Contributed by the Technical Committee on Vibration and Sound for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received March 1999; revised Feb. 2001. Associate Editor: A. F. Vakakis.

This note is abstracted from Childs 1 more complete discussion of the influence of a radial clearance on spiral vibrations and is limited to a discussion of the kinematics assumptions involved in developing Kellenberger’s 2 model for spiral vibrations. Black’s 3 model and notation are used to define the rotor and stator interaction force.

Black’s 3 model is illustrated in Fig. 1. The rotor is a Jeffcott (Laval) rotor with mass $mr,$ stiffness $kr,$ and damping $cr.$ The stator is a particle of mass $ms,$ connected to ground through a spring $ks$ and linear dashpot $cs.$ A radial clearance $Cr$ exists between the rotor and stator...