Modal analysis of the hydro turbine shaft with cracks

Abstract

The design process for the elements which are the parts of the structures and equipment in power industry includes both of stress and strain state calculations, as well as an analysis of natural mode shapes and frequencies. During operation of the machine elements and systems, periodic vibration measurement in unloaded and loaded state is essential for high level of availability of the equipment operation. This is especially important after the reparation of particular elements of mechanical systems, when the vibration monitoring is source of the information necessary for their proper and safe use. Therefore, the previous numerical calculations of the eigen frequency and modal analysis give the necessary information for appropriate operation loading. In this paper the dynamics of the Kaplan turbine shaft is analyzed in accordance with these preferences. The Finite Element Analysis is used for numerical simulations and calculations. The real case of the shaft failure is chosen and the analyses are performed for the shaft before and after damage appearance. The cracks of different depth are modeled at the shaft to flange transition zone, in accordance with the real damages. Also, the model of the shaft with the shape and dimensions after the reparations is analyzed in order to compare the shaft dynamics with changed transition radius. Conclusions and discussion about the obtained results are given in comparison with the real operation conditions for the analyzed case study.