Shaft Vibration

[sow]

My understanding of modes of vibration / failure of drive shafts is as follows

1) Torsional
2) Lateral (with/ without rotation)
3) Whirl (of shaft, not bearings)

However there seems to be a lot of confusion about what is whirl and what is lateral vibrations, some sources say they are the same thing (or rather whirl is caused by the onset of lateral resonance).

Other sources suggest that whirl is an issue in its own right, and the only governing factor is a critical number based on a simple equation.

Some sources ignore whirl it all together.

I have a supplier providing a fairly long vertical drive shaft at fairly high rpm, and need to brush up on my shaft design headline issues!

Thanks in advance.

 

[tygerdawg]

My parents owned a newspaper & my father purchased a used Webendorfer offset press made in Heidelberg in 1933. It was a glorious work of pre-WW2 German mechanical engineering design and working around it as a youngster put me on my path to Mechanical Engineering. If memory serves, the drive shaft was probably 2 inches diameter and about 10 feet long, supported at both ends. I assure you, "whirl" is real. I've seen the math in my three Mech Vibrations classes I took. Designs should be done to accommodate the stresses caused by those vibratory motions.

TygerDawg
Blue Technik LLC
Virtuoso Robotics Engineering

http://www.bluetechnik.com

 

[zekeman]

Lateral vibration
induced by transverse motion.
For example consider a single degree of system with mass at the center of a shaft with end bearings.
1)If the spring constant is k, then the natural lateral resonant frequency would be wn=Sqrt(k/M). If the lateral driving frequency is w, then the undamped motion amplification would be (w/wn)^2/{1-(w/wn)^2}
2) same system, only this time the mass is rotating, but its CM is initially offset by e.Same resonant frequency, wn. The whirling radius would be
r=e*(w/wn)^2/{1-(w/wn)^2}
which shows that whirling depends on an offset CM .
Without e , no whirling.