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Description
Condition monitoring focuses on detecting and identifying changes in a machine's dynamics. In rotor dynamics, flexible connection elements such as bearings and joints are critical. Over time, the dynamics of these components can change, e.g., due to aging, which changes the overall dynamic behavior of the rotor system. Condition monitoring uses response data acquired during operation that is caused by operational forces. The contribution presents a practical approach to monitor the bearings' stiffness and damping, using transfer path analysis and frequency-based substructuring.
Transfer path analysis (TPA) is a method that considers the assembly of a source structure with an unknown excitation and a receiver structure. Typically, the goal of TPA is to characterize the excitation of the source and predict the responses of the receiver. However, in the context of condition monitoring, the goal is different. From an equivalent force and a measured response, the dynamics (i.e., transfer functions) of the system should be calculated. Using the calculated transfer functions, the dynamics of the bearings can be extracted by using frequency-based substructuring.
This contribution presents a workflow that uses TPA and frequency-based substructuring to identify the bearings of a rotor system in operation. In a TPA step, the bearings are considered part of the receiver system, and the rotor is considered the source system. An equivalent force at the interface that represents the operational excitation is determined. Measurements of the response on the interface are used to obtain some transfer functions of the system at the interface. These transfer functions are used in a frequency-based substructuring step to isolate the dynamics of the bearings, which are then used to detect changes. Previously, a numerical example of a beam with an operational excitation that is connected to the environment via spring-damper elements was presented. This contribution gives an experimental application of the novel procedure on an academic rotor test rig with magnetic bearings and artificial excitation.
