Experiences in performing a high-intensity, direct-field acoustic test on a contamination sensitive system

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A direct-field acoustic test (DFAT) was performed on a Sandia system in order to verify survival due to an acoustic environment of 146.7 dB OASPL. The DFAT technique' performed by surrounding a test article with a wall of speakers and controlling the acoustic input with a closed-loop control system' was chosen as the test method in order to meet a critical schedule. In choosing this test method, other challenges became apparent, such as how to obtain the high-intensity acoustic levels and what occurs to that environment inside the bagged frame constructed to maintain a contamination-free system. In addition, the vast amounts of data measured during a single test necessitated a way for the test director to quickly visualize the acoustic environment, saving time and provide insight for input adjustments if necessary. Finally, even though the specified acoustic environment was successfully obtained, the results illustrated some drawbacks of the current DFAT method. This paper will detail the DFAT setup used to obtain the test specification, the effects of the contamination frame on the acoustic environment, the quick-look data program created for visual analysis of the acoustic field, and ideas for performing more diffuse DFAT tests in the future.

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Aero-acoustic loading has been established as the primary source of excitation for a Flight System at Sandia National Laboratories. However, flight data of this system does not exist, limiting estimations of system or component response in this environment. Therefore, an experimental acoustic simulation was performed on a heavily-instrumented Flight System, using the direct-field acoustic test (DFAT) method with a multi-input multi-output (MIMO) control system. The combination of DFAT and MIMO resulted in attaining uniform and gradient acoustic fields as high as 127 dB OASPL. This paper will discuss the design of the test, the speaker and controller configurations, and the test results of this unique test method. Additionally, an overview of the method used to apply the measured test data to the pressure-loading finite element simulations of the Flight System will be discussed as well.
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