| Lightweight panel structures are widely used in vehicles,rail transportation,power grid equipment,and aerospace.How to reduce the weight of the structure while maintaining its excellent sound insulation performance is an important issue in engineering applications.Most of the current sound insulation theories assume that the sound field incidence conditions are plane waves or diffuse sound field,while in practice,many occasions the sound field incidence conditions can be approximated as a point source or surface source(such as aircraft cockpit noise caused by aircraft engines),when the incident acoustic wavefront is approximately spherical or a superposition of several spherical acoustic waves.Spherical wave incidence conditions in the thin plate structure sound insulation characteristics and plane wave incidence have significant differences.Therefore,it is of great academic and engineering value to conduct in-depth research on the sound insulation characteristics of typical thin plate structures under spherical wave incidence.In this thesis,the calculation formula of sound insulation of constrained damped plate and double-layer plate under the condition of spherical wave incidence is derived,and the general rule of sound insulation amount is obtained;in addition,the engineering method and finite element method are compared and analyzed with the engineering application of reactor sound insulation.The main research contents of the article and the results obtained are as follows.(1)The calculation formula of sound transmission loss of constrained damping panel under spherical wave incidence is derived,and the sound insulation characteristics of constrained damping panel under spherical wave incidence are analyzed theoretically,and it is found that its sound insulation quantity follows the following rule: the sound insulation quantity increases by 3-6dB when the panel mass or frequency is doubled.In addition,the effects of point source distance,material,thickness of viscoelastic layer,shear modulus,and damping and loss factors on the sound transmission loss of damped sandwich panels under spherical wave sound field incidence were analyzed.(2)The sound transmission loss calculation equations for double-layer infinite panel and double-layer finite panel structures under spherical wave incidence conditions were derived respectively.It is found that the sound insulation of the double-layer plate structure under spherical wave incidence follows the following rules: for the double-layer infinite plate,the sound transmission loss follows the rule of 9dB/oct when the mass of the panel per unit area or the frequency is doubled above the first resonant frequency;while for the double-layer finite plate,the sound transmission loss is between 9dB/oct and 18 dB/oct when the mass of the panel per unit area or the frequency is doubled,and it depends greatly on the distance between the plate and the source and the size of the plate.largely depends on the distance between the panel and the sound source and the size of the panel.This law is significantly different from the plane wave(or diffuse sound field)incidence: plane wave incidence,double-layer finite large plate sound insulation in the mid-frequency region follows the law of doubling the mass or frequency of the unit surface,the amount of sound insulation increased by 18 dB.In addition,the effects of panel material,panel thickness and cavity thickness parameters on the sound transmission loss of the double-layer panel structure were further analyzed.(3)The engineering method and the finite element method were used to calculate and analyze the afferent loss of the acoustic enclosure,and the experimental verification was carried out.The results showed that both the engineering method and the finite element method can predict the trend of the acoustic loss of the acoustic enclosure to a certain extent,but compared with the finite element method,the engineering method is more efficient in calculation and faster and simpler in application. |
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