Modal Synthesis of Large Structures with Nonlinear Joints from Vibration Tests,
ECOLE CENTRALE DE LYON ECULLY (FRANCE) DEPT DE MECANIQUE DES SOLIDES
Pagination or Media Count:
The fundamental idea of modal synthesis methods is to describe the movement of the structure assembly as a superposition of the lower modes of each substructure. The first method, proposed by Hurty, utilized the fixed constraint modes of each substructure obtained by clamping the internal boundaries. Initially, this method utilized constraint modes and rigid body modes to describe the movement at the connection points. Later, Craig and Bampton showed that it was not necessary to differentiate between these two sets of modes and that both could be regarded as constraint modes. This substructure synthesis method is based on the Rayleigh-Rita procedure. The other possibility is to utilize the free modes of each substructure and to impose the displacement boundary conditions. The coupling procedure can be implicit or explicit. The latter alternative corresponds to the utilization of Lagrange multipliers. As Meirovitch and Hale clearly showed in recent studies, the utilization of unconstrained models leads to two basic problems. The first involves model truncation and the second, the choice of the weighting functions which guarantee the compatibility conditions together with the residual methods. The influence of modal truncation is to increase the calculated natural frequencies and thus compensate for the fact that the set of constraint functions is truncated in the case of continuous interfaces, according to the Weinstein method.