Dynamic Analysis of Complex Mechanical Structures Using a Combination of Numerical and Experimental Techniques

Abstract

A systematic methodology is applied, leading to an accurate prediction of the dynamic response of a large and geometrically complex mechanical structures (e.g., a vehicle superstructure supported on a given chassis). The basic idea is to first measure the acceleration time histories at the connection points of the vehicle superstructure with its suspension system and use them subsequently as a base excitation in a finite element model of the superstructure. The reliability of the methodology applied was tested in a small scale nonlinear laboratory vehicle model. In this model, first the study is purely numerical and the emphasis is placed in demonstrating and verifying the accuracy and validity of the methodology applied. Then, the method is applied and examined, using real measurements. Next, the method applied in the superstructure of a real large military vehicle. The vehicle superstructure is first discretized by finite elements. The model is then updated through an experimental modal analysis procedure in a support-free state. Then, a series of experimental trials is performed in real operating conditions, aimed at recording the acceleration time histories at the connection points of the superstructure with the chassis. These time histories are used as a ground excitation for the FE model of the superstructure and the stresses developed are evaluated. In this way, the critical points of the superstructure can be identified by numerical means. The reliability of the methodology applied was tested by placing strain gauges at the critical points of the superstructure and performing a new set of measurements for the vehicle under similar loading conditions. Direct comparison of the numerical and experimental data obtained in this manner verified that the hybrid methodology applied is quite reliable.