Abstract
Rolling element bearing is a vital component in rotating machinery, such as a wind turbine (WT) system. By accurately monitoring its health condition, the faults can be detected at an early stage, providing sufficient lead time to perform maintenance and hence reducing accidents and economic losses. Bearing usually suffers from various wears and tears, which result in a gradual increase in clearance through its lifetime. Insufficient understanding of vibration characteristics under different clearances brings difficulties for bearing condition monitoring. Thus, this paper presents a nonlinear bearing vibration model with six degrees of freedom (DOF) to investigate the vibration characteristics under different radial clearances and load conditions. Then, a dedicated bearing test is established to verify the reasonability and effectiveness of the vibration model. Furthermore, a comprehensive simulation analysis is conducted to study the vibration characteristics over an extended range of the internal radial clearance and external load. Results show that the dynamic force on each ball presents an impulse whose magnitudes increases whereas the pulse width reduces with clearance increases. Ball pass frequency of outer race (BPFO) is the dominant modulation component and the frequency is in accordance with the number of dynamic force impulses. Two indicators, i.e., root mean square (RMS) value and spectral centroid, are proposed to indicate clearance changes. In general, they show an uptrend with the increase in clearance, which is in line with the dynamic force increasing with clearance, especially the spectral centroid of the low frequency band. However, it should be noted that the RMS value and spectral centroid exhibit a fluctuating behavior due to nonlinear vibration responses. For the first time, this study shows the details of vibration characteristics with clearance variations and provides a foundation for monitoring the bearing conditions before any obvious local defects on raceways.
Highlights
Wind energy, as a kind of renewable and clean energy resource, has become the fastest-growing energy source [1]
1000rpm rpmwere werecarried carried studythe theinfluence influenceofofrotational rotationalspeed, speed, simulations simulations under out out to make a comparison with rpm based on the spectral centroid values of the low and to make a comparison with 1500 rpm based on the spectral centroid values of the low andhigh high frequency bands in in thethe load direction, as as shown in in frequency bands load direction, shown
From all the above analysis, the dynamic force on each rolling element shows a linear increase with the increase in the clearance and load, it is very difficult to obtain a linear vibration indicator related to bearing clearance
Summary
As a kind of renewable and clean energy resource, has become the fastest-growing energy source [1]. In view of structural vibrations highly influencing the propagation of wear [15], significant efforts need to be dedicated to study the vibration characteristics under different bearing clearances before obvious local defects appearing, which could provide more guidance for bearing condition monitoring. A few studies have begun to focus on bearing clearances and paved the foundations for this study, several problems existed in these studies, such as a lack of mechanism research, incomplete vibration characteristics and insufficient reasonable monitoring indicators These deficiencies bring difficulties to bearing condition monitoring and maintenance of WT systems. To bridge the gap, a nonlinear bearing vibration model is proposed to investigate the vibration characteristics for bearing condition monitoring under different internal clearances, as well as external loads. The main contribution of this paper lies in the non-linear vibration model and the influence of continuously changing clearances on dynamic force and vibration characteristics
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