| In this thesis, the acoustic absorption of a composite sound absorption structure based on the micro-perforated plate and internal resonance system is investigated. The analytical formula for calculating the absorption coefficient of the composite sound absorption structure is derived by employing the modal expedition solution of the classical plate equation coupled with the acoustic wave equation. The proposed theory is validated with FEM results.The thesis introduces and assorts the studies of the micro-perforated absorber first, and then gives the absorption formula of the micro-perforated absorber. The effects of the parameters of the micro-perforated absorber on the absorption coefficient are investigated. The results show that, the radius of the perforations needs to be sub-millimeter to make the absorber impendence match the air characteristic impedance when the maximum value of the absorption coefficient can be obtained; the absorption bandwidth can be expanded by reducing the orifice diameter, panel thickness or increasing perforation ratio; when the cavity depth increases, the first resonance absorption bandwidth will become narrow and the peak in absorption coefficient curve occurs at a lower frequency.Then a composite sound absorption structure based on the micro-perforated plate and internal resonance system is proposed. The absorption formula is developed for the composite sound absorption structure based on the modal analysis solution. The sound absorption performance at low frequencies can be improved by adjusting the parameters of the internal resonance system, while sound absorption characteristic at the middle and high frequencies can be optimized by optimizing the parameters of the micro-perforated panel and the cavity depth.Finally a FEM modal of the proposed micro-perforated absorption structure is built. With the FEM modal, the sound absorbing coefficient can be directly obtained without calculating the impedance of micro-perforated panel in advance. The numerical simulation results are consistent with those calculated by the analytical solution and therefore the FEM modal is validated. |
