NORMAL MODES AND NATURAL FREQUENCIES OF COMBINED STRUCTURES

The normal modes and natural frequencies of a structure are determined from a knowledge of the normal modes and natural frequencies of its components parts. Only linear elastic structures resting on an immovable base are considered. The total structure is mentally broken down into a primary structure (part including base points) and one or more substructures. The displacement of the total structure is expressed as a series expansion of the scaled normal modes of the primary structure. The scaling factors involved are determined from the equilibrium equations of the primary structure with the secondary structures removed and replaced by their internal forces of connection. © 1968, Acoustical Society of America. All rights reserved.