ABSTRACT
Usually, but not always, the potential for rotor dynamic beam-bendingtype deflections significantly contributes to the LRV characteristics. The significance of LRV rotor bending increases with bearing-to-rotor stiffness ratio and with rotor spin speed. Consequently, in some rotating machines with a low operating speed and/or low bearing-to-rotor stiffness ratio, the LRV is essentially of a rigid rotor vibrating in flexible bearings or supports. The opposite case (i.e., a flexible rotor in essentially rigid bearings) is also possible but rotor dynamically less desirable, because it lacks some vibratory motion at the bearings which often provides that essential ingredient, damping, to keep vibration amplitudes at resonance conditions within tolerable levels. For the same reason, it is generally undesirable to have journal bearings located at nodal points of important potentially resonant modes; i.e., the squeeze-film damping capacity of a bearing cannot dissipate vibration energy without some vibratory motion across
it. Figure 1 shows a case with significant participation of both rotor bending and relative motion at the bearings. This is the most interesting and challenging LRV category to analyze.
