Showing papers on "Slip ratio published in 2017"

Study on Self-Tuning Tyre Friction Control for Developing Main-Servo Loop Integrated Chassis Control System

Abstract: The inherent flexibility of hierarchical structure scheme with main-servo loop control structure is proposed to the problem of integrated chassis control system for the vehicle. It includes both main loop, which calculates and allocates the aim force using the optimal robust control algorithm and servo loop control systems, which track and achieve the target force using the onboard independent brake actuators. In fact, for the brake actuator, the aim friction is obtained by tracking the corresponding slip ratio of target force. For the coefficient of tire-road friction varying with different road surface, to get the nonlinear time-varying target slip ratio, the most famous quasi-static magic formula is proposed to estimate and predict real-time coefficient of different road surface and the constrained hybrid genetic algorithm (GA) is used to identify the key parameters of the magic formula on-line. Then, a self-tuning longitudinal slip ratio controller (LSC) based on the nonsingular and fast terminal sliding mode (NFTSM) control method is designed to improve the tracking accuracy and response speed of the actuators. At last, the proposed integrated chassis control strategies and the self-tuning control strategies are verified by computer simulations.

Fluid flow and heat transfer of non-Newtonian nanofluid in a microtube considering slip velocity and temperature jump boundary conditions

Abstract: Forced convection of non-Newtonian nanofluid, aqueous solution of carboxymethyl cellulose (CMC)–Aluminum oxide through a microtube is studied numerically. The length and diameter of tube are L = 5 mm and D = 0.2 mm, respectively which means the length is long enough compared to the diameter. The effects of different values of nanoparticles volume fraction, slip coefficient and Reynolds number are investigated on the slip velocity and temperature jump boundary conditions. Moreover the suitable validations are presented to confirm the achieved results accuracy. The results are shown as the dimensionless velocity and temperature profiles; however the profiles of local and averaged Nusselt number are also provided. It is seen that more volume fraction and slip coefficient correspond to higher Nusselt number especially at larger amounts of Re.

The effects of different nano particles of Al2O3 and Ag on the MHD nano fluid flow and heat transfer in a microchannel including slip velocity and temperature jump

Abstract: The forced convection of nanofluid flow in a long microchannel is studied numerically according to the finite volume approach and by using a developed computer code. Microchannel domain is under the influence of a magnetic field with uniform strength. The hot inlet nanofluid is cooled by the heat exchange with the cold microchannel walls. Different types of nanoparticles such as Al2O3 and Ag are examined while the base fluid is considered as water. Reynolds number are chosen as Re=10 and Re=100. Slip velocity and temperature jump boundary conditions are simulated along the microchannel walls at different values of slip coefficient for different amounts of Hartmann number. The investigation of magnetic field effect on slip velocity and temperature jump of nanofluid is presented for the first time. The results are shown as streamlines and isotherms; moreover the profiles of slip velocity and temperature jump are drawn. It is observed that more slip coefficient corresponds to less Nusselt number and more slip velocity especially at larger Hartmann number. It is recommended to use Al2O3-water nanofluid instead of Ag-water to increase the heat transfer rate from the microchannel walls at low values of Re. However at larger amounts of Re, the nanofluid composed of nanoparticles with higher thermal conductivity works better.

Evolution of shear fabric in granular fault gouge from stable sliding to stick slip and implications for fault slip mode

Abstract: Laboratory and theoretical studies provide insight into the mechanisms that control earthquake nucleation, when fault slip velocity is slow (<0.001 cm/s), and dynamic rupture when fault slip rates exceed centimeters per second. The application of these results to tectonic faults requires information about fabric evolution with shear and its impact on the mode of faulting. Here we report on laboratory experiments that illuminate the evolution of shear fabric and its role in controlling the transition from stable sliding ( v ∼0.001 cm/s) to dynamic stick slip ( v > 1 cm/s). The full range of fault slip modes was achieved by controlling the ratio K = k / k c , where k is the elastic loading stiffness and k c is the fault zone critical rheologic stiffness. We show that K controls the transition from slow-and-silent slip ( K > 0.9) to fast-and-audible ( K v = 3 cm/s, slip duration 0.003 s) slip events. Microstructural observations show that with accumulated strain, deformation concentrates in shear zones containing sharp shear planes made of nanoscale grains, which favor the development of frictional instabilities. Once this fabric is established, fault fabric does not change significantly with slip velocity, and fault slip behavior is mainly controlled by the interplay between the rheological properties of the slipping planes and fault zone stiffness.

Unsteady flow and heat transfer of power-law nanofluid thin film over a stretching sheet with variable magnetic field and power-law velocity slip effect

Abstract: This paper studies the flow and heat transfer of the power-law nanofluid thin film due to a stretching sheet with magnetic field and velocity slip effects. Unlike classical work, Fourier's law is modified by assuming that the thermal conductivity is power-law-dependent on the velocity gradient. Meanwhile, the power law wall temperature and the power law velocity slip effects are taken into account. Three different types of nanoparticles, Al 2 O 3 , TiO 2 and CuO are considered with ethylene vinyl acetate copolymer (EVA) used as a base fluid. The governing equations are solved by using DTM–NIM which is combined the differential transform method (DTM) with Newton Iteration method (NIM). The results show that for the specific physical parameters, the two different velocity profiles have always an intersection which goes from a far-field region to the stretching sheet as increasing velocity slip parameter. Furthermore, CuO–EVA nanofluid has better enhancement on heat transfer than TiO 2 /Al 2 O 3 –EVA.

Radiation effects on stagnation point flow with melting heat transfer and second order slip

Abstract: This article examines the effects of melting heat transfer and thermal radiation in stagnation point flow towards a stretching/shrinking surface. Mathematical formulation is made in the presence of mass transfer and second order slip condition. Numerical solutions to the resulting nonlinear problems are obtained by Runge-Kutta fourth fifth order method. Physical quantities like velocity, temperature, concentration, skin friction, Nusselt and Sherwood number are analyzed via sundry parameters for stretching/shrinking, first order slip, second order slip, radiation, melting, Prandtl and Schmidt. A comparative study with the previously published results in limiting sense is made.

Influence of velocity slip and temperature jump conditions on the peristaltic flow of a Jeffrey fluid in contact with a Newtonian fluid

Abstract: n this paper, we investigate the peristaltic transport of a two layered fluid model consisting of a Jeffrey fluid in the core region and a Newtonian fluid in the peripheral region. The channel is bounded by permeable heat conducting walls. The analysis is carried out in the wave reference frame under the assumptions of long wave length and low Reynolds number. The analytical expressions for stream function, temperature field, pressure-rise and the frictional force per wavelength in both the regions are obtained. The effects of the physical parameters associated with the flow and heat transfer are presented graphically and analyzed. It is noticed that the pressure rise decrease with increasing slip parameter β in the pumping region (ΔP>0). The temperature field decreases with increasing Jeffrey number and the velocity slip parameter; whereas the temperature field increases with increasing thermal slip parameter. Furthermore, the size of the trapped bolus increases with increasing Jeffrey number and decreases with increasing slip parameter. We believe that this model can help in understanding the behavior of two immiscible physiological fluids in living objects.

Heat and mass transfer analysis on peristaltic flow of particle–fluid suspension with slip effects

Abstract: In this paper, the effect of heat and mass transfer on particle–fluid suspension due to peristaltic motion is examined with of slip effects. The governing equations of fluid phase and particulate phase for Casson fluid model with embedded particles are interpreted under the approximation of long wavelength and neglecting the inertial forces. The obtained coupled resulting partial differential equations are solved analytically and an exact form of solutions are conferred. The impact of various sundry parameters are plotted and discussed for velocity, temperature and concentration distribution for both fluid and particle phase. Numerical solution is evaluated for pressure rise along the whole channel. The present analysis reveals various interesting behavior that warrant further analysis on various Newtonian and non-Newtonian fluids. In the present flow problem, the influence of slip represents opposite attitude on the walls of the channel whereas due to the impact of particle volume fractions, the velocity...

The lubrication performance of water lubricated bearing with consideration of wall slip and inertial force

Abstract: The lubrication mechanism and the performance parameters with consideration of wall slip and inertial force are studied in this paper. Based on the modified Reynolds equation, the finite difference method is used to study the lubrication mechanism and the performance. Effects of the wall slip and the inertial force on the performance parameters are obtained, and found in good agreement with the results of FLUENT. It is shown that the wall slip and the inertial force do not significantly change the distribution of the pressure, the load capacity and the friction force. The inertial force slightly increases the pressure and the load capacity by 1.2% and 4.8%, while the wall slip reduces them by 8.0% and 17.85%. The wall slip and the inertial force increase the friction by about 15.98%, 2.33%, respectively. Compared with the wall slip, the inertial force is smaller, but cannot be neglected.

Inelastic non-Newtonian flow over heterogeneously slippery surfaces

Abstract: In this study, we investigated inelastic non-Newtonian fluid flow over heterogeneously slippery surfaces. First, we simulated the flow of aqueous xanthan gum solutions over a bubble mattress, which is a superhydrophobic surface consisting of transversely positioned no-slip walls and no-shear gas bubbles. The results reveal that for shear-thinning fluids wall slip can be increased significantly, provided that the system is operated in the shear-thinning regime. For a 0.2 wt% xanthan gum solution with a power-law index of n=0.4, the numerical results indicate that wall slip can be enhanced 3.2 times when compared to a Newtonian liquid. This enhancement factor was also predicted from a theoretical analysis, which gave an expression for the maximum slip length that can be attained over flat, heterogeneously slippery surfaces. Although this equation was derived for a no-slip/no-shear unit length that is much larger than the typical size of the system, we found that it can also be used to predict the enhancement in the regime where the slip length is proportional to the size of the no-shear region or the bubble width. The results could be coupled to the hydrodynamic development or entrance length of the system, as maximum wall slip is only reached when the fluid flow can fully adapt to the no-slip and no-shear conditions at the wall.

Slip flow by a variable thickness rotating disk subject to magnetohydrodynamics

Abstract: Objective of the present study is to determine the characteristics of magnetohydrodynamic flow by a rotating disk having variable thickness. At the fluid–solid interface we consider slip velocity. The governing nonlinear partial differential equations of the problem are converted into a system of nonlinear ordinary differential equations. Obtained series solutions of velocity are convergent. Impact of embedded parameters on fluid flow and skin friction coefficient is graphically presented. It is observed that axial and radial velocities have an opposite impact on the thickness coefficient of disk. Also surface drag force has a direct relationship with Hartman number.

Integrated traction control strategy for distributed drive electric vehicles with improvement of economy and longitudinal driving stability

Abstract: This paper presents an integrated traction control strategy (ITCS) for distributed drive electric vehicles. The purpose of the proposed strategy is to improve vehicle economy and longitudinal driving stability. On high adhesion roads, economy optimization algorithm is applied to maximize motors efficiency by means of the optimized torque distribution. On low adhesion roads, a sliding mode control (SMC) algorithm is implemented to guarantee the wheel slip ratio around the optimal slip ratio point to make full use of road adhesion capacity. In order to avoid the disturbance on slip ratio calculation due to the low vehicle speed, wheel rotational speed is taken as the control variable. Since the optimal slip ratio varies according to different road conditions, Bayesian hypothesis selection is utilized to estimate the road friction coefficient. Additionally, the ITCS is designed for combining the vehicle economy and stability control through three traction allocation cases: economy-based traction allocation, pedal self-correcting traction allocation and inter-axles traction allocation. Finally, simulations are conducted in CarSim and Matlab/Simulink environment. The results show that the proposed strategy effectively reduces vehicle energy consumption, suppresses wheels-skid and enhances the vehicle longitudinal stability and dynamic performance.

Slip Analysis at Fluid-Solid Interface in MHD Squeezing Flow of Casson Fluid through Porous Medium

Abstract: An unsteady squeezing flow of Casson fluid having Magneto Hydro Dynamic effect and passing through porous medium channel with slip at the boundaries has been modelled and analyzed. Similarity transformations are applied to the governing partial differential equations of the Casson model to get a highly non-linear fourth order ordinary differential equation. The obtained equation is then solved analytically using the Homotopy Perturbation Method (HPM) for uniform and non-uniform slip at the boundaries. Five cases of boundary conditions, representing slip at upper wall only, uniform slip at both walls, non-uniform slip where slip at upper wall is greater than that of lower wall, non-uniform slip where slip at lower wall is greater than that of upper wall, and slip at lower wall only are considered and thoroughly investigated. Validation is performed by solving the equation numerically using fourth order explicit Runge Kutta method (ERK4). Both analytical and numerical results show good agreement. Lastly, the effects of various fluid parameters on the velocity profile are investigated for each case graphically. Analysis of these plots show that the positive and negative squeeze numbers have opposite effect on the velocity profile throughout all the cases. It is also observed that various fluid parameters like Casson, MHD, and Permeability have similar effects on the velocity profile in the cases when slip is occurring at the upper wall only, and non-uniform slip at both the boundaries with slip at lower wall is greater than upper wall. Furthermore, similar effects have been observed when slip is uniform at both the boundaries, and in case of non-uniform slip with slip at lower wall is less than the upper wall.

Determination of slip and characteristic velocities in reactive extraction with experiments in the Oldshue-Rushton column and presence of samarium and gadolinium metals

Abstract: The slip and characteristic velocities of the reactive system (samarium, gadolinium and D2EHPA) were investigated in the pilot plant Oldshue-Rushton extraction column The experiments were carried out at the extraction and stripping stage The influences of the agitation speed, dispersed as well as continuous phase velocity were studied An increase in dispersed phase velocity led to the increase of the slip velocity while it decreased with agitation speed and continuous phase velocity More buoyancy and faster upward movement of larger drops accelerate the slip velocity in the stripping condition as compared with the case of extraction condition The experimental data were compared with the proposed correlations by Asadollahzadeh et al, and the related deviation was within 26% from these equations Therefore, the modified correlations for prediction of slip and characteristic velocities were proposed with the experimental data and the data from the physical systems in the literature

Dynamic wall slip behavior of yield stress fluids under large amplitude oscillatory shear

Abstract: Wall slip occurs under large amplitude oscillation shear (LAOS) for yield stress fluids. In this work, we investigated how the boundary conditions affect the nonlinear behavior under LAOS and proposed a simple methodology based on the geometric average of Lissajous curves to study the dynamic wall slip behavior under oscillatory shear. The results show that the stress-mean strain curve is a good candidate to define material's functions since it is almost not influenced by the wall slip effect. Meanwhile, the stress-mean strain rate curves from smooth plates and rough plates can be used to determine the wall slip velocity. It is found that the intercycle maximum slip strain rate follows the generalized Navier's law, while the intracycle slip behavior can be well described by a Maxwell-like dynamic slip model, which helps to determine the slip relaxation time. It is also found that the slip Deborah number is independent of the angular frequency and is a monotonically decreasing function of the reduced stres...

Analysis of rheology and wall depletion of microfibrillated cellulose suspension using optical coherence tomography

Abstract: A rheometric method based on velocity profiling by optical coherence tomography (OCT) was used in the analysis of rheological and boundary layer flow properties of a 0.5% microfibrillated cellulose (MFC) suspension. The suspension showed typical shear thinning behaviour of MFC in the interior part of the tube, but the measured shear viscosities followed interestingly two successive power laws with an identical flow index (exponent) and a different consistency index. This kind of viscous behaviour, which has not been reported earlier for MFC, is likely related to a sudden structural change of the suspension. The near-wall flow showed existence of a slip layer of 2–12 μm thickness depending on the flow rate. Both the velocity profile measurement and the amplitude data obtained with OCT indicated that the slip layer was related to a concentration gradient appearing near the tube wall. Close to the wall the fluid appeared nearly Newtonian with high shear rates, and the viscosity approached almost that of pure water with decreasing distance from the wall. The flow rates given by a simple model that included the measured yield stress, viscous behavior, and slip behavior, was found to give the measured flow rates with a good accuracy.

Provide a suitable range to include the thermal creeping effect on slip velocity and temperature jump of an air flow in a nanochannel by lattice Boltzmann method

Abstract: The thermal creeping effect on slip velocity of air forced convection through a nanochannel is studied for the first time by using a lattice Boltzmann method. The nanochannel side walls are kept hot while the cold inlet air streams along them. The computations are presented for the wide range of Reynolds number, Knudsen number and Eckert number while slip velocity and temperature jump effects are involved. Moreover appropriate validations are performed versus previous works concerned the micro–nanoflows. The achieved results are shown as the velocity and temperature profiles at different cross sections, streamlines and isotherms and also the values of slip velocity and temperature jump along the nanochannel walls. The ability of the lattice Boltzmann method to simulate the thermal creeping effects on hydrodynamic and thermal domains of flow is shown at this study; so that its effects should be involved at lower values of Eckert number and higher values of Reynolds number especially at entrance region where the most temperature gradient exists.

Core-annular miscible two-fluid flow in a slippery pipe: A stability analysis

Abstract: This study is motivated by the preliminary direct numerical simulations in double-diffusive (DD) core-annular flows with slip at the wall which displayed elliptical shaped instability patterns as in a rigid pipe case; however, slip at the pipe wall delays the onset of instability for a range of parameters and increases the phase speed. This increased our curiosity to have a thorough understanding of the linear stability characteristics of the miscible DD two-fluid flow in a pipe with slip at the pipe wall. The present study, therefore, addresses the linear stability of viscosity-stratified core-annular Poiseuille flow of miscible fluids with matched density in a slippery pipe in the presence of two scalars diffusing at different rates. The physical mechanisms responsible for the occurrence of instabilities in the DD system are explained through an energy budget analysis. The differences and similarities between core-annular flow in a slippery pipe and in a plane channel with velocity slip at the walls are explored. The stability characteristics are significantly affected by the presence of slip. The diffusivity effect is non-monotonic in a DD system. A striking feature of instability is that only a band of wavenumbers is destabilized in the presence of moderate to large inertial effects. Both the longwave and shortwave are stabilized at small Reynolds numbers. Slip exhibits a dual role of stabilizing or destabilizing the flow. The preliminary direct numerical simulations confirm the predictions of the linear stability analysis. The present study reveals that it may be possible to control the instabilities in core-annular pressure driven pipe flows by imposing a velocity slip at the walls.

Slip length for transverse shear flow over a periodic array of weakly curved menisci

Abstract: By exploiting the reciprocal theorem of Stokes flow, we find an explicit expression for the first order slip length correction, for small protrusion angles, and for transverse shear over a periodic array of curved menisci. The result is the transverse flow analogue of the longitudinal flow result of Sbragaglia and Prosperetti [“A note on the effective slip properties for microchannel flows with ultrahydrophobic surfaces,” Phys. Fluids 19, 043603 (2007)]. For small protrusion angles, it also generalizes the dilute-limit result of Davis and Lauga [“Geometric transition in friction for flow over a bubble mattress,” Phys. Fluids 21, 011701 (2009)] to arbitrary no-shear fractions. While the leading order slip lengths for transverse and longitudinal flow over flat no-shear slots are well-known to differ by a factor of 2, the first order slip length corrections for weakly protruding menisci in each flow are found to be identical.