Studies on Effect of Rotor Crack on Dynamics Characteristic Using Numerical Methodology

Abstract

In present work, dynamic analysis of cracked rotor is presented with a generalized formulation. After formulating the problem, dynamic analysis is conducted to find natural frequencies and dynamic response. Initially, transfer matrix approach was used with an interactive computer program. By using the field and point matrices of the shaft, bearing, disk, and crack, the resultant transfer matrix is obtained. A single crack on an element is considered in terms of stress intensity factor. Natural frequencies, mode shapes and response of the system are obtained at various crack depths. Results are validated with ANSYS model. Further, a two plane bending problem is considered using finite element method with a Maye’s breathing crack model to show the effect of crack depth and crack angle on dynamic response. A model consisting of a symmetrical shaft with central disk supported over bearings at ends is considered for illustration. A scaled prototype is fabricated and modal analysis experiments are conducted with and without transverse crack. The rotor is operated at various speeds and at each speeds, the output response at bearing is recorded to show the effect of crack on overall dynamics. Main contribution of the present work is generalized computer program formulation, where user can select the crack depth, crack angle, type of method and location of crack.