On the dynamic instability of components in complex structurest

The case where one structural member of a larger complex structure experiences a dynamic instability is addressed. An averaged integral representation of the overall structure is chosen, except for the structural member of interest which is modelled precisely by means of the conventional methods of vibration theory. Material damping and the energy dissipation between components are taken into account by means of a distributed elastic-plastic rheological model. Particular attention is paid to keeping the intrinsic nonlinear properties of the energy dissipation. Structural members prove to act as dynamic absorbers with respect to the primary structure. The phenomenon of vibration saturation in complex structures is revealed and discussed. Full-scale vibration testing of a complex structure driven by an electromagnetic shaker is considered as an application of the concept. The moving coil of an electromagnetic shaker is shown to be dynamically unstable if an experiment is not properly designed. The influence of the Iarge vibrating structure on the stability chart of the shaker turns out to be considerable and it changes the shaker’s atability chart drastically. 0 1997 Elsevier Science Ltd.