Implementation of Transfer Matrix Analysis of Multi-section Rotors Using Ansys Parametric Design Language

Critical speed analysis of rotor systems is a difficult process due to the fact that there exists no direct formula to determine the natural frequency of a multi-section rotor. Finite Element packages provide a suitable platform for such an analysis but demand considerable experience on part of the user to perform modeling, meshing, solving and post-processing. The primary objective of this paper is to identify a suitable method for determining rigid bearing critical speeds of multi-section rotors in order to validate the results obtained through traditional FEA package and also to simplify the latter. The only drawback of transfer matrix analysis is the existence of mathematical equations and multiple roots which makes it a cumbersome process by solving manually. This problem has been tackled in this present work through the use of Ansys Parametric Design Language (APDL). The strength of APDL as a macro language have been taken advantage of in this present work to develop an interactive macro which mimics the Finite Element Method and thus relaxes the rigorous routine involved in a traditional tool-based finite element analysis. The results thus obtained through Transfer Matrix Analysis and FEM macro are compared with traditional ANSYS results.