

A computational simulation of two-dimensional magnetic-Carreau fluid in a suspension of gyrotactic microorganisms past a slendering sheet with variable thickness is investigated for slenderness parameters varied in the range of –0.2 to 1.0. Owing to the noticeable implication in various engineering applications, the effects of multiple slip is considered in the present simulation along with the Soret and the Dufour effects for the heat and mass transfer controlling process. The numerical values of the velocity, temperature, concentration, and the density of the motile organisms are computed by the robust Runge–Kutta-based Newton’s scheme. The thermal and concentration boundary layer are changed with the increase in the multiple slip parameters such as velocity slip, temperature slip, concentration slip, and diffusion slip parameters. With the rise in the Carreau fluid power index parameter, the velocity field increases while it declines with the velocity slip and magnetic field parameter. The increasing values of velocity slip, Dufour number, Soret number, and magnetic parameter boost up the density of the motile organism profiles for different slenderness parameter considered in the present study. The effect of the nondimensional factors on the skin friction, local Nusselt, local Sherwood, and the density numbers of the motile organisms are discussed with the assistance of the table for three different slenderness parameters. It is found that multiple slip parameters enable to control the heat and mass transfer rate. Finally, both the qualitative and quantitative comparisons of the present results with previous study are presented in the tabular form and are found to be in excellent agreement.

Unsteady MHD Slip Flow with Radiative Heat and Mass Transfer over an Inclined Plate Embedded in a Porous Medium

The combined effects diffusion-thermo, chemical reaction, buoyancy forces, radiative heat flux, velocity slip and magnetic field on an unsteady hydromagnetic mixed convective flow of an electrically conducting fluid with heat and mass transfer over an inclined vertical porous plate embedded in a porous medium is studied. The imposed thermal boundary conditions include prescribed uniform plate surface temperature (PST) and prescribed heat flux (PHF). The governing equations are solved analytically with the help of two term perturbation technique. The influence of various thermophysical parameters on the fluid velocity, temperature and species concentration are presented graphically while numerical values of skin friction, Nusselt and Sherwood numbers are presented in tabular form for different values and discussed. A special case of our results show excellent agreement with the earlier results in the literature.

A numerical analysis for non-linear radiation in MHD flow around a cylindrical surface with chemically reactive species

Abstract Boundary layer flow around a stretchable rough cylinder is modeled by taking into account boundary slip and transverse magnetic field effects. The main concern is to resolve heat/mass transfer problem considering non-linear radiative heat transfer and temperature/concentration jump aspects. Using conventional similarity approach, the equations of motion and heat transfer are converted into a boundary value problem whose solution is computed by shooting method for broad range of slip coefficients. The proposed numerical scheme appears to improve as the strengths of magnetic field and slip coefficients are enhanced. Axial velocity and temperature are considerably influenced by a parameter M which is inversely proportional to the radius of cylinder. A significant change in temperature profile is depicted for growing wall to ambient temperature ratio. Relevant physical quantities such as wall shear stress, local Nusselt number and local Sherwood number are elucidated in detail.

Homotopy perturbation method for analysis of squeezing axisymmetric flow of newtonian fluid under the effects of slip and magnetic field

Homotopy perturbation method for analysis of squeezing axisymmetric flow of newtonian fluid under the effects of slip and magnetic field

Energy performance of a tractor according to the escalation of gears and engine speeds

This study aimed to evaluate the energy performance of a tractor-disk set under different combinations of speed and engine revs. The experiment was conducted at the Federal University of Mato Grosso, Sinop Campus, MT. The design consisted of randomized blocks with eight treatments and four replications being 1Ax1550rpm (4km h -1 ), 5Bx1500rpm (4km h -1 ), 5Bx1950rpm (5 km h -1 ), 1Ax2000rpm (5 km h -1 ), 6Bx1650rpm (6 km h -1 ), 2Ax1900rpm (6 km h -1 ), 2Ax2150rpm (7 km h -1 ) and 6Bx1950rpm (7 km h -1 ). We evaluated the tractor wheel slip, hourly consumption, operating consumption and effective field capacity. The tractor wheel slip was not influenced by the variation of combinations gear and engine speed. The escalation of gears and engine speed influenced on field capacity of the assembly and, consequently, the operating consumption. The hourly fuel consumption is lower when working with the gear 6B and 1650 engine rpm. Operating fuel consumption is lower when working with 6B march 1950 and engine speed

Micromechanical modeling of intrinsic and specimen size effects in microforming

Size effect is a crucial phenomenon in the microforming processes of metallic alloys involving only limited amount of grains. At this scale intrinsic size effect arises due to the size of the grains and the specimen/statistical size effect occurs due to the number of grains where the properties of individual grains become decisive on the mechanical behavior of the material. This paper deals with the micromechanical modeling of the size dependent plastic response of polycrystalline metallic materials at micron scale through a strain gradient crystal plasticity framework. The model is implemented into a Finite Element software as a coupled implicit user element subroutine where the plastic slip and displacement fields are taken as global variables. Uniaxial tensile tests are conducted for microstructures having different number of grains with random orientations in plane strain setting. The influence of the grain size and number on both local and macroscopic behavior of the material is investigated. The attention is focussed on the effect of the grain boundary conditions, deformation rate and the grain size on the mechanical behavior of micron sized specimens. The model is intrinsically capable of capturing both experimentally observed phenomena thanks to the incorporated internal length scale and the crystallographic orientation definition of each grain.

A reduced micromorphic single crystal plasticity model at finite deformations. Application to strain localization and void growth in ductile metals

A micromorphic single crystal plasticity model is formulated at finite deformations as an extension of Mandel’s classical theory based on a multiplicative decomposition of the deformation gradient. It involves a single microslip degree of freedom in addition to the usual displacement components. Two main variants of the constitutive equations are proposed. The first one relies on a Lagrangian microslip gradient and leads to a Laplace term in the isotropic hardening law. In contrast, the second formulation, based on a generalized strain measure defined with respect to the intermediate configuration, is shown to induce both isotropic and kinematic enhanced hardening. The first formulation is implemented in a 3D finite element code. The model is applied first to strain localization phenomena in a single crystal in tension undergoing single slip. The regularization power of the model is illustrated by mesh-independent simulations of the competition between kink and slip bands. The model is then used to investigate void growth and coalescence in FCC single crystals. Cylindrical and spherical voids are considered successively. The simulations show, for the first time in the case of spherical voids embedded in a single crystal matrix, that smaller voids grow slower than bigger ones, and that the onset of void coalescence is delayed for smaller voids. These results are related to the fact that the field of plastic slip is found to be more diffuse around smaller voids.

Dislocation Creep: Climb and Glide in the Lattice Continuum

A continuum theory for high temperature creep of polycrystalline solids is developed. It includes the relevant deformation mechanisms for diffusional and dislocation creep: elasticity with eigenstrains resulting from vacancy diffusion, dislocation climb and glide, and the lattice growth/loss at the boundaries enabled by diffusion. All the deformation mechanisms are described with respect to the crystalline lattice, so that the continuum formulation with lattice motion as the basis is necessary. However, dislocation climb serves as the source sink of lattice sites, so that the resulting continuum has a sink/source of its fundamental component, which is reflected in the continuity equation. Climb as a sink/source also affects the diffusion part of the problem, but the most interesting discovery is the climb-glide interaction. The loss/creation of lattice planes through climb affects the geometric definition of crystallographic slip and necessitates the definition of two slip fields: the true slip and the effective slip. The former is the variable on which the dissipative power is expanded during dislocation glide and is thus, the one that must enter the glide constitutive equations. The latter describes the geometry of the slip affected by climb, and is necessary for kinematic analysis.

Reconstruction of faults in elastic half space from surface measurements

We study in this paper a half-space linear elasticity model for surface displacements caused by slip along underground faults. We prove uniqueness of the fault location and (piecewise-planar) geometry and of the slip field for a given surface displacement field. We then introduce a reconstruction algorithm for the realistic case where only a finite number of surface measurements are available. After showing how this algorithm performs on simulated data and assessing the effect of noise, we apply it to measured data. The data were recorded during slow slip events in Guerrero, Mexico. Since this is a well studied subduction zone, it is possible to compare our inferred fault geometry to other reconstructions (obtained using different techniques) found in the literature.

Thermodynamics Analysis of Unsteady MHD Mixed Convection with Slip and Thermal Radiation over a Permeable Surface

This paper discusses the thermodynamics irreversibility in an unsteady hydromagnetic mixed convective flow of an electrically conducting optically dense fluid over a permeable vertical surface under the combined influence of thermal radiation, velocity slip, temperature jump, buoyancy force, viscous dissipation, Joule heating and magnetic field. The governing partial differential equations are reduced to ordinary differential equations by using similarity variable. A local similarity solution is obtained numerically using shooting technique coupled with Runge-Kutta Fehlberg integration method. The influence of various thermophysical parameters on velocity and temperature profiles, skin friction, Nusselt number, entropy generation rate and Bejan number are presented graphically and discussed quantitatively. It is found that velocity slip, surface injection and temperature jump can successfully reduce entropy generation rate in the presence of an applied magnetic field. A comparison of numerical solution is made with the exact solution under a special case scenario and excellent agreement is found.

Determining Fault Geometries From Surface Displacements

We introduce a new algorithm for determining the geometry of active parts of faults. This algorithm uses surface measurements of displacement fields and local modeling of the Earth’s crust as a half-space elastic medium. The numerical method relies on iterations alternating non-linear steps for recovering the geometry and linear steps for reconstructing slip fields. Our algorithm greatly improves upon past attempts at reconstructing fault profiles. We argue that these past attempts suffered from either the restrictive assumption that the geometry of faults can be derived using only uniformly constant slips or that they relied on arbitrary assumptions on the statistics of the reconstruction error. We test this algorithm on the 2006 Guerrero, Mexico, slow slip event (SSE) and on the 2009 SSE for the same region. These events occurred on a relatively well-known subduction zone, whose geometry was derived from seismicity and gravimetric techniques, see Kostoglodov et al. (Geophys Res Lett 23(23):3385–3388, 1996), Pardo and Suarez (J Geophys Res 100(B7):357–373, 1995), Singh and Pardo (Geophys Res Lett 20(14):1483–1486, 1993), so our results can be compared to known benchmarks. Our derived geometry is found to be consistent with these benchmarks regarding dip and strike angles and the positioning of the North American Trench. In addition, our derived slip distribution is also consistent with previous studies (all done with an assumed fixed geometry), see Larson et al. (Geophys Res Lett 34(13), 2007), Bekaert et al. (J Geophys Res: Solid Earth 120(2):1357–1375, 2015), Radiguet et al. (Geophys J Int 184(2):816–828, 2011, J Geophys Res 2012), Rivet et al. (Geophys Res Lett 38(8), 2011), Vergnolle et al. (J Geophys Res: Solid Earth 115(B8), 2010), Walpersdorf et al. Geophys Res Lett 38(15), 2011), to name a few. We believe that the new computational inverse method introduced in this paper holds great promise for applications to blind inversion cases, where both geometry and slip distribution are unknown.

Micromechanical Modelling of Size Effects in Microforming

Abstract This paper deals with the micromechanical modelling of the size dependent mechanical response of polycrystalline metallic materials at micron scale through a strain gradient crystal plasticity framework. The model is implemented into a Finite Element software as a coupled implicit user element subroutine where the plastic slip and displacement fields are taken as global variables. Uniaxial tensile tests are conducted for microstructures having different number of grains with random orientations in plane strain setting. The influence of the grain size and number on both local and macroscopic behavior of the material is investigated. The model is capable of capturing both size effect due to statistical distribution of the grains and their size taking into account the grain boundary conditions.

Crystal plasticity modelling and HR-DIC measurement of slip activation and strain localization in single and oligo-crystal Ni alloys under fatigue

Single crystal (CMSX4) and oligocrystal (MAR002) nickel have been studied using three-point beam bending under conditions of cyclic loading. SEM images have enabled identification of slip activation, and high resolution digital image correlation has been utilized to quantify the developing strain fields and the strain localization in both single and oligocrystals in fatigue. The single and oligocrystal microstructures have been replicated within crystal plasticity finite element models and the fatigue loading analysed such that grain-by-grain comparisons of slip may be carried out. Single and multiple slip activation, slip localization and microstructure-sensitive stress evolution have been examined.Single crystal bend fatigue gives rise to non-symmetric slip fields and localization depending on crystallographic orientation. Modelling correctly captures slip activation and the developing non-symmetric slip fields. Oligocrystal slip is markedly heterogeneous, with grain misorientations driving strong variations, also reasonably captured by the model. Microstructure behaviour is found to vary spatially and include elastic-plastic hysteresis which is stable, and which undergoes mean stress relaxation so that plastic shakedown occurs. Remarkable variations occur between locations either side of grain boundaries, providing appropriate opportunities for fatigue crack nucleation.

Effects of Second-Order Slip and Magnetic Field on Mixed Convection Stagnation-Point Flow of a Maxwellian Fluid: Multiple Solutions

In this paper, we investigate the effects of second-order slip and magnetic field on the nonlinear mixed convection stagnation-point flow toward a vertical permeable stretching/shrinking sheet in an upper convected Maxwell (UCM) fluid with variable surface temperature. Numerical results are obtained using the bvp4c function from matlab for the reduced skin-friction coefficient, the rate of heat transfer, the velocity, and the temperature profiles. The results indicate that multiple (dual) solutions exist for a buoyancy opposing flow for certain values of the parameter space irrespective to the types of surfaces whether it is stretched or shrinked. It is found that an applied magnetic field compensates the suction velocity for the existence of the dual solutions. Depending on the parametric conditions; elastic parameter, magnetic field parameter, first- and second-order slip parameters significantly controls the flow and heat transfer characteristics. The illustrated streamlines show that for upper branch solutions, the effects of stretching and suction are direct and obvious as the flow near the surface is seen to suck through the permeable sheet and drag away from the origin of the sheet. However, aligned but reverse flow occurs for the case of lower branch solutions when the mixed convection effect is less significant.

Velocity, thermal and concentration slip effects on a magneto-hydrodynamic nanofluid flow

This article examines the magneto-hydrodynamic (MHD) flow of nanofluid bounded by a stretching surface. The slip conditions are utilized in the present analysis. The involved differential systems are solved for the velocity, temperature and mass fraction. Graphical and numerical results are reported for the analysis of various parameters of interest entering into the modeled problems. Combined effects of thermal and concentration jump are analyzed. Various tables are constructed to show the rheological effects of different physical parameters. Streamlines are plotted showing the rheology for the slip and no slip flow regime. Plots of skin friction are also prepared for the slip and magnetic field effects.

Simulations of peristaltic slip-flow of hydromagnetic bio-fluid in a curved channel

The influence of slip and magnetic field on transport characteristics of a bio-fluid are analyzed in a curved channel. The problem is modeled in curvilinear coordinate system under the assumption that the wavelength of the peristaltic wave is larger in magnitude compared to the width of the channel. The resulting nonlinear boundary value problem (BVP) is solved using an implicit finite difference technique (FDT). The flow velocity, pressure rise per wavelength and stream function are illustrated through graphs for various values of rheological and geometrical parameters of the problem. The study reveals that a thin boundary layer exists at the channel wall for strong magnetic field. Moreover, small values of Weissenberg number counteract the curvature and make the velocity profile symmetric. It is also observed that pressure rise per wavelength in pumping region increases (decreases) by increasing magnetic field, Weissenberg number and curvature of the channel (slip parameter).

Micropolar crystal plasticity simulation of particle strengthening

The yield and work hardening behavior of a small-scale initial-boundary value problem involving dislocation plasticity in an idealized particle strengthened system is investigated using micropolar single crystal plasticity and is compared with results for the same problem from dislocation dynamics simulations. A micropolar single crystal is a work-conjugate higher-order continuum that treats the lattice rotations as generalized displacements, and supports couple stresses that are work-conjugate to the lattice torsion-curvature, leading to a non-symmetric Cauchy stress. The resolved skew-symmetric component of the Cauchy stress tensor results in slip system level kinematic hardening during heterogeneous deformation that depends on gradients of lattice torsion-curvature. The scale-dependent mechanical response of the micropolar single crystal is dictated both by energetic (higher-order elastic constants) and dissipative (plastic torsion-curvature) intrinsic material length scales. We show that the micropolar model captures essential details of the average stress–strain behavior predicted by discrete dislocation dynamics and of the cumulative slip and dislocation density fields predicted by statistical dislocation dynamics.

Peristaltic flow with convective mass condition and thermal radiation

The primary objective of present investigation is to introduce the novel aspects of convective mass condition and thermal radiation in the peristaltic transport of fluid. Magnetohydrodynamic (MHD) fluid was considered in a symmetric channel. Heat and mass transfer characteristics were analyzed in the presence of Soret and Dufour effects, and the results were presented via two forms of thermal radiation. The temperature, concentration and pressure rise per wavelength were examined. It is observed that the velocity slip and magnetic field parameters have opposite effects on the pressure rise per wavelength. Temperature of fluid is a decreasing function of the radiation parameter. Further, the temperature of fluid decreases by increasing the heat transfer Biot number. It is notified that the heat transfer rate at the wall is a decreasing function of radiation parameter.

MHD mixed convection slip flow near a stagnation-point on a nonlinearly vertical stretching sheet

The problem of magnetohydrodynamic (MHD) mixed convection flow near a stagnation-point region over a nonlinear stretching sheet with velocity slip and prescribed surface heat flux is investigated; this has not been studied before. Using a similarity transformation, the governing equations are transformed into a system of ordinary differential equations, and then are solved by employing a homotopy analysis method. The effects of the nonlinearity parameter, the magnetic field, mixed convection, suction/injection, and the boundary slip on the velocity and temperature profile are analyzed and discussed. The results reveal that the increasing exponent of the power-law stretching velocity increases the heat transfer rate at the surface. It is also found that the velocity slip and magnetic field increase the heat transfer rate when the free stream velocity exceeds the stretching velocity, i.e. $\varepsilon< 1$ , and they suppress the heat transfer rate for $\varepsilon> 1$ .