Abstract
Appearance of transverse cracks in rotor systems mainly affects their stiffness content. The stability of such systems at steady-state running is usually analyzed by using the Floquet’s theory. Accordingly, the instability zones of rotational speeds are dominated by negative stiffness content in the whirl response in the vicinity of critical rotational speeds. Consequently, an effective stiffness measure is introduced here to analyze the effect of the crack and the unbalance force vector orientation on the intensity of negative potential and stiffness content in the whirl response. The effective stiffness expression is obtained from the direct integration of the equations of motion of the considered cracked rotor system. The proposed effective stiffness measure is applied for steady-state and transient operations using the Jeffcott rotor model with open and breathing crack models. The intensity of negative potential and stiffness content in the numerical and experimental whirl responses is found to be critically depending on the propagation level of the crack and the unbalance force vector orientation. Therefore, this can be proposed as a crack detection tool in cracked rotor systems that either exhibit recurrent passage through the critical rotational speeds or steady-state running.
Highlights
In another series of publications, several models of cracked rotor systems were employed with several damage detection techniques for studying the vibration whirl signature of cracked rotor systems at steady-state running[18,19,20,21,22,23,24,25]
I n19,20, a coupled radial, axial and torsional vibration whirl response was analyzed for crack detection and identification. In21, a static rotor system with an open crack model in the shaft was considered for vibration whirl analysis to predict the transverse crack depth and its location
An effective time-domain identification algorithm based on the Extended Kalman Filter (EKF) was employed in[25] for rotor damage detection where the neural networks accompanied with power spectral density characterization have been applied in26 for crack damage identification
Summary
In another series of publications, several models of cracked rotor systems were employed with several damage detection techniques for studying the vibration whirl signature of cracked rotor systems at steady-state running[18,19,20,21,22,23,24,25]. The changes in experimental whirl amplitudes with respect to the shaft rotational speed are plotted in Fig. 9 for crack depth μ = 0.2 at two different unbalance force vector angles β = 4π/9 rad and β = 8π/9 rad .
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