Modal Response of a Flexible Rotor in Fluid-Film Bearings

An analysis is presented for calculating the response of a general flexible rotor in fluid-film bearings to forced and transient excitation. It is a modal method where the governing system equations are transformed by means of normal coordinates into a set of decoupled, first-order equations which can be solved in closed form. The transformation is based on the orthogonal complex modal functions (“mode shapes”) associated with the eigenvalues of the system. The method has been applied to an industrial multistage compressor. Numerical results are given for the response to selected unbalance distributions and, also, the transient response to a shock pulse.