Predicting the fatigue life of synchronous motor-driven compressor using the complex modal reduction technique

In this paper, the low cycle fatigue life for rotor systems driven by synchronous motors is predicted using the complex modal reduction technique. The system torsional model is derived using the lumping technique where, for accuracy, large number of stations is considered. The effect of bearing viscous damping is accounted for in the equations of motion. The Miner's rule is adopted for calculating the commutative stresses for predicting the low cycle fatigue life for the full and the reduced-order models. The procedure is applied to an actual 19 000 hp synchronous motor driving a high-speed compressor. Simulation results showed excellent agreement in predicting the transient stresses between the full model and the 2-modes reduced model with vast reduction in computatiional time, i.e. around 90%. Moreover, the predicted fatigue life in terms of number of startups shows excellent agreement with a maximum error of about 4.2% in the predicted life. (C) 2000 Elsevier Science S.A. All rights reserved.