ABSTRACT
Until now, we have concentrated on the transverse and torsional vibration analyses of rotor-bearing systems, e.g. free vibrations, forced responses, and instability analysis. These analyses are useful tools for designers of rotating machineries to predict the behavior of such machineries before their manufacturing and commissioning. These analyses help in the modification of design if the operating speed is close to critical speeds or in instability zones. In the present and subsequent chapters, we will address another class of practical and common problems related to rotating machineries that practicing engineers face during the commissioning of new rotating machine, during operation, or after every major overhaul of such machineries. Some of these faults are unbalances, misalignments, rotor-stator rubs, bent or bowed shafts, fatigue cracks, the wear and tear of various moving and stationary components, loose components, and faults related to components of bearings, gears, couplings, blades, seals, electric motors, alternators, generators, and pumps. Among various kinds of faults, the most common fault is inherent unbalances (or residual unbalances) in machineries that occur due to manufacturing errors (fits and tolerances), material in-homogeneity, improper commissioning, thermal deformation, the wear and tear during operation, residual stresses, and so on. The basic definition of unbalance and its type for rigid rotors has been introduced earlier in Chapter 2. To prevent excessive vibration due to unbalances, we must first decrease this unbalance (or balance the rotor), which is the major source of vibration.
