The Best Force Design of Pure Modal Test Based Upon a Singular Value Decomposition Approach

Abstract

Pure normal mode test, a routine ground vibration test (GVT) for large aircrafts, needs many shakers. When conducting such test for a pure mode, two major problems remain unsolved: One is how to determine the best shaker number; another is how to determine the best distribution of the shakers after shaker number is determined. This paper will answer these two important questions. When one mode is to be excited, the number of the shakers and the corresponding locations of shakers can be determined by a singular value decomposition approach, an algorithm proposed in this paper. The force appropriation can also be solved by SVD method with FRF matrix. The force appropriation effect is quantified by two indexes, the pure index and effective index. And the complete FRF matrix can be constructed by modal parameters of initial modal test or FEM. At the first section of this paper, the pure normal mode test theory development is reviewed. At the end, a simulation example is given to help understanding the new theory.