Because no material can be infinitely stiff, these alternating torques applied at some distance on a shaft cause twisting vibration about the axis of rotation.
Therefore, and to ensure that the coupling is not damaged due to this (temperature could be very high, depending on the load), this is verified through torsional vibration calculation.
Then, the generated electromagnetic torque is also influenced by additional time-varying electromechanical interactions, which lead to further torsional vibrations of the drive system.
For this purpose, by means of measurement results, i.e., empirically, formulas have been developed that provide good approximations for the electromagnetic external excitations produced by the electric motor.
[8] In many cases, such simplifications yield sufficiently useful results for engineering applications, but they can lead to inaccuracies since many qualitative dynamic properties of the mechanical systems, e.g., their mass distribution, torsional flexibility, and damping effects, are neglected.
Thus, an influence of the oscillatory behaviour of drive systems on the electric machine rotor angular speed fluctuations, and in this way on the electric current oscillations in the rotor and stator windings, cannot be investigated with a satisfactory precision, excepting numerical methods, which can provide arbitrarily high accuracy.
[9] Torsional vibrations in railway vehicle drivetrains are generated by many coupled mechanisms, which are very complex and can be divided into two main parts: An interaction of the adhesion forces has nonlinear features which are related to the creep value and strongly depend on the wheel-rail zone conditions and the track geometry (especially when driving on a curve section of the track).
Often the study of railway vehicle dynamics using the rigid multibody methods without torsionally deformable elements are used [14] This approach does not enable analysis of the self-excited vibrations, which have an important influence on the wheel-rail longitudinal interaction.
Torsional vibration specific codes are more versatile for design and system validation purposes and can produce simulation data that can readily compared to published industry standards.
These codes make it easy to add system branches, mass-elastic data, steady-state loads, transient disturbances and many other items only a rotordynamicist would need.