An improved subspace iteration method with shift for structures with multiple natural frequencies

An efficient and numerically stable eigensolution method for structures wit h multiple natural frequencies is presented. The proposed method is develop ed by improving the well-known subspace iteration method with shift. A majo r difficulty of the subspace iteration method with shift is that because of singularity problem, a shift close to an eigenvalue cannot be used, result ing in slower convergence. In this paper, the above singularity problem has been solved by introducing side conditions without sacrifice of convergenc e. The proposed method is always non-singular even if a shift is on a disti nct eigenvalue or multiple ones. This is one of the significant characteris tics of the proposed method. The non-singularity is proved analytically. Th e convergence of the proposed method is at least equal to that of the subsp ace iteration method with shift, and the operation counts of the above two methods are almost the same when a large number of eigenpairs are required. To show the effectiveness of the proposed method, two numerical examples a re considered. (C) 1999 Academic Press.