Modal parameter identification of structure under base excitation using vibration test data

Abstract

In the active flight phase, the spacecraft suffers the rigorous external vibration environment which comes from the engine at the bottom of rocket. In course of the ground test, the shaker simulates such excitation through the base movement, and the modal parameters identification method which employs the vibration test data is to the more extent in line with the operating state. In this paper, a specified method is applied for parameter estimation of lumped-mass mechanical system in the vibration test. The modal parameters under the fixed and free–free constrained state can be identified at the same time by this technique. In addition, when the analytical model which includes the test article and the shaking table is adopted, the relations between the response transfer function (RTF) and frequency response function (FRF) are clarified, and some misconceptions in the engineering practice are cleared. Because of the uncertain of the connection impedance between the test article and the shaking table, only the partial parameters of the fixed mode can be identified, such as natural frequency, modal damping ratio and modal shape. As the interface force transfer function (IFTF) can eliminate the influence of the connection impedance and the fixed impedance matrix of the test piece is transformed into the free impedance matrix, the identified parameters of the free mode are complete. Furthermore, the influence of the constraint degree of freedom (DOF) on the parameter identification of the IFTF is discussed preliminarily. Finally, the numerical simulation and the vibration test of discrete structure verify the validity of the proposed method.