rotordisplacement

Rotordisplacement is a term used in rotor dynamics to describe the motion of a rotating shaft away from its nominal centered position during operation. It encompasses both radial displacement (lateral movement of the shaft centerline) and angular displacement (tilt or canting of the rotor) relative to bearings and supporting structures. The magnitude and phase of rotordisplacement are functions of operating speed, loading, and the dynamic properties of the machine.

Causes of rotordisplacement include unbalance of the rotor mass, misalignment of shafts or couplings, bearing clearance and stiffness variations, shaft bow or runout, thermal growth, and rotor-stator rubbing at clearance seals. Dynamic effects such as gyroscopic coupling at high speeds and resonance near critical speeds can amplify displacement.

Measurement and analysis are conducted using sensors such as proximity probes, eddy current or capacitive sensors, and sometimes laser Doppler vibrometry for validation. Data are analyzed in time, frequency, or orbit domains to identify amplitude, phase, and orbit shape. Models like the Jeffcott rotor and more complete multibody dynamics are used to predict displacement as a function of speed, damping, and stiffness. Experimental modal testing and condition monitoring employ displacement data to assess health and estimate critical speeds.

Implications of excessive rotordisplacement include rubs, wear, seal damage, elevated vibration and noise, reduced efficiency, and potential bearing failure. Design and maintenance practices aim to minimize displacement through balanced rotors, proper alignment, sufficient damping, and ongoing monitoring.

Standards such as ISO 10816 and ISO 7919 provide guidelines for measuring and evaluating vibration and shaft displacement in rotating machinery. Related concepts include rotor dynamics, unbalance, critical speed, bearing stiffness, rotor whirl, and rub.