Experiment And Simulation Analysis Of Sound Transmission Loss Of Laminated Composite Cylindrical Shell

Composite material fairing is mostly used in new launch vehicles,which not only has the advantages of light weight,high temperature resistance and fatigue resistance,but also reduces the redundant mass of spacecraft and improves the payload ratio.With the development of the launch vehicle technology towards large thrust and large diameter ratio,the problem of low and medium frequency noise in the cavity becomes more and more prominent,which increases the risk of damage to the payload of precision instruments,so the acoustic characteristics and noise reduction measures of the composite fairing cavity need to be studied in depth.Usually the payload is placed in the cylindrical section of the fairing,as a result,the composite cylindrical shell is chosen as the research object in this work,the method of combining simulation analysis with experimental test is used to analyze the influence of the layer angle,shell thickness and material parameters of the composite cylindrical shell on the sound transmission loss at low and medium frequency of0-1000 Hz,on this basis,studying the influence of the thickness,the type of acoustic material and the multi-layer laying in the cavity on the sound transmission loss of the cylindrical shell,which provides guidance and reference for the sound field optimization of similar structures.The main research work and achievements are as follows:(1)The experimental study on the acoustic characteristics of the intracavity of the laminated composite cylindrical shell structure was carried out.The composite model of the cylindrical shell and the related acoustic experimental device were set up.The intracavity noise response of the cavity without laying material and with the laying of melamine foam,450 g/m~2 sound-absorbing cotton and butyl rubber+melamine foam were tested by experiments to investigate the acoustic characteristics of the cavity.The results show that the laminated composite structure has the largest sound transmission loss(13.53 dB)in the 0-200 Hz frequency band and the lowest sound transmission loss(7.17 dB)in the 800-1000 Hz frequency band;40 mm melamine foam,10 mm sound-absorbing cotton,2 mm butyl rubber+6 mm melamine foam reduces the intracavity noise by 7.95 dB,6.57 dB,and 4.01 dB,respectively,and the intracavity noise response of the acoustic material is reduced with increasing frequency in the frequency range of 0-1000 Hz.(2)The simulation analysis of sound transmission loss of laminated composite cylindrical shells was carried out.The finite element model of laminated composite cylindrical shell was established,and the correctness of the finite element model was verified by comparison with noise experimental data;on this basis,the effects of factors such as the layer angle,thickness and material parameters of the composite cylindrical shell on the sound transmission loss of the structure were studied by simulation.The results show that the laying angle has a great influence on the sound transmission loss of the structure,when the axial tensile stiffness of the shell is not less than the circumferential tensile stiffness,the noise reduction effect of the structure is better;the sound transmission loss of the structure increases with the increase of the total thickness of the cylindrical shell;the change of longitudinal elastic modulus and transverse elastic modulus of single-layer composite has a great influence on the sound transmission loss of cylindrical shells,while the change of shear modulus and Poisson’s ratio has little effect.(3)The influence of laying different acoustic materials in the cylindrical cavity on the transmission loss of composite cylindrical shells was studied.The finite element model of composite cylindrical shells with different acoustic materials in the cavity was established,and the correctness of the finite element model was verified by comparing with the noise experimental data;on this basis,the effects of the single layer melamine foam and sound-absorbing cotton on the sound transmission loss of cylindrical shell under the same thickness and the same quality were studied by simulation;at the same time,in the condition of multi-layer laying of butyl rubber and melamine foam,the influence of the thickness of each layer,the proportion of different materials and the total thickness of the multilayer material on the sound transmission loss of cylindrical shell was simulated;the effects of cylindrical shells with different materials on sound transmission loss were compared.The results show that the sound transmission loss of the cylindrical shell increases with the increase of the total thickness of the laying acoustic materials;when only one layer of material is laid,the noise reduction of the sound-absorbing cotton is about 1.26 times of the melamine foam under the same thickness,under the same quality conditions,the noise reduction of melamine foam is about 1.42 times of sound-absorbing cotton,when laying multi-layer materials,the greater the thickness of butyl rubber is laid,the better the noise reduction effect;secondly,in the frequency range of 150-400 Hz,the sound transmission loss of composite cylindrical shell is better than that of aluminum alloy with the same quality,in the frequency range of 400-1000 Hz,the sound transmission loss of aluminum alloy structure is better than that of composite cylindrical shell.