Question

In a three rotor system, for the middle rotor, if the stiffness of both the length either side of the rotor is increased to two times what will be the effect on total stiffness of the middle rotor?

(a) Remains constant

(b) Decreases by two times

(c) Increases by two times

(d) Increases by 4 times

The question was asked in a job interview.

My question is from Free Torsional Vibrations of a Three Rotor System in section Torsional Vibrations of Machine Dynamics

Answer 1

Correct option is (c) Increases by two times

Best explanation: In a three rotor system, each length to either side of the middle rotor is twisted through the same angle therefore the total stiffness is the sum of individual stiffness.