In rotating machinery, what sign is most indicative of crossing the critical speed?

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Multiple Choice

In rotating machinery, what sign is most indicative of crossing the critical speed?

Explanation:
Crossing a critical speed happens when the rotor’s rotational speed aligns with a natural frequency of the rotor-support system, causing resonance. When this occurs, the vibration amplitude grows dramatically because the system is being excited at its own natural tendency to oscillate. The most telling sign is the turbine vibrating violently, often with higher dynamic forces on bearings and supports. Stalling, runaway acceleration, or overheating aren’t the characteristic indicators of hitting a critical speed, so violent vibration is the best cue.

Crossing a critical speed happens when the rotor’s rotational speed aligns with a natural frequency of the rotor-support system, causing resonance. When this occurs, the vibration amplitude grows dramatically because the system is being excited at its own natural tendency to oscillate. The most telling sign is the turbine vibrating violently, often with higher dynamic forces on bearings and supports. Stalling, runaway acceleration, or overheating aren’t the characteristic indicators of hitting a critical speed, so violent vibration is the best cue.

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