Identification of modal parameters, generalized and effective masses during base-driven tests

Abstract

Structural dynamics identification is a common, long-standing procedure performed on large aerospace structures in order to investigate their dynamic behaviour. Usually, the experimental identification is accomplished by a set of single exciters placed at suitable structural points. An alternative to multiple point excitation is a driven-base test using a multi-axial shaker table. Multi-axis shaker facilities have been developed for experimental dynamic load simulation. However, they can be used for structural dynamics identification as well, whereby the overall structure is accelerated by the vibration table and the structural responses are measured. Based on these data, the structural dynamics of the structure can be identified. A common procedure for this identification is the determination of the modal paramaters, i.e., the eigenfrequencies, modal damping values, and mode shapes. A complete set of modal parameters requires the determination of the generalized mass as well. The measurement and evaluation of the interface forces between the structure and the multi-axial shaker facility makes the determination of the missing property possible. The present article develops the theoretical background for the identification and elucidates the experimental requirements. The application on a laboratory test structure as well as on two more complex structures is described. Typical measurement data and the extracted modal parameters are presented. The advantages and limitations of the test procedure are pointed out.