Theoretical Research On Low-frequency Absorption Characteristics Of Novel Semi-active Acoustic Anechoic Coating With Subwavelength Piezoelectric Arrays

With their unique maneuverability and concealment,submarines have won the favor of major naval powers and become strategic weapons to defend national sovereignty over territorial waters.Driven by the competitive development of sonar detection technology,active research on acoustic stealth technology of submerged vehicles is essential to enhance the hidability,attack and service life of our submarines,and is indispensable for maintaining world peace.The key of submarine acoustic stealth technology is to control the sound field and acoustic target characteristics of underwater vehicles,and reduce the detection probability and distance of the active/passive sonar mounted on enemy boats,so as to weaken the opponent's underwater attack power,and improve the operational performance of our subs in target detection,tracking,positioning and precision attack.However,acoustic covering technology is the only acoustic stealth technology that can simultaneously suppress the echo and vibroacoustic response of the hull.In view of the fact that passive sonar detection technique is gradually limited with the reduction of submarine radiation noise(RN),active sonar detection technology emerges and flourishes,and the corresponding working frequency moves to a lower frequency band by degrees.Therefore,this dissertation proposes a novel semi-active acoustic anechoic coating with periodic subwavelength piezoelectric arrays for the submarine acoustic stealth technology in response to the new active sonar in the future;which focuses on the absorbing characteristics of the proposed coating,and carries out research on theoretical modeling,regularity analysis,and mechanism revealing of multiple energy dissipation.The main research contents and achievements are as follows:A theoretical analysis model for predicting the underwater acoustic properties of the sound absorber formed by coupling an equivalent thin-plate with periodic subwavelength piezoelectric arrays and a backing cavity is developed in this dissertation.Based on piezoelectric shunt technology and effective medium method(EM),an equivalent model of the thin-plate structure with subwavelength piezoelectric arrays is established and the corresponding dual equivalent characteristics are analyzed.In the meantime,the acoustic wave equation and Kirchhoff's thin-plate theory are introduced to found the theoretical model for analyzing the acoustic characteristics of the absorber,and the accuracy of theoretical results is validated by the finite element simulation technique.The effects of structural parameters such as depth of the backing cavity,lattice constant,substrate thickness and patch sizes on the sound absorption characteristics of the sound absorber are examined in detail.This dissertation constructs an acoustic characteristic prediction model for the composite coating with periodic subwavelength piezoelectric arrays,namely a global fourterminal network model,which is based on the aforementioned equivalent model of subwavelength thin-plate and the theory of wave propagation in layered media.The accuracy of the theoretical model is verified by using finite element simulation technology and standing-wave tube(SWT)testing technology.Then,variation laws of the sound absorption coefficient for the composite coating are studied in-depth to reveal the multicoupling energy dissipation mechanism.The corresponding independent variables cover the material and geometric parameters of rubber layers and the interlayer containing subwavelength piezoelectric arrays.Taking into account the role of double-hull backing structure,a theoretical model for sound absorption characteristics of the integrated coating is established in this dissertation.On the premise of fusing all inertia of ribs in sandwich backing,the vibration control equation of the upper and lower facesheets are deduced by space harmonic method,and the displacement response amplitude coefficients are separated by the virtual work principle to analyze the surface input impedance of the backing structure.In terms of the global fourterminal network method mentioned above,the theoretical prediction model for absorbing performances is built.Meanwhile,a criterion for the truncation convergence of harmonic components of the backing structure is proposed,and the infinite control equations of facesheets in the orthogonal rib-stiffened sandwich backing are limitedly truncated.Furthermore,an acoustic-structure fully coupled finite element model of the contrast overburden is set up to confirm the theoretical prediction results,and a test sample is developed to carry out the sound-absorbing test of a traveling-wave tube(TWT)at atmospheric pressure and complete the experimental verification.The influence of material and geometric parameters of the sandwich backing on acoustic properties of the integrated coating is investigated to reveal the corresponding energy dissipation mechanisms.In this dissertation,an analytical model for sound absorption characteristics of the integrated coating in a hydrostatic environment is initially established.Considering the effect of hydrostatic pressure on geometric deformations of the overburden,the constitutive models suitable for a non-uniform rubber layer with cylindrical cavity and a uniform rubber layer are,respectively,proposed based on the phenomenological theory,and then the equilibrium control equations for the corresponding rubber layer are constructed in conjunction with periodic conditions of the lining.Moreover,the finite deformation analysis of the rubber layer of isotropic incompressible neo-Hookean material is combined with the stress boundaries and volume incompressibility.By synthesizing the convergence criterion of equivalent stratification for non-uniform layers,the finite deformation of each sublayer is used to approximate the deformation result of the inhomogeneous layer 2 with truncated cone cavities.Thus,the deformation of each rubber layer is incorporated into the global transfer matrix under atmospheric pressure to establish a theoretical analysis model for sound absorption characteristics of the integrated coating.Based on finite element simulation technology and TWT testing technology for pressurized constant pressure condition,the accuracy and reliability verifications of the theoretical model are expected to be completed.Change laws of sound-absorbing properties of the integrated lining under different hydrostatic loads are explored,and the multiple energy consumption mechanisms are further revealed.