ALTERNATIVE APPROACH FOR EVALUATING NATURAL FREQUENCIES AND STABILITY OF ELASTIC ROTORS.

The dynamical behavior of elastic rotors supported on journal bearings was evaluated using numerical solutions such as lumped masses, transfer matrix, and finite element analysis. In this paper, the problem was solved alternatively using the Mode Summation Method (MSM). The equation of motion was discretized to the finite degree of freedom in terms of the generalized coordinates. The presented model is considered a general rotor consisting of a flexible shaft carrying a disc supported by two oil-lubricated journal bearings. The various effects of the dynamic forces and moments arising from the bearing hydrodynamics and gyroscopic, unbalancing, lateral, and rotational inertia effects were included. The present analysis can be modified to include additional rotor configurations such as multi-d discs, anisotropic bearing, seal pressure, fluid flow pressure, and thick shaft behavior (Timoshenko beam). In this work, the natural frequencies, threshold speed of instability, and whirl frequencies were investigated. The validity of the present analysis was carefully checked by comparing it with the RDA software. The results showed good agreements where the maximum error did not exceed 7%. The convergence of the present solution was also tested. The results showed that using a few modes (not more than 6) is sufficient for accurate analysis. [ABSTRACT FROM AUTHOR]