In the previous lecture we looked at a simple rotor wherein the disc was centrally located on the shaft and we studied the effect of unbalance. Now we will try and gain an appreciation of some more interesting problem situations in the field of rotor dynamics.

Fig 2.2.1 An offcenter Rotor

Fig 2.2.2 Two Position of the rotor

Consider the shaft system shown in Fig 2.2.1, wherein the disc is located at a point away from the mid-length of the shaft. Fig. 2.2.2 shows two positions and the point of interest is the orientation of the disc. As per Euler-Bernoulli beam bending theory, a plane cross-section remains plane and normal to the neutral axis even after bending. Thus we observe that the disc has actually rotated about an axis perpendicular to the plane of the figure. The moment of inertia of the disc therefore plays a significant role in this rotation of the disc and has an affect on the dynamics of the rotor-shaft system.