Estimation of damping in rotors using complex morlet wavelet transform

In a rotor-bearing system running with uniform angular acceleration, after running through the resonance, typical beat vibrations occur because the response of the system consists of the natural and excited motion. Shortly after resonance both are vibrations with frequencies close to each other. The present study explains a method for estimating damping of rotor-bearing systems from transient beat characteristics observed during the run-up stage. A mathematical justification is provided that the transient response of the rotor-bearing system consists of a beat response when the system crosses resonance. It is also clear from the mathematical model that the beat phenomenon observed depends on the level of damping in the system. The beat time period is also dependent on the angular acceleration of the system. This beat response is considered for wavelet analysis and the damping is estimated. Angular acceleration (α) of the rotor often increases the damping effects. This paper investigates how the damping ratio changes with respect to different angular acceleration values of the rotor-bearing system. Experimental validation of the beat phenomenon and damping identification is done for a rotor-bearing system. Validation for the above proposed method is done by the half-power bandwidth method of the run-up response and logarithmic decrement method of the beat response. A damping estimation from the impulse response of the stationary rotor by using wavelet transforms is also presented and validated using the logarithmic decrement method.