Study On Vibro-acoustic Model And Characteristics Of Cylindrical Shell Partially Filled With Liquid

As a basic structure,the cylindrical shell is widely used in ship and ocean engineering,aerospace,and oil pipeline transportation.There are many types of liquid or ballast water tanks inside underwater vehicles.In addition to ensuring the requirements for structural strength,stiffness,and stability,the requirements for its vibration and acoustic quality are more and more stringent.In the recent vibro-acoustic research of underwater shells,little concentration is given to the influence of fluid inside the structure on the vibro-acoustic characteristics of the structure.And the mechanism of coupling vibration and acoustic radiation between the internal and external fluid medium and the structure during free liquid surface sloshing has not yet been revealed.In this paper,the structure of the underwater vehicle containing the liquid tank is simplified,and the vibro-acoustic model and characteristics of the partially liquid-filled cylindrical shell are studied.First,a semi-analytical method is proposed for solving the free surface sloshing problem of 3D partially filled rigid cylindrical shells.By establishing polar coordinate systems on the cylindrical shell and the free liquid surface,the two coordinate systems of the cylindrical shell and the free liquid surface are linked according to the transformation relationship of the two coordinate systems.Based on the assumption of an incompressible ideal fluid,the velocity potential function of the free liquid surface is obtained according to the Laplace equation.And then,the governing equation of the free liquid surface is obtained according to the boundary conditions and coordinate relations.The fluid sloshing frequency is solved by the Galerkin method.The free liquid surface sloshing experiments of cylindrical shells with different liquid filling depths were carried out,and the correctness of the method was verified by comparing it with the experimental and published results.The influence of liquid surface depth and other parameters on the sloshing motion is discussed,which provides a theoretical basis for the vibro-acoustic analysis of partially liquid-filled elastic cylindrical shells considering free liquid surface sloshing.Then,a theoretical model of the coupled vibration of a partially liquid-filled threedimensional elastic cylindrical shell considering the sloshing motion of the free liquid surface is established in this paper.Based on the Flügge shell theory,the displacement function of the cylindrical shell is expanded in the form of double series using the wave propagation method.Based on the fluid potential function and the continuity condition of the cylindrical shell-internal fluid,a unified solution method can simultaneously solve the liquid surface sloshing,and the coupled vibration of the liquid-filled cylindrical shell is proposed.Further considering the external fluid acoustic medium,the vibro-acoustic theoretical model of the coupling system of the external flow field-cylindrical shell-internal flow field is established.The far-field acoustic radiation of the coupling system is calculated using the acoustic barrier column model combined with the steady phase method.The method’s accuracy is verified by comparing it with other numerical methods.The influence of structural and internal liquid parameters on the vibro-acoustic characteristics of the coupling system is analyzed,and the coupling mechanism of internal liquid sloshing and shell vibration is revealed.Next,the vibration and acoustic radiation studies of a partially liquid-filled underwater cylindrical shell with a horizontal partition inside are carried out.The theoretical model of internal flow field-inner cylindrical shell with horizontal partition-external flow field is established.Using the coupling force and bending moment at the junction of the cylindrical shell and the internal partition,the governing equations of motion for the cylindrical shell with the diaphragm are derived.The governing functions of the coupling force and bending moment are determined by the propagation of bending waves in the shell and the inner plate to make sure.Compared with the calculation results of finite element and boundary element methods,the method’s accuracy is verified.The effects of the free liquid surface and structural parameters on natural frequency,mode shape,forced vibration response,and farfield sound pressure are analyzed.The paper breaks through the theoretical modeling method and solution method of the coupling vibro-acoustic problem between the internal-external flow field and the complex cylindrical shell,which considers the linear sloshing effect.What’s more,the influence of internal and external fluid coupling on the shell vibration and acoustic radiation is analyzed in this paper.The theoretical system of the vibro-acoustic research of the underwater cylindrical shell coupling system is further enriched.And the relevant conclusions can provide a reference for the acoustic design of the shell structure with internal liquid and structure.