Characterisation of rotating machinery dynamics within limited frequency intervals using modal analysis

Abstract

The possibility of characterising the dynamics of rotating machinery structures using modal analysis is explored. The paper is based on a recently-developed method by which the left-eigenvectors can be computed from their right counterparts and their corresponding eigenvalues. This method is aimed at obtaining the complete set of modal parameters of a machine without the need to measure a complete row plus a complete column of the frequency response function (FRF) matrix, as is customary for non-self-adjoint systems. The applicability of the method to the derivation of reduced-order modal models of continuous systems from measured FRFs is discussed. It is shown that the new method is applicable if the response of the continuous system at hand is only affected significantly by a limited number of modes within the frequency interval of interest. It is also shown that a simplification of the measurement scheme made available by this new method depends on the selection of degrees of freedom used to study the structure. A numerical example is given to illustrate this point.