Shaft critical speed calculation
Shaft critical speed calculation
(OP)
Hi All,
I have a shaft supported by 3 bearings (we'll consider them simple supports) on the ends and one in the middle. The shaft has 2 masses, one on each side of the middle bearing. The shaft is indeterminate so I replace the middle bearing with a force and set the displacement to 0.
Now, when I use Rayleigh's method for lumped masses, do I consider the masses to produce a force in the same direction (Static beam), or do I consider them acting in opposite directions (as would happen in dynamic deflection, likely mode 1).
When I sum w*y^2, I get a negative sign which of course cannot be used in Rayleighs equation. Any help is greatly appreciated.
Thanks,
Tyler
I have a shaft supported by 3 bearings (we'll consider them simple supports) on the ends and one in the middle. The shaft has 2 masses, one on each side of the middle bearing. The shaft is indeterminate so I replace the middle bearing with a force and set the displacement to 0.
Now, when I use Rayleigh's method for lumped masses, do I consider the masses to produce a force in the same direction (Static beam), or do I consider them acting in opposite directions (as would happen in dynamic deflection, likely mode 1).
When I sum w*y^2, I get a negative sign which of course cannot be used in Rayleighs equation. Any help is greatly appreciated.
Thanks,
Tyler





RE: Shaft critical speed calculation
I think Dunkerley is one way to attack this: Choose one of the masses, displace it by a certain amount, , determine associated shaft deflection (which will be opposite on the two sides of center bearing), compute resonant frequency using Raleigh for that one-mass configuration... repeat for the other mass... combine resonant frequency estiamtes using 1/w^2 = 1/w1^2 + 1/s2^2
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(2B)+(2B)' ?
RE: Shaft critical speed calculation
Have a look at this site:-
http://www
Go down till you see Dunkerley's method as E.Pete suggested.
Can you post a sketch or pic of your situation?
desertfox