Self-Identification Experiments Using Variable Inertia Systems for Flexible Beam Structures

The concept of self-identification and its feasibility are experimentally investigated. The modal parameters changed by the variable inertia systems, which are controlled by control input, are used to obtain linear equations about unknown structural parameters to overcome the lack of modes in vibration testing. We derive the controllability of the modal parameters as the requested conditions for implementing self-identification using sensitivity analyses of the modal parameters with respect to the control input. Also, a criterion for the self-identification is proposed to measure the controllability. To examine the present method, the self-identification experiments are performed using a flexible cantilevered beam with controllable additional mass attached to the beam. In the experiments, we simulate the self-identification of a flexible structure with variable inertia systems, where lower vibration modes are changed by the variable inertia system adapting to the lack of modes in identification of unknown parameters. It is shown that the identification error of the bending stiffness and mass per unit length of the beam are ranging from about 8% to 12% and 1% to 7%, respectively, and they depend on the mode number because the mode shape estimation from strain sensors and cubic spline interpolation also depends on the mode. Furthermore, the factor for the identification error is discussed in detail through numerical analysis, and the results show the clear relationship between the present criterion and the identification accuracy in experiments.