2. When rotor is mounted on a shaft its centre of
gravity usually not coincide with the rotation of the
shaft. This C.G. is displaced from axis of rotation
although amount of displacement may very slow.
As a result shaft is subjected to a centrifugal force
when it begain rotate.
The CF acting radially outward, which make the
shaft to bend in the direction of eccentricity of the
C.G.`
3. This unbalance CF, a shaft start vibrating violently
in the direction perpendicular to the axis of the
shaft. This phenomenon is known as whirling of
shaft.
The speed at which the shaft start to vibrate
violently in the direction perpendicular to the axis
of the shaft is known as critical speed.
4. Consider a vertical shaft having negligible inertia
and carrying a single rotor is shown in fig.
5.
6.
7.
8. Consider vertical rotating shaft having negligible
inertia and carrying a single rotor of mass ‘m’.
9.
10.
11.
12. 1. rayleigh method
This method is based on the principle that the
maximum kinetic energy is equal to te maximum
potential energy.
