A linear least-squares version of the algorithm of mode isolation for identifying modal properties. Part II: Application and assessment

Abstract

The latest modifications of the algorithm of mode isolation (AMI) for identification of modal properties from frequency response data are tested with synthetic data derived from an analytical model of an elastic frame in which flexure and torsion are coupled. The parameters of this model are selected to cause the occurrence of localized modal patterns in two modes having close natural frequencies. The response data is contaminated with white noise at a level sufficient to almost mask the two close modes. Results for the real and imaginary part of the eigenvalues are tabulated. The analytical modal patterns of displacement and torsional rotation are depicted graphically, accompanied by the discrete values obtained from AMI. Excellent agreement is found to occur for each mode, other than one of the pair of close modes. The poorer quality of that mode’s identified properties is shown to be a consequence of its localized modal pattern. Results for the eigenvalues obtained by the rational fraction polynomial algorithm, which is an alternative modal identification technique, are found to be substantially less accurate as a consequence of difficulty in the presence of noise.