Farouk O. Hamdoon, Hussein R. Al-Bugharbee, Azzam S. Hameed


During startup process of rotating machinery and due to the rotor’s inherent unbalance, transient vibration is
introduced as the machinery passes through critical speeds. In the present paper, time domain simulation is performed
using ANSYS software to investigate the transient unbalance response of rotor – bearing system. The transient vibration
response of the rotor system passing through the critical speeds is analysed under different startup speed profiles.
Startup speed profile is represented by exponential formula with single parameter (δ) that indicates whether the startup
speed is rapid or slow. The results show that for slow machine startup; the system will remain at the critical speeds for
a long period allowing the vibration response to be increased. On the other hand, rapid machine startup passing through
the critical speeds will reduce the vibration response. In addition, the numerical simulation results show that applying
initial slow startup speed profile followed by instantaneous switch to rapid startup speed profile can reduce the
vibration response significantly and more than for applying only rapid startup speed profile.

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