Sound Radiation Analysis Of Finite Cylindrical Shells Partially Covered With Viscoelastic Layer In Fluid

Finite cylindrical shells are the main structures of the pressure and non-pressure hull of submarine. To coate with viscoelastic layer on the hull of submarine is one of the main methods of vibration contral and noise reduction. Because of practical reasons in engineering, it is impossible to coate on all of the surface of the hull of submarine with viscoelastic layer. It is significant for noise reduction to study the vibroacoustic characteristics of partially covered cylindrical shell immersed in fluid. In this paper, the vibroacoustic characteristics of partially covered cylindrical shells driven by a harmonious point force are studied. The viscoelastic layer is taken to be messless spring, having dissipative properties but without thickness. The shell is simply supported and its displacement is expanded in a series of its in-vacuo eigenmodes. The shell motion is described by Flügge thin shell theory. The sound pressure treated as reaction forces which act on the shell are applied into the general controlling shell equation. The sound pressure brought by the shell vibration is also expressed as the function of the shell displacement using Helmholtz equation in fluid and Fourier integral imposed to the finite shell. Lastly, the coupling vibration equation of the acoustic-fluid-structure is gotten. After solving the coupling equation, several parameters, which indicate the general characteristics of the shell vibration and sound radiation are calculated. The parameters are the acoustic radiated power level, the radial quadratic velocity level and the radiation efficiency.The focus of the numerical calculation is the analysis of the difference between the vibroacoustic characteristics of the partially covered shells and those of the bare shell. The discussion is favorable for noise reduction of the stiffened shells.