Study Of Underwater Sound Absorption Mechanism And Characteristics Of Hydroacoustic Anechoic Coating Embedded With Infiltrated Micro-perforated Panel

Micro-perforated panel is an important and basic acoustic structure.Because of the simple,clean,and pollution-free structure,MPP is widely used in indoor noise reduction,muffler design,and other sound absorption fields.The current research and application of micro-perforated panels are mostly limited to air medium.This paper attempts to introduce the micro-perforated panel structure into the underwater anechoic coating,combine the acoustic impedance-matching characteristic of piezoelectric composite material and the energy-dissipation mechanism of the shunted piezoelectric and design anechoic coating with broadband and low-frequency sound absorption performance.The interest of this paper lies in the acoustic and vibration characteristics of liquid-immersed micro-perforated panel and the engineering application for sound absorption underwater.Combining with multiphysics finite element simulation,underwater hydroacoustic testing,this research mainly focuses on theoretical analysis methods,and studies on the acoustic and vibration mechanism,modeling,and characteristic analysis of the underwater coating.Main contents of this research are shown as follows:(1)The acoustic-structure coupling calculation model and the sound absorption performance prediction model of infiltrated flexible MPP are established.Based on the viscous motion equation in the liquid-filled rigid short tube,the acoustic impedance characteristic of the micro-perforated panel is corrected with the end acoustic radiation effect,the interaction between the perforation,and the heat conduction.Based on modal analysis solution from Kirchhoff's theory on a thin plate,acoustic wave equation,and continuous conditions of sound pressure and particle velocity,the author established the acoustic-vibration coupling model between the flexible infiltrated micro-perforated panel and the backing liquid layer.Based on the modal simulation of the infiltrated microperforated panel,the author simplified the calculation process and studied the influence of the vibration coupling effect on the acoustic characteristics of the infiltrated microperforated panel.The author also studied the influence factors of the infiltrated microperforated panel absorber and discussed the broadband sound absorption characteristics of the multilayer infiltrated micro-perforated panel structure periodically arranged in series.(2)The underwater sound absorption prediction model of the MPP-rubber coating(MPPRC)is established and also verified in the underwater acoustic impedance tube.Based on Hooke's law in solid medium,combining the scalar potential function and vector function of the displacement field,the transfer matrix of the state variables in the viscoelastic layer and liquid are both derived.The sound absorption performance prediction model of the MPPRC is established based on the transfer matrix method in the parallel composites in different backing conditions,included rigid backing condition,impedance-matching condition,and pressure-release condition.Underwater measurement is conducted by the impulse response method and the transfer function method.The sound absorption mechanism of the MPPRC structure is studied,the synergistic sound absorption mechanism of the micro-perforated panel,the front rubber,and the thickness is proposed,and the influence of the structural parameters of the MPPRC on its acoustic performance is explored.(3)The influence of the infiltration rate on the sound absorption characteristics of the infiltrated micro-perforated panel is studied,and the acoustic calculation for the periodic structure of the double-sided orthogonally reinforced micro-perforated panel is established.Based on the sound absorption theory of micro-perforated panels,an acoustic calculation model of inadequate-infiltrated micro-perforated panels is established,and the sound absorption characteristic of MPPRC structures in the inadequately infiltrated condition is studied.This dissertation also designs the acoustic calculation model of the double-sided orthogonally reinforced micro-perforated panel to improve the infiltration rate.Based on the Fourier transform and spatial wavenumber method,the vibration influence of the ribs is studied,which concludes that the negligible influence of the stiffed ribs.(4)A theoretical calculation method for sound absorption of piezoelectric composite layers with shunt circuits is established,and a dynamic broadband impedance-matching method is proposed to optimize the design of parameters in the shunt circuit.Equivalent parameters of the 1-3 piezoelectric composite layer are obtained according to the Voigt hybrid model.Based on the acoustic wave equation and piezoelectric equation,this dissertation derived the transfer matrix model and explores the effects of piezoelectric phase volume fraction and circuit element parameters on the sound absorption performance of the composite layer.The broadband dynamic acoustic impedance matching method is proposed to optimize the parameters of circuit components in the low-frequency range in a rigid backing condition to achieve the target of dynamic frequency matching impedance.And also,the acoustic prediction model of a composite structure containing piezoelectricmicroperforated plates is established and verified on the COMSOL simulation platform,the cover layer sample containing the piezoelectric resonant layer of the shunt circuit is produced,and the optimized low-frequency sound absorption performance of the cover layer of the shunted circuit is tested and verified.(5)The influence of heat conduction absorption in an infiltrated micro-perforated panel is taken into account,and the influence of temperature on the composite structure is studied.Based on the Fourier heat conduction formula,the temperature field distribution of the covering layer with a series-parallel composite structure is established and verified by simulation.The dynamic modulus parameters of the rubbery polymer in a wide temperature range are obtained by measurement.Based on the temperature-frequency equivalence principle and WLF equation,the wide-frequency dynamic mechanical property of polymer materials with temperature changes is obtained.The influence of constant and nonlinear temperature field distribution on the sound absorption performance of the composite anechoic coating is studied.