Torsional vibration involves angular oscillations of the rotors of a machine. For large rotating machinery the mechanical system often consists of several rotors that are connected by relatively slender shafts and couplings. For some machines involving geared rotor connections, for example, there may be several rotor axes of rotation. The twisting oscillations following severe torsional disturbances to a machine may be sufficient to cause fatigue damage to the machine’s shafts and other components.