Application of nonlinear dynamics tools for diagnosis of cracked rotor vibration signatures

Abstract

The nonlinear model of the cracked Jeffcott rotor is investigated, with the particular focus on study of rotor's vibrational response using tools of nonlinear dynamics. The considered model accounts for nonlinear behavior of the crack and coupling between lateral and torsional modes of vibrations. Load torque is applied to the rotor which is laterally loaded with a constant radial force (gravity force) and unbalance excitation. The co-existence of frequencies of lateral modes in the frequency spectra of torsional mode are characteristics of the coupling response of lateral and torsional vibrations. When only the lateral excitations are applied, vibration amplitude bifurcation plot with the shaft speed as a control parameter, demonstrates some speed ranges for which vibrations of the rotor dramatically increase. Furthermore, the torsional response amplitude at the same speed ranges also increases and chaotic behavior can be observed due to the lateral excitations. These phenomena cannot be observed for pure lateral vibration response with the torsionally rigid rotor assumption.A cracked Jeffcott rotor with lateral and angular (torsional) degrees of freedom is considered. The rotor is subjected to a constant radial load (gravity force), rotating unbalance force, and the externally applied torque. The coupled torsional-

Condition Monitoring of Rotor Using Active Magnetic Actuator

“…The topic of cracked rotor vibrations has been analyzed in a great number of published works, for example [7][8][9][10][11][12][13][14]. They have been focused on the study of dynamic behavior of rotors with the so-called breathing type of crack during the passage through a critical speed at constant angular acceleration or deceleration.…”

“…They have been focused on the study of dynamic behavior of rotors with the so-called breathing type of crack during the passage through a critical speed at constant angular acceleration or deceleration. For example, Sawicki et al [7][8][9][10] studied the dynamics of accelerating cracked rotors, the crack-induced coupling between the torsional and lateral vibrations, and the application of nonlinear dynamics tools for crack diagnosis. Gasch [10] provided a comprehensive investigation of the stability behavior of a cracked Jeffcott rotor.…”

A Two‐Disk Extended Jeffcott Rotor Model Distinguishing a Shaft Crack from Other Rotating Asymmetries

“…This allows one to study the rotor dynamic response with or without the rotor weight dominance assumption by taking nonsynchronous whirl into account. Sawicki et al [10] investigated the nonlinear dynamic response of a cracked onemass Jeffcott rotor by means of bifurcation plots. When a rotor with the crack depth of 0.4 spins at some speed ranges, both the lateral and torsional vibration responses sustain periodic, quasiperiodic, or chaotic behavior.…”

Intermittent behaviour of a cracked rotor in the resonance region

“…One should notice that the dynamics of the rotor is related to the coupling of torsional and lateral vibrations and the whole system is nonlinear. The crucial point is related to the model of the "breathing" crack, indicating that cracks involve additional parametric excitations with the frequency equal to an angular velocity of the rotor rotation [8,7]. The crack introduces extra nonlinearity terms and produces coupling terms of lateral and torsional modes.…”

“…Finally, Ishida and Inoue [17] considered the response of a horizontal rotor to harmonic external torques. Furthermore, Sawicki et al [18,19,7] examined transient response of the cracked rotor, including the stalling effect under the constant driving torque.…”