Analysis of Rotor Dynamics Acceptance Criteria in Large Industrial Rotors

Rotating machinery is extensively used in the industry today. The dynamics of rotating machines and the critical issues associated with them have been the principal focus of a large part of the research and development in industry in recent times. The rotating machines are one of the most essential components of machinery in industry as they play a vital role in the process of transferring power from one place to another. The assemblies of the important industrial machinery such as gas turbines, compressors, hydroelectric systems, locomotives, vehicles etc. are made of different rotating parts. Therefore it becomes necessary to analyze the dynamic behavior of the rotating systems in order to understand the level of stresses to which these components are subjected to during their operation. This pre-design phase analysis can greatly contribute to the trouble shooting of the critical issues. However, the dynamic behavior of rotating machinery is quite complex which necessitates the need for understanding the mechanics behind the operation of these devices thoroughly. The complexity of the analysis increases further whenever there is an unbalance in the rotating components which leads to an undesirable whirling response. The gyroscopic effects present in the rotating disks amplify at higher rotating speeds of shafts thereby inducing some undesirable stresses in the components. Due to the complexity of these rotating structures, they are subjected to stresses during the industrial processes. So, it becomes necessary to perform the vibration analysis for predicting their behavior prior to their application phase. This analysis would be of great aid in determining the natural frequencies and the associated mode shapes of the system. Initially, a free vibration analysis is carried out which is followed by the forced vibration analysis to predict their behavior when subjected to the excitations arising from the residual unbalance and any other external excitations. The primary goal of this dissertation is to analyze the dynamic behavior of the industrial rotors and address the critical issues associated with them. Initially, a simple Jeffcott rotor is analyzed in detail to determine its natural frequencies, critical speeds from the Campbell diagram, the forward and backward whirl modes. This is followed by the analysis of an actual industrial rotor in ANSYS in order to understand its dynamic behavior which involves the detailed analysis of the Campbell diagrams, critical speeds, effect of the gyroscopic moments etc. The phenomenon called ‘Curve veering’ was observed from the inspection of the obtained natural frequencies of the system and discussed. Campbell diagrams are obtained and critical speeds, effect of the gyroscopic moments etc. are identified and discussed.