Parameter Identification With Noncollocation of Force and Measurement Locations Using Nonsynchronous Perturbation and Optimization Techniques

Abstract

Nonsynchronous perturbation techniques developed over the last few years have proven to be a very powerful tool for parameter identification of rotating systems. In order to obtain interpretable results, some limitations have had to be imposed on the analytical models and rotor systems used in the process, such as applied forces, and measurement transducers had to be located near major masses on the rotor. In the laboratory environment these limitations can usually be accommodated, but not always, while in the field, compliance is almost impossible. This paper explores the use of finite element modeling, measured vibration response data, and optimization techniques to extend the applicability of parameter identification through nonsynchronous perturbation techniques to those systems in which the perturbation forces and/or resultant response measurements cannot be conveniently located at the mass centers. In this technique, a finite element model of the rotor system is constructed, and all known information about the system parameters input to a computer program designed to operate on a personal computer. The program then computes the theoretical response of the system, by processing user-supplied initial conditions for the unknown system parameters, and compares these results with the vibration responses measured on the machine, and collected by the data acquisition system. The unknown parameters are then modified using local convergence optimization techniques until the error between the theoretical and measured responses is acceptably small. If the system parameters under investigation coincide with the unknown parameters in the computer program, they are identified in the process. This technique was applied to an experimental rotor system constructed such that the parameters under investigation, the direct and quadrature dynamic stiffness components for a plain oil-lubricated journal bearing operating at low eccentricity, could be determined by both this technique and conventional unbalance force testing. The results of the nonsynchronous tests are presented in the paper.