Hybrid Element Method for Compsoite Structures Subjected to Boundary Layer Loading

In many situations, aerospace structures are subjected to a wide frequency spectrum of mechanical and/or acoustic excitations and therefore, there is a need for the development of numerical modeling techniques that are applicable for the resolution of dynamic response of complex systems spanning the entire frequency spectrum. Further, the modeling of composite structures becomes more and more important since many new vehicle designs incorporate increased amount of composite structural components due to weight specific advantages of composites. Thus, we propose to develop techniques that will allow the prediction of noise in the interior of an enclosure such as aircraft due to the transmission of turbulent boundary layer loading in the presence of composite structural components. This innovative Hybrid Element Method (HEM) solution tool for mid-frequency analysis, which utilizes elements of DEA, together with conventional low frequency FEM tools and high frequency EFEM tools, will provide a unified framework that is applicable for the solution of full frequency spectrum vibroacoustic prediction of nonuniform aerospace structures including metallic/composite configurations, accurately and efficiently.

The proposed development will extend and enhance the computational modeling capabilities in many industries such as automotive, naval, heavy equipment and consumer products. Customers equate quality of a product with the sound the product makes. As a result of elevated demand for quieter products from customers together with the increased government regulations, manufactures of products with noise problem in all industries are searching for effective ways to make products with improved noise characteristics. For example, in automotive industry, the increased use of multi-media and telemetric devices demands quieter vehicle interiors and the manufactures and suppliers of interior products not only need to consider functionality, but also the noise control capability of the products. Consequently, there is increasing demand for tools based on computer simulation that can be used to guide design at the early design stage. In addition to interior noise prediction and optimization, the software can be adapted to evaluate and improve radiated noise from engines, exhaust, tires, etc. It can be used to evaluate and improve consumer products such as compressors, air conditioners, hairdryers, vacuum cleaners, and washing machines.

The development of space vehicles and space stations requires the prediction of vibration levels to asses the fatigue life of critical components and noise levels to assess the comfort and functionality levels of crew members. The software product developed as part of the proposed project will enable NASA to effectively evaluate and apply noise and vibration control procedures spanning the entire frequency spectrum. It will also substantially reduce the effort involved in the design of products since the proposed development is based on finite element method that is already used extensively for low frequency noise and vibration analysis. Since low frequency (FEM), mid frequency (HEM) and high frequency (EFEM) analyses can be performed using mostly the same database, the modeling effort associated will be substantially reduced. The software will also enhance NASA's ability to evaluate the acoustic environment and resulting vibration in the payload bay of launch vehicle, diffuse sound field excitation on payloads during rocket launch and ground qualification, and structural integrity of airframe. Manufacturers of aircraft engines and components will also find the software useful for analysis and design.

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