Is the dissipation induced by ‘‘fuzzy’’ substructures real or apparent?

Abstract

There continues to be confusion whether the dissipation which can be induced in a master structure by a multitude of small attached substructures is ‘‘real’’ or only apparent. It is shown that the dissipation is real during steady-state vibration and can cause the master structure to have a larger loss factor than that of the substructures inducing the loss. The dissipation involves the continuous transfer of vibratory power from the master structure to the substructures and its continuous conversion into heat. During transient excitation, however, some of the initial dissipation in the master structure may be only ‘‘apparent,’’ involving the storing of some of the transferred power as vibratory energy in the substructures and its cyclical transfer back and forth between master and substructures until eventually dissipated, at a rate which in this case depends on the loss factors of the substructures. Examples of the two cases will be shown.