Simulation Study On Noise Reduction Of Cylindrical Shell With Reinforced Sandwich Filled With Porous Material

The stiffened sandwich cylindrical shell structure is a common form of construction for structures such as aircraft,submarines and deep-water propulsion,With the development of science and technology,the impact of noise generated by internal vibrations of aerospace equipment,deep-water equipment,launchers and the friction of surrounding fluid media on the invisibility,reliability and stability of the system is becoming increasingly severe.In order to reduce the radiated noise of navigational vehicles,acoustic coverings are usually laid in reinforced double cylindrical shells to improve their acoustic stealth performance,but the introduction of foam fillers exacerbates the complexity of the mechanical properties and acoustic radiation characteristics of sandwich composite architectures,especially the problem of noise control in the low and medium frequency bands becomes the key to noise reduction in the cavity.In this paper,we adopt a combination of experimental tests and finite element simulations to study the influence of geometrical structure parameters,porous material acoustic parameters and porous material filling methods on the noise reduction of cylindrical shells in the low and medium frequency bands,in order to provide useful reference for future integrated noise reduction design of porous material structures.The main research work and the research results obtained in this paper are as follows:(1)Using the stiffened sandwich panel as the research object,a finite element analysis model of the stiffened sandwich panel was established and the relevant experimental setup was built for verification.Through the comparison between the structural modal finite element simulation and the experimental test data,it can be seen that the first 8 orders of modal vibration and inherent frequency,the error is within 10%,which verifies the correctness of the finite element modelling.The comparison between the finite element simulation of radiation noise and the experimental test data shows that the sound power level curves in the frequency band of 150-1000 Hz are basically the same,and the wave peaks basically match,and the consistency of the results is good,which again verifies the correctness of the finite element modelling.(2)A finite element model of the cylindrical shell of the stiffened sandwich structure is established and a study of the modal and radiation noise of the cylindrical shell structure is carried out.The effect of different reinforcement methods,reinforcement geometry parameters,shell material properties,inner shell thickness,excitation position and direction on the radiation noise of the reinforced sandwich structure cylindrical shell was obtained by means of finite element simulation analysis.The results show that: when the number of reinforcement is 12,the total sound power level of the ring rib reinforced shell is reduced by 16.19 d B compared with that of the longitudinal reinforced shell;increasing the number and thickness of reinforcement both reduce the structure radiation noise,while the structure radiation noise increases when the reinforcement length increases to a certain value;in the frequency band of 1-400 Hz,the increase of shell density and Young’s modulus can effectively reduce the structure radiation noise,in the 400-1000 Hz frequency band,shell Young’s modulus,Poisson’s ratio increases and density decreases can effectively reduce the structural radiation noise;the more the excitation position is far from the center of the shell,the closer the excitation position is to the ring rib or the smaller the incidence angle of the excitation direction,the lower the structural radiation of the cylindrical shell.(3)A study on the effect of filling different porous materials on the radiation noise of reinforced sandwich cylindrical shell was carried out.By filling five different porous materials and comparing the noise reduction results,it can be seen that in the frequency band of 1-1000 Hz,the polyurethane foam has the best noise reduction effect when filled with porous materials of the same thickness and different quality,and the total noise reduction can reach 13.06 d B,while when filling the same quality of different thickness of porous materials,although the noise reduction per unit mass of polyurethane foam reaches 3.72 d B,the best noise reduction performance,but with the corresponding highest filling weight.Filled with the same thickness of polyurethane foam,the greater the flow resistance and curvature factor of the material,the greater the amount of structural noise reduction,while the appropriate reduction in porosity can effectively reduce the structural radiation noise,the material viscous characteristic length and thermal characteristic length have less influence on the structural radiation noise.(4)A study of the effect of porous material filling methods on the radiation noise of stiffened sandwich cylindrical shells was carried out.In the frequency band of 1-1000 Hz,the greater the filling thickness and filling rate,the greater the amount of noise reduction but the smaller the increase,and with different filling rates and filling positions,the closer the filling rate increases,the better the noise reduction effect on the structure.Under the condition that the mass of the filling porous material must be less than 1% of the total mass,comparing the different filling methods,a polyurethane foam with a thickness of 20 mm and a filling rate of 75%has the lowest radiation noise,and the total noise reduction can be further increased by 3.09 dB.