Influence of External Damping on the Stability and Response of a Horizontal Rotor with Anisotropic Bending Stiffness

Abstract

Design features, such as keyways of blind holes, produce noncircular cross-sections which introduce anisotropies in the bending stiffness churacterirtics of rotor shafb. Rotors with appreciable stiffness anisotropy have been found to exhibit vibrations at one-half the synchronous frequency. In horizontal single-disk rotors with anisotropic bending stiffness characteristics, gravity induces vibrations at one-half the synchronous frequency. Previous studies have neglected the damping effect of the surrounding medium and have predicted the operation of the rotor in between the two critical speeds to be unstable. This investigation examines the influence of external damping on rotor response to imbalance of gravity excitations and shows that sufficient amount of damping can suppress the reported instability caused by anisotropic bending stiffness characteristics.

Nonlinear secondary whirl of an overhung rotor

“…critical speed (Smith 1933). The relevant literature primarily identifies these gravity critical speeds (Coleman & Feingold 1958;Genta 2005), with subsequent linear analyses under various idealizations: Jeffcot rotor models on rigid bearings (Taylor 1940;Childs 1993;Rajalingham et al 1993;Genta 2005), Jeffcot rotors on flexible pedestals (Kondo & Kimura 1991), Euler-Bernoulli beam models (Bishop & Parkinson 1965;Sakata et al 1983) and three-dimensional finite element (FE) models (Rao & Sreenivas 2003). Experimental results on horizontal cantilever shafts were reported, for example, by Hull (1961), and on a simply supported shaft with a centrally mounted wheel were reported by Bishop & Mahalingam (1965).…”

Evolution of whirl in flexible isotropic rotors : modelling and experimental study

“…Wettergren and Olsson [10] considered a horizontal rotor with a flexible shaft supported in flexible bearings and found that major instabilities appear near the imbalance resonance and remarked that the resonances due to gravity near one half of the major critical could be reduced with enhanced material damping. Rajalingham et al [15] considered the influence of external damping on the stability and dynamic response of single disk horizontal rotors with anisotropic bending stiffness characteristics Campos et.al [19] reported a study on the dynamics of a Jeffcott rotor through Bond Graph formulation which provides for modelling of various nonlinear and multi-energetic systems. They validated their results through experiments on a carefully designed test setup obtaining a good agreement between the model predictions and the measured response Chang and Cheng [22] considered the dynamics of a rotating shaft-disk system and particularly addressed the question of instability.…”