Modal Surveys of Weakly Coupled Systems

The emergence of digital signal processing equipment and associated computer programs has caused a strong interest in modal survey investigations using this type of equipment. It will be shown, however, in this paper that in certain types of physical systems, mode shapes are so highly sensitive to small changes in the physical properties of the system that close agreement between computed and experimentally measured mode shapes cannot be expected. It will be shown, for example, that in certain situations stiffness changes in the order of five percent give rise to changes in coupled mode shapes of the order of fifty percent.