Which of the following parameters has higher value during whirling of a shaft?

This question was previously asked in
BPSC AE Paper 6 (Mechanical) 2012 Official Paper
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  1. Speed
  2. Acceleration
  3. Frequency
  4. Amplitude

Answer (Detailed Solution Below)

Option 4 : Amplitude
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Detailed Solution

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Explanation:-

Critical or whirling speed of a shaft

  • When the rotational speed of the system coincides with the natural frequency of lateral/transverse vibrations, the shaft tends to bow out with a large amplitude. This speed is termed as critical/whirling speed.
  • Whirling speed or Critical speed of a shaft is defined as the speed at which a rotating shaft will tend to vibrate violently in the transverse direction if the shaft rotates in the horizontal direction.
  • In other words, the whirling or critical speed is the speed at which resonance occurs.
  • Hence we can say that Whirling of the shaft occurs when the natural frequency of transverse vibration matches the frequency of a rotating shaft.
  • It is the speed at which the shaft runs so that the additional deflection of the shaft from the axis of rotation becomes infinite is known as critical or whirling speed.

F1 Ashiq 21.9.20 Pallavi D4

Deflection of the shaft due to transverse vibration of the shaft.

\(y = \frac{e}{{{{\left( {\frac{{{\omega _n}}}{\omega }} \right)}^2} - 1\;}}\)

26 June 1

At critical speed,

\(\omega = {\omega _n} = \sqrt {\frac{k}{m}} = \sqrt {\frac{g}{\delta }} \)

where,

ω = Angular velocity of the shaft, k = Stiffness of shaft, e = initial eccentricity of the center of mass of the rotor

m = mass of rotor, y = additional of rotor due to centrifugal force.

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