Combined Crack and Unbalance Response Simulation for a Spinning Rotor

Abstract

Rotor unbalance is omnipresent in rotating machinery components and possibility of appearance of crack in such rotors also exists. Analysis of cracks in rotors attracts high merit for analysis and research. This is because of the detrimental effects in way of broken rotor and financially burdening downtimes associated with such failures. Rich literature exists on analysis and identification of cracks in spinning rotors; but a comprehensive theory on crack, its propagation, identification and localization is still incomplete. The present paper discusses the most likely response that would be generated from a cracked rotor. Variation of out of balance force and response has a linear relationship with magnitude of unbalance and parabolic relationship with spin speed of the rotor. A comprehensive study has been performed to visualize the cracked rotor response under different unbalance level and different spin speeds. In physical system, continuous change of unbalance represents situation of material loss during spinning, as it is the case with most rotors. The continuous spin speed variation relates to ramp up and coast down of the rotor during starting and shutting down. The equation of motion has been developed using Newtonian mechanics and response generated by solving the equation of motion by a fourth-order Runge–Kutta solver. The three-dimensional plot of interrelationship of rotor response with unbalance and spin speed obtained as result of the simulated experiment gives a clear idea of the crack presence.