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Research Papers

Draft: Stick-Slip Motions of a Rotor-Stator System

[+] Author and Article Information
Nicholas Vlajic

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20742
e-mail: vlajic@umd.edu

Chien-Min Liao

Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20742
e-mail: gimmy@umd.edu

Hamad Karki

Department of Mechanical Engineering,
The Petroleum Institute,
Abu Dhabi, UAE
e-mail: hkarki@pi.ac.ae

Balakumar Balachandran

ASME Fellow
Department of Mechanical Engineering,
University of Maryland,
College Park, MD 20742
e-mail: balab@umd.edu

1Corresponding author.

Contributed by the Design Engineering Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received March 22, 2012; final manuscript received October 28, 2013; published online December 16, 2013. Assoc. Editor: Yukio Ishida.

J. Vib. Acoust 136(2), 021005 (Dec 16, 2013) (8 pages) Paper No: VIB-12-1078; doi: 10.1115/1.4025994 History: Received March 22, 2012; Revised October 28, 2013

In the current study, the authors examine the torsional vibrations of a rotor enclosed within a stator subjected to dry friction. Through the experiments, it is demonstrated that forward whirling of the rotor occurs while in contact with the stator, backward whirling occurs with contact, as well as impacting motions, which are characterized by nonsynchronous whirling with rotor-stator collisions. While undergoing these motions, the torsional oscillations are excited by stick-slip interactions. Experimental data are presented to show the presence of a stable torsional mode dominated motion while subjected to stick-slip forces during dry-friction whirling. In this motion state, the torsional oscillation response occurs at a combination of frequencies including drive and whirl frequencies. A finite dimensional model is constructed and simulations carried out by using this model are able to capture the system dynamics, including the torsional responses observed during dry-friction whirling. Numerical results obtained by using this model are consistent with experimental observations. The findings of this study are relevant to whirling motions experienced by rotating, long flexible structures, such as drill strings used in oil-well explorations.

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References

Figures

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Fig. 1

Experimental arrangement of laboratory scale drilling apparatus

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Fig. 6

Model of the string and rotor-stator system used to generate the equations of motion

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Fig. 5

Experimentally observed torsional strain: (a) time history and (b) single sided Fourier spectra of the time history

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Fig. 4

Experimentally observed impacting motions: (a) trajectory of rotor center within the stator, (b) time histories of the v(L, t) and w(L, t) displacement components, and (c) Fourier spectra of complex displacement quantity

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Fig. 3

Experimentally observed backward whirling motions: (a) trajectory of rotor center within the stator, (b) time histories of the v(L, t) and w(L, t) displacement components, and (c) Fourier spectra of complex displacement quantity

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Fig. 2

Experimentally observed forward whirling motions: (a) trajectory of rotor center within the stator, (b) time histories of the v(L, t) and w(L, t) displacement components, and (c) Fourier spectra of complex displacement quantity

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Fig. 7

Comparisons for the same input parameters: (a) experimental results and (b) numerical results

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Fig. 8

System response during dry-friction whirl: (a) relative speed, (b) torsional displacement time history, and (c) Fourier spectrum of the torsional response

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Fig. 9

Phase diagram of the torsional response during dry-friction whirl for the data presented in Fig. 8

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