Virtual testing for vibration tests: methodology to assess facilities performance and modal coupling

摘要

The Test Centre Division of the Directorate of Technical and Quality Management at ESAESTEC has been developing simulation tools for “virtual-testing” large spacecrafts on shaker facilities for the past three years. In the domain of Spacecraft testing, mechanical engineers involved with vibration testing are aiming at the following conditions: a theoretically fix-free interface, a desired profile (acceleration) with a certain frequency content characterised by tight margins in terms of amplitude deviation (and minimum cross-coupling), and an unchanged damping for the spacecraft eigenmodes. This is difficult to achieve in practice for large structures. Moreover, this is not addressed in the procedures of the standards and it can lead to faulty correlations and overtesting for the spacecraft. Virtual Testing consist in performing a test simulation representative of a vibration test on a specific facility, and taking account of all the parameters which may impact or alter the dynamic behaviour of the test specimen. In this paper, the aforementioned approach is thoroughly explained, highlighting the sensitive parameters which may impact test performance for large dynamic test facilities. Two practical examples are detailed: the 6-DOF’s hydraulic shaker HYDRA, and the new QUAD vertical shaker, recently installed at ESA/ESTEC Test Centre.