Tham khảo tài liệu 'rotating machinery vibration 2011 part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Lateral Rotor Vibration Analysis Models 79 100 p mm Simulated Condition 100 000 Pound Unbalance Force At A Last-Stage Blade Row Of The Low-Pressure Steam Turbine Illustrated in L Figure 2-15 3 600 rpm Fixed-Arc Bearings Pivoted-Pad Bearings 20 40 60 Frequency Hz Figure 18 FFT of peak-to-peak journal vibration displacement amplitudes. jump phenomenon and into a quite nonlinear dynamic motion detailed by the results in Fig. 16 for a 100 000 pound unbalance force. The explanation for the results in Figs. 16 and 17 can be seemed to well-established knowledge of fixed-arc and pivoted-pad journal bearings concerning instability self-excited vibrations. The A-y signals displayed in Fig. 16a and b contain sequentially numbered timing marks for each one-half rotor revolution time interval at 3600 rpm. The observed steady-state motions therefore require three revolutions to complete one vibration cycle for both cases shown in Fig. 16. Thus these steady-state motions both fall into the category of a period 3 motion because they both contain a J subharmonic frequency component along with a once-per-revolution synchronous component. But these two cases are clearly in stark contrast to each other. With the partial-arc bearings. Fig. 16a steady-state motion is dominated by the ỳ subharmonic component and the journal motion virtually fills up the entire bearing clearance circle. However in the second case which employs a tilting-pad bearing model the I subharmonic component is somewhat less than the synchronous component and the journal motion is confined to the lower portion of the bearing clearance envelope. As is clear from Fig. 17 with partial-arc bearings motion undergoes a nonlinear jump phenomenon as unbalance magnitude is increased. With pivoted-pad bearings a nonlinear jump phenomenon is not obtained. This contrast is even more clear when the motions are transformed into the frequency domain as provided by fast Fourier Transform FFT in Fig. 18. The journal-to-bearing
