Numerical modelling of a rotor-bearing system for Machinery Condition Monitoring.

The real-time monitoring of rotors is used to speed up the identification of damage and allows to reduce the risk of failures. The detected vibration signal needs algorithms to be analysed and classified, moreover require an accurate placement of sensors. It is also possible to create a digital replica of the physical systems to simulate the behaviour of the machine and to carry out all the necessary tests. Vibration monitoring analysis offers lots of information about anomalies that could be present inside rotating machines. These usually generate inside bearings which are critical elements for the safety of the entire system. The work of this master’s degree thesis focuses on the creation of an analytical-numerical model to describe the behaviour of a flexible rotor supported by rolling elements bearings. This model can be adopted to perform two kind of monitoring activities: “in-monitoring”, where a continuous identification of the operating conditions is performed on the bearing itself, to detects the possible presence of defects inside the component through the dynamic firm of the system, and “out-monitoring”, as an indirect measurement, which allows to identify the defects affecting one part of the machine and to determine the dynamic signature of the entire system. In this work the model is studied considering the presence of different types of localized defects, that can be located inside the bearings: on the inner ring, on the outer ring and on the rolling elements. The mains parameters of the system and the defects are described with an analytical approach, to obtain a Digital Twin of the real system where the goal is to identify and classify damages through the monitoring activity. It is then studied how the vibrations, produced by bearings, affects the behaviour of the rotor. The simulation is obtained through a complete analysis of the contact between bodies, and the acceleration signal, produced by the vibration of the system, is studied in different locations on the shaft. The dynamic analysis of the signals is performed considering the presence of each defect separately, and obtaining the particular features of the vibration signal, both in the time and frequency domain.