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Since Statistical Energy Analysis (SEA) is based on lumped parameters, acoustic responses predicted by SEA are spatially discontinuous. However, in many practical applications, the ability to predict spatially continuous energy flow is useful for guiding the design of systems with improved acoustical characteristics. A new approach, utilizing integral equations derived from energy flow concepts, is developed to predict the continuous variation of acoustic field such as sound pressure level in the interior of acoustic domains using structural response predicted by SEA. The computer code developed based on energy flow boundary integral equations is initially validated by analyzing sound propagation in a duct.

Noise transmission paths in an aircraft include, in many cases, both components with a few modes and others with a high modal density. The components with few modes display a long wavelength behavior and are usually modeled using the Finite Element Method (FEM). On the other hand, components with many modes show a short wavelength behavior and suit the application of the Statistical Energy Analysis (SEA). An example of this kind of transmission path is given by the vibration transmission from the fuselage to the floor panels through the floor beams. The fuselage and the floor panels possess a high modal density while the floor beams are considerably stiff and display a small number of modes. The prediction of the vibro-acoustic response of such systems is commonly called the “mid frequency problem” and, until recently, was difficult to be handled with traditional modeling approaches. A Hybrid method that rigorously couples SEA and FEM has been recently proposed.

The Hybrid FE-SEA method has been used to create a fast/efficient model to predict structure-borne noise propagation in a fully trimmed vehicle over the frequency range from 200 to 1000 Hz. The method was highlighted along with the modeling process and extensive validation results in previously published papers [1-3]. The use of the model to analyze structure-borne noise in the full vehicle, and to design and evaluate the impact of counter measures was described. In this study, the Hybrid FE-SEA method is used identify potential design changes to improve the acoustic performance. First, results from a noise path analysis are used to identify key contributors to interior noise. Next, potential design strategies for reducing the interior noise are introduced along with implications on the model. Finally, sample prediction results illustrating the impact of design changes on interior noise levels are shown along with experimental validation results.