It is well known that the bearing coefficients of oil film journal bearings are speed dependent. From the derivation of Tiwari et al., the numbers of unknown coefficients are twice the number of the equations relating to unbalance responses. That means at least two unbalance test runs are necessary to solve the bearing coefficients, no matter how many measurements are made, and the rotating machines have to stop once to adjust the unbalance configurations for the second test run. In this study, second order polynomials are assumed to fit the bearing coefficients in a specific speed range, and unbalance measurements are made at several rotating speeds in that speed range to solve for the polynomial coefficients. The advantages of this approach are that it fulfills the conditions of speed-dependent coefficients, the bearing coefficients can be obtained without stopping the machines, and on-line identification of bearing coefficients can be achieved. Noise reduction and interpolation for the bearing coefficients at other speeds can also be easily attained.
Closure to “Discussions of ‘The Influence of Oil-Film Journal Bearings on the Stability of Rotating Machines’” (1947, ASME J. Appl. Mech., 14, pp. A77–A78)