ABSTRACT
While fulfilling very important roles in machinery, the rotors are, at the same time, the main source of perturbation of normal operation of the machines. Rotational motion around an appropriate axis, at rated, design-imposed, rotational speed, represents the crucially required dynamical state for rotors. In all practical cases in rotating machinery, the accumulated rotational energy cannot, however, be fully used for the design purpose. This energy has a potential for serious leaks and can easily be transformed into other forms of energy. Naturally, as in all other mechanical elements, some energy loss due to dissipative mechanisms always occurs, irreversibly transforming the rotor rotational energy into thermal energy, which eventually gets irreversibly dissipated. Except for this type of side effect, in rotors there exist additional sources of energy leaks, transforming the rotor rotational energy into other forms of mechanical energy. In other words, the rotational motion of rotors, associated with useful work that it is supposed to accomplish, is accompanied by
energy transfer — from rotation to other forms of motion — the rotor rotation may be
itself occur. They may have diverse forms of varying intensity. All three main modes of rotor vibrations — lateral, torsional, and axial modes — may be present during rotor operation. Among these modes, the lateral modes of the rotor are of the greatest concern. Most often,
machines and mechanisms (Figure 1.1.1). Rotational motion is employed to achieve transla-
‘‘mechanical side effects’’ (Figure 1.1.2). Due to several factors, which contribute to the
accompanied by various modes of vibrations (Figure 1.1.3). First, vibrations of the rotor
they represent the lowest modes of the entire machine structure. Next, through the supporting bearings and through the fluid encircling the rotor (unless the rotor operates in vacuum), the rotor lateral vibrations are transmitted to the nonrotating parts of the machine. Eventually, the vibrations spread to the machine foundation, to adjacent equipment, building walls, and to the surrounding air in the form of acoustic waves.
