N. D. Pagar^1,, S. H. Gawande²

Accurate prediction of critical speeds in rotating machinery is of great importance to designer and many attempts have been made to calculate it exactly. At the design stage it is necessary to predict accurately the dynamic behavior of rotating system of rotating parts of Wankelengine in order to avoid resonant conditions at operating speeds. Critical speed of a rotating shaft differs from its non-rotating natural frequency. The main reason for this difference is known to be the gyroscopic momentum. So it is quite great important to determine the natural frequency of the eccentric shaft in non-rotating condition (free-free condition) i.e. degrees of freedom are not restricted. In this study the natural frequency and mode shapes are predicted for the eccentric shaft in free-free condition (non-rotating) by using the commercial software package (ANSYS) in its modal analysis option. And results obtained from it are compared with experimental modal analysis (FFT analyzer). The verified results leads to the prediction of the dynamic behavior of the eccentric shaft viz. design calculations, natural frequencies, mode shapes.

modal analysis, natural frequency, resonance, finite element analysis (FEA), fast fourier transform (FFT)