On post-resonance backward whirl in an overhung rotor with snubbing contact
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ORIGINAL PAPER
On post-resonance backward whirl in an overhung rotor with snubbing contact Mohammad A. AL-Shudeifat . Michael Friswell . Oleg Shiryavev . C. Nataraj
Received: 12 March 2020 / Accepted: 24 June 2020 Ó Springer Nature B.V. 2020
Abstract Rotordynamic systems are central to many aerospace and heavy-duty industrial applications. The vibrational response of such systems is usually associated with forward whirl (FW) and backward whirl (BW) precessions. It is well known in the literature that the BW precession generally precedes the passage through the critical FW resonance precession. Therefore, it can be named as a pre-resonance BW frequency (Pr-BW). However, another kind of BW has been recently observed to be immediately excited after the passage through the critical FW M. A. AL-Shudeifat (&) Department of Aerospace Engineering, Khalifa University of Science and Technology, Abu Dhabi, PO Box 127788, United Arab Emirates e-mail: [email protected] M. Friswell College of Engineering, Swansea University, Bay Campus, Fabian Way, Crymlyn Burrows, Swansea SA1 8EN, UK e-mail: [email protected] O. Shiryavev Department of Mechanical Engineering, University of Alaska Anchorage, 3211 Providence Dr., Anchorage, AK 99508, USA e-mail: [email protected] C. Nataraj Villanova Center for Analytics of Dynamic Systems, Villanova University, 800 Lancaster Ave., Villanova, PA 19085, USA e-mail: [email protected]
resonance frequency in cracked rotors with anisotropic supports during run-up and coast-down operations. Consequently, this kind of BW can be named as a postresonance backward whirl (Po-BW) precession. The Pr-BW and Po-BW phenomena are investigated here with an overhung rotor system that exhibits snubbing contact and stiffness anisotropy in the supports. Incorporating the snubbing moment couple into the equations of motion of the considered overhung rotor model yields a piecewise and strongly nonlinear system. Full-spectrum analysis is employed to capture the BW zones of rotational speeds in the whirl response. Wavelet transform spectrum analysis is also employed to determine the frequency content in the Pr-BW and the Po-BW zones. Three cases are considered in this numerical study to explore the effect of the support stiffness isotropy and anisotropy with active and inactive snubbing contact on the PoBW excitation. For all cases, the Po-BW zones of rotational speeds are found. Moreover, the broadness and recurrence of the Po-BW zones of rotational speeds are more prominent for the cases of active snubbing contact. Even though the Pr-BW and Po-BW zones are excited at different shaft rotational speeds, they are found to possess nearly similar BW frequencies which are less than the FW resonance frequency of the considered system. Keywords Backward whirl Overhung rotor Postresonance backward whirl Full-spectrum analysis Rotor system
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1 Introduction It is important to understand the dynamic behavior of rotor
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