Hybrid finite element developments for vibroacoustic analysis of vehicle systems in the mid-frequency range

New developments in the hybrid Finite Element Analysis (hybrid FEA) are presented in this Thesis. The hybrid FEA mothod combines conventional FEA methods with energy FEA for analysis over a complete frequency range. Formulations for mid-frequency analysis of plates spot-welded to beams are developed. Conventional FEA models are employed for modeling the behavior of the stiff members in a system. Appropriate damping elements are introduced in the connections between stiff and flexible members in order to capture the presence of the flexible members during the analysis of the stiff ones. The component mode synthesis method is combined with analytical solutions for determining the driving point admittance at joints between stiff and flexible members and for defining the properties of the damping elements which represent the flexible members when analyzing the stiff components. The hybrid FEA developments are validated by comparing results of the hybrid FEA with results from very dense Finite Element Analyses (FEA) for structures of increasing complexity. A new formulation for computing the radiation efficiency of a plate radiating into a finite acoustic cavity is also developed. It allows the capture of the modal characteristics of the acoustic cavity which can be important in the mid-frequency range. The coupling effect between the acoustic cavity and the flexible plate is fully accounted in the formulation. The new radiation efficiency development is employed in the hybrid FEA formulation when an acoustic cavity is considered in the interior of a structural system. The new development is validated by comparing results of the hybrid FEA with results of a very dense FEA analysis for a structural-acoustic system. Finally, a case study that integrates conventional and energy based boundary element analyses for a seemless acoustic prediction over a wide frequency range is presented. The acoustic signature of a military vehicle is computed from 10Hz ∼ 2,000Hz using both methods (BEA from 10Hz ∼ 500Hz, EBEA from 500Hz ∼ 2,000Hz). Then, the detection distance of the vehicle is computed by employing the ADRPM (Acoustic Detection Range Prediction Model) software.