Influence of Spin Softening on Natural Frequencies of a Steam Turbine Rotor Assembly with Interference-Fit

Vibration is the default state of all mechanical systems that causes them to possess a natural frequency. The significance of natural frequency cannot be emphasised enough, considering the fact that its study is essential in averting resonance which causes violent swaying motions and catastrophic failures in improperly constructed structures. In case of rotating structures, the study of natural frequency is incomplete without the understanding of spin softening. This paper presents an ANSYS based analysis to study natural frequency variation due to spin softening, but in a faster and more accurate way than conventional GUI-based ANSYS analysis. The conventional GUI based ANSYS procedure is a laborious time consuming process, with the user having to perform multiple iterations of model analysis involving different rotational velocities to examine the variation of natural frequencies of the system. Through this paper, a novel way has been suggested to bring down the time and effort involved in such a study by using an advanced ANSYS feature called ANSYS Parametric Design Language (APDL). The results obtained have been found to validate spin softening.