DAMAGE DETECTION IN ROTORS USING WAVELET ANALYSIS OF OPERATIONAL DEFLECTION SHAPES

Fatigue cracks in high speed rotating machinery are a vital source of catastrophic failures. Hence, the diagnosis of fatigue crack location identification in uninterrupted rotating systems is still an active and challenging research problem in equipment predictive maintenance. In the available literature, many damage detection techniques have been proposed with their own advantages and limitations. The operating deflection shape (ODS), which represents the deflection of a vibrating structure at a particular frequency to a specific structural loading, has been gaining importance for crack detection in recent years. In this study, obtained ODS of cracked rotor are processed, using continuous wavelet transforms to detect, localize and quantify the fault severity. Steady state or run-up vibration data will only provide information about the presence of the damage. On the other hand using spatial vibration information such as operation deflection shapes or mode shapes is more likely to detect the location of the fault. In the present study the operational deflection of displacement and strain energy are extracted from the finite element model at a particular speed of the rotor. The difference vectors obtained between undamaged and damaged ODS are used as input vectors for the wavelet transform analysis. The performance of the displacement and strain energy based damage detection is tested by including noise of signal data. The quantification of the damage severity is estimated using a parameter formulated from the distribution of wavelet coefficients with respect to the scales. The choice of mother wavelet selection and effect of scales on the quantification of the defect is evaluated. Diagnosis results for different damage cases such as single and multiple damages are presented.