1. Different rotor operating speeds

Transient regimes, corresponding to variations over time in the average speeds of the rotors (acceleration or braking of the system, application of torque, etc.), can lead to sudden failures due to instabilities induced, in most cases, by a resonance phenomenon. Less spectacularly, another consequence can be local overstepping of permissible stress limits, leading to a significant reduction in the plant's service life.

For a steady state characterized by a constant average speed for each rotor making up the installation (nominal operating point), the state of stress in the shafts breaks down into a constant average value – associated with the transmission of the average torque – and a set of pulsed components whose periodic variation over time is directly linked to the existence of axial, transverse or torsional...