Numerical and experimental analysis of a continuous overhung rotor undergoing vibro-impacts

This work aims in obtaining the transient response of an overhung rotor undergoing vibro-impacts due to a defective bearing. An overhung rotor clamped on one end, with a flywheel on the other and impacts occurring in between, due to a bearing with clearance, is considered. The variation of this system, popularly known as the Jeffcot rotor, has been considered in previous works, but there, the system has been reduced to a single degree of freedom for ease of analysis. In this work the system is modeled as a continuous rotor including gyroscopic effects and the governing partial differential equations are set up and numerically solved. The method of assumed models is used to discretize the system in order to solve the partial differential equations (PDE) by partially decoupling them and solving numerically. These partially decoupled equations are more accurate and less time consuming than the ones produced by finite elements or other numerical schemes. The most important step in the success of this method is the selection of suitable modes for decoupling the system. It is not simply enough to select orthonormal modes for decoupling the PDEs, but care must be taken to select the modes as close to the actual system as possible. Using this method numerical experiments are run and representative results are presented. The different numerical issues involved are also discussed. An experimental setup was also built to run experiments and validate the results. In the setup a defective bearing is introduced at the flywheel end of the shaft to create radial impacts on the shaft. Laser sensor non-contact probes are used to measure the displacement of the shaft a specified locations. Experimental observations show satisfactory qualitative agreement when compared to the numerical integrations.