Modal Rotor Identification by Base Excitation with Interface Force Measurements.

Abstract

Most of the commonly used modal testing methods are based on multiple point excitation. An alternative to this kind of excitation is driven-base testing using a multi-axis shaker table. Driven base tests excellently deliver all the eigenmodes of vibration which significantly react to a total acceleration of the structure through its interface to a primary structure in real operation. As a typical example, the article presents the modal identification of a large propeller which was performed on DLR's multi-axis vibration table MAVIS in Goettingen. For the first time, the interface forces between the structure and the shaker table were measured during the investigation of such a dynamically complex structure under base excitation. The analysis of interface forces and moments yields the effective and generalized masses of the structure, whereas the analysis of the structural responses deliver the eigenfrequencies, modal damping values, and mode shapes. The paper summarizes the theoretical background, elucidates the test procedure and test data evaluation, and presents typical test results which emphasize the measured interface forces.