Modal disparity and its experimental verification

Abstract

This paper describes an analytical and experimental investigation of the property of modal disparity in a vibrating structure. For a given structure, the concept of modal disparity describes the structure's ability to generate significant changes in the mode shapes by some type of on-the-fly structural modification. In the present study we consider a vibrating beam that experiences a controlled stiffness change, induced by the activation and deactivation of an electromagnetic brake that causes a spatially localized change in the bending stiffness. Using a finite element model and an experimental apparatus it is shown that significant amounts of energy can be shifted back and forth between sets of modes in a systematic and predictable manner. This confirmation of modal disparity for a specific structural system provides evidence that this concept is feasible, and thereby opens the door for a number of potential applications in passive and active control of vibrating structures.