Modal Analysis of Multi-Axis Transient Tests via Time Domain Identification.

Abstract

A time domain identification method analysing forced vibrations is utisized for evaluation of a base driven transient test. A structural model of a satellite mounted onto a multi-axis vibration simulator was excited by transient base point acceleration signals typical of those occuring during launch of spacecraft. Time histories of base point accelerations and structural responses were measured. These data were preprocessed and then analysed by the identification algorithm. The theoretical basis of the method is outlined and fundamental equations are summarized. The solution of the identification equation by three different methods is described and the concept of the employed reduction transformation is explained. Data preprocessing consists of calculation of relative accelerations, digital filtering and time integration. Modal analysis using various time windows is described. Results for modal parameters are compared with those of a frequency domain modal analysis. Effects of some evaluation parameters and the type of estimation method on the quality of the results are considered.