Characteristics and recognition of non-linear vibratory systems - Free, forced and self-excited vibrations
|Publication Date:||1 December 2014|
|ICS Code (Vibrations, shock and vibration measurements):||17.160|
Non-linearities are properties of an oscillatory system. Its vibration responses under excitation are incorrectly referred to as non-linear vibrations although their occurrence is in fact due to the nonlinear system. Non-linearities are always system properties but no exciter properties.
In the evaluation of the oscillatory mechanical systems of solid bodies phenomena are repeatedly encountered which, on the basis of the theory of linear vibrations, cannot simply be explained by the excitation and by linear system properties. One possible reason for this could be the fact that the oscillatory system under investigation has nonlinear properties. These could, for example, be due to:
- manufacturing defects
- discontinuities in materials
- wear and fracture
- effects arising from overloading
non-linear characteristics of bearing elements
This standard is primarily intended to assist in assessing from measurement results whether the presence of non-linear properties can be detected in an oscillatory system. Excitation as a possible cause of inexplicable phenomena should thereby be ruled out.
Furthermore for a number of known cases this guideline should provide assistance in identifying the cause of the non-linearity (for example, the presence of cracks or play).
With a knowledge of non-linearities in a system and the diverse vibration responses which arise thereby, it then becomes possible to selectively reduce these non-linearities and their unwanted effects, or even to prevent them completely.
In many respects the non-linear property of a system can be used equally methodically. On the one hand non-linearities are built in, for example, to limit the magnitude of amplitudes in resonances or to use the shock-like processes generated by backlash as a way of compacting granular substances. On the other hand not only the existence of nonlinearities but also their quantity and/or quality can be used as a characteristic for evaluating the condition of a system or its wear or overloading.
This standard provides information about the effects of non-linearities. It describes effects occurring in an oscillatory system and provides information about possible causes.
In what follows we shall only be concerned with the mechanical vibrations of solid bodies.