A large number of commercial systems for condition monitoring of most common planetary gearboxes used in wind turbines and mining machinery have been developed for years. However nowadays, multistage constructions are encountered in industries. These are not necessarily planetary, but generally epicyclic. Current state of the art, according to the authors knowledge, does not give general equations for a case where multistage systems are considered, where some of the gears consist all moving parts. Hence, currently available CMS systems are not suitable for condition monitoring of these kinds of systems.
The paper presents a new general equation, which allows calculating the characteristic frequencies of any kind of multistage gear sets, as a result of theoretical investigation. Illustrated solution does not assume a fixed speed of any element. Moreover, presented equation takes into account corrected teeth, making developed equations most general from all available in tribology science. Presented scientific development is currently implemented in a modern European CMS.
The paper illustrates a general equation in a new form, which allows calculating the characteristic frequencies of any kind of epicyclic gear sets with a ring, a sun, and planets. Moreover, presented equation takes into account corrected teeth (i.e. where the equality 2P+S=R is not fulfilled). This happens when gearboxes contain gears where corrected teeth procedure was adopted during designing stage. Presented solution can refine the configuration modules of the Condition Monitoring Systems (CMS) in such a way that allows to configure systems into larger groups than now available, i.e. multistage gear sets systems with epicyclic gears. Such CMS are capable of early mechanical faults detection, which prevents from costly critical repairs. For instance, fault detection of wind turbines is typically based on vibration and process signals analysis. Illustrated possible enhancement of configuration module is the basis for determining the energy bands in the spectra and envelope spectra in the process of identifying characteristic frequencies caused by gear defects.
The last few decades have seen a significant increase in research interest related to nonlinearities in micro-cracked and cracked solids. As a result, a number of different nonlinear acoustic methods have been developed for damage detection. The paper investigates nonlinear crack-wave interactions used for damage detection in plate-like structures. Semi-analytical modelling is used to investigate wave propagation in the vicinity of the crack. The focus is on non-classical crack model leading to wave modulations. Various physical phenomena (including fluctuation of temperature gradient) associated with these modulations are investigated. The work presented can be used for better understanding of nonlinear crack-wave interactions that are used for damage detection in structural health monitoring applications.
The paper presents a novel damage detection method that combines Lamb wave propagation with nonlinear acoustics.
Low-frequency excitation is used to modulate Lamb waves in the presence of fatigue cracks. The work presented shows
that the synchronization of the interrogating high-frequency Lamb wave with the low-frequency vibration is a key
element of the proposed method. The main advantages of the proposed method are the lack of necessity for baseline
measurements representing undamaged condition and lack of sensitivity to temperature variations. Numerical
simulations and experimental measurements are performed to demonstrate the application of the proposed method to
detect fatigue crack in aluminum beam.