Current Issue : April - June Volume : 2013 Issue Number : 2 Articles : 5 Articles
The precise knowledge of the force and moment generated by the air squeezed under the read-write slider by the rotating disc is an\r\nengineering necessity in designing the air bearing surface slider. This paper reviews methods addressing the thin gas film bearings\r\nproblem. It firstly reviews briefly the relatively well-known two methods of calculations of the microgas flows under flying head\r\nsliders, the generalized Reynolds equation, having given a number of useful results of slider design, and the DSMC method, which\r\nis precise and appropriate for the flow of complex configurations but is restricted to miniature (~micrometer) size sliders. The\r\nmain purpose of the paper is to introduce to the reader an alternative method, the information preservation (IP) method, for use\r\nin simulation of the flows under air bearing surfaces. Some recent results of IP simulation of slider flows published on conference\r\nproceedings are introduced here....
Efficiency is becoming a main concern in the design of power transmissions. It is therefore important, especially during the design\r\nphase, to have appropriate models to predict the power losses. For this reason, CFD (computational fluid dynamics) simulations\r\nwere performed in order to understand the influence of geometrical and operating parameters on the losses in power transmissions.\r\nThe results of the model were validated with experimental results....
In a rolling element system, the period of transition between motion commencement and the attainment of steady state, gross\r\nrolling, and termed prerolling is of common concern to many engineering applications. This region is marked by hysteresis friction\r\nbehavior, with a characteristic friction-displacement curve, which is in particular relevant to motion characterization and control\r\nissues. In a previous paper, the authors carried out a theoretical analysis of tractive prerolling, leading to a model for simulating this\r\nphenomenon. The present paper is dedicated to the experimental investigation of tractive prerolling friction behavior, including\r\nvalidation of the theoretical model. Firstly, a kinematic analysis of the rolling motion in V-grooved tracks is carried out. Secondly,\r\nthe influence of the normal load on the frictional behavior, in prerolling up to the attainment of gross rolling, is investigated on\r\na dedicated test setup. Finally, the newly developed theoretical model is validated by comparison with the experimental results.\r\nSatisfactory agreement is obtained between theory and experiment....
The knowledge of the film thickness values is very important in lubricated contacts to verify the lubrication conditions. Optical interferometry\r\nis one of the most used methodologies for film thickness and shape determination of Elastohydrodynamic-lubricated\r\ncontacts. An image processing programme has been developed for the analysis of white light interferograms. The programme,\r\nbased on the analysis of the hue channel, has been developed in order to process big amounts of images, as often generated under\r\ntransient conditions. The measurement range is currently limited to a maximum film thickness of 0.7 �µm. The programme has\r\nbeen used for analysing several images recorded in tests carried out with a ball on disc contact under steady-state as well as transient\r\nconditions for different velocities and slide-to-roll ratios. Under transient conditions, the entraining velocity is varied with a\r\nsinusoidal law for two different frequencies. The results obtained evidenced an asymmetric reduction of the film thickness when\r\nincreasing the percentage of sliding, both for stationary and transient conditions. Under transient conditions with increasing test\r\nfrequency, film thickness loops of increasing amplitude have been found that reduce their amplitude more when the ball is running\r\nfaster than the disc. Squeeze and thermal effects can explain the results obtained....
The improvement of mechanical contacts or microcontacts seeks a nearly uniform current density over most of contact area.\r\nWhen microtopography is homogeneous, this aim is achieved if nominal shape of contacting surfaces yields a nearly uniform\r\ncentral pressure which decreases monotonously to zero in contour points. These authors derived recently this shape for circular\r\ncontacts by employing high-order surfaces. This paper extends this result to elliptical contacts. Some results are used to this end,\r\nderived for elliptical elastic contacts between high-order surfaces. As homogeneous high order surfaces lead to a highly nonuniform\r\npressure distribution, central pressure is flattened by making the first derivatives of pressure vanish in contact center. Then, the\r\ncontacts between fourth, sixth, and eighth, order surfaces are analyzed and recurrence relations for pressure distribution and\r\ncontact parameters are proposed....
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