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Ground based environmental testing is a necessity to ensure the survivability of hardware during launch of spacecrafts (SCs). Testing methodologies for this purpose must provide a safe, effective and efficient control strategy to synthesize the dynamic loads an aerospace structure, - system or component – will encounter during its operational life. In case of the environmental acoustic test the dynamic loads to be reproduced consist of the ones induced by the sound field inside the fairing of the SC during ignition and lift-off launch stages.
Direct Field Acoustic eXcitation Test (DFAX) is a recently developed testing methodology which does not require a dedicated facility and consists in setting an array of loudspeakers around the test specimen, as shown in figure 1. Through a MIMO closed-loop control strategy DFAX has shown good performance achieving the test requirement between certain tolerance levels. In this context, the purpose of the MIMO feedback controller is the automatic computation of the random signals driving the loudspeakers and the update of the drives when necessary (i.e. based on the comparison between a user-defined test reference and the responses provided by multiple acoustic control sensors). In order to compute the random signals, prior to the full-level DFAX test the electroacoustic system must be identified through an experimental low-level pre-test where the system is driven by uncorrelated white noise. This is the so-called system identification (SI) procedure.
A previous work studied the use of vibro-acoustic numerical simulations for synthesis of the electroacoustic frequency response functions and for pre-test purposes (e.g. optimal sensors placement). On top of that, an experimental approach has also investigated how the modal parameters of the mechanical structure under test can be estimated by Operational Modal Analysis (OMA) during the SI. In order to de-risk a DFAX test, it seems that the natural step following these findings would be the update of the vibro-acoustic numerical model based on the experimental data provided by the SI, allowing in this way to predict the forced responses when the drives computed by the MIMO controller are partially correlated. Providing these reliable numerical tools for pre-test purposes is of paramount importance to improve the efficiency of the DFAX set-up process. In addition, these tools are imperative because over-testing responses on the specimen, as well as on the pressure field, must be avoided ensuring a safe testing environment for the flight-model test specimen. This work presents the status of this simulation-test hybrid approach towards the integral simulation of DFAX tests with MIMO random control strategies for pre-test purposes.