Modal analysis and characterization of mounting cart used for testing in the combined environment acoustic chamber

Abstract

The ability to simulate the aeroacoustic and thermoacoustic loading typically experienced by space access vehicles and hypersonic flight vehicles is accomplished through the use of a progressive wave tube (PWT) housed in the Combined Environment Acoustic Chamber (CEAC). Simulating these types of acoustic loading requires the test article be mounted flush with the wall of the PWT, exposing the test article to the propagating pressure wave. This mounting capability is achieved through the use of a strong-back fixture, referred to in this work as a test cart, whose initial design was to withstand static pressure loading on the front face where a test article is mounted. However, this test cart experiences dynamic loading during these acoustic tests. Preliminary modal evaluations of test articles mounted to the cart have indicated that the test cart has several natural frequencies in the testing frequency range of interest (0–1000 Hz). The interaction between the test cart and test article is undesirable because it contradicts the analytical rigid boundary conditions and could also lead to unrealistic failure as a result of over excitation of the specimen if the same mode exists in the test cart and test article. The goal of this work is to characterize the test cart using experimental modal analysis and evaluate the need for modification or complete redesign of the test cart to eliminate modes below 1000 Hz and maintain the intended functionality of the cart.