Use of Finite Element-Models for Preparation of Ground Vibration Test

Abstract

The paper discusses possibilities to make use of the finite element model (FE model) to prepare and analyse ground vibration tests (GVT) on large aircrafts. It reports about experiences gained in the preparation stage and of a research GVT on an Airbus A340-300. The observability and controllability of the expected structural modes can be investigated on the basis of FE calculations during the preparation of the GVT. By this means, the engineering skill strictly necessary to set up a GVT can be backed up with analytical findings potentially resulting in improvements of the pick-up and excitation plan. During and after the test the performance of orthogonality checks as well as the calculation of generalized masses on the basis of the measured mode shapes and the analytical mass matrix provide usefull additional information for the evaluation and interpretation of test results. The detection of deviations of the measurements from the analytical model might influence the test procedure drawing the attention towards the least precisely predicted modes which can prove to be very useful for the updating of the FE model. A prerequisite for any activity related to the FE model is a proper association of the test data with the analytical calculations. For this task the use of a generalized static expansion technique is recommended which is a suitable tool during both, the preparation and analysis stage of a GVT.