Autonomous Identification of the Fast Time-Varied Modal Parameters

Abstract

When the modal parameters are changed quickly with time, they need to be identified at many moments to obtain the changing trend. To complete all the analysis manually is a very tremendous work, so the autonomous analysis is obligatory. Besides, for the test in which parameters are always changed with time, the data for computing FRF is short and excitation force is continuous. All these things make it difficult to obtain the precise FRFs which are necessary for autonomous modal analysis. To obtain the precise FRFs, in the paper, a direct time domain devolution method is presented to calculate the Impulse Response Functions (IRFs) for the first time. In the devolution algorithm, time-consuming inversion of matrix with large size is necessary. To avoid the matrix inversion, an effective iterative algorithm is put forward which can speed the calculation greatly at the cost of little accuracy reduction. In order to complete the modal analysis automatically, first, the modal analysis is completed manually at initial time and this analysis result will be as a preliminary reference model, the modal analysis of other times are completed total automatically. In the process, the previous analysis result is as the reference model, the stability diagram of current time is obtained by some methods such as ERA, PRCE, PolyMAX. Some poles are selected automatically by computing the pole weighted Modal Assurance Criterion (pwMAC) with the reference model. At the end of this paper, the real engineering example is introduced and the automatic analysis results are promising.