Numerical study of the three-span shaft critical speedand develop a new method to compute critical speed

Critical speed is one of the most important characteristic features of rotating machinery. If the running speed of machinery is matched with critical speed, vibration amplitude increases until severe damage results in the machine. By increasing the constraints of the rotor shaft system, the complexity of calculating the critical speed is increased. In this study, a new method based on finite element analysis (FEA) is developed for the computing critical speed of the machinery with four bearings (supports). The modal analysis by FEA is selected to calculate the natural frequency of the shaft. In this regard, FEA is implemented in the exper-imental setup, and results are compared to verify the validity of the model. The FEA analysis is used for several case studies for different shaft lengths. By validation of the FEA model, it is used to develop a new method for the calculation of the rotor shaft critical system. In the developed method, four equations were derived for four ranks of critical speed. Briefly, the developed method is an algorithm in which the entrance of its mechanical properties of the shaft and its output is four ranks of the critical speed. It will be shown that the first natural frequency of the three-span shaft varies from the fixed-fixed shaft with the length of the mid-dle span to a simple support beam with the length of the middle span shaft. The output of this study helps to calculate the natural frequency of the three-span shaft in which the close solu-tion is complex

کلیدواژه ها:

shaft critical speed ، finite element analysis (FEA) ، natural frequency ، three-span shaft