Squeeze and Entraining Motion in Nonconformal Line Contacts. Part II—Elastohydrodynamic Lubrication

1989 ◽  
Vol 111 (1) ◽  
pp. 8-16 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock
Keyword(s):  
Transient Process ◽  
Peak Pressure ◽  
Initial Conditions ◽  
Hydrodynamic Lubrication ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Maximum Pressure ◽  
Steady State Condition ◽  
Maximum Peak ◽  
Line Contacts

A fast numerical approach to the solution of elastohydrodynamic lubrication (EHL) of line contacts in combined entraining and normal squeeze motion is developed. The initial conditions for the pressure profile, the central normal squeeze velocity, and the location of the outlet boundary at any specified dimensionless load and dimensionless entraining velocity were obtained from the hydrodynamic lubrication study in Lee and Hamrock (1988). The pressure and film thickness were obtained by solving the transient Reynolds, elasticity, rheology, and time-dependent central squeeze velocity equations. The squeeze effect on this transient EHL problem has been proved in that the maximum peak pressure was always higher than the maximum pressure calculated at the steady-state condition. The needle-shaped pressure profile during the transient process produced a dimpled shape near the center of the contacts. In general, the maximum peak pressure increased with increasing dimensionless load, decreasing dimensionless entraining velocity, and increasing dimensionless materials parameter. The dynamic performance parameters were plotted and are a function not only of the dimensionless velocity parameter (as described in Lee and Hamrock, (1988)), but also of the dimensionless load, the dimensionless entraining velocity, and the dimensionless materials parameter. The major factor causing the pressure gradient to be infinity during the transient process was the viscosity. A non-Newtonian fluid is suggested to execute the problem for high load and low entraining velocity.

A fast thermoelastic model based on the half-space theory applied to elastohydrodynamic lubrication of line contacts involving free boundaries

2021 ◽  
pp. 1-29
Author(s):  
Ali Yalpanian ◽  
Raynald Guilbault
Keyword(s):  
Finite Dimension ◽  
Elastohydrodynamic Lubrication ◽  
Contact Problems ◽  
Pressure Profile ◽  
Distribution Center ◽  
Maximum Pressure ◽  
Free Boundaries ◽  
Heat Flows ◽  
Line Contacts ◽  
Contact Models

Abstract This study allows contact models based on semi-analytical methods including the impacts of thermoelastic deformations in contacts of finite dimension bodies. The proposed method controls heat flows crossing free boundaries. A comparison with FEA reveals that the proposed method can reduce the calculation times by more than 98%. The paper introduces the thermoelasticity effects into thermal-elastohydrodynamic lubrication (TEHL) modeling of line contact problems. The analysis reveals that including thermoelastic deformations changes the pressure profile and tends to localize the pressure close to the distribution center. Compared to TEHL simulations, the examined configurations caused an overall increase in the maximum pressure by about 9%, an overall film thickness reduction of about 7%, and an overall temperature increase of about 2 K.

Squeeze and Entraining Motion in Nonconformal Line Contacts. Part I—Hydrodynamic Lubrication

1989 ◽  
Vol 111 (1) ◽  
pp. 1-7 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock
Keyword(s):  
Hydrodynamic Lubrication ◽  
Dynamic Performance ◽  
Elastohydrodynamic Lubrication ◽  
Constant Load ◽  
Initial Guess ◽  
Maximum Pressure ◽  
Performance Parameters ◽  
Velocity Parameter ◽  
Dimensionless Velocity ◽  
Line Contacts

An analytical solution to the problem of combined entraining and normal squeeze motion in nonconformal line contacts hydrodynamically lubricated with an isoviscous, incompressible lubricant has been obtained without any limitations on dimensionless load, dimensionless entraining velocity, and dimensionless velocity parameter. The dimensionless load and entraining velocity are fixed for a complete range of operating parameters for both normal approach and separation. Results show that the lubrication of the outlet boundary and the location of the maximum pressure move upstream into the inlet region as the central film thickness decreases or the dimensionless velocity parameter increases from negative (normal approach) to positive (normal separation). All the dynamic performance parameters relating to the steady-state bearing performance parameters have been found to be functions of only the dimensionless velocity parameter with constant load and entraining velocity. The dimensionless velocity parameter significantly influenced those dynamic performance parameters. The results of this study will be used as the initial guess for the elastohydrodynamic lubrication of nonconformal line contacts.

The Effect of Oil Supply Pressure on the Circumferential Pressure Profile in Hydrodynamic Journal Bearing

2013 ◽  
Vol 315 ◽  
pp. 809-814 ◽  
Author(s):  
Mohamad Ali Ahmad ◽  
Salmiah Kasolang ◽  
Rob Dwyer-Joyce ◽  
Nik Rosli Abdullah
Keyword(s):  
Journal Bearing ◽  
Hydrodynamic Lubrication ◽  
Pressure Profile ◽  
Journal Bearings ◽  
Maximum Pressure ◽  
Oil Supply ◽  
Supply Pressure ◽  
Machine Elements ◽  
Hydrodynamic Journal Bearing ◽  
Circumferential Pressure

In hydrodynamic lubrication, the pressure condition of the fluid is critical to ensure good performance of the lubricated machine elements such as journal bearings. In the present study, an experimental work was conducted to determine the effect of oil supply pressure on pressure profile around the circumference of a journal bearing. A journal diameter of 100mm with a ½ length-to-diameter ratio was used. The oil supply pressure was set at three different values (0.3, 0.5, 0.7 Mpa) and the circumferential pressure results for 400, 600 and 800 RPM at different radial loads were obtained. It was observed that the maximum pressure values were affected by changes in oil supply pressure.

Thermal Non-Newtonian Elastohydrodynamic Lubrication of Rolling Line Contacts

1991 ◽  
Vol 113 (3) ◽  
pp. 481-491 ◽  
Author(s):  
H. Salehizadeh ◽  
N. Saka
Keyword(s):  
Film Thickness ◽  
Contact Region ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Shear Stresses ◽  
Hertz Contact ◽  
Minimum Film Thickness ◽  
Line Contacts ◽  
Pressure Spike ◽  
Heavy Loads

The two-dimensional thermal elastohydrodynamic equations were numerically solved for a Ree-Eyring type lubricant under pure rolling conditions. Profiles of lubricant pressure, film thickness, and temperature were obtained for medium to heavy loads and moderate to high rolling speeds. The pressure results generally show a small secondary peak near the outlet, but at the highest load considered no pressure spike is obtained and the pressure profile is almost Hertzian. The film thickness results show an increase in minimum film thickness with increasing rolling speeds, but at a lesser rate than those predicted for a Newtonian fluid under isothermal conditions. It is found that unless the lubricant becomes non-Newtonian in the inlet region, the reduction in minimum film thickness at high rolling speeds is completely due to thermal effect. The lubricant temperature profile and the amount of heat generated and dissipated in the contact region were also calculated. The lubricant temperature reaches a maximum just before the entrance to the Hertz contact region. Both shear and compression heating are found to be important in raising the lubricant temperature in the inlet. As the lubricant enters the Hertz contact zone, the temperature first drops rapidly, because of the rapid heat conduction to the rollers, and then remains almost constant for most of the Hertz contact. Near the exit where the pressure gradients are large, the lubricant temperature drops rapidly below the ambient because of lubricant expansion. The lubricant then heats up rapidly before leaving the contact area as a result of heat generated by shear stresses.

Time Dependent Line EHD Lubrication Using the Multigrid/Multilevel Technique

1992 ◽  
Vol 114 (1) ◽  
pp. 68-74 ◽  
Author(s):  
K. F. Osborn ◽  
F. Sadeghi
Keyword(s):  
Elastohydrodynamic Lubrication ◽  
Time Dependent ◽  
Operating Parameters ◽  
Response Behavior ◽  
Steady State Condition ◽  
Elasticity Equations ◽  
Ehd Lubrication ◽  
Line Contacts ◽  
Lubricated Contact ◽  
Analysis Models

A numerical solution of time dependent compressible elastohydrodynamic lubrication of line contacts has been obtained. The results show the effects of various operating parameters on the transient response behavior of a lubricated contact. The analysis models a startup situation where the surfaces are initially at rest and in contact. Then, with the contacts operating at a given load and speed, the analysis is run until the pressure and film thickness reach a steady-state condition. A multigrid/multilevel technique is used to simultaneously solve the time dependent Reynolds and elasticity equations. The effects of various loads and speeds have been investigated. Results are presented for nondimensional loads ranging from W = 2.0 × 10−5 to W = 2.3 × 10−4 and nondimensional speeds ranging from U = 1.0 × 10−12 to U = 1.0 × 10−10.

Elastohydrodynamic lubrication of coated finite line contacts

2017 ◽  
Vol 232 (9) ◽  
pp. 1077-1092 ◽  
Author(s):  
Shivam S Alakhramsing ◽  
Matthijn B de Rooij ◽  
Dirk J Schipper ◽  
Mark van Drogen
Keyword(s):  
Mechanical Properties ◽  
Film Thickness ◽  
Surface Profile ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Maximum Pressure ◽  
Lubrication Performance ◽  
Line Contacts ◽  
Finite Line ◽  
Axial Surface

In this work, a finite element-based model is presented that simulates elastohydrodynamic lubrication in coated finite line contacts. Using this model, the film thickness and pressure distributions, between a straight roller with rounded edges on a plate, were analyzed. The model was successfully validated against representative results reported in literature. Parameter studies were conducted to study the influence of varying operating conditions, axial surface profile parameters and coating mechanical properties on the overall elastohydrodynamic lubrication behavior of the contact. It was found that in contrast with typical elastohydrodynamic lubrication behavior, the maximum pressure and minimum film thickness, which are located at the rear of the contact, are largely influenced by variations in load. Results also reveal that axial surface profile parameters and coating mechanical properties may act as amplifiers to the effect of load on pressure and film thickness distribution and can thus, if smartly chosen, significantly enhance lubrication performance.

Bio–Based Lubricants for Numerical Solution of Elastohydrodynamic Lubrication

2012 ◽  
Vol 58 (2) ◽  
Author(s):  
Dedi Rosa Putra Cupu ◽  
Jamaluddin Md Sheriff ◽  
Kahar Osman
Keyword(s):  
Numerical Solution ◽  
Vegetable Oils ◽  
Peak Pressure ◽  
Contact Region ◽  
Roller Bearing ◽  
Elastohydrodynamic Lubrication ◽  
Infinite Cylinder ◽  
Line Contacts ◽  
Cylindrical Roller Bearing ◽  
Cylindrical Roller

This paper presents a numerical solution of elastohydrodynamic lubrication (EHL) problem in line contacts which is modeled through an infinite cylinder on a plane to represent the application of cylindrical roller bearing. In this work, the contact between roller element and raceway of outer ring of the cylindrical roller bearing is simulated using vegetable oils as bio-based lubricants. Temperature is assumed to be constant at 40oC. The results show that the EHL pressure for all vegetable oils was increasing from inlet flow until the center, then decrease a bit and rise to the peak pressure. The shapes of EHL film thickness for all tested vegetable oils are almost flat at contact region.

PAPER PHYSICS. The web structure in relation to the furnish composition and shoe press pulse profiles during wet pressing

2012 ◽  
Vol 27 (4) ◽  
pp. 798-805 ◽  
Author(s):  
Collin Hii ◽  
Øyvind W. Gregersen ◽  
Gary Chinga-Carrasco ◽  
Øyvind Eriksen ◽  
Kai Toven
Keyword(s):  
Porous Structure ◽  
Peak Pressure ◽  
Pulse Length ◽  
Pressure Profile ◽  
Steam Consumption ◽  
Web Structure ◽  
Wet Pressing ◽  
Solids Content ◽  
In The Beginning ◽  
The Web

Abstract This study shows that wet-pressing TMP and DIP with a shoe press pulse may yield similar afterpress solids, provided that an adequate shoe pulse length with similar pressure profile is applied. A wet web with more porous structure in the sheet dewatering (felt) layer seems to contribute to the increased dewatering during wet pressing. In addition, a shoe press pulse with high peak pressure at the end yields higher solids content after wet-pressing and higher bulk compared to a pulse with a peak pressure in the beginning. The increased dewatering during wet-pressing implies a reduction of steam consumption in the dryer.

Risk assessment in mission planning of uninhabited aerial vehicles

2019 ◽  
Vol 233 (10) ◽  
pp. 3499-3518 ◽  
Author(s):  
Giulio Avanzini ◽  
David S Martínez
Keyword(s):  
Initial Conditions ◽  
Mission Planning ◽  
Unmanned Aerial Systems ◽  
Steady State Condition ◽  
Motion Primitives ◽  
Uninhabited Aerial Vehicles ◽  
Aerial Systems ◽  
The Impact ◽  
Navigation Errors ◽  
Time Of Failure

A procedure for evaluating the risk related to the use of unmanned aerial systems over populated areas is proposed. A nominal trajectory, planned for performing a given mission, is represented by means of motion primitives, that is segments and arcs flown in a steady-state condition. The risk of hitting a person on the ground after catastrophic failure is evaluated as a function of vehicle reliability and population density (assumed known), and position of the impact point (which depends on initial conditions at the time of failure and trajectory flown afterwards). In the deterministic case, a lethal area is introduced and the risk at each point on the ground is proportional to the amount of time spent by the point inside the lethal area. Under the assumptions of a ballistic fall, the position of the lethal area with respect to the nominal trajectory depends only on altitude and velocity at the time of failure. When the effect of navigation errors is introduced, impact points are described by a statistical impact footprint, assuming that position and velocity errors at time of failure are normally distributed with known standard deviations. The two approaches are compared for a fictitious, yet realistic, mission scenario.

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