Abstract

It is widely acknowledged from literature that material or structural imperfections of the shaft crack type are capable, in some cases, of generating coupled forms of lateral-axial-torsional vibrations in the rotating machine. Such information, however, pertains to smal] or model objects of that type. In the paper presented are investigations into the influence of the shaft gack on the dynamic state of a large, multi-supported rotating machine. Determined have been the cases where the crack is capable of inducing pronounced forms of vibrations, which can serve as basis for more reliable and effective diagnostics, or the cases, where the mechanism of couplings deteriorates, despite the existence of cracks with significant depths. Determined has been the degree of sensitivity of non-linear and mutually coupled system vibrations on mock propagation and conducted had been the assessment of their applicability as a diagnostic determinant of a the dynamic state in a large rotating machine. Indicated have also been the cases, where traditional diagnostics, based on the analysis of constituent vibration spectra of 2X type in the case of lateral vibrations and 1X and 2X for axial and torsional vibrations can be misleading. Conducted have also been investigations into the influence of crack location  and propagation on operation of rotating machine after exceeding the stability threshold and hence system operation under conditions of existence and formation of oil whirls. It turned omr that the crack can sustain and reinforce existing sub-harmonic components in the vibration spectrum whereas oil whirls efficiently impair the effect of vibrations coupling. Investigations have been conducted based on the advanced models and suites ofcomputer codes for the analysis of complex systems of the type: line of rotors-slide bearings-foundation, enabling generation of dfrngnostic relations defect-symptom also in cases of large displacements and strongly non-linear externall interactions occurring the system. Presented have been the examples of experimental wńcation of applied research tools.