Improved Subspace Method with Application in Linear Time-Varying Structural Modal Parameter Identification
Pang Shiwei,Yu Kaiping,Zou Jingxiang
(Department of Astronautics and Mechanics, Harbin Institute of Technology, Harbi n, 150001, P.R.China)

Abstract: An improved subspace method using ensemble response sequence wasd eveloped. The original method can identify the pseudo-modal parameter of time-varying structure efficiently, but is sensitive to the noise severely. Considering that the key of this method is to find a matrix whose eigenvalues are the same to the system matrix, the process of finding this matrix was converted to a Least Square (LS) problem. Using generalized observability instead of the output matrix,an improved method was obtained, where the sensitivity to noise was a bated,but the computational complexity increased. The orthogonality of the left singular matrix was once considered, the process of computing the pseudo-inverse of the matrix in LS problem was simplified into finding the transposed itself to greatly reduce the computational complexity. The improved method was verifiedvia identifying pseudo-modal parameters of a 2DOF spring-mass model with three kinds of time-varying stiffness.
Keywords: modal parameter estimation, subspace method, time-varying structural system.