This paper describes a combined theoretical and experimental investigation of the eight oil film stiffness and damping coefficients for a novel low impedance hydrodynamic bearing. The novel design incorporates a recess in the bearing surface which is connected to a standard commercial gas bag accumulator; this arrangement reduces the oil film dynamic stiffness and leads to improved machine response and stability. A finite difference method was used to solve Reynolds equation and yield the pressure distribution in the bearing oil film. Integration of the pressure profile then enabled the fluid film forces to be evaluated. A perturbation technique was used to determine the dynamic pressure components, and hence to determine the eight oil film stiffness and damping coefficients. Experimental data was obtained from a laboratory test rig in which a test bearing, floating on a rotating shaft, was excited by a multi-frequency force signal. Measurements of the resulting relative movement between bearing and journal enabled the oil film coefficients to be measured. The results of the work show good agreement between theoretical and experimental data, and indicate that the oil film impedance of the novel design is considerably lower than that of a conventional bearing.

A novel bearing design is presented. The bearing consists of a partial arc bearing into which two recesses are machined. Attached to the two recesses, via remote-controlled valves, are two accumulators. The ability to be able to open and close the valves gives the new bearing design four independent operating modes. Steady state operating characteristics for the bearing were predicted using a finite difference solution to Reynolds' equation. A new mathematical model is proposed for the recess boundary. The model is based on flow continuity and enables afinite difference node to be positioned on the recess boundary. It is demonstrated that the theoretical model proposed predicts steady state characteristics which agree favourably with previously published work and with experimental data. The model was further utilized, in a pressure perturbation algorithm, to obtain predictions of the bearing's dynamic operating characteristics. It is demonstrated that by switching the valves from open to closed, or vice versa, the bearing's characteristics can be altered in situ. I t is also demonstrated that the inclusion of the recesses and accumulators has little effect on the steady state characteristics whencompared to those of a conventional partial arc bearing. It is suggested that the bearing design proposed in this paper has major advantages to offer the rotating machine designer. Use of the bearing enables the operator to vary support characteristics without major re-machining. Furthermore, support characteristics may be varied in situ, without signifcant cost penalties and with little additional maintenance overheads.

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A novel form of hydrodynamic oil-flm bearing has been examined experimentally to establish both steady state and dynamic characteristics. The novel bearing design is based on a 120" partial arc bearing but contains two recesses to which are attached accumulators. The facility to open or close a valve located between the accumulator and the recesses enables the engineer to effectively tune the in situ. This bearing also has the benefit of being similar in cost to a standard bearing. The oil-film coeficients were obtained F y om t efrequency response function obtained when the system was excited by a pseudo random binary sequence signal. The use of the generalized matrix inversion method to determine the oil-film coefficients from thefrequency response function was found to be some 10 per cent faster than the least squares curve-jitting method. Both methods were shown to produce reliable estimates to extract oil-film coefficients.

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