Substructure system identification from coupled system test data

System identification in the context of linear structural dynamics and mechanical vibrations is addressed. More specifically, the focus is on large systems built up by components and the identification of its subsystems using test data of the complete system. A method based on reconstruction of the interface forces acting between the unknown subsystem and its neighbour is presented. Theoretical aspects regarding frequency domain load identification are illuminated. The causes and consequences of an ill-conditioned matrix inversion are emphasized. It is shown that the load identification and thus also the subsystem identification is sensitive to the existence of general anti-resonances in the frequency domain of interest. Different methods for validation of an identified subsystem are discussed. Two numerical examples with artificial test data are given to illustrate the procedure: a simple lumped parameter system and a slightly more complex distributed parameter system. The technique is also successfully applied to a physical test setup consisting of a plane frame structure built up from two components.