Research On Sound Radiation Characteristics And Vibration Control Technology Of Complex Thin Shell Structure

With the development of industry, the operating power of dynamic machinery equipment increases, and its vibration energy is heightened. Nevertheless, the engineering structure develops towards light and thin increasingly, which makes the structural vibration and sound become more severe. Therefore, in the product design stage, provided that the vibro-acoustic characteristics of product were predicted validly, the effective measures to proceed low noise design were carried out in advance, the designs and trial-manufactures repeatedly would be avoided, the cost of design would be reduced and the schedule of manufacture would be accelerated. As the thin shell structure has been widely used in automobile, ship hull and underwater navigation structure and so on, the prediction and control technology on the vibro-acoustic characteristics of complex thin shell structure in wide frequency domain will show great significance not only in astronavigation, automobile, ship, but also in machinery industry.In this paper, taking complex thin shell structure as research object, the vibration and radiation characteristics and control technology of stiffened plate (sheet-beam) structure, sandwich structure, base structure, cylindrical shell and its supporting structure and ship model have been studied in the wide range of frequency. A new pattern hollow blocking mass structure with excellent vibration-isolating performance was put forward. Besides, a kind of butyl-rubber composite damping rubber sheet with high damping characteristics was developed, and whose vibration damping performance in thin shell structure was uncovered from the perspective of engineering application. The cylindrical shell experimental model containing several equipment supporting pedestals was designed, and the vibration transmission and noise radiation characteristics of these inner supporting structures were studied. In addition, the composite blocking technology of supporting structure was put forward, a series of vibro-acoustic prediction were carried out on the complex thin shell structure such as cylindrical shell and ship cabins in the wide range of frequency, and a good effect on reducing vibration and noise was obtained. The main research contents and conclusions of this paper as follows:Base on the hybrid FE-SEA method applied on the vibro-acoustic characteristic analysis of complex structure in the mid-high frequency domain, the parameters of the ratio of characteristic dimension to wavelength used to divide each effective frequency domain of FEM, SEA and hybrid FE-SEA method was defined, which improved the efficiency of building complex thin shell structural hybrid FE-SEA model.A new type pattern hollow blocking mass structure was put forward, whose vibration-isolating mechanism was studied by numerical calculation and experiment. Compared with solid blocking mass, the impedance mismatching of hollow blocking mass was increased, which lead to its blocking performance be improved. The effective blocking frequency shifted toward low frequency domain, which widened the blocking frequency domain of hollow blocking mass. The stiffeners of thin shell structure could reduce the vibration of plates in low frequency to some extent, while the blocking mass had an excellent vibration-isolating performance in mid-high frequency domain.A kind of self-adhesive composite damping rubber sheet, with butyl rubber as main raw material, has good damping vibration attenuation performance for the thin shell structure such as ship in the wide range of frequency. After pasted with these composite damping sheets, the average structural loss factor of thin shell structure increased significantly in the wide range of frequency, whose damping performance increased with the propagation distance.One underwater cylindrical shell experimental model containing3kinds of equipment supporting pedestals was designed. By the analysis method of transfer function sensitivity, the finite element model of cylindrical shell structure was amended. The calculation errors of the first10order natural frequencies of the cylindrical shell and the internal platform structure were less than8%and2%respectively after amended. Besides, the trends of calculated transfer function were basically identical with experimental results. On this basis, the influence rule on the vibration transmission characteristics of supporting structures inside the cylindrical shell in low frequency was analyzed, which provided the foundation for the acoustic design of supporting structures.By analyzing the vibration transmission characteristics from pedestals to cylindrical shell structure, the influences on vibration transmission characteristics of pedestal type, structural parameters and layout were revealed. The vibration transfer function and transmissibility from pedestals to cylindrical shell structure had connection with structural modal parameters, which was influenced by pedestal and cylindrical shell structural vibration modes obviously in low frequency. The equivalent transmissibility from the same type pedestals to the cylindrical shell approached identical much the same, and the adjustment of the local structural parameters of pedestals also had a little effect on the equivalent transmissibility. Taking mechanical admittance and transmissibility as evaluation index, the distributional trends and essential characteristics of mechanical admittance and transmissibility from pedestals to the cylindrical shell were identical. In the mid-high frequency domain, taking the equivalent mechanical admittance and equivalent transmissibility as evaluating the average vibration characteristics of cylindrical shell was provided.The composite vibration-isolating technology combining blocking mass and damping vibration attenuation was provided, and the study on the composite blocking performance of the internal supporting structures was carried out. The results showed that the composite vibration-isolating technology was advantageous than rigid blocking or damping vibration attenuation technology solely, which could improve the vibration and noise reduction performance and widened the effective vibration-isolating frequency domain.In this paper, the structural styles of thin shell structural blocking mass was developed, and a kind of butyl-rubber composite damping rubber sheet was also developed. Based on studying the mass blocking and damping vibration attenuation performance, the composite vibration-isolating technology of inner structure was put forward, and the vibro-acoustic performance hybrid modeling and numerical prediction method on complex thin shell structure in wide frequency domain was studied, which deepened the vibration transmission control technology of inner structure and carried out creative work in order to improve the acoustic design level of complex thin shell structure. Thus a series of conclusion and achievements with engineering practical value were obtained, which had a reference value in the low noise design of the complex thin shell structures in automobile and ship hull and so on.