Vibration analysis of periodically time-varying rotor system with transverse crack

This paper proposes the vibration analysis for the periodically time-varying rotor system with transverse crack based on the complex modal analysis by introducing the modulated coordinates. From the feasibility of the crack modeling by harmonically varying stiffness, for which the dynamic behaviors of breathing crack depending on two modeling structures are investigated, the vibration analysis associated with modal characteristics, whirling, instability, directional frequency response functions (dFRFs) and directional spectrum (dS) is carried out. Using the feature of the reverse dFRFs strongly representing the effect of the crack and the interpretation of the dS patterns, the effective method to identify the modes due to the presence or propagation of a transverse crack is suggested.