THE DETERMINATION OF FREQUENCIES AND MODES OF UNDAMPED STRUCTURES USING FINITEELEMENT STIFFNESS AND CONSISTENT-MASS MATRICES.
MASSACHUSETTS INST OF TECH CAMBRIDGE AEROELASTIC AND STRUCTURES RESEARCH LAB
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An analysis and a computer program which permit determining the natural mode shapes and frequencies for undamped structures are given. The program is designed to operate on stiffness and consistent-mass matrices which are derived from a finite-element representation of the structure, since it has been shown that superior accuracy is achieved compared with conventional lumped-parameter methods with an equal number of idealized elements. The consistent-mass matrix is a symmetric-mass matrix with nonzero offdiagonal elements it is this symmetric nondiagonal feature which the present analysis handles conveniently. In particular, the present method represents a convenient and economical synthesis of existing methods, and may be used to calculate the natural mode shapes and frequencies for any system which is described by a set of symmetric mass and stiffness matrices. Author