Calculation of Polynomial Curves for Speed-Dependent Bearing Coefficients Available to Purchase

Estimating bearing coefficients based on the vibration responses under operating conditions is the most precise approach that reflects the true conditions of the bearings. For speed-dependent bearing coefficients, such as oil-film journal bearings, the numbers of unknown coefficients are twice the number of the equations relating to unbalance responses, as pointed out by Tiwari et al.. At least two unbalance test runs are necessary to solve the bearing coefficients from unbalance responses, which means the rotating machines have to stop at least once to adjust the unbalance configurations for the second test run. This research aims at identifying the bearing coefficient curves in only one test run by using the unbalance responses at different rotating speeds within a specific speed range. In a wider range of operating speeds, the variations of bearing coefficient curves may have two bends, as well as the critical speeds may occur within the speed range. Third-order polynomials, which can follow the two-bend trends, are used to approximate the coefficient curves of speed-dependent bearings in this paper. The coefficients of the polynomials are calculated from the unbalance responses directly. The merits of identification with one test run are that it does not require the rotating machines to stop for the setting of independent unbalance configurations and is suitable for on-line identification of the bearing coefficients. The feasibility of the proposed method is studied by simulation and the noise effects around critical speeds are also investigated.