Showing papers on "Slip ratio published in 1993"

Slip transition of a polymer melt under shear stress.

Abstract: We present the first direct measurements of the local velocity of a sheared polymer melt within the first 100 nm from the solid-liquid interface. For high enough shear rates we observe a sharp transition between weak and strong slip (i.e., a nonzero boundary fluid velocity) in the case of weak polymer-surface interactions [polydimethylsiloxane (PDMS) on silanated silica surfaces]. For strong polymersurface interactions the slip is strongly reduced. These results are compared to a theoretical model recently proposed by Brochard and de Gennes

The rheology of concentrated dispersions of weakly attracting colloidal particles with and without wall slip

Abstract: It is demonstrated that weakly flocculated, concentrated colloidal dispersions show slip flow when sheared between smooth concentric cylinders. The precise pattern of behavior seen depends upon the stress and upon how long the flow is left to establish prior to measurement. With delay times of order hours, slip is not seen until a critical stress is exceeded (typically about 1 Pa) and, thus, the true low‐shear viscosity can be determined provided care is taken to ensure the stress does not exceed the critical level. With short delay times of order minutes, slip is seen irrespective of how small the stress is and the low‐shear viscosity can be underestimated by several orders of magnitude. Comparisons of flow curves obtained using smooth and roughened cylinders show that slip only occurs at the inner cylinder, and also that bulk flow is re‐established at higher stresses where the dispersions start to shear thin. The apparent low‐shear, relative viscosity measured in the presence of slip appears, to a first...

Wall slip in the extrusion of linear polyolefins

Abstract: A molecular model, based on the concept of the activation rate theory, is developed for slip of a polymer as it flows through a die. The model correctly predicts the dependence of the critical shear stress for the onset of slip and the slip velocity of high molecular weight, linear polyethylene resins on temperature, pressure, wall shear stress, and molecular weight. It also predicts the increased slip which occurs when die surfaces are coated with a fluoropolymer having a low surface tension. It is not applicable at and above the critical shear stress for the onset of gross melt fracture.

Stick and Slip Behaviour of Confined Oligomer Melts under Shear. A Molecular-Dynamics Study.

Abstract: The flow behaviour of melts of short chains, confined in molecularly thin Couette flow geometries, is studied with molecular-dynamics simulations. The effect of wall attraction and confinement on the density and velocity profiles is analysed. In these highly inhomogeneous films, a strong correlation between the density and velocity profile is found. Sticking of the interfacial layer on the wall and slip on the wall and inside the film is manifested by changes in the velocity profile. The location of the slip is determined by the strength of the wall attraction.

Anti-skid braking method and system

Abstract: An anti-skid braking method is provided for controlling, on the basis of a slip ratio of a wheel and an acceleration of the wheel, braking force to be applied to the wheel. The anti-skid braking method comprises the following steps: where the slip ratio is found to fall outside an appropriate range during slip ratio computation, adding differences between a limit defining the appropriate range and the respective slip ratio values so computed; and when the integral of the differences is at least equal to a predetermined value and the acceleration of the wheel is detected to be low, enhancing the control of the braking force, the control being performed based on the wheel acceleration and the slip ratio, so that the slip ratio is brought back into the appropriate range. An anti-skid braking system suitable for use in practicing the anti-skid braking method is also described.

Simulation method and device for aiding the design of a fluid torque converter

Abstract: In a method and device for simulating properties of a fluid torque converter such as torque ratio, capacity factor and efficiency involving the execution of the steps of finding a plurality of parameters including a fluid passage angle and a fluid passage resistance from a vane profile of a vane wheel of a fluid torque converter, and simulating the properties of said fluid torque converter according to said parameters and an input and output torque relationship based on an angular momentum theory, said fluid passage angle is corrected according to a slip ratio between rotational speeds of input and output ends of the fluid torque converter for the purpose of accounting for the influences of the occurrence of flow separation. Good results can be obtained by correcting the outflow angle of a stator vane array by using a correction value given as a mathematical function of the slip ratio. Thus, the accuracy of simulation can be substantially improved with a minimum increase in the computer time.

Anti-skid braking method

Abstract: In a first mode, an integral (JD1) of a high-frequency component of a longitudinal acceleration of a vehicle body is modified in accordance with an average (FGS) of a low-frequency component of the longitudinal acceleration by road roughness computing means (75) and a slip ratio is then corrected in accordance with the modified integral (JD2) to obtain a corrected slip ratio (HJDR,HJDRR). In a second mode, the value of a high-frequency component of a longitudinal acceleration of the vehicle body is modified by a wheel acceleration (FGrr,FGrl), sensed through a high-pass filter (71), an absolute value device (72) and a multiplier (73); a slip ratio is then corrected in accordance with the modified value of the high-frequency component of the longitudinal acceleration to obtain a corrected slip ratio (HJDR,HJDRR).

Normalization of Tire Force and Moment Data

Abstract: Semi‐empirical theories of tire mechanics are employed to determine appropriate means to normalize forces, moments, angles, and slip ratios. Force and moment measurements on a P195/70R 14 tire were normalized to show that data at different loads could then be superimposed, yielding close to one normalized curve. Included are lateral force, self‐aligning torque, and overturning moment as a function of slip angle, inclination angle, slip ratio, and combinations. It is shown that, by proper normalization of the data, one need only determine one normalized force function that applies to combinations of slip angle, camber angle, and load or slip angle, slip ratio, and load. Normalized curves are compared for the effects of inflation pressure and surface water thickness. Potential benefits as well as limitations and deficiencies of the approach are presented.

A critique of slip and stick hydrodynamics for ellipsoidal bodies

Abstract: Translational friction coefficients of hard prolate ellipsoids (having aspect ratios of 1–10) have been calculated by solving the linearized Navier-Stokes equations of hydrodynamics, using the method of Faxen's theorem. When the stick boundary condition was used, the present results reproduce the famous work of Lamb. The new information derived from this study arises from the analysis of the friction under the influence of the slip hydrodynamic boundary condition. It was found that the slip friction perpendicular to the long axis of the prolate ellipsoid increases monotonically with aspect ratio, whereas the parallel component of the friction decreases monotonically to an apparent limiting value. The ratio f ⊥/f ‖ of friction coefficients perpendicular and parallel to the long axis of the particle, calculated using slip hydrodynamics, scales roughly as the aspect ratio of the ellipsoid, in accord with the findings from an Enskog (uncorrelated binary collision) kinetic theory of hard ellipsoids and from th...

Slip flow in converging and diverging channels

Abstract: The classical problem of Jeffery-Hamel flow is considered in which the fluid is allowed to slip along the walls of the channel The problem is solved analytically and the volumetric flow rate is computed and compared with that of the corresponding no-slip flow In the converging channel case, it is found that the slip boundary condition enhances flow rates through the channel, although the effect is minimal when the Reynolds number is large

Traction control apparatus for automotive vehicle

Abstract: A traction control apparatus for carrying out a traction control process of an automotive vehicle in order to control a throttle position of a throttle valve. The apparatus includes: a feedback control part for performing a feedback control process to adjust a throttle position of a sub-throttle valve based on a slip ratio of driving wheels of the vehicle, so as to prevent the vehicle from undergoing excessive slippage at the driving wheels when the vehicle is accelerating; an inhibiting part for setting the throttle position of the throttle valve to a first value by inhibiting the performing of the feedback control process when a traction control process is started; a first control part for enabling the inhibiting part to inhibit the performing of the feedback control process until a slip ratio convergence is detected; and a second control part for setting the throttle position of the throttle valve to a second value smaller than the first value when the driving wheel slip ratio is not converging after the throttle position has been changed to the first value at the start of the traction control process.

Anti-lock brake device

Abstract: PURPOSE:To prevent erroneous brake control by correcting slip ratio in accordance with vibration speed of an axle shaft, and road surface frictional force in accordance with vibratory acceleration of the axle shaft, in an anti lock brake device which controls brake force based on variation of the slip ratio of a wheel and variation of road surface frictional force. CONSTITUTION:A wheel speed sensor 12, a road surface frictional sensor 13, an a vertical drag sensor 14 are provided on a wheel 2; and output signals of those sensors are fed to a control device 1. An acceleration sensor 15 for detecting vibratory acceleration of the wheel is attached to the axle shaft of the wheel 2, and an acceleration component following the deceleration of a car body is removed from the output by means of a high-pass filter 16 and only acceleration component following the vibration of the axle shaft is fed to the control device 1. The control device 1 calculates the slip ratio of the wheel according to wheel speed and car body speed, and accelerates the vibratory speed of the axle shaft to the car body speed to correct the slip ratio. Further, inertia force component following to the axle shaft vibration included in the detected value of the road surface frictional force is canceled from the vibratory acceleration of the axle shaft, so as to correct the road surface frictional force.

Traction control apparatus in which a driving force is increased when a stalling condition is detected

Abstract: A traction control apparatus includes a determining part (11) for determining a slip ratio of driving wheels (27, 28) of a vehicle (20), a drive torque control part (12) for performing a traction control process in which a driving force of the driving wheels is controlled such that the driving force is lowered to a smaller value when the slip ratio determined by the determining part (11) is greater than a reference value, a detecting part (13) for detecting a stalling condition of the vehicle, and a changing part (14) for changing the traction control process performed by the drive torque control part (12) when a stalling condition is detected by the detecting part (13), so as to increase the driving force of the driving wheels.

Fem predictions for two‐phase flow in a vertical pipe without the use of any external correlations

Abstract: A mathematical model is developed for the description of the thermohydraulics of the two‐phase flow phenomenon in a vertical pipe. Using an additional momentum equation for the slip velocity, it is shown that the computation of slip and pressure drop from the model equations is possible without the use of any external correlations. The finite element method is used to solve the governing equations. The predictions for a steam‐water two‐phase flow in vertical upflow with constant wall heat flux agree well with experimental results and with widely used correlations.

A model for predicting slip velocity during extrusion with fluoropolymer processing additives

Abstract: A molecular model, based on the concept of the activation rate theory, is developed for slip of a polymer as it flows through a die. The model correctly predicts the dependence of the apparent slip velocity of high molecular weight, linear polyethylene resins on wall shear stress, up to the onset of gross melt fracture. It also predicts the increased slip which occurs when die surfaces are coated with a fluoropolymer processing aid having a low surface tension.

Laminar Flow with Slip in Channels with Uniformly Porous Walls

Abstract: The assumption of no slip does not accurately characterize momentum transfer near permeable walls. The influence of nonzero slip velocities on velocity profiles, pressure distribution, and friction coefficient are reported for laminar flow in a parallel plate channel with uniform suction or injection through its porous boundaries. The 2‐D Navier‐Stokes equations are reduced to a third‐order, nonlinear, ordinary differential equation with one free parameter by introducing an appropriate stream function that is then solved numerically. This solution is valid for arbitrary values of the wall Reynolds number Rw, based on the half‐channel height and the suction wall velocity. Suction at the porous boundary appears to have a greater impact on fluid mechanics compared to injection. It is observed that at a fixed value of the slip coefficient, increasing suction results in thinner momentum boundary layers whereas for a fixed wall Reynolds number, velocity profiles approach plug flow with increasing slip. It is al...

Characteristics of Granular Flow in an Inclined Open Channel

Abstract: The experiments of granular flow were made in an inclined open chanel under three kinds of bed condition; one was a rough fixed bed and the others were smooth fixed beds of plywood and acrylic board. Vertical velocity profile, surface velocity and depth of the flows were measured by using a high-speed video camera.Uniform velocity profile is observed on the smooth beds, while high shear flow on the rough bed. The ratio of surface velocity to friction velocity doesn't change with an increase in the ratio of flow depth to grain diameter on the smooth beds. On the other hand, the former ratio increases with the latter ratio on the rough bed. The ratio of average velocity to friction velocity has almost same value as that for debris flow.

Drive wheel slip control device

Abstract: PURPOSE:To prevent overheating of an exhaust gas purification device when an engine output is reduced, in a drive wheel slip control device CONSTITUTION:In stationary operating conditions, a table 1 is selected and, according to increase in slip ratio output by an overslip detecting means of drive wheels, an engine output is reduced progressively by an ignition retard, air-fuel ratio leaning of all cylinders, and a means including combination of air-fuel ratio leaning with fuel cut When a condition in which both an engine speed and a slip ratio exceed a specified limit continues for a specified period, a table 2 is selected and an engine output is reduced progressively by a means not including the ignition retard and the air-fuel ratio leaning of all cylinders, whereby overheating of an exhaust gas purification device can be prevented Also, in place of the condition in which both the engine speed and the slip ratio exceed specified limits continues for a specified period, even if timing for switching over from the table 1 to the table 2 is set at a time when the floor temperature of the exhaust gas purification device exceeds a specified limit, the overheating of the exhaust gas purification device can be prevented

Lone drawing method for extra fine wire

Abstract: PURPOSE:To prevent the occurrence of problems such as disconnection by constantly controlling a slip ratio. CONSTITUTION:In a lubricating oil, a line drawing is performed on a extra fine wire through plural numbers of dies having a prescribed diameter decrease ratio and through the circumference of a capstan. Then, a slip type line drawing, in which the linear velocity of the extra fine wire is different from the circumferential speed of the capstan, is performed. In a slip ratio controller 15, a specific arithmetic operation is performed from each signal that is inputted in the controller, the results are inputted in a slip ratio display device 17 and displayed in the display device 17. Also, the results from other arithmetic operations are outputted to a take-up motor controller 18 as a revolution setting signal for the driving motor of a take-up spool. Thus, the slip ratio is constantly controlled.

Front wheel drive force control device in four-wheel drive asphalt finisher

Abstract: PURPOSE:To provide a good pavement finish surface by controlling drive force of a front wheel so that a value of slip ratio is in a range of obtaining a maximum friction coefficient, and controlling a peripheral speed of the front wheel synchronized with a rear wheel, so that effective traction force is generated in the front wheel to prevent its racing. CONSTITUTION:Based on rotational speeds N1, N2 detected by rotational speed detectors 72, 52, front/rear wheel peripheral speeds V1, V2 are calculated, and based on each value V1, V2, slip ratio S of a front wheel 6 is calculated. By comparing this slip ratio S with preset slip ratio alpha, in the case of S

Wheel slip ratio control device

Abstract: PURPOSE:To set a slip ratio corresponding to a running condition so as to improve operation stability by calculating lateral force based on handle angle and handle angular speed and longitudinal force based on brake pressure and brake pressure increase ratio, and setting the slip ratio. CONSTITUTION:A handle angle sensor 1 and a brake pressure sensor 2 are provided, and their output signals are input to a controller 3. When the handle angle is large or the handle angular speed is large, a slip ratio attaching importance to lateral force is set in the controller 3, and when the brake pressure is high or the increase ratio of brake pressure is large, a slip ratio attaching importance to longitudinal force is set. The optimum slip ratio set in this way is output to an actuator driver 4, and a prescribed actuator is appropriately operated so as to realize safe running of the vehicle.

Evaluation of open channel flow with varying aspect ratio and roughness ratio

Abstract: A flow pattern with varying aspect ratio (breadth/depth) and boundary roughness ratio (bed roughness/side wall roughness) in open channel is proposed in this paper. The distribution of boundary shear and the mean boundary shear are studied. On the basis of this, velocity distribution and flow resistance are further discussed. The evaluation formulae of boundary shear, velocity distribution and flow resistance are derived systematically. The results are suitable for all aspect ratio and roughness ratio, and are better in agreement with a wide range of experimental data. These are much helpful to the study of sediment transport, flow diffusion, river engineering, etc.