Modal analysis of an isolated nonlinear response mode using the Nyquist circle properties: Numerical case

Abstract

Modal testing practitioners are well accustomed to FRFs which, nowadays, can be measured and analysed by a large variety of methods and tools. However, most of the tools for linear modal analysis are practically unusable when the frequency response is amplitude dependent. Hence, the methods based on the properties of the Nyquist circle become unavailable because of the loss of its circularity and completeness. Nevertheless, FRFs of well-isolated modes can still be processed by calculating the modal parameters for every pair of receptance points taken at equal amplitude either side the maximum response peak. The major limitation of this method is the absence of one branch of the response function due to unstable dynamics. The objective of this work is to show that incomplete FRF functions can be still processed to obtain the modal parameters. The method is benchmarked against a single degree of freedom both for linear and nonlinear response conditions