Seminar: Vibration Analysis of Spinning Rotors with Flexible Bearings and Housing Supports
Rotary machines appear everywhere in our daily life ranging from jet engines to computer hard disk drives. Every rotary machine consists of three basic elements: a rotary part (rotor), a stationary part (housing), and multiple bearings that connect the rotary and stationary parts. The rotor can be axisymmetric (e.g., hard disk drives) or cyclic symmetric (e.g., wind turbines).
In this presentation, we will discuss how bearings and housing affect vibration of a spinning rotor. Mathematical models are developed through use of Lagrange equation, finite element analyses and component mode synthesis. The mathematical modeling leads to the following conclusions. First, when a rotor is assembled to housing via bearings, some vibration modes will not change their natural frequencies and mode shapes. These modes have the characteristics of zero inertia force and inertia moment. Therefore, they are called “balanced modes.” Otherwise, a vibration mode is called an “unbalanced mode.” Only unbalanced modes will be coupled to the housing and bearings. Second, for axisymmetric rotors, unbalanced modes will appear in the form of precession or axial translation when they are coupled with the housing and bearings. In the case of hard disk drives, one-nodal-diameter disk modes present precession and axisymmetric disk mode present axial translation. Disk modes with 2 or more nodal diameters are balanced modes. Third, for cyclic symmetric rotors, balanced or unbalanced modes will depend on the number of repeated substructures and a “phase index” , which determines the phase angle between two neighboring substructures. A vibration mode is a balanced mode if , , or . Finally, when mistuning is present in a cyclic symmetric rotor, localized vibration modes may appear. Presence of bearings may introduce more localized modes and may couple the housing to the rotor. Localized modes are unbalanced with larger bearing forces.
Majority of the mathematical predictions have been validated via calibrated experiments.
About the Speaker
Professor Steve Shen received his B.S. and M.S. degrees from National Taiwan University and Ph.D. from the University of California (Berkeley), both in Mechanical Engineering. Professor Shen's general research area is vibration, dynamics, sensing, and actuation. In particular, his expertise includes PZT thin-film micro-sensors/actuators, flapping-wing micro aerial vehicles, medical devices (hearing and dental implants), and spindle and rotor dynamics.
Professor Shen is a Fellow of American Society of Mechanical Engineers (ASME). He is currently the Technical Editor of ASME Journal of Vibration and Acoustics. Professor Shen is a recipient of ASME N. O. Myklestad Award and IBM Partnership Award.
Hosted by Professor Kiran D'Souza