Showing papers on "Critical speed published in 1968"

Critical-speed analysis of flexibly mounted rigid rotors

Abstract: A general solution of the frequency equation for rigid rotors in undamped bearings is m e solution is applied to a wide range of derived for forward and backward precession. speeds and shapes, with variation in center-of-gravity location, to obtain maps of the frequency characteristics and locate major and nonsynchronous critical speeds. When the center of gravity is at the bearing centerline midpoint, a set of two solutions exists. An additional set of two solutions appears, however, when the center of gravity is away from this point. of-inertia ratio equals or exceeds the critical-speed ratio. With the center of gravity midway between single-row ball bearings and the polar and diametral moments of inertia equal, a nonsynchronous critical speed exists at all rotor speeds. No forward-precession high-frequency critical speeds exist if the moment-

On the Vibrations of Horizontal Shaft Supported in Oil Lubricated Journal Bearings

Abstract: Based on a pressure solution for an infinitely long journal bearing clarified in the previous paper, the vibrations of a rotating shaft which is supported in oil lubricated journal bearings is investigated theoretically and experimentally. The results are as follows : 1) A system in which a rigid shaft is supported in oil lubricated journal bearings has in general an angular natural frequency slightly less than ω/2 (ω is angular velocity of rotating shaft). Although the free vibration with angular frequency about ω/2 is stable at low rotational speeds, it becomes self-excited when the rotational speed increases to a high enough value. 2) In the case of a flexible shaft, the system has three angular natural frequencies, one of which is slightly less than ω/2 and the others are nearly equal to Ω (Ω is a fundamental angular frequency of flexural vibration of the shaft). Only one of the vibrations with frequency Ω becomes unstable when the rotational speed increases above about twice the critical speed of the shaft.