Researches On The Acoustic Properties Of Periodically Stiffened Micro-perforated Thin Plates

As the applications of periodically stiffened thin plates and the acoustic absorber based on the thin plates in aviation, shipping, architecture, mechanism and so on improve, many researches on the acoustic properties of the structure have been done by scholars. Based on the fundamental theory of the micro-perforated plate of Maa, the acoustic properties of periodically stiffened micro-perforated thin plates excited by the plane sound pressure are investigated, meanwhile the effects of some parameters upon the acoustic properties of the studied structure are also discussed.First of all, the radiation acoustic pressures of infinite single-periodically stiffened micro-perforated thin plates are analyzed. Based on the fundamental acoustical theory about the micro-perforated plate of Maa and Takahashi, the vibrating response equation of infinite single-periodically stiffened micro-perforated thin plates is established. By using the Fourier transform, constructed function method, Fourier inverse transform, the radiation acoustic pressures of infinite single-periodically stiffened micro-perforated thin plates are obtained. In order to improve the acoustical properties of infinite periodically stiffened micro-perforated thin plates, the two-periodically stiffened micro-perforated thin plate is introduced. Based on the theory of single-periodically stiffened micro-perforated thin plates, by using the space harmonic method, the radiation acoustic pressures of infinite two-periodically stiffened micro-perforated thin plates, which are expressed as a sum of infinite sets of Floquet harmonic waves, are obtained. In order to analyze the acoustical properties of the multi-leaf studied structure conveniently, the radiating matrix of the infinite two-periodically stiffened micro-perforated thin plate is proposed and calculated. Thus, by using the cascaded connection method, the radiating matrix of multi-leaf two-periodically stiffened micro-perforated thin plates is constructed and the radiation acoustic pressures and absorbing coefficients are calculated.Finally, we compare the transmission acoustic pressure of thin plates and periodically stiffened micro-perforated thin plates, the results show that the micro-perforation and stiffeners can affect the radiation acoustic pressures. The influences of micro-perforation and stiffeners on the transmission acoustic pressure are discussed numerically. Then the comparison between the single and multi-leaf two-periodically stiffened micro-perforated thin plate with a rigid back wall is carried out numerically, which show the multi-leaf plate structure has better acoustical properties. The influences of the micro-perforation, the stiffener and the distance between the plates on the absorbing coefficient of multi-leaf two-periodically stiffened micro-perforated thin plates with a rigid back wall are studied numerically. Based on those principles, a numerical optimization is carried out, which shows that an ideal absorption performance in low and middle frequency range can be gotten by controlling those parameters.