7. Results and Discussions The main important features to show the achieved improvements through the current proposed simulation approach are shown by comparing the power spectrum density for both the faulty and good bearings for simulated and measured signals. A further comparison is made to show the improvement for the good and faulty cases after removing the discrete components. This comparison is done at the cyclic frequency of the shaft speed (10 Hz) and also at zero frequency. Although the graphs shown are to a different scale or dynamic range, the main intention here is to compare the shape of the spectra and the dB difference between the good and the faulty bearing. 7.1 Extended inner race fault – PSD comparison The experimental results for the smooth extended inner race fault were compared with the results of three different simulations namely; LPM, HUMS [22] and the current simulation model (Fig 8). Note that the comparison of the power spectra at this stage is made without removing the contribution of the gears, so as to show the overall spectrum shape. It can be said that the overall shape of the spectrum has improved significantly through this current simulation (8.d) as compared to earlier model (8.b and 8.c). This is seen in the low/mid frequency range up to 6 kHz. A number of resonances are also clearly noticed in the high frequency region. The structural damping used to extract the FRF needs to be adjusted (increased) to give a better correspondence. This will be investigated and updated at a later stage. Fig 8: PSD comparison: showing overall response in the useful frequency band (a) Experimental (b) LPM (C) HUMS (no pink noise added) (d) Current model (Forces from the condensed model convolved with the frequency response from the total gearbox) 406
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