ACCURACY EVALUATION OF EXPERIMENTALLY DERIVED DYNAMIC COEFFICIENTS OF FLUID FILM BEARINGS .1. DEVELOPMENT OF METHOD

The goal of many experimental studies of fluid film bearings is the determination of the eight linearized stiffness and damping coefficients. These coefficients cannot be measured directly; they are derived from a series of other measurements, in many cases, the coefficients are found by applying known steady-state sinusoidal loads to excite a journal on a rigid rotor and measuring the resulting displacement, velocity, and acceleration orbits. This paper relates how uncertainties in these measurements affect the accuracy of the derived coefficients. The analysis can also be used for the proper selection of test procedures and transducers to measure the primary variables and estimate results beforehand. For an example case, it was found that bearing coefficients are entirely subject to test conditions, meaning not only sensor accuracy but where in an orbit data is taken. Stiffness coefficients had about an order of magnitude less uncertainty in their evaluation (-3 percent) than the damping coefficients (-25 percent). Uncertainty in velocity measurements dominated the total uncertainty in all coefficients. © 1990 Taylor & Francis Group, LLC.