Modal parameter identification algorithm based on pure normal mode test technology

Abstract

There is common denominator for the FRFs of mode test which determine the modal frequency and damping. For the modal parameter identification of SIMO or MISO, one row or one column of FRF matrix is known, by applying pure normal mode test technology which is often used in the Ground Vibration Test (GVT) of aeroplane, a group of real coefficients can be computed out, each coefficient corresponds to one FRF, the sum of all the FRF multiplying the computed coefficient constructs one new FRF which includes only one mode. By this way, the precise modal frequency and modal damping can be identified. Changing the coefficients, the other mode’s frequency and damping can also be identified. For MIMO test, one new group FRFs which include only one mode can be constructed in similar way. The precise modal frequency, modal damping and modal shape can be identified. Changing the coefficients, the other mode’s parameter can also be identified. Even if the number of FRF groups for MIMO is not enough, one new group FRFs can be obtained which greatly deleting the nearest mode’s influence, improve the preciseness of identified modal parameters, especially the modal shape. In this paper, the method of computing the coefficients are introduced for SIMO, MISO and MIMO test. The real engineering example is given to verify the effective and correct of new algorithm. For mode test with very big damping, the coupling of different modes is very seriously, the new algorithm can realize the decoupling easily and obtain the precise modal parameters.