effect of shaft torque on critical speed
effect of shaft torque on critical speed
(OP)
I'm looking at a simple shaft problem, there are no distributed masses. The shaft is supported between crowned splined couplings. My questions,
1. is there are relationship between torque in the shaft and critical speed
2. are there standard formulae for the effect of initial curvature and eccentricity
3. my end constraints can rotate and slide axially, how do I factor this into the critical speed calculation
Many thanks for any pointers......
1. is there are relationship between torque in the shaft and critical speed
2. are there standard formulae for the effect of initial curvature and eccentricity
3. my end constraints can rotate and slide axially, how do I factor this into the critical speed calculation
Many thanks for any pointers......





RE: effect of shaft torque on critical speed
I am no expert in this area but from my mechanics book I would say that the torque would only play apart in the critical speed of the shaft if that torque was directly related to the shaft speed.The standard formula for critical speed of shaft's accounts for the static deflection of the shaft which would be the same if the shaft were a beam. The formula I have here are for various
cases ie:- uniform plain shaft with long and short bearings, uniform shaft with one end free etc.The formula for the first two cases these are as follows and are probably the
ones most useful for your situation:-
Nc (short bearings)= (1.57/L^2)*(E*I/m)
Nc (long bearings)= (3.57/L^2)*(E*I/m)
where L= length of shaft
E= modulus of elasticity of shaft material
I= second moment of area
m= mass per unit length of shaft
regards desertfox
RE: effect of shaft torque on critical speed
RE: effect of shaft torque on critical speed
The effect of the end constraints is very significant. But the main thing you need to know is their rotational stiffness in the plane of the shaft.
See Blevins - Formulas for natural frequency and mode shape. See in particular "Natural frequencies of a pinned-pinned beam with unequal torsion springs at the pinned joints".
RE: effect of shaft torque on critical speed
RE: effect of shaft torque on critical speed
RE: effect of shaft torque on critical speed
Guess that's why I'm not a roto-dynamic engineer
RE: effect of shaft torque on critical speed
Anyway, for 'normal' driveshafts the torque carried makes no difference to the actual resonant frequency.
I find it hard to believe that any single low friction bearing would behave as better than a pin joint, for these purposes.
Incidentally don't expect too much accuracy from hand calcs in this field, testing is the way to go.
Remember to account for foundation stiffnesses as well.
Cheers
Greg Locock
RE: effect of shaft torque on critical speed
RE: effect of shaft torque on critical speed