Acoustic Performance Analysis And Optimal Design Of Sound Absorbing Cover And Composite Acoustic Panel

As a formidable naval equipment,submarine acoustic stealth performance is the premise and important index to ensure the submarine's survivability and combat effectiveness.So,noise reduction is one of the important design objectives of submarine.There are two effective ways to reduce the noise of submarine,to lay the sound absorbing coating outside the hull and to apply the sound insulation material inside the hull.Sound absorption coating can not only reduce its own radiation noise,but also reduce the reflection of the detection sound,and "absorb" more detection sound waves to improve the invisibility.The use of lightweight composite sound insulation plate can improve the sound insulation performance of the internal components and reduce the radiated noise of the hull.The design of the hollow cavity structure and shape of the acoustic overlay can change the damping distribution and vibration characteristics of the material and cause the change of the acoustic performance of the material.The reasonable design of the distribution and thickness of the carbon fiber composite layers can adjust the distribution of the stiffness and damping of the material,so as to change the reflection and propagation of the sound waves,and cause the change of the material's sound insulation and vibration isolation performance.Therefore,it is necessary to construct the performance analysis and optimization method of materials to obtain sound absorption and sound insulation materials with higher performance of vibration and noise reduction.In this paper,an acoustic analysis model with multi-layer cylindrical cavity is established,and an optimization method for the cavity structure of acoustic overlay is proposed.A multi-software numerical analysis model of carbon fiber composite soundproof board was constructed.The influence of different material distribution and thickness on sound insulation performance of the soundproof board was compared and analyzed,and the thickness distribution of carbon fiber composite soundproof board was optimized to improve sound insulation performance.Specific research contents and results are as follows:(1)The optimization method of acoustic cover layer structure with multiple cylindrical cavities.Aiming at the research object of the viscoelastic(rubber-like)acoustic cover layer with variable cross-section cylindrical cavity as the research object,an optimized design method for the structure of the composite acoustic cover layer with multi-layer cylindrical cavity is established.By using a one-dimensional acoustic model,the single-layercylindrical cavity structure is equivalent to a special equivalent medium,and an analytical expression of equivalent parameters(equivalent density and equivalent modulus)is obtained.Combined with the transfer matrix method,the sound absorption performance analysis model of the composite acoustic cover with multiple cylindrical holes is established.Using the aperture size of the multi-layer cylindrical cavity as the design variable,the genetic algorithm was used to optimize the design of the cavity structure of the sound-absorbing cover layer,and the pore structure of the sound-absorbing cover layer with the maximum sound absorption coefficient in a specific frequency band was obtained The influence of the number of cavity layers and the acoustic frequency band on the optimal configuration has resulted in several new covering structures with higher sound absorption coefficients.(2)Performance prediction and shape optimization design of acoustic cover layer with periodic cavity.Based on the analysis and calculation of commercial finite element software,the sound absorption performance of the acoustic covering layer with periodic cavity is optimized for different cavity shapes.The two-dimensional symmetrical finite element model of acoustic overlay is used and compared with the analytical solution to prove that the finite element model is correct and effective for the prediction of acoustic overlay performance.The sound absorption performance of two typical cavities(trapezoidal and exponential)and the acoustic cladding of the new cavity structure is discussed.It is found that the cavity shape has an important influence on the sound absorption performance,and it is verified that the new cavity structure has a higher sound absorption coefficient than the exponential cavity structure.At the same time,the influence of the material and structural parameters of the cover layer on the acoustic performance is analyzed.The new cavity structure obtained in Chapter 2 was curve-fitted,and the analytical expression of the new cavity structure pore pattern was obtained.Combined with the linear programming method,the shape optimization design of the typical cavity structure and the new cavity structure was carried out,and the optimal cavity structure in the design frequency band was obtained.(3)Analysis and optimization design of sound insulation performance of composite sound insulation board.The material of each layer of the composite sound insulation board is equivalent to a uniform material with equivalent parameters.The natural frequencies and modal shapes of the carbon fiber composite sound insulation board with the core materials of honeycomb and PET foam are calculated.Based on the finite element method,the sound insulation performance calculation model of the sound insulation board is established to realize the calculation of the sound insulation performance of the composite material sound insulation board,which is compared with the sound insulation curve of the existing sound insulation test.Calculate the sound insulation performance of the composite sound insulationboard of various schemes,and analyze the influence of the material layer thickness and material distribution on the sound insulation performance of the sound insulation board.The optimized design of sound insulation performance of composite carbon fiber material sound insulation board was constructed.The optimization method of linear programming was used to optimize the thickness of each layer of the sound insulation board with symmetric structure and sound insulation board with asymmetric structure.In addition,the thickness of the material layer of the sound insulation board with increased material weight and no increase of material is optimized,which is helpful for the comparison and optimal selection of sound insulation performance of different composite sound insulation boards.