SHOCK SPECTRA ANALYSIS OF ROTOR-BEARING SYSTEMS

A shock response spectrum procedure is developed to estimate the peak displacement response of linear flexible rotor-bearing systems subjected to a shock load such as encountered by blade loss, base acceleration pulse or a step turn maneuver. A response spectrum is established for each of these types of shock loads. The spectrum for blade loss consists of a progressive and a retrograde part. The blade loss and base acceleration pulse spectra are expressed in a unique nondimensional form. The blade loss spectrum is a function of the modal damping ratio and the ratio of rotor spin speed to modal damped whirl speed. The spectrum associated with a base acceleration pulse is expressed as a function of the modal damping ratio and the ratio of excitation frequency to damped whirl speed. The turn maneuver spectrum is a function of the modal damping ratio and damped whirl speed. Modal decomposition using complex modes is utilized to make use of the unique feature of the spectra for the estimation of the peak displacement response of rotor systems when excited by a shock load. The procedure is developed and then applied to four example rotor systems using several superposition strategies. The results are compared to true peak displacements obtained by a separate time transient response analysis. The results for one of the examples are also compared with experimental data obtained by Pratt and Whitney Aircraft from a blade out test rig.