Question

Increasing which of the following factor would result in increase of free torsional vibration?

(a) Radius of gyration

(b) Mass moment of inertia

(c) Polar moment of inertia

(d) Length

The question was posed to me in an interview for internship.

The query is from Effect of Inertia of the Constraint on Torsional Vibrations topic in division Torsional Vibrations of Machine Dynamics

Answer 1

Right choice is (c) Polar moment of inertia

For explanation I would say: The free torsional vibration frequency of a single rotor system depends by the following relation

f = \(\frac{1}{2}\sqrt{(\frac{C.J}{l.I})}\)

Hence increase in polar moment of inertia results in increase in vibration frequency.