Abstract
A general, CFD-based frequency response method for obtaining the dynamic coefficients of hydrodynamic bearings is presented. The method is grounded in experimental parameter identification methods and is verified for an extremely long, slider bearing geometry as well as short and long journal bearing geometries. The influence of temporal inertia on the dynamic response of the bearings is discussed and quantified through the inclusion of added mass coefficients within the mechanical models of the hydrodynamic bearing films. Methods to separate the dynamic stiffness into static stiffness and added mass contributions are presented and their results compared. Harmonic perturbations are applied to the bearings at varying frequencies to determine the frequency dependence of the dynamic coefficients and to facilitate the decomposition of the dynamic stiffness into its constituents. Added mass effects are shown to be significant for the extremely long slider bearing geometry and negligible for the short and long journal bearing geometries under operating conditions motivated by those typical of marine bearings.
Highlights
In their review paper, Dimond et al [1] presented methods for the identification of bearing dynamic coefficients based on experimentally measured data.They discussed bearing coefficient identification employing force excitation using incremental loading, impulse, pseudo-random, and unbalance excitation applied to a moving shaft and fixed bearing housing, or viceversa
Proceeding, the frequency response functions (FRFs) results will be presented owing to the generality of the method and prevalence in experimental parameter identification techniques
For the long journal bearing, the mesh density was 10 × 100 × 120 and like the short bearing, the predicted dynamic coefficients fell within 2% of a finer, 15 × 100 × 120 mesh
Summary
Dimond et al [1] presented methods for the identification of bearing dynamic coefficients (stiffness, damping, and added mass) based on experimentally measured data. Kanki et al [5] used a special testing system to determine the dynamic characteristics of water lubricated bearings by applying sinusoidal excitation forces in the x- and y-directions (perpendicular to the rotor axis) by means of hydraulic actuators and measuring the journal displacement to determine the transfer function. The direct stiffness and damping coefficients were found to be frequency independent if an added mass term, smaller than the test device modal mass, was introduced Both the parameter identification procedure and the experimental technique were based on the earlier work of Rouvas and Childs [16] with water-lubricated bearings.
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