Multilevel dynamic substructure iteration method (iterative eigensolution of a multilevel substructure system)

A method is presented for the calculation of the first vibration modes of a structure subdivided in substructures organized in a multilevel tree. The eigensolutions obtained are exact (that is they can be obtained with the required accuracy, defined by a convergence tolerance). The method, called MDSI, is the adaptation, to a substructure tree, of the well-known subspace iteration method, with the additional improvement of a method for the calculation of very good starting iteration vectors. The method, though requiring iterative calculations on the whole system of substructures, can be implemented in a very efficient way in computer programs provided with substructure capabilities. The method is actually implemented in the Ansaldo program PAS and has been extensively tested, and shown to be competitive, on large models, with other programs (which usually require, however, for a comparatively efficient solution, the use of approximate dynamic condensation techniques). The method is free from numerical problems and converges very fast (due to his good starting vectors). (orig.)