A Finite Element Model for Distributed Parameter Turborotor Systems

Abstract

A specific numerical calculation procedure is outlined for a general turborotor-bearing system in which distributed inertia and elasticity are consistently represented. Bearings are represented by up to sixteen linear cross coupled coefficients each for stiffness and for damping. Discrete (as well as distributed) masses are allowed. As an example, for stability analysis (free response) a non-dimensional parameter study is made for the special case of a simple rotor supported on two short (Ocvirk) fluid film bearings. A comparison of discrete and distributed parameter rotor representations shows that the discrete parameter model predicts onset of instability at a lower speed ratio and is, therefore, more conservative. For unbalanced response (forced response), comparison is made to Prohl’s method, which represents mass discretely. A considerable reduction in the number of degrees of freedom necessary for accurate system representation is observed with the finite element formulation.