| With its extraordinary concealment and mobility,submarines have won the favor of navies worldwide and have gradually become a weapon for the country to defend the sovereignty of territorial waters.Driven by the low frequency of sonar technology,actively promoting the research on the acoustic stealth performance of submarines is of great significance to enhancing the aggressiveness,stealth,and lifespan of submarines in active service.Acoustic coatings with periodic cavity arrangements have been widely used in underwater vehicles to meet the needs of reducing acoustic radiation and reducing structural self-noise.Therefore,it is essential to design a series of acoustic layers with high sound absorption or sound insulation performance to meet certain specific working conditions.This paper takes the acoustic coatings with an axisymmetric cavity structure as the research object.It uses the research methods of theoretical analysis and numerical simulation to investigate the sound absorption and sound insulation performance optimization of the acoustic coatings and the sound absorption and sound insulation mechanism.The paper introduces the transfer matrix theory(TMT)and finite element simulation method(FEM)for calculating the sound absorption coefficient and sound insulation of the cavity structure acoustic coatings.Two methods are used to calculate the influence of material parameters,cavity size,and position on the acoustic performance of the covering layer.The calculation results of the two methods are in good agreement,which mutually verifies the accuracy of the two methods.An optimization method is proposed to establish an interpolation function that characterizes the shape of the cavity bus bar of the axisymmetric cavity structure.The acoustic optimization problem is transformed into finding the optimal position of each point composing the bus bar.The Nelder-Mead algorithm is used to analyze the cavity structure of the model.It is optimized with material parameters,and different weighting strategies are used to successfully move the peak frequency of the sound absorption and sound insulation curve to the target position,thereby obtaining a cavity structure with better low-frequency acoustic performance.The research results show that the optimization of the cavity structure has a limited effect on the low-frequency optimization of effective sound absorption and sound insulation frequency bands.The optimization of the coupling material parameters can broaden the sound absorption sound insulation range and significantly improve the low-frequency acoustic performance.Due to the unique working environment of the underwater acoustic coatings,this paper predicts the acoustic performance of the model under 1MPa and3 MPa based on the moving mesh technology.It compares the simulation results of the sound insulation under different pressure conditions with the experimental values,and the two are consistent well.The research results show that the sound absorption performance of the acoustic coatings is more affected by cavity deformation than the sound insulation performance.The model with superior sound insulation performance under normal pressure can still maintain relatively superior sound insulation performance under other pressure conditions.However,the sound absorption performance becomes unpredictable under large cavity deformation.Finally,by drawing the displacement mode diagram at the peak frequency,the acoustic mechanism of sound absorption and sound insulation of the acoustic coatings is analyzed.The resonance in the cavity is more intense at frequencies with a higher sound absorption coefficient,which shows that cavity resonance dissipation is the basis of good sound absorption performance.In contrast,the resonance of the surface of the acoustic coating is more evident in the frequency band with better sound insulation performance.The reflection of the end face of the sound wave incident domain and the dissipation of the cavity are essential factors that affect the amount of sound insulation. |
