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The work described is concerned with the behavior of plain, hydrodynamic joulnal bearings during starting and stopping under a steady load.The starting behavior indicated that a rapid buildup of hydrodynamic forces occurred i n all cases. A hydrodynamic film was formed i n a very short time, after which the shaft moved in a spiral shaped whirling locus to the steady state operating position. Prior to separation of the shaft and bearing srcfaces, the contact was mainly a sliding situution with little or no initial rolling. At stopping, the shaft followed a typical Iiydrodynamic locus until rotation ceased and then a squeeze film trajectory to the final resting position.

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The majority of hydrostatic thrust bearings are designed on the assumption that the bearing surfaces are parallel but, with the possibility of manufacturing and assembly errors and structural deformations, this condition is rarely, if ever, achieved in practice. With the increasing demands being made in modern machinery, more detailed design information is required. An experimental and theoretical investigation was carried out into the effects of tilt on the operation of circular hydrostatic thrust pads, the results of which show that, for static conditions, the characteristics of a tilted pad can be reliably predicted, assuming the lubricant to be isoviscous. With this information, a thrust pad can be designed to operate in any specified tilted configuration or can be incorporated in a rigorous structural design. In many applications, however, it may be difficult to specify the tilt and in such situations it is more useful for the designer to have some indication of how the operating conditions may be modified by tilt when the design is based on parallel surfaces. For a system which is supplied from a constant pressure source through a viscous external restrictor, the modified operating conditions can be predicted. The effect of tilt on the operating conditions depends on the pad geometry and design resistance ratio but significant changes may occur in mean pad clearance, required flow rate and static stiffness. Although this investigation was limited to static conditions, the results are still valid for sliding conditions where the hydrodynamic effects are small compared with the hydrostatic contribution. The general effects of tilt observed with circular pads are indicative of what may be expected with pads of other geometries.

The use of porous materials in externally pressurized thrust bearings i s attractive. Compared with conventional externally pressurized bearings, there is a more even distribution of pressure at the thrust face and a n external restrictor is not required, which leads to a compad design.A theoretical analysis of a n externally pressurized, circular, porous thrust pad i s presented and the effects of pad geometry and permeability anisotropy on the load and flow characteristics are demonstrated. The pumping power and stiffness characteristics are derived for a range of pad geometries and show the conditions for minimum power consumption and maximum stiffness. The characteristics are such that it is possible to operate a bearing so that the power and stiffness are both close to their optimum values.