A stiffness optimization method for a shaft-bearing-pedestal system based on the dynamics

The shaft and pedestal deformations can produce large misalignments and displacements of shaft-bearing-pedestal systems (SBPSs). The phenomena have a great influence on the working performances of the SBPS. Thus, the shaft and pedestal stiffness should be properly optimized to minimize the system vibrations during the design process of the SBPSs. To overcome this issue, a new shaft and pedestal stiffness optimization strategy of a SBPS based on both the time- and frequency-domain vibrations is conducted in this work, which cannot be addressed by the previous methods considering single shaft or pedestal stiffness. Moreover, this method can be used to avoid the unexpected resonance frequencies of the rotor system during the design processing. A dynamic model of the SBPS considering both the flexible deformations of shaft and pedestal is presented. The effects of the shaft and pedestal stiffness on the vibration performances of the SBPS are discussed. The results give that the shaft and pedestal stiffness have a great effect on the time-domain waveform, magnitude, and peak frequencies of the vibrations of the SBPS. The relationships between the peak frequencies in the spectra of SBPS and two stiffness coefficients are nonlinear ones. However, they have no effect on the bearing passing frequency and its harmonics in the envelop spectra. It represents that the SBPS with the larger shaft and pedestal stiffness has a smaller vibration level. The obtained results can provide some guidance for the SBPS design with a low vibration level.