Abstract
This work develops novel numerical approaches and experiments to implement an acoustic system containing a vibrated structure radiating sound in the interior domain through an opening to the exterior domain.During the numerical investigation, a convected acoustic wave equation derived by linear acoustic theory is adopted for modeling the acoustic system. Based on the variational method, a generalized three-dimensional acoustic finite element model is first developed to analyze acoustic characteristics in the interior domain with mean flow. The convective effects induced by mean flow are taken into the stiffness, damping and mass matrix of the finite element model. In addition, the boundary conditions, including non-reflex terminations and absorptive materials, are derived for transmission loss (TL) analysis.In addition, this work also develops a novel technique combining FEM and BEM to resolve the sound radiation problem without mean flow. In the acoustic system, the eight-node solid acoustic finite element and the four-node planar acoustic boundary element model the interior and exterior domains, respectively. By using the proposed technique, the interfacial acoustic characteristics between the interior and exterior domains are analytically determined by the admittance matrix derived from the BEM model developed for the exterior domain. By doing so, the acoustic behavior in the interior domain can be resolved using only FEM analysis. This approach averts the disadvantages of asymmetry and lack of bandwidth encountered in the direct acoustic FEM-BEM coupling method, substantially reducing the computation time. The effects of flange size and wave frequency on impedance, sound pressure, and sound directivity are studied as well.Several examples, including those of a cylindrical horn, piezoelectrical buzzer, muffler, loudspeaker and acoustic board demonstrate the feasibility of the proposed approach. In addition, the experimental work including the vibration velocity, sound pressure level and sound absorption coefficient measurement is also carried out for verification and analysis purposes. A good correlation is found between the numerical and experimental / referenced results. The novel design on the acoustic board and muffler are also noted. Therefore, this approach can be effectively applied to industrial product development.