An numerical method which can analyze the eigenproblem for very large structural systems with multiple or close eigenvalues is presented. This method is formulated by applying of the accelerated Newton-Raphson method to eigenproblems which is obtained from solving a constrained stationary value problem.
The step length which is used in the accelerated Newton-Raphson method is calculated from the least square concept. This method can calculate the natural frequencies and mode shapes without any numerical instability which may often occurred in the subspace iteration method or the determinant search method which has been mainly used for solving eigenvalue problem.
The efficiency of this method is verified by comparing convergence and solution time for numerical examples with those of the subspace iteration method and the determinant search method.
