Nonlinear secondary whirl of an overhung rotor

Nandakumar, K and Chatterjee, Anindya (2010) Nonlinear secondary whirl of an overhung rotor. In: Proceedings of the royal society a-mathematical physical and engineering sciences, 466 (2113). pp. 283-301.

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Abstract

Gravity critical speeds of rotors have hitherto been studied using linear analysis, and ascribed to rotor stiffness asymmetry. Here, we study an idealized asymmetric nonlinear overhung rotor model of Crandall and Brosens, spinning close to its gravity critical speed.Nonlinearities arise from finite displacements, and the rotor's staticlateral deflection under gravity is taken as small. Assuming small asymmetry and damping, slow modulations of whirl amplitudes are studied using the method of multiple scales. Inertia asymmetry appears only at second order. More interestingly, even without stiffness asymmetry, the gravity-induced resonance survives through geometric nonlinearities. The gravity resonant forcing does not influence the resonant mode at leading order, unlike the typical resonant oscillations. Nevertheless,the usual phenomena of resonances, namely saddle-node bifurcations, jump phenomena and hysteresis, are all observed. An unanticipated periodic solution branch is found. In the three-dimensional space oftwo modal coefficients and a detuning parameter, the full set of periodic solutions is found to be an imperfect version of three mutually intersecting curves: a straight line,a parabola and an ellipse.

Item Type:	Journal Article
Publication:	Proceedings of the royal society a-mathematical physical and engineering sciences
Publisher:	The Royal Society
Additional Information:	copyright of this article belongs to The Royal Society.
Keywords:	gravity critical speed;overhung rotor;stiffness asymmetry;multiple scales;periodic solution.
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	13 Jan 2010 05:38
Last Modified:	19 Sep 2010 05:53
URI:	http://eprints.iisc.ac.in/id/eprint/25141

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