Modal Parameters Identification of Variable-Stiffness Adaptive Structures Based on Rate of Change in Frequency Response Amplitude

Paper number

IAC-07-C2.5.03

Author

Dr. Atsuhiko Senba, Tokyo Institute of Technology, Japan

Coauthor

Mr. Kaoru Ohashi, Tokyo Institute of Technology, Japan

Coauthor

Prof. Hiroshi Furuya, Tokyo Institute of Technology, Japan

Year

2007

Abstract

Modal parameters identification techniques for space structures usually use both input and output data obtained by sensors in structures. However, there are difficulties in measuring exact input data for space structures because unknown external forces always exist in orbit. A method that does not need measuring input force is, therefore, suitable for such issue. In this study, we investigate a possibility of modal identification based on only frequency response amplitude of structures, where semi-active stiffness control of adaptive structures is used so that input force data are not required for process of identification. 

Since the frequency response amplitude of structures with variable-stiffness devices can be changed and its rate of change can be assumed to be a function of unknown modal parameters, we investigate a possibility of updating natural frequency based on the rate of change of frequency response amplitude by using the variable-stiffness devices. In particular, we focus on the use of variable-stiffness members in adaptive truss structures. To demonstrate the proposed procedures, basic experiments for identifying the first modal frequency of a 10-bay truss structure are conducted. Using an electromagnetic exciter, the frequency response amplitude of the truss for low-stiffness state and high-stiffness state are measured, and then the rate of change of them is calculated. The obtained rate of change of frequency response amplitude is finally used to implement proposed method. 

Experimental results show that the proposed method is effective and the accuracy of identified parameters depends on the relationship between the first natural frequency for low and high stiffness states and the excitation frequency. It is indicated that the identification accuracy becomes higher when the rate of change of frequency response amplitude is nearly zero. The factors of identification error are discussed with numerical simulations on adaptive truss model. Furthermore, the effect of the change of mode shape, damping ratio on the identification accuracy is investigated to improve the accuracy. 

Abstract document

IAC-07-C2.5.03.pdf

Manuscript document

IAC-07-C2.5.03.pdf (🔒 authorized access only).

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