Dynamical Behavior of Rotating Machinery in Non-Stationary Conditions: Simulation and Experimental Results

Condition monitoring of rotating machinery is generally performed in stationary conditions or quasi-stationary conditions. Assuming linearity of the system its dynamic behaviour can be simulated in the frequency domain. Simulated results are then compared to measured results and the comparison allows to apply model based diagnostic procedures. As soon as the system presents strong non-linearity, simulation must be performed in the time domain, including also iterative procedures, which may become cumbersome. When the dynamic behaviour of linear or non-linear systems in non-stationary conditions is simulated, the time domain integration must be necessarily used. Accuracy of simulated results gets weaker; comparison with measured results for diagnostic purposes becomes difficult or ineffective; model based diagnostic approach seems not applicable. Monitoring of machines in “strong” non-stationary conditions is generally performed only by means of accurate signal analysis, without modelling the machine or the process. In this paper the simulation of some typical behaviour of rotating machines in weak or strong non-stationary conditions in the time domain is presented and discussed. Some experimental results are also presented and compared to simulations. Further examples of systems with strong non-linearity, that in stationary conditions exhibit non-stationary vibrations, are also given.