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.

Keywords:

• Rotating machinery
• modal analysis
• modal testing
• non-self-adjoint
• gyroscopic
• left eigenvectors
• model reduction
• test planning

Additional information

Notes on contributors

E S Gutiérrez-Wing

Enrique is a vibration engineering consultant and researcher of the Department of Mechanical Engineering at the Centro Nacional de Investigación y Desarrollo Tecnológico in Cuernavaca, México. He obtained his PhD degree in 2003 from the University of London/Imperial College London. His research interests are on modal analysis, rotordynamics and vibration signal processing.

He has collaborated in several research projects in the fields of modal analysis and rotordynamics with funding from the Consejo Nacional de Ciencia y Tecnología of México, the EPSRC of the United Kingdom and the European Union.