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• Vibration transmission mechanisms of the shell with immersed elastic connections are studied. • The forced vibration test is conducted on the double-layer shell with six immersed isolators. • An analytical approach is proposed to predict the vibration response of the double-layer shell. • The vibration test provides benchmark experimental results for future studies. • The energy transmission is quantitatively partitioned with respect to elastic connection stiffness. This paper investigates vibration transmission characteristics of the double-layer cylindrical shell with fully immersed elastic connections through experimental and analytical approaches. A test sample of the double-layer cylindrical shell connected by six vibration isolators is firstly manufactured and a forced vibration test is done with fully immersed interlayer. Meanwhile, a novel analytical approach is developed to calculate vibration responses of an unequal double-layer cylindrical shell with fully immersed elastic connections. The substructure receptance method and wave propagation method are combined in the coupling theoretical model. Springs are utilized to simulate elastic connections, that are considered as substructures. By comparing the achieved analytical and experimental vibration responses, good agreements are gained and the two approaches are demonstrated. Then the transmission characteristics are gradually analyzed with respect to the double-layer shell with elastic connections, double-layer shell with interlayer fluid and double-layer shell with fully immersed elastic connections. It is found that the interlayer water between the inner and outer shells plays a "short-circuit" role in vibration transmission, which greatly reduces the isolation performance of vibration isolators. Nevertheless, the fully immersed isolators with small stiffness still have the non-ignorable vibration isolation effect compared with the case of rigid connection. [ABSTRACT FROM AUTHOR]

In order to study the vibration isolation characteristics in water, based on the Flügge theory, a double-walled cylindrical shell model with spring connection is established using the wave propagation method. The fluid inside the inner shell is considered in the model. The reliability of the theoretical method is verified by comparing the calculation results of the mean square velocity with those of the finite element method. The effects of spring stiffness, spring number, fluid load, and inter-shell fluid thickness on vibration transmission of inner and outer shells are studied. The results show that the fluid loading effect of the water medium inside the inner shell can act on the inner shell and the outer shell simultaneously, while the fluid loading effect of the outboard fluid only acts on the outer shell. Under the condition of keeping the total spring stiffness unchanged, increasing the number of springs can reduce the vibration transmission from the inner shell to the outer shell, especially the vibration transmission from the inner shell to the outer shell at low frequencies. The "vibration short circuit" effect easily occurs in the inter-shell water, which is independent of the thickness of inter-shell water. When the elastic connection stiffness is small, the inter-shell water plays a leading role in vibration transmission in the whole frequency range. When the stiffness of elastic connection is large, the inter-shell water plays a leading role in vibration transmission at low frequencies, while the elastic connection plays a leading role in vibration transmission at high frequencies. [ABSTRACT FROM AUTHOR]