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Rolling Element Bearing is one of the most common mechanical components to be found in critical industrial rotating machinery. Since the failure of bearings will cause the machine to malfunction and may quickly lead to catastrophic failure of the machinery, it is very important to detect any bearing deterioration at an early stage. In this thesis, novel signal processing methods based on Acoustic Emission measurement are developed for bearing condition monitoring. The effectiveness of the proposed methods is experimentally demonstrated to detect and diagnose localised defects and incipient faults of rolling element bearings on a class of industrial rotating machinery – the iGX dry vacuum pump. Based on the cyclostationary signal model and probability law governing the interval distribution, the thesis proposes a simple signal processing method named LocMax-Interval on Acoustic Emission signals to detect a localised bearing defect. By examining whether the interval distribution is regular, a localised defect can be detected without a priori knowledge of shaft speed and bearing geometry. The Un-decimated Discrete Wavelet Transform denoising is then introduced as a pre-processing approach to improve the effective parameter range and the diagnostic capability of the LocMax-Interval method. The thesis also introduces Wavelet Packet quantifiers as a new tool for bearing fault detection and diagnosis. The quantifiers construct a quantitative time-frequency analysis of Acoustic Emission signals. The Bayesian method is studied to analyse and evaluate the performance of the quantifiers. This quantitative study method is also performed to investigate the relationships between the performance of the quantifiers and the factors which are important in implementation, including the wavelet order, length of signal segment and dimensionality of diagnostic scheme. The results of study provide useful directions for real-time implementation.

Air-riding bearing and seal technology comprises rotor and stator elements separated by a thin air-film and experiencing relative rotational motion. The Navier- Stokes equations for compressible flow lead to a modified Reynolds equation incorporating additional high-speed rotation effects. The dynamics of the system are investigated when the axial position of the stator is prescribed by a finite amplitude periodic forcing. Two different physical configurations of air-riding technology are considered in this thesis; a squeeze-film thrust bearing and a pressurised air-riding face seal. Details are provided of a finite-difference, time-stepping scheme and a Fourier spectral collocation scheme to compute the periodic pressure distributions and rotor heights. For changing values of a selected physical parameter the method of arc-length continuation is employed to track branches of solutions computed using the spectral collocation scheme. For both configurations of air-riding technology the effect of different frequencies and amplitudes of stator forcing is identified for a range of rotation speeds and the influence of the rotor support structures is analysed. For air-riding face seals a critical shaft speed is identified that maintains no-net flow by balancing inertia and pressurisation effects The potential for resonant rotor behaviour is identified through asymptotic and Fourier analysis of the rotor motion. Changes in the minimum rotor-stator clearance are presented as a function of the rotor stiffness to demonstrate the appearance of resonance. Both the minimum rotor-stator clearance and the total mass flux of air through the seal are used to evaluate the limits of stable periodic operation without resonant rotor dynamics and incorporating high operating speeds.

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No description available.